434

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NOAA Technical Report NMFS Circular 434

Osteology, Phylogeny, and

Higher Classification of

the Fishes of the

Order Plectognathi

(Tetraodontiformes)

James C. Tyler OCTOBER 1980 ; Marina Biological Laboratory ] libra:iy OCT 141992

Woods Hoio. iViuSS.

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service
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NOAA Technical Report NMFS Circular 434

^'^m

^"'i^Emof^^

Osteology, Phylogeny, and

Higher Classification of

the Fishes of the

Order Plectognathi

(Tetraodontiformes)

James C. Tyler OCTOBER 1980

Marine Biological Laboratory LIBRARY OCT 14 1992 Woods Hole, Mess.

U.S. DEPARTMENT OF COMMERCE

Philip M. Klutznick, Secretary National Oceanic and Atmospheric Administration

Richard A. Frank, Administrator National Marine Fisheries Service

Terry L. Leitzell, Assistant Administrator for Fisheries
The National Marine Fisheries Service (NMFS) does not approve, rec- ommend or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to NMFS, or

to this publication furnished by NMFS, in any advertising or sales pro- motion which would indicate or imply that NMFS approves, recommends

or endorses any proprietary product or proprietary material mentioned

herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NMFS

publication.
CONTENTS

INTRODUCTION 1 Preface 1 Methods 2 PROLOGUE 4

Synopsis of the phylogeny of the Plectognathi 4 Synopsis ofthe higher classification of the Plectognathi 7

Historical review of the classification of the Plectognathi 7

Historical review of the nonclassificatory anatomical work on the Plectognathi 28

Relationship of the Plectognathi to the Perciformes 40 SYSTEMATIC SECTION 41

Definition and synopsis of the osteology of the Order Plectognathi (Tetraodontiformes) 41 Suborder Balistoidei (Sclerodermi) 44 Comparative diagnosis (contrast with that ofthe Tetraodontoidei) 44

Infraorder Triacanthoideo [and Superfamily Triacanthoidea] 44 Comparative diagnosis (contrast with that of the Balistoideo) 44 Family Triacanthodidae 46 Comparative diagnosis (contrast with that of the Triacanthidae) 46

Detailed description of Para/io//ardia lineata 47 Comparative diagnoses of subfamilies (Spinacanthinae, Eoplectinae, Hollardiinae, Triacanthodinae) 56 Anatomical diversity 56

Generic relationships 69

Subfamilial relationships, and relationships to the Triacanthidae and Gymnodontes 73 Family Triacanthidae 78 Comparative diagnosis (contrast with that of the Triacanthodidae) 78

Detailed desciiption of Pseudotriacanthus strigilifer 79 Comparative diagnoses of subfamilies (Protacanthodinae, Cryptobalistinae, Triacanthinae) 88 Anatomical diversity 92 Generic relationships 98

Infraorder Balistoideo 99 Comparative diagnosis (contrast with that of the Triacanthoideo) 99 Superfamily Balistoidea 99 Comparative diagnosis (contrast with that ofthe Ostracioidea) 99 Family Balistidae 101 Comparative diagnosis (contrast with that of the Monacanthidae) 101 Detailed description of Ba/ts£apusundu/atus 102 Anatomical diversity 110 Generic relationships 120 Relationship to the Monacanthidae 123 Relationship to the Triacanthidae 131 Family Monacanthidae 135 Comparative diagnosis (contrast with that ofthe Balistidae) 135 Detailed description of Monacant/iusci7iatus 136 Anatomical diversity 1^

Generic relationships 1"^^ Superfamily Ostracioidea 1^3 Comparative diagnosis (contrast with that of the Balistoidea) 183 Family Aracanidae ^85 Comparative diagnosis (contrast with that ofthe Ostraciidae) 185

Detailed description of Kentrocapros acu/eafus 185 Anatomical diversity 1^5 Generic relationships 204

Relationship to the Ostraciidae 206

Relationship to the Balistidae 207 Family Ostraciidae 211 Comparativediagnosis(contrast with that ofthe Aracanidae) 211 Detailed description of A canthostracionquadncomis 211
Anatomical diversity 220

Generic relationships and comparative diagnoses ofsubfamilies(Ostraciinae and Lactophrysinae) . . . 238 Suborder Tetraodontoidei (Gymnodontes) 243 Comparative diagnosis (contrast with that of the Balistoidei) 243

Infraorder Triodontoideo [and Superfamily Triodontoidea, Family Triodontidae] 243 Comparative diagnosis (contrast with that of the Tetraodontoideo) 243 Detailed description of Triodon macropterus 244 Anatomical diversity 254

Relationships to the Balistoidei and to the other Tetraodontoidei 260

Infraorder Tetraodontoideo 263 Comparative diagnosis (contrast with that of the Triodontoideo) 263 Superfamily Tetraodontoidea 264 Comparative diagnosis (contrast with that of the Moloidea) 264 Family Tetraodontidae 265 Comparative diagnosis (contrast with that of the Diodontidae) 265 Comparativediagnosesof subfamilies (Tetraodontinae and Canthigasterinae) 265 Detailed description of Lagocep/ia/us/aeui^atus 266

Detailed description of Canthigaster rostrata 274 Anatomical diversity and generic relationships 286 Summary of generic relationships and intrafamilial classification 341 Relationships to the Diodontidae and to the other Tetraodontoidei 342 Family Diodontidae 343 Comparative diagnosis (contrast with that of the Tetraodontidae) 343

Detailed description of D(odon/io/ocan(/ius 343 Anatomical diversity 351 Generic relationships 365

Relationship to the other Tetraodontoidei 368 Superfamily Moloidea [and Family Molidae] 368 Comparative diagnosis (contrast with that of the Tetraodontoidea) 368

Detailed description oiMola mola 368 Anatomical diversity 377 Generic relationships 391 Relationship to the other Tetraodontoidei 392 Material examined 393 Recent species 393

Fossil species 398 EPILOGUE, Remaining problems 400 ACKNOWLEDGMENTS 401 LITERATURE CITED 403 INDEX OF DISCUSSION OF GENERA 421

Figxires

1. Flowing-line illustrated version of hypothesized familial and subfamilial groupings of the Plectognathi 5

2. Angular-line versionof hypothesized familial and subfamilial groupings of the Plectognathi 6

3. Flowing-line illustrated version of hypothesized familial, subfamilial, and generic relationships of the Superfamily Triacanthoidea, the basal Plectognathi 45

4. Range of diversity in body form in the Recent Triacanthodidae: Parahollardia lineata and Halimochirurgus alcocki 47

5. Parahollardia lineata: external features 48

Parahollardia lineata, composite based on several specimens, 45.7-86.1 mm SL, Gulf of Mexico to South Carolina:

6. lateral view of entire specimen 57

7. lateral view of head 58

8. dorsal and ventral views of skull 58

9. posterior view of orbit; posterior view of skull; posterior and lateral views of first abdominal verte- bra 59

10. dorsal view of branchial arches; lateral view of hyoid arch and urohyal 60

11. lateral view of pectoral girdle 60

12. lateral view of caudal fin supporting structures 61
13. Parahollardia lineata, 62.2 mm SL, Florida: dorsal, lateral, and ventral views of pelvis and pelvic fin 61

14. Parahollardia lineata, 82.0 mm SL, Florida: lateral and anterior views of first two dorsal spines 61

15. Protobalistum imperiale, lateral view of holotype, 522 mm SL, Eocene of Monte Bolca, Italy 62

16. SpiVwcanf/juscunei/ormis, lateral view of holotype, 104 mm SL, Eocene of Monte Bolca, Italy 63

17. £op/ecfUA' 6/o(i, lateral view of holotype, 65.2 mm SL, Eocene of Monte Bolca, Italy 64

18. Zjgnoic/if/iysofe/ongus, lateral view of holotype, ca. 161 mm SL, Eocene of Monte Bolca, Italy 65

Lateral views of entire specimens of other representative triacanthodid genera of the Subfamily Tria- canthodinae:

19. Triacanf/iodesanoma/us, 71.5 mm SL, Japan, example of a relatively generalized member 67

20. Tydemanfa/iat^igaforjs, 64.4 mm SL, Bay of Bengal, example of a moderately specialized member .... 68

21. Macror/jomp/iosodesuradoi, 69.9 mm SL, Japan, example of a highly specialized member 69

22. Hollardia hollardi: lateral views of moderate-sized specimen, 62.7 mm SL, and extremely large specimen, 174 mm SL, both from Caribbean 70

23. Para/3o//ardiasc/im;d(i, lateral view of head, 62.0 mm SL, Nicaragua 71

24. Tn'acanf/iodesanoma/us, lateral view of head, 71.5 mm SL, Japan 71

25. Parafn'acant/iodesrefrospmis, lateral view of head, 85.3 mm SL, Mozambique 71

26. Johnsonina eriomma, lateral view of head, 67.0 mm SL, Puerto Rico 72

27. Atrophacanthus japonicus, lateral view of head, 43.1 mm SL, Celebes 72

28. Tydemanianai'igatons, lateral view of head, 64.4 mm SL, Bay of Bengal 72

29. Macrorhamphosodes uradoi, lateral view of head, 69.9 mm SL, Japan 73

30. //a/imoc/z(>urgusceAj(nscoides, lateral view of head, 99.2 mm SL, Bay of Bengal 73

31. Typical body form in the Recent Triacanthidae iPseudotnacant/iusstrJ^i/i/er 78 Pseudotriacanthus strigilifer: 32. external features 79

33. lateral view of entire specimen, 79.0 mm SL, India 89

34. lateral view of head, 79.0 mm SL, India 90

35. dorsal, ventral, and posterior views of skull, 79.0 mm SL, India 90

36. posterior view of orbit, 130 mm SL, Thailand 90

37. Tripodichthys angustifrons: dorsal view of branchial arches; lateral view of hyoid arch and urohyal;

137 mm SL, Australia 91

38. Triacanthus biaculeatus: lateral and anterior views of first two dorsal spines, 113 mm SL, Borneo 91

39. A, Parahollardia lineata, 45.7 mm SL, Florida, and B, Triacanthus biaculeatus, 113 mm SL, Borneo;

lateral views of pelvis and pelvic fin; anterior views of the base of the pelvic spine 91

40. Trixiphichthys weberi: lateral view of entire specimen, 101 mm SL, Bay of Bengal 92

41. Trixiphichthys weberi: lateral view of head, 101 mm SL, Bay of Bengal 93

42. Protacanthodesombonii: lateral views of holotype, 112 mm SL, Eocene of Monte Bolca, Italy 94

43. Protacanthodes ombonii: lateral view of abdominal region, holotype, 112 mm SL, Eocene of Monte

Bolca, Italy 95

44. Acanthopleurus serratus: lateral view of entire specimen, syntype, ca. 91 mm SL, Oligocene of Canton

Glarus, Switzerland 96

45. Acanthopleurus serratus: lateral views of entire specimens, 153 mm SL and 127 mm SL, and A. col- /e«ei, ca. 120 mm SL and 96.2 mm SL, paratypes, Oligocene of Canton Glarus, Switzerland 96

46. Charts showing two proportional measurements as percent of standard length that differentiate Acanthopleurus serratus and A. collettei 97

47. Marosichthys huismani: lateral view of anterior part of body of holotype, ca. 36 mm head length, Miocene of the Celebes 98

48. Crs'ptobalistes brevis: lateral view of holotype, ca. 88 mm SL, Oligocene of Canton Glarus, Switzer- land 99

49. Rangeof diversity in body form in the Recent Balistidae: Balistapus undulatus and Odonus niger 101

50. Balistapus undulatus: external features 102 Balistapus undulatus, composite based on several specimens, ca. 120-124 mm SL., western Pacific:

51. lateral view of entire specimen Ill

52. lateral view of head 112

53. dorsal and ventral views of skull 112

54. posterior views ofskuU and orbit; posterior and lateral views of first abdominal vertebra 113

55. dorsal view of branchial arches; lateral view of hyoid arch and urohyal 114

56. lateral view of pectoral girdle 114

57. medial view of upper jaw; lateral view of pelvis and encasing scales at end of pelvis; posterior view of end of pelvis 115

58. lateral view of spiny dorsal fin and its pterygial supports 116
59. dorsal view of pterygial supports of spiny dorsal fin; posterior view of first dorsal spine and anterior view of second dorsal spine 116

60. lateral view of caudal fin supporting structures 116 External features of other representative balistid genera:

61. Abalistes stellaris 117

62. Canthidermis maculatus 117

63. Xanthichthys ringens 117

64. Odonusniger 118

65. Fossil balistids: A, Balistomorphus ovalis, lateral view of holotype, 121 mm SL; B, B. ovalis, lateral view of entire specimen, 119 mm SL; C, B. spinosus, lateral view of holotype, ca. 90 mm SL; D, B. orbi- culatus, lateral view of holotype, 65.6 mm SL—specimens A through D from Oligocene of Canton Glarus, Switzerland; E, Oligobalistes robustus, lateral view of syntype, ca. 60 mm SL, Maikop deposits of the Oligocene of the Caucasus 119

66. Hypothesized phylogenetic relationships ofthe genera of Balistidae 121

67. Dentition of representative balistids: A, Batistes polylepis, 56.1 mm SL, Galapagos; B, Xanthichthys

lineopunctatus, 181 mm SL, Hawaii; C, Odonus niger, 173 mm SL, New Guinea; D, Melichthys niger, 147 mm SL, locality unknown 121

68. Scalesjustabovetipof pectoral fin of fia/tstoidesuindescens, 114 mm SL, Indonesia 122

69. Batistes polylepis, lateral view of entire specimen, 56.1 mm SL, Galapagos 124

70. Su/Z/amen/renatus, lateral view of entire specimen, 74.3 mm SL, Somalia 125

71. fl/imecanf/iusrecfangu/us, lateral view of entire specimen, 37.4 mm SL, Phoenix Islands 126

72. Cant/iidermismacu/atus, lateral view of entire specimen, 80.1 mm SL, Alabama 127

73. Xant/iic/it/iys/meopunctatus, lateral view of entire specimen, 181 mm SL, Hawaii 128

74. Lateral views of relatively normal balistid skulls: Batistes capriscus, ca. 360 mm SL, Gulf of Mexico; B.

polylepis, ca. 390 mm SL, Mexico 129

75. Lateral view of most specialized balistid skull and suspensorium, Odonus niger, 173 mm SL, New

Guinea 130

76. Batistes polylepis: ventral and dorsal views of skull, ca. 390 mm SL, Mexico 131

77. Batistes capriscus: ventral view of skull, ca. 360 mm SL, Gulf of Mexico 132

78. Range of diversity in body form in the Monacanthidae: A, Monacanthus citiatus; B, Amanses scopas;

C, Brachatuteres trossulus; D, Psitocephalus barbatus 135 Monacanthus citiatus: 79. external features 136

80. lateral view of entire specimen, 81.3 mm SL, Florida 145

81. lateral view of head, 81.3 mm SL, Florida 145

82. dorsal and ventral views of skull, 51.3 mm SL, Colombia 146

83. posterior views of skull and orbit, 81.3 mm SL, Florida 147

84. dorsal view of branchial arches; lateral view of hyoid arch and urohyal; 75.7 mm SL, Florida 147

85. lateral view of pelvis and encasing scales at end of pelvis; detail of the end of pelvis; 81.3 mm SL,

Florida 148 External features of other representative monacanthid genera:

86. Monacanthus chinensis 148

87. Stephanotepis cirrhifer 149

88. Chaetoderma spinosissimus 149

89. Paramonacanthus curtorhynchus 149

90. Pervagormetanoceplmlus 150

91. Rudarius ercodes 150

92. Navodon hypocrepis 150

93. Eubalichthys spilomelanurus 151

94. Cantherhines pultus 151

95. Amanses scopas 151

96. Alutera monoceros 151

97. Psitocephalus barbatus 152

98. Oxymonacanthus longirostris 152

99. Pseudatuteres nasicornis 152

100. Paratuteres prionurus 152

101. Brachatuteres trossulus 153

102. Step/iano/epw/iispidus, lateral view of entire specimen, 50.4 mm SL, Florida 155

103. Paramonacant/iuscrypfodon, lateral view of entire specimen, 68.5 mm SL, Thailand 156

104. C/iaetoderma spinosissimus, lateral view ofentire specimen, 33.0 mm SL, Malaya 157
105. Peryagorspi/osomus, lateral view of entire specimen, 80.0 mm SL, Hawaii 158

106. i?udanusmmufus, lateral view of entire specimen, 17.9 mm SL, Borneo 159

107. Amansesscopas, lateral view of entire specimen, 167 mm SL, Japan 160

108. /lcanf/ra/uferesspi7ome/anurus, lateral view of entire specimen, 63.7 mm SL, Australia 161

109. A/uiera/ieude/otii, lateral view of entire specimen, 107 mm SL, Florida 162

110. PsiVocep/ja/us 6ar6atus, lateral view of entire specimen, 137 mm SL, Singapore 162

111. Brac/ia/uferestrossu/us, lateral view of entire specimen, 55.5 mm SL, Australia 163

112. Para/uterespnonurus, lateral view of entire specimen, 46.4 mm SL, Seychelles 164

113. Oivmomicani/ius/ongirostns, lateral view of entire specimen, 34.2 mm SL, Seychelles 165

114. Pseuda/uteresmjstcornjs, lateral view of entire specimen, 108 mm SL, Philippines 166

115. Sfep/iano/epis/iispidus, lateral view of head, 50.4 mm SL, Florida 168

116. ParamonacoMt/iuscrypiodon, lateral view of head, 68.5 mm SL, Thailand 168

117. Pervagor spilosomus, lateral view of head, 80.0 mm SL, Hawaii 169

118. Amanses scopas, lateral view of head, 167 mm SL, Saipan 169

119. A/ufera /leude/ofii, lateral view of head, 107 mm SL, Florida 170

120. Psilocephalus barbatus, lateral view of head, 137 mm SL, Singapore 170

121 Brachaluteres trossulus, lateral view of head, 55.5 mm SL, Australia 171

122. OAfymo/iacant/jus fofigirosfm, lateral view of head, 26.5 mm SL, Seychelles 171

123. Pseudaluteres nasicornis, lateral view of head, 108 mm SL, Philippines 172

124. Dorsal views of skulls of: A, Pseudaluteres nasicornis. 108 mm SL, Philippines, highly specialized; B, Paraluteres prionurus, 46.4 mm SL, Seychelles, moderately specialized; C, Chaetoderma spinosissimus,

33.0 mm SL, Malaya, relatively generalized 174

125. A, Paraluteres prionrus, ventral view of skull, 46.4 mm SL, Seychelles; B, Pervagor spilosomus, ventral view of skull, ca. 65 mm SL, Hawaii; C, Psilocephalus barbatus, dorsal and ventral views of skull, 137 mm SL, Singapore 175

126. Dorsal view of branchial arches and lateral view of hyoid arch and urohyal of: Alutera heudelotii, 114 mm SL, Florida, and Psilocephalus barbatus, 139 mm SL, Singapore 176

127. Medial views of upper and lower jaws of: A, Alutera heudelotii, 114 mm SL, Florida; B, Monacanthus

ciliatus, 51.3 mm SL, Colombia; C, Psilocephalus barbatus, 137 mm SL, Singapore; D, Amanses scopas,

167 mm SL, Saipan;E, Acanthaluteres spilomelanurus, 63.1 mmSL, Australia 177

128. Hypothesized phylogenetic relationships of the genera of Monacanthidae 178

129. Typical body form in the Recent Aracanidae: Aracana aurita 185 Range of diversity in body form and external features of representative aracanid genera:

130. Strophiurichthys inermis and S. robustus 186

131. Aracana aurita 187

132. Anoplocapros amygdaloides 187

133. Capropygia unistriata 187

134. Caprichthys gymnura 187 Kentrocapros aculeatus:

135. lateral view of entire specimen, 90.0 mm SL, Japan 196

136. lateral view of head, 90.0 mm SL, Japan 197

137. dorsal and ventral views of skull, 90.7 mm SL, Japan 197

138. posterior views of skull and orbit, 90.7 mm SL, Japan 198

139. dorsal view of branchial arches, lateral view of hyoid arch and urohyal, 90.7 mm SL, Japan 199

140. Strop/iiunc/jf/j.vs ro6usfus, lateral view of entire specimen, 150 mm SL, Australia 200

141. Aracana aunta, lateral view of entire specimen, 87.3 mm SL, Tasmania 201

142. Aracana omafa, lateral view of entire specimen, 70.5 mm SL, Australia 202

143. Lateral views of heads of typical aracanids: Strophiurichthys robustus, 150 mm SL, Australia, and

Aracana aurita, 87.3 mm SL, Tasmania 203

144. Ventral views of the two types of configuration of the ventral surface of the vertically expanded anterior portion of the parasphenoid: A, Caprichthys gymnura, 74.1 mm SL, Australia; B, AracarM aurita, 87.3 mm SL, Tasmania 203

145. Proaracana dubia: lateral view of entire specimen; composite based on three specimens, including the

holotype, 31.4-54.5 mm SL, all specimens from the Eocene of Monte Bolca, Italy 204

146. Hypothesized phylogenetic relationships ofthe genera of Aracanidae 205

147. Typical body form in the Recent Ostraciidae: Ostracion lentiginosum 210

148. Acant/iostracionQuadricomis: external features 211 Acanthostracion quadricornis, composite based on several specimens, 58.2-350 mm SL, Gulf of Mexico

and Caribbean:

149. lateral view of entire specimen 221
150. lateral view of head 222

151. dorsal and ventral views of skull 223

152. posterior views of skull and orbit 224

153. lateral and medial views of palatopteroquadrate region 224

154. Acanthostracion quadricornis, 77.7 mm SL, Florida: lateral view of occipital region of skull and the fused firstfiveabdominal vertebrae; posterior view of fused first five abdominal vertebrae 224 Acanthostracion quadricornis, composite based on several specimens, 58.2-350 mm SL, Gulf of Mexico and Caribbean:

155. medial and lateral views of pectoral girdle 225

156. ventral views of vertebral column from the fused first five abdominal vertebrae to the fourth caudal

vertebra and of the basal pterygiophores of the anal fin 225

157. dorsal view of branchial arches; lateral view of hyoid arch; lateral and dorsal views of urohyal 226

158. lateral view of caudal fin supporting structures 226

External features of other representative ostraciid genera:

159. A, Rhinesomus bicaudalis, B and C, R. triqueter 227

160. Lactophrys trigonus 227

161. Lactoria fornasinii 227

162. Tetrosomus gibbosus 227

163. Ostracion lentiginosum 227

164. Rhynchostracion nasus and R. rhinorhynchus 227 Number of teeth in upper and lower jaws in relation to standard length and the relatively negligible in- crease in number of teeth with increasing standard length at sizes greater than about 40 mm SL:

165. Lactophrys trigonus, Rhinesomus triqueter, R. bicaudalis 228

166. Ostracion tuberculatus, O. lentiginosum, Acanthostracion quadricornis, A. polygonius 229

167. /?/imesomustn(7ue(er, lateral view of entire specimen, 134 mm SL, Colombia 230

168. Lactona cornuta, lateral view of entire specimen, 104 mm SL, Philippines 231

169. Tetrosomus concatenatus, lateral view of entire specimen, 43.4 mm SL, Thailand 232

170. Os(rac(on(Li6ercu/a(us, lateral view of entire specimen, 54.5 mm SL, Aldabra Atoll 233

171. Rhinesomus triqueter, lateral view of head, 134 mm SL, Colombia 234

172. Ostracion fu6ercu/atus, lateral view of head, 54.5 mm SL, Aldabra Atoll 234

173. Tetrosomus concaferiatus, lateral view of head, 43.4 mm SL, Thailand 235

174. Lactoria cornuta, ventral view of skull, 88.2 mm SL, Philippines 235

175. Lactoria fornasinii, posterior view of orbit, 65.2 mm SL, Hawaii 236

176. Rhynchostracion rhinorhynchus: ventral and dorsal views of skull, 88.2 mm SL, Java 237

177. Lactoria cornuta, dorsal view of branchial arches; lateral view of hyoid arch and urohyal; 88.2 mm SL,

Philippines 238

178. Hypothesized phylogenetic relationships ofthe genera of Ostraciidae 239

179. Eolactoria sorbinii: lateral view of holotype, 15.5 mm SL, Eocene of Monte Bolca, Italy 242

180. Body form in the only known Recent species of Triodontidae: Triodon macropterus 243 Triodon macropterus:

181. external features 244

182. lateral view of entire specimen, 391 mm SL, Philippines 255

183. lateral view of head, 391 mm SL, Philippines 256

184. dorsalandlateral views of skull, 391 mm SL, Philippines 256

185. posterior views ofskull and orbit, 391 mm SL, Philippines 257

186. dorsal view of branchial arches; lateral view of hyoid arch; dorsal and lateral views of urohyal; 391 mm

SL, Philippines 257

187. lateral view of pectoral girdle, 391 mm SL, Philippines 258

188. lateral view of scapula and first actinost in representatives of all superfamilies 258

189. lateral views of alternate pleural ribs and their epipleurals; dorsal view of lower jaw; 391 mm SL, Phil- ippines 259

190. lateral and dorsal views of rudimentary spiny dorsal fin and its basal pterygiophores, 463 mm SL, Japan 259

191. ventral, dorsal, and lateral views of pelvis, 391 mm SL, Philippines 259

192. lateralviewofcaudalfinsupportingstructures, 391 mm SL, Philippines 260

193. Range of diversity in body form in the Recent Tetraodontidae: A, Lagocephalus spadiceus, B, Xenopterusnaritus;C, Amblyrhynchotes piosae; andD, Canthigaster rostrata 264

194. Lagocephalus laeuigatus, with L. lunaris and L. sc/erafus for comparison: external features 266
Lagocephalus laevigatas, composite based on several specimens, 61.4-166 mm SL, Gulf of Mexico:

195. lateral view of entire specimen 275

196. lateral view of head 276

197. dorsal and ventral views of skull 276

198. posterior view of skull; lateral and posterior views of first abdominal vertebra; posterior view of

orbit 277

199. dorsal view of branchial arches and lateral and medial views of hyoid arch 278

200. lateral view of pectoral girdle 278

201. lateral view of caudal fin supporting structures 279

202. Canthigasterrostrata, with C. ualentini and two renditions of C. amboinensis: external features 279

Canthigaster rostrata, composite based on several specimens, 55.2-96.5 mm SL, Texas:

203. lateral view of entire specimen 286

204. lateral view of head 287

205. dorsal and ventral views of skull 288

206. posterior view of skull; lateral and posterior views of first abdominal vertebra; posterior view of orbit 288

207. dorsal view of branchial arches; lateral and medial views of hyoid arch 289

208. lateral view of pectoral girdle 290

209. lateral view of caudal fin supporting structures 290

210. External features of other representative tetraodontid genera: A, Sphoeroides nephelus; B, S. testudi- neus; C, S. dorsalis; D, S. lobatus; E, S. pachygaster 291

211. Nasal organs and olfactory lamellae of representative species of Sphoeroides and Lagocephalus: A, Sphoeroides trichocephalus; B, S. spengleri; C, S. maculatus; D, Lagocephalus spadiceus; E, L. lago- cephalus; F, L. inermis 292

External features of other representative tetraodontid genera:

212. Guentheridia formosa 292

213. Colomesus psittacus 292

214. A, Amblyrhynchotes piosae; B, A. honckenii; C, A. richei 293

215. Torquigener pleurostictus and T. hamiltoni 293

216. Fugu vermicularis 293

217. Arothron armilla and A. immaculatus 294

218. A, Tetraodon miurus; B, T. lineatus; C, T. kretamensis; and D, T. schoutedeni 294

219. Ephippionguttifer of decreasing sizes (325, 232, and 101 mm SL) 295

220. Photographic detail of interdigitated scale plates from lower side of body of Ephippion guttifer, 325 mm SL 295 External features of other representative tetraodontid genera:

221. Chelonodon patoca and C. fluviatilis 295

222. Monotreta palembangensis and M. leiurus 296

223. Chonerhinos modestus 296

224. Xenopterus naritus 296

225. Carinotetraodon lorteti 297

226. Sphoeroides macu/atus, lateral viewof entire specimen, 97.5 mm SL, Virginia 299

227. Sp/ioeroides pachygaster, lateral view of entire specimen, 80.6 mm SL, Nigeria 300

228. Guent/iendia/ormosa, lateral view of entire specimen, 175 mm SL, Panama (Pacific) 300

229. Co/omesuspsjUacus, lateral view of entire specimen, 178 mm SL, Surinam 301

230. Amftiyr/iync/ioteshoncfeemi, lateral view of entire specimen, 70.7 mm SL, India 301

231. Amb/yr/iynchoiesric/iei, lateral view of entire specimen, 59.4 mm SL, New Zealand 302

232. Amb/yr/iynchotes piosae, lateral viewof entire specimen, 33.8 mm SL, Australia 302

233. Fu^u c/irysops, lateral view of entire specimen, 98.6 mm SL, Japan 303

234. Fugu o6/orj^us, lateral view of entire specimen, 46.2 mm SL, India 303

235. i4ro(/iroMs«e//atus, lateral view of entire specimen, 292 mm SL, India 304

236. Arot/iron armi/te, lateral view of entire specimen, 61.3 mm SL, Australia 305

237. Tetraodofimbu, lateral view of entire specimen, 47.7 mm SL, Congo 306

238. Ephippion guttifer, lateral view of entire specimen, 108 mm SL, Guinea 306

239. Che/onodon/ZuDJah/is, lateral view of entire specimen, 84.7 mm SL, Thailand 307

240. Monotreta leiurus, lateral view of entire specimen, 61.5 mm SL, Thailand 308

241. Choner/iinos modestus, lateral view of entire specimen, 31.0 mm SL, Borneo 308

242. Xenopterus mzn'tus, lateral view of entire specimen, 143 mm SL, Bay of Bengal 309

243. Carmotetraodon/orteti, lateral view of entire specimen, 35.9 mm SL, locality unknown 310

244. Cant/iigaster amboinerasi's, lateral view of entire specimen, 80.3 mm SL, Hawaii 311
245. Sphoeroides maculatus, lateral view of head, 97.5 mm SL, Virginia 313

246. Co/omesuspsiffacus, lateral view of head, 178 mm SL, Surinam 314

247. /lm6/yr/ivnc/T0fesric/iej, lateral view of head, 59.4 mm SL, New Zealand 314

248. Fugu chrysops, lateral view of head, 98.6 mm SL, Japan 315

249. Fugu oblongus, lateral view of head, 46.2 mm SL, India 315

250. Arothron stellatus, lateral view of head, 292 mm SL, India 316

251. Tetraodon mbu, lateral view of head, 47.7 mm SL, Congo 316

252. C/ie/onodon/Zuuiafi'/is, lateral view of head, 84.7 mm SL, Thailand 317

253. Monotreta leiurus, lateral view of head, 61.5 mm SL, Thailand 317

254. C/ioner/imosmodestus, lateral view of head, 31.0 mm SL, Borneo 318

2.55. Xenopferus aarif us, lateral view of head, 143 mm SL, Bay of Bengal 318

256. Carmofetraodofi /ortett, lateral view of head, 35.9 mm SL, locality unknown 319

Dorsal views of skulls: 257. Sphoeroides maculatus, 12.4-201 mm SL, New Jersey and Virginia 320

258. A, Sphoeroides dorsalis, 155 mm SL, Florida; B, S. nephelus, 128 mm SL, Bahamas; C, S. lobatus, 67.5 mm SL, Panama (Pacific) 321

259. A, Sphoeroides angusticeps, 172 mm SL, Galapagos; B, S. spengleri, 92.8 mm SL, Nicaragua; C, S. maculatus, 179 mm SL, Virginia 322

260. A, Sphoeroides greeleyi, 60.8 mm SL, locality unknown; B, S. trichocephalus, 57.1 mm SL, Panama

(Pacific); C, S. pachygaster, 117 mm SL, Mozambique 323

261. Sphoeroides testudineus, 68.5 mm SL, Venezuela, and S. annulatus, 174 mm SL, locality unknown . . . 324

262. Guentheridia formosa, 175 mm SL, Panama (Pacific), and Colomesus psittacus, 179 mm SL, Suri- nam 325

263. A, Lagocephalus inermis, 52.2 mm SL, Bay of Bengal; B, L. scleratus, 80.9 mm SL, Philippines; C,

L. lunaris, 62.3 mm SL, Bay of Bengal 326

264. Lagocephalus spadiceus, 98.2 mm SL, Mozambique, and L. lagocephalus, 214 mm SL, Malpelo Is- lands 327

265. /lm6/yr/iync/iotes/ioncfeem7, 97.4 mm SL, Mozambique, and A. n'c/iei, 59.4 mm SL, New Zealand .... 328

266. Torquigener pleurogramma, 113 mm SL, Australia, and Amblyrhynchotes piosae, 33.8 mm SL, Australia 329

267. Torqujgenerp/eurosfjctui, 87.1 mm SL, Australia, and Fugu c/irysops. 98.6 mm SL, Japan 330

268. Fugu oblongus, 46.2 mm SL, India, and F. rubripes, 151 mm SL, Japan 331

269. Aro</irofjste//a(us, ca. 420 mm SL, Seychelles, and A. armi7/a, 61 .3 mm SL, Australia 332

270. Tetraodon lineatus, 222 mm SL, French Equatorial Africa, and T. mbu, 47.7 mm SL, Congo 333

271. Ephippionguttifer, 101 mm SL, Guinea 334

272. Chelonodon patoca, 70.6 mm SL, New Guinea, and C. fluviatilis, 84.7 mm SL, Thailand 335

273. Monotreta gularis, 46.8 mm SL, Burma, and M. leiurus, 61.5 mm SL, Thailand 336

274. C/ioner/imosmodestus, 54.5 mm SL, Borneo, and Xenopfems narjtus, 143 mm SL, Bay of Bengal .... 337

275. Carinotetraodon lorteti, 33.1 mm SL, locality unknown 338

276. Ventral views of skulls of: Sphoeroides maculatus, 179 mm SL, Virginia, and Arothron stellatus, ca. 420 mm SL, Seychelles 339

277. Dorsal views of branchial arches and lateral views of hyoid arches of: Xenopterus naritus, 108 mm SL, Bayof Bengal, and Arot^onmgropunctatus, 56.8 mm SL, Solomon Islands 339

278. Hypothesized phylogenetic relationships ofthe genera of Tetraodontidae 341

279. Range ofdiversity in body form in the Diodontidae: Diodonholocanthus and Chilomycterusschoepfi . . 343

280. Diodon holocanthus, with Chilomycterus schoepfi for comparison: external features 344 Diodon holocanthus, composite based on several specimens, 12.3-124 mm SL, Gulf of Mexico and Carib- bean:

281. lateral view of entire specimen 352

282. lateral view of head 353

283. dorsal and ventral views of skull 354

284. posterior view of skull; lateral and posterior views of first abdominal vertebra; posterior view of orbit; dorsal view of lower jaw 355

285. dorsal view of branchial arches; lateral and medial views of hyoid arch 356

286. lateral view of pectoral girdle 357

287. lateral view of caudal fin supporting structures 357

288. Lateral view of entire specimen of another representative diodontid genus: Chilomycterus schoepfi,

60.1 mm SL, Louisiana 359

Dorsal views of skulls: 289. Chilomycterus schoepfi, 60.1 mm SL, Louisiana, and C. affinis, 310 mm SL, Galapagos 360
290. Diodon jacuUferus, 53A mmSh, AuatialiA, and Chilomycterus orbicularis, 12.9 mmSL, Somalia .... 360

291. Dicotylichthys punctulatus, 226 mm SL, Australia 361

292. Chilomycterus schoepfi: dorsal view of branchial arches and lateral view of hyoid arch, 168 mm SL,

Florida 361

293. Nasal apparatuses of representative diodontids: A, Chilomycterus mauretanicus; B, C. orbicularis; C,

C. schoepfi; D, C. antennatus; E, C. reticulatus; F, C. atinga; G, Diodon hystrix; H, D. holocanthus; I, D. jaculiferus; J, Dicotylichthys punctulatus; K, D. nicthemerus 361

294. Ventral views of upper jaws to show trituration tooth plates: A, Chilomycterus orbicularis, 77.0 mm SL, Somalia, and 158 mm SL, Philippines; B, C. schoepfi, 62.5 mm SL, Texas, and 168 mm SL, Florida .... 362

295. Chilomycterus schoepfi: lateral view of upper jaw; cross section through middle of one of the individual

flattened disklike trituration teeth; outline of about one-half of a trituration tooth; 168 mm SL, Flor- ida 362

Cross sections of upper and lower jaws just to one side of the midline:

296. Diodon hystrix, 88.3 mm SL, 228 mm SL, 505 mm SL 363

297. Diodon holocanthus, 63.4 mm SL, 122 mm SL, 183 mm SL, 375 mm SL 364

298. Chilomycterus schoepfi, 97.6 mm SL, 166 mm SL 365

299. Chilomycterus antillarum, 116 mm SL 365

300. Chilomycterus atinga, 173 mm SL 365

301. Chilomycterus mauretanicus, 92.2 mm SL 366

302. Chart showing the increased number of trituration plates in the upper jaw in Diodon holocanthus, D.

hystrix, Chilomycterus schoepfi, C. mauretanicus, C. atinga, C. antillarum, and C. reticulatus 366

303. Hypothesized phylogenetic relationships of the genera of Diodontidae 367

304. Rangeofdiversity in body fnrmintheMolidae: Mola mola and Ramania laevis 368

305. Mola mola: external features 369 Mola mola, composite based on two specimens, 306 and 310 mm SL, California: 306. lateral view of entire speciinen 378

307. lateral view of head 379

308. dorsal and ventral views of skull 380

309. posterior view of skull; lateral and posterior views of first abdominal vertebra; posterior view of orbit; dorsal viewof lower jaw 381

310. dorsal viewof branchial arches; lateral viewof hyoid arch 382

311. lateral view of pectoral girdle 382

312. lateral view of pseudocaudal fin supporting structures 383 External features of other representative molid genera:

313. Masturus lanceolatus 383

314. Romania laevis 383

315. Masfurns /anceo/afus, lateral view of entire specimen, 127 mm SL, Florida 385

316. /Tanzania /aei'is, lateral viewof entire specimen, 65.1 mm SL, Hawaii 386

317. Masturus /anceo/afus, ventral and dorsal views of skull, 127 mm SL, Florida 387

318. Kanzania /aei;js, ventral and dorsal views of skall, 65.1 mm SL, Hawaii 388

319. Masturus lanceolatus, lateral viewof head, 127 mm SL, Florida 388

320. Ramania laevis, lateral viewof head, 65.1 mm SL, Hawaii 388

321. Dorsal views of branchial arches and lateral views of hyoid arches: Ramania laeuis, 66.9 mm SL, Hawaii, and Masturus lanceolatus, 127 mm SL, Florida 389

322. Masturus lanceolatus: dorsal viewof lower jaw, 127 mm SL, Florida 389

323. Ramania laevis: dorsal view of lower jaw and ventral view of upper jaw, 493 mm SL, Hawaii; dorsal view

of lower jaw, 65.1 mm SL, Hawaii 389

324. Ramania laevis: diagrammatic representation of the relationships between the basal pterygiophores of the dorsal, anal, and pseudocaudal fins and the neural and haemal spines of the supporting vertebrae;

65.1 mm SL, Hawaii 390

325. Ramania laevis: scales from upper middle region of body; 493 mm SL, Hawaii 390

326. Hypothesized phylogenetic relationships of the genera of Molidae 392

Tables

1. Characteristics ofthe hyoid and branchial arches in families of Tetraodontiformes 413

2. Total number of vertebrae and vertebral formulas of Recent plectognath fishes examined as radiographed and as cleared and stained specimens 414

3. Numbers of teeth in the upper and lower jaws of ostracioids 420

Osteology, Phylogeny, and Higher Classification

of the Fishes of the

Order Pleetognathi (Tetraodontiformes)^

JAMES C. TYLER'

ABSTRACT

The osteologj- of over 160 species of fossil and Recent plectognath or tetraodontiform fishes is described and illustrated in relation to the supposed phylogeny and proposed higher classiflcation (subfamilial to ordinal levels) of this group of approximately 320 Recent species of primarily tropical and temperate forms of the Atlantic. Pacific, and Indian oceans. The history of the classification and

of the previous work on the osteology of the order is reviewed, while one new species (^ Acanthopleurus

collettei, Oligocene of Canton Glarus. Switzerland) and one new genus {lEotetraodon, Eocene of Monte Bolca. Italy) are described. Comparative inclusive and exclusive definitions are given for all higher categories based on both external and internal anatomical features. The Order Pleetognathi

(Tetraodontiformes) is divided into two suborders, the Sclerodermi or Balistoidei and the Gymnodontes or Tetraodontoidei, with a variety of other infraordinal and superfamilial categories, and 10 families, with subfamilial groupings in 4 of the latter. INTRODUCTION

Preface

The Pleetognathi are widely, but not unanimously,

recognized as one of the major orders or phyletic lines of teleostean fishes derived of perciform ancestors. The

primary reason that there is any doubt concerning the

naturalness of the Pleetognathi, regardless at what tax- onomic level it is recognized, is that it is a highly diversified group for which adequate definitions have not yet been given either for it as a whole or for most of its subdivisions. Until there appears and is accepted a consistent and systematic general osteological survey and

comparison of the basic types of organization found among the fossil and Recent species of plectognaths, both generalized and highly modified, it will be impossible to state without reasonable refutation that they are

all closely related, and more similar to one another than

to any other group of fishes. The aims of the present monograph are: first, to anatomically define, especially with osteologically based

characters, the higher categories in the classification of the plectognaths proposed here, these categories being from the subfamilial to ordinal levels; and second, to inContribution No. 77-25M from the Southeast Fisheries Center Miami

Laboratory, Miami, Fla. 'Southeast Fisheries Center Miami Laboratory, National Marine Fisheries Service, NOAA, Miami, FL 33149, and Research Associate, Depart- ment of Ichthyology, American Museum of Natural History, New York, NY 10024; present address; Office of Marine Mammals and Endangered , Species, National Marine Fisheries Service, NOAA, 3300 Whitehaven

Street, N.W., Washington, DC 20235.

terpret the phylogenetic relationships between these

divisions and most genera of the fossil and Recent Pleetognathi, dating back to the upper portion of the lower Eocene, approximately 60 million years ago. This is done by pointing out, as much by illustrations as by written descriptions, the many common os- teological features of numerous representatives of each of the families of plectognaths, including both relatively generalized and specialized species when available. The

totality of these characteristics of the fossil and Recent

species demonstrates beyond question the distinc- tiveness and phylogenetic naturalness of the plectognath

fishes, while at the same time providing the bases for the

detailed comparative diagnoses given here for the tax- onomic subdivisions of the Pleetognathi. As classified here, the Order Pleetognathi (or Tetraodontiformes), comprising today about 320 species

of mostly shallow-water, cireumtropical, and subtropical marine forms, is divided into two suborders (Sclerodermi or Balistoidei and Gymnodontes or Tetraodontoidei), a variety of categories from infra- orders to superfamilies, and into 10 families, in 4 of which subfamilies are recognized. The Pleetognathi are much more diversified than the great majority of fish groups of a comparable number of species. Relative to its comparatively few species, mostly marine, the Pleetog- nathi are as highly diversified as that prime example of

diversity among fishes, the speciose freshwater characids

of South America and Africa. Just as interesting as the plectognath's diversity itself.
is an analysis of the evolutionary mechanism leading to

it. This presents a strikingly clear case of intraordinal evolution primarily through the processes of reduction,

simplification, and loss of elements, especially of the bony parts. Reductive tendencies in the evolution of

vertebrates, including many groups of fishes, are not un- common (Myers 1958), and the reductions that have

taken place in plectognaths are of especial interest only because of the extreme exaggeration of the tendency

in this order. The reductive trend in the evolution of plectognaths obviously is not absolute, and certain morphological units in circumscribed groups show an

opposite tendency, e.g., the stomach and complex musculature of tetraodontoids, the pectoral girdle of ostracoids, the scales in nearly all groups except a few tetra- odontids, etc. The main point, however, is that the generalized members of the order, the triacanthoids, possess only slightly

less than the percoid complement of bones, but many

bones have become reduced or simplified, fused with

others, or entirely lost in what appear to be clear evolutionary lines derived from these basal plectog- naths. This is especially evident in the: branchial apparatus; caudal, dorsal, and anal fin supporting structures; dorsal fin spines; pelvic fin and girdle; jaws and

teeth; and myodome. The plectognaths are also of biological interest because

of their supposed position at one of the major end lines of modern teleost radiation and because of their great

diversification in structure, size, behavior, way of life, and habitat (Tyler 1965c). They range from 22 mm and

30 g to 2 m and 1,000 kg in adult length and weight, from

relatively normal shapes to strangely specialized forms

with long tubular snouts or aborted caudal regions, from

scaleless to heavily armored, from nearly toothless to

equipped with massive crushing beaks, from drably

colored to gaudy, from palatable to poisonous flesh, etc., and with comparable contrariety in behavior, habits, and

habitats. They include the spikefishes, triplespines, trig- gerfishes, filefishes, boxfishes, trunkfishes, pursefishes,

pufferfishes, porcupinefishes, and giant ocean sunfishes. The plectognaths are of some commercial interest

directly, for the dried skins or encasements of the weirder

forms are sold as curios, while a few species are sold for hu- man consumption, such as tetraodontids, called sea squabs on the east coast of the United States and fugu in Japan, but

of greater worth indirectly — the young of many plectog- nath species are important forage for such popular large oceanic fishes as dolphins, tunas, and billfishes. The Plectognathi are thought to have been derived from a percoid ancestry related to the same line which

gave rise to the acanthuroids (the surgeonfishes and their

allies) in the late Cretaceous, but the evidence of this hypothesized relationship is not yet conclusive (Tyler

1968, 1970c). The osteology of the fossil and Recent

acanthuroids is not well known, but with the osteologj' of the plectognaths being made better known here, it will be

easier to search among the acanthuroids for a group which shows a preplectognath type of organization and

which may be related to the speculated ancestral stock common to the two groups. Because the plectognaths are often of exotic form and

occur in European waters, even though their center of

diversification is the Indo-Pacific, a few species were

described by early naturalists from Aristotle and Pliny to Linnaeus. But some species still remain to be described, many others are inadequately known, and much confusion remains about the systematics of the group, even

at the familial level.

Methods

The majority of the specimens of the Recent species studied for this monograph were prepared by potassium

hydroxide clearing, alizarin staining, and glycerin preser- vation, prior to the advent of techniques using trypsin. A

few specimens were prepared by maceration as dry or alcohol wet whole skeletons, or parts thereof, while

limited dissections were made on alcohol - preserved whole materials. For fossil species, only superficial sur- face preparation with chipping and weak acid washes was employed. A list of the species examined, along with the numbers of specimens and their sizes, general localities, and

catalogue (or other identifying) numbers of their repositories, appears toward the end of this work. Length of specimens is always standard length (SL),

unless otherwise noted, taken from the anteriormost middle point of the upper jaw (often from the tip of the exposed upper teeth) to the middle of the line of flexure

at the caudal fin base, and measured and recorded with a

needlepoint dial caliper to the nearest 10th of a millimeter (mm), but with lengths given here of over 100 mm

rounded off to the nearest mm (0.5 and above to the next

highest integer). The survey of the osteology of the order was hindered by the poor showing of internal features in several fossil forms, by the relative unavailability of specimens for clearing and staining of about one-fifth of the described

species currently considered valid, by a lack of time and

purpose to describe and illustrate each available species

(especially in genera with large numbers of osteologically similar forms), and by the demands of space conser- vation and publication costs. It is felt, however, that the

species selected for osteological inclusion (167 studied, and 115 illustrated, for one skeletal region or another, of the approximately 320 Recent species, and nearly all of the fossil forms) adequately cover the anatomical diversity of the group, and almost always cover the entire range of external and osteological differences of the more

highly modified as well as more normal representatives of each family. I find it difficult to believe that

there is a missing link or living relic among those Recent and fossil plectognaths not examined for this work which
would materially change the concepts of the phylogeny and classification presented here. For each of the 10 families treated here, one relatively generalized species is described in detail and extensively

illustrated, with other species as appropriate described and illustrated less fully, except in the Tetraodontidae,

with two species representative of the two subfamilies

that have often been considered as separate families being given the fuller descriptive and illustrative treat- ment to aid in comparisons of their osteological distinctiveness. Line drawings show the most diagnostically important or anatomically interesting external features

of representatives of each group.

Lateral view illustrations of the entire skeleton are usually supplemented by other views of various parts of the skeleton showing features of particular phylogenetic

or morphological interest. Statements concerning the numbers of such serial elements as basal pterygiophores, epipleurals, neural and haemal spines, epurals, and hypurals are based

mostly on cleared and stained specimens and not on

radiographs, because all of the members of such series of these elements usually are not clearly defined in radio- graphs due to the often thickened nature of the scales. Vertebral counts are based on both cleared and stained specimens and radiographs, except for those of diodontids in which radiographs of the vertebral column are usually undeciferable because of the massive roots of the

skin spines. The lateral view illustrations of entire skeletons and of most of the skeletal parts were prepared by photo- graphing the skeleton or its parts submerged in a gly- cerin solution. The 35 mm negatives were projected and

outline drawings showing as much detail as possible made, of about 40 to 50 cm length in the case of entire

skeletons. Details were filled in by examination through

a dissecting microscope of the photographed skeleton or

part. The completed pencil drawings were transferred by

ink tracing on paper, with contours and depth approxi- mately shown by varying intensities of stippling. While

the pencil drawings and ink tracings are all by the

author, the stippling is by a combination of the author and his illustrators listed in the Acknowledgments.

Photographed entire specimens and/or one or more additional specimens of the same species were partially disarticulated in order to prepare, if necessary, drawings

of selected parts or views of regions of diagnostic or morphological interest, as well as generally to examine the

skeleton and its parts in greater detail. A few of the simpler supplemental illustrations were made with the aid of proportional dividers rather than photography. Some of the drawings are composite, based on several specimens, and are so indicated. Fin rays usually are shown only partially and diagrammatically as an outline of the positions of the bases of the

rays, with, for the caudal fin, the unbranched rays in- dicated by solid bases and the branched rays by open

bases. Only the pelvic fin rays and uppermost pectoral

fin ray routinely were fully drawn. Epipleurals, especially if slender, usually are shown in solid black rather than

stipple. The finer details of the surface sculpturing of the bones usually is not shown, for, even though it is beautiful, it is exceedingly time consuming to accurately portray and normally is of little value to an understanding of the relationships of the species in question. The otoliths of the species treated here are not illus- trated, for they only rarely were intact and uncorroded enough in the cleared and stained study material to be

useful. The osteological descriptions of the species treated in greatest detail were written from microscopic reexamination of the skeletons or parts thereof, and corrections were made in the drawings whenever necessary. Corrections were frequent, for nothing brings to light the errors

in illustrations more quickly than having to verbally

describe the shapes of bones and, particularly, their ar- ticulations. The osteological terminology used here is conservative, and hopefully that most readily understandable by

the majority of ichthyologists. For the most part, it is that of Starks (1901), although such terms as ptero- sphenoid, ectopterygoid, first pharyngobranchial,

cleithrum, and scapula are substituted, respectively, for Starks alisphenoid, pterygoid, suspensory pharyngeal,

clavicle, and hypocoracoid. Certain names, such as

prefrontal rather than lateral ethmoid or dermethmoid,

are used in order to be deliberately topological and to avoid implications of the dermal versus endochondral

origin of the bone. Subsequent to the beginning of this monograph, and of the pervasive decisions on the names of bones to be employed in the text and illustrations, several

researchers have provided more precise and homologously correct terminologies for certain skeletal regions than

used here. It has not been possible for reasons of practicality to make the numerous desirable changes, es- pecially in labeling of the illustrations, that would be

necessitated by incorporating these changing ter- minologies into the present work. Examples of the more modem and accurate names for certain skeletal regions, such as the branchial arches and lower jaw, are found in the exemplary publications of Weitzman (e.g., 1967 et

seq.) and Nelson (e.g., 1969 et seq.). In describing the types of articulations between bones, purely descriptive phrases often are used, for the technical terminology is not standardized and it is sometimes more precise than my observations. Whenever an amount of cartilage observable under the dissecting microscope (ca. 30x ) is seen to intervene between the ar- ticular faces of two bones, these bones are said to ar- ticulate through cartilage. When bones have relatively smooth articular faces held to one another without the

intervention of cartilage, they are said to articulate by

fibrous tissue. A large number of bones £ire said to ar- ticulate with one another by interdigitation, and this simply means that the closely apposed surfaces of two

bones have their articulation strengthened by delicate to coarse emarginations of one bone fitting into similar in- dentations of the other bone. At its fullest development,

this interdigitation can be distinguished from fusion only
by attempting to disarticulate the bones after long maceration. When a bone is said to be cartilage filled along a particular edge, this refers to the presence of car- tilaginous material extending into the otherwise ossified substance of the bone so that an upper and a lower layer

of bone, separated by cartilage, are distinguishable at the edge of the bone. Such a condition, of course, is only possible in endochondral bones. As a general rule, the amount of interdigitation between bones increases with

increasing specimen size, while at the same time the amount of cartilage at the edges of endochondral bones

decreases. The suffix oideo is adopted for the names of infraor- dinal categories. Throughout the text, vernacular versions of the

classically based and more formal superfamilial,

familial, and subfamilial names, ending respectively in oidea, idae, and inae, are employed, with the last two

vowels dropped for adjectival usage and with these replaced by an "s" for nominative usage, so that superfamilies end in -oid or -oids (triacanthoid, balistoid, os- tracioid, triodontoid, tetraodontoid, moloid), families in

-id or -ids (triacanthodid, triacanthid, balistid, monacanthid, aracanid, ostraciid, triodontid, tetraodontid, diodontid, molid), and subfamilies in -in or -ins (spina- canthin, eoplectin, hollardiin, triacanthodin, protacanthodin, cryptobalistin, triacanthin, ostraciin, lactophrysin, tetraodontin, canthigasterin). The names of two of the familial categories, the Triacanthodidae and Triacanthidae, unfortunately are rather similar, and the distinc- tion between such terms as triacanthoid, triacanthodid, and triacanthid is a necessary mental excercise.

PROLOGUE

Synopsis of the Phylogeny of the Plectognathi The anatomical data on the fossil and Recent Plectog- nathi presented in this monograph indicate that the

family Triacanthodidae contains the most generalized

fossil and Recent species of the order, and that these

basal plectognaths gave rise on the one hand to the line leading to the triacanthids, their nearest relatives, and

through them to the balistoids and ostracioids, while, on

the other hand, and with even greater modification away

from the ancestral level of organization, the triacan- thodids gave rise to the triodontids, and through them to the tetraodontoids and molids. The triacanthodids and

their anatomically and phylogenetically closest derivative groups, the triacanthids, balistoids, and ostracioids, are here considered to represent the suborder Scleroder- mi or Balistoidei, while the other major line of plectog- nath radiation, that has diverged even further from the

ancestral triacanthodid type, comprising the triodontids, tetraodontoids and molids, is here considered to represent the suborder Gymnodontes or Tetraodontoidei. Two fossil forms of the basal triacanthoids from the Eocene are thought to be especially pertinent to the phylogeny of the plectognaths, for Protacanthodes forms a

strong link between the triacanthodids and the triacan- thids and thus to the other derived scleroderms

(balistoids and ostracioids), while Eoplectus is nearly a

perfect intermediary between the triacanthodids and the

triodontids, the most generalized of the gymnodonts, and

thus to the derived tetraodontoids and molids. More particularly, of the four subfamilies of Triacanthodidae recognized here, it is obvious that the Triacanthidae are derived from the HoUardiinae rather than

from the Triacanthodinae or the fossil Spinacanthinae and Eoplectinae because of similarities in the shapes and

positions of the bones in the rear of the skull and of the shape of the pelvis and because there is every reason to believe that the Spinacanthinae were evolutionary dead

ends without issue surviving today and that the Eoplectinae were ancestral to the triodontids and the other gymnodonts. The evolution of the Triacanthidae from the Triacan- thodidae was probably mediated through a form like Protacanthodes, the Eocene representative of the most

generalized subfamily of triacanthids. Of the other two

subfamilies of triacanthids, the triacanthins include all of the Recent species and obviously evolved from such

Oligocene forms as Acanthopleurus, while the aberrant cryptobalistins of the Oligocene were, like the

spinacanthin triacanthodids, failed evolutionary ex- periments that did not give rise to forms living today. The balistoids and ostracioids are reasoned to share a common ancestral line to the triacanthids in the Eocene, and it is unquestioned that the balistids gave rise to the monacanthids and that the aracanids are ancestral to the

ostraciids. Two subfamilial lines of evolution are evident

in the ostraciids. The recent discovery of the eoplectin triacanthodids, with a well-developed spiny dorsal fin, the best developed pelvic fin among plectognaths, and a generally triacanthodid appearance, but with a fully developed gymnodontlike crushing beak, tends to confirm that the triacanthodids gave rise to a line of triodontidlike forms which in turn were ancestral to the two main radiations

of the gymnodonts, the molids on the one hand and the

tetraodontids and diodontids on the other hand. The

tetraodontids show two subfamilial phyletic lines, the

tetraodontins for the vast majority of diversified forms,

related through Carinotetraodon to the canthigasterins.

In summary, it seems clear, especially in the light of our present knowledge of Protacanthodes and Eoplectus, as discussed by Tyler (1973b), that the basic diversification of the plectognaths was a relatively rapid event

of the lower Eocene. In the upper portion of the lower Eocene of Monte Bolca, Italy, alone, there are represen-
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tatives of most of the families of plectognaths (and nearly modern acanthurids as well). The triacanthodids are represented there by the Spinacanthinae, which

probably became extinct, and the Eoplectinae, which are

ancestral to the gymnodont families. The triacanthids, derived from the triacanthodids, are represented by the Protacanthodinae, in many ways intermediate between

the triacanthodids and triacanthids. The aracanids are represented by Proaracana, not much different from Recent genera, while the ostraciids, derived from the

aracanids, are also found in the Eocene beds of Monte

Bolca in the form of Eolactoria, again not much dif- ferent from Recent genera. Among these scleroderms.
only the balistids and the derivative monacanthids are not found in the Eocene. The balistids, of triacanthid

derivation, are first known from the Oligocene, with

genera rather similar to those alive today, while the monacanthids as yet have no known fossil record. The

fossil record of the gymnodonts is not as impressive for overall antiquity, quantity, or quality as that of the

scleroderms, with only the diodontids and, probably, the

tetraodontids known from the Eocene, again from Monte

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Bolca. Triodontids have been described from the Eocene

of Africa and Europe (not including Monte Bolca), but

only on the basis of jaws alone, with the dentaries fused

into a single piece and the premaxillaries separate. The

teeth in these jaws are small rounded units such as are found in Triodon and diodontids, but this is scarcely sufficient evidence of a fish of truly 7>iodon-like general

configuration in the Eocene. Molids are first known from

the Miocene.
Synopsis of the Higher Classification of the Plectognathi

Order Plectognathi Suborder Balistoidei (Sclerodermi)

Infraorder Triacanthoideo Superfamily Triacanthoidea Family Triacanthodidae: spikefishes Subfamily Spinacanthinae (Eocene) Subfamily Eoplectinae (Eocene) Subfamily HoUardiinae (Recent) Subfamily Triacanthodinae (Recent) Family Triacanthidae: triplespines Subfamily Protacanthodinae (Eocene) Subfamily Cryptobalistinae (Oligocene) Subfamily Triacanthinae (Oligocene to Recent)

Infraorder Balistoideo Superfamily Balistoidea Family Balistidae (Oligocene to Recent): triggerfishes Family Monacanthidae (Recent): filefishes Superfamily Ostracioidea Family Aracanidae (Eocene to Recent): boxfishes Family Ostraciidae (Eocene to Recent): trunkfishes Subfamily Ostraciinae Subfamily Lactophrysinae Suborder Tetraodontoidei (Gymnodontes)

Infraorder Triodontoideo Superfamily Triodontoidea Family Triodontidae (Eocene to Recent): pursefishes Infraorder Tetraodontoideo

Superfamily Tetraodontoidea Family Tetraodontidae (Eocene to Recent): pufferfishes Subfamily Tetraodontinae Subfamily Canthigasterinae Family Diodontidae (Eocene to Recent): porcupinefishes

Superfamily Moloidea Family Molidae (Miocene to Recent): giant ocean

sunfishes. Alternative arrangements of subordinal and lower groupings are obviously possible and perhaps equally appealing to some. One of these would be to recognize the triacanthodids as subordinally distinct from both of the two major lineages to which they gave rise, a suborder

Sclerodermi (Balistoidei), in this case comprising the

triacanthids, balistoids, and ostracioids but minus the triacanthodids, and a suborder Gymnodontes

(Tetraodontoidei), with the triodontids, tetraodontoids, and molids. Another would be to recognize both the triacanthodids and triacanthids as subordinally distinct from both the remainder of the suborder Sclerodermi (in this case only the balistoids and ostracioids) and the suborder Gymnodontes (as above). Or, as Winterbottom

(1974) has so ably suggested, a recognition of a suborder

for the triacanthodids and triacanthids as distinct from a suborder for all of the other plectognaths, with the latter divided into two superfamilies, one for the balistoids and

ostracioids (the remnants of the Sclerodermi) and one for the gymnodonts (as above) along with the Eocene

Eoplectus and its relatives.

It is felt here that the entire constellation of overall

similarities and differences in both generalized and

specialized features between the various species and

higher categories support the reasonableness of con- tinuing to divide the Plectognathi into two suborders: the Sclerodermi for the basal triacanthodids and their closely related triacanthids as well as the

balistoids and ostracioids derived from the latter, and

the Gymnodontes for the more modified tetraodontoids and molids linked together through the triodontids to the Eocene eoplectin triacanthodids.

Historical Review of the Classification of the Plectognathi

Since representatives of most of the major subgroups

of plectognaths occur in the Mediterranean and off the

Atlantic coast of Europe, they were familiar to the early Greeks and Romans. A rather long article could be

devoted to just the pre-Linnaean occidental knowledge of the plectognaths, for almost every naturalist who dealt with fishes, from Aristotle to Marcgrave, made promi- nent mention of various balistoids, ostracioids,

tetraodontoids, and molids (the similar oriental, primarily Chinese, history of the plectognaths cannot be

dealt with here). Passing over those nearly 2,000 years

that intervened between Aristotle and the person who is most often considered the founder of modem ich- thyology, Peter Artedi, only one example of the type of

classificatory scheme that preceded Artedi's work need

be cited.

In his "Historia Piscium," WiUughby (1686:22-25) divided "fishes" (including elasmobranchs and

cetaceans) into 11 major categories, one of which was the

Pinnis uentalibus carentes, containing the plectognaths, syngnathids, and swordfishes. Within any one of the 11 categories were described a

variable number of species, most of them based on the

literature of such previous naturalists as Clusius, Rondelet, Gesner, Marcgrave, Belon, Salviani, and Al- drovandi, but with a few supposedly new species also described. The types of fishes that occurred (Willughby

1686:143-164) in the "de Piscibus corpore contractiore vel

saltern non admodum lubrico, qui pinnis ventralibus

carent," or "Pinnis ventralibus carentes," were for the most part plectognaths. This section consisted of 14 chapters, each of which described either a single species
or a group of supposedly related species. For example, Chapter I (p. 143-148) was devoted to "De Orbe Pisce" and described 11 species in which the first word of the binomial or polynomial was, in all but two cases, Orbis. The two exceptions had the species name beginning with Orbibus or Histrici and are diodontids. One might ex- pect that all of the Orbis species would be tetraodontids

or diodontids and in fact they are, with a single exception: the Orbis Ranae rictu (p. 145, fig. 2 of pi. 19, after Clusius) is Cyclopterus lumpus. Another species, Orbis oblongus Testudinis capite (p. 147-148, fig. 3 of pi. 19, after Clusius) is probably a tetraodontoid, but the figure shows a creature whose front end reminds one of a fetal seal but whose hind end is fishlike. Chapters II (p. 148) and III (p. 148-149) described, respectively, Ostracion

Nili and Ostracion prior, both of which are ostraciids, as

is Pisces triangularis of Chapter IV (p. 149-150). Chapter V (p. 150-151) described Monoceros pisces, which is probably a monacanthid, while Chapter VI (p. 151-152) was devoted to the Mola of Salviani or Orthagoriscus

of Rondelet. Chapter VU (p. 152-156) described the

balistid Capriscus pesce Balestra, but an appendix to this chapter described three species of Orbes: a

tetraodontid, a diodontid, and an ostraciid. The remaining seven chapters described nonplectognaths, these being, to use only the "generic" term, Stromateus (a butterfish), Hippocampus (a seahorse), Acus (a pipefish), Acui (a syngnathid), Scolopax (Macrorhamphosus), and

Xiphias (a swordfish). The latter seven types have little,

if anything, in common with the plectognaths, making

for an odd mixture of forms within the "Pinnis ventralibus carentes," but it is more realistic to dwell on the

fact that by the 17th century the plectognaths were al- ready placed together in the same subgroup of fishes. In an appendix, written by Lister, to Willughby's

(1686) "Historia Piscium," an illustration of a shallow- water triacanthid was given, based on the Hoornvisch of the Dutch East Indies first described by Nieuhof (1682)

in his work on the fishes of Batavia. An account of

this species of triacanthid was not to reappear until Bleeker (1852b) formally described this first-mentioned

triacanthid as Triacanthus Nieuhofii, while in the in- terim the first triacanthid to be binomially described was

Batistes Biaculeatus Bloch 1786. By contrast, the deep- water triacanthodids were not described until Schlegel

(1850). With the advent of Artedi, the classification of fishes

in general as well as that of the plectognaths was placed on a much more refined basis, for the groupings of supposedly related forms were far superior to any that had

previously appeared. In his "Genera Piscium," Artedi

(1738) recognized five basic divisions within his Pisces. One of these, the Plagiuri, had the caudal fin horizontal and is the Cetacea, while the other four divisions (Malacopterygii, Acanthopterygii, Branchiostegi, and

Chondropterygii) had the caudal fin perpendicular and

are true fishes. The Branchiostegi contained the fol- lowing genera: Batistes, Ostracion, Cyctopterus, and

Lophius. The generic categories of Artedi are usually recognized today at the familial or ordinal levels. The name

Branchiostegi {branchio, gills, and stegein, to be

covered) implies that Batistes, Ostracion, Cyctopterus, and Loph'us should have the superficial similarity of the

gills being relatively well hidden from external view by

the constricted aperture of the branchial cavity. We now

know, of course, that the last two genera mentioned

above are neither closely related to one another nor to Batistes and Ostracion. Ostracion contained 22 species which represent not only the ostraciids but also the

tetraodontids, diodontids, and molids. It should be noted

that the Ostracion category was composed of species of extreme diversity in external appearance, which are

nevertheless closely related to one another. Moreover,

the group was not as heterogeneous as it might superficially seem to be, for within it the species were de- scribed successively in a manner which shows that Artedi had an insight into the relative closeness of relationship

of the various forms. Thus, the first 10 species are ostraciids, and the next 3 species are tetraodontids. All of the next seven species (nos. 14 to 20) are diodontids, with

the exception of species no. 17, which is the Orbis Ranae

rictu of Willughby and of Clusius, a cyclopterid. The

next to the last species (no. 21) is probably a tetraodontid, but since it was based on the poorly figured Orbis ob- tongus Testudinis capite of Willughby and of Clusius, one could scarcely have expected Artedi to have placed it with his other tetraodontids. The last species (no. 22) is the commonest (as an adult, at least) of the molids, Mola

mola. The Batistes group contains five balistoids and a macrorhamphosid (the only nonplectognath included).

In short, Artedi did justice to those plectognaths which

he had actually seen or which were reasonably described

in the literature, and the several errors were only the

result of occasionally being forced to rely solely on poor

descriptions by earlier naturalists. The plectognaths appeared in a somewhat different assemblage in Klein's (1742) "Historiae Piscium

Naturalis." Like previous workers since the time of

Aristotle, Klein included in his Pisces both cetaceans and fishes, separating them from one another on the

basis of possession of lungs or gills. Whereas Artedi's first dichotomous division of the true fishes was on the basis

of bone as opposed to cartilage in the skeleton, Klein's was on whether the gills were hidden or easily observed. Thus, the Branchiis Apertis contained a large array of

relatively normal fishes, such as Siturus, Acipenser,

Xiphias, Mastacembetus, Sotea, Tetragonopterus, etc. By contrast, the Branchiis Occultis contained a less plausible association of 15 genera, including elas- mobranchs and cyclostomes. The plectognaths were all included in Crayracion

(Klein 1742:17) and Capriscus (p. 23), which, along with Batrachus and Conger, supposedly had the following combination of characters: paired fins present; branchial cavity with a single aperture; gills placed

laterally and hidden from view. Klein's Batrachus is the same as Artedi's Lophius, while Artedi's Cyctopterus ap- peared as a part of Klein's Crayracion. The addition of a number of eels, as Conger, to a place of proximity with
the plectognaths and Lophius and the placement of all of these with the elasmobranchs and cyclostomes were major differences in the treatment of the plectognaths by

Artedi and Klein. Klein's Crayracion and Capriscus are more or less synonymous with, respectively, Artedi's Ostracion and Batistes. Both of Artedi's groups con- tained only plectognaths (except for Macrorhamphosus). but the same cannot be said of Klein's. The lat- ter described 32 species of Crayracion, of which most are

ostraciids, tetraodontids, diodontids, or molids, but

species 7 (p. 19) and 11 (p. 19) are Cyclopterus and

species 32 (p. 23) is a syngnathid. On the other hand, all 11 species of Klein's Capriscus are balistoids. In his "Museum Ichthyologicum," Gronovius (1754) followed precisely the classification adopted by Artedi, with Pisces containing the Plagiuri, Malacopterygii,

Acanthopterygii, Branchiostegi, and Chondropterygii. The Branchiostegi again contained four types: Balistes, Ostracion, Cyclopterus, and Lophius. Gronovius made

no innovations in the Balistes category; on the contrary, one of his species of Balistes appears to be Marcgrave's

antenneriid frogfish from Brazil. However, Gronovius did go a step beyond Artedi in his handling of the Ostracion

group. Gronovius divided his Ostracion into three sub- groups on the basis of body shape, thus: Corpore quadrangulo, with three ostraciids; Corpore triangutato, with

three more ostraciids; and Corpore cathetoplateo, uel rotundo. with two tetraodontids and a molid. Although

Gronovius' (1763) subsequent "Zoophylacium" is post- Linnaean chronologically, it is pre-Linnaean in its ter- minology. His Pisces were now divided into Plagiuri, Chondropterygii, Branchiostegi, and Branchiales, the

latter group being roughly equivalent to his previously used Malacopterygii and Acanthopterygii. Within these groups the species were segregated according to fin structure. Thus, his Branchiostegi were arranged as follows:

Pinnis Ventralibus nullis: Muraena, Gymnotus, Syngnathus, Ostracion. Pinnis Ventralibus spuriis: Balistes, Cyclopterus,

Cyclogaster. Pinnis Ventralibus veris praesentibus: Gonorynchus,

Cobitis, Uranoscopus, Lophius. New groups were added to the Artedian Branchiostegi, and, beyond that, Gronovius (1763) added a fur- ther subdivision to the Ostracion category. The Balistes category remained a simple descriptive list of a number

of balistoids and a macrorhamphosid. The four Ostracion subgroups that Gronovius recognized were: Corpore

quadrangulo, with four ostraciids; Corpore triangulato, with three more ostraciids; Sphaerico, uel oblongo- rotundo corpore, with two diodontids and one tetraodontid; Corpore cathetoplateo, with two tetraodontids and

two molids. When comparison is made between the

classification of the nonbalistoid plectognaths of Gronovius and that of Linnaeus, it is obvious that Gronovius simply incorporated into his Ostracion sub- groups a few of Linnaeus' ideas without an excess of

recision.

With the 10th edition of Linnaeus' (1758) "Systema

Naturae," a basic division of the plectognaths into four genera (Balistes, Ostracion, Tetraodon, Diodon) was

presented for the first time. Five groups of Pisces were

recognized by Linnaeus: Apodes, Jugulares, Thoracici, Abdominales, and Branchiostegi. The latter contained

the following genera: Mormyrus, Balistes, Ostracion, Tetraodon, Diodon, Centriscus, Syngnathus, and

Pegasus. But to the above Pisces must be added the fishes which

Linnaeus placed in the Amphibia Nantes, containing Petromyzon, Raja, Squalus, Chimaera. Lophius, and

Acipenser. Such a classification shows an eclectic approach to the systems of previous workers. The Branchiostegi of Artedi

is a much smaller group than that of Linnaeus, and the

only species that are common to the Branchiostegi of both are the plectognaths. Thus, Cyclopterus and

Lophius appeared in Artedi's Branchiostegi, but Lin- naeus placed Cyclopterus in the Thoracici and Lophius

in the Amphibia Nantes. Mormyrus, Centriscus, Syngnathus, and Pegasus of the Linnaean Branchiostegi are found among the Acanthopterygii and Malacopterygii of Artedi. In short, as far as the plectognaths are concerned, Linnaeus (1758) had followed Artedi's views, only adding generic names to the four plectognath sub- groups that Artedi had at least implicitly recognized. The Linnaean Balistes contained seven balistoids and a macrorhamphosid; Ostracion, nine ostraciids; Tetraodon

(spelled Tetrodon on p. 243 in the list of genera of Branchiostegi but Tetraodon on p. 332 where defined),

five tetraodontids and one molid; Diodon, seven diodontids. Linnaeus thus recognized 29 plectognath species, only two more than Artedi had recognized 20 years

previously. Many of Klein's 43 species of Crayracion and

Capriscus were synonymized by Linnaeus, or dis- regarded as unrecognizable.

In the 12th edition of Linnaeus' (1766) "Systema

Naturae" a major change took place in the classification

of the plectognaths—Branchiostegi was eliminated. All

of the genera of the former Branchiostegi were placed in the Amphibia Nantes, except for Mormyrus, which was

placed in the Abdominales. The Amphibia Nantes then

consisted of an odd assortment of types: Petromyzon,

Raja, Squalus, Chimaera, Lophius, Balistes, Ostracion, Tetrodon, Diodon, Cyclopterus, Centriscus, Syngnathus, Acipenser, and Pegasus. The motive behind the placement of the plectognaths in the Amphibia Nantes

was the erroneous report sent to Linnaeus by Dr. Garden, a physician in Charleston, S.C, who informed Lin- naeus that Diodon possessed a lung. A combination of three anatomical peculiarities in Diodon probably led to the confusion, for Diodon not only has a distensible diverticulum of the oesophagus that can be filled with

either air or water (at the time of Linnaeus it was thought

to undergo inflation only by the intake of air), but the swim bladder is bilobed anteriorly and the well- developed kidneys are placed far forward. Linnaeus

wrote (1766:348) that "Garden in America habitant!,

petere, vellet dissecare Diodontis respirationis organa &
inquirere numne Pulmones haberent." It is possible that Garden mistook either the swim bladder, kidneys, or dis- tensible diverticulum of the oesophagus for lungs. Broussonet (1780:680) believed that it was the distensible diverticulum that had been misinterpreted, but Cuvier

(1817:146) thought that it was the kidney, and the particular source of Garden's error is impossible to identify. Severe as was the elimination of the Branchiostegi, the only significant change in the assemblage of species of plectognaths described was the synonymizing of several

of his previously numerous species of Diodon, so that

only two species of that genus were recognized. Among the 29 Linnaean species were representatives of the balistids, monacanthids, both subfamilies of ostraciids, the tetraodontin tetraodontids, diodontids, and

molids. As discussed in the preceding section on

Willughby, the triacanthids were known before 1758, even though Linnaeus did not recognized them, and they were not binomially described until Bloch (1786), while

triacanthodids were not described until Schlegel (1850). As discussed in the succeeding section on Cuvier, the aracanids and triodontids were not formally described

until well after Linnaeus, respectively by Shaw (1798) and Cuvier (1829), but see Tyler (1967) for a history of the impressionistic pre-Linnaean illustrations of TVt'o- don. Several names for canthigasterin tetraodontids were inadvertently listed by Linnaeus as synonyms for several species of tetraodontin tetraodontids (e.g., see Shipp 1974 for Lagocephalus) , but the first binomial

description of a canthigasterin was in a now mostly

forgotten publication by Paterson (1786), as Tetrodon

electricus, and the currently used specific name of one of the more common Indo-Pacific species of Canthigaster may have to be changed. Gmelin's 13th edition (1788) of the "Systema Naturae"

reestablished the Branchiostegi in the Pisces and entirely eliminated the Amphibia Nantes, while at the same time

the "Systema Naturae" introduced the Chrondropterygii. Fishes were thus all included in six categroies of

Pisces: the Apodes, Jugulares, Thoracici, Abdominales,

Branchiostegi, and Chondropterygii. This general classification was a distinct improve- ment over any of those in previous editions of the "Systema Naturae" and was largely the synthesis of Gmelin himself. Within the Branchiostegi the genera ap- peared in the following order: Mormyrus, Ostracion with 10 species of ostraciids, Tetrodon with 12 species of tetraodontids and 2 species of molids, Diodon with 6

species of diodontids and 1 species of molid, Syngnathus, Pegasus, Centriscus, Batistes with 18 species of balistoids, Macrorhamphosus, Cyclopterus, and

Lophius. Thus, the treatment of the individual genera of plectognaths was inferior to that of previous editions, for molids were placed in both Tetrodon and Diodon, while

Balistes was spatially separated from the other plectog- naths by the intervening Syngnathus, Pegasus, and

Centriscus. Even if this separation of Balistes was

deliberate, its significance, if any, is unknown. The classification adopted by Goiian (1770:94) in his "Historia Piscium" divided the Pisces into three main

groups, the Acanthopterygii, Malacopterygii, and

Branchiostegi, each with the same four subdivisions: the Apodes, Jugulares, Thoracici, and Abdominales. Such subdivisions of the three major categories have a deductive simplicity that is truly alluring, but, unfortunately, fishes are not constructed to fit into such

logical pigeonholes. The Acanthopterygii and Malacopterygii contained the expected genera, and the Branchiostegi sorted out to:

Apodes: Syngnathus, Balistes (with a footnote saying that certain Balistes have ventral fins and thus must be placed in the Abdominales), Ostracion, Tetraodon, Diodon.

Jugulares: Lophius.

Thoracici: Cyclopterus. Abdominales: Centriscus, Pegasus (and, according to the footnote, a few Balistes, which are not specifically named, but may imply Macrorhamphosus).

Only genera were described, but the species of Balistes

or of other plectognaths that would have to have been

placed in the Branchiostegi Abdominales are the triacanthoids, which had not yet been described binomially. The above treatment of the Branchiostegi is basically that of Gmelin's 13th edition of the "Systema Naturae,"

except that Mormyrus was placed by Goiian in the Malacopterygii Abdominales.

In Bonnaterre's (1788) "Tableau Encyclopedique," the plectognaths reverted to the cartilaginous fishes, for five classes were recognized: the Cartilagineux, Apodes,

Jugulares, Thoracici, and Abdominales. These five groups are those of the 12th edition of Linnaeus' (1766) "Systema Naturae," the only difference being the substitution of the term Cartilagneux for Amphibia Nantes. The Cartilagineux contained exactly the same genera as the Amphibia Nantes, differing only in that Petromyzon

was called Lampetra. The value of Bonnaterre's work to the study of plectognaths rests on the fact that of the 41

species described, the great majority were figured with some accuracy, and outline cross sections of the body

were given for many.

If fishes were ever to fit into a deductively logical scheme of classification, they were given a chance to do

so in Lacepede's (1798, 1800, 1802a, b, 1803) categories, as outlined in his "Histoire Naturelle," even more so than in Goiian's work. The "Classe des Pois- sons" was divided into the Sous-classe Poissons Cartilagineux and the Sous-classe Poissons Osseux. Each of these subclasses was split into the same four divisions, and each of these divisions was split into the same four

orders. Thus, there was a dichotomy followed by two successive sets of quadrichotomies, to give a total of 32

orders in eight sets of Apodes, Jugulaires, Thoracins, and Abdominaux (following Gouan). The balistoids were in the third order (Thoracins) of the second division of the
Poissons Cartilagineux, while the other plectognaths were in the first order (Apodes) of the fourth division, well separated from the balistoids. When one considers the "Poissons Cartilagineux" as a

whole, the plectognaths were associated with much the same genera as they were in Gmelin's 13th edition (1788)

of the "Systema Naturae." Again, just as in Gmelin,

Batistes was separated from the other plectognaths, although in a more definite manner. One innovation was

Lacepede's handling of the plectognath genera. His con- temporaries had accepted four genera {Balistes, Ostracion. Tetrodon, and Diodon) but Lacepede admitted six (Balistes, Ostracion, Tetrodon, Les Ovoides, Diodon, and Les Spheroides). It happened that his two new

genera were based on artifacts or misinformation and

thus lost their value, except for nomenclatural purposes. Les Ovoides (Lacepede 1798:520) was based on a damaged specimen described by Commerson which lacked dorsal, caudal, and anal fins. Lacepede had never seen the

single specimen used by Commerson but thought that it probably represented a new genus, and so named it. Les

Spheroides (Lacepede 1800:22) was likewise said to lack

dorsal, anal, and caudal fins. It was based on an unpublished figure by Plumier of the anterior view of the body

of what we know now as Sphoeroides spengleri. Lacepede

did somewhat better with his other genera, for each of these was divided into unnamed subgenera.

Balistes (Lacepede 1798:332) contained four subgenera; the first for those forms with more than one spine

in both the pelvic and first dorsal fins; the second for those with more than one spine in the pelvic fin but only one spine in the first dorsal fin; the third for those with

only one spine in the pelvic fin but more than one spine

in the first dorsal fin; the last for those with but a single spine in both the pelvic fin and first dorsal fin. The first subgenus should only contain triacanthoids, which by common definition are those plectognaths with

well-developed pelvic spines. Lacepede mistook the en- larged scales that occur in the midventral line of the ab- dominal region of many balistoids between the end of the

pelvis and the anus for pelvic fin spines. These scales strengthen the "abdominal fan" of those balistoids whose pelvis is especially movable around its anterior ar- ticulation with the pectoral girdle. The distal ends of the

enlarged scales are tapered into narrow shafts which

often project out through the skin on either side of the midventral line (see Monod 1959a), and it is not sur- prising that they should have been considered to be some kind of pelvic fin spines. Lacepede also observed

the thickened scales that encase the posterior end of the

pelvis and mostly obscure from view the modified fin-ray element of most balistoids, and understandably thought them also to be a pelvic fin spine, as had others before him and afterward (e.g., Garman 1891). For these reasons Lacepede's first subgenus contained not only the

single binomially described triacanthid then known but

also three balistids. His second subgenus contained a

single monacanthid, whose modified scales in the ab- dominal fan were again mistaken for pelvic fin spines. The third subgenus was by far the largest of his subgenera, containing numerous balistids and a few

monacanthids. The fourth subgenus contained two

monacanthids.

Intervening between the descriptions of Balistes and

the next group of plectognaths {Ostracion) were the

descriptions of Chimaera, Polyodon, and Acipenser. Ostracion (Lacepede 1798:441) was divided into four sub- genera on the basis of the four logical combination possibilities of the presence, or absence, of cuirass spines in the ocular region and of the presence, or absence, of cuirass spines in the caudal region. These categories are

superficial and have not withstood the test of time. Tetrodon (Lacepede 1798:474) had three subgenera, of which the first two were described as not having the body

particularly compressed and consisted of tetraodontids, while the third subgenus was said to have a compressed body and contained a single molid. Diodon (Lacepede

1800:1) had no subgenera and contained four diodontids

as well as two molids, one of which was the same species that also occurred in the third subgenus of Tetrodon. Lacepede's only subgeneric groups of lasting value were those of Balistes, which have since, at least in part, been elevated to familial rank. His contribution to the plectognaths was primarily the recognition of the fact that the Linnaean genera could, and should, be subdivided. His subgenera tended to be arbitrarily drawn

and factual errors pervaded his descriptions, but he began the trend of subdivision of the Linnaean categories

of plectognaths. Like that of Lacepede, the classification adopted by

Bloch and Schneider (1801) in their "Systema Ich- thyologiae" was deductively logical and equally artificial. Eleven classes of fishes were recognized on the

basis of the number of fins, i.e., Hendecapterygii (11 fins) to Monopterygii (1 fin). Each class was divided, on the

basis of pelvic fin position, into such orders as Apodes,

Jugulares, Thoracici, Abdominales, and Achiri ( =

without hands, but with reference to pelvic rather than

pectoral fins, and thus would seem to be equivalent to Apodes). The plectognath genera fell within the fol- lowing classes and orders (Bloch and Schneider 1801:Lm-LVni):

Classis VI: Hexapterygii [i.e., two dorsals, an anal, a caudal and two pectorals] Ordo Apodes: Balistes, Rynchobdella [a mastacembelid] Ordo Pinna Anali Carentes: Trachypterus, Gymnetrus [= Regalecus]

Classis VII: Pentapterygii [i.e., a dorsal, anal, caudal, and two pectorals] Ordo Apodes: Ophidium, Pomatias, Gnathobolus, Muraena, Stromateus, Ammodytes, Sternoptyx, Anarrhichas, Channa, Sternarchus, Ostracion, Tetrodon, Orthagoriscus, Diodon, Syngnathus.

This was the manner of listing in the index, but in the

text the Pentapterygii were placed in two orders (Bloch and Schneider 1801:484-516), Apodes for the genera from
Ophidium to Anarrhichas, Achiri for the genera Channa

to Syngnathus. Thus, Batistes, along with the mastacembelids, was one of the Apodes Hexapterygii,

while the other plectognaths, along with Channa and the

syngnathids, were Achiri Pentapterygii. Such a system

could scarcely be more artificial, but several new species were described and the use of Orthagoriscus for molids

set a generic usage to be followed for the next hundred

years. One of the widest separations of the balistoids from the

other plectognaths was that made by Rafinesque (1810)

in his "Indice d'lttiologia Siciliana." He recognized two

subclasses of fishes, the Pomniodi (branchial apparatus

with both an operculum and branchiostegal membrane)

and the Atelini (branchial apparatus incomplete). The

Sotto-Classe Pomniodi contained four divisions based on

pelvic fin position; Guigulari, Toracici, Abdominali, and

Apodi. Each of these four "Divisione" was subdivided

into a variable number of "Sezione," which in turn con- tained the orders. Tetrodon, Diodon, and Orthagoriscus were placed in the Ordine Gli Odontini (Rafinesque

1810:40; all but the pelvic fins present; jaws in the form

of a bony beak), while Ostracion was placed in the Ordine Ostracidi (p. 39; body covered by a cuirass; all but

pelvic fins present; jaws with teeth not formed as a bony

peak). Both of these orders were in the Sezione Branchiosomi (body short; spherical or elliptical) of the

Divisione Apodi of the Pomniodi. Batistes, however, was

elevated as the Ordine Balistini of the Divisione Gli Omnanchidi (branchial apparatus with a branchiostegal membrane but without an operculum) of the Atelini. Rafinesque's treatment of the plectognaths is best remembered as a nomenclatural curiosity. The name of Cuvier looms large, of course, in the study

of plectognaths, and not only because it was he who es- tablished them as a natural group at the ordinal level. In

his "Legons d'Anatomie Comparee," Cuvier (1805) fol- lowed a classification (folding sheet at end of volume 1) that borrowed heavily from previous systems. Fishes were divided into those with "a squelette cartilagineux" and those with "a squelette osseux," with the bony fishes subdivided into Apodes, Jugulares,Thoraciques,and Abdominaux. The cartilaginous fishes were subdivided into two groups of Chondropterygiens and six groups of Branchiosteges, of which two were the "bouche au bout du museau; des dents" for Batistes and Ostracion, and

the "os des machoires tenant lieu de dents" for Tetrodon, Ouoides, Mota, and Diodon. The plectognaths were thus associated with much the same genera as in the 12th edition of Linnaeus' (1766) "Systema Naturae." An important improvement was

made, however, by the fact that Batistes and Ostracion were placed together as a subgroup distinct from the

other plectognaths. This was the first time that such a

distinction had been made so clearly. Cuvier further contributed to the study of plectognaths in this work, for throughout all five volumes numerous anatomical notes were given for this group. Cuvier (1817) put this anatomical information to good

use in his "Le Regne Animal," in which the Order Plectognathi was established, as one of the six orders of Pois- sons Osseux (in contrast to Chondropterygiens), as fol- lows;

Ordre Plectognathes. La premiere famille, ou les Gymnodontes. La deuxieme famille, ou les Sclerodermes.

Cuvier placed the Plectognathi as the first order of Poissons Osseux, just after the Chondropterygiens, because (1817:144) "il se rapproche un peu par I'imperfection des machoires, et par le durcissement tardif du

squelette; cependant ce squelette est fibreux, et en

general toute sa structure est celle des poissons or- dinaries." He continued with the diagnosis of the order,

of which "Le principal caractere distinctif tient a ce que

I'os maxillaire est soude ou attache fixement sur le cote de I'intermaxillaire qui forme seul la machoire, et a ce que I'arcade palatine s'engrene par suture avec le crane,

et n'a par consequent aucune mobilite." He added that

the operculum and branchiostegal rays were hidden under the thick skin and that the branchial aperture was

restricted. He further stated that there were only vestiges of ribs, no pelvic fins, a large intestine without

caeca and usually a large swim bladder. The Gymnodontes (p. 145) were defined as those Plectognathi which

"A, au lieu de dents apparentes, les machoires gamies

d'une substance d'ivoire, divisee interieurement en

lames," while the operculum was small and there were

five branchiostegal rays. Three genera were described; Diodon, Tetrodon, and Orthagoriscus. The

Sclerodermes (p. 149-150) were defined as being dis- tinguished by "le museau conique ou pyramidal prolonge depuis les yeux, termine par une petite bouche armee de

dents distinctes en petit nombre a chaque machoire. Leur peau est generalement apre ou revetue d'ecailles dures; leur vessie natatoire ovale, grande et robuste." Five generic groups were recognized, three of them for the first time: Batistes, Les Monacanthes, Les

Aluteres, Les Triacanthes, and Ostracion.

This, then, was the basic anatomical classification of the Plectognathi upon which all subsequent work on the group rests. It is perhaps unfortunate that the order was

not more carefully diagnosed, for subsequent workers found it easy to erode the structure that Cuvier had

erected. For instance, the principal character used by

Cuvier, the suturing (or at least immovable attachment)

of the maxillary to the premaxillary is true for all plec- tognaths, except for the triacanthoids. But since Cuvier had examined Triacanthus biaculeatus he might have

been expected to have noticed that his principal diagnostic character of the Plectognathi did not apply to one

of the genera. The definition of the order can also be

criticized because some nonplectognaths also have the two bones of the upper jaw intimately connected. These

criticisms, of course, are valid, but by far the more important point is that it was Cuvier who clearly saw in the

early 19th century the naturalness of the plectognaths as

a group, elevated them to ordinal rank, and defined the
basic subgroups within the two families. His families are now of subordinal rank, and his genera have become the bases for most of the families now recognized.

In only one group did Cuvier miss an important major

distinction, i.e., the ostracioids can be divided easily into

ostraciids and aracanids, but Cuvier could not have been

very familiar with the aracanids, for these mostly Japanese and Australian deepwater forms were rarely collected

at that time and known primarily from a single species

(aurita, Shaw 1798 illustration and 1804 description). Of

the 10 families of plectognaths presently recognized, only

the triacanthodids and triodontids were unmentioned by

Cuvier, and they were not to be discovered for another decade or more. Cuvier's description of Reinwardt's specimen of the unique Triodon bursarius (= macropterus) appeared in the second edition of Cuvier's "Le

Regne Animal" (1829:370) as the fourth genus of the

family Gymnodontes, while the first triacanthodid was

described by Schlegel (1850). In summary, most of the

basic groupings of plectognaths were made known by

Cuvier, with the notable exception of the two subdivisions of the ostracioids. At about the same time that

his (1817) first edition of "Le Regne Animal" appeared,

Cuvier (1818) published a short paper on Diodon, describing some new species, but, more importantly, cor- recting a number of anatomically erroneous statements about diodontids made by such workers as Broussonet,

Plumier, and Bloch. The appearance of the classifications of Latreille (1825) and Risso (1826) shortly after Cuvier's (1817) "Le Regne Animal" set the precedent for the thereafter nearly unanimous ordinal recognition of the Plectognathi. Risso followed Cuvier rather closely, and as far as the plectognaths are concerned, added nothing to their

classification. In his (1825) "Families Naturelles,"

Latreille used Cuvier's definition of the Ordre Plectog- nathes, but placed them in a different relationship with

other orders (with the sturgeons and lophobranchs). At about this time Geoffroy Saint-Hilaire (1827) published his "Poissons du Nil." His description (p. 176-214,

pis. 1-2) of Tetrodon physa (= lineatus Linnaeus), the common pufferfish of the Nile, was the finest description of a plectognath that had appeared up to that time,

describing the general anatomy, habits, distribution, and

nomenclature of the fish and gently setting aside the er- rors made by Bloch and by Lacepede on the inflation mechanism, showing the sac to be a diverticulum of the oesophagus and describing its general structure and musculature. The year 1833 saw the begiiming of the publication of Agassiz's "Recherches sur les Poissons Fossiles" [vols. 1 (1844a) and 2 (1833, 1842, 1844b)], which was to make a major (or at least temporarily so) change in the

classification of nearly all groups of fishes. Based on the

configuration and composition of the scales, Agassiz hoped to establish a more natural grouping of orders than had previously been available. Agassiz's system as a whole did not stand the test of time, and his association

of the plectognaths with the ganoids was a major error. His Ordre des Ganoides (1844a: 169) contained six

groups: Acipenserides, Siluroides, Lophobranches, Gymnodontes, Sclerodermes, and Sauroides. To Agassiz the plectognaths were ganoides for various

reasons. The scales of Ostracion were described (Agassiz

1844a:75) as consisting of a homy substance deposited in strata and covered with a thick layer of dentine characterized by ramifying calcareous tubes like those of the

teeth. The major references to plectognaths, however, were contained in a section (1844b:248-267) entitled "De

la famille des Gymnodontes" where brief osteological descriptions of a Tetraodon and a Diodon were given, along

with a comparison of the structure of the teeth and spines

of these two gymnodonts. Agassiz found the gymnodont

spines to be similar to the scales of scleroderms, in that both possessed a dentine layer with calcareous tubes, while the teeth of gymnodonts were said to be similar to the teeth of sharks. Agassiz (1857) also published a brief note on the structure of Mola.

Agassiz (1833:1-2) listed the six families of his Ordre

Ganoides as: Famille Lepidoides (with Acanthodes,

Palaeoniscus, Osteolepis, Lepidotus, etc.); Famille

Sauroides (with Leptolepis, Sauropsis, etc.); Famille Pycnodontes (with Placodus, Pycnodus, Microdon, etc.); Famille Sclerodermes; Famille Gymnodontes; and

Famille Lophobranches (with Syngnathus, etc.). It is strange to see the plectognaths associated in the same

order with such forms as the placoderm Acanthodes, the

crossopterygian Osteolepis, and the isospondyl Leptolepis. Even stranger, however, was the assemblage in- cluded in the Sclerodermes (1844b: 248- 267). Not only were Balistes, Ostracion, the Balistes-like fossil Acanthoderma, and the Triacanthus-Vike fossil Acanthopleurus placed there, but also included in the Sclerodermes were such obviously nonplectognath fossils as Blochius (which Woodward, 1901:591, referred to the Blenniiformes), Dercetis (which Woodward, p. 171, referred to the Isospondyli), and Rhinellus (which Woodward, p. 266, referred to the Isospondyli). Agassiz rec- ognized in later years that his classification was highly

artificial (see Agassiz 1860). With the appearance of Miiller's (1844) "Ueber den Bau und die Grenzen der Ganoiden," the Ganoides of Agassiz were modified to a considerable extent. Miiller purged the Ganoides of the plectognaths, lophobranchs, and most of the other living species placed there by Agassiz. Muller pointed out that the true ganoids had, among

other characteristics, more than two valves in the conus

arteriosus, while the teleosts had only two. Among the supposed ganoids of Agassiz that Muller had examined

for this characteristic were Balistes, Ostracion, and Tet- raodon. The classification at which Muller arrived

(1844:85-88) recognized six subclasses of Pisces, with the Subclass Teleostei containing the Order Plectognathi and its three families: Balistini, Ostraciones, and Gymnodontes. Muller pointed out (1844:6) that whereas the true ganoids are physostomes with abdominal pelvics, the Plectognathi are physoclists and that when obvious pel- vic fins are present, as in the triacanthoids, they are not abdominal. He also disagreed (p. 7) with Agassiz's con-
tention that the scales of plectognaths have much in common with those of ganoids. Just as Muller had purg- ed the Ganoides, so he also rid (p. 26) the Scleroderms of Agassiz's Blochius, Dercetis, and Rhinellus. Elsewhere

(p. 78-79) Muller gave systematic notes on the tetraodontoids, based on the structure of the nasal aperture and

tube. The character of the nasal organ was thereafter to play an important (and exaggerated) role in the classi- fication of the tetraodontoids. Muller made a clear state- ment (p. 84) of the fact that the maxillary and premaxillary are not fused or firmly attached to one another in all of the plectognaths, as Cuvier had said that they were,

for he noted that in the triacanthoids these two bones have a more normal relationship to one another.

Muller's contribution to the classification of fishes was

so outstanding that the outline given above in relation to the plectognaths cannot do it justice, for his was the

finest classification of fishes to appear up until that time, and in the magnitude of the changes it wrought in ich- thyology it was at least equal to the work of Artedi and

Cuvier. With Agassiz saying one thing about the highly modified scales and teeth of plectognaths and with Muller saying something else, a controversy broke out in the literature which has not yet been fully resolved (see references under subsequent discussion of Owen). Some of Muller's classificatory conclusions came in for immediate criticism. Vogt (1845) took exception to Muller's recognition of the Orders Pharyngognathi and

Plectognathi. Vogt thought these orders to have been

founded on insufficient criteria, i.e., the fusion of the lower pharyngeals in the Pharyngognathi and the fusion

of the upper jaw bones in the Plectognathi. Muller's classification is discussed here slightly out of chronological order so that it can be more easily compared with that of Agassiz. Intervening between these two monumental works were the classifications of Swainson, Nardo, and Bonaparte.

In his (1832) "Saggio d'una Distribuzione Metodica"

Bonaparte adopted a classification that was basically that of Cuvier's (1817) "Le Regne Animal," but with sig- nificant changes in the rank of the groups recognized. Bonaparte introduced here for the first time, in a consistent manner, the "idae" ending for familial and the

"ini" for subfamilial names for his Classe Pisces. Bonaparte recognized two monotypic orders in his Sezione 3, or Plectognathi: the Gymnodontes (for the family Tetraodontidae) and the Sclerodermi (for the family

Balistidae). The Tetraodontidae contained the usual four genera: Diodon, Tetraodon, Orthagoriscus, and Triodon. The

Balistidae contained three genera: Ostracion, Triacanthus, and Balistes (with the latter divided into four subgenera: Batistes, Balistapus, Monacanthus, and Aluterus)

In his (1841a) magnum opus, the "Iconografia della Fauna Italica," Bonaparte treated the plectognaths as one of the three sezione (along with the Micrognathi and

Teleostomi) of the Sottoclasse Pomatobranchii (in contrast to the Elasmobranchii, Lophobranchii, and Marsipobranchii) as follows:

Sezione Plectognathi Ordine Sclerodermi Famiglia Balistidi [sic] [Subfamily] Balistini [Subfamily] Ostraciontini Ordine Gymnodontes

Famiglia Tetraodontidae

[Subfamily] Tetraodontini [Subfamily] Diodontini Famiglia Orthagoriscidae [Subfamily] Orthagoriscini [Subfamily] Molini.

In the same year, Bonaparte (1841b) published his "A New Systematic Arrangement of Vertebrae Animals," and the classification adopted was that outhned above, with only minor changes. In the plectognaths, for ex- ample, the one difference was that in the family

Orthagoriscidae only one subfamily was recognized, the

Orthagoriscini, which was thus equal to his previous two subfamilies, Orthagoriscini and Molini. The classification used by Swainson (1838, 1839) in his "Natural History of Fishes, Amphibians, and Reptiles" was, like the rest of his work, a careless hodge-podge. The

pseudometaphysical "systems" by which Oken (1816) compared orders of fishes with various classes of inver- tebrates and vertebrates obviously made an impression on Swainson, for the latter carried on where the former had left off. To Swainson the plectognaths were equated

with such groups as amphibians and turtles, whereas Oken had equated them with mammals. Swainson

(1838:189) included all of the plectognaths (or Cheloni- form Order) in a family Balistidae, in which were

recognized five subfamilies: Balistinae, Ostracinae, Cephalinae, Diodoninae, and Tetraodinae, each of which

included the expected forms. Nardo (1842) presented a brief outline of his classi- fication of the Sclerodermi, in which he closely followed Bonaparte (1832), but attributed all of the familial names to himself. The first person after Cuvier to extensively analyze the

classification of the plectognaths as a whole was Dareste. His first paper ( 1849) dealt with the osteology of Triodon

macropterus, the monotypic representative of its family. Dareste saw that Triodon had many features in common

with the gymnodonts, but that it also possessed certain

characteristics of the scleroderms. One might expect that

this would strengthen the union of these two groups in an

Order Plectognathi. Such was not the interpretation of Dareste, however, for he concurred with Vogt's (1845:67)

belief that the Order Plectognathi was ill-defined, unnatural, and not long for this world. Although Dareste made this point in his work on Triodon, he did not substantiate it with a discussion until 1850, in his "Recherches sur la Classification de i'Ordre des Plectog- nathes." In the latter work Dareste took apart Cuvier's

definition of the Order Plectognathi sentence by sentence. To review very briefly Dareate's critique, he stated
that: Mola is the only plectognath with a skeleton less ossified than that of the majority of fishes (but Cuvier had stated only that the ossification was "tardif," while

otherwise like that of other fishes); the premaxillaries and maxillaries are fixed firmly to one another in a number of fishes other than plectognaths; the palatine is movable in certain scleroderms (Cuvier implied that it was sutured to the cranium in all plectognaths); the operculum and branchiostegal rays are hidden beneath

the skin in a number of fishes other than plectognaths; Triodon possesses ribs; some scleroderms possess pelvic

fins (Cuvier said that they are always absent in plectog- naths); Mola does not have a swim bladder (Cuvier said

that it is well developed in all plectognaths). Dareste (1850) went too far when he criticized Cuvier

for not knowing that Triodon possessed ribs. In the first edition of the "Le Regne Animal," Cuvier (1817) stated that the plectognaths had only very small vestiges of ribs. Triodon was not to be discovered until after the first edi- tion of the "Le Regne Animal," and while its original description appeared in the second edition (1829), it was

still not known that Triodon possessed well-developed

ribs until Dareste published his 1849 paper. Cuvier could

scarcely have been expected to have known the osteology

of an as yet undiscovered fish, or to have personally in- vestigated the ribs of every species offish, plectognath or otherwise, described in the "Le Regne Animal." The only features that Dareste (1850) believed the

plectognaths to have in common were a reduced oper- culum, a rodlike interoperculum, and a low number of vertebrae. To Dareste these characteristics were not im

portant enough to merit the recognition of the plectog naths as an order, or even as a natural group. One must admit that Cuvier's definition was im

precise, but Dareste temporarily neglected (see Dareste

1872c:1019) the fact that ordinal definitions are besi founded on a combination of characters possessed by the group in question and not by other fishes. Even ac

cepting Cuvier's far-from-perfect diagnosis, it is doubt

ful that any fishes other than plectognaths would fit into

it. Unfortunately, a significant number of plectognaths

also would be excluded from it, but this could be cured by a little rewording. Dareste proceeded to split the plectognaths into

(1872c: 117) "cinq petites families bien distinctes les unes

des autres" which were numbered as follows:

Premiere Famille - Diodon and Tetraodon Deuxieme Famille - Triodon

Troisieme Famille - Orthagoriscus Quatrieme Famille - Batistes (which included "les

petits generes Batistes, Alutere, Monacanthe et Triacanthe") Cinquieme Famille - Ostracion. His definitions of these families were anatomically, and

especially osteologically, founded, and included not only

a good summation of the contemporary knowledge of the plectognaths but also some original observations.

In his later publications Dareste (1872a, b, c) confined himself to the placement of the scleroderms "among the Acanthopterygians, in the vicinity of the Acanthuri and other fishes belonging to the small family

of the Teuthyes" (1872b:68). However, he despaired of showing the relationships of the gymnodonts, for he said

(1872c: 1088): "Ce type est assez difficile a definir, par

suit de la diversite des formes sous lesquelles il se presente, et qui en font une famille par chaine, plutot qu'une famille en groupe" and (1872c: 1089): "Le

Triodon differe notablement des autres Gymnodontes, et forme par consequent un type a part, quoique voisin." Dareste (1872b:69-70) pointed out the many characteristics held in common by the "Acanttiuri and Balistidae, especially the true Balistes, which are more nearly

allied to the Acanthuri than the Triacanthi, Monacanthi

and Aluterae." The particular features he noted in Balistes and acanthurids were: firm and immovable

union of the premaxillary and maxillary; general shape

of skull; supraoccipital with a long forward extension and

an elevated crest; ethmoid elongate; parasphenoid as a

vertical plate anterior to the orbit; vomer small and

toothless; palatine small, toothless, and movable; in- teroperculum at least partially rodlike and hidden beneath the preoperculum; pelvis elongate, its two

halves more or less fused together; few vertebrae. In comparison to these similarities, Dareste said (1872b:70) that "The differences between the skeletons of the Acanthuri and Balistes are but few and of slight importance," these

differences being: the presence of suborbitals in acanthurids and their absence in balistids; the spiny dorsal and soft dorsal fins of acanthurids being continuous, but

separated in balistids; the branchial aperture of acanthurids being larger than in balistids, due to the shape of the preoperculum; the acanthurids possessing true ribs, but not balistids. Great credit is due to Dareste for having so definitely pointed out these similarities. They are for the most part

correct, although just as Dareste had torn apart Cuvier's

definition so also could a person familiar with both acanthurids and balistids find many osteological details at variance with the above information. But the only reasonable ana useful criticism that can be made of Dareste's scheme is that the comparison was made

between acanthurids and balistids rather than between

acanthurids and triacanthoids. The triacanthoids are obviously the most generalized of the plectognaths and the

balistids show every indication of having arisen from

triacanthoid ancestors, perhaps not long after the

triacanthoids had themselves arisen from an ancestral stock which also gave rise to the acanthurids. Dareste's arguments are still convincing, but they would have been

even more so had the comparison been between the acanthurids and triacanthoids. At the same time that Dareste was attempting to dis- mantle the Order Plectognathi, another Frenchman took

a diametrically opposed view. Hollard stands second to no one in the study of the plectognaths. While Dareste's primary contribution was to relate scleroderms to acanthurids, Hollard's was to describe the anatomy and rela- tionships of the families within the Plectognathi.
HoUard's (1853, 1854a, b, 1855) first contribution was the "Monographie de la Famille des Balistides," which described the differences and similarities of Batistes, Monacanthus, and Triacanthus, the three genera he recognized. Whereas Alutera had previously been

recognized as a distinct genus by many workers, Hollard

relegated it to subgeneric rank, with the genus Monacanthus containing two subgenera, Monacanthus and

Aluteres. He believed these two types to be essentially the same, except that the posterior end of the pelvis protruded and was covered by modified scales (his "pointe pelvienne") in Monacanthus, while the pelvis remained covered by skin in Aluteres. One might notice

that in the excellent review of the group by Berry and

Vogele (1961) this concept still stands. Not only did Hollard described the general anatomy, including os- teology, viscera, integument, muscles, etc., but he also gave systematic descriptions of all of the then known

species of balistoids and triacanthoids and described many new species. Several years later, Hollard's (1857a) "Monographie

de la Famille des Ostraciontides" treated trunkfishes in the same fine style as he had done with the other sclero- derms. Hollard pointed out that, in the progression from

Triacanthus to Batistes to Monacanthus and Aluteres, the pelvic fin and spiny dorsal fin elements decrease in number and that in Ostracion there is no trace of either. Thus, to Hollard (1857a: 125) the acanthopterygians and

malacopterygians "ne s'en separent pas d'une maniere

absolue, et que le caractere tire de la presence des rayons epineux n'a qu'une valeur relative et conditionelle, bien

inferieure a celle que lui attribuaient Artedi et G.

Cuvier." Regarding the actual classification of the trunkfishes, it must be remembered that at this time a great number of new species of plectognaths were being made

known by Bleeker and a host of others, and that Kaup

(1855) had just reviewed the ostracioids. Kaup synony- mized many of Bleeker's species and defined a number of new generic groups, as follows: Cibotion Kaup,

Laetophrys (sic) Swainson, Ostracion Linnaeus, Acerana

(sic) Gray (with four subgeneraAcerana Gray,

Capropygia Kaup, Kentrocapros Kaup, Anoplocapros

Kaup), Centaurus Kaup (for the larval Mola described by Richardson [1845:52] as Ostracion boops). Hollard

did not wish to recognize as many generic and subgeneric categories as Kaup had given. Whereas Kaup

had placed great importance on the number and place- ment of cuirass spines, Hollard thought them to be of a

superficial or secondary nature and of no real value to an

understanding of the phylogeny of the trunkfishes. Thus,

Hollard recognized only two genera, Ostracion and

Aracana. Since Hollard had never seen a specimen of Ostracion boops, he was correctly skeptical of it and

mentioned it only in passing—quite in contrast to Kaup's establishing a new genus for it. The next in Hollard's (1857b) series of papers was the "Etude sur les Gymnodontes," of the same high quality

as the preceding works. The osteological illustrations that Hollard presented here were to be used by all sub- sequent workers on plectognaths, and they were even

reproduced by Gill (1892a). Hollard had at his dis- position the unpublished manuscript left upon the death

of Bibron, who had been reviewing the pufferfishes and

had established in his manuscript numerous new genera, some of which were in name only, for the diagnoses had

not yet been written. This manuscript was published al- most in its original condition, with only a few notes added by Dumeril (1855), its editor. Bibron had completed

the diodontids, but was still working on the tetraodontids at the time of his death. Suffice it to say that, on the

whole, Bibron's generic groupings were highly artificial and are unacceptable in a modem phylogenetic classi- fication. Hollard, for example, synonymized seven of Bibron's genera {Dilobomycter, Aphanacanthus, Amblyrhynchotus, Stenometopus, Geneion,

Epipedorhynchus, Promecocephalus) into one genus, to which, unfortunately, he gave yet another new name,

Apsicephalus. The last, summarizing, article in Hollard's (1860)

series was the "Memoire sur le Squelette des Poissons Plectognathes," in which he condensed all his anatomical observations and arrived at the following

classification (p. 46; genera were not listed, but are here

inserted below as he recognized them in his previous

three articles):

Plectognathes ou Echinoides

Sclerodermes

Balistides Triacanthiens TYiacanthus

Balistines Batistes Monacanthiens Monacanthus

subgenus Monacanthus

subgenus Aluteres

Ostracionides Aracaniens Aracana

Ostraciens Ostracion Gymnodontes

Loganiosomes ou

Triodoniens Triodon Spherosomes (Orbes epin.) Tetrodoniens Rhynchotus

Xenopterus

Batrachops

Apsicephalus Brachycephalus Monotreta

Diodoniens Diodon mes ou

Orthagorisciens

Ort- agoriscus.
The above classification was rarely accepted in its entirety by subsequent researchers on the plectognaths, and it was not a radical departure from previous ar- rangements of the order. By present-day standards,

Hollard's osteological observations were often incorrect, with two inaccuracies being of particular prominence. The bone now called the parasphenoid was thought by

Hollard to be composed of two entities, a large anterior

piece or "sphenoide anterieur" and a small posterior

piece or "sphenoide posterieur." What is presently termed the frontal was recognized as such by Hollard, except

that he believed a small portion at its posteromedial end

to be separated from it, and called this small piece the

"parietal." But Hollard had to rely, for the most part, on

dried skeletons, and if he occasionally saw a few too many bones in the cranium, it is readily understandable. With the present techniques of clearing and

staining, the sutural regions between bones are much

easier to define, and surface sculpturing of individual bones is less likely to be confusing. Hollard's contribution, then, was that he systematically made known

for the first time the general morphological structure of

all of the primary types of plectognath fishes. Coming after Dareste's (1850) critique of Cuvier's or- dinal recognition of the Plectognathi but before the

general plectognath classification of Hollard (1860) was

the "Ichthyologie Analytique" by Andre Dumeril (1856), father of the August Dumeril who had edited Bibron's manuscript. In probable deference to Dareste, the elder Dumeril did not recognize an Order Plectognathi, but, on

the other hand, his families Sclerodermes and "Gymnognathes" followed one another in his subclass Chondrostichthes, as outlined in the large folding sheet between pages 92 and 93:

Famille Lophobranches (syngnathids) Famille Podopteres (Cydopterus, Lophius, antennariids, ogcocephalids, etc.) Famille Sclerodermes (scleroderms) Famille Gymnognathes (gymnodonts)

Famille Hypostomates (climaerids, Polyodon, Acipenser, Pegasus). Whereas the two plectognath groups were listed one

after the other in the folding sheet, in the text they were

described discontinuously. Dumeril did not seem to have

any confidence in the validity of the Plectognathi. In the

section on "Les Chondrostes Gymnognathes," Dumeril

(1855:159-160) simply and conservatively listed the four genera he recognized: Diodon, Triodon, Tetraodon, and "Cephale" (= Mola). "Les Chondrostes Sclero- dermes" (p. 173-182) were treated in only a slightly more detailed manner. Two groups were recognized, the Ostracides and the Balistides. There were four genera of trunkfishes {Ostracion, Aracana, Cibotion, and

Doryophrys) and the standard four genera (Monacanthe,

Alutere, Triacanthe, and Baliste) in his Balistides. One

will notice that the term "Gymnognathes" (of Bleeker)

replaced Cuvier's "Gymnodontes." But the term Gymnodontes was not simply stricken from the record, for

Dumeril used it as the name of one of the families of his Ordre Hemisopodes. This "Famille Gymnodontes" in- cluded such items as Gerres, sparids, Upeneus, mullids,

etc.In Dumeril's (1806) much earlier "Zoologie Analyti- que," the fish classification of Lacepede was followed with only the addition of a large number of familial and

ordinal names.

Perhaps the fish classification that appears in ths vari- ous editions of the Encyclopaedia Britannica can be

taken as an example of the standard or average condition

of our knowledge of that subject. Richardson's (1856)

article on "Ichthyology" (8th edition) recognized the Order Plectognathi (p. 312-314) within the teleosts. For

the arrangement of the families of plectognaths Richardson followed Kaup (1855). Kaup, however, had not fin- ished his major groupings of plectognaths in that paper, and Richardson filled in the missing categories with what he thought to be Kaup's logic, as follows: Family Balistidae Sub-Family Balistini: Pyrodon, Melichthys, Xanthichthys, Canthidermis, Batistes, Balistapus. Sub-Family Monacanthini: Monacanthus, Aluterius, Triacanthus. Family Ostraciontidae

Cibotion, Doryophrys, Ostracion, Aracana (with

four subgenera: Aracana, Capropygia, Kentrocapros, Anoplocapros) , Centaurus. Family Diodontidae Sub-Family Diodontini: Diodon, Dicotylichthys,

Cyclichthys, Cyanichthys, Chilomycterus. Sub-Family Tetraodontini: Tetraodon (with four subgenera, after Miiller: Physogaster, Chelonodon, Cheilichthys, Arothron). Sub-Family Orthagoriscini: Orthagoriscus.

There are two obvious errors in the above scheme, one

of omission and the other of commission. The unique

Triodon is not even mentioned, and all of the triacan- thids (Triacanthus) were placed in the Monacanthini. The explanation is that when Kaup treated the

Balistidae he included all the balistid species he de- scribed under the Sub-Family Balistini, but did not mention £uiy other subfamily since he was not describing any triacanthoids or monacanthids. Richardson as- sumed that if in the Balistidae there was a Sub-Family

Balistini, then there should be a counterbalancing subfamily, so he set up the Sub-Family Monacanthini to in- clude all the other nonostracioid scleroderms. This treat- ment of the Plectognathi was later adopted by Fitzinger

(1873), but after that it fortunately disappeared from

use.After the turn of the 18th century there was an almost unanimous, with the few exceptions to be discussed later, belief that the plectognaths of Cuvier were indeed a

natural group, although there would continue to be much

discussion about the rank at which they were to be recognized. Attention was then turned to better descriptions, diagnoses, and eirrangements of the species within the
order. This task would have been long delayed had it not been for Bleeker, that great describer of the Indo-Australian ichthyofauna. As with so many other orders of

fishes, a knowledge of the Indo-Pacific representatives of the plectognaths is indispensable to an understanding of

their evolution. Here is to be found a far greater number

and diversity of species of plectognaths than in all other

areas of the world combined. If the Indo-Pacific was not

the cradle of the evolution and distribution of the plec- tognaths, then at least it is their present center of greatest speciation and morphological diversity.

It is impossible to give here a full review of Bleeker's contributions to the study of plectognaths, or to mention more than a few of the numerous papers in which he de- scribed new species of that order. Of particular descriptive, but not classificatory, interest is Bleeker's

(1852a) "Bijdrage tot de Kennis der Blookakige (Gymnognathen)" in which numerous new species were de- scribed and his (1852b) "Bijdrage tot de Kennis der

Balistini en Ostraciones." Of most importance to this discussion, however, is Bleeker's complete classification

of the plectognaths, which appeared in two places: in volume 5 (1865) of his monumental "Atlas Ich- thyologique" and in his 1866 "Systema Balistidorum, Ostracionidorum, Gymnodontidorumque Revisum." The

classification was the same in both works, and that which is here condensed is that of the "Systema" only because the definitions of the categories were more complete there and all of the ordinal names were latinized, which they were not in the "Atlas." Bleeker never used

the term Order Plectognathi, since he gave each of his three major groups of plectognaths ordinal rank, but he

obviously thought of them as a natural assemblage, as examination of the titles of his articles will show. His

classification was as follows:

Ordo Balistidi Familia I. Triacanthoidei Subfamilia I. Triacanthiformes TriacanthusA Acanthopleurus

Subfamilia II. Paratriacanthiformes

Triacanthodes, Hollardia Familia 11. Balisteoidei Subfamilia I. Balistidiformes

Leiurus, Erythrodon, Melichthys, Balistes (with

five subgenera: Parabalistes, Pseudobalistes, Balistapus, Balistes, Canthidermis)

Subfamilia II. Monacanthiformes

Phalanx 1. Monacanthini

Monacanthus, Chaetodermis, Paramonacanthus, Amanses, Pseudomonacanthus, Liomonacanthus, Oxymonacanthus

Phalanx 2. Aluterini Brachaluteres, Acanthaluteres, Ceratacanthus,

Paraluteres, Pseudaluteres, Aluteres Phalanx 3. Psilocephalini Psilocephalus

Ordo Ostracionidi Familia Ostracionoidei Ostracion (with four subgenera: Ostracion, Laetophrys, Tetrosomus, Acanthostracion), Aracana (with four subgenera: Aracana, Capropygia, Kentrocapros, Anoplocapros) , Centaurus Ordo Gymnodontidi

Familia I. Orthagoriscoidei Orthagoriscus Familia 11. Tetraodontoidei Subfamilia I. Diodontiformes Phalanx 1. Trirhizacanthini Chilomycterus, Diodon

Phalanx 2. Dirhizacanthini Atopomycterus, Paradiodon, Trichodiodon

Subfamilia 11. Tetraodontiformes Phalanx 1. Tetraodontini

Tetraodon, Crayracion, Leiodon, Chonerhinus, Ephippion

Phalanx 2. Canthogasterini Canthogaster

Familia HI. Triodontoidei

Triodon.

The precise separation of the triacanthids from the triacanthodids and of the tetraodontins from the canthigasterins appeared here for the first time. Although his groupings of the balistoids owed much to the work of Hollard, they were well defined and concisely executed. If one bears in mind that what Bleeker called Diodon we now refer to as Chilomycterus, then one sees that he also realized the natural division of the diodontids into those with erectile two-rooted spines (Phalanx Dirhizacanthini) and those with permantly fixed three-rooted

spines (Phalanx Trirhizacanthini). In short, Bleeker made good use of what had come before him and added much new information based on both observation and

synthesis in his own right. His is a reasonable classifica- tion even today, and at the time of its appearance it was

superb. Owen (1840 & 1845) in his "Odontography" gave what

are now the classic descriptions of the teeth of plectog- naths. The fish classifications he used in his various

publications were not his own, but they are cited here to show the variable handling of the plectognaths that one

finds up until the turn of the 19th century. In his "Odontography," which appeared several years after Agassiz's

(1833) "Poissons Fossiles," Owen placed the plectog- naths in two groups (scleroderms and gymnodonts)

within the ganoid fishes, and an Order Plectognathi was

not recognized. But in his "Lectures on Comparative Anatomy," which appeared after Miiller's (1844) "Ueber

den Bau," Owen (1846) recognized the Order Plectognathi, with three families: Balistinae, Ostraciones, and Gymnodontes. The same plectognath groups were

recognized by Owen in his (1853) "Descriptive Catalogue of the Osteological Series," but a new term for a
higher plectognath category appeared in his (1866) "On

the Anatomy of Vertebrates." In the latter work, the Order Plectognathi was composed of two suborders: Sclerodermi, with the family Balistini; and

Apleuri, with the families Ostraciontidae and Gymnodontidae. This is not the place to discuss the histological struc- ture and composition of the plectognath teeth and scales, nor to attempt to summarize the highly conflicting infor- mation available. But since some recent workers are not aware of all the older literature dealing with this subject, it is useful to list the more important references to the histology of the scales and teeth of plectog- naths: Bom 1827 (teeth of gymnodonts). Owen 1839

(teeth of Tetraodon and Diodon); 1840 & 1845 (teeth of

Balistes, Tetraodon, and Diodon). Williamson 1851

(scales of Balistes and Ostracion). Hollard 1857a

(scales of Ostracion). Cleland 1862 (bony tubercles in skin of Mola). Turner 1862 (bony tubercles in skin of Mola). Hertwig 1881 (scales of numerous plectog- naths, mostly gross morphology, but some his- tology). Hilgendorf 1886 (mostly gross morphology of teeth of Tetraodon and Diodon); 1893 (teeth of Mola,

Tetraodon, and Diodon). Wortman 1886 (teeth of Balistes and Diodon). Green 1901 (subdermal tissue of Mola). Green and Tower 1902 (albuminoids in scales of Mola and Sphoeroides) . Ghigi 1905a, 1905b (teeth of Balistes); 1921 (teeth of Ostracion and

Tetraodon). Rosen 1913 (scales of numerous plectog- naths); 1916b (scales of plectognaths in comparison

with those of other fishes). Kaschkaroff 1914a (scales of numerous plectognaths). Rauther 1919, 1927a (scales of

Balistes); 1927b (teeth of numerous plectognaths). Tretjakoff 1924a, b, 1926a, b (scales of numerous

plectognaths); 1925 (pectoral fin rays of Tetraodon compared with body scales); 1926c (teeth of numerous plec- tognaths). Pflugfelder 1930 (teeth of Tetraodon and Diodon in particular, but also of Ostracion and

Balistes). Grieb 1935 (pharyngeal teeth of

Sphoeroides). Arsuffi 1939 (teeth of Tetraodon). Bartolini 1941 (general discussion of plectognath

teeth). Isokawa 1955 (teeth of Monacanthus and

Cantherhines). Soule 1969a, b, 1970 (tooth attach- ment in balistids). More recently Roberto Andreucci and his colleagues in Brazil have begun a systematic reexamination of the histology of plectognath teeth (so

far confined to gymnodonts): Andreucci 1966a, b, 1967a, b, 1968a, b, 1969, 1970; Andreucci and

Britski 1968a, b, 1969a, b, 1970, 1971; Britski and

Andreucci 1971; Andreucci and Blumen 1971. A landmark in the study of almost all groups of fishes was the publication of Gunther's "Catalogue of the Fishes

in the British Museum." Here was a consistent, stan- darized description of nearly every order, family, genus, and species of known fishes. The Plectognathi appeared

in volume 8, published in 1870. In the subclass Teleostei, six orders were recognized: Acanthopterygii,

Acanthopterygii Pharyngognathi, Anacanthini,

Physostomi, Lophobranchii, and Plectognathi. The plec- tognaths were divided as follows:

Order Plectognathi Family Sclerodermi

First Group: Triacanthina

Triacanthodes, Hollardia, Triacanthus Second Group: Balistina

Balistes (with six subgenera: Liurus, Balistes, Canthidermis, Parabalistes, Melanichthys, Erythrodon), Monacanthus (with two subgenera: Monacanthus and Aluteres), Anacanthus

Third Group: Ostraciontina Ostracion (with two subgenera: Ostracion and

Aracana) Family Gymnodontes

First Group: Triodontina TYiodon Second Group: Tetrodontina

Xenopterus, Tetrodon (with 10 subgenera: Tetro- don, Hemiconiatus, Gastrophysus, Cheilichthys, Liosaccus, Crayracion, Chelonodon, Monotretus,

Arothron, Anosmius), Diodon, Chilomycterus,

Dicotylichthys, Atopomycterus, Trichodiodon,

Trichocyclus Third Group: Molina

Orthagoriscus (with two subgenera: Orthagoriscus and Ranzania).

The classification of the Plectognathi followed by Gunther (1880) in his "An Introduction to the Study of Fishes" was essentially the same as that given above. There was nothing special about Gunther's (1870) treat- ment of the Plectognathi, and it could be held to be dis- tinctly inferior to that given 4 years earlier by Bleeker

(1866). Gunther's most notable failure was his handling of the admittedly difficult "Tetrodontina." The tetraodontids are a far larger and more diversified group than the

diodontids, yet Gunther recognized only two genera of the former (albeit with 10 subgenera, but these were based

primarily on the form of the nostril, an unreliable character when used alone rather than in conjunction with a number of other anatomical systems) but six genera of the latter (defined by the form of the nasal tentacle and

the movability of the spines). In his (1871a) "Observations on the Systematic

Relations of the Fishes," Cope, while giving credit to Muller as (p. 580) "the father of modern ichthyology,"

nevertheless thought that within the teleosts the Plectog- nathi and Lophobranchii were not of equal rank with

the Physostomi and Physoclisti. Thus, within the Subclass Actinopteri (= Muller's Teleostei and Ganoidei), Cope recognized three tribes: the Chondrostei ( =

Mailer's Order Chondrostei of the Subclass Ganoidei), Physostomi, and Physoclisti. The Physoclisti contained

10 orders, including the Plectognathi. Cope stated

(1871a:582) that phylogenetic lines radiate out from the Percomorphi and that "one leads from the Chaetodontidae, through the Acroneuridae [= Acanthuridae], to the Plectognathi, by the similarity in the arrangement of
the posttemporal and forms of the pharyngeal apparatus." In the same year Cope (1871b) again ex- pressed the idea that the Plectognathi and Lophobranchii were natural groups, but that Miiller had given them too high a rank in comparison with the other

teleosts. Cope's opinion is almost unanimously accepted

today. Winther (1877), in part three of his "Fiskenes Ansigt: en Comparativ-Anatomisk Unders«igelse," briefly de- scribed the general anatomy, especially of the head

region, of such representative plectognaths as Triacanthus, Batistes, Monacanthus. Ostracion,

Tetraodon, Diodon, and Mola. He was the last person with a knowledge of the plectognath fishes as a whole who did not believe that they were a natural group. Like

others before him, Winther criticized Cuvier's character

of the intimate fixation of the upper jaw bones to one

another as being neither unique to, nor characteristic of,

all of the plectognaths. He believed the plectognaths to represent three families: Triacanthini, Sclerodermi (in- cluding balistoids and ostracioids), and Gymnodontes. He was unsure of the relationship of the triacanthoids to

his Sclerodermi, but he concurred with Dareste that the

balistoids were related to the acanthurids. For some

unaccountable reason, Winther thought that the Gymnodontes were related to the Discoboli (Cyclopterus). A good summary of the then prevailing feeling about

plectognaths by knowledgeable ichthyologists is found

in Gill's (1882) "Arrangement of the Families of Fishes . . .," published shortly after Bleeker's "Atlas,"

Giinther's "Catalogue," and Cope's "Systematic Relationships." While Gill's arrangement was drawn up to serve as the fish filling system to be used at the Smithsonian Institution, it was more than a mere list of families, for Gill gave numerous comments on the phylogeny of the higher

categories. After reviewing the characteristics of the plec- tognaths. Gill expressed the contemporary view that (1872:XLI) "the many common characters justify their association together, and the characters that are peculiar

to them sanction their isolation as a group," while "Their

differences sink into comparative insignificance." Gill agreed that the scleroderms "have been deemed more

related to ordinary Acanthopterygian types than to the

other admitted Plectognaths. And it is quite true that they (and especially the Triacanthids) are much more

similar to the ordinary fishes than are the typical Plectog- naths. This, however, is quite explicable by the supposition that they are the most generalized, and repre- sent the immediate line of descent . . . ." It was thus

agreed that the work of Dareste and others related the scleroderms to the acanthurids and that the gymnodonts were obviously highly specialized offshoots of the scleroderms. This was then, as it is now, the more or

less accepted view. In the actual arrangement used by

Gill, the Plectognathi were divided into three major subgroups, as had been done by Muller and Bleeker, in- stead of into two major subgroups, as had Cuvier, HoUard, and Giinther. The families that Gill recognized

in each of the three subgroups were those as recognized by Bleeker.

Several years later Gill (1885) published his "Synopsis of the Plectognath Fishes." This was a skillful diagnosis, based almost entirely on the literature, of the

characteristics of the various plectognath subgroups, and

of the nomenclatural labyrinth that surrounds the order.

Gill relied heavily for the osteological information in his diagnoses on the various publications of HoUard, whose

papers he thought had been unwisely neglected. Gill's classification of the plectognaths was much more

elaborate than that of his "Arrangement of the Families

of Fishes," and although it has much in common with

Bleeker's system, it is sufficiently different to merit

citation:

Order Plectognathi Suborder Sclerodermi Family Triacanthidae Subfamily Triacanthodinae Subfamily Triacanthinae Family Balistidae Subfamily Balistinae Subfamily Monacanthinae

Subfamily Psilocephalinae Suborder Ostracodermi Family Ostraciontidae Suborder Gymnodontes

Superfamily Triodontoidea Family Triodontidae Superfamily Tetrodontoidea Family Tetrodontidae Subfamily Tetrodontinae Subfamily Colomesinae Family Psilonotidae Family Chonerhinidae

Superfamily Diodontoidea Family Diodontidae

Superfamily Moloidea

Family Molidae

Family Molacanthidae.

The above scheme differs only slightly from Bleeker's handling of the scleroderms, the difference being that the elongate monacanthid Psilocephalus was elevated by

Gill to familial rank. In regard to the gymnodonts. Gill recognized a great many more higher categories than had

Bleeker, but few of Gill's extra divisions have continued

to be recognized. To Gill's credit, however, was the fact that all of the subgroups were diagnosed, and his sys- tematic handling of the maze of names that have been

applied to the various plectognath groups was a boon to

all subsequent researchers. A number of years later Gill (1892a) published his "Notes on the Tetraodontoidea," in which he expanded

on his nomenclatural treatment of the tetraodontids, without any basic change in the classification he had

previously used. In a series of notes, Gill (1888a, b, 1889, 1892b, 1897) dealt effectively with a number of other nomenclatural problems which need not be dis- cussed here. In the same vein, Eigenmann's (1885) only
paper on plectognaths might be noted, since he worked

out the 36 specific names that had been applied to the six species of diodontids that occur off the American coasts, while that of Goode (1880) did the same for ostraciids. No mention has yet been made of works on fossil plec- tognaths, other than Agassiz's species descriptions, for the simple reason that until part IV of Woodward's

"Catalogue of Fossil Fishes" (1901) appeared, there was

no systematic account of them. The order Plectognathi was not recognized by Woodward; rather, the plectog- naths occurred in the families Balistidae and Gymnodontidae, which, along with the Chaetodontidae and

Acronuridae (= acanthurids), composed the Division Chaetodontiformes of the Suborder Acanthopterygii. Admittedly the higher categories adopted by Woodward for the purpose of his pioneering catalogue were somewhat

artificial, but it is significant that the one person who

had reviewed the fossil plectognaths felt that they were

so closely related to the acanthurids and chaetodontids

that all of these groups should be placed in the same

higher category. The plectognaths were the first of the long series of orders that Regan (1903a) revised; his "On the Classification of the Fishes of the Suborder Plectognathi" was

in sharp contrast to Gill's plectognath work. Whereas

Gill concentrated on examining the literature, and particularly Hollard's figures, Regan made direct use of the

skeletal material of the British Museum and nearly completely shunned nomenclatural matters. Gill having al- ready straightened out most of the latter. Not only were

the research styles much different but the classifications arrived at were equally dissimilar. Regan recognized the Plectognathi as one of the suborders of the Acanthopterygii in close relationship with

the acanthurids. He (1903a:285) felt that the "feature of most importance in diagnosing the suborder Plectog- nathi is the absence of ribs, although in some well-ossifed epipleurals are present which have been mistaken

for ribs," but he pointed out that, like everyone else since Dareste and HoUard, he had not had the opportunity to examine Triodon and only supposed that it also lacked

ribs. On the other hand, Regan believed that "the

coalescence of the teeth in the jaws is a feature of little importance, and has, as probably as not, originated in- dependently . . ." in the gymnodonts and scleroderms. One could not do justice to Regan's classification without

quoting in full his brief but excellent osteologically grounded diagnoses for the various subdivisions, but

space forbids and in outline his system was as follows: Suborder Plectognathi

Division Sclerodermi Family Triacanthidae: Triacanthus, Triacanthodes, Halimochirurgus Family Triodontidae: Triodon Family Balistidae: Balistes, Monacanthus, Paraluteres, Pseudaluteres, Pseudomonacanthus,

Alutera, Psilocephalus Family Ostraciontidae: Aracana, Ostracion, Lactophrys

Division Gymnodontes

Family Tetrodontidae: Tetrodon, Ephippion,

Tropidichthys, Chonerhinus, Xenopterus

Family Diodontidae: Diodon, Lyosphaera Family Molidae: Mola, Ramania.

The most obvious feature of Regan's classification is that it was much more conservative than that of such

predecessors as Bleeker and Gill, but the differences were more basic than a simple and inevitable "lumper-splitter" disagreement. The unique Triodon had always been

placed in the Gymnodontes because of the fusion of its teeth, following the lead of Cuvier (1829) in the second

edition of the "Le Regne Animal." Regan (1903a:285), however, thought that "the structure of the pectoral arch and vertebral column, as well as the presence of a pelvis and well-ossifed epipleurals" related it to the triacan- thoids and balistids, and thus Triodon for the first time appeared in the Sclerodermi. Contrary to Miiller and

Bleeker, who recognized three subdivisions of the Plectognathi, Regan followed Hollard and Giinther in recog- nizing only the original two Cuvierian subdivisions, for the "Ostraciontidae do not seem to me to differ sufficiently from the Sclerodermi to rank as another division—Ostracodermi" (Regan 1903a:285). Whereas

Gill recognized three families of tetraodontids, Regan

preferred a single family. Regan pointed out that Gill based his diagnoses of the tetraodontid families on the

figures given by Hollard of the top of the skull of various

puffers, but that "the figures of Hollard have met with

too ready an acceptance, that author having mistaken

ridges on and fissures in the frontal bones for sutures" (p. 293). Regan's objection to Hollard's figures and Gill's use

of them was entirely correct. In short, Regan gave

excellent diagnoses for the limited number of plectognath subgroups that he recognized, and corrected numerous

osteological errors that had prevailed up to that time. Unfortunately, as was typical of most of Regan's revisions, only a few figures were given to accompany the great amount of osteological information that was discussed in the text. It is impossible, for example, to tell what Regan

meant by the presence of an "ossified praeorbital" in the

Balistidae. But these are relatively minor criticisms of the work'that became the standard treatment of the major plectognath subgroups. Regan's only other effort devoted solely to the plectog- naths was a brief, but useful at its time, revision of the genus Triacanthus (1903b). In the only complete fish classification that Regan ever presented, his "Fishes"

(1929) in the 14th edition of the Encyclopaedia Britannica, the plectognaths were discussed and diagnosed as

in his 1903 revision of the order. But now the Plectog- nathi were an order of the Neopterygii rather than a suborder of the Acanthopterygii. Thus, in the years that intervened between his revision of the plectognaths and

his general fish classification, the plectognaths would seem to have grown in stature in Regan's view. After Regan's (1903a) plectognath classification, the diagnoses that were there given were used to a greater or
lesser extent by all subsequent ichthyologists. For example, Boulenger's "A Synopsis of Suborders and Families

of Teleostean Fishes" (1904a) and "Fishes, Systematic Account of Teleostei" (1904b) followed Regan without

deviation, and Boulenger's (1907) only other interest in plectognaths was his lateral view illustration of the skeleton of the Nile puffer, Tetraodon fahaka (=

lineatus Linn.). On the other hand, Jordan (1905) accepted Regan's work more critically, for while sparingly using Regan's

diagnoses, Jordan had his own ideas about the plectog- nath subdivisions. For one thing, Jordan continued to recognize three suborders of the Plectognathi, with the Ostracodermi being one of them, rather than being

relegated, in Regan's fashion, to familial rank within the Sclerodermi. Like Regan, Jordan (1905, 2:411) wished to

stress the close association of the plectognaths and

acanthurids, and did so by recognizing a "Series Plec- tognathi" which is "derived directly from the Acanthuridae, from which they differ by progressive steps

of degeneration." But since the plectognaths "differ from one another more widely than the highest or most

generalized forms differ from the Acanthuridae, we do

not regard it as a distinct order. The forms included in it differ from the Acanthuridae much as the swordfishes

differ from ordinary mackerel" (Jordan 1905, 2:411). It is a matter of opinion whether the magnitude of dif- ference, external and internal, between such plectog- naths as Mola and Triacanthus is of a higher degree than that between the swordfish and mackerel, but in any case Jordan was restating Dareste's acanthurid-plec- tognath relationship. In Jordan's somewhat vague ter- minology, the Chaetodontidae, Zanclidae,

Acanthuridae, and related forms comprised the Squamipinnes, which gave rise to the Series Plectognathi. But in 1898 Jordan and Evermann, in their "The

Fishes of North and Middle America" (part 2) made the same point, the Plectognathi being called either an

"Order" (p. XVU) or a "Group" (p. 1696); and in 1923, Jordan, in his "A Classification of Fishes," recognized an Order Plectognathi with the following conservative subgroupings:

Order Plectognathi Suborder Sclerodermi fFamily Spinacanthidae [for all fossil triacanthoids] Family Triacanthidae Family Balistidae Family Monacanthidae

Family Psilocephalidae Suborder Ostracodermi Family Ostraciidae Suborder Gymnodontes

Family Triodontidae Family Tetraodontidae Family Canthigasteridae Family Diodontidae Family Molidae. Of more importance than the above classification were

Jordan's collaborative reviews of various families of plec- tognaths, making known many new species and redescribing poorly known ones: Jordan and Edwards (1887); Jordan and Snyder (1901); Jordan and Fowler (1903). Before continuing on to other researchers, it should be noted

that Jordan's belief in the close relationship of the plec- tognaths and acanthurids was reinforced by the osteological observations of his colleague Starks (1907:217) on the Siganidae and Acanthuridae. An example of the combined effect that Woodward's

(1901) "Catalogue" and Jordan's numerous publications had on the subsequent handling of the plectog- naths can be seen in Goodrich's (1909) "Cyclostomes and Fishes." Woodward had used the Division

Chaetodontiformes for plectognaths, acanthurids, and

chaetodontids, while Jordan had stressed again and

again the close relationship of his "Series Plectognathi" with his Squamipinnes. These messages were taken to heart by Goodrich, for, even though he made free use of Regan's osteological diagnostic information, he adopted

a modification of Woodward's and Jordan's views about

the placement of the Plectognathi. The eclectic result was as follows: Subtribe Chaetodontiformes

(of the Tribe Perciformes)

Division A, Squammipennes

Chaetodontidae Drepanidae

Division B, Plectognathi Subdivision A

Teuthididae

Siganidae Acanthuridae

Subdivision B

Branch 1, Sclerodermi

Series 1 Triacanthidae

Balistidae Monacanthidae

Series 2 Ostraciontidae Branch 2, Triodontes Triodontidae Branch 3, Gymnodontes A

Tetrodontidae Diodontidae B

Molidae.

Although the above "Plectognathi" was the logical ex- tension of Jordan's championing of Dareste's ideas, it is nevertheless the first time that the term Plectognathi had included within its folds the acanthuridlike fishes. More important, however, was the fact that the plectog- naths proper (Subdivision B) were divided into three major groups, one of which had never been recognized

previously at that level. The Triodontidae had formerly 22
been placed in either the Sclerodermi or Gymnodontes,

and thus had always had a subordinate position until Goodrich gave it equal ranking with the two Cuvierian

divisions. However, Goodrich's (1909:439) remarks on why Triodon had been so elevated were only that this is "a family intermediate between the first and third subgroups, whose exact position it is difficult to deter- mine." Thus, the new third category was only a matter of convenience. In his (1930) "Studies of the Structure and

Development of Vertebrates," Goodrich followed exactly

the same classification. The handling of the acanthurid-plectognath line in Gregory's (1933) "Fish Skulls" was modified from that of Goodrich. Gregory recognized a Balistoidei as one of the

23 subdivisions of the Acanthopterygii. The Balistoidei contained five large assemblages: acanthurids, zanclids, siganids, teuthids, and plectognaths (Gregory

hesitated to give any of them a precise rank). His

Balistoidei was therefore equal to the expanded "Plec- tognathi" (or Division B of the Subtribe Chaetodontiformes) of (Goodrich. Goodrich's "Squammipennes"

(Division A of the Subtribe Chaetodontiformes) became

the Chaetodontoidei of Gregory, a group equal in rank

with the Balistoidei. Gregory felt that the chaetodontids, acanthurids, and plectognaths formed a natural

series, but he split apart Goodrich's Chaetodontiformes

because it was his opinion (1933:281) "that the cleft between the typical chaetodonts and acanthurids is much greater than that between the latter and the plec- tognath stem as represented by the balistids." Just as with Dareste, one wonders why the comparison was not made between acanthurids and triacanthoids, which are the most generalized of the plectognaths, rather than between acanthurids and balistids, which are obviously of triacanthoid derivation. Gregory even illustrated the

skull of a triacanthid (1933:282, fig. 160), but no mention at all was made of it in the text. Highly useful as Gregory's plectognath figures (1933:figs. 160-172) are for obtaining a general idea of cranial construction, they

lack detail. The tentative classification as seen in Gregory's (1933) "Fish Skulls" was a great change from that Gregory

(1907) used in his much earlier "Orders of Teleostomous

Fishes." In the earlier work Gregory recognized the Plec- tognathi as one of the 10 orders of the Superorder

Acanthopteroidei. The Plectognathi were subdivided in the same way as Regan had done, with the exception that

the monacanthids were recognized as two separate

families (with the Alutera-like species as a distinct family) rather than being placed in the Balistidae. One other paper should be mentioned in connection with Gregory. Gregory and Raven (1934) discussed the anatomy and

relationships of Mola and supported previous workers' placement of the molids in close association with the

diodontids. During the period 1912 to 1916 a number of papers of great importance to the study of plectognaths were published by Rosen in Sweden and Kaschkaroff in Russia. Rosen produced five successive articles in his "Studies on

the Plectognaths" which dealt, respectively, with the

anatomy of the blood-vascular system (1912), the air- sac and intestine (1913a), the integument (1913b), the body muscles (1913c), and the skeleton (1916a). In the

introduction to the series, Rosen (1912:1) explained his purpose to be the study of a number of anatomical sys- tems, since "to base the building up of a phylogenetical

tree solely on one anatomical system is a great error which far too many anatomists commit." He then promised to "end this series of studies on the Plectog- naths with a section in which all the phylogenetical

results attained independently from the study of each or- gan will be discussed together" (1912a:2). Unfortunately, such a last summary article on phylogeny never appeared, the last of the series being the 1916 paper on the

skeleton, in which almost no phylogenetic conclusions were drawn. One can go to his earlier papers for his tentative views on the phylogeny of plectognaths, but he cer- tainly would not have drawn his final conclusions until

after the osteological paper had appeared. The ten- tativeness of the conclusions that will be quoted from his

earlier work should be stressed, for the series is a good

anatomical survey of the plectognaths, but his phylogenetic remarks based on the blood-vascular, intestinal, and integumentary systems do not seem to me to be

substantiated by the osteology of the order. Rosen's ideas were most clearly expressed in his paper on the air-sac and intestine (1913a:19) in which he stated that, "The

Molids and the Ostraciontids, which possess no such sac, must have developed independently of the other

families. The inquiry given above on the air-sac has

clearly shown that we have every reason to believe that

the families Triacanthidae, Balistidae (including the genus Monacanthus), Diodontidae, and Tetrodontidae form a continuous series of development. This is an evi- dent proof against the present classification of the Plec- tognaths into two subgroups, Sclerodermi and Gymnodontes, as proposed by Regan." Rosen's work on the integument confirmed his opinions and he (1913c:25-26) added that "The Molids and Ostraciontids are primitive Plectognaths, both groups separately specialized." The

fourth paper in the series, like the fifth, contained no

phylogenetic remarks.

Regardless of how the above statements would have

been modified in a summarizing article, Rosen's series was highly useful as a pioneering survey of the soft, as

well as the osteological, anatomy of the plectognaths. His

first four papers are presently the only publications that even attempt to treat as a whole all of the main nonosteological systems of the plectognaths, although Winterbottom's (1974) superb myological analysis is a major

step in that direction. Rosen added much new infor- mation and reviewed the then existing knowledge. Without going into details, a few of the leading structural peculiarities summarized by Rosen in his first paper of the series should be mentioned as examples of the type of information with which he dealt. He was particularly impressed by the fact, known since the time of Cuvier, that Mola has a larger, and supposedly rather

primitive, number of valves in its conus arteriosus and

atrioventricular region than do the other plectognaths,
which are normal in this respect. This fact, along with his observations of the primitive condition of the "circulus cephalicus" vessels in Lactophrys and Balistes (the only scleroderms in which he was able to examine the vas- cular system) and of its highly specialized condition in the gymnodonts, led Rosen (1912:19) to comment on

"the occurrence of a great number of both primitive and

highly specialized characters not only within the group

but also in the same form." Thus, he felt that "Judging

from the number of primitive characters that we have

found in some Plectognaths we have all reason to believe, that this fish group has branched off rather early from

the Teleostean main stock" (1912:20). On matters of osteology, and considering that he had

examined only four species of Plectognathi, Rosen's observations were generally quite accurate. He was able to substantially improve our knowledge of the plectog- naths and to correct one of Regan's major errors. Regan

had said in his diagnoses of the Sclerodermi and Gymnodontes that the former had all of the neural arches forming single spines, while in the latter the anterior vertebrae had bifid neural spines. Rosen correctly pointed out that in balistoids the first vertebra has a bifid neural spine and no bony roof over the neural canal. One

would probably disagree, however, with Rosen's assess- ment of Regan, whose contribution Rosen (1916a:l) said "does not seem to me to have increased our knowledge

either of the skeleton or of the phylogeny of the group."

Rosen's description of the developmental and adult

cranial osteology of Sphoeroides was well done, for he de- scribed it with more precision than had been given to a plectognath up until that time. But like Regan before him, Rosen included very few figures of the structures he

discussed so well. However, since Rosen described these

was not until 3 years after he had finished his manuscript

that he had seen Rosen's first three articles. Kaschkaroff

(1914a:365) simply said that he found them "sehr in- teressante." Whereas only a small, but highly sig- nificant, part of Rosen's output was devoted to osteology, the majority of Kaschkaroffs work concerned the os- teology of the plectognaths and the histology of their bones, and only minor excursions were taken into soft anatomy. In this respect Kaschkaroffs treatment of the order was similar to that of HoUard. Whereas HoUard

produced the first work that could be called a monograph

on the osteology of the plectognaths, Kaschkaroff produced what until now is the last such work. Kaschkaroff began his study at one of the end points of plectognath radiation, for he (1914a:265) admitted that "Meines Erachtens ist Orthagoriscus mola die interes- santeste Form genannter Gruppe." That view has many

advocates, as attested to by the practically infinite number of distributional and natural history notes that have

been devoted to that species. Kaschkaroff proceeded to describe, with many more illustrations than had Rosen,

the general osteology of members of all the major groups

of plectognaths, with the exception of Triodon, of which

he had no specimens. While on the whole Kaschkaroffs work is highly valuable, it contains a number of serious observational errors that will be mentioned in the os- teological section of this monograph. Regardless of os- teological errors, Kaschkaroff had intelligently examined

a large number of plectognaths and the conclusions at which he arrived are important to note. These conclusions were best summarized in the diagram he

presented (1914a:359), while cautioning the reader that

this was only a chart of anatomical similarity and not

necessarily a phylogenetic tree.

Tetrodon Diodon Triodon Orthagoriscus Balistes Monacanthus Ostracion Triacanthus /

Der Vorfahr

structures in some detail, it is not overly difficult to reconstruct what he saw. The same cannot be said of Regan's telegraphic summaries of his osteological observations. In the middle of the 4-year period during which

Rosen's series was published, there appeared Kaschkaroffs (1914a) "Vergleichendes Studium der Organisation von Plectognathi." This was evidently to be

the first of a series of anatomical monographs concerned

with "Materialen zur Vergleichenden Morphologie der

Fische," but, just as with Rosen, something in those troubled times was to cut short the series. Kaschkaroff was not aware of Rosen's work until after completing his own studies, for he said at the close of his paper that it

The only outstanding peculiarity of the above was the

close association of Orthagoriscus (= Mola) with Triodon, but there was no explanation in the text as to the reasoning that lead to this association. Kaschkaroff went on to say, however, that HoUard's classification was acceptable, and the latter was presented by Kaschkaroff (1914a:360) with the statement that "die alte Klassifikation von

Hollard erscheint mir vollkommen begrundet." Kaschkaroff discussed what "Der Vorfahr" of the Plec- tognathi should be, listing the characteristics of this hypothetical ancestor. The list (1914a:359) added up, in essence, to a triacanthoid with a large amount of carti- lage in its skeleton. He did not believe that the plectog- naths arose from an acanthurid stock, for the latter did
not possess a large amount of cartilage in the skeleton, a

characteristic he considered to be of great importance.

Rather, he felt that the plectognaths might possibly best be placed in association with the Lophobranchii and

Lophius. If one wishes to place such an emphasis on the amount of cartilage present in the skeleton of some plec- tognaths, then one could just as well relate the order to Cycloptenis as well as to Lophius, and return to the Artedian Branchiostegi.

In his "Studien iiber die Flossenmuskulatur der

Teleostier," Grenholm (1923:245) supported Rosen's view that "Die alte Zweiteilung der Plectognathen in Gymnodontes und Sclerodermi ist nach meiner Ansicht

. . . schwer aufrecht zu erhalten," while at the same time

admitting that the Plectognathi were a distinct group

related through the Acanthuridae to the other

acanthopterygians. It is of interest that Grenholm's

research on the fin muscles and Rosen's on the soft anatomy lead to the same conclusion, a conclusion not supported by the great majority of osteologically based

works, nor by Winterbottom's (1974) general myology of the plectognaths. Whenever one wishes to identify most plectognath

genera, there is only one place to which one usually

turns, and that is to the long series of revisionary papers by Eraser- Brunner (1935a, b, 1940a, b, c, 1941a, b, c, 1943, 1950, 1951). For species identification the

story is somewhat different. Fraser-Brunner

simply listed under the keyed-out genus the species which he found to be recognizable. Only for the molids and several genera of monacanthids were keys to the species provided. However, since Fraser-Brunner

typically drew his generic lines rather finely, there are usually only a few species within any one genus and the

practical matter of species identification is not as dif- ficult as it might first appear. The exemplary service that Fraser-Brunner performed will be appreciated by anyone who attempts to identify plectognaths, especially those from the Indo-Pacific. Throughout the series Fraser-Brunner promised eventually to publish a comprehensive monograph on the

order, but, since that has not yet appeared, there is presented below his tentative classification as brought

together from his various publications. No genera will be

listed by name, for with Fraser-Brunner the number

usually accepted was greatly increased:

Order Plectognathi Suborder Balistoidea Division Triacanthiformes Family Triacanthodidae (10 genera) Family Triacanthidae (2 genera)

Division Balistiformes Family Balistidae (13 genera) Family Aluteridae Subfamily Aluterinae (21 genera) Subfamily Anacanthinae (1 genus) Suborder Ostraciontoidea Family Aracanidae (6 genera)

Family Ostraciontidae Subfamily Ostraciontinae (3 genera) Subfamily Lactophrysinae (3 genera) Suborder Tetraodontoidea

Division Moliformes Family Molidae

Subfamily Ranzaniinae (1 genus) Subfamily Molinae (2 genera) Division Tetraodontiformes

Subdivision Tetraodontines Family Canthigasteridae (1 genus) Family Lagocephalidae Subfamily Lagocephalinae (1 genus) Subfamily Sphaeroidinae (3 genera) Family Colomesidae (1 genus) Family Tetraodontidae Subfamily Tetraodontinae (2 genera) Subfamily Arothroninae (1 genus) Family Chonerhinidae (2 genera) Subdivision Diodontines Family Diodontidae (3 genera).

The above is obviously not complete, for Fraser-Brunner has not yet assigned a place to Triodon, although he

(1943:4) did say that the "Tetraodontoidea are almost

certainly derived from the Triacanthiformes, a some- what fragile connection between the two being provided by the existing Triodon."

Fraser-Brunner's classification is basically similar to that of Bleeker's, with, of course, the refinements made

possible by Fraser-Brunner's own skill and by the results of the researchers who intervened between these two. It is nevertheless a compliment to Bleeker that Fraser- Brunner should, nearly a hundred years later, arrive at essentially the same classificatory scheme—although

Fraser-Brunner's diagnoses are, naturally, incomparably

better. Fraser-Brunner relied heavily on Regan's os- teological observations and pointed out (1943:1), e.g., that Regan's diagnosis of the Gymnodontes "here re- garded as the Suborder Tetraodontoidea, cannot be

surpassed, and its salient features are given below, practically unaltered." This is not to imply that Fraser-Brunner relied only on previous diagnoses of the subgroups,

for he contributed many original and significant obser- vations on the osteology of various families, notably in the tetraodontids, triacanthodids, and ostracioids. His

strong point was his combination of his own and

previously published osteological observations with his knowledge of the relative importance of external characteristics in arriving at his familial categories. This is particularly evident in his diagnoses of the tetraodontid subgroups, in which osteology (albeit only the top of the cranium in most cases) is uniquely combined with the

structure of the nostril and lateral line, two systems

notoriously misleading in this group when used by themselves. In one of his more recent papers, Fraser-Brunner

(1950) speculated about the basic phylogeny within the

Plectognathi. There is little doubt today about the
naturalness of the triacanthoid-balistid-monacanthid

line, but from what stock the tetraodontoids and ostracioids arose is an open question. After examination of the

larvae of a triacanthodid, Fraser-Brunner suggested that both the tetraodontoid and ostracioid lines may have

been derived neotenously from the triacanthodids. Whereas Miiller and Bleeker had started the trend toward the recognition of three major subgroups of plec- tognaths, rather than the original two of Cuvier, Berg's

(1940) "Classification of Fishes" went one step further and recognized four. Berg came to the following classi- fication on the basis of his analysis of the works of Regan,

Rosen, Kaschkaroff, Gregory, and Fraser-Brunner:

Order Tetraodontiformes (Plectognathi) Suborder Balistoidei (Sclerodermi) tFamily Spinacanthidae Family Triacanthidae Subfamily Triacanthini Subfamily Halimochirurgini Family Triodontidae Family Balistidae Subfamily Balistini Subfamily Monacanthini

Subfamily Psilocephalini Suborder Ostracioidei (Ostracodermi) Family Ostraciidae Suborder Tetrodontoidei (Gymnodontes)

Family Tetrodontidae Family Diodontidae Suborder Moloidei Family Molidae.

Other than the fact that the molids were given subordinal rank, this was a very conservative classification, based entirely on works already mentioned. Breder and Clark's (1947) "A Contribution to the Visceral Anatomy, Development and Relationships of the Plectognathi" is a useful, and interesting, comparison of the anatomy of the acanthurid-plectognath line. It is in- dicative of the then current state of our knowledge of plectognath anatomy (Breder and Clark 1947:312-313,

table 2) that these two authors, on the basis of the litera- ture and their own research, were unable to state whether

the palatine was movable in either Triodon or the trunkfishes. One also sees in table 2 that even greater gaps

exist in our knowledge of the characteristics associated with reproduction. It has been mentioned several times

in this historical review that the rarity of museum

specimens of Triodon had hampered the phylogenetic in- vestigations of all workers after the time of Dareste and

Hollard. Breder and Clark were able to make a partial dissection of one of the Stanford University specimens of Triodon obtained by Herre in the Philippines in 1931. Their report on the intestine was the first addition that had been made in 1(K) years to our knowledge of Triodon. This same specimen has been utilized for the present monograph.

The classification adopted by Breder and Clark was

modified from that of Fraser-Brunner: Order Plectognathi Suborder Sclerodermi tFamily Spinacanthidae Family Triacanthidae Subfamily Triacanthodinae Subfamily Triacanthinae Family Balistidae Family Monacanthidae

Subfamily Monacanthinae

Subfamily Aluterinae Family Triodontidae Suborder Ostracodermi Family Ostraciidae Subfamily Aracaninae Subfamily Ostraciinae Suborder Gymnodontes

Family Tetraodontidae Subfamily Canthigasterinae Subfamily Lagocephalinae Subfamily Colomesinae Subfamily Tetraodontinae Subfamily Chonerhininae Family Diodontidae Suborder Moloidei Family Molidae. On the basis of their research, Breder and Clark (1947)

felt that the trunkfishes deserved subordinal rank rather than inclusion in the Sclerodermi: "In view of the marked differences in the ontogeny from that of Monacanthus and its resemblance to that of Spheroides, we

cannot feel justified in holding these fishes within the Sclerodermi almost solely on the basis of cranial characters" (p. 311). Their justification for following Berg's handling of the molids was that "Although these fishes represent an offshore modification of the gymnodontid

type, they are so much further modified as, in our judge- ment, to warrant such a separation. The fact they have

lost their tail and its associated musculature ... in- dicates a fundamental change in the whole plan of or- ganization" (p. 311). Breder and Clark's views were summarized in a phylogenetic tree (p. 315, fig. 8) that is one

of the most sensible and understandable that has been

presented for the plectognaths, and the reader is referred

to it. The extensive work by Y. Le Danois (1954, 1955, 1956, 1959, 1961a, b) on the osteology, myology and other

soft anatomy, taxonomy, and phylogeny of the plectog- nath fishes, including monographs on the tetraodontoids and ostracioids, has not had a favorable reception. The osteology and systematics were criticized by Tyler

(1963b) and the myology by Winterbottom (1974). To

more fully comment on the controversial aspects of Le

Danois' work would require hundreds of pages, and it must suffice to summarize Le Danois' conclusions: the triacanthoids and balistoids are of acanthurid origin; the other plectognaths (Orbiculati) are not even of percoid
derivation, being related to the isospondylous fishes; and

Canthigaster is related to the ostracioids rather than the

tetraodontids. Le Danois' classification of the "Orbiculati" is as follows:

Sous-ordre Orbiculati

Division Orbispiniformes ou Tetraodontoidea

Families: Xenopteridae, Colomesidae, Diodontidae,

Tetraodontidae, Lagocephalidae.

Division Ostracioniformes ou Ostraciontoides

Families: Canthigasteridae, Aracanidae, Ostracionidae. Division Moliformes ou Moloidea

Families: Ranzanidae, Molidae.

Division Triodontiformes ou Triodontoidea

Famille: Triodontidae.

To what order the "Orbiculati" belong is not stated. Le Danois' work can be dismissed, except nomenclaturally. Although not directly concerned with the general phylogeny and higher classification of the plectognath fishes, several outstanding recent works on the systematics of limited groups of plectognaths have made certain species complexes far better known than in the past, and repre- sent the basic building blocks upon which such revisions

as this monograph are based, de Beaufort (1962) sys- tematically treated all of the more common species of the

Indo-Pacific plectognaths (104 species) for the first time

since Bleeker, immensely aiding the often difficult task

of specifically identifying the plectognaths of that region. Berry and Vogele (1961) carefully analyzed the sys- tematics of the Atlantic species of monacanthids, and

Berry and Baldwin (1966) did the same for the Pacific

balistids. Shipp (1970, 1972a, b, 1974) and Shipp and Yerger (1969a, b) have brought order to the nu- merous Atlantic species of Sphoeroides, discussing external morphological features, delimiting distributional

patterns, and describing new species. With such exemplary work as that of Berry and Shipp and colleagues, the American balistoids and tetraodontoids have become the

best known of their respective families. In Asia the ex- ceptionally speciose and mainly freshwater pufferfishes

of the genus Tetraodon received their first systematic

review by Dekkers (1975), who placed them in five species groups and unraveled most of the systematic

snarls that previously surrounded them. Similarly, the marine species (primarily of Arot/iroM and Canthigaster)

of tetraodontids from Taiwan were redescribed by Shen

and Lim (1974a) and Shen et al. (1975) in that general area for the first time since the series of articles by Abe

(1942, 1944, 1949a, b, c, 1950-51, 1952, 1954, 1960), while Shen and Lim also reviewed the ostracioids (1973) and

balistids (1974b) of Taiwan. Allen and Randall (1977) pro- vided an excellent and superbly photographed review of the Indo-Pacific pufferfishes of the subfamily Canthigasterinae, recognizing 22 species, of which 7 were described

as new, in this group of notoriously difficult tetraodontids, while Leis (1978) has performed a similarly fine service for

the five species of Diodon he recognizes worldwide. The fossil and Recent triacanthoids were redefined and revised by

Tyler (1968), which monograph was reviewed by Myers (1970). The provisional reclassification of fishes by Green- wood et al. (1966), which is wisely accepted as the con- temporary standard, does not attempt to include new in- formation on the plectognaths. While I agree with their basic subgroupings of the Recent Plectognathi, I consider

their families as superfamilies, a matter of opinion that I hope is supported by the numerous differences given here between the 6 superfamilies and their included 10

families as recognized in this monograph.

In Gosline's (1971) combination of functional morphology and fish classification, the plectognaths are recognized in 7 superfamilies with 12 families (the Aluteridae recognized as distinct from the Monacanthidae, and the Canthigasteridae from the

Tetraodontidae) in the usual two suborders, while Gosline (1968:16) had previously related the acanthuroids and plectognaths. The tentative classification of the plectognaths

proposed by Tyler (1974), with 7 superfamilies and 11

families, is modified here by the combination of the Canthigasteridae with the Tetraodontidae and of the Diodontoidea with the Tetraodontoidea.

It is pleasant to be able to conclude this historical review of the higher classification of the plectognaths with praise for the latest significant publication, that by Winterbottom (1974) on "The Familial Phylogeny of the Tetraodontiformes (Acanthopterygii: Pisces) as Evidenced by Their Comparative Myology." This is a beautifully

illustrated and thoroughly analyzed survey of the muscles of numerous representative plectognaths and of

its implications to the phylogeny and classification of the

order. It is unquestionably the finest comparative

myological study of any major group of fishes. A phylogenetic interpretation is given for the condition of every main muscle (75 in toto) in representatives of every plec- tognath family and of various reinterpretations of these

data. It is a forcefully reasoned analysis based on an ex- ceptional amount of myological data. A hallmark of Winterbottom 's work is a rigorous application of the principal that only synapomorphies

(shared specialized characters) can be used to link together related groups, while symplesiomorphies

(shared generalized or primitive characters) are not valid as phylogenetic indicators. The excellence of Winterbot- tom 's contribution can best be seen by perusal of his

brilliant monograph, and only the highlights of his phylogenetic conclusions and an outline of his proposed

major reclassification can be given here. Winterbottom (1974:ii) states in his abstract that "... using only those characters of a shared specialized (synapomorph) nature . . . suggests that the Triacanthodidae and Triacanthidae are sister groups, and separated

off first from the ancestral stock. The remaining families

are divided into two lines. On the one hand, the

Balistidae form the sister group of the Monacanthidae, and together form the sister group of the Aracanidae and

Ostraciidae. In the other linage, the Triodontidae
separated off first, followed by the Molidae. The Diodontidae form the sister group of the Tetraodontidae plus Canthigasteridae." The classification based on this phylogeny divides the plectognaths into two suborders in a rather different way than ever proposed before, revised as

follows (Winterbottom 1974:99): Order Tetraodontiformes Suborder Triacanthoidei Family Triacanthodidae Subfamily Triacanthodinae tSubfamily Cryptobalistinae Subfamily HoUardiinae Family Triacanthidae Subfamily Triacanthinae tSubfamily Protacanthinae Suborder Tetraodontoidei Superfamily Balistoidea tFamily Spinacanthidae Family Balistidae Subfamily Balistinae Subfamily Monacanthinae

Family Ostraciidae Subfamily Aracaninae Subfamily Ostraciinae Superfamily Tetraodontoidea tFamily Eoplectidae tFamily Zignoichthyidae Family Triodontidae Family Tetraodontidae Subfamily Tetraodontinae Subfamily Canthigasterinae Family Diodontidae Family Molidae.

The phylogenetic conclusions reached by Winter- bottom on the basis of the myology of the plectognaths and those presented here on the basis of their osteology

are in general agreement, although the hypotheses of this monograph emphasize the role on the one hand of a

hollardiinlike Eocene stock of triacanthodids as ancestral to triacanthids through a protacanthodinlike line, with the basal triacanthids giving rise to the balistoids and ostracioids, and on the other hand of an eoplectinlike Eocene stock of triacanthodids as ancestral to the

triodontids and hence to the tetraodontoids and molids. Even though the phylogenies based on Winterbottom's

myological analysis and that of the osteology given here

are not far apart, and differ mainly in details of the rela- tionships of fossil forms for which there is no myological

evidence, the classifications adopted are widely divergent. While finding Winterbottom's philosophy of classifica- tion highly worthwhile, eminently logical and entirely defensible, the preference followed here is to weigh and

balance the value of both the generalized and specialized

features of the fossil and Recent species, rather than to

rely on the specialized alone, and the classification sug- gested here reflects that bias. Winterbottom and I plan to prepare a joint paper after the publication of this monograph discussing the merits

of alternatives to our respective modes of phylogenetic

interpretation and classification of various plectognath

linages and subgroups. Until then, the reader is left to

his own inclination.

Historical Review of the Nonclassificatory Anatomical Work on the Plectognathi, with notes on certain anatomical systems of special historical interest.

Comments are given in the preceding section on the contributions of such anatomically oriented workers as Cuvier, Dareste, Hollard, Winther, Regan, Kaschkaroff, Rosen, Gregory, Fraser-Brunner, and Le Danois, all of whom were using an osteological framework for their

classifications of the plectognath fishes. A number of other workers have described the general osteology of one

or several species of Plectognathi from a more or less purely anatomical point of view, without concerning

themselves with questions of phylogeny and classification. Specific details of these works are mentioned in the subsequent analysis, but some of these shorter contributions are of sufficient importance to merit brief general comment.

Wellenbergh (1840) was the first person to treat an in- dividual plectognath species in a manner similar to that

of Geoffroy Saint-Hilaire's (1827) anatomy of the Nile

puffer. Wellenbergh's description of the bones of the

skull of Mola leaves much to be desired by con- temporary standards, but the branchial and hyoid arches were described rather accurately. After Wellenbergh's work there came a veritable flood of literature on the anatomy of molids. Goodsir (1841) described with some

detail the histology of the shagreenlike skin and the

gelatinous subdermal tissue of Mola, as well as its general myology. His work is of importance here because

of his description of the abortive nature of the posterior end of the molid vertebral column. Cleland (1862) like-
wise gave a general account of the soft anatomy of Mola,

with an emphasis on the structure of the caudal region,

its bony supports, cartilaginous pterygials, and unusual

fin rays. Two of Cleland's most often quoted statements

were that Mola possessed no otoliths and had only two

semicircular canals. Cleland was not aware that Cuvier

(1805, 2:456-457) had described the otoliths of Mola as being gelatinous and mucoid, rather than calcareous, and that he had even figured (pi. 18, fig. 1) the three semicircular canals. Cleland's error has been corrected a number of times: vide, Harting (1865), Thompson

(1888), and Meek (1904). Harting's (1865) general anatomy of Mola contained

very few references to osteology, but he did give a brief description of the long, sharp-pointed teeth on the upper

pharyngeals. Walgren's (1867) work on Mola was mostly confined to external characteristics, but brief notes were given on the skeleton, and the jaws, with their trituration plates, were well described and figured. The

first worker to publish on the general anatomy of the dis- tinctive molids of the genus Ranzania was Trois ( 1883-

1884), whose osteological interest, however, was mainly

confined to the comparison of the histology of the bones

of Ranzania with that of Masturus and Mola. He pointed

out, for example, that Ranzania has a much more completely ossified skeleton than that of the other molids.

Trois' histologically oriented work was soon followed by

Beauregard's (1893) descriptive osteology of Ranzania. Beauregard gave us our basic knowledge of the general

osteology of Romania, and the information that he

presented was not supplemented until Raven (1939b) published his brief article on its anatomy. One of the more accurate of the early general osteologies of Mola

was that of Steenstrup and Liitken (1898); the various

figures (unnumbered; occurring on p. 91-94) of the skull and branchial apparatus are, with the exception of the

orbital region, notably accurate, and the lateral view of the entire skeleton (pi. 2) is only questionable in the

region of the pseudocaudal fin. Two other papers should

be mentioned here in relation to molid anatomy, that of Gregory and Raven (1934) on Mola and that of Raven

(1939a) on Masturus. Both of these papers were primarily concerned with the myology, but information was also given on the osteology of the supporting structures of the pseudocaudal fin. Of a much more ambitious nature than any of the above-mentioned papers on molid anatomy was Briihl's (1856) "Osteologisches aus dem Pariser Pflanzengarten," in which there appeared (p. 58-70) brief os- teological descriptions of Balistes, Ostracioh, Alutera, Tetraodon, and Diodon. Briihl confined himself almost

entirely to the cranium, and the few figures which he gave of various regions of the plectognath skeleton show

very little detail, but if one takes the time to translate the sirchaic terminology of the bones, one finds that

Bruhl's osteological observations were substantially correct. It is hard to explain, however, how he mistook part

of the sphenotic in Diodon for a parietal; possibly it was

because Wellenbergh had found a "parietal" in Mola, and thus one might expect to also find one in Diodon, if

one believed very strongly in the close relationship of those two types. In his "Zootomie," Bruhl (1880) presented excellent illustrations (pi. 24, with two un- numbered pages of explanation; also see Briihl 1891) of

Balistes, and the only serious error in his various figures

of the skeleton is the presence of an extra suture between

the parasphenoid and basioccipital. A work very similar to Briihl's (1856) "Osteologisches"

in its conception, but broader in its scope of coverage, was Klein's (1884, 1885, 1886) "Bildung des Schadels der Knochenfische." In this general work on the teleost skull, Klein discussed the cranial osteology of representatives

of most of the major plectognath subgroups. His descriptions were, on the whole, accurate, and since his illus- trations were so well executed, it is unfortunate that

there were so few of them. Klein corrected a great many

of Hollard's osteological errors, and stressed (1886:230-

234) the presence of a myodome in the nonostracioid scleroderms and its absence in the gymnodonts. In an

earlier paper Klein (1872) had described the cranial os- teology of four species of Balistes, and while his descriptions were relatively accurate, his illustrations were so reduced in size for publication that little detail can be

seen. Klein (1881) published one other paper on plectog- nath osteology, devoted primarily to the description of the spiny dorsal fin locking mechanism in triacanthoids and balistoids. Rosenthal (1839) produced rather accurate lateral views of the entire skeletons and other detailed views of

Balistes, Ostracion, Tetraodon, and Diodon.

Several other papers of special importance to the os- teology of particular species should be mentioned here. The osteology of the skull of Balistes and Mola was

described and reasonably well illustrated by Supino

(1905), as was the branchial apparatus of each species, the latter being an important anatomical system which had all too often been neglected by previous workers. Much of the information that Supino published in his 1905 paper appeared again in his more general work

(1907) on "II Crano dei Pesci." Awati and Bal ( 1933) initiated a series of papers on the anatomy of Indian puffers with a description of the

skeleton of Tetraodon (= Fugu) ohlongus, but their os- teological descriptions suffer from numerous serious

defects, as will be detailed later. The second paper in this

series (Awati and Bal 1934) dealt with the blood vas- cular system, and the third paper (Bal 1937) with the nervous system. A far more detailed and accurate survey

of the functional anatomy of the head of that species was

given by Sarkar (1960) in a published doctoral dissertation. A work of importance to the generic classification of the tetraodontids is Kuronuma's (1943) survey of the

configuration of the top of the cranium of 14 species of Japanese puffers. Besides giving a photograph of the top

of the cranium of each of these species, diagrammatic il- lustrations were presented of lateral views of the skulls of species representative of the three genera to which the

species belong. Kuronuma's osteology is correct and he

has made available much information of diagnostic value
for the genera and species studied. Kiausewitz (1964) ac- curately described and illustrated the skull of an

Arothron, and Rishi (1969) that of a Chelonodon. The otic region of the skull of plectognaths has been

the subject of much misinterpretation in the literature. One source of the error has evidently been the feeling that the plectognaths, like most other fishes, should

possess a pair of parietals. But the plectognaths have lost

all trace of the parietals and what have been called the

parietals in plectognaths are portions of the epiotics, sphenotics, or frontals. Wellenbergh (1840) referred to a portion of the epiotic in Mola as a parietal. Bruhl (1856) described the parietals as being absent in all plectog- naths except Diodon and Mola, calling the posterior part of the sphenotic in Diodon a parietal and accepting

Wellenbergh's statement that a parietal existed in Mola.

In HoUard's (1853, 1854a, b, 1855, 1857a, b, 1860) various

publications the posterior portion of the frontal is called the parietal, although a definite suture between the bones is not usually shown in his figures. Goeldi (1884) pointed out that many of the sutures shown by Hollard were artifacts and criticized Hollard for the excessive number of bones that had been described as separate ele- ments. What Siebenrock (1901) described as a parietal in Balistes, even though he could not find one in Tria- canthus, or Monacanthus, is probably a part of the

epiotic. Supino (1905) thought that in Balistes the

parietals were fused to the frontals, but in Mola he

described the medial half of the pterotic as being a

parietal. Kaschkaroff (1914a) described a parietal as being present only in Balistes, his parietal evidently being

part of the epiotic. Kaschkaroff believed that the frontal

of Mola might represent the product of the fusion of the

frontal with the parietal. Rosen (1916a:13) said that the

parietals were absent in plectognaths, and expressed the

prevailing view that "they have perhaps fused with the

frontals." The above statements are exclusive of those in- stances in which there is a purely nomenclatural dif- ference, e.g., Regan's (1903a) use of the term "parietal"

as being synonymous with "epiotic." Since Rosen's time, no knowledgeable worker has described a parietal in a

plectognath fish, and if that bone has fused with the

frontal it has done so indistinguishably. Not even a trace

of a separate ossification which could conceivably be

referred to as a parietal has been seen in any of the developmental stages of various plectognaths examined

for this work. Under these circumstances it would seem

best to assume that the parietal simply fails to develop in plectognaths. The other major source of error in the interpretation of the otic region has been the description of the upper and

lower surfaces of the epiotic as two separate and distinct bones, because of a certain anatomical peculiarity of the development of the endochondral bones, particularly in the otic region. The otic bones begin to develop in the normal manner as small ossifications in the appropriate

region of the chondrocranium. From this center of ossification in a plate of cartilage, the gradual peripheral movement of the ossification does not proceed evenly. Rather, the ossification spreads through the upper surface and through the lower surface of the cartilage, so that toward its edges the bone is composed of an upper and a lower layer separated by cartilage. The two layers are continuous with one another only at their original center of ossification. As the specimen becomes larger, there is a slow and gradual ossification that fills in the otherwise cartilaginous area between the two peripheral

layers of the bone. It is only in extremely large specimens

that all of the cartilage between the double-layered

peripheral parts of the bone is replaced by ossified tis- sue. Thus, in the descriptions given here of the otic and

other regions, there is reference to these endochondral

bones having the edges filled with cartilage, simply

because in all but the largest specimens of any particular species the replacement of the cartilage between

the upper and lower layers in the peripheral region of the bone is incomplete. This double-layered condition is particularly evident in the epiotic and sphenotic, and is progressively less evident in the pterotic, prootic, exoccipital, supraoccipital, and the other endochondral bones

of the skull. In adult specimens the cartilage-filled edges

of these endochondral bones are usually not evident on

external examination, and they can be seen only when

the bones are disarticulated. The reason that this condition is not particularly ap- parent is that the edges of the upper layers of two adjacent bones, e.g., epiotic and sphenotic, may inter- digitate with one another, hiding the fact that just below

this interdigitated surface there is a thin layer of cartilage separating the upper and lower layers of the bones.

It is usually true, except in large adults, that when the upper layers of two bones articulate by interdigitation, the lower layers of these bones are separated from each

other by a small amount of cartilage, this cartilage ex- tending for a short distance into the substance of each of the bones. It must be emphasized that even though a bone such as the epiotic has an upper and a lower layer separated by cartilage peripherally, these two layers converge toward one another centrally to be connected by a core of bone representing the original center of ossifi- cation. This central core of bone is delicate enough in some cases to be easily broken when skeletal material is prepared by drying, because of the contorted shrinkage

of the cartilage that lies between the double-layered

peripheral regions of the bone. If the drying of the skele- ton does not break the central core, then the process of

disarticulation of the skull often will.

It is thus not surprising to find that Klein (1872, 1881,

1884, 1885, 1886) stated that in plectognaths there is an

epiotic which is covered over by a parietal. Klein's

"parietal" was simply the upper layer of the epiotic, which had become separated from its lower layer during

the drying and disarticulation of the skull by breaking of the central ossified core which normally makes the two

layers continuous. Awati and Bal (1933) have done essentially the same thing in their study oiFugu oblongus, for they refer to the ventral surface of the epiotic as the

"epiotic," but to its dorsal surface as the "parietal." Furthermore, they refer to the ventral surface of the sphenotic as the "sphenotic," but to its dorsal surface as
the "squamosal." Like Klein, they were using dried

skeletal material. Rosen (1916a) had some insight into this problem of the "double-layered" condition, which is especially prominent in the otic region of tetraodontids. In his brief description of Sphoeroides testudineus he contradicted

Klein's statement that the epiotics are covered by the

parietals, for Rosen stated (1916a: 19) that "I have not been able to find distinguishable such elements either in adult specimens or in young ones (18 mm. in length)." But, quite unaccountably, Rosen went on a few lines

later to say, without any elaboration, that there were

"Parietals present." Unfortunately, there were no figures

of plectognath skulls in that paper, and one can only

guess that Rosen was referring to a portion of the posterior end of the frontal in Sphoeroides as the parietal. Rosen's most interesting statements, however, were about the sphenotic and pterotic in Sphoeroides, for he

described them as follows: "Sphenoticum. Sections of specimens 18 mm in length show that this bone orig- inated as two elements: a dermosphenoticum and an

autosphenoticum in the same mode as, e.g., squamosum. Squamosum is formed by the fusion of a dermo- squamosum and an autosquamosum." No other com- ments were made about this condition of the otic region, nor were any figures presented of it. Rosen was obviously aware of the double-layered condition in the otic region, but why he did not notice it in the epiotic is a mystery. Rosen was probably incorrect in assuming that the upper

layers of the sphenotic and pterotic were of dermal

origin, for in the many young tetraodontids examined for the present work, this upper layer is obviously ossified in the upper region of the cartilage of the chondrocranium.

This is not to say, however, that there is not any dermal

ossification eventually incorporated into the external

surface of the upper endochondral layer of the otic bones, but only that the great bulk of these bones is endochondral in origin. In ParahoUardia and other triacan- thodids, for example, most of the substance of the part of the pterotic that overlies the sphenotic and epiotic ap- pears to be of dermal origin, but this is only a very small, and irregular, portion of the pterotic. A number of workers have erroneously referred to cer- tain portions of the pterotic as the "opisthotic." Awati and Bal (1937) did so in Fugu oblongus, and Gamaud

(1956) did likewise in Batistes. Kaschkaroff (1914a:351) seems to be the one who began the mistake, for he said that an opisthotic was present in scleroderms but not in gymnodonts. Kaschkaroffs "opisthotic" is only a region

of the pterotic. A well-developed myodome has long been known to be

present in triacanthoids and balistoids, and more recently in triodontids (Tyler 1962a), but it was thought to be

absent in all other plectognaths. Klein (1884, 1885, 1886) was the first person to point out the diagnostic value of

this structure (see part 1:150-152 and part 3:230-234) in plectognaths, but Regan (1903a) rather unaccountably

stated that the Sclerodermi have the "basis cranii more

or less distinctly double" (p. 280) and that the Gymnodontes have the "basis cranii simple" (p. 291), which

implies that the ostracioids have a myodome. Kaschkaroff (1914a:351) described the longitudinal concavity on the ventral surface of the basioccipital in Triacan

thus, Balistes, and Monacanthus, but he did not men

tion that this channel leads into the myodome. Holm

gren and Stensio (1936:488) contended that the myodome of plectognaths and a few other fishes cor- responds to the dorsal part of the myodome of Salmo

because it encloses only the M. recti externi. Be that as it may, the important fact that Triodon possesses a well developed myodome was overlooked by Dareste (1849) and Hollard (1857b), and it is significant to know that at

least a rudiment of the dorsal roofing of the myodome is present in some tetraodontids (Tyler 1963b). Frost (1930:621) gave cursory descriptions of the

otoliths of a few plectognaths and said that they "are

curiously aberrant in form, showing little affinity with

those of the other orders."

In the orbital region there has been much controversy

in the literature concerning the bones with which the

frontal articulates posteriorly. The difficulty stems from

Hollard's (1857b) inaccurate figures of the top of various gymnodont skulls. Gill's (1885, 1892a) reproduction and

use of these figures could only lead to erroneous diagnoses, with the tetraodontids being said to have the frontals in contact with the supraoccipital, except for Canthigaster and Chonerhinus, which were supposed to have these bones separated from one another by the in- tervention of the sphenotics. This erroneous difference between the tetraodontins and canthigasterins was used by Jordan and his associates (Jordan and Edwards 1887; Jordan and Evermann 1898; Jordan and Snyder 1901) and thus it gained popularity. However, Regan (1903a) showed that the differences were purely in Hollard's

figures and presented figures of his own which showed

the correct relationships of the bones of the top of the

skull in a tetraodontin and a canthigasterin. Fraser- Brunner (1943) used the fact that the sphenotic separates

the frontal and epiotic in diodontids as one of the diagnostic characteristics of that group. Sexual dimorphism

in the size of the frontals has been pointed out by Ebina

(1932) in filefishes, and supposedly by Le Danois (1954)

in diodontids. In relation to this discussion of the frontal,

it is worthwhile to mention that none of the dermal bones

of the head develop in conjunction with the sensory canal system, a fact first stated by Rosen (1916a:20). The der- mal bones show no trace of canals, bridges, or troughs

that could in any way be associated with the cephalic sensory canal system, which is confined entirely to the

skin in plectognaths. Le Danois' (1956) statements to the

contrary are unproven. A basisphenoid is present only in two groups of plectog- naths

Triodon and molids. Neither Dareste (1849) nor Hollard (1857b) observed the basisphenoid in Triodon, but that of molids has been described often, although under a variety of names. A few workers have described the

anterior region of the prootic in various scleroderms as a "basisphenoid" (Klein 1884; Supino 1905; Rosen 1916a),

but, strangely, there has been agreement (as early as Stannius 1854:61) that gymnodonts, except for molids.
do not possess a basisphenoid. It is indeed food for thought that a basisphenoid occurs only in Triodon, which by all odds is the most primitive of the Recent

gymnodonts, and in molids, which are one of the end

lines of gymnodont radiation. Starks (1905:755), in dis- cussing the myodome of fishes, noted that "the dichost

( = basisphenoid of Huxley) is always absent when the myodome is. I know of no case where it is at all ossifed when the myodome is absent." Molids are thus an ex- ception to the rule. The basisphenoid of Triodon is relatively normal in appearance, but that of molids is ex- panded anterodorsally until it makes contact with the pterosphenoids (in Mola and Masturus) or frontals (in Ranzania).

In the ethmoid region the size and shape of the eth- moid have been prominently used in the classification of the tetraodontids by Fraser-Brunner (1943). While the- ethmoid of tetraodontids is sometimes rather small, by

far the most reduced state of the bone is found in diodontids, where there is a thin plate of bone that represents the only remains of the ossifications of the entire eth- moid region of the skull in a position analogous to that of both the vomer and the ethmoid. For that reason, this bone is called here the ethmoid-vomer, supposing that it represents the fused rudiments of both elements. Starks

(1926:286) recognized the dual anatomical position of

this bone in Diodon, but preferred to call it the ethmoid.

It should be mentioned briefly that in HoUard's various

publications the medial portion of the plectognath eth- moid was called the "ethmoid," while its lateral portions were referred to as the "nasals." Hollard did not, however, show any sutures between these two regions, so

his terminology was undoubtedly based on theoretical considerations. Awati and Bal (1933) divided the eth- moid of their tetraodontid in the Hollardian manner, but

referred to the medial portion of the ethmoid as the

"lateral ethmoid" and to the lateral portions of the eth- moid as the "nasals." Swinnerton (1902) found the eth- moid and palatine regions of balistids and acanthurids to be similar. The vomer of tetraodontids and ostracioids is sometimes so closely interdigitated, or even fused, with the ethmoid and parasphenoid that even a relatively knowledgeable worker such as Kaschkaroff (1914a:350) mistakenly said that the vomer was absent in those groups.

In the mandibular region the presence of a symplectic has sometimes been overlooked. Cope (1871:591) stated that in the Phyaoclisti "the symplectic is present, except in Ostracion, where it is not ossified," but Regan

(1903a:290) corrected Cope's error. In view of Regan's

statements, it is surprising to find that Kaschkaroff

(1914a:352) extended Cope's misstatement to include Triacanthus as well as Ostracion, both of which Kaschkaroff said lacked a symplectic. Raven (1939b:4) said that the symplectic was absent in Ranzania, but figures 316 and 320 given here show it to be long and prominent.

In the palato-pterygoid region the size, shape, and

articulations of the palatine have been used as important diagnostic features for a number of plectognath

subgroups, sometimes erroneously. A summary of the

condition of the palatine in plectognaths, with brief comments on the literature, follows. In triacanthoids the

palatine is basically a flattened rectangular or squarish bone with a small posterodorsal lobe about midway along

its upper edge for firm anchoring through fibrous tissue with a region of the ethmoid-prefrontal-vomer, while

ventrally the palatine is firmly anchored by fibrous tis- sue with the ectopterygoid, except in the long-snouted

species in which it forms a portion of the tubelike snout; an anterior process of the palatine movably articulates with the recessed dorsolateral surface of the maxillary so that the latter can rotate around this articulation and

allow for a slight protraction of the upper jaw, except in the long-snouted species in which the protractibility of the upper jaw is not so directly associated with a maxillary-palatine articulation. In balistids what is the squarish ventral portion of the palatine in most triacanthoids becomes shaftlike and the whole palatine T-shaped,

with the ventral shaft firmly anchored by fibrous

tissue with the ectopterygoid, the posterodorsal end

similarly held to the ethmoid and vomer, and the anterodorsal end movably articulated with a slight concavity on the lateral surface of the maxillary, around which

point of articulation the upper jaw rotates, without being

protracted. In monacanthids the palatine is rodlike, but sometimes with a bulge on its ventral surface representing the long foot of the T as found in balistids, con- nected ventrally by a long ligament to the anterior edge

of the ectopterygoid, while posteriorly the rod is anchored by fibrous tissue to the ethmoid and anteriorly

is movably articulated with a slight concavity on the

lateral surface of the premaxillary and maxillary. The differences in the shape of the palatine in the tria- canthoids, balistids, and monacanthids have long been known, but with Regan's (1903a) use of these features as diagnostic characteristics an error crept into the

literature. Regan said that the triacanthoids had the

palatine immovably articulated with the other bones of the skull, but that the balistoids had it either movably

articulated with the ectopterygoid (balistids) or entirely

free from it (monacanthids), and Fraser-Brunner (1941b) has said much the same thing. The differences in the shape of the bone are real enough, but the palatine im- movably articulates with the ectopterygoid and with the ethmoid-vomerine region in all of these groups. It is the

firm anchoring of the palatine to these two regions which

provides the upper jaw with the immovable prop around

which it can rotate. The ventral edge of the palatine and

the dorsal edge of the ectopterygoid in triacanthoids and

balistids are often not in close contact with one another, but the sheet of tough fibrous tissue that binds the

palatine to the ectopterygoid and to the ethmoid- vomerine area makes the palatine immovable for all practical purposes.

In ostracioids the palatine is a relatively small and

elongate block of bone, representing an enlarged foot of the T-shaped balistid palatine, which is usually

extensively interdigitated with the dorsal end of the

ectopterygoid and mesopterygoid. The rounded dorso- medial edge of the palatine is firmly held by fibrous
tissue primarily to the vomer, usually to a slight concavity on the surface of the latter. The palatine is so small and closely apposed to the ectopterygoid that most

authors have been noticeably vague about its articulation or even about is presence, although Hollard (1860:

fig. 6 of pi. 3) presented an accurate figure of it. The palatine in the gymnodonts is a much larger bone

than it is in the scleroderms. The ventral edge of the

palatine in gymnodonts always immovely articulates, usually by interdigitation, with the ectopterygoid.

Posteroventrally the palatine articulates with the mesopterygoid, and in some cases with the metapterygoid as

well. The anterodorsal edge of the palatine supports the upper jaw, primarily through a flexible fibrous tissue ar- ticulation with the concave facet on the maxillary. There

is some variability, however, in the immovable ar- ticulation of the palatine with the ethmoid region of the

skull. In Triodon the medial surface of the palatine ar- ticulates with the ethmoid, vomer, parasphenoid, and

prefrontal. Rather unexpectedly, the shape and ar- ticulation of the palatine in molids is strikingly similar to that in Triodon. The characteristic feature of the

palatine in tetraodontids is that its posterodorsal region

possesses an anteriorly directed cleft which fits closely around some type of flange on the lateral surface of the vomer. With the almost total reduction of the ethmoid

region in diodontids, the palatine becomes extensively

interdigitated with the frontals and makes only a sec- ondary and functionally unimportant contact medially

with the ethmoid-vomer.

Gregory (1933:287) presented highly diagrammatic

figures of the palato-pterygoid region of the skull in Triacanthus, Balistes, Alutera, and Psilocephalus to il- lustrate the progressive elongation of the snout in that

series. Fraser-Brunner (1941a:423) showed, with more

detailed illustrations, the changes that take place in the

palato-pterygoid region when the same type of elongation of the snout takes place in the triacanthodid genera Johnsonina, Tydemania, and Macrorhamphosodes,

while Tyler (1968) did so for all the genera of that family. The figures and descriptions given by Thilo (1920) of the jaws and palato-pterygoid region of Triacanthus,

Balistes, and Tetraodon are too crude to be of any value, but those of Winther (1877) are much more useful. Others have presented accurate descriptions and figures of the palato-pterygoid region in particular species, e.g., Steenstrup and Liitken (1898) for Mala, and Supino

(1905, 1907) for Mola and Balistes. In the opercular region the length and posterior

articulation of the interoperculum have been used as diagnostic familial characters. A summary of the inter- operculum in plectognaths with brief comments on the

literature follows. The interoperculum is best developed

in the triacanthoids, in which it is relatively broad and

rounded posteriorly and only gradually tapers to a point

anteriorly. Posteriorly the interoperculum articulates

closely with the suboperculum. In balistoids the inter- operculum is a short rod which never extends posteriorly past the level of the epihyal. The posterior end of the interoperculum in balistoids has its main articulation

with the epihyal, while more posteriorly it connects by a

long band of fibrous tissue with the operculum, or with

the region of articulation between the operculum and

the suboperculum. In ostracioids the interoperculum

is even slightly shorter than it is in most balistoids, and

similarly it has its main posterior articulation with

the epihyal. In contrast to the balistoids, however,

the long band of fibrous tissue running posteriorly from

the ostracioid interoperculum attaches exclusively to the suboperculum, rather than to the operculum or to both the operculum and suboperculum. Among the gymnodonts the interoperculum is relatively long and

well developed in all groups, except in the molids. In the latter group the interoperculum is reduced to a thin but sometimes long splint of bone entirely embedded in the long ligament which runs between the angular and

suboperculum. In tetraodontids and diodontids the rodlike interoperculum always has a ventral flange in about

the middle of its length wWch articulates by fibrous

tissue with the epihyal. The bifurcate posterior end of the interoperculum in Triodon is unique among the

plectognaths, with it being hypothesized that the ventral process of the bifurcate portion corresponds to the

ventral flange of the interoperculum in tetraodontids and

diodontids. The interoperculum articulates posteriorly with the anteriorly directed process of the suboperculum

in Triodon, diodontids, and molids, but in tetra- odontids it articulates with the operculum. While many early workers described the unusual shape

of the interoperculum in this order, and Dareste (1850)

said that it was one of the few characters that the plec- tognath fishes had in common, it was not until Regan

(1903a) that the structure of the interoperculum was

used diagnostically for various plectognath subgroups. Regan incorrectly said that in the Sclerodermi the inter- operculum was attached to the suboperculum, while in the Gymnodontes it was attached to the suboperculum in

all groups except the tetraodontids. Fraser-Brimner

(1943) similarly used this supposed difference in the posterior articulation of the interoperculum as a diagnostic

character. In his various publications on the respiratory ap- paratus of plectognaths and related forms, Willem (1941, 1942, 1944, 1945, 1947, 1949) pointed out the correlation between the presence of a distensible diverticulum of the oesophagus and the size of the suboperculum (i.e., the suboperculum is relatively well developed in the tetra- odontids and diodontids) and discussed the role of the in- teroperculum in coordinating the opening of the lower jaw with the expansion of the opercular apparatus at the beginning of the inspiration phase of the respiratory cycle.The structure of the jaw8 of plectognaths has played such an important role in the diagnoses of various

families since the founding of the order that it must be summarized here. Cuvier's (1817) term Plectognathi (from the Greek: plektos, plaited or twisted together; gnathos, jaw) refers to the intimate and inflexible union

of the premaxillary and maxillary in all families except

the triacanthoids.
In all plectognaths except the triacanthoids, the upper jaw is nonprotractile and the premaxillary immovably

articulates, usually by extensive interdigitation, with the

maxillary. In triacanthoids the premaxillary and maxillary movably articulate with one another and the upper jaw is slightly protractile. The premaxillary of triacan- thoids is more or less L-shaped, with the long arm of the L forming the posteriorly directed ascending process which slides over the dorsal surface of the ethmoid in the

process of protracting and retracting the upper jaw. In

balistoids and ostracioids the posteriorly directed process

of the premaxillary is essentially absent, and the postero- medial end of the premaxillary articulates with the anterior edges of the ethmoid and vomer, particularly with

the former. Along its anterior edge the premaxillary of the scleroderms bears a variable, but usually small, number of discrete teeth. The premaxillary of gymnodonts is modified, in conjunction with the teeth, into a crushing plate which is often and aptly referred to as a

parrotlike beak. The posteromedial end of the premaxillary articulates with the ethmoid, and to a lesser extent with the vomer, in Triodon, but in most tetraodontids

this articulation is primarily with the vomer. In Triodon and in the tetraodontids the medial edges of the two pre- maxillaries are closely apposed and articulate with one

another by fibrous tissue. Emarginations from the medial surfaces of each of the premaxillaries in tetra- odontids alternate with one another and strengthen the

articulation between the two elements. In diodontids and

molids the two premaxillaries are indistinguishably fus- ed together into a large U-shaped bone. Hollard (1857b:308) did not believe that fusion of the

premaxillaries, or dentaries, was a character of much sys- tematic importance, possibly because it was known that the premaxillaries and dentaries of extremely large specimens of tetraodontids occasionally fuse together in the same way as do those of diodontids. More interesting, however, is Reuven's (1894:130) observation of a phenomenon in Mola of just the opposite nature to that

occasionally observed in tetraodontoids. In his description of a young Mola, Reuven said that he "found that

the maxilla superior is splitted up in the middle, the in- ferior is not cleft," and a figure was presented (pi. 5) to show this "tetraodont" condition of the upper jaw.

Hollard's view that too much importance has been at- tributed to the fusion of the premaxillaries, or dentaries,

as a major indicator of phylogenetic affinity seems well taken. It might be mentioned here that the premaxillary and maxillary are often said to be fused or coalesced, when in actuality they, at least in the great majority of instances, only extensively interdigitate with one

another. Only very rarely is an extremely large specimen

of a tetraodontid or diodontid found in which the pre- maxillary and maxillary are for all practical purposes

fused. One of the more extreme statements about the fu- sion of the various jaw bones in plectognaths is that of Wagner (1845:190) who said that the upper jaw bone

"coalesces with the vomerine, palatal and nasal bones to form a single bone, which unites, however, with that of the other side by suture, as in Orthagoriscus." Such a

condition would certainly be the death of any plectog- nath and whether Wagner had ever actually examined a molid is problematical, although he had (1841) once

presented a figure of the skeleton of a balistid. Only in the triacanthoids is the maxillary movably ar- ticulated and not closely apposed to the premaxillary, for

in all other plectognaths the maxillary firmly articulates, usually by extensive interdigitation, with the pre- maxillary. In triacanthoids the lateral surface of the rounded dorsal end of the maxillary movably articulates with the anterior process of the palatine. In balistids the

palatine articulates with a slight concavity on the sur- face of the maxillary and premaxillary, but in monacanthids the maxillary scarcely makes contact with the

palatine or is even entirely excluded from articulation with it. With reduction of the palatine in ostracioids the maxillary articulates with only the anterior edges of the vomer and ethmoid. In gymnodonts the maxillary al- ways articulates over a broad, and usually slightly concave, area with the anterodorsal end of the palatine, and

it is this articulation which is the major source of support for the upper jaw in gymnodonts. In triacanthoids the support of the upper jaw is shared about equally between the articulation of the maxillary with the

palatine and the articulation of the premaxillary with

the ethmoid and vomer, but in balistoids the palatine-maxillary articulation becomes progressively less important and in ostracioids it is completely absent. The

posterior edge of the maxillary of most balistoids and ostra- cioids bears an indentation which is characteristic of these two groups, but not of the other plectognaths. The

lateral surface of the maxillary is relatively flat in all plectognaths except the diodontids, in which this sur- face is upraised into a stout flange for muscle attach- ment. The lower end of the maxillary forms the lower

part of the anterior edge of the upper jaw in all plec- tognaths. Among Shufeldt's (1917) nearly totally erroneous observations on the osteology of Diodon, there occurs the statement that an "admaxillary" is present on

the dorsal edge of each maxillary, but since no description or illustration was given of this structure, that

author's statement is best forgotten, as is his other work

(1926) on plectognaths.

In scleroderms the teeth are usually few in number but

they are always individually recognizable units. In the gymnodonts, however, the teeth are so highly modified

that they are scarcely recognizable as such. The number

and shape of the teeth in the jaws are discussed in the

diagnoses of the familial groupings recognized here and

are summarized below. The number and shape of the teeth vary most in the

triacanthodids, and Gunther (1870), Myers (1934), Fraser-Brunner (1941a), and Tyler (1968) have all made

prominent use of dental formulae in their revisions of the

family. The teeth of Recent triacanthodids are usually

conical and usually occur in a single series. This outer

series contains the majority of teeth, which usually vary

in number from about 10 to 50, but with reduced numbers (sometimes absent) in the long-snouted genera. When teeth in an inner series are present, in the more
generalized genera, they vary from 1 to about 10 in number. The teeth of the upper and lower jaws are basically

similar, but there are usually a few more teeth in the lower jaw than in the upper. In a few moderately to highly specialized genera the teeth are truncate rather than conical, while the fossil genera sometimes have en- larged teeth. In triacanthids there is an outer series of about 8 to 10 heavy incisors in each jaw, internal to which are several more or less molariform teeth, usually 4 (2 in one genus)

in the upper jaw and 2 in the lower. The structure and number of the teeth in balistids are strikingly similar to those found in triacanthids, for in balistids the heavy in- cisors invariably (with rare individual exceptions) occur

in an outer series of eight teeth and an inner series of six teeth in the upper jaw, while in the lower jaw there is only a single series (corresponding to the outer series of the upper jaw) of eight teeth. The number of teeth becomes further reduced in monacanthids to six in an

outer series in the upper jaw and six (sometimes only

four) in the outer series of the lower jaw, with an inner

series of four teeth in the upper jaw and no inner series teeth in the lower jaw. The dental formulae of the various balistoids have

been common features of the diagnoses of that group ever

since the time of Bleeker ( 1866:8- 10) , who was the first to give prominent attention to these differences. The

development of balistoid teeth from deep sockets in continuity with the pulp cavity was accurately described for the first time by Owen (1840 & 1845:82-85). Goodrich

( 1909:438, fig. 448) gave a figure of the replacement teeth developing in Balistes, and Isokawa (1955) presented a

description of the general development and histology of the teeth in monacanthids. The teeth of ostracioids are elongate and rodlike, with between 6 and 17 teeth in a

single series in each jaw. The teeth of gymnodonts are so highly modified that they have attracted a great deal of attention in the

literature. There is, however, a phyletically important

distinction to be made about the teeth of the various gymnodont subgroups which usually is not clearly

stated. In Triodon and diodontids the teeth always take

the form of relatively small £uid discrete units which become densely packed with one another and incor- porated with the bony matrix of the premaxillary and

dentary. In tetraodontids the teeth are relatively more

discrete long rods which lie parallel to the biting edge of the jaws. There are no discrete teeth present in the jaws

of molids, nor can any individual tooth primordia be found in the pulp cavity. The intimate incorporation of the teeth with the bony matrix of the premaxillary and

dentary has reached its zenith in the molids, and one can

only speculate that the highly irregular surface of the

floor of the pulp cavity, with its numerous individual "tooth" or bone forming cavities, indicates that the molid condition has evolved from the Triodon and

diodontid type rather than from the tetraodontid type. The structure, and even the mere presence or absence,

of a trituration plate is also of diagnostic interest. In Triodon a trituration plate composed of right and left

halves is present in the upper jaw, while the trituration plate of the lower jaw is undivided. In both jaws about

five individual teeth can be seen at the posterior edge of the trituration plate to each side of the midline. In diodontids and molids there is a trituration plate in each

jaw, but the number of dental units that go into its make

up differs. In diodontids there is a single dental unit along the posterior edge of each half of the trituration plate in each jaw, except for one species with several dental units. In molids there is a single dental unit along the

posterior edge (and sometimes anteriorly) of each half of the trituration plate in the upper jaw, but in the lower jaw several such teeth are present. Steenstrup and Lutken (1898) described the dif- ferences between the trituration plates in two genera {Mola and Rumania) of molids, as did Hilgendorf (1893). Wahlgren (1867) gave one of the earliest and best descriptions of the trituration plate in Mola, and his figure of that structure was reproduced by Steenstrup and Lutken. Trituration plates are never developed in canthigasterins, but, contrary to Fraser-Brunner (1943), they are sometimes present in tetraodontins. In the upper jaw of many tetraodontids there is a single longitudinal series of

a small number of teeth, to each side of the midline. In

the lower jaw, however, these trituration teeth are of less frequent occurrence. They have been reported in the

lower jaws of several tetraodontids by Kaschkaroff

(1914a:317-318), in the lower jaw of the tetraodontid Colomesus by Pinto (1959), and in many other tetra- odontids described here. There are a number of papers

describing the general structure of the teeth in plectog- naths to which the reader should be referred before passing on to other topics. Cuvier (1805, vol. 3) gave descriptions of the gross morphology of the teeth in plectog- naths, but it was not until Owen (1840 & 1845) that their detailed structure was made known. Owen took exception to the view advocated by Cuvier (1805, 3:125) and by Bom (1827) that the dental lamellae in gymnodonts

develop by the "apposition or the transudation of layers

of calcareous matter from the pulp's surface" (Owen

1840:77). On the contrary, Owen showed that these lamellae developed by "intus-susception or the deposition of calcareous tubes in the pulp's substance." Owen

pointed out that whereas the teeth of the biting part of the jaws in diodontids and tetraodontoids were dif- ferent, there was a marked similarity between the dental

lamellae of the trituration plate of diodontids and the

elongate dental lamellae of the biting portion of the jaws

in tetraodontids. A more modem treatment of the

general anatomy of the teeth in gymnodonts is that presented by Pflugfelder (1930), Andreucci (1966a, b, 1967a, b, 1968a, b, 1969, 1970), Andreucci and Britski (1968a, b, 1969a, b, 1970, 1971), and Andreucci and Blumen (1971). The rodlike structure of the dental units

of tetraodontids and the platelike trituration lamellae have been described by a number of workers other than

those mentioned above, notably by Goodrich (1909), Ghigi (1921), and Tretjakoff (1926c). Jenyns (1842:150) was probably the first to call attention to the discrete dental units that are visible on the external surface of the
crushing beak of diodontids in his description of a species

of Diodon: "the true teeth appear on the surface of the jaws like minute scales, as in several species of the genus

Scarus."

It will be recalled that Regan (1903a) placed the genus

Triodon in the Sclerodermi, and, as a consequence of

this, it was necessary for him to state (p. 285) that "the

coalescense of the teeth in the jaws is a feature of little importance, and has, as probably as not, originated in- dependently in . . . [the Sclerodermi] . . . and in the Gymnodontes." That view is not followed here, as the placement of Triodon in the Gymnodontes indicates. For a discussion of the surface structure of plectog- nath teeth in relation to sound production by stridula- tion the reader is referred to Burkenroad (1931:22-24), Fish et al. (1952:189-190), Fish (1954:62-77), Moulton

(1958:359-362), and Vincent (1963). The two dentaries are indistinguishably fused with one

another in Triodon, diodontids, and molids. The fibrous

tissue articulation of the two dentaries in tetraodontids is strengthened by emarginations from the medial edges of the two bones, just as is the case with the premaxillaries. In triacanthodids and molids the articular and dentary are firmly held to one another mainly by fibrous tis- sue, but in other plectognaths there is normally an ex- tensive interdigitation between the surfaces of these two

bones. It is not true, however, that the dentary and ar- ticular are fused into a single piece, as was maintained

by Gill (1872:XL; 1885:412) for plectognaths in general, and as Smith (1935:359) gave as a characteristic of the

balistoids. Regan (1903a:286) correctly stated that the dentary and articular are not fused in the gymnodonts,

but, rather unaccountably, he agreed with Gill that these two bones are fused in the scleroderms. In the descriptions of the representative plectognaths given here no at- tempt is made to differentiate between a dermal and an

endochondral portion of the articular, for this requires

histological study of the developing bone for consistant accuracy. Only two papers in the literature treat this subject in plectognaths. Rosen (1916a: 19) simply said, without any elaboration, that in Sphoeroides the "articulare develops as an autarticulare and a dermarticulare." Haines (1937:14-21) gave a detailed description of the growth and fate of Meckel's cartilage and the surrounding ossifications in Tetraodon, and concluded

that the endochondral portion of the articular was either greatly reduced or absent. The sesamoid articular is pres- ent in all plectognaths, except some tetraodontids and

molids. It has been described in a number of different plectognath genera by Starks (1916:32-33), who said that

in Sphoeroides annulatus "the sesamoid articular more

evidently originates within the tendon than in any other examples I have encountered." With the exception of Rumania, which has lost the

sixth branchiostegal ray, all gymnodonts have six such

rays, and statements in the literature giving a lesser number probably reflect the loss of a ray during dissection, while Hubbs (1919:69) pointed out that "in Tetrao- don the uppermost ray basally is an unossified ligament," which is true also of some other tetraodontids where the sixth ray tends to be an especially slender

shaft. McAllister (1968) accurately surveyed the number of branchiostegal rays and the structure of the hyoid

arch in a wide selection of plectognaths, far more so than

ever previously attempted, and found them to be related

to the acanthopterygian type. Wellenbergh (1840) gave an accurate description and

figure of the six branchiostegal rays in Mala, but Kaschkaroff (1914a:282) and Van Dobben (1935) stated that

there are only five branchiostegal rays present in Mola. Roon and Pelkwijk (1939) and Roon (1942) have again

called attention to the fact that there are six branchiostegal rays in Mola. Thilo (1899a, 1914) first pointed out that species such as Stephanolepis setifer and

Brachaluteres trossulus possess only five branchiostegal

rays. In contrast to Ranzania, however, it is not the sixth branchiostegal that is lost; rather, it is the second

branchiostegal. The branchiostegal counts given by

Willen (1941, 1942, 1944, 1945, 1947, 1949) are not

reliable. He said that there were six branchiostegals in Triacanthus, Monacanthus, Ostracion and Mola, but that

there were seven in Batistes and five in Tetraodon and

Diodon. The supposed "seventh ray" of balistids was

neither figured nor well described, and it is only possible

to guess that Willem may have mistaken the rodlike in- teroperculum for a seventh branchiostegal. The branchial region is one of the most neglected anatomical systems of fishes, for cleared and stained specimens and especially delicate dissections are re- quired, although Nelson (1969 et seq.) has made great

strides in rectifying this situation. In plectognaths the

extensive variation in branchial structure reported here (Table 1) forms an important part of the diagnoses of the

higher categories recognized and of the phylogenetic inter- pretations offered, and yet the only previous survey of

the plectognath branchial apparatus is the cursory one by Kaschkaroff( 1914a). There are, however, a few papers

containing descriptions of the branchial or hyoid arches

of particular genera, such as Awati and Bal (1933) for Tetraodon, Borcea (1907) for Batistes, Steenstrup and

Liitken (1898) for Mola, Supino (1905) for Balistes and

Mola, and Wellenbergh (1840) for Mola. The condition of the plectognath branchial apparatus, with comments on the literature, is summarized below. A basihyal is always present but the dorsal hypohyal is absent in many tetraodontids and a few

diodontids. The hypohyals are enlarged in ostracioids, and it was probably the size of the dorsal hypohyal that

lead Horshelmann (1866:23) to say that Ostracion

possessed a tongue while the other plectognaths did not. The ceratohyal and epihyal are always present, while

the interhyal is absent in diodontids and most tetra- odontids. The urohyal is well developed only in triacan- thoids and balistoids, although it is present in a muchreduced state in ostracioids and in Triodon. The

branchiostegal rays usually are present in the 2-1-4

arrangement typical of percoid fishes (Hubbs 1919), al- though the second and sixth branchiostegal rays are absent in a few species of monacanthids and aracanids, and
the sixth absent in one of the molids. There are a number of diagnostically important differences given here in the manner by which the branchiostegal rays are articu- lated to the ceratohyal and in the form of the modified

first branchiostegal ray of many gymnodonts.

Thilo (1899b, 1914) drew attention to the obvious cor- relation between the presence of an inflation mechanism

in many gymnodonts and the enlargement of the first branchiostegal ray, and described the pumping action of that platelike element. Thilo (1914) contended that when

the distensible diverticulum of the oesophagus is not

well developed (as in Fugu rubripes and Lagocephalus

scleratus, according to Thilo) the first branchiostegal ray

is as small as it is in most balistoids. Thilo is guilty of exaggeration, for the first branchiostegal ray in those two

species is much larger than it is in any balistoid, even though it is somewhat reduced in size from that seen in more typical gymnodonts.

There are always three basibranchials (except in the monacanthid Psilocephalus with two), three pairs of hypobranchials, five pairs of ceratobranchials, and four

pairs of epibranchials (except in Psilocephalus with

three), but the number of pharyngobranchials is variable and of much diagnostic interest. There are always at

least two pharyngobranchials, those of the second and

third arches, except that in diodontids they are of the

first and second arches. The pharyngobranchial of the

first arch is absent in monacanthids, molids, and some

ostraciids, while that of the fourth arch is absent in

balistids, monacanthids, ostraciids, tetraodontids, and

diodontids and that of the third arch absent only in diodontids. The dentition of the pharyngobranchials is also of great diagnostic use, for teeth are present on the pharyngobranchial of the first arch in diodontids and some tetraodontids, on that of the second arch in all but

a few aracanids, on that of the third arch in all but some

ostraciids and diodontids, and on that of the fourth in triacanthodids, triacanthids, aracanids, triodontids, and

molids. The fifth ceratobranchial is toothed in triacan- thodids, triacanthids, balistids, triodontids, and, with minute teeth, in a few diodontids.

In Canthigaster the first three ceratobranchials are more compressed and deeper than in other tetraodontids, while in molids the ceratobranchials are so deep

that in Mola they have been called (Barnard 1935:657)

"knife-like bones." These support the enormous gills of molids, which were well illustrated as long ago as Ales- sandrini (1839). The first pharyngobranchial in triacanthoids, balistoids, and triodontids is usually a toothless, often rodlike, suspensory element. Grieb (1935) has said that teeth are present on the

lower pharyngeals of "Spheroides sp.," but that has not been found to be the case in any tetraodontids examined

here. The reader is referred to Al-Hussaini (1947) for an

interesting discussion of the correlation between diet, length of intestine, and development of pharyngeal teeth

in a number of plectognaths. Iwai (1964) has carefully surveyed the taste buds on the gill rakers and gill arches

of Fugu and Rudarius.

In the pectoral girdle the position of the supracleithrum varies from more or less vertical in scleroderms to being

obliquely placed in relation to the skull in triodontids and tetraodontids, while in diodontids and molids it is almost horizontal to the skull. Regan (1903a) used the

position of the supracleithrum as one of the distinguish- ing features between the Sclerodermi and Gymnodontes.

It was probably Gill (1872, 1885) who made best known

that there is some rudiment of a posttemporal present between the supracleithrum and pterotic in at least some

plectognaths, and much the same was said by Regan

(1903a:285), Rosen (1916a:21), and Berg (1940:495). Even though relatively small and closely sutured and in- terdigitated to the skull, careful examination reveals its presence in all scleroderms except one monacanthid, and

its absence in all gymnodonts.

Siebenrock's (1901) descriptions of the pectoral girdle

in a number of plectognaths are so erroneous that they

are useless, and Regan (1903a:291) called attention to the

incorrectness of Seibenrock's contention that the supra- cleithrum of Mola was really a posttemporal. Sjirensen's (1883) mainly myological description of the pectoral

region of Tetraodon is highly detailed. Both the dorsal and the ventral postcleithra are pres- ent in most plectognaths as distinct elements, hut in monacanthids, diodontids, and molids the two elements

tend to indistinguishably fuse. Fraser-Brunner (1941c:307) used size of the postcleithra as one characteristic to distin- guish aracanids from ostraciids. The suture between the dorsal and ventral postcleithra is difficult to trace in many

ostracioids, and it is possible that the two elements oc- casionally fuse together. The anteriorly directed process, which lies just lateral to the actinosts, of the fused postcleithra of molids is a diagnostic feature of that group. Kuronuma (1943) has used the shape of the ventral post- cleithrum in tetraodontids as a systematic character and

Parr (1927) gave an interesting discussion of the function of the postcleithra in gymnodonts, while Winterbot- tom (1971) has thoroughly surveyed the matter. Thilo

(1899b) was surely in error in saying that the postcleithra could be moved through an arc of 90° . The role played by the postcleithra and cleithra in sound production has been discussed by Mobius (1889), Cunningham

(1910:117), and Fish (1954:69). For a general survey of the endochondral bones of the plectognath pectoral gir- dle the reader is referred to Starks' (1930:206-210) excellent work on that subject. Sound production by pectoral

fin drumming is reviewed by Salmon et al. (1968), and by

this and other methods by Schneider (1961). The scapula completely encloses the scapular foramen

in most scleroderms and in Triodon, but in tetraodontids and diodontids the foramen is incomplete, being enclosed by both the scapula and the cleithrum. In molids the scapular foramen is essentially absent or highly incomplete, being represented only by a small hole in the sheet

of fibrous tissue holding the bottom half of the scapula to the cleithrum. In scleroderms and in Triodon the dorsal edge of the scapula always bears an emargination to which is attached the first pectoral fin ray, but in the

other plectognaths no such emargination is present. Four
actinosts are present in all plectognaths, except in molids, which have three. The close connection of the scapula with the first actinost is such that Regan (1903a:291) drew attention to the fact that "On a superficial examination there ap- pears to be no scapula, and the pectoral fin to be supported by a series of four enlarged pterygials. In fact, the united upper pterygial and scapula together resemble one of the enlarged pterygials." Even after this state- ment, others (e.g., Kaschkaroff 1914a:355; Awati and Bal

1933:91) continued to misidentify the actinosts and

scapula. On the other hand, Regan's (1903a) statement

that the scleroderms have the "pterygials (pectoral

basalia) not enlarged, movably attached by ligament to the scapula and coracoid, three to the former and one to the latter" (p. 286) while the gymnodonts have the "lower three pterygials enlarged and immovable united

to the coraco-scapula" (p. 291) is only partially true (see above). In molids what was the first actinost of other plectognaths is either lost or fused with the scapula, so that only three actinosts are present. Somewhat understandably, a number of workers have mistaken the scapula of Mola for an actinost and have concluded that Mola possessed four actinosts and no scapula. However,

Gregory and Raven (1934:148) described Mola as having

four actinosts (i.e., three actinosts and a scapula), as well as a "vestigial scapula" represented by a "bone which is crowded between the expanded first pterygial and the

posterior recurved border of the cleithrum." It is impossible to state what it was that Gregory and Raven saw,

for their description is brief and there is no illustration of the vestigial scapula. The structure of the pelvis and pelvic fin in plectog- naths has been the cause of much confusion in the

literature, for the relatively normal pelvic apparatus of triacanthoids is replaced by a highly modified and

specialized structure in balistoids that has been often misinterpreted. Tyler (1962b) has surveyed in detail the reduction and eventual loss of the pelvic apparatus in plectognaths, and these features are used prominently in the diagnoses given here, while Winterbottom (1970) sur- veyed the muscles of the triacanthoid pelvic fin. The

locking mechanism of the triacanthoid pelvic spines (continuous series of positions of erection in triacan- thodids and two positions in triacanthids) is also treated by Tyler (1962b). HoUard (1853:107) and Thilo (1896a, 1896b:327, 1898, 1899a, 1900) incorrectly described only a

single position of erection in Triacanthus, but the twoposition mechanism has been correctly described by

Sorensen (1884:69, 1897) and Monod (1959c). The true nature of the rudimentary pelvic fin element

in balistids was first made known by Monod (1959a), in excellent style for Balistes forcipatus. As detailed in the accounts of each family given here, the number of vertebrae in plectognaths varies from 16 to 30

(Table 2) but is usually less than 24 and normally in the range of 17 to 21, while the structure of the vertebral column is highly modified in some groups, especially the

ostracioids (Tyler 1963a) and molids. In aracanids the

first two, and in ostraciids the first four or five, abdominal vertebrae are at least partially fused to the

skull, and the whole vertebral column is relatively in- flexible except in the caudal peduncular region ex- tending outside of the carapace. Another unusual feature

of the ostraciid vertebral column, first pointed out by

Fraser-Brunner (1941c:307), is that the course of the haemal canal is displaced to one side or the other from

the midline, while Tyler (1963a) called attention to the uniquely divergent positions away from the midline of the anal fin basal pterygiophores. Abe (1942) presented an extensive study of the variation in the form and number of elements of the tetraodontid vertebral column.

Ford (1937) compared the balistid and zeoid vertebral columns. The fact that true or pleural ribs are found in the monacanthid Pseudaluteres and in the gymnodont

Triodon negates Regan's (1903a:285) statement that "the

feature of most importance in diagnosing the suborder

Plectognathi is the absence of ribs." The sequence of vertebrae to which the epipleural bones are attached is a character of systematic importance, as first shown by Fraser-Brunner (1941b: 176) in

his differentiation of the triacanthodids from the triacan- thids and of the balistids from the monacanthids. The

epipleurals in some monacanthids tend to become swollen (hyperostotic) and closely applied to the transverse

processes of the vertebrae, and it is not surprising that they have been misinterpreted (e.g., Smith 1935). The

development of the epipleurals has been studied in several monacanthids by Goeppert (1895) and Goette

(1879). The structure and reduction in number of elements in the caudal fin supports is documented by Tyler (1970b), while comments are given by Pope (1945), Okada (1950), Randall (1964), and Tyler (1970d) on abnormalities of vertebral structures. The work of Abe (1949b) should be

consulted for a detailed survey of hypural fusion in tetra- odontids. The description given by Whitehouse (1910) was one of the earlier accurate accounts of a balistid caudal skeleton. Monod (1968) accurately surveyed and

illustrated the ural structures of a wide variety of plec- tognaths, and agreed with Dareste (1850) and Le Danois

(1955) that the triacanthoids and balistoids are not closely related to the ostracioids and gymnodonts (the Orbiculates). Gosline (1961:269) pointed out that "there seems to have been a general trend toward fusion of parts in the caudal skeleton of teleostean fishes that has occurred

repeatedly and independently in various lineages." The

Plectognathi are certainly a perfect example of this, since

there are several uroneurals, one epural, and six hypurals in the primitive triacanthodids, but the number of elements becomes reduced in the triacanthid-balistid- monacanthid series and becomes even more reduced in the ostracioids. The same reduction takes place in- dependently in the gymnodonts. Gosline said that the caudal skeletons of Zanclus, Acanthurus, and the plec- tognath fishes form a series, but Monod (1959b:728) has

said that the caudal skeleton of Acanthurus and Balistes are "toutefois profondement diff6rente" and thus the
acanthurids and balistids "ne sauraient etre tenues pour

tres eloignees." What Monod did not realize was that if the caudal skeleton of a triacanthodid is compared with

that of an acanthurid, one finds the two to be rather

similar. Just as the number of epurals, uroneurals, and hypurals becomes reduced in the more specialized plectog- naths, so also the number of caudal fin rays becomes

reduced. In triacanthoids and balistoids there are 12 caudal fin rays; the uppermost ray and the lowermost ray unbranched, the others branched (except Psilocephalus)

In aracanids there are 11 rays, but in ostraciids the number is further reduced to 10. As with the other sclero- derms, the uppermost ray and the lowermost ray are unbranched, but the others are branched. Triodon has 12

principal caudal fin rays, but in addition to these it also possesses a series of procurrent rays. Triodon is thus the only Recent plectognath with more than 12 fin rays in the caudal fin, but its number of principal caudal fin rays is still the same as in triacanthoids and balistoids. In tetra- odontids there are usually 11 caudal fin rays; the upper- most ray and the lowermost two rays unbranched, the

others branched. As a part of his long and useful series of papers (1942, 1944, 1949a, 1950-51, 1952, 1954, 1960), Abe extensively and accurately surveyed the variability of the caudal fin rays (1949b) in tetraodontids, showing the i, 8, ii arrangement to be the normal condition

for all of the numerous species he studied. In diodontids

the number of caudal fin rays is either 9 or 10, with the uppermost ray and the lowermost ray unbranched, and the other rays branched. The complicated subject of the pseudocaudal fin of molids can only be summarized here. A number of early workers (Wellenbergh 1840; Goodsir 1841; Cleland 1862; Wahlgren 1867; Putnam 1871) gave brief descriptions of the highly modified structures of the caudal fin of molids, but it was not until Ryder's (1886) work that the

origin of this fin was adequately discussed. Ryder

described some of the developmental stages of the molid

caudal fin and came to the conclusion that that struc- ture was a gephyrocercal tail; the true caudal fin having been lost and replaced by posteriorly migrated dorsal and anal fin rays. Ryder said that molids and carapids were the only two groups with gephyrocercal tails. Ryder's opinion did not meet with unanimous acceptance, and Kaschkaroff (1914a), Grenholm (1923), and

Gregory and Raven (1934) continued to describe it as a true caudal fin, while Whitehouse (1910) and Regan

(1910) both agreed that the structure was a gephyrocercal tail. With typical thoroughness, Gudger (1935; 1936; 1937a, b, 1939) and Gudger and MacDonald (1935) reviewed the literature on the subject and also per- sonally examined a few developmental stages of molids. Gudger came to the conclusion that both Mala and

Masturus have a gephyrocercal tail, and Raven (1939a) agreed with that analysis. Raven (1939b) described the

tail of Ramania as also being gephyrocercal. Fraser- Brunner (1951) was in basic agreement with Gudger and Raven on this subject, but Fraser-Brunner stated that

the few fin rays that are found in the "nipple" part of the

tail of Masturus are the remnants of the true caudal fin rays, whereas the rest of the caudal structure is gephyrocercal. In short, there is general agreement that

the entire caudal structure in Mola and in Ramania is gephyrocercal, and that in Masturus at least the great majority of the caudal structure is gephyrocercal. It is also agreed that the bony supporting elements of the pseudocaudal fin in molids are posteromedially migrated

dorsal and anal fin basal pterygiophores. Owen's

(1846:64) description of these pterygiophores as "rudimental vertebrae . . . blended together at right angles to the rest of the column" does not seem plausible. The variability in the number of fin rays said to be pres- ent in Mola (summarized by Beauregard 1893) attests to the fact that it is difficult to delimit the pseudocaudal fin from the dorsal and anal fins, as well as to the fact that a

great many of the descriptions of Mola in the literature are actually based on Masturus (summarized by Gudger

1937a). To complicate matters even more, Fraser-Brunner (1951) attempted to distinguish two species of Mola,

partially on the basis of the number of fin rays borne on

modified basal pterygiophores. Barnard (1935) has

pointed out the diagnostic value of the degree of branching of the fin rays of the pseudocaudal fin in molids. The dorsal and anal fins, and especially the dorsal fin spines, being highly visible and variable between groups

of plectognaths, have been featured prominently in nearly all diagnoses, including here, as summarized below.

In triacanthodids there are six dorsal fin spines sup- ported by five basal pterygiophores, with the first two

spines always prominent and visible externally, the third

to fifth either normally developed or rudiments buried beneath the skin or barely protruding to the surface, and

the sixth spine either a short protruding element or a rudiment buried beneath the skin or barely protruding to the surface. There are 12 to 18 dorsal fin rays and 11 to 16

anal fin rays in Recent species. In triacanthids there are nearly always six dorsal fin spines, except that the fifth and sixth spines are sometimes absent in one Recent species and perhaps in several fossil forms, supported by four, rarely only three, basal pterygiophores, with the first four spines always

visible externally, the fifth spine usually very short but

nearly always protruding at least a short distance through the skin, and the sixth spine nearly always pres- ent as a buried rudiment. There are 19 to 26 dorsal fin rays and 13 to 22 anal fin rays. In balistids there are three dorsal fin spines, the second more than one-half the length of the first, supported by

two basal pterygiophores and a supraneural strut. In monacanthids there are usually two dorsal fin spines, but sometimes only one, the second spine, when present, not more than one-third the length of the first, with both

spines supported by a single basal pterygiophore, without a supraneural strut. In balistoids there are 23 to 52 dorsal fin rays and 20 to 66 anal fin rays. The locking mechanism of the spines of triacanthoids is described by

Tyler (1968), and that of balistoids by the references given in the description of Balistapus undulatus.

In ostracioids there is no spiny dorsal fin, and the dor-
sal and anal fins are both short-based, with 9 to 13 rays

each. Among the gymnodonts only Triodon has even a trace

of a spiny dorsal fin, as a minute structure composed

usually of two spines, occasionally only one but with possible rudiments of a third spine, borne on two basal

pterygiophores, present in most specimens of one of the populations (Indonesia to Japan) of the single species, with the second basal pterygiophore succeeded by two

supraneural elements.

It is possible that the supraneural elements in gymnodonts are rudiments of the basal pterygiophores of the now absent spiny dorsal fin. The structure and position

of the single supraneural element in tetraodontids give no indication of its possible derivation from a spiny dorsal fin pterygiophore, but the structure and number of the supraneurals in Triodon are reminiscent of the spiny

dorsal fin pterygiophores of triacanthids. An at least analogous situation is present in ostracioids, for the aracanids have a very long supraneural element which

extends throughout almost the entire distance between

the supraoccipital and soft dorsal fin, but in ostraciids

this supraneural is short and confined to a position just

in front of the soft dorsal fin. One should refer to Bridge (1896) and Rosen (1916a)

for descriptions of the cartilaginous distal pterygio- phores in the dorsal and anal fins of several plectog- naths. Hora's (1924, 1925) descriptions of Kanduka as a genus of tetraodontid without a dorsal fin and with the

anal fin at least rudimentary, if not absent, are to be

looked upon skeptically. His two small (14 and 54 mm

SL) specimens were highly inflated, and the fins were undoubtedly hidden beneath the skin. The fact that Hora's radiographs did not show these fins probably

only means that the pictures were overexposed and that

the specimens were still weakly ossified. Much has been said in the literature about the general

structure of the bones of plectognaths. Some of the early workers obviously thought the plectognaths to be

similar to the "cartilaginous" fishes, probably because of the relatively late ossification of the bones that is seen in some plectognaths and because of misinterpretation of the spongy nature of the ossifications in Mala and of the

large amount of cartilage that is present even in the adult Mola. The consensus, however, seems to be that while many plectognaths simply have a relatively late ossifica- tion of the endochondral bones of the skull, the composition of the ossification is normal. This is more or less what Cuvier (1817:144) said in his definition of the Order

Plectognathi. The principal references to the histology of the bones of plectognaths are the following: Quekett

(1850-1855, bones of a number of plectognaths), Leydig

(1857, bones of Mola), Kolliker (1859, bones of numerous plectognaths; 1860, bones of Mola), Harting

(1865, bones of Mola), Goette (1879, epipleurals of Monacanthus), Trois (1883-1884, bones of Ranzania and Mola), Goeldi (1884, general bone structure in Balistes), Goeppert (1895, development of epipleurals

of Monacanthus), Stephan (1900, bones of Mo/a, Tetra- odon, and Balistes), Supino (1904, bones of Mola), Nowikoff (1910, bones of Mola), Kaschkaroff (1914a and 1925, bones of numerous plectognaths; 1914b and

1916, bones oi Mola), Studnicka (1916, bones of Mola), Rauther (1927b, epipleurals and vertebrae oi Monacanthus), Haines (1937, Meckel's cartilage in Tetraodon). The literature on the muscles of plectognaths has been

thoroughly reviewed by Winterbottom (1974) and duplication of that laudable effort is avoided here. The smatterings of information available on other sys- tems (such as the blood-vascular, digestive, renal, neural, chromosomal, cellular, physiological, developmental,

etc.) are too incomplete for plectognaths to be of im- mediate value to the present studies, and this literature

will not be routinely reviewed here. It will be analyzed in a forthcoming synopsis of the biological data on plectog- naths, and specific papers will only be cited here if they have direct bearing on other matters discussed.

Relationship of the Plectognathi to the Perciformes

As indicated in the historical review of the classifica- tion of the Plectognathi, it is commonly thought that the plectognaths are a derivative of the perciform fishes, and

perhaps most closely related to the acanthurid surgeonfishes. The features of the osteology of the Recent acanthurids most pertinent to an interpretation of their

classification and interrelationships have been reviewed by Tyler (1970c), aiming especially at ascertaining what

is generalized versus specialized in that family. The complementary analysis of the fossil forms of acanthurids is not yet completed, and the necessary comptirisons between them and the fossil plectognaths studied here, especially those of both groups from the Eocene, must

await a subsequent publication under preparation by

J. Blot (Mus. Nat. Hist. Nat., Paris) and the author. However, as indicated by Tyler (1968), it is obvious

that the skeletal structure of acanthurids is not far

removed from that of triacanthoids, the basal plectog- naths, differing mainly in the presence of a number of bones absent in triacanthoids and in a greater number of

certain meristic elements. In general appearance the acanthurid skeleton is closer to that of triacanthids among the plectognaths rather than to that of the more

generalized triacanthodids. This might suggest that if the triacanthoids and thus the other plectognaths share a common Upper Cretaceous ancestral stock (as sug- gested by Patterson 1964:400) with the acanthurids, that

the Recent acanthurids are not as generalized a group as the triacanthodids are relative to the triacanthids. Acanthurids differ most significantly from plectog- naths by having: two or three anal fin spines (none in plectognaths); a relatively better developed pelvic fin varying from 1,5 to 1,3, with the rays cross-striated and

branched (one spine followed by, at the most, two much

40
smaller unbranched rays without cross-striations in Recent triacanthodids, but with the Eocene Eoplectus

having a spine and four long branched and presumedly

cross-striated rays); 16 principal caudal fin rays (12 in triacanthodids, the maximum for the order); the presence

of a folding spine or fixed plates on the caudal peduncle

(folding spine lacking in all plectognaths but with fixed

plates in some scleroderms); a complete series of suborbital bones (none in plectognaths); nasal or other bones

lateral to the ethmoid and anterior to the prefrontal (none in plectognaths); parietals (none in plectognaths);

true or pleural ribs (lacking in all plectognaths except in one monacanthid and in the primitive gymnodont Trio- don); a basisphenoid (lacking in all plectognaths except Triodon and molids); a relatively normal percoid type

pelvis without a long extension posterior to the level of the pelvic fin origin (a long extension of the pelvis pres- ent only in triacanthoids posterior to the level of the pel- vic fin origin, this portion being at least half, and usually more, of the total length of the pelvis); very short premaxillary pedicels and a nonprotractile upper jaw

(premaxillary pedicels well developed and upper jaw

protractile only in triacanthoids); and a dorsal fin consisting of an anterior portion of 4 to 9 (rarely 3 or 10) spines not decreasing much, if at all, in length posteriorly in the series (except in the young of some species) and followed without spatial interruption or indentation

of the membrane by about 20 to 33 rays (as many as six dorsal spines present only in triacanthoids, decreasing

greatly in length posteriorly in the series, except in the Eocene Spinacanthus, and followed either without

spatial interruption or with only a slight spatial inter- ruption, but always with an indentation of the membrane to the base of the fin, by 12 to 26 rays in Recent

species of triacanthoids and as few as about eight in Spinacanthus; no more than three dorsal spines in other

plectognaths). A number of other features of acanthurids (e.g., the

ridged surfaces, deep indentations, and hooks found on

the distal articular areas of the first basal pterygio- phores of the spiny dorsal and anal fins and the laterally expanded distal ends of many of the others; the usually

highly modified dentition; less restricted gill opening;

longer and more anteriorly placed ethmoid; two or three more vertebrae; fewer and less well-developed branchiostegal rays anteriorly in the series, etc.) distinguish them

from triacanthoids and other plectognaths, but these will be dealt with in detail along with their similarities to triacanthoids in a subsequent work comparing the fossil acanthurids and triacanthoids.

SYSTEMATIC SECTION

Definition and Synopsis of the Osteology of the Order Plectognathi (Tetraodontiformes)

Until such time as most other orders of fishes have

been extensively studied anatomically, and especially os- teologically, it is impossible to give a comparative in- clusive diagnosis of the Plectognathi that would clearly and succinctly distinguish them at once from all other

orders of Acanthopterygii, and especially from all sub- groups of the Order Perciformes, of which order the plec- tognaths are most likely a specialized derivative. The

perciform suborder Acanthuroidei has often been

thought to be the closest extraordinal relative of the plec- tognaths, the implication being that the acanthurids and

plectognaths share a common ancestral line in the Cretaceous, with Patterson (1964:400) having suggested

that this was the Pharmacichthyidae. Tyler (1968:42-43)

briefly pointed out that the Recent acanthurids differ from the most generalized plectognaths, the triacan- thodids, mainly in the retention of a number of bones not now found in triacanthodids and in a greater number of certain meristic elements. I subsequently studied the os- teology of numerous additional Recent species (the major

features summarized in Tyler 1970a, c) and of a large majority of the specimens of fossil acanthurids available (unpubl. data), mainly from the Eocene of Monte Bolca,

Italy. These subsequent studies of acanthurids tend to support the view that acanthurids are probably relatively generalized (except in dentition, caudal peduncle ar- mature, and dorsal and anal spine locking mechanisms)

representatives of the same ancestral line which gave rise to the plectognaths, with at least the majority of plectog- naths becoming far more specialized than the acanthurids in most respects. These matters will be discussed in a subsequent paper

on the anatomy of fossil and Recent acanthurids by

J. Blot and the author, and then on their differences from and similarities to the plectognaths. For the moment, the Order Plectognathi is defined below by listings of the bones that are either constantly

present throughout the order or are of variable oc- currence. Certain bones apparently are always present in plectog- naths, although in many cases these bones are highly

variable in size and shape from one family or genus to the

next. Those elements which are constantly present are: basioccipital; exoccipital; supraoccipital; pterotic; sphenotic; epiotic; prootic; frontal; parasphenoid; eth- moid; vomer (with the possible exception of diodontids); hyomandibular; quadrate; metapterygoid; symplectic;

palatine; ectopterygoid; operculum; suboperculum; pre- operculum; premaxillary; maxillary; dentary; articular; angular; ventral hypohyal; ceratohyal; epihyal; four branchiostegal rays (at least one in the anterior group and three in the posterior group); two basibranchials (of the second and third arches); three hypobranchials (of the first to third arches); five ceratobranchials (support-
ing at least three gills, of the first to third arches); three epibranchials (of the second to fourth arches); two

pharyngobranchials (at least of the second and third arches; except in diodontids, of at least the first and sec- ond arches); supracleithrum; cleithrum; postcleithrum

as at least a single piece; coracoid; scapula; three acti- nosts (second to fourth sequentially from anterodorsal to posteroventral); between 9 and 25 pectoral fin rays (fin placed in about middle of side of body); between 7 and 52

dorsal fin rays and a similar or only slightly lesser number of basal pterygiophores; between 7 and 66 anal fin rays and a similar or only slightly lesser number of basal

pterygiophores; between 16 and 30 vertebrae (usually

less than 24); gill rakers on the anterior and posterior edges of the first to third arches. Those elements which are present in some plec- tognaths, but not in others, are: basisphenoid (consistently present only in triodontids and molids, but rarely present in at least one species of triacanthodid); sesamoid articular (absent only in several species of tetraodontids and molids); basihyal (present only in triacanthodids); dorsal hypohyal (absent only in a few

diodontids and many tetraodontids); interhyal (absent

only in diodontids and most tetraodontids); second and

sixth branchiostegal rays (one or both absent only in a few species of monacanthids and aracanids; the sixth absent in one species of molid), urohyal (absent in all Tetraodontoidei except triodontids); first and fourth pharyngobranchials (pharyngobranchial of first arch

absent in monacanthids, molids, and some ostraciids; that of the fourth arch absent in balistids, monacanthids, ostraciids, tetraodontids, and diodontids) and

third pharyngobranchial (absent only in a few diodontids); teeth on the pharyngobranchials (that of the

first arch with teeth in diodontids and some tetra- odontids; that of the second with teeth in all but a few

aracanids; that of the third with teeth in all but some os- traciids and diodontids; that of the fourth with teeth in triacanthodids, triacanthids, aracanids, triodontids, and

molids); teeth on fifth ceratobranchial (toothed in triacanthodids, triacanthids, balistids, and triodontids and with minute teeth in a few diodontids);

basibranchial and epibranchial of the first arch (absent

only in one species of monacanthid); first actinost (ab- sent only in molids); pterosphenoid (absent only in one

species of tetraodontid); prefrontal (absent only in two

species of tetraodontids and several species of diodontids); posttemporal (absent in one species of monacanthid and in all Tetraodontoidei); mesopterygoid (ab- sent in most species of triacanthids and in one species of tetraodontid); interoperculum (absent only in one

species of molid); pelvis (absent in aracanids, ostraciids, tetraodontids, diodontids, molids); well-developed pel- vic fin spine (present only in triacanthodids, with the

possible exception of several Eocene species, and triacanthids; thoracic in position, placed under pectoral fin base); well-developed pelvic fin rays (present only in one Eocene species of triacanthodid, with four rays); poorly developed pelvic fin rays immediately following the spine

(one or two present in many species of triacanthodids;

one even less well-developed ray present in some species

of triacanthids); a rudimentary but complex composite

pelvic fin element at the posterior end of the pelvis mostly hidden from view by enlarged encasing scales (present only in balistids and many monacanthids); pleural ribs (present only in triodontids, one species of monacanthid, and probably in one of the Eocene species of both

the triacanthodids and the tetraodontids); epipleurals (present in all triacanthodids, with the possible exception

of one of the Eocene species, and in all triacanthids,

balistids, monacanthids, and triodontids); a separate

epural (absent in aracanids, ostraciids, and molids and

in at least most diodontids); uroneurals (present as one

or two pairs in triacanthodids, triacanthids, and triodontids, and, rarely, in at least one species of balistid); a separate parhypural (autogenous in triacanthodids,

balistids, monacanthids, triodontids, and tetraodontids); one or more separate hypurals (usually five, sometimes only three or four, separate hypurals in triacanthodids, four in triodontids, one in triacanthids,

balistids, and tetraodontids, and one in at least most

monacanthids); a separate haemal spine of the penul- timate vertebra (autogenous in triacanthodids, balistids, monacanthids, aracanids, triodontids, tetraodontids, and a few species of ostraciids); a separate haemal spine

of the antipenultimate vertebra (autogenous only in trio- dontids); procurrent caudal fin rays (present in triodontids and in at least one species of Eocene triacanthodid);

principal caudal fin rays (apparently absent in at least two of the three species of molids, but perhaps represent- ed in the other species by the rays in the central nipple of the pseudocaudal fin otherwise formed of posteriorly migrated dorsal and anal fin rays; 12 principal rays in triacanthodids, triacanthids, balistids, monacanthids, and triodontids, 11 in aracanids (10 in one species) and

tetraodontids, 10 in ostraciids, and 9 or 10 in diodontids;

in all cases the uppermost ray and the lowermost ray being unbranched and the intervening rays branched, ex- cept in tetraodontids in which the uppermost ray and the two lowermost rays are unbranched, and in one species of monacanthid in which several rays both above and below

are unbranched); dorsal fin spines and their basal pte- rygiophores (six spines, the last four of which may be rudimentary and mostly buried beneath the skin, the

spines borne on five basal pterygiophores in triacanthodids; usually six spines, rarely only four or five, the sixth spine nearly always a buried rudiment, the spines borne on four, rarely three or five, basal pterygiophores in triacanthids; three spines borne on two basal pteryg- iophores in balistids; two spines, rarely only one, borne on one basal pterygiophore in monacanthids; two, possibly three, rudimentary spines borne on two basal pte- rygiophores in triodontids; no spines in aracanids, os- traciids, tetraodontids, diodontids, and molids); supraneural elements (one, as a strut supporting the sec- ond basal pterygiophore, in balistids; one in aracanids and ostraciids; one in several molids and in most tetrao- dontids; absent in all monacanthids and diodontids); ossified Baudelot's ligament (present only in aracanids and

ostraciids); trituration teeth or teeth internal to the ma-
jor outer series (present in both the upper and lower jaws

of a few triacanthodids and in all triacanthids, diodontids, and molids; present only in the upper jaw of

balistids and monacanthids; present in the upper jaw of many tetraodontids and, to a lesser extent, in the lower

jaw; absent in all aracanids and ostraciids); gill rakers along anterior edge of first gill slit (present only in molids); gill rakers along anterior edge of fourth arch (ab- sent only in a few diodontids); gill rakers along posterior edge of fourth arch (absent in tetraodontids and diodontids); gill rakers along anterior edge of fifth arch (present

in monacanthids, aracanids, ostraciids, and molids);

scales (present on at least a part of the body in all species except a few tetraodontids). The few major features in the soft anatomy of plec- tognaths treated here are about as variable between or within various families as the bony parts just discussed. Of most importance here, neglecting for the moment the musculature that has been so superbly studied by Winterbottom (1974), is the presence of four gills and a gill slit between the fourth and fifth arches in all groups ex- cept tetraodontids and diodontids, which have lost the

gill of the fourth arch and the slit between it and the

fifth. A pseudobranch is present in all species, but the degree of development and number of lamellae are highly

variable, the number of lamellae ranging from only 4 or 5

to about 70, with balistids and a few tetraodontids tending to have the pseudobranch the least well developed. The olfactory epithelium is in the form of a rosette in triacanthodids, triacanthids, and triodontids, but it is variously modified in all other families as folds (often ex- tensive but never as a rosette), ridges, pits and

plications, or relatively smooth. There are two nostrils in

all families, except in tetraodontids and diodontids in which there are either one or two nostrils. There is basically a single lateral line on the body in all families, except in tetraodontids in which there are one, two, or three lateral lines on the body. A well-developed air bladder is present in all families, except that it is absent

in molids, at least as adults. An inflatable diverticulum

of the gut is well developed only in tetraodontids and

diodontids, while an expansible dewlap of skin between

the end of the rotatable pelvis and the anus is moderately

developed in most balistids, well developed in many

monacanthids, and greatly developed in triodontids. Whether a slighly inflatable diverticulum of the gut is present in a few monacanthids (especially

Brachaluteres) is still debateable (see Thilo 1899b, 1914; Rosen 1912; Breder and Clark 1947; Clark and Gohar

1953; Arbocco 1957), but, if so, it is far less well de- veloped than in tetraodontids and diodontids and has undoubtedly been independently evolved. Molids may

be unique among plectognaths by having a single ovary

(according to Cleland 1862 and Wahlgren 1867 for Mola, and Pellegrin 1912 for Ranzania). With the possible ex- ception of molids, all plectognaths have hard otoliths of normal size, but these are usually so corroded or other- wise dissolved in the formaldehyde-preserved, cleared, and stained study material that they cannot be ade- quately described or figured, and are not further discussed here. Cleland (1862) said that otoliths were absent in Mola, while Cuvier (1805) and Thompson (1888; repeated by Kaschkaroff 1914a) found that the otoliths in Mola were represented by small calcareous granules grouped together. It is not known whether this is also the

case in Masturus and Ranzania, but there is no evidence

of otoliths in the present study specimens. The large number of bones not mentioned above in either of the two lists (constant versus variable occurrence) that are often found in perciform fishes are absent in plectognaths and will help form a large segment

of the defining characteristics of the Order Plectognathi when the other orders and suborders of acanthopterygian fishes are better known anatomically. Some of these

structures typical of perciforms that have been lost by

plectognaths are: anal fin spines; suborbital bones;

parietals; at least one and usually several of the other- wise five pelvic fin rays, and in all but the Eocene

triacanthodid Eoplectus of the branched and cross- striated structure of the fin rays that are retained;

nasals; tabulars; scale bones; intermuscular bones other than 5 to 11 epipleurals; intercalars or "opisthotics"; supramaxillae; any sheath or surface concavity for the upper jaw; canals in the skull bones for the lateral line system; vomerine and palatine teeth, and of any other

teeth except those of the dentary, premaxillary, pharyngobranchials, and fifth ceratobranchials; reduced or- namentation of the skull bones and lack of spiny

processes; simplification of the posttemporal to a

relatively flat rod sutured along all of its medial surface

to the skull (mostly to the pterotic); development of a small and only slightly, if at all, protractile mouth, al- though often with massive jaws, and the relatively great

restriction of the gill opening (never ending ventrally very far below the pectoral fin base); the complete covering by scaly to scaleless skin of the branchiostegal region, and the usual development of relatively spinulose or heavy scales probably derived from ctenoid scales. The two suborders of plectognaths (Balistoidei and

Tetraodontoidei) are difficult to comparatively diagnose, primarily for two reasons. One reason is that both

groups contain an anatomically highly diverse assemblage of families. For example, the diagnosis of the Balistoidei must encompass such widely anatomically dif- ferentiated families as the Triacanthodidae and Ostraciidae, and that of the Tetraodontoidei has to include such similarly diverse families as the Triodontidae and

Molidae or Diodontidae. Moreover, the diagnoses must

also take into account the great diversity found within

certain families, such as the differences between a generalized monacanthid such as Stephanolepis and a highly

specialized one like Psilocephalus, or the differences be- tween a generalized tetraodontid such as Sphoeroides and a highly specialized one like Xenopterus. However,

the most important reason that the two suborders of plec- tognaths are difficult to comparatively diagnose is that we are fortunate in having alive today a very generalized

or primitive Recent member of the Tetraodontoidei,

Triodon, and that we also have available the speciaHzed Eocene fossil subfamily of triacanthodid Balistoidei, the
Eoplectinae, that was ancestral to Triodon and the other Tetraodontoidei. From the very fact of their close ancestor-derivative relationship, many of the characteristics of the eoplectins and triodontids bridge what are otherwise

the morphological gaps between the known fossil and Recent Balistoidei and Tetraodontoidei.

SUBORDER BALISTOIDEI

(SCLERODERMI)

Comparative diagnosis (contrast with that of the Tetraodontoidei). —Teeth relatively large (small in one

highly specialized genus of triacanthodids) and discrete separate units protruding out from sockets in the jaws, except in the Eocene eoplectin triacanthodids in which

the teeth are small, nonprotruding, and fully incor- porated into the matrix of the jaw bones just as in many

of the Tetraodontoidei, to which they are ancestral; dentaries and premaxillaries never fused to their opposite members, except in at least some eoplectins; the medial

articulation of the premaxillaries to one another not strengthened by alternating emarginations and indentations; posttemporal present, except in one highly

specialized species of monacanthid; urohyal present; pelvis present, except in the ostracioids, the most specializ- ed superfamily; pelvic fin present, at least as a rudiment

at the posterior end of the pelvis, except completely absent in many of the more specialized monacanthids and

in all ostracioids; palatine relatively small and not firmly sutured to both the ethmoid-vomerine region and the pterygoid arch, except probably so sutured in the eoplectins; myodome with a complete dorsal roof present, ex- cept small to absent in ostracioids; prootic shelf under

the orbit present, except in triacanthoids, the most

generalized superfamily, and in several highly specializ- ed monacanthids; supracleithrum placed vertically or only slightly obliquely to the axis of the skull; scapular foramen complete, except in two highly specialized

species of monacanthids; scapula with a knob or crest for articulation with the uppermost pectoral fin ray; at least some of the distal pterygiophores of the soft dorsal and

anal fins ossified, except in ostracioids; spiny dorsal fin varying from six well -developed spines to a single slen- der spine, or, in ostracioids, absent altogether, but when

present having its origin above or close behind the skull;

first branchiostegal ray relatively unmodified, without an inturned dorsomedial edge.

Infraorder Triacanthoideo

Comparative diagnosis (contrast with that of the

Balistoideo), which is also that of its only contained

Superfamily, the Triacanthoidea.—Premaxillary with

a well-developed pedicel or ascending process, the

pedicel usually a sturdy rodlike shaft (but variously

modified in the two long-snouted genera of triacanthodids) sliding along the dorsal surface of the ethmoid

and, sometimes, vomer as well; premaxillary movably

articulated with the maxillary, allowing for a slight protraction of the upper jaw; maxillary deeply indented

dorsally for articulation with the anterior end of the

palatine, except in the long-snouted triacanthodids;

palatine usually with a squarish or oblong major portion

(as seen laterally) from which arises an anterior prong for articulation with the maxillary, although much modified

in the long-snouted triacanthodids, but never as a T- shaped bone or a simple rod, or as a bony column sutured

to the palato-pterygoid arch; ethmoid with a more or less evenly convex upper surface, without a laterally ex- panded dorsal or dorsolateral region and always nar- rower dorsally than ventrally; no prootic shelf developed under the orbit in front of and above the major articula- tion of the posterior region of the parasphenoid with the

prootics; dorsal end of the hyomandibular articulated with the prootic, pterotic, and sphenotic; interoper- culum long and, at least posteriorly, relatively deep and

flattened, never as a stout rod throughout its length, and

extending posteriorly well behind the level of the epihyal and interhyal to approach closely and connect by a short ligament to the anterior edge of the suboperculum; dorsal fin spines usually six, rarely only five, supported by

five or four, and rarely only three, basal pterygiophores;

the first dorsal spine not lockable in an erected position through the agency of the second spine, but with an in- dependent locking mechanism between the base of the

first spine and its basal pterygiophore; first basal pteryg- iophore of spiny dorsal fin with a high dorsomedial

flange articulating through an anteroposterior canal in the basal region of the first dorsal spine; pelvic fin consisting of at least a large erectile and lockable spine, sometimes followed by one to four rays of greatly varying

degrees of development, at about the middle of the length of the pelvis, except in several Eocene

triacanthodids in which the spine may have been reduc- ed in size and possibly absent; pelvis either shaftlike or basinlike posterior to the pelvic spines and never with a

dorsal lobe posteriorly, but always with a laterally ex- panded portion anterior to the spines; pelvis not particularly rotatable in life around its anterior articulation with the cleithra and no expansible dewlap of skin pres- ent between the posterior end of the pelvis and the anus; one or two sets of uroneurals usually present; vertebrae

nearly always 8 -I- 12 = 20 (9 -(- 11 = 20 in one Eocene

species); three pharyngobranchials with prominent large protruding teeth; posteromedial edges of epiotics slightly

to decidedly inturned to form, in association with the

exoccipitals and neural spine of the first vertebra, a pocket in which the shaftlike base of the first basal pterygiophore of the spiny dorsal fin is held, with the probable exception of the Oligocene triacanthid Cryptobalistes: mesopterygoid in neither direct nor indirect contact with the quadrate and ectopterygoid, except sometimes very slightly so with the quadrate by the agency of the symplectic making contact with both the quadrate and mesopterygoid.

Family Triacanthodidae Comparative dia^osis (contrast with that of the Triacanthidae) (modified from Tyler 1968:58-62).—

not especially strongly sutured skull and a variety of body forms none of which are built for particularly active, strong swimming; many areas of cartilage visible on

the external surface of the skull between the limited areas

of suturing between the bones in the otic and occipital

regions; teeth in the jaws various, conical or truncate,

in a single series or with a numerous outer series fol- lowed by a few teeth in an inner series, or absent al- together (in adults of one of the long-snouted genera, Macrorhamphosodes) in the upper jaw, or of numerous

rounded dental units incorporated into the matrix of the premaxillary and dentary in beaklike jaws in the Eocene

Eoplectus, but never as heavy incisor teeth (except per- haps somewhat so in the Eocene Protobalistum); a nor- mal ethmoid-frontal complex for support of jaws without massive dentition (except in the Eocene Eoplectus, with

a modified ethmoid-vomer-palatine complex to support

the massive beaklike jaws); the prefrontal without a long

anterior extension sutured to the ethmoid and vomer, and the vomer without posterolateral extensions toward

the prefrontal; premaxillary pedicels when retracted reaching most of the way along the dorsal surface of the ethmoid, almost to the tip of the frontals, except in both

of the long-snouted genera (Halimochirurgus and Macrorhamphosodes), in which the premaxillary is far removed from both the ethmoid and frontal, and in the Eocene Eoplectus, which has only very short premaxillary pedicels and a nonprotractile jaw; supraoccipital

either domelike with a convex posterior surface, or mostly flattened with a small dome or laterally compressed

crest; epiotics meeting one another in the midline on the

dorsal surface of the skull and separated from the frontals by the sphenotics in one group (those with a flat- tened supraoccipital) but separated from one another on

the dorsal surface of the skull in the other group by the

supraoccipital and meeting medially only on the posterior surface of the skull, and articulating anterolateral

ly with the frontals (for illustrations see Tyler 1968:fig. 4a-d); pterosphenoids not meeting in the midline of the

posterior wall of the orbit; neural processes of the first vertebra not meeting in the midline above the neural

canal, forming in conjunction with the exoccipitals an

only partially enclosed bony region (without a bony bot- tom) in which the shaftlike end of the first basal pte- rygiophore of the spiny dorsal fin is immovably held; parasphenoid in region of orbit relatively straight or with

a ventral arch and with a poorly developed ventral flange below the orbit, the flange not deeper than the depth of the shaftlike portion of the bone, except in the Eocene

Eoplectus, with a much deeper flange; hyomandibular

without a prominent groove and crest along its lateral surface; pterotic without a ventral process overlying the hyomandibular; supracleithrum usually placed obli- quely to the horizontal axis of the skull, only the approx- imate lower half of its length overlying the cleithrum; mesopterygoid always present as a separate element.

sometimes sutured along its ventral edge with the metapterygoid; olfactory cavity between the ethmoid and prefrontal not well defined by bony outlines; basi- hyal present; lower two branchiostegal rays more or less

like the others, not enlarged; operculum more or less triangular; air bladder usually thin walled, somewhat

rounded, extending posteriorly to no more than the level of about two-thirds the length of the abdominal cavity;

pelvis either a sturdy shaft more or less triangular or broadly heart-shaped in cross section (the apex or round- ed surface ventrally) just behind the level of the pelvic spine or a flat basin with upturned edges; the two halves

of the pelvis only lightly sutured to one another; the side

of the pelvis at the level of the flange of the pelvic spine

either smooth and allowing for only a single position of

erection of the spine or with numerous small grooves

allowing for numerous, continuous positions of erection

of the spine, but never with a single relatively large oblique crest allowing for only two positions of erection; the

ventrolateral surface of the pelvis at the base of the spine with a complete foramen through which the two sides of the base of the spine meet medially; the haemal arch and

spine of the penultimate vertebra usually autogenous

(occasionally extensively sutured to the centrum), the other haemal arches and spines fused to their centra; the

epural, parhypural, and five hypurals usually separate elements articulated by connective tissue to each other and to the centrum, but occasionally a few of the middle

hypurals may be partially to fully fused to one another; usually two pairs of uroneurals present; slender

epipleurals present from the first or second abdominal

vertebra to the seventh or eighth abdominal vertebra, and, sometimes, on the first or second, rarely third, caudal vertebra, except in the Eocene Eoplectus, in which epipleurals, if present, probably did not occur on

at least the more posterior abdominal vertebrae; fifth basal pterygiophore of spiny dorsal fin present, normally

developed; first basal pterygiophore of spiny dorsal fin with anterior and posterior medial flanges well developed, many times the width of the relatively slen- der shaftlike portion of the bone, except in the Eocene

Eoplectus in which the flanges are only moderately

developed and in Halimochirurgus in which they are poorly developed (in the Eocene Protobalistum and

Spinacanthus the more anteriorly placed spiny dorsal fin probably was supported high on the rear of the skull by

basal pterygiophores with short shafts and poorly developed anterior and posterior medial flanges); first basal pterygiophore of spiny dorsal fin with a medial

flange dorsally completely enclosing a foramen through which the two sides of the first dorsal spine meet medially; second to fifth basal pterygiophores of spiny dorsal fin well developed, their shafts reaching ventrally to or between the distal regions of the neural spines of the

fourth to eighth abdominal vertebrae; at least the first two basal pterygiophores of spiny dorsal fin sutured

together distally; spiny dorsal fin base (including rudi- ments) much longer than soft dorsal fin base, except in the Eocene Eoplectus, with these two bases of equal

length; neural spines of all eight abdominal vertebrae
placed anterior to first basal pterygiophore of soft dorsal

fin (the Eocene Eoplectus with nine abdominal vertebrae, all but the last with their neural spines anterior to the first soft dorsal fin basal pterygiophore); first anal fin basal pterygiophore either with or without a medial

flange anterior to its lateral flanges, the pterygiophore

either T- or + -shaped in cross section; well-developed

lateral flanges for muscle attachment present only on the

first anal fin basal pterygiophore, those present, if any, on the other pterygiophores very poorly developed; no

lateral flange present horizontally along the last cen- trum or on the hypurals; soft dorsal fin basal pterygio- phores 11 to 16, anal fin basal pterygiophores 11 to 13, these pterygiophores not sutured to one another distally (probably fewer basal pterygiophores in both fins in the Eocene Spinacanthus); distal pterygiophores of soft dorsal and anal fins always ossified in adults, usually as two

separate halves; sixth dorsal spine either a short (probably longer in the Eocene Spinacanthus)

protruding element or a rudiment buried beneath the

skin or barely protruding to the surface; third to fifth spines either normally developed or rudiments buried beneath the skin or barely protruding to the surface; first and second spines always prominent and visible externally; dorsal fin rays 12 to 18; anal fin rays 11 to 16 (fewer

rays in both fins in the Eocene Spinacanthus); pelvic fin with a large (smaller in the Eocene Protobalistum and

Spinacanthus) spine followed in the Eocene Eoplectus by

four well-developed branched rays but in all Recent

species by no more than one or two small unbranched

rays, both of which, but especially the second, become in some species buried rudiments in adults; adults of some

species with one or two protruding pelvic rays; dorsal and

pelvic spines with deep lengthwise grooves, obscured by

the overlying scale plates except at the naked distal end

(one-half to one-tenth or less of the length); uppermost

pectoral fin ray short but not reduced to a nubbin, the two halves of the ray of about equal length and the basal

region of the medial half not immensely larger than that

of the lateral half; the slightly overlapping basal plates of the scales of the body bearing a vertical row of upright

spinules arising from individual bases, large specimens of some species acquiring supplemental spinules in front of and behind the principal row (the Eocene Eoplectus with

a single upright spinule per scale plate and the body not completely covered with scales, some of the plates being

isolated and nonoverlapping, and the Eocene ProtobalisFigure 4.—Range of diversity in body form in the Recent Triacanthodidae: Parahollardia Uneata (left) and Halimochirurgus alcocki (right).

turn with huge more or less hexagonal plates bearing numerous rounded tubercules, as in ostracioids); peritoneum light tan to jet black, except in Hollardia meadi in which it is pale or silvery; coloration basically reddish, often with darker red, blue, yellow, or green markings; lateral line inconspicuous; scaly skin not forming a definite low sheath along the bases of the soft dorsal and anal fins; olfactory lamellae 9 to 20, relatively plump; anterior nostril with a tube, lowest in front, highest in back; posterior nostril more or less flush with

the surface, or with a slightly upraised rim anteriorly; gill rakers laterally on first arch relatively long, as long as or longer than the width of the fleshy arch; two to seven,

rarely only one, rakers laterally on the upper limb of the

first arch above the angle; caudal peduncle relatively

short, 10 to 19'^c SL (24'~c SL in the Eocene Eoplectus), not distinctly tapered and without a narrow transversely indented region above and below just in front of the caudal fin base; least depth of the caudal peduncle 5 to

12'^c SL (21% SL in the Eocene Eoplectus); caudal peduncle deeper than wide; caudal fin rounded to al- most truncate.

Detailed description of Parahollardia Uneata. Material examined. —Seven cleared and stained specimens, 4.5.7-86.1 mm. The large amounts of cartilage

visible on the surface of the skull, particularly in the otic and occipital regions, is the norm for the family, in contrast to the closely related and derivative Triacanthidae. Even as large specimens, all species of Triacanthodidae

retain cartilaginous regions between some of the cranial bones, although the amount slightly decreases with in- creasing specimen size. The largest specimen of a Recent

triacanthodid presently recorded (Tyler 1968:64) is a 174 mm female Hollardia hollardi (ANSP 97654) which has subsequently been cleared and stained. As can be seen in Figure 22, areas of cartilage are still present on the sur- face of the skull in the occipital and otic regions, al- though the various bones are more extensively inter- digitated to one another than in the 62.7 mm specimen

illustrated by Tyler (1968:fig. 198) and relatively less cartilage is present. SKULL.

Occipital Region.

Basioccipital. —A short column, dorsolateral^ ex- panded; cartilage filled along its anterior and anterodorsal edges; articulates through cartilage posterolaterally
Figure H.—Parahollardia lineata: with

dots representing the course of the inconspicuous

lateral line; lower left, scales from upper middle

region of body, including two lateral line canal

bearing scales; lower right, nasal region as seen

externally (above) and the olfactory lamellae as

seen with the top of the nasal sac removed.

with the exoccipitals, anterolaterally with the prootics, and, with sHght interdigitation, anteroventrally with the

overlying posterior end of the parasphenoid. The rim of the round concave posterior end of the basioccipital ar- ticulates by fibrous tissue with the rim of the concave anterior face of the centrum of the first vertebra. A deeply concave medial channel is present on the anterior half of the ventral surface of the basioccipital, but the channel

is mostly hidden from view by the overlying para- sphenoid. Posteriorly this channel is open to the exterior

at the base of the posterior bifurcation of the para- sphenoid, while anteriorly it opens into the myodome

where the anterior end of the basioccipital forms the

posterodorsal and posterolateral walls of the myodome.

Exoccipital. —Cartilage filled at its dorsal, lateral, and ventral edges; articulates through cartilage dorsally with the epiotic, anteroventrally with the prootic, ventro- medially with the basioccipital; articulates laterally through cartilage and slight interdigitation with the

overlying pterotic. Medially the exoccipital forms the

lateral and ventral walls of the foramen magnum, the foramen being closed dorsally by the cartilage between

the dorsomedial edges of the two exoccipitals. Postero- medially the exoccipitals are firmly attached by fibrous

tissue and slight interdigitation to the anterior surface of the elongate, laterally expanded, bifid neural spine of the

first vertebra. The exoccipital condyle is a short posterior prolongation of the posterior edge of the bone just

above its articulation with the basioccipital, forming a

plate which overlies the lower anterolateral surface of the

neural arch of the first vertebra just above the region of the centrum.

Supraoccipital. —Dome-shaped, its stout rounded

anterodorsal edge forming the apex of the cranium and

its posterior surface convex; cartilage filled along all of

its ventral edges; articulates posteroventrally through

cartilage with the epiotics and anteroventrally through

cartilage and slight interdigitation with the overlying

frontals.

Otic Region.

Pterotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates posterodorsally through cartilage and extensive inter- digitation with the epiotic, posteroventrally through cartilage and slight interdigitation with the exoccipital, anterodorsally through cartilage with the sphenotic, and

anteroventrally through cartilage with the prootic. Along

the middle of the anterior half of its ventral surface the

pterotic articulates with the hyomandibular through

fibrous tissue, the articulation being somewhat flexible. Posterolaterally the pterotic is broadly overlain by the posttemporal to which it is firmly interdigitated.

Sphenotic. —Cartilage filled along all of its edges of articulation with the other cranial bones; articulates through cartilage posterodorsally with the epiotic, posteroventrally with the slightly overlying pterotic, ven- tromedially with the prootic and dorsomedially with the pterosphenoid. Dorsally the sphenotic is broadly overlain by and slightly interdigitated with the frontal. On its ventral surface the medial edge of the sphenotic ar- ticulates by fibrous tissue with the hyomandibular.

Epiotic. —Cartilage filled along all of its edges of articulation with the other cranial bones; articulates through cartilage dorsally with the supraoccipital, anterodorsally with the occasionally slightly overlying

frontal, anteriorly with the sphenotic, and posteroventrally with the exoccipital. Ventrolaterally the epiotic ar- ticulates anteriorly through cartilage with the pterotic, but more posteriorly the pterotic broadly overlies and in- terdigitates with the epiotic. Along the lower portion of

its posteromedial edge the epiotic bends anteriorly so that a shallow, vertical depression or groove is formed where the two epiotics articulate through cartilage with one another medially. The ventral end of the stout shaft

of the first basal pterygiophore of the spiny dorsal fin fits into this depressed area and is held tightly to it by

fibrous tissue. This depression in the back of the skull is continued ventrally by a similar intuming of the upper

third of the medial edges of the exoccipitals.

Prootic. —Cartilage filled along all of its edges of

articulation with the other cranial bones, except anteriorly; articulates through cartilage anterodorsally with
the pterosphenoid, anterolaterally with the sphenotic,

posterolaterally with the pterotic, posteriorly with the

exoccipital, and posteromedially with the basioccipital. Anteromedially the prootic articulates for most of its length through cartilage with the parasphenoid, but at

its extreme anteromedial end the articulation of the

prootic with the short dorsal wing of the parasphenoid is by slight interdigitation. It is at this place of interdigitation between the prootic and parasphenoid that the first pharyngobranchial makes a firm ligamentous connection with the cranium. Along its ventral surface the anterior half of the lateral edge of the prootic helps support

the dorsal head of the hyomandibular. The lateral walls

of the myodome are formed by the ventromedial sur- faces of the prootics, while the dorsal walls of the myo- dome are formed by medially directed horizontal shelves, which are attached to one another medially by fibrous

tissue, from the ventromedial surfaces of the two

prootics. The prootics also form most of the anterior wall

of the myodome.

edges of the prootics and thus form the lower part of the

anterior edge of the myodome. Behind this restricted area of interdigitation with the anteroventral edge of the

prootic, the lateral edges of the parasphenoid articulate through cartilage with the medial edges of the prootics and thus form the floor of the myodome. Anteriorly the parasphenoid broadly overlies and interdigitates with

the dorsal surface of the posterior shaftlike portion of the vomer, and, to a much lesser extent, with the ventral sur- face of the latter. The anterior end of the parasphenoid

thus essentially possesses a deep concavity into which

the shaft of the vomer fits. Anterodorsally the para- sphenoid is tightly held to the ethmoid cartilage, and

hence to the ethmoid and prefrontals.

Pterosphenoid. —Cartilage filled along all of its edges, except medially; articulates through cartilage ventrally with the prootic and ventrolaterally with the

sphenotic. Dorsolaterally the pterosphenoid is held by

fibrous tissue to the overlying frontal.

Orbital Region. Ethmoid Region.

Frontal. —Wide posteriorly but tapering to a point

anteriorly; articulates posterodorsally and posteroventrally by overlying and slightly interdigitating with,

respectively, the supraoccipital and sphenotic. Occasionally the most posterior portion of the frontal slightly overlies the anterodorsal portion of the epiotic. Posteromedially on its ventral surface the frontal some- what overlies and articulates by fibrous tissue with the pterosphenoid. Anteriorly the frontal overlies the eth- moid cartilage and articulates by fibrous tissue with the ethmoid and prefrontal. Ventrally the medial edges of the frontals are widely separated by a large cartilaginous mass which is continuous anteriorly with the ethmoid

cartilage.

Prefrontal. —In the form of a basally expanded

column; cartilage filled along its dorsomedial and ventro- medial edges; articulates through cartilage along all of its medial surface with the ethmoid and ethmoid cartilage; articulates by fibrous tissue dorsally with the frontal and

anteroventrally with the posterior end of the palatine. The prefrontal articulates ventrally with the dorsal sur- faces of the vomer and parasphenoid, by way of the fact that the ethmoid cartilage is firmly attached to the dorsal surfaces of the posterior region of the vomer and the

anterior region of the parasphenoid.

Parasphenoid. —An elongate shaft with a slight keel along its ventral surface in the region of the orbit. A

deep, anteriorly directed cleft is present in the wide posterior portion of the parasphenoid, giving rise to the fork- ed region which broadly overlies and interdigitates with

the basioccipital and at the same time covers over the medial groove on the ventral surface of the basioccipital leading into the rear of the myodome. About two-thirds

the way back, the parasphenoid possesses paired dorsolateral wings which interdigitate with the anteroventral

Ethmoid. —The ethmoid remains largely cartilaginous, the ossification being restricted to the sur- face regions. It articulates through cartilage dorsally with

the slightly overlying frontals, posterolaterally with the

prefrontals, and ventrally with the vomer and para- sphenoid. Vomer. —Large and rounded anteriorly, but

tapering to a stout shaft posteriorly which interdigitates with the concavity at the anterior end of the para- sphenoid. Dorsally the vomer is attached by fibrous tis- sue to the base of the ethmoid cartilage and thus secondarily with the bases of the ethmoid and prefrontals. At

the lateral edges of its rounded anterior portion the vomer articulates by tough fibrous tissue with the medial

surfaces of the palatines. Mandibular Region. Hyomandibular. —Somewhat expanded dorsally, tapering to a stout shaft anteroventrally; cartilage filled at its dorsal and anteroventral edges; articulates by fi- brous tissue at its dorsal head with the pterotic posteriorly, the sphenotic anterolaterally, and the prootic anteromedially. Along the lower three-fourths of its posterior edge it articulates by fibrous tissue with the pre- operculum. Just above the dorsal end of the preoper- culum, the hyomandibular articulates by fibrous tissue

at a small groove on its posterior edge with the knob at the dorsal end of the operculum. Anteriorly the hyomandibular ends at the cartilaginous plate that lies between

it and the symplectic and metapterygoid.

Quadrate. —Wide posteriorly, tapering to a knob

anteriorly for articulation through fibrous tissue with the

articular in the lower jaw; cartilage filled along its posterior edge; with a long posteriorly directed process from
its posteroventral region; articulates by fibrous tissue dorsally with the ectopterygoid, ventrally with the preoperculum, and anteriorly with the articular.

Posteriorly the quadrate articulates through cartilage with the metapterygoid and symplectic.

Metapterygoid. —Broad anteriorly, narrowing posteriorly; cartilage filled along its anterior and ventral

edges; articulates through cartilage anteriorly with the

quadrate, ventrally with the symplectic, and posteriorly with the cartilaginous area in front of the anterior end of the hyomandibular. Dorsally the metapterygoid ar- ticulates by fibrous tissue with the mesopterygoid.

Symplectic. —Long and rod-shaped; cartilage filled at its anterior and posterior ends; articulates through

cartilage anteriorly with the quadrate, dorsally with the metapterygoid, posteriorly with the cartilaginous area in front of the anterior end of the hyomandibular. Ventrally the symplectic articulates by fibrous tissue with

the preoperculum.

Palato-Pterygoid Region.

Palatine. —Cartilage filled at its anterior and posterior ends; articulates by fibrous tissue anteriorly with

the dorsolateral surface of the maxillary, medially with

the lateral surface of the expanded portion of the vomer,

posteriorly with the mesopterygoid. A posterodorsal projection from its dorsal edge articulates by fibrous tissue with the base of the ventrolateral surface of the prefrontal, and also connects to a band of fibrous tissue that runs over and above the premaxillary pedicels to join with the posterodorsal wing of the palatine on the other

side. The palatine is firmly held in place by these fibrous

tissue articulations even though it is not sutured to any

of the surrounding bones,

Ectopterygoid. —Somewhat triangular in shape; ar- ticulates closely by fibrous tissue along its ventral edge

with the quadrate, while along its posterodorsal edge it articulates through a sheet of fibrous tissue with the

palatine and mesopterygoid.

Mesopterygoid. — Relatively well developed, only

slightly smaller than the metapterygoid; articulates by

fibrous tissue anterodorsally with the palatine, anteroventrally with the ectopterygoid, and ventrally with the metapterygoid.

Opercular Region. Operculum. —Thin and broad ventrally, nar- rowing to a stout shaft dorsally; articulates by fibrous tis- sue dorsally with a groove on the upper posterior edge of the hyomandibular. Ventrally the operculum slightly

overlies and is held by fibrous tissue to the suboper- culum.

Suboperculu -Rounded anteriorly, tapering to

a point posteriorly; with a small dorsal projection located

in about the middle of its dorsal edge; articulates by fi- brous tissue dorsally with the operculum, and anteriorly with the interoperculum.

Interoperculum. —Very elongate; wide and rounded

posteriorly but tapering to a point anteriorly; articulates by fibrous tissue posteriorly with the suboperculum,

while anteriorly it makes a ligamentous attachment

to the angular in the lower jaw. In the posterior half

of its length the dorsal edge of the interoperculum connects by a band of fibrous tissue to the epihyal in the

region where the epihyal articulates with the interhyal.

Preoperculum. —Slightly expanded posteroventrally; the dorsal edge along the anterior half of the bone

slightly expanded laterally for articulation with the quadrate; articulates by fibrous tissue along the posterior region of its dorsal edge with the hyomandibular,

along the middle region of its dorsal edge with the car- tilaginous plate between the symplectic, metapterygoid, hyomandibular, and quadrate, along the anterior region of its dorsal edge with the quadrate. Upper Jaw.

Premaxillary. —L-shaped, with the long posterior arm (pedicel) movably articulated by fibrous tissue along the dorsal surface of the vomer and ethmoid, allow- ing for protraction of the upper jaw. When fully retracted the pedicel reaches most of the way along the dorsal sur- face of the ethmoid, almost to the tip of the frontals. The

shorter ventral arm of the premaxillary forms the anterior edge of the upper jaw, except for a short distance

ventrally where the maxillary forms the border. The pre- maxillary articulates by fibrous tissue along the middle

of the lateral surface of its posterior arm with the medial

surface of the upper exptmded portion of the maxillary, while along the medial surface of its posterior arm the premaxillary articulates with its opposite member. The

ventral arm of the premaxillary articulates by fibrous tis- sue along its posterior edge with the anterior edge of the

maxillary. Six to seven bluntly conical teeth, decreasing

in size laterally, are borne in deep sockets along the anterior edge of the premaxillary. Behind and internal to

this outer row of teeth there is usually a single conical

tooth, about half the size of the largest tooth in the outer

series, but several such inner teeth may be present on

each premaxillary. The teeth are replaced by new ones

developing in new sockets just above and external to the

sockets of the outer row of teeth. After a new tooth erupts through the surface of the premaxillary, it gradually migrates slightly forward and downward into the area of the socket of the older tooth which it is replacing.

Maxillary. —Rounded dorsally, constricted in the middle, and only slightly expanded ventrally; ar- ticulates by fibrous tissue dorsally along the lateral sur- face of its rounded portion with the anterior end of the

palatine, while along the medial surface of its rounded
portion it attaches to the lateral and ventral surfaces of the premaxillary. Ventrally the medial surface of the maxillary articulates by tough fibrous tissue with the

lateral surface of the posterodorsal part of the dentary, while along its anteroventral edge the maxillary ar- ticulates similarly with the premaxillary. Lower Jaw.

Dentary. —The posterior end concave to accom- modate the anterior end of the articular, which it broadly overlies laterally but only slightly overlies medially;

articulates by fibrous tissue anteromedially with its opposite member, posteroventrally with the angular, and

posteromedially with the articular. Along the posterodorsal region of its lateral surface the dentary ar- ticulates by tough fibrous tissue with the medial surface

of the ventral portion of the maxillary. Seven to eight bluntly conical teeth, decreasing in size laterally, are borne in deep sockets along the anterior edge of the dentary. Behind and internal to this outer row of teeth there

is usually a single conical tooth, about half the size of the

largest tooth in the outer series, but several such inner

teeth may be present on each dentary. The teeth of the

outer series are replaced by new ones developing in new

sockets just below and external to the sockets of the outer row of teeth, in the same manner as described for the

premaxillary.

Articular. —More or less triangular in shape;

cartilage filled at its anterior edge, where it is con- tinuous with the remains of Meckel's cartilage; ar- ticulates by fibrous tissue dorsally, ventrally, and

laterally with the broadly overlying dentary, posteroventrally with the angular, and posteriorly at the groove on its posterior edge with the knob at the anterior end of the quadrate. The sesamoid articular is a small ossifica- tion held by fibrous tissue to the region of juncture of Meckel's cartilage and the anteromedial surface of the

articular.

Angular. —Small; articulates by tough fibrous tis- sue with the dentary and articular. Posteriorly the angular connects by ligament to the anterior end of the interoperculum. BRANCHIAL APPARATUS.

and with the ceratohyal, while they articulate by fibrous

tissue anteromedially with their opposite members, and

in the case of the dorsal hypohyal with the region of ar- ticulation between the basihyal and first basibranchial. The ventral edge of the ventral hypohyal articulates by

fibrous tissue with the urohyal.

Ceratohyal. —Large, somewhat expanded posteriorly; cartilage filled at its anterior and posterior edges; articulates through cartilage anteriorly with both

of the hypohyals and posteriorly with the epihyal. The

six branchiostegal rays articulate by fibrous tissue with

the ceratohyal; the first two rays to about the middle of the ventral edge and the last four rays to the lateral sur- face of its posteroventral region. EpihyaL —Large; cartilage filled at its anterior and

ventral edges; articulates through cartilage anteriorly with the ceratohyal and posterodorsally by fibrous tis- sue with the interhyal.

Interhyal. —Short, columnar; cartilage filled at its dorsal and ventral edges; articulates by fibrous tissue ventrally with the epihyal and dorsally with the car- tilaginous plate between the symplectic and hyomandibular.

Branchiostegal rays. —Six in number, increasing in length posteriorly in the series; the first ray somewhat

flattened or laterally compressed, the succeeding rays

less compressed so that the sixth ray is rodlike; ar- ticulate by fibrous tissue with the ceratohyal as de- scribed above.

Urohyal. —Thick at its dorsal and anterior edges, otherwise very thin; articulates by fibrous tissue with the ventromedial surfaces of the ventral hypohyals.

Branchial Arches.—All the elements are cartilage

filled at their edges of articulation with the other ele- ments of the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and four pairs of pharyngobranchials. Four gills are present, with a slit between the

fourth arch and the lower pharyngeal. Hyoid Arch, Branchiostegal Rays, and Urohyal.

Basihyal. —Elongate; slightly expanded laterally at posterior end; cartilage filled at posterior end; ar- ticulates by fibrous tissue posteriorly with the first basibranchial and laterally with the dorsal hypohyals.

Hypohyals. —Both hypohyal elements well de- veloped; dorsal hypohyal cartilage filled at its ventral and posterior edges, the ventral hypohyal cartilage filled at its dorsal and posterior edges. The dorsal and ventral hypohyals articulate through cartilage with one another

First Arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basibranchial

short, laterally compressed in the middle of its length; displaced forward so that it articulates posteriorly mainly with the second basibranchial and only secondarily

posterolaterally with the first hypobranchials, while anteriorly it articulates with the basihyal. First hypobranchial the largest of the hypobranchial elements, which decrease in size posteriorly in the series; ar- ticulates mainly with the anterior half of the lateral sur- face of the second basibranchial, and to a lesser extent

along its extreme anteroventral edge with the first basi-
branchial. First ceratobranchial the shortest of the

ceratobranchial elements, which, except for the fifth, in- crease slightly in size posteriorly in the series; possesses a

ventrally directed flange along most of its ventral surface, this flange on the succeeding ceratobranchials becoming progressively less developed until it is nonexistent on the fifth. First epibranchial with the dorsal one-third of its length bifurcate into two projections; the anterior projection articulating with the base of the

first pharyngobranchial, and the posterior projection ar- ticulating with the second pharyngobranchial. First pharyngobranchial (suspensory pharyngeal) a narrow

rod articulating ventrally with the anterior projection of the first epibranchial and dorsally by fibrous tissue with

the area of articulation of the dorsolateral wing of the parasphenoid with the anteroventral edge of the prootic.

Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial the largest of the three basibranchial elements;

articulates anteriorly with the first basibranchial,

anterolaterally with the first hypobranchials, posteriorly with the third basibranchial, and posterolaterally with

the second hypobranchials. Second hypobranchial very wide ventrally; articulates ventrally with the posterior end of the second basibranchial and anterior end of the

third basibranchial, articulates dorsally with the second

ceratobranchial, which in turn articulates dorsally with

the somewhat laterally expanded second epibranchial. The second pharyngobranchial is the first of the tooth bearing pharyngobranchials, having seven or eight teeth,

set in sockets, in a single row on its ventral surface. The

teeth are of the same type as those of the jaws, although

slightly smaller and with sharper points. They are replaced by new teeth developing in new sockets just anterior to the sockets of the old teeth, in the same manner

as in the replacement of the teeth in the jaws.

Third arch. —Basi-, hypo-, cerato-, epi-, and pharyngobranchial elements present. Third

basibranchial articulates anteriorly with the second

basibranchial, anterolaterally with the second hypobranchials, posterolaterally with the third hypobranchials, and posteriorly with the fourth cerato- branchials. Third hypobranchial with an anteroventral

process which articulates by fibrous tissue with the

posterodorsal edge of the urohyal; at its posterodorsal end it articulates medially with the posterior end of the

third basibranchial and laterally with the ventral end of the third ceratobranchial. Third ceratobranchial ar- ticulated dorsally with the third epibranchial, which in turn articulates with the third pharyngobranchial, the

largest of the three tooth-bearing pharyngobranchial

elements. It possesses six to seven teeth in a row along its anterior edge and about three more teeth irregularly placed behind the anterior row. The teeth are similar to those described for the second pharyngobranchial. The

third pharyngobranchial closely articulates by fibrous

tissue with the other two toothed pharyngobranchials

(second and fourth).

Fourth arch. —Cerato-, epi-, and pharyngobranchial

elements. With the disappearance of the fourth basi- branchial and fourth hypobranchial, the fourth cerato- branchial articulates ventrally with the posterior end of the third basibranchial. Fourth epibranchial an elongate

rod which articulates ventrally with the fourth cerato- branchial and dorsally with the small fourth pharyngobranchial. The latter is the smallest of the toothed pharyngobranchial elements, and closely articulates by

fibrous tissue with the third pharyngobranchial. It bears

five or six teeth in an anterior row and three or four more

teeth, irregularly placed, behind this anterior row.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial wide anteroventrally but tapering to a short stout column dorsally. Teeth more or less placed in three rows, with those of the

posterior row the largest; 7 to 10 teeth in the anterior row, 7 to 9 teeth in the middle row, and 7 to 11 teeth in the posterior row. The teeth are of the same type as those

of the pharyngobranchials. Ventrally the fifth cerato- branchial articulates with the base of the fourth cerato- branchial.

PAIRED FIN GIRDLES.

Pectoral Fin.

Posttemporal. —A straight shaft of bone without

evidence of a forked condition, broadly overlying and

strongly interdigitated to the pterotic in the lower twothirds of its length and to the epiotic above. The rounded

ventral head of the posttemporal articulates by fibrous

tissue with the concave dorsal end of the supracleithrum.

Supracleithrum. —Located slightly obliquely

anterodorsally to posteroventrally in relation to the axis

of the body; articulates by fibrous tissue dorsally with

the ventral head of the posttemporal, and ventrally with

the cleithrum, which it broadly overlies.

Cleithrum. —Laterally expanded along the ventral two-thirds of its length; articulates by fibrous tissue dorsolaterally with the overlying supracleithrum, while dor- somedially it overlies the dorsal postcleithrum. Along the middle of its posterior surface the cleithrum articulates by fibrous tissue with the scapula and the rounded

anterodorsal portion of the coracoid. Ventromedially the cleithrum articulates by tough fibrous tissue with its opposite member, while just above this region the anterior end of the pelvis is firmly held between the cleithra.

Postcleithra. —The postcleithra form a long

posteroventrally directed strut from the dorsomedial

region of the cleithrum along the abdominal wall musculature to the region just above the middle of the

posterior half of the pelvis. The dorsal postcleithrum is expanded into a thin plate dorsally and articulates by
fibrous tissue anterolaterally with the somewhat overly- ing cleithrum and posteroventrally with the ventral postcleithrum. The ventral postcleithrum is a slightly compressed shaft which articulates by fibrous tissue anterodorsally with the dorsal postcleithrum in the

region behind the pectoral fin rays.

Coracoid. —Rounded dorsally, tapering ventrally to a narrow shaft; produced posterodorsally into a prong

below the lowermost actinosts; cartilage filled along the

dorsal and anterior edges of its rounded dorsal region and

at the end of its ventral shaft; articulates by fibrous

tissue anterodorsally and anteroventrally with the

posterior surface of the cleithrum, dorsally through cartilage with the scapula and through fibrous tissue with

the bases of the last two actinosts.

Scapula. —Completely encloses the scapular foramen; cartilage filled at its anterior and ventral edges; articulates anteriorly by fibrous tissue with the

cleithrum and ventrally through cartilage with the cor- acoid. Posteriorly the scapula articulates by fibrous tis- sue with the following elements, in order from dorsal to ventral; the first pectoral fin ray, the small first actinost, the second actinost, and the dorsal part of the base of the

third actinost. The first fin ray is supported on a stubby

projection, and the first actinost on a flattened surface

just posteroventral to the articulation of the first fin ray.

the lateral edge of the pelvis, as well as ventrally with the

pelvis by an anteroventral flange from the base of the

spine, and dorsally with the pelvis by a smaller dor- somedial flange (the anterior direction of the ventral

flange and the medial direction of the dorsal flange are

for the unerected spine). The spine can be envisioned to lock in an erect position by a combination of three movements. The whole spine is rotated approximately 70° forward and outward around its base of articulation with

the pelvis. By this movement the ventral flange, that was

originally directed anteriorly, is now directed medially, and the dorsal flange, that was originally directed

medially, is now pointed posteriorly and is no longer in contact with the dorsal surface of the pelvis, but rather is lying just lateral to the edge of the pelvis. The spine is then slightly rotated so that the dorsal flange very slightly overlies the ventrolateral edge of the pelvis. When the

spine is then rotated slightly backward and inward, the

dorsal flange hits flatly against the ventrolateral surface

of the pelvis and any further backward and inward move- ment of the spine is stopped. The spine is unlocked by

the simple rotation of the spine slightly forward and out- ward, and then slightly backward and upward, until the

dorsal flange is out of contact with the ventrolateral sur- face of the pelvis and is lying just lateral to it. The spine can then be drawn back to its unerected position, with

the dorsal flange sliding over the dorsal surface of the

pelvis to its original medially directed position.

Actinosts. —Four elements; all cartilage filled at both ends; the first two actinosts articulating with the

scapula, the third actinost articulating with the dorsal edge of the region of articulation between the scapula and coracoid, the fourth actinost articulating with the

coracoid; distally the actinosts support all of the pectoral

fin rays, except for the first. The actinosts increase in size from the first to the fourth. Fin rays. —Thirteen fin rays in most specimens;

the first ray normal, of two equal halves, but only onefifth to one-fourth the length of the second ray and ar- ticulating directly with the scapula rather than with the

actinosts, as do the other fin rays; the first two rays and

the last or lowermost ray unbranched, the intervening

rays branched. First ray without cross-striations; all other rays with cross-striations.

Pelvic fin. Pelvis.—Formed of two distinct lateral halves

tightly bound together medially by fibrous tissue; tapers

to a sharp point posteriorly, but terminates bluntly

anteriorly where it is tightly held by fibrous tissue between the medial edges of the cleithra; expanded ventrolaterally in the area anterior to the articulation

of the pelvic spines so that a large basin for muscle at- tachment is formed on the ventral surface of the pelvis.

Pelvic spine. —Large and strong; articulates broadly by fibrous tissue at its concave medial edge with

Fin rays. —Two rays present, only the first of which

can be seen externally. The first ray short, about onethird the length of the spine, unbranched and without

cross-striations, the two halves of the ray distinct from

one another throughout their lengths and held together by fibrous tissue. Basally the two halves of the first ray

are widely divergent, the base of the medial half of the

ray articulating broadly across the ventral surface of the

pelvis, while the base of the lateral half of the ray articulates along the lateral surface of the pelvis. The second

fin ray is small and easily overlooked, for it lies flat against the ventral surface of the pelvis and is completely

covered by the thick spinulose skin of the body. Like the

first ray, the second ray is composed of two distinct halves that are held together by fibrous tissue. The

medial half of the second ray is wider than the lateral half and both halves are unbranched and without crossstriations. No pterygial elements are present. See Tyler

(1962b) for additional details on the pelvis and pelvic fin, and Winterbottom (1970) for their muscular evolution. VERTEBRAL COLUMN. —All vertebrae with bi- concave centra, except the last, which ends posterodorsally in the urostyle. Abdominal Vertebrae.

First vertebra. —Neural spine enlarged, laterally expanded dorsally, bifid to the centrum and hence

without a bony roof over the neural canal; articulates over all of the anterior surface of its neural spine by
fibrous tissue with the epiotics and by slight interdigitation with the exoccipitals. Over the anterior half of the neural arch area just above its centrum, the first vertebra

articulates by fibrous tissue with the overlying posteriorly directed exoccipital condyles. The rim of the concave

anterior end of the centrum articulates with the rim of the concave posterior end of the basioccipital. Posteriorly the first vertebra articulates with the second vertebra by

apposition of the rims of their centra and by the short, but wide, neural postzygapophysis of the first vertebra

slightly overlying the neural prezygapophyseal area of the second vertebra. No haemal zygapophyses are present.

Other abdominal vertebrae. —In 17 specimens the abdominal vertebrae numbered eight. Except for the

first vertebra, all of the abdominal vertebrae, as well as the caudal vertebrae, have a bony roof over the neural

canal and a single, undivided, neural spine. The basal

regions of the neural spines and dorsal regions of the neural arches become progressively more anteroposteriorly expanded from the second to the eighth ab- dominal vertebra. This expansion involves both the neural pre- and postzygapophyses, which become

broadened into large articular surfaces, with the pre- zygapophyses of the seventh and eighth (sometimes sixth

to eighth) abdominal vertebrae slightly overlying the postzygapophyseal area of the vertebrae anterior to them. No haemal pre- or postzygapophyses are present. Each neural arch has a neural foramen along the middle

of its lateral surface. The first three abdominal vertebrae have no transverse or haemal processes, but the fourth and fifth vertebrae have transverse processes from the

anterolateral edges of their centra, the process of the fifth being somewhat longer and more ventrally curved than

that of the fourth. The sixth vertebra has a slightly longer transverse process, which differs from that of the

fourth and fifth vertebrae in that the two processes of the

sixth vertebra possess medial projections that meet and

are continuous in the midline beneath the centrum,

enclosing the haemal canal and thus representing a haemal arch without a haemal spine. The seventh

vertebra has the haemal arch more strongly developed and possesses ventrally directed processes from each side

of the haemal arch representing a bifid haemal spine. The haemal apparatus of the eighth vertebra is like that

of the seventh, except larger. Six epipleurals or inter- muscular bones are present in the myocommata between

the epaxial and hypaxial musculature, and borne on the second to seventh abdominal vertebrae. The first and second epipleurals articulate with the neural arches

of, respectively, the second and third abdominal

vertebrae. The third epipleural articulates with the dorsal surface of the short transverse process of the fourth abdominal vertebra; the fourth epipleural with the dorsal surface of the transverse process of the fifth ab- dominal vertebra. The fifth and sixth epipleurals articulate with the ventrolateral surfaces of the haemal arches

of, respectively, the sixth and seventh abdominal

vertebrae.

Caudal Vertebrae. —In 17 specimens the caudal

vertebrae numbered 12. As is true with the last two or three abdominal vertebrae, the first four to six caudal

vertebrae have the neural spine area around and above

the neural zygapophyses expanded into large articular surfaces so that the neural prezygapophyses of the first four or five caudal vertebrae overlie the neural postzyga- pophyseal area of the vertebrae anterior to them. With

the exception of the last two vertebrae, each neural arch

has a completely enclosed neural foramen. All of the abdominal vertebrae have a bony roof over the neural

arch and a single, undivided, neural spine. The haemal

arches and spines are well-developed and normal, except

for those of the first caudal vertebra, which has the haemal spine single and undivided for the upper onethird of its length, but bifid for the ventral two-thirds

of its length. The bifid portion of this spine overlies the upper anterior surface of the first basal pterygiophore of the anal fin. The haemal arch of the penultimate verte- bra is not fused to its centrum, but, rather, is tightly held to it by fibrous tissue. The haemal arch of the last vertebra is described below.

Caudal Skeleton. —The caudal skeleton consists of the last vertebral centrum, one epural, two pairs of uroneurals, five hypurals, and the parhypural, with the whole complex receiving support from the prolonged

neural and haemal spines of the penultimate vertebra. The last vertebral centrum is prolonged posterodorsally

into a urostyle and supports along its posterior edge the

five hypurals and the parhypural. From the dorsolateral surface on each side, the centrum bears anterodorsal projections which do not meet in the midline dorsally. These projections represent the lateral walls of the

neural arch of the last vertebra and its neural pre- zygapophyses, since they form the lateral borders of the

neural canal and at their dorsal ends articulate by

fibrous tissue with the neural postzygapophyses of the penultimate vertebra. The epural is a long rod articulat- ing by fibrous tissue along its posterior edge with the uroneurals and at its anteroventral edge with the area between the dorsal ends of the two anterodorsal projec- tions of the last vertebral centrum. The epural thus forms

the dorsal roof of the neural canal of the last vertebra and

it is, evidently, the very little modified neural spine of the last vertebra. The uroneurals in this and the other

species of triacanthodids are highly variable in shape,

size, number and condition of pairing, as described in detail by Tyler (1970b; see fig. 1 for illustrations of the uroneurals in six specimens of P. lineata). There

is usually clear evidence of two pairs of uroneurals, with the first pair usually smaller and more variable than the second, more posterior, pair. In the caudal

skeleton of P. lineata illustrated here, the first pair

of uroneurals is represented by a single small rounded

plate above the anterior end of the second uroneural,

it being obvious that either one half of the first uroneural has failed to develop or that the two halves have fused

into one piece. One other study specimen also has a

single first uroneural ossification, but three others have a
pair of pieces and another has three small pieces, as dis- cussed by Tyler (1970b:5). The second pair of uroneurals

is represented by two long separate pieces in three of the specimens, while in the other three specimens the two

halves are fully fused anteriorly. The hypurals decrease in length from the first (lower- most) to the fifth. Fifth hypural directed posterodorsally from just behind and slightly below the uppermost point

of the urostyle; more or less rod-shaped; supports, along with the uppermost edge of the fourth hypural, the up- permost caudal fin ray. Fourth hypural the deepest of the hypural elements; articulates anteriorly with the posterior edge of the urostyle and posteriorly supports the uppermost five caudal fin rays, although it shares the support of the uppermost and lowermost of these five rays with, respectively, the fifth hypural and third hypural. Third hypural broad posteriorly but becoming

narrow anteriorly where it articulates with the posterior edge of the urostyle; posteriorly it supports the upper of the middle two caudal fin rays and partially supports the lowermost of the upper five caudal fin rays. Second

hypural similar to third hypural, but slightly larger; ar- ticulates anteriorly with the posterior edge of the

urostyle, while posteriorly it supports the lower of the middle two caudal fin rays. First hypural articulated

anteriorly with the posterior edge of the urostyle, while

posteriorly it supports three fin rays. The parhypural the

largest of the hypural series and enclosing the end of the haemal canal with its deeply concave anterior end; the

lateral edges of its concave anterior end articulate by

fibrous tissue with the posterolateral surfaces of the cen- trum. A slight indentation on the anterodorsal edge of the parhypural marks the end of the haemal canal. The

parhypural is thus the not greatly modified haemal arch and spine of the last vertebra. Caudal fin rays. —Twelve in number; the upper- most ray and the lowermost ray unbranched, the others becoming increasingly branched toward the two middle

fin rays, which are branched in triple dichotomies. The

fin rays articulate at their bifid bases by fibrous tissue with the hypurals, as described above.

DORSAL AND ANAL FINS.

Dorsal Fin.

Spines and pterygiophores. —Six spines borne on

five basal pterygiophores, without the intervention of

distal pterygial elements. The first spine long, the others decreasing in length posteriorly in the series. First spine with its generally concave base somewhat expanded ventrolaterally. The ventrolateral flanges of the first spine

are in close contact with one another medially, although

they are not fused together. Just above the basal area of

close apposition of the flanges, a hole is present anteroposteriorly through the middle of the spine. The generally concave basal surface of the spine fits over the generally convex upper surface of the first pterygiophore, while

at the same time a high medial flange from the upper

surface of the pterygiophore fits into the hole through the base of the first spine. The medial flange of the pterygio- phore possesses a large hole through which the two

medial surfaces of the base of the first spine come into

close fibrous tissue contact. The first spine is thus impossible to disarticulate from its pterygiophore without

cutting the fibrous tissue or breaking either the base of the spine or the medial flange of its pterygiophore. The

first spine can be held in an erect position by a very simple mechanism. The ventral articular surface of the first spine and the dorsal articular surface of the first pterygiophore, on either side of its medial flange, are rough and irregular. When the spine is erected at a right angle to the dorsal surface of the pterygiophore and then

pulled slightly downward, a firm contact is established between the two roughened articular surfaces and the

spine is effectively locked in position. The spine is unlocked by relaxation of the strong, vertically directed pressure of the spine against the pterygiophore, so that

the articular surface of the spine can slide forward over

the articular surface of the pterygiophore without undue

frictional resistance. The second spine articulates at its concave ventral end with the generally convex surface of the first pterygiophore directly behind the articular area

of the first spine, but the second spine has no function in the locking mechanism of the first spine. There is a small medial flange of the pterygiophore that fits loosely into the slight concavity in the middle of the base of the sec- ond spine. The third to the sixth spines articulate to their individual basal pterygial elements and have, from

the third to sixth, progressively less concave articular surfaces fitting against the progressively less convex ar- ticular surfaces of their pterygiophores, so that the ar- ticulation of the sixth spine to its pterygiophore is at the

relatively flat surfaces of both elements. The first basal pterygiophore has a strong anteroventrally directed columnar process which fits into a

groove formed by the intumed posteromedial surfaces of the ventral half of the epiotics and the dorsal one-third of the exoccipitals, as well as by the medial surfaces of the

bifid neural spine of the first vertebra, which overlies these regions of the epiotics and exoccipitals. The columnar portion of the first pterygiophore is held in this groove by tough fibrous tissue. The second to fifth pterygiophores bear, respectively, the third to sixth dorsal fin spines. The ventral regions of the second to fifth pterygiophores articulate, respectively, between the

neural spines of the third and fourth vertebrae, the fifth and sixth vertebrae, the sixth and seventh vertebrae, and

the seventh and eighth vertebrae. The pterygial elements

are cartilage filled at their extreme ventral edges.

Fin rays and pterygiophores. —Sixteen fin rays

usually present; the first two rays and the last ray unbranched, the others branched in single or double

dichotomies. Each fin ray has a small pair of distal pterygiophores as two distinct halves between the bifur- cate base of the ray, except for the last one or two rays, in which these elements, if present, are unossified. Basally
the fin rays are supported by about 14 basal pterygia- phores, which decrease in size posteriorly in the series. The more anterior of the pterygiophores have weakly

developed lateral flanges along their lengths, but these

lateral projections for muscle attachment become reduc- ed posteriorly in the series and are entirely absent from

the more posterior pterygiophores. The basal pterygio- phores articulate by fibrous tissue ventrally with the neural spines of the vertebrae. The first and second basal pterygiophores of the soft dorsal fin are usually located between the neural spines of the eighth abdominal and

first caudal vertebrae while the last basal pterygiophore

is located between those of the sixth and seventh caudal

vertebrae. The basal pterygial elements are cartilage fill- ed at their dorsal and ventral ends. Anal Fin.

Fin rays and pterygiophores. —Fourteen fin rays

usually present; the first ray and the last ray un- branched, the others branched in single or double

dichotomies. Each fin ray has a small pair of distal pterygiophores as two distinct halves between the bifur- cate base of the ray, except for the last one or two rays, in which these elements, if present, are unossified. Basally

the fin rays are supported by about 13 basal pterygio- phores, which decrease in size posteriorly in the series. They possess weakly developed lateral flanges for muscle attachment along their lengths, as in the case of the dorsal fin basal pterygiophores, and they are cartilage filled at their dorsal and ventral ends. The first basal pterygio- phore is by far the largest of the series and has well- developed lateral flanges for muscle attachment along each side of its anterior surface. It articulates by fibrous

tissue to the posterior surface of the bifid portion of the haemal spine of the first caudal vertebra and to the

anterior surface of the haemal spine of the second caudal

vertebra. The 2d to 13th basal pterygiophores articulate by fibrous tissue to the haemal spines of the 2d to 7th caudal vertebrae.

pelvic fin, if it is present at all. Two species: Protobalis- tum imperiale (Massalongo 1857) and Spinacanthus

cuneiformis (Blainville 1818). The Eocene Eoplectinae differ from both the Spinacanthinae and the Recent species in having: gymnodontlike jaws and upper jaw suspension, with numerous small rounded dental units incorporated in the matrix of the premaxillary and dentary, with the premaxillary and maxillary immovably articulated, and

the jaws probably nonprotrusible; a well-developed

pelvic fin of one spine and four long branched rays; the

ventral shaft of the second basal pterygiophore of the spiny dorsal fin directed anteroventrally and articulated

either to the base of the skull or between the neural

spines of the first and second vertebrae; 9 4-11 vertebrae

in a highly arched column; decidedly more soft dorsal and anal fin rays than basal pterygiophores. Two

species: Eoplectus bloti Tyler (1973b) and

Zignoichthys oblongus (Zigno 1874a). The Recent species are divided into two subfamilies mainly on the basis of the shape of the posterior portion

of the skull, the placement of the epiotics and the shape

of the pelvis, none of which features are known for the

fossil species. Comparative diagnoses of the two Recent

subfamilies follows: Hollardiinae. The dorsal surface of the supraoccipital

entirely domelike, without a broad flat expanse, the posterior surface of the dome convex; epiotics not meeting

medially on the dorsal surface of the skull, separated

there by the supraoccipital and meeting medially only on

the posterior surface of the skull, and articulating

anteriorly with the frontals; pelvis a sturdy shaft more or

less triangular or broadly heart-shaped in cross section;

first anal fin basal pterygiophore tending to be -t- -shaped

in cross section, with an anteromedial process; teeth conical. Four western Atlantic species and one from Hawaii,

in two genera (Hollardia and Parahollardia)

Comparative diagnoses of subfamilies (Spinacanthinae, Eoplectinae, Hollardiinae, Triacanthodinae). —As discussed in greater detail by Tyler (1968, 1973b), there are four subfamilies of triacanthodids, two fossil, and two Recent, whose most pertinent diagnostic

features are summarized below. See Sorbini (1968) and

Blot (1969) for the upper portion of the lower Eocene

age of the Monte Bolca, Italy, fish beds. The Eocene Spinacanthinae differ from both the Eocene Eoplectinae and the Recent species (Hollardiinae and Triacanthodinae) in having: enormously elongate

dorsal fin spines (50 to 90% SL) in an exceptionally long- based fin (slightly over 50% SL), with the soft dorsal and

anal fins exceptionally short-based (about 11 to 12% SL);

the spiny dorsal fin origin over the level of the middle or

front of the eye; the eye small (5 to 7% SL) and placed

high in the head; a probably only poorly developed

Triacanthodinae. The dorsal surface of the supraoccipital with a broad flat expanse, anteromedially on which is an upraised area varying in shape from a small dome to a laterally compressed thin crest; epiotics meeting medially on the dorsal surface of the skull as

well as on the posterior surface, and separated anteriorly from the frontals by the sphenotics; pelvis a flat basin with upturned edges; first anal fin basal pterygiophore T-shaped in cross section, without an anteromedial

process; teeth conical or wider than thick and more or

less truncate distally. Of the 14 species in 9 genera, 13

species belong to 8 genera (Triacanthodes, Mephisto, Paratriacanthodes, Atrophacanthus, Bathyphylax,

Tydemania, Macrorhamphosodes, Halimochirurgus) in the Indo-western Pacific, and 1 species belongs to a monotypic genus (Johnsonina) in the western Atlantic. Anatomical diversity. —The anatomical diversity of the two Recent subfamilies has been treated in detail by
Tyler (1968), while the Eoplectinae were described subsequently (Tyler 1973b), and the features of these three subfamilies need be only briefly summarized here. The

Spinacanthinae were discussed by Tyler (1968) on the

basis of the literature alone, but the holotypes and only known specimens of the two species of this subfamily have been examined for the present work and are redescribed below. Protobalistum imperiale (Massalongo 1857:775), in counterpart, MCSNV T9 (head left)-10, 522 mm SL, and

655 mm TL (total length), is gigantic by comparison to the other members of the superfamily Triacanthoidea,

^i*" <^^<.e*^-^'

the largest triacanthodid otherwise known being a 174 mm SL specimen of Hollardia hollardi and the largest triacanthid a 272 mm SL specimen of Triacanthus

biaculeatus (Tyler 1968:64; 1970f:5). The spiny dorsal fin

is enormous, with five well-developed strong spines decreasing in length posteriorly in the series, with the

possibility that a much smaller sixth spine is present just behind the base of the fifth spine but hidden there by a

slightly misplaced scale plate. All of the spines are covered with the same kind of granulations as those of
-Parahollardia Uneata

omposite based on several

45.7-86.1 mm SL, Gulf of Mexico to South Carolina.

lateral view

I specimens.

maxillary

premaxillary

pterosphenoid parasphenoid

cartilage prefrontal palatine \ ethmoid

frontal supraoccipital
the scale plates of the body. The first dorsal spine, in- cluding the groove representing at least part of the missing distal end of the spine, is at least 279 mm (53.6% SL),

the second at least 273 mm (52.4% SL), the third at least 210 mm (40.3% SL), the fourth at least 139 mm (26.6%

SL), and fifth, which seems complete even distally, 90.3 mm (17.3't SL). There are about nine dorsal

fin rays, of which the fourth is the longest, 79.5 mm

(15.2% SL). The anal fin is directly below the soft dorsal

fin and likewise has about nine rays, of which the third is the longest, 91.3 mm (17.5'c SL). The spiny dorsal fin base is about 276 mm (53'^c SL) long, while the bases of the soft dorsal and anal fins are both about 57 mm (11%

SL) long. All but the first ray in the soft dorsal and anal

fins are extensively branched. The broadly rounded caudal fin is 133 mm (25.6% SL) and has 12 rays, of which the uppermost ray and the lowermost ray are unbranched and the intervening 10

rays extensively branched. The length of the caudal peduncle (from end of anal fin base to middle of caudal

fin base) is 126 mm (24.1% SL) and its least depth 55.0 mm (10.5% SL). The greatest body depth is about 210 mm (40% SL). The eye is placed high in the head just below the base of the first dorsal spine and has an ap- proximate diameter of 39 mm (7% SL). There are remains of pectoral fin rays, but the number

cannot be counted. It is impossible to state whether a

pelvic fin was present or not. In redescribing the species,

Figure H.—Parahollardia lineata: dorsal (left) and ventral (right) views of skull; composite based on

several specimens. 45.7-86.1 mm SL,

Gulf of Mexico to South Carolina.

Figure 9.—Parahollardia lineata: posterior view of

orbit (left) (cross section of skull; dashed lines represent cut surfaces of frontals and parasphenoid);

posterior view (right) of skull: below, posterior and lateral views of first abdominal vertebra: composite based on several specimens, 45.7-86.1 mm SL, Gulf of Mexico to South Carolina.

Zigno (1887a:4) said that there was a pelvic spine of 30 mm length, bent backward along the side of the body. Along the lower edge of the body at the level between the bases of the second and fourth dorsal fin spines, there is a

ridge of bone with the same type of surface granulation as found on the scale plates, described below. This ridge is about 173 mm long (33% SL) but is discontinuous, with some segments showing surface granulations and others

the bone beneath the granulations. Zigno may have had

one of these granular segments in mind for the pelvic

spine. If this ridge does represent a pelvic spine, then it was almost as well developed as the more anterior dorsal

fin spines. However, it is at least equally likely that this ridge is simply the ventrolateral curved edge of the carapace of scale plates that fully covers this region of the body, as described below. In short, it is not known at present whether Protobalistum had pelvic spines. The teeth are well-preserved. They are large and

relatively massive, some with straight or rounded distal edges as in incisors but others with a distinct cusp or distal constricted region. The teeth with more rounded distal edges may represent those toward the middle of the jaws that have been worn down through use. There are about four or five teeth in each half of the upper and
JL'^ — Tag's ^N

ox'S"*-"'!--

S .Sf X -2 -ii -S « "S Sillily

a " o S .

.1 -1 -5 .- -3 1^*

Figure 15.—Protobalistum imperiale: top. lateral views of the two counterparts; middle left, lateral view of head, showing pharyngeal and jaw teeth; lower right, lateral view of caudal region; bottom, lateral view of middle of body (head to right), showing remains of scale plates, pectoral fin rays, coracoid, and pharyngeal teeth; holotype, 522 mm SL, Eocene of Monte Bolca, Italy.

lower jaws, but it cannot be determined if they occurred

in a single series or in a major outer series internal to which were a few other teeth. Pharyngeal teeth are pres- ent in the appropriate area at the intersection of the

levels of the horizontal through the middle of the mouth

and the vertical to the base of the second dorsal fin spine. They are small and more elongate versions of the cusped

teeth of the mouth. The anterior half of the body exclusive of the head

(i.e., in the region below the bases of the second to fifth dorsal spines) is completely (taking into account missing

pieces) covered by relatively huge, thick bony plates with numerous rounded bumps or granulations on their surface. Many of these plates are distinctly hexagonal, and

all of them articulate to one another along all of their edges of apposition by intermeshed delicate denticulations, all of this being remarkably similar to the scale plates in ostracioids. Measurements of a few of the more

complete scale plates are as follows: a plate below the bases of the fourth and fifth dorsal spines is 56.9 mm

(lO.g'^o SL) deep and 64.3 mm (12.3% SL) wide; a plate

just below the former is 51.6 mm (9.9% SL) deep and 52.3 mm (10.0% SL) wide; one of the few scale plates on the head, approximately midway between the eye and

mouth, is about 31 mm (5.9% SL) deep and 27 mm (5.2% SL) wide. While a continuous ostracioidlike carapace ap- parently is present only on the anterior half of the body

exclusive of the head, there are numerous, usually much
smaller, isolated scale plates with the same kind of sur- face granulations on the head, especially dorsally and

ventrally, and on the body posterior to the carapace in the region between the soft dorsal and anal fins and on

the caudal peduncle. The scale plates, and apparently

thick skin, on the caudal peduncle completely obscure

the vertebral column. The possible phylogenetic implications of the presence

of ostracioidlike scales in the triacanthodid

Protobalistum is discussed in the section on subfamilial

relationships. Spinacanthus cuneiformis (Blainville 1818:359), a

single plate, MNHN (LP) 10918, 104 mm SL, presently is a very incomplete and poorly preserved specimen which

appears to have lost some of its surface and bony struc- ture since it was studied by Volta (1796), Blainville

(1818), and Agassiz (1839 illustration, 1844c description). Much less can be seen in the specimen today than in the

illustrations of it by Volta and Agassiz. The spiny dorsal

fin is even more enormous than in Protobalistum, with

the first spine, even with a slight amount of the distal tip missing and not measurable, being 95.7 mm (92.0'

SL). The second to fourth dorsal spines are missing too much of their distal ends to be measureable, but ap- parently they were almost as long as the first spine. The

fifth spine is about 35 mm (34% SL) long, and a smaller

sixth spine, if present, cannot be detected. There are

large retrorse thomlike barbs along the anterior edge of

at least the basal third of the first dorsal spine. There

appear to have been about 10 fin rays in both the ap- posed soft dorsal and anal fins. The slightly rounded

caudal fin is poorly preserved, but it had about 12 rays

(Agassiz thought 7 or 8 branched rays plus an un- branched ray above and below). The pectoral fin has about 12 or 13 rays (Agassiz thought 12). Agassiz es- timated the number of vertebrae to be no more than 20,

and I would guess at about 20 judging on the basis of the

size of those that show and of the space available for those that do not show. The length of the caudal peduncle is 26.0 mm (24.9% SL) and its depth at least 7.0 mm

(6.7% SL). The greatest body depth is 39.0 mm (37.4%

SL). The eye is placed high in the head just below the base of the first dorsal spine and has a diameter of 7.2 mm (6.9% SL). The branchiostegal rays from both sides are evident, and in the more clearly seen set there appear to be six rays. The prefrontal is one of the few bones that are rela- tively well preserved, and it has an appropriately moderate size. Agassiz thought that a pelvic spine was

present and displaced in the region of the branchiostegals. At least at present I find no structure in the

branchiostegal region that could possibly be interpreted

as a pelvic spine. However, just posterior to the branchiostegals and below the pectoral fin is a vague indication

of a long rodlike strut of bone oriented vertically. It is possible that this is the structure seen by Agassiz, and it might possibly be a thin, weakly developed barbless

pelvic spine. It would appear to me more likely to be a

part of the pectoral girdle, perhaps the thickened posterior edge of the coracoid. As with Protobalistum, it is not known with surety whether Spinacanthus had a

pelvic fin. The teeth in the lower jaw are well-preserved. There

appear to have been about seven of them in the left dentary. A few of these teeth are especially fully exposed and

can be seen clearly in three dimensions. One of these is 2.0 mm (1.9% SL) long from its flat circular base to its distal tip. The tooth tapers only very slightly from basally to distally throughout most of its length, but in the

Figure 16.—Spinacanthus cuneiformis:

lateral view of holotype, 104 mm SL, Eocene of Monte Bolca, Italy.
distal one-fifth of the length the tooth is strongly constricted into a blunt nipple. In the distal halves of their lengths the teeth bear about 10 annularlike rings, which

I doubt are artifacts. In the upper jaw, grooves represent where teeth once were present, and perhaps of their sockets. More than 20 pharyngeal teeth are present in the

region in front of the pectoral fin base, these being

similar to those of the jaws but much smaller, the largest being about 0.5 mm (0.5% SL) long. The body bears numerous, mostly isolated, scale plates of moderate size. Each plate has a strong rela- tively high central spine peripheral to which are much

smaller and lower rounded bumps or granulations similar

to those of Protobalistum. The more or less isolated

plates, which probably covered only about one-fourth of the surface of the body, seem to become more numerous

ventrally, where they may have been placed in more or

less regular horizontal rows, with some contact between

individual plates. The plates are largest and most

regularly arranged along the ventral edge of the body

from the region of the branchiostegals posteriorly to the

anal fin base, the largest plates being in the abdominal

area. The largest plates have a diameter of about 5.0 mm

(4.8% SL). Very few scale plates are evident on the head.

the only one clearly seen being on the profile of the snout about midway between the mouth and eye. The scale covering of Spinacanthus is comparable to that found on

Protobalistum anterior and posterior to its carapace of articulated hexagonal plates. The anatomical features of the Eoplectinae, recently described by Tyler (1973b), are summarized briefly below. The Eoplectinae are represented by two species known

only from their holotypes, only one of which (Eoplectus)

is well preserved.

In most of its features Eoplectus bloti Tyler (1973b) is a generalized plectognath at the triacanthodid level of organization. It has at least five and probably six dorsal

fin spines, a rounded caudal fin of 12 rays (i, 10, i), a generalized caudal skeleton, a short caudal peduncle, and the most generalized condition of the pelvic fin known among the plectognaths, this being a spine and

four well-developed branched rays. The overall configuration of the body is also triacanthodid. However,

Eoplectus has the jaws and dentition modified into a crushing beak, with numerous small rounded dental

units incorporated into the matrix of the premaxillary and dentary. This condition otherwise is found among

Figure U.—Eoplectus bloti: lateral view of holotype,

65.2 mm SL, Eocene of Monte Bolea, Italy.
the plectognaths only in the suborder Gymnodontes

(Tetraodontoidei), and it is closely similar to that of Triodon, the monotypic representative of the Triodontidae and the most generalized member of its suborder. Eoplectus is similar to Recent triacanthodids and

differs from Triodon in the following ways: 1) Recent

triacanthodids have the most fully developed pelvic fin among plectognaths, in more generalized forms consisting of a spine and two unbranched rays, while in Eoplectus this fin is even better developed as a spine and

four branched rays, the better development in Eoplectus

being less reduced than in triacanthodids from the

ancestral perciform condition of one spine and five branched rays; 2) the rounded i, 10, i caudal fin, without

procurrent fin rays; 3) the short caudal peduncle; 4) six dorsal fin spines borne on five well-developed basal

pterygiophores; 5) first basal pterygiophore of the spiny

dorsal fin articulated low on the base of the skull and

bearing the first two spines; 6) third to fifth basal pterygiophores of the spiny dorsal fin with their shafts directed ventrally or posteroventrally in relation to the

vertebral axis and articulated with the neural spines of the fifth to eighth vertebrae; 7) 20 vertebrae; 8) probably no ribs; 9) small prefrontal not extensively sutured to the

frontal, parasphenoid and ethmoid; 10) moderately large eye located about midway between the snout and spiny

dorsal fin origin; 11) relatively large numbers of dorsal and anal fin rays. Eoplectus is similar to Triodon and differs from the

other triacanthodids in the following ways: 1) the small

individual rounded dental units intimately associated with the matrix of the premaxillaries and dentaries to form a crushing beak; 2) premaxillary probably im- movably held by suturing to the maxillary, the ascending

process of the premaxillary poorly developed and the upper jaw probably nonprotrusible, rotating around a ball and socket joint between the palatine and the maxillary;

3) the palatine probably immovably sutured to the ethmoid-vomerine region; 4) vertebrae in a 9 -I- 11 ar- rangement.

Eoplectus is similar to both the other triacanthodids and to Triodon in the following ways: 1) the pelvis with

a long anterodorsal shaft probably held between the anteromedial edges of the cleithra; 2) a generalized caudal skeleton with the parhypural, numerous

hypurals, and single epural probably not fused to one

another or to the last centrum.

Eoplectus differs from both the other triacanthodids and Triodon in the following ways: 1) probably no

uroneurals, or only very small ones at the most; 2) the

great depth of the caudal peduncle; 3) the placement of the well-developed shaft of the second basal pterygio- phore of the spiny dorsal fin, directed strongly anteroventrally and articulating either with the base of the

skull or between the neural spines of the first and second

vertebrae; 4) the spiny dorsal fin base equal in length to the soft dorsal fin base rather than either much greater or much less than it; 5) soft dorsal and anal fin rays far more numerous than the basal pterygiophores supporting them; 6) the extremely well developed ventral flange of

Figure iS.—Zignoichthys oblongus:

lateral view of holotype, ca. 161 mm SL, Eocene of Monte Bolca, Italy.

the parasphenoid versus weakly to moderately

developed; 7) the highly arched vertebral column; 8) the body with an incomplete covering of scales, many of which are isolated and nonoverlapping. The other species of Eoplectinae is the extremely poorly known Zignoichthys oblongus (Zigno 1874a, b) from

the same strata of the Eocene of Monte Bolca, Italy, in which Eoplectus occurs. Of its few known features, re- described by Tyler (1973b) and briefly summarized here, the most important is the huge jaw bone composed of two equal sides fully fused together in the midline with no evidence of any kind of separation or suture between

the right and left halves. The biting edge of the beaklike jaw is not exposed, but the teeth can be expected to be

small dental units incorporated into the matrix of the bone much as in Eoplectus, Triodon, and some of the other gymnodonts. The body is covered with numerous

small scales with numerous upright spinules, and the caudal fin has about 12 principal rays in addition to at

least two or three procurrent rays both above and below. Among plectognaths, procurrent rays are otherwise known only in Triodon. It is not known with surety whether dorsal fin spines were present, for most of the appropriate region of the body is missing, but it is probably best to assume that a spiny dorsal fin of un- known size was present. The region where one would ex- pect to find a pelvic fin if one were present is relatively well preserved, and no pelvic fin is apparent, and it can

probably be assumed that the pelvic spine, if present at

all, was of reduced size. Too few critical features are known of Zignoichthys to allow a precise placement of it among the plectognaths, and it has very tentatively been associated (Tyler 1973b) with Eoplectus and the Eoplectinae of the Triacanthodi- dae for the following reasons. It has a generalized condition of the caudal fin and caudal peduncle, and of the

soft dorsal and anal fins and scales consistant with the

triacanthodids, and, if a spiny dorsal fin was present, it would probably have been longer based than the soft dorsal fin, judging from the space available for it, while the jaw that is exposed is similar to that of Eoplectus.
The Eoplectinae differ from the other fossil subfamily

of triacanthodids, the Spinacanthinae, mainly by having

a larger eye located about midway between the snout and

spiny dorsal fin origin, the lesser development of the spiny dorsal fin and its shorter base and more posterior

position, better developed and longer based soft dorsal and anal fins, and the massive beaklike jaws. The anatomical diversity of the two Recent subfamilies of triacanthodids is summarized below from

Tyler (1968). Of greatest phylogenetic significance is the arrangement and form of the bones of the posterodorsai

region of the skull and in the shape of the pelvis, which

features divide the Recent species into different subfamilies. In the Hollardiinae, which form a compact group of

five species in two genera, the supraoccipital is domelike and separates the epiotics on the dorsal surface of the

skull, while the epiotics directly contact the frontals and

the pelvis is a sturdy shaft with a more or less triangular shape in cross-section. In the Triacanthodinae, whose 14

species in 9 genera range from relatively normal species through intermediates to weirdly specialized forms with extremely long tubular snouts, the supraoccipital

basically is a broad flat bone with a variously developed

crest and does not separate the epiotics on the dorsal sur- face of the skull, while the epiotics are separated from

the frontals by the sphenotics and the pelvis is a broad

flat basin with upturned edges. The two genera of Hollardiinae differ mainly in that Parahollardia retains a small number of teeth internal to the major outer series while the inner teeth on the premaxillary and dentary are lost in Hollardia.

Similarly, in the Triacanthodinae, one genus

(Triacanthodes) retains inner series teeth which are lost

in the other eight genera. In the Triacanthodinae the

teeth are usually conical, as they are also in the Hollardiinae, but in a few genera the teeth are large, thin, and

wide, much compressed from front to back, and either truncate (Tydemania) or truncate to rounded or pointed (Macrorhamphosodes) distally. In Johnsonina the conical teeth are smaller and far more numerous than in the

other genera of triacanthodins, while in Halimochirurgus the teeth are small and conical but of low to moderate (3 to 15) number in both jaws. In one species, Macrorhamphosodes platycheilus, the few upper jaw

teeth are lost in adults. The snout in most triacanthodins is of short to moderate length and normal shape, but in one of the two

species of Bathyphylax, the snout, although of only moderate length, is decidedly concave in front of the

eyes, giving it a tubular appearance, while in Macro- rhamphosodes and Halimochirurgus the snout is enor- mously (26 to 49% SL; least so in young) elongate and

tubular. The mouth is more or less terminal in Triacanthodes, Mephisto, and Paratriacanthodes, as it is in the

Hollardiinae, but it is slightly supraterminal in Johnsonina and Atrophacanthus, slightly to decidedly supra- terminal in Bathyphylax, and decidedly supraterminal

in Tydemania, Macrorhamphosodes, and Halimochirurgus.

The bones of the long tubular snouts of Macrorhamphosodes and Halimochirurgus are strangely rearranged from the condition of other members of the family. In both species of Halimochirurgus and in M. uradoi the upper three-fourths of the tube is composed, from anteriorly

to posteriorly, more or less successively by the ecto- pterygoids, palatines, and vomer, which are thin, curved, and elongate plates. In M. platycheilus, however, the vomer extends further forward than in the others to form

the roof of the anterior region of the snout to the exclusion of the ectopterygoids and palatines. The ventrolateral region of the tube in all four species is formed by

the elongate quadrate and the long slender anterior prolongation of the preoperculum. The premaxillary

pedicels of M. uradoi are prolonged posteriorly as thin filaments but in none of the four long-snouted species do

the pedicels extend posteriorly to the region of the ethmoid, as they do in other triacanthodids. The bones of the snout of Halimochirurgus more completely roof over

the tube than in Macrorhamphosodes, and the tube is narrower and more elongate in Halimochirurgus than in Macrorhamphosodes.

In Halimochirurgus the lips are of normal

triacanthodid size and shape, while in Macrorhamphosodes the lips form a wide disklike structure around

the mouth. The size of the lips in Tydemania is more or

less intermediate between that of Macrorhamphosodes

and other triacanthodids. In Macrorhamphosodes the mouth becomes twisted to the left or right, usually

progressively so with increasing specimen size, while in Halimochirurgus it is symmetrically placed at all sizes. The spiny dorsal fin is relatively well developed, with

all six spines protruding through the surface and of gradually decreasing length posteriorly in the series in Triacanthodes, Mephisto, Paratriacanthodes, and Johnsonina, as in the Hollardiinae, while in Bathyphylax the

fourth spine is much shorter than the third but protrudes through the surface and is clearly seen, with the fifth and

sixth spines only slightly shorter than the fourth and

protruding only slightly less. In Atrophacanthus, Tydemania, Macrorhamphosodes, and Halimochirurgus the last three dorsal spines are rudimentary and usually only barely, if at all, protrude through the

surface, while in Halimochirurgus the third spine also tends to be rudimentary.

Triacanthodes, Johnsonina, and Paratriacanthodes

herrei usually have two pelvic fin rays, although in large specimens the second may tend to become a buried rudi- ment and be resorbed, while in P. retrospinis, Mephisto,

Atrophacanthus, Bathyphylax, Tydemania, Macrorhamphosodes, and Halimochirurgus there is only a single pelvic fin ray. The size of the gill opening varies from relatively huge

for a plectognath fish in Mephisto, in which the slit ex- tends down well below the level of the lower edge of the

pectoral fin base, to simply large, as in Triacanthodes, Halimochirurgus centriscoides, and Macrorhamphosodes platycheilus, in which the slit extends down to or around the level of the lower edge of the pectoral fin base, to moderate or short, as in all the other species, in
which it extends to somewhere between the level of about

one-third to three-fourths down the pectoral fin base, the

slit being especially short in Halimochirurgus alcocki and Macrorhamphosodes uradoi. The length of the pseudobranch, more or less corre- lated with its number of lamellae, varies from especially

long, as in Triacanthodes, in which it extends below the

level of the lower edge of the pectoral fin base, to short, as

in Mephisto, Bathyphylax, and Macrorhamphosodes, in which it extends to the level of the upper edge of the pectoral fin base, with the other genera variously in- termediate. The greatest depth of the body in adults of Triacanthodes, Mephisto, Paratriacanthodes, Johnsonina, and
Bathyphylax, as in the hollardiins, is about 40 to 65%

SL, while in Atrophacanthus and Tydemania it is about

30 to 35% SL, and in Macrorhamphosodes and Halimochirurgus about 15 to 25% SL. The eye of Johnsonina is larger than in any other triacanthodid at comparable

size, and it is the only genus to feature a large ocellated eye spot on the body, just below the soft dorsal fin. In Triacanthodes, Mephisto, Johnsonina, and Paratriacanthodes herrei, as in hollardiins, the basal flange of the pelvic spine and the region of the pelvis against which it slides are smooth, allowing for only a single posi- tion of locking the erected spine against the pelvis, while

in P. retrospinis, Atrophacanthus, Bathyphylax, Tydemania, Macrorhamphosodes, and Halimochirurgus these two regions are grooved, allowing for multiple positions of locking the erected spine against the pelvis.
The crest on the otherwise flattened supraoccipital of triacanthodins is best developed in Triacanthodes and

Johnsonina, being high and relatively wide at the

anterior edge, while in all the other genera the crest is low and thin. Other features of the anatomical diversity of the triacanthodids are discussed by Tyler (1968), and for the muscles by Winterbottom (1974). Generic relationships. —Parahollardia and Hollardia

are obviously very closely related, with the former slightly the more generalized of the two, based on the evidence

of its retention of a series of teeth internal to the major
branchiostegal rays

row, while the similarity in the configuration of the posterodorsal region of the skull and of the pelvis clearly indicates that these two genera, forming the hoUardiins,

represent a line of triacanthodid evolution distinct from

that of the other nine Recent genera, the triacanthodins. The relationships of these two Recent subfamilies to the two fossil subfamilies are discussed in the following sec- tion on subfamilial relationships. Among the triacanthodins, as summarized from Tyler

(1968:29-31), the deeper bodied genera with well- developed spiny dorsal fins are more generalized than the

others, and of these generalized genera, Triacanthodes, which retains a series of teeth internal to the major outer

series and which has a deep body, well-developed spiny

dorsal fin, and long gill opening, is the most generalized

of all. Mephisto and Paratriacanthodes are close derivatives of the same ancestral stock which gave rise to Triacanthodes and are simply progressively more

modified from it. Johnsonina is also a derivative of a Triacanthodes-like ancestral stock which has independently further specialized in most ways from it beyond

the levels of Mephisto and Paratriacanthodes. Atrophacanthus, Bathyphylax, and Tydemania are probably independent derivatives of a stock of ParatriaFigure 22.—Hollardia hollardi: lateral view

of heads of moderate-sized specimen, 62.7 mm SL, (above) and extremely large specimen. 174 mm SL

(the largest Recent triacanthodid fish recorded), Caribbean, showing the change in configuration, increased suturing in the occipital-otic region and decreased amount of cartilage

visible externally in large specimens.

canthodes-like level of organization. An Atrophacanthus-like form, with the last three dorsal spines rudi- mentary, the second pelvic ray absent, and the mouth

slightly but distinctly supraterminal, is probably not

ancestral to any other living triacanthodid, for the tendencies it shows are for the snout to slightly decrease

in length and the conical teeth to increase in number

while becoming smaller and more sharply pointed. These

tendencies are not compatible to ancestry of any of the

other moderately or highly specialized genera. However, a Tydemania-Vike form is ancestral to Macrorhamphosodes, while a Bathyphylax-Uke one is ancestral to Halimochirurgus. Thus, the two long- snouted genera which are superficially closely related in actuality have independently evolved long snouts and

are not as closely related to one another as to other

genera. Tydemania and Macrorhamphosodes are the only two

genera of triacanthodids in which the teeth are wide and

thin and variously pointed to rounded to truncate distally. Tydemania has a snout of moderate length, a distinctly supraterminal mouth of moderate width with wide

fleshy lips, the truncate teeth well developed in both

jaws but slightly fewer in the upper than in the lower jaw,

the last three dorsal spines rudimentary, and the second

pelvic ray absent. These are all characteristics that one would expect to find in an ancestor of Macrorhamphosodes, in which the elongate snout bears a distinctly supraterminal mouth in a wide fleshy disk, the teeth are more or less truncate and well developed in the lower jaw

but few in number or absent in the upper jaw, the last three dorsal spines are rudimentary, and the second

pelvic fin ray is absent.

In Halimochirurgus the distinctly supraterminal mouth has thin lips and feeble teeth in reduced number

in both jaws at the end of an extremely long tubular
Figure 23.

ParahoUardia schmidti

lateral view of head;

62.0 mm SL. Nicaragua.

Figure 24.—Triacanthodes anomalus:

lateral view of head;

71.5 mm SL, Japan.

Figure 25.—Paratriacanthodes

retrospinis: lateral view of head;

85.3 mm SL, Mozambique.
Figure 2^.—Johnson

eriomma: lateral head; 67.0 mm SL, Puerto Rico.

Figure 21 .—Atrophacanthus

japonicus: lateral view of head

4.3.1 mm SL. Celebes.

Figure 2». —Tydemania navigatoris

lateral view of head: H4.4 mm SL, Bay of Bengal. 72
tu prooccipital ipiwnoric

Figure 29.—Macrorhamphosodes uradoi:

lateral view of head; 69.9 mm SL, Japan. branchiottagal rays intaropwculum

•pihyal

snout, the last three dorsal spines rudimentary and the second pelvic fin ray absent, all of which features are foreshadowed in Bathyphylax, in which the snout is of moderate width, the mouth slightly to distinctly supraterminal, the lips thin, the teeth conical and slightly reduced in number in both jaws, the last two or three dorsal spines rudimentary, and the second pelvic fin ray absent. Subfamilial relationships, and relationships to the Triacanthidae and Gymnodontes.—Since the shape of the posterodorsal region of the skull and of the portion of the pelvis posterior to the pelvic spines, the primary dis- tinguishing features of the two Recent subfamilies, is not known in the two fossil subfamilies, a pertinent question about the basal genus in each of the two Recent subfamilies is which comes closest in basic structure to the

ancestral stock which gave rise to them: was it a stock

with a domelike supraoccipital separating the epiotics on

the dorsal surface of the skull and with a shaftlike pelvis, or a stock with a flattened supraoccipital bearing a medial crest and allowing the epiotics to meet on the dorsal surface of the skull and with a basinlike pelvis, or perhaps a stock with intermediate conditions? In the absence of a solution from the fossil triacanthodids there

is but one clue as to which condition is more likely to have been that of the early triacanthodids, and that is the condition of the supraoccipital and epiotics in the

acanthurids, which are often considered to have evolved

in the Eocene from the same Cretaceous stock (perhaps

the Pharmacichthyidae, according to Patterson 1964) as that which gave rise in the Eocene to the triacanthodids and other plectognaths. The supraoccipital of acanthurids is basically domelike and without a flattened basal portion, while the

epiotics are separated from each other medially on the

Figure 30.—Halimochirurgiu centrUcoidee:

lateral view of head; 99.2 mm SL, Bay of Bengal.
dorsal surface of the skull, basically the same condition

as found in the hollardiins and in contrast to that of the

triacanthodins. The acanthurid epiotic is separated for a

short distance from the frontal by a parietal, a bone lost in all plectognaths, but the epiotic in acanthurids ap- proaches the frontal closely enough to be more similar to the condition in hollardiins than to that in triacan- thodins. The indication from the acanthurids is that the domelike supraoccipital excluding the epiotics from the midline of the dorsal surface of the skull in hollardiins is the more generalized of the two and ancestral to the

flattened condition of the supraoccipital found in triacanthodins. The phylogenetic implications of the shaftlike pelvis of

hollardiins versus the basinlike pelvis of triacanthodins

are unknown, for these differentially shaped portions of the pelvis are long extensions behind the level of the

pelvic fins, and most fishes, including acanthurids, have

no such structure with which that of triacanthodids can

be compared. While the triacanthodins are more speciose and

anatomically diversified than the other Recent subfamily, from which they were derived, they apparently are not

ancestral to any other group of plectognaths, for it is the

hollardiins that are ancestral to the triacanthids, and

that same line probably is ancestral to the balistoids and

ostracioids as well, while the gymnodonts are derived from the eoplectins, as discussed below. The hoUardiin

ancestry of the triacanthids is attested to by the similarity in the domelike shape of the supraoccipital, which ex- cludes the epiotics from meeting on the dorsal surface of the skull, and in the shaftlike nature of the pelvis posterior to the pelvic spines found in this subfamily of triacanthodids and in the derived triacanthids. Since the nature of the supraoccipital and pelvis is not known in the fossil Eoplectinae and Spinacanthinae, it is impossible to say whether one was more closely related

to the hollardiin or triacanthodin line of triacanthodid

radiation than the other. However, it is clear that the

eoplectins were ancestral to the gymnodonts and that the spinacanthins were perhaps an unsuccessful experiment

of the early triacanthodids that gave rise to at least one species with some superficial similarities to os- tracioids but which became extinct without derivatives

alive today. The phylogenetic significance of the Eoplectinae is dis- cussed in detail by Tyler {1973b) and need be only briefly summarized here. It is assumed to be extremely unlikely that the highly specialized condition of small and numerous dental units intimately incorporated into the matrix of the premaxillaries and dentaries, forming a

parrotlike crushing beak, has arisen independently in two or more lines of plectognath radiation. It is more par- simonius to assume that this highly specialized condition

arose in only one basic line of plectognaths, that leading

to the gymnodonts, whose most generalized family is the Triodontidae, and that all plectognaths with this condition are phylogenetically related. Eoplectus basically is triacanthodid and generalized (general body shape, well- developed pelvic and spiny dorsal fins, rounded i, 10, i

caudal fin) in most of its structure, but has a distinctly triodontid and highly specialized dentition and jaw

structure. It represents almost precisely the kind of Eocene ancestral line that has been speculated (Tyler 1962a:793) between the triacanthodids and triodontids, and thus between the basal scleroderms and the derivative gymnodonts. The conversion of an Eoplectus-like form into a Triodon-Vike one involves mostly reductive tendencies, which are well-known to be of great importance in the

evolutionary diversification of the plectognaths, as

follows: 1) complete loss of pelvic fin but retention of

pelvis; 2) reduction of spiny dorsal fin and its basal pterygiophores into a posteriorly migrated rudimentary

structure; 3) reduction in number of soft dorsal and anal

fin rays; 4) great increase in length and decrease in depth

of caudal peduncle concomitant with conversion of rounded into forked caudal fin; 5) decrease in height of neural and haemal spines of caudal peduncular vertebrae and development of anterolateral flanges on neural

spines, associated again with elongation and slenderization of peduncle for more powerful swimming with forked caudal fin; 6) increased covering of scales with more

elaborate surface spinulation and development of ex- pansible dewlap of skin between finless pelvis and anal

region; 7) increase in size of prefrontal and of its sutural connections to surrounding snout bones for stronger buttressing of crushing beak; 8) probable similar increase in

size of palatine for same reason; 9) decrease in depth of ventral flange of parasphenoid; 10) straightening of vertebral column associated with elongation of body. Triodon has only two anatomical features known to be more generalized than in Eoplectus: the presence of procurrent caudal fin rays and of well-developed ribs and

epipleurals. It is unlikely that these are de novo acquisitions of Triodon, and the ancestry of Triodon should have

these structures. In fact, the Eocene Zignoichthys, ap- parently closely related to Eoplectus, does have

procurrent caudal fin rays, indicating that these were

simply lost by Eoplectus after it gave rise to the line leading to Triodon. It is possible that small ribs and

epipleurals were present on the obscured anterior ab- dominal vertebrae of Eoplectus, but it still must be assumed that well -developed ribs and epipleurals were

lost by Eoplectus only after it gave rise to the Triodonlike line. Thus, E. bloti must be considered a slightly specialized member of the Eoplectinae line which gave

rise to the Triodon line, and not the immediate direct ancestor of Triodon. The number of dorsal and anal fin rays in Eoplectus is in the high part of the range for triacanthodids, but the number of basal pterygiophore supports is in the low part

of the range, and even lower for the dorsal pterygio- phores. The fact that there are many more rays than

pterygiophores, especially in the posterior regions of these fins, may indicate a prelude to an eventual reduction in the number of rays from posteriorly to anteriorly

in the series leading to the Triodon condition. This

reduction in number of rays would also tend to lengthen

the caudal peduncle, which would probably continue to
lengthen by posterior elongation as less reliance was

placed on the soft dorsal and anal fins for locomotion and

greater emphasis was placed on the caudal fin as it gradually became forked and more heavily muscled in the tapering peduncular region. Perhaps as it became a more sustained rapid swimmer there was less advantage

to having a large defensive spiny dorsal fin, which eventually was reduced to a rudimentary structure, such as in Triodon, in which it is sometimes absent altogether. The spiny dorsal fin of Eoplectus has one important

characteristic which may shed light on the phylogeny of the other scleroderras, and that is the placement of the second basal pterygiophore, perhaps seemingly trivial. The long shaft of this pterygiophore is oriented distinctly anteroventrally and articulates either between the neural

spines of the first and second vertebrae or between the neural spine of the first vertebra and the base of the

skull just behind the shaft of the first pterygiophore. This

is a decidedly nontriacanthodid arrangement, in which

the shaft of the second pterygiophore is otherwise always

directed ventrally or posteroventrally and articulates with the neural spine of the fourth vertebra. In direct contrast to the triacanthodids, the short shaft of the sec- ond pterygiophore of triacanthids is directed slightly to distinctly anteroventrally toward the region between the neural spines of the first and second vertebrae. This is similar to the situation in Eoplectus, except that the

shaft as well as the rest of the pterygiophore is of much

reduced size, as could be expected by the much smaller

size of the spine it bears in triacanthids relative to Eoplectus. A forward shift in the orientation of the shaft

of the second pterygiophore (and of those posterior to it) occurred somewhere in the line of evolution between the

ancestral triacanthodids and the derived triacanthids, and Eoplectus shows such a shift of the second pterygio- phore (but not of those posterior to it). It is entirely possible that a pre-£op/ectus-like fish, before the jaws and dentition had become 7>wdon-like, was on the line of hollardiin triacanthodids that gave rise to the triacanthids, undoubtedly through a line of evolution including the Eocene Protacanthodes, the most

generalized or triacanthodidlike of all the triacanthids. Protacanthodes has a reduced spiny dorsal fin whose

base is much shorter than that of the long-based soft dorsal fin, an apparently shaftlike pelvis with a well- developed spine and other features typical of triacanthids, while retaining from its triacanthodid ancestry a deep and only slightly tapered caudal peduncle and a

large well-rounded caudal fin. A pre-Eoplectus-like fish with: 1) a hollardiin domed

posterodorsal region of the skull; 2) shaftlike pelvis;

3) generalized triacanthodid jaws with well-developed ascending premaxillary processes and discrete conical teeth in sockets; 4) approximately one to one ratio of dorsal and anal fin rays to their basal pterygiophores; 5) uro- neurals; 6) full-scale covering; 7) only moderately

developed parasphenoid ventral flange; 8) 8 -f 12 ar- rangement of vertebrae; etc., could be on a line ancestral

to the beak-jawed Eoplectus and hence to Triodon and

the other gymnodonts on the one hand, and on the other

hand to the line ancestral to the Recent hoUardiins, from which latter line early arose the Eocene Protacanthodes and its decendent Recent triacanthids. This hypothetical generalized triacanthodid ancestral

line of pre-Eoplectus-like configuration could well have

diverged into two distinct radiations: one retained dis- tinct well-developed individual teeth protruding from

sockets in the jaws, as well as relatively well-developed

spiny dorsal and pelvic fins, and the 8-1-12 vertebral arrangement; the other specialized the jaws and dentition into a crushing beak, while eventually losing the spiny dorsal and pelvic fins and converting to a 9 -(- 11 vertebral arrangement. The evolution of Protacanthodes from a conically toothed pre-£op/ectus-like line would involve: 1) an in- crease in the number of soft dorsal fin rays and of their basal pterygiophores; 2) an elongation of the soft dorsal

fin base concomitant with a reduction in the size of the second and subsequent dorsal spines and of their basal

pterygiophores; 3) a shortening of the spiny dorsal fin base; 4) a slight elongation of the caudal peduncle; 5) a reduction in the number of pelvic fin rays and of their

size. All of this is well within the range of possibility. Somewhere along the line between the pre-Eoplectuslike form, Protacanthodes, and the Recent triacanthids, the enlargement of the prefrontal and its anterior extension alongside the ethmoid and vomer, and other such

typical triacanthid specializations, could have taken

place, while the caudal peduncle structure and caudal fin shape would not have changed until between the Protacanthodes and Recent triacanthid stage. The configuration of the first three basal pterygio- phores of the spiny dorsal fin in Eoplectus is also of in- terest to the phylogeny of the balistids, for it in some

ways represents what one might expect a balistid ancestral group to have, at least in this one respect. That

is, there is a large open space between the second

(anteroventrally directed shaft) and third (postero- ventrally directed shaft) pterygiophores. The third pterygiophore already seems to be acting partially as a

strut supporting the posterodorsal end of the second

pterygiophore and has the ventral end of its shaft in contact with the neural spine of the fifth vertebra, as in

balistids. If the first two pterygiophores in Eoplectus had

greatly reduced ventral shafts so that the first pterygio- phore articulated high on the rear of the skull and the second pterygiophore to the posterior end of the first, with the latter concurrently becoming anteriorly elongate

to reach the rear of the skull, then a prototype of the

balistid structure is achieved. The spine of the third pterygiophore would become lost and the sole function of

this pterygiophore would be to brace the developing

specialized carina accommodating the complex locking mechanism of the first two spines, with the third spine, borne on the small second pterygiophore forming the

rear end of the carina, becoming reduced in size. At the same time that these transformations would be taking

place, the fourth and fifth pterygiophores and their spines would also become reduced in size and eventually

entirely lost. Such is a reasonable scenario for the de-
velopment of the balistid spiny dorsal fin apparatus. The above hypothesis in no way implies that Eoplectus

is directly ancestral to the balistids, for the balistids

clearly are derived from triacanthids. However, fishes

like the Recent triacanthids are too specialized to be considered as the ancestral group to the balistids, and it is simply suggested that balistids could have evolved from

an early line of Protacanthodes-like triacanthids in the Eocene still having an Eoplectus-hke arrangement of the

first three basal pterygiophores of the spiny dorsal fin. The Spinacanthinae appear to me to represent an extinct lineage of triacanthodids not ancestral to any of the Recent groups of plectognaths, although with our present

negligible knowledge of the internal anatomy of the two

species of this subfamily, almost any phylogenetic state- ment about them is mostly speculation. If the Spinacanthinae were evolutionary dead ends, this sub- family of triacanthodids joins the Cryptobalistinae subfamily of triacanthids as the only two groups of fossil plectognaths not clearly on evolutionary lines leading to Recent groups of plectognaths. The reasons for considering the Cryptobalistinae as an evolutionary dead

end are discussed at length by Tyler (1968:243-249) and

for the Spinacanthinae below. The Spinacanthinae seem to have been an unsuccessful experiment in specialization from a more normal

basal triacanthodid configuration. These specializations include: 1) the enormous elongation of the dorsal

fin spines and increased length of the fin base; 2) the reduction in number of fin rays in the soft dorsal and

anal fins and the shortening of the fin bases; 3) the ex- tremely high placement of the small eye in the head;

4) the forward migration of the spiny dorsal fin origin to above the eye; 5) the probably reduced size of the pelvic

fin spine, if present at all; 6) the steep profile of the

snout; 7) the immense size of the body of one of the

species; 8) the development of enormous more or less hexagonal scale plates forming a complete carapace over

the anterior part of the body behind the head in one of the species. The trend for the elaboration of the dorsal fin spines and lengthening of its base concomitant with a reduction

in the number of soft dorsal and anal fin rays and a shortening of their bases is not compatible with a possi- ble ancestry of the triacanthids or balistids, both of which have reduced the spiny dorsal fin and elaborated

the soft dorsal and anal fins. The position of the eye and

the origin of the spiny dorsal fin in spinacanthins are, respectively, higher and further forward than in any

triacanthids or balistids, and the snout is much steeper than in those two families. Additionally, there is good

evidence that the hollardiin triacanthodids gave rise to the triacanthids through a Protacanthodes-\ike line, and

that the balistids were derived from the early triacanthids before they became as specialized as the Recent species. All of this would seem to me to exclude the

spinacanthins from further consideration as possible ancestors of the triacanthids and balistids, and, even

neglecting the role of the eoplectins as the ancestors of the gymnodonts, there is nothing compelling in the composition of spinacanthins to think of them as possibly

related to the gymnodonts, other than that the pelvic fin may have been reduced in size or absent and that the soft dorsal and anal fins are reduced in size. This leaves but one group of plectognaths to be considered as hypothetically derivable from spinacanthins: the ostracioids. Ostracioids, like spinacanthins, have short-based soft dorsal and anal fins and have completely lost the pelvis and pelvic fin, while in spinacanthins the pelvic fin may have been of reduced size or absent, and the condition of the pelvis is unknown. The

scales in one of the two genera of spinacanthins, Proto- balistum, are large thick hexagonal plates which form a continuous cuirass around the anterior half of the body

behind the head, the plates interdigitating along their edges of contact and having surface granulations. In os- tracioids the plates of the carapace are remarkably

similar to those of Protobalistum, although they cover

the head as well as most of the body. It is easy to envision a transition from the mostly isolated and approximately

circular scale plates of Spinacanthus, with surface granulations and a higher central spine, to the hexagonal carapace plates in the partial body cuirass of Protobalistum, with surface granulations and interdigi- tated edges, to the fuller carapace covering of ostracioids. While the teeth of Protobalistum are too large and

heavy to be conveniently ancestral to those of os- tracioids, the smaller more conical teeth of Spinacanthus

could easily be ancestral to those of ostracioids. The

profile of the snout of some ostracioids is as equally steep

as in spinacanthins, and the eye of ostracioids, although somewhat larger than in the two species of

spinacanthins, is located high in the head. However, it is difficult to compare eye position between two groups in which one has a spiny dorsal fin and the other does not. Weighing against any phylogenetic significance to these similarities between spinacanthins and ostracioids

are three factors: 1) the presence of an enormously well- developed spiny dorsal fin in spinacanthins, which one would expect to be at least no larger than in other triacanthodids if not of greatly reduced size in a line leading to the ostracioids; 2) enlarged scale plates, whether or not with granulations and hexagonal pattern, are not unique to Protobalistum and ostracioids among the plectognaths, but are found in some

tetraodontids and molids as well, and the scales of

balistids can easily be envisioned as ancestral to those of

ostracioids; 3) the osteological evidence from Recent

species indicates that the ostracioids are derived from

the same ancestral line as that which gave rise to the

balistids, while it is discussed above why the spinacanthins are unlikely to be ancestral to the triacanthids and

balistids. The low number of fin rays and short base of the soft dorsal fin in spinacanthins is probably correlated with

the trend for the enormous enlargement of the spiny dorsal fin, while for hydrodynamic reasons the apposed anal

fin would similarly become reduced in size to match its equivalent above it. Thus, the short-based soft dorsal and anal fins in spinacanthins could have no phy-
logenetic relationship to the short-based soft dorsal and

anal fins of ostracioids. Nevertheless, considering the

reductive tendencies in the spiny dorsal fin in the plec- tognaths, it is not inconceivable that a group like the spinacanthins at one time early in their history greatly enlarged the spiny dorsal fin, an experiment which eventually proved a failure and gave way to the more usual

trend of reduction, leading to a spinacanthin line with

the spiny dorsal fin reduced in size and eventually lost, leaving a hypothetical form much more suitable for consideration as an ancestral line to the ostracioids than are the two presently known species. The scales in the tetraodontid Ephippion guttifer are

relatively normal prickles in the young, with two or three

radiations from the basal plate supporting the projecting

spine. By about 100 mm SL, however, only the prickles on the belly retain the normal shape, those of the body

having the basal plate enlarged and elongate, and the

projecting spine reduced in size. By 200 mm SL the basal

plates of the scales between the levels of somewhat

behind the pectoral fin base and the soft dorsal and anal

fin origins are further enlarged into irregularly rounded

plates, with irregularly granular surfaces, closely held

together by numerous interdigitations along their edges

of contact. The scale plates anterior and posterior to the

girdle of sutured plates are progressively more distantly spaced from one another and elongate rather than rounded. The scales of the belly, below the carapace girdle, re- main as normal prickles. At larger sizes, as illustrated for a 325 mm specimen, the scales of the girdle become

progressively larger and thicker and the girdle itself ex- tended further anteriorly and posteriorly. The surface sculpturing of the plates becomes more regularly granular and the firmness of the interdigitation between

the plates along all their edges of contact stronger and

less flexible, the largest and heaviest plates mostly in the

ventral region of the girdle. The plates have relatively ir- regular outlines, but many range from triangular to hexagonal. This girdle of interdigitated thickened scale plates in Ephippion adults is fully as strong and solid as that of

ostracioids, and only slightly more flexible, mainly

because it does not completely enclose the body, the belly always retaining normal prickles, and the girdle not extending onto the head. In four specimens, the size of the largest scale plates increased as follows: 3.6% SL at 101 mm; 4.3% SL at 232 mm; 7.1% SL at 325 mm; 9.2% SL at 391 mm. In ostracioids the largest scale plates range from about 6 to 13% SL relatively independent of specimen size beyond juvenile stages. Among the molids the individual scale plates are

relatively small. In Mola and Masturus the basal plates

are more or less rounded and flexibly articulated with one another by delicate denticulations. In Ramania,

however, the basal plates become thicker with in- creasing specimen size and the extent of the interdigitation also increases so that adults have nearly the entire body covered by an only slightly flexible carapace of small (in two specimens, 0.8% SL at 65.1 mm and 1.2% SL at 493 mm) minutely denticulated and irregularly

geometrically arranged basal plates with only low and in- conspicuous surface sculpturing, ranging from 3 to 12

sided, but with some distinctly hexagonal. This carapace

of scale plates never attains the thickness of that of os- tracioids or Ephippion.

In balistids the thick scale plates are usually rhomboidal with slightly overlapping edges (plates not over- lapping in Canthidermis) and usually with low surface sculpturing of wide variety, while some plates (es- pecially on the caudal peduncle) may bear higher spiny

processes. Although usually rhomboidal, the anterior and posterior apices sometimes are flattened, the plate then having a decidedly hexagonal shape. Scale plates such as found in balistids could easily be ancestral to those of ostracioids, by an increase in thickness and sur- face area, more usual hexagonal shape, and conversion from slightly overlapping edges to apposed inter- digitated edges. The strongest reason, however, for not considering the spinacanthins as ancestral to the ostracioids is that the

osteological evidence from Recent species indicates that

the balistids and ostracioids evolved from a common

triacanthid ancestral stock, as discussed fully under the

relationships of the ostracioids, but basically because

balistids and ostracioids have a well-developed prootic

shelf, the hyomandibular supported by the prootic and

pterotic but not by the sphenotic, an expanded

parasphenoid, and similarities in the shape or size of the interoperculum, operculum, suboperculum, premaxillary, and maxillary. Thus, for the present at least and until more is known

of the internal anatomy of the spinacanthins, it seems to me reasonable to tentatively consider the spinacanthins an extinct line of early triacanthodid experimentation

not ancestral to any of the other known subgroups of plectognaths.

In summary, there is good evidence that the HoUardiinae are ancestral to the Triacanthidae and the Eoplectinae to the Tetraodontoidei, while probable that the Triacanthodinae are derived from the hollardiins and

possible that the Spinacanthinae were an evolutionary dead end.

In fact, the Eoplectinae are so obviously ancestral to the Gymnodontes that the eoplectins could be considered as the most basal family of that suborder, even more generalized than the Triodontidae, rather than as a subfamily of the Triacanthodidae with highly specialized

jaws. Similarly, the Protacanthodinae are so obviously

ancestral to the Recent Triacanthidae and intermediate between them and the Triacanthodidae that the

protacanthodins could be considered a specialized sub- family of the Triacanthodidae rather than as the most

generalized subfamily of the Triacanthidae. It is on the

basis of my own personal assessment of the overall

similarities and differences between most triacan- thodids, Eoplectus, Zignoichthys, and triodontids and

between triacanthodids, Protacanthodes, and most

triacanthids that I subjectively feel that Eoplectus and

Zignoichthys are best placed in the Triacanthodidae and

Protacanthodes in the Triacanthidae.
Family Triacanthidae Comparative dia^osis (contrast with that of the Triacanthodidae) (modified from Tyler 1968:234-

236). —A compact, strongly sutured skull and a muscular body built for active swimming near the bottom;

very little cartilage visible on the external surface of the

skull between the regions of apposition of the bones in the otic and occipital regions, the bones usually strongly sutured to one another along all edges of proximity; an

outer series of about 8 to 10 heavy incisor teeth in each

jaw, internal to which are several more or less molariform

teeth, usually four (two in Trixiphichthys weberi) in

Figure 31.—Typical body form in the Recent

Triacanthidae: Paeudotriacanthus strigilifer.

the upper jaw and two in the lower; a large sturdy eth- moid-frontal complex for the support of the massive dentition; the prefrontal with a long anterior extension, sutured medially to the ethmoid and anteriorly to the

posterolateral extensions of the vomer; premaxillary

pedicels when fully retracted reaching only to the anterior basal region of the ethmoid, well-separated from

the frontals (probably least so in the Eocene

Protacanthodes); supraoccipital domelike, its posterior surface concave; epiotics separated on the dorsal surface

of the skull by the supraoccipital and meeting medially

only on the posterior surface of the skull and ar- ticulating anterolaterally with the frontals; ptero- sphenoids meeting and suturing in the midline of the

posterior wall of the orbit; neural processes of the first vertebra meeting and suturing in the midline above the neural canal, forming with the exoccipitals a completely

enclosed bony well (with a bony bottom) in which the

shaftlike end of the first basal pterygiophore of the spiny

dorsal fin is immovably held (a different arrangement

present in the Oligocene Cryptobalistes); parasphenoid

in region of orbit with a dorsal arch and a well-developed

ventral flange below the orbit, the flange about 2 or 3 times as deep as the upper shaftlike portion of the bone

(except in the Eocene Protacanthodes, the shaft relatively straight and the flange not much deeper than the

shaft); hyomandibular with a well-developed groove and

crest along its lateral surface more or less transversely;

pterotic with a ventral process overlying and firmly ar- ticulating with the upper posterior portion of the hyomandibular; supracleithrum placed vertically to the

horizontal axis of the skull, nearly its entire length overlying the cleithrum; mesopterygoid absent (at least in adults) in all but one species {Trixiphichthys weberi), and when present small and difficult to distinguish from

the metapterygoid, to which it is mostly fused; olfactory cavity between the ethmoid and prefrontal well defined, with distinct bony boundaries; basihyal absent; lower two branchiostegal rays enlarged (except in the Eocene

Protacanthodes), much wider than the upper branchiostegal rays; operculum elongate, usually widest in the middle, not triangular; air bladder thick walled, somewhat elongate, large and extending posteriorly al- most the entire length of the abdominal cavity; pelvis a

sturdy shaft; the two halves of the pelvis variously fused

or extensively interdigitated, like a railroad rail in cross section just behind the level of the pelvic spine (except in the Oligocene Cryptobalistes, which has a basinlike pelvis); a single oblique crest on the side of the pelvis at the

level of the flange of the pelvic spine, allowing for two, and only two, positions of locking the erected spine (probably a different arrangement in the Oligocene

Cryptobalistes); the ventrolateral surface of the pelvis at the base of the spine without a complete foramen and the two sides of the base of the spine not meeting medially;

all haemal arches and spines of adults fully fused to their centra; only the epural and uppermost hypural as separate elements articulated by fibrous tissue to each

other and to the centrum, the other hypurals and the parhypural fully fused to one another and to the cen- trum (probably some separation of the middle hypurals

in the Eocene Protacanthodes); a single pair of uroneurals present; thick epipleurals present from the

third or fourth abdominal vertebra to the first or second, sometimes the third and rarely the fourth, caudal

vertebra; fifth basal pterygiophore of the spiny dorsal fin usually absent, rarely present as a tiny buried bony

splint beneath the usually rudimentary sixth dorsal

spine; first basal pterygiophore of the spiny dorsal fin a

stout shaft (except very short in the Oligocene Cryptobalistes) with poorly developed anterior and posterior medial flanges, the flanges never wider than the shaft;

first basal pterygiophore of spiny dorsal fin with a medial

flange dorsally not completely enclosing a foramen; sec- ond to fourth basal pterygiophores of spiny dorsal fin reduced in size, their shafts not reaching ventrally to between the tips of the neural spines (but associated with

those of the first to third vertebrae, except in the Eocene

Protacanthodes, in which the shafts reach to the distal ends of the neural spines of the second to fourth

vertebrae) and the fourth pterygiophore occasionally

missing; none of the basal pterygiophores of the spiny

dorsal fin sutured to one another distally; spiny dorsal fin base (including rudiments) much shorter than soft dorsal fin base (except the Eocene Protacanthodes, with

spiny dorsal base slightly longer than soft dorsal base); only four or five (six in the Eocene Protacanthodes and

perhaps in the Oligocene Cryptobalistes) abdominal

vertebrae anterior to the first basal pterygiophore of the

soft dorsal fin; first anal fin basal pterygiophore with a

sturdy medial flange anterior to its lateral flanges, the
pterygiophore + -shaped in cross section; well developed

lateral flanges for muscle attachment present along most

of the length of most of the basal pterygiophores of the

soft dorsal and anal fins; a sturdy lateral flange present

horizontally along the middle of the posterior half of the

last centrum and the anterior region of the hypural

plate; soft dorsal fin basal pterygiophores 20-26, anal fin basal pterygiophores 14-19, most of these pterygiophores sutured to one another distally; distal pterygiophores of

soft dorsal and anal fins often unossified, the ossification, when present, always as a single piece and not as a

pair of elements to either side of the midline; sixth dorsal spine nearly always present as a rudiment, in all but

very young specimens usually as a splint of bone buried beneath the skin, but sometimes protruding to the sur- face even in adults; the fifth spine usually very short, but

nearly always protruding at least a short distance through the skin; the first four spines always visible externally, but the fifth and sixth spines sometimes absent

in one Recent species and perhaps in several fossil forms;

dorsal fin rays 19-26; anal fin rays 13-22; pelvic fin with a

large spine followed in some species by a single ray which becomes a buried rudiment in adults; adults never with a protruding pelvic ray; dorsal and pelvic spines with numerous shallow lengthwise grooves (except in the Miocene Marosichthys, in which the grooves seem to be

deep), mostly obscured by the overlying scale plates ex- cept at the naked distal end (one-tenth or less of the

length); uppermost pectoral fin ray nubbinlike, the two

halves of the ray about equally short or the lateral half

shorter, the basal region of the medial half always im- mensely larger than that of the lateral half; the slightly overlapping basal plates of the scales of the body bearing

either an emarginate cruciform ridge or an anterior to posterior series of vertical emarginate ridges (except in the Eocene Protacanthodes, with numerous upright

spinules, and in the Oligocene Cryptobalistes, without

elaborate ornamentation); peritoneum pale, often with

silvery overtones; coloration basically silvery-gray, with

yellowish or greenish overtones; lateral line relatively conspicuous (least so in Trixiphichthys weberi); scaly skin forming a definite low sheath along the bases of the

soft dorsal and anal fins; olfactory lamellae 23-54,

relatively thin; anterior nostril with an upraised rim posteriorly, essentially flush with the surface anteriorly, the rim not tubelike; posterior nostril with an upraised rim

anteriorly; gill rakers laterally on first arch relatively

short, shorter than the width of the fleshy arch; usually only one, rarely two, rakers laterally on the upper limb of the first arch above the angle; caudal peduncle relatively

long, 16 to 31% SL, distinctly tapering to a narrow transversely indented region above and below just in front of the caudal fin base (except in the Eocene

Protacanthodes, which has a relatively deep and only

slightly tapered peduncle); least depth of the caudal

peduncle, between the precaudal grooves, 2 to 5% SL (ex- cept in the Eocene Protacanthodes, the depth 15% SL, and in the Oligocene Acanthopleurus collettei, the depth

5 to 8% SL, versus 4 to 5% SL in the Oligocene A. ser- ratus and 2 to 4% SL in Recent species); the caudal

peduncle wider than deep at this point (except in A. collettei, the width probably about equal to the depth, and

in the Eocene Protacanthodes, the width unknown but

obviously less than the depth); caudal fin deeply forked

(except in the fossil genera Protacanthodes, with a rounded caudal, and Cryptobalistes, with an almost

truncate caudal).

Figure 32.~Pseudotriacanthus strigilifer: showing the course of the lateral line; lower

left, scales from upper middle region of body, including two lateral line canal bearing scales: lower right, nasal

region as seen externally (above) and

the olfactory lamellae as seen with the top

of the nasal sac removed.

Detailed description o{ Pseudotriacanthus atrigilifer. Material examined. —Five cleared and stained speci- mens, 79.0-145 mm.

Occipital Region.

Basioccipital. —A short column, dorsolateral^ expanded; cartilage filled along its anterior and anterodorsal edges; articulates by extensive interdigitation

posterolaterally with the exoccipitals, anterolaterally with the prootics and anteroventrally with the overlying

posterior end of the parasphenoid. The rim of the round

concave posterior end of the basioccipital articulates by

fibrous tissue with the rim of the concave anterior face of the centrum of the first vertebra. A deeply concave

medial channel is present on the anterior three-fourths of the ventral surface of the basioccipital. The anterior end

of this channel is mostly hidden from view by the overlying parasphenoid. Posteriorly this channel is open to the
exterior at the base of the posterior bifurcation of the parasphenoid, while anteriorly it opens into the myodome where the anterior end of the basioccipital forms the posterodorsal and posterolateral walls of the myodome.

Exocclpital. —Cartilage filled at its dorsal, lateral, and ventral edges; articulates by interdigitation dorsally with the epiotic, anteroventrally with the prootic, ventro- medially with the basioccipital and laterally with the

pterotic, while dorsomedially it interdigitates with its opposite member above the foramen magnum. The

foramen is entirely surrounded by the exoccipitals, ex- cept ventromedially where it is bounded by the upper

surface of the basioccipital. Posteromedially the exoccipitals interdigitate with the neural spine of the first vertebra. An exoccipital condyle is present only in the' form of a slightly posteriorly elongate region of the

posteroventral end of the exoccipital, the short condyle

overlying the anterolateral surface of the lower neural arch region of the vertebra just above the region of the centrum. The neural processes from either side of the

first vertebra meet and interdigitate in the midline above

the neural canal, forming, in conjunction with the exoccipitals to which they are also sutured, a completely

enclosed bony well in which the shaftlike end of the first basal pterygiophore of the spiny dorsal fin is immovably

held by fibrous tissue. The bony bottom of this well is formed mainly by the exoccipitals where they meet

medially to roof over the foramen magnum.

Supraoccipital. —Dome-shaped; its stout rounded

anterodorsal edge forming the apex of the cranium and

its posterior surface concave; cartilage filled along most

of its ventral edges; articulates through interdigitation posteroventrally with the epiotics and anteroventrally with the frontals, the frontals overlying the anterolateral edges of the supraoccipital.

Otic Region.

Pterotic. —Cartilage filled along most of its edges

of articulation with the other cranial bones; articulates through extensive interdigitation posterodorsally with

the epiotic, posteromedially and ventromedially with the

exoccipital, anteromedially with the prootic, and anterolaterally and anterodorsally with the sphenotic. The

anteroventral end of the pterotic is the main support for the hyomandibular, its extreme anteroventral edge abutting against the rear half of the dorsal end of the hyomandibular while a sturdy ventral flange from its ventrolateral edge broadly overlies the posterodorsal region of the lateral surface of the hyomandibular. While the ar- ticulation between the pterotic and hyomandibular is through fibrous tissue, it is very firm and relatively im- movable, especially so because of the presence of the ventral flange of the pterotic broadly overlying the hyomandibular. Much of the posterolateral surface of the

pterotic is overlaid by the posttemporal, to which it is firmly interdigitated.

Sphenotic. —Cartilage filled along all of its edges of articulation with the other cranial bones; articulates by

extensive interdigitation anteromedially with the

prootic, pterosphenoid, and frontal in the posterior wall

of the orbit, respectively from below to above. Laterally on the skull the sphenotic articulates by interdigitation dorsally with the frontal and epiotic and posteriorly with

the pterotic. Posterodorsally the sphenotic interdigitates for a short distance with the anterodorsal edge

of the posttemporal. Anterolaterally the sphenotic helps form the concave groove that supports the dorsal edge of the hyomandibular. The sphenotic forms the anterolateral part of the groove, the anteromedial part being formed by the prootic and the posterior half by the

pterotic. The articulation of all these bones with the hyomandibular is through fibrous tissue.

Epiotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates through extensive interdigitation posterodorsally with

the supraoccipital and anterodorsally with the frontals. Medially the edges of the two epiotics interdigitate with one another, while posteroventrally they interdigitate with the exoccipital and pterotic. Anteroventrally the

epiotic interdigitates with the posterodorsal region of the

sphenotic, while the extreme posterolateral edge of the

epiotic is broadly overlain by the upper end of the post- temporal, with which it interdigitates. Ventromedially on the posterior surface the epiotic helps form a very

short portion of the upper anterior region of the bony well supporting the shaft of the first basal pterygiophore of the spiny dorsal fin, while the main support for this shaft

is the portion of the well formed by the exoccipitals and

neural spine of the first vertebra.

Prootic. —Cartilage filled along all of its edges of articulation with the other cranial bones, except anteriorly; articulates by extensive interdigitation anterodorsally with the pterosphenoid, anterolaterally with the

sphenotic, posterolaterally with the pterotic, posteriorly with the exoccipital, and posteromedially with the

basioccipital. The prootic interdigitates along all of its length medially with the parasphenoid, while laterally the prootic helps support the dorsal head of the hyomandibular. The lateral walls of the myodome are formed by

the ventromedial surfaces of the prootics, while the dorsal walls of the myodome are formed by the medially

directed horizontal shelves, which are attached to one

another through extensive interdigitation, from the ven- tromedial surfaces of the two prootics. The prootics also form the upper two-thirds to three-fourths of the anterior wall of the myodome.

Orbital Region.

Frontal. —Wider posteriorly than anteriorly where

it tapers to a blunt point above the posterior end of the ethmoid and medial to the prefrontals; articulates by ex- tensive interdigitation posteromedially with the supraoccipital, whose anterior edge it broadly overlies, pos-
teriorly with the epiotic, posterolaterally with the

sphenotic, anteriorly with the ethmoid, and anterolaterally with the prefrontal. Posteromedially on its ventral surface in the rear of the orbit the frontal inter- digitates medially with the pterosphenoid and ventrally with the sphenotic. Medially the two frontals are in close apposition with one another and articulate either through fibrous tissue or interdigitation, but at one or more places along their lengths there is usually a small amount of cartilage visible between the two halves. The

frontal interdigitates anteriorly with the ethmoid and

anterolaterally with the prefrontal, both of which bones

it overlies.

Prefrontal. —Cartilage filled along most of its broad medial surface except for the long anterior strut that lies alongside the ethmoid. Posteromedially the edges of the two prefrontals interdigitate with one

another but anteromedially the prefrontals articulate through cartilage with the ethmoid, except for the long

anterior strut which lies alongside and interdigitates with the lateral surface of the anterior half of the eth- moid, the shaft at its extreme anterior end also inter- digitating with the posterolateral wing of the vomer.

Posteroventrally the prefrontal articulates through cartilage with the dorsal surface of the parasphenoid below.

Parasphenoid. —An elongate shaft with a well- developed keel along its ventral surface in the region of the orbit. A deep, anteriorly directed cleft is present in the posterior portion of the parasphenoid, giving rise to the forked region which broadly overlies and inter- digitates with the basioccipital and at the same time

covers over the medial groove on the basioccipital leading to the rear of the myodome. About two-thirds of the way back the parasphenoid possesses paired dorsolateral wings which interdigitate with the anteroventral edges of the prootics and thus form the lower part of the

anterior edge of the myodome, while more posteriorly the parasphenoid forms the floor of the myodome. Posterior

to its articulation with the prootics, the parasphenoid

overlies and interdigitates with the basioccipital. Just below its region of articulation with the anteroventral ends of the prootics, the lateral surface of the para- sphenoid is slightly expanded into a knob, anterior to which the keeled portion of the bone is slightly concave.

It is to this concavity that the upper elements of the

branchial arches are held by fibrous tissue, especially the epibranchials and pharyngobranchials. The first pharyngobranchial or suspensory element articulates through fibrous tissue to the lateral surface of the para- sphenoid in this region. In the region of the orbit the parasphenoid is slightly arched dorsally and the keel is 2

to 3 times the depth of the more rounded shaftlike portion above it. At its extreme anterior end the ventral sur- face of the parasphenoid is somewhat concave to receive and interdigitate with the posterior shaftlike portion of the vomer, while dorsally at its anterior end the para- sphenoid articulates through cartilage with the prefrontals £md ethmoid.

Pterosphenoid. —Cartilage filled along its lateral edges; articulates by interdigitation dorsally with the

frontals, posteriorly with the sphenotic, and ventrally with the prootic. Along the middle of its medial edge the pterosphenoid possesses a medial extension which meets

with that of its opposite member to interdigitate in the

midline. Ethmoid Region. Ethmoid.—The ethmoid remains largely car- tilaginous, the ossification being mostly restricted to the

surface regions. However, the ossification is more ex- tensive than in triacanthodids. The bone is widest along

the middle of its lateral surface where it interdigitates with the long forward extensions of the prefrontals. Posterodorsally the ethmoid interdigitates with the overlying anterior end of the frontal. Posterolaterally it ar- ticulates through cartilage and some interdigitation with

the prefrontals, and ventrally through cartilage with the

dorsal surface of the parasphenoid and shaftlike portion

of the vomer. Anteromedially the ethmoid has a pro- longation which interdigitates with the posteromedial

region of the dorsal surface of the vomer. The surface of the medial region of the anterior one-fourth of the eth- moid is somewhat thickened, this being the region over which the premaxillary pedicel slides in the opening and

closing of the mouth.

Vomer. —The vomer is expanded laterally at its anterior end, while its flattened shaftlike posterior ex- tension fits into and interdigitates with a concave area on

the ventral surface of the petrasphenoid. Posterolaterally the vomer has a pair of extensions which extensively in- terdigitate with the anterior ends of the extensions from

the prefrontals alongside the anterior end of the eth- moid. The dorsal surface of the vomer helps support the premaxillary pedicel, while laterally the expanded anterior region of the vomer articulates by tough fibrous tis- sue with the medial surface of the middle region of the

palatine. Posteromedially the vomer interdigitates with

the anterior end of the parasphenoid, while the dorsal surface of the posterior shaft of the vomer abuts against

the ethmoid cartilage above it.

Mandibular Region. Hyomandibular. —A stout rectangular shaft whose

dorsal end firmly articulates by fibrous tissue with the groove on the lateral surface of the underside of the skull formed anterolaterally by the sphenotic, anteromedially by the prootic, and posteriorly by the pterotic, the latter bone also having a ventral flange which broadly overlies the posterodorsal region of the lateral surface of the hyomandibular. A well-developed crest for muscle at- tachment is present about midway along the lateral sur- face of the hyomandibular. Posteriorly the hyomandibular articulates by fibrous tissue along most of its length to the anterior edge of the upper region of the preoperculum, just above the end of which latter bone
the hyomandibular articulates by fibrous tissue with the

anterodorsal head of the operculum. Anteriorly the hyomandibular ends in the cartilaginous plate between it and the metapterygoid.

Quadrate. —Wide posteriorly, tapering anteriorly

to a head for articulation through fibrous tissue with the

articular of the lower jaw; cartilage filled along posterior edge; with a long posteriorly directed process from its posteroventral region which articulates by inter- digitation and fibrous tissue with the anteroventral edge

of the symplectic in large specimens, whereas in smaller specimens intimate contact between the symplectic and

posterior extension of the quadrate is not made and the

articulation is purely by fibrous tissue. Along the posterior edge the quadrate articulates through cartilage with the anterior edge of the metapterygoid, at this region being cartilage filled. Ventrally the quadrate ar- ticulates through fibrous tissue with the dorsal surface of the anterior end of the preoperculum.

Metapterygoid. —A more or less flat plate; cartilage

filled along its anterior, ventral, and posterior edges; ar- ticulates through cartilage anteriorly with the quadrate,

while along its ventral edge it extensively interdigitates with the symplectic in large specimens but only ar- ticulates to it through fibrous tissue in smaller

specimens. Posteriorly the metapterygoid articulates through cartilage with the hyomandibular.

Symplectic. —Long and rod-shaped; cartilage filled at its posterior end; articulates dorsally by inter- digitation (in large specimens, see above) with the metapterygoid and anteriorly variously through inter- digitation and fibrous tissue with the posteroventral end

of the quadrate. Posteriorly the symplectic is in contact with the cartilaginous plate between the metapterygoid and hyomandibular. The upper end of the epihyal is at- tached by fibrous tissue to this cartilaginous plate immediately behind the posterior end of the symplectic.

Ventrally the symplectic articulates by fibrous tissue with the dorsal surface of the preoperculum.

Palato-Pterygoid Region.

Palatine. —Cartilage filled at its extreme posterior end; articulates by fibrous tissue anteriorly with the dorsolateral surface of the maxillary, medially with the

lateral surface of the expanded portion of the vomer,

posteroventrally by fibrous tissue to the posterior end of the ectopterygoid, and directly posteriorly through cartilage and fibrous tissue to the anterodorsal region of the metapterygoid. The posterodorsal wing of the palatine connects to a broad band of fibrous tissue that runs over and above the premaxillary pedicels to join with the

posterodorsal wing of the palatine on the other side. Al- though not sutured to any of the surrounding bones the

palatine is in effect firmly held in place by its extensive

fibrous tissue articulations.

Ectopterygoid. —Somewhat in the shape of an

elongate rectangle; articulates along all of its ventral edges by interdigitation with the quadrate. Dorsally it articulates by fibrous tissue with the posteroventral

region of the palatine and posteriorly through cartilage to the anterodorsal region of the metapterygoid.

Mesopterygoid. —Absent in this and all other species of triacanthids with the exception of Trixiphichthys

weberi, in which it is a small plate of bone closely inter- digitated to the posterior third of the dorsal edge of the

far larger metapterygoid.

Opercular Region. Operculum. —A thin sheet of bone broadest in the middle and tapering to a point ventrally; with a short

dorsally prolonged flange above its anterodorsal head

which articulates by fibrous tissue with a groove on the

posterior edge of the hyomandibular just above the dorsal tip of the preoperculum. Ventrally the operculum

slightly overlies and articulates by fibrous tissue with the suboperculum.

Suboperculum. —Rounded anteriorly, tapering to a

dorsally directed point posteriorly; articulates by fibrous

tissue dorsally with the operculum and anteriorly with

the interoperculum.

Interoperculum. —Very elongate and flat; rounded

posteriorly but tapering to a point anteriorly; articulates by fibrous tissue posteriorly with the suboperculum and

anteriorly ligamentously with the angular in the lower

jaw. In the posterior half of its length the dorsal edge of the interoperculum connects by a band of fibrous tissue

to the epihyal in the region where the epihyal articulates with the interhyal.

Preoperculum. —Slightly expanded posteroventrally in the region below the hyomandibular; the dorsal edge along the anterior half of the bone slightly thicken- ed for articulation by fibrous tissue with the quadrate;

articulates dorsally in about the middle of its length

variously by fibrous tissue and through cartilage with the

symplectic, metapterygoid, and anterior end of the hyomandibular, whereas the main articulation to the hyomandibular is by fibrous tissue along the posterodorsal edge of the preoperculum. Upper Jaw.

Premaxillary. —L-shaped, with the long dorsal arm

(pedicel) much longer than the ventral arm and movably

articulated by fibrous tissue along the dorsal surfaces of the vomer and the extreme anterior end of the ethmoid,

allowing for a slight protraction of the upper jaw. When

fully retracted, the pedicel reaches to the anterior basal

region of the ethmoid. The shorter ventral arm of the pre- maxillary forms the upper two-thirds of the anterior edge

of the upper jaw, the rest of the border being formed by
the maxillary. The premaxillary articulates by fibrous

tissue along the middle of the lateral surface of the posterior arm with the medial surface of the upper portion of the maxillary, while along the medial surface of its posterior arm the premaxillary articulates through fibrous

tissue with its opposite member. The ventral arm of the premaxillary articulates through fibrous tissue along its posteroventral edge with the anterior edge of the maxillary. There are usually five incisorlike teeth, decreasing

in size laterally, borne in shallow sockets along the anterior edge of the premaxillary. Behind and internal to

this outer row of teeth there are usually two additional

teeth, the more medial of the two being the largest, of a

size and shape similar to that of the large most medial

tooth in the outer row, and the lateral inner tooth similar

to the small outermost tooth in the outer row. The teeth

are replaced by new ones developing in new sockets which have pores to the exterior just above and external

to the sockets of the outer row of teeth. After a new tooth

erupts through the surface of the premaxillary, it gradually migrates slightly forward and downward to the

area of the socket of the older tooth which it is replacing.

Maxillary. —A more or less heavy rectangular

bone, rounded ventrally and less so dorsally, and slightly constricted above the middle region; articulates by fi- brous tissue dorsally along the lateral surface of its round- ed portion with the anterior end of the palatine, while

along the medial surface of its rounded portion it at- taches to the lateral and ventral surfaces of the posterior arm of the premaxillary. Ventrally the medial surface of the maxillary articulates by tough fibrous tissue with the

lateral surface of the posterodorsal part of the dentary, while along the middle of its anterior edge the maxillary

articulates by similar tissue with the ventral arm of the

premaxillary.

Lower Jaw.

Dentary. —The posterior end concave on the medial surface to accommodate the anterior end of the

articular, which it broadly overlies laterally but only

slightly overlies medially and to which it articulates by

fibrous tissue; articulates anteromedially by fibrous tis- sue to its opposite member in the midline and posterolaterally by interdigitation with the small angular. Along

the posterodorsal region of its lateral surface the dentary

articulates by tough fibrous tissue with the medial sur- face of the ventral portion of the maxillary. There are usually five incisorlike teeth borne in shallow sockets along the anterior edge of the dentary and usually a

single tooth behind and internal to the outer series, the

single inner tooth being of a size comparable to that of the two larger more medially placed teeth in the outer

series. The lower jaw teeth have the same form as the upper jaw teeth and are replaced by teeth developing in the same manner as described for the premaxillary.

Articular. —More or less triangular in shape;

cartilage filled at its anterior end, where it is continuous

with the remains of Meckel's cartilage; articulates by fi- brous tissue dorsally, ventrally, and laterally with the broadly overlying dentary, posteroventrally by inter- digitation with the angular, and posteriorly at the groove on its posterior edge with the knob at the anterior end of the quadrate. The sesamoid articular is a small ossifica- tion held by fibrous tissue to the region of juncture of Meckel's cartilage and the anteromedial surface of the

articular.

Angular. —A small block of bone; articulates by

interdigitation dorsally with the articular and anteriorly with the dentary. Posteriorly the angular connects by

ligament to the anterior end of the interoperculum. BRANCHIAL APPARATUS.

Hyoid Arch, Branchiostegal Rays, and Urohyal. Hypohyals. —-Both hypohyal elements well de- veloped; dorsal hypohyal cartilage filled along its ventral and posterior edges, the ventral hypohyal cartilage

filled at its dorsal and posterior edges. The dorsal and

ventral hypohyals articulate through cartilage with one

another and with the ceratohyal, while they articulate by

fibrous tissue anteromedially with their opposite members, and in the case of the dorsal hypohyal with the anterior third of the first basibranchial, which is held between the posterior halves of the medial edges of the apposed dorsal hypohyals. The ventral edge of the ventral hypohyal articulates by fibrous tissue with the

urohyal. In large specimens there is sometimes a slight amount of interdigitation between the dorsal and ventral hypohyals.

Ceratohyal.—A large plate expanded posteriorly; cartilage filled at its anterior and posterior edges; ar- ticulates through cartilage anteriorly with both of the hypohyals and posteriorly with the epihyal, the ar- ticulation with the epihyal sometimes strengthened by

interdigitation in large specimens. The six branchiostegal rays articulate by fibrous tissue with the cera- tohyal; the first two rays along the ventral edge of the posterior half of the ceratohyal and the last four rays

to the posterodorsal edge of the ceratohyal and, in the

case of the uppermost one or two rays, to the lower lateral surface of the epihyal.

Epihyal. —Large; cartilage filled at its anterior and

ventral edges; articulates anteriorly through cartilage with the ceratohyal, this articulation sometimes being

strengthened by interdigitation, while posterodorsally

it articulates by fibrous tissue with the interhyal.

Interhyal. —Short, columnar; cartilage filled at its dorsal and ventral edges; articulates by fibrous tissue ventrally with the epihyal and dorsally with the car- tilaginous plate between the symplectic and hyomandibular immediately behind the posterior end of the symplectic.
Branchiostegal rays. —Six in number; increasing only slightly in length posteriorly in the series. The

branchiostegal rays are mostly flat plates of decreasing width posteriorly in the series and articulate anteriorly by fibrous tissue variously to the posterior end of the

ceratohyal and the lower lateral surface of the epihyal, as described above. The decreasing width of the rays posteriorly in the series makes the last few rays somewhat

rodlike rather than flat plates.

Urohyal. —Laterally expanded and thickened

along its anterior edge and, to a lesser extent, for a short distance anterodorsally. Otherwise a flat, thin plate ar- ticulating by fibrous tissue anterodorsally primarily with

the undersurfaces of the ventral hypohyals.

Branchial Arches. —All of the elements are cartilage

filled at their edges of articulation with the other elements of the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and four pairs of pharyngobranchials. Four gills are present, with a slit between the

fourth arch and the lower pharyngeal.

First arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basibranchial the shortest of the three basibranchial elements, laterally compressed in the anterior half of its length, where it is held by fibrous tissue between the medial edges of the

dorsal hypohyal, while posteriorly it articulates mainly

with the anterior end of the second basibranchial and

only secondarily posterolaterally with the first hypobranchials. First hypobranchial about the same size as the second hypobranchial but more rectangular in form;

articulates ventrally with an indented region along the

lateral surface of the anterior half of the second basi- branchial. First ceratobranchial slightly the longest of the ceratobranchial elements, which decrease slightly in

size or length posteriorly in the series; a more or less columnar shaft of bone without a prominent ventral keel. First epibranchial a more or less rectangular block of bone except distally where it slightly bifurcates into two

short projections; the anterior projection articulating with the base of the first pharyngobranchial, or suspensory element, and the posterior projection articulating with the second pharyngobranchial. First pharyngobranchial (suspensory pharyngeal) a short sturdy rod of bone articulating ventrally with the anterior projection of the first epibranchial and dorsally by fibrous tissue to the

lateral surface of the ventral keel of the parasphenoid in the region just below the articulation of the anteroventral edge of the prootic with the parasphenoid.

Second arch.—Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial slightly the longest of the three basibranchial

elements, with concave lateral surfaces in the anterior half of its length for articulation with the ventral ends of

the first hypobranchials; articulates anteriorly with the

first basibranchial, posteriorly with the third basi- branchial and posterolaterally with the second hypobranchials. Second hypobranchial expanded ventro- medially where it articulates with the posterior end of the second basibranchial and the anterior end of the third basibranchial; articulates dorsally with the second

ceratobranchial, which in turn articulates dorsally with

the laterally expanded basal portion of the second epi- branchial. The second pharyngobranchial is the first of the tooth bearing pharyngobranchials, having six or seven teeth, set in deep sockets, in a single row along its ventral edge. The teeth are laterally compressed and

taper to blunt points distally and are much smaller than

those in the jaws. They are replaced by teeth which

develop in new sockets just anterior to the sockets of the

old teeth, much in the same manner as in the replace- ment of the teeth in the jaws. Third arch.—Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Third basi- branchial articulates anteriorly with the posterior end

of the second basibranchial, anterolaterally with the second hypobranchials, posterolaterally with the third hypobranchials, and posteriorly, more distantly, with the

fourth ceratobranchials. Third hypobranchial with an

anteroventral process which articulates by fibrous tissue with the posterodorsal edge of the urohyal; at its posterodorsal end it articulates medially with the posterior end

of the second basibranchial, anterolaterally with the end of the third ceratobranchial. Third ceratobranchial

articulates dorsally with the third epibranchial, which is about equal in size to the second pharyngobranchial. Third pharyngobranchial bears six to seven teeth in a

single row along its ventral edge, similar to those on the second pharyngobranchial. The three tooth bearing pharyngobranchial elements (second to fourth) are more

or less closely held to one another by fibrous tissue. Fourth arch. —Cerato-, epi-, and pharyngobranchial elements present. In the absence of a fourth basibranchial and fourth hypobranchial, the fourth

ceratobranchial articulates ventrally with the posterior ends of the third basibranchial and hypobranchials. Fourth epibranchial a more or less rodlike element,

slightly expanded ventrally; articulates ventrally with

the fourth ceratobranchial and dorsally with the small

fourth pharyngobranchial. The fourth pharyngobranchial is the smallest of the three tooth bearing

elements, and bears four or five teeth in a single row

along its ventral edge, these teeth being smaller than

those on the second and third pharyngobranchials but of similar shape.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial wider in the middle

than anteriorly where it is generally rounded or posteriorly where it tapers to a short shaft, bearing teeth more or less placed in three rows, with those of the posterior row the largest. All of the teeth tend to be more

84
bluntly rounded than are the teeth of the upper pharyngeals. There are up to 15 teeth in the anterior series and

only slightly fewer on the average in the larger posterior row, with 5 to 8 teeth in the middle row. Ventrally the

fifth ceratobranchial articulates with the base of the

fourth ceratobranchial.

PAIRED FIN GIRDLES.

Pectoral Fin.

Posttemporal. —A straight sheift of bone without

evidence of a forked condition, broadly overlying and

strongly interdigitated to the pterotic in the lower half of

its length and to the epiotic above, and, to a much lesser extent, with the posterodorsal part of the sphenotic. The

rounded ventral head of the posttemporal articulates by

fibrous tissue with the concave dorsal end of the supracleithrum.

Supracleithrum. —Located more or less vertically

in relation to the axis of the body; articulates by fibrous

tissue dorsally with the ventral head of the posttemporal and ventrally with the cleithrum, which it broadly overlies for its entire length.

Cleithrum. —Laterally expanded along the ventral two-thirds of its length; articulates by fibrous tissue dorsolaterally with the overlying supracleithrum, while dor- somedially it overlies the dorsal one-sixth or one-fifth of the postcleithrum. Along the middle of its posterior sur- face the cleithrum articulates by fibrous tissue with the scapula and the anterodorsal region of the coracoid, which it slightly overlies and mildly interdigitates with

in larger specimens. Ventromedially the cleithrum ar- ticulates by tough fibrous tissue with its opposite member, while just behind the top of this region the anterior end of the pelvis is firmly attached to the rear edge of the

cleithra.

Postcleithrum. —The postcleithrum forms a long

posteroventrally directed, sturdy, more or less flattened

shaft from the dorsomedial region of the cleithrum along

the abdominal wall musculature to the region over the

posterior third to one-half of the posterior half of the pelvis. The postcleithrum is a single piece without evidence, even in small specimens, of being divided into an upper and lower portion. The middle region of the postcleith- rum is strengthened on the inner surface by a thick shaft.

Coracoid. —Rounded dorsally, tapering ventrally to

a narrow shaft; produced posterodorsally into a prong

below the lowermost actinost; cartilage filled along its dorsal edge and at the extreme anteroventral end; ar- ticulates anterodorsally by fibrous tissue and slight inter- digitation with the posterior edge of the cleithrum, which

slightly overlies it; articulates dorsally through cartilage with the scapula and by fibrous tissue with the base of the lowermost actinost.

Scapula. —Completely encloses the scapular foramen; concave and cartilage filled at its anterior and

ventral edges; articulates anteriorly by fibrous tissue with the cleithrum which overlies its extreme anterior

region, while ventrally it articulates through cartilage with the coracoid. Posteriorly the scapula articulates by

fibrous tissue with the following elements, in order from

dorsal to ventral; the first pectoral fin ray borne on a long knoblike projection and just behind it the small first or uppermost actinost followed by the second and third ac- tinosts which articulate along the lower third of the posterior edge of the scapula.

Actinosts. —Four elements; cartilage filled at the

dorsal end and, to a lesser extent, at the ventral end; the

three uppermost actinosts articulating with the scapula,

the lower actinost being supported by the posterodorsal edge of the coracoid; distally the actinosts support all of the pectoral fin rays except for the first. The actinosts in- crease in size from the first to the fourth.

Fin rays. —Usually 13 or 14 fin rays; the first ray

very short, only about one-tenth the length of the second

ray, the medial half much larger than the lateral half and

articulated directly with the scapula rather than with the

actinosts as are the other fin rays; the first two rays and

the last or lowermost ray unbranched, the intervening

rays branched. The small first ray without cross-striations; all other rays with cross-striations.

Pelvic Fin.

Pelvis. —A sturdy shaft, the two halves either variously fused or extensively interdigitated together so that the impression is that of a solid bone like a raiboad

rail in cross section behind the level of the pelvic spine. A

single oblique crest on the side of the pelvis at the level of the flange of the pelvic spine allowing for two and only two positions of locking the erected spine. The shaft of the pelvis tapering to a point posteriorly. Anterior to the

level of the pelvic spine, the anteroventral end of the pelvis bifurcates into a concave region for muscle attach- ment, extending up along the anterior base of the anterodorsal shaft of the pelvis. The anterodorsal shaft of the

pelvis articulates by strong fibrous tissue just above the

region of close medial articulation of the two cleithra.

Pelvic spine. —Large and strong; the medial end ar- ticulating to the pelvis in much the same manner as

previously described for the triacanthodid Parahollardia

lineata. However, in the Triacanthodidae the side of the

pelvis at the level of the flange of the pelvic spine is either smooth and thus allowing for a single position of

erection of the spine or it has numerous small grooves

allowing for numerous, continuous positions of erection

of the spine, rather than as in the Triacanthidae, ex- emplified by Pseudotriacanthus strigilifer, in which

there is a single relatively large oblique crest allowing for only two positions of erection. The rotation of the spine is
the same as described for Parahollardia lineata, the dif- ference being only that when the erected spine is return- ed to its unerected position it can have its flange, after the latter is out of contact with the ventrolateral edge of the pelvis, stopped by the oblique groove on the lateral surface of the pelvis, permitting the second or partial position of erection of the spine.

Fin rays. —No pelvic fin rays have been found in any of the cleared and stained specimens or in other specimens examined closely in the pelvic axil but not

cleared and stained. However, this is perhaps partially attributable to the relatively large size of the specimens

examined, as explained in Tyler (1968:290), for a single rudimentary fin ray is present in the young of some

species of triacanthids, the ray being resorbed in adults. VERTEBRAL COLUMN. —All vertebrae with bicon- cave centra, except the last, which ends posterodorsally

in the urostyle.

Abdominal Vertebrae.

First vertebra. —Neural spine thick, the left and

right halves meeting above the neural canal to come into

close apposition and interdigitation posteromedially; from this point of meeting the neural spine spreads

anterolaterally to form the posterior half of the walls of the bony well surrounding the ventral end of the stout

shaft of the first basal pterygiophore of the spiny dorsal

fin, the well also forming a bony roof over the neural canal in this region. The anterolateral edge of the neural arch and lower region of the neural spine articulate by

extensive interdigitation with the exoccipital and, in some cases, with the extreme posteroventral edge of the

epiotic as well, but the articulation is mainly to the exoccipital. Over the anterior third of the neural arch region

just above the centrum, the first vertebra extensively in- terdigitates with the short and irregularly shaped exoccipital condyles that overlie this region. The rim of the concave anterior end of the centrum of the first vertebra

articulates with the rim of the concave posterior end of the basioccipital. Posteriorly the first vertebra ar- ticulates with the second vertebra by apposition of the rims of their centra and by the short and bluntly rounded

neural postzygapophysis of the first vertebra slightly overlying the neural prezygapophyseal area of the second

vertebra. No haemal zygapophyses are present. Other abdominal vertebrae. —In 21 specimens the abdominal vertebrae numbered eight. All of the ab- dominal vertebrae, as well as the caudal vertebrae, have

a bony roof over the neural canal and a single undivided

neural spine. The neural spine of the second abdominal

vertebra is of about the same size as that of the first, while the neural spines of the third and subsequent

vertebrae are longer than those of the first two ab- dominal vertebrae and of approximately the same size. The last abdominal vertebra has its neural prezy- gapophysis overlying the neural postzygapophyseal area

of the preceding vertebra. No haemal pre- or post- zygapophyses are present. Each neural arch has a neural foramen along the middle of its lateral surface. The first three abdominal vertebrae have no transverse or haemal

processes, but the fourth to last abdominal vertebrae

variously have transverse processes or haemal arches and

spines which bear the intermuscular bones. These trans- verse processes become more ventrally directed until they eventually form complete haemal arches. The

processes of the fourth to sixth vertebrae are incomplete, whereas those of the seventh and eighth vertebrae form

complete haemal arches with very short spines. Eight

epipleurals or intermuscular bones are present in the myocommata between the epaxial and hypaxial musculature, five borne on the fourth to eighth abdominal

vertebrae, followed in series by three others on the first three caudal vertebrae. The epipleurals articulate basally by fibrous tissue with the lateral surfaces of the trans- verse processes of the fourth to sixth abdominal

vertebrae and of the haemal arches and spines of the seventh abdominal to third caudal vertebrae. Caudal Vertebrae. —In 21 specimens the caudal

vertebrae numbered 12. The haemal spine of the first caudal vertebra articulates by fibrous tissue with the anterior surface of the dorsal one-fifth of the first anal fin basal pterygiophore. The neural spine of the first caudal

vertebra is similar to that of the preceding vertebra, but

the other caudal vertebrae have progressively slightly

less long neural spines. The haemal spines similarly decrease slightly in size from the second caudal vertebra

to the penultimate vertebra, which has its neural and

haemal spines of slightly increased length. The neural prezygapophyses of the more Euiterior of the caudal

vertebrae overlie the neural postzygapophyseal area of the preceding vertebrae. The haemal spines of the caudal

vertebrae support the anal fin basal pterygiophores by

fibrous tissue but do not make close contact with them. The same is true of the neural spines of the abdominal and caudal vertebrae that support the basal pteryg- iophores of the soft dorsal fin. With the exception of the

last vertebra, each neural arch has a completely enclosed neural foramen along the middle of the neural arch region, and all have a bony roof over the neural and

haemal canals. All of the haemal arches and spines are fused to their centra.

Caudal Skeleton. —The parhypural and all but the uppermost hypural are indistinguishably fused to the

last vertebral centrum. There is a free epural and a uro- neural represented by a single solid piece, the two halves

of the uroneural apparently having fused together. The

low neural arch of the vertebral centrum bifurcates anteriorly but comes together in the midline over the neural

canal posteriorly. It is to this anterior bifurcate region that the ventral end of the epural articulates by fibrous

tissue. The single free hypural is rodlike and articulates along the oblique upper anterior edge of the fused hypural plate, the anterior end of the free hypural being

just behind the posterior end of the short neural arch of
the last vertebral centrum. The uroneural is located between the epural and free hypural and has a tube through its length enclosing the neural canal. The tube

also extends through the distal region of the epural to

exit near to the tip of the neural spine of the penul- timate vertebra. A large foramen just below the middle of the fused hypural plate represents the region of fusion of the parhypural with the hypurals above it, but other- wise the hypurals (except for the uppermost free ele- ment) and the parhypural are indistinguishably fused with the last vertebral centrum. As explained by Tyler

{1970b: 10) the single uroneural probably represents the second pair of uroneurals of triacanthodids, in which the

first of the two pairs usually is much smaller and more

variable in occurrence than is the second pair. A promi- nent horizontal crest is present on the fused centrumparhypural-hypural plate for muscle attachment.

Caudal fin rays. —Twelve in number; the upper- most ray and the lowermost ray unbranched, the others becoming increasingly branched toward the two middle

rays, which are branched in triple to quadruple

dichotomies. The upper unbranched ray has its bifur- cate base articulated with the distal end of the free hypural and the extreme dorsal end of the fused hypural

plate. The uppermost two or three branched rays have

their bifurcate bases overlapping the fused hypural

plate, whereas the middle four to five rays to not overlap

the plate. Similarly, the lower unbranched ray slightly overlaps the fused parhypural-hypural plate, and the branched rays above increasingly less so.

DORSAL AND ANAL FINS.

Dorsal Fin.

Spines and pterygiophores. —Six spines of greatly decreasing length posteriorly in the series and only four basal pterygiophores, without the intervention of ossified distal pterygial elements. The first two spines are borne on the first basal pterygiophore, whereas the third, fourth, and fifth spines are borne on their own indivi- dual basal pterygiophores. There is no basal pterygio- phore supporting the minute rudimentary sixth spine which is buried beneath the skin. The concave medial

region of the base of the first spine rotates over a low medial flange at the dorsal surface of the first basal pte- rygiophore. However, this medial flange more posteriorly becomes a tall, somewhat anteriorly directed prong which fits into a transverse hole through the base of the

spine. It is around this dorsal flange of the pterygiophore

that the first spine rotates. The spine can be erected and

locked in any of a continuous series of positions by the

close apposition of the base of the first spine with the dorsal articular surface of the first pterygiophore on either

side of its medial flange, both surfaces being somewhat

rough and irregular. This mechanism is basically the same as that described for the triacanthodid Parahollardia lineata, although the medial flange of the basal

pterygiophore in the case of triacanthids is much less elaborately developed than it is in triacanthodids (see Tyler 1968:fig. 7 for a comparative illustration of the

structure in the two families of triacanthoids). The sec- ond spine articulates basally with the dorsal surface of the first basal pterygiophore just behind the posterior edge of the anterodorsal flange around which the first spine rotates, at a slight concavity on the surface of the pterygiophore in this region. This slight concavity has a very small medial flange fitting into the concave base of the second spine. The third to the fifth spines articulate

at their generally rounded basal ends with simple shal- low concavities in the dorsal surfaces of their individual

pterygiophores. The sixth spine is rudimentary and has no basal pterygiophore supporting it. The first basal pterygiophore is a very stout shaft of bone with only narrow anteromedial and posteromedial

flanges for muscle attachment. Basally the stout shaft is firmly held in place by fibrous tissue within the deep bony well formed posteriorly by the neural spine of the

first abdominal vertebra and anteriorly by the exoccipitals. This is a relatively immovable articulation. The

second to fourth basal pterygiophores are much smaller than is the stout first pterygiophore and each bears its own individual dorsal spine of decreasing length in the

series. The four basal pterygiophores articulate to one

another by fibrous tissue or, in some cases, by a very

slight interdigitation of their apposed surfaces. The sec- ond to fourth pterygial elements are cartilage filled at

their extreme ventral ends, at the end of the vertical shaft along their lateral surfaces. The second and third pterygiophores also often remain cartilaginous at the ex- treme posterodorsal tip.

Fin rays and pterygiophores. —Usually 21 or 22 fin rays are present; the first 1 or 2 rays unbranched, the

others branched in single to double dichotomies. No ossified distal pterygiophores are present between the

bifurcate bases of the rays in the specimens of P.

strigilifer studied, but in some other species of

triacanthids ossified distal pterygiophores are present, at

least in large adult specimens (see Tyler 1968:268). When

ossified distal pterygiophores are present they are a

single piece in the midline rather than a pair of pieces as found in triacanthodids. Basally the fin rays are supported by a number of basal pterygiophores similar in number to that of the fin rays. The pterygiophores ex- tensively interdigitate with one another in their upper

regions just below the apposed concavities in their anterior and posterior edges which give rise to the round

holes between the distal heads of the pterygiophores that

are present at least anteriorly in the series. Lateral

flanges for muscle attachment are very well developed

along the lengths of the pterygiophores. These flanges are widest toward the distal end of the pterygiophore where

they form prominent hooklike processes. The first basal pterygiophore of the soft dorsal fin usually is located between the neural spines of the fourth and fifth ab- dominal vertebrae, while the last few basal pterygio- phores lie between the neural spines of the fifth and sixth
caudal vertebrae. The pterygial elements are cartilage

filled at their dorsal and ventral ends.

Anal Fin.

Fin rays and pterygiophores. —Usually 15 or 16 fin rays are present; the first ray and sometimes the second

ray unbranched, the others branched in single to double

dichotomies. No ossified distal pterygiophores are pres- ent between the bifurcate bases of the rays. Basally the

fin rays are supported by a number of basal pterygio- phores equal to or sometimes one less than the number of

rays. The pterygiophores articulate to one another by ex- tensive interdigitation in a manner similar to that described for the basal pterygiophores of the soft dorsal

fin and possess holes distally between the apposed

anterior and posterior edges of the pterygiophores, at

least anteriorly in the series. Well-developed lateral flanges with hooklike processes are present just as with

the basal pterygiophores of the soft dorsal fin. The first basal pterygiophore of the anal fin is by far the largest of the series, the others decreasing in length posteriorly in the series. There is a prominent crest anterodistally on

the first basal pterygiophore of the anal fin in addition to the lateral flange similar to that which is present on the other basal pterygiophores. The first basal pterygio- phore is held immovably by fibrous tissue against the

posterior edge of the haemal spine of the ninth vertebra, making the latter by definition the first caudal

vertebra. The last several basal pterygiophores of the

anal fin articulate by fibrous tissue between the neural

spines of the fifth and sixth caudal vertebrae, just as the

last few basal pterygiophores of the soft dorsal fin are held between the neural spines of the same two

vertebrae. Comparative diagnoses of subfamilies (Protacanthodinae, Cryptobalistinae, Triacanthinae). —There

are three subfamilies of triacanthids: two exclusively

fossil (one from the Eocene and one from the Oligocene) and one with both fossil (Oligocene and Miocene) and

Recent species. These three subfamilies are comparatively diagnosed as follows, modified and expanded

from Tyler (1968), especially on the basis of the reexamination of the holotype of the Eocene Protacanthodes. The Eocene Protacanthodinae have: the pelvis

shaftlike posterior to the region of the pelvic spines and

probably not bifurcate anterior to the spines and of un- known cross-sectional shape; the spiny dorsal fin base

slightly longer than the soft dorsal fin base; six ab- dominal vertebrae anterior to the first basal pterygio- phore of the soft dorsal fin; second to fourth basal pterygiophores of the spiny dorsal fin with well- developed ventral shafts oriented more or less vertically

in relation to the vertebral axis and with their proximal

ends in contact with the distal ends of the neural spines

of the second to fourth abdominal vertebrae; ventrally directed portion of the first basal pterygiophore of the spiny dorsal fin long and well developed, articulated

with the middle to basal region of the posterior surface of

the skull; most neural spines relatively oblique; skeletal appearance similar to that of the Recent triacanthids and not to that of balistids; caudal peduncle only slightly tapering toward the tail, deeper than wide at the place of

least depth; caudal fin extremely long (53% SL) and

rounded; scales with numerous upright spinules. A single

species, Protacanthodes ombonii (Zigno 1887a). The Oligocene Cryptobalistinae have: the pelvis basinlike from the region of the pelvic spines posteriorly, but bifurcate anterior to the spines; pelvis in cross section behind the pelvic spines flat, with upturned edges forming a concave dorsal surface, wider than deep; spiny dorsal fin base much shorter than the soft dorsal fin base; probably six abdominal vertebrae anterior to the first basal pterygiophore of the soft dorsal fin; second to third

(fourth, if present, unknown) basal pterygiophores of the spiny dorsal fin essentially without ventral shafts, these pterygiophores far removed from the distal ends of the

neural spines of the abdominal vertebrae; ventrally directed portion of the first basal pterygiophore of the spiny dorsal fin very short, articulated with the upper

region of the posterior surface of the skull; most neural

spines relatively vertical; skeletal appearance generally

similar to that of the balistids rather than to that of Recent triacanthids; caudal peduncle probably tapered to a

constricted region in front of the caudal fin, and probably about as wide as deep; caudal fin of moderate length (31% SL), basically truncate, with a slight medial concavity; scales apparently without elaborate ornamentation. A single species, Cryptobalistes brevis (Rath 1859). The Oligocene to Recent Triacanthinae have: the

pelvis shaftlike from the region of the pelvic spines posteriorly and not bifurcate anterior to the spines; pelvis in cross section behind the pelvic spines like a railroad rail, deeper than wide or at least about as deep as wide, the

lateral edges not upturned; spiny dorsal fin base much

shorter than the soft dorsal fin base; four or five ab- dominal vertebrae anterior to the first basal pterygio- phore of the soft dorsal fin; second to fifth basal pterygio- phores of the spiny dorsal fin with moderately developed

ventral shafts, usually directed anteroventrally toward

the region between the neural spines of the first to third abdominal vertebrae but not in direct contact with them,

usually well separated from them; ventrally directed

shaft of the first basal pterygiophore of the spiny dorsal

fin long and well developed, articulated with the middle

to basal region of the posterior surface of the skull; most

neural spines relatively oblique; skeletal appearance

similar to that of the Recent triacanthids and not to that

of balistids; caudal peduncle tapered to a narrow trans- versely indented region above and below in front of the caudal fin, wider than deep at this point; caudal fin of

short to moderate length (15 to 30% SL), deeply forked;

scales with low emarginate ridges. Seven Recent species

in four genera (Triacanthus, Trixiphichthys, Pseudotriacanthus, Tripodichthys) in the Indo-western Pacific, two

fossil species in a single Oligocene genus (Acanthopleurus), and one species from the Miocene (Marosichthys).

Figure 34.— Paeudotriacanthus strigilifer: lateral view of head; 79.0 mm SL, India.

Figure 35.—Pseudotriacanthus strigilifer: above, dorsal (left) and ventral (right) views of

skull; below, posterior view of skull;

79.0 mm SL, India, with a few details from 130 mm SL, Thailand.

in. ^^-^^\ ,,w — -4J

Figure Se.—Paeudotriacanthus strigilifer: posterior view of orbit (cross section of skull; dashed lines represent cut surfaces of frontals and parasphenoid);

130 mm SL, Thailand. 90
basibranchials

epibranchials pharyngobranchials

iterhyal hi

epihyal

hypobranchials

ceratobranchials urohyal

dorsal hypohyal

Figure 3S.—Triacanthiu biaculeatut:

lateral (left) and anterior (right) views

of first two dorsal spines (erected), with basal pterygiophore shown in lateral view in both cases, 1 13 mm SL, Borneo.

Figure 37 .—Tripodichthys angustifrona: dorsal view of branchial arches (extended on lower side); lateral view of hyoid arch and urohyal; 137 mm SL, Australia.

Figure 39.— A, Parahollardia lineata, 45.7 mm SL,

Florida, and B, Triacanthus biaculeatus, SL, Borneo: lateral views of pelvis and pelvic fin in place (above) and of

pelvis with pelvic fin removed (middle); anterior views of the base of the pelvic spine (below), show the structural differences in the locking mechanism of the Triacanthodidae (indefinite number of positions of erection) and

Triacanthidae (two positions of erection).
Anatomical diversity.—The anatomical diversity of

this family has been treated in detail by Tyler (1968) and

the major features need be only briefly summarized here. The Recent species form a very slightly diversified group of four rather finely split genera that in the near

past were all accommodated in one genus. The heavy in- cisorlike teeth of Triacanthus, Pseudotriacanthus, and

Tripodichthys occur in an outer series of 10 in both jaws,

the upper jaw with an inner series of four molariform

teeth and the lower jaw with two. In Trixiphichthys, however, the teeth are smaller and the number of inner

series teeth in the upper jaw is reduced to two, while the snout is longer and the mouth is narrower than in the

other three genera. A mesopterygoid is absent except in Trixiphichthys, in which it is small. The caudal peduncle

is much shorter and the lateral line slightly less con-
Figure i\ .—Trixiphichthya weberi: latei head, 101 mm SL. Bay of Bengal

spicuous in Trixiphichthys than in the other three

genera. The second dorsal fin spine is best developed in Pseudotriacanthus (greater than half the length of the

first spine), next best developed in Trixiphichthys (about half the length of the first spine) and relatively short in the other two genera (about one-third or less the

length of the first spine). The scales in Pseudotria- canthus have an anterior to posterior series of high thin

distally emarginate vertical ridges, while in the other

three genera the scales have a low, distally emarginate

cruciform ridge. The shaft of the pelvis posterior to the

pelvic spines tapers to a sharp point posteriorly in Pseudotriacanthus and Tripodichthys, but does not

taper to a sharp point in Triacanthus and Trixi- phichthys. The length of the anal fin base is shorter

(usually about 2 times in the soft dorsal fin base) in Pseudotriacanthus than in the other three genera (usually about 1.4 to 1.7 times in the soft dorsal fin base). The

lateral edge of the sagitta is relatively straight or somewhat convex in Triacanthus, but has a distinct in- dentation or cavity in the other three genera. The base of the pseudobranch has a forward pointed apex about onethird down its length in Trixiphichthys but is an even

curve without an apex in the other three genera, which

usually have a shorter base to the pseudobranch and

fewer lamellae. There are fewer dorsal, anal, and pectoral

fin rays in Pseudotriacanthus than in the other three

genera. The sixth, and last, dorsal fin spine is more often completely lost in Triacanthus biaculeatus than in the

other six species. Externally visible rudiments of the

pelvic fin ray buried in the skin are retained longer in Tripodichthys oxycephalus than in the other six species. The fossil triacanthids include at least one genus

highly similar to the Recent species, another genus

highly dissimilar to the Recent species, and one genus

obviously intermediate in many respects between the

triacanthodids and triacanthids. These were treated by

Tyler ( 1968) mainly on the basis of the literature, but some of the specimens have subsequently been re- examined, and notes are given here on their anatomy. The Eocene Protacanthodes ombonii, the only repre- sentative of the Protacanthodinae, is known from a single specimen which has recently been reexamined. The

holotypic specimen, in counterpart, IGUP 10.901 (head

to left) - 902, from the upper portion of the lower Eocene

of Monte Bolca, Italy, is 112 mm SL, an excellent impression with well-preserved scales that obscure many

osteological features. Proportional measurements (percent of standard

length in parentheses) for P. ombonii are: greatest depth 45.7 mm (40.7% SL); snout to base of first dorsal spine 44.2 mm (39.3% SL); eye 11.4 mm (10.1% SL);

spiny dorsal fin base 25.8 mm (23.0% SL); soft dorsal fin base 23.5 mm (20.9% SL); anal fin base 12.4 mm (11.0%

SL); daudal peduncle length 26.2 mm (23.3% SL); least caudal peduncle depth 16.4 mm (14.6% SL); caudal fin length 50.6 mm (45.0% SL); length of pelvis posterior to the base of the pelvic spine 17.9 mm (15.9% SL); length

of pelvic spine 27.9 mm (24.8% SL); soft dorsal fin height

10.5 mm (9.3% SL); anal fin height 10.0 mm (8.9% SL); and the approximate lengths of the dorsal fin spines are

as follows: first 36.5 mm (2.5% SL), second 10.5 mm

(9.3% SL), third 6.0 mm (5.3% SL), fourth 5.0 mm (4.4%

SL), fifth 1.9 mm (1.7% SL), sixth 1.4 mm (1.2% SL). The six dorsal spines, which decrease greatly in length

posteriorly in the series, are followed by 19 fin rays, the

distal ends of those that show being branched. The dis- tance between the last spine and the first ray (5.1 mm,
(.

Figure 42.—Protocont/iodes ombonii: of the heads of the two counterparts; of the two counterparts, to show the above, lateral views of the two below, lateral views of the dorsal six dorsal spines; holot.vpe, 112 mm

counterparts; middle, lateral views parts of the head and anterior body SL, Eocene of Monte Boica, Italy.
4.5% SL) is slightly greater than that between the last few spines (4.1 mm, 3.6% SL). The anal fin has 14 rays, the distal ends of those that show being branched. The

elongate rounded caudal fin has 12 rays, the uppermost

ray and the lowermost ray unbranched and the inter- vening 10 rays branched. The pectoral fin rays cannot be

counted, nor are any pelvic fin rays evident, although a small ray or two could well be present but obscured by

the pelvic spine. The branchiostegal rays are 2 + 4 = 6, and the first two rays are not much wider than the others. There are clearly 12 caudal vertebrae and probably 8 ab- dominal vertebrae. The supracleithrum is placed vertically in relation to the axis of the skull. The

parasphenoid is relatively straight in the region of the orbit, and the ventral flange seems to have been only moderately developed, probably only slightly deeper than the depth of the shaftlike portion of the bone above

it. The prefrontal is very large and sturdy, and has at

least a moderate anteroventral extension alongside the

lower region of the ethmoid, although it is not clear whether this extension took the form of a long process which also sutured anteriorly with the posterolateral wing of the vomer, as in Recent triacanthids. The upper

half of the prefrontal apparently was well separated from

the upper half of the ethmoid by a block of cartilage

larger than in the Recent species. The ethmoid appears

to have been large and sturdy, with a steeply oblique

anterior face that then tapered posterodorsally to suture with the frontal and prefrontal, much as illustrated by

Tyler (1968:361, fig. 206) for Triacanthus biaculeatus, but with the frontal extending a little further forward. The upper jaw apparently is unnaturally displaced

posteriorly, for the tip of the upper jaw is well behind

that of the lower jaw, a functionally unlikely arrange- ment in this family. As presently placed, the posterior end of the premaxillary pedicel abuts against the top of the oblique anterior face of the ethmoid just anterior to the anterior end of the frontal. In life, however, the

pedicel undoubtedly never was retracted this far posterodorsally and probably slid along the anterior basal region

of the ethmoid when the mouth was protracted, as in the Recent species. The moderate-sized eye is located just above the middle of the distance between the snout and

the spiny dorsal origin. The pelvis posterior to the pelvic spines appears to be a stout shaft of bone. The anterior and lateral surfaces of the first dorsal spine and the

anterior, dorsal, and ventral surfaces of the pelvic spine

are covered with low spiny processes, probably asperities on the scales covering these spines. The caudal fin supporting structures are not well preserved, but grooves indicate that there was probably a good separation between what in generalized tria- canthoids are the second and third hypurals. The condition of the parhypural, epurals, and uroneural elements,

if present and separate, is unclear. The first basal pterygiophore of the spiny dorsal fin (supporting the first two spines) has a strong ventral shaft directed ventrally

to between the middle to basal region of the skull and

what is probably the neural spine of the first vertebra

closely applied to the skull. The second basal pterygioHI

-\.)r

Figure 43.—Protocant/iodes ombonii: lateral view of abdominal region (head to left) to show the pelvis and pelvic spine (one from

each side), holotype, 112 mm SL, Eocene of Monte Bolea. Italy.

phore (supporting the third spine) has its shaft angled

slightly anteroventrally and in contact with the distal end of the neural spine of the second vertebra. The third and fourth basal pterygiophores have their shafts directed ventrally, about vertical to the vertebral column, and in contact, respectively, with the distal ends

of the neural spines of the third and fourth vertebrae. If a fifth basal pterygiophore supporting the slender, minute sixth spine was present, it apparently was very

small, for it does not show in either plate. The first basal pterygiophore of the soft dorsal fin is placed between the

neural spines of the sixth and seventh abdominal

vertebrae, and there appears to have been an approxi- mately one to one ratio between the number of dorsal and

anal fin rays and their basal pterygiophore supports. The teeth are relatively large incisors, about five in each half of each jaw judging from the size of the somewhat scattered elements. It is not possible to tell whether an inner series of teeth was present in addition

to the major outer series. The largest teeth, antero- medially in each jaw, have stout bases toward the sockets but taper into blunt nipplelike caps distally, while the

teeth more laterally in each jaw have lesser cusps and, in some cases, almost rounded distal edges. Protacanthodes differs from the other triacanthids mainly by having: 1) a deep and only slightly tapered

caudal peduncle; 2) an extremely elongate rounded

caudal fin; 3) the spiny dorsal fin base slightly longer than the soft dorsal fin base; 4) better developed spiny

dorsal fin basal pterygiophores whose ventral shafts are

slightly differently arranged; 5) the upper shaftlike portion of the parasphenoid in the region of the orbit rela- tively straight and its ventral flange only slightly deeper than the depth of the shaftlike portion; 6) the lower two

branchiostegal rays not enlarged; 7) possibly less fusion

of the hypurals; 8) one more abdominal vertebra anterior

to the first basal pterygiophore of the soft dorsal fin; 9) and in having scales with a row of upright spinules. All

of these features of difference between Protacanthodes and Recent triacanthids relate Protacanthodes to the
Figure ii.~Acanthopleurus serratus:

lateral view of entire specimen, syntype,

ca. 95 mm SL, Oligocene of Canton Glarus, Switzerland (Agassiz 1842:pl. 75).

triacanthodids and establish it as an intermediate between the two famiHes, as discussed more fully in the preceding section on the relationships of the Triacanthodidae. The fossil species of Triacanthinae are represented mainly by several dozen specimens of the Oligocene Acanthopleurus. These specimens are little more than

impressions, although in some cases rather complete, left in the black schist of Canton Glarus, Switzerland, and 18

of them have recently been reexamined for this work. The general appearance of all the specimens is decidedly

like that of Recent triacanthids. The specimens of Acanthopleurus examined fall naturally into two

groups: 1) moderately elongate, like most of the Recent

species; and 2) decidedly elongate, much more so than any of the Recent species. The moderately elongate specimens differ from all the Recent species by having a

slightly deeper (5-8% SL vs. 2-4% SL) caudal peduncle,

i.e., less constricted just in front of the caudal fin base. Only one specific name is available in Acanthopleurus,

this being serratus Agassiz (1842 illustration, 1844b

description), based on decidedly elongate specimens. The deeper bodied Acanthopleurus is described here as

collettei in honor of Bruce B. CoUette, National Marine

Fisheries Service, National Systematics Laboratory, who

is a valued colleague, diving companion, editor of this monograph, and a responsible agent for having it published. It is diagnosed on the basis of the depth of its body and caudal peduncle, as specified above and in the measurements given below and in Figure 46. The seven

type specimens of collettei are designated in the list of

fossil specimens examined for this work.

Proportional measurements as percent of standard

length for A. collettei are as follows, with the number of specimens on which data were recorded for the character preceding in parenthesis the range, which is followed by

the average value in parenthesis when appropriate: greatest depth (7) 24.0-31.4 (27.7)% SL;

least caudal peduncle depth (6) 5.5-8.3 (6.7)% SL; length

of pelvic spine (6) 20.0-30.8 (25.5)% SL; length of first dorsal spine (6) 20.3-35.2 (27.1)% SL; length of second

dorsal spine (6) 6.1-10.3 (8.2)% SL; length of third dorsal spine (5) 2.6-3.9 (3.7)% SL; length of fourth dorsal spine

Figure iH.—Acanthopleurus serratus (above), lateral views of entire specimens, left, 153 mm SL, and,

right, 127 mm SL. to contrast with the deeper bodied

A. collettei (below), left, ca. 120 mm SL, paratype, an(

right, 96.2 mm SL, paratype: all specimens from

the Oligocene of Canton Glarus, Switzerland.
150
counted in any of them, although they presumedly numbered eight as in the Eocene Protacanthodes, the Oligo- cene Cryptobalistes, and the Recent species of the family. On the basis of the configuration o( Acanthopleurus,

the Triacanthinae have changed very little from at least the Oligocene. The other fossil species of Triacanthinae is the very

poorly known Marosichthys huismani (de Beaufort

1926), based on a single very incomplete specimen from

the Miocene of the Celebes comprising the head and upper anterior part of the body. The dorsal fin spines are

better developed than in Acanthopleurus, and the body

deeper, but Marosichthys can be considered to be at the same level of organization as Acanthopleurus, as discuss- ed by Tyler (1968:241-242). The Oligocene Cryptobalistes brevis (Rath 1859), the only representative of the Cryptobalistinae, is known

from a single specimen (perhaps two, see Winterbottom

1974:96) from the same black schist of Canton Glarus, Switzerland, in which the apparently thoroughly modem

Acanthopleurus is found. The specimen of Cryptobalistes was not reexamined for this work, for the holotype cannot be located, and the following very briefly summarizes the long phylogenetic discussion of the species presented by Tyler (1968:243-249). Cryptobalistes is an enigma. In general appearance it

is rather balistoid, although it has (probably) 20 rather than 18 vertebrae, 12 of which are caudal, at least four

dorsal spines and no locking mechanism of the first by

the second, no supraneural strut bracing the last spiny dorsal fin basal pterygiophore, a large pair of pelvic spines, and a relatively wide, dorsally concave, basinlike pelvis.

Although Cryptobalistes is in most ways an excellent anatomical intermediate between the triacanthids and

balistids, the shape of its pelvis negates the other

evidence, and the balistoid appearance of Cryptobalistes

is presumed to be due to parallelism. Cryptobalistes

represents an extinct lineage, for in the same Oligocene

strata in which it is found there are also thoroughly modem balistids (Balistomorphus) not much different from genera alive today, and these Oligocene balistids already posses a stout shaftlike pelvis with a dorsal

lobe, three dorsal fin spines with a locking mechanism,

a carina with a supraneural supporting strut, and no

pelvic spines. While Cryptobalistes represents an

evolutionary dead end, it greatly increases the known

anatomical diversity of the Triacanthidae and proves

that the triacanthids were capable to giving rise to

balistidlike forms. Generic relationships. —As discussed by Tyler

(1968:250), the four Recent genera fall naturally into two

groups on the basis of the structure of the posterior shaft

of the pelvis, Triacanthus and Trixiphichthys having a

relatively untapered pelvis and Pseudotriacanthus and

Tripodichthys a distinctly tapering pelvis ending in a

point. On the meager evidence of the better development

of the second dorsal spine and shorter anal fin base in Pseudotriacanthus, conditions closer to those of the

ancestral triacanthodids, Pseudotriacanthus can be considered slightly more generalized than Tripodichthys. On

the basis mainly of the specialized reduced dentition and

of the elongate and narrow snout, Trixiphichthys is less generalized than Triacanthus. The relationship between

the two more generalized genera in the two basic subdivisions of the Recent species is not clear, but both are cer- tainly closely related to the Oligocene Acanthopleurus,

with the Miocene Marosichthys of unknown relationship

to Acanthopleurus. The Oligocene Cryptobalistes is of uncertain relationship with the other triacanthids, while

the Eocene Protacanthodes is clearly on the line directly intermediate between the ancestral triacanthodids and

the derived triacanthids, as discussed in the preceding

section on the relationships of the Triacanthodidae. The relationship of the Triacanthidae to the Balistidae

is discussed under the latter, with the conclusion being

that Protacanthodes is not far removed from the line of

early triacanthids that gave rise to the balistids and

aracanids, and thus, respectively, to the monacanthids and ostraciids as well. In spite of its name, Protriacanthus gortanii d'Erasmo

(1946:116), from the upper Cretaceous, is not a plec- tognath (see Patterson 1964:429-432).

Figure il .—Marosichthys huismani: lateral view of anterior part of bod.v of holot.vpe, ca. 36 mm head length, Miocene of the Celebes

(de Beaufort 1926; fig. 5 of pi. 5).
Figure iS.—Cryptobalisles brevis: lateral view of holotype, with insets from left to right showing the spiny dorsal fin, the

pelvis in dorsal view, scale plates, and

the pelvic spine, ca. 88 mm SL,

Oligocene of Canton Glarus, Switzerland (Rath I859:fig. 4 of pi. 5).

Infraorder Balistoideo Comparative diagnosis (contrast with that of the Triacanthoideo).— Premaxillary without a pedicel or ascending process, the blunt posterodorsal end of the premaxillary rotating around the anterior ends of the ethmoid and vomer; premtixillary immovably articu- lated with the maxillary, often by suture, and the upper jaw not even slightly protractile; maxillary only slightly

if at all indented dorsally for articulation with the

anterior end of the palatine; palatine varying from Tshaped (as seen laterally) to a simple rod and not sutured

to other bones, or as a bony column sutured to the palatopterygoid arch; ethmoid with a laterally expanded

dorsal or dorsolateral region, at least anteriorly, and

never narrower dorsally than ventrally, forming a strong

buttress for the rotation of the upper jaw; a prootic shelf

of varying size developed under the orbit in front of and

above the major articulation of the posterior region of the parasphenoid with the prootics, except secondarily lost in two closely related genera of highly specialized monacanthids; dorsal end of the hyomandibular articulated only with the prootic and pterotic, not in direct contact with the sphenotic; interoperculum a short rod extending

posteriorly no further than the level of the epihyal and

interhyal, connecting to the suboperculum or operculum

around the anterior edge of the region of overlap of these two bones only by way of a long unossified ligament; dorsal fin spines three, two, one, or absent altogether, if pres- ent supported by one or two basal pterygiophores; the

first dorsal spine capable of being locked in an erected

position through the agency of the second spine, if present, but without an independent locking mechanism

between the base of the first spine and its basal pterygio- phore; first basal pterygiophore of spiny dorsal fin without a high dorsomedial flange and no anteroposterior canal present in the basal region of the first dorsal

spine; pelvic fin present or absent, when present never as

a prominent erectile and lockable spine at about the middle of the pelvis, but as a rudiment at the extreme

posterior end of the pelvis consisting of delicate, poorly

ossified, partially fused together flexible filaments or bony nubbins mostly, or entirely, hidden from external view by modified scales; pelvis present or absent, when

present laterally compressed and shaftlike throughout its length, and with or without a dorsal lobe posteriorly; pelvis usually slightly to greatly rotatable around its anterior articulation with the cleithra and a slightly to greatly expansible dewlap of skin usually present between the posterior end of the pelvis and the anus;

uroneurals rarely present; vertebrae (6-10) -I- (8-23) = 18-

30, but rarely, if ever, 8 + 12 or 9 -t- 11; no more than two

pharyngobranchials with prominent large protruding

teeth; posteromedial edges of epiotics not inturned and

neither they nor the exoccipitals and neural spine of the

first vertebra associated with the articulation of the first basal pterygiophore of the spiny dorsal fin, when present;

articulation of the mesopterygoid varying from direct contact with both the quadrate and ectopterygoid to in- direct contact with both of them through the agency of, respectively, the symplectic and mesopterygoid.

SUPERFAMILY BALISTOIDEA

Comparative diagnosis (contrast with that of the

Ostracioidea).—Head and entire body (except in the

relatively naked monacanthid Paratuteres prionurus and

in the snout region of several balistids) covered with a more or less continuous field of scales whose edges are

either slightly separated from one another (the balistid Canthidermis and several monacanthids) or slightly overlapping, but never with apposed interdigitated

edges, the basal plates thick and usually rhomboidal in balistids but thin and variously rounded to rectilinear in monacanthids; body outline in cross section a simple

gently rounded and laterally compressed oblong; a spiny

dorsal fin of one to three spines; soft dorsal and anal fins
long-based, with 23 to 52 dorsal rays and 20 to 66 anal

rays, and usually a slightly lesser number of basal

pterygiophores; caudal fin with 12 rays; pelvis always

present but a modified rudimentary pelvic fin either pres- ent (balistids and some monacanthids) or absent at the

posterior end of the pelvis; teeth relatively large and

compressed, more or less notched and incisorlike, six to eight in an outer series and four to six in an inner series in the upper jaw and four to eight in a single series in the lower jaw; lateral line associated with grooves or spiny

processes of the scale plates (with the possible exception

of the monacanthid Pseudaluteres nasicornis); branchiostegals usually 2-1-4, but sometimes 1 -I- 4 or 1 -I- 3, with none of the rays in the posterior division as broad and

laterally compressed as those in the anterior division;

distal end of last branchiostegal ray usually not closely held to inner surface of suboperculum; elements of the hyoid arch less compacted together anteroposteriorly and

most elements more elongate or less deep bodied; urohyal relatively large and more or less L-shaped, with a

ventral flange of varying degrees of development; fifth ceratobranchial either toothed or toothless; pharyngobranchials consisting of two elements bearing large protruding teeth, with an anterior toothless suspensory element present or absent; epibranchials usually four, but three in the monacanthid Psilocephalus; gill rakers present or absent along anterior edge of fifth cerato- branchial (posterior edge of last gill slit); caudal fin supporting structures only moderately consolidated, always

having at least the epural and parhypural autogenous and usually having an autogenous uppermost hypural as

well; haemal spine of penultimate vertebra autogenous;

neural and haemal arches of the last vertebra in- complete, the neural and haemal canals at least partially open respectively above and below; uroneurals rarely present; vertebrae normally 7 -I- 11 = 18 (balistids) or (6- 8) -I- (12-23) = 19-30 (monacanthids), but never nine or more abdominal vertebrae; the first vertebra of normal

size and firmly sutured but not fused to the rear of the

skull; five (balistids) or four to eight (monacanthids) ab- dominal vertebrae with neural spines anterior to the first basal pterygiophore of the soft dorsal fin; four to six caudal vertebrae posterior to the last basal pterygio- phores of both the soft dorsal and anal fins; at least three and usually four soft dorsal fin basal pterygiophores plac- ed between at least some of the successive neural spines; most neural spines positioned only slightly obliquely in relation to the axis of the vertebral column; haemal

spines above the anal fin basal pterygiophores with rela- tively long stout shafts similar to those of the neural

spines and penetrating into the proximal region of the

series of anal fin basal pterygiophores; soft dorsal fin basal pterygiophores 22 to 51; anal fin basal pterygio- phores 20 to 64; prominent thin lateral flanges present along at least a part of the length of the soft dorsal and

anal fin basal pterygiophores; distal pterygiophores pres- ent as ossified single or paired pieces in both the soft dorsal and anal fins, except often absent or unossified under the more posterior rays in both fins; all anal fin basal pterygiophores in the midline of the body; one or

two basal pterygiophores supporting the anteriorly placed spiny dorsal fin of one to three spines, but no supraneural element present anteriorly from the dorsal end of the first basal pterygiophore of the solt dorsal fin; epipleurals always present on some of the abdominal vertebrae and

sometimes on some of the more anterior caudal

vertebrae, while ribs are rarely present; uppermost pectoral fin ray never of two relatively well -developed halves

of about equal length, either a single piece without a foramen or a larger medial half and a much smaller

lateral nubbin; actinosts flexibly articulated with the scapula and coracoid, not sutured to them or to one

another; coracoid and cleithrum not especially enlarged; coracoid not expanded ventrally, much less wide there than dorsally, without prominent flanges; coracoid always with a well-developed posterior prong just below

the lowermost actinost; scapular foramen usually complete, incomplete only in a few monacanthids; cleithrum without an anterior flange from its lower anteromedial

edge; postcleithrum usually as a single piece, rarely with two halves, in the form of a long sturdy rod directed

strongly obliquely toward the end of the pelvis; at least the proximal end of the supracleithrum not in contact with the cleithrum, and usually slightly less firmly held

to the cleithrum and posttemporal; Baudelot's ligament

not ossified; posttemporal usually relatively small; palatine varying from T-shaped to a simple rod of bone

representing the top of the T and not sutured to any of the bones with which it articulates, the foot of the T con- nected by ligament to the anterodorsal edge of the ecto- pterygoid and the top of the T primarily connected to the maxillary and ethmoid; vomer not especially enlarged, having a moderately laterally expanded anterior end and

a long posterior tapering shaft fitting into a deep concavity in the parasphenoid; ventral edge of the ventral flange

of the parasphenoid not at all laterally expanded; ventral

flange of parasphenoid with a deep indentation at about

the level of the prefrontal; parasphenoid without a dorsal

flange in the medial septum of the orbit, the para- sphenoid and pterosphenoids not being in contact there and there being no anteroventral extensions of the ptero- sphenoids into the medial septum; the medial edges of the pterosphenoids in contact in the posterior wall of the

orbit, usually in light contact dorsally and broader

sutural contact ventrally; myodome large; apposed sur- faces of parasphenoid and basioccipital excavated to form a canal leading anteriorly into the myodome cavity;

epiotics broadly in contact and sutured to one another

medially on the posterior surface of the skull, not

separated there by the more anteriorly placed supraoccipital; supraoccipital never with a posterior crest, but

with or without an anterior crest on the surface of the main body of the bone; prootic shelf usually relatively smaller, never with a prominent ventral or ventrolateral flange from its lateral edge; the major foramen in the

prootic shelf relatively small and rounded, and completely enclosed by the prootic alone; anterior edge of upper

part of preoperculum articulated only along the rear edge

of the hyomandibular; hyomandibular a more or less flattened shaft, not greatly expanded.
Family Balistidae Comparative diagnosis (contrast with that of the Monacanthidae).—Teeth very sturdy, more or less in- cisorlike, developed more for crushing than nibbling, four outer and three inner on each premaxillary and four in a

single series on each dentary; pharyngobranchials consisting of a toothless suspensory element and two uniserially toothed elements; fifth ceratobranchial toothed but without gill rakers along its anterior edge (posterior edge of last gill slit); three dorsal spines, the second more

than one-half the length of the first and ending ventrally

in large sturdy ventrally directed processes from either

side; dorsal fin spines supported by two basal pterygio- phores and a supraneural strut; dorsal spines and their basal pterygiophores placed behind the posterodorsal apex of the skull, the anterior edge of the first basal pterygiophore abutting against the rear of the posterodorsal surface of the skull; first basal pterygiophore with

a large lateral foramen to accommodate the ventral prong

of the second dorsal spine; supraoccipital large and stur- dy, with a variously high (usually) to low (Rhinecanthus)

but sturdy vertical crest medially throughout its length, the crest expanded laterally at its posterior end to help support the anterior end of the first basal pterygiophore;

posterior region of the epiotic expanded dorsally, the medial edges of the two epiotics well-separated dorsally, bounding the posterolateral region of the deep foramen

in the skull between the epiotics and the supraoccipital

in which the short anteroventral shaft of the first basal pterygiophore is held; palatine T-shaped, the long foot of the T directed ventrally or posteroventrally to connect by

a short ligament with the anterior edge of the ec- topterygoid; exoccipital meeting its opposite member in the midline above the foramen magnum between the medial edges of the bifid neural spine of the first vertebra; prefrontal relatively large and heavy, firmly ar- ticulated, often by interdigitation, with the frontal, ethmoid, and parasphenoid; parasphenoid only slightly expanded laterally just behind the orbit, the medial edge

of the pterotic on the ventral surface of the skull only narrowly separated from its opposite member there by

the basioccipital and parasphenoid; parasphenoid much

expanded dorsally in front of the orbit, broadly overlying

the ethmoid and contacting the prefrontal; the laterally expanded dorsal region of the ethmoid wide and thick.

Figure 49.—Range of diversity in body

form in the Recent Balistidae: Balistapus

undulatus, left; Odonus niger, right.

about as wide as or wider than the depth of the ventral

platelike portion; ventral platelike flange of the ethmoid

thick and sturdy, relatively shallow, not much if at all deeper posteriorly than anteriorly, and broadly overlain by the parasphenoid; posttemporal held in a deep groove on the lateral surface of the pterotic; medial edge of dentary either denticulate or smooth; prootic shelf well developed, extending forward at least to the level of the middle of the orbit; posterior edge of supracleithrum

with a posteriorly directed process or hump; post- cleithrum with a dorsal spur from its upper dorsal edge supporting the ventral region of the tympanum

regardless of whether enlarged scales are present there or not; postcleithrum either a single piece or divided into dorsal and ventral segments; branchiostegal rays always

2-1-4; pelvis always with a dorsal lobe posteriorly on its dorsal surface; encasing scales at the posterior end of the

pelvis in four segments, always flexible (least and only

slightly so in Canthidermis); a relatively well-developed rudimentary pelvic fin element always present, running

the length of the last two segments and protruding to the

exterior through a foramen in the fourth segment (except

in Melichthys and Xanthichthys, in which the element is reduced in size and does not protrude, and in Canthidermis, in which the ray is an even smaller nubbin of bone not protruding to the exterior); vertebrae 18 (7 +

11); vertebrae anterior to the first basal pterygiophore of the soft dorsal fin always five, those posterior to the last basal pterygiophores of both the soft dorsal and anal fins always four; neural and haemal arches of the last cen- trum relatively well developed although incomplete; the

last centrum with a vertical crest for muscle attach- ment; uroneurals rarely present; an upper free hypural always present; lateral flanges on the soft dorsal and anal

fin basal pterygiophores not ending distally in prominent

hooklike lateral expansions; the basal pterygiophores extending proximally relatively closely to the neural and

haemal arches throughout the length of the series; the

great majority of the dorsal, anal, and pectoral fin rays branched, only the first few rays, and sometimes the last, being unbranched; scales large, with thick basal plates and relative coarse spinulation, the basal plates broadly

overlapping (except in Canthidermis) and more or less regularly arranged; scales above the pectoral fin base

usually enlarged and more or less separated, forming a

flexible covering to the tympanum (scales unmodified in Canthidermis and only slightly modified but unenlarged

in Xanthichthys); species relatively large, adults usually reaching well over 200 mm.
Figure 50.—Balistapug undulatusi upper

left, scale plates of the tympanum region

just behind the gill slit and above the pectoral fin base; upper middle, scales from

upper middle region of body, including

lateral line canal bearing scales; upper right, ventral view of encasing scales

at end of pelvis (anterior to left), with arrow indicating major region of flexibility (two terminal branches of modified fin-r>y element protrude posteriorly); lower left, nasal region as seen externally (above) and the olfactory lamellae as seen with

the top of the nasal sac removed.

Detailed description of Balistapus undulatua. Material examined.—Two cleared and stained

specimens, 122-124 mm, and three wet partially disar- ticulated skeletons of approximately the same size as the two previous specimens, prepared by maceration.

Occipital Region.

Basioccipital. —A short column, expanded anterodorsally; cartilage filled at its anterior and dorsal edges;

articulates by interdigitation dorsally with the exoccipitals, anterolaterally with the prootics, and antero- medially with the overlying posterior end of the para- sphenoid. The rim of the round concave posterior end of the basioccipital articulates by fibrous tissue with the concave anterior face of the centrum of the first vertebra. The ventromedial surface of the basioccipital is deeply concave throughout its length. This concave channel is mostly hidden from view by the overlying parasphenoid, but the channel opens to the exterior posteriorly at the base of the posterior bifurcation of the parasphenoid.

Anteriorly the channel opens into the myodome where

the anterior end of the basioccipital forms the posterolateral and posterodorsal walls of the myodome.

Exoccipital.—Cartilage filled at its ventral edge;

articulates by interdigitation dorsally with the epiotic,

laterally with the pterotic and ventromedially with the

basioccipital. Posteriorly the exoccipitals form the

lateral and ventral walls of the foramen magnum, while

dorsally the foramen is closed by the thin piece of cartilage between the dorsomedial edges of the two exoccipitals. The posterior surface of the exoccipitals firmly

articulates by fibrous tissue and slight interdigitation with the anterior surface of the bifid neural spine of the

first vertebra. The posteromedial portion of the exoccipital, which forms the lateral wall of the myodome and

the firmest place of attachment of the neural spine of the

first vertebra, is stout and thickened, probably repre- senting the much modified region of the exoccipital condyle.

Supraoccipital. —Wide posteriorly, tapering to a

point anteriorly; expanded dorsomedially throughout its length into a low crest; cartilage filled at its edges of ar- ticulation with the other cranial bones; articulates by in- terdigitation anterolaterally with the slightly overlying

frontals and posterolaterally with the epiotics. The

posterodorsal end of the supraoccipital is expanded into a thickened articular face with a medial concavity to support the anteroventral shaft of the first basal pterygiophore of the spiny dorsal fin. This medial concavity is partially bordered by the epiotics. The anteroventral shaft of the pterygial element is held by tough

fibrous tissue to both the supraoccipital and the epiotics.

Otic Region.

Pterotic. —Cartilage filled along all of its edges of articulation with the other cranial bones; articulates by

interdigitation dorsomedially with the epiotic, anterolaterally with the sphenotic, anteroventrally with the

prootic, and anteromedially on its ventral surface with

the basioccipital. More or less transversely along its ventral surface, the pterotic is produced into a sturdy flange whose depth is greatly increased in about the middle of

its length. The anterior surface of this stout and elongate

portion of the ventral flange of the pterotic articulates by

fibrous tissue with the posterodorsal edge of the hyomandibular. Just anterior to its ventral flange, the pterotic bears a slight depression which continues anteriorly over

the prootic and into which the dorsal head of the hyo- mandibular is held by fibrous tissue. In about the middle

of its lateral surface, the pterotic bears a deep vertical groove into which the posttemporal fits and is held im- movably by extensive interdigitation.
Sphenotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates by

interdigitation anterodorsally with the frontal and

pterosphenoid, posterodorsally with the epiotic, posteroventrally with the pterotic and posttemporal, and antero- ventrally with the prootic.

Epiotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates by

interdigitation dorsally with the supraoccipital, dorsolaterally with the frontal, laterally with the sphenotic,

ventrolaterally with the pterotic and a short section of the posttemporal, posteroventrally with the exoccipital, and medially with its opposite member. The posterodorsal edge of the epiotic is deeply concave where it inter- digitates with the supraoccipital, forming, with the latter bone, the concavity in the skull in which is held by

fibrous tissue the anteroventral shaft of the first basal pterygiophore of the spiny dorsal fin.

Prootic. —Cartilage filled along all of its edges of

articulation with the other cranial bones, except antero- medially; articulates by interdigitation medially with

the lateral surface of the parasphenoid, anteromedially

with the ascending fork of the parasphenoid, anterodorsally with the pterosphenoid, anterolaterally with the

sphenotic, and posteriorly with the pterotic. A concavity

is present in the middle of the ventral surface of the

prootic in which is held by fibrous tissue the anterior

half of the dorsal head of the hyomandibular. The medial

edges of the prootics form the lateral walls of the myodome, while medially directed shelves from the medial edges of the prootics interdigitate with one

another in the midline to form the dorsal roof of the myodome. The anterior edge of the myodome is formed by the prootics, except ventrally where it is formed by

the parasphenoid. The anterior end of the prootic is prolonged anteriorly as a subocular shelf which serves for muscle attachment.

Orbital Region.

Frontal. —Widest posteriorly, tapering to a point

anteriorly; its lateral edge above the orbit slightly uprais- ed and thickened; articulates by interdigitation postero- medially with the supraoccipital, which it slightly

overlies, posterolaterally with the sphenotic and posteriorly with the epiotic. Posteriorly in the rear of the orbit it interdigitates with the pterosphenoid. The frontal

interdigitates anteriorly with the ethmoid and anterolaterally with the prefrontal. On its ventral surface, the medial edges of the frontals are narrowly separated by

the cartilaginous mass which is continuous anteriorly with the remains of the ethmoid cartilage.

Prefrontal. —Large and elongate; cartilage filled along its medial edge; articulates by interdigitation dor- somedially with the frontal, ventrally with the para- sphenoid, and anteriorly with the ethmoid. Along most

of its medial edge, the prefrontal is continuous with the remains of the ethmoid cartilage. Parasphenoid. —Elongate, running almost the

entire length of the skull; ventrally expanded into a thin

keel along the anterior half of its length. The bifurcate

posterior end of the parasphenoid broadly overlies and

interdigitates with the basioccipital, roofing over the

longitudinal concavity in the ventral surface of the

basioccipital. Under the posterior region of the orbit, the parasphenoid possesses a pair of short, slightly forked,

dorsolateral projections which interdigitate with the

prootics and form the anterior edge of the ventral region

of the myodome. Posterior to these dorsal wings, the parasphenoid interdigitates with the ventromedial edges

of the prootics and, more posteriorly, with the ventral

surface of the basioccipital. Just anterior to the orbit, the parasphenoid interdigitates with the base of the prefrontals. Anterior to the level of its articulation with the

prefrontals, the dorsal edge of the parasphenoid becomes

concave and fits around the ventral edge of the ethmoid

keel. At its anterior end the parasphenoid possesses a

short, narrow concavity into which fits and interdigitates the posterior shaftlike portion of the vomer.

Pterosphenoid. —Cartilage filled along all of its edges of articulation with the other cranial bones; ar- ticulates by slight interdigitation dorsally with the frontal, laterally with the sphenotic, and ventrally with the

prootic. Medially the pterosphenoid articulates broadly through cartilage and interdigitation with its opposite member.

Ethmoid Region. Ethmoid. —Wide and elongate; slightly expanded

laterally and ventrally at its anterior end; produced ventrally into a keel which is relatively low along most of its length, but which increases in depth at its anterior end

above the shaftlike portion of the vomer; cartilage filled at its posteroventral edge where it is continuous with the remains of the ethmoid cartilage. The ventral edge of the

ventral flange of the ethmoid articulates by fibrous tissue with the concave dorsal edge of the platelike portion of the parasphenoid. At its posterior end the ethmoid ar- ticulates by interdigitation laterally with the prefrontal and dorsally with the frontal. The ethmoid articulates by

fibrous tissue anteroventrally with the anterior edge of the vomer, while directly anteriorly the ethmoid supports

the posterodorsal edge of the upper jaw.

Vomer. —Short; laterally expanded anteriorly but

tapering to a shaft posteriorly; articulates posteriorly by

slight interdigitation of its posterior shaftlike portion with the concavity at the anterior end of the para- sphenoid; articulates by fibrous tissue dorsally with the

anteroventral surface of the ethmoid and anterolaterally with the medial surfaces of the palatines and the posterodorsal edges of the upper jaw.
Mandibular Region. Hyomandlbular. —Somewhat expanded dorsally, but tapering to a stout shaft ventrally; cartilage filled at

its posterodorsal and anteroventral edges; articulates by

fibrous tissue dorsally with the longitudinal groove on

the ventral surfaces of the prootic and pterotic, while

posterodorsally the hyomandlbular abuts against and is firmly held by fibrous tissue along the medial surface of the elongate portion of the ventral flange of the pterotic. Along the lower three-fourths of its posterior edge the hyomandlbular articulates by fibrous tissue with the preoperculum. Just posterior to the dorsal end of the preoperculum, the ventral edge of the hyomandlbular is thickened and bears a concavity with which the dorsal end of the operculum articulates by fibrous tissue. The

anterior end of the hyomandlbular articulates variously through cartilage and fibrous tissue with the metapterygoid, symplectic, interhyal, and preoperculum.

Quadrate. —Widest posteriorly, tapering to a knob

anteriorly for articulation with the articular in the lower

jaw; cartilage filled at its posterior edge; deeply cleft along its lower posterior edge to accommodate the

anterior end of the symplectic; articulates by slight inter- digitation dorsally with the ectopterygoid, while it ar- ticulates by fibrous tissue posteriorly with the

metapterygoid and symplectic, both of which somewhat

overlie the quadrate. Ventrally the quadrate articulates by fibrous tissue with the preoperculum.

Metapterygoid. —Large; a more or less rounded flat plate; cartilage filled at its anterior edge; articulates by

fibrous tissue anteriorly with the quadrate, posteriorly with the interhyal and hyomandlbular; articulates by

slight interdigitation dorsally with the mesopterygoid,

anterodorsally with the ectopterygoid, and ventrally with

the symplectic.

Symplectic. —Large; cartilage filled at its anterior and posterior edges; dorsally expanded in the middle of

its length; articulates by fibrous tissue anterodorsally and anteroventrally with the quadrate; articulates by

slight interdigitation posterodorsally with the

metapterygoid, while along its posteroventral edge the symplectic is attached to the fibrous tissue sheet that is present between the preoperculum, hyomandlbular, and

metapterygoid.

Palato-Pterygoid Region.

Palatine. —T-shaped; articulates by fibrous tissue ventrally with the ectopterygoid, anterodorsally with the premaxillary and maxillary, and posterodorsally with the

laterally expanded anterior ends of the ethmoid and

Ectopterygoid. —Elongate; articulates by slight interdigitation anteroventrally with the quadrate, which

it somewhat overlies, posteroventrally with the

metapterygoid, and posterodorsally with the mesopterygoid. Along the middle of its anterior edge it articulates by tough fibrous tissue with the base of the palatine. Mesopterygoid. —Small; articulates by inter- digitation anteriorly with the ectopterygoid and ventrally with the metapterygoid.

Opercular Region.

Operculiun. —Thin and flat, except dorsally where

it thickens into a rounded articular facet; articulates by

fibrous tissue with the slightly upraised area on the ventral surface of the posterodorsal region of the hyomandlbular, while ventrally it overlies and articulates by fi- brous tissue with the suboperculum.

Suboperculum. —Very thin and flat, slightly wider

anteriorly than posteriorly; held to the overlying oper- culum by fibrous tissue.

Interoperculum. —A straight rod, slightly wider

posteriorly than anteriorly; extends from the region of the interhyal to about the anterior end of the preoper- culum; articulates by a tough ligament anteriorly with

the angular in the lower jaw, while at its posterior end

two ligaments are present. One of these ligaments is short and connects with the dorsal surface of the epi- hyal, while the other one is long and runs posteriorly to connect with the anterior edge of the operculum just above the point where the operculum begins to overlie the suboperculum.

Preoperculum. —Not greatly expanded in its middle region; its dorsal surface only slightly flattened for ar- ticulation with the quadrate; articulates by fibrous tis- sue along the posterior portion of its dorsal edge with the hyomandlbular, along the middle portion of its dorsal edge with the symplectic, metapterygoid, and interhyal, and along the anterior portion of its dorsal edge with the quadrate. Upper Jaw.

Premaxillary. —A slightly curved plate, wider dorsally than ventrally; its posterodorsal edge slightly con- cave to articulate by fibrous tissue with the anterior ends

of the ethmoid and vomer. It also articulates by fibrous

tissue laterally with the medial surface of the palatine. The anterior edge of the premaxillary forms the border of the upper jaw, except for a short distance ventrally where

the maxillary does so. The premaxillary is in close apposition with the maxillary and articulates immovably

with it by fibrous tissue and slight interdigitation. The

flat dorsomedial edges of the two premaxillaries are held

closely to one another by fibrous tissue. Each premaxillary bears seven teeth, four in an outer row and three in an inner row. Both of these rows are in close contact with
one another. The teeth are borne in very shallow depressions on the surface of the premaxillary in their fully formed condition. They develop, however, from large deep sockets which open to the surface just anterior to the base of the old tooth which they will replace. As the

tooth erupts to the surface to replace an old tooth, the

socket from which it arose seems to become overgrown or

filled in with bone and to disappear so that the tooth

rests flatly against the surface of the premaxillary. Most

of the interior of the premaxillary is given over to the dental pulp cavity, this cavity communicating with the

exterior through a foramen in the posterodorsal surface of the bone as well as through numerous smaller holes on

the inner and outer surfaces of the bone.

Maxillary. —Widest ventrally, becoming narrower

dorsally; articulates firmly with the premaxillary by fi- brous tissue and slight interdigitation. The medial sur- face of the ventral region of the maxillary articulates by

fibrous tissue with the lateral surface of the upper portion of the dentary. The posterodorsal surface of the maxillary articulates by fibrous tissue with the lateral expansions of the ethmoid and vomer and with the medial surface of the palatine.

Lower Jaw.

Dentary. —Wide posteriorly; its posterior edge con- cave to accommodate the anterior portion of the articular, with which it articulates by interdigitation. Posteroventrally the dentary articulates by inter- digitation with the angular. From the lateral surface of

its posterodorsal region the dentary articulates by fi- brous tissue with the medial surface of the maxillary. Ventromedially the flat surface of the dentary articulates by fibrous tissue with its opposite member. Each dentary bears four teeth in a single row, corresponding to the outer row of teeth in the premaxillary. The teeth are borne flush against the surface and are replaced by new

teeth developing in deep sockets, just as described for the

teeth of the upper jaw. Most of the interior of the dentary

is filled with the dental pulp, the cavity opening to the

exterior at the concave posterior edge of the dentary, as

well as at pores on the inner and outer surface of the

bone.

Articular. —Wide along its posterior edge, with a concave facet for articulation by fibrous tissue with the

anterior knob of the quadrate; articulates by inter- digitation with the concave posteromedial surface of the

dentary. Along its ventral edge the articular inter- digitates with the angular. The sesamoid articular is a small but thick nodule of bone closely held by fibrous tis- sue to the medial surface of the articular just in front of the concave articular facet of that bone. Angular. —Small, squarish; articulates by inter- digitation dorsally with the articular and anteriorly with

the dentary. Posteriorly the angular connects by liga- ment with the interoperculum.

BRANCHIAL APPARATUS.

Hyoid Arch, Branchiostegal Rays, and Urohyal. Hypohyals. —Both hypohyal elements well de- veloped, the ventral element considerably larger than

the dorsal element; the dorsal element cartilage filled at

its dorsal Eind posterior edges; the two elements ar- ticulate with one another through the cartilage that lies between them; the dorsal and ventral elements ar- ticulate by fibrous tissue at their anteromedial edges with their opposite members. The dorsal hypohyal ar- ticulates by fibrous tissue at its dorsal edge with the

lateral surface of the first basibranchial. The ventral hypohyal articulates through cartilage at its posterior edge with the ceratohyal, and by fibrous tissue from its ventromedial surface with the urohyal.

CeratohyaL —A short shaft, wider posteriorly than

anteriorly; cartilage filled at its anterior and posterior edges; articulates through cartilage anteriorly with the

ventral hypohyal; articulates posteriorly through cartilage and interdigitation with the epihyal. The first two

branchiostegal rays articulate with slight depressions on

the ventral edge of the ceratohyal. The ventralmost one

or two rays of the remaining four rays have their fibrous

tissue articulation principally with the ceratohyal.

EpihyaL —Large; cartilage filled at its ventral

edge; articulates through cartilage and interdigitation ventrally with the ceratohyal, while dorsally it ar- ticulates by fibrous tissue with the interhyal and inter- operculum.

InterhyaL-A short, thick rod; cartilage filled at both ends; articulates by fibrous tissue ventrally with the

epihyal and dorsally with the symplectic.

Branchiostegal rays. —Six in number; increasing

slightly in length posteriorly in the series; first ray considerably flatter and wider than the others. The first two

rays articulate by fibrous tissue with shallow grooves on

the ventral edge of the posterior half of the ceratohyal. The other four rays articulate by fibrous tissue with the

ceratohyal and epihyal. The more ventral of these four rays have their connective tissue fibers attached principally to the ceratohyal, while the more dorsal rays have them attached principally to the epihyal.

Urohyal. —Thick along its dorsal and anterior

edges, otherwise a thin plate; articulates by fibrous tis- sue anteroventrally with the medial surface of the ventral hypohyal, while posteriorly it articulates with the

ventral surface of the first two basibranchial elements.

Branchial Arches. —All the elements are cartilage

filled at their edges of articulation with the other elements of the series, and the articulations are usually 105
through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and three pairs of pharyngobranchials. Four gills are present, with a slit between the

fourth arch and the lower pharyngeal.

branchial; about 12 to 15 teeth present in a single row,

the teeth like those of the outer series of the jaws, but much smaller and with sharper points. The teeth decrease in size posterolaterally in the series and are replaced by new teeth developing in sockets below the

bases of the old teeth.

First arch.—Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basibranchial

short, wider posteriorly than anteriorly, displaced for- ward so that it articulates posteriorly with the second

basibranchial and posterolaterally with the first hypobranchials. First hypobranchial very wide, more so posterodorsally than ventrally; the largest of the hypobranchial elements, which decrease in size posteriorly in the series; articulates ventrally with the region of ar- ticulation between the first and second basibranchials and dorsally with the first ceratobranchial. First cerato- branchial a sturdy rod; the longest of the cerato- branchial elements, which decrease in length posteriorly

in the series; no ventrally directed flange present on the

ceratobranchials, although from the second to the last ceratobranchial the ventral ends of the elements become

increasingly enlarged; articulates dorsally with the first epibranchial. First epibranchial with its ventral end

rounded and its dorsal end forming two divergent stubby

projections; its rounded ventral end articulates with the

first ceratobranchial, while the anterior projection of its dorsal end articulates with the first pharyngobranchial, and the posterior projection of its dorsal end with the

dorsal end of the second epibranchial and the ventral end

of the second pharyngobranchial. First pharyngobranchial (suspensory pharyngeal) short, slightly wider

ventrally than dorsally; articulates ventrally with the

first epibranchial and dorsally by fibrous tissue with the

ventral edge of the keel of the parasphenoid at the level of the middle of the orbit.

Third arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Third basi- branchial narrow anteriorly and posteriorly, but ex- panded in the middle; articulates anteriorly with the sec- ond basibranchial, anterolaterally with the second

hypobranchials, posterolaterally with the third hypobranchials, and posteriorly with the fourth cerato- branchials. Third hypobranchial rounded posteriorly but

with a tapering anteroventral process that articulates by

fibrous tissue anteriorly with the ventral surface of the more anterior basibranchials; articulates posterolaterally with the third ceratobranchial and posteromedially with the posterior end of the third basibranchial. Third ceratobranchial with a much expanded ventral end; articulates ventrally with its opposite member

and with the third hypobranchial, and dorsally with

the third epibranchial. Third epibranchial a short rod

with a slightly expanded base and a short projection posteriorly from the basal part of its posterior edge; ar- ticulates dorsally with the third pharyngobranchial; the

projection from the basal portion of its posterior edge ar- ticulates by fibrous tissue with a similar projection from

the anterior edge of the fourth epibranchial. Third pharyngobranchial like the second pharyngobranchial,

except slightly smaller and with its ventral arm shorter and wider; teeth in about the same number and arrange- ment as described for the second pharyngobranchial; ar- ticulates with the dorsal ends of the third and fourth epi- branchials. The two toothed pharyngobranchial

elements are held to one another by fibrous tissue.

Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial longer than the first basibranchial and about

the same length as the third basibranchial, but wider than either of the other two; articulates anteriorly with

the first basibranchial, anterolaterally with the first hypobranchials, posteriorly with the third basibranchial and posterolaterally with the second hypobranchials. Sec- ond hypobranchial squarish, with a short posterior ex- tension; articulates ventrally with the area of ar- ticulation between the second and third basibranchial and dorsally with the second ceratobranchial. Second

ceratobranchial a long rod with a slightly expanded ventral end; articulates dorsally with the second epi- branchial. Second epibranchial a short rod; articulates dorsally with the second pharyngobranchial and the

posterodorsal arm of the first epibranchial. Second

pharyngobranchial with an elongate tooth bearing portion and a short arm for articulation with the second epi- branchial and the posterodorsal arm of the first epiFourth arch. —Cerato- and epibranchial elements

only. Fourth ceratobranchial much expanded ventrally;

articulates ventrally with the ventral end of its opposite member and with that of the third ceratobranchial. Fourth epibranchial rodlike; longer than the second and

third epibranchials; articulates ventrally with the fourth ceratobranchial and dorsally with the base of the third pharyngobranchial, and, from a short projection on its lower anterior edge, with the third epibranchial.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial the shortest of the

ceratobranchial elements; wider ventrally than dorsally, with a short anterior projection from its anteroventral

edge; articulates ventrally with the base of the fourth

ceratobranchial; bearing two rows of teeth, the posterior row much larger than the anterior row; teeth in both rows

similar to those of the pharyngobranchials, and becoming smaller dorsally; about 25 teeth in the anterior row and 15 in the posterior row.
PAIRED FIN GIRDLES.

Pectoral Fin.

Posttemporal. —A slender wedge of bone ventrally where it is held in a deep concavity on the lateral surface

of the pterotic, but slightly expanded posterodorsally where it contacts the sphenotic and, to a lesser extent, the epiotic. It is firmly and immovably held to all three of these bones, and especially to the pterotic, by a combination of fibrous tissue and interdigitation. Ventrally

the posttemporal articulates by fibrous tissue with the supracleithrum.

Supracleithrum. —More or less vertical in position

in relation to the axis of the body; articulates im- movably by fibrous tissue dorsally with the rounded ventral head of the posttemporal and ventrally with the

cleithrum, which it broadly overlies.

Cleithrum. —Laterally expanded at its anterior

edge, particularly in the middle one-third of its length;

articulates by fibrous tissue dorsally with the overlying supracleithrum and with the dorsal postcleithrum, which

it overlies. Along its posterior edge the cleithrum broadly

overlies and articulates by fibrous tissue with the anterior edges of the scapula and coracoid. Ventromedially

the cleithrum articulates by fibrous tissue with its opposite member, and just above this region the anterior end of the shaftlike pelvis is held between the cleithra.

Postcleithra. —The postcleithra form a long

posteroventrally directed strut from the dorsomedial sur

face of the cleithrum along the abdominal wall muscula

ture to the area just above the dorsal lobe of the pelvis The dorsal postcleithrum is wide anteriorly where it ar

ticulates by fibrous tissue with the overlying cleithrum

with a short dorsal projection from about the middle of

its length supporting the posteroventral edge of the enlarged scales of the tympanum; tapering to a point posteriorly where it broadly overlies and articulates by fi- brous tissue with the anterodorsal region of the ventral postcleithrum. The ventral postcleithrum a simple shaft, tapering to a point posteriorly.

Coracoid. —Wide dorsally, tapering to a blunt

point ventrally; with a short spinelike process under the lowermost actinost from its posteroventral edge; the upper one-third of its posterior edge with an inturned flange

directed anteromedially, forming a broad basin for muscle attachment; cartilage filled at its dorsal edge and for a short distance at its anteroventral edge; articulates by

fibrous tissue anteriorly with the cleithrum, which

broadly overlies the dorsal one-half of its anterior edge;

articulates anterodorsally through cartilage and inter- digitation with the scapula; articulates dorsally by fi- brous tissue with the bases of the ventralmost two actinosts.

Scapula. —Completely encloses the scapular foramen; cartilage filled at its anterior and ventral edges;

articulates anteriorly and anteroventrally by fibrous tis- sue with the overlying cleithrum; articulates posteroventrally through cartilage and interdigitation with the

coracoid. Along its posterodorsal edge the scapula ar- ticulates by fibrous tissue with the following elements, in order from anterodorsal to posteroventral: the first pectoral fin ray, the small first actinost, the second actinost, and the anterior half of the base of the third actinost. The articulations with the first pectoral fin ray and the

first actinost occur at upraised areas on the dorsal edge of the scapula, the stubby projection supporting the first pectoral fin ray being slightly larger than that supporting the first actinost.

Actinosts. —Four elements; all cartilage filled at both ends; first actinost small, the others increasing

slightly in size posteroventrally in the series; first two actinosts articulated to the scapula as described in the preceding section; third actinost articulated with the

dorsal edge of the articular area between the scapula and

coracoid and the fourth actinost with the coracoid; all the articulations are by fibrous tissue. Distally the actinosts support by fibrous tissue all of the fin rays, ex- cept for the first, which is supported by the scapula.

Fin rays. —Fourteen fin rays in most specimens,

with the first ray about one-fifth the length of the second

ray and articulated directly with the scapula, rather than

with the actinosts, as are the other rays. First ray with its medial half enlarged and thickened at its basal region of articulation with the scapula; its lateral half reduced to a

thin, short splint closely held to the medial half, or even

fused to it. First two rays and the last ray unbranched,

the others branched. First ray without cross-striations,

all the other rays cross-striated.

Pelvic Fin.

Pelvis. —A stout shaft; not divided into separated

right and left halves; anterior half of its lateral surface with a concavity for muscle attachment; a large dorsal

lobe present from its posterodorsal region which serves as a place of tough fibrous tissue attachment for the overlying skin of the distensible abdominal area or ventral

flap (dewlap). A series of enlarged scales encircles the

posterior end of the pelvis and obscures from view the rudimentary fin-ray (or spinous) element present in the midline just behind the end of the pelvis. The lateral sur- face of the posterior end of the pelvis bears several ridges

for articulation with these scales. The scales occur in four segments, the anteriormost of which is immovably held

to the end of the pelvis, while the other three segments

are movable in a dorsoventral plane against the scales of the first segment and the end of the pelvis. The fin-ray element is deeply bifurcate anteriorly into divergent

dorsal and ventral halves, as described in detail by Tyler

(1962:228-229, figs. 30-37). The anterior one-third of the
dorsal surface of the element has a groove in the midline which superficially separates the element into right and

left halves, but the ventral surface shows no such groove.

Posteriorly the element becomes divided into four slender rods, the tips of which project posteriorly a short distance beyond the end of the encasing scales, through a

hole in the posterodorsal surface of the last scale seg- ment. A large plug of cartilage intermediates between

the bifurcate anterior end of the fin-ray element and the

posterior end of the pelvis. The fin-ray element is movable in a dorsoventral plane around the posterior end

of the pelvis, for ligaments are attached to the dorsal and

ventral halves of the anterior end of the element, and the ligaments connect anteriorly to strong muscles. The ventral ligament runs along a concavity on the ventral sur- face of the pelvis to its muscle, while the dorsal ligament

runs anteriorly through a longitudinal tunnel in the basal

region of the dorsal lobe of the pelvis to make contact with its muscle, which is housed in a concavity along the

dorsal surface of the pelvis anterior to the dorsal lobe. The pelvis itself is movable in a dorsoventral plane around its fibrous tissue attachment between the ventro- medial edges of the cleithra. VERTEBRAL COLUMN. —All vertebrae with bicon- cave centra, except the last, which posteriorly ends in a

plate representing the fused centrum, hypurals, and

parhypural. Abdominal Vertebrae.

First vertebra. —Neural spine enlarged, somewhat

laterally expanded, bifid to the centrum and thus not forming a bony roof over the neural canal; articulates by

fibrous tissue and slight interdigitation along all of the

anterior face of its neural spine with the exoccipitals. The

rim of the concave anterior face of its centrum ar- ticulates by fibrous tissue with the rim of the concave

posterior end of the basioccipital, while the rim of its posterior face articulates similarly with the rim of the anterior face of the second vertebra. From about the middle of its posterolateral surface, the centrum possesses a

posteroventrally directed process which makes fibrous

tissue contact over the anterior half of the lower surface

of the centrum of the second vertebra. The neural pre- zygapophysis of the second vertebra makes close fibrous

tissue contact with the dorsolateral surface of the first vertebral centrum.

Other abdominal vertebrae. —In five specimens the abdominal vertebrae numbered seven. Except for the

first vertebra, all the abdominal vertebrae, as well as all of the caudal vertebrae except the last, possess bony

roofs over the neural canal and have single, undivided

neural spines. The neural spine of the third vertebra is the largest of those of the abdominal vertebrae, for it is much expanded dorsally. The basal regions of the neural

spines and the dorsal regions of the neural arches become

increasingly anteroposteriorly enlarged, from the second

to the last abdominal vertebra, into broad articular surfaces. These enlarged neural spines may have their anterior and posterior edges interdigitated with the preceding and succeeding neural spines in large specimens, but normally they articulate with one

another only by fibrous tissue. Each neural arch has a neural foramen in its lateral surface. Short haemal post- zygapophyses are present which slightly overlie the ventrolateral surface of the succeeding vertebral centra, but

there are no haemal prezygapophyses. The second to the seventh abdominal vertebrae possess processes from

their centra which bear all but one of the seven

epipleural ribs. These processes become increasingly longer and stouter posteriorly in the series. The second

vertebra bears a short lateral projection from its cen- trum just below the anterior region of the neural arch, and this projection articulates by fibrous tissue with the

first epipleural. The third to fifth vertebrae bear their transverse processes progressively lower on their centra,

so that the fifth vertebra has its transverse process taking

its origin from the anteroventral edge of the centrum,

while the process itself is directed posteroventrally. The

third to the fifth vertebrae bear, respectively, the second

to fourth epipleurals from the dorsal surfaces of their transverse processes. The processes of the sixth and

seventh vertebrae differ from those anterior to them in that from the medial surface of the process on each side

of the centrum there is a medially directed projection which meets and is continuous with that of its opposite member, completely enclosing the haemal canal. The

haemal arch of the sixth vertebra does not have a haemal

spine, but that of the seventh vertebra does. The haemal

spine of the seventh vertebra, however, is not a single medial piece. Rather, it is bifid and forms a short

posteroventrally directed process on either side of the

midline. The sixth and seventh vertebrae bear, respectively, the fifth and sixth epipleurals from the lateral sur- faces of their haemal arches. The neural spine of the fifth vertebra articulates by fibrous tissue dorsally with the supraneural strut that supports the posterior end of the

spiny dorsal fin pterygial elements, while posterodorsally it articulates with the first basal pterygial element

of the soft dorsal fin. The neural spines of the sixth and

seventh vertebrae articulate by fibrous tissue between,

respectively, the first and second and the second and

third basal pterygial elements of the soft dorsal fin.

Caudal Vertebrae. —The caudal vertebrae numbered

11 in five specimens. As with the more posterior of the abdominal vertebrae, the first two caudal vertebrae have

their neural spines enlarged. From the third to the last vertebra, however, the degree of enlargement progressively decreases so that the more posterior caudal verte- brae have relatively normal neural spines. All of the caudal vertebrae, except the last, possess complete

neural and haemal arches. There are no haemal pre- zygapophyses, and small haemal postzygapophyses are only developed on a few of those vertebrae supporting the

anal fin. The first caudal vertebra has a thick haemal

spine that articulates firmly by fibrous tissue with the upper anterior surface of the enlarged first anal fin basal
pterygiophore. From the lateral surface of the haemal

spine of the first caudal vertebra, just below the level of the haemal arch, the seventh or last epipleural ar- ticulates by fibrous tissue. The second caudal vertebra has the largest haemal spine of any of the vertebrae, and

posterior to this vertebra the length of the haemal spines

progressively decreases until the 10th caudal vertebra is reached. The 10th caudal vertebra has its haemal spine

longer than those just anterior to it, and in contrast to all the others, its haemal spine is autogenous. The lengths of the neural spines decrease from the first to the 10th caudal vertebra. The 10th caudal vertebra has its neural

spine longer than those just anterior to it. The haemal

and neural spines of the last caudal vertebra are de- scribed below.

Caudal Skeleton. —The caudal complex consists of an

epural, a free upper hypural, a free parhypural, and a

large plate composed of the centrum fused to most of the hypural elements. The epural is a narrow shaft dorsally but an expanded plate ventrally, where it articulates by

fibrous tissue with the neural arch of the centrum, sometimes more closely than that in the illustrated specimen. The free upper hypural is wider dorsally than ventrally and is held by fibrous tissue between the edges of the

epural and the posterior half of the dorsal edge of the fus- ed hypural plate. The parhypural is a flattened rod

similarly held between the edges of the posteroventral

half of the autogenous haemal spine of the penultimate

vertebra and the ventral lobe of the fused hypural plate. The large hypural plate is the centrum fused to what in more generalized plectognaths are the first to fourth

hypurals, the deep indentation on the posterior edge of the plate representing what would be the division between the second and third hypurals. The centrum

region is thickened into a broad vertical crest for muscle

attachment. The two halves of the neural arch of the last centrum diverge anteriorly, but more posteriorly they sometimes approach each other more or less closely in the midline, although they do not interdigitate or fuse. The neural canal is thus relatively open above, never being more than very partially roofed over. Similarly, the two halves of the haemal arch closely approach one

another ventromedially, but do not interdigitate or fuse and leave the haemal canal only partially roofed over. The haemal canal courses through the haemal arch to

exit at the deep notch in the anteroventral end of the fus- ed hypural plate. The parhypural thus represents only

the haemal spine of the last vertebra, and not both the

spine and arch. As discussed and illustrated by Tyler (1970b:14, fig. 22) three of the five study specimens show no evidence of uroneurals, nor do any of the other species of balistids ex- amined, but two of the specimens of Balistapus undulatus do. In one of these specimens there is a pair of small nubbins of bone resting on the dorsal surface of the upper free hypural and directly behind the posterior edge

of the epural, these apparently being the two halves of a rudimentary uroneural. In the other specimen, the "uro- neural" elements are much further forward, being a pair

of ossifications just above and behind the posterodorsal

region of the neural arch of the last centrum. Whether

these elements are homologous to the uroneurals of the

other specimen is questionable, for they could also be unconsolidated neural arch material, as sometimes found in triacanthodids, which have relatively well-developed

uroneurals.

Caudal fin rays. —Twelve in number; the upper- most ray and the lowermost ray unbranched, the others becoming increasingly branched toward the middle fin rays, which are branched in triple dichotomies. The bifid bases of the fin rays articulate by fibrous tissue with the caudal skeleton as follows: the uppermost two rays to the upper free hypural; the lowermost ray to the parhypural and the remaining eight rays to the lobes of the

fused hypural plate, four to the dorsal lobe and four to the ventral, with the lowermost branched ray receiving

partial support from the parhypural as well. DORSAL AND ANAL FINS.

Spines and pterygiophores. —Three spines borne on two basal pterygiophores. First spine long and stout; sec- ond spine slightly shorter and narrower; third spine about one-fourth the length of the first spine. The first two spines are borne on the enlarged first pterygiophore and the third spine on the much smaller second pterygiophore. The mechanism by which the bifid bases of the

first two dorsal spines rotate over the medial upraised

portion of the dorsal surface of their pterygiophore and

lock themselves in an erected position, with the postero- ventral edge of the first spine resting against the anteroventral edge of the second spine, has been described so

often in the past that a detailed redescription of it here seems superfluous. For such descriptions see Hollard

(1853:102), Bnihl (1856:59; 1880; 1891:pl. 24), Mayer

(1864:fig. 4 of pi. 7), Bliss (1872:10), Thilo (1879:12; 1896b:291; 1902), Klein (1881:350), S(<rensen (1884:50;

1897), Mohr (1928), Jacobs (1935:156-157), Clothier

(1939), Smith (1949a:406), and Monod (1950, 1960). The

papers of S</rensen, Clothier, and Monod are particularly recommended. Anteriorly the first pterygio- phore has a short, bluntly rounded, ventral process which

is firmly held by fibrous tissue in the concavity in the midline of the posterodorsal region of the skull formed

dorsally by the supraoccipital and laterally and ventrally by the epiotics. Posteriorly the first pterygiophore

is broadly overlain by the anterior region of the second

pterygiophore, with which it interdigitates. On the ventral edge of the second pterygiophore, there is a shallow

indentation where fibrous tissue articulation is establish- ed with the thick shaftlike supraneural element. The

supraneural slants posteroventrally from its articulation with the second pterygiophore to make fibrous tissue contact with the dorsal edge of the neural spine of the

fifth abdominal vertebra and with the lower anterior edge of the first basal pterygiophore of the soft dorsal fin. 109
Fin rays and ptery^ophores. —Twenty-six fin rays

are present in most of the study specimens; the first ray unbranched, the others branched in single or double

dichotomies. Each fin ray has a small, unpaired, distal pterygiophore between the bifurcate base of the ray. Basally the fin rays are supported by 27 basal pterygio- phores. Each basal pterygiophore has a well-developed

lateral flange throughout its length, except at the very proximal and distal ends of the element, for muscle at- tachment. The lateral flanges decrease slightly in height

posteriorly in the series. The first basal pterygiophore is somewhat shorter, but stouter, than those just posterior

to it, and articulates by fibrous tissue ventrally between

the neural spines of the fifth and sixth abdominal verte- brae, while anteroventrally it supports the base of the

supraneural. Posterodorsally the first basal pterygio- phore interdigitates with the second basal pterygio- phore, and all of the subsequent basal pterygiophores ex- tensively interdigitate to one another along their edges of contact, the more posterior elements only slightly less ex- tensively so than more interiorly. The last few basal pterygiophores articulate between the neural spines of the seventh and eighth caudal vertebrae. The degree of

interdigitation between the pterygiophores, and their closeness of apposition with the neural spines, increases with increased size of the individual, so that in very large specimens a massive, almost solid plate is present between the vertebrae and the soft dorsal fin. The basal

pterygial elements are cartilage filled at their dorsal and

ventral edges. In all but one of the five study specimens

the number and arrangement of the basal pterygial elements is as described above, but slight variation in the number of elements is to be expected.

Fin rays and pterygiophores. —Twenty-three fin rays are present in most of the study specimens; first ray unbranched, the others branched in single or double

dichotomies. Each fin ray with a small, unpaired, distal pterygiophore between its bifurcate base. Basally the

rays are supported by 22 basal pterygiophores, like those

of the dorsal fin. The first basal pterygiophore is by far the largest of the series and has its anterior edge ex- panded laterally. It articulates by fibrous tissue dorsally between the haemal spines of the first and second caudal

vertebrae, while posteroventrally it interdigitates with

the second basal pterygiophore, and all of the sub- sequent basal pterygiophores are extensively inter- digitated to one another, as in the soft dorsal fin, with the

interdigitation and closeness of apposition to the haemal

spines increasing with increasing specimen size. The last few basal pterygiophores articulate between the haemal

spines of the seventh and eighth caudal vertebrae. Anatomical diversity.—The balistids are one of the

least anatomically and otherwise diversified families of plectognaths, of a degree of diversity comparable to that

of the Triacanthidae, Aracanidae, and Diodontidae.

Internally the balistids differ remarkably little from one

another in fundamental plan. The vertebral column (7 -(- 11), basal pterygiophore support system of the soft dorsal and anal fins, and the caudal fin supporting struc- tures are basically the same in all species. The skulls

differ mainly in the degree of development and massiveness of the supraoccipital and epiotic supports of the

basal pterygiophores of the spiny dorsal fin (least developed in Rhinecanthus), perhaps correlated at least

in part with the size of the third spine, and of the degree

of anterior displacement of the suspensorium (most dis- placed in Xanthichthys and, especially, Odonus), cor- related with the degree of upturning of the mouth. The genera of balistids are, in fact, distinguishable mainly by external features such as: the degree of development of a cusp or enlargement on the medial end

of the biting edge of the teeth (least developed in Melichthys, in which at least the more medial of the cusped

teeth of young specimens become truncate true incisors with increasing size; best developed in Xanthichthys

and, especially, Odonus, in both of which the most

medial tooth of the premaxillary is smaller than that just

lateral to it, whereas it is the medial tooth that is the

largest in all other balistids; the enlarged cusp of the sec- ond most medial tooth in Odonus projecting far beyond

the others and resting on the lower lip as a fang when the jaws are closed); the presence or absence of a deep groove

in front of the eye and below the nostrils of unknown

functional significance (absent in Balistapus and Rhinecanthus, and only weakly present in Pseudobalistes); the presence or absence of enlarged, rounded, or otherwise modified nonoverlapping and flexible scales covering the tympanum (not enlarged in Canthidermis and

Xanthichthys); scales and spinulation patterns on the head and body; degree of development of the third dorsal spine (least developed in Melichthys, Rhinecanthus, and Xanthichthys; becoming minute in large specimens

of Canthidermis and Balistoides conspicillum) , these

diagnostic features supplemented by the shape of the caudal peduncle and caudal fin. These and other features

in the anatomical diversity of the Recent species are dis- cussed further in the section on generic relationships. The balistids have changed little since the Oligocene.

In the black schist of Canton Glarus, Switzerland, there

are three species of balistids placed in the genus Balisto- morphus that are, from what little is known of them from

their impressions, thoroughly modem in appearance. The holotypes and a few additional specimens of these

three species have recently been reexamined and data on them is given below. Balistomorphus ovalis (Agassiz 1842 illustration, 1844b

description) is the most slender bodied of the three

species in the genus. The holotype, IGUN uncatalogued

(but XXXVH scratched on the back of the plate), a

single impression (head left) is 121 mm SL. The depth of the body between the soft dorsal and anal fin origins is 45.3 mm (37.3% SL). The least depth of the caudal peduncle is 12.8 mm (10.5% SL). The length of the first dorsal spine is 25.7 mm (21.2% SL). The second dorsal spine cannot be measured, but the third spine is 4.5 mm

(3.7% SL). There are 11 caudal vertebrae, as in Recent

prefrontal frontal pterosphenoid supraoccipital

metapterygoid hyomondibular

ethmoid

frontal

prootic pterotic porosphenoid

operculum

ethmoid

parasphenoid

prefrontal

sphenotic

C2) " pterotic posttemporal

supraoccipital "s^' \l

epiotic

pterotic / ^ posttemporal

basioccipital ' exoccipital exoccipital

epiotic

112
Figure 52. (opp. page, upper)—Baliatapus undulatus: lateral view of head, composite ba§ed on several specimens.

ca. 120-124 mm SL, western Pacific.

posttemporal\ ^/ V / /r, ^

posterior myodome cavity

parasphenoid

pital basioccipital foramen magnur

neural spine

Figure 53. (opp. page, \ovieT)—BalUtapus

undulatus: dorsal (left) and ventral (right) vi< of skull, composite based on several specimen

ca. 120-124 mm SL, western Pacific.

Figure 54.

Balistapus undulatus: posterior view of orbit (left) (cross section of skull; dashed lines represent cut surfaces of

fronlals, supraoccipital, and parasphenoid) and posterior view of skull (right); below,

posterior and lateral views of first abdominal vertebra; composite based on several specimens, ca. 120-124 mm SL, western Pacific.

113
ilil 8 S « . 2 f' = J

llli

...sl.-l... llli

1 1 1 .1

0,0-- « a:

Figure 5><.—Balistapus undulatus:

lateral view of spiny dorsal

fin and its pterygial supports, composite based on several specimens,

ca. 120-124 mm SL, western Pacific.

basal pterygiophore

r~ 3 fin I

Figure 59.—Balistapus undulatus:

left, dorsal view of pterygial supports

of spiny dorsal fin, with the spines removed; right, posterior view of first dorsal spine and anterior view of second dorsal spine to show their articular facets; composite based on

several specimens, ca. 120-124 mm SL, western Pacific.

Figure SO.—Balistapus undulatus:

lateral view of caudal fin supporting structures, composite based on several specimens,

ca. 120-124 mm SL, western Pacific.

caudal vertebrae
Figure 61.—External features of other representative balistid genera: Abalistes

etetlaris— upper left, scale plates of the tympanum region just behind the gill slit and above

the pectoral fin base; upper middle, scales from upper middle region of body, including

lateral line canal bearing scales; upper

right, ventral view of encasing scales at end of pelvis (anterior to left), with arrow

indicating major region of flexibility (two terminal branches of modified

fin-ray element protrude posteriorly); lower

left, nasal region as seen externally (above) and the olfactory lamellae as seen with the top of the nasal sac removed.

Figure 62.—External features of other

representative balistid genera: Canthidermis maculatus—upper left, scales of the relatively unmodified tympanum region

just behind the gill slit and above the

pectoral fin base; upper middle, scales from upper middle region of body, including

lateral line canal bearing scales; upper

right, ventral view of encasing scales at end of pelvis (anterior to left), with arrow indicating major region of Hexibility (modified fin-ray element not protruding); lower left, nasal region as seen

externally (above) and the olfactory lamellae as seen with the top of the nasal sac removed.

Figure 63.—External features of other representative balistid genera: Xanthichthya ringens—

upper left, scales of tympanum

region just behind the gill slit and above the pectoral fin base; upper middle, scales from

upper middle region of body,

including lateral line canal bearing scales; upper right, ventral view of encasing scales

at end of pelvis (anterior to

left), with arrow indicating major region of flexibility (three terminal branches of modified fin-ray element protrude

posteriorly); lower left, nasal region as seen externally (above) and the olfactory lamellae as seen with the top

of the nasal sac removed.
Figure 64.—External features of other representative balistid genera : Odonua niger—

upper left, scale plates of the tympanum

region just behind the gill slit and above the pectoral fin base; upper middle,

scales from upper middle region of body, including lateral line canal bearing scales; upper right, ventral view of encasing

scales at end of pelvis (anterior to left), with arrow indicating major region of

fiexibility (two terminal branches of modified fin-ray element protrude posteriorly); lower left, nasal region as seen externally (above) and the olfactory lamellae as seen with the top of the nasal sac removed.

species, and room for about seven abdominal vertebrae,

also as in Recent species, although only the last four ab- dominal vertebrae can be seen relatively clearly. There

appear to be about 12 caudal fin rays in a slightly rounded fin. There is a well-developed supraneural strut supporting the rear end of the carina. The basal pterygio- phores that are best shown, anteriorly in the soft dorsal

fin, have well-developed lateral flanges. The form and number of the teeth do not show. The stout pelvis has a small but distinct dorsal lobe posteriorly. The scales, best seen posteriorly on the body, bear one or more low

longitudinal ridges along the basal plate, those in the

region of the caudal peduncle being larger and longer than elsewhere and oriented in longitudinal rows, just as

in many Recent species. An additional specimen from the black schist of Canton Glarus, NSKG 178b, 119 mm SL, can be assigned to Balistomorphus oualis, mainly on the basis of its slender body, the depth between the soft dorsal and anal fin origins being about 36 mm (30% SL). It is a poor impression that at one time was in counterpart, but the head to the right plate (presumably numbered 178a) cannot be

found. The caudal peduncle depth is 12.4 mm (10.4%

SL). The first dorsal spine is 22.8 mm (19.2% SL), the second 9.5 mm (8.09; SL), and the third 5.1 mm (4.3%

SL), all of which measurements are compatible with that

of the holotype of B. oualis from the same strata, as are the well-developed supraneural strut supporting the car- ina and the approximately 11 caudal vertebrae. Little

else of interest can be seen. Balistomorphus spinosus (Agassiz 1842 illustration, 1844b description) is a moderately deep bodied species. The holotype, and only relatively complete specimen

available, BMNH P. 3973, a single impression (head

right) is 92.0 mm SL. The depth of the body between the

soft dorsal and anal fin origins is 46.0 mm (50% SL). The

least depth of the caudal peduncle is 12.2 mm (13.3%

SL). The length of the first dorsal spine, which bears low

asperities laterally, is 21.0 mm (22.8% SL). The second

dorsal spine cannot be measured, but the third spine is

5.0 mm (5.4% SL). The vertebral column can be inter- preted either as 7 + 11, as in Recent species, or as 8 + 10. The caudal fin appears to have 12 rays. There is a well- developed supraneural strut supporting the rear end of the carina. The basal pterygiophores have well- developed lateral flanges. The form and number of the

teeth do not show. There is a slight indication that the

stout pelvis had a low dorsal lobe posteriorly. The scales are not as well indicated as in B. oualis, but low granulations of some sort were present on the basal plates. The

anal fin base seems to have been substantially shorter than the soft dorsal fin base, more so than in B. oualis. An additional specimen from the black schist of Canton Glarus, NSKG 189a and b, which is too poor an impression in counterpart to accurately measure, can

probably be assigned to B. spinosus on the basis of its moderately deep body, as can another not listed in the material examined (BMNH P. 1819) from the same

strata whose bones are too disorganized to measure. These additional specimens add little to our knowledge

of the species, except that the first dorsal spine in one of them bears even better developed asperities laterally, and apparently anteriorly, than does the holotype of B. spinosus. Balistomorphus orbiculatus (Heer 1865, see also 1876)

is an extremely deep bodied species. The holotype, and

only known specimen, NSKG 2688, a single impression (head left), is 65.6 mm SL. Heer's illustration of the specimen shows the head facing right, so either the illus- tration was reversed or, less likely, the specimen was

originally in counterpart and only the head to left half remains in the Glarus collection. Woodward (1901:568) believed the great depth of the specimen to be due to dis- tortion, but, as with the other specimens of Balistomor- phus (and of the Oligocene triacanthid Acanthopleurus, which see) from the black schist of Canton Glarus, the

neural and haemal spines of the vertebrae have a normal

relationship with the basal pterygiophores of the soft dorsal and anal fins and the patterns of the scales are nor- mal, neither of which would be the case if B. orbiculatus
Figure 65. —Fossil balistids: A. Balistomorphus ovalU, lateral view

of holotype, 121 mm SL, Oligocene of Canton Glarus, Switzerland (Agassiz

1842:pl. 75); B, B. ovalis, lateral view of entire specimen, 119 mm SL,

Oligocene of Canton Glarus, Switzerland:

C, B. spinosus. lateral view of holotype,

ca. 9U mm SL, Oligocene of Canton

Glarus, Switzerland (Agassiz 1842:pl. 75); D, B. orbiculatus, lateral view of holotype, 65. G mm SL, Oligocene of Canton

Glarus, Switzerland; E, Oligobalistes robustus, lateral view of syntype,

ca. 60 mm SL, Maikop deposits of the Oligocene of the Caucasus (Danil'chenko

1960:175, fig. 32).
were unnaturally drawn out vertically. The depth of the body between the soft dorsal and anal fin origins is 63.6 mm (97.0% SL). The least depth of the caudal peduncle

is 20.1 mm (30.6% SL), this being substantially deeper than in the other two species of the genus. The length of the first dorsal spine is 24.6 mm (37.5% SL). The second

dorsal spine cannot be measured, but the third spine is 3.9 mm (5.9% SL). The number of dorsal and anal fin rays appears to have been similar, and between about 20 and 25. The vertebral column cannot be seen in the ab- dominal region, but the caudal series can be interpreted

as either 11, as in Recent species, or 12. The caudal fin appears to have 12 rays. There is a well-developed, es- pecially obliquely placed, supraneural strut supporting

the rear end of the carina. The basal pterygiophores have

exceptionally well-developed lateral flanges. The form and number of the teeth are poorly indicated as large incisors, with at least three probably located in an outer

series in the upper jaw. The stout pelvis has a low but

distinct dorsal lobe posteriorly, and there is some in- dication that the scales between the posterior end of the

pelvis and the anus were enlarged and elongate to support a small fan or dewlap in this region, as in most Recent species. The scale pattern is relatively well preserved, and the basal plates appear to bear two or three more

or less vertically oriented low emarginate ridges, substantially different from the condition of spinulation in the other two species of the genus.

In addition to the three species of Balistomorphus, one

other species of balistid is known from the Oligocene seas

of Europe. Oligobalistes robustus Danil'chenko (1960), known from three specimens of 27 to 60 mm SL from the Maikop deposits of the Caucasus, is the best preserved

fossil balistid. It has not been reexamined for this work, and the following is based on the description by

Danil'chenko. Oligobalistes differs from Balisto- morphus by having no surface sculpturing on the scale

plates, and by the better development of the second and

third dorsal spines (respectively 15 and 10% SL in Oligobalistes versus 8 and 4 to 6% SL in Balisto- morphus), although the first dorsal spine of Oligobalistes

is slightly less well developed (30% SL) than in one of the

species of Balistomorphus (B. orbiculatus, 37.5% SL). DanH'chenko believed Oligobalistes to differ from all of the Recent genera by the large size of the first dorsal spine and the presence of longitudinal rows of spinules along its anterior edge. The first dorsal spine is slightly longer, but not stouter, than in the adults of any Recent

genera, some of which (e.g., Rhinecanthus) have

longitudinal rows of spinules along the anterior and

lateral edges of the scales that are as well developed as in Oligobalistes. If the scales of Oligobalistes are completely smooth then it also differs in this respect from the Recent genera, all of which have at least low emarginations or spinules. The teeth in Oligobalistes were described as numbering four to six in each jaw, but presumedly any number above the four in an outer series (as found in all Recent species) represent misplaced teeth from another

outer series or from any of the inner series. The vertebral

column was described as 7 -I- 10, but the illustration clearly shows 11 caudal vertebrae, and a 7 -I- 11 column,

as in all Recent species. Danil'chenko thought Oligobalistes most closely

related to the Recent Balistes, but because of the ab- sence of a preocular groove, Oligobalistes is probably more closely related to Balistapus and Rhinecanthus, as discussed under Generic Relationships.

Generic relationships.—The generic relationships within the Balistidae are not especially clear on the basis

of the present work. Features that a priori seem generalized on the basis of the evolution of balistids from tria- canthids are a terminal mouth, well -developed third dorsal spine and overlapping scale plates. The relatively straight-edged or gently curved heavy

crushing incisors of triacanthids contrast to the slightly fewer in number, but at least superficially larger, notch- ed teeth basic to balistids. While slightly larger in sur- face area, balistid teeth are thinner edged and less heavy

than in triacanthids, except in very large individuals of most species of balistids, in which the teeth become just as massive if not more so than in triacanthids, while still retaining at least some degree of notching. The presence

of unnotched edges on the more medial teeth in adult Melichthys is not an indication of a generalized condition, for Berry and Baldwin (1966:449) have shown that

the teeth are normally cusped in juveniles and only

gradually do the more medial teeth become worn down to a relatively straight edge in adults, definite remnants of the notching always being present on the more lateral teeth. However, the dentition of Xanthichthys and Odonus

can surely be considered a specialization, with the en- largement of the second most medial tooth in the premaxillary and, in Odonus, of its cusp, into a fang. The

second most medial tooth in the dentary is also often

slightly larger in Xanthichthys and Odonus than it would be in other balistids. In contrast to all other

balistids, which have white teeth, the teeth oi Xanthichthys have a dark tinge, at least as adults (Berry and

Baldwin 1966:456), and those of Odonus are a deep red. Also in contrast to other balistids, the teeth in Xanthichthys and Odonus, as well as in Canthidermis, the only

truly oceanic balistid, do not become exceedingly massive and thickened in large adults, the dietary changes between juveniles and large adults in these three genera

apparently not being at all as extensive as in other The specialized condition of the anterior displace- ment of the suspensorium and lower jaw is found most

prominently in Xanthichthys and, especially, Odonus,

the mouth being distinctly supraterminal. The mouth in Melichthys is slightly supraterminal, but in other

balistid genera it is essentially terminal. Probably not much importance should be placed on

the size of the third dorsal spine as an indicator of

specialization and relationship. The third spine is not in- volved in the locking mechanism of the first two spines, and it has neither a complex basal articulation 120
Odonus

Xanthichthys

Melichthys

Sufflamen

Pseudobalistes

Balistomorphus

Oligobalistes (Oligocene)

Figure 66.—Hypothesized phylogenetic

relationships of the genera of Balistidae.

mechanism with its basal pterygiophore nor a complex

extensive musculature. The third spine functionally seems rather insignificant, and great variation in such a

structure can be expected, the variation from genus to genus or within a genus being of little value to deter- mining relationships. Thus, the minute third dorsal spine found in Rhinecanthus, Melichthys, and

Xanthichthys probably does not indicate close relation- ship between these three otherwise relatively dissimilar genera, nor does it necessEirily indicate that they are

specialized in the face of almost any other evidence to the

contrary. The third dorsal spine is well developed in the Oligocene genera Balistomorphus and, especially,

Oligobalistes. The significance of the presence of a preocular groove and of specialized flexibly articulated nonoverlapping

scales over the tympanal region above the pectoral fin base is difficult to interpret. Neither structure is present

in triacanthids. They occur only in balistids and not in the derived monacanthids. The fossil record of the balistids,

first known from the Oligocene, consists of less than a dozen specimens, many of them rather imperfect. The

specimens assigned to the three species of Balisto- morphus from the Oligocene of Switzerland, including

the holotypes of each, have recently been reexamined, and there is no indication of a preocular groove or of specialized tympanal scales, but these regions are not

well shown on any of the specimens. However, in describing the well-preserved Oligobalistes robustus from

the Oligocene of Russia, Danil'chenko (1960:173-174)

specifically says that a preocular groove is absent, while

his statement that there is a "small body plate with

radial sculpture situated directly behind gill slit, level

Figure 67.—Dentition of representative balistids: A. Baliatea polylepis, 56.1 mm SL, Galapagos;

. Xanthichthys lineopunctatus, 181 mm SL, Hawaii

C, Odonug niger, 173 mm SL, New Guinea:

3, Melichthys niger, 147 mm SL, locality unknown.
with dorsal end of latter" would seem to describe a modified tympanal scale. The two Recent genera which lack large tympanal

scales, Canthidermis and Xanthichthys, are otherwise

very different in structure and surely are not closely

related. It is simply impossible to say precisely at present whether the generalized condition of balistids is the presence of enlarged plates which have subsequently been lost by a few genera, or whether the basal balistids lacked specialized tympanal scales which were subsequently developed by most genera. I think the former view to be the more likely, and that the development of specialized tympanal scales aiding in and refining sound

production was one of the major features of the basal

balistids which led to their differentiation from the

triacanthids, concomitant with the reduction of the spiny dorsal fin and development of a complex locking mechanism of the first two spines, the reduction of the

pelvic fin and modification of the pelvis into a stout

rotatable shaft, and increased sturdiness of the skull to support the nonprotrusible jaws with a change in dentition. In this view, Canthidermis lacks specialized tympanal scales simply because all of its scales have become

relatively small and nonoverlapping, perhaps associated with the more flexible body covering necessary for lateral flexion of the caudal peduncle in a strong swimming and

truly oceanic species. Xanthichthys, on the other hand, seems closely related to Odonus, which has large specialized tympanal scales, and I have no explanation

for the lack of them in Xanthichthys, except that in Xanthichthys the scales in the tympanal region are smaller than those surrounding them, but they are not

overlapping and are just about as flexible as those of the tympanal region of other balistids. It would seem that

Xanthichthys has not truly lost the specialized tympanal scales, but simply reduced their size. It would be of

interest to know if the sound productions associated with

the drumming of the pectoral fin against the side of the body (and thereby against the anterolateral end of the swim bladder) differ in Canthidermis and Xanthichthys

from other balistids.

If the supposed absence of a preocular groove in the

fossil species of balistids, of which relatively complete specimens are known only from the Oligocene, is correct, then that structure is a more recent acquisition by

all genera except BaUstapus and Rhinecanthus. The

latter two genera are very closely related, differing only by Rhinecanthus having a lower supraoccipital crest, a much smaller third dorsal spine and a more constricted caudal peduncle with fewer rows of spine bearing scales. In fact, BaUstapus could serve as a model for a generaliz- ed balistid. The mouth is terminal, the third dorsal spine

well developed, the large specialized tympanal scales well developed, the encasing scales at the end of the pelvis with great flexibility (although with a slightly reduc- ed number of scales in one of the segments) and well- cusped teeth at all sizes and the teeth of decreasing size laterally in both jaws. It is possible, but hardly proven

here, that BaUstapus is a relative generalized balistid and that its lack of a preocular groove may also represent

the generalized condition. One final character must be considered, that of the

degree of development and massiveness of the supraoccipital and epiotic supports of the basal pterygiophores of the spiny dorsal fin. Is a high sturdy supraoccipital crest, such as found in most balistids, the generalized condition? In the early development of balistids from

triacanthids, it is reasonable to expect that the process of conversion of the domelike uncrested supraoccipital of ^W Figure 68.—Scales just above tip of pectoral fin of Balistoides viridescens

114 mm SL, Indonesia, to show

the hexagonal shape often obtained by

the scale plates in adults as the anterior and posterior edges of the rhomboid plate become flattened.

^* >£
triacanthids into the flatter and crested supraoccipital of

balistids passed through a low crest stage such as is found today in Rhinecanthus before achieving the higher and sturdier buttressing crest found in most other Recent

balistids. However, the low crest of Rhinecanthus could

well be a secondary reduction of the crest from a high

crested ancestral stock and simply be associated with the low nape of Rhinecanthus.

In short, the generic relationships within the

Balistidae are not clear on the basis of the osteological data presented here, nor are many of them clear on the

basis of external features. However, Xanthichthys and,

especially, Odonus, are two of the most specialized genera and are probably closely related, the former ancestral to the latter. Canthidermis is also specialized, in a much different way, for an oceanic existence, the scales

all being reduced in size and nonoverlapping and the body thus more flexible. Canthidermis is also specialized

in having the full ossification of the skeleton much

delayed, as well as in having the most rudimentary pel- vic apparatus among the balistids. Instead of the firm ossification and sturdiness of the skeleton of all other

balistids, the bones of specimens of Canthidermis under

about 100 mm remain poorly ossifed and slightly spongy, although not to the extent found in the molids Mola and

Masturus, but less ossifed than in the molid Ranzania. Only in fully adult specimens of Canthidermis is the

skeleton fully ossified. The pelvic fm ray of Canthidermis

is discussed below. Balistapus and Rhinecanthus are also obviously closely related, as explained above, the latter probably being

a specialized offshoot of the former. Likewise, Batistes (including Nematobalistes and Verrunculus, properly synonymized with Batistes by Berry and Baldwin

1966:435) and Pseudobalistes seem closely related, the

latter a derivitive of the former with reduced cheek scales and preocular groove. Sufftamen may be related to

Batistes, and Metichthys to Xanthichthys, hnt Abatistes and Batistoides are not clearly (to me) related closely to any of the groups of genera discussed above. I suppose

that the basic question is whether the Batistes-like genera are more generalized than the Batistapus-like genera. I suspect the latter are the more generalized, but

have no firm evidence of it. Fraser-Brunner (1935a:660-661) thought Canthidermis to be the most primitive genus, "since there is no

evidence that it is derived from any of the forms having

ossified plates behind the gill opening." With this I do

not agree, Canthidermis simply having lost the overlap- ping body scales found in all other genera, but from what

stock Canthidermis is derived I cannot say, although I would suspect a Batistes-like origin. Fraser-Brunner thought Abatistes to be a slightly modified derivative of Batistes on a line leading to Batistoides, Sufftamen, and Batistapus, with Rhine- canthus a derivative of the latter. He also thought

Batistoides to be ancestral to Pseudobalistes on the one hand and to Metichthys and hence Xanthichthys on the

other, with Odonus a derivative of Metichthys. I can add

nothing to these unproven speculations.

Relationship to the Monacanthidae.—Balistids are

clearly derived from triacanthids, with the major

changes involving the sturdier, stronger skull structure

associated with the nonprotrusible jaws with less massive crushing teeth, and heavier scales with less body

flexibility but more delicacy of swimming movements

associated with the sacrifice of speed for defensive

features, including the development of the complex

locking mechanism of the first two spines and a rotatable

pelvis. Balistids are likewise clearly ancestral to monacanthids, the major changes involving a reduction

in massiveness of the skull associated with the thinner, more sharply edged teeth serving a more nibbling

function with finer food and thinner, less regularly over- lapping scales associated with a sacrifice in defensive

features such as the reduction of the spiny dorsal fin and

less swimming strength for a more secretive and often

cryptic existence, blending into the environment rather than standing out conspicuously from it. The more

secretive monacanthids also tend to be much smaller in

size than balistids, which are among the largest of plec- tognaths (exclusive of molids), except that the four species oi Atutera all reach sizes in excess of 200 mm;

one, A. monoceros, reaching over 5(X) mm SL (Berry and Vogele 1961). The more important osteological differences between

the balistids and monacanthids, as pointed out in the comparative diagnosis of each, are mostly concerned

with the reduction in size and forward displacement of the spiny dorsal fin and its basal pterygiophores and the

features associated with the more delicate teeth and jaws and their supporting structures. The heavy crested supraoccipital of balistids supporting the front end of the first basal pterygiophore of the spiny dorsal fin becomes, at least posteriorly, a

delicate flattened plate in monacanthids upon which the

ventral surface of the basal pterygiophore rests, at least

in part. However, a few genera of monacanthids retain a

vestige of the large vertical crest of balistids as a smaller

crest on an anterior prolongation of the bone above the

orbit, the crest supporting the ventral edge of the vertical platelike anterior region of the basal pterygiophore. The deep hole in the balistid skull surrounded by the

supraoccipital and epiotics in which is held the short anteroventral shaft of the first basal pterygiophore is lost in monacanthids, and the epiotics in the latter no longer have the dorsal extension that in balistids helps buttress the apex of the skull for the support of the anterior end of the first basal pterygiophore. The second basal pterygiophore of balistids supporting the third spine is lost by monacanthids along with the third spine and the supraneural strut that in balistids supports the posterior end of the carina against the vertebral column. The second dorsal spine of balistids becomes much reduced in size in monacanthids, but the locking mechanism, involving

only the basal regions of the two spines, remains the same. The massive first dorsal spine of balistids becomes

more slender in monacanthids, and usually more highly ornamented with spinules and barbs. However, the first
124
125


Mltl

dorsal spine in some balistids (especially Rhinecanthus)

has its anterior face well ornamented with relatively large barbs, while some monacanthids have the first dorsal spine absolutely smooth. The first dorsal spine of

balistids serves, among other defensive functions, to wedge the fishes into holes and cavities that they seek out in danger and in rest. I suspect that the first dorsal spine in most monacanthids is used less in this manner

and more as a rapid vibrator in communication during

agonistic and breeding behavior. In some monacanthids

the spine can be vibrated back and forth with such speed

that it blurs before the eyes. The typical crushing dentition of balistids has been

converted in monacanthids to more of a nibbling form, while the massive supporting structures of the balistid jaws give way in monacanthids to a much more delicate suspensorium, the palatine being reduced in size and less intimately connected with the ectopterygoid, and the ethmoid and parasphenoid far less massive. The pharyngeal apparatus of balistids is changed in monacanthids

by the loss of the suspensory pharyngobranchial, the loss of teeth on the fifth ceratobranchial, and the usual loss of the second branchiostegal ray. A balistidlike pelvis is found in the more generalized monacanthids, although it usually is not quite so massive as in balistids. However, the main difference between the pelvic apparatus in balistids and generaliz- ed monacanthids is in the reduction in the size of the rudimentary fin ray (or spinous element) at the end of the pelvis and of the number of series of specialized

scales surrounding it. In all balistids there are four series of encasing scales, and in all but Canthidermis these

series have a dorsoventral flexibility. In the great majority of balistids the rodlike ossification extending posteriorly from the end of the pelvis, representing a com- pound formed from a right and left rudimentary and

highly modified fin ray or spine (see Tyler 1962b) of the otherwise absent pelvic fin, exits through a foramen in the fourth and last segment of encasing scales to protrude to the exterior. The compound rod usually is branched distally, although it has lost its segmentation. This is the condition found in the various species ex- amined of Batistes, Balistoides, Abalistes, Hemibalistes,

Balistapus, Rhinecanthus, Sufflamen, and Odonus. Of

the two species of Xanthichthys examined, the ray is like that in most other balistids in X. ringens, but in X.

lineopunctatus the ray is shorter, and, while branched

distally, it does not protrude to the exterior and there is no foramen in the last series of encasing scales in the

single large (181 mm) specimen examined. Since the ray

itself is similar in X. ringens and X. lineopunctatus other than the shorter distal portion in the latter, it is possible that small specimens of X. lineopunctatus have the ray protruding through a foramen which eventually closes over while the distal portion of the ray is resorbed. However, I have no small specimens of the relatively rarely collected X. lineopunctatus to examine for this. In both of the two species of Melichthys examined the fin- ray element is a large cone-shaped ossification representing only the anterior end of the element as found in most
Figure 74.—Lateral views of

relatively normal balistid skulls: above, Batistes capriscus. ca. 360 mm SL

Gulf of Mexico; below, B. polytepis,

ca. 390 mm SL, Mexico.

Other balistids. It does not project to the exterior and

there is no foramen in the last series of scales. In Melichthys the encasing scales are flexible in young specimens

but tend to become less flexible in large adults (Berry and Baldwin 1966). In Canthidermis, in which the en- casing scales are only slightly flexible even in young

specimens and more or less immovable in large adults, the fin-ray element is even more reduced than in Melichthys, being only a small conelike ossification at the end of the pelvis which is far too short to protrude to the exterior even if a nonexistant foramen in the last series of encasing scales were present.

In the more generalized monacanthids there are three

series of encasing scales, and there is always at least one

region of great dorsoventral flexibility between them. One of the encasing scale series of balistids has been lost,

but the flexibility retained, as is a dorsal lobe of the pelvis to strengthen the support of the modified enlarged

scales of the distensible skin between the end of the pelvis and the anus. In these generalized monacanthids the

fin-ray element is much more rudimentary than in

balistids, and, in contrast to the single rodlike piece of

balistids (except a stubby cone in Melichthys and

Canthidermis), the element in monacanthids is always

further reduced in size and divided into a dorsal and ventral half widely separated by the plug of cartilage on which they rest at the end of the pelvis. These two splints represent only the anterodorsal and anteroventral ends of the element as found in balistids. As discussed under the anatomical diversity of the Monacanthidae, about half of the species of that family examined have the above de- scribed generalized condition of the pelvic apparatus, a
supraoccipito

reduced but functionally similar version of that of

balistids, but the other monacanthids have further reduced the apparatus variously to the point of the total absence of a fin -ray element, encasing scales and dorsal

pelvic lobe. It is clear, however, that it was a balistid group with a flexible series of encasing scales that gave

rise to the monacanthids, the most generalized of which

also have a flexible series of scales. Probably associated with a greater body flexibility in monacanthids, the constant 7 + 11 = 18 vertebral for- mula of balistids is changed in monacanthids by an in- crease of at least one vertebra in the caudal series, and

often more. In balistids the basal pterygiophores of the

soft dorsal and anal fins bear a flange for muscle attach- ment along their lengths. This is true also of monacanthids, but in the latter family the crest is fur- ther elaborated, particularly distally, where it is es- pecially expanded laterally into a more or less hooklike

process partially separating the inclinator, erector, and

depressor muscles of each fin ray from those of the preceding and succeeding rays. The distal pterygio- phores are much less different between the two groups. Those of most balistids, like their triacanthid ancestral group, have the right and left halves fused into a single

piece, although far posteriorly in the soft dorsal and anal

fins the right and left halves may remain separate. The

distal pterygiophores of balistids may also be expected to be in separate halves in very young specimens. Of the

Figure 75.—Lateral view of most specialized

balistid skull and suspensorium: OdonuB niger, 173 mm SL, New Guinea.

balistids examined, only Balistes polylepis, B. capriscus, B. ueluta, and Sufflamen verres have most of the distal pterygiophores as separate halves, but the specimens of these are all relatively small, and the distal pterygiophores can be expected to be fused into a single piece in adult specimens of these species. Only in Canthidermis maculatus do the distal pterygiophores re- main as separate halves even in large specimens. In an

80.1 mm specimen nearly all the distal pterygiophores have separate halves, while in a large 217 mm adult

those in approximately the anterior one-third of the soft dorsal and anal fins have the two halves fused into a

single piece while more posteriorly they remain separate. The retention of mostly separate halves in the distal pterygiophores of Canthidermis is probably related in some way both to its oceanic existence and late develop- ment of full ossification. In the derived monacanthids, nearly all of the distal pterygiophores are single pieces even in small specimens, and always so in large specimens.
Figure 76.—Batistes polylepis: ventral

(left) and dorsal (right) views of skull, ca. 390 mm SL, Mexico.

Relationship to the Triacanthidae.—The presence

in balistids of such features as a well-developed spiny

dorsal fin, a well-developed pelvis with a pelvic fin (even though highly modified), discrete teeth in the jaws, a caudal fin with 12 rays, supported by a complex

with a free epural and parhypural, and a free palatine obviously relates the balistids to the triacanthoids, while a number of characteristics shared by balistids and triacanthids but not by triacanthodids indicates that the triacanthids are the most closely related ancestral group of the balistids.

The main features of similarity between balistids and

triacanthids, followed by the dissimilar condition in triacanthodids, as mostly summarized from Tyler (1968),

are: 1) large heavy incisorlike teeth in an outer series and more molariform teeth in the inner series versus

relatively smaller, conical to wide and thin in an outer

series £md, when present, of the same type in an inner

series; 2) hyomandibular with a well-developed crest across its outer surface versus no such crest; 3) pterotic with a large ventral flange over the posterodorsal end of the hyomandibular versus no such flange; 4) operculum
expanded in the middle about equally anteriorly and

posteriorly versus triangular in shape; 5) basihyal absent versus present; 6) pterosphenoids suturing to one

another in the midline of the posterior wall of the orbit versus not in contact there; 7) spiny dorsal fin base much

shorter than soft dorsal fin base (except Protacanthodes,

the bases about equal) versus much longer (except

Eoplectus, the bases about equal); 8) epipleurals

relatively thick versus thin; 9) basal pterygiophores of

soft dorsal and anal fins with lateral flanges along their lengths and sutured to one another distally versus without flanges and not sutured; 10) a single free hypural

(probably more in Protacanthodes) versus three or more

free hypurals; 11) uppermost pectoral fin ray very short, the lateral half smaller than the medial, versus moderately short, the two halves of about the same size.

It is extremely unlikely that this great array of. similarities between balistids and triacanthids in conil spine of Ist vertebra

of 1st vertebra

centrum of 2nd vertebra

Figure 77.BatUtes capriscus: ventral view

of sltull, ca. 360 mm SL, Gulf of Mexico.

tradistinction to triacanthodids has been arrived at in- dependently. There are only three important ways in which balistids are more similar to triacanthodids than to

triacanthids: 1) the parhypural is free; 2) the haemal

spine of the penultimate vertebra is autogenous; 3) and

the caudal peduncle is relatively shorter in balistids and triacanthodids than in triacanthids, except

Protacanthodes. These specializations of the Recent

triacanthids are associated with their more rapid sus- tained swimming in comparison to balistids and

triacanthodids, and it must be assumed that balistids evolved from triacanthids at a level of organization less specialized than that of the Recent species, probably at about the level of Protacanthodes. Although balistids (and, by implication, the monacanthids and ostracioids, which see) are clearly derived from triacanthids, the number of ways in which

balistids differ from triacanthids is impressive. Most of these differences are associated with the development in

balistids of: 1) a locking mechanism of the first dorsal spine through the agency of the second spine; 2) an even

heavier skull structure for greater buttressing of nonprotractile jaws adapted to an even heavier crushing or biting function of the teeth than found in triacanthids; 3) a rudimentary but complex pelvic fin-ray element; 4) heavier scales and less flexible body for less powerful sus- tained swimming but with greater delicacy of movement. The principal differences between balistids and

triacanthids, summarized and modified from Tyler

(1968), are as follows: There are usually six, and rarely only five, dorsal fin spines and usually four, rarely three

or five, basal pterygiophores supporting them in triacanthids, while in balistids there are only three

spines supported by two basal pterygiophores, although

the supraneural element of balistids is homologous to the

third basal pterygiophore of triacanthids, as discussed

subsequently.

In triacanthids there is an autogenous mechanism of locking the first dorsal spine in an erected position in- volving the apposition of its roughened ventral end

against the similarly roughened dorsal surface of the first basal pterygiophore below it, the first spine having an

anteroposterior canal through its base which rotates around a high dorsal pronglike flange on the basal pteryg- iophore, the locking mechanism not directly involving

the second spine. In balistids the locking of the first spine

is not autogenous, depending on a roughened area on the

slightly convex anteroventral surface of the second spine

fitting into a roughened medial concavity on the posteroventral surface of the first spine, while the first spine has no anteroposterior canal through it and the basal pteryg- iophore no pronglike flange. In triacanthids the first basal pterygiophore is of simple structure, being a stout vertical shaft articulated between the lower rear of the skull and the neural spine

of the first vertebra, except in the Oligocene Cryptobalistes in which it has only a short ventral shaft and ar- ticulates high on the rear of the skull and apparently out

132
of contact with the first vertebra. In balistids the first basal pterygiophore is a highly complex, horizontally elongate structure articulated high on the rear of the

skull by a short ventral shaft. The pterygiophore features

a concave dorsal surface in the region of the first two

spines that opens laterally through the wall of the pte- rygiophore to admit the muscles controlling the locking mechanism, there being nothing similar to this in tria- canthids.

In triacanthids the second basal pterygiophore, bearing the third spine, is relatively small, has a relatively

flat dorsal surface, and is not sutured to the first basal

pterygiophore, while in balistids it is relatively large, deeply concave dorsally, and is firmly sutured to the

first. The third basal pterygiophore of triacanthids, bearing the fourth spine, is probably the pterygiophore modified in balistids into the supraneural strut bracing

the rear end of the carina (formed by the first two pterygiophores) against the tip of the neural spine of the fifth vertebra and the anteroventral edge of the first basal pterygiophore of the soft dorsal fin. The articulation of the carina high on the rear of the

skull in balistids has drastically changed the configuration of the skull in this region, but it still bears evidence

of the triacanthid ancestry of the balistids. In both the

triacanthids and balistids the posterior surface of the

supraoccipital is concave, and while the supraoccipital of

balistids is so modified that it is no longer a simple dome,

it does exclude the epiotics from meeting one another on

the dorsal surface of the skull, and the epiotics contact

the frontals, just as in triacanthids and their ancestral hoUardiin triacanthodids, and not as in the tria- canthodin triacanthodids. The face that one Oligocene triacanthid {Cryptobalistes) has the otherwise

triacanthidlike spiny dorsal fin articulated high on the

rear of the skull by a short ventral shaft, even though the more numerous basal pterygiophores are small and do

not form a carina, and there is neither a supraneural

strut nor a locking mechanism between the first two

spines, shows the potentiality and preadaptation of the

triacanthids to give rise to the balistid-type spiny dorsal

fin and pterygiophores.

In triacanthids the premaxillary pedicels are well developed and help allow the protusibility of the upper

jaw, while the premaxillary and maxillary are movably

articulated to one another through fibrous tissue. In

balistids there are no premaxillary pedicels, the upper

jaw is not protrusible and the premaxillary and maxillary are immovably held to one another, often by suturing. The palatine in triacanthids is a flat squarish bone

with an anterior prong articulating with the deeply

recessed dorsolateral surface of the maxillary, while in balistids the palatine is T-shaped, the anterior end of the

cross bar articulated with a slight concavity on the dorsolateral surface of the maxillary. In triacanthids there are usually five teeth in an outer series in each half of each

jaw, internal to which are one or two teeth in each half of the upper jaw and one in each half of the lower jaw. In

balistids there are always four teeth in an outer series in each half of each jaw, and three inner series teeth in each

half of the upper jaw but none in the lower jaw. Thus,

balistids have slightly reduced the number of teeth as found in triacanthids, and also modified their form. In triacanthids the edges of the teeth are straighter than in the typically notched teeth of balistids, and while the

size of the teeth in balistids is usually larger than that of triacanthids, they are thinner and less massive, except in most large adult balistids in which the teeth become just as massive as in triacanthids. The teeth in the balistids Canthidermis, and, to a lesser extent, Odonus and

Xanthichthys, do not tend to become so massive in large

adults. In triacanthids the pelvis is shaftlike only posterior to the level of the pelvic spines in about the middle of its length and cannot be rotated around its anterior ar- ticulation with the cleithra. In balistids the pelvis is shaftlike throughout its length and can be rotated in a

vertical plane around its anterior articulation with the

cleithra, while the pelvic fin is represented by a rudimentary but complex structure representing the fused fins from each side at the posterior end of the pelvis, sur- rounded by enlarged encasing scales. Whether this complex fusion product of the pelvic fins represents the

spines or rays of triacanthids is problematical. One sus- pects that because the fin rays in triacanthids are

relatively rudimentary and often lost while the spines are always well developed, that, in the process of reduction

of the pelvic fin from that of triacanthids to that of

balistids, the rays would be irrevocably lost early in the

process, leaving the spine alone to become further reduc- ed in size and eventually fused with its opposite member

at the rear of the pelvis. As the spine became of relatively minute size and less fully ossifed, it may have secondarily become branched distally, as in many balistids, this branching of the unstriated element perhaps not at all homologous to that of rays.

It is possible that the reduced spine migrated posteriorly along the shaftlike posterior portion of the pelvis eventually to arrive at its extreme posterior end while at the same time the anterior half of the pelvis became

shaftlike and rotatable. This seems more likely to me

than to account for the position of the balistid pelvic fin as a result of the loss of the shaftlike posterior half of the

triacanthid pelvis at the same time that the spine was

reduced and the anterior half of the pelvis was becoming

shaftlike and rotatable and also greatly elongate so that

the stationary spine was moved posteriorly to the anal

region by the growth of the anterior half of the pelvis rather than by migration. The shaftlike form of at least the posterior half of the pelvis in balistids, triacanthids, and hoUardiin

triacanthodids is additional evidence of the phylogenetic validity of their relationship. The vertebrae of triacanthids are 8 -f 12, while those of

balistids are 7 -(- 11. In triacanthids there are three tooth- ed pharyngobranchials following the toothless suspensory element, but only two toothed elements in balistids. In triacanthids the hyomandibular is supported dorsally by the prootic, pterotic, and sphenotic, but in balistids only by the prootic and pterotic. In triacanthids there is 133
no prootic shelf such as is present in balistids. In triacanthids the interoperculum extends posteriorly to the suboperculum, but in balistids it is shorter and more

rodlike, not extending posteriorly beyond the epihyal. In triacanthids the parasphenoid is a relatively narrow

shaft in front of the orbit, but it is greatly expanded there

into a thick plate in balistids. In triacanthids the vomer

is larger and less concave anteriorly than in balistids, which lack the posterolateral wings that in triacanthids suture to the long forward extensions of the prefrontal (with the possible exception of Protacanthodes) . In triacanthids the posttemporal is larger and more superficially held to the skull than in balistids. The above outline of the similarities and differences between triacanthids and balistids clearly indicates that while balistids are highly differentiated from

triacanthids, the latter are the closest ancestral group of the balistids, and that the level of organization of the Recent triacanthids (and their close Oligocene relatives) is too specialized in a few ways for their consideration as being ancestral to balistids. Moreover, the same line of triacanthids that gave rise to the balistids also gave rise to the a^acanids, and the few features of both balistids and aracanids that are more generalized than in Recent

triacanthids must have been present in the early triacanthids leading to the balistids and aracanids. These few generalized features required of the early triacanthids are: 1) a free parhypural; 2) haemal spine

of penultimate vertebra autogenous; 3) caudal peduncle

relatively deep and not yet elongate and highly tapered and the caudal fin not deeply forked; 4) soft dorsal fin base probably not yet highly elongate; 5) the uppermost

pectoral fin ray only moderately reduced in size and the two halves still of about equal length; 6) the teeth not yet enlarged to massive incisors but somewhat intermediate between conical and incisorlike; 7) the prefrontal not yet with a long forward extension alongside the ethmoid

sutured anteriorly with posterolateral wings of the vomer; 8) the second and third basal pterygiophores of the spiny dorsal fin not yet greatly reduced in size. Among the fossil triacanthids, the Oligocene Acanthopleurus and Marosichthys are so like the Recent

triacanthids that they are unlikely to be closely related to the line of early triacanthids giving rise to the balistids and aracanids, while the Oligocene Cryptobalistes has

certain balistid features in its configuration which shows

the possibility of triacanthids being able to give rise to certain balistidlike features, even though Cryptobalistes seems to have been an evolutionary dead end unrelated

to the line of triacanthids which were ancestral to the

balistids. The Eocene Protacanthodes, which is inter- mediate between the triacanthodids and triacanthids, is the only known example of the early triacanthids, and of those features of its anatomy that are exposed it is generalized enough to encompass some of the critical generalized features required of the triacanthid line leading to the balistids and aracanids as listed above.

In Protacanthodes the condition of the uppermost pectoral fin ray, the parhypural and the haemal spine of the penultimate vertebra are not known, but the caudal

peduncle is relatively deep and of only moderate length and the caudal fin is rounded. These are conditions to be

expected in the balistid-aracanid ancestral line, except

that the caudal peduncle of Protacanthodes is probably

already somewhat too long for that line. The more medial

of the teeth in the jaws aie large incisors with constricted distal ends, and thus somewhat notched, while more laterally the edges were relatively straighter. While

the teeth in Protacanthodes may have been slightly smaller than in Recent species (except Trixiphichthys), they are probably already slightly too enlarged and in- cisorlike to be conveniently ancestral to those of the

balistid-aracanid line, even assuming that early balistids had less massive teeth than at present and that those of

early aracanids were larger and less conical than at present. The prefrontal in Protacanthodes is large and has

at least a moderate anteroventral extension alongside the ethmoid, although there is no evidence that it formed a

long process articulating anteriorly with the vomer, and

it is better separated anterodorsally from the ethmoid

than in Recent triacanthids. Thus, the prefrontal of Protacanthodes is not known to have been much more

specialized than in the balistid-aracanid line, although it may have been slightly more specialized. The soft dorsal

fin base in Protacanthodes is not yet greatly elongate, and the second and third basal pterygiophores of the

spiny dorsal fin are still moderately large, even though

the spiny dorsal fin base is much shorter than in the ancestral triacanthodids. The second basal pterygiophore

articulates ventrally with the tip of the neural spine of the second vertebra and the third basal pterygiophore to that of the third, so that the articulations of both of these pterygiophores has already shifted forward relative to the

condition in triacanthodids. In the line ancestral to

balistids and aracanids the third basal pterygiophore would be expected to retain an articulation with a more

posteriorly located neural spine, as in triacanthodids, and especially as in Eoplectus, as discussed in detail

there. Thus, the second and third basal pterygiophores of Protacanthodes are already slightly too specialized to be

conveniently ancestral to the condition postulated to be

necessary in the balistid-aracanid line. While Protacanthodes is by far the most generalized of the triacanthids, a number of its characteristics (caudal peduncle length, tooth size and shape, placement of

third basal pterygiophore of spiny dorsal fin) are already

slightly too specialized for it to have given rise to the

balistids and aracanids. The divergence of the balistid- aracanid line must have taken place among the early triacanthids at a slightly more generalized (that is, more

triacanthodidlike) level of organization than as seen in certain anatomical regions of Protacanthodes. In this

light the line of early triacanthids derived of a hollardiinlike triacanthodid ancestry diverged into one line leading with little change to Protacanthodes and to another line which after far greater change gave rise to the balistids and aracanids, the latter diverging the furthest from the common triacanthid ancestral stock, and the

Protacanthodes line continuing on to give rise to the Triacanthinae and probably Cryptobalistinae as well.
Family Monacanthidae

Comparative dia^osis (contrast with that of the

Balistidae).—The more or less incisorlike teeth relatively more delicate, developed for nibbling, three outer and

two inner on each premaxillary, and three, occasionally only two, in a single series on each dentary; pharyngobranchials consisting only of two uniserially toothed

elements; fifth ceratobranchial toothless but with a

series of gillrakers along its anterior edge (posterior edge

of last gill slit); usually two dorsal spines, sometimes

only one, the second spine, when present, not more than

about one-third the length of the first, and usually much

smaller, ending ventrally in delicate ventrolaterally directed prongs from either side; dorsal fin spines sup- ported by a single basal pterygiophore, without a supraneural strut; dorsal spines and at least most of the length

of the basal pterygiophore placed over the top of the

skull; no lateral foramen in the basal pterygiophore to ac- commodate the venterolateral prongs of the second dorsal spine; at least the posterior region and usually all of the supraoccipital a flat or slightly rounded thin plate without a vertical crest and broadly overlain (only slightly in Psilocephalus) by the first basal pterygiophore above it, while in some genera an anterior prolongation of the supraoccipital above the orbit bears a vertical crest

for articulation with the ventral edge of the vertical platelike portion of the anterior region of the first basal

pter>-giophore; posterior region of the epiotic not ex- panded dorsally, the medial edges of the two epiotics in contact throughout their lengths, there being no large foramen in the skull between the epiotics and the supraoccipital; palatine more or less rodlike, never distinctly T-shaped, but sometimes with a bulge or short process on

its ventral edge representing a rudiment of the long foot of the T as found in balistids, usually connected by a long ligament with the anterior edge of the ectoptergiod; exoccipital not meeting its opposite member in the midline above the foramen magnum, only slightly if at all

protruding medially beyond the medial edge of the bifid neural spine of the first vertebra; prefrontal relatively small and delicate, articulated by fibrous tissue mainly

with the frontal and sometimes, to a much lesser extent, with the ethmoid, but never directly contacting the para- sphenoid; parasphenoid moderately to much expanded

laterally just behind the orbit (except in the elongate

Psilocephalus), the medial edge of the pterotic on the

ventral surface of the skull broadly separated from its opposite member there by the basioccipital and para- sphenoid; parasphenoid not expanded or only very

slightly expanded dorsally in front of the orbit, only

slightly if at all overlying the ethmoid and not contacting the prefrontal; the laterally expanded dorsal

region of the ethmoid relatively narrow and thin, much

less wide than the depth of the ventral platelike portion

ventral platelike flange of the ethmoid thin and delicate

relatively deep, much deeper posteriorly than an

teriorly, and only slightly if at all overlain by the para

sphenoid; posttemporal (absent in Psilocephalus) held more superficially and in a much less deep groove on the

lateral surface of the pterotic; medial edge of dentary al- ways denticulate; prootic shelf less well developed (and sometimes absent), not extending forward to the level of the middle of the orbit, except in Psilocephalus in which

it reaches the front of the orbit; posterior edge of supra- cleithrum relatively straight and not posteriorly ex- panded; postcleithrum without a dorsal spur on its dorsal edge and no specialized tympanal region present; postcleithrum always a single piece; branchiostegal rays

2 -(- 4, 1 -I- 4, or 1 -I- 3; pelvis with or without a dorsal lobe

posteriorly on its dorsal surface; encasing scales at the

posterior end of the pelvis in three or fewer segments, or

of indeterminate number or absent, when present either

flexible or fixed; a rudimentary pelvic fin element either present or absent; vertebrae 19 (usually 7 -I- 12, sometimes

6 + 13) or more (7 or 8 -I- 13 to 23), up to 30; vertebrae

Figure 78.—Range of diversity in body form in the Monacanthidae:

A. Monacanthus ciliatus; B. Amansea acopas;

C. Brachaluteres trossulus; D, Pnlocephalua barbatua.
anterior to the first basal pterygiophore of the soft dorsal

fin four to eight, those posterior to the last basal pteryg- iophores of both the soft dorsal and anal fins four to six; neural and haemal arches of the last centrum poorly developed and nearly always incomplete (complete in Brachaluteres trossulus); the last centrum with a

horizontal crest for muscle attachment (reduced to a prong in B. trossulus); uroneurals never present; an

upper free hypural occasionally absent; lateral flanges on the soft dorsal and anal fin basal pterygiophores ending distally in prominent hooklike lateral expansions, except in Chaetoderma spinosissimus and Rudarius

minutus; the basal pterygiophores extending proximally

relatively closely to the neural and haemal arches

usually only anteriorly in the length of the series; all of the dorsal, anal, and pectoral fin rays unbranched;

scales small, with thin basal plates and usually fine spinulation, the basal plates either overlapping or well separated but usually not regularly arranged; scales above the pectoral fin base unmodified; most species

relatively small, adults usually being 2(X) mm or smaller, except for some species of a few genera (e.g., Cantherhines, Nauodon) that have larger adults and, especially, Alutera. at least one species (monoceros) of which

reaches over 5(K) mm (Berry and Vogele 1961:66).

Detailed description of Monacanthua ciliatua. Material examined.—Twelve cleared and stained specimens, 38.3-119 mm.

SKULL.

Occipital Region.

Basioccipital. —A short column, expanded anterodorsally; cartilage filled at its anterior and anterodorsal

edges; articulates by interdigitation dorsally with the

exoccipitals, anteroventrally with the prootics, and

anteromedially with the overlying posterior end of the parasphenoid. The rim of the round concave posterior end of the basioccipital articulates by fibrous tissue with

the concave anterior face of the centrum of the first vertebra. The ventromedial surface of the basioccipital is deeply concave throughout its length. This concave

channel is mostly hidden from view by the overlying parasphenoid, but the channel opens to the exterior posteriorly at the base of the posterior bifurcation of the parasphenoid. Anteriorly the channel opens into the myodome where the anterior end of the basioccipital forms the posterolateral and posterodorsal walls of the myodome.

Exoccipital. —Cartilage filled along most of its ventral, anterior, and dorsal edges; articulates through cartilage and slight interdigitation dorsally with the epiotic,

laterally through cartilage and interdigitation with the

pterotic, and ventromedially mainly through inter- digitation with the basioccipital. Posteriorly the exoccipitals form the lateral and ventral walls of the foramen magnum, while dorsally the foramen is closed by the

epiotics. The posterior surface of the exoccipitals is firmly attached by fibrous tissue and interdigitation with

the anterior surface of the bifid neural spine of the first vertebra. A short posterior process from the postero- medial portion of the exoccipital overlies the upper anterior region of the centrum of the first vertebra, this posterior extention representing the modified exoccipital condyle.

Supraoccipital. —Widest posteriorly, where its relatively flat dorsal surface is mostly obscured from ex- ternal view by the large basal pterygiophore of the spiny

dorsal fin, but with a long forward extension above the

orbit with a vertical crest intervening between the frontals and the anterior third of the basal pterygiophore;

cartilage filled along all of the edges of its posterior flat- tened surface; articulates dorsally by interdigitation with

the basal pterygiophore of the spiny dorsal fin, posteriorly through cartilage and interdigitation with the

epiotics, laterally and anteriorly, and ventrally on its anterior prolongation, through interdigitation with the

frontals, while the extreme anterior end of the anterior extension reaches to the posterior end of the ethmoid in large specimens.

Figure 79.—Monacanthua ciliatus: upper left, nasal region as seen

externally (far left) and the olfactory lamella as seen with the top of the nasal

sac removed; middle left, scales from

upper middle region of body, including two lateral line canal bearing scales: lower left, ventral view of encasing scales

at end of pelvis (anterior to left).
Otic Region.

Pterotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates through cartilage and interdigitation dorsally with the

epiotic, posteriorly with the exoccipital, ventromedially on the ventral surface of the skull with the basioccipital and parasphenoid, anterolaterally with the sphenotic,

laterally through extensive interdigitation with the posttemporal which overlies a portion of its lateral surface, and anteroraedially in the region of the orbit by interdigitation with the prootic. The anteroventral

region of the pterotic is prolonged ventrally as a shaft

like projection overlying and extending ventral to the

posterodorsal end of the hyomandibular, to which it articulates by fibrous tissue. Just anteromedial to its ventral shaft the pterotic bears a deep depression which

continues over the prootic and to which depression the

dorsal head of the hyomandibular is held by fibrous tisSphenotic. —Cartilage filled along all of its edges of articulation with the other cranial bones except for its anteroventral prong; articulates in the orbit through cartilage and interdigitation anteromedially with the ptero- sphenoid, prootic, and pterotic; articulates anterolaterally by extensive interdigitation with the frontal, posterodorsally through cartilage and slight inter- digitation with the epiotic, and posteroventrally with the

pterotic.

Epiotic. —Cartilage filled along all of its edges of articulation with the other cranial bones; articulates dor- somedially by extensive interdigitation with the overlying basal pterygiophore of the spiny dorsal fin. Below

this articulation with the basal pterygiophore the dor- somedial edge of the epiotic articulates through cartilage and interdigitation with its opposite member in the

midline. Anteriorly the epiotic articulates through

cartilage and interdigitation dorsally with a short portion of the posterior edge of the supraoccipital and

through extensive interdigitation along most of its anterior edge with the frontal, while anteroventrally

it articulates through cartilage and interdigitation with the posterodorsal edge of the sphenotic. Ventrally

the epiotic articulates through cartilage and inter- digitation with the pterotic and exoccipital, while the

posterolateral surface of the lower half of the epiotic

is broadly overlain and articulates by interdigitation with the bifid neural spine of the first abdominal

vertebra.

Prootic. —Cartilage filled along all of its edges of

articulation with the other cranial bones, except antero- medially; articulates by interdigitation medially with

the lateral surface of the parasphenoid, anteromedially

with the ascending fork of the parasphenoid, through

cartilage and interdigitation anterodorsally with the pterosphenoid, anterolaterally with the sphenotic, and

posteriorly with the pterotic. A deep concavity on the

ventral surface of the prootic articulates by fibrous tissue with the anterior half of the dorsal head of the hyomandibular. The medial edges of the prootics form the lateral walls of the myodome, while medially directed shelves from the medial edges of the prootics meet in the midline and articulate through cartilage and fibrous tissue with one another to form the dorsal roof of the myodome. The

anterior edge of the myodome is formed by the prootics, except ventrally, where it is formed by the para- sphenoid. The anterior end of the prootic is prolonged

anteriorly as a subocular shelf which serves for muscle at- tachment.

Orbital Region.

Frontal. —Widest posteriorly, tapering to a point

anteriorly; its lateral edge above the orbit only slightly upraised and thickened; articulates by interdigitation posteromedially with the flattened posterior portion of the supraoccipital, which it slightly overlies, posteriorly with the epiotic, and posteroventrally with the sphenotic.

Posteriorly in the rear of the orbit it articulates by fibrous

tissue with the pterosphenoid and by interdigitation with

the sphenotic. Medially above the orbit the frontal

slightly overlies and articulates by fibrous tissue and

slight interdigitation with the ventrolateral edge of the

anterior extension of the supraoccipital, just posterior to which the frontal is broadly overlain and articulates by

extensive interdigitation with the laterally expanded

middle region of the basal pterygiophore of the spiny dorsal fin. The frontal interdigitates anteriorly with the eth- moid, whose posterodorsal surface it broadly overlies, while laterally at the front of the orbit the frontal articulates by interdigitation with the dorsolateral surface of the prefrontal. On its ventral surface, the medial edges of the frontals are separated by the cartilaginous mass

which is continuous anteriorly with the remains of the ethmoid cartilage.

Prefrontal. —Expanded dorsolaterally;

filled along its medial edge below the frontal; articulates by interdigitation dorsomedially with the frontal, while ventromedially it is continuous with the ethmoid

cartilage lying between it and its opposite member and

the posterior end of the ethmoid.

Parasphenoid. —Elongate, expanded laterally only

posteriorly in the region below the rear of the orbit; ventrally expanded into a thin keel in the region below and

just anterior to the orbit. The bifurcate posterior end of the parasphenoid broadly overlies the ventral surface of the basioccipital in the region of the deep concave groove

in the latter, roofing over in this region the channel

leading into the myodome. Articulates posteriorly by in- terdigitation with the basioccipital, pterotics, and

prootics. Under the posterior region of the orbit the para- sphenoid possesses a pair of short, slightly forked, dorsolateral projections which interdigitate with the prootics and form the anterior edge of the ventral region of the myodome. Anterior to the orbit the dorsal surface of the 137
parasphenoid is concave and receives the rounded ventral edge of the platelike portion of the ethmoid, to which

it articulates by fibrous tissue. The anterior end of the parasphenoid is deeply concave to receive the posterior

shaftlike portion of the vomer, to which it is held by

fibrous tissue.

Pterosphenoid. —Cartilage filled along all of its lateral edges of articulation with the other cranial bones;

articulates through cartilage and fibrous tissue with the

frontal, which broadly overlies it, and through cartilage and interdigitation with the sphenotic and prootic. Medially the pterosphenoid possesses a projection toward

the midline which interdigitates with a similar projection from its opposite member, the pterosphenoids here meeting in the midline. The pterosphenoids also are iri contact through cartilage at their extreme dorsomedial

ends.Ethmoid Region. Ethmoid. —Elongate and deep; expanded laterally along its dorsal region but a deep flattened plate ventrally, the rounded edge of the ventral plate fitting into a concavity along the dorsal surface of the anterior end of the parasphenoid and held there by fibrous tissue. More

anteriorly the ventral edge of the ethmoid articulates by

fibrous tissue and light interdigitation with the dorsal surface of the anterior half of the vomer. Posterolaterally the dorsal surface of the ethmoid is overlain and

interdigitated to the extreme anterior ends of the frontals. Posteriorly the ethmoid articulates through its cartilage filled posterior edge with the anteroventral car- tilaginous ends of the prefrontals. The anterior end of the ethmoid is somewhat more laterally expanded than is the

dorsal edge behind it, especially ventrally where a flange protrudes anteroventrally and articulates through

fibrous tissue with the posterior end of the palatine. The

extreme anterior end of the ethmoid remains somewhat

cartilaginous centrally, and it is against this cartila- ginous face that the rear edge of the premaxillary abuts

in rotation. Vomer. —An elongate shaft except anteriorly where

it is laterally expanded; articulates posteriorly at its shaftlike portion by fibrous tissue to the concavity at the

anterior end of the parasphenoid; articulates by fibrous

tissue and slight interdigitation dorsally with the anteroventral end of the ethmoid, while anteriorly it helps support the posterior end of the upper jaw.

Mandibular Region. Hyomandibular. —A flat shaft for most of its length, somewhat expanded dorsally; cartilage filled anteroventrally; the posterior edge thickened for articulation by fibrous tissue with the preoperculum and, just above the dorsal end of the latter, with the anterodorsal head of the operculum; articulates by fibrous tissue dorsally with the groove on the ventral surfaces of the

prootic and pterotic, while posterodorsally the hyomandibular abuts against and is firmly held by fibrous tissue along the medial surface of the elongate portion of the

ventral flange of the pterotic. The articulation with the head of the operculum is at a slight bulge of the hyo- mandibular whose concave face is cartilage filled and

abuts against the similarly cartilage filled head of the operculum. The anteroventral end of the hyomandibular articulates variously through cartilage and fibrous

tissue with the posterior end of the metapterygoid,

symplectic, interhyal, and preoperculum.

Quadrate. —Widest posteriorly, tapering to a knob

anteriorly for articulation with the articular in the lower

jaw; cartilage filled at its posterior edge; deeply cleft along its posterior edge to accommodate the anterior end

of the symplectic; articulates dorsally by extensive inter- digitation with the ectopterygoid, while posteriorly it ar- ticulates through cartilage with the mesopterygoid and

metapterygoid; articulates by fibrous tissue and inter- digitation with the symplectic. Ventrally the quadrate

articulates by fibrous tissue with the preoperculum.

Metapterygoid. —A large flat plate curving

medially along its dorsal edge; cartilage filled at its anterior and posterior edges; articulates anteriorly through cartilage with the quadrate while anterodorsally it is overlain and interdigitated with the

mesopterygoid and anteroventrally extensively inter- digitated with the symplectic. Along the middle of its ventral edge it articulates through fibrous tissue with the

dorsal end of the interhyal. Posteroventrally the metapterygoid articulates through fibrous tissue and cartilage with the preoperculum and anteroventral edge of the hyomandibular.

Symplectic. —A flattened shaft; relatively large; cartilage filled at its posterior and, to a lesser extent, anterior edges; articulates by extensive interdigitation posterodorsally with the metapterygoid and anteriorly with the indented region of the quadrate; ventrally ar- ticulates by fibrous tissue and, in some cases, by slight interdigitation with the dorsal edge of the preoperculum. The posterior cartilaginous end of the symplectic is in contact with the region of articulation between the in- terhyal and metapterygoid.

Palato-Pterygoid Region.

Palatine. —A more or less simple short rod with a

slight bulge along its ventral edge for articulation by

fibrous tissue with the extreme anterodorsal edge of the

ectopterygoid; articulates anteriorly by fibrous tissue with the dorsal head of the maxillary and posteriorly with the lateral flanges of the ethmoid and, to a lesser extent, with the anterolateral expansion of the vomer.

Ectopterygoid. —Elongate; more or less triangular, the apex of the triangle being anterior in the middle of its length where the ectopterygoid articulates through
fibrous tissue with the middle of the ventral edge of the

palatine; articulates by extensive interdigitation ventrally with the quadrate and posteriorly with the

mesopterygoid.

Mesopterygoid. —A small plate extensively inter- digitated anteriorly with the ectopterygoid and, to a

slight extent, with the quadrate in some specimens, and

posteriorly with the metapterygoid; its anteroventral edge in contact with the cartilaginous region between the quadrate and the mesopterygoid.

Opercular Region. Operculum. —More or less thin and flat, except

dorsally where it thickens into a rounded shaft with an

articular facet for articulation by fibrous tissue with the

posterior edge of the dorsal region of the hyomandibular,

while ventrally it overlies and articulates by fibrous

tissue with the suboperculum.

Suboperculum. —Very thin, flat, and oblong; held

to the overlying operculum by fibrous tissue.

Interoperculum. —A straight rod, tapering slightly to a point anteriorly; extends from the region of the in- terhyal to just beyond the anterior end of the preoper- culum; articulates by a tough ligament anteriorly with

the angular in the lower jaw, while at its posterior end

two ligaments are present. One is short and connects

with the dorsal surface of the epihyal just below the ar- ticulation of the latter with the interhyal, while the other one is long and runs posteriorly to connect to the anterior edge of the operculum just above the point where the operculum begins to overlie the suboperculum.

Preoperculum. —Expanded in its middle region; its dorsal surface only slightly flattened for articulation with

the quadrate; articulates along the posterior portion of

its dorsal edge by fibrous tissue with the hyomandibular, along the middle portion of its dorsal edge through

cartilage and fibrous tissue with the symplectic,

metapterygoid, and interhyal, and along the anterior portion of its dorsal edge by fibrous tissue with the quadrate.

Upper Jaw.

Premaxillary. —A medially curved plate, wider

dorsally than ventrally; its posterodorsal edge slightly concave to articulate by fibrous tissue with the anterior ends of the ethmoid and vomer. It also articulates by

fibrous tissue laterally with the medial surface of the

palatine, although the main articulation of the latter is with the maxillary. The anterior edge of the premaxillary forms the entire anterior border of the upper jaw and only

shares the border with the maxillary ventrally. The

premaxillary is in close apposition with the maxillary and articulates immovably with it by fibrous tissue and

slight interdigitation. The flat dorsomedial edges of the

two premaxillaries are held closely to one another by

fibrous tissue. Each premaxillary bears five teeth, three

in an outer row and two in an inner row. Both of these rows are in close contact with one another. The teeth are borne in very shallow depressions on the surface of the premaxillary in their fully formed condition. They

develop, however, from large deep sockets which open to the surface just at the base of the old tooth which they

will replace. As a tooth erupts to the surface to replace an

old tooth, the socket from which it arose apparently is overgrown or filled in with bone and disappears and the

tooth rests only in a shallow depression on the surface of the premaxillary. Most of the interior of the premaxillary

is given over to the dental pulp cavities, these cavities communicating with the exterior through numerous

holes on the inner and outer surfaces of the bone.

Maxillary. —Widest ventrally, becoming narrow in the middle, and expanded again dorsally where it ar- ticulates with the anterior head of the palatine; articulates firmly with the premaxillary by fibrous tissue and

slight interdigitation. The medial surfaces of the ventral

rti-ioiis of the maxillary and, to a lesser extent, of the premaxillary articulate with the lateral surface of the upper portion of the dentary, by fibrous tissue. The posterodorsal surface of the maxillary articulates by fibrous

tissue with the lateral expansions of the ethmoid and vomer and with the medial surface of the palatine.

Dentary.—Wide posteriorly; its posterior edge

concave to accommodate the anterior portion of the £tr- ticular, with which it articulates by interdigitation. Posteroventrally the dentary articulates by fibrous tissue and slight interdigitation with the angular. From the

lateral surface of its posterodorsal region the dentary ar- ticulates by fibrous tissue with the medial surfaces of the maxillary and, to a lesser extent, of the premaxillary. Ventromedially the dentary has broad denticulations with which it articulates through fibrous tissue with its opposite member. Each dentary bears three teeth in a

single row, corresponding to the outer row in the premaxillary. The teeth are borne in shallow sockets on the sur- face of the dentary and are replaced by new teeth developing in deep sockets just as described for the teeth

of the upper jaw. Most of the interior of the dentary is filled with the pulp cavity of the developing teeth, the

cavity opening to the exterior at the concave posterior edge of the dentary as well as at pores on the inner and

outer surface of the bone.

Articular.—Wide along its posterior edge, with a concave facet for articulation by fibrous tissue with the

anterior knob of the quadrate; articulates by interdigi- tation with the concave posteromedial surface of the dentary. At its extreme posteroventral edge the articular

interdigitates slightly with the angular. The sesamoid ar- ticular is a small nubbin of bone closely held by fibrous
tissue to the medial surface of the articular just in front

of and above the concave articular facet of that bone.

Angular. —A small wedge of bone articulated by

interdigitation dorsally with the articular and anteriorly with the dentary. Posteriorly the angular connects by

ligament with the interoperculum. BRANCHIAL APPARATUS.

Hyoid Arch, Branchiostegal Rays, and Urohyal. Hypohyals. —Both hypohyal elements well de- veloped, and of about equal size; the dorsal element

cartilage filled at its ventral and posterior edges, the ventral element cartilage filled at its dorsal edge; the two

elements articulate with one another through the cartilage that lies between them; the dorsal and ventral elements articulate by fibrous tissue at their antero- medial edges with their opposite members. The dorsal hypohyal articulates posteromedially by fibrous tissue with the lateral surface of the first basibranchial. The

posterior edge of the ventral hypohyal and a short portion

of the posteroventral edge of the dorsal hypohyal articulate through cartilage and fibrous tissue with the

ceratohyal, while the medial surface of the ventral hypohyal is held by fibrous tissue to the anterodorsal

region of the urohyal.

Ceratohyal. —A flat shaft, wider posteriorly than

anteriorly; cartilage filled at its lower posterior edge; ar- ticulates through cartilage anteriorly with the ventral hypohyal and, to a lesser extent, with the dorsal hypohyal; articulates posteriorly through cartilage and

interdigitation with the epihyal. K six branchiostegal

rays are present, the first two rays articulate in about the middle or just behind the middle of the ventral edge of the ceratohyal. However, only five branchiostegal rays

are usually present and only one articulates to the ventral edge of the ceratohyal. Of the four branchiostegal

rays always present in the posterior group, the lower two

or even three have their fibrous tissue articulation primarily with the lateral surface of the posterior end of the ceratohyal in the region immediately below the inter- digitation with the epihyal.

Epihyal. —Large, about the same size as each of the hypohyals; cartilage filled at its ventral edge; articulates through cartilage and interdigitation anteriorly with the ceratohyal, while dorsally it articulates by

fibrous tissue with the interhyal and interoperculum.

Interhyal.—A short, thick rod; cartilage filled at both ends; articulates by fibrous tissue ventrally with the

epihyal and dorsally with the extreme posterior end of the symplectic and the ventral edge of the metapterygoid

just behind the symplectic.

Branchiostegal rays. —Usually five in number. Of

the 12 specimens examined, 11 have five branchiostegals on each side, one articulated to the middle of the

ventral surface of the ceratohyal and four articulated to the lateral surfaces of the posterior and ventral ends of, respectively, the ceratohyal and epihyal. However, one specimen has five branchiostegals on one side and six on

the other. The side with the five branchiostegals has a

typical arrangement of one ray articulated to the ventral

surface of the ceratohyal and four articulated to the

lateral surface of the ceratohyal and epihyal. On the one

side with six branchiostegals, two are articulated to the

ventral surface of the ceratohyal and the other four more

posteriorly. In the illustration of the branchial apparatus

of M. ciliatus. the additional branchiostegal ray occasionally present is indicated by dashed lines, this being

the branchiostegal ray immediately behind the large

first branchiostegal articulated to the ventral surface

of the ceratohyal. The branchiostegal rays are all articulated by fibrous tissue to the ceratohyal or epihyal. The first branchiostegal is much wider than are the succeeding rays, the more posterior of which are so narrow that they are, in essence, slender rods.

Urohyal. —Thick along its anterior and anterodorsal edges, otherwise a relatively thin plate; articulates by

fibrous tissue anterodorsally between the medial edges of the ventral hypohyal, while posteriorly it articulates with

the ventral surfaces of the posterior end of the first basibranchial and the anterior end of the second

basibranchial.

Branchial Arches.— All the elements are cartilage

filled at their edges of articulation with the other elements of the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and two pairs of pharyngobranchials. Four gills are present, with a slit between the

fourth arch and the lower pharyngeal.

First arch.—Basi-, hypo-, cerato-, and epibranchial elements present. First basibranchial short, wider

posteriorly than anteriorly; articulates posteriorly with

the second basibranchial and posterolaterally with the

first hypobranchial. First hypobranchial of increasing width posterodorsally; the largest of the hypobranchial

elements, which decrease in size posteriorly in the series; articulates ventrally with the region of articulation between the first and second basibranchials and dorsally with the first ceratobranchial. First ceratobranchial a

stout rod; the longest of the ceratobranchial elements, which decrease in length posteriorly in the series; no ventrally directed flange present on the ceratobranchials, ex- cept for the fourth, which is somewhat compressed and

has a small ventral flange basally; articulates ventrally with the first hypobranchial and dorsally with the first epibranchial. First epibranchial a flattened plate, rounded ventrally where it articulates with the cerato-
hyal but then diverging into two prongs; the anterior prong articulates by fibrous tissue with the ventral

keel of the parasphenoid just anterior to the middle of the orbit, while the posterior prong articulates with

the anteriormost pharyngobranchial (that of the second

arch) and the dorsal end of the second epibranchial. The

pharyngobranchial element of the first arch is absent.

Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial the longest of the three elements of the series and slightly wider posteriorly than anteriorly; articulates anteriorly with the first basibranchial, anterolaterally with the first hypobranchials, posteriorly with

the third basibranchial, and posterolaterally with the second hypobranchials. Second hypobranchial wider

posterodorsally than anteroventrally; articulates ventrally with the area of articulation between the second and

third basibranchials and dorsally with the second cerate- branchial. Second ceratobranchial a long rod with a

slightly expanded ventral end; articulates dorsally with

the second epibranchial. Second epibranchial a short

rod; articulates dorsally with the second pharyngobranchial and, to a lesser extent, with the posterodorsal arm of the first epibranchial. Second pharyngobranchial

(the first of the two remaining elements of the series) an

oblong block bearing on its ventral surface a row of about

five slender sharply pointed teeth and articulating ventrally with the dorsal end of the second epibranchial and

the posterodorsal projection of the first epibranchial. New teeth develop in sockets just behind and below the bases of the old teeth.

Third arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Third basibranchial a short column, widest in the middle; articulates

anteriorly with the second basibranchial, anterolaterally with the second hypobranchials, posterolaterally with

the third hypobranchials, and posteriorly with the

fourth ceratobranchials. Third hypobranchial rounded

posteriorly but with a short tapering anteroventral

process that articulates by fibrous tissue anteriorly with the ventral surface of the more anterior basi- branchials and the posterior arm of the urohyal; arti- culates posterolaterally with the third ceratobranchial and posteromedially with the posterior end of the third basibranchial. Third ceratobranchial expanded ventrally but shaftlike more distally; articulates ventrally with its opposite member and with the third hypobranchial, and

dorsally with the third epibranchial. Third epibranchial

rodlike distally and expanded in the middle region; ar- ticulates dorsally with the third pharjoigobranchial; the expanded middle region is directed anteriorly and ar- ticulates with the basal region of the second

epibranchial. Third pharyngobranchial like the second

pharyngobranchial except smaller and usually with only

three teeth, the teeth slightly smaller than those of the

other pharyngobranchial; articulates ventrally with the

distal ends of the third and fourth epibranchials. The two

pharyngobranchial elements are held to one another by

fibrous tissue. Fourth arch. —Cerato- and epibranchial elements

only. Fourth ceratobranchial more compressed than the

other ceratobranchials and with a narrow ventral flange;

articulates ventrally with the ventral end of its opposite member and that of the third ceratobranchial. Fourth

epibranchial rodlike, only slightly larger in the middle

than at either end; articulates ventrally with the fourth ceratobranchial and dorsally with the third pharyngobranchial.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial the shortest of the

ceratobranchial elements; ntirrowest dorsally, widest in the middle, and with an expanded base articulating with

the base of the fourth ceratobranchial; toothless.

PAIRED FIN GIRDLES.

Pectoral Fin.

Posttemporal. —A short relatively straight shaft broadly overlying the lateral surface of the pterotic and,

to a lesser extent, the sphenotic and extensively inter- digitated to both, and therefore immovably held to the

skull; articulates ventrally through fibrous tissue with

the dorsal head of the supracleithrum.

Supracleithrum. —A straight shaft of bone oriented more or less vertically to the axis of the body; most of its medial surface broadly overlying and held by fibrous

tissue to the lateral surface of the upper end of the

cleithrum, while dorsally it articulates immovably

through fibrous tissue with the head of the posttemporal.

Cleithrum. —Laterally expanded at its anterior edge in the middle of its length; articulates by fibrous

tissue dorsally with the overlying supracleithrum and

with the upper end of the postcleithrum, which it broadly

overlies. Along its posterior edge the cleithrum overlies the anterior region of the scapula and coracoid and ar- ticulates with both through fibrous tissue and slight in- terdigitation. Along the ventral two-thirds of its length

the medial edges of the two cleithra are firmly held to one

another by fibrous tissue, while ventromedially they also

articulate through strong fibrous tissue with the anterior end of the shaftlike portion of the pelvis which is closely held between the two cleithra.

Postcleithrum. —The postcleithrum is a long

flattened strong strut not divided into dorsal and ventral

parts. The dorsal end of the postcleithrum articulates by

fibrous tissue with the dorsomedial surface of the cleith- rum. The postcleithrum is angled obliquely down from

its upper point of attachment toward the region of the abdominal wall in front of the dorsal lobe of the

pelvis.
Coracoid. —Widest dorsally, tapering to a shaft

ventrally; with a slender spinelike process under the lowermost actinost from its posteroventral edge; the upper one-third of its posterior edge with an intumed flange medially; cartilage filled at its dorsal end and at the tip of its ventral shaft; articulates by fibrous tissue and in- terdigitation anteriorly with the cleithrum, which

overlies the upper anterior edge of the coracoid; articulates anterodorsally through cartilage with the scapula;

posterodorsally the edge of the coracoid supports the lowermost and largest actinost and sometimes, to a les- ser extent, the lower edge of the base of the third acti- nost.

Scapula. —Completely encloses the scapular foramen; cartilage filled at its anterior and ventral edges;

articulates anteriorly by fibrous tissue and slight inter- digitation with the cleithrum, while ventrally it articulates through cartilage with the coracoid. Along its posterodorsal edge the scapula articulates by fibrous tissue with the following elements, in order from anterior to posterior or above to below: the first and uppermost

pectoral fin ray attached to a projection from the surface

of the scapula, immediately below which the scapula

supports on a small flange the small uppermost actinost, with the second and third actinosts articulating along

the relatively unmodified posterior edge of the sca- pula, although the posterodorsal edge of the coracoid

helps to support the lower basal region of the third acti- nost.

Actinosts. —Four elements; all cartilage filled at both ends; the first actinost small, the others increasing

slightly in size from above to below in the series; articu- lated to the scapula and coracoid as described in the preceding section. Distally the actinosts support by

fibrous tissue all of the fin rays except the first, which is supported by the scapula.

Fin rays. —Twelve fin rays in most specimens, with

the first ray about one-tenth the length of the second ray and articulated directly with the scapula, rather than

with the actinosts, as are the other rays. First ray with its medial half enlarged and thickened at its basal region of

articulation with the scapula; its lateral half reduced to a

thin short splint closely held to the medial half. All of the

pectoral fin rays unbranched; the first ray without crossstriations, all the other rays cross-striated.

Pelvic Fin.

Pelvis. —A stout shaft; not divided into separate

right and left halves; anterior three-fourths of its lateral surface with a concavity for muscle attachment; a large

relatively slender dorsal lobe present from its posterodorsal region which serves as a place of tough fibrous

tissue attachment for the overlying skin of the highly dis- tensible abdominal area or ventral flap (dewlap). A

series of enlarged scales encircle the posterior end of the

pelvis and obscure from view the rudimentary fin-ray element present in the midline just behind the end of the

pelvis. The lateral surface of the posterior end of the

pelvis bears several ridges for articulation with these

scales. The scales occur in three segments, with only the

distal segment movably articulated, the major region of

flexibility in the series being between the second and

third series. The fin-ray element is reduced to a single nubbin of bone above and below the plug of cartilage that extends posteriorly from the end of the pelvis, as describ- ed in detail by Tyler (1962b:229-232, figs. 38-45). These bony nubbins, representing the remains of a fin-ray (or spinous) element, are closely held by fibrous tissue to the

cartilaginous plug. Running anteriorly from each of the nubbins is a tendon. The tendon from the dorsal nubbin

courses through a hole in the dorsal flange of the pelvis to attach to a muscle housed in the concave region on the

dorsal surface of the pelvis, while the tendon from the

ventral nubbin runs along a similar concavity on the ventral surface of the pelvis. The fin-ray nubbin and the at- tached plug of cartilage at the end of the pelvis are movable in a dorsoventral plane around the posterior end

of the pelvis by the contractions of the muscles on the

dorsal and ventral surface of the pelvis to which they are connected by ligament. The pelvis itself is movable in a dorsoventral plane around its fibrous tissue attachment

between the ventromedial edges of the cleithra.

VERTEBRAL COLUMN. —All vertebrae with

biconcave centra, except the last, which posteriorly ends

in a plate representing the fused centrum, hypurals, and

parhypural. Abdominal Vertebrae.

First vertebra. —Neural spine shorter than those of the succeeding vertebrae but sturdy; laterally expanded,

bifid to the centrum and thus not forming a bony roof over the neural canal; articulates by extensive interdigi- tation along most of its anterior face with the exoccipitals and epiotics. The rim of the concave anterior face

of its centrum articulates by fibrous tissue with the rim

of the concave posterior end of the basioccipital, while

the rim of its posterior face articulates similarly with the rim of the anterior face of the second vertebra. Anteriorly between the region of the centrum and the neural arch, the first vertebra is slightly overlain by the short exoccipital condyle. From the lower region of its posterolateral surface the centrum possesses a short posteroventrally directed process which makes fibrous tissue contact over the anterior fifth of the lower surface of the centrum of the second vertebra, although this is mostly

obscured from lateral view by the lateral flange of the second vertebra. Other abdominal vertebrae. —In 12 specimens the abdominal vertebrae numbered six. Except for the first vertebra, all the abdominal vertebrae, as well as all of the 142
caudal vertebrae except the last, possess bony roofs over

the neural canal and have single, undivided neural

spines. The neural spines of the abdominal vertebrae are

all of about the same length but they are of increasing width posteriorly in the series. Their edges of apposition

articulate with one another through fibrous tissue and, in some cases, slight interdigitation. Each neural arch has a

neural foramen in its lateral surface. Haemal prezyga- pophyses are weakly developed on a few vertebrae, but mostly they are absent or insignificant. Except for the

first, all of the abdominal vertebrae have transverse

processes which bear epipleural ribs. These processes become increasingly laterally expanded and stouter posteriorly in the series. The transverse process of the second

vertebra arises in about the middle of the anterior region

of the centrum, but the transverse processes of the subse- quent vertebrae originate low on the centrum. The

epipleurals articulate by fibrous tissue to the dorsolateral surfaces of the transverse processes. The trans- verse processes of the fifth and sixth abdominal

vertebrae have posteromedial flanges from each side which make contact with the haemal regions of the succeeding vertebrae, roofing over the haemal canal under the fifth and sixth vertebrae, while more anteriorly the haemal canal is open. The first basal pterygiophore of the soft dorsal fin articulates between the neural spines

of the fourth and fifth vertebrae, the articulation being by fibrous tissue. The second basal pterygiophore of the

soft dorsal fin articulates similarly between the neural

spines of the fifth and sixth abdominal vertebrae.

Caudal Vertebrae. —The caudal vertebrae number 11

in 12 specimens. The neural spines of the caudal

vertebrae become less expanded anterodorsally and in- creasingly shorter posteriorly in the series, except for the

last few vertebrae, behind the soft dorsal and anal fin bases, which have the neural and haemal spines expanded. All of the caudal vertebrae, except for the last, possess complete neural and haemal arches and spines. Haemal pre- and postzygapophyses are essentially absent, but neural pre- and postzygapophyses are distinctly developed in both the caudal and abdominal series. The

sturdy haemal spine of the first caudal vertebra is somewhat concave ventrally along its posterior surface and slightly bifurcate at its extreme distal end. It is against the posterior surface of this haemal spine that

the first basal pterygiophore of the anal fin is firmly held by fibrous tissue. The haemal spines of the second and

third caudal vertebrae are progressively slightly longer than that of the first, but more posteriorly the length of the spines decreases until those of the 10th to 12th

vertebrae, which are of increased length. The length of the neural spine similarly decreases posteriorly in the

series and then increases behind the soft dorsal fin base. The haemal spine of the penultimate vertebra is auto- genous. The haemal and neural spines of the last caudal

vertebra are described below.

Caudal Skeleton. —The caudal complex usually

consists of an epural, a free parhypural, and a large plate composed of the centrum fused to the hypural elements. The free epural and parhypural are of about equal size. The neural arch of the last centrum is incomplete, the

neural canal not being roofed over. Similarly the haemal

canal is not roofed over and its presence is simply in- dicated by an indentation in the anteroventral edge of the hypural plate just below the centrum and above the

dorsal end of the parhypural. The fused hypural plate bears a horizontal keel for muscle attachment on the rear portion of the centrum area and anterior region of the

fused hypurals. There is also a deep indentation on the middle of the posterior edge of the fused plate, this in- dentation representing what would be the division between the second and third hypurals in a more

generalized plectognath having five free hypurals. The

above is the condition found in 10 of the 12 study

specimens. However, as described and illustrated by

Tyler (1970b:16, fig. 31), 2 of the 12 specimens have an

upper free hypural, representing the fifth hypural of generalized plectognaths. The presence of an upper free hypural is the norm for the family, all species examined

having one with the exception of, usually, M. ciliatus, and the several specimens of Rudarius ercodes and

R. minutus cleared and stained or radiographed, and

the single specimen of Amanses scopas cleared and

stained.

Caudal fin ra.vs. —Twelve in number; the uppermost

ray and the lowermost ray unbranched, the others becoming increasingly branched toward the middle fin rays, which are branched in triple dichotomies. The bifid bases of the fin rays articulate by fibrous tissue with the caudal skeleton as follows: the upper six rays to the upper half of the fused hypural plate and the lower six rays

to the lower half of the plate.

DORSAL AND ANAL FINS.

Dorsal Fin Spines and pterygiophores. —Two spines borne on a

large and elongate basal pterygiophore. First spine long and moderately stout; second spine much smaller, consisting of a basal rounded region, a slender tapering distal end and, from the ventrolateral edge of the basal ex- panded region, a laterally projecting flange for muscle

attachment. The concave ventromedial region of the first spine rotates over a low medial flange on the pterygio- phore, while posteromedially the first spine has a ventrally directed flange which rotates into a deep concavity on the basal pterygiophore just behind the medial flange. The thick posterior region of this posteromedial flange of the first spine is roughened and makes contact with the

similarly roughened anterior edge of the basally expanded portion of the second spine to form the locking mechanism. The concave ventral surface of the second

spine rotates over a low medial flange on the pterygio- 143
phore just posterior to that supporting the first spine. The second spine also has a very short and blunt pos- teromedial expansion which is accommodated in a low

concavity on the pterygiophore just behind the medial

flange over which the base of the spine rotates. The lock- ing mechanism of the two spines is basically similar to that in the Balistidae and continuous positions of erec- tion from partial to full are possible. The ventral surface of the basal pterygiophore is strongly interdigitated with the top of the skull, especially with the frontals, and extends forward to the level of the prefrontals. In addition to the frontals, the basal pterygiophore is interdigitated with the supraoccipital and epiotics. The pterygiophore is especially sturdy and

laterally expanded in the region below the first dorsal

spine.

Fin rays and pterygiophores. —There are usually between 30 and 36 fin rays; all of the rays unbranched,

but with cross-striations. In the illustrated specimen the

31 fin rays are borne on an equal number of basal

pterygiophores. Each fin ray has a small, unpaired, distal pterygiophore between the bifurcate base of the ray. Each basal pterygiophore, except for the last several, has

a well-developed lateral ridge along its length, except at the very proximal and distal ends of the element, for muscle attachment. The lateral ridges decrease slightly

in height posteriorly in the series. Distally the ridge is es- pecially laterally expanded and curved slightly ventrally

to form a hooklike process. The first basal pterygiophore

is slightly the largest in the series, the other pterygio- phores decreasing slightly in length posteriorly in the

series. The first basal pterygiophore articulates by

fibrous tissue between the neural spines of the fourth and

fifth abdominal vertebrae, while the last few basal pterygiophores are between those of the 9th and 10th caudal vertebrae. Posterodorsally the first basal

pterygiophore interdigitates with the second basal pterygiophore, and all of the subsequent basal pterygio- phores are extensively interdigitated to one another

along their edges of contact, except for the last few basal pterygiophores which are held to one another mainly by

fibrous tissue instead of extensive interdigitation. Just below their distal ends the successive pterygiophores are not in close contact and a foramen is formed between

their apposed edges. The degree of interdigitation between the pterygiophores decreases slightly in the

series posteriorly, as does their degree of contact with the

neural spines supporting them. The basal pterygial elements are cartilage filled at their dorsal and ventral

edges.

Fin rays and pterygiophores. —There are usually between 30 and 35 fin rays supported by an equal number of basal pterygiophores or by only one or two less than the number of rays; all of the rays unbranched but

with cross-striations. In the illustrated specimen the 31

fin rays are supported by 29 basal pterygiophores. Each

fin ray has a small, unpaired, distal pterygiophore between its bifurcate base. The basal pterygiophores of the anal fin are similar to those of the soft dorsal fin and

bear the same kind of lateral flanges for muscle at- tachment along most of their lengths. The first two basal pterygiophores of the anal fin articulate by fibrous tissue between the haemal spines of the first and second caudal

vertebrae, while they articulate by extensive interdigi- tation with one another, as do the other pterygiophores in the series. This interdigitation decreases posteriorly in the series to the extent that the last few pterygiophores

articulate to one another mainly by fibrous tissue. The

pterygiophores decrease slightly in length posteriorly in the series, as does the height of their lateral flanges. There are usually three to four anal fin basal pterygio- phores articulated between successive haemal spines, whereas in the dorsal fin there are usually only two or three basal pterygiophores between successive neural

spines, this because the number of basal pterygiophores

in the dorsal and anal fins is similar, whereas the dorsal

fin is longer based and extends over more vertebrae than

does the anal fin.

Anatomical diversity. —The monacanthids are one of the more diversified families of plectognaths, comparable in many ways to the degree of diversity found in the Recent triacanthodids, although without as much

diversity in dentition and with no indication of two major

phyletic lines within the family such as is evident in the Recent triacanthodids. Fossil species of monacanthids

are not yet known, although the ancestral balistids have

been found as early as the Oligocene. The monacanthids, with about 90 species, are one of the most

speciose families of plectognaths, only the tetraodontids having more species, perhaps a few over 100. Even

though two subfamilies of tetraodontids (tetraodontins and canthigasterins) are easily recognizable and none

such are in the monacanthids, the latter still are probably more anatomically diversified than the former. That is, there is no sharp break in the structural continuity of monacanthids, while there is in tetraodontids between Canthigaster and the tetraodontins, only partially bridged by Carinotetraodon. Most monacanthids have an only slightly elongate body form, similar to that of balistids, although they

tend to be thinner bodied (more laterally compressed) than balistids. However, monacanthids range from those

of nearly perfectly rounded outline {Brachaluteres, Chaetoderma), in which the greatest body depth, in- cluding the normal pelvic region expansion, approaches

the standard length, to the extremely elongate Psilocephaluti, whose depth is contained many times in the standard length. Although always over the top of the head, the place- ment of the first dorsal spine is variable, ranging from

over the rear edge of the eye (many genera) to well forward of the eye (Pseudaluteres only), while in most

genera it originates somewhere over the rear half of the

eye. Two dorsal spines are present in all genera except

basal pterygiophi

Figure »2.—Monacanthu» ciliatus: dorsal (left) and ventral (right) views of skull, 51.3 mm SL, Colombia.

Brachaluteres and Psilocephalus, in which only the first spine remains. The single spine of Brachaluteres is rela- tively well developed, but that of Psilocephalus is very

short and weak, as is its pterygiophore. In most genera

the first dorsal spine is ornamented with downward and

backward projecting spiny processes, especially along the two posterolateral edges, while the anterior surface is usually ornamented with smaller and less regularly ar- ranged barbs, these oriented either upward, downward,

or straight forward. However, a few genera have the barbs on the anterior face of the spine as well developed,

or almost so, as on the posterolateral edges: Laputa, Chaetoderma, Arotrolepis, and Acanthaluteres . Others have a relatively low and plain ornamentation over most

of the surface of the spine which is not greatly rougher

than that of the skin: Amanses, Cantherhines, and

Alutera. In a few genera (Brachaluteres and Pseudaluteres) there are low barbs mainly on the anterior face, these continued onto the posterior face only distally. In two genera, Paraluteres and Psilocephalus, there are no

barbs at all. In Paraluteres the barbs have obviously been lost in conjunction with the role of this filefish as a mimic of the pufferfish Canthigaster valentini, the spine being covered by smooth scaleless skin and probably not

fully erectile in life. The smoothness of the spine of Psilo- cephalus is undoubtedly related to the reduction of the

spine in that genus. The second dorsal spine is always much smaller than

the first and is absent in Brachaluteres and Psilocephalus. The second spine always has a sturdy rounded basal 146
Figure S3.—Monacanthut cUiahu: posterior views of skull (left) and

of orbit (right) (cross section of skull; dashed

lines represent cut surfaces of frontals, supraoccipital. basal pterygiophore of spiny

Jorsal fin and parasphenoid), 81.3 mm SL, Florida.

region for locking contact with the posterior edge of the posteromedial flange of the first spine and has a pair of ventrolateral processes for muscle attachment, but the

length of the thin narrow distal shaft of the second spine

is variable. The distal shaft is usually so short that it is difficult to see as it lies buried in the narrow band of skin between the posterior edge of the first spine and the dor- somedial edge of the body just behind it, and even when

relatively long, it never conspicuously protrudes through

the skin.

Figure 84.

Monacanthus ciliatus: dorsal view of branchial arches

(extended on lower side); lateral view of hyoid arch and urohyal;

75.7 mm SL, Florida.

^epibranchials '^pharyngobranchials

rohyal

dorsal hypohyal

ceratohyal

branchiostegal rays 147
lateral flanges

dorsal tendon

dorsal portion o(

fin ray element

muscle attachment ventral portion of

fin ray <

Figure S5.—Monacanthus ciliatus: above, lateral view of pelvis and encasing scales at end of

pelvis which completely obscure from external view the rudimentary fin-ray element; below,

detail of the end of the pelvis, with the encasing scales removed to expose the rudimentary

rin-ray element and its cartilage plug and

tendons: 81.3 mm SL, Florida.

Figure 86.—External features of Monacanthus chinenais. for comparison

with those of M. ciliatus:

'

, nasal region as seen externally

(far left) and the olfactory lamella as seen with the top of the nasal sac removed;

middle left, scales from upper middle region of body, including two lateral line canal bearing

scales; lower left, ventral view of encasing

scales at end of pelvis (anterior to left).
Figure 87.—External features of other representative monacanthid

genera: Stephanolepis cirrhifer— upper left, nasal region as seen

externally (far left) and the

olfactory lamella as seen with the top of the nasal sac removed;

middle left, scales from upper middle

region of body, including two

lateral line canal bearing scales; lower

left, ventral view of encasing scales

at end of pelvis (anterior to left). -Hr%^"^^

Figure 88.—External features of other representative monacanthid

genera: Chaetoderma spinosissimus- upper left, scales from upper middle

region of body, including two

lateral line canal bearing scales; middle left, nasal region as seen externally (olfactory lamella, if present, indistinct in specimen examined); lower left, ventral view of encasing scales at end of pelvis (anterior to left).

Figure 89.—External features of other representative monacanthid

genera: Paramonacanthus curtorhynchuaupper left, nasal region as seen

externally (far left) and the olfactory lamella as seen with the top of the nasal sac removed; middle left, scales from upper middle region of body, including ivio lateral line canal bearing scales; lower left, ventral view of encasing scales at end of

pelvis (anterior to left).

149
Figure 90.—External features of other representative monacanthid

genera: Pervagor melanocephalusupper left, nasal region as seen

externally (far left) and the

olfactory lamella as seen with the

top of the nasal sac removed;

middle left, scales from upper

middle region of body, including

three lateral line canal bearing

scales; lower left, ventral view of encasing scales at end of pelvis (anterior to left).

Figure 91. —External features of other

representative monacanthid genera: Rudarius ercodes —upper left, nasal

region as seen externally (olfactory lamella, if present, indistinct in specimen examined); middle left, scales from upper middle region of body, including two lateral line canal bearing

scales; lower left, ventral view of encasing scales at end of pelvis (anterior to left).

Figure 92.—External features of other

representative monacanthid genera: Navodon hypocrepis —upper left, nasal

region as seen externally (far left) and

the olfactory lamellae as seen with the

top of the nasal sac removed; middle left, scales from upper middle region of body, including a lateral line canal bearing

scale; lower left, ventral view of encaging scales at end of pelvis (anterior to left).

150
Figure 93.— External features of other

representative monacanthid genera: Eubalichthys spilomelanurus —upper

left, nasal region as seen externally

(far left) and the olfactory lamella as seen with the top of the nasal sac removed;

lower left, scales from upper middle

region of body, including a lateral line canal bearing scale; no encasing scales at end of pelvis (or below it).

Figure 94.—External features of other

representative monacanthid genera: Cantherhines pullus—upper left, nasal

region as seen externally (far left) and

the olfactory lamella as seen with the

top of the nasal sac removed: middle

left, scales from upper middle region of body, including two lateral line canal bearing scales; lower left, ventral view of encasing scales at end of pelvis (anterior to left).

Figure 95.—External features of other

representative monacanthid genera: Amanses scopas—upper left, nasal

region as seen externally (far left) and

the olfactory lamellae as seen with

the top of the nasal sac removed; middle

left, scales from upper middle

region of body, none of which have

apparent lateral line canals or pores; lower

left, ventral view of encasing scales at end of pelvis (anterior to left).

Figure 96.—External features of other

representative monacanthid genera: Alutera monoceros —upper left, nasal

region as seen externally (far left) and

the olfactory lamella as seen with the top

of the nasal sac removed; low-er left, scales from upper middle region of body,

including a lateral line canal bearing

scale; no encasing scales at end of pelvis

(or below it).
Figure 97.—External features of other

representative monacanthid genera

Pailocephalus barbalus—upper left, nasal region as seen externally

(olfactory- lamella, if present,

indistinct in specimen examined); lower

left, scales from upper middle region of body, including a series of numerou>>

lateral line canal bearing scales; no

encasing scales at end of pelvis (or below it).

Figure 98.—External features of other

representative monacanthid genera Oxymonacanthus longiroatris— upper left, scales of upper middle region of body, includin three lateral line canal bearing scales, middle left, nasal region as seen externally

(olfactory lamella, if present, indistinct

in specimen examined); ventral view of

scales at end of pelvis (anterior

to left).

Figure 99.—External features of other

representative monacanthid genera: Pseudaluterea nasicornU—upper left, nasal region as seen externally

(olfactory lamella, if present,

indistinct in specimen examined); lower

left, scales of upper middle region of body (specialized lateral line canal or pore-bearing scales absent); no encasing

scales at end of pelvis (or below it).

Figure 100.—External features of other

representative monacanthid genera: Paraluterea prionurus—upper left, nasal

region as seen externally (olfactory lamella, if present, indistinct in specimen

examined); lower left, scales from upper middle

region of body, including a lateral line canal bearing scale; no encasing scales at end of

pelvis (or below it).

152
Figure 101.—External features of other

representative monacanthid genera: Brachaluteres trossulus —upper left, nasal

region as seen externally (olfactory lamella.

if present, indistinct in specimen examined):

lower left, scales from upper middle region

of body, including a lateral line canal bearing scale; no encasing scales at end of

pelvis (or below it).

The size and shape of the basal pterygiophore supporting the spiny dorsal fin are highly diverse among the monacanthids. It is expectedly least developed in Psilo- cephalus, in which only a single, short, thin rudi- mentary spine is present. The basal pterygiophore of Psilocephalus is a thin triangular bone (as seen in lateral view) whose dorsal edge is only slightly expanded laterally and whose ventral edge is held by fibrous tissue only

anteriorly to the dorsal surface of the supraoccipital. The

dorsal surface of the pterygiophore at the place of articulation of the spine is only slightly expanded laterally and

upraised to support the equally only slightly laterally ex- panded base of the spine, the whole mechanism being far

less complex than in other monacanthids.

In all other monacanthids the basal pterygiophore is relatively much larger and sturdier than in Psilocephalus. Most typically, as illustrated for Monacanthus ciliatus, it is a large bone whose flattened or gently curved ventral surface is closely applied by fibrous

tissue and sometimes interdigitation to the dorsal sur- face of the skull from the level of the front or middle of the eye posteriorly, obscuring much of the supraoccipital from view. It is laterally expanded in about the middle of its length into two thick buttresses supporting

the articular facets of the base of the first spine, while

posteriorly an upraised medial buttress supports the sec- ond spine, posterior to which the basal pterygiophore becomes a thick vertical plate with a laterally expanded,

slightly concave, dorsal edge. Anterior to the large lateral expansion supporting the first spine, the pterygiophore

rapidly narrows into a thinner vertical plate whose dorsal edge is slightly expanded laterally and either flatten- ed or convex. The region of the pterygiophore posterior to the second spine is supported mainly by the epiotics, while the middle region is supported by the supraoccipital, and, especially in the case of the buttresses for the first spine, by the frontals. Anterior to the first spine, the laterally compressed portion of the pterygiophore is supported by the frontals alone in most genera, but by

the supraoccipital as well in those three genera (Monacanthus, Stephanolepis, Paramonacanthus) in which

that bone extends far forward above the orbit as a low

vertical crest (the possible phylogenetic significance of which is discussed under the section on generic relationships). The above applies well to most of the genera in which

the first dorsal spine is above or behind the middle of the

eye, with the basal pterygiophore extending from behind

the skull to about the level of the front of the eye. In Paraluteres, with the dorsal spine distinctly in front of the eye, the basal pterygiophore is enormously elongate, reaching nearly the entire length of the skull, although it retains the same basic makeup as in more normal monacanthids. The basal pterygiophore in Paraluteres articulates posteriorly with the supraoccipital, which it broadly

overlies, and along the ventral edge of its laterally compressed plate with the epiotics, while the middle twothirds of its length is firmly held to the frontals and its anterior end to the ethmoid. Many of the specializations

of Paraluteres are associated with its mimetic rela- tionship with a Canthlgaster pufferfish (Tyler 1966). The basal pterygiophore in the especially deep-bodied Chaetoderma is very high and domelike, while in the

species ofAlutera it is slightly smaller than in most other monacanthids, having only a short anterior vertical crest

in front of the level of the first spine, and the pterygio- phore is not as broadly held ventrally to the supraoccipital and epiotics. In two genera the basal pterygiophore is of more or less normal size in lateral surface area, but much thinner than in other monacanthids {Psilocephalus excepted). In the deep-bodied Brachaluteres the pterygiophore supporting the single but well-developed dorsal spine is es- pecially high, but it is much thinner and less heavy than

normal, the buttresses for the spine being only slightly expanded laterally and most of the surface of the ptery- giophore being a thin compressed plate. In Paraluteres,

in which the two skin covered dorsal spines are probably

not fully erectible in life, the pterygiophore is of reduced

sturdiness and of relatively short length, although the

buttressing for the spines is more or less normal.

In comparison to the spiny dorsal fin, there is even
greater diversity in the pelvic apparatus of monacanthids. The number of segments of scales in the encasing

series ranges from three to two to one to none, and a rudi- mentary fin ray represented by a pair of bony splints above and below a plug of cartilage at the end of the

pelvis is variously present or absent. The encasing scales are either flexible or fixed, the dorsal lobe to the pelvis varies from greatly to only slightly developed or absent

altogether, and the pelvis itself ranges from relatively massive and extending to the region of the anus to slender and reduced in length.

In what can be considered the most generalized condition of the pelvic apparatus in monacanthids (i.e., the

least reduced from that of balistids), the pelvis is well- developed and has at least a moderate dorsal lobe, the encasing scales are flexible and in three series, and a fin- ray element is present as two bony splints. This generalized condition is found in Monacanthus, Paramonacanthus, Stephanolepis, Pervagor, and Laputa. Tendons

attach to the splints and run forward to muscles on the

dorsal and ventral surface of the pelvis, the dorsal tendon

passing through a horizontal tube in the basal region of the dorsal lobe, as described by Tyler (1962b) for Monacanthus ciliatus. The splints representing the fin-ray ele- ment are of moderate size, about like that illustrated by

Tyler (1962b) for M. ciliatus, in all of the species examined of the above genera, except that they are longer in M.

mylii and M. chinensis and shorter in Paramonacanthus

barnardi. In one other genus a fin-ray element and flexi- ble encasing scales are present, this being the monotypic

Chaetoderma, in which there are only two series of en- casing scales and the fin-ray splints are minute. The only genus not examined which has a flexible encasing scale

series, Arotrolepis, can be expected to have fin-ray

splints. In all of the genera examined in which the encasing

scales are fixed or absent, the fin-ray splints are absent, although in a few species tendons still attach to the small

cartilaginous plug at the end of the pelvis, as described by Tyler (1962b) for Cantherhines sandwichiensis. Tyler

(1962b) attributed three series of encasing scales to that

species. Examination of additional specimens of C. sandwichiensis and of other species of Cantherhines makes it unclear to me now whether the scales are in two or three

series; perhaps it should be counted as two and a half

series, the half series being a pair of scales scarcely if at

all meeting in the midline ventrally between the larger anterior and posterior pair. Whether these represent two

or three series of scales is problematical, but, in any case, when the encasing scale series is inflexible, the length of the series is shorter than in those genera in which there

are clearly three series and in which flexibility is present.Of the genera examined with an inflexible series, there

are two and a half or clearly only two series of encasing

scales in Amanses, Cantherhines, Nauodon, and Acanthaluteres, and there is no fin-ray element. This is probably also the case in the other genera with fixed en- casing scales: Scobinichthys, Pseudomonacanthus, and Meuschenia; and, questionably, in Eubalichtys, as

discussed below. In Rudarius there are two series of en- casing scales and no fin-ray element in R. ercodes, but

only a single series and no ray in R. minutus, the reduction of the series into a single, although highly spinous,

series in the latter perhaps being associated with the ex- tremely small adult size of that species. In Oxymonacanthus there is no fin-ray element and no precisely delineated series of encasing scales; rather, the scales bordering the ventral surface of the posterior end of the

pelvis simply gradually become larger and more spinous

distally so that the encasing scales are of indeterminate number. The genus Alutera provides an example of the process

of loss of the encasing scales. No fin-ray element is present, but Berry and Vogele (1961) have shown that in small specimens of three of the four species (A. heudelotii, A. scripta, and A. monoceros) there is a single enlarged spinous scale present on the midline below the

ventral edge of the pelvis, this being the last remnant of the encasing scales. This scale becomes unornamented

and then lost in large adults. In A. schoepfi there is no

rudimentary encasing scale at any size (Berry and Vogele

1961). In Acanthaluteres, the specimens of the single species here examined {spilomelanurus, if I have it properly

identified, and I am not sure) lack encasing scales, whereas Fraser-Brunner (1941b: 178) gives as a key character for the genus "Pelvic shield present at all stages (sometimes minute or inconspicuous)." It is possible that

there are allometric changes in the encasing scales, just as in Alutera. This may also be true of Eubalichthys, of which Fraser-Brunner (1941b: 180) says: "Pelvic shield minute, inconspicuous." There are no encasing scales or fin-ray elements in Psilocephalus, Brachaluteres, Paraluteres, and Pseudaluteres, and, according to Fraser-Brunner (1941b:181), in Blandowskius. The structure of the pelvis itself is highly diversified in monacanthids. In those species with flexible encasing

scales, the pelvis is always, relatively well developed and

has a dorsal lobe of at least moderate height. The dorsal

lobe is largest in the genus Monacanthus, the species of which are noted for the especially large size of the fan of

distensible skin with enlarged scales that can be flared out between the anus and pelvis when the latter is rotated downward and forward. However, the presence of

a dorsal lobe is not absolutely correlated with the expansion of the abdominal dewlap, for one genus (see below) without a lobe has the ability to flare a remarkably large

fan.In general, however, most of the genera (Pseudaluteres, Paraluteres, Brachaluteres, Alutera) without a

dorsal lobe also do not flare fans, the exception being

Psilocephalus, which not only has no dorsal lobe but also the most slender and weakly developed pelvis in the

family, and yet can flare as large a fan as in Monacanthus. The presence of a dorsal lobe is probably more

strictly correlated with the presence of enlarged scales along the posterior edge of the fan, these scales being supported by the lobe. The scales along the posterior 154



t


%





edge of the fan in Psilocephalus are not much enlarged or differentiated from those just anterior to them. The dorsal lobe is poorly developed in Oxymonacanthus, which

flares only a small or moderate sized fan and which has no modified scales in the fan. Of the genera with fixed encasing scales, the pelvis ranges from very strongly (e.g., Amanses) to only moderately (e.g., Oxymonacanthus) developed. Of the genera

with no encasing scales, none have a dorsal lobe, and the

size of the pelvis ranges from massive (e.g., Alutera), to normal (Brachaluteres), to slightly reduced in size {Pseudaluteres and Acanthaluteres), to short and

somewhat slender (Paraluteres) , and to long but very weak and slender {Psilocephalus}.

In Pervagor alone the lateral surface of the anterior

region of the pelvis has a lateral knoblike expansion which articulates with a similar expansion on the posterior edge of the coracoid, forming the point of pivot around which the pelvis is rotated downward and

forward to flare the fan. There is little variation in the branchial apparatus in the monacanthids, except for the number of branchiostegal rays. All species with the exception of Psilocephalus barbatus have three basibranchials, three hypobranchials, five ceratobranchials (the last toothless), four epibranchials, and two pharyngobranchials (both

toothed). In Psilocephalus there are only two basi- branchials and three epibranchials, and all of the various

pieces in the arches are more or less reduced in massiveness, although the ceratobranchials are more

elongate. There are six branchiostegals in a 2 -(- 4 arrangement in the various species examined of Nauodon, Acanthaluteres, Alutera, Cantherhines, and Amanses, but only

four branchiostegals, in a 1

-(- 3 arrangement, in Psilo- cephalus. The great majority of species examined,

however, have five branchiostegals, in a 1

-)- 4 arrange- ment, these being of the genera Monacanthus, Stephanolepis, Paramonacanthus, Pervagor, Laputa, Rudarius, Oxymonacanthus, Chaetoderma, Paraluteres, Brachaluteres, and Pseudaluteres. When five rays are present, it is the second of the anterior group of two that has been

lost, while in Psilocephalus, with four rays, one has also been lost from the posterior series of four. It is of interest that of 12 specimens of Monacanthus ciliatus examined,

11 had the 1-1-4 arrangement on both sides, but one had

1 -(- 4 on one side and 2 -f 4 on the other, the second ray of the anterior group being present on one side only. There are great differences in the number, size, and

placement of epipleural bones in monacanthids, which

has led to confusion. Fraser-Brunner (1941b:176), in his diagnoses of the Balistidae and Monacanthidae, stated

that in balistids epipleurals were found on no more than

the first two caudal vertebrae, while monacanthids had

epipleurals on the first four or five caudal vertebrae. From the materials examined here, it appears that most

balistids have epipleurals on the second abdominal to the first caudal vertebra, but in the species of the genus Rhinecanthus they extend back from the second ab- dominal to the fifth or even sixth caudal vertebra. In

most monacanthids the epipleurals begin on the second abdominal vertebra and usually but not always extend

onto the caudal vertebrae. However, in a number of

species the epipleurals are confined to the abdominal

vertebrae. In the species of Alutera, for example, the

epipleurals extend from the second abdominal only to the sixth (next to last) or, rarely, seventh (last) ab- dominal vertebra, while in Pseudaluteres they are pres- ent from the second to the eighth (next to last) ab- dominal vertebra and in Psilocephalus from the second

to sixth (next to last) abdominal vertebra. As an ex- amination of the lateral view illustrations of monacanthids presented here will show, the epipleurals of other genera extend posteriorly variously anywhere from the

first to fifth caudal vertebrae, while in Rudarius (both er- codes and minutus) and Brachaluteres they are present

only from the third abdominal to the second to fourth caudal vertebrae, being absent on the second abdominal

vertebra. Thus, here is no absolute familial distinction concerning the epipleurals between the balistids and

monacanthids. The epipleurals in monacanthids are usually slender

splints, less sturdy than in most balistids, but they are

ver\' sturdy in at least the single large adult oi Amanses

examined, and relatively well developed with large sur- face area in Brachaluteres and Alutera. In Alutera the

epipleurals become hyperostotic in large adults. True ribs have previously been found among plec- tognaths only in the primitive gymnodont Triodon macropterus (see Tyler 1962a:798 for discussion), and in the monacanthid scleroderm Pseudaluteres nasi- cornis as well (see Tyler 1973b). The latter would be

a less amazing occurrence of ribs, in light of the ancestral balistids lacking true ribs, were Pseudaluteres at

least a primitive monacanthid rather than being, as discussed under generic relationships, surely one of the most specialized. The genetic information on constructing ribs would

appear to have been retained in the otherwise ribless monacanthids and their ancestral balistids and their ancestral and equally ribless triacanthids and triacan- thodids from the doubtless rib bearing basal group of plectognaths from which both the scleroderms and gymnodonts evolved. What peculiarity in the functional life of Pseudaluteres has made it advantageous to have ribs when other monacanthids (and Recent scleroderms) do

not is a mystery to me, but it would not appear to be as- sociated with its two other primary specializations; the

far forward placement of the dorsal fin spine in front of the eye or of the lack of encasing scales and loss of the rudimentary pelvic fin-ray element. A posttemporal is present in all monacanthids examined except Psilocephalus barbatus, none of the three adult specimens of which shows any evidence of one. Whether

the ossification center for the posttemporal is lost or in- corporated indistinguishably with that of the pterotic remains problematical. The dorsal head of the supra- cleithrum in Psilocephalus articulates directly with the

lateral surface of the pterotic. This loss of the posttemporal is undoubtedly correlated with the greatly reduced

167
Figure Ma.—Stephanolepii hUpidiu: lateral view of

50.4 mm SL, Florida.

basal pterygiophi

Figure W^.—Paramonacanthu

cryptodon: lateral view of hea

68.5 mm SL, Thailand.
Figure in.—Pervagorapiloeomus: lateral view of head, 80.0 mm SL, Hawaii.

premaxillary

quadrate sy^plect mefapterygoid preoperculum
1st dorsal spine basal pterygiophore 2nd dorsal spine

Figure \19.—Alutera heudelotii

lateral view of head,

107 mm SL, Florida.

preroric hyomandibula

operculum

suboperculum

preoperculum

metapterygoid

articularangular

interoperculum

symplectic mesopterygoid

ectopterygoid

Figure 120.—Psilocephalus barbatua: lateral view of head, 137 mm SL, Singapore. 170
Figure 12\ .—Brachaluterea trosaulus: lateral view of head, 55.5 mm SL, Australia.

Figure 122.— Oxymonacanthut

longirostris: lateral view of head, 26.5 mm SL, Seychelles.
Figure \23.—Pseudaluteres

nasicornis: lateral view of head, 108 mm SL, Philippines, with inset above showing

detail of the snout region

size of the pectoral girdle and of the fin it supports, with

the rays reduced in number to eight (usually) or nine, plus the uppermost rudimentary ray. This attests to the

far greater reliance in Psilocephalus on the especially long-based and many-rayed soft dorsal (43-52 rays; average of five specimens 49) and anal (53-66 rays, average 58) fins for locomotion. Psilocephalus is the only monacanthid regularly to have far more anal than dorsal

fin rays. As in balistids, the scapula completely encloses its foramen in most monacanthids, but in Pseudaluteres and Psilocephalus the scapular foramen is incomplete

anteriorly, being bounded by the cleithrum. In Psilocephalus this is probably correlated with the reduced size of the pectoral girdle and fin, but Pseudaluteres

has a well-developed pectoral girdle and a moderate number (11-13) of rays. Variation in the monacanthid caudal skeleton mainly

concerns the presence or absence of an upper free hypural. There is always a single epural and usually a free upper hypural in contrast to the other hypurals which are fused to one another and to the centrum, and a free parhypural. A free upper hypural is absent in the majority of specimens of Monacanthus ciliatus examined and

in those of Rudarius ercodes and R. minutus and in the

single specimen of Amanses scopas examined (Tyler

1970b: 15, erroneously implied that R. ercodes has an upper free hypural). Of 12 specimens of M. ciliatus examin-
ed, only 2 had a free upper hypural. Other variation in the monacanthid caudal skeleton (discussed in Tyler

1970b) is that the usually horizontal crest for muscle at- tachment on the last centrum is reduced to a prong in Brachaluteres trossulus, and its neural and haemal

canals are better developed than in other monacanthids,

being roofed over distally rather than open. In Psilocephalus only the middle 6 to 8 rays of the ex- tremely elongate caudal fin are branched, rather than

having 10 branched rays as in all other monacanthids. The posterior edge of the fused hypural plate is much

more convex in Psilocephalus than in all other monacanthids, while in Brachaluteres the cleft in the posterior edge of the fused hypural plate, that marks the region of fusion between what in generalized plectognaths like triacanthodids are the second and third hypurals, is much deeper than in all other monacanthids.

In balistids and in all but two genera of monacanthids

the side of the rear part of the cranium just above the

region of articulation of the upper end of the hyomandibular is formed by the sphenotic anteriorly and by the

pterotic posteriorly, the hyomandibular articulating with

a groove across the surface of the prootic and pterotic. The sphenotic usually has a well -developed (least developed in Rudarius) ventrally or anteroventrally

directed prong from its lower edge and the pterotic a

larger ventrally directed flange that overlies the posterodorsal end of the hyomandibular. The anterolateral edge

of the sphenotic forms the lower rear margin of the orbit, with the frontal forming the margin more dorsally. The two exceptions to these conditions are Oxymonacanthus and Pseudaluteres, in both of which the sphenotic is displaced posteriorly by a ventral extension

of the frontal, the side of the rear of the cranium above

the articulation of the hyomandibular being formed by

the frontal anteriorly and the pterotic posteriorly, with

the sphenotic squeezed in between. The sphenotic

retains a short ventrally directed prong and the pterotic a normally developed large flange overlying the posterodorsal end of the hyomandibular, which articulates in a normal manner with a groove across the surface of the

prootic and pterotic. The frontal, which forms all of the

posterior margin of the orbit in these two genera to the

exclusion of the sphenotic, has a ventrally directed prong

from its anteroventral end in this region. This prong on

the frontal is comparable to that on the sphenotic of all other monacanthids, where it forms the lower rear margin of the orbit. Monacanthids always have the prootic shelf much less strongly developed than in balistids. The shelf in monacanthids does not extend as far forward as the level of the middle of the orbit, except in Psilocephalus, in which the shelf is long, thin, and delicate and reaches to the front of the orbit. Within these limits, the prootic

shelf of monacanthids is variously developed, from

relatively well to only moderately, and in two genera it is completely absent, these being Oxymonacanthus and

Pseudaluteres.

All monacanthids have an outer series of three and an

inner series of two teeth in each premaxillary, the inner

series closely applied to the inner (or under) surface of the outer series and to the bone. In the dentary there is a

single series of teeth, corresponding to the outer series of the upper jaw, usually three in number, but reduced to two in Psilocephalus barbatus, Rudarius ercodes and R. minutus, Brachaluteres trossulus and (according to Clark and Gohar 1953:46) B. baueri and (according to Scott 1969:40) B. wolfei, Paraluteres prionurus, and Oxy- monacanthus longirostris (presumedly also only two

teeth in the closely related 0. halli Marshall as well). While three teeth are present in the dentary of Pseudaluteres nasicornis, the outermost tooth is much smaller than in other monacanthids with three dentary teeth. In

all monacanthids the medial edges of articulation of the apposed dentaries are well-denticulated. The teeth are relatively thinner and have more

delicate cutting edges than in balistids, but they are usually notched in basically the same way in both

families. The least notched condition of the teeth among

the monacanthids examined is found in Acanthaluteres

spilomelanurus, in which the two most medial teeth in both the upper and lower jaws (the most medial tooth of both premaxillaries and both dentaries) are relatively straight edged, forming a broad relatively sharp straight nipping edge along the front of the mouth. The position

of the mouth tends to be terminal or only slightly supra- terminal in most monacanthids, but it is distinctly supraterminal in the elongate Psilocephalus barbatus. The mouth of Oxymonacanthus is relatively small and

laterally compressed, with the teeth also relatively nar- row but elongate, for what is probably a specialized mode

of feeding between the branches of coral of this strictly reef-dwelling species. Among the monacanthids examined, the teeth are most massive in Amanses scopas, but

this could in large part be a function of the large size of the single specimen examined. It will be of interest to know the size of the teeth in juveniles and young adults

of Amanses, which have yet to be collected (Randall

1964:335). While the number of vertebrae in the ancestral

balistids is almost invariably 7 -(- 11 = 18 (in contrast to

their ancestral triacanthoids in which it is 8 -I- 12 = 20), the number of vertebrae in monacanthids is highly

variable, although the most frequent formula is 7 H- 12 =

19 and none of the species examined normally has as few

as the 18 vertebrae of balistids. Only a few species of monacanthids have other than seven abdominal verte- brae, most of the variation in total number being in the caudal series. The only monacanthids normally with six abdominal vertebrae are the two Atlantic species of Monacanthus {ciliatus and tuckeri, the subgenus Leprogaster of Fraser-Brunner, with 6 -I- 13 = 19 in contrast

to the 7 -I- 12 = 19 of the Indo-Pacific species) and

Acanthaluteres spilomelanurus (6 -I- 14 = 20). The only monacanthids normally with eight abdominal vertebrae

are Oxymonacanthus longirostris (8 -(- 17 = 25) and

Pseudaluteres nasicornis (8 -I- 18 = 26). When the number of vertebrae is increased beyond what is probably the generalized number of 19, it is usually by the addition of one or more vertebrae in the 173
caudal series (as well as, in Oxymonticanthiu and

Pseudaluteres, by one in the abdominal series), as ex- emplified by Alutera, whose four species have normal

vertebral counts ranging from 20 to 23 but all of which re- tain 7 abdominal vertebrae. The greatest increase in number of vertebrae is in the extremely elongate body of Psilocephalus barbatus, the increase again being confined to additions in the caudal series. Four of the five specimens of P. barbatus cleared and stained or radio- graphed have 7 abdominal and 22 or 23 caudal verte- brae, while one has 8 abdominal and 22 caudal verte- brae. The neural spines of the abdominal vertebrae anterior

to the first basal pterygiophore of the soft dorsal fin vary from relatively narrow long slender shafts (e.g., Brachaluteres) to short slender shafts (e.g., Chaeto- derma) to broadly anteroposteriorly expanded plates

(e.g., Pseudaluteres), with intermediate conditions found in other genera. As in balistids, which always have

five vertebrae anterior to the first basal pterygiophore of the soft dorsal fin, the great majority of monacanthids

also have five so placed. The only exceptions are the two

Atlantic species of Monacanthus (ciliatus and tuckeri), the single species of Acanthaluteres examined, nd one

of the two species of Rudarius (minutus), all of which

have only four vertebrae anterior to the first soft dorsal

Figure 124.—Dorsal viewi of skull* of: A, Pnudalutereg nasicomis, 108 mm SL,

Philippines, highly specialized; B, Paraluteres prionurue, 46.4 mm SL,

Seychelles, moderately specialized; C, Chaetoderma spinosiasimus, 33.0 mm SL, Malaya, relatively generalized.

fin basal pterygiophore, and Pseudaluteres nasicornis with six and Psilocephalus barbatus with eight. As in balistids, the lateral line system in most monacanthids is inconspicuous, and can usually only be fol- lowed in cleared and stained specimens examined under

a microscope. However, it can be relatively easily seen with the unaided eye even in alcohol preserved speci- mens of a few species of Monacanthus (especially chinensis), Paramonacanthus, and Paraluteres prionurus, and,

to a lesser extent, in Psilocephalus barbatus. The scales of the lateral line in monacanthids typically have a foramen in the basal plate with an upright spiny

process like that of the other scales bordering the foramen above and below. The only species examined in which such lateral line scales could not be found was

Pseudaluteres nasicornis. In all species except Paraluteres prionurus the head and body are more or less fully covered with scales whose

upright spinulations usually give a shagreenlike quality
to the skin. In P. prionurus the skin is smooth to the

touch, except on the caudal peduncle of mature males

where there are two pairs of retrorse barbs and a patch of short upright setae extending forward to the level of the

anal fin origin. The fact that there are very low weakly

developed spinulose scales on the head and ventral sur- face from the mouth to the anus is only readily apparent

in cleared and stained specimens. The scales of monacanthids vary greatly in the degree and structure of the spinulation and in the size and

degree of overlap (if any) of the usually rounded to rectilinear basal plates, but they are always much smaller than in balistids. In most species the basal plates more or

less broadly but irregularly overlap, while in others (e.g., Chaetoderma) there is little if any overlapping of the

relatively large and more or less triangular plates. The

scales of Chaetoderma are more or less regularly ar- ranged in rows, and, according to Fraser-Brunner

(1941b: 178), they are in distinct longitudinal tracts in

Figure 125.— From left to right: A, Paraluteres prionurus. ventral view of

skull, 46.4 mm SL, Seychelles; B. Pervagor

apilosomus, ventral view of skull, ca. 65 mm SL, Hawaii; C, Psilocephalus

barbatu^, dorsal and ventral views

of skull, 137 mm SL, Singapore.

Arotrolepis, while in the great majority of monacanthids

the arrangement is irregular. There is always at least one

upright spinule (least developed in Paraluteres, best in Chaetoderma) per scale plate, and often many. The in- dividual scale plates are largest in Chaetoderma, in which many of the upright spinules support large der- mal flaps, and smallest in Psilocephalus.

All monacanthids, like balistids, have two nostrils in a

scaleless area on both sides, each nostril usually at the end of a short tube, but sometimes more or less flush with

the surface (especially Paraluteres and Psilocephalus).
basibranchials :^^^ '

' ^'"

' ' "^ -"^^v' " hypobranchials

^ - ceratobranchials

urohyal

-c:2ss.

S. f-^

branchiostegal rays

The nasal sac beneath the surface usually has a single longitudinal upraised fold or lamella. Generic relationships. —Given their evolution from

balistids, one would expect generalized monacanthids to have a relatively well-developed pelvis with a dorsal lobe and at least rudiments of the fin-ray element hidden

within a flexible series of encasing scales of a maximum

number of segments. Likewise, the basal pterygiophore supporting the dorsal fin spines would be expected to be

well developed and over the rear part of the skull (i.e., the least distance migrated forward) and with the skull the least flattened for articulation with it (i.e., with some

remnant of the medial supraoccipital crest of balistids). Other generalized features to be expected a priori would be an only slightly elongate body and terminal mouth, six branchiostegals, a groove posterior to the dorsal spines into which they are folded more or less flush with the surface when unerected, the least reduction in the number of teeth, the least increase in the number of

vertebrae, and the presence of an upper free hypural. Of the above features, I tend to place greatest emphasis on the pelvic apparatus and the form of the top of the skull in relation to the basal pterygiophore of the spiny dorsal fin. The supraoccipital is best developed in Stephanolepis, Monacanthus, and Paramonacanthus,

reaching to the front of the eye, and only in these three genera does the supraoccipital retain a vertical medial

crest anteriorly for articulation with the laterally compressed platelike anterior region of the spiny dorsal fin basal pterygiophore. I take this low anteriorly placed

supraoccipital crest as the remnant of the much sturdier

crest that is found more or less throughout the length of the balistid supraoccipital and which ends posteriorly in the thick lateral expansion which helps, along with the

epiotics, to support the anterior end of the first basal pterygiophore of the spiny dorsal fin. Stephanolepis, Monacanthus, and Paramonacanthus

also have the pelvic apparatus well developed, with the

dorsal lobe of the pelvis of moderate to large size and

with the maximum monacanthid number of three seg- ments of flexible encasing scales surrounding a hidden

fin-ray element to which muscles attach through ten- dons running along the dorsal and ventral surface of the

pelvis, the dorsal tendon coursing through a canal in the base of the dorsal lobe. In all three of these genera the

dorsal spines are placed relatively posteriorly on the

skull, at a level behind the middle of the eye. In most other genera of monacanthids examined (Pervagor, Amanses, Cantherhlnes, Acanthaluteres, Oxymonacanthus, Rudarius, Laputa, Navodon, Pseudaiuteres, Paraluteres, Psilocephalus) the supraoccipital does not extend as far forward as in Stephanolepis, Monacanthus, and Paramonacanthus and there is no

crest at all. With the exception of Laputa (and Chaeto- derma as well), the former group of genera are also specialized in having an inflexible series of encasing

scales, or none at all, and no fin-ray element, other than sometimes a mere cartilaginous plug at the end of the

pelvis. Laputa is the only genus with flexible encasing scales and a rudimentary fin-ray element (small in the single species examined) in which the supraoccipital does not extend far forward and is without a crest, although the 176
Figure 126. (opp. page)—Dorsal view of branchial arches

(extended on lower side) and

lateral view of hyoid arch and

urohyal of: left, Alutera heudelotii,

114 mm SL. Florida (labeled), and right, Psilocephalug

barbatus, 1,39 mm SL. Singapore (unlabeled).

Figure 127.— Medial views of upper (left) and lower (right) jaws of: A. Alutera heudelotii, 114 mm SL. Florida; B, Monacanthu« ciliatus, 51.3 mm SL, Colombia;

C. PBilocephalus barbatus, 137 mm SL. Singapore; D. Amanses scopas, 167 mm SL, Saipan;

E, Acanthaluteres apilomelanurus,

63.7 mm SL, Australia.
Figure 128.—Hypothesized phylogenetic relation- ships of the genera of Monacanthidae.

dorsal spines are placed posteriorly on the head. Thus, Laputa is as generalized as Stephanolepis, Monacanthus, and Paramonacanthus except for the shorter and more flattened condition of the supraoccipital.

In Chaetoderma there are only two encasing scale seg- ments, a slight specialization, but minute remnants of the fin-ray element remain and the encasing scale segments are flexible, the minuteness of the fin-ray ele- ment also being a slightly specialized condition. Moreover, Chaetoderma has a relatively well developed

forward extension of the supraoccipital, almost to the

front of the eye and only slightly shorter than in Stephanolepis, Monacanthus, and Paramonacanthus. The forward extension of the supraoccipital in Chaeto- derma bears a thin low crest over the middle and posterior regions of the eye which is probably a remnant of that found in the three genera in which the crest is well developed.

In two other genera besides Chaetoderma the supraoccipital extends forward only slightly less than the front of the eye, but both are obviously specialized by the total

loss of the pelvic fin-ray element and the dorsal lobe of the pelvis, as well as by either the total loss of the en- casing scale series or its reduction to a single scale that is lost in large adults. These two genera are Alutera, in which all four species have a low supraoccipital crest on

the forward extension, and the single species of Brachaluteres examined (trossulus), in which there is no

crest in the smaller of the two specimens but a very low

crest present from the middle of the eye posteriorly in the

larger specimen. One other genus must be mentioned in connection

with the shape of the supraoccipital, that being Psilo- cephalus, in which there is no true long forward and

mainly medial extension of the supraoccipital as found in the genera just discussed. In Psilocephalus the supraoccipital is represented only by the relatively larger more

laterally expanded posterior portion. But probably

because of the relative shortening of the posterior part of the skull and the great elongation of the snout, the anterior end of the supraoccipital in Psilocephalus does ex- tend forward to the level of the dorsal end of the prefrontals, although still short of the front of the eye. In my opinion, the combination of the most generaliz- ed condition of the pelvic apparatus and that of the

supraoccipital supporting the basal pterygiophore and its dorsal spines placed over the rear of the eye points to Stephanolepis, Monacanthus, and Paramonacanthus as representing the most generalized group of monacanthids. Of the other features listed in the opening paragraph of this section as being considered generalized

a priori on the basis of the structure of the ancestral

balistids, these three genera have terminal mouths with

the most typical monacanthid number of teeth (the minimum reduction from balistids), 19 vertebrae (the minimum increase in number from balistids), and an up- per free hypural, except that only a minority of specimens of one of the species {ciliatus) of Monacanthus have a free upper hypural. However, Stephanolepis, Monacanthus, and Para- monacanthus are among those majority of monacanthids with 1-1-4 branchiostegals, rather than the 2 +

4 arrangement found in balistids and in Navodon,

Acanthaluteres, Alutera, Cantherhines, and Amanses among the monacanthids, and in having no relatively distinct and deep groove medially behind the basal

region of the dorsal spines into which the latter are received and held more or less flush with the surface, as found in balistids and in the monacanthids Acanthaluteres, Cantherhines, Amanses, Meuschenia, Oxymonacanthus, Eubalichthys, and most but not all species of Pervagor. The 2 + 4 versus 1 + 4 number of branchiostegals and

the degree of development of a groove for the reception of the dorsal spines seem in this case to be less important

indicators of the overall generalized condition of monacanthids than do the other outstanding features dis- cussed above, this especially in light of the fact that, as described here, Monacanthus ciliatus at least sometimes

has the 2 + 4 branchiostegal number and that among the apparently closely related species of Pervagor, most have

a groove behind the dorsal fin, while at least one species (tomentosus, according to Fraser-Brunner 1941b: 183) does not. The three most generalized genera, Stephanolepis, Monacanthus, and Paramonacanthus, seem very closely

related, and only a single genus has often been recog- nized for the species now placed in Stephanolepis and

Monacanthus. The latter two genera have been best dif- ferentiated by Berry and Vogele (1961:63, 68), mostly on

the basis of the spinulation of the scales. Monacanthus

has unbranched and relatively fewer spinules per scale than does Stephanolepis, which has branched spinules, although the number of spinules increases greatly with

increasing specimen size in both genera, just as in most

other monacanthids. Berry and Vogele also pointed out

that the ventral dewlap between the end of the pelvis and

178
the anus is much larger in Monacanthus, in which it ex- tends out far beyond the end of the encasing scales, than

in Stephanolepis, in which it extends out only to the distal end of the encasing scales. In Paramonacanthus the ventral dewlap is especially

short, extending posteriorly only to the anterior edge of the encasing scale series, so that the end of the pelvis protrudes prominently from the ventral contour. The

scales in Paramonacanthus have unbranched spinules, as in Monacanthus and the vast majority of other monacanthids, but the spinules are less coarse than in Monacanthus and the skin of Paramonacanthus thus has much the same velvety shagreen consistency as found in Stephanolepis, rather than the rougher consistency of Monacanthus. In Paramonacanthus the scale spinules

are unmodified, while, as described in detail by Berry and Vogele (1961), mature males of Stephanolepis

develop a patch of bristles on the caudal peduncle and

mature males of Monacanthus have bristles and retrorse barbs, females of Monacanthus developing smaller posteriorly pointed barbs on the caudal peduncle but very

little if any bristle patch.

In Monacanthus the dorsal lobe of the pelvis is very

large, the longest among monacanthids, being as- sociated with support of the modified scales in the enor- mous dewlap. In the various species of Stephanolepis and Paramonacanthus the dorsal lobe is only moderately

developed, about that normal for the family when a dorsal lobe is present at all. In Paramonacanthus and Stephanolepis there is always a free uppermost hypural, as is also the case in the Indo-Pacific species of Monacanthus. In the two

Atlantic species of Monacanthus, one species (tuckeri) usually has a free upper hypural (present in three out of

four cleared and stained specimens) while the other

species iciliatus) usually lacks the free hypural (present

in 2 out of 12 cleared and stained specimens).

In Stephanolepis and Paramonacanthus epipleurals

usually extend back to the fifth caudal vertebra while in Monacanthus they usually extend back only to the sec- ond or third caudal vertebra (one specimen of M. chinensis with epipleurals on the fourth caudal vertebra).

In Stephanolepis, Paramonacanthus and the IndoPacific species of Monacanthus there are 7 abdominal

and 12 caudal vertebrae, with 5 of the abdominal verte- brae anterior to the first basal pterygiophore of the soft dorsal fin, this being the most common vertebral condition in the family. In the two Atlantic species of Monacanthus the total number of vertebrae remains 19, but it is the haemal spine of the seventh rather than that

of the eighth vertebra that supports the anterodorsal end

of the first basal pterygiophore of the anal fin, and the neural spine of the fourth rather than that of the fifth vertebra supports the anteroventral end of the first basal pterygiophore of the soft dorsal fin, M. ciliatus and

tuckeri thereby having only 6 rather than 7 abdominal

vertebrae and only 4 rather than 5 predorsal vertebrae. With the similarities and differences discussed above between the three genera here considered to be the most

generalized monacanthids, the question is whether one of

them can be considered closer to the ancestral group

than the other two. There is little to go on.

In balistids the ventral fan is only moderately

developed, with the expansible skin extending posteriorly across most of the length of the encasing scale

series, ending at about the beginning of the most distal of the four segments of scales. This condition is somewhat

intermediate between that of Paramonacanthus, with a very short dewlap, and Stephanolepis, with a moderate

dewlap, but closer to that of Stephanolepis. The moderate dorsal lobe of the pelvis of Paramonacanthus and Stephanolepis is closer to that of balistids than is the extremely large one of Monacanthus. The upright spinules on small basal scale plates in monacanthids is so different from the structure of the

scales of balistids that it is impossible to say whether the branched spinules of Stephanolepis are more generalized

or specialized than the unbranched spinules in Monacanthus and Paramonacanthus, and in any case many of the scales of the head and extreme upper and

lower parts of the body in the Indo-Pacific species of Monacanthus have branched spinules, while those of most of the body are unbranched but sometimes notched

along their anterior edge. The phylogenetic implications of the presence of enlarged caudal peduncular scales forming a patch of

bristles or spines in mature males of Stephanolepis and

in mature males and, to a lesser extent, in mature

females of Monacanthus, but in neither sex of Para- monacanthus, is difficult to interpret. Among balistids only two genera (Balistapus and Rhinecanthus) have

well-developed caudal armature, in the form of large

spines, but numerous genera (e.g., Sufflamen, Melichthys, Xanthichthys, Abalistes, Balistoides) have

horizontal ridges formed by upraised areas on the successive rows of scales on the caudal peduncle and posterior region of the body, and only a few genera are totally lacking these ridges (e.g., Balistes and Odonus). Without knowing from what type of balistids the monacanthids have been derived, it cannot be said at present whether the caudal armature present in a few monacanthids is a generalized holdover from their balistid ancestors or a relatively specialized feature.

I would guess that Stephanolepis is the most generaliz- ed of the three genera, basically because of its moderate

dorsal lobe of the pelvis and moderate dewlap. Monacanthus would be a slightly specialized close derivative

of Stephanolepis whose evolutionary trend is for a great

increase in the size of the dewlap and of the dorsal lobe supporting it, while in another direction Paramonacanthus is an equally close relative of a Stephanolepislike stock, specialized by a great reduction in the size of the dewlap but not of the dorsal lobe. Fraser-Brunner (1941b: 181) considered Pervagor the most generalized monacanthid, stating that: "Pervagor,

in which dorsal and pelvic spines are better developed than in the succeeding [i.e., all the other] genera, exhibits two features which are not found among the other forms possessing a movable pelvic spine - the forward

position of the dorsal spine and the presence of a deep
groove in which it is received when depressed (the latter character, however, being lacking in the subgenus

Acreichthys noted [described as new| below). On the one hand it leads to the rest oi' the genera retaining the pelvic spine but having the dorsal spine behind the eye and

without groove; of these, Stephanolepis seems to be the group round which the specialized forms such as Chaeto- derma and Monacanthus are clustered. On the other hand extends the large series of genera in which the pelvic spine has been lost. ..."

I do not find that the dorsal spines and encasing scales

in Pervagor are better developed than in most other

genera, and certainly they are no better developed than

in Stephanolepis, Monacanthus, and Paramonacanthus. Moreover, I do not think that the somewhat for- ward position of the dorsal spine (over the middle of the

eye) can be considered the generalized condition when

the ancestral balistids have the dorsal spines behind the

eye.As discussed previously, the least forward migration of the dorsal spines is the most generalized monacanthid

condition, with the spines over the rear of the eye. Per- vagor does not possess the generalized monacanthid condition of the supraoccipital, for it lacks the forward ex- tension with vertical crest to the front of the eye that is a remnant of the condition of the balistid supraoccipital. In fact, the only definitely generalized feature of Per- vagor to my way of thinking is its pelvic apparatus, with

it having a moderate dorsal lobe, three segments in the

flexible encasing scale series and moderately well- developed rudiments of the fin-ray element. As dis- cussed previously, a groove behind the dorsal spines would seem a priori a generalized condition in monacanthids since the ancestral balistids have such a groove. But of the genera of monacanthids with a groove behind

the dorsal spines, only Pervagor has a generalized pelvic apparatus, all the other genera having the segments of encasing scales reduced in number and inflexible or absent entirely, and without a fin-ray element.

All of the genera with the groove behind the dorsal spines have the most specialized condition of the

supraoccipital, without a long or even moderate forward

extension and no crest. It seems as likely that the monacanthid postdorsal groove is a de novo develop- ment in moderately specialized forms as it is that it is a hold over from the ancestry of the monacanthids, the most generalized Recent species of which would then have to be presumed to have subsequently lost it. A similar situation occurs with the interpretation of the 2-1-4 branchiostegal number found only in a few

genera of monacanthids, these all being genera with a

specialized pelvic apparatus in which the fin-ray element

is absent and the segments of encasing scales are reduced

in number and inflexible or absent entirely, a small dorsal lobe is present on the pelvis, and there is either no

forward supraoccipital extension (Nauodon, Acanthaluteres, Cantherhines, Amanses) or only a small extension to above the middle of the eye {Alutera). Thus, on

all of the most important grounds, the genera with the 2 + 4 number of branchiostegals are much more specialized in general than are many of the genera with the 1 -t- 4 number, including Stephanolepis, Monacanthus, and

Paramonacanthus.

Pervagor also possesses one unique feature found in neither the other monacanthids nor in balistids. The

lateral surface of the anterior region of the pelvis has a protuberance for articulation with a similar

protuberance from the posterior edge of the coracoid, the

pelvis rotating around this joint when the dewlap is ex- panded.

In short, Pervagor cannot be considered one of the most generalized monacanthids, but, rather, it is probably a derivative of a Paramonacanthus-like stock. In both Paramonacanthus and Pervagor the dewlap is short, not extending out beyond the beginning of the en- casing scale series, which protrude conspicuously from

the ventral contour. The specializations of Pervagor beyond the Paramonacanthus level are the loss of the for- ward extension of the supraoccipital, the more anterior

position of the dorsal spines, the greater elongation of the body, and the development of the rotation processes on

the coracoid and pelvis. Two other genera with a flexible encasing scale series and rudiments of the fin-ray element are Laputa and

Chaetoderma, both of which also have the dorsal spines placed in the generalized location over the rear of the eye. Chaetoderma has a relatively well-developed forward

extension of the supraoccipital and at least a low weak

crest, the forward extension being not much less extensive than in Stephanolepis, Monacanthus, and Para- monacanthus. The most outstanding specializations of Chaetoderma are that the encasing scale segments have

been reduced to two, while retaining their flexibility, and

that the two rudiments of the fin-ray element are minute. The ventral flap of Chaetoderma is small and

similar to that of Paramonacanthus. Chaetoderma could

well be a derivative of Paramonacanthus, specialized by

the increased depth of the body, the great development

of dermal flaps on the skin, the reduction in the number

of segments of encasing scales and in the size of the rudi- ments of the fin-ray element, and the slight reduction in the size of the forward extension of the supraoccipital. However, the scales of Chaetoderma are strongly reminiscent of those of the rough skinned Monacanthus,

especially those of the Indo-Pacific species, in which the

strong central upright spinule is backwardly directed and

bears a notch along its anterior or outer edge. The scales

of Chaetoderma are an elaborate version of this, with a deep cleft in the usually strong single spinule dividing

the spinule into a smaller upwardly or anteriorly directed prong and a larger posteriorly directed prong.

I suspect that the Australasian Chaetoderma is deriv- ed from the Indo-Pacific stock of Monacanthus, by all the ways of specialization mentioned above in comparison to Paramonacanthus, and additionally by the

loss of caudal peduncle armature and the great reduction in the size of the dewlap probably associated in some

way with the camouflage value of the extensively developed dermal flaps. Additional evidence for a close Chaetoderma and Indo-Pacific Monacanthus relation-
ship is that at least some species of the latter have at

least poorly developed dermal flaps. In Laputa there is a full complement of three seg- ments in the flexible encasing scale series and the fin-ray rudiments, while small, are not minute. The dorsal lobe

of the pelvis is of moderate size and the dewlap just as short as in Paramonacanthus. The most prominent

specializations of Laputa in comparison to the other genera with flexible encasing scales and fin-ray elements

are that the forward extension of the supraoccipital has been lost and that the encasing scale series is somewhat

reduced in size. I suspect that Laputa is on the same line as that leading from Paramonacanthus to Pervagor, with Laputa being a derivative of the forerunner of Pervagor

in which the dorsal spine had not yet migrated forward to above the middle of the eye. In addition to Stephanolepis, Monacanthus, and Paro' monacanthus, with fully developed forward extensions of the supraoccipital bearing a relatively well-developed

crest, and Chaetoderma, with a somewhat shorter for- ward extension and very shallow crest, two other genera have a moderately developed forward extension and low

crest, a still rather generalized condition, and another genus has the forward extension but no crest. These are

Alutera, Brachaluteres, and Psilocephalus, in all of which the forward extension reaches to between the middle and almost the front of the eye, with the crest

relatively distinct in Alutera but only very poorly developed in Brachaluteres and absent in Psilocephalus.

All three of these genera have highly specialized pelvic apparatuses, with no dorsal lobe to the pelvis, no pelvic

fin-ray element, and either no encasing scales or a single enlarged scale representing the remnant of the series (some Alutera), even this being lost in large adults. The first dorsal spine is placed over about the middle

of the eye in Alutera and Brachaluteres, and only slightly more posteriorly in Psilocephalus, while Brachaluteres and Psilocephalus are further specialized by having lost the small second dorsal spine, and Psilocephalus by the

great elongation of the body, increased number of verte- brae and development of a long chin barbel. In fact, of the genera studied here, I suspect that at least the majority of those without a dorsal pelvic lobe, with the en- casing scale series essentially absent and with no fin-ray element, form a natural group representing two diver- gent lines of diversification from a more or less Aluteralike ancestral group, which itself evolved from some

derivative of the Stephanolepis-Paramonacanthus level of organization, perhaps from an early Rudarius-like group that still retained the forward extension of the

supraoccipital, and which had the dorsal spine placed

over the middle of the eye and a tendency for the reduction of the fixed encasing scale series, such as is evident

in the two Recent species, R. ercodes with two segments and R. minutus with only one. The Alutera-\ike ancestral group referred to above is envisioned as being essentially like Recent Alutera, with

the exception of having a better developed spiny dorsal

fin basal pterygiophore more closely applied to the skull. This ancestral group is seen as diverging into two lines.

One line leads to Alutera and Psilocephalus by a

decrease in the size and closeness of association of the

basal pterygiophore with the skull, reduction in the size of the first dorsal spine, and elongation of the body and

increased number of vertebrae, as found in some Recent

Alutera (vertebrae 20 to 23) and carried to an extreme in Psilocephalus (vertebrae 29 or 30). In Psilocephalus the

basal pterygiophore is greatly reduced in size and only

closely attached to the skull anteriorly, while the first dorsal spine is slender and delicate and the second spine

is lost, and the pelvis is reduced to a thin narrow shaft. The other line of evolution from the Alutera-Uke ancestral group would seem to lead to those genera with a

simplified pelvic apparatus (no dorsal lobe, no encasing

scales, no fin-ray element) but with a well-developed

spiny dorsal fin basal pterygiophore and a relatively well- developed first dorsal spine. On this line is Brachaluteres, which retains the forward extension of the supraoccipital and at least a remnant of the crest, as well as the relatively low number of 20 vertebrae found also in one species of Alutera, while the body depth is increased

rather than decreased. Part of the increased size of the deep basal pterygiophore in Brachaluteres may be as- sociated with this increased depth of the body and thus

of the muscle bands attaching to the sides of the pterygiophore. The first dorsal spine of Brachaluteres is strong, but the second spine is absent. Brachaluteres has the same kind of elaboration and branching of the epi- pleurals as found in some Alutera. Undoubtedly also on this line and closely related to Brachaluteres is Paraluteres, with an equally low number of vertebrae, an even more reduced pelvis and neither

a forward extension of the supraoccipital nor a crest. The

basal pterygiophore, while strong and closely held to the

skull, is placed a little further back on the skull than in Brachaluteres, and the dorsai spine is over the rear rather than the middle of the eye, perhaps in conjunction with the resculpturing of the skull that took place as Paraluteres developed its mimicry of Canthigaster valentini, with it being advantageous for the dorsal spine to be

able to be laid back inconspicuously against the body

rather than jutting out prominently from the head. In

fact, the dorsal spine in Paraluteres is covered with thick

scaleless skin and in life is probably not capable of being

erected at a full 90° to the dorsal profile, even though the second dorsal spine and presumedly also the locking mechanism are present. Paraluteres probably evolved from the same ancestral group as Brachaluteres, but before the second dorsal spine was lost and the body depth so greatly increased. From this same ancestral group from which Brachaluteres and Paraluteres evolved also probably came Oxy- monacanthus and Pseudaluteres, with much the same

tendencies for elongation and increased number of verte- brae as in the Alutera-Psilocephalus line, but with the

exact opposite trend with the basal pterygiophore and

dorsal spine, the pterygiophore remaining large and

closely associated with the skull, as in Brachaluteres and

Paraluteres.

In Oxymonacanthus the basal pterygiophore of the
spiny dorsal fin is prolonged anteriorly over the posterior one-third of the surface of the ethmoid, and the first dorsal spine is placed over the front of the eye. In Pseudaluteres the basal pterygiophore is even further prolonged

anteriorly, being of such great length that it covers nearly

the entire length of the dorsal surface of the skull, the

dorsal spines being placed further anteriorly than in any

other monacanthid, distinctly in front of the eye. As discussed before, there is no counterpart in any

other scleroderm plectognath fish of the true or pleural

ribs found in Pseudaluteres. Oxymonacanthus and Pseudaluteres share a specializ- ed condition of the sphenotic found in no other monacanthids. In other monacanthids the lower region of the

side of the cranium, just above the region of articulation

of the upper end of the hyomandibular, is formed by the sphenotic anteriorly and by the pterotic posteriorly, the former ending ventrally as a ventrally or anteroventrally

directed prong and the latter having a larger ventrally directed prong that overlies the posterodorsal region of the hyomandibular. In both Oxymonacanthus and

Pseudaluteres, as explained in detail in the section on

anatomical diversity, the sphenotic is displaced posteriorly by a ventrally directed portion of the posterior region of the frontal bearing its own ventrally directed prong, the side of the cranium just above the ar- ticulation of the hyomandibular thus being formed by

the frontal anteriorly and the pterotic posteriorly, with

the sphenotic squeezed in between and with a relatively small ventral prong. Moreover, Oxymonacanthus and

Pseudaluteres are the only two genera of monacanthids

to have completely lost the prootic shelf. Oxymonacanthus is speculated to be an early offshoot

of the line leading to Pseudaluteres, an offshoot of the pie-Alutera group before the dorsal lobe of the pelvis was

lost and the encasing scales nearly entirely lost. In Oxy- monacanthus the dorsal lobe of the pelvis is only slightly developed and the encasing scales are reduced to an in- determinate number of scales gradually and slightly in- creased in size from those of the surrounding region, while the number of vertebrae is increased to about 25

(only 1 less than in Pseudaluteres), and the forward ex- tension of the supraoccipital is absent. Except for its specialized small nipping mouth (with reduced number of dentary teeth) and slightly elongate

snout, a form such as Oxymonacanthus could easily have

given rise to Pseudaluteres by the continued reduction in the dorsal lobe and encasing scales and the further migration forward of the dorsal spine and the anterior elongation of the basal pterygiophore. The shared highly

specialized nature of the sphenotic in both genera is as- surance of their close relationship.

All of the other genera of monacanthids examined

here, but not yet discussed, form the middle group of moderately specialized genera intermediate in many

ways between the basal Stephanolepis-Monacanthus- Paramonacanthus group and their close relatives and the group of genera of several lines thought to be derived from a pre-A/u(era-like form. The middle group contains genera without a forward extension of the supraoccipital and without a fin-ray element, but with encasing

scales usually present in an inflexible series or only minutely developed, with 19 or 20 vertebrae and the body

not especially either elongate or deepened. These are Amanses, Cantherhines, Rudarius, Navodon, and

Acanthaluteres. Of these, Amanses and Cantherhines have two and a

half segments of encasing scales, Navodon two, Rudarius two or one, and Acanthaluteres only minute series when

present. Amanses, Cantherhines, and Acanthaluteres have a deep groove posterior to the dorsal spines which is not present in Navodon and Rudarius, while the first dorsal spine is placed behind the middle of the eye in Navodon, Rudarius, and Acanthaluteres, but over the middle or front of the eye in Amanses and Cantherhines,

the latter two genera also having relatively plain dorsal spine ornamentation. Amanses and Cantherhines have long been considered

closely related, rightly so I think, and have been well characterized by Randall (1964), who showed them to

differ primarily in spinulation {Amanses with coarser

scales and a patch of long quill-like spines on the side of the body between the soft dorsal and anal fins) and a deeper caudal peduncle and lower numbers of soft dorsal and anal fin rays. Amanses is obviously a slightly specialized spinier scaled version of Cantherhines, and

Randall (1964:332) has suggested that Scobinichthys and

Meuschenia (neither studied here) are also closely related to Cantherhines.

I suspect that Cantherhines and its close relatives are derived from a Pervagor-like stock (prior to the develop- ment of the special rotation joint between the pelvis and

coracoid), some species of which have a groove behind

the dorsal spines located above the middle of the eye, by

a decrease in the amount of ornamentation of the first dorsal spine and sometimes of its slight forward migration, and by the reduction of the encasing scale series from a flexible three segments around a fin-ray element

to an inflexible two and a half segments without a fin-ray element. Whether Acanthaluteres, with a deep groove behind

the dorsal spines, is related to the Cantherhines-hke

genera is difficult to say, for it has a more generalized

dorsal spine position over the rear of the eye but a more

specialized pelvic apparatus, the dorsal lobe being es- sentially absent and the encasing scales either absent or minute. I suspect that Acanthaluteres is an offshoot of the line leading to the pre-/l/ufera-like group hy- pothesized here as containing the Alutera-Psilocephalus

line and the Brachaluteres-Paraluteres and the Oxy- monacanthus-Pseudaluteres lines. Rudarius is probably a derivative of the line leading from a Pervagor-\\ke form to those of the Cantherhineslike genera, but with the placement of the dorsal spine remaining a little more posterior, usually just behind the middle of the eye, while the trend of reducing the in- flexible encasing scale series continued further to only two segments in one of the species and to one segment in the other, while the dorsal lobe and ventral dewlap

remained of moderate to small size.
The dense patch of setae found on the caudal peduncle

of male Rudarius ercodes is similar to that found in males of some species of Cantherhines (others have pairs

of retrorse spines; see Randall 1964 and Tyler 1970e), while the much longer posteriorly directed spines on the caudal peduncle of male R. minutus are undoubtedly a

specialized development from the ancestral R. ercodeslike form and are not in any way related to the even

longer quills further forward on the body of Amanses.

Similarly, the large dermal flaps found in R. minutus

have a much smaller counterpart in some species of Cantherhines (see Randall 1964). Navodon shares many characteristics with Rudarius,

as pointed out by Fraser-Brunner (1941b:178-179), and

the two are probably closely related, both specialized in their own way, Rudarius with a relatively deep small body and only two teeth in each dentary and Navodon

with a larger more elongate body and a full complement

of three dentary teeth but a more forwardly placed gill

slit and reduced size of the ventral dewlap. Four genera not examined for this work and not dis- cussed above should be briefly mentioned, these being

Arotrolepis, Pseudomonacanthus, Blandowskius, and

Eubalichthys. According to the data in Fraser-Brunner

(1941b), these four genera can be characterized as fol- lows:

Arotrolepis has the dorsal spines originating behind

the middle of the eye, a flexible encasing scale series (presumedly of three segments and with a fin-ray ele- ment) of small size, the ventral dewlap of no more than moderate size, and the scales usually with a single strong

central spinule and arranged in distinct longitudinal

tracts. Fraser-Brunner thought Arotrolepis most closely related to Monacanthus, although in his key to the genera (which he cautions does not show the true rela- tionships of some of the genera) it is coupled with Chaetoderma. I suspect that he is right and that

Arotrolepis is on the Monacanthus-Chaetoderma line. It obviously would be of great interest to know the form of the supraoccipital in Arotrolepis. Pseudomonacanthus (most data from Fraser-Brunner

1940c) has the dorsal spines originating over the middle

or behind the middle of the eye and an inflexible short

series of encasing scales (presumedly of less than three segments and with the fin-ray element absent) and no

dorsal pelvic lobe. Blandowskius, which Fraser-Brunner thought was

most closely related to Pseudomonacanthus, has no

encasing scales at all and the dorsal spines over the

rear of the eye, with both genera being intermediate between the Rudarius and the Alutera levels of organization. Eubalichthys, with the dorsal spines over or in front of the middle of the eye and followed by a groove for their reception, and with the inflexible encasing scale series much reduced in size until it is minute and inconspicuous, was thought by Fraser-Brunner to be a

derivative of the Cantherhines-Amanses line.

In short, many of the generic relationships within the monacanthids remain unclear, and will probably continue to be unclear until many more species, representing all genera, have been examined osteologically than it has been possible to do here. However, it does seem clear that the most generalized forms are those with an

anteriorly elongate supraoccipital bearing a vertical crest and with a well-developed series of flexible encasing

scales of three segments covering over a rudimentary fin- ray element, and with the dorsal spine placed behind the middle of the eye. The genera sharing these conditions

are Stephanolepis, Monacanthus, and Paramonacanthus. A Stephanolepis-like stock is probably ancestral to both Monacanthus and Paramonacanthus. Chaeto- derma (and probably Arotrolepis) seems a derivative of a Monacanthus-like stock, while Laputa is probably deriv- ed from Paramonacanthus along with Pervagor. It is sus- pected that a Pervagor-\\ke stock is ancestral to the

various moderately specialized genera with inflexible en- casing scale series and no fin-ray element. An Aluteralike stock is suspected to have evolved from some

derivitive of a Paramonacanthus-like stock, perhaps

from a form like Rudarius or Navodon, and to have

diverged in two directions, one leading to Alutera and

Psilocephalus and the other to two lines leading to Brachaluteres and Paraluteres and to Oxymonacanthus

and Pseudaluteres.

SUPERFAMILY OSTRACIOIDEA

Comparative diagnosis (contrast with that of the

Balistoidea). —Head and most of body encased in a

relatively inflexible (except on cheek in front of gill slit) cuirass of especially thick and mostly hexagonal scale plates whose apposed edges are articulated by minute in- terdigitations, the portion of the body posterior to the carapace with or without isolated scale plates of various shape but never continuously covered by scales; body

outline in cross section less laterally compressed and

always with two or more angles or ridges; no spiny dorsal

fin; soft dorsal and anal fins short-based, with 9 to 13 rays and a slightly lesser number of basal pterygio- phores; caudal fin with 10 or 11 rays; pelvis and pelvic fin absent; teeth relatively small and more or less conical or only slightly compressed basally but often constricted

distally, between 6 and 17 in a single series in both jaws;

lateral line not associated with grooves or spiny processes on the scale plates; branchiostegals usually 2-1-4 but sometimes 1 -I- 4 or 2 -I- 3, at least some of the rays in the

posterior division as broad and laterally compressed as those in the anterior division; distal end of last branchiostegal ray always articulated to the inner surface of the suboperculum; elements of the hyoid arch more compacted together anteroposteriorly and most elements less elongate and more deep bodied; urohyal much reduced in

size, a more or less flattened plate or a slightly curved

rod, a ventral flange either absent or very poorly developed; fifth ceratobranchial (lower pharyngeal) al-
ways toothless; pharyngobranchials consisting either of a

toothless suspensory element followed by three elements

bearing small but protruding or minute nonprotruding

teeth, or a toothless suspensory element (absent in some

Acanthostraclon) followed by two elements, one or both

of which bear minute nonprotruding teeth; epi- branchials always four; gill rakers always present along

anterior edge of fifth ceratobranchial (posterior edge of

last gill slit); caudal fin supporting structures extremely

consolidated, the epural, hypural, parhypural, and cen- trum elements fully fused into a single plate; haemal

spine of penultimate vertebra either autogenous or fused

to its centrum; neural arch of the last vertebra complete, the canal accommodated in a tube through the

plate exiting on the posterior half of the dorsal edge, while the haemal arch is either complete and the canal accommodated in a tube through the plate or the arch is essentially absent, the haemal region of the plate solid and not pierced by the canal; uroneurals never present; vertebrae normally 9 -I- 9 = 18 or 10 -I- 8 = 18, but 9 -I- 10 = 19 in one species, and always 9 or 10 abdominal verte- brae; the first 2 to 5 vertebrae reduced in size at least anteroposteriorly and at least partially fused to the rear

of the skull; 7, more rarely 8, abdominal vertebrae with

neural spines anterior to the first basal pterygiophore of the soft dorsal fin; 3 to 5 caudal vertebrae posterior to the

last basal pterygiophores of both the soft dorsal and anal

fins; usually no more than 2, rarely 3, soft dorsal fin basal pterygiophores placed between successive neural spines; most neural spines positioned strongly obliquely in rela- tion to the axis of the vertebral column; haemal spines above the anal fin basal pterygiophores relatively

shorter, either rudimentary or well developed as anteroposteriorly expanded plates but never long and shaftlike and not penetrating into the proximal region of the series of anal fin basal pterygiophores, and at least some of these haemal spines markedly different in shape and size from the neural spines above them; soft dorsal fin basal pterygiophores 8 to 10; anal fin basal pterygiophores 8 to

10; prominent thin lateral flanges not present on the soft dorsal and anal fin basal pterygiophores; distal pteryg- iophores either absent or unossified in both the soft dorsal and anal fins; 4 to 6, or about half, of the anal fin basal pterygiophores with only their distal ends placed in the midline of the body, their proximal regions in- creasingly divergent variously to the left and right of the midline in the musculature bordering the rear of the ab- dominal cavity; no spiny dorsal fin and hence no spiny

dorsal fin basal pterygiophores, but a supraneural ele- ment present anteriorly from the dorsal end of the first basal pterygiophore of the soft dorsal fin, this supraneural element representing a modified basal pterygiophore, per- haps the supraneural strut of balistids; epipleurals and

ribs never present; uppermost pectoral fin ray either of two relatively well-developed halves of about equal length (aracanids) or of a single piece bearing a foramen basally

(ostraciids); actinosts inflexible and articulated by

suturing to one another and to the scapula and coracoid; coracoid and cleithrum enlarged; coracoid expanded

ventrally, as wide as or wider there than dorsally, with

prominent broad flanges; coracoid with or without a posterior prong along its posterodorsal edge, the prong when

present not so well -developed or closely associated with

the lowermost actinost; scapular foramen always complete; cleithrum with an anterior flange from its lower anteromedial edge; postcleithrum usually with two dis- tinct halves, rarely as a single piece, the bone directed

posteriorly or only slightly obliquely downward and

variously slightly to enormously expanded posteriorly and ventrally into a flat relatively thin plate, but never

as a long sturdy rod; nearly the entire length of the supra- cleithrum overlying the cleithrum, or cleithrum and

postcleithrum, and the supracleithrum very firmly held

to them and the posttemporal; Baudelot's ligament ossified as a stout heavy rod between the posterior region of the parasphenoid and the region of articulation of the supracleithrum, cleithrum, and posttemporal; posttemporal usually relatively large; palatine an elongate block

of bone representing an enlarged foot of the T-shaped

balistid palatine and firmly sutured along all but the distal end of its medial surface to the ectopterygoid and

mesopterygoid while its distal end is held by ligament

primarily to the vomer; vomer much enlarged, having

either a strongly laterally expanded anterior end and a

relatively short posterior tapering shaft fitting into a shallow concavity in the parasphenoid (aracanids) or a

strongly expanded lateral surface throughout its length,

so that the bone is more or less square and has a flat- tened posterior surface that sutures to the similarly flat- tened anterior end of the parasphenoid (ostraciids); ventral edge of the ventral flange of the parasphenoid

laterally expanded slightly to moderately and only partially along its length (aracanids) or well expanded along

all of its length anterior to the level of about the prefrontal (ostraciids); ventral flange of the parasphenoid

without a deep indentation at about the level of the prefrontal; parasphenoid with a high dorsal flange in the medial septum of the orbit which sutures broadly or only

slightly with long anteroventral extensions of the ptero- sphenoids into the medial septum; the medial edges of the pterosphenoids not in contact in the posterior wall of the orbit, well separated there; myodome small or absent; apposed surfaces of the parasphenoid and basioccipital not excavated and no canal between them leading

anteriorly into the myodome cavity; epiotics not in contact medially on the posterior surface of the skull, widely

separated there by the more posteriorly placed supraoccipital; supraoccipital either with or without a posterior

crest, but never with an anterior crest on the surface of the main body of the bone; prootic shelf usually relatively larger, always with a prominent ventral or ventrolateral flange from its lateral edge; the major foramen in the prootic shelf relatively large and elongate, and not completely enclosed by the prootic, being bounded

laterally by the prootic and medially by the para- sphenoid; anterior edge of the upper part of the preoper- culum articulated below along the rear edge of the hyomandibular but above to a groove on the lateral sur- face of the hyomandibular; hyomandibular a greatly ex- panded plate, without much of a shaftlike portion.
Family Aracanidae

Comparative diagnosis (contrast with that of the

Ostraciidae). —Supraorbital region of the skull relatively strong, the frontal relatively thick in this region and

not held extraordinarily firmly to the undersurface of the carapace; frontal with a long forward extension broadly

overlying the dorsolateral surface of the ethmoid to, or very nearly to, the extreme anterior end of the snout;

supraoccipital with a long, thin, vertical crest extending

posteriorly well beyond the level of the base of the skull; epiotic much prolonged posterolaterally, well beyond the

level of the base of the skull, and beyond the level of the

distal end of the supraoccipital crest; prootic shelf with a recurved wing from its lateral edge which makes contact with the anterior edge of the laterally expanded posterior region of the bone; myodome small but distinct; four pharyngobranchials, the first a toothless suspensory element, the second either toothless or with minute

teeth, the third and fourth with few but large teeth; branchiostegals usually 2 -t- 4, but sometimes 1 -I- 4 or 2

-I- 3; ethmoid relatively deep and platelike and not much

laterally expanded anteriorly; pterosphenoid and para- sphenoid with a broad region of suturing in the interorbital septum; parasphenoid anterior to its region of suturing with the anteromedial edges of the prootic shelves either not much expanded laterally or expanded

laterally only for a portion of its length there, the laterally expanded portion being either anteriorly near the vomer or posteriorly near the prootic shelf, but not forming a complete hard palate over the roof of the oral

cavity; posterodorsal region of the coracoid with a moderately to well-developed posterior prong; two small

vertebrae, represented mostly by neural arch material, at the front of the vertebral column variously fused and

sutured to one another and to the exoccipitals and

basioccipital, the fusion region without a ventral process below the level of the centra; vertebrae immediately fol- lowing the fusion region with long neural spines and

anteroposteriorly much compressed centra with well- developed transverse processes; the centra of the first several vertebrae anterior to the caudal plate not much

compressed anteroposteriorly; haemal arch and spine of the penultimate vertebra relatively well developed and

autogenous; caudal fin rays i, 9, i (except the Eocene

Proaracana, with i, 8, i); postcleithrum (especially the

ventral piece) greatly expanded posteriorly into a deep

thin plate reaching the level of the anterodorsal ends of the more anterior anal fin basal pterygiophores; supraneural long and well developed, with a relatively deep

ventral flange making contact with most or all of the neural spines of the predorsal vertebrae (exclusive of those of the small first two fused vertebrae), extending

anteriorly well beyond the level of the anteroventral end

of the first dorsal fin basal pterygiophore; haemal spines on the more posterior abdominal and on most of the caudal vertebrae well developed, especially those above

the anal fin basal pterygiophores which they support

through a connective tissue sheet rather than by close apposition; first anal fin basal pterygiophore without

Figure 129.—Typical body form in the Recent Aracanidae: Aracana aurita.

anterolateral wings from its distal end; haemal canal entirely straight, in the midline under the vertebral centra and relatively well enclosed by well-developed haemal

arches and spines on all but the more anterior ab- dominal vertebrae; none of the vertebrae posterior to the

anteriormost two fused vertebrae sutured to one another; uppermost pectoral fin ray relatively well developed,

consisting of two halves with a few cross-striations distally, the two halves of about the same length or one half, usually the lateral, only slightly shorter than the other; body relatively deep, the distance between the distal ends of the first dorsal and anal fin basal pterygiophores being contained less than 3 times in the SL and the dis- tance between the top of the rear of the cranium and the ventralmost edge of the pectoral girdle being contained about one and three-fourths to slightly more than twice

in the SL; carapace open behind the dorsal and anal fins; carapace with a well to only slightly developed ventral

keel; caudal peduncle always with scale plates isolated from the carapace proper, often almost completely, if not

completely, encircling it.

Detailed Description of Kentrocapros aculeatus. Material examined.—Two cleared and stained

specimens; 90.0-90.7 mm.

Occipital Region.

Basioccipital. —A short column, slightly expanded

anterolaterally; cartilage filled anterodorsally; ar- ticulates through cartilage and interdigitation dorsally with the exoccipitals and anterolaterally with the

prootics, while its ventromedial surface is broadly overlain by and extensively interdigitated with the bifurcate

posterior end of the parasphenoid. The upper region of the extreme posterolateral surface of the basioccipital is more or less indistinguishably fused with the basal region

of the rudimentary first two abdominal vertebrae, as ex- plained in the section on the vertebral column.
Figure 130.—Range of diversity in body form and external features of representative aracanid genera: Strophiurichthya inermis (above) and

S. ro6u«(u«—in front of each, above, nasal region as seen externally (far

left) and the olfactory lamellae as seen with the top of the nasal sac removed, and. below,

outline of cross section of middle of body.

Exoccipital. —Cartilage filled along all of its edges

of articulation with the other cranial bones; articulates through cartilage posteromedially with its opposite member and posterodorsally with the supraoccipital; articulates through cartilage and extensive inter- digitation posterolaterally with the epiotic, ventro- medially with the basioccipital, and anteroventrally with

the prootic, while ventroiaterally it articulates mainly

through cartilage but with some interdigitation with the

pterotic. The lateral surface of the extreme posterior end

of the exoccipital is overlain by and interdigitated with

the neural spines of the rudimentary first two ab- dominal vertebrae, as explained in the section on the

vertebral column. In this region the exoccipitals form the

lateral wails of the foramen magnum, while the dorsal

wall is formed by the cartilaginous sheet between the posteromedial edges of the two exoccipitals; the ventral

surface of the foramen magnum is bounded by the basioccipital.

Supraoccipital. —Laterally expanded and with a well-developed supraoccipital crest directed posteriorly; cartilage filled along all of its edges of articulation with

the other cranial bones; articulates by extensive inter- digitation anteriorly and anterolaterally with the frontals, while it articulates through cartilage laterally with

the epiotics and ventrally with the exoccipitals.

Otic Region.

Pterotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates through cartilage and interdigitation anteroventrally with the prootic, posteroventrally with the exoccipital, posterodorsally with the epiotic, and anterodorsally with

the sphenotic; the posterodorsal portion of the sphenotic

intervening between the pterotic and frontal so that the

latter two bones do not articulate directly with one

another. For a short distance medially along its anteroventral edge the pterotic supports through cartilage the

posterodorsal edge of the hyomandibular. The anterolateral region of the pterotic is prolonged ventrally into a

stout shaft whose medial edge articulates through fi- brous tissue with the posterodorsal region of the hyomandibular while laterally it is broadly overlain and extensively interdigitated with the posttemporal and medially

it helps to support by fibrous tissue the expanded lateral end of the ossified Baudelot's ligament.

Sphenotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates through cartilage and interdigitation posterodorsally with the pterotic and, to a lesser extent, with the epiotic, while anterodorsally it interdigitates with the frontal; medially in the posterior wall of the orbit the sphenotic

articulates through cartilage and interdigitation with the pterosphenoid, prootic, and pterotic. The dorsolateral surface of the sphenotic is broadly overlain by the frontal.

Epiotic. —A rounded sturdy cone anteriorly but

prolonged posteroventrally into a thin flange; cartilage

filled along all of its edges of articulation with the other

cranial bones; articulates through cartilage and inter- digitation dorsally with the frontal, anteroventrally along its lateral edge with the sphenotic and pterotic and

posteroventrally with the exoccipital and medially, through cartilage only, with the supraoccipital.

Prootic. —Cartilage filled along all of its edges of articulation with the other cranial bones, except anteriorly and ventrally where it articulates with the para- sphenoid; articulates by interdigitation ventromedially

with the laterally compressed keellike dorsal region of
Figure 131.— Range of diversity in body form and

external features of representative aracanid genera: Aracana aurita—upper left, nasal region as seen externally (olfactory lamellae, if present.

indistinct in specimen examined); lower left, outline of cross section of middle of body.

Figure 132.—Range of diversity in body

form and external features of representative aracanid genera: Anoplocapros amygdatoides—

upper left, nasal region as seen

externally (far left) and the olfactory lamellae as seen with the top of the nasal sac removed: lower

left, outline of cross section of middle of body.

Figiire 133.—Range of diversity in body form and external features of representative aracanid genera: Capropygia untstnafa—uppei

left, nasal region as seen externally

(olfactory lamellae, if present, indistinct in specimen examined); lower left, outline of cross section of middle of body.

Figure 134.—Range of diversity in body

form and external features of representative aracanid genera: Caprichthys gymnura—upper

left, nasal region as seen externally (olfactory lamellae, if present, indistinct in specimen

examined); lower left, outline of cross

section of middle of body.
the parasphenoid; articulates through cartilage and in- terdigitation ventrolaterally with the pterotic, postero- ventrally with the basioccipital and exoccipital, dorso- medially with the pterosphenoid, and dorsolaterally with

the sphenotic. Along a short distance of the anterior edge

of its laterally expanded posterior portion the prootic ar- ticulates through cartilage with the posterodorsal end of the hyomandibular. The anteromedial region of the

prootic possesses a long forward extension under the orbit which makes contact by interdigitation with the parasphenoid at the level of the prefrontals. A recurved

portion of this prootic subocular shelf is directed posterolaterally and makes contact with the anterolateral region

of the rear half of the prootic, the two parts of the bone

interdigitating in this region just medial to the ar- ticulation of the prootic with the dorsal edge of the hyomandibular. Just ventral to this region of contact between the posterolateral wing of the prootic shelf with

the rest of the prootic, the wing is thickened and ar- ticulates by fibrous tissue with the dorsal surface of the

lateral region of the ossified Baudelot's ligament. The

medial edges of the prootics form the lateral walls of the myodome, while medially directed shelves from the medial edges of the prootics more or less meet in the midline and articulate through cartilage with one another to form the dorsal roof of the myodome. The anterior edge

of the myodome is formed by the prootic, except ventrally where it is formed by the parasphenoid.

Orbital Region.

Frontal. —Wide in the posterior half of its length, then rapidly tapering to a point anteriorly; extending

throughout almost the entire length of the skull and a

relatively sturdy bone throughout its length; articulates through cartilage and interdigitation posteromedially

with the supraoccipital and posterolaterally with the

epiotic and sphenotic, broadly overlying the latter. In the

posterior wall of the orbit the frontal articulates through

cartilage and interdigitation with the pterosphenoid and

sphenotic. The anterior prolongation of the frontal broadly overlies and is held by fibrous tissue to the dorsolateral surface of the ethmoid. Immediately posterior to where it begins to overlie the ethmoid, the ventral sur- face of the frontal is held by fibrous tissue to the dorsal surface of the prefrontal.

Prefrontal. —Large and wedge-shaped; cartilage

filled along its medial edge where it is continuous with

the ethmoid cartilage; articulates by fibrous tissue dorsally with the broadly overlying frontal and ventrally with the dorsal edge of the parasphenoid, the latter ar- ticulation perhaps strengthened by slight interdigitation. Its major surface of articulation, however, remains with the ethmoid cartilage, that broadly inter- venes between the prefrontal and the ethmoid.

Parasphenoid. —An elongate, mostly laterally compressed, slab of bone; expanded in the middle of its

length for articulation by interdigitation with the antero- medial edges of the prootic shelves, and, more posteriorly along its ventral edge, where it interdigitates with the prootics and basioccipital. Dorsally in the region

of the orbit the parasphenoid has a large dorsal flange which meets and interdigitates with the ventral flanges

of the pterosphenoids. Just anterior to this dorsal flange the parasphenoid articulates by fibrous tissue and per- haps slight interdigitation with the ventral end of the

prefrontal. Anterodorsally the parasphenoid articulates by fibrous tissue and interdigitation with the ventral edge of the ethmoid, while the extreme anteroventral edge of the parasphenoid becomes concave for reception

of the posterior end of the vomer, with which it inter- digitates. At its extreme posterior end the parasphenoid

bifurcates in the region that overlies the ventral surface

of the anterior half of the basioccipital. However, there is no apparent opening into the myodome in this region such as is found in triacanthoids and balistoids. Along its laterally expanded ventral surface in the region of the

rear of the orbit the parasphenoid articulates by fibrous

tissue and perhaps slight interdigitation with the medial ends of the ossified Baudelot's ligaments from either

side.

Pterosphenoid. —Cartilage filled along all of its edges of articulation with the other cranial bones, ex- cept for a very short distance anteroventrally; ar- ticulates through cartilage and interdigitation posterodorsally with the frontal, which somewhat overlies it, posteriorly with the sphenotic, and posteroventrally with

the prootic. The anterior end of the pterosphenoid is prolonged anteroventrally into a process which inter- digitates with the dorsal edge of the dorsal flange of the parasphenoid in about the middle of the orbit. Ethmoid Region. Ethmoid. —Elongate; laterally expanded and somewhat rounded dorsally, but ventrally becoming

laterally compressed where it articulates by inter- digitation and fibrous tissue with the parasphenoid, which in the posterior region of the articulation overlies the ventrolateral edges of the ethmoid; cartilage filled at

its posterior edge, where it is continuous with the eth- moid cartilage; articulates by fibrous tissue dorsally with

the anterior prolongation of the frontal, which broadly

overlies the dorsolateral surface of the ethmoid. Anteroventrally the ethmoid articulates through cartilage and

slight interdigitation with the dorsal surface of the vomer. At its anterior edge the ethmoid helps support, through fibrous tissue, the upper jaw. Vomer. —A short, squarish block of bone with two

lateral expansions and a posterior tapering shaft; ar- ticulates through cartilage and interdigitation dorsally with the ethmoid and by interdigitation posteriorly where its shaft fits into the concave anteroventral edge of the parasphenoid. The anterior end of the vomer sup-
ports, through fibrous tissue, the upper jaw. The con- cave region between the two lateral expansions of the vomer articulates by strong fibrous tissue with the medial surface of the palatine, holding it immovably to

Mandibular Region. Hyomandibular. —Expanded posteriorly, and

slightly narrowed anteriorly where it ends bluntly; cartilage filled at its posterior and anterior edges; ar- ticulates by fibrous tissue posteriorly with the extreme

lateral edge of the posterior portion of the prootic and

with the anteromedial edge of the pterotic, as well as along the medial surface of the ventral shaft of the

pterotic. Dorsomedially the hyomandibular is firmly held by fibrous tissue to the lateral edge of the prootic

shelf and its posterolateral wing. Anteriorly the hyo- mandibular articulates along its dorsal edge by fibrous

tissue with the posteroventral end of the metapterygoid,

while its extreme anteroventral edge articulates through

cartilage and fibrous tissue to the fibrous tissue sheet between the metapterygoid, symplectic, and preoper- culum. In about the middle of its length the posterior edge of the hyomandibular has a blunt process with a concave head for articulation by fibrous tissue with the head of the operculum. Just anterior to this articular

area, the hyomandibular bears an elongate groove along

its posterolateral surface into which the slender posterodorsal end of the preoperculum fits and is tightly held by

fibrous tissue.

Quadrate. —Wide posteriorly, tapering anteriorly

to a knob for articulation with the articular in the lower

jaw, while from its posteroventral edge it possesses a well-developed posteriorly directed process; cartilage fill- ed at its posterior edge; articulates by interdigitation

dorsally with the ectopterygoid, and, to a lesser extent, with the extreme ventral edge of the mesopterygoid; ar- ticulates posteriorly through cartilage with the metapterygoid; at the indented region on its lower posterior edge the quadrate articulates by fibrous tissue and some

interdigitation with the anterior end of the symplectic, which broadly overlies its lateral surface. Along most of

its ventral edge the quadrate articulates by fibrous tis- sue with the preoperculum.

Metapterygoid. —A more or less elongate, rec- tangular plate, somewhat wider anteriorly than posteriorly; cartilage filled at its anterior edge; articulates anterodorsally by interdigitation with the mesopterygoid, which it broadly overlies; articulates anteroventrally through cartilage with the quadrate, while along

the anterior half of its ventral edge it articulates by inter- digitation with the symplectic. The posterior and

posteroventral edges of the metapterygoid are firmly held by fibrous tissue to the anterodorsal edge of the hyomandibular. The dorsal end of the interhyal articulates by

fibrous tissue with the ventral edge of the metapterygoid

just posterior to the posterodorsal end of the symplectic and just in front of a ventral process of the metapterygoid.

Symplectic. —Slender and somewhat triangular in shape; slightly filled with cartilage at its anterior and, to a lesser extent, posterodorsal end; articulates by fibrous

tissue and interdigitation anteriorly with the quadrate, which it broadly overlies, and posterodorsally by fibrous

tissue and extensive interdigitation with the anteroventral surface of the metapterygoid, which it also overlies. The posterior edge of the symplectic is in contact with

the fibrous tissue sheet between the symplectic, metapterygoid, hyomandibular, and preoperculum, and its posterodorsal end is closely adjacent to the region where

the dorsal end of the interhyal articulates with the metapterygoid.

Palato-Pterygoid Region.

Palatine. —A sturdy dome; articulates by extensive interdigitation ventrally with the ectopterygoid and

mesopterygoid. Dorsomedially the palatine articulates by fibrous tissue with the concave region on the lateral surface of the vomer between the two laterally expanded

processes of the vomer.

Ectopterygoid. —Elongate, slightly widest in the middle; articulates by extensive interdigitation dorsally with the palatine, posteriorly with the mesopterygoid, and ventrally with the quadrate, which broadly overlies

its posteroventral region.

Mesopterygoid. —A large triangular slab whose

lateral surface is broadly overlain by the metapterygoid,

to which it is extensively interdigitated; anteriorly the mesopterygoid extensively interdigitates with the

palatine and ectopterygoid and, to a much lesser extent, with the upper posterior edge of the quadrate. Opercular Region. Operculum. —A relatively flat plate except at its upper end where it is expanded into a facet for ar- ticulation by fibrous tissue with the slight concavity on

the ventrally directed knob of the posterior edge of the hyomandibular. Ventrally the operculum broadly overlies and articulates by fibrous tissue with the suboper- culum.

Suboperculura. —A thin plate, widest anteriorly, its ventral region broadly rounded, tapering to a point posteriorly; articulates by fibrous tissue dorsally with the broadly overlying operculum. At the anterior edge of the

region where the operculum overlies the suboperculum, a

strong ligament coming from the interoperculum makes

contact with the suboperculum and, to a lesser extent, with the operculum.

189
Interoperculum. —A short rod of somewhat ir- regular shape but usually slightly wider in the middle

region than at either end; extends from the level of the

anterior end of the preoperculum to the level of the posterior end of the epihyal; connects by a strong ligament

anteriorly to the angular in the lower jaw, while posteriorly it connects by a short ligament to the epihyal and

by a longer more diffuse ligament to the anterior edge of the suboperculum and, to a lesser extent, of the oper- culum.

Preoperculum. —Relatively short; moderately ex- panded in the middle region and tapering to narrow ends

anteriorly and posteriorly; articulates by fibrous tissue anteriorly along its dorsal edge with the quadrate, while

posteriorly the narrow shaft of the preoperculum is held by fibrous tissue along the ventral edge of the hyoman-

'dibular and, more dorsally, in the shallow groove on the

lateral surface of the hyomandibular. The middle of the

dorsal edge of the preoperculum also connects to the fi- brous tissue sheet between the symplectic, hyomandibular, and metapterygoid.

the vomer and ethmoid, and ventromedially with the

dorsolateral surface of the dentsu^. Lower Jaw.

Dentary. —Wider posteriorly than anteriorly; its posteromedial surface concave dorsally to accommodate

the articular, with which it interdigitates. Just below the

articular, the dentary interdigitates with the angular. The ventromedial edges of the two dentaries are held

closely together by fibrous tissue. Laterally from its posterodorsal region the dentary articulates by fibrous

tissue with the medial surface of the maxillary. Each

dentary bears four teeth, like those of the upper jaw, in deep grooves on its outer surface, each of the tooth bearing grooves ending posteriorly in a deep socket in which new teeth develop. The sockets are in communication

with the large pulp cavity that fills most of the hollow in- terior of the dentary. The pulp cavity communicates

with the exterior not only at the sockets but also at its posterior concave region of articulation with the artic- ular. Upper Jaw.

Premaxillary. —A slightly curved plate, wider dorsally than ventrally; its posterodorsal region flattened for articulation by fibrous tissue with the anterior edges of the vomer and ethmoid; the anterior edge of the upper jaw formed by the premaxillary, except for a short dis- tance ventrally where it is formed by the maxillary; the dorsomedial edges of the two premaxillaries held in close apposition by fibrous tissue. Each premaxillary bears

four teeth in a single row in the two specimens examined. The teeth are borne in relatively deep and elongate grooves on the outer surface of the premaxillary. The

lowermost teeth are shaftlike and taper to sharp points, but more dorsally they are flattened and blunter at the

distal ends, except when they first erupt through the gum

as replacement teeth, at which time they too are sharp

pointed but apparently rapidly become worn down to bluntness through use. At the posterior end of each tooth bearing groove there is a deep socket in which new teeth develop before moving forward to replace the old ones. Most of the interior of the premaxillary contains the dental pulp from which the new teeth develop. This pulp

cavity communicates with the exterior not only by the deep sockets in which the new teeth develop but also by a

large hole in the posterodorsal surface of the maxillary. The premaxillary articulates by extensive inter- digitation with the maxillary along all of its posterior edge, except for a short distance dorsally.

Maxillary. —Widest ventrally, with a deep in- dentation along its lower posterior edge; articulates by

extensive interdigitation anteriorly along all of its length except extremely ventrally with the premaxillary, which

it somewhat overlies. The maxillary articulates by fi- brous tissue posterodorsally with the anterior edges of

Articular. —Small; its posterior edge with a concavity for articulation by fibrous tissue with the anterior knoblike process of the quadrate. Anteriorly the articular

interdigitates with the concave upper half of the postero- medial surface of the dentary. On the medial side of its ventral edge the articular interdigitates with the angular, but the lateral surfaces of the two bones are not in contact; rather, they are slightly separated by the dentary. The sesamoid articular is a flattened nubbin of bone

mostly held to the medial surface of the anterior end of the articular just behind the region where the upper

medial edge of the articular meets the medial surface of the dentary.

Angular. —Small and mainly confined to the medial surface of the lower jaw; articulates by inter- digitation dorsomedially with the articular, while dorsolaterally, anteriorly, and ventrally it interdigitates with

the dentary. Posteriorly the angular connects by liga- ment with the anterior end of the interoperculum. BRANCHIAL APPARATUS.

Hyoid Arch, Branchiostegal Rays, and Urohyal.

Hypohyals. —Both elements well developed; ventral element larger than the dorsal element; dorsal ele- ment cartilage filled at its ventral and posterior edges, the ventral element cartilage filled at its dorsal and posterior edges. The two elements articulate with one

another and with the ceratohyal mainly through cartilage, but on their medial surfaces the two hypohyals have thin extensions which interdigitate with one

another. The anteromedial edges of both elements ar- ticulate by fibrous tissue with their opposite members. The dorsomedial edge of the dorsal hypohyal articulates
by fibrous tissue posteriorly with the first basibranchial and anteriorly with the reduced urohyal, while the dorso- medial edge of the ventral hypohyal also articulates by

fibrous tissue with the urohyal.

Ceratohyal. —A wide flat plate; shortened anteroposteriorly and expanded dorsoventrally, particularly

posteriorly; cartilage filled along all of its edges except

for the indented regions dorsally and ventrally; ar- ticulates through cartilage anteriorly with the dorsal and

ventral hypohyals, and posteriorly with the epihyal. The

first two branchiostegal rays articulate by fibrous tissue with slight concavities on the anterior half of the ventral edge of the ceratohyal. The next three branchiostegal

rays articulate by fibrous tissue with the posteroventral edge of the ceratohyal, and the last ray with the ventral

region of the lateral face of the epihyal and, to a lesser extent, the lateral face of the extreme posterior end of the

ceratohyal.

Epihyal. —Large, elongate dorsoventrally; cartilage

filled at its anterior, anterodorsal, and ventral edges; ar- ticulates through cartilage anteriorly with the ceratohyal, while posterodorsally it supports the interhyal by

fibrous tissue. Just anterior to its articulation with the

interhyal, the lateral surface of the epihyal articulates by

fibrous tissue with the posterior end of the interoper- culum.

Interhyal. —A short column; cartilage filled at both

ends; articulates by fibrous tissue ventrally with the epi- hyal and dorsally with the concavity on the ventral edge

of the metapter>'goid immediately behind the posterodorsal end of the symplectic.

Branchiostegal rays. —Six in number; the last ray

slightly longer than the others; articulates by fibrous tis- sue to the ceratohyal and, to a lesser extent, the epihyal,

as explained under those bones.

Urohyal. —Reduced to a somewhat irregularly curved rod without a ventral keel; articulates by fibrous

tissue anterodorsally with the anteromedial edge of the

dorsal hypohyal and the dorsomedial edge of the ventral hypohyal; articulates by fibrous tissue posterodorsally with the ventral surface of the first basibranchial.

branchial short, only slightly wider posteriorly than anteriorly; displaced forward so that it articulates posteriorly with the second basibranchial and anteriorly with the hypohyals and urohyal, but with no direct connection with the first hypobranchials. First hypobranchial a square block of about the same size as the second hypobranchial; articulates ventrally with the

lateral surface of the second basibranchial and dorsally with the first ceratobranchial. First ceratobranchial a sturdy rod; about equal in length to the other cerato- branchial elements; somewhat greater in depth ventrally than dorsally, this increased depth at the ventral end increasing from the first to the last ceratobranchial,

the last being widest in the middle region; no ventrally

directed flange present on any of the ceratobranchials;

articulates ventrally with the first hypobranchial and

dorsally with the first epibranchial. First epibranchial a sturdy column; articulates anterodorsally with the base

of the first or suspensory pharyngobranchial. First pharyngobranchial a toothless flattened plate; ar- ticulates dorsally by fibrous tissue to the undersurface of the extreme anterior end of the prootic suborbital shelf

just lateral to the region where the prootic interdigitates with the laterally expanded portion of the parasphenoid

in the anterior region of the orbit. Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial the largest of the three elements in the series; articulates anteriorly with the first basibranchial,

laterally with the first hypobranchial, and posteriorly with the third basibranchial. Second hypobranchial ar- ticulated ventrally with area of articulation between the second and third basibranchials and dorsally with the second ceratobranchial. Second ceratobranchial ar- ticulated dorsally with the second epibranchial. Second

epibranchial a wide heavy column; articulates dorsally with the base of the second pharyngobranchial. Second

pharyngobranchial the largest of the four pharyngobranchial elements and the first of the tooth bearing

elements. The teeth are very small and difficult to see and in life may largely be buried in the pharyngeal tis- sues. The 15 to 20 minute teeth on the second pharyngobranchial are much shorter than those on the third and

fourth pharyngobranchials, and are grouped together in the central region of the ventral face of the element.

Branchial Arches. —AH the elements are cartilage

filled at their edges of articulation with the other elements in the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and four pairs of pharyngobranchials. Four gills are present, with a small slit between the fourth arch and the lower pharyngeal.

First arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basiThird arch. —Basi-, hypo-, cerato-, epi-, and pharyngobranchial elements present. Third

basibranchial a short column, the shortest of the three

basibranchials; articulates anteriorly with the second basibranchial, anterolaterally with the second

hypobranchials, posterolaterally with the third hypobranchials and third ceratobranchials, and posteriorly to the region between the fourth certobranchials. Third hypobranchial a long slender rod, directed anteroventrally and with only its extreme posterodorsal end at the

level of the other hypobranchial elements; articulates posterolaterally with the third ceratobranchial and
posteromedially with the third basibranchial, while its ventraily directed anterior end articulates by fibrous tis- sue with the undersurface of the more anterior branchial

elements, although I am unable in the two study specimens to see exactly where the attachments end. Third ceratobranchial articulated ventraily with the

posterior end of the third hypobranchial and third basibranchial, and dorsally with the third epibranchial. Third epibranchial slender dorsally and somewhat ex- panded ventraily; articulates dorsally with the third pharyngobranchial. Third pharyngobranchial smaller than the second pharyngobranchial but larger than the

fourth; bearing a single row of four or five long slender

teeth with relatively sharp points on the compressed

ventral edge of the bone; articulates ventraily with the

third epibranchial and is held by fibrous tissue more or

less closely to the second and fourth pharyngobranchials.

Fourth arch. —Cerato-, epi-, and pharyngobranchial elements present. Fourth ceratobranchial ar- ticulated ventraily with the cartilaginous area between

the third ceratobranchials and the third basibranchial, and dorsally with the fourth epibranchial. Fourth epi- branchial the longest of the epibranchial elements; rodlike; articulates dorsally with the fourth pharyngobranchial. Fourth pharyngobranchial a very small plate bearing a single row of two or three long slender teeth much like those of the third pharyngobranchial but

slightly smaller.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial the widest and

shortest of the ceratobranchial elements; much ex- panded in the middle region of its length; articulates ventraily with the cartilaginous region between the bases

of the fourth ceratobranchials; toothless. PAIRED FIN GIRDLES.

Pectoral Fin.

Posttemporal. —A large long shaft broadly overlying the lower half of the lateral surface of the pterotic, to which it is firmly interdigitated; anterodorsally it also

interdigitates with the sphenotic, while its ventral head

is firmly held by fibrous tissue to the supracleithrum. On

its ventromedial surface the posttemporal helps, along

with the pterotic and, to a far lesser extent, the cleith- rum, to support by fibrous tissue the expanded lateral end of the ossified Baudelot's ligament.

Baudelot's ligament. —This ligament is fully ossified as a large stout laterally expanded shaft giving

great support to the pectoral girdle. It interdigitates in the midline with its opposite member and is firmly held by fibrous tissue at its medial end to the ventral surface

of the parasphenoid just below the level of the origin of the prootic shelf. Its expanded lateral end is firmly held by fibrous tissue mainly to the ventromedial surface of

the ventral flange of the pterotic and to the ventral end of

the posttemporal, and, to a much lesser extent, to the ex- treme dorsal end of the cleithrum. Along its dorsal edge,

just lateral to its middle region, Baudelot's ligament connects by fibrous tissue with the recurved portion of the

prootic shelf, while its ventral edge helps support by a

fibrous tissue sheet the dorsal edge of the medially ex- panded platelike portion of the cleithrum.

Supracleithrum. —Located slightly obliquely

posterodorsally to anteroventrally in relation to the axis

of the body; relatively short and overlain for a short dis- tance anterodorsally by the ventral end of the posttemporal, to which it is articulated firmly and relatively im- movably by fibrous tissue. The medial surface of the supracleithrum broadly overlies and is firmly held by

fibrous tissue to the anterodorsal surface of the

cleithrum.

Cleithrum. —Greatly expanded both laterally and

medially along all the length of its anterior edge, except

for a short distance ventraily, so that a large thin vertical plate is formed at right angles to the axis of the body;

also greatly expanded posteriorly in the ventral twothirds of its length; articulates dorsally by fibrous tissue on its lateral surface with the broadly overlying supra- cleithrum and on its medial surface with the anterior end

of the dorsal postcleithrum; along its posterior edge it ar- ticulates by fibrous tissue and interdigitation with the

anterior edge of the scapula, which it somewhat overlies

ventraily, while more ventraily along its posterior edge it articulates through cartilage and slight interdigitation with the coracoid. Ventromedially the cleithrum ar- ticulates by fibrous tissue with its opposite member,

while the dorsal edge of its medially expanded platelike portion is held by fibrous tissue to the ventral surface of Baudelot's ligament.

Postcleithra. —The postcleithra are greatly expanded into an extremely wide, thin plate whose

lateral surface is closely held by fibrous tissue to the

cuirass. There are distinct dorsal and ventral segments,

the ventral segment much larger than the dorsal. The

anterior end of the dorsal segment articulates by fibrous

tissue with the medial surface of the dorsal end of the

cleithrum, while posteriorly it interdigitates with the ventral postcleithrum. The ventral edges of both

postcleithra are thicker than the dorsal region, and the

anterior end of the dorsal postcleithrum is thickened and

shaftlike in the area of its articulation with the

cleithrum.

Coracoid. —Somewhat wider ventraily than

dorsally; its posterior edge with a laterally directed

flange throughout its length, the flange ending dorsally

as a posteriorly directed prong below the lowermost actinost; cartilage filled at its dorsal and anterior edges; an

upraised flange present on its lower lateral surface, running, with increasing height of the flange, from postero-
dorsally to anteroventrally where it contacts the posteroventral end of the cleithrum; articulates dorsally through cartilage with the scapula, while posterodorsally it articulates through cartilage (and interdigitation

in one of the two study specimens) with the third actinost and through cartilage and interdigitation with the fourth

actinost. It is probable that in large specimens the third

actinost would also interdigitate with the coracoid. Anteriorly the coracoid articulates through cartilage and

in some places slight interdigitation with the posterior edge of the cleithrum.

Scapula. —Completely encloses the scapular foramen; cartilage filled at its posteroventral and

anterior edges; articulates by fibrous tissue and inter- digitation anteriorly and anteroventrally with the

cleithrum, while posteroventrally it articulates through

cartilage with the coracoid. Posterodorsally the scapula

articulates through fibrous tissue and interdigitation with the bases of the first two actinosts and, in one of the two study specimens, with the anterior end of the base of the third actinost. Just anterior to its articulation with

the first actinost the scapula bears a projection with a concave surface for support of the short uppermost pectoral fin ray, to which it is held by fibrous tissue.

Actinosts. —Four elements; cartilage filled at their ventral edges; first actinost the smallest, the others of

slightly increasing size posteriorly in the series; all four elements held to one another by interdigitation; first and

second actinosts articulated ventrally by interdigitation with the posterodorsal edge of the scapula; third actinost

articulated ventrally either through cartilage or by inter- digitation with the dorsal edge of the coracoid; fourth actinost interdigitated with the posterodorsal edge of the

coracoid. Distally the actinosts support by fibrous tissue

all of the fin rays, except for the first, which is supported

by the scapula, and perhaps the second, which may be

supported in part by the scapula as well as by the first actinost.

Fin rays. —Twelve to thirteen fin rays in most

specimens, with the first ray only about one-fourth or one-fifth the length of the second ray and articulated

directly with the scapula instead of with the actinosts, as

are all the other rays with the possible exception of the

second, which articulates more or less in the region of in- terdigitation between the scapula and first actinost; first ray with its two halves distinct and of about equal size. The first two rays unbranched, the others branched. The

first ray has cross-striations at its extreme distal end and

the other rays are more fully cross-striated. VERTEBRAL COLUMN. —All vertebrae with

biconcave centra, except the last, which ends posteriorly

in the fused hypural plate, and the highly modified first two vertebrae. However, the third and fourth vertebrae

particularly are much compressed anteroposteriorly and

the biconcaveness of the centra is only slightly indicated.

Abdominal Vertebrae.

First two vertebrae. —In the two adult study

specimens, the first two abdominal vertebrae are rudimentary and are not only fused to one another and to the skull but are much smaller than any of the subse- quent vertebrae. The neural arches of the first two

vertebrae are slender and the arches from each side do

not meet their opposite members in the midline above

the spinal cord. They are distinct from one another in the

dorsal halves of their lengths and are fused to one

another and to the exoccipitals and basioccipital only

basally. The fused centra of the first two vertebrae are so compressed anteroposteriorly and shortened dorsoventrally that they form only a thin plate fused to the dorsal

region of the posterior end of the basioccipital. The

neural arches of both vertebrae bear small neural foramens. The structure of the first two vertebrae and of the vertebral column in general has been described by

Tyler (1963a:164-171). Other abdominal vertebrae. —As used here the term abdominal vertebrae refers to all of those vertebrae

anterior to the vertebra to which is attached the first anal

fin basal pterygiophore. In the case of ostracioids, with

their highly unusual anal fin basal pterygiophore ar- rangement, this definition is not applicable. The more

anterior of the anal fin basal pterygiophores of os- tracioids do not remain in the midvertical plane of the body, but, rather, are laterally divergent from their medially placed bases and thus no longer connected with

the ventral surface of the vertebral column. Only the last three or four basal pterygiophores are invariably in the midline of the body, and the proximal ends of even these pterygiophores in ostracioids do not make as close a contact with the vertebrae as in other plectognaths. Under

these circumstances (discussed more fully by Tyler

1963a: 169) it is necessary to arbitrarily state that the first caudal vertebra is that vertebra to which the proximal end of the first basal pterygiophore that consistently lies entirely in the midline of the body is most closely associated. Although this divides the vertebral column

into abdominal and caudal segments that are not comparable to those of other plectognaths, it has consistency

within the superfamily, for all specimens of ostracioids examined have, by this definition, 9 abdominal

vertebrae, regardless of how many of the anterior elements are fused together, and either 9 (usually) or 10 caudal vertebrae. In Kentrocapros aculeatus the first basal pterygiophore of the anal fin that lies entirely in the midline of the body is supported or most closely as-

.sociated with the sequentially 10th vertebra, which ar- bitrarily is thus defined as the first caudal vertebra. The

third to ninth abdominal vertebrae have normal, unfused, centra, and complete neural arches with well-de- veloped neural spines. These abdominal vertebrae differ from the more anterior of the caudal vertebrae only in that the first few vertebrae following the two rudimentary vertebrae (i.e., the third to about the sixth
vertebrae), have their centra anteroposteriorly compressed, the degree of which decreases posteriorly in the

series, and by the fact that the third to eighth abdominal

vertebrae have transverse processes laterally from the

centra. The posterolaterally directed transverse process

of the third abdominal vertebra arises from the upper

part of the centrum and the lower part of the neural arch. The processes of the fourth and fifth abdominal

vertebrae are placed successively lower on the centra and

the processes of the sixth to eighth vertebrae are low on

the ventral edge of the centra. None of these abdominal

vertebrae, up to and including the eighth, have haemal

arches or spines. The ninth and arbitrarily designated

last abdominal vertebra has a short haemal arch and

spine differing from those in the caudal series only by its smaller size. The neural spines of the third to seventh ab- dominal vertebrae lie anterior to the first basal pterygio- phore of the dorsal fin. The neural spines of the third, fourth, and sometimes fifth abdominal vertebrae are held distally in a narrow concavity along the ventral edge

of the ventral keel of the supraneural element or carina, while the neural spines of the fifth to seventh vertebrae simply articulate by fibrous tissue with the ventral edge

of the keel. The neural spines of the eighth and ninth ab- dominal vertebrae articulate by fibrous tissue between

the basal pterygiophores of the anterior region of the dorsal fin. The haemal arch and spine of the ninth abdominal vertebra is symmetrically placed in the midline below the centrum and there is no indication here or on any of the more posterior vertebrae that the haemal

canal lies other than in the midline, in contrast to the condition in the Ostraciidae. The neural spine and arch

of the seventh abdominal vertebra bears a low ridge along its length, while a similar ridge is present on the eighth and ninth abdominal vertebrae, but much more

prominently developed, ending ventrally on the anterior end of the centrum as a flange.

Caudal Vertebrae. —The caudal vertebrae numbered

nine in two specimens. All of the caudal vertebrae possess complete neural and haemal arches and spines. The

haemal spine of the first caudal vertebra is better de- veloped than that of the last abdominal vertebra, but

still shorter than that of the second caudal vertebra, which is the largest in the series. Posterior to the second

caudal vertebra the haemal spines decrease gradually in size in the series to the seventh caudal vertebra. The

haemal spine of the eighth caudal vertebra is larger than

that preceding it and it is autogenous to the centrum. The neural spines decrease in length gradually in the

series from the first to the seventh caudal vertebrae, while the neural spine of the eighth caudal vertebra is somewhat larger than that preceding it. The haemal

spines of the first to fourth caudal vertebrae support the

distal ends of the last four basal pterygiophores of the anal fin, these being the only four which consistently lie in the midline of the body, rather than being divergent from it as are the more anterior pterygiophores. The

neural and haemal canals lie in the midline of the body and are not divergent from it. Each of the caudal vertebrae, as with the abdominal vertebrae, possesses a neural foramen low on the neural arch region. Caudal Skeleton. —The caudal complex consists of a

large rectangular plate, with a rounded expansion in the middle region of its anterior edge representing the cen- trum of the last caudal vertebra, and a deep cleft in the middle of its posterior edge representing the division be- tween what in more generalized plectognaths such as triacanthodids would be the second and third hypurals. However, the hypurals are fully fused to the centrum and

to themselves and no real distinction can be made be- tween them. The anteroventral region of the rectangular

plate represents the parhypural which is fully fused to the centrum and hypurals. That this is the region of the parhypural is indicated by the haemal canal penetrating

the anterior region of the rectangular plate just below the centrum and exiting at a foramen a short distance posterior to where it first enters the plate. This foramen

represents the region of fusion between the parhypural and the hypurals. The anterodorsal region of the rec- tangular plate represents the completely fused epural,

for the neural canal penetrates the plate, again just above the centrum, and courses through it to exit about midway along the dorsal edge of the plate. Caudal fin rays. —Eleven fin rays are present in both specimens and generally throughout the Aracanidae; the uppermost ray and the lowermost ray unbranched, the intervening nine rays branched; all rays with cross-striations. The fin is vaguely divided into an

upper and lower lobe, the upper lobe containing five rays

articulated to the fused hypural plate above the indentation in its posterior edge and the lower six rays articu- lated to the lower half of the plate. The bifid bases of the

rays do not overlap the hypural plate, to which they are

articulated through fibrous tissue. The branched fin rays become increasingly branched toward the center of the

fin, where the rays are branched in up to incomplete quadruple dichotomies.

DORSAL AND ANAL FINS.

Dorsal Fin.

Fin rays and pterygiophores. —Eleven fin rays are present in both study specimens; the first ray unbranched, the other rays branched in single to triple dichotomies. Distal pterygiophores are either absent or

unossified. The bifid bases of the fin rays are supported

through fibrous tissue by 9 or 10 basal pterygiophores. The specimen with 9 basal pterygiophores (the il- lustrated specimen) has the last pterygiophore a com- pound element obviously representing the fusion product

of 2 pterygiophores, for in the other study specimen there

are 2 separate basal pterygiophores in this region for a

total of 10. With the exception of the first and last pterygiophores the basal pterygiophores are more or less slender rods, cartilage filled at both ends, and of slightly
decreasing length posteriorly in the series. At their dorsal ends the pterygiophores are slightly expanded into ar- ticular knobs. The pterygiophores articulate with one

another and with the neural spines supporting them by

fibrous tissue with little or no interdigitation between the

pterygiophores. Just below their expanded articular faces the pterygiophores are slightly constricted so that there

is a definite gap between their apposed surfaces. The first pterygiophore is unlike the others only in that it is much

larger and more expanded anteriorly and posteriorly in- to a thin plate filling the space between the distal regions

of the neural spines of the seventh and eighth abdominal

vertebrae. Anterodorsally the first basal pterygiophore

articulates by fibrous tissue and interdigitation with the

posterior end of the supraneural element or carina. The

supraneural is a long strut reaching nearly to the posterior end of the skull. Its dorsal surface is laterally ex- panded and its bears a deep ventral keel. Anteriorly the

ventral edge of the keel is concave to enclose the distal

tips of the neural spines of the third, fourth, and, in one

specimen, fifth abdominal vertebrae, articulating with them by fibrous tissue. The distal tips of the neural

spines of the sixth and seventh vertebrae end at the ventral edge of the keel and do not penetrate it. The dorsal surface of the supraneural lies just below the cuirass. The

basal pterygiophores of the dorsal fin articulate between

the neural spines of the seventh abdominal to third caudal vertebrae.

Fin rays and pterygiophores. —Eleven fin rays are present; the first ray unbranched, the others branched in up to incomplete triple dichotomies. Distal pterygio- phores are either absent or unossified. The bifid bases of the fin rays articulate by fibrous tissue to nine basal

pterygiophores. These pterygiophores are basically similar to those of the dorsal fin except that they tend to be longer, more anteroposteriorly expanded and much

more firmly held to one another, usually by extensive in- terdigitation. However, while all of the dorsal fin basal pterygiophores lie in the midvertical plane of the body,

only the last four anal fin basal pterygiophores consistently lie entirely in this medial plane, the five pterygiophores anterior to them diverging to the right and to the left from their ventral ends, which are in the

midvertical plane. The sixth to ninth basal pterygio- phores have their dorsal ends held by fibrous tissue at some distance from the ventral ends of the haemal spines

of the first to fourth caudal vertebrae. The second to fifth pterygiophores have their slightly expanded ventral ar- ticular ends in the midvertical plane, but their long more

or less rodlike anterodorsally directed portions lie to the

right or to the left of the midline in the anterior portion of the large muscle mass connected to the anal fin. In the two study specimens three of these pterygiophores

diverge to the right and two to the left. The first basal pterygiophore is expanded just above its knoblike distal end into a thin plate which lies only slightly to one side of the midline. It has the largest keellike expansion of any

of the pterygiophores. It is the second to the fifth pterygiophores that diverge widely from the midline, two

to the left and two to the right. The second to fifth pterygiophores remain rodlike throughout their lengths, while the sixth to ninth pterygiophores, that lie in the midline of the body throughout their lengths, are

variously expanded into thin plates for parts of their lengths. The knoblike distal ends of these more posterior basal pterygiophores are closely apposed to one another and articulate by fibrous tissue but they are not fused or sutured. The shafts of the first to fifth pterygiophores are

tightly held to one another in the midline before they di- verge to the right or left, and the surfaces of apposition seem to be at least extensively interdigitated, if not, in some cases, perhaps even fused. The concave region on

the posteroventral edge of the last basal pterygiophore

rests against the edge of the carapace, just as the similarly indented region on the last dorsal basal pterygiophore

supports the carapace in that region. Anatomical diversity. —Very little anatomical

diversity is present in this small family of deepwater box

fishes comprising about 10 species from the Indo-Pacific (Hawaii to South Africa), but mainly from Australia. They have been relatively poorly collected and the genera as presently recognized (McCulloch and Waite

1915; Fraser-Brunner 1935b, 1941c) seem extremely finely split, the distinctions based exclusively on carapace

characteristics, many of which are rather trivial (number of spiny processes and degree of development of iso- lated caudal peduncular scale plates). Three of the genera {Kentrocapros,^ Capropygia, Caprichthys) are monotypic, while Aracana and Strophiurichthys each have two species, and Anoplocapros two, perhaps three

(if grayi is valid). The carapace in all genera except Kentrocapros and

Aracana has six major ridges or angles: single dorsal and ventral crests and two paired ridges along the side of the body, dorsolateral and ventrolateral in position. In Kentrocapros and Aracana there is no dorsal crest, the back being relatively flat or gently convex rather than

high crested, so that there is a total of five ridges. In the

single fossil species of the family, Proaracana dubia

(Blainville 1818) from the Eocene of Monte Bolca, Italy, the dorsal crest is well -developed and terminates at its greatest height in a large spiny process similar to that of the ventral crest, spines in these positions being unique

in the family. In addition to the major ridges, a mediolateral ridge or

slightly convex region may be present about midway

between the dorsolateral and ventrolateral ridges, but it is usually less distinct than the other ridges. The carapace extends further posteriorly and the caudal fin is less strongly developed in Caprichthys and

Capropygia than in the other genera.

Posterior to the carapace there are always isolated

Aracanostracion Smith (1949b) is tentatively considered a synonym

of Kentrocapros, until the single known specimen, the type of rosapinto, can be examined.

Figure \3S.—Kentrocapros aculeatus: lateral of head, 90.0 mm SL, Japan.

Figure \37.—Kentrocapros aculeatug:

ventral (left) and dorsal (right) views of

skull, 90.7 mm SL, Japan.
ring around the rear of the peduncle, and another set of

plates more anteriorly just behind the bases of the dorsal and anal fins form broad saddles above and below the peduncle which do not meet one another mediolaterally.

In Kentrocapros, Aracana, and Strophiurichthys the two

anterior saddles are similar to those of Capropygia and

Anoplocapros, except that the individual scales making

up the anterior saddle in Kentrocapros and Aracana are

less well-consolidated into a single unit than they are in Strophiurichthys, Capropygia, and Anoplocapros.

Posteriorly, instead of a complete ring around the peduncle as in Capropygia and Anoplocapros, there are similar saddles over the dorsal and ventral regions of the pe- duncle that fail to meet mediolaterally, although in large specimens the edges of these two posterior saddles are al- most in contact. In the Eocene Proaracana the dorsal and

Figure 139.—Kentrocapros aculeatus:

dorsal view of branchial arches

(extended on lower side); lateral view of hyoid arch and urohyal;

90.7 mm SL, Japan. lU^i

1111=1

scale plates on the caudal peduncle. These plates are

least developed in Caprichthys, in which there are only one to three relatively small scutes dorsally and ventrally on the anterior region of the caudal peduncle just behind

the bases of the dorsal and anal fins. The caudal plates

are best developed in Capropygia and Anoplocapros, in which a posterior set of plates forms a completely closed

ventral regions of the caudal peduncle are covered with numerous semi-isolated small scale plates that do not form compact saddles, and the mediolateral region is scaleless. The center of each carapace scale plate in most species usually bears a spinule larger than those of the rest of the plate, while large prominent spiny processes are vari- ously developed. In Kentrocapros there is a small

supraorbital spine, a larger one on the dorsolateral ridge and several on the mediolateral and ventrolateral ridges. Aracana is similar to Kentrocapros, but with the

supraorbital spine larger and with two or more spines on

the dorsolateral ridge. In Capropygia and Caprichthys

there is a single large spine on the dorsolateral and ventrolateral ridges, with Caprichthys additionally having a

small supraorbital spine in the young which is resorbed

in the adult. In Anoplocapros and Strophiurichthys prominent spines of the magnitude found in the other genera are absent, although in large adults of one of the

species of the latter genus, S. robustus, there is a small

supraoccipital spine and the central spinule of many of the individual scale plates of the carapace is relatively much larger than the others, forming spines intermediate in size between those on the ridges of such genera as Kentrocapros, Aracana, Capropygia, and Caprichthys, and those of the center of the plates in all other species. Young specimens of all species probably have the
basibranchiaU

I rT~_3—hypobranchials

pharyngobranchials

mterhyal "^^

^1 ,/^ ^ dorsal hypohyal

epihyal U ^^

anchiostegal rays

spinules of the individual scale plates, including the

variously enlarged central spinule, better developed than

in adults, i.e., the plates in the young are more highly sculptured and ornamented than in adults. Aracanids generally have between 10 and 13 dorsal and

anal fin rays, with Capropygia and Caprichthys tending

to have closer to 13 dorsal and 12 anal and the other genera tending to have closer to 10 or 11 in these fins, the

anal with the same number, or one less, than the dorsal.

All of the species tend to have either 10 or 11 pectoral fin rays in addition to the small uppermost ray. There are usually 8 to 10 teeth in the upper jaw and 8

in the lower. The numbers of teeth found in the jaws of the specimens examined (including alcohol preserved

material) are as follows, with the total in the upper jaw

followed by that of the lower jaw: Strophiurichthys

robustus, 9 and 8 in four specimens, 8 and 8 in one, 10 and 7 in one; S. inermis, 10 and 8 in one; Kentrocapros

aculeatus, 8 and 8 in one, 7 and 8 in one; Aracana aurita, 8 and 8 in one; A. ornata, 8 and 8 in two; Caprichthys gymnura, 10 and 8 in two; Capropygia unistriata, 10 and 8 in two.

In most osteological characteristics the aracanids are remarkably similar, closely following the same general plan in genus after genus.

In Capropygia and Caprichthys, with relatively high numbers of dorsal and anal fin rays, there are usually 12 dorsal fin basal pterygiophores and 11 anal fin basal

pterygiophores, while in the other genera these range in number from 8 to 10. There are always seven predorsal

vertebrae, the more numerous rays and basal pterygio- phores in Capropygia and Caprichthys being accommodated toward the rear of the fin; e.g., the last pterygio- phore of the dorsal fin in these two genera being placed between the neural spines of the 13th and 14th verte- brae, while in the other genera it is placed between the

12th and 13th. The branchiostegal rays are usually 2-1-4, except that

the single specimen of Caprichthys gymnura examined

had 2 -I- 4 on one side and 1 -(- 4 on the other, and that of the two species of Aracana examined, the single speci- men of A. aurita had 1 -(- 4 on both sides, while of the two

specimens of A. ornata examined one had 1 -I- 4 on both

sides and the other had 1 -(- 4 on one side and 2 -I- 3 on the

other. It would appear that in Aracana the branchiostegals are usually reduced to five, while the normal sit- uation in Caprichthys awaits the examination of further specimens, as it does also in Anoplocapros, no species

of which have been examined internally for this work.

In Kentrocapros, Aracana, and Strophiurichthys the second pharyngobranchial bears minute teeth, while in Caprichthys and Capropygia it is entirely toothless. The

number of large teeth respectively on the third and

fourth pharyngobranchials are as follows for single speci- mens of each of the species closely examined for this fea- ture: Strophiurichthys robustus 6 and 6 (plus a few

smaller teeth on the third element in addition to the larg- er ones); Aracana ornata 6 and 3; Aracana aurita 4 and 2; Kentrocapros aculeatus 4 and 3; Caprichthys gymnura 3 and 2; Capropygia unistriata 3 and 2. Thus, Strophi- urichthys has the best developed pharyngobranchial

dentition and Caprichthys and Capropygia the least, with Aracana and Kentrocapros more or less intermediate. The ventral flange of the carina or supraneural is deeper for a greater proportion of its length in the high

crested Strophiurichthys, Capropygia, and Caprichthys

than it is in the relatively flat-backed Kentrocapros and

Aracana.

In Kentrocapros the autogenous haemal spine of the penultimate vertebra is smaller than in the other genera.

In Kentrocapros, Aracana, and Strophiurichthys the haemal canal enters the fused centrum-epural-hypural- parhypural plate at the end of the vertebral column and

exits shortly behind at a prominent foramen low on the

plate, the foramen marking the region of fusion between what would be the parhypural and lowermost hypural in more generalized forms. In Capropygia and Caprichthys

this foramen is either absent or minute (Tyler 1970b: 18) and the haemal canal which pierces the front edge of the

plate either stops within the plate or has only a minute

foramen that could not be detected in either of the single specimens examined of the two species involved.

In one of the species of Aracana, A. ornata, the snout becomes convex and laterally expanded in adults, this
*

200
^v^x^V^UUUuy

Figure 143 —Lateral views of heads of tvpical aracanids

left, Strophturichthye robiutiu,

150 mm SL, Australia; right, Amcana

.3 mm SL, Tasmania.

from a great enlargement of the anterior prolongation of the frontals from the level of the eye forward. This swell- ing of the snout is more prominent in males {ornata) than

in females (the synonymous flavigaster) and occurs in the family only in this species, even the closely related A.

aurita showing no signs in large specimens of any snout

or other enlargements. The structure of the parasphenoid presents variation

of special interest. In Kentrocapros and Strophiurichthys

the ventral edge of the vertical platelike portion of the parasphenoid anterior to its articulation with the anteromedial edges of the prootic shelves is relatively un- expended laterally throughout its length, being only

slightly wider anteriorly where it sutures with the vomer

than more posteriorly. In Aracana the ventral edge of the

Figure 144.—Ventral views of the two types

of configuration of the ventral surface of the

vertically expanded anterior portion of the parasphenoid: A, Caprichthys gymnura,

74.1 mm SL, Australia, representative of the shape in Caprichthya and Capropygia;

B, Aracana aurita, 87.3 mm SL, Tasmania,

representative of the shape in the two species of Aracana. 203
,.r

If^

parasphenoid is relatively as narrow as in Kentrocapros and Strophiurichthys in the anterior half of its length

anterior to the prootic shelves, but it is much expanded

laterally just in front of the shelves, forming a partial hard palate over the rear of the oral cavity. In Caprichthys and Capropygia the ventral edge of the parasphenoid is relatively as narrow as in Kentrocapros and Strophiurichthys throughout most of its length

{interior to the prootic shelves, but it becomes laterally expanded anteriorly behind the vomer, forming a partial hard palate over the front of the oral cavity. The possible phylogenetic implications of these differences and of the

others mentioned above stfe discussed in the section on

generic relationships that follows. Generic relationships. —Probably having been deriv- ed from the same line of fishes that connects the tria- canthids and balistids, the primitive aracanids also probably had a laterally compressed body whose cross- sectional outline would be a dorsoventrally elongate oval. The body was probably fully covered with enlarged, per- haps slightly overlapping, scale plates. While the

balistids retained a more flexible body and flexible scale covering, the aracanids specialized in a thicker and less

Figure H5.—Proaracana dubia: lateral view

of entire specimen, composite based on three specimens, including the holotype, 31.4-54.5 mm SL,

all specimens from the Eocene of Monte

Bolca, Italy (Tyler 1973a:fig. 7).

flexible scale covering with a concomitant reduction in swimming ability but greatly increased protection from

the exoskeleton. The relatively complete covering of somewhat flexible scales would have become consolidated into a relatively inflexible carapace of hex- agonal plates with marginal interdigitations, except that many of the scale plates on the check remained small and free from one another to allow for respiratory movements and that the scales around and behind the dorsal and anal fins remained similarly small and free from one

another to allow for lateral flexion of the caudal peduncle when the caudal fin was used in rapid swimming. The

tendency would be for the scales that originally entirely covered the caudal peduncle to become reduced in size and in coverage of the peduncle, within the limits of also providing some protection from the bites of predators. The Eocene Proaracana dubia provides a firm example

of an early aracanid, the carapace over most of the body

being fully consolidated and the caudal peduncle bearing 204
a large number of small, at least semi-isolated, scale plates

in a long patch both dorsally and ventrally but not

mediolaterally. The carapace is high crested both dorsally and ventrally so that in cross-sectional outline it would be in the form of a laterally compressed oval. The

carapace does not extend posteriorly beyond the level of the rear of the bases of the dorsal and anal fins. This can

probably be taken as the generalized aracanid carapace

condition, and the one on which the Recent species have

modified mainly only in a greater specialization of the caudal peduncular scale plates. Unfortunately, the in- ternal anatomy of P. dubia is mostly unknown, being

largely hidden from view by the carapace in the few specimens presently available. However, the more posterior portion of the vertebral column is relatively easily seen in some of the specimens, and the indications are. that the caudal plate is as fully fused together as in Recent species and that the anterior anal fin basal pteryg- iophores diverged from the midline. The teeth were dis- crete and low in number, similar to those of Recent

species. Proaracana has only one known specialized

feature relative to the Recent species of the family, this being that it has only 10 caudal fin rays rather than the

11 found in all Recent species. In triacanthids and balistids the ventral edge of the parasphenoid anterior to the orbit is narrow, and the pharyngobranchials consist of a toothless suspensory ele- ment followed by three (triacanthids) or two (balistids) elements bearing large teeth. One would expect that the more generalized of the aracanids would have been

derived from these conditions. Strophiurichthys and

Kentrocapros have the ventral edge of the parasphenoid

the least expanded in the family, and Strophiurichthys has the best developed dentition on the two pharyngobranchials (third and fourth) bearing large teeth, as well

as minute teeth on the second pharyngobranchial. Kentrocapros has minute teeth on the second pharyngobranchial but fewer large teeth on the third and fourth pharyngobranchials than in Strophiurichthys.

Strophiurichthys has a high dorsal crest, similar in magnitude to that of Proaracana if the high dorsal spiny

process in the latter is ignored.

In short, of the genera examined, Strophiurichthys ap- pears to be the most generalized of the Recent forms. A

form like it probably gave rise on the one hand to a line leading to Kentrocapros and hence Aracana and on the

other hand to a line leading to Anoplocapros (not studied

internally) and Capropygia-Caprichthys, the latter two

monotypic genera being so similar that they scarcely merit distinction. In the line leading to Kentrocapros the high crested dorsal ridge was lost, with the back becoming flattened or only very gently convex, while the ventral carapace ridge was also reduced in size. The pharyngeal dentition was slightly decreased and the degree of development of large spiny processes increased. Aracana

is obviously closely related to Kentrocapros, sharing with

it a flattened back and a more or less comparable

pharyngeal dentition, and differing from it externally only by a continuing slight increase in the number of

large spiny carapace processes and the probable retention from a slightly more generalized ancestor than the Recent Kentrocapros of a deeper ventral carapace ridge. Internally Aracana is further specialized by the apparently usual loss of one of the two anterior branchiostegal rays, and, more importantly, by the development of a wide lateral expansion of the ventral edge of the para- sphenoid just in front of its articulation with the antero- medial edges of the prootic shelves. In one respect Kentrocapros and Aracana have remained slightly more

generalized than the ancestral Strophiurichthys-like form in that the individual scale plates of the two anterior caudal peduncular saddles are less fully consolidated into functionally single pieces. Probably a close derivative of the ancestral Strophiurichthys-like form is Anoplocapros, whose internal structure has not been studied but which is very similar

to Strophiurichthys externally in the features of its relatively spineless high crested carapace. Anoplocapros

differs from Strophiurichthys mainly in having a complete ring of scales around the posterior region of the caudal peduncle instead of two saddles. However, this is surely a minor distinction, and McCulloch and Waite

(1915:479) pointed out that the ring "may be incomplete

in the young." In short, the two only narrowly separated

posterior peduncular saddles as found in Strophiurichthys have simply met mediolaterally in adult Anoplocapros. The Strophiurichthys-Anoplocapros line probably also gave rise to Capropygia and Caprichthys, both of which are specialized by the loss of even minute

teeth on the second pharyngobranchial and the reduction in number of large teeth on the third and fourth pharyngobranchials, while the carapace extends back

further posteriorly than in any of the other genera. The most distinctive internal feature linking Capropygia and Caprichthys is the development of a moderate

lateral expansion of the ventral edge of the para- sphenoid just behind its articulation with the vomer, in contrast to the more posteriorly placed lateral expansion

Aracana

Kentocapros

Caprichthys Capropygia

Anoplocapros

Strophiurichthys

Figure 146.— Hypothesized phylogenetic

relationshipg of the genera of Aracanidae. 205
just in front of the prootics found in Aracana. Capropygia and Caprichthys differ almost exclusively on the

basis of the caudal peduncular scales, although Caprichthys sometimes develops a supraorbital spine whereas

Capropygia never does. In both Caprichthys and Capropygia the small scale plates that make up what are the

anterior peduncular saddles in other genera are less consolidated and do not form distinctive saddles that are functionally single pieces. This can be considered a reduction from the condition seen in Strophiurichthys and Anoplocapros. The posterior series of peduncular

plates forms a complete ring around the peduncle in Capropygia, just as in Anoplocapros, while the posterior

plates are completely lost in Caprichthys.

It seems evident that Capropygia is a derivative of an

Anoplocapros -like ancestral stock specialized by the reduction of the anterior peduncular plates, a posterior elongation of the carapace, a reduction in the size of the caudal fin, the development of prominent spiny

processes on the carapace, the reduction in the pharyngeal dentition and the development of a partial hard

palate over the front of the oral cavity. Caprichthys is simply a closely related derivitive of Capropygia in which

the anterior peduncular plates are further reduced in size and the posterior plates completely lost, and with a ten- dency for one more carapace spine to develop. Capropygia and Caprichthys have a slightly higher number of dorsal and anal fin rays than do the other

genera, and a relatively large number of fin rays might be

expected to be a primitive character in a group derived from a posttriacanthid and prebalistid ancestral stock, both of which families have long-based and many-rayed

dorsal and anal fins. However, Proaracana has only 10 or

11 dorsal and anal fin rays, like all of the Recent genera

except Capropygia and Caprichthys. I suspect that the number of dorsal and anal fin rays in Capropygia and

Caprichthys is a de novo increase associated with the

greater dependence on these two fins for locomotion demanded by the longer posterior extension of the carapace and concomitant reduction in lateral flexibility of the caudal peduncle, at the end of which is a caudal fin

less well developed than ii; all of the other genera. Relationship to the Ostraciidae.—The deepwater

aracanids are so obviously closely related and ancestral

to the shallow water, more speciose (about 20 species),

ostraciids, that it is needless to belabor the point. The

changes from the aracanid to ostraciid levels of or- ganization mostly are associated with the increased

length of the carapace and its more complete enclosure

posterior to the dorsal and anal fins of the more elongate body concomitant with a reduction in the size and

strength of the orbital and postorbital regions of the skull and an extensively sutured, inflexible, generally weaker

vertebral column within the carapace, with four or five rather than only two vertebrae involved in the variously fused and sutured complex at the rear of the skull, and a

general reduction in the size of most of the neural and

haemal arches. The caudal fin supporting apparatus in

the more generalized ostraciids is similar to that of aracanids, except that there are only 10 fin rays rather than 11, while the apparatus becomes highly specialized

in most other ostraciids. Differences in the type of food available in deep versus shallow water that the aracanids and ostraciids are specialized in feeding on may account for the slight dif- ferences in dentition between the two families, ostraciids having a much reduced pharyngobranchial dentition but

usually a few more teeth in the jaws, especially in the upper jaw, relative to aracanids. The differences in the

structure of the ethmoid supporting the upper jaw and of the completeness of the parasphenoid forming a hard

palate over the roof of the oral cavity between the two

families are also undoubtedly related to differences in

diet, the shallow-water ostraciids perhaps making

greater use of plant material in their omnivorous diet than do the deepwater aracanids. Other evolutionary trends from the aracanids to the os- traciids are the reduction in the size of the postcleithral apparatus, perhaps associated with a lesser need for buttressing the side of the carapace in the more completely and solidly enclosed ostraciid body, the reduction of the

size of the uppermost pectoral fin ray, the development

variously by the basal pterygiophores and neural and

haemal spines of a firmer system of support for the carapace around the dorsal and anal fins, the diversion of the haemal canal away from the midline and its close apposition to the ventral surface of the centra, perhaps a space saving device in a crowded abdominal region from which even muscles are largely excluded laterally, the

loss of the ventral keel of the carapace and the reduction

in the number of isolated scale plates on the caudal peduncle posterior to the carapace. With the aracanids obviously ancestral to the ostraciids, a critical question is whether the latter can be shown to have evolved from one or the other of the two main evolutionary lines postulated here as diverging from a Strophiurichthys-\ike ancestral stock, or whether

it was from such a generalized form as Strophiurichthys

or Proaracana. This is discussed under the section on

generic relationships of the Ostraciidae, with the conclusion being that the ostraciids, and more particularly the lactophrysins, the more generalized of the two subfamilies, probably evolved from one of the two lines possessing a laterally expanded parasphenoid shelf over

the roof of the oral cavity, but whether from the line with

the shelf placed posteriorly (Aracana) or anteriorly (Capropygia and Caprichthys) cannot be determined.

It is of interest that in both the triacanthoids, in which

the deepwater Triacanthodidae are clearly ancestral to the derived shallow-water Triacanthidae, and in the os- tracioids, in which the deepwater Aracanidae are clearly ancestral to the derived shallow-water Ostraciidae, all of the families occur together in the same strata of the upper portion of the lower Eocene of Monte Bolca, Italy. The Triacanthodidae are represented there by

Spinacanthus cuneiformis, Protobalistum imperiale, and

Eoplectus bloti, all so different from the Recent species
of the family that they are placed in different sub- families than the Recent species, while the

Triacanthidae are represented by Protacanthodes ombonii, a somewhat intermediate form between the Triacanthodidae and Triacanthidae and different enough from the Recent triacanthids and those known

from the Oligocene and Miocene to be placed in a separate subfamily. By contrast, of what little is known of them, the single species of Eocene aracanid and ostraciid are relatively modem enough in general countenance to be easily ac- commodated in the same higher categories as the Recent

species. The diversifications of the families apparently was rapid and in both cases with the derived families

specialized for a shallow-water existence coextant with

the ancestral families successful continuance in deeper

waters. Relationship to the Balistidae.—The derivation of the ostracioids presents a slight enigma. Both families of ostracioids appeared in the Eocene with genera not markedly different from Recent genera, and paleontology offers no clue as to what plectognath group the os- tracioids are most closely related. As pointed out in the

historical section of the Introduction, the ostracioids have been considered variously as a third major subordinal group of plectognaths, or as members of both the Sclerodermi and Gymnodontes. Regardless of how they have been classified, their relationships to the

triacanthoids and balistoids, with which they are usually

placed, have never been analyzed much beyond the simple statement that ostracioids have individual discrete teeth protruding from the jaws and hence show an af- finity with the scleroderms and that since they lack the spiny dorsal and pelvic fins, they are probably related to the balistoids, which have the spiny dorsal and pelvic

fins at least reduced in size or in number of elements in relation to the triacanthoids. This is not to belittle the clue that the presence of dis- crete protruding relatively normal teeth and lack of spiny

dorsal and pelvic fins in ostracioids affords, for I agree

that they are important indications of their relationship with the balistoid scleroderms. Any such clues are important, for ostracioids are so highly modified for life within

a shell that many of their features are unique. The divergence of many of the anal fin basal pterygio- phores away from the midline is not found in fishes other than ostracioids, while the fusion of several abdominal

vertebrae to the skull and the heavy ossification of Baudelot's ligament are at least highly unusual features among fishes. Other features of the ostracioids that are

less distinctive, but at least unique among the plectog- naths, are the heavy lateral expansions of the ventral edge of the parasphenoid forming a partial hard palate, the articulation of the preoperculum with a groove on the

lateral surface of the hyomandibular, the complete fu- sion of all epural, hypural, and parhypural elements into a single largo plate, the displacement in ostraciids of the haemal canal to one side or the other of the midline, and

the great expansion in aracanids of the postcleithrum. Beset with a multitude of such specializations one is for- tunate to find even a few structures in ostracioids that

give evidence concerning the origin of the group. The forward extension of the prootics as a shelf under

the orbit is unusual among fishes, and in the plectog- naths it is found only in the balistoids and ostracioids. The interoperculum is a short and simple rod not ex- tending posteriorly past the level of the epihyal only in balistoids and ostracioids among the plectognaths, and

the operculum and suboperculum are about equally reduced in the two groups. Only in balistoids and os- tracioids is the hyomandibular supported dorsally by the

prootic and pterotic alone, without contacting the

sphenotic. The palatine in balistoids and ostracioids is reduced in size in comparison to other plectognaths, al- though it is articulated differently in these two superfamilies. The shape and size of the inflexibly articulated premaxillary and maxillary are very similar in balistoids and ostracioids, as is the rotation of the upper jaw around

a laterally expanded and buttressed ethmoid-vomerine

region. The shape of the teeth of Recent ostracioids is somewhat intermediate between that of triacanthodids and that of triacanthids and balistids, but there is an in- dication that the teeth of the Eocene ostracioids were more balistidlike than at present (see description of

Eolactoria). The ostracioids do not show any such similarities with any of the gymnodonts, and it is obvious from the above

that they have their closest anatomical affinity with the

balistoids. Since the ostracioids have completely lost the spiny dorsal and pelvic fins, and the pelvis, one must

consider the possibility that they are, among the

balistoids, more closely related to the derivative monacanthids than to the ancestral balistids, for it is among

the monacanthids that the reduction in size and number

of dorsal fin spines (to the presence of a single and

sometimes weakly developed spine in a few genera) and

in the size of the pelvic fin (completely lost in many

genera) and pelvis (to a relatively slender shaft in a few

genera) has reached its extreme for the superfamily. However, the monacanthids possess a number of

specialized features in comparison to balistids that show,

as discussed below, that the ostracioids are more closely related to balistids than to monacanthids. The T-shaped palatine of balistids, with the foot of the T articulated against the ectopterygoid and the crossbar

articulated between the maxillary and ethmoid-vomerine region, becomes a simple rod in monacanthids repre- senting only the crossbar of the balistid palatine, and it is usually well removed from the ectopterygoid, even though connected to it by a strong ligament. The columnar

palatine of ostracioids, with its ventral end sutured to the

ectopterygoid and its dorsal end firmly held to the eth- moid-vomerine (especially to the latter) region is dif- ficult to derive from the highly specialized and greatly reduced in size monacanthid condition but easy to derive from the balistid condition. The ostracioid palatine

represents basically the shaftlike foot of the T-shaped
balistid palatine, the foot now sutured to the ectoptery- goid (and mesopterygoid) rather than simply ar- ticulated closely to it through a short ligament, with the top of the ostracioid palatine probably representing a combination of the top part of the shaft and the posterior part of the crossbar held by ligament to the eth- moid-vomerine (especially the former) region in

balistids. The specialized nibbling incisors of monacanthids are

far less like the dentition of ostracioids than is that of

balistids. Balistids have four teeth in an outer series in each half of the upper and lower jaws, while the derived monacanthids have reduced the number to three in the upper jaw and to three or, in some cases, only two in the lower jaw. In ostracioids there are usually four or five teeth in each half of both the upper and lower jaws. It is unlikely that the reduced in number and relatively broad

incisors of monacanthids could be ancestral to the more

elongate and basically conical teeth in greater numbers

as found in ostracioids. While the number of teeth in the outer series in balis- tids is similar to that in the single series in ostracioids, their shapes, at least at present, are not. The teeth in balistids are somewhat wider, thicker, and more notched

than in Recent ostracioids. However, the teeth of the two

species of Eocene ostracioids probably were wider,

thicker, and more notched than in the Recent species, approximating the balistid condition. It is suggested here simply that the Eocene balistids (for which there are

as yet no fossils from that period) and ostracioids could

easily have had rather similar numbers, sizes, and shapes

of teeth, those of balistids somewhat smaller and less notched than at present and those of ostracioids some- what larger and more notched. There are marked similarities between the balistid and

ostracioid parasphenoid, ethmoid, and prefrontal that do

not exist in the monacanthids. In balistids and os- tracioids the prefrontal is relatively well developed and

extends ventrally to articulate with a thickened region of the parasphenoid, while in monacanthids the prefrontal

is greatly reduced in size and is far removed from any

contact with the parasphenoid. In balistids and os- tracioids the ethmoid has only a relatively shallow ventral keel, if present at all, while in monacanthids the ventral keel is always extremely well developed. In balistids and ostracioids the parasphenoid is expanded dorsally

into a thick plate in front of the orbit, but no such ex- pansion is present in monacanthids. The large, thick, usually rhomboidal scale plates of balistids are far closer

to the larger, even thicker, usually hexagonal scale plates

of ostracioids than are the small, thin, usually more or

less rounded to rectilinear scale plates of monacanthids, and in some balistids the scale plates are hexagonal.

In all ostracioids there are 18 vertebrae, with the ex- ception of one specialized genus with a secondary in- crease to 19, and all balistids normally have 18 vertebrae

also, while monacanthids always have 19 or more verte- brae. Balistids and ostracioids have mostly branched

rays in the soft dorsal, anal, and pectoral fins, while these

rays are all unbranched in monacanthids. A supraneural

is present in both balistids and ostracioids, although it is possible that their origins are different, while a supraneural is absent in monacanthids. The lesser reduction in number of pharyngobranchial elements in balistids ver- sus monacanthids is more similar to the condition in most ostracioids. In balistids and ostracioids the para- sphenoid is only slightly, if at all, expanded laterally just behind the orbit, while in monacanthids it is moderately

to greatly expanded there, except in one highly specializ- ed genus. In balistids and ostracioids the postcleithrum

is sometimes composed of two pieces, while in monacanthids it is always a single piece. By contrast, there are only a few ways in which monacanthids are more similar to ostracioids than £U"e balistids. In monacanthids and ostracioids the medial

edges of the pterotics on the ventral surface of the skull are widely separated, while they are only narrowly

separated in balistids. However, balistids and monacanthids are similar in that the separation is by the para- sphenoid and basioccipital, while in ostracioids it is by

the prootic and exoccipital, a rather different arrange- ment. The posttemporal of monacanthids and os- tracioids is more superficially held to the skull than is that of balistids, which is always placed in a deep groove on the skull. However, the posttemporal in ostracioids is usually much larger and more extensively sutured to the

pterotic than is that of monacanthids, and the slight resemblance between the posttemporal of monacanthids and ostracioids is probably coincidental and of no phylogenetic significance. In monacanthids and ostracioids the supracleithrum is not posteriorly expanded and the postcleithrum does not have a dorsal prong, while in balistids a posterior expansion and dorsal prong are present. However, these struc- tures in balistids probably are involved with support of the specialized tympanal region above the pectoral fin base only found in balistids and not to be expected in groups lacking a tympanum. In monacanthids and os- tracioids the fifth ceratobranchial is toothless but has a

series of gill rakers along its anterior edge, while in balistids the fifth ceratobranchial bears teeth but no gill rakers. These differences are surely correlated with the

usually coarser diet of balistids versus monacanthids and

ostracioids, and the loss of teeth from and the gain of gill rakers along the anterior edge of the fifth cerato- branchial probably occurred independently in monacanthids and ostracioids. It is perhaps instructive that in triacanthoids, from which the balistids are derived, the

fifth ceratobranchial also is toothed but lacks gill rakers. Thus, the evidence strongly indicates that it is the

balistids among the balistoids to which the ostracioids

are most closely related, and not to the monacanthids

that are derivatives of the balistids. Moreover, since the

ostraciids are clearly derived from the aracanids, and the aracanids have remained far more generalized, the

closest relationship of the balistids to the ostracioids is to the aracanids and not to the ostraciids. There are only a few ways in which balistids are more
specialized than aracanids, and these are mostly con- cerned with dentition and correlated with the coarser

diet of balistids. In balistids there are only three pharyngobranchials, a toothless suspensory element followed by two elements bearing prominent teeth, while in aracanids the toothless suspensory element is followed by

three elements, the first of which is either toothless or with minute teeth but the third and fourth elements with

teeth almost as well developed as in balistids but usually

of lesser number. The relatively conical teeth of aracanids are more generalized than the heavier notched

incisors of balistids in the sense that they are closer in structure to those of the more generalized

triacanthodids, the basal plectognaths, while those of

balistids are more similar to those of the triacanthids derived from the triacanthodids. However, as indicated

previously, there is evidence that the structure of the

teeth in balistids and aracanids might not have been much different in the Eocene. By the retention of an in- ner series of teeth in the upper jaw, balistids are more

generalized than aracanids, while the variable presence

in aracanids of a fifth tooth in what is the outer series of

balistids, which always have only four in each half of both jaws, is slightly more generalized than in balistids. The uppermost pectoral fin ray of aracanids is relatively well developed and the two halves are of about equal

length, while in balistids this ray is greatly reduced in

size and the medial half is larger than the splintlike nubbin that represents the lateral half of the ray. Here again

the condition in aracanids is similar to that in triacanthodids while that of balistids is similar to that in triacanthids, although the lateral half of the ray in balistids is even more reduced than in triacanthids. It is presumed here that these few more specialized features

of balistids were acquired after the divergence of the common triacanthoid phyletic line leading on the one hand to balistids and on the other to aracanids, as dis- cussed subsequently. The conversion of a balistidlike fish into an aracanid

requires mainly the following: 1) the complete loss of the pelvis along with its rudimentary pelvic fin-ray ele- ment and encasing scales; 2) the complete loss of the

three dorsal fin spines and of their three pterygial and

supraneural supports, with the possible exception of one

of them; 3) a rearrangement of the posterodorsal part of the head that no longer supports the spiny dorsal fin, in- cluding the development of a posteriorly projecting

supraoccipital crest, subsequently to be lost by the ostraciids; 4) a flattening of the dorsal surface of the

supraoccipital; 5) the elimination of the articulation foramen of the first basal pterygiophore of the spiny dorsal fin between the epiotic and supraoccipital, and a reduction in the posteromedial region of the exoccipitals

so that they no longer are closely apposed to one another

in the midline on the posterior wall of the skull; 6) the development of a dorsal flange on the parasphenoid into the orbital septum to meet an anteroventral prolongation of the pterosphenoids; 7) an enlargement of the vomer with a broader surface of suturing to the ethmoid

and parasphenoid; 8) a reduction of the anterior cross- bar of the T-shaped palatine and a firm suturing of the

foot of the T to the ectopterygoid and mesopterygoid; 9) the loss of the inner series of teeth but the retention of a

slightly more generalized form and number in the outer

series than in Recent balistids; 10) a foreshortening and

deepening of many of the hyoid arch elements along with

the reduction in width of the first branchiostegal and the development of a constant articulation between the last branchiostegal and the suboperculum; 11) the retention

of a third toothed pharyngobranchial and the reduction

in size of the teeth on the first of the toothed elements;

12) loss of teeth on the fifth ceratobranchial and develop- ment of gill rakers along its anterior edge; 13) great reduction in the size of the urohyal; 14) great increase in the size of the hyomandibular, posttemporal, postcleith- rum, cleithrum, coracoid, epiotic, and pterotic; 15) reduction in the size of the myodome and the elimination

of the posterior opening into it; 16) the ossification of Baudelot's ligament; 17) the elaboration of the prootic

shelf including a recurved lateral wing; 18) a wider

separation of the pterotics on the ventral surface of the

skull; 19) the reduction in size and the fusion of the first two vertebrae to the skull; 20) the loss of epipleurals; 21) complete fusion of all the caudal fin supporting elements

of the last vertebral centrum; 22) an increase in the size of the neural spines of the predorsal vertebrae and a great reduction in length but a broadening of the haemal

spines of most of the caudal vertebrae; 23) a great reduction in the number of dorsal and anal fin rays and of their basal pterygiophores and the development of divergent

anal fin basal pterygiophores; 24) concomitant with the reduction in the dorsal and anal fins, an increase in the number of vertebrae with neural or haemal spines anterior to the first basal pterygiophores of both fins (i.e., an increase in predorsal and abdominal vertebrae); 25) development of lateral flanges on many of the more centrally located vertebrae; 26) loss of one branched caudal

fin ray; 27) the enlargement and thickening of the scales

into heavy, more or less hexagonal, plates over the head and body anterior to about the level of the ends of the

dorsal and anal fin bases; 28) the enlargement of a supraneural element into a long strut projecting anteriorly from the dorsal fin base; 29) the suturing of the actinosts

to one another and to the scapula and coracoid. Some of these above changes from the balistid to aracanid type of organization are not shared by the ostraciids. For example, ostraciids do not have: 1) the

posteriorly prolonged supraoccipital crest; 2) the es- pecially elongate supraneural in front of the dorsal fin; 3) the immensely enlarged postcleithrum; 4) the posteriorly prolonged epiotic and generally more elongate

postorbital region of the head; 5) the elongate neural

spines of most of the predorsal vertebrae. This indicates

either that the ostraciids diverged from the aracanids at

a time before the ancestral line had developed these

latter differences with balistids or that the ostraciids at any early stage had similar differences with balistids which they have subsequently modified. I suspect, with-
out proof, that it is mainly a case of the latter, but it could well be some combination of both possibilities. As in the evolution of the triacanthoids and balistoids, the major features in the diversification of the aracanids from a prebalistidlike group and of ostraciids from

aracanids are largely reductive.

It is not suggested here that the aracanids evolved from a group with a level of organization like that of the Recent or few known fossil balistids, but rather that aracanids and balistids share a common ancestry at a lower level of organization, around that of the

triacanthids. However, this joint ancestral line of the aracanids and balistids must have been more generalized than any of the Recent triacanthids, and probably split off from the triacanthids at a level of organization somewhat like that exemplified by Protacanthodes, the Eocene ancestral triacanthid that probably evolved from

hoUardiinlike triacanthodids. That is, the triacanthid

line leading to the balistids and aracanids probably did

not yet have such specialized features as found in the Recent triacanthids as: 1) the especially large notched in- cisors; 2) the forward extension of the prefrontal suturing

to the vomer; 3) a fully elongate soft dorsal fin with many

more rays than the anal fin; 4) the uppermost pectoral

fin ray much reduced in size and one half smaller than

the other; 5) the second and third basal pterygiophores of the spiny dorsal fin greatly reduced in size; 6) the ab- sence of a free parhypural and autogenous haemal spine

of the penultimate vertebra; 7) an elongate tapering caudal peduncle with a deeply forked caudal fin. The

triacanthid line leading to the balistids and aracanids would have had to retain from its triacanthodid ancestry more generalized conditions of these features, much as did Protacanthodes, the basal triacanthid. Whether the

balistid-aracanid ancestral line diverged from the early triacanthids at a level of organization slightly more

generalized than that represented by Protacanthodes or

at a level between that oi Protacanthodes and the Recent

triacanthids is difficult to ascertain, for too many critical features of Protacanthodes remain unknown, but it was

probably the former, as discussed under the Balistidae. This ancestral pretriacanthid line is seen as diverging

into two radiations, one line leading with little change to the Eocene Protacanthodes and the other triacanthids on

the one hand, and the other line leading through greater changes to the balistids and aracanids, with the balistids

(as discussed under that family) remaining more

generalized and thus anatomically closer to their pre- triacanthid ancestors than did the aracanids, whose

specializations are built around the defensive shell that encases their bodies. While the balistid line continued to lengthen the soft dorsal and anal fin bases and to develop

a locking mechanism between the first two dorsal spines and an elaborate flexing mechanism of rudimentary rays

at the end of the pelvis, the aracanid line lost the spiny

dorsal fin and pelvic apparatus completely while

shortening the bases and decreasing the number of rays

in both the soft dorsal and anal fins. When the aracanid line split off from that of the prebalistids it rapidly lost, still in the Eocene, the spiny dorFigure 147.—Typical body form in the Recent

Ostraciidae: Ostracion lentiginoaum.

sal and pelvic fins as the developing carapace took on the major line of defensive protection. The aracanids became

less flexible and less swift in sustained swimming as the

soft dorsal and anal fins were reduced in number of rays and basal pterygiophores. While the pelvis was completely lost, there remains some trace of either the now

absent spiny dorsal fin supports or of those of the now absent anterior part of the originally longer based soft dorsal fin. The long supraneural element of aracanids that extends out from the anterior end of the dorsal fin is un- doubtedly a modified basal pterygiophore, but whether

from the spiny dorsal fin or the anterior region of the soft dorsal fin is impossible to say with assurity, because as the spiny dorsal was being lost so was some of the soft dorsal fin, probably from anteriorly to posteriorly judging from the position of that which remains.

In balistoids the tendency has been for the spiny dorsal fin and its pterygiophores to migrate anteriorly as the

fin is reduced in size and number of elements from

balistids to monacanthids, and the latter retain no remnants of the third spine, second pterygiophore, and

supraneural element of balistids. If the spiny dorsal fin of aracanids migrated anteriorly as it became rudimentary, it may have left free one of the more posterior pte- rygiophores (corresponding in balistids to either the second pterygiophore or to the supraneural strut, the lat- ter itself being a modified third pterygiophore) which

then became enlarged to support the carapace. Conversely, in the only group of plectognaths other than

aracanids to lose the spiny dorsal fin, the gymnodonts,

the loss of the fin, on the evidence of Triodon, has been

by the posterior migration of the spines and pterygio- phores as they became rudimentary. If the loss in aracanids was by posterior migration, then the supraneural still represents an enlarged pterygiophore, or an

enlarged consolidation of two or more of them. Equally

possible is that the aracanid spiny dorsal fin, regardless

of whether it migrated anteriorly or posteriorly, lost not

only the spines but also all the pterygiophores, and that

the supraneural is actually an enlarged pterygiophore, or an enlarged consolidation of two or more of them, from

the soft dorsal fin that became available for carapace

support as the soft dorsal was shortened from anteriorly

to posteriorly.
Family Ostraciidae Comparative diagnosis (contrast with that of the Aracanidae). —Supraorbital region of the skull rela- tively weak, the frontal extremely thin in this region and

tightly held to the undersurface of the carapace; frontal without a long forward extension anterior to the orbit, ending anteriorly over or only slightly in front of the

prefrontal and not overlying the ethmoid; supraoccipital

crest absent; epiotic little, if any, prolonged posterolaterally, scarcely if at all beyond the level of the base of the skull; prootic shelf without a recurved wing; myodome either small and shallow or essentially absent;

usually three pharyngobranchials, occasionally only two,

the first a toothless suspensory element and sometimes

absent, the second with a series of small to minute teeth, and the third either toothless or with minute rudi- mentary teeth; branchiostegals 2 -I- 4; ethmoid a more or

less rounded shaft posteriorly and much expanded

laterally in the anterior one-third or more of its length; pterosphenoid and parasphenoid with only a very limited

region of suturing in the interorbital septum; para- sphenoid much expanded laterally throughout its length

anterior to its region of suturing with the anteromedial

edges of the prootic shelves, forming a complete hard

palate over the roof of the oral cavity; posterodorsal

region of coracoid without a posterior prong; four or five vertebrae, represented by both neural arch and centrum

material, at the front of the vertebral column variously fused and sutured to one another and to the exoccipitals and basioccipital, the fusion region with a prominent

ventral process below the level of the centra; vertebrae immediately following the fusion region with relatively short neural spines and with centra of about normal

length without transverse processes; the centra of two or more of the vertebrae immediately preceding the caudal

plate much compressed anteroposteriorly; haemal arch and spine of the penultimate vertebra relatively small and either autogenous or fused to the centrum, in which

latter case it may be rudimentary; caudal fin rays, i, 8, i; postcleithrum of moderate size, formed of one or two

pieces, and not extending posteriorly much beyond the

level of the posterior edge of the pectoral girdle; carina

(supraneural) relatively short and either without a ventral flange or with only a weak shallow one, not extending

anteriorly as far as the level of the anteroventral end of the first dorsal fin basal pterygiophore and not in contact with any of the neural spines of the predorsal vertebrae;

haemal spines poorly developed and absent on many of

the abdominal and caudal vertebrae, except for the heavy haemal spine(s) which supports by close apposition and sometimes interdigitation the last anal fin basal

pterygiophore, the other anal fin basal pterygiophores

that lie in the midline of the body also making relatively

close contact along their distal ends with the vertebral column; first anal fin basal pterygiophore expanded

anterolaterally at its distal end into wings supporting the

carapace; haemal canal not entirely straight, diverted under the centra of the more posterior abdominal

vertebrae (usually between the seventh abdominal to

first caudal vertebrae) either to the left or to the right of the midline, or alternatively to the left and right, and

relatively poorly enclosed under most vertebrae by weakly developed haemal arches and spines; most of the

vertebrae posterior to the anteriormost four or five fused

vertebrae and anterior to the postanal vertebrae sutured

to one another (suturing between at least the fifth and

sixth abdominal vertebrae to the third and fourth caudal

vertebrae); uppermost pectoral fin ray short, composed

of a single piece without cross-striations and bearing a foramen representing the region of otherwise complete

fusion between the original halves of the ray; body (ex- clusive of vertical carapace spines) relatively less deep,

the distance between the distal ends of the first dorsal and anal fin basal pterygiophores being contained more

than 3 times in SL, and the distance between the top of the rear of the cranium and the ventralmost edge of the

pectoral girdle being contained about 2.3 to 2.5 times in SL; carapace closed behind the anal fin and, with the ex- ception of one species, behind the dorsal fin as well; carapace never with a ventral keel; caudal peduncle

usually without scale plates isolated from the carapace

proper. Detailed description o( Acanthostracion quadricorMaterial examined: —Thirteen cleared and stained specimens, 8.2-350 mm; three dry skeletons, 130-163 mm.

Occipital Region.

Basioccipital. —A short column, expanded anterolaterally; cartilage filled along its anterior and dorsal edges; articulates by interdigitation dorsally with the

exoccipitals, anterolaterally with the prootics and

anteriorly with the overlying posterior end of the paraFigure 148.

Acanthostracion quadricornis: upper left, nasal region as seen externally

(olfactory epithelium relatively smooth in this and all other species of ostraciids); lower left, outline of cross section of middle

of body; pattern of scale plates shown

only behind pectoral fin.
sphenoid. The posterior half of the basioccipital is hidden from view by the forward displacement of the

highly modified first five abdominal vertebrae, as ex- plained in the section on the vertebral column.

Exoccipital. —Cartilage filled along all of its edges

of articulation with the other cranial bones; articulates by interdigitation posterodorsally with the epiotic, ventrolaterally with the pterotic, ventromedially with the

basioccipital, and anteroventrally with the prootic. Posteriorly the exoccipitals form the lateral walls and

most of the dorsal walls of the foramen magnum, while

ventrally the foramen is closed by the dorsal surface of the basioccipital. Posterodorsally the medial edges of the

exoccipitals closely approach, but do not meet, one

another and are held together by a thin sheet of fibrous

tissue. More anteriorly, however, the dorsomedial edges

of the exoccipitals are more distantly separated and the space between them is filled by a thin sheet of cartilage. The lateral surface of the extreme posterior end of the

exoccipital is overlain by and interdigitated with the more anterior of the highly modified first five abdominal

vertebrae, as explained in the section on the vertebral column.

Supraoccipital. —Laterally expanded; no supraoccipital crest; cartilage filled along all of its edges of ar- ticulation with the other cranial bones; articulates by

interdigitation anteriorly and anterolaterally with the

frontals and posterolaterally with the epiotics.

Otic Region.

Pterotic. —Cartilage filled along all of its edges of articulation with the other cranial bones; articulates by

interdigitation posterodorsally with the epiotic, anterodorsally with the sphenotic, anteroventrally with the

prootic and posteroventrally with the exoccipital. For a

short distance medially along its anteroventral edge the

pterotic supports by fibrous tissue the posterodorsal edge

of the hyomandibular. The anterolateral region of the

pterotic is prolonged ventrally into a stout shaft that is mostly obscured from lateral view by the broadly overlying posttemporal, to which it is interdigitated. At the ventromedial end of this shaft the pterotic helps to support by fibrous tissue the laterally expanded end of the

ossified Baudelot's ligament and medially the posterolateral edge of the hyomandibular.

Sphenotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates by

interdigitation posterodorsally with the frontal, posteroventrally with the pterotic and for a short distance with

the anterodorsal end of the posttemporal, dorsomedially

with the pterosphenoid, and ventromedially with the

prootic. The dorsolateral surface of the sphenotic is broadly overlain by the frontal.

Epiotic. —More or less rounded, but with a short

ventrally directed process from its ventrolateral edge;

cartilage filled along all of its edges of articulation with

the other cranial bones; articulates by interdigitation

dorsally with the frontal, anteroventrally along its lateral edge with the sphenotic and pterotic, posteroventrally with the exoccipital, and medially with the supraoccipital. For a short distance the medial edge of the

epiotic is in contact with the cartilaginous plate that

separates the medial edges of the exoccipitals.

Prootic. —Cartilage filled along all of its edges of

articulation with the other cranial bones, except at its anteriormost region of articulation with the para- sphenoid; articulates by interdigitation ventromedially

with the laterally compressed keellike dorsal region of the parasphenoid, ventrolaterally with the pterotic, posteroventrally with the basioccipital and exoccipital, dor- somedially with the pterosphenoid and dorsolaterally with the sphenotic. Along most of the anterior edge of its laterally expanded posterior portion the prootic possesses

a slight concavity with which the dorsal head of the hyo- mandibular articulates by fibrous tissue. The antero- medial region of the prootic possesses a long forward

extension under the orbit which makes contact by inter- digitation with the parasphenoid at the level of the

prefrontals. A bony myodome is essentially absent.

Orbital Region.

Frontal. —Wide posterolaterally; extremely thin and delicate anterolaterally, where it is in close contact with the ventral surface of the cuirass; articulates by in- terdigitation posteriorly with the supraoccipital and

posterolaterally with the epiotic and sphenotic, broadly

overlying the latter. Anteroventrally, in the orbital region, the frontal interdigitates with the ptero- sphenoid. Anteriorly the frontal is prolonged into a very

thin projection that overlies the dorsomedial edge of the

prefrontal and the dorsal surface of the ethmoid cartilage and reaches almost to the posterior end of the ethmoid.

Since the thin anterolateral expansion of the frontal is closely held by fibrous tissue to the ventral surface of the

cuirass over the orbital region, a large portion of the frontal is very easily torn away when the cuirass is removed.

Thus, the few figures of the skulls of trunkfishes that have been previously published usually show the frontal incompletely and unrealistically with ragged edges.

Prefrontal. —Large and wedge-shaped; cartilage

filled along its medial edge where it is continuous with

the ethmoid cartilage; articulates by fibrous tissue dor- somedially with the frontal, while ventrally it articulates by fibrous tissue and, in large specimens, by slight interdigitation with the parasphenoid. Its major surface

of articulation, however, remains with the ethmoid cartilage that broadly intervenes between the prefrontal and

the ethmoid.

Parasphenoid. —Elongate, running almost the

entire length of the skull; expanded ventrally along nearly all of its length into a thin keel, which itself is laterally
expanded along the anterior third of its ventral edge to form a slightly concave horizontal plate over the roof of the oral cavity. The parasphenoid articulates by inter- digitation posterolaterally with the prootics, while at its extreme posterior end it broadly overlies and interdigi- tates with the basioccipital. At its blunt anterior end the parasphenoid is deeply and firmly interdigitated with both the ethmoid and vomer, and in large specimens

(over approximately 200 mm) these articulations become

truly fused. Anterodorsally the parasphenoid interdigi- tates with the ethmoid, while dorsally in about the middle of its length the parasphenoid becomes slightly ex- panded laterally and articulates by fibrous tissue and, in large specimens, by interdigitation with the bases of the

prefrontals. In the anterior half of the orbital cavity the parasphenoid is present as a thin flat plate, the extreme

posterodorsal edge of which makes contact, in large specimens at least, with the extreme anterior end of the pterosphenoid. In large specimens the articulation of the parasphenoid and pterosphenoid is by interdigitation, whereas in smaller specimens the articulation is through

the interorbital sheet of fibrous tissue. In about the middle of its length, where it is laterally expanded, the para- sphenoid makes contact by interdigitation with the

anterior prolongation of the prootics.

Pterosphenoid. —Cartilage filled along all of its edges of articulation with the other cranial bones, except

anteriorly; articulates by interdigitation posterodorsally with the somewhat overlying frontal, posteriorly with the sphenotic and posteroventrally with the prootic. The

anterior edge of the pterosphenoid is prolonged anteriorly

into a flattened process which makes contact with the

posterior edge of the platelike orbital expansion of the parasphenoid, as explained above.

Ethmoid Region. Ethmoid. —Elongate; a rounded shaft posteriorly, but becoming laterally expanded anteriorly; cartilage

filled at its posterior edge, where it is continuous with the ethmoid cartilage; articulates by interdigitation ventrally along the posterior two-thirds of its length with the parasphenoid, while ventrally in the anterior one-third of

its length it firmly articulates by extensive interdigi- tation with the vomer. In large specimens the articulation between the ethmoid and vomer becomes fused. At

its anterior edge the ethmoid helps support, through

fibrous tissue, the upper jaw.

Mandibular Region. Hyomandibular. —Much expanded posteriorly, tapering gradually to a blunt end anteriorly; cartilage

filled at its posterior and anterior edges; articulates by

fibrous tissue posteriorly with the slight concavity on the

anterior edge of the laterally expanded posterior portion

of the prootic and, for a short distance, with the continuation of that concavity on the anteromedial edge of the pterotic, as well as along the medial surface of the

ventral shaft of the pterotic. The dorsomedial edge of the hyomandibular is also supported through fibrous tissue by the lateral surface of the ventral flange of the prootic

shelf. The hyomandibular possesses a slight concavity on

its ventral edge in which the rounded dorsal end of the operculum is held by fibrous tissue. Just anterior to this articular area the hyomandibular bears an elongate

groove on its lateral surface into which the slender posterodorsal end of the preoperculum fits and is tightly held by fibrous tissue. Anteriorly the hyomandibular is attached to the fibrous tissue sheet between the

metapterygoid, symplectic, and preoperculum.

Quadrate. —Wide posteriorly, tapering anteriorly

to a knob for articulation with the articular in the lower

jaw, while from its posteroventral edge it possesses a

short posteriorly directed process; cartilage filled at its posterior edge; articulates by interdigitation dorsally with the ectopterygoid, posterodorsally with the mesopterygoid and posteroventrally with the symplectic. Along the posterior two-thirds of its ventral edge the quadrate articulates by fibrous tissue with the preoper- culum.

Metapterygoid. —Elongate; wide anteriorly but becoming narrower posteriorly; cartilage filled at its anterior edge; articulates by interdigitation anterodorsally with the mesopterygoid and anteroventrally with

the symplectic, which it somewhat overlies. Posteriorly the metapterygoid articulates by fibrous tissue with the hyomandibular and interhyal.

Symplectic. —Slender and elongate; no cartilage

filled edges evident; articulates by interdigitation anteriorly with the quadrate, posteriorly with the metapterygoid and by fibrous tissue posteroventrally with the preoperculum and hyomandibular.

Palato-Pterygoid Region. Vomer. —Short, slightly expanded laterally in about the middle of its length; articulates by interdigi- tation dorsally with the ethmoid and posteriorly with the parasphenoid, but in large specimens both of these ar- ticular surfaces become fused. Anterolaterally, just in front of its laterally expanded region, the vomer supports through fibrous tissue the palatines, while at its extreme

anterior end it supports the upper jaw. A slight concavity

in the lateral surface of the vomer marks the place of ar- ticulation between the vomer and palatine.

Palatine. —A small wedge of bone; articulates by

interdigitation ventrally with the ectopterygoid and, to a

lesser extent, with the mesopterygoid. Even though the

palatine has often been said to be absent in ostraciids, it

is distinct from the ectopterygoid even in large specimens and the suture between the two can be seen upon close examination. Dorsomedially the palatine articulates by

fibrous tissue from a slightly rounded prominence on its upper medial surface with the slight concavity on the

lateral surface of the vomer.
Ectoptcrygoid. —Elongate; articulates by inter- digitation dorsally with the palatine, posteriorly with the mesopterygoid, which it somewhat overlies, and ventrally with the quadrate, which it also overlies.

Mesopterygoid. —Large; articulates by inter- digitation posteroventrally with the metapterygoid,

while anteriorly it interdigitates with and is somewhat

overlain by the palatine, ectopterygoid, and quadrate. Opercular Region. Operculum. —Relatively short and thin; more or

less rounded in outline, with a protuberance dorso- medially for articulation by fibrous tissue with a slight concavity on the ventral edge of the hyomandibular.

Ventrally the operculum broadly overlies and ar- ticulates by fibrous tissue with the suboperculum.

Suboperculum. —Very thin; widest in the middle,

broadly rounded anteriorly, tapering to a point posteriorly; articulates by fibrous tissue dorsally with the broadly overlying operculum. At the anterior edge of the

region where the operculum overlies the suboperculum, a

strong ligament coming from the interoperculum makes

contact with the suboperculum and, to a lesser extent, with the operculum.

Interoperculum. —A short rod; extends from the

level of the anterior end of the preoperculum to the level of the junction of the ceratohyal and epihyal; connects by

a strong ligament anteriorly to the angular in the lower

jaw, while posteriorly it connects by a short ligament to the epihyal and by a longer more diffuse ligament to the

anterior edge of the suboperculum and, to a lesser extent, of the operculum.

Preoperculum. —Relatively short; not much ex- panded in its middle region, and tapering to narrow ends

anteriorly and posteriorly; articulates by fibrous tissue anteriorly along its dorsal edge with the quadrate and, to a slight extent, with the symplectic; posteriorly the nar- row shaft of the preoperculum is held by fibrous tissue in an elongate concavity on the lower lateral surface of the hyomandibular.

Upper Jaw.

Premaxillary. —A slightly curved plate, wider dorsally than ventrally; its posterodorsal region somewhat

concave for articulation by fibrous tissue with the anterior edges of the vomer and ethmoid; the anterior edge

of the upper jaw formed by the premaxillary, except for a

short distance ventrally where it is formed by the maxillary; the dorsomedial edges of the two premaxillaries held in close apposition by fibrous tissue. Each pre- maxillary in adults usually bears five or six teeth in a

single row. The teeth are borne in relatively deep and

elongate grooves on the outer surface of the premaxillary. The lowermost teeth are shaftlike and taper to

sharp points, but more dorsally and medially they are

flattened and blunter at their distal ends. At the posterior end of each tooth-bearing groove there is a deep

socket in which new teeth develop before moving for- ward to replace the old ones. Most of the interior of the premaxillary contains the dental pulp from which the new teeth develop. This pulp cavity communicates with

the exterior not only by the deep sockets in which the new teeth develop but also by a large hole in the posterodorsal surface of the premaxillary. The premaxillary ar- ticulates by extensive interdigitation with the maxillary

along all of its posterior edge, except for a short distance

dorsally.

Maxillary.—Widest ventrally, constricted in the middle of its length; articulates by extensive interdigita- tion anteriorly along all of its length with the pre- maxillary, which it somewhat overlies. The maxillary ar- ticulates by fibrous tissue posterodorsally with the

anterior edges of the vomer and ethmoid and ventro- medially with the dorsolateral surface of the dentary.

Lower Jaw.

Dentary. —Wider posteriorly than anteriorly; its posteromedial surface concave dorsally to accommodate

the articular, with which it interdigitates. Just below the

articular, the dentary interdigitates with the angular. The ventromedial edges of the two dentaries are held

closely together by fibrous tissue. Laterally from its posterodorsal region the dentary articulates by fibrous

tissue with the medial surface of the maxillary. Each

dentary in adults usually bears four or five teeth, like those of the upper jaw, in deep grooves on its outer surface, each of the tooth-bearing grooves ending posteriorly in a deep socket in which new teeth develop. The

sockets are in communication with the large pulp cavity

that fills most of the hollow interior of the dentary. The

pulp cavity communicates with the exterior not only at the tooth sockets but also at its posterior concave region

of articulation with the articular.

Articular. —Small; its posterior edge with a concavity for articulation by fibrous tissue with the anterior knoblike process of the quadrate. Anteriorly the articular

interdigitates with the concave upper half of the postero- medial surface of the dentary. On the medial side of its ventral edge the articular interdigitates with the angular, but the lateral surfaces of these two bones are not in contact; rather, they are slightly separated by the dentary. The sesamoid articular is a roundish nubbin of bone

closely held to the medial surface of the articular just behind the region where the upper medial edge of the ar- ticular meets the medial surface of the dentary.

Angular. —Small, slightly elongate; articulates by

interdigitation dorsomedially with the articular, while

dorsolaterally, anteriorly, and ventrally it interdigitates with the dentary. Posteriorly the angular connects by

ligament with the anterior end of the interoperculum.
BRANCHIAL APPARATUS.

Hyoid Arch, Branchiostegal Rays, and Urohyal.

Hypohyals. —Both hypohyal elements well de- veloped; ventral element larger than the dorsal ele- ment; dorsal element cartilage filled along its posterior and ventral edges, the ventral element cartilage filled along its posterior and dorsal edges. The two elements ar- ticulate with one another and with the ceratohyal through cartilage; the anteromedial edges of both

elements articulate by fibrous tissue with their opposite members. The dorsomedial edge of the dorsal hypohyal

articulates by fibrous tissue posteriorly with the first basibranchial and anteriorly with the reduced urohyal, while the dorsomedial edge of the ventral hypohyal also articulates by fibrous tissue with the urohyal.

Ceratohyal. —A wide flat plate; shortened anteroposteriorly and expanded dorsoventrally to such an ex- tent that the former dimension is shorter than the latter; cartilage filled along all of its edges except at the in- dented regions posterodorsally and anteroventrally; ar- ticulates through cartilage anteriorly with the ventral hypohyal, anterodorsally with the dorsal hypohyal and

posteriorly with the epihyal. The first two branchiostegal rays articulate by fibrous tissue with slight depressions on the ventral edge of the ceratohyal at the anterior edge of its deeply indented anteroventral region. The next three branchiostegal rays articulate by fibrous

tissue with the posteroventral edge of the ceratohyal, and

the last ray with the ventral edge of the area of ar- ticulation between the epihyal and ceratohyal.

Epihyal. —Large, elongate dorsoventrally; cartilage

filled at its anterior, anterodorsal and ventral edges; ar- ticulates through cartilage anteriorly with the ceratohyal, while posterodorsally it supports the interhyal by

fibrous tissue. Just anterior to its articulation with the

interhyal, the lateral surface of the epihyal articulates by

fibrous tissue with the posterior end of the interoper- culum.

Interhyal. —A short, slender rod; cartilage filled at both ends; articulates by fibrous tissue ventrally with the

epihyal and dorsally with the slight concavity on the ventral edge of the metapterygoid immediately behind the

posterodorsal end of the symplectic.

Branchiostegal rays. —Six in number; the first ray

shorter than the second; the third to fifth rays of about

the same length as the first ray; the sixth ray by far the

longest. The rays articulate by fibrous tissue to the

ceratohyal and, to a lesser extent, the epihyal, as ex- plained under those bones.

Urohyal. -—Reduced to a short depressed plate without a ventral keel; articulates by fibrous tissue anterodorsally with the anteromedial edge of the dorsal hypohyal and dorsomedial edge of the ventral hypohyal;

articulates by fibrous tissue posteriorly with the ventral

surfaces of the first two basibranchial elements.

Branchial Arches. —All the elements are cartilage

filled at their edges of articulation with the other elements in the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and two (sometimes three) pairs

of pharyngobranchials. Four gills are present, with a small slit between the fourth arch and the lower pharynFirst arch. —Basi-, hypo-, cerato-, epi-, and, sometimes, pharyngobranchial elements present. First basibranchial short, slightly wider posteriorly than anteriorly; displaced forward so that it articulates posteriorly with the second basibranchial and anteriorly with the hypohyals and urohyal, but with no direct connection with the first hypobranchials. First hypobranchial wide dorsally but very narrow ventrally; the

largest of the hypobranchial elements, which decrease in size posteriorly in the series; articulates ventrally with

the lateral surface of the middle region of the second

basibranchial and dorsally with the first ceratobranchial. First ceratobranchial a long sturdy compressed rod; the longest of the ceratobranchial elements, which decrease in length posteriorly in the series; from

the first to the fourth ceratobranchial the ventral regions become increasingly enlarged (the degree of compression

of the rods, and hence their width, appears to increase somewhat with increasing specimen size); no ventrally directed flange present on any of the ceratobranchials;

articulates ventrally with the first hypobranchial and

dorsally with the first epibranchial. First epibranchial a

short rod, somewhat narrowed in the middle; articulates dorsally with the anterolateral surface of the second pharyngobranchial and with the base of the first or suspensory pharyngobranchial when such is present; the

shortest of the epibranchial elements, which increase slightly in size posteriorly in the series. First pharyngobranchial absent, at least as an ossification, in the majority of the specimens examined, but present in 3 out of 13 specimens as a short slender toothless rod whose

distal end is held by fibrous tissue to the medial surface

of the extreme anterior end of the ventral flange of the

prootic shelf just lateral to the region where the prootic

interdigitates with the laterally expanded portion of the parasphenoid in the anterior region of the orbit.

Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial the longest of the basibranchials, the first and

third being of about the same length, but of different widths; articulates anteriorly with the first basi- branchial, laterally with the first hypobranchials, and

posteriorly with the third basibranchial. Second hypobranchial somewhat wider dorsally than ventrally; ar- ticulates ventrally with the area of articulation between

215
the first and second basibranchials, and dorsally with the second ceratobranchial. Second ceratobranchial only

slightly shorter than the first ceratobranchial; slightly expanded anteroventrally; articulates dorsally with the second epibranchial. Second epibranchial a short rod; ar- ticulates dorsally with the posterolateral surface of the second pharyngobranchial. Second pharyngobranchial

the first and larger of the two toothed pharyngobranchial elements; even in the largest specimen studied

(350 mm) it remains partially unossified, because a large cartilaginous region is present anterodorsally in its mass; more or less squarish in outline, except for its concave and vertically oriented posterior surface; articulates along its lateral surface posteriorly with the second epi- branchial and anteriorly with the first epibranchial; ar- ticulates along its concave posterior surface by fibrous

tissue to the rounded anterior surface of the third pharyngobranchial. The posterior surface of the second

pharyngobranchial is more deeply concave ventrally than dorsally, so that the ventral surface of the element

is U-shaped. It bears an irregular band of up to about 25 minute teeth on its ventral surface along the bend of the

U. The teeth are so small that it is doubtful if they are functional or even if they protrude to the surface through

the skin of the oral cavity.

Third arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Third basi- branchial the widest of the basibranchial elements; rec- tangular in shape; articulates anteriorly with the second

basibranchial, anterolaterally with the second hypobranchials, posterolaterally with the third hypobranchials and third ceratobrtmchials, and posteriorly with the fourth ceratobranchials. Third hypobranchial a

relatively straight and slender rod; articulates posterolaterally with the third ceratobranchial and postero- medially with the third basibranchial, while its ventrally directed anterior end articulates by fibrous tissue with the under surface of the more anterior basi- branchial elements. Third ceratobranchial articulated

ventrally with the posterior ends of the third hypobranchial and third basibranchial, and dorsally with the

third epibranchial. Third epibranchial rodlike; slightly expanded anteriorly in the middle of its length, at which

place it makes fibrous tissue contact with the posterior surface of the second epibranchial; articulates dorsally with the lateral surface of the third pharyngobranchial. Third pharyngobranchial smaller than the second

pharyngobranchial; more or less columnar; its ventral

surface concave; better ossifed than the second pharyngobranchial, but nevertheless with several cartilaginous areas present; articulates anteriorly with the concave

posterior surface of the second pharyngobranchial and

laterally with the dorsal ends of the third and fourth epi- branchials. It usually bears one to six minute and nonprotruding teeth in a row along the anterior edge of its ventral surface, but no such even rudimentary teeth could be found in some of the specimens examined.

Fourth arch. —Cerato- and epibranchial elements

only. Fourth ceratobranchial much expanded ventrally;

articulates ventrally with the posterior end of the third basibranchial and dorsally with the fourth epibranchial. Fourth epibranchial the longest of the epibranchial elements; much wider ventrally than dorsally; ar- ticulates dorsally with the lateral surface of the third pharyngobranchial.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial the shortest of the

ceratobranchial elements; much expanded ventrally throughout the middle region of its length; articulates ventrally with the ventral end of the fourth cerato- branchial; toothless.

PAIRED FIN GIRDLES.

Pectoral Fin.

Posttemporal. —A large long shaft broadly overlying the lower half of the lateral surface of the pterotic,

to which it is firmly interdigitated; anterodorsally it also interdigitates, to a much lesser extent, with the

sphenotic, while its ventral head is firmly held by fi- brous tissue to the supracleithrum. On its ventromedial

surface the posttemporal helps, along with the pterotic and, to a far lesser extent, the cleithrum, to support by fi- brous tissue the expanded lateral end of the ossified Baudelot's ligament.

Baudelot's ligament. —The ligament fully ossified as a large stout shelf giving great support to the pectoral

girdle. It articulates firmly by fibrous tissue at its medial end with the extreme posterolateral edge of the pttra- sphenoid immediately anterior to the posteriormost

point of contact between the parasphenoid and basioccipital. Its expanded lateral end is firmly held by fibrous

tissue mainly to the ventromedial surface of the ventral

flange of the pterotic and to the ventral end of the post- temporal, and, to a much lesser extent, to the extreme

dorsolateral end of the cleithrum. The dorsal edge of the medially expanded platelike portion of the cleithrum is firmly held by a sheet of fibrous tissue to the ventral sur- face of Baudelot's ligament.

Supracleithrum. —Located slightly obliquely posterodorsally to anteroventrally in relation to the axis of the body; relatively short and broadly overlain by the posttemporal; articulates firmly by fibrous tissue, and

slight interdigitation in large specimens, dorsally with

the overlying posttemporal and ventrally with the cleith- rum, which it broadly overlies.

Cleithrum. —Greatly expanded both laterally and

medially along all the length of its anterior edge, except

for a short distance ventrally, so that a large thin vertical plate is formed at right angles to the axis of the body; also greatly expanded posteriorly in the ventral

half of its length; articulates dorsally by fibrous tissue 216
and slight interdigitation with the broadly overlying supracleithrum and by fibrous tissue with the anterior edge of the dorsal postcleithrum; posteriorly in about the middle of its length it articulates by fibrous tissue and

slight interdigitation with the scapula and coracoid. Ventromedially the cleithrum articulates by fibrous tissue with its opposite member, while the dorsal edge of its medially expanded platelike portion is held by fibrous

tissue to the ventral surface of Baudelot's ligament.

Postcleithra. —The postcleithra form a thin wide

plate, closely held by fibrous tissue to the cuirass, from

the upper end of the cleithrum to about the level of the posteriormost point of the pectoral girdle. The dorsal postcleithrum is widest and thickest at its anterior edge where it articulates by fibrous tissue with the cleithrum.

Posteriorly the dorsal postcleithrum articulates by fi- brous tissue, and in large specimens by slight inter- digitation, with the ventral postcleithrum. The ventral postcleithrum is an extremely thin plate of variable shape, but it is always much smaller than the dorsal postcleithrum. The two postcleithra overlie one another

in a variable manner at their region of articulation.

Coracoid. —Wider ventrally than dorsally; its posterior edge with a laterally directed flange throughout its length, except at the extreme dorsal and ventral ends; a

short dorsal projection present from its posterodorsal edge which makes contact with the posterior edge of the

last actinost; cartilage filled at its dorsal edge; an upraised flange present on its lateral surface, running, with

increasing height of the flange, from posterodorsally to anteroventrally; articulates dorsally through cartilage with the scapula, while posterodorsally its small dorsally directed flange interdigitates with the posterior edge of the last actinost. Dorsally along its anterior end

the coracoid articulates by fibrous tissue and slight in- terdigitation with the cleithrum, which broadly overlies

it.

Scapula. —Completely encloses the scapular foramen; cartilage filled at its ventral and posterior edges; articulates by fibrous tissue and slight inter- digitation anteriorly and anteroventrally with the cleith- rum, and through cartilage ventrally with the coracoid; posterodorsally the scapula interdigitates with the bases

of the first two actinosts, while more anteriorly on its dorsal edge it bears a concavity to which the reduced first pectoral fin ray articulates by fibrous tissue.

Actinosts. —Four elements; all cartilage filled at

their dorsal edges; first actinost the smallest, the others

of slightly increasing size posteriorly in the series; all four elements held to one another by interdigitation; first and

second actinosts articulated ventrally by interdigitation with the posterodorsal edge of the scapula; third actinost

articulated ventrally by fibrous tissue with the scapula

and coracoid; fourth actinost articulated by fibrous tis- sue ventrally with the coracoid, as well as by inter- digitation posteriorly with the dorsally directed process

of the coracoid. Distally the actinosts support by fibrous

tissue all of the fin rays, except for the first, which is supported by the scapula, and the second, which is sup- ported by both the scapula and first actinost.

Fin rays. —Twelve fin rays in most specimens, with

the first ray about one-sixth the length of the second ray and articulated directly with the scapula instead of with

the actinosts, as are all the other rays, except for the sec- ond, which articulates with the region of interdigitation between the scapula and first actinost; first ray with its two halves fused together, the division between the two

halves being indicated only by an oblong cavity running

horizontally through the base of the ray; the medial half

of the ray larger than the lateral half. The first two rays unbranched, the others branched. The first ray without

cross-striations, the other rays cross-striated.

VERTEBRAL COLUMN. —All vertebrae with bicon- cave centra, except the last, which ends posteriorly in the fused hypural plate, and the highly modified first five vertebrae.

Abdominal Vertebrae.

First five vertebrae. —What has usually been called the first vertebra is in fact a compound element resulting from the fusion of the first five abdominal vertebrae to themselves and to the posterior end of the basioccipital

(as described in detail by Tyler 1963a). In adult specimens there is slight evidence of this fusion of the

first five vertebrae into a single piece, for there are five neural foramina in the upper half of the lateral surface of the fusion product and its neural arch shows, except in extremely large specimens, a division or lobation dorsally into five successive regions separated from one

another by clefts which extend downward about onethird to one-half the distance from the top of the neural arch to the region of the centrum. In the 8.2 mm

specimen each of the last three of the first five vertebrae

possesses a very thin centrum and neural arch in a single continuous piece separate from that succeeding and

preceding it. The first and second vertebrae are even

thinner than the others and their centra are in close apposition and may even be fused at this early develop- mental stage. These two centra, in turn, appear to be in the process of fusing with the basioccipital, but their neural arches are still separate from one another. In the

15.3 mm specimen the first two vertebrae have their centra and the lower one-fourth of their neural arches indis- tinguishably fused, while the centra are similarly fused

to the basioccipital. The third and fourth vertebrae have

their centra and the lower three-fourths of their neural

arches indistinguishably fused, but separate from the fused first two vertebrae and the fifth vertebra. In the 217
study specimens of 25.0 mm and larger the centra of the

first five vertebrae are all fully fused to one another and

to the basioccipital, while their neural arches become

progressively more fused together until only the lobation

dorsally remains from their original distinctness (see Tyler 1963a: 158- 160 for details). After the centra have

fused with the basioccipital I am unable to distinguish where the one ends and the other begins. In the adult, the

posterior end of the fused basioccipital and first five vertebral centra is a concave rounded surface which ar- ticulates by fibrous tissue with the sixth abdominal

vertebra. One can suppose that this concave articular surface is formed from material contributed by the cen- trum of the fifth vertebra. At least the first two vertebrae seem to lie principally lateral to the posterior region of the basioccipital, for it appears that they have fused not

to the extreme posterior end of the basioccipital but

rather to its posterolateral surface. The neural arch of the

first vertebra overlies and interdigitates with the posterodorsal surface of the exoccipitals. Ventrolaterally from

each side of the fused first five vertebral centra there is a

wide, but delicate, ventral process which attaches by fi- brous tissue posteriorly with a similar pair of projections from the sixth abdominal vertebra. The small muscles which attach to these ventral projections have a complex relationship with the air bladder. The dorsomedial

edges of the neural arches of the first five vertebrae meet

in the midline and are held together at first by fibrous

tissue, but in large specimens this articulation becomes

interdigitated to form a complete bony roof over the neural canal. No neural spines are present. The lower

half of the posterior edge of the fused neural arches of the

first five vertebrae strongly interdigitates with the anterior edge of the lower portion of the neural arch of the

sixth abdominal vertebra.

Other abdominal vertebrae. —As explained in the preceding section on the Aracanidae, the first caudal

vertebra is arbitrarily designated as the anteriormost

vertebra whose ventral surface is most closely associated with the proximal end of the first anal fin basal pteryg- iophore which consistently lies in the midvertical plane

of the body. In 13 specimens there are nine abdominal

vertebrae; which is to say that the first five vertebrae are fused into a single piece, and that this element is fol- lowed by four separate and distinct vertebrae. The sixth abdominal vertebra articulates by fibrous tissue at its concave anterior end with the posterior concave surface

of the fused first five vertebrae and basioccipital, while

laterally the lower half of the anterior edge of the neural

arch of the sixth vertebra is extensively interdigitated with the lower posterior edge of the neural arch of the fus- ed first five vertebrae. The sixth abdominal vertebra

possesses a short and thin neural spine along most of the

length of the dorsal surface of its neural arch. The

haemal processes from the ventrolateral edges of the anterior end of the sixth vertebra are anteriorly expanded

at their distal ends. The distal ends of these processes do

not fuse to one another in the midline of the body; rather, they are held to one another by fibrous tissue. This incomplete haemal arch is held by fibrous tissue anteriorly to the similar structure from the fused first five vertebrae and, like the latter, it is a point of attachment

for a complex of muscles associated with the air bladder. The seventh to ninth abdominal vertebrae have large neural spines and complete, although much reduced, haemal arches without haemal spines. The sixth to ninth abdominal vertebrae articulate with one another not only by fibrous tissue between their concave articular faces but also by deep and firm interdigitation of the edges of

the neural arches. The neural spine of the seventh ab- dominal vertebra is long, thin, and delicate; the anteroposterior depth of its basal region is about equal to that

of the vertebra, but the spine tapers to a point distally. The posterior edge of the neural spine of the seventh ab- dominal vertebra articulates by fibrous tissue with the

first dorsal fin basal pterygiophore. The neural spines of the eighth and ninth abdominal vertebrae are narrow

rods arising from the posterodorsal surfaces of their neural arches and directed posterodorsally between the

dorsal fin basal pterygiophores almost to the distal ends

of the latter elements. The neural spine of the eighth ab- dominal vertebra lies between the first and second

pterygiophores, and the neural spine of the ninth between the third and fourth pterygiophores. The neural

spines and pterygiophores are held to one another by a

sheet of fibrous tissue. The haemal arches of the seventh

to ninth abdominal vertebrae are complete, although

thin and very delicate and of somewhat variable shape

from specimen to specimen. No haemal spines are present. The haemal arches arise from the anterior end of the

ventrolateral surfaces of the centra and do not project very far ventrally, thus enclosing only a shallow cavity through which the haemal canal runs. The arches of the

eighth and ninth vertebrae are distinctly displaced to one

side of the midline of the body, usually to the right. The

longitudinal concavity on the ventral surface of the seventh to ninth vertebrae, which marks the course of the haemal canal, is likewise displaced to a greater or lesser degree to one side of the midline of the body. The

longitudinal concavity on the ventral surface of the sixth vertebra is in the midline of the body, as it is on the anterior end of the seventh vertebra. As the concavity

passes from the anterior to the posterior end of the seventh vertebra, it is displaced usually to the right of

the midline, and along the eighth and ninth vertebrae it

is similarly usually displaced to the right of the midline. The ventrolateral edges of the seventh to ninth ab- dominal vertebrae are interdigitated with one another. The eighth and ninth abdominal vertebrae possess

slightly upraised ridges diagonally across the lateral sur- faces of their centra from the bases of the neural spines to the anterolateral edges of the centra. The neural foramen

of each of the abdominal vertebrae from the sixth to ninth emerges relatively low on the lateral surface of the

vertebra.

Caudal Vertebrae. —The caudal vertebrae numbered

10 in 13 specimens, although all other species of ostraciids, including the other three species of Acantho-
stracion, have only 9 caudal vertebrae (see Tyler

1965b:268). The first and second caudal vertebrae are

like the eighth and ninth abdominal vertebrae, except

that their neural spines are shorter and that their anteroventral surfaces support by fibrous tissue the first two

anal fin basal pterygiophores which lie entirely in the

midvertical plane of the body. The neural spine of the

first caudal vertebra lies between the fifth and sixth dorsal fin basal pterygiophores. The haemal arches of the

first, second, and third caudal vertebrae are delicate and

complete, like those of the seventh to ninth abdominal

vertebrae. The haemal arches of the second and third caudal vertebrae are more or less symmetrically placed

in the midline of the body, but that of the first caudal

vertebra is displaced somewhat to the right. The longi- tudinal concavity present on the ventral surfaces of the

first to fourth caudal vertebrae, which marks the course

of the haemal canal, is more or less in the midline, ex- cept in the case of the first caudal vertebra, where the concavity is displaced to the right at the anterior end of the vertebra. The fourth caudal vertebra usually

possesses only the longitudinal concavity on its ventral

surface, and no haemal arch. The third and fourth anal

fin basal pterygiophores that lie in the midvertical plane

of the body articulate by fibrous tissue with the anteroventral surfaces of, respectively, the third and fourth caudal vertebrae. The neural spine of the third caudal

vertebra is anteroposteriorly expanded into a flattened

plate which along the dorsal half of its anterior edge is firmly articulated by fibrous tissue with the posterior edge of the last dorsal fin basal pterygiophore, while

along its posterior edge it is deeply interdigitated with

the anterior edge of the neural spine of the fourth caudal

vertebra. The neural spine of the fourth caudal vertebra

is anteroposteriorly expanded into a flat plate which is firmly interdigitated at its anterior and posterior edges

with, respectively, the posterior edge of the neural spine

of the third caudal vertebra and the anterior edge of the

neural spine of the fifth caudal vertebra. Whereas the

third caudal vertebra is the last caudal vertebra to make

contact with the dorsal fin basal pterygiophores, the fifth caudal vertebra is the last to make contact with the anal

fin basal pterygiophores. The fifth caudal vertebra has

its neural spine anterodorsally expanded, with its anterior edge interdigitating with the posterior edge of the

neural spine of the fourth caudal vertebra, while its posterior edge is well separated fi-om the neural spine of the

sixth caudal vertebra and is held to the latter only by fi- brous tissue. The fifth caudal vertebra possesses a well- developed haemal arch and spine, with the haemal arch running the length of the vertebra. The haemal spine of the fifth caudal vertebra is a thick compressed plate which is concave along the lower half of its anterior edge and articulates by fibrous tissue with the middle region

of the posterior surface of the last anal fin basal pterygiophore. The sixth to ninth caudal vertebrae are basically similar to one another. They possess sturdy neural arches and spines and haemal arches and spines, all of which

decrease slightly in size posteriorly in the series. The centra of these four vertebrae are much shortened anteroposteriorly and are held to one another by fibrous tissue. These vertebrae, and the last vertebra, are thus the only

vertebrae which can be laterally flexed to any appreciable extent, since all the vertebrae anterior to the

sixth caudal vertebra are interdigitated with one another

over large areas of their surfaces of contact. Thus, the

third to sixth caudal vertebrae are interdigitated with one another along the surfaces of contact of their neural

arches and spines; the seventh abdominal to the second

caudal vertebrae are interdigitated with one another not

only along the surfaces of contact of their neural arches but also at their ventrolateral edges of contact; the sixth abdominal vertebra is interdigitated along the anterior and posterior edges of its neural arch with the vertebrae

anterior and posterior to it; the first five abdominal

vertebrae are completely fused to one another.

Caudal Skeleton. —The caudal complex consists of a

large rectangular plate, with a rounded expansion in the middle region of its anterior edge representing the cen- trum of the last caudal vertebra, and a deep cleft in the middle of its posterior edge representing the division between what in more generalized plectognaths would be

the second and third hypurals. However, the hypurals

are fully fused to the centrum and to themselves and no

real distinction can be made between them. Examination of young specimens shows that the anterior portion

of the caudal skeleton develops from a centrum which

has a complete neural arch and spine and haemal arch and spine. The neural (epural) and haemal (parhypural) apparatus in the 8.2 mm specimen already appear to be continuous with the centrum, although a deep indentation in the dorsal edge of the plate partially separates the epural from the fused hypurals. In all of the small specimens a urostylar thickening can be seen projecting a

short distance posterodorsally from the posterior end of the last vertebra, just in front of the anterodorsal edge of the hypural region. This complex that represents the last caudal vertebra corresponds to about the anterior one- seventh of the adult caudal skeleton. Posterior to the

region of the last caudal vertebra in the 8.2 mm

specimen, and continuous with it, is the hypural plate, representing the hypural elements fully fused already to one another and to the last vertebra, except in the region

of the deep cleft in the posterior edge, the cleft being much deeper in young specimens than in adults. In adults all of these elements are simply more extensively and indistinguishably fused into the single rectangular

plate already apparent at 8.2 mm. A small foramen is present in the anteroventral region of the plate and this is the last opening into the haemal canal, which forms a short tube in the substance of the plate anterior to the foramen and is continuous with the haemal canal of the more anterior vertebrae. This foramen thus marks the

region of fusion of the lower hypural region with the parhypural. The neural canal enters the anterior edge of the plate just above the centrum and courses through the

plate to exit at a foramen on its posterodorsal edge. The

region of the plate above the neural canal represents the

fully fused epural. 219
Caudal fin rays. —Ten in number, the uppermost

ray and the lowermost ray unbranched, the others becoming increasingly branched toward the middle rays, which are branched in triple dichotomies. The five upper

rays articulate by fibrous tissue at their bifid bases with

the upper lobe of the fused hypural plate and the lower

five rays with the lower lobe. DORSAL AND ANAL FINS.

Fin rays and pterygiophores. —Ten fin rays are present in most specimens; the first ray unbranched, the

other rays branched in single or double dichotomies. Distal pterygiophores are either absent or unossified. The

bifid bases of the fin rays are supported through fibrous

tissue by nine basal pterygiophores. With the exception

of the first pterygiophore, all of them are slender rods,

cartilage filled at both ends and of decreasing length posteriorly in the series. At their dorsal ends these rodlike pterygiophores are somewhat compressed and are closely held to one another by fibrous tissue and slight inter- digitation, with the degree of interdigitation between them increasing with increased specimen size. From the second to the ninth pterygiophore, slight concavities are present in the surfaces of contact of the pterygiophores with each other, so that gaps are present in the other- wise interdigitated surfaces. The first pterygiophore is unlike the others only in that it is expanded anteriorly throughout most of its length into a thin flange. The

anterodorsal edge of the first pterygiophore inter- digitates with the posterior edge of the supraneural. The

supraneural is a short, laterally expanded, plate whose

dorsal surface is convex and whose ventral surface is concave. The dorsal surface of the supraneural is in close fi- brous tissue contact with the cuirass. The dorsal fin basal pterygiophores articulate by fibrous tissue between the

neural spines of the seventh abdominal to third caudal

vertebrae. The articulation of the ninth pterygiophore is somewhat different from the others in that it makes a much more intimate contact with the adjacent neural

spine than do the others, for it lies in close apposition with the concave anterior edge of the neural spine of the

third caudal vertebra.

Fin rays and pterygiophores. —Ten fin rays are present in most specimens; the first ray unbranched, the

others branched in single or double dichotomies. Distal pterygiophores are either absent or unossified. The bifid bases of the fin rays are supported through fibrous tissue by 9 (occasionally 10) basal pterygiophores. These

pterygiophores are basically similar to those of the dorsal fin in that they are slender rods, compressed at their ventral ends into flattened narrow plates held to one

another by fibrous tissue and slight interdigitation. Concavities are present in their surfaces of contact with each

other so that gaps are present in their otherwise interdigitated surfaces. Whereas all of the dorsal fin pteryg- iophores lie in the midvertical plane of the body, only the

last four anal fin pterygiophores lie entirely in this medial plane, the five pterygiophores anterior to them

diverging to the right and to the left from their ventral

ends, which are in the midvertical plane. The sixth to ninth pterygiophores have their dorsal ends held by fi- brous tissue to the anteroventral surfaces of, respectively, the first to fourth caudal vertebrae. The middle

region of the posterior edge of the ninth pterygiophore is also held by fibrous tissue to the concavity on the anterior edge of the haemal spine of the fifth caudal vertebra. The second to fifth pterygiophores have their flat- tened ventral regions in the midvertical plane, but their long rodlike anterodorsally directed portions lie to the

right or to the left of the midline in the anterior portion of the large muscle mass connected to the anal fin (only the two pterygiophores that diverge to the left are shown in the figure of the lateral view of the entire skeleton). The

anterodorsal rodlike portion of the first anal fin basal pterygiophore is placed only very slightly to one side of the midvertical plane, either to the right or to the left depending on the individual. The ventral edge of its rodlike portion is expanded into a low and thin keel throughout most of its length. The first pterygiophore has by far the largest distal end of any of the pterygiophores. Its base is expanded anterolaterally to either side to form a U-shaped projection which lies just under the cuirass. In

large specimens the usually rodlike dorsal portions of the second to fifth pterygiophores may become laterally ex- panded into thin flanges in the region where these pterygiophores converge toward the midvertical plane of the body.

Anatomical diversity.—The carapace extends well behind the level of the posterior ends of the dorsal and

anal fins and completely encloses the fin bases in all species of the family except Lactophrys trigonus, the lat- ter having the carapace somewhat extended beyond the

dorsal and anal fin bases but only completely closed behind the anal fin. Posterior to the dorsal fin in L. trigonus the two posterodorsal extensions of the carapace

often closely approach one another in the midline, es- pecially in large specimens, and are separated from one

another and from the anterior half of the large fi-ee plate that lies just behind the dorsal fin only by a very narrow

scaleless space. In one especially large specimen of L. trigonus examined (ANSP 102757, 366 mm) externally, the posterodorsal extensions of the carapace and the

usually free plate are in intimate contact and are as fully interdigitated with one another as are the other scale plates of the carapace, the carapace in this specimen

forming a complete wide bridge over the caudal peduncle behind the dorsal fin. In most genera (Acanthostracion, Rhinesomus, Lactophrys, Tetrosomus) the carapace has a basically tri- angular shape, the horizontal distance between the

ventrolateral ridges being greater than between the

dorsolateral ridges, with the carapace extended above

into a dorsal ridge. A mediolateral ridge is scarcely devel-
oped, if at all, and there is no ventral ridge, the flattened bottom of the carapace being either gently convex or slightly concave. At the opposite extreme to the forms with a

triangular carapace is Ostracion, with a rectangular carapace in which the distance between the dorsolateral ridges is about equal to that between the ventrolateral ridges, and with both the back and belly flattened

or only gently convex, the dorsal and ventral ridges
Fi({ure laO.—Acanthostracion quadricornis:

lateral view of head, composite based on

several specimens, 58.2-350 mm SL, Gulf of Mexico and Caribbean. pterosphenoid

frontal prefrontal

maxillary premaxillaryXp"'*"'"*

dentary

articular anguia

quadrate

-interoperculom

ectopterygoid

parosphenoid

cartilage ' ethmoid \ V#f^^

vomer

supraoccipital

sphenotic

symplectic

basioccipital

prootic \ parasphenoid

metapterygoid , operculum ^ preoperculum \ i» i "^^^'y^J^ suboperculum hyomandlbular PO^«emporal

essentially being absent. Two other genera are in various ways intermediate between the two extremes of carapace

shape. In Lactoria the carapace is basically pentagonal, with the distance between the ventrolateral ridges much

greater than that between the dorsolateral ridges, but

with only a low dorsal ridge, extended in two species (for- nasinii and diaphana) into a prominent spine. In Rhynchostracion the carapace in one species

(rhinorhynchus) is as rectangular as in Ostracion, while

in the other species (nasus) there is a prominent and

relatively high dorsal ridge so that the carapace is pentagonal. In the pentagonal carapace of R. nasus the dis- tance between the ventrolateral ridges is only very slightly greater than that between the dorsolateral ridges and

this shape may be most closely related to the rec- tangular form, while the pentagonal carapace of Lactoria, with the distance between the ventrolateral ridges much greater than that between the dorsolateral ridges, may be most closely related to the triangular form.

Isolated scale plates on the caudal peduncle behind

the carapace are found only in Acanthostracion quadricornis (commonly) and in A. polygonius (rarely, see Tyler 1965a:8), in addition, of course, to the single large plate found in Lactophrys trigonus, discussed above.

In the only known fossil specimen of ostraciid, Eolactoria sorbinii from the Eocene of Monte Bolca, Italy, it is impossible to say with assurity whether the carapace was

triangular, pentangular, or rectangular. However, there

is a slight indication (Tyler 1973a: 108) that the scale plates along the region that would be the dorsolateral

ridge had larger central tubercules or spines than the sur- rounding plates, suggesting that the dorsolateral ridge

was prominent and that there was a dorsal crest, the carapace perhaps being pentangular as in the Recent

Lactoria and Rhynchostracion rhinorhynchus. Spiny processes are present on the carapace except in Ostracion, Rhynchostracion, and Rhinesomus triqueter. In Acanthostracion, Lactoria, and the Eocene Eolactoria there are paired preorbital and postanal spines, with Eolactoria having in addition an unpaired anteriorly directed spine between the eyes and Lactoria having a well-developed spine on the dorsal ridge in some

species. In Lactophrys and Rhinesomus bicaudalis there

are postanal spines, while in Tetrosomus there are three

to five spines along the ventrolateral ridge, a supraorbital spine and one or two spines along the dorsal ridge. In general, the carapace of ostraciids is slightly more

fully consolidated than in aracanids, the only region with much flexibility and unsutured scale plates being the

cheek, whereas in aracanids many of the scale plates around the mouth and along the ventral region and

around the anus are often unsutured and slightly flexi- ble.The number of teeth is slightly variable in ostraciids, which tend to have a few more teeth in the jaws, es- pecially the upper, than in aracanids. Most ostraciids have 10 to 12 teeth in the upper jaw and 8 to 10 in the lower jaw. There is only a slight tendency for an increase

in the number of teeth with increasing specimen size, ex- cept in Lactoria diaphana, a relatively small species which at sizes below about 30 mm tends to have 10 to 12 teeth in the upper jaw and 6 to 7 in the lower jaw, but at

larger sizes to have about 13 to 16 in the upper and 7 to 9

in the lower. The numbers of teeth in the upper and lower 222
jaws of those species for which the most counts were made are shown in Table 3 and Figures 165-166 (for Lactoria cornuta, L. fornasinii, and L. diaphana; Ostracion

tuberculatus and 0. lentiginosum; Acanthostracion quadricomis and A. polygonius; Lactophrys trigonus; and Rhinesomus triqueter and R. bicaudalis). There is nothing out of the ordinary in the tooth counts recorded

for the fewer specimens of the other species of ostraciids examined but not listed above. In the Eocene Eolactoria

the total number of teeth in the jaws is not known, but

they seem to be slightly wider basally and more decidedly constricted distally or cusped than in the Recent

species, somewhat reminiscent of the teeth of balistids (Tyler 1973a).

In all species of the Indo-Pacific genera (Lactoria, Tetrosomus, Ostracion, and Rhynchostracion) the dorsal and anal fin rays are modally 9 and the pectoral fin rays modally 10, excluding the uppermost rudimentary

pectoral ray. In all of the species of the Atlantic genera

{Acanthostracion, Rhinesomus, and Lactophrys) the

dorsal and anal fin rays are modally 10 and the pectoral

fin rays modally 12 in all but Acanthostracion quadFigure 151.

Acanthostracion quadricornis:

dorsal (left) and ventral views of skull, composite based on several specimens, 58.2-350 mm SL, Gulf of Mexico and Caribbean.

ricornis, which has only 11 (see Tyler 1965a, b). Correlated with the differences in the number of dorsal and

anal fin rays are similar differences in the number of basal pterygiophores. In the Indo-Pacific genera there are modally eight dorsal and anal fin basal pterygiophores and in the Atlantic genera nine. In both cases the anterior divergent anal fin basal pterygiophores number

five. When one more than the modal number of rays is present, there is also often one additional basal pterygiophore. In all ostraciids there are two nostrils on each side, nearly always in the form of two short upright tubes. However, in Rhinesomus bicaudalis the anterior tube is extremely bulbous (see Bohlke and Chaplin 1968:678, fig. 212; and Fig. 159 here) at all specimen sizes, while in Lactophrys trigonus it becomes bulbous, to about half the extent of that in R. bicaudalis, in large specimens.
Figxire 152.—Acanthost

quadricomis: posterior views

skull (left) and of orbit (right) ( section of skull: dashed lines represent

cut surfaces of frontals, pterosph(

prootics, and parasphenoid). composite based on several specimens,

58.2-350 mm SL, Gulf of Mexico and Caribbean.

Figure l53.—Acantho»tracion quadricomia: lateral (to left) and

medial views of palatopteroquadrate

region, composite based on several specimens, 58.2-350 mm SL, Gulf of Mexico and Caribbean.

Figure \5i.—Acantho8tracion

quadricornig: (left) lateral view of

occipital region of skull and the fused five abdominal verte- brae; (right) posterior view of fused first five abdominal vertebrae;

77.7 mm SL, Florida.
1st 2nd 3rd

Figure \55.—Acantho8tracion quadricomis: medial (left) and

lateral (right) views of pectoral

girdle, composite based on several specimens, 58.2-350 mm SL, Gulf of Mexico and Caribbean.

Figure 156.—/Icanf/iostrocion quadricomis: above, ventral view

of vertebral column from the fused first five abdominal vertebrae

to the fourth caudal vertebra, showing the haemal spines and the displacement of the haemal canal; below, ventral view of the basal pterygiophores of the anal fin, showing the displacement of the more anterior pterygiophores to the left and to the right of the midline; composite based on several specimens, 58.2-350 mm SL, Gulf of Mexico and Caribbean.
ceratobranchials

epibranchials rS^'

pharyngobranchials

::;= basibranchials hypobranchials

epihyal

' }j ventral hypohyal

ceratohyol

Figure 159. (opp. page)—External features

of other representative ostraciid genera:

A, Rhinesomus bicaudalis— upper left, nasal region as seen

externally and, lower left, outline of cross section of middle of body; B, R. triqueter—

to show the course of the inconspicuous lateral line canals and their major pores. as decifered by placing drops

of ink on each pore found by

microscopic search of a partially drying specimen; C, R. triqueter— upper left, nasal region as seen externally and. lower

left, outline of cross section

of middle of body, with pattern

of scale plates shown only behind pectoral fin on main

body illustration.

branchlostegal rays

Figure 157.—4cant/io»tracion lateral and dorsal views of urohyal; quadricomig: dorsal view of composite based on several specimens,

branchial arches (extended on lower 58.2-350 mm SL, Gulf of

side); lateral view of hyoid arch; Mexico and Caribbean. Figure 158.—4conf/io»trocion quadri- comis: lateral view of caudal fin supporting structures, composite based on several specimens,

58.2-350 mm SL, Gulf of Mexico

and Caribbean.

l;^

I u~^i
Figure 162.— External features of other representative

ostraciid genera: Tetrosomus gibboeus—upper left, nasal region as seen externally; lower left, outline of cross section of middle of body; pattern of scale plates shown only behind pectoral fin.

Figure 163.—External features of other representative

ostraciid genera: Ostracion lentiginosum—upper

left, nasal region as seen externally; lower left, outline of cross section of middle of body; pattern

of scale plates shown only behind pectoral fin.

Figure 160. —External features of other representative

ostraciid genera: Lactophrys trigonus —upper left, nasal region as seen externally; lower left, outline

of cross section of middle of body; pattern of

scale plates shown only behind pectoral fin.

Figure 161.— External features of other representative

ostraciid genera: Lactoria forntuinii—upper left, nasal region as seen externally; lower left, outline

of cross section of middle of body; pattern of

scale plates shown only behind pectoral fin.

Figure 164.— External features of other representative

ostraciid genera: Rhynchostracion nasus (above) and

R. rhinorhynchua—in both cases, upper left, nasal

region as seen externally; lower left, outline of cross section of middle of body; pattern of scale plates shown only behind pectoral fin. 227
L. TRIGONUS • O

R. TRIQUETER V

R. BICAUDALIS I f

The fundamental plan of the skull is even more conservative in the ostraciids than in the aracanids, and

nearly all of the differences between the species to be

pointed out involve the vertebral column.

In all of the species of the Indo-Pacific genera (Lactoria, Tetrosomus, Ostracion, and Rhynchostracion) a small but distinct myodome is present, while in all of the

species of the Atlantic genera (Acanthostracion, Rhine- somus, and Lactophrys) the myodome is essentially absent. In the Atlantic species there is no anterodorsal roof

to the prootic at the appropriate place over the posterior eye muscles, although in the rear of the orbit where the

prootics are in contact medially the two bones are curved upward to form a shallow concavity bounded posteriorly by a low crest, which region can be considered as the posterior and posterodorsal walls of a rudimentary myodome. If these surfaces of the prootics in the Atlantic species were a little more concave and the posterior myodome region more uplifted and anterodorsally

oriented, a small myodome could be said to be present, but such is not quite the case. In the Indo-Pacific species a small and shallow myodome is more distinctly present.

In all of the species of the more generalized family Aracanidae, a small but distinct myodome is present. In all of the Indo-Pacific species at least two of the

vertebrae posterior to the last which helps support the

last dorsal fin basal pterygiophore have trifid neural

spines, while none of the neural spines are trifid or even

bifid in the Atlantic species. The greatest number of

trifid neural spines is found in Lactoria cornuta, in which

the 14th to 17th vertebrae have them. In L. fomasinii

there is one less, the trifid spines being present on the

14th to 16th vertebrae. In Tetrosomus concatenatus and

T. gibbosus well-developed trifid neural spines are pres- ent on the 15th and 16th vertebrae, and a less strongly developed one may be present or absent on the 17th

vertebra. In Ostracion lentiginosum they are trifid on the

15th to 17th vertebrae, as they also are in 0. tuber- culatus and Rhynchostracion rhinorhynchus, except that

the spine of the 17th vertebrae is sometimes single rather than trifid. The trifid neural spines apparently afford a broader surface of support for the carapace in this region than does the single neural spine. In all of the Atlantic species and in the Indo-Pacific Lactoria fornasinii the first five vertebrae are involved in the fusion complex with the base of the skull, while all of the Indo-Pacific species except L. fornasinii have only

the first four vertebrae involved in the fusion complex. Of

the two species of Ostracion examined, at least one has

slightly less fusion between the first four vertebrae than

in the other Indo-Pacific species. In Ostracion tuber- culatus the first two vertebrae are fully fused to one

i »

7 8 9 10 NUMBER OF TEETH

Figure 165.—Number of teeth in upper (solid symboU) and lower (open symbols) jaws in relation

to sUndard length, to show the slightly greater number of teeth in the upper versus the lower jaw, and the relatively negligible increase in number of teeth with increasing standard length at sizes greater than about 40 mm SL; Lactophry» trigonut Rhinesomiu triqueter, R. bicaudalit.
O. TUBERCULATUS • O a LENTIGINOSUM D

A. OUADRICORNIS V

A. POLYGONIUS • O

I I

8 9 10 11 12 13 JUMBER OF TEETH

another and to the basioccipital and exoccipital basally, while distally there is only partial fusion of their neural

spines. The third and fourth vertebrae are similarly fully fused with one another basally, while their neural spines

are only partially fused. The degree of fusion of the

neural spines increases with increased specimen size, much as described by Tyler (1963a) (or Acanthostracion

quadricomis. But even in the two largest specimens of 0. tuberculatus examined (96.7-122 mm) the fused first- second vertebrae and the fused third-fourth vertebrae re- main distinct from one another. In 0. lentiginosum the two smallest specimens examined (24.4-33.2 mm) have

the first and second vertebrae fully fused to themselves and to the basioccipital and exoccipital basally, with the neural spines only partially fused, and the third and

fourth vertebrae are similarly fused to themselves, with

the second and third remaining separate. But in all of the

larger specimens (68.2-115 mm) the fused first-second vertebrae and the fused third-fourth vertebrae are at

least partially fused together between the second and

third, and in the largest specimens almost completely

fused. However, this variously partial to almost complete fusion between the two fusion complexes in 0. len- tiginosum is less complete and occurs at a larger specimen size than in the other Indo-Pacific genera. The divergence of the haemal canal away from the midline under most of the unfused abdominal vertebrae

is highly variable. There follows a listing of the course of the divergence in the specimens closely examined for

it: Tetrosomus concatenatus, to the right of the midline in 1 specimen; T. gibbosus, left in 1; Lactoria cor- nuta, right in 4, left in 1, alternately right and left in 2, almost straight in 1; L. fornasinii, right in 1, essentially straight in 2; Ostracion lentiginosum, right in 4, left in 1; 0. tuberculatus, right in 5; Rhynchostracion rhinorhynchus, right in 1; Acanthostracion quadricornis, right in 6, left in 2; A. polygonius, right in 1, alternately right and

left in 1; A. guineensis, alternately right and left in 1; A. notacanthus, right in 1; Lactophrys trigonus, right in 2, left in 1, alternately right and left in 2; Rhinesomus

bicaudalis, left in 2; R. triqueter, left in 2, alternately

right and left in 2, almost straight in 1. Thus, in both the

Indo-Pacific species and in the Atlantic species, the canal can be diverted to either the right or left, or al- ternately to the right and left. If enough specimens were examined it might be possible to show that there was a

greater frequency of right deviation in the Indo-Pacific

species and of left or alternately right and left deviation

in the Atlantic species, but such cannot yet be done. The structure of the last few vertebrae shows interest- ing variation, as described by Tyler (1970b) and briefly

Figure 166.—Number of teeth in upper (solid symbols) and lower (open symbols) jaws in relation

to standard length, to show the slightly greater number of teeth in the upper versus the lower jaw, and the relatively negligible increase in number

of teeth with increasing standard length at sizes greater than about 40 mm SL: Ostracion

tuberculatus, O. lentiginosum, Acanthostracion

quadricornis, A. polygonius. 229
%


/4^
Figure i~ I .—Rhinesomus triqueter: lateral view of head, 134 mm SL, Colombia.
angular

metapterygoid

symplectic ectoDterygoid quadrate

interoperculum

parasphenoid posttemporol

pterotic hyomandibular

Figure 173.—Tetrosomu*

concatenatua: lateral view of head, 43.4 mm SL, Thailand.

Figure m.—Lactoria comuta: ventral view of skull, 88.2 mm SL, Philippines.
Figure 175.—Lactoria fomaainii: posterior view of

orbit (cross section of skull; dashed lines represent cut surfaces of frontals. pterosphenoids,

prootics, and parasphenoid), 65.2 mm SL, Hawaii.

summarized here. The most generalized condition of the caudal skeleton is found in Lactophrys trigonus and the two species of Rhinesomus, the haemal spine of the penultimate vertebra being relatively large and autog- enous and the haemal canal passing through it and into the caudal plate to exit at a foramen just below the

region of the centrum, the foramen marking the region of

fusion between what in more generalized plectognaths

are the parhypural and lowermost hypural. All three

species have three postanal vertebrae. The moderately

specialized condition of the caudal skeleton is found in Lactoria cornuta and the four species of Acanthostracion, the haemal spine of the penultimate vertebra being reduced in size and fused to its centrum, while the haemal canal pierces and exits in the caudal plate just as

in Lactophrys and Rhinesomus. There are three post- anal vertebrae in Lactoria cornuta, four in A. polygonius,

A. guineensis, and A. notacanthus, and five in A. quadricornis. Since all ostracioids with the exception of A. quadricornis have 18 vertebrae, and quadricornis 19, it is assumed that 18 is the generalized number and that the

addition of a vertebra in quadricornis has taken place in the postanal series. The most specialized condition of the caudal skeleton

is found in Lactoria fomasinii, the two species of Ostracion, the two species of Tetrosomus, and in Rhynchostracion rhinorhynchus. In these species the haemal

arches and spines of all the postanal vertebrae are usually much reduced in size, solid, fused to the centra, and

not pierced by the haemal canal, which also does not

enter the foramenless caudal plate. Of these species, the

solid haemal spines are best developed in Ostracion

tuberculatus (illustrated here), the haemal spines being

shorter in 0. lentiginosum (Tyler 1963a:fig. 13, which in- correctly shows nontrifid neural spines) and just as rudimentary if not more so in Tetrosomus and Rhynchostracion. There are four postanal vertebrae in Ostracion and Rhynchostracion, and three in Lactoria and

Tetrosomus.

All species of ostraciids have 9 abdominal and 9 caudal

(10 caudal in A. quadricornis) vertebrae, and all have 7 predorsal vertebrae, with the postanal, flexibly ar- ticulated, vertebrae varying from 5 to 3. The postcleithrum is nearly always composed of two

pieces, both of which, but especially the ventral piece, are relatively thin and delicate, only the anterior end of the dorsal piece around its region of articulation with the cleithrum being of much strength. Only in the single specimens examined of the two species of Tetrosomus was the division into two pieces not seen, and it may

have simply escaped notice in the posterior half of the bone which tends to break away from the front portion during dissection and hold fast to the carapace.

In all ostraciids the distal end of the first anal fin basal pterygiophore is expanded into a pair of anterolateral wings more or less surrounding the rear half of the anus and supporting the carapace in this region. The carapace

has additional specialized supporting structures around

both the dorsal and anal fins in the Indo-Pacific species, but not in those of the Atlantic. In addition to the trifid neural spines of two or more of the postdorsal vertebrae

that broaden the base of support for the carapace in the

Indo-Pacific species, the last dorsal and anal fin basal pterygiophores are also variously modified to help support the carapace. Just above its distal end the last anal fin basal pteryg- iophore is always laterally expanded into a shelf upon

which the carapace rests. In Lactoria cornuta the shelf is mainly a simple lateral expansion, but in L. fomasinii and all of the other Indo-Pacific species it is expanded

anteriorly as well as laterally into a pair of broad anterolaterally directed prongs supporting the carapace. The last dorsal fin basal pterygiophore, just below the

distal end, is variously expanded laterally and posteriorly into a supporting flange. In Ostracion, Rhynchostracion, and Lactoria cornuta this basal portion of the last dorsal fin basal pterygiophore is much expanded anteroposteriorly and closely held between the stout neural

spines of the 11th and 12th vertebrae, while the distal portion of the pterygiophore is expanded both laterally and posteriorly into a shelf upon which the carapace

rests. The posterior expansion of the distal end of the pterygiophore usually makes contact with the neural

spine of the 13th vertebra. In Lactoria fornasinii the distal end of the last dorsal fin basal pterygiophore is only

slightly expanded laterally and posteriorly into a supporting shelf and the basal portion is rodlike, not ex- panded anteroposteriorly. Moreover, the trifid neural

spines of the 14th to 16th vertebrae are not as massive in

L. fornasinii as in L. cornuta, and the neural spine of the

13th vertebra in L. fornasinii is long and slender and not

in contact with the last pterygiophore rather than massive and in contact with it, while that of the 12th verte-
bra is also much smaller than in L. comuta and only contacts the basal half of the rodlike portion of the last pterygiophore. The last dorsal fin basal pterygiophore in the two

species of Tetrosomus is similar to that of L. fornasinii, but the neural spines of the vertebrae below it are even more reduced in size. In Tetrosomus the distal end of the pterygiophore is only slightly expanded laterally and

posteriorly and the basal portion is rodlike, its extreme

basal end being supported variously by the long neural

spine of the Uth vertebra. The rest of the length of the pterygiophore is not in contact with any other vertebrae, mainly because the posterior extension of the distal end

is short and the neural spines of the 13th and 14th verte- brae are extremely low. As in L. fornasinii, the trifid neural spines of the 15th and 16th vertebrae in Tetrosomus are not massive. The degree of development of lateral flanges extending down from the neural spines across the lateral sur- faces of the centra to end in broad transverse processes extending out anterolaterally from the lower surface of the centra is difficult to compare between species other than relatively subjectively. The flanges are best developed in Lactoria and Ostracion, moderately

developed in Tetrosomus and Rhynchostracion and only

slightly, if at all, less so in Rhinesomus, and poorly developed in Lactophrys and, especially, Acanthostracion. Thus, there is a tendency for the Indo-Pacific

species to have the lateral flanges better developed than

in at least most of the Atlantic species. Probably associated with the more bulbous snout of Rhynchostracion is the fact that the ethmoid in this ge- nus is wider and more massive than in all other genera. Variation in the branchial arches of ostraciids is mainly confined to the presence or absence of minute and per- haps nearly functionless teeth on the third pharyngobranchial. The second pharyngobranchial in all species bears equally minute or only slightly larger teeth than

those of the third pharyngobranchial. The first pharyngobranchial is a toothless suspensory element that is

Figure 176.—Rhynchostracion

rhinorhynchus: ventral (left) and dorsal

(right) views of skull, 88.2 mm SL, Java.
tyO CO basibranchials

l_J' —hypobranchials

branchiostegal

ventral hypohyal

ceratohyal

Figure ill .—Lactoria comuta: dorsal view of branchial arches (extended on lower side); lateral view

of hyoid arch and urohyal; 88.2 mm SL, Philippines.

present in all species, with the exception that only a minority of the specimens of Acanthostracion quadricornis examined had a first pharyngobranchial present,

at least as an ossification, and that the first pharyngobranchial may also have been absent in the single specimen of A. notacanthus examined, the specimen

having been poorly cleared and crudely dissected in this region and the presence or absence of that pharyngobranchial now being impossible to decipher. In most of the species examined the third pharyngobranchial is toothless, but minute teeth are present on it in Lactophrys trigonus, Tetrosomus concatenatus, and in most

but not all of the specimens examined of Acanthostracion quadricornis and Lactoria cornuta. Such variation is to be expected in what appear to be highly rudimentary structures, and if more specimens of the

species in which no third pharyngobranchial teeth were found had been examined, the suspicion is that at least some of these species could be added to the list above of those known to at least sometimes have teeth on this ele- ment.

Generic relationships and comparative diagnoses

of subfamilies (Ostraciinae, Lactophrysinae).—Fra- ser-Brunner (1941c) divided the ostraciids into two subfamilies, the Indo-Pacific Ostraciinae and Atlantic Lactophrysinae, on the basis of the lower number of dorsal, anal, and pectoral fin rays in the former and of supposed

vertebral differences between the two groups. Tyler

(1963a:185) showed that the vertebral differences mentioned by Fraser-Brunner did not stand close examination of a larger number of species than Fraser-Brunner

apparently had examined, but Tyler only hinted at a few other vertebral characters that might eventually be used to separate the two groups. These and additional characters that distinguish the two subfamilies are dis- cussed more fully in the preceding section on anatomical

diversity in the family. The separation of the ostraciids into two phyletic lines of subfamilial rank seems justified to me on the basis of the following differences: OSTRACIINAE

dorsal and anal fin rays modally 9

dorsal and anal fin basal pterygio- phores modally 8 pectoral fin rays modally 10

four vertebrae involved in the fu- sion complex at the rear of the

skull, except for one species with

five two or more postdorsal vertebrae with trifid neural spines

last anal fin basal pterygiophore

laterally or anterolaterally ex- panded into a prominent fiange

for carapace support

last dorsal fin basal pterygiophore moderately or greatly expanded

laterally and posteriorly for cara- pace support haemal spine of penultimate verte- bra fused to the centrum, either with a foramen or solid myodome small and shallow, but

present

Indo-Pacific distribution.

LACTOPHRYSINAE

dorsal and anal fin rays modally 10

dorsal and anal fin basal pterygio- phores modally 9 pectoral fin rays modally 12, ex- cept one species with 11

five vertebrae involved in the fu- sion complex at the rear of the

sliull

all vertebrae with unbranched

neural spines

last tinal fin basal pterygiophore

not expanded for carapace support

last dorsal fin basal pterygiophore

not expanded for carapace support haemal spine of penultimate verte- bra autogenous or fused to the centrum, always with a foramen myodome essentially absent

Atlantic distribution (to South

Africa).

If, as suggested, the two subfamilies represent separate

phyletic lines, it is assumed that the involvement of the

fifth vertebra in the anterior fusion complex of the IndoPacific Lactoria fornasinii has taken place independently by convergence from that in the Atlantic species, and that the fusion of the haemal spine of the penultimate vertebra to its centrum in the four species of Atlantic Acanthostracion has been similarly indepen- dent from that in the Indo-Pacific species. This, it seems

to me, is far easier to believe than that the entirely constant differences: 1) the numbers of dorsal, anal, and

pectoral fin rays; 2) the structure of the neural spines of two or more postdorsal vertebrae; 3) the structure of the

last basal pterygiophore of the dorsal and anal fins; and

4) the different distributions and myodome develop- ment, between the two groups have no phylogenetic meaning.
Generalized conditions in ostraciids can be considered

those which deviate the least from the structure of the

ancestral aracanids. Only two anterior vertebrae are fus- ed in aracanids, so the involvement of only four vertebrae

in the fusion complex of all but one species of ostraciins is less specialized than the involvement of five in the lacto- phrysins. Aracanids have single unbranched neural

spines, as do lactophrysins, and the trifid neural spines of some of the vertebrae in ostraciins can be considered as

specialization. Aracanids have no lateral or other expansions toward the distal ends of the last dorsal and anal fin basal pterygiophores for support of the carapace, nor do

the lactophrysins, and the expansions of these pterygio- phores in ostraciins can be considered a specialization. The higher numbers of dorsal, anal, and pectoral fin rays, and of the dorsal and anal fin basal pterygio- phores, in lactophrysins is more similar to that of aracanids than are the lower numbers found in ostraciins, the latter again more specialized. In aracanids the haemal spine of the penultimate vertebra is autogenous,

while only among the lactophrysin ostraciids are there

species with the penultimate haemal spine autogenous,

the ostraciins again having the more specialized condition. Moreover, it is only among the species of ostraciins that the penultimate and the preceding one or two haemal spines are reduced in size, solid and without a foramen for the haemal canal, the ostraciins again at

least tending to have a more specialized caudal fin supporting apparatus than in the lactophrysins. The

moderate degree of lateral flange development across the

surface of the centra in aracanids is about intermediate between that of the moderate to well-developed flanges found in ostraciins and that of the moderate to poorly developed flanges of lactophrysins.

In only two ways can ostraciins be considered more

generalized than lactophrysins. In aracanids and os- traciins a small myodome is present, but this has been

essentially lost by lactophrysins. Aracanids and ostraOstracion

Rhynchostracion

Acanthostracion

Eolactoria (Eocene)

Figure 178.—Hypothesized phylogenetic relation- ships of the genera of Ostraciidae.

ciins both have an Indo-Pacific distribution, while that

of lactophrysins is Atlantic.

In short, in most of the anatomical characters discuss- ed above, with the notable exception of the anterior

vertebral fusion and mydome development, the lacto- phrysins are seen as the more generalized of the two subfamilies. It seems best to assume that the lactophrysins have remained more generalized than the ostraciins in nearly all respects, except that the myodome became

reduced and the fifth vertebra became involved in the

anterior fusion complex in all species, while the generally more specialized ostraciins retained from the same

generalized stock that gave rise to both subfamilies a

slightly better developed myodome and a less extensive

anterior vertebral fusion complex. In this view it is likely that the Ostraciidae diverged into two lines in the IndoPacific, with the more specialized ostraciins eventually becoming dominant there to the exclusion of the lacto- phrysins, which remained anatomically closer to the

ancestral stock, and were only permanently successful in the Atlantic, in what is perhaps at least a partially relict distribution. Within the Lactophrysinae three genera were recogniz- ed by Fraser-Brunner (1935b:317, 1941c:307), exclusively on the basis of carapace characters, Acanthostracion for the species (quadricornis, polygonius,

guineensis, and notacanthus) with the carapace closed behind the dorsal fin and with preorbital as well as postanal carapace spines, Rhinesomus for the two species

(bicaudalis and triqueter) with the carapace closed behind the dorsal fin, no preorbital carapace spines but

with the postanal spines present or absent, and Lacto- phrys for trigonus, with the carapace open behind the

dorsal fin, no preorbital carapace spines but with

postanal spines. Since the presence of preorbital spines seems to have no more magical phylogenetic quality than

the presence of postanal spines, one could with equal

simplicity group together those species with postanal

spines (Acanthostracion, Lactophrys, and Rhinesomus

bicaudalis) as distinct from R. triqueter, and within the former group split off R. bicaudalis and L. trigonus from

Acanthostracion on the basis of the presence or absence

of preorbital spines, and further separate R. bicaudalis and L. trigonus on the basis of whether the carapace is closed behind the dorsal fin. A great many such combinations are as logically valid on the basis of carapace

characteristics alone. With this in mind, most workers have not recognized all three genera as valid, variously lumping them all together in one genus (Lactophrys) or recognizing Lactophrys for the three species without

preorbital spines and Acanthostracion for the four

species with preorbital spines. Several skeletal characters indicate the advisability of recognizing two genera rather than one or three for the Lactophrysinae. In Lactophrys and Rhinesomus the penultimate haemal spine is autogenous while in Acanthostracion it is fused to the centrum. In Lacto- phrys and Rhinesomus there are three postanal (posterior to the last vertebra supporting the anal fin) vertebrae while in Acanthostracion there are four in three
species and five in one (quadricornis) , i.e., the 15th

vertebra helps to support the last anal fin basal pteryg- iophore in Lactophrys and Rhlnesomus but not in Acanthostracion. In Lactophrys and Rhlnesomus suturing be- tween adjacent vertebrae extends from the 5th and 6th back to between the 12th and 13th, while in Acanthostracion it extends back to between the 13th and 14th

(erroneously stated by Tyler 1963a:171, to be between

the 12th and 13th in A. quadricornis). Lateral flanges

across the centra are slightly better developed in Lacto- phrys and Rhlnesomus than in Acanthostracion. On the basis of the above, only two genera should be

recognized in the Lactophrysinae, with Lactophrys =

Rhlnesomus being more generalized in all of the characteristics listed above than Acanthostracion. Whether the condition of having the carapace slightly open behind the

dorsal fin in L. trlgonus is a hold over from the ancestral aracanids that gave rise to the ostraciids or is a case of the subsequent reduction of the carapace in this region from a more immediate ancestor with a complete bridge

across the back behind the dorsal fin is impossible to say

with assurance. In the only fossil ostraciid, the Eocene

Eolactorla, the carapace is complete behind the dorsal

fin. I suspect, especially in light of the fact that the carapace is complete behind the dorsal fin at least oc- casionally in large specimens of L. trlgonus just as it is in Eolactorla and all other ostraciids, that the condition in

L. trlgonus is a secondary reduction of the posterior end

of the carapace and not the retention of a primitive condition. It seems possible that L. trlgonus and R. blcaudalis are slightly more closely related to one

another than to R. trlqueter, despite the behind the dorsal fin carapace similarity between blcaudalis and trl- queter. In addition to blcaudalis and trlgonus both having postanal carapace spines, both have the anterior

nostril bulbous, more so in blcaudalis and at all sizes, and less so and only in large specimens of trlgonus. It would be intriguing to know whether the anterior nostril

in trlqueter, which is a smaller species than the other

two, would become bulbous were it to reach sizes comparable to trlgonus. Acanthostracion is probably derived from a Lacto- phrys = Rhlnesomus-Vike stock, undoubtedly from a form with the carapace closed behind the dorsal fin and

with postanal spines. Acanthostracion is specialized in- ternally in the ways mentioned above, while the presence

of preorbital spines could indicate either that they are a new development from the Lactophrys = Rhlnesomuslike line which give rise to it or that the immediate

ancestry of the Lactophrys = Rhlnesomus line had preorbital spines which were lost by the Recent species of that group but retained by the line leading to Acanthostracion. Within Acanthostracion, quadricornis is obviously the most specialized form (the addition of 1 vertebra to the postanal series for a total of 5 in the series and 19 for the entire column, both unique in the family, and the total number of vertebrae unique in the superfamily; the modal reduction by one of the number of pectoral fin rays, unique in the subfamily; the frequent

presence of isolated scale plates above and below on the

caudal peduncle, unique in the family), and notacanthus, polygonlus, and gulneensls are more closely related

to one another than to quadricornis, with the rela- tionship between notacanthus and polygonlus being es- pecially close on the basis of the coloration, carapace, and caudal fin shape characteristics discussed by Tyler

(1965b:275).

In the Ostraciinae the generic relationships, and which

genera are generalized versus specialized, are less clear than in the lactophrysins. The rectangular carapace of Ostraclon and Rhynchostraclon rhlnorhynchus can be

considered a specialization, being further removed from

the laterally compressed oval of aracanids and the high

crested triangle of lactophrysins and of Tetrosomus, with

the high crested but otherwise rectangular form of R. nasus being a variant of the Ostraclon and R. rhlno- rhynchus form and the pentangular carapace of Lactorla

a low crested variant of the triangular form.

In the caudal skeleton the presence of a haemal canal

piercing the more posterior haemal spines and entering

the caudal plate, as found only in Lactorla cornuta among the ostraciins, is clearly a relatively generalized condition in comparison to the highly specialized solid postanal haemal spines, usually reduced in size and

never pierced by the haemal canal, which also does not

enter the caudal plate, found in L. fornaslnll, Tetro- somus, Ostraclon, and Rhynchostraclon. The reduction

in size of several of the neural spines below the last dorsal fin basal pterygiophore, so that the pterygiophore is supported only basally by a neural spine, as found in L. fornaslnll, and, especially, Tetrosomus, seems special- ized in comparison to the more normal neural spines in

this position found in L. cornuta, Ostraclon, and Rhynchostraclon. However, the relatively small size and poor development of shelves supporting the carapace on this pterygiophore in L. fornaslnll and Tetrosomus are much

closer to the condition found in the lactophrysins and

aracanids, and must be considered either more generalized than or a secondary reduction in size from the far more massive last dorsal fin basal pterygiophore with

well-developed specialized shelves found in L. cornuta,

Ostraclon, and Rhynchostraclon. The only moderately developed lateral flanges across the centra in Tetrosomus and Rhynchostraclon would seem slightly less specialized than the larger flanges of Lactorla and Ostraclon. The relatively small lateral shelf

for carapace support on the last anal fin basal pterygio- phore in L. cornuta seems the least removed from the condition in lactophrysins and aracanids and thus less specialized than the much larger anterolateral shelf found in L. fornaslnll, Tetrosomus, Ostraclon, and

Rhynchostraclon. The number of postanal vertebrae, three in Lactorla and Tetrosomus and four in Ostraclon and Rhynchostraclon, can be compared only to the condition in lacto- phrysins. In aracanids there is a far less close association

of the last (and other) anal fin basal pterygiophore with

the haemal spines of the caudal vertebrae (with only the proximal end of the element at all associated with a particular haemal spine instead of most of its posterodorsal
edge closely in contact with several vertebrae) which

leads to incomparably high postanal counts. In lacto- phrysins the more generalized group, Lactophrys =

Rhinesomus, have three postanal vertebrae and the more

specialized group, Acanthostracion, four, while Ostracion and Rhynchostracion would thus be considered to have a more specialized number of postanal vertebrae. Trifid neural spines on some of the postdorsal

vertebrae being a specialization found in all ostraciins, it seems reasonable to assume that the greater the number

of vertebrae with trifid neurals, the greater the degree of specialization in this character. The greatest number,

four, is found in L. cornuta, with L. fornasinii having

three, and Tetrosomus, Ostracion, and Rhynchostracion

either two or three. While the number of vertebrae involved in the fusion complex with the rear of the skull in all species of the subfamily is four, except five in L. fornasinii, the lack of fusion between the fused first-second vertebrae and the

fused third-fourth vertebrae in 0. tuberculatus even in large adults and of the sometimes only partial fusion in this region in 0. lentiginosum seem more generalized than having at least the basal regions of the four elements fully fused, as in Rhynchostracion, Lactoria, and Tetrosomus. As seen above, no one genus has a relatively full complement of either the specialized or generalized characteristics discussed, all of the genera having a difficult to interpret mixture of both. What follows is a highly speculative interpretation of the evidence. The probably triangularly or pentagonally carapaced

ancestral group of the Ostraciidae had no more than four vertebrae involved in the anterior fusion complex, the haemal spine of the penultimate vertebra autogenous,

the last dorsal and anal fin basal pterygiophores without

shelves for carapace support, and the neural spines of the more posterior vertebrae undivided. This ancestral group

gave rise on the one hand to the Lactophrysinae, which

remained relatively unchanged from the ancestral condition except for subsequently involving the fifth vertebra

in the fusion complex and having the penultimate haemal spine become fused to the centrum in the most

specialized genus, in which the number of postanal

vertebrae was also increased. On the other hand the

ancestral group gave rise to the Ostraciinae, which

retained the ancestral condition of the anterior vertebral

fusion complex but which specialized in a number of ways mostly involving the simplification of the postanal haemal spines and of the development of carapace supporting structures on the last dorsal and anal fin basal pterygiophores and on some of the neural spines of the

postdorsal vertebrae. The line immediately ancestral to the Recent ostraciins is envisioned as having the last dorsal and anal fin basal pterygiophores moderately well developed (i.e., larger than in the lactophrysins), with moderate shelves (probably less well developed than in their greatest development in the Recent species), and with only two or

three of the postdorsal vertebrae with trifid neural

spines. This hypothetical ancestral line leading from the

immediate ancestry of the lactophrysins would probably have had a triangular or pentangular carapace, and it is postulated to have diverged into two lines of Recent

species, one line containing basically triangular forms

with many carapace spines {Lactoria and Tetrosomus) and the other basically rectangular forms with a rela- tively spineless carapace (Ostracion and Rhynchostracion). In the Lactoria- Tetrosomus line of ostraciins, a form

close to L. cornuta, but with a still only moderately

enlarged last dorsal fin basal pterygiophore and only two

or three trifid neural spines, was probably ancestral, L. cornuta being the only species to have the haemal canal

pierce the fused haemal spine of the penultimate

vertebra and enter into and exit from the caudal plate and to have a relatively moderate lateral shelf on the last anal fin basal pterygiophore. The L. cornuta-like (with

the exceptions noted) ancestral line probably gave rise to

L. cornuta on the one hand by the further enlargement of the last dorsal fin basal pterygiophore and its shelf and

by the trifid division and enlargement of additional post- dorsal neural spines. On the other hand the pre-L. cornuta ancestor is seen

as having given rise to L. fornasinii with no increase in the number and size of trifid neural spines, the reduction

of the size of the haemal arches of the postanal vertebrae, and the elimination of their foramina so that they are

solid and not pierced by the haemal canal which also does not pierce the caudal plate, an enlargement of the moderate shelf on the last anal fin basal pterygiophore

into a more substantial anterolateral shelf, a reduction in the size of the neural spine of the vertebra (13th) between

that which supports the base of the last dorsal fin basal pterygiophore and the most anterior of the three vertebrae (14th to 16th) with trifid neural spines, and a

slight reduction in the size of the last dorsal fin basal pterygiophore and its posterior carapace shelf so that the

basal portion of the pterygiophore is rodlike rather than

anteroposteriorly expanded while the posterior end of the

distal shelf does not make contact with any neural

spines. Probably a close derivative of the immediate ancestor

of L. fornasinii is Tetrosomus. Tetrosomus shows the same tendencies, but more strongly, as L. fornasinii does

in the reduction of the size of the neural spines below the

last dorsal fin basal pterygiophore and in the size of the

latter. In Tetrosomus the size of the neural spines of the

12th to 14th vertebrae is greatly reduced, and that of the

14th is no longer trifid. The trifid neural spines of the 15th and 16th vertebrae are of about the same moderate

size as in L. fornasinii, the anterolateral shelf on the last anal fin basal pterygiophore just as massive, and the

solid haemal spines of the postanal vertebrae just as reduced in size and not pierced by the haemal canal, which likewise does not enter the caudal plate. Thus, L. fornasinii shares many peculiarities with Tetrosomus, and a form like it is very likely to have been ancestral to Tetrosomus. The higher crested carapace in Tetrosomus

could be either an enlargement of the lower crest in Lactoria or a hold over from the line leading from the pre-
fornasinii-like ancestor, which may have been higher

crested than the Recent Lactoria.

In the Ostracion-Rhynchostracion line of ostraciins derived from a probably pentangular form, there seems

to have been a tendency for the distance between the

ventrolateral ridges to be decreased to about the same as that between the dorsolateral ridges, while the dorsal carapace crest tended to be reduced in height, leading to a basically rectangular form with overtones of the

ancestral pentangular form depending on the degree of development, if any, of the dorsal crest. Ostracion and

Rhynchostracion probably evolved from the same pre- Lactoria comuta-\ike line that gave rise to Lactoria and

Tetrosomus. The Ostracion-Rhynchostracion line is en- visioned as diverging from them in the shape of the carapace and in the loss of spines from the probably

spiny carapaced ancestor, while developing large last basal pterygiophores with large carapace supporting

shelves in both the dorsal and anal fins and reducing the

size of the haemal spines of the four postanal vertebrae, with the haemal spines losing the foramen and being

solid. Ostracion shows the extreme in dorsal carapace crest reduction and increased distance between the dorsolateral ridges, the carapace being essentially rectangular, while it retains the most generalized ostraciid condition

of the anterior vertebral fusion complex. In Rhynchostracion, however, one species {nasus) retains a rela- tively well-developed dorsal carapace crest while in the

other (rhinorhynchus) it is obsolete, the carapace being almost as rectangular as in Ostracion, with both species

of Rhynchostracion having the anterior four vertebrae

fully fused to one another. Rhynchostracion has the additional slight specialization of a bulbous or protruding

snout. Ostracion and Rhynchostracion can be viewed as

closely related sibling genera from a common ancestral group, with Rhynchostracion slightly more specialized in the greater anterior vertebral fusion and expanded

ethmoid region while retaining a slightly more generalized carapace shape. The Eocene Eolactoria is impossible to place with confidence in either one or the other of the two subfamilies

recognized here for the Recent species, simply because its dorsal, anal, and pectoral fin rays are not preserved and

none of the internal features equally diagnostic between

the two subfamilies can be seen (Tyler 1973a). The

presence of enormous preorbital and postanal carapace

spines in Eolactoria would seem to relate it to either the

Atlantic Acanthostracion (Lactophrysinae) or the IndoPacific Lactoria (Ostraciinae), from both of which it differs in the immensity of the elongation of the spines

(equal to the standard length of the fish) and in the presence of a much shorter unpaired spine directed

anteriorly from between the front of the eyes, the latter unique in the family. Without knowing the appropriate

critical diagnostic characteristics, Eolactoria is simply

placed here questionably in the Lactophrysinae, the more generalized of the two subfamilies, on the theory

that an Eocene ostraciid is more likely to be generalized

in most respects than specialized. It is possible that

FifTure i79.—Eolactoria aorbinii: lateral view

of holotype, 15.5 mm SL, Eocene of Monte Boica,

ItalyCIVlerigrSaifig. 1). 242
Eolactoria is a representative of the line which gave rise to Acanthostracion on the one hand and to Lactophrys =

Rhinesomus on the other, with the latter variously losing the preorbital and postanal carapace spines, and that another more specialized derivative of the Eolactoria to Acanthostracion line gave rise to that of Lactoria and

Tetrosomus on the one hand and to that of Ostracion and

Rhynchostracion on the other, with the latter two genera

also losing the preorbital and postanal carapace spines. Since all ostraciids have the ventral edge of the para- sphenoid laterally expanded into a roof over the oral cavity anterior to the level of the prefrontals, they can be expected to have evolved from one of the two lines of aracanids with a similar but less extensive expansion of the ventral edge of the parasphenoid, either the Aracana

line with the expansion limited to a posterior region or the Capropygia-Caprichthys line with the expansion

limited to an anterior region. However, it is impossible to say with any confidence which one of these two lines was

more likely ancestral to the ostraciids (see discussion under Aracanidae).

SUBORDER TETRAODONTOIDEI

(GYMNODONTES)

Comparative diagnosis (contrast with that of the

Balistoidei). —Teeth either small rounded units or long

rodlike structures, but always nonprotruding and fully incorporated into the matrix of the jaw bones, in one

family indistinguishably so, the otherwise discrete teeth

in molids no longer distinguishable from the bony

matrix, at least at 30 magnifications; dentaries and/or

premaxillaries often fused to their opposite members;

the medial articulation of the premaxillaries to one

another, if unfused, strengthened by alternating emarginations and indentations, least developed in Triodon,

the most generalized member of the suborder; post- temporal absent; urohyal absent, except in Triodon;

pelvis absent, except in Triodon; pelvic fin always absent; palatine relatively large and massive, always firmly sutured or otherwise closely and immovably held to both

the ethmoid-vomerine region and the pterygoid arch; myodome with a complete dorsal roof absent, except in Triodon; prootic shelf under the orbit never present; supracleithrum always placed distinctly obliquely to the

axis of the skull; scapular foramen incomplete, except in Triodon; scapula without any special knob or crest for ar- ticulation with the uppermost pectoral fin ray, except in Triodon; distal pterygiophores of the soft dorsal and anal

fins always unossified; spiny dorsal fin absent, except

present as a rudiment placed far behind the skull in Triodon; first I ^ranchiostegal ray modified, with a slightly (Triodon) to enormously enlarged and inturned dorso- medial edge, except unmodified in molids.

Figure 180.—Body form in the only known Recent

species of Triodontidae: Triodon macroptenis.

Infraorder Triodontoideo

Comparative diagnosis (contrast with that of the Tetraodontoideo), which is also that of its only contained Superfamily, the Triodontoidea, and family, the Triodontidae. —A rudimentary spiny dorsal fin of one or, more usually, two small spines borne on two basal pte- rygiophores present in most specimens of one of the populations (Indonesia to Japan) of the single included Recent species, the second basal pterygiophore succeed- ed by two supraneural elements; ribs and epipleurals present; caudal fin with 12 principal rays and numerous

procurrent rays; caudal fin deeply forked; caudal

skeleton with four separate hypurals, two uroneurals, and a hypurapophysis; haemal spine of antipenultimate

vertebra autogenous; neural and haemal spines of penul- timate vertebra long rounded shafts oriented highly

obliquely and directly supporting caudal fin rays; caudal peduncle distinctly tapered to narrow transversely in- dented regions above and below just in front of the caudal fin, the least depth of the peduncle being about 3% SL and the least width at this region always greater than the least depth; many of the caudal vertebrae with

large anterolateral processes from the region of the neural arch and base of the neural spine; pelvis present; a huge

expansible dewlap of skin between the end of the pelvis and anus, but no inflatability of the abdominal region; cleithrum greatly elongate anteriorly, reaching forward

to between the lower jaw; basisphenoid a small rod plac- ed far posteriorly in the interorbital septum and articu- lated with the anterior edge of the dorsal roof of the myodome; a large myodome present with a complete dorsal roof; a shallow channel present between the apposed

surfaces of the parasphenoid and basioccipital leading

into the myodome; scapular foramen complete, entirely enclosed by the scapula; scapula with a distinct knob for articulation with uppermost pectoral fin ray; four actinosts, none of which are sutured to one another or to the scapula or coracoid; urohyal present; four pharyngobranchials present; fifth ceratobranchial well-covered with prominent teeth; dentaries and premaxillaries

totaling three separate pieces; premaxillaries articu- lated to one another by interdigitation or by only minute

243
more regular interlocking emarginations; sphenotic rela- tively small and confined to the posterior wall of the orbit, not reaching the lateral or dorsal surface of the skull;

first branchiostegal ray with its dorsal edge slightly in- tumed, articulated with the ventrolateral surface of the

ceratohyal; interoperculum with a ventral flange and a

short posterior shaft extending only slightly behind the

ventral flange and level of the epihyal; pterotic prolonged

posteroventrally as a stout laterally compressed shaft broadly articulating with the hyomandibular and supracleithrum; epiotic confined to the lateral region of the top

of the skull, separated from the supraoccipital by the

exoccipital; exoccipital in contact with the frontal; frontal in contact posteriorly with the pterotic in the rear of the orbit; olfactory epithelium in the form of a rosette, the lamellae radiating out from a horseshoe-shaped base, the olfactory sac below the surface of the body and the two nostrils more or less flush with the surface, the

anterior nostril with an upraised flap posteriorly and the

posterior nostril with an upraised flap anteriorly.

Detailed description of Triodon macropterus. Material examined. —Two cleared and stained

specimens, 391-463 mm. It will be advantageous in the

future to compare the amount of interdigitation in the

skull structure of these two large adult specimens with

that in a young specimen, but the species as yet is known

only from several dozen relatively large (about 285-480 mm, see Tyler 1967:90) adults. This species has often been called T. bursarius, but Boeseman (1962) has thor- oughly reviewed the literature £md shown T. macropterus

to have priority. SKULL.

Occipital Region.

Basioccipital. —A very short column, slightly expanded anterodorsally; cartilage filled at its anterior

ledge; articulates by extensive interdigitation anteriorly with the overlying parasphenoid, anterolaterally with the

prootics, and posterolaterally with the exoccipitals. A

slight depression is present medially on the ventral sur- face of the anterior end of the basioccipital just behind

the region where it is overlain by the parasphenoid. This

depression continues anteriorly as a narrow canal between the otherwise interdigitated surfaces of the

basioccipital and parasphenoid, and opens into the ex- treme posterior end of the myodome. The extreme posteroventral portion of the wall of the myodome is formed

by the anterodorsal end of the basioccipital. The rim of the round concave posterior end of the basioccipital ar- ticulates by fibrous tissue with the rim of the concave

anterior face of the centrum of the first vertebra.

Exoccipital. —Extremely large; cartilage filled along its dorsal and dorsolateral edges; articulates by ex- tensive interdigitation dorsomedially with the supraoccipital, anterodorsally with the frontal, dorsolaterally

Figure 181.Triodon macropterus: showing the course

of the lateral line; lower left, the nasal region as seen externally (above) and the olfactory lamellae

as seen with the top of the nasal sac removed; lower

right, scales from upper middle region of body, including three lateral line canal bearing scales.

with the epiotic and pterotic, ventrolaterally with the

prootic, and ventromedially with the basioccipital. The

posteromedial edges of the two exoccipitals form the ventral and lateral walls of the foramen magnum, while dorsally the wall of the foramen is formed mostly by the

exoccipitals, but also for a short distance medially by the

ventral edge of the supraoccipital. Strong condyles project from the posteromedial portions of the exoccipitals and make fibrous tissue contact over the anterior half of the lateral surfaces of the centrum of the first vertebra.

Supraoccipital. —Somewhat expanded anteriorly, but drawn out into a short, stout, laterally compressed

spine posteriorly; cartilage filled along all of its edges of

articulation with the other cranial bones, except posteroventrally; articulates by interdigitation anteriorly and anterolaterally with the frontals and posterolaterally with the exoccipitals.

Otic Region.

Pterotic. —Very large; cartilage filled along its medial edge; articulates by interdigitation anterodorsally with the epiotic, anteroventrally with the

sphenotic, ventromedially with the prootic, and postero- medially with the exoccipital. Posteroventrally the

pterotic is prolonged into a stout, laterally compressed

shaft which articulates by fibrous tissue along its anterior edge with the hyomandibular and along its posterior edge with the supracleithrum. The articulation with the supracleithrum appears to also involve some interdigi- tation in the smaller specimen, but not in the larger; in neither case is the articulation very flexible. The more

normal articulation of the pterotic with the supracleith- rum is through fibrous tissue along the slightly concave

ventral surface of the extreme posterodorsal region of the

pterotic. Just anterior to the base of its stout shaft the

pterotic is deeply concave to receive and articulate by fi- brous tissue with most of the length of the dorsal end of the hyomandibular.
Sphenotic. —Relatively small and confined to the

posterior wall of the orbit; cartilage filled along all of its edges of articulation with the other cranial bones; ar- ticulates by interdigitation anterodorsally with the frontal, posterodorsally with the pterotic, anteroventrally with the pterosphenoid, and ventrally with the prootic. The ventral edge of the sphenotic is deeply concave for articulation by fibrous tissue with the anterolateral region of the dorsal head of the hyomandibular. This concavity of the sphenotic is continuous with that along the

lateral edge of the prootic, which supports the antero- medial region of the head of the hyomandibular, and with

that of the pterotic forming the main support for that head.

Epiotic. —Relatively large, but thin; cartilage filled along its medial edge; articulates by interdigitation

anteriorly with the frontal, medially with the exoccipital and posteriorly with the pterotic.

Prootic. —Cartilage filled along all of its edges of

articulation with the other cranial bones, except anteriorly; forms all of the walls of the myodome, except for the medial portion of the ventral wall and the short section of the anterior wall formed by the parasphenoid and for the extreme posterior portion of the wall formed by the

basioccipital; articulates by interdigitation anteriorly with the dorsolateral wing of the parasphenoid, dorso- medially with the pterosphenoid, dorsolaterally with the

sphenotic, ventrolaterally with the pterotic, ventro- medially with the parasphenoid and basioccipital, and

posteriorly with the exoccipital. From its oblique medial

surface the prootic gives rise to the horizontal plate of bone which meets its opposite member in the midline to form the dorsal roof of the myodome. These two projections interdigitate with one another in the midline and

each possesses a small foramen laterally near its dorsal edge. Another pair of foramina are present in the ventral

wall of the myodome to either side of the midline, where

there is a slight gap in the interdigitated surfaces of the

prootics and the parasphenoid. Anteromedially from the

dorsal roof of the myodome the prootics support by fi- brous tissue the posterior end of the basisphenoid. At the concavity along its lateral edge the prootic articulates by

fibrous tissue with the anteromedial region of the dorsal head of the hyomandibular.

Orbital Region.

Frontal. —Large and massive; laterally expanded

posteriorly but tapering to a bluntly rounded end anteriorly. Throughout its entire length the medial edge of the frontal is broadly, but not deeply, concave and covers

a core of cartilage that is continuous anteriorly with the

cartilage of the ethmoid region and posteriorly with that

of the occipital region. The frontal articulates by inter- digitation dorsomedially in the posterior half of its length with its opposite member, while directly postero- medially it interdigitates with the supraoccipital.

Posterolaterally on its dorsal surface it interdigitates

with the exoccipital and epiotic. Posteroventrally it in- terdigitates with, from anterior to posterior, the ptero- sphenoid, sphenotic, and pterotic. The ventromedial

edges of the two frontals are in close fibrous tissue contact for most of their lengths, diverging from one another

only posteroventrally just in front of the pterosphenoids and anteriorly just behind the prefrontals. Anteriorly the

frontal broadly overlies and slightly interdigitates with

the ethmoid, while anterolaterally it interdigitates with

the dorsomedial edge of the prefrontal.

Prefrontal. —Relatively large, both dorsally and

ventrally; cartilage filled along all of its ventromedial

edges where it is continuous with the ethmoid cartilage; articulates dorsally by interdigitation with the frontal and

the posterolateral edges of the ethmoid, while posteroventrally it articulates through cartilage and fibrous tis- sue with the anterodorsal surface of the parasphenoid. Along most of its ventral edge the prefrontal articulates through cartilage and interdigitation with the long posterior portion of the palatine. In about the middle of its medial surface the prefrontal is deeply concave, so that a

horizontal canal is formed between the prefrontal and

the ethmoid cartilage, with which the prefrontal is otherwise continuous. The nerves and blood vessels that

course through this canal run not only to the olfactory organ but also to the anteriormost regions of the head by way of a similar canal between the palatine and ethmoid.

Parasphenoid. —Elongate, with a thin ventral keel throughout most of its length. The anterior end of the parasphenoid is deeply concave to accommodate the

posterior end of the vomer, with which it is interdigi- tated. The parasphenoid also interdigitates anterolaterally with the posterior portion of the palatine, while

anterodorsally it articulates through cartilage and fi- brous tissue with the prefrontal. Posteriorly the para- sphenoid somewhat overlies and strongly interdigitates with the basioccipital, while at the same time leaving open the small canal in the midline between their otherwise interdigitated surfaces. About five-sixths of the way back in its length, the parasphenoid gives rise to

its paired dorsolateral wings which interdigitate with the anteromedial edges of the prootics and form a section of the anterior wall of the myodome. On its ventral surface between the level of its dorsolateral wings and its meeting with the basioccipital, the lateral edges of the parasphenoid interdigitate with the ventromedial edges

of the prootics, and in so doing the parasphenoid forms

the medial portion of the ventral wall of the myodome.

At the posterior end of its ventral keel the parasphenoid becomes thickened and posterolaterally expanded into a bony knob to which the distal end of the first (suspensory) pharyngobranchial and associated muscles are at- tached.

Pterosphenoid. —A thick plate; broadly cartilage

filled along its dorsal and lateral edges; articulates by in- terdigitation dorsally with the frontal, posterolaterally with the sphenotic, and posteroventrally with the prootic.
Basisphenoid. —Laterally compressed throughout

its length, except posteriorly where it is laterally expanded into a rounded process which articulates by fibrous

tissue with the anterior edge of the dorsal roof of the myodome in the smaller specimen, while in the larger specimen the posterior end is attached more dorsally to the membranous wall between the two pterosphenoids. From its posterior place of attachment to the prootics, the basisphenoid is directed anteroventrally and ends in the fibrous tissue sheet of the interorbital septum. This

anterior edge, which is slightly cartilage filled, is some

distance removed from the dorsal surface of the para- sphenoid below it.

culum and anteriorly with the symplectic and interhyal, as well as with the slightly overlying posterior edge of the metapterygoid.

Quadrate. —Widest posteriorly, tapering to a knob

anteriorly for articulation by fibrous tissue with the ar- ticular in the lower jaw; cartilage filled at its posterior edge; prolonged from its posteroventral edge into a thin process which articulates by fibrous tissue with the

symplectic; articulates by fibrous tissue anterodorsally with the ectopterygoid, ventrally with the preoperculum,

posteriorly with the metapterygoid, and posterodorsally with the mesopterygoid. Ethmoid Region. Ethmoid. —Large and wide; relatively thin in the

posterior half of its length, but becoming much deeper

anteriorly; the posterior half of its ventral surface

irregularly concave and continuous with the ethmoid cartilage; articulates posterodorsally by interdigitation with

the overlying frontals and posterolaterally through cartilage and interdigitation with the prefrontals. Anterolaterally the ethmoid is extensively interdigitated with

the medial edges of the palatines. The medial region of

the anteroventral surface of the ethmoid is extensively

interdigitated with the dorsal surface of the vomer in the smaller specimen, but only lightly interdigitated to it in the larger. The more or less vertical anterior face of the ethmoid supports the posteromedial ends of the premaxillaries and maxillaries. The lateral surface of the anteri- or one-third of the ethmoid is concave, so that when it articulates laterally with the equally concave medial sur- face of the palatine a spacious canal is left between the two bones. Through this canal run the nerves and blood

vessels from the similar canal between the medial surface

of the prefrontal and lateral surface of the ethmoid cartilage.Vomer. —A narrow shaft throughout its length, except anteriorly where it becomes somewhat expanded

dorsally to articulate by fibrous tissue with the postero- medial arms of the premaxillary and maxillary; articulates by interdigitation posteriorly with the concave

anterior end of the parasphenoid, laterally with the

palatines, and anterodorsally with the ethmoid. Posterodorsally the ethmoid cartilage intervenes between the

dorsal surface of the vomer and the ventral surface of the ethmoid.

Mandibular Region. Hyomandibular. —Very wide for most of its length, only tapering to a stout shaft for a short distance anteroventrally; cartilage filled at its dorsal and anteroventral

edges; articulates by fibrous tissue dorsally with the elongate concavity formed anterolaterally by the

sphenotic, anteromedially by the prootic, and pwsteriorly by the pterotic. The hyomandibular articulates by

fibrous tissue along its posterior edge with the preoperMetapterygoid. —Large, thick, more or less square;

cartilage filled at its anterior edge; articulates by fibrous

tissue anterodorsally with the mesopterygoid, anteriorly with the quadrate, and posteriorly with the hyomandibular. Ventrally the metapterygoid slightly overlies and

interdigitates with the symplectic and also articulates by

fibrous tissue with the interhyal.

Symplectic. —Large and elongate; cartilage filled at

its posterior edge; articulates dorsally by slight inter- digitation with the overlying metapterygoid, while it ar- ticulates by fibrous tissue posteroventrally with the preoperculum and interhyal, and anteroventrally with

the overlying quadrate.

Palato-Pterygoid Region.

Palatine. —Expanded into a thick plate posteroventrally, but becoming laterally expanded anterodorsally; articulates by firm interdigitation along the anterior half of its dorsomedial edge with the ethmoid and

along the anterior half of its ventromedial edge with the vomer. The palatine is equally firmly interdigitated posterodorsally with the prefrontal and posteroventrally with the parasphenoid. The medial surface of the upper

region of the anterior half of the palatine is concave, so that a canal is formed between it and the ethmoid, as de- scribed previously. The medial and anterior surface of the anterodorsal end of the palatine forms the articular

facet for support through fibrous tissue of the lateral sur- face of the posteromedial wing of the maxillary.

Ectopterygoid. —Expanded posteriorly; only

slightly curved along its anterior edge; articulates by fi- brous tissue dorsally with the palatine and ventrally with

the quadrate, while posteriorly it articulates by fibrous

tissue and slight interdigitation with the mesopterygoid. The palatine and quadrate slightly overlie the ec- topterygoid, while the ectopterygoid slightly overlies the mesopterygoid.

Mesopterygoid. —Thin; irregular in its posterior and ventral outline; articulates by slight interdigitation anteroventrally with the ectopterygoid and by fibrous

tissue anteriorly with the palatine, ventrally with the quadrate and posteroventrally with the metapterygoid. 246
Opercular Region. Operculum. —Thin and expanded ventrally; a

dorsally directed process for muscle attachment present above its articular region with the preoperculum; articulates ventrally by fibrous tissue with the suboperculum, which it broadly overlies, while along its upper anterior edge the operculum is slightly expanded laterally into the articular facet whose concave face attaches by fi- brous tissue to the preoperculum.

Suboperculum. —Thin and delicate in its regions that lie behind and below the operculum, but slightly thicker at its anterodorsal end; articulates by fibrous tis- sue dorsally with the overlying operculum, while at the end of its emterodorsal process it connects by a ligament

with the upper prong at the posterior end of the in- teroperculum.

Interoperculum. —A long sturdy rod for all of its length, except posteriorly where it bifurcates into two

thin prongs. The more ventral of these two prongs lies in the fibrous tissue sheet between the branchiostegal rays and the region of the operculum and suboperculum. The

dorsal prong connects by ligament with the anterodorsal

process of the suboperculum. Anteriorly the interoper- culum connects by ligament with the angular in the lower jaw. Just in front of its ventral prong the medial

surface of the interoperculum is held by fibrous tissue to the area of articulation between the epihyal and in- terhyal.Preoperculum. —Relatively thin and narrow

throughout its length, being only slightly expanded ventrally in its middle region in the smaller specimen, but about one-third wider in the larger specimen; articulates by fibrous tissue along the posterior half of its dorsal edge with the hyomandibular and along the anterior

half of its dorsal edge with the quadrate and the region of the symplectic, metapterygoid, and interhyal. Along the upper portion of its posterior edge the preoperculum

possesses a slight convexity for articulation through fi- brous tissue with the operculum.

Upper Jaw.

Premaxillary. —Posteromedial arm thick and

sturdy; together with the fused teeth forms a massive

crushing plate; its anterior edge forming the anterior border of the upper jaw, except for a short distance ventrally where the maxillary forms the border. The dorso- medial surfaces of the two premaxillaries are firmly held

to one another by fibrous tissue and extensive interdigitation, which, especially in the larger specimen, takes

the form of numerous small projections from the

otherwise flattened medial surfaces of apposition of each

premaxillary alternating with one another. The posterolateral surface of the premaxillary is strongly interdigi- tated with the overlying maxillary. The premaxillary

contains an elongate internal cavity which houses the dental pulp and which communicates with the exterior by two openings on the posterior edge of the interdigi- tated surfaces of the premaxillary and maxillary, as well

as at numerous smaller openings along the lateral surface

of the tooth bearing region, especially dorsally. The pos- teromedial arm of the premaxillary articulates by fi- brous tissue posteriorly with the vertical anterior face of the ethmoid. The fused teeth of the jaws retain much of

their individual identity and are particularly clearly seen

at the edge of the jaw. About 25 to 30 of these small dental units, with the rounded faces oriented toward the

biting edge of the jaw and the apparently slightly con- cave edges oriented toward the pulp cavity, can be seen packed closely together at the edge of the jaw, being held immovably in place by an extremely dense bony matrix. How much fusion actually takes place between the tooth elements themselves and between the tooth elements and the bony matrix of the premaxillary could only be

told by a histological examination not attempted here. The tooth elements become less and less distinctly seen

at the surface further away from the edge of the jaw, ex- cept at the extreme dorsal edge of the tooth bearing

lateral surface, where the primordia of the individual

teeth can be seen forming in the small pockets in the matrix that open by pores to the exterior on the lateral surface. The primordia obviously move gradually toward

the distal crushing edge of the jaw and become more fully impacted with the matrix of the premaxillary as new

primordia form behind it. There are about 10 to 15 such

small teeth in various stages of incorporation with the matrix between the generative region at the inner edge of the tooth bearing surface and the crushing outer edge of the jaw. In the medial region of its ventral surface the premaxillary bears a massive trituration plate formed of fused teeth. The process by which this plate is formed on

the undersurface of the premaxillary can be seen at the

posterior edge of the plate. Four or five anteroposterior^ compressed teeth are formed in deep sockets at the posterior edge of the plate and are clearly evident as entirely individual and separate units held relatively loosely in their sockets. Immediately in front of this row of newly formed teeth in their individual sockets, the surface of the trituration plate no longer shows individual tooth

elements, and only the ridges and grooves on the surface

give evidence of what are evidently the now fused teeth

that had moved up from the formation area. The medial

edges of the trituration plates of either premaxillary do

not meet in the midline but, rather, are separated by a

slight gap.

Maxillary. —Somewhat curved forward at both

ends; forms the anterior border of the upper jaw at its ventral end. Posteromedially the maxillary possesses a

relatively long, but thin, process which overlies the

lateral and most of the ventral edges of the postero- medial arm of the premaxillary. The lateral surface of

this posteromedial arm of the maxillary is slightly concave, forming the articular surface which makes fibrous

tissue contact with the medial surface of the anterodor-
sal region of the palatine. The posterior edge of the pos- teromedial arm of the maxillary is supported against the

anterior vertical face of the ethmoid. The maxillary is firmly interdigitated along most of its medial surface with the premaxillary, except at the extreme ventral end

where it no longer overlies the premaxillary and articulates by fibrous tissue with the lateral surface of the posterodorsal end of the dentary. In the larger of the two

specimens the posteromedial arm of the premaxillary is narrower and that of the maxillary wider than that illus- trated for the smaller specimen, and the maxillary,

rather than the premaxillary, forms the major articu- lation with the ethmoid and vomer. Lower Jaw.

Dentary. —Dentaries indistinguishably fused

together at what would normally be their medial edges of contact, so that the combined dentaries form a massive U-shaped bone. No medial line of fusion between the two

halves can be observed externally or internally, but the two canals leading into the pulp cavity occur side by side

to either side of the midline. The pulp cavity of the combined dentaries is smaller than that of the premaxillaries. The teeth of the crushing jaw are exactly like those described for the premaxillary, as are those of the tri- turation plate, and are formed from primordia in the same way. The trituration plate of the dentaries, however, is a single, almost squarish, massive block which shows no evidence of the fusion line between what may be assumed to have been at one time the separate

right and left halves. The posterior end of the dentary is extremely concave to accommodate the articular, to which it attaches by interdigitation. Posteroventrally the dentary articulates by fibrous tissue with the angular. The dorsolateral surface of the dentary articulates by fi- brous tissue with the ventromedial surface of the maxillary.

Articular. —More or less triangular in shape; its posterior edge somewhat laterally expanded; cartilage

filled at its anterior edge where it is continuous with the remains of Meckel's cartilage; articulates by interdigi- tation over most of its lateral surface and over the anterior portions of its medial surface with the dentary.

Posteroventrally it interdigitates with the angular. At

the concave surface of the lateral expansion on its lower

posterior edge the articulfir is supported through fibrous

tissue by the anterior knob of the quadrate. The sesa- moid articular is a slightly elongate nubbin of bone held

alongside the anteromedial edge of the articular just above the remains of Meckel's cartilage and just below

the posteromedial edge of the dentary, and is relatively much larger in the larger specimen than in the smallAngular. —Small; articulates dorsally by inter- digitation with the articular and anteriorly by fibrous tis- sue with the dentary. Posteriorly it connects by ligament

with the anterior end of the interoperculum.

BRANCHIAL APPARATUS.

Hyoid Arch, Branchiostegal Rays, and Urohyal. Hypohyals. —Both hypohyal elements present, the

dorsal the larger of the two; dorsal hypohyal cartilage fill- ed at its posterior and ventral edges, ventral hypohyal

cartilage filled at its posterior and dorsal edges; both

hypohyals articulate through cartilage and, in the larger

of the two specimens, by slight interdigitation of their medial edges with one another and with the ceratohyal; dorsomedially the dorsal hypohyal articulates by fibrous

tissue with its opposite member.

Ceratohyal. —Elongate; dorsoventrally expanded

at both its anterior and posterior ends; cartilage filled at

its anterior and posterior edges; articulates through cartilage anteriorly with the dorsal and ventral hypohyals and posteriorly with the epihyal, strengthened in the

case of the larger of the two specimens by slight inter- digitation. Of the six branchiostegal rays, the first three

are held directly to the ceratohyal and the fourth is held near the posterior edge of the ceratohyal on the cartilage separating the latter from the epihyal. The somewhat

enlarged first branchiostegal ray is held to the lower

lateral surface of the ceratohyal about one-third the way

back its length. The second branchiostegal ray is held to a very slight concavity in about the middle of the ventral edge of the ceratohyal or slightly dorsomedial to it, while

the third branchiostegal attaches to the lower posterolateral surface of the ceratohyal.

Epihyal. —Rounded posteroventrally but slightly prolonged anterodorsally; cartilage filled at its ventral and anterior edges; articulates through cartilage and, in the larger specimen, by interdigitation anteriorly with

the ceratohyal, while at a slight prominence on its posterodorsal edge it articulates by fibrous tissue with the

interhyal. Just below its articulation with the interhyal, the epihyal articulates by fibrous tissue laterally with the interoperculum.

Interhyal. —An elongate column; cartilage filled at

its dorsal and ventral edges; articulates by fibrous tissue ventrally with the epihyal and dorsally with the fibrous

tissue sheet between the hyomandibular, metapterygoid, symplectic, and preoperculum.

Branchiostegal rays. —Six in number; the first branchiostegal ray shorter but, in the anterior two-thirds

of its length, wider than the other rays; its dorsal edge

distinctly curved medially while its ventral platelike ex- pansion lies in the vertical plane; articulates by fibrous

tissue with the lower lateral surface of the ceratohyal about one-third the way back its length. The second

branchiostegal ray is a long thin shaft held to about the middle of the length of the ventral edge of the ceratohyal

in the smaller specimen (illustrated), but distinctly on

the medial surface just above the middle of the ventral edge in the larger specimen. The third and fourth branchiostegal rays are slightly shorter, and much

stouter anteriorly, than the second ray. The third ray is
held to the lower posterolateral surface of the ceratohyal, while the fourth is held to the posterior edge of the

ceratohyal and to the cartilage between the epihyal and

ceratohyal. The fifth and sixth branchiostegal rays are held to the lateral surface of the epihyal; the sixth branchiostegal is the longest of the branchiostegal rays.

All of the branchiostegal rays articulate with the

ceratohyal or epihyal by fibrous tissue.

Urohyal. —Thin and shallow; laterally expanded

and wider than long; articulates by fibrous tissue posterodorsally with the anterior edge of the first basi- branchial and anterodorsally with the dorsomedial sur- face of the dorsal hypohyal; in the larger specimen the urohyal is even more laterally expanded than as illus- trated for the smaller specimen.

Branchial Arches. —All the elements are cartilage

filled at their edges of articulation with the other elements of the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and four pairs of pharyngobranchials. Four gills are present, with a slit between the

fourth arch and the lower pharyngeal.

First arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basi- branchial elongate, slightly compressed in the middle;

displaced forward so that it articulates posteriorly with

the second basibranchial and only posterolaterally with

the first hypobranchials. First hypobranchial an elongate

rod; articulates with the anterior end of the second basi- branchial and the posterior end of the first basi- branchial. First ceratobranchial a narrow rod; slightly shorter than the second ceratobranchial but of about the same length as the third and fourth ceratobranchials; ar- ticulates ventrally with the first hypobranchial and dorsally with the first epibranchial. First epibranchial

rodlike ventrally but becoming wider and flatter dorsally; the largest of the epibranchials; its dorsal end with two articular prominences, the anterior of which connects with the first pharyngobranchial, while the posterior process connects with the base of the second

pharyngobranchial. First pharyngobranchial (suspensory pharyngeal) a curved rod; toothless; articulates ventrally with the first epibranchial and dorsally with the lateral surface of the base of the large ventral process of the

posteroventral surface of the parasphenoid.

posteromedially with the second basibranchial and dorsally with the second ceratobranchial. Second cerato- branchial the longest of the ceratobranchial elements;

articulates dorsally with the second epibranchial. Second

epibranchial columnar, with a slight expansion posteroventrally; articulates dorsally with the second pharyngobranchial. Second pharyngobranchial roughly L-shaped,

with an irregular series of about 25 well-developed and

sharp-pointed teeth borne on the slightly longer of its two

arms. The toothless arm of the pharyngobranchial ar- ticulates ventrally with the posterodorsal process of the

first epibranchial and with the dorsal end of the second

epibranchial. The teeth are borne in individual sockets and are replaced by new teeth developing in sockets

irregularly scattered between the sockets of the old teeth. The second pharyngobranchial is closely held to the

other two toothed pharyngobranchials by fibrous tissue.

Third arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Third basi- branchial the longest of the basibranchials; laterally ex- panded in the anterior two-thirds of its length; articulates anteriorly with the second basibranchial, posterolaterally with the third hypobranchials, and posteriorly with the fourth ceratobranchials. Third hypobranchial produced anteroventrally, at which end it articulates by

fibrous tissue with the ventral surface of the first basi- branchial; articulates posteromedially with the third basibranchial and posterolaterally with the third cerato- branchial. Third ceratobranchial like the others; ar- ticulates dorsally with the third epibranchial. Third epi- branchial triangular in shape; articulates anterodorsally with the third pharyngobranchial and posterodorsally with the middle of the anterior edge of the fourth epi- branchial. Third pharyngobranchial rounded ventrally, only slightly expanded dorsally; toothed in the same

manner as the second pharyngobranchial, but with somewhat fewer teeth on its slightly shorter and thicker tooth-bearing edge.

Fourth arch. —Cerato-, epi-, and pharyngobranchial elements present. Fourth ceratobranchial like the others; articulates ventrally with the third basi- branchial and dorsally with the fourth epibranchial. Fourth epibranchial a column expanded posteriorly in the middle of its length; articulates dorsally with the

fourth pharyngobranchial. Fourth pharyngobranchial

the smallest of the toothed pharyngobranchials, but with

the widest tooth-bearing surface; teeth like those of the

other pharyngobranchials, except slightly smaller. Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial only slightly longer than the first basi- branchial, but much wider; articulates anteriorly with

the first basibranchial, anterolaterally with the first hypobranchials, posterolaterally with the second hypobranchials, and posteriorly with the third basibranchial. Second hypobranchial the largest of the hypobranchials; much expanded anterolaterally; articulates

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial a stout shaft; rounded anteroventrally but tapering to a narrow blunt end

posterodorsally; articulates anteroventrally with the base of the fourth ceratobranchial. The rounded anterior

region of the fifth ceratobranchial bears teeth like those

of the pharyngobranchials, except slightly smaller, but more posteriorly on the dorsal surface of the shaftlike portion the teeth are extremely small. 249
PAIRED FIN GIRDLES.

Pectoral Fin. Supracleithrum. —In position at about a 45° angle

to the axis of the body; a massive straight shaft, very

thick dorsally but thinner ventrally. At its wide dorsal edge the supracleithrum articulates by fibrous tissue with the ventral surface of the posterolateral portion of the pterotic, while anterodorsally the supracleithrum

abuts against the posterior edge of the posteroventral

flange of the pterotic and articulates with it by fibrous

tissue and, in the smaller specimen, by interdigitation, the supracleithrum being immovably held to the

pterotic. Ventrally the supracleithrum broadly overlies the cleithrum and anterior end of the dorsal post- cleithrum, to both of which bones it is firmly held by fi- brous tissue. There is no evidence in either of the two

study specimens of a posttemporal bone intervening between the supracleithrum and pterotic, even as a small bone extensively interdigitated or partially fused to one

of them. It would be of interest to know whether young

specimens of this species, the most generalized of the Recent gymnodonts, give evidence to the fate of the post- temporal in gymnodonts.

Cleithrum. —Extremely long, reaching anteriorly to between the dentaries in the lower jaw; laterally expanded along most of its length but expanded posteriorly only

to a very slight extent in the area of the scapula; articulates by fibrous tissue dorsolaterally with the overlying supracleithrum and posterodorsally with the anterior edge of the dorsal postcleithrum. Along its upper medial

edge the cleithrum articulates by fibrous tissue with the

anterior edge of the dorsal postcleithrum. Along its upper

medial edge the cleithrum articulates by fibrous tissue with the anterior edge of the scapula and the anterodorsal edge of the coracoid. The ventral end of the coracoid

also articulates by fibrous tissue with the medial edge of the cleithrum about one-third the way back the length of the cleithrum. At their extreme anterior ends the medial

surfaces of the two cleithra are firmly bound to one

another by fibrous tissue, while just posterior to this region the medial surfaces of the two cleithra support the

anterior end of the pelvis.

Postcleithra. —The postcleithra form a long strut from the ventral end of the supracleithrum along the ab- dominal wall musculature to about one-third the way

back the length of the abdominal cavity. The dorsal post- cleithrum articulates by fibrous tissue anteriorly with

the posterodorsal edge of the cleithrum and anterolaterally with the posteromedial surface of the overlying supracleithrum. Along nearly all of its ventral edge the

dorsal postcleithrum articulates by fibrous tissue with

the dorsal edge of the anterior half of the ventral postcleithrum, which is a somewhat slimmer shaft than the

dorsal postcleithrum.

Coracoid. —Rounded anterodorsally, but tapering

to a slender shaft in the ventral half of ito length, a large

posterodorsally directed process present from the posterior edge of the rounded portion of the coracoid; cartilage

filled along the anterior edge of its rounded portion; ar- ticulates by fibrous tissue anteriorly with the cleithrum and posterodorsally with the third and fourth actinosta; anterodorsally it articulates through cartilage with the

scapula.

Scapula. —Scapular foramen entirely enclosed by

the scapula; cartilage filled at its anterior and ventral

edges; articulates by fibrous tissue anteriorly with the cleithrum and ventrally through cartilage with the cor- acoid. Along the upper half of its posterior edge the scapula possesses two slightly protruding articular

facets, the more dorsal for articulation with the first fin ray and the other for articulation with the ventral edge of the first actinost. At the bottom of its posterior edge the scapula supports the second actinost.

Actinosts. —Four elements; all cartilage filled at both ends; first actinost by far the smallest of the elements and articulated by fibrous tissue with the upraised area on the posterodorsal edge of the scapula; sec- ond, third, and fourth actinosts much larger than the

first and articulated by fibrous tissue with the postero- ventral edge of the scapula in the case of the second actinost and to the dorsal edge of the coracoid in the case of the third and fourth actinosts. Distally the actinosts support through fibrous tissue all of the pectoral fin rays, ex- cept for the small first fin ray, which articulates with the

scapula.

Fin rays. —Fifteen fin rays present on both sides of the smaller specimen and 16 on both sides of the larger; the first ray short, composed of two distinct halves throughout its length, the medial half being by far the

stouter of the two; first ray articulated with the scapula, but the other rays articulated with the actinosts. The

first two rays and the last ray unbranched, the other rays branched; first ray without cross-striations, the other

rays cross-striated.

Pelvic Fin. Pelvis.—An extremely long and stout shaft; its posterior half tapering to a thin rod, while its anterior

half becomes ventrolaterally expanded and then tapers

to a bluntly rounded anterior end; the two halves of the

pelvis firmly interdigitated with one another, except at the narrow posterior end where the interdigitation becomes so extensive that distinct halves can no longer be recognized and where fusion of the medial surfaces of each half may have taken place. The ventral surface of

the anterior half of the pelvis is deeply concave and

houses the muscle mass whose contraction causes the downward and forward rotation of the pelvis around its anterior articulation with the cleithra in the process of expansion of the huge ventral flap or dewlap. A small gap

is present in the otherwise interdigitated medial surfaces

of the two halves at a point just behind the middle of the 260
length of the pelvis. Anteriorly the pelvis articulates by

tough fibrous tissue with the medial edges of the two

cleithra in the region below the quadrate. There is no

trace of pelvic fins or of any of the rudimentary fin ray elements such as are found in balistoids. VERTEBRAL COLUMN. —All vertebrae with bicon- cave centra, except for the last, which ends posteriorly in the urostyle.

Abdominal Vertebae.

First vertebra. —Lateral wall of neural arch from

each side of the centrum meeting its opposite member

dorsally above the neural canal but not continuous or in- terdigitated with it; rather, the medial edges are held to one another by fibrous tissue; the dorsal surface of this articular area is slightly upraised medially to give the

suggestion of a neural spine. The upper anterior portion

of the centrum and lower portion of the neural arch are deeply concave and form a facet for articulation by fi- brous tissue with the exoccipital condyle. Other abdominal vertebrae. —Nine abdominal

vertebrae in two specimens, all of which, except for the

first and ninth in the smaller specimen, bear true ribs; from the first to the ninth vertebrae the neural spines become increasingly well developed; the two halves of the neural spine of the second vertebra, like that of the

first, are not fused together above the neural canal, but

are held to one another by fibrous tissue, while the neural

spines of the more posterior vertebrae are single pieces. The first to the sixth abdominal vertebrae do not possess haemal arches, but the seventh to ninth have complete haemal arches and progressively better developed haemal spines which project slightly posterior to the haemal arch, that of the seventh with only a short posterior tapering to the haemal arch. Haemal prezyga- pophyses are not developed and haemal postzyga- pophyses only begin to develop from about the seventh

vertebra and never extend posteriorly even to the level of the end of the centrum above them. Neural postzyga- pophyses are present on the abdominal vertebrae, but

the greatest development of the zygapophyses involves the neural prezygapophyses. The neural prezygapophyses, and particularly the portions of the neural

arches and spines above them, become enlarged from the second to about the seventh and eighth abdominal verte- brae. At its full development the region anterior to the thickened shaftlike part of the neural spine becomes en- larged into a relatively flat plate which projects anteriorly slightly past the anterior edge of its vertebral cen- trum to fit below the posteriorly projecting neural spine

of the preceding vertebra. These anterior expansions are held by fibrous tissue to the posterior edge of the neural

spine region of the preceding vertebra and increase the

rigidity of the vertebral column. The tip of the neural

spine of the fourth vertebra supports the anteroventral edge of the first supraneural ( = first basal pterygiophore

of the spiny dorsal fin when the latter is present), while

the neural spines of the fifth and sixth abdominal verte- brae articulate with the ventral edge of this element fur- ther back along the length of the latter. The neural spine

of the seventh abdominal vertebra articulates dorsally with the ventral edges of the second and third supraneurals (terminology when no spiny dorsal fin is present) and posteriorly with the anterior edge of the first soft dorsal fin basal pterygiophore. The neural spines of the

eighth and ninth abdominal vertebrae articulate be- tween the more anterior dorsal fin basal pterygiophores.

Ribs and epipleurals. —True ribs are present on all of the abdominal vertebrae in the large specimen, but are absent on the first and last abdominal vertebrae in the smaller (illustrated) specimen. The point of articulation

of the rib with the vertebra is at first with the lower

anterolateral surface of the centrum, but it becomes

progressively lower on the centrum until finally the ribs on the last few abdominal vertebrae articulate with the

lateral surfaces of the haemal arches. The ribs become

progressively longer from the first to the fourth or fifth, and then become slightly shorter again. The ribs border

the internal surface of the abdominal cavity and there can be no doubt that they are pleural ribs. The first two

ribs (attached to the first and second vertebrae) of the

larger specimen and the first rib (attached to the second

vertebra) of the smaller specimen do not bear epi- pleurals (intermuscular bones), but all of the other ribs have well-developed epipleurals attached to their dorsal

surfaces. In the smaller of the two study specimens the

epipleurals attached to the second to fifth abdominal

vertebrae are composed of two pieces which are variously branched. The two pieces of these intermuscular bones

are held together by fibrous tissue. The epipleurals at- tached to the sixth and seventh ribs are composed of a

single unbranched piece, and while that of the sixth vertebra is held by fibrous tissue to the pleural rib, that

of the seventh vertebra is fused to the rib. The ninth ab- dominal vertebra has an unbranched epipleural attached by fibrous tissue to the lateral surface of its haemal arch. Short, unbranched epipleurals are attached by fibrous

tissue to the lateral surft e of the haemal arches of the

first five caudal vertebrae. In the larger study specimen

the epipleurals are more extensively branched, and only

one, that attached to the fifth abdominal vertebra, is composed of two pieces. The epipleurals of the second abdominal vertebra are both unbranched, while those of the third are branched on one side and unbranched on

the other. The epipleurals of the fourth to seventh ab- dominal vertebrae are extensively branched, while those on the eighth and more posterior vertebrae are un- branched. Whereas in the smaller specimen the

epipleurals extend to the fifth caudal vertebra, in the

larger there are epipleurals on both sides of the sixth caudal vertebra as well. Caudal Vertebrae. —Eleven caudal vertebrae in two

specimens; all, except the last, with well-developed haemal arches and spines; neural spines well developed
on all but the last of the caudal vertebrae; neural spines decreasing in length from the first to the eighth, but in- creasing in length from the 9th to 10th. As the neural

spines of the first to sixth caudal vertebrae decrease in height, they become laterally compressed into anteroposteriorly extended plates. The neural spines of the first to third caudal vertebrae are placed between, and ar- ticulate by fibrous tissue with, the dorsal fin basal pterygiophores. The anterior edge of the neural spine of the

fourth caudal vertebra articulates by fibrous tissue with

the posterior edge of the 11th, or last, basal pterygio- phores. The neural spine of the 9th caudal vertebra

elongates almost directly posteriorly to form a roof over

the 10th caudal vertebra for almost the entire length of the centrum of the latter. The neural spine of the 10th caudal vertebra is an elongate shaft which distally supports the first 4 or 5 procurrent caudal fin rays. The anterior ends of the neural arches and bases of the neural

spines of all of the caudal vertebrae, except for the last two or three, are prolonged anterolaterally into thick

spinelike processes to which are attached large muscle

masses. Just above the centrum on the lower anterior edge of the neural arch there is a shorter anterior process which articulates by fibrous tissue with the posterolateral surface of the neural arch and base of the neural

spine of the preceding vertebra. This anterior process, representing the neural prezygapophysis, is increasingly

well developed from the first to about the fifth and sixth caudal vertebrae, posterior to which it becomes

progressively smaller again. The haemal arches and

spines of the first to fifth or sixth caudal vertebrae bear

epipleurals laterally and the first to fifth support through

fibrous tissue ventrally the basal pterygiophores of the

anal fin. Along most of its posterior edge the haemal

spine of the first caudal vertebra supports the upper anterior edge of the enlarged first basal pterygiophore of the anal fin. The haemal spines of the second to fourth caudal vertebrae support most of the anal fin basal

pterygiophores. The posterolaterally expanded and

slightly concave anterior surface of the large haemal

spine of the fifth caudal vertebra supports the small

ninth, or last, pterygiophore. The ventrolateral surface of the posterior half of each centrum from the first to fifth caudal vertebrae becomes increasingly expanded ventrally to form the side walls of the trough through which

the haemal canal courses. At the sixth caudal vertebra

these ventral expansions articulate by fibrous tissue with

the dorsal edge of the posteriorly prolonged flange of the haemal spine. There are thus, in effect, two arches over

the haemal canal—the haemal arch proper and the arch formed by the meeting of the haemal spine with the ventral flange from either side of the posteroventral surface

of the centrum. The seventh and eighth caudal verte- brae have the same arrangement, except that the sur- face of contact between the haemal spine and the ventral flanges is fused, leaving only a foramen to indicate what was formerly the wide space between the dorsal edge of the posteriorly directed haemal spine and the

ventrolateral surface of the centrum. The haemal spine

of the 9th caudal vertebra, like its neural spine, is

prolonged posteriorly to form a roof over the haemal arch and base of the haemal spine of the 10th caudal vertebra. The haemal spine of the 10th caudal vertebra, like

its neural spine, forms a long shaft that distally supports most of the procurrent rays of the lower lobe of the caudal

fin. The haemal arches and spines of the 9th and 10th caudal vertebrae are autogenous. Caudal Skeleton. —The caudal fin supporting struc- tures are composed of the Uth caudal vertebra and its urostylar projection, an epural, two pairs of uroneurals,

four hypurals, and a parhypural, as well as the shaftlike neural spine and haemal spine of the 10th caudal vertebra. The centrum of the 11th caudal vertebra is prolong- ed posterodorsally into a urostylar process whose posterior edge is concave and supports the upper three hypurals, while its anterodorsal edge is similarly con- cave and helps support the uroneurals. Because of its concave anterodorsal and posterior surfaces, the upper

half of the urostyle is forked into right and left halves, since there is no bony material in the midline of the urostyle in this region. From the anterolateral region of its dorsal surface the centrum possesses an anteriorly directed prong or neural prezygapophysis which ar- ticulates by fibrous tissue with the posterolateral sur- face of the neural spine of the 10th caudal vertebra. The

dorsomedial edges of the two sides of the neural arch of

the last centrum are not in close contact in the midline

over the neural canal, only partially roofing over the latter. The epural is a large column of bone which is con- cave along the upper half of its posterior edge. It ar- ticulates by fibrous tissue anteriorly with the posterior edge of the neural spine of the 10th caudal vertebra, posteriorly with the first uroneural and ventrally with the

dorsal edges of the incomplete neural arch of the 11th caudal vertebra. The second uroneural is a long rounded

shaft, with a medial groove along its length representing

the region of complete fusion of its two halves, whose

anteroventral edge rests against the concave dorsal sur- face of the urostyle mainly in the region of its pwsterior bifurcation. The posterodorsal end of the second

uroneural supports the deeply forked base of the first principal ray of the upper lobe of the caudal fin. Along

the ventral two-thirds of its round anterior surface the second uroneural has closely applied to it a large, but

very thin, pair of bones, the first uroneurals, which ar- ticulate with it, and with each other medially, by fibrous

tissue. Along their anteroventral edges the first uro- neurals articulate by fibrous tissue with the dorsal sur- face of the neural arch and urostyle of the last centrum. The fourth hypural, or uppermost, is more or less triangular in shape, with the lower two-thirds of its anterior edge resting against the concave posterior surface

of the urostyle. Along its ventral edge the fourth hypural

is closely held by fibrous tissue to the dorsal edge of the

third hypural. The third hypural is widest posteriorly, narrow anteriorly to a slightly convex and laterally ex- panded articular facet which fits against a concavity on

the anterior one-third of the dorsal edge of the second

hypural. The extreme anterior end of the second hypural
makes only slight contact with the posterior edge of the

urostyle. The anterior end of the second hypural rests against the lower posterior edge of the urostyle, while its dorsal edge is slightly expanded laterally along the anterior one-third of its length into a concave articular facet

for contact with the anterior end of the third hypural, as explained above. The ventral edge of the second hypural

articulates with the dorsal edge of the first hypural by fi- brous tissue posteriorly but more anteriorly by slight in- terdigitation. The first hypural articulates dorsally with

the second hypural as just described, while anteriorly it rests against, and possibly slightly interdigitates with, the posteroventral edge of the last centrum. The first hypural articulates ventrally with the dorsal edge of the parhypural by fibrous tissue posteriorly but more anteriorly by slight interdigitation. The parhypural is obviously the haemal arch and spine of the last, or 11th, caudal vertebra, but, like the haemal arches and spines

of the 9th and 10th caudal vertebrae, it is autogenous.

Dorsally the parhypural articulates with the first hypural through fibrous tissue and interdigitation, as described

above. The portion of the dorsolateral surface of the parhypural that lies below the anterior one-third of the

first hypural is laterally expanded into a flange to which

caudal fin-ray muscles are attached. A similar, but much

smaller, lateral flange is present from the anterior edge of the first hypural. The anterior end of the flange from the

first hypural overlies the anterodorsal surface of the

flange from the parhypural. The combined flanges from

the parhypural and first hypural compose the hypurapophysis. The anterior half of the dorsal articular sur- face of the parhypural is concave, so that where it inter- digitates with the last centrum and with the anteroventral end of the first hypural, a canal is formed in the midline of the otherwise interdigitated surfaces between the

three bones. The canal opens to the exterior posteriorly

at a slight gap in the articulated surfaces of the parhypural and first hypural just behind the lateral flange of the parhypural. The canal is continuous anteriorly with

the haemal canal of the preceding vertebrae.

Caudal fin rays. —Twelve principal (branched rays

plus the unbranched ray directly above and directly below the series of branched rays) fin rays preceded by

eight (smaller specimen) or nine procurrent rays above and six (smaller specimen) or seven procurrent rays below. The 10 branched rays become increasingly branched toward the middle 2 rays, which are branched

in triple dichotomies. The uppermost branched ray and

the lowermost branched ray are the longest of the caudal

fin rays, while the two middle rays are the shortest, being about one-half the length of the longest branched rays. The two unbranched principal caudal rays are some- what shorter than the longest branched rays, and the

procurrent caudal rays rapidly decrease in length anteriorly in the series. The first two or three procurrent

rays are without cross-striations, while all the other procurrent rays and principal rays are cross-striated. The

upper unbranched principal caudal ray articulates with

the second uroneural; the lower unbranched principal

caudal ray with the parhypural. The upper three and

lower two branched rays of the dorsal lobe articulate, respectively, with the fourth hypural and with the third hypural. The upper two and lower three branched rays of the ventral lobe articulate, respectively, with the second

hypural and with the first hypural. All the rays ar- ticulate by fibrous tissue with the supporting elements.

DORSAL AND ANAL FINS.

Spines and pterygiophores. —The presence or ab- sence of a spiny dorsal fin in T. macropterus has been

discussed by Tyler (1962a:794-796; 1967:92-93), it being shown that most specimens from Japan to Indonesia have a minute spiny dorsal fin, usually of two spines, while the specimens now known from the Indian Ocean

lack the spiny dorsal fin. The smaller of the two

specimens studied for the present work, SU 13747, from

the Philippines, had been skinned, then cleared and

stained, and then dissected by the author prior to his dis- covery of a spiny dorsal fin in other whole specimens, and

it is impossible to say, upon reexamination of the cleared and stained SU 13747 specimen, whether spines had

been present or not. Being from the Philippines, it probably did have spines which were lost during its processing as an osteological preparation. The larger study specimen, ANSP 98917, from the Volcano Islands south of Japan, was processed with the knowledge of its possession of a spiny dorsal fin. The lateral view illus- tration of the entire skeleton presented here is based on SU 13747, except that the dorsal spines are based on ANSP 98917, as are the detailed lateral and dorsal views

of the spiny dorsal fin. When dorsal spines are present, the first is longer than

the second, and both can be laid back in a shallow groove

in the skin in the midline of the body. The bases of the two spines are relatively close together, the first ar- ticulating with the posterodorsal surface of the long first basal pterygiophore ( = first supraneural when no spiny

dorsal fin is present), and the second spine articulating

in the middle of the much shorter second basal pterygio- phore. From the anterolateral surface on either side of the base of the first spine a tendon runs anteroventrally along a groove in the dorsal and lateral surfaces of the

first basal pterygiophore to connect to a small muscle whose contraction causes the erection of the spine. The

second spine does not have such muscles and tendons as- sociated with it, but a low membrane connects the first and second spines so that the erection of the first spine causes the erection of the second as well. The ventral ends of both spines articulate by fibrous tissue to the

relatively flat surfaces of their basal pterygiophores. There are rudiments of what is probably another dorsal spine in the form of two nubbins of bone, one to either

side of the midline, lying beneath the skin on the dorsal surface of the first basal pterygiophore immediately in front of the base of the first relatively well-developed dor-
sal spine. How constant this pair of nubbins are in their occurrence cannot be determined until more specimens

of this species are available for clearing and staining, but

I suspect that the nubbins represent the right and left basal regions of a rudimentary spine. In all other plec- tognaths with two or more dorsal spines, the first two

spines are always borne on the first basal pterygiophore, while the spines posterior to them are each borne on in- dividual basal pterygiophores, which additionally leads me to believe that the paired nubbins in T. macropterus

are homologous to the first dorsal spine in other plec- tognaths and that the two relatively well -developed

spines in T. macropterus are homologous to the second and third spines of other plectognaths. U that is true, Triodon exhibits a feature not seen in other plectog- naths with a spiny dorsal fin, for when the size and number of the dorsal spines decreases in the

triacanthoids and balistoids it is always by reduction and

loss of elements from posteriorly to anteriorly in the

series, and the first spine is always much larger than the

others. Two other bony elements without intemeural processes are placed above the dorsal ends of the neural spines be- tween, and in series with, the two basal pterygiophores supporting the dorsal spines and the first basal pterygio- phore of the soft dorsal fin. When a spiny dorsal fin is not

present, these four elements anterior to the anterodorsal end of the first basal pterygiophore of the soft dorsal fin would be called supraneurals. But where the two more

anterior elements in the series support dorsal spines, they must be referred to as basal pterygiophores, even

while the two more posterior elements technically remain

supraneurals. Thus, the distinction between supraneurals and basal pterygiophores in Triodon is ar- bitrary, and indicates that the supraneural element that occurs in ostracioids and gymnodonts is probably a

simplified basal pterygiophore that no longer supports

dorsal fin spines. Of the four elements that are supraneural in position

in Triodon, the first (the first basal pterygiophore when a spiny dorsal fin is present) is by far the largest and ar- ticulates by fibrous tissue anteriorly with the distal end

of the neural spine of the fourth abdominal vertebra,

ventrally with the distal ends of the neural spines of the

fifth and sixth abdominal vertebrae, and posteriorly with

the anterior edge of the second element. The second ele- ment is much shorter than the first and articulates by fi- brous tissue anteriorly with the first, ventrally with the

neural spine of the seventh abdominal vertebra and posteriorly with the anterior edge of the third element. The

third element is slightly shorter than the second and ar- ticulates anteriorly by fibrous tissue with the second and

with the neural spine of the seventh abdominal vertebra. Posteriorly the third element slightly interdigitates with the anterior edge of the fourth, while posteroventrally it articulates by fibrous tissue with the first basal pterygiophore of the soft dorsal fin. The small fourth ele- ment articulates by interdigitation ventrally with the

first basal pterygiophore of the soft dorsal fin and anteriorly with the third element.

Fin rays and ptery^ophores. —Eleven fin rays present; the first ray unbranched, the others branched in

single, double, or triple dichotomies; third and fourth

rays longest; first ray about equal in length to the next to

last ray. Each fin ray has a well-developed pair of distal pterygiophores as two distinct halves between the bifur- cate base of the ray. In the smaller specimen the two

halves are not in close contact with one another, while in the larger specimen the two halves have their medial

edges in close apposition and are held firmly together by

fibrous tissue and in some cases apparently by slight in- terdigitation. The fin rays are supported basally through

fibrous tissue by ii basal pterygiophores, which ar- ticulate with one another and with the neural spines of the vertebrae by fibrous tissue. The dorsal ends of the

basal pterygiophores are slightly enlarged and are in close contact with one another. The upper lateral sur- faces of the first three or four basal pterygiophores

possess shallow lateral flanges, but these flanges decrease in size posteriorly in the series and are effectively absent on the last few pterygiophores. The pterygio- phores are cartilage filled at both ends. The intemeural

portions of the pterygiophores articulate between the

neural spines of the seventh abdominal to the fourth caudal vertebrae.

Anal Fin.

Fin rays and pterygiophores. —Ten fin rays present; the first ray unbranched, the others branched in

single, double, or triple dichotomies; third and fourth

rays longest; first ray about as long as the last ray. Each

fin ray has a well-developed pair of distal pterygiophores

as two distinct halves between the bifurcate base of the

ray, with the two halves in close apposition medially only

in the larger specimen, just as with the soft dorsal fin. The fin rays are supported basally through fibrous tissue by nine basal pterygiophores, which are cartilage filled at both ends. At their distal ends the pterygiophores are

slightly expanded anteroposteriorly, but they do not make as close a fibrous tissue contact with one another as do the soft dorsal fin basal pterygiophores. Other than at

their distal ends, the anal fin pterygiophores, with the exception of the first, are slender shafts without any

lateral projections or flanges from their surfaces. The

first pterygiophore is a much stouter shaft and ventrally

it possesses a large lateral flange to either side of its anterior edge. The second pterygiophore is extremely thin, and is held between the first and third pterygiophores without reaching dorsally to make contact with a haemal

spine. The other pterygiophores articulate by fibrous tis- sue dorsally with the haemal spines of the first to fifth caudal vertebrae. Anatomical diversity.—The single Recent species of

this family apparently consists of two at least partially reproductively isolated populations (Tyler 1967) differ- ing grossly only in that the population from Japan to In- donesia usually retains a rudimentary spiny dorsal fin 254
while the Indian Ocean population usually completely

lacks even rudimentary dorsal fin spines. Fragments of premaxillaries and fused dentaries with

small rounded teeth incorporated into the matrix of the

biting edge, found as early as the Eocene of Europe (see Material Examined), have been assigned to the Triodontidae as Triodon antiquus Leriche (1905, 1906, 1919,

1920), entirely on the rationale that the jaws are in three major pieces rather than the two of diodontids or four of tetraodontids. Tetraodontids would be eliminated from consideration for the antiquus jaw fragments because in antiquus

the individual dental units are small and rounded as in triodontids and diodontids rather than long rods as in tetraodontids. Diodontids can be eliminated from consideration only because the premaxillaries in antiquus remain separate from their opposite members, while they
parasphenoid

prefrontal frontal

Fiffure 183.

Triodon macropterus:

lateral view of tiead, 391 mm SL,

Philippines.

premaxillcry

bosisphenoid epiotic

angular

interopercolum quadrate sympleetic \ mesopterygoid metapterygoid
Flsure liS.—Triodon iruicroptenu: poitcrior view of skull (left), with, below, lateral and

posterior views of Hrst abdominal vertebra;

posterior view of orbit (right) (cross section of

skull; dashed lines represent cut surfaces of

frontals and parasphenoid), with, below, lateral view of basisphenoid (anterior to left); 391 mm SL, Philippines.

ceratobranchials '^C^ C^C=^ basibranchials

epibranchials // jT //^ <??/ "hypobranchials

pharyngobranchials

Figure 184. (opp. page)—TViodon

macropterus: dorsal (left) and

lateral (right) views of skull, 391 mm SL, Philippines. .^

T4

interhyal pihyal

Figure 186. (right)— TViodon

macropterus: dorsal view of branchial

arches (extended on lower side); lateral view of hyoid arch; dorsal and lateral views of urohyal;

391 mm SL, Philippines.

dorsal

lateral urohyal

dorsal hypohyal

ventral hypohyal

branchiostegol rays
dorsal postcleithrum

ventral postcleithrum

Figure 187.— Triodon macropterus: lateral view of pectoral girdle, with inset showing

full extent of scapula in lateral view,

391 mm SL, Philippines.

Parahollardia lineala Balistapus undulatus Acanthostracion quadricomis

Triodon macropterus Lagocephalus laevigatus Carrthigaster rostrata

Dicxion holocanthus

Figure 188.— Lateral views of scapula and

first (uppermost) actinost in representatives

of all superfamilies, showing the completely

enclosed scapular foramen of Triodon macropterus, unique among the gymnodonts and similar to the scleroderms.
Figure lS9.—Triodon macroplenu: lateral views

of alternate pleural ribs and their epipleurals

(left); dorsal view of lower jaw (right) to show

the trituration plate; 391 mm SL, Philippines.

Figure 190.— Triodon macropterua: lateral (above) and dorsal views of rudimentary spiny

dorsal fln and its basal pterygiophores,

463 mm SL, Japan.

Figure 191.—TWodon macroptenu: ventral, dorsal, and lateral views of pelvis, 391 mm SL, Philippines.
2nd uroneural epural

neural spines

haemal spines

caudal vertebrae procurrent fin rays

are fully fused together in diodontids. Even accepting

this reasoning, the presence of Triodon-like jaw frag- ments tells us nothing about what the fish behind the jaws was like, there being no guarantee that the general form of antiquus was at all like that of the Recent

Triodon macropterus . Moreover, apper jaws without fus- ed premaxillaries but with small rounded dental units in the matrix are what one would expect to find in the Eocene ancestors of the early to late Eocene diodontids such as Prodiodon and Progymnodon.

Relationships to the Balistoidei and to the other

Tetraodontoidei. —The relationship of the Triodontidae as an intermediary between the eoplectin Triacanthodidae and the other more specialized Tetraodontoidei is discussed under the subfamilial rela- tionships of the Triacanthodidae, it being shown, in es- sence, that Triodon, which is by far the most generalized

of the gymnodonts, clearly is derived from the eoplectins, which retain many generalized triacanthodid features while having highly specialized gymnodontlike jaws with

small rounded dental units incorporated into the matrix

of the premaxillaries and dentaries. Since it is highly improbable that such complex dentitional changes as found

in the gymnodonts have arisen independently in various

lines, the eoplectins are obviously ancestral to the gymnodonts, with their closest relatives among the gymnodonts being the triodontids. While the evolution of small rounded dental units in- corporated into the matrix of the jaw bones is a highly complex matter that has arisen only once among plec- tognaths (although similar dentition has been in- dependently developed in some of the Scaridae among

the perciform fishes), the same is not true of the fusion of the dentaries and premaxillaries to their opposite memFigure \92.— Triodon macropterus: lateral view of caudal fin supporting structures

(see T>ler 1970b:figs. 42a and 42b,

for details), 391 mm SL, Philippines.

bers, which, relative to the dentitional and general structural changes involved in developing a crushing or biting beak, is a simple matter. The relative superficiality of the jaw bone fusion is attested to by the fact that the dentary and premaxillary of very large specimens of tetraodontids occasionally fuse to their opposite members and that Reuvens (1894:130) described a young

molid in which the dentaries were fused but the pre- maxillaries were separate. Thus, the form of the dental

units in the biting edge of the jaws is a far more

anatomically complex and phylogenetically important

indicator than is the fusion or lack of fusion of the dentaries and premaxillaries. The fusion of these bones to their opposite members

undoubtedly at least slightly increases the rigidity and

strength of the beak beyond that which it would possess

if the premaxillaries and dentaries remained separate, but I doubt that the difference is functionally of great magnitude, for the two halves of the upper and lower jaws of tetraodontids are firmly and relatively inflexibly held together medially by a combination of interlocking emarginations and thick bands of tough fibrous tissue. The two halves of the upper jaw in Triodon, for example,

are so extensively interdigitated that they are ex- ceedingly difficult to force apart, and I doubt that much

more pressure would be needed to break apart the fused

dentaries than to separate the interdigitated premaxillaries. The most generalized dentitional condition in gymnodonts is small rounded units incorporated into the
matrix of the biting edge of the premaxillaries and dentaries, as found in the triodontids, the most generalized gymnodonts, and in their ancestral eoplectin triacan- thodids (as well as in the moderately specialized diodontids). Of the two known eoplectins, the biting edges of the jaws are exposed only in Eoplectus, which has small rounded dental units, but this can also be expected to be

the condition in the related Zignoichthys. The eoplectins undoubtedly evolved from a group of early triacanthodids with a generalized dentition of numerous

conical teeth in an outer series, internal to which there were a smaller number of conical inner series teeth. Conversion of this generalized dentition into that as found in eoplectins and triodontids probably involved a

great increase in the number of outer series teeth and

their placement in more than one row concomitant with

a great reduction in size of the individual teeth, which

eventually protruded less and less to the exterior beyond

their basal sockets in the premaxillaries and dentaries and finally became entirely nonprotrudant, being fully surrounded by the matrix of the bone. It is not known

whether eoplectins had trituration plates internal to the

biting edges of the jaws, but it is probable that they did,

for trituration plates are found in all triodontids, diodontids, molids, and in many tetraodontids, and the jaws of eoplectins are just as massive as in most gymnodonts and

the eoplectin diet probably consisted of hard shelled in- vertebrates for which trituration plates would be useful

in crushing and grinding. These trituration plates are obviously formed from modified internal series teeth as found in the more generalized triacanthodids, the teeth becoming greatly increased in number, and sometimes in

size, to form a series of rows which variously retained much of their individual identity or became incor- porated into a plate in which some of the teeth lost their individual identity, especially anteriorly in the plate away from the posterior region of tooth replacement. However, the development of trituration teeth, whether

as plates or not, is probably a highly labile feature in various lines of gymnodonts closely correlated with

dietary changes as species evolved in differing habitats. The generalized gymnodont dentition of small rounded

units in the biting edge has been retained by triodontids and diodontids, but tetraodontids and molids have greatly modified the dentition of the biting edge. In molids

discrete dental units are no longer present, at least as observed at 30 magnifications, the ancestral small rounded

units apparently indistinguishably fused to the bony

matrix. In tetraodontids the ancestral small rounded units have been modified into less numerous long rods lying

in series approximately parallel to the biting edge. The

tetraodontid dental units of the biting edge obviously did

not become specialized long rods until after the division

of the joint tetraodontid-diodontid ancestral line, for diodontids retained small rounded units from this line.

It seems reasonable to assume that the tetraodont jaw

type (but not tooth type), with both the premaxillaries and dentaries closely articulated but not fused to their opposite members, was the primitive condition of early gymnodonts, and that both the triodont jaw type, with

only the dentaries fused to their opposite members, and

the diodont jaw type, with both the dentaries and pre- maxillaries fused to their opposite members, are derived from a tetraodont jaw type ancestry, either in- dependently or with the diodont type perhaps having been preceded by a triodont type ancestral group.

It is not known whether the premaxillaries and dentaries were fused or articulated to their opposite members in the Eocene triacanthodid Eoplectus, but in the apparently closely related Zignoichthys from the same

strata, at least one of the jaws, probably the lower, had

the two halves (presumedly dentaries) fully fused

together.

If these two Eocene triacanthodids, representing the subfamily Eoplectinae, are indeed representatives of the

ancestral line leading to Triodon and the other gymnodonts, then at least Zignoichthys is already too

specialized in its jaw structure (which must be either triodont or diodont type) to be considered as ancestral to the tetraodontids. It seems to me extremely unlikely that once the full fusion of the dentaries and/or premaxillaries was established in a line of gymnodont evolution

that consistent reversal to an unfused condition could

take place, especially in light of the intricate inter- locking interdigitations that are almost always present when the premaxillaries or dentaries are articulated to one another rather than fused.

It is assumed here that the immediate ancestry of the few known eoplectins and thus of the triodontids had the

premaxillaries and dentaries separate from their opposite members, and that the tetraodontids diverged from this ancestral line at a time in the Eocene when at

least some members of that line retained separate pre- maxillaries and dentaries. This line was probably

TViodon-like except in the retention of separate dentaries and also probably before the elongate tapered caudal peduncle as seen in the Recent Triodon had been

fully established. Since it is here considered that the diodontids are more closely related to tetraodontids than

to molids, an additional implication of the above reasoning is that the fusion of the premaxillaries and dentaries

in molids and diodontids has taken place in- dependently, that in diodontids from a tetraodontid ancestral group, and that in molids from the same eoplectin-triodontid line retaining separate premaxillaries and

dentaries from which tetraodontids are evolved. The features in the conversion of an eoplectinlike fish into a triodontidlike one are discussed under Eoplectus

in the account of the Triacanthodidae. The conversion of a triodontidlike fish into a fish like that of any of the

other derived families of gymnodonts involves primarily

the loss of most of its more generalized or triacanthodidlike features. The features of Triodon that are lost by all other gymnodonts are: 1) the rudimentary spiny dorsal fin and all but one of the basal pterygiophores and supraneural elements supporting it; 2) the ribs and epipleurals; 3) the

pelvis; 4) uroneurals and hypurapophysis, and the consolidation of the hypurals so that only one free element is present and the conversion from an autogenous to fused
haemal spine on the antipenultimate vertebra; 5) the

procurrent caudal fin rays and at least one of the principal rays (from the upper lobe of the fin); 6) a complete

dorsal roof to the myodome and the channel leading into

it posteriorly; 7) the knob on the scapula for articulation with the uppermost pectoral fin ray, and the complete

scapular foramen; 8) urohyal; 9) one of the pharyngobranchials and well-developed teeth on the fifth cerato- branchial; 10) the deep olfactory sac and normal olfac- tory rosette; 11) four actinosts, none of which are sutured

to one another or to the scapula or coracoid. Triodon, as represented by the single Recent species upon which our entire knowledge of the family is based

except for the fossil jaw fragments possibly related to it, has certain features found in neither the triacanthodids nor in other gymnodonts. These undoubtedly are

specializations which were acquired by Triodon after its ancestral stock had given rise to the lines leading to the molids on the one hand and to the tetraodontids and

diodontids on the other hand. These specialized features

of Triodon are: 1) the long caudal peduncle tapering to a transversely indented region just in front of the base of the deeply forked caudal fin; 2) the prominent anterolateral processes from the neural arch region of many of the caudal vertebrae and the long rodlike neural and

haemal spines of the penultimate vertebrae, all as- sociated with the musculature and support of the caudal peduncle and caudal fin used for apparently sustained

rapid swimming; 3) the rotatability of the pelvis and the expansible dewlap of skin between the end of the pelvis and the anus; 4) the great anterior elongation of the cleithrum; 5) the small sphenotic entirely confined to the

rear of the orbit; 6) the articulation of the first branchiostegal ray on the ventrolateral surface of the ceratohyal; 7) the short posterior shaft of the interoperculum behind the level of the epihyal; 8) the posteroventrally prolonged shaft of the pterotic articulating broadly with

the hyomandibular; and 9) the exoccipital in contact with the frontal and excluding the epiotics from contact with the supraoccipital. Since neither the triacanthodids nor any of the other gymnodonts possess anything similar to these specializations of Triodon, the ancestral line leading to the Recent

Triodon can be expected to have had more triacanthodidlike conditions in these features and that they remained relatively generalized in them until after the

other gymnodont linages split off from the early Triodonlike fishes. The ancestral line connecting the eoplectin tri- acanthodids and the triodontids is hypothesized as having given rise to the line leading to the great diversifica- tion of the gymnodonts, this line diversifying in two basic

directions, one leading to the molids and one to the

tetraodontids and diodontids, at a pre-Recent Triodon

level of organization, i.e., at a level of organization that

retained all of the generalized features of Triodon but

that did not yet have the specialized features of the Recent Triodon noted above, as well as with both the pre- maxillaries and dentaries unfused and the first branchiostegal ray entirely unmodified.

The molid line of radiation from the pre-Recent Triodon level of organization is represented by only a few

species, at least surviving today, which became vastly modified for a slow swimming oceanic and mostly pelagic existence and relatively huge size within a protective

wall of thickened skin, while retaining from its triodontid ancestry several generalized features lost in the tetraodontid-diodontid line of radiation. Molids have

retained: 1) the basisphenoid; 2) fourth gill and gill slit between the fourth and fifth arches; 3) unmodified first branchiostegal ray; 4) uninflatable gut; and 5) un- sutured ceratohyal and epihyal. Moreover, the configuration of the bones of the snout

in molids is in many ways remarkably similar to that in Triodon, far more so than is the case in the tetraodontid- diodontid line. In Triodon and molids the ethmoid tends

to be a large squarish block of bone bordered on either

side by the large palatines and prefrontals, with the

palatine broadly held medially to the ethmoid, vomer

(unossified in Ranzania), parasphenoid and prefrontal. The shape and size of the frontals in Triodon and molids

is also remarkably similar. An anteriorly directed prong

in the suboperculum, as found in Triodon and diodontids, is retained in molids, even though the molid oper- culum and suboperculum are greatly reduced in size. While these similarities between Triodon and molids

indicate the relationship between the two groups, molids

possess an array of specializations beyond the generaliz- ed Triodon level of organization, many of which are centered around the aborted rear end of the body and the support of the continuous dorsal, anal, and pseudocaudal fins. The major ways in which molids differ from

Triodon, other than those already mentioned above that

distinguish Triodon from all other gymnodonts, whether

they be the generalized triacanthodidlike features of Triodon that are lost or the specialized features of Triodon developed after the radiation of the other gymnodonts from a triodontid ancestral group, are: 1) the apparently indistinguishable incorporation of the dental

material into the matrix of the jaws, along with the fu- sion of the premaxillaries, even though well-developed

individual trituration teeth are retained in both the upper and lower jaws; 2) the loss of an ossified sesamoid articular; 3) the great enlargement of the basisphenoid and

the complete loss of the dorsal roof of the myodome and

of the posterior opening into it; 4) the loss of teeth on the

fifth ceratobranchial and the development of gill rakers along the front of the fifth ceratobranchial and along the

anterior edge of the first gill slit, even though only Triodon and molids among the gymnodonts retain the

fourth gill, well-developed teeth on all three of the tooth- ed pharyngobranchials, unsutured ceratohyal and

epihyal, the consistent presence of both dorsal and ventral hypohyals and the interhyal, and a relatively unmodified first branchiostegal ray; 5) the loss of the pharyngobranchial of the first arch; 6) the loss of the first or uppermost actinost; 7) the consolidation of the postcleithra into a single piece and the development of an anterior spur from it to the region of the actinosts; 8) the development of a dome or posterior prolongation on the
epiotics; 9) the development of a posterior prolongation

of the pterotics broadly articulating with the supracleithrum; 10) the dorsal prolongation of the basioccipital excluding the exoccipitals from contact with the

first vertebra; 11) the loss of haemal arches and spines on

at least some of the abdominal vertebrae and the reduction in size of their neural spines; 12) the loss of all of the supraneural elements and the vast rearrangements of the

vertebral column and basal pterygiophores of the dorsal and anal fins in the formation of the continuous fin around the posterior end of the body with the abortion of the true caudal fin and its supporting structures and the development of a pseudocaudal fin of posteriorly migrated dorsal and anal fin rays and their basal ptery- giophores; 13) reduction in the number of vertebrae from

20 to between 16 and 18; 14) reduction in the size of the

olfactory apparatus; 15) development of thickened or hardened skin; 16) reduction in the size of the gill opening; and 17) the loss of the air bladder. The tetraodontid-diodontid line of radiation from the pre-Recent Triodon level of organization diversified

greatly, with well over a hundred species alive today, and

have become in many ways just as morphologically dif- ferent if not more so from triodontids as have molids, while retaining none of the few generalized characters shared by triodontids and molids, even though in general body form the tetraodontid-diodontid line is more

similar to that of Triodon (exclusive of the expansible dewlap) than is that of molids. The major ways in which tetraodontids and diodontids differ from Triodon, other than those previously mentioned that distinguish Triodon from all other gymnodonts, whether they be the generalized triacanthodidlike features of Triodon that are lost or the specialized

features of Triodon developed after the radiation of the other gymnodonts from a triodontid ancestral group,

are: 1) the loss of the basisphenoid; 2) the loss of the

fourth gill and of the gill slit between the fourth and fifth arches; 3) the loss of at least well-developed teeth on the

fifth ceratobranchial and on one of the three pharyngobranchials; 4) the loss of the pharyngobranchial of the

fourth arch; 5) the loss of gill rakers behind the anterior edge of the fourth arch; 6) the great expansion of the first branchiostegal ray into a horizontal pumping plate ar- ticulated to the medial surface of the ceratohyal; 7) the development of an inflatable diverticulum of the gut; 8) the suturing of the ceratohyal with the epihyal; 9) the

frequent loss of the interhyal and dorsal hypohyal; 10) the loss of at least most of the dorsal roof of the myo- dome and of the posterior opening into it; 11) the loss of

all, or all but one, of the supraneural elements; 12) the development in one of the two families of long rodlike dental units and of the frequent reduction in size or loss of the trituration plates or teeth; 13) the development of a more limited area of articulation of the palatine with

the cranium either at a notch and flange between the

palatine and ethmoid-vomerine region or by extensive

suturing between the palatine and frontal; 14) a reduction in the massiveness of the prefrontal and supracleithrum; 15) the usual better development of the

mesopterygcid (except absent in one species) and its firm

suturing to the metapterygoid as well as to the palatine; and 16) the development in three or more of the ab- dominal vertebrae of bifid neural spines, always in- cluding the first three abdominal vertebrae. Thus, even though Triodon is by far the most

generalized gymnodont and retains many primitive

features of its triacanthodid ancestry, the structure of the

only species of which we have knowledge other than jaw

fragments, the Recent Triodon macropterus, is too

specialized for an Eocene fish closely similar to it to have

been the ancestral line from which the molid and tetrao- dontid-diodontid lines radiated. This ancestral triodontid line had a more generalized organization than that of

T. macropterus, not yet possessing such specializations

as the small size and entirely orbital placement of the sphenotics allowing the frontals and exoccipitals to meet, and the elongation and tapering of the caudal peduncle and associated vertebral modifications. Nevertheless, an

early Eocene Triodon-like fish minus the specializations

as seen in the single Recent species is undoubtedly ancestral to the other two major subgroups of gymnodonts

and itself evolved from the eoplectin triacanthodids in the early Eocene.

Infraorder Tetraodontoideo

Comparative diagnosis (contrast with that of the Triodontoideo).—Spiny dorsal fin completely absent and no more than one supraneural element present; ribs and epipleurals absent; caudal fin with 11 or fewer principal rays and no procurrent rays; caudal fin varying from moderately forked to rounded; caudal skeleton with no more than one separate hypural, and no uroneurals and hypurapophysis; haemal spine of antipenultimate

vertebra fused to its centrum; neural and haemal spines

of penultimate vertebra various but not long rounded

shafts directly supporting caudal fin rays; caudal peduncle not distinctly tapered to narrow transversely in- dented regions above and below just in front of the caudal fin, the least depth of the peduncle being about 6% SL or greater, and the least width at this region al- ways less than the least depth; none of the caudal verte- brae with anterolateral processes above the centra; no

pelvis; no expansible dewlap of skin in front of the anus, but inflatability of the abdominal region present in all families except molids; cleithrum not elongate an

teriorly, reaching forward no further than about the level of the middle of the ceratohyal; basisphenoid either ab

sent or present as a large plate in the interorbital sep tum; myodome either absent or present only as a rudi ment of the dorsal roof represented by medial wings ol the prootics, the roof always highly incomplete; no chan

nel present between the apposed surfaces of the para

sphenoid and basioccipital; scapular foramen incomplete, closed anteriorly by the cleithrum; scapula without a distinct knob for articulation with the upper- most pectoral fin ray; three or four actinosts, if four pre- sent at least some sutured either to one another or to the
scapula or coracoid, the uppermost always sutured to the

scapula; urohyal absent; no more than three pharyngobranchials present; fifth ceratobranchial usually toothless, rarely with even a small patch of minute teeth; dentaries and premaxillaries totaling either two or four separate pieces; premaxillaries, if separate, articulated

to one another by prominent regular interlocking emarginations; sphenotic relatively large and not confined to the posterior wall of the orbit, but present on

both the lateral and dorsal surfaces of the skull as well;

first branchiostegal ray with its dorsal edge either not in- turned at all and articulated to the ventral edge of the

ceratohyal or greatly inturned into a huge plate and ar- ticulated to the medial surface of the ceratohyal; inter- operculum with a ventral flange and a long posterior

shaft extending well behind the ventral flange and level of the epihyal, except in molids in which the interoper- culum is a short to long simple slender rod without a ventral flange; pterotic not prominently prolonged posteroventrally as a stout shaft; epiotic placed more medially on the top of the skull, always in contact with the

supraoccipital; exoccipital never in contact with the

frontal; frontal never in contact posteriorly with the

pterotic in the rear of the orbit, separated from it by the

sphenotic, while in some tetraodontins posterolateral wings from the dorsal surface of the frontal make contact with the pterotic on the top of the rear of the skull; olfactory epithelium smooth, pitted or in parallel folds, never in a rosette, the olfactory sac either above the sur- face in a tube or tentacle with one or two nostrils, or at or below the surface and rudimentary.

SUPERFAMILY TETRAODONTOIDEA

Comparative diagnosis (contrast with that of the Moloidea). —Inflatable diverticulum of the gut present;

first branchiostegal ray with the dorsal edge inturned and enormously enlarged into a more or less horizontal pumping plate articulated to the medial surface of the

ceratohyal; air bladder well developed; three gills, not

greatly expanded dorsally; no gill slit between the gill- less fourth and fifth arches and no gill rakers along the

posterior edge of the fourth arch and the anterior edge of the fifth arch; no gill rakers along the anterior edge of the

first gill slit; pharyngobranchials with moderate to minute teeth, and one sometimes toothless, the three elements being those of the first to third arches (that of the third sometimes absent); ceratobranchial and epi- branchial sutured to one another; interhyal and dorsal hypohyal often absent; teeth in biting edge of jaws

retaining much of their individual identity; basi- sphenoid absent; caudal fin relatively normal, with 9 to

11 rays supported by variously consolidated and fused but normal vertebral elements; most dorsal, anal, caudal, and pectoral fin rays less extensively branched

but with a normal amount of cross-striations, these not

confined to only the distal ends of the rays; sesamoid ar- ticular usually present; postcleithrum without an anteriorly directed process; four actinosts; supracleithrum

less elongate, only its extreme proximal end articulated

directly to the pterotic; coracoid less long and slender, with a posterodorsal prong below the lower actinost al- ways developed to some degree; operculum and sub- operculum of much greater complexity of structure and

lateral surface area; interoperculum with a ventral flange and posterior shaftlike portion extending posteriorly well beyond the level of the epihyal; basioccipital not prolonged dorsally behind the exoccipitals, the exoccipitals bordering all but the bottom edge of the foramen magnum; exoccipitals with condyles and in contact with

the first vertebra, which articulates anteriorly with both

the basioccipital and exoccipitals; epiotic without any

kind of posterodorsal prolongation; pterotic not prolong- ed posteriorly, not reaching posteriorly to the level of the end of the basioccipital; bony canal, when present, for the nerves and blood vessels running from the orbit to the

nasal region nearly always incomplete, surrounded by

the prefrontal laterally, above and below, but not

medially; palatine receiving its main support dorsally

either by a complex interlocking with the vomer and eth- moid or by extensive suturing to the frontal; at least the

first three abdominal vertebrae with bifid neural spines

projecting dorsally or dorsolaterally on each side of the

neural arch; centra of at least some of the abdominal

vertebrae always with ventral or ventrolateral processes

of some sort, whether or not forming complete haemal

arches or zygapophyses; dorsal and anal fin rays not

widely separated from their basal pterygial supports by a

large block of cartilage; scales, when present, small to

large, the basal plates not forming a completely con- tinuous covering over the entire body, and some of the

scales always forming prominent prickles or spines; one

or two nostrils in a prominent upraised sac or tentacle, or a single minute nostril in a low tube; lateral line present, whether conspicuous or inconspicuous, but nearly al- ways clearly seen within 30 magnifications.
Family Tetraodontidae Comparative diagnosis (contrast with that of the Diodontidae). —Teeth incorporated into the matrix of the biting edge of the jaws as long slender rods; pre- maxillaries and dentaries not fused to their opposite members in the midline, the articulation strengthened by interlocking emarginations; lateral surface of maxillary neither deeply indented nor laterally flanged, the

surface relatively even; the jaws usually less massive;

small trituration teeth often present in the upper and,

less frequently, lower jaw as well, but seldom with a large

trituration plate in both jaws; first pharyngobranchial

with small or, usually, minute teeth, or sometimes toothless, but second and third pharyngobranchials with small

teeth; dorsal hypohyal often absent; interhyal sometimes present; anterior edge of ectopterygoid distinctly concave; ethmoid and vomer relatively well developed and sturdy, although sometimes at least partially fused

together; palatine with a notched region posterodorsally

for firm articulation with a crested region of the vomer

and/or ethmoid, and never making contact with the frontal; prefrontal usually well developed, absent only in two

closely related specialized genera, Xenopterus and

Chonerhinos; frontals less wide and massive, except in Xenopterus; anterior end of parasphenoid less wide and

less deeply concave, the concavity filled by the posterior articulating shaft of the vomer; rear margin of the orbit formed by the frontal and sphenotic; sphenotic often

laterally expanded anteriorly, but never as a long, slender lateral prong; frontal not in contact posteroventrally in the rear of the orbit with the prootic, separated from it by the sphenotic and pterosphenoid; suboper- culum without an anteriorly directed prong, and the in- teroperculum articulated posteriorly by a short ligament

to the anterior edge of the operculum; supracleithrum

usually positioned at about a 45° angle to the axis of the body, but with great variation between species on the degree of obliqueness to the body; postcleithrum in two

pieces, and much longer than the distance along the scapula to the lowest actinost; supraoccipital spine

laterally compressed and mainly in a vertical plane, al- though its dorsal edge may be thicker than the ventral

plate; exoccipital condyles well developed; at least the

first two vertebrae anterior to the first basal pterygio- phore of the dorsal fin without bifid neural spines, only

the first three to five abdominal vertebrae with bifid divergent neural spines; none of the vertebrae with prominent lateral flanges from the centra; neural spines

of the vertebrae supporting the basal pterygiophores of the dorsal fin relatively normal long slender shafts penetrating relatively deeply the interspaces between the

Figure 193.—Range of diversity in body form in the Recent Tetraodontidae:

A. Lagocephalus spadiceus,

B, Xenopterus naritua, C, AmblyrhynchoteB pioaae, D, Canthigaater rogtrata.

pterygiophores; a supraneural element often present; at

least some of the basal pterygiophores of the dorsal and

anal fins usually, but not always, interdigitated with one

another; one or more of the more posterior abdominal

vertebrae usually, but not always, with a complete haemal arch; none of the vertebrae posterior to the bases

of the last basal pterygiophores of the dorsal and anal

fins anteroposteriorly compressed, of about the same

centrum length as those more anteriorly; abdominal

vertebrae usually fewer in number than the caudal vertebrae, sometimes of equal number but never of greater number; dorsal and anal fins more anterior in position;

at least four vertebrae fully posterior to that whose hae- mal spine is the last support of the last anal fin basal

pterygiophore; caudal fin supporting skeleton with a free epural, one free uppermost hypural that in a few species may be partially fused to the centrum, a free parhypural and an autogenous haemal spine of the penultimate

vertebra; no prominent lateral flange present on the fus- ed hypural-centrum plate; haemal canal penetrating the

last vertebral complex to exit between the parhypural and fused hypural-centrum plate; caudal fin rays 11, the two lowermost rays unbranched; scales always relatively smaller, even when best developed, as in the moderate

quills of Torquigener piosae or the enlarged basal plates

of adult Ephippion guttifer. Comparative diagnoses of Subfamilies (Tetraodontinae and Canthigasterine). —Subfamily Tetraodontinae: ethmoid varying from long to short, and of a vari- ety of shapes, but never distinctly T-shaped in cross

section; supraoccipital with an only moderate to low

crest, usually arising from a flattened anterior region

of the bone from which it is prolonged posteriorly, the

posterior end of the crest not visible externally through

the skin; posterolateral region of frontal variously laterally expanded or not, but never as two flanges whose distal ends closely approach or are in contact with one another

to form a bony well around the muscle mass leading to the operculum; sphenotic a prominent component of the

dorsal surface of the skull, and usually extended anterodorsally at least a short distance forward of the rear edge

of the orbit; base of prefrontal always either in contact with or in very close proximity to the vomer; trituration teeth often present; one or two nostrils in a moderately

low to high sac or tube, or a single or bifid tentacle or

flap, but always conspicuous; lateral line conspicuous

(with the possible exception of the long-spined Tor- quigener piosae); gill opening usually extending ventrally below the level of the middle of the pectoral fin base; vertebrae modally 17 to 29; vertebral column

usually not highly arched anteriorly, the axis of the anterior portion of the column usually not especially oblique to that of the skull; haemal arches and spines

usually not especially well developed on most of the ab- dominal vertebrae. Subfamily Canthigasterinae: ethmoid long and T- shaped in cross section, its upper surface a laterally ex-
panded more or less flat plate of decreasing width anteriorly and its lower surface a similarly flat vertical plate of decreasing depth anteriorly; supraoccipital with

a high well-developed crest throughout most of its length, the dorsal edge of the posterior end of the crest of- ten indicated externally by a break in the contour of the

dorsal profile; posterolateral region of frontal prolonged

laterally as two flanges whose distal ends closely ap- proach or are in contact with one another to form a partial to complete bony well around the muscle mass

leading to the operculum; sphenotic mostly excluded

from the dorsal surface of the skull, mostly confined to the ventrolateral surface of the skull behind the orbit; base of prefrontal well removed from the vomer, broadly

separated from it by the ethmoid and parasphenoid;

trituration teeth never present; a single nostril on each

side, set in a very low inconspicuous tube; lateral line in- conspicuous, apparent only with magnification; gill opening restricted, extending ventrally no further than about the level of the middle of the pectoral fin base; vertebrae always modally 17; vertebral column highly arched anteriorly, the axis of the arched portion highly

oblique to that of the skull; haemal arches and spines es- pecially well developed on most of the abdominal verte- brae.

Detailed description of Lagocephalus laevigatus. Material examined—Three cleared and stained

specimens, 61.4-166 mm; one wet completely disarticulated specimen, approximately 290 mm, prepared by

maceration; one dry skeleton, approximately 290 mm.

Occipital Region.

Basioccipital. —A short column, slightly expanded

anteriorly; cartilage filled at its anterior and anterolateral edges; articulates by interdigitation anteriorly with the slightly overlying parasphenoid, anterolaterally with the prootic and laterally with the exoccipitals. The

anterodorsal end of the basioccipital reaches to and

forms the lower posterior wall of the vestigial myodome

(see description of the prootic). The rim of the round con- cave posterior end of the basioccipital articulates by fi- brous tissue with the rim of the concave anterior face of the centrum of the first vertebra. The posterodorsal sur- face of the basioccipital forms the ventral wall of the foramen magnum.

Exoccipital. —Cartilage filled at its anterior and

ventromedial edges; articulates by interdigitation ventromedially with the basioccipital, posterolaterally with

the pterotic, anterodorsally with the epiotic, and anteroventrally with the prootic. Dorsomedially the exoccipital forms the lateral wall of the foramen magnum,

while the dorsal wall of the foramen is formed by the

close fibrous tissue articulation of the extreme dorso- medial edges of the two exoccipitals. Ventrally the foramen magnum is closed not by medial projections of

Figure 194.—Lagocephalus laevigatus (above), with L. lunaris (center) and

L. scleratus (below) for comparison: in all three examples, upper left, nasal region as

seen externally (far left) and the olfactory lamellae as seen with the top of the nasal

sac removed (center), and the outline of an

anteroposterior cross section of the sac and

lamellae; center left, scales from upper

middle region of body, including, in L. lunaris and L. scleratus, the small scales associated with the lateral line.
the exoccipitals, but, rather, by the posterodorsal sur- face of the basioccipital. From the posterior end of its ventromedial edge the exoccipital possesses a modified

condyle in the form of a posteroventral process that ar- ticulates by fibrous tissue with the lateral surface of the neural arch and centrum of the first vertebra.

Supraoccipital. —A rounded plate anteriorly, but drawn out posteriorly into a long, laterally compressed

spine; cartilage filled along all of the edges of its rounded

anterior portion; articulates by interdigitation posterolaterally with the epiotics and anteriorly and anterolaterally with the frontals. Along the middle of its anterior end, as seen dorsally, the supraoccipital is broadly

overlain by the posteromedial edges of the frontals. The

supraoccipital spine is drawn out posteriorly between the

bifid neural spine of the first vertebra and sometimes

reaches posteriorly to above the second vertebra. The anterior half of the ventral edge of the supraoccipital spine

articulates by tough fibrous tissue with the dorsomedial

edges of the epiotics and exoccipitals.

Otic Region.

Pterotic. —Cartilage filled along its anteromedial

edge; articulates by interdigitation posteromedially with

the exoccipital, dorsomedially with the epiotic, anterodorsally and along the lateral part of its anteroventral edge with the sphenotic, and anteroventrally with the

prootic. At the anterodorsal edge of its most laterally ex- panded portion the pterotic articulates by fibrous tissue with the posterolaterally projecting arm of the frontal. Along the middle of its posterior surface the pterotic has

a concavity for articulation by fibrous tissue with the supracleithrum. In the middle of its ventral surface the

pterotic articulates by fibrous tissue with the hyomandibular.

Sphenotic. —Broadly cartilage filled at its medial

edge; articulates by interdigitation anterodorsally and

dorsomedially with the frontal, posteromedially on its dorsal surface with the epiotic, posterodorsally with the

pterotic, posteromedially on its ventral surface with the pterosphenoid, and anteroventrally with the frontal. Posteromedially on its ventral surface the sphenotic ar- ticulates with the hyomandibular by fibrous tissue.

Epiotic. —Flat, more or less rounded; broadly

cartilage filled along all of its edges of articulation with

the other cranial bones; articulates by interdigitation anteriorly with the frontals, anteromedially with the rounded anterior portion of the supraoccipital, anterolaterally with the sphenotic, posterolaterally with the pterotic, and posteromedially with the exoccipital. The medial

edges of the two epiotics articulate with one another and

with the ventral edge of the supraoccipital spine by fi- brous tissue.

teriorly; articulates by interdigitation anteroventrally with the dorsolateral wing of the parasphenoid, anterodorsally mostly with the sphenotic but also with the pterosphenoid, laterally with the sphenotic, posterolaterally with the pterotic, and anteromedially with the parasphenoid. From about the middle of its vertical anteromedial edge the prootic possesses a thin splint of bone projecting medially almost to the midline of the

skull, where it articulates by fibrous tissue with the

splintlike projection from the other prootic. These

delicate spines are evidently all that remains of the dorsal roofing of the myodome. The small myodome is now

roofed over only by a sheet of dense fibrous tissue which

begins anteriorly where it binds together the two medial

projections of the prootics and continues on posteroventrally to the floor of the cranial cavity, attaching posteriorly to the region where the parasphenoid and basioccipital interdigitate with the prootics. The myodome is thus enclosed dorsally mainly by a fibrous tissue sheet, and only at its upper anterior edge is the roof enclosed by

the medial projections of the prootics. Laterally the myodome is bordered by the medial surfaces of the

prootics, ventrally by the dorsal surface of the para- sphenoid, and posteriorly by the anterior end of the

basioccipital.

Orbital Region.

Frontal. —Laterally expanded in the middle of its length; with a long posterolaterally directed arm. The

bone is generally dense and hard, but along the approxi- mately anterior two-thirds of its medial portion a layer of spongy connective tissue is present between the medial

surfaces of the two frontals. This spongy connective tis- sue layer extends laterally into the frontal for about onefourth or one-fifth the width of the bone and anteriorly it becomes cartilaginous and continuous with the ethmoid

cartilage. The frontal articulates by interdigitation dor- somedially in the midline of the skull with its opposite member, anteriorly with the ethmoid, which it broadly

overlies, anterolaterally with the prefrontal, posterolaterally with the sphenotic, posteriorly on its dorsal sur- face with the epiotic, and posteromedially on its dorsal surface with the supraoccipital. From above the region where it articulates with the sphenotic, the frontal possesses a long posterolaterally directed process that ar- ticulates by fibrous tissue with the anterodorsal edge of the most laterally expanded portion of the pterotic. The

lateral fossa thus enclosed is bordered above by the frontal and below by the sphenotic and pterotic. On its ventral surface the frontal sends a ventromedially directed

process into the deeply concave dorsal surface of the vertical interorbital projection of the parasphenoid, with ex- tensive interdigitation occurring between the two bones. Just lateral to its ventromedial projection, the frontal is broadly overlain by the pterosphenoid, with slight inter- digitation occurring between the two surfaces.

Prootic. —Cartilage filled along all of its edges of articulation with the other cranial bones, except anPrefrontal. —In the form of a dorsolaterally ex- panded column; cartilage filled at its rounded ventral 267
edge; articulates by fibrous tissue ventrally with the

region of articulation between the vomer and para- sphenoid; articulates at its dorsal surface by interdigi- tation anteromedially with the ethmoid and postero- medially and posteriorly with the frontal. Along most of

its medial surface it is attached to the ethmoid cartilage, with which it is continuous.

Parasphenoid. —Elongate, with a well-developed

ventral keel in the suborbital region. The anterior end of the parasphenoid is deeply concave and into this concavity the shaftlike posterior end of the vomer interdigitates. The parasphenoid articulates laterally by fibrous

tissue with the base of the prefrontal in this region. Posteriorly the parasphenoid slightly overlies the anterior end of the basioccipital and strongly interdigitates with

it. About three-fourths the way back its length the para- sphenoid gives rise to its paired dorsolateral wings that

interdigitate with the anteromedial edges of the prootics. Posterior to this area of interdigitation with the antero- medial edges of the prootics, the lateral edges of the parasphenoid interdigitate with the ventromedial edges

of the prootics. In about the middle of its length the para- sphenoid gives rise to an interorbital projection into whose deeply concave dorsal surface the ventromedial

projections of the frontals interdigitate.

Pterosphenoid. —A thin plate; cartilage filled along

its dorsal edge; articulates by interdigitation posteroventrally with the prootic and posterolaterally with the

sphenotic. For most of its length the pterosphenoid overlies the posteromedial portion of the ventral surface of the frontal, and slightly interdigitates with it.

ncave anterior end of the parasphenoid. Along the dorsolateral surface of the vomer there is a laterally projecting bony shelf above and below which fits the deeply notched posterodorsal region of the palatine, the articulation being by fibrous tissue.

Mandibular Region. Hyomandibular. —Expanded dorsally, tapering to a

stout shaft anteroventrally; cartilage filled at its anteroventral and dorsal edges; articulates by fibrous tissue dorsolaterally with the sphenotic and pterotic and dorso- medially with the prootic and pterotic. Along the ventral

three-fourths of its posterior edge it articulates by fibrous

tissue with the preoperculum, while just above the dorsal end of the latter the hyomandibular supports the articular face of the operculum. Anteriorly the hyomandibular

articulates by fibrous tissue principally with the posterior region of the metapterygoid and symplectic. Quadrate. —Wide posteriorly, but tapering to a knob anteriorly for articulation with the articular in the

lower jaw; a short, posteriorly directed process present from its posteroventral edge; cartilage filled at its posterior edge; articulates by fibrous tissue anteriorly with

the articular, anterodorsally by interdigitation with the

slightly overlying ectopterygoid, dorsally by interdigi- tation with the broadly overlying mesopterygoid, and

ventrally by fibrous tissue with the preoperculum.

Posteriorly the quadrate articulates through cartilage with the metapterygoid and symplectic, the anterior part

of the latter being overlain by the short posterior process

of the quadrate.

Ethmoid Region. Ethmoid. —Large, more or less rectangular; articulates by interdigitation posterodorsally with the overly- ing frontals and posterolaterally with the prefrontals. Along the anterior half of its ventral surface the ethmoid

articulates with the vomer, the posterior part of this ar- ticular surface showing interdigitation, while more

anteriorly the two bones are completely fused. In small specimens (under approximately 100 mm) it can be seen

that the anterior edge of the ethmoid region is actually formed by the upturned anterior edge of the vomer, even though in large specimens no such distinction can be made. Anterolaterally the ethmoid articulates by fibrous

tissue with the palatine, although the main articulation

of the latter is with the vomer. In large specimens the ethmoid tends to become swollen and porous, or hyperostotic. Just behind its articulation with the vomer,

the posteroventral surface of the ethmoid is continuous

with the remains of the ethmoid cartilage. Vomer. —Broad anteriorly, but tapering to a stout

shaft posteriorly; articulates with the ethmoid by fusion anterodorsally but by interdigitation posterodorsally. The posterior shaft of the vomer interdigitates with the

Metapterygoid. —Broad anteriorly; cartilage filled at its anterior edge; articulates through cartilage anteriorly with the quadrate and ventrally with the

symplectic, the latter also slightly overlying and inter- digitating with the metapterygoid. The metapterygoid

articulates by fibrous tissue posteroventrally with the hyomandibular, preoperculum, and interhyal, while

anterodorsally it broadly overlies and slightly interdigi- tates with the mesopterygoid.

Symplectic. —Small, somewhat irregular in shape

from specimen to specimen; cartilage filled at its posterior edge; articulates through cartilage and slight inter- digitation anteriorly with the overlying process of the quadrate and dorsally with the metapterygoid; articulates by fibrous tissue posteroventrally with the preoper- culum and interhyal.

Palato-Pterygoid Region.

Palatine. —Expanded posteriorly; a deep, anteriorly directed cleft present in its upper posterior edge which fits tightly above and below the thin lateral shelf of the vomer, articulating with it by fibrous tissue. Anteroventrally the palatine interdigitates with the ec- topterygoid, while posteriorly it overlies and interdigi-
tates with the mesopterygoid. Anterodorsally the palatine is expanded laterally to form the articular facet for support of the maxillary through fibrous tissue.

Ectopterygoid. —Somewhat V-shaped, with the apex directed posteriorly; articulates by interdigitation dorsally with the palatine, posteriorly with the mesopterygoid, which it broadly overlies, and ventrally with the quadrate, which slightly overlies it.

Mesopterygoid. —Variable in shape, but usually

thin anteriorly and thickened at its posterior edge. It ap- pears to be relatively small as seen laterally, because it is overlain by each of the four bones with which it articulates by interdigitation; anterodorsally with the palatine, anteriorly with the ectopterygoid, anteroventrally with the quadrate, and posteroventrally with the

metapterygoid.

Opercular Region. Operculum. —Thin and expanded posteroventrally; a dorsally directed process from its dorsal surface present for muscle attachment; articulates by

fibrous tissue dorsally at its flattened articular surface with the upper posterior edge of the hyomandibular,

while ventrally it articulates with the deeply cleft region

of the suboperculum, which it slightly overlies. In about

the middle of its anterior edge the operculum articulates by a tough ligament with the rodlike interoperculum. Suboperculum. —Thin; deeply and broadly cleft in

its upper region; the portion of the bone anterior to the

cleft somewhat prolonged dorsally; articulates by fibrous

tissue along the edges of its cleft region with the slightly overlying operculum.

Interoperculum. —A long rod, with a small ventral

flange from about the middle of its ventral edge; articulates by strong ligaments posteriorly with the operculum

and anteriorly with the angular in the lower jaw. The

ventral flange articulates by fibrous tissue with the

lateral surface of the epihyal. Preoperculum. —Large; expanded posteroventrally; slightly convex laterally; the anterior half of its dorsal edge somewhat laterally expanded to present a broad

surface for fibrous tissue articulation with the ventral edge of the quadrate; articulates by fibrous tissue along

the posterior half of its dorsal edge with the quadrate,

symplectic, interhyal, and metapterygoid. Upper Jaw.

Premaxillary. —Posteromedial arm short; together with the fused teeth forms a massive crushing plate; its anterior edge forming the anterior border of the upper

jaw, except for a short distance ventrally where the maxillary forms the border. The premaxillaries articulate dorsomedially with one another by fibrous tissue, with

the articulation strengthened by a single row of a dozen

or more well-developed medial projections from the dor- somedial surface of each premaxillary. These projections alternate with one another and decrease in size anteriorly. The short posteromedial arm of the premaxillary articulates by fibrous tissue with the anteroventral

surface of the vomer. Posteriorly and laterally the premaxillary is firmly articulated by extensive interdigi- tation with the broadly overlying maxillary. The

premaxillary contains an internal cavity which communicates with the exterior through a small opening placed

just lateral to the posteromedial arm that articulates with the vomer. This cavity in the premaxillary contains

the dental pulp, which continually gives rise to the long,

thin, rodlike, highly modified teeth. These teeth lie parallel to the anterior edge of the premaxillary and are constantly being moved forward to replace those dental

lamellae worn down through use. There are usually 5 to 10 of these dental lamellae present in each premaxillary,

of which only the most anterior one or two are actually exposed at the edge of the jaw. However, the lamellae

posterior to them can be seen easily through the very thin portion of the premaxillary covering them, giving the impression that many more of the dental lamellae are ex- posed than is actually the case. On its ventral surface the premaxillary bears a variable number (two to six) of more or less anteroposteriorly compressed blunt teeth,

set in shallow sockets, in a longitudinal row just lateral to

its medial edge. These teeth, like the dental lamellae, are replaced from the posterior end of the series by the activity of the pulp tissue.

Maxillar>'. —Curved forward and slightly expanded

dorsally and ventrally; broadly overlies and firmly inter- digitates with the premaxillary along all of its length, ex- cept for a short distance ventrally where it is free of the premaxillary and forms the anterior border of the upper

jaw. Posterodorsally at a slight groove on its surface the

maxillary is supported through fibrous tissue by the

anterodorsal edge of the palatine. The ventromedial surface of the maxillary articulates by fibrous tissue with

the dorsolateral surface of the dentary.

Lower Jaw.

Dentary. —Somewhat squarish; articulates posteriorly by fibrous tissue and interdigitation with the articular, which it broadly overlies laterally but only slightly

overlies medially. Posteroventrally the dentary articulates by fibrous tissue, or in large specimens by inter- digitation, with the angular. The dorsolateral surface of the dentary articulates by fibrous tissue with the ventro- medial surface of the maxillary. The dentary is hollow in- ternally, although not as extensively so as the premaxillary. The cavity contains the dental lamellae producing

pulp material, which functions in the same way as de- scribed for the premaxillary. The pulp cavity opens to the exterior at the region of articulation of the anterior end of the articular with the dentary. Only long, thin, rodlike, dental lamellae are produced, there being no
stubby trituration teeth as there are on the ventral sur- face of the premaxillary. Ventromedially the dentary ar- ticulates by fibrous tissue with its opposite member, with about 15 stubby projections strengthening the articulation, as in the case of the premaxillary.

Articular. —More or less triangular in shape, with

the apex pointing anteriorly into the hollowed out posterior part of the dentary; cartilage filled at its anterior edge where it is continuous with the remains of Meckel's

cartilage; articulates by fibrous tissue and interdigi- tation anteriorly with the dentary, posteriorly by fibrous

tissue at a groove on its surface with the knoblike

anterior end of the quadrate, posteroventrally by fibrous

tissue, and interdigitation in large specimens, with the

angular. The sesamoid articular is a rod of bone lying alongside the anteromedial surface of the articular just posterior to the region where the latter interdigitates with the dentary.

Angular. —Small; articulates by fibrous tissue with

the dentary and articular, or in large specimens by inter- digitation with both of these bones. Posteriorly the angular makes ligamentous connection with the anterior end

of the interoperculum. BRANCHIAL APPARATUS.

Hyoid Arch and Branchiostegal Rays. Hypohyals. —Both hypohyal elements present but

not large, the dorsal hypohyal being particulfirly small;

dorsal hypohyal cartilage filled at its ventral edge and

ventral hypohyal cartilage filed at its posterior edge. The

hypohyals articulate through cartilage with one another and with the ceratohyal, while they articulate by fibrous

tissue anteromedially with their opposite members.

Ceratohyal. —Elongate, somewhat expanded posteriorly; cartilage filled at its anterior and posterior edges; articulates through cartilage anteriorly with the hypohyals and through cartilage and interdigitation posterodorsally with the epihyal. Of the six branchiostegal rays, only five usually articulate by direct contact through fibrous tissue with the ceratohyal.

Epihyal. —Rounded posteriorly; cartilage filled at

its anterior edge; articulates anteriorly through cartilage and interdigitation with the ceratohyal and by fibrous

tissue posterodorsally with the interhyal and laterally with the ventral flange of the interoperculum.

Interhyal. —Short and columnar; cartilage filled at

its dorsal and ventral edges; articulates by fibrous tissue ventrally with the epihyal and dorsally with the fibrous

tissue sheet between the symplectic, metapterygoid, and

preoperculum.

Branchiostegal rays. —Six in number; the first branchiostegal ray a large, relatively flat horizontal plate

with a down-turned lateral edge which anteriorly be- comes a thick vertical flange for articulation by fibrous

tissue with a vertical groove in the middle of the medial

surface of the ceratohyal. The second branchiostegal ray

is the longest of the six elements and it is a normal unex- panded shaft articulating by fibrous tissue with the ventral edge of the ceratohyal just posterior to the region of

articulation of the first branchiostegal ray. The third, fourth, and fifth branchiostegal rays are also normal in shape, increasing slightly in length from the third to fifth and articulating by fibrous tissue with the lateral sur- face of the posteroventral region of the ceratohyal. The

sixth branchiostegal ray is sometimes broad posteriorly, but always tapers to a narrow shaft anteriorly where it articulates by fibrous tissue with the dorsal edge of the

fifth branchiostegal ray, rather than with the ceratohyal.

Branchial Arches. —All the elements are cartilage

filled at their edges of articulation with the other ele- ments of the series, and the articulations are usually mediated through cartilage and fibrous tissue. The branchial arches are composed of three basibranchials, three

pairs of hypobranchials, five pairs of ceratobranchials,

four pairs of epibranchials, and three pairs of pharyngobranchials. Three gills are present; the fourth arch possesses no gill and there is no slit between it and the lower pharyngeal.

First arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basi- branchial elongate and rodlike; displaced forward so that

it articulates posteriorly with the second basibranchial and posterolaterally with the first hypobranchials. First hypobranchial slightly expanded dorsally; the largest of the hypobranchial elements, which decrease in size posteriorly in the series; articulates ventrally with the re- gion of articulation of the first basibranchial with the second basibranchial and dorsally with the first cera- tobranchial. First ceratobranchial the shortest of the

ceratobranchial elements, which, except for the fifth ceratobranchial, increase in size posteriorly in the series; possesses a ventrally directed flange along most of its ventral surface, this flange on the succeeding cera- tobranchials decreases in size posteriorly until it is al- most absent on the last ceratobranchial; articulates dorsally with the first epibranchial. First epibranchial a nar- row rod; the shortest of the epibranchial elements, which

increase in length posteriorly in the series; articulates dorsally with the first pharyngobranchial. First pharyngobranchial (suspensory pharyngeal) a rounded plate with a short ventral process for articulation with the first epibranchial; toothless; placed in line with the two tooth bearing pharyngobranchials rather than being oriented toward, and having its distal end attached by fibrous

tissue to, the ventral surface of the skull. The dorsal re- gions of the branchial arches are held to the ventral sur- faces of the parasphenoid and prootics by fibrous tissue attaching to the dorsolateral surfaces of the epibranchials and pharyngobranchials.
Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial short, but much expanded laterally both

anteriorly and posteriorly; articulates anteriorly with the

first basibranchial, posteriorly with the third basi- branchial, anterolaterally with the first hypobranchials, and posterolaterally with the second hypobranchials. Second hypobranchial a short rod; articulates ventrally with the posterolateral surface of the second basi- branchial and dorsally with the second ceratobranchial, which in turn articulates dorsally with the second

epibranchial. Second epibranchial a slender rod; articulates dorsally with the ventral arm of the second

pharyngobranchial. Second pharyngobranchial roughly L-shaped; bearing a single row of 12 to 17 well-de- veloped teeth, which are relatively sharp pointed and

curved slightly posteriorly, along the larger of the two

wings of the L. The toothless ventral wing articulates principally with the second epibranchial, but also, to a

lesser extent, with the third epibranchial. The teeth are

set in shallow sockets and are replaced by new teeth de- veloping in sockets just anterior to and below the bases of the old teeth. The second pharyngobranchial is held to the other two pharyngobranchial elements by fibrous tisThird arch. —Basi-, hypo-, cerato-, epi-, and pharyngobranchial elements present. Third basibranchial

like second basibranchial, but larger; articulates

anteriorly with the second basibranchial, posteriorly with the fourth ceratobranchials and posterolaterally with the third hypobranchials. Third hypobranchial with an anteroventral process that articulates by fibrous

tissue with the ventral surface of the first basibranchial;

posteriorly it articulates with the posterolateral surface

of the third basibranchial and with the ventral edge of the third ceratobranchial. Third ceratobranchial articu- lated ventrally with the third hypobranchial and dorsally with the third epibranchial. Third epibranchial a stout

rod, with a stubby projection from its posterolateral sur- face articulating by fibrous tissue with a similar process from the fourth epibranchial; articulates dorsally with

the second and third pharyngobranchials. Third pharyngobranchial roughly L-shaped, with the larger of the two arms bearing about 10 to 12 teeth in a single row; teeth

similar to those of the second pharyngobranchial and

replaced in a similar manner; articulates by the smaller

of its two arms ventrally with the third and fourth

epibranchials.

Fourth arch. —Cerato- and epibranchial elements

only. Fourth ceratobranchial the longest of the cerato- branchial elements; articulates ventrally with the third basibranchial and dorsally with the fourth epibranchial. Fourth epibranchial an elongate rod, the longest of the

epibranchial elements; possesses a stubby projection from its anterolateral edge which articulates through

fibrous tissue with the similar process on the third epibranchial; articulates dorsally with the third pharyngobranchial.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial a stout rod, slightly expanded medially in about the first one-third of its length; toothless; articulates ventrally with the base of the fourth ceratobranchial.

PAIRED FIN GIRDLES.

Pectoral Fin.

Supracleithrum. —In position at about a 45° angle

to the axis of the body; a stout shaft with a lateral flange along most of its length; articulates by fibrous tissue dorsally with a slight concavity on the posterior surface of

the pterotic and ventrally with the cleithrum, which it overlies. Cleithrum. —Laterally expanded along most of its length; articulates by fibrous tissue dorsally with the

overlying supracleithrum and with the dorsal post- cleithrum, which it overlies. Along its posterior surface it articulates by fibrous tissue with the scapula and coracoid. Ventromedially the cleithrum articulates by tough

fibrous tissue with its opposite member in the midline of the body between the medial edges of the horizontal

platelike portions of the first branchiostegal rays.

Postcleithra. —The postcleithra form a long strut, widened posteriorly, along the abdominal wall musculature from the supracleithrum to about halfway back the

length of the abdominal cavity. The dorsal postcleithrum

articulates by fibrous tissue anterolaterally with the

overlying cleithrum and posterolaterally with the ventral postcleithrum, which is much deeper and more laterally compressed than the dorsal postcleithrum.

Coracoid. —Rounded dorsally, but tapering to a point anteroventrally; a posterodorsally directed spinelike process present from its posteroventral edge; carti- lage filled at its dorsal edge; articulates anteriorly by

fibrous tissue with the cleithrum and dorsally through

cartilage with the scapula and the second to fourth actinosts.

Scapula. —Scapular foramen not entirely enclosed by the scapula, but, rather, with its anterior edge closed by the cleithrum; cartilage filled at its dorsal, ventral, and anterior edges; articulates by fibrous tissue anteriorly with the cleithrum, posteriorly by slight interdigi- tation dorsally with the small first actinost and ventrally with the base of the second actinost, and through carti- lage ventrally with the coracoid.

Actinosts. —Four elements; all cartilage filled at both ends, except for the first, which is only cartilage fill- ed at its dorsal edge. The first actinost is reduced to a

small wedge between the upper regions of the scapula and the second actinost, articulating with the former by

interdigitation and with the latter through cartilage. The

second and third actinosts are constricted in the middle, 271
with the third being slightly larger than the second. The

fourth actinost is only concave on the side toward the

third actinost. The actinosts articulate with one another

dorsally through cartilage and ventrally, except for the small first actinost, with one another by slight interdigi- tation. The second actinost interdigitates anteroventrally with the base of the scapula, while the second

to fourth actinosts articulate ventrally through cartilage with the coracoid. Distally the actinosts support all of the fin rays, except for the small first fin ray, which ar- ticulates with the scapula.

Fin rays. —Usually 17 to 19 fin rays present; the

first ray small, its medial half thicker than its lateral

half; first ray articulated with the scapula, but the other

rays articulated to the actinosts. The first two rays and

last ray unbranched, the other rays branched. First ray without cross-striations, the other rays cross-striated.

VERTEBRAL COLUMN. —All vertebrae with bicon- cave centra, except the last, which ends posteriorly in the modified urostyle and fusion with some of the hypurals. Abdominal Vertebrae.

First vertebra. —Neural spine befid and relatively

short; neural arch with a complete bony roof over the neural canal, as do all the other vertebrae; articulates by

fibrous tissue laterally at a shallow but broad concavity

over the upper anterior half of its centrum with the

posteroventrally projecting spinelike exoccipital condyles. Along the lizn of its concave anterior end the centrum articulates by fibrous tissue with the rim of the round posterior end of the basioccipital. The first vertebra articulates by fibrous tissue poaterodorsally at a

shallow concavity on its lateral surface with the neural prezygapophysis of the second vertebra, while

posteroventrally from its lateral edge it sends a large process posteriorly to fit under a shallow groove on the

anterior half of the ventrolateral surface of the centrum

of the second vertebra. Other abdominal vertebrae. —In 12 specimens, the abdominal vertebrae numbered eight. The second and

third abdominal vertebrae have bifid neural spines very

similar to that of the first vertebra. The fourth abdominal vertebra, however, has the neural spine bifid anteriorly but single posteriorly. All the vertebrae, both abdominal and caudal, posterior to the fourth abdominal

vertebra have undivided neural spines. The neural spines

of the fifth to eighth abdominal vertebrae become in- creasingly thiimer and longer. From the second to eighth abdominal vertebrae the neural and haemal prezy- gapophyses gradually become larger, but the haemal

postzygapophyses remain about the same size so that each of the last few abdominal vertebrae articulates ventrally by the apposition of its posteroventrally projecting haemal postzygapophyses with the anteroventrally projecting haemal prezygapophyses of the vertebra posterior to it. No haemal arches or spines are present. The

neural spine of the seventh abdominal vertebra articulates by fibrous tissue along its posterior edge with the

first basal pterygiophore of the dorsal fin, while the neural spine of the eighth abdominal vertebra articulates between the first and second basal pterygiophores

of the dorsal fin.

Caudal Vertebrae. —In 12 specimens, the caudal

vertebrae numbered 11 in 10 specimens and 10 in 2 speci- mens. All the caudal vertebrae, and only the caudal

vertebrae, possess haemal arches, while only those verte- brae just below and posterior to the last basal pterygio- phore of the anal fin possess large haemal spines. The

haemal arches of the first four caudal vertebrae (those without conspicuous haemal spines) are modified for ar- ticulation by fibrous tissue with the dorsal ends of the

basal pterygiophores of the anal fin. From the haemal

prezygapophyses of each of these vertebrae there is one

projection directed anteriorly and another directed pos- teromedially. The anterior projections from the haemal

prezygapophyses on each side of the vertebra do not meet

in the midline under the centrum, while the postero- medial projections from each side do meet and fuse in the midline under the centrum at the open area between the

anterior projections from the haemal prezygapophyses of the vertebra behind it. Thus, the posteromedial projections from the haemal prezygapophyses form the haemal

arch, which is here displaced posterodorsally from the

position it would more normally assume. The anterior projections from the haemal prezygapophyses are much

shorter than the posteromedial projections, except in the

case of the first caudal vertebra, in which the anterior

projection is much enlarged and somewhat ventrally di- rected for support along its ventral surface of the dorsal end of the enlarged first basal pterygiophore of the anal

fin. The anterior projections from the haemal prezyga- pophyses of the second and third caudal vertebrae support through fibrous tissue, respectively, the second and

third anal fin basal pterygiophores. The fourth caudal

vertebra supports the fourth and fifth anal fin basal pterygiophores from, respectively, its anterior haemal

prezygapophyseal projections and from its haemal arch. The fifth caudal vertebra supports the sixth anal fin basal pterygiophore from its haemal arch. The fifth caudal vertebra, in all but one of the study and radio- graphed specimens, possesses a haemal spine. The pos- teromedial projections of the haemal prezygapophyses of the fifth caudal vertebra not only fuse to each other in the midline, but also fuse to the ventrolateral edges of the centrum, leaving open a medial canal beneath the centrum and enclosing a large foramen laterally. From

the area of fusion with the centrum, a long haemal spine

is given off ventrally from the fifth caudal vertebra to support by fibrous tissue the last anal fin basal pterygio- phore. The haemal apparatus of the sixth to ninth verte- brae is similar to that of the fifth vertebra in that the haemal arch fuses posterolaterally to the centrum and

completely encloses the haemal canal, except laterally at the foramen. The haemal spines of the sixth and seventh
caudal vertebrae are the largest of those of the caudal

vertebrae. In large specimens (over 200 mm) these two haemal spines become enlarged and swollen, taking on

the hyperostotic consistency that is also characteristic of the ethmoid in large specimens. The haemal structures

of the last two vertebrae are autogenous. The neural spines of the first five caudal vertebrae are slender rods which support most of the basal pterygio- phores of the dorsal fin. They arise from the posterodorsal surface of the neural arches at the region of the neural postzygapophyses. The neural spine of the first caudal

vertebra is placed between the third and fourth basal pterygiophores and that of the fourth caudal vertebra behind the ninth and last basal pterygiophore. The

neural spine of the fifth caudal vertebra is larger than

those of the caudal series anterior to it, but it is rela- tively small in comparison to the neural spine of the sixth caudal vertebra. Posterior to the sixth caudal vertebra

the neural spines become progressively smaller. It is of

interest to note that whereas the haemal spines of the

sixth and seventh caudal vertebrae are swollen and

spongy in the two largest study specimens, the neural

spines of these same vertebrae are normal thin hard

plates.

Caudal Skeleton. —The supporting structure of the caudal fin appears to be a single large block of bone, square in its lateral outline, but it is a compound struc- ture formed of four separate bony elements firmly inter- digitated with one another. The ventral portion of the caudal skeleton is formed by the parhypural. A slight concavity is present in about the middle of its dorsal sur- face just below a similar concavity on the ventral surface

of the bony element that lies above it, which is the fused centrum-lower hypurals. The parhypural and the fused centrum-lower hypurals are extensively interdigitated with each other, except in the region where the concavities occur in their apposed surfaces so that a foramen is enclosed between them. This foramen is the last opening

into the haemal canal, the latter being connected to the

canal in the preceding vertebrae by a small longitudinal groove along the articular surface between the

parhypural and the centrum-lower hypural element

anterior to the foramen. Anteriorly the parhypural is laterally expanded to form haemal prezygapophyses. The epural is much like the parhypural in shape, but it is shorter and only forms the dorsal margin of the anterior two-thirds of the caudal skeleton. Along most of its ventral surface it firmly interdigitates with the centrum but

posteriorly it interdigitates with the autogenous upper

hypural plate. Concavities exist on the ventral and dorsal

surfaces, respectively, of the epural and centrum so that

a foramen is enclosed by the otherwise apposed surfaces

of the two bones. A deep longitudinal groove is present along the ventral surface of the epural and the dorsal sur- face of the centrum which permits the neural canal to be

present in the midline of the otherwise interdigitated sur- faces of these two elements. The neural canal opens

anteriorly into the neural canal of the preceding vertebrae, while posteriorly it opens to the exterior between

the posterior end of the epural and the dorsal surface of the autogenous upper hypural plate. The anterior end of the epural is expanded laterally to form the neural prezygapophyses. The fused centrum-lower hypurals form the largest bone of the caudal skeleton, its anterior portion corresponding to the last vertebral centrum and

abbreviated urostyle, and its posterior portion corres- ponding to what in generalized plectognaths would be

the first and second hypurals. The anterior portion inter- digitates dorsally with the epural, posterodorsally with

the upper hypural plate and ventrally with the

parhypural. The posterodorsal region of the anterior portion, which represents the urostyle, is extensively inter- digitated with the anteroventral edge of the upper

hypural plate. The posteroventrally expanded portion

representing the lower hypurals articulates by interdigi- tation dorsally with the upper hypural plate and ventrally with the parhypural. There is a short concavity, or blindly ending tube, proceeding posteriorly and slightly dorsally into the lower hypural region from the area of the haemal foramen between the centrum and parhypural. This tube probably encloses the end of the haemal

canal. The lower hypural region supports the lower six caudal fin rays, with the support of the lowermost ray shared with the parhypural. The autogenous upper

hypural plate forms the posterodorsal region of the caudal skeleton and represents what in generalized plec- tognaths would be the third to fifth (or, in Triodon, third and fourth) hypurals. It interdigitates strongly with the centrum-lower hypural plate and with the posterior end

of the epural. The upper hypural plate supports the upper five caudal fin rays.

Caudal fin rays. —Eleven in number, the upper- most ray and lowermost two rays unbranched, the inter- vening rays becoming increasingly branched toward the middle rays, which are branched in at least triple dichotomies. The upper five rays articulate by fibrous tissue at

their bifid bases to the upper hypural plate and the lower

six rays mainly to the lower hypural region, as described

above.

DORSAL AND ANAL FINS.

Fin rays and pterygiophores.—Fi/tecn fin rays pres- ent in most specimens, the first two rays and the last one

or two rays unbranched, the others branched in single or double dichotomies. The first ray is small and rudimentary, barely protruding to the surface, formed of two

separate halves and without cross-striations, while all the other rays are cross-striated. Distal pterygiophores

are either absent or unossified. The fin rays are supported below by nine basal pterygiophores which are strongly interdigitated with one another dorsally. The in- temeural processes of these pterygiophores are large anteriorly in the series but decrease in size posteriorly. The first and second basal pterygiophores are placed well
in advance of the base of the dorsal fin. The intemeural

process of the first basal pterygiophore lies between the neural spines of the seventh and eighth abdominal verte- brae and those of the last two basal pterygiophores between those of the third and fourth caudal vertebrae. On the upper end of each of the basal pterygiophores

there is a short columnar projection whose deeply con- cave surface is cartilage filled, except for the last pterygiophore, which has two of these facets with which

the fin rays articulate by fibrous tissue. The pterygio- phores are also cartilage filled at their ventral edges. From its anterodorsal edge the first basal pterygiophore has an anteriorly directed process, lying in the midline of the body just beneath the skin, which reaches to about

the level of the tip of the neural spine of the sixth ab- dominal vertebra. At its anterior end it is attached by

fibrous tissue to a rodlike supraneural. The supraneural

lies just below the skin in the midline of the body from

the level of the tip of the neural spine of the sixth ab- dominal vertebra to about the region above the fourth abdominal vertebra. The supraneural is surrounded by a

longtitudinal band of muscles which lies between the dorsomedial edges of the general epaxial muscle masses. This longtitudinal band of muscles continues anteriorly and partially fills the space between the bifid neural

spines of the first three abdominal vertebrae and ends by

connecting firmly with the supraoccipital spine. The

ninth, or last, basal pterygiophore has a posteriorly di- rected spine from its posterodorsal edge that ends over

the neural spine of the fifth caudal vertebra. The fact that the ninth basal pterygiophore bears two columnar

articular facets may indicate that it is a fusion product of two originally separate basal pterygial elements. None of the basal pterygiophores possess lateral projections along

its length for muscle attachment.

the sixth basal pterygiophore, which usually has three of them. From these columnar facets the fin rays articulate by fibrous tissue. The pterygiophores are also cartilage

filled at their dorsal ends. As is the case with the last basal pterygiophore of the dorsal fin, the presence of more than one columnar articular process may indicate that the first and the last anal fin basal pterygiophores

are the fusion products of two or more originally separate elements. The sixth basal pterygiophore bears from

its posteroventral edge a posterior projection that ex- tends back under the haemal spine of the sixth caudal

vertebra. None of the pterygiophores possess lateral pro- jections along their lengths for muscle attachment.

Detailed description of Canthigaster rostrata. Material examined. —Five cleared and stained speci- mens, 10.0-59.6 mm, and one dry, partially disarticu- lated skeleton, approximately 96.5 mm.

SKULL.

Occipital Region.

Basioccipital. —A long column, laterally expanded

anteriorly; cartilage filled at its anterior and posterolateral edges; articulates anteriorly by interdigitation with the slightly overlying parasphenoid, anterolaterally with the prootics, and laterally with the exoccipitals. The

posterior concave end of the basioccipital is somewhat

depressed, its rim articulating by fibrous tissue with the rim of the anterior concave face of the first vertebra. The

dorsal edge of the basioccipital forms the ventral wall of the foramen magnum.

Anal Fin.

Fin rays and pterygiophores. —Fourteen fin rays present in most specimens, the first two rays and the last one or two rays unbranched, the others branched in single or double dichotomies. The first ray is small and

rudimentary, like that of the dorsal fin. Distal pterygio- phores are either absent or unossified. The fin rays are supported below by six basal pterygiophores which are strongly interdigitated with one another ventrally. The

"interhaemal" processes of these pterygiophores are

large anteriorly in the series but decrease in size posteriorly, with the first basal pterygiophore being by far the largest of the series. The first, second, third, and

fourth basal pterygiophores articulate by fibrous tissue dorsally with the haemal prezygapophyses of, respectively, the first, second, third, and fourth caudal vertebrae. The fifth and sixth basal pterygiophores articulate similarly with about the middle of the haemal arches of, respectively, the fourth and fifth caudal vertebrae. On

the ventral surface of each pterygiophore there is a short columnar projection whose ventral edge is deeply con- cave and cartilage filled, except for the first basal

pterygiophore, which has two of these projections, and

Exoccipital. —Cartilage filled at its anterior and

ventromedial edges; articulates by interdigitation ventromedially with the basioccipital, ventrolaterally with

the pterotic, anterodorsally with the epiotic, and dorso- medially with the supraoccipital. At the extreme posterior end of its dorsomedial edge the exoccipital inter- digitates with its opposite member to form the dorsal

wall of the foramen magnum, while the posteromedial

edges of the exoccipitals form the lateral walls of that foramen. From its posteroventral edge the exoccipital condyle projects posteriorly well past the posterior end of the basioccipital and articulates by fibrous tissue over

the lateral surface of the anterior half of the centrum of the first vertebra.

Supraoccipital. —Flattened anteriorly, but drawn

out into a deep laterally compressed spine posteriorly; cartilage filled along its anterior edge; articulates by in- terdigitation anteriorly with the frontals, which somewhat overlie it, laterally with the epiotics and posterolaterally with the exoccipitals. The posterior edge of

the supraoccipital spine is slightly expanded laterally, particularly in the dorsal region. The spine does not project posteriorly far beyond the end of the skull.
Otic Region.

Pterotic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates by

interdigitation anterodorsally with the sphenotic, dorso- medially with the epiotic, ventromedially with the exoccipital, and anteroventrally with the prootic and

sphenotic. Placed transversely along the middle of its ventral surface, the pterotic possesses a low ventrally di- rected flange for muscle attachment. Anterior to this ventral flange the pterotic has a slight concavity on its surface for articulation by fibrous tissue with the posterior half of the dorsal edge of the hyomandibular.

Sphenotic. —Cartilage filled at its medial edge; ar- ticulates by interdigitation anterodorsally with the

frontal, anteromedially with the pterosphenoid, ventro- medially with the prootic, posteroventrally and posterodorsally with the pterotic, and posteromedially on its dorsal surface with the epiotic. On its ventral surface the medial edge of the sphenotic articulates with the anterior end of the dorsal edge of the hyomandibular by fibrous

tissue.

Epiotic. —Somewhat expanded laterally; cartilage

filled along all of its edges of articulation with the other

cranial bones; articulates by interdigitation anteriorly with the frontal, anterolaterally with the sphenotic,

laterally with the pterotic, posteriorly with the exoccipital, and medially with the supraoccipital.
Figure l%.—Lagocephalus laevigatua:

lateral view of head, composite based on several specimens,

61.4-166 mm SL, Gulf of Meitico.

^-^r

W

Figure \97 .—Lagocephaliu laevigaliu: dorsal

(left) and ventral (right) views of skull, with in at top right showing a ventral view detail of

the articulation of the upper jaw with the

palatines and vomer, composite based on several

61.4-166 mm SL, Gulf of Mexico. 276
Fipire \9S.—Lagocephalus laevigatua:

posterior view of skull (left); above,

lateral and posterior views of first abdominal vertebra; posterior view of

orbit (right) (cross section of skull; dashed lines represent cut surfaces of

frontals, pterosphenoids, and parasphenoid); composite based on several

61.4-166 mm SL, Gulf of Mexic

Prootic. —Cartilage filled along all of its edges of articulation with the other cranial bones, except

anteriorly; articulates by interdigitation anteroventrally with the dorsolateral wing of the parasphenoid, anterodorsally with the pterosphenoid and sphenotic, ventrolaterally with the sphenotic, ventromedially with the parasphenoid, and posteromedially on its ventral sur- face with the basioccipital. The more or less vertical an- teromedial edge of the prootic possesses a slight medial

protuberance which probably marks the former dorsal

limit of the now absent bony myodome and corresponds

to the medially directed prongs representing the rudi- ments of the bony dorsal roof of the myodome in such

tetraodontids as Lagocephalus laevigatas. The functional myodome is roofed over by a fibrous tissue sheet between the two prootics and the region of articulation between the parasphenoid and basioccipital. The functional myodome is thus bounded dorsally by a fibrous

tissue sheet, laterally by the prootics, ventrally by the

dorsal surface of the parasphenoid, and posteriorly by

the anterior end of the basioccipital.

Orbital Region.

Frontal. —Thin throughout most of its length, ex- cept posterolaterally; articulates by slight interdigi- tation dorsomedially with its opposite member, while its ventromedial edge makes fibrous tissue contact with the

cartilaginous rod which is continuous anteriorly with the ethmoid cartilage; articulates by slight interdigitation

anteriorly with the ethmoid, which it slightly overlies, anterolaterally with the prefrontals, which it broadly

overlies, posteromedially with the supraoccipital, which

it slightly overlies, posteriorly with the epiotic, and posterolaterally with the sphenotic. In the posterior wall of the orbit the frontal articulates laterally with the sphenotic and medially with the pterosphenoid. The most dis- tinctive feature of the frontal concerns the shape of its laterally expanded posterior portion. Just behind the

region that forms the posterolateral wall of the orbit, the

dorsal surface of the frontal possesses a thin laterally di- rected flange. This flange makes contact with the ex- treme posterolateral edge of the frontal, just above the

area of articulation between the frontal and sphenotic. In small specimens the articulation between the flange of the frontal and the posterolateral edge of the portion of the orbital wall formed by the frontal is by close apposition through fibrous tissue, but in larger specimens these two surfaces of the frontal tend to fuse together. The

space between the lateral flange and the posterolateral region of the orbital wall is filled with a muscle mass

which connects ventrally with the uppermost end of the operculum (see Winterbottom 1974).

Prefrontal. —Thin and more or less flattened

dorsally, but tapering to a stout column anteroventrally;

cartilage filled at its ventromedial edge, where it is con- tinuous with the ethmoid cartilage; articulates by slight interdigitation posterodorsally with the frontal, anterodorsally with the ethmoid, and anteroventrally with the parasphenoid.

Parasphenoid. —Elongate, with a well-developed

ventral keel in the suborbital region. The anterior end of the parasphenoid is concave and receives the posterior end of the vomer, with which it interdigitates. The dorsal edge of the parasphenoid anterior to the orbit is slightly concave and interdigitates with the posterior half of the

ventral edge of the ethmoid, while just posterior to this region it interdigitates with the base of the prefrontal. The flattened, somewhat laterally expanded, posterior end of the parasphenoid slightly overlies and interdigi-
ceratobranchials

epibranchials

Figure l99.—Lagocephalus taevigatut: dorsal view of branchial arches (extended on lower side); lateral (above) and medial (below, upside down)

views of hyoid arch; composite based on several specimeiu, 61.4-166 mm SL, Gulf of Mexico. — basibranchials

1st branchiostegal rays

epihyal

Figure 200.—Lagocephalns laevigatus: lateral view of pectoral girdle, composite based on

several specimens, 61.4-166 mm SL, Gulf of Mexico.
caudal vertebrae

Figure 201.—Lagocephalus laevigatas: lateral view of caudal Rn supporting structures, composite based on

several specimens, 61.4-166 mm SL, Gulf of Mexico.

Figure 202.—Canthigaater roatrata (A, above), with C. valentini (B) and two renditions

of C. amboinensia (C): the lower showing

the course of the lateral line canals and their major pores as decifered by

placing drops of ink on each pore found by microscopic search of a partially drying specimen; in front of the top three figures, nasal

region as seen externally (above) and scales from upper middle

region of body.
tales with the anterior end of the basioccipital, while just anterior to this region the parasphenoid interdigitates with the ventromedial edges of the prootics. About three- fourths the way back its length the parasphenoid gives

rise to its dorsolateral wings which interdigitate with the anteromedial edges of the prootics.

Pterosphenoid. —A small, thin plate; cartilage

filled at its dorsal and lateral edges; articulates by slight interdigitation dorsally with the frontal, laterally with

the sphenotic and ventrally with the prootic. Ethmoid Region. Ethmoid. —More or less T-shaped in cross section;

its dorsal surface laterally expanded, increasingly so posteriorly, while its ventral surface is drawn out into a thin medial flange in the posterior two-thirds of its length; ar- ticulates by slight interdigitation pwsteriorly with the

frontals and prefrontals, posteroventrally with the some- what overlying parasphenoid and anteroventrally with

the vomer. Vomer. —Thin and laterally compressed posteriorly, but dorsoventrally depressed anteriorly; anterior end concave; anterolateral edge with a deep indentation around which the anterodorsal forked region of the palatine fits and is held by fibrous tissue; articulates by slight interdigitation dorsally with the ethmoid and pos- teriorly with the concave anterior end of the

Mandibular Region. Hyomandibular. —Expanded dorsally, tapering

gradually to a stout shaft anteroventrally; cartilage filled at its dorsal and anteroventral edges; articulates by

fibrous tissue dorsolaterally with the sphenotic and

pterotic and dorsomedially with the prootic and pterotic. The ventral three-fourths of the posterior edge of the hyo- mandibular articulates by fibrous tissue with the preoperculum, while just above the dorsal end of the

latter the hyomandibular supports the articular face of the operculum. At its anteroventral end the hyo- mandibular makes fibrous tissue contact mainly with the preoperculum, and only secondarily with the symplectic and metapterygoid.

Quadrate. —Somewhat wider posteriorly than

anteriorly; prolonged posteroventrally into a thin tapering piece below the metapterygoid; cartilage filled only

for a short distance along its posterodorsal edge; articulates by fibrous tissue anteriorly with the articulfir in the lower jaw and ventrally with the preoperculum. It ar- ticulates by interdigitation dorsally with the overlying

ectopterygoid, while posterodorsally it overlies and inter- digitates with the metapterygoid.

Metapterygoid. —A more or less rounded plate; cartilage filled only for a short distance along its anteroventral edge; articulates by interdigitation anteriorly with the ectopterygoid and palatine, dorsally with the mesopterygoid, anteroventrally with the quadrate, and

posteroventrally with the symplectic.

Symplectic. —A thin delicate rod; cartilage filled at

its posterior edge; articulates by interdigitation dorsally with the metapterygoid and by fibrous tissue ventrally with the preoperculum.

Palato-Pterygoid Region.

Palatine. —Expanded posteriorly; a short

anteriorly directed cleft present in the anterior part of its dorsal edge; articulates anterodorsally by firm fibrous

tissue attachment of its cleft surface in the anterolateral indentation of the vomer; articulates by interdigitation ventrally with the ectopterygoid, posteroventrally with

the metapterygoid, and posterodorsally with the

mesopterygoid.

Ectopterygoid. —Roughly triangular, its posterior end tapering to a blunt point; articulates by interdigi- tation dorsally with the palatine, posteriorly with the metapterygoid, and ventrally with the quadrate, which it broadly overlies.

Mesopterygoid. —Broad anteriorly, but becoming

narrower posteriorly; articulates by interdigitation

anteriorly with the palatine and ventrally with the metapterygoid, both of which bones overlie the mesopterygoid to a variable extent. Opercular Region. Operculum. —Elongate; wide in the middle of its length, but tapering gradually to points anteriorly and

posteriorly; its dorsolateral surface produced into a

strong keel which extends dorsally as a stout shaft above

the articular facet for connection with the hyomandibular. This dorsal process serves as a place of attachment

for the muscles originating on the posterolateral surface

of the frontal. The operculum articulates by fibrous

tissue anterodorsally with the upper posterior edge of the hyomandibular and ventrally with the suboperculum, which it overlies. In about the middle of its anterior edge

the operculum makes ligamentous contact with the rodlike posterior end of the interoperculum. Suboperculum. —Thin and delicate; rounded

ventrally but produced dorsally into two processes, the more anterior of which is by far the longer. The posterior edge of the more anterior of these two dorsal processes ar- ticulates by fibrous tissue with the anterior edge of the operculum. The lateral surface of the rounded ventral

portion of the suboperculum is broadly overlain by the

ventral end of the operculum.

Interoperculum. —A long rod, with a ventral flange along the middle region of its ventral edge; articulates by
ligaments posteriorly with the operculum and anteriorly with the angular in the lower jaw. The ventral flange ar- ticulates by fibrous tissue with the lateral surface of the

epihyal.Preoperculum. —Large, expanded posteroventrally; slightly expanded laterally along the anterior half of

its dorsal edge for articulation by fibrous tissue with the

ventral surface of the quadrate; articulates by fibrous tis- sue posterodorsally with the hyomandibular and antero- dorsally with the symplectic, metapterygoid, and

quadrate.

Upper Jaw.

Premaxillary. —Posteromedial arm short; together with the fused teeth forms a relatively sharp-edged cutting plate; its anterior edge forming the anterior border of the upper jaw, except for a short distance ventrally where

the maxillary forms the border. The dorsomedial edges of the two premaxillaries articulate with one another by

fibrous tissue, with the articulation strengthened by 15 to 20 short but firm projections, which decrease in size anteriorly in the series, from the dorsomedial edge of each premaxillary. The posteromedial arms of the

premaxillaries articulate by fibrous tissue with the

posteroventral surface of the vomer. Posterolaterally the premaxillary articulates by interdigitation with the

overlying maxillary. The premaxillary is relatively hol- low interiorly to accommodate the dental pulp. The long,

thin, rodlike teeth produced by the dental pulp lie parallel to the edge of the premaxillary and are continuously moved forward to replace those being worn away by use

at the biting edge. About 15 to 20 such rodlike dental

lamellae are present in each premaxillary. Only the most

anterior one or two lamellae are exposed at the cutting edge of the jaw, but the other lamellae are easily seen

posterior to them because of the thinness of the overlying

anterior region of the premaxillary. The pulp-filled inter- nal cavity of the premaxillary is open to the exterior through a small canal just lateral to the base of its posteromedial arm.

Maxillary. —Not especially curved forward; widest

ventrally where it forms the border of the upper jaw; broadly overlies and firmly interdigitates with the pre- maxillary along all of its length except at its expanded

ventral edge, where its medial surface articulates by

fibrous tissue with the dorsolateral surface of the dentary. The maxillary articulates posterodorsally by

fibrous tissue at a groove on its surface with the palatine.

Dentary- —Somewhat squarish; its posterior end

concave to accommodate and interdigitate with the

anterior portion of the articular; the dentary overlies the

articular more extensively laterally than medially.

Posteroventrally the dentary articulates by fibrous tissue

or slight interdigitation with the angular, while antero- medially it articulates by fibrous tissue with its opposite member. The connection with its opposite member is strengthened by about 15 stubby medial projections from

each dentary which alternate with one another and decrease in size anteriorly, as is the case with the pre- maxillary. The dorsolateral surface of the dentary at- taches by fibrous tissue to the ventromedial surface of the maxillary. About 15 dental lamellae are present in the dentary, in the same manner as described for those of the premaxillary. The dentary is filled with the pulp

cavity that produces these rodlike teeth, and the cavity opens to the exterior at the concave posterior end of the dentary just in front of the anterior end of the articular.

Articular. —Somewhat triangular in shape; carti- lage filled at its anterior edge; the anterior portion of the

articular fits into and interdigitates with the concave

posterior end of the dentary. The posterior edge of the ar- ticular is thickened around the concavity at which it ar- ticulates by fibrous tissue with the quadrate. Posteroventrally the articular articulates by fibrous tissue with

the angular, but in larger specimens this articulation is by interdigitation. The sesamoid articular is a thin nubbin of bone lying alongside the medial surface of the ar- ticular just behind the articulation of the latter with the

dentary.Angular. —Small; articulates by fibrous tissue, or

slight interdigitation in larger specimens, with the dentary and articular. Posteriorly it articulates by a liga- ment to the anterior end of the interoperculum.

BRANCHIAL APPARATUS.

Hyoid Arch and Branchiostegal Rays.

Urohyal, basihyal, and interhyal—Absent.

Hypohyal. —Dorsal hypohyal absent; ventral hypohyal wide posteriorly but tapering to a blunt point

anteriorly; cartilage filled at its posterior edge; articulates through cartilage posteriorly with the ceratohyal and by fibrous tissue medially with its opposite member.

Ceratohyal. —Elongate and slightly expanded posteriorly; cartilage filled at its anterior and posterior edges; articulates anteriorly through cartilage with the hypohyal and posterodorsally by interdigitation with the

epihyal. The ceratohyal supports by fibrous tissue all of the six branchiostegal rays.

Epihyal. —Cartilage filled at its anterior and

ventral edges; articulates anteriorly by interdigitation with the ceratohyal. Along its lateral surface the epihyal

articulates by fibrous tissue with the ventral flange of the interoperculum, while dorsally it connects, without the

intervention of an interhyal, with the symplectic-metapterygoid region.
Branchiostegal rays. —Six in number; first branchiostegal ray a large flat oblique plate with a downturned lateral edge which becomes thickened anteriorly

to form the articular facet for contact with the vertical groove on the ventromedial surface in about the middle

of the length of the ceratohyal; like that described for Lagocephalus laevigatas, except that it is held in a much

more oblique position. Second branchiostegal slightly

laterally compressed; articulates at its knoblike anterior end with a slight depression on the ventral surface of the ceratohyal just behind the articular area of the first branchiostegal; second branchiostegal ray about the same length as, or slightly longer than, the third to sixth

rays. Third to sixth branchiostegal rays of about the same length, but the sixth ray much narrower than the

others; all four rays held by fibrous tissue to the lateral surface of the posteroventral region of the ceratohyal.

Branchial Arches. —All the elements are cartilage

filled at their edges of articulation with the other ele- ments in the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs

of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and three pairs of pharyngobranchials. Three gills are present; the fourth arch has no gill and there is no slit between it and the lower pharyngeal.

First arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basi- branchial wider posteriorly than anteriorly; displaced forward so that it articulates posteriorly with the second

basibranchial and posterolaterally with the first hypobranchials. First hypobranchial a slender rod, slightly wider dorsally than ventrally; the longest of the hypobranchial elements, which decrease in size posteriorly in the series; articulates ventrally with the region of articulation between the first and second basibranchials and

dorsally with the first ceratobranchial. First cerato- branchial the shortest of the first four ceratobranchial

elements, which increase in length posteriorly in the

series, except for the fifth ceratobranchial which is slightly shorter than the first ceratobranchial; first ceratobranchial with a ventrally directed flange along most of its ventral surface, while a similar flange is pres- ent on the second and third ceratobranchials, as well as on the fourth ceratobranchial in a much reduced state; a

large posterodorsally directed flange is present from the

dorsal edge of the ventral region of the first cerato- branchial, and a similar, although slightly smaller,

flange is present on the second and third cerato- branchials; articulates ventrally with the first hypobranchial and dorsally with the first epibranchial. First epibranchial a slender rod, the shortest of the epibranchial elements; articulates dorsally with the first pharyngobranchial. First pharyngobranchial a rounded

plate with a ventral shaftlike process for articulation with the first epibranchial; bears about 15 to 25 small

sharply pointed teeth in a single but somewhat irregular row along the edge of the rounded platelike region; the

teeth smaller than those of the second and third pharyngobranchials. The dorsal regions of the branchial arches

are held to the ventral surfaces of the parasphenoid and

prootics by fibrous tissue attaching to the dorsolatertd surface of the epibranchials and phaiyngobranchials.

Second arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Second basi- branchial somewhat constricted in the middle of its length; articulates anteriorly with the first basibranchial, anterolaterally with the first hypobranchials,

posterolaterally with the second hypobranchials and posteriorly with the third basibranchial. Second hypobranchial a short slender rod; articulates ventrally with

the posterolateral edge of the second basibranchial and

dorsally with the second ceratobranchial, which in turn

articulates dorsally with the second epibranchial. Second

epibranchial slender, rodlike; articulates dorsally with a stubby projection on the ventral arm of the second

pharyngobranchial. Second pharyngobranchial the largest of the pharyngobranchial elements; more or less Lshaped, bearing a single row of about 10 to 15 sharply pointed teeth along the edge of the wider of the two arms

of the L. The teeth are set in shallow sockets and are curved slightly posteriorly. They are replaced by new

teeth developing in new sockets alongside the sockets of

the old teeth. The teeth of the second pharyngobranchial are of about the same size as those of the third. The second pharyngobranchial is held by fibrous tissue

to the other two pharyngobranchials.

Third arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Third basi- branchial large, rather squarish, articulates anteriorly with the second basibranchial, posterolaterally with the

third hypobranchials and posteriorly with the fourth

ceratobranchials. Third hypobranchial a slender L- shaped bone whose ventral arm articulates by fibrous

tissue with the ventral surface of the first basibranchial;

articulates posterodorsally with the posterolateral edge

of the third basibranchial and with the ventral edge of the third ceratobranchial. Third ceratobranchial articu- lated dorsally with the third epibranchial. Third

epibranchial a slender rod, with a stubby projection from

about the middle of its posterior edge which articulates by fibrous tissue with a similar process from the fourth epibranchial; articulates dorsally with the third pharyngobranchial. Third pharyngobranchial like the second pharyngobranchial, but much smaller and bearing only about 7 to 10 small sharply pointed teeth in a

single row; articulates ventrally with the third and fourth

epibranchials. Fourth arch. —Cerato- and epibranchial elements

only. Fourth ceratobranchial a slender rod with only a

very low ventral flange along a short portion of its length;

articulates ventrally with the third basibranchial and

dorsally with the fourth epibranchial. Fourth epibranchial a slender rod with a low flange along its posterior edge, and a stubby emargination from about the middle
of its anterior edge which articulates by fibrous tissue with the third epibranchial; the dorsal end of the fourth epibranchial articulates with the third pharyngobranchial.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial a stout shaft with a small medial expansion in about the middle third of its length; articulates ventrally with the base of the fourth

ceratobranchial; toothless. PAIRED FIN GIRDLES.

Pectoral Fin.

Supracleithruin. —In position at about a 45° angle

to the axis of the body; a stout shaft with a lateral flange along most of its length; articulates by fibrous tissue anterodorsally with the slight concavity on the lateral ex- pansion of the pterotic and ventrally with the cleithrum, which it broadly overlies.

Cleithrum. —Laterally expanded along most of its length; articulates by fibrous tissue dorsally with the

overlying supracleithrum and with the anterior end of the dorsal postcleithrum, which it overlies; along its posterior edge it articulates by fibrous tissue with the scapula and coracoid. Ventromedially the cleithrum articulates by fibrous tissue with its opposite member in the midline of the body between the medial edges of the

platelike portions of the first branchiostegal rays.

Postcleithra. —The postcleithra form a stout strut along the abdominal wall musculature from the supracleithrum to halfway back the length of the ab- dominal cavity. The dorsal postcleithrum articulates by

fibrous tissue anterolaterally with the overlying

cleithrum and posteroventrally with the ventral postcleithrum, which tapers to a point posteriorly. The dorsal and ventral postcleithra are only slightly laterally compressed.

Coracoid. —Rounded dorsally but gradually

tapering to a stout shaft ventrally; along the dorsal third

of its length the posterior edge of the coracoid is in- turned to form a medial flange whose dorsal edge is pro- longed into a spinelike process below the fourth actinost;

cartilage filled at the edge of its rounded dorsal portion and at its extreme ventral edge; articulates by fibrous

tissue anteriorly with the cleithrum and through cartilage dorsally with the scapula and last two actinosts.

Scapula. —Scapular foramen not entirely enclosed by the scapula, but, rather, with its anterior edge closed by the cleithrum; cartilage filled at its anterior and ventral edges; articulates anteriorly by fibrous tissue with

the cleithrum, ventrally through cartilage with the coracoid, posterodorsally by slight interdigitation with the

anterior edge of the first actinost, and posteroventrally by slight interdigitation with the ventral edge of the sec- ond actinost.

Actinosts. —Four elements; all cartilage filled at both ends, except for the first actinost, which is filled with cartilage only at its dorsal edge. First actinost reduced to a triangular wedge between the upper parts of the scapula and second actinost, to both of which ele- ments it interdigitates. Second actinost rounded dorsally, constricted in the middle and reduced ventrally to a narrow splint that interdigitates ventrally with the scapula and posteriorly with the base of the third acti- nost; articulates by interdigitation anterodorsally with

the first actinost and posterodorsally with the third acti- nost. Third and fourth actinosts slightly constricted in the middle; the third actinost articulating dorsally and

ventrally by interdigitation with the second and third

actinosts, while it articulates through cartilage just be- low its base with the coracoid; the fourth actinost ar- ticulating by interdigitation anterodorsally and anteroventrally with the third actinost and ventrally through

cartilage with the coracoid. Distally the actinosts support all of the fin rays.

Fin rays. —Usually 17 fin rays present; the first fin ray short, about one-third or one-fourth the length of the second ray, but normal in shape and symmetry, its two

halves of equal size; all rays articulated by fibrous tissue with the dorsal ends of the actinosts. The first tv/o or three rays unbranched, the other rays branched. The first ray without cross-striations, the others cross-striated.

VERTEBRAL COLUMN. —All vertebrae with bicon- cave centra, except the last, which ends posteriorly in the

urostylar process and fusion with some of the hypurals.

Abdominal Vertebrae.

First vertebra. —Neural spine bifid and relatively

short; neural arch with a complete bony roof over the neural canal, as do all the other vertebrae; articulates by

fibrous tissue over the anterior half of the lateral surface

of its centrum with the posteriorly projecting exoccipital condyles, while the rim of the concave anterior face of its centrum articulates with the rim of the concave posterior end of the basioccipital. Posteroventrally on its lateral surface the centrum of the first vertebra possesses a flattened posterior process which fits under the

anterior half of the ventrolateral surface of the centrum

of the second vertebra. Other abdominal vertebrae. —In 17 specimens the abdominal vertebrae numbered eight. The second and

third abdominal vertebrae have their neural spines bifid, but somewhat longer than that of the first vertebra. The fourth vertebra has its neural spine enlarged anteroposteriorly, and while it is bifid anteriorly, it becomes

single posteriorly. All of the vertebrae, both abdominal

and caudal, posterior to the fourth abdominal vertebra have undivided neural spines. The neural spines of the

fifth and sixth abdominal vertebrae are of about the same height as that of the fourth vertebra, but they are
less anteroposteriorly expanded than the latter. The

seventh and eighth abdominal vertebrae have their neural spines in the form of long stout shafts between which

the first basal pterygiophore of the dorsal fin articulates. Small neural prezygapophyses are present from about

the fourth to the last abdominal vertebra, and increase in

size posteriorly in the series. From the posterolateral sur- face of the second vertebral centrum a stout ventrally di- rected process is present which makes fibrous tissue contact with a similar ventrally directed process from the

anterolateral surface of the centrum of the third vertebra. These ventral processes from either side of these two

centra do not meet their opposite members in the midline to completely enclose the haemal canal. However,

the abdominal vertebrae posterior to the third vertebra have stout ventrally directed processes from the anterolateral surfaces on either side of their centra which do meet and fuse in the midline to enclose completely the haemal canal. The haemal spines possess posteriorly di- rected flanges along their posterior edges just below the haemal canal. The haemal spines increase in size posteriorly in the series and form broad surfaces for muscle

attachment.

Caudal Vertebrae. —In 17 specimens the caudal

vertebrae numbered nine. All of the caudal vertebrae

possess neural arches and spines and haemal arches and

spines. Neural prezygapophyses are present on all of the caudal vertebrae, although they decrease in size posteriorly so that the last caudal vertebra has them only weakly developed. The neural spines of the first two caudal vertebrae are slender but strong shafts which dis- tally support the more posterior of the dorsal fin basal

pterygiophores. These two neural spines are shorter than

the last two neural spines of the abdominal vertebrae, which support the more anterior of the dorsal fin basal

pterygiophores. The neural spines of the third to sixth caudal vertebrae are slender but strong shafts which are

slightly longer than those of the two preceding caudal

vertebrae. The neural spine of the seventh caudal verte- bra is enlarged anteroposteriorly, and that of the eighth caudal vertebra is even more enlarged. The neural spines

of these two vertebrae make close fibrous tissue contact with one another and form a large thin plate above their centra. Each neural arch possesses a small neural fora- men. The haemal arches and spines of the first three caudal vertebrae are like those of the abdominal vertebrae

just anterior to them, except that the haemal spine of the

first caudal vertebra is even more enlarged posteriorly than are the others and ventrally supports by fibrous

tissue the much expanded first basal pterygiophore of the

anal fin. The posteriorly expanded platelike portions of the haemal spines of the second and third caudal verte- brae ventrally support through fibrous tissue the second

to the fifth (last) anal fin basal pterygiophores. The

haemal spine of the fourth caudal vertebra is less anteroposteriorly expanded than are those anterior to it, but it

is somewhat longer. The haemal spines of the fifth to seventh caudal vertebrae become increasingly expanded

anteroposteriorly so that the haemal spine of the seventh

is a rounded flat plate whose posterior edge makes

fibrous tissue contact with the anterior edge of the much

modified haemal spine of the eighth caudal vertebra. Whereas the centrum and the neural arch and spine of the eighth caudal vertebra are fused together, the haemal

arch and its spine are autogenous and held to the cen- trum by fibrous tissue and interdigitation. The haemal

spine of the eighth caudal vertebra is much enlarged, and

possesses a posterior extension which reaches almost to the base of the lowermost caudal fin ray. The edge of the haemal apparatus of the eighth caudal vertebra that makes contact with the centrum is somewhat concave so that a haemal canal is present throughout the length of the region of articulation of the two elements. The hae- mal canal is continuous anteriorly with the haemal canal

of the preceding vertebrae, while posteriorly it is continu- ous with the canal between the surfaces of contact of the parhypural and the centrum of the last vertebra.

Caudal Skeleton. —The caudal complex is composed

of four separate bony elements closely held to one

another variously by fibrous tissue and interdigitation. The ventral portion of the caudal skeleton is formed by

the parhypural, which is broad anteriorly but tapers to a

stout shaft posteriorly where it supports the lowermost

caudal fin ray. Anteriorly it is extensively interdigitated with the posterodorsal edge of the haemal spine of the penultimate vertebra. A distinct notch is present in its dorsal edge a little forward of its middle region. Anterior

to this notch the dorsal edge of the parhypural is extensively interdigitated with the region of the centrum of the

large bony plate above it, which is the fused centrumlower hypurals. The notch in the parhypural is the last opening into the haemal canal, the latter being con- nected to the canal in the preceding vertebrae by a longi- tudinal groove medially along the otherwise interdigi- tated articular surface between the parhypural and the centrum anterior to the foramen. The dorsal surface of the parhypural posterior to the foramen is held by fibrous

tissue to the ventral edge of the hypural region of the fus- ed centrum-lower hypural plate. The epural is a flat- tened plate closely held by fibrous tissue between the

posterior edge of the neural spine of the penultimate

vertebra and the anterior edge of the urostylar region of the fused centrum-lower hypural plate and of the anteroventral region of the upper edge of the autogenous upper

hypural plate. Ventrally the epural slightly interdigi- tates with the incomplete neural arch region of the last vertebra, forming the dorsal roof of the neural arch. The

neural canal thus enclosed is continuous anteriorly with

the canal in the preceding vertebrae, while posteriorly the canal opens to the exterior just behind the end of the

area of articulation between the epural and the neural arch of the last vertebra. In large specimens (over 1(X) mm) the articulation between the epural and the lateral walls of the neural arch of the last vertebra tends to be- come more intimately interdigitated and perhaps even

fused. Similarly, the articulation of the epural with the

neural spine of the penultimate vertebra and the urostylar region of the last vertebra tends to become slightly
interdigitated in large specimens. The largest element of the caudal skeleton is that formed from the fusion of the centrum of the last vertebra posteroventrally with the lower hypurals, which in generalized plectognaths would

correspond to the first and second hypurals but which are here indistinguishably fused with one another and with

the centrum. The concave anterior face of the centrum

portion of this fusion element articulates in a normal manner with the concave posterior face of the centrum of the penultimate vertebra, but immediately below this fibrous tissue articulation the ventral expansions of these two vertebrae interdigitate with one another, while ventrally that of the last centrum interdigitates with the

anterodorsal end of the parhypural, except at the medial

longitudinal groove between their apposed surfaces enclosing the haemal canal. The urostyle of the last cen- trum is represented by a tapering thickened shaft ex- tending posterodorsally from the centrum portion of the composite plate and is extensively interdigitated along

its posterior edge with the anterior edge of the autogenous upper hypural plate. The anterior edge of the urostylar region articulates by fibrous tissue, and by interdigita- tion in larger specimens, with the epural. The ventral edge of the hypural region of the fused centrumlower hypurals articulates by fibrous tissue with the

posterodorsal edge of the parhypural, while its dorsal edge is extensively interdigitated with the anteroventral end of the autogenous upper hypural plate. The upper

hypural plate is composed of indistinguishably fused hypurals corresponding to what in generalized plectog- naths would be the third to fifth elements, the plate being extensively interdigitated with the urostylar and

hypural regions of the fused centrum-lower hypural

plate, and held for a short distance anterodorsally by

fibrous tissue to the epural. In the smallest specimen ex- amined, 10.0 mm, the lower hypurals are as fully and in- distinguishably fused to one another and to the centrum

as in adults, while the autogenous upper hypural plate, the epural and parhypural are, as expected, scarcely if at

all interdigitated with the fused centrum-lower hypurals, but the upper hypural plate more so than the epural and

parhypural. Caudal fin rays. —Eleven in number, the upper- most ray and the lowermost ray unbranched, the others becoming increasingly branched toward the middle rays, which are branched in triple dichotomies. The upper- most five rays are held by fibrous tissue to the auto- genous upper hypural plate, the lowermost ray to the parhypural and the upper five rays of the lower lobe to the hypural region of the fused centrum-lower hypural

plate.DORSAL AND ANAL FINS.

Dorsal Fin. Fin rays and pterygiophores. —Ten fin rays are pres- ent in most specimens, the first one or two rays unbranched, the others branched in single or double dichotomies; the first ray almost as long as the longest ray. Distal pterygiophores either absent or unossified. The

fin rays are supported basally by eight basal pterygio- phores which are broadly interdigitated with one another and which decrease slightly in length posteriorly in the

series. The first basal pterygiophore is by far the largest and fills much of the space between the neural spines of the seventh and eighth abdominal vertebrae. The second

to fourth basal pterygiophores have their ventral or in- temeural portions between the neural spines of the

eighth abdominal and first caudal vertebrae, while those

of the fifth to seventh basal pterygiophores are between

the neural spines of the first and second caudal verte- brae. The eighth basal pterygiophore has its ventral region placed just behind the upper end of the neural

spine of the second caudal vertebra. The pterygiophores

articulate with the neural spines by fibrous tissue. Each

pterygiophore ends dorsally in a short columnar projection whose deeply concave dorsal edge is cartilage filled.

It is to these columnar projections that the fin rays are held by fibrous tissue. The ventral ends of the pterygio- phores are all deeply cartilage filled. The anterodorsal edge of the first pterygiophore is slightly prolonged

anteriorly and articulates by fibrous tissue with the rounded shaftlike supraneural. The supraneural extends from above the posterior region of the neural spine of the

fourth abdominal vertebra to just in front of the dorsal end of the neural spine of the seventh abdominal vertebra. The supraneural is connected with a band of longi- tudinal muscles in the midline of the body which

anteriorly connects with the supraoccipital spine. None

of the pterygiophores possess lateral flangelike projec- tions along their lengths for muscle attachment,

although they are slightly thicker in the middle regions throughout their lengths than they are anteriorly or posteriorly.

Fin rays and pterygiophores. —Nine fin rays are present in most specimens, the first one or two rays un- branched, the others branched in single or double

dichotomies; the first ray only slightly shorter than the

longest ray. Distal pterygiophores either absent or unossified. The anal fin rays are supported through fibrous

tissue by five basal pterygiophores which are interdigi- tated with one another only for a short distance ventrally. Posterior to the enlarged first pterygiophore, the re- maining pterygiophores decrease only very slightly in length posteriorly in the series. The dorsal ends of the

pterygiophores articulate by fibrous tissue with the ventral edges of the haemal spines of the caudal vertebrae, with the first pterygiophore attached to the first caudal

vertebra and the remaining pterygiophores attached to the second and third caudal vertebrae. Like the pterygio- phores of the dorsal fin, those of the anal fin are carti- lage filled proximally, while distally they possess short columnar projections whose deeply concave edges are

cartilage filled. Whereas the second to fourth pterygio- phores possess a single columnar projection distally, the
w

first pterygiophore possesses two and the last pterygio- phore possesses two or three columnar projections. The

presence of more than one such projection may indicate that the first and last pterygiophores are fusion products

of two or more originally separate basal pterygial ele- ments. The fin rays are articulated by fibrous tissue to these columnar distal ends of the pterygiophores. Like

the dorsal fin pterygiophores, the anal fin pterygio- phores are slightly thicker in the middle regions throughout their lengths than they are anteriorly or posteriorly.

Anatomical diversity and generic relationships. —The fossil record of tetraodontids is meager. The

only relatively complete specimen of a tetraodontid is Tetraodon pygmaeus Zigno (1887b) from the Eocene of
prefrontal frontal pterosphenoid supraoccipital

frontal parasphenoid

maxillary palatine premaxillary

dentary

epiottc

pterotic

basioccipital

suboperculum

mesopterygoid

ectopterygoid metapterygoid I preoperculum

quadrate interoperculum symplectic

Monte Bolca, Italy. The holotype and only known speci- men, IGUP 6890-91, 18.2 mm SL, in counterpart, is small and only moderately well preserved. It is a lateral impression and the medial region of the upper and lower jaws is not exposed. Thus, it cannot be told at present how the dentaries and premaxillaries articulate to their opposite members. However, the body is covered by very

fine small prickles and the abdominal vertebrae (either 9

or 10) are fewer than the caudal vertebrae (12), while the

rodlike postcleithrum is in two pieces, all these features being more characteristic of tetraodontids than diodontids. There are about 10 or 11 dorsal and anal fin rays, and the caudal fin seems to have 12 rays, one more than

in any Recent species of tetraodontid, but the same number of principal rays as in the ancestral gymnodont

triodontids and scleroderm eoplectins. Moreover, there is a strong indication that there are slender ribs present on many of the abdominal vertebrae, while ribs are absent

in all Recent gymnodonts except the basal triodontids (and one of the two species of scleroderm eoplectins also seems to have ribs). The above are the only features of in- terest that I can distinguish in the specimen, which is sufficiently distinct from all Recent species to merit

separate generic recognition, and Eotetraodon is pro- posed herein for pygmaeus Zigno (type-species by monotypy and original designation). The only other tetraodontid fossil materials are jaw

fragments found from the Miocene onward, and usually

referred to as Tetraodon lecointrae Leriche and T. lawleyi Carraroli. They indicate only that the individual dental units incorporated into the biting edge of the jaws

were elongate rods such as in the Recent species.

Figiire 204.—Canthigaster

roBtrata: lateral view

of head, composite based on several specimens,

55.2-96.5 mm SL, Texas.

The three external characters that have been

prominently used in conjunction with internal features in subdividing the Recent tetraodontids (the number of

dorsal and anal fin rays, the form and number of the

lateral lines, and the form of the nasal apparatus) will be

discussed here first, followed by an analysis of the osteological diversity of the family. In the two most recent

revisions of the group (Fraser-Brunner 1943 and Le

Danois 1959, 1961a) five families have been recog- nized in what is here considered a single family with two

subfamilies, and the term Tetraodontidae as used here is senso lato, although closely corresponding to that in general use in the contemporary ichthyological

literature. Chonerhinos and Xenopterus have the dorsal and anal

fins longer based and with more rays than in other tetra- odontids. In Chonerhinos there are about 23 to 29 dorsal rays and in Xenopterus about 32 to 38, with the anal fin

in both cases having several less rays than the dorsal fin. In other tetraodontids the number of dorsal fin rays ranges modally from about 7 to 18, with the anal fin having either the same number or one to several rays less than the dorsal fin. Sanzo (1930) was the first to describe in detail the

lateral line of tetraodontids, and Fraser-Brurmer (1943) the first to call attention to its systematic importance.

Figure 205. (opp. page)—Canthigaater

roBtrata: dorsal (left) and

ventral (right) views of skull, with

inset at top right showing a ventral view detail of the articulation of the upper jaw with the palatines and

vomer, composite based on several specimens, 55.2-96.5 mm SL, Texas. ceratobranchials

epibranchials

pharyngobranchials

ClI)Cl3c= — basibranchials

hypobranchials

^>

^::s

Figure 206. (opp. page)—Canfftt^osfer

roatrata: posterior view of skull (left); below, lateral and posterior views of

first abdominal vertebra; posterior view

of orbit (right) (cross section of

skull; dashed lines represent cut surfaces of frontals and parasphenoid); composite based on several specimens,

55.2-96.5 mm SL, Texas.

Figure 207.—Conf/i«<Mtcr rostrata: dorsal view of branchial arches (extended on lower

side); lateral (above) and medial (below, upside down) views of hyoid arch; composite based on

several specimens, 55.2-96.5 mm SL, Texas.
Wiedersheim (1887a, b; 1888) was the first to describe in

detail the nasal apparatus of tetraodontids, while its systematic importance was first stressed by Bibron (see Dumeril 1855), although an overemphasis on the nasal apparatus has led to confusion. Dunker and Mohr (1931) described the changes in the nasal tube in Chelonodon

with increasing body size, and Barnard (1927) showed

the variety of nasal organs in South African puffers, while Le Danois (1959) illustrated it for an even larger selection of tetraodontids. Inger (1953) illustrated the differences in the olfactory epithelium between

Tetraodon kretamensis and Chelonodon fluviatilis. Chonerhinos and Xenopterus have the lateral line more elaborately developed than in other tetraodontids, with three lines on the body rather than only one or two.

Figure 20S.~Canthiga8ter rostrata: lateral view of pectoral girdle, composite based on

several specimens, 5.5.2-96.5 mm SL, Texas.

while in Canthigaster the lateral line system is so in- conspicuous that it can only be seen with the aid of magnification. Nasal specializations also distinguish

these genera from other tetraodontids. In Chonerhinos and Xenopterus (the Chonerhinidae of Fraser-Brunner)

the nasal apparatus is larger than in other tetra- odontids, in the form of a large, low open cup with numerous lamellae or folds, while in Canthigaster (the Canthigasteridae of Fraser-Brunner) the nasal apparatus

is much smaller than in other tetraodontids, in the form

of a small, low simple tube with a single opening.

In other tetraodontids the nasal apparatus ranges from

an upright sac with two nostrils (in Lagocephalus,

Sphoeroides, Guentheridia, Amblyrhynchotes, Fugu, and Torquigener, these being the Lagocephalidae of Fraser-Brunner, except that for purposes of the present

discussion the genera are more finely split than as recog- nized by Fraser-Brunner, and in Colomesus, the Colomesidae of Fraser-Brunner) to a tube with a single

nostril or a bifid tentacle or a simple single flap (Ephippion, Arothron, Monotreta, Chelonodon, Carinotetraodon, and Tetraodon, the Tetraodontidae of Fraser- Brunner, except, as above, for purposes of the present

discussion, more finely split). While the lateral line systems in Chonerhinos-Xenopterus and in Canthigaster are each in their own way just as distinctive as

their nasal apparatuses, the situation is not so neatly simple in the other tetraodontids. Among those genera with the relatively normal nasal apparatus as an upright sac with two nostrils, Sphoeroides and Guentheridia have a single lateral line on the body, although short segments of an additional lower line are sometimes present (see illustrations of S. lobatus, S. dorsalis, and G. formosa), while in Lagocephalus, Amblyrhynchotes, Fugu, Torquigener, and Colomesus two lateral lines usually are present, the

Figure 209.— Canthigaster

roBtrata: lateral view of caudal fin supporting

structures, composite based on several specimens.

55.2-9G.5 mm SL, Texas.
lower one always better developed than in the traces of it sometimes found in Sphoeroides and Guentheridia, even though the lower line may not run the full length of the caudal peduncle (see illustration of Torquigener pleurostictus). Possible exceptions are Amblyrhynchotes

piosae, in which the exceptionally long spines mostly obscure the lateral line, so that in the single alcohol- preserved specimen examined I am unable to find any

lateral line at all on the caudal peduncle, and A. richei, in which I cannot find a lower lateral line in any of the 10

alcohol preserved specimens examined, although Le

Danois (1959:172) showed it as present. A distinctly upraised horizontal ridge of skin is present ventrolaterally along the caudal peduncle in all species of Logocephalus, in most species of Torquigener (absent in pleurostictus) and Fugu (absent or only weakly

developed in chrysops), in at least some species of Amblyrhynchotes (honckenii and hyselogenion) and

Sphoeroides (e.g., see illustrations of lobatus, testudineus, and dorsalis), but it is absent in Guentheridia and

Colomesus. The presence or absence of this ridge is of very limited systematic interest at the generic level, while the presence or absence of a second, lower, lateral

line is more variable within certain genera than previously thought.

In those genera with a single nostril or a nasal tentacle, there is a single lateral line in Arothron, while in Chelonodon and Monotreta the upper lateral line nor- mally curves ventrally to join the lower lateral line in the

region above the anal fin, the lower line continuing posteriorly to the tail as well as anteriorly to the abdominal

region from the point of juncture with the upper lateral

line. Tetraodon has some species with basically the same

arrangement as in Chelonodon and Monotreta (see illus- trations of T. lineatus and T. mbu), but in at least one

species (see illustration of T. miurus) there seems to be

no lower lateral line, the upper line continuing directly onto the tail, while in another (see illustration of T.

Figure 210.— External features of other

representative tetraodontid genera:

A, Sphoeroides nephelus, upper left, nasal

region as seen externally (far left) and

olfactory lamella as seen with front of nasal sac removed, and, lower left, scales from upper middle region of body; B, S. testudineua, upper left, nasal region as seen externally (olfactory lamella, if present, indistinct in specimen examined),

and, lower left, scales from upper middle

region of body; C, S. dorsalis, upper left, nasal

region as seen externally (far left) and

olfactory lamella as seen with front of nasal sac removed, and, lower left, scales from upper middle region of body; D. S. lobatus, upper left, nasal region as seen externally

(olfactory lamella, if present, indistinct

in specimen examined), and, lower left, scales from upper middle region of body

(larger markings on rear of body, and one

on dorsum, represent flaps rather than

scales); E. S. pachygaster. lower left, nasal region

as seen externally and, upper left, olfactory lamellae as seen with front of nasal sac removed, showing more

lerous lamellae than in other species

of Sphoeroides (scales absent).

291
Figure 211.—Nasal organs and

olfactory lamellae of representative

species of Sphoeroides (top row, A-C) and Lagocephalus (D-F):

to left in each set, the nasal

region as seen externally, and

to its right the olfactory lamellae

as seen with top or front of nasal

sac removed, and to its right,

in Lagocephalus, the outline of an anteroposterior cross section

of the sac and lamellae. A, Sphoeroides trichocephalus;

B, S. spengleri; C, S. maculatus

D, Lagocephalus spadiceus;

E, L. lagocephalus: F, L.

Figure 212.—External features of other representative tetraodontid genera: Guentheridia formoaa—upper

left, nasal region as seen externally

(far left) and the pitted olfactory epithelium as seen with the top of the nasal sac removed; lower left, scales from upper middle

region of body.

Figure 213.—External features of other representative tetraodontid genera: Colomesus psittacus—upper

left, nasal region as seen externally

(far left) and the olfactory lamella

as seen with the front of the nasal

sac removed; lower left, scales

ft'om upper middle region of body.
Figure 214.—External features of other representative tetraodontid genera: A, Amblyrhynchotea pioaae—

upper left, nasal region as seen

externally (far left) and the olfactory lamellae as seen with the front of the nasal sac removed, and, lower left, scales from upper middle region of body

(spines on caudal peduncle surrounded

by fleshy flaps which are better developed there than more anteriorly); B, A. honckenii—upper left, nasal

region as seen externally (far left) and the olfactory lamellae as seen with the top of the nasal sac removed,

and, lower left, scales from upper

middle region of body; C, A. richei—

upper left, nasal region as seen

externally (two lower figures), indicating that I out of 10 specimens

has the nostrils confluent and the nasal tube with a single large opening, with the upper figure showing the

olfactory lamellae with the top of the nasal sac removed, and, lower left, scales from upper middle region of body.

Figure 215.—External features of other

representative tetraodontid genera: Torquigener pleuroalictus (above) and

T. hamiltoni—in both cases, upper left, nasal region

as seen externally (far left) and the

olfactory lamella(e) as seen with the

front of the nasal sac removed, and, lower left, scales from upper middle region of body.

Figure 216.—External features of other representative tetraodontid genera: Fugu vermicularis—left, bottom to top, nasal region as seen externally, the olfactory lamellae as seen with

the front of the nasal sac removed, and the outline of an anteroposterior

cross section of the sac and lamellae.
Figure 217.— External features of other representative tetraodontid genera: Arothron armilla (above) and

A. immaculatus—in both cases, upper

left, nasal region as seen externally and, lower left, scales from upper

middle region of body (nasal epithelium

of A. immaculatus pitted as shown;

that of A, armilla, not exposed in the illustration, is only a slightly irregular medial surface of the

single simple nasal flap).

Figure 218.— External features of other representative tetraodontid genera: A, Tetraodon miurug,

B, T. lineatua. C, T. kretamensis, and

D, T. achoutedeni—in all cases, upper

left, nasal region as seen externally (with inset below for T. schoutedeni showing the pitted nasal epithelium) and, lower left, scales from upper

middle region of body.
Figure 219.—External features of other representative tetraodontid genera: Ephippion guttifer of decreasing sizes, from top to bottom

(325, 232, and 101 mm SL) to show

the enlargement of the scale plates with increasing standard length

until, in large adults, a firm saddle is formed over the back and

sides (but not belly); other two

insets show nasal region as seen

externally; scales of 101 mm SL

shown for both beUy

Figure 220.—Photographic detail of interdigitated scale plates from lower

side of body of Ephippion guttifer, 325 mm SL, also shown in Figure 219 (greatest length of largest scale plate 23.0 mm).

Figure 221.—External features of other representative tetraodontid genera: Chelonodon patoca (above) and

C. fluviatilis—in both cases, upper

left, nasal region as seen externally, and, lower left, scales from upper

middle region of body.
Figure 222.—External features of other

representative tetraodontid genera: Monotreta palembangensis (above) and M. leiurus—in both cases, upper

left, nasal region as seen externally, and, lower left, scales from upper

middle region of body.

Figure 223.—External features of other

representative tetraodontid genera: Chonerhinos modestus—upper left, nasal region as seen externally

(far left) and the olfactory lamellae as seen with the

top of the nasal sac removed; lower left, scales from upper middle region of body.

Figure 224.—External features of other representative tetraodontid genera: Xenopteriui naritua—upper left, nasal region as seen

externally; lower left, scales from upper middle region of body.
Figure 225.—External features of other representative tetraodontid genera: Carinotetraodon torteti— upper left, nasal

region as seen externally; lower left, scales from upper middle region of body.

kretamensis) the course of the lateral line was found to be impossible to trace posteriorly in the single alcohol- preserved specimen examined. In Carinotetraodon a

well -developed lower lateral line is present, but, at least

in the few specimens examined, it does not join with the upper lateral line, continuing on directly to the tail (see

illustration). In Ephippion a lower lateral line is present, but its juncture with the upper line is highly variable within the single species, as is the length of its extension

anterior to the point of juncture (see illustrations). None

of the genera with a single nostril or nasal tentacle have an upraised ridge of skin ventrolaterally along the caudal

peduncle.

In short, it can be said that, of those genera with two

nostrils, Sphoeroides and Guentheridia have only a

single well-developed lateral line on the body, while in Lagocephalus, Amblyrhynchotes, Fugu, Torquigener, and Colomesus two lateral lines usually are present, and

that of those genera with a single nostril or nasal ten- tacle, Arothron has a single lateral line, while

Chelonodon, Monotreta, and Ephippion have two which

usually merge on the caudal peduncle, Carinotetraodon

usually has two which do not merge, and Tetraodon has

either two which merge or, in at least a few species, a

single lateral line. There is also intraspecific variation in the form of the

nasal apparatus, although probably less than that described here subsequently for the Diodontidae. In one

species with two nostrils {Amblyrhynchotes richei), 9

(18.9-47.3 mm, ANSP 109916) out of 10 specimens ex- amined had the normal arrangement of two nostrils separated by a broad band of tissue, but one specimen

(49.1 mm, ANSP 109916) had apparently resorbed the middle region of the band in both the right and left nasal apparatuses to leave the nostrils confluent, and only in- completely separated by two flaps of skin (see illus- tration). In the genera with a single nostril or nasal tentacle, the

olfactory epithelium is usually relatively smooth, but in at least a few species (see illustrations of Arothron im- maculatus and Chelonodon fluviatilis) the inner surfaces

of the bifid tentacles are deeply pitted. In the genera with two nostrils, the olfactory epithelium ranges from smooth to highly folded into numerous successive lamellae, but in the monotypic

Guentheridia formosa the olfactory epithelium is deeply

pitted just as in some of the species with bifid tentacles

(all of the relatively normal species oi Arothron and one

of the species of Chelonodon). The degree of lamellar development is variable within some genera. For example, in Lagocephalus lamellae are exceptionally well

developed in all species as folds that cover the entire in- ner surface of the nasal sac, with one or two of the folds on the rear wall enlarged as protruding flaps which themselves bear lamellae, except in L. scleratus, in which

folds are present only on the rear wall of the sac and the two prominent protruding flaps are not themselves extensively folded. Similarly, in Sphoeroides, most species have the olfactory epithelium either smooth or with only one or two prominent folds or horizontal ridges on the

rear wall, but one species, S. pachygaster, has the folds on the rear wall much better developed and more

numerous, between five and eight in number. While the

habitat of L. scleratus is similar to that of some (e.g., the

equally streamlined and open water L. lagocephalus) of the other species of Lagocephalus with extensive olfac- tory flap development, S. pachygaster, in contrast to all other species of Sphoeroides, is a deepwater species, which may rely more heavily on olfaction than do the

shallower water species. In Fugu the folds are only slightly less well developed than in most Lagocephalus and oc- cur on the entire inner surface of the nasal sac, although

the larger folds on the rear wall never become so extensively folded themselves as they do in most species of Lagocephalus. The numbers and size of the lamellae are

especially great in F. oblongus. In the species of Colomesus, Torquigener, and Amblyrhynchotes ex- amined, one to about four folds or ridges are developed on the rear wall of the sac. There is variation in the size of the prickly spines and

in their coverage of the body. Among the materials ex- amined there are four genera in which most of the species have prickles but in which one or two species are completely spineless. In the speciose Sphoeroides most

species have spines on both the back and belly but two

species are spineless, S. angusticeps in the eastern

Pacific and S. pachygaster (of which Liosaccus cutaneus

is one on many synonyms, according to Shipp 1974:44-

47) in the Atlantic and Indo-Pacific to Japan. These two

species are not closely related within the genus, as dis- cussed subsequently, and the loss of prickles undoubtedly has occurred independently in the two species. Moreover, Shipp and Yerger (1969a) and Shipp (1974:98) reported that a minority of specimens of S. nephelus are completely spineless, and nephelus does not seem closely related to either pachygaster or angusticeps.

In the equally speciose Fugu, most species have spines on both the back and belly but two species are spineless,

F. chrysops and F. uermicularis, which on the basis of the

osteological data presented by Kuronuma (1943) do not seem closely related within the genus and are placed in different subgenera by Abe (1952). Here again, the loss of
spines in these two species has occurred independently.

T. Abe (pers. commun.) has informed me that, additionally, F. pardalis is at least superficially spineless. Lagocephalus and Tetraodon each contain a spineless

species, L. inermis and T. mbu. In T. mbu, and, to a far

lesser extent, in the two scaleless species of Fugu, there

are pits in the skin that appear to be filled with a

secreted matter, which is presently under histological investigation by the author. In L. inermis, and, to a lesser extent, in S. pachygaster, the skin of the belly is irregular

in comparison to the smooth skin of the rest of the body, but no spines are present. With the exception of these spineless species (and

there are probably others among the species of tetra- odontids not examined for this work), spines are always

present on the belly of tetraodontids, but there is great

variation both between and within genera in the degree

of covering by prickles dorsally and laterally on the body.

In Lagocephalus, for example, several species (lagocephalus and laevigatus) have spines only on the belly, while

others (lunaris, scleratus, and spadiceus) have prickles variously developed on the dorsum in front of the dorsal

fin. In Sphoeroides prickles are present (except in the two naked species) on the belly and dorsum, but are about as frequently absent as present on the side of the body (see Shipp 1974). In Torquigener prickles usually

are absent from the sides of the body, but in Amblyrhynchotes they are present there. In Ephippion the

prickles on the sides of the body become enormously

enlarged into plates forming a partial carapace (see illus- tration for form of spines at three specimen sizes), while one species of Amblyrhynchotes (piosae) has the pro- jecting portion of the prickle much longer than in any

other tetraodontid. In Chonerhinos and Xenopterus the

prickles of the belly and sides of the body tend to be

larger than in other tetraodontids.

In a few tetraodontids the scales along the course of the

lateral line are modified, being much smaller, more

numerous, and with less development of the protruding

spinule. For example, in Lagocephalus, the three species

(lunaris, scleratus, spadiceus) which have prickles along

the back and upper sides in the region of the lateral line show great differentiation of the small scales immediately along the line from those adjacent to them. In the

other tetraodontids examined, there is no differentiation

of the prickles immediately along the line from those adjacent to them, although the course of the lateral line is sometimes clearly indicated in cleared and stained specimens by a wider spacing of the prickles leading to a spineless stripe along the course of the line (especially

clearly marked in the two species of Colomesus, and, to a

lesser extent, in a few species of Monotreta). The internal anatomical diversity of the tetraodontids

is much greater than the external. The long-based, many-rayed dorsal fin in Chonerhinos and Xenopterus is reflected in a greater number of vertebrae than in other

tetraodontids, Chonerhinos has 26 vertebrae modally

(25-27), of which 10 are usually abdominal, while Xenopterus has 29 or 30 vertebrae, of which 10 or 11 are ab- dominal. All other tetraodontids have modal values

ranging from 17 to 23, the only species with modal values above 20 being numerous species of Fugu and some of Monotreta and Torquigener. At the opposite extreme, 17 vertebrae modally, are all of the species of Canthigaster,

that of Carinotetraodon and of Guentheridia, and several species of Lagocephalus, Sphoeroides, and Tetra- odon, the formula always being eight abdominal and

nine caudal when the total is modally 17. Since both the Eoplectinae and Triodontidae, ancestral to the tetra- odontids, have 20 vertebrae (9 -(- 11), as do the other

basal Triacanthodidae (8 -(- 12), the presence of somewhere around 20 vertebrae can be considered generalized in tetraodontids, and the great increase in number

in Chonerhinos and Xenopterus as well as the decrease in number to as low as 17 can both be considered speciali- zations. Moreover, since the Eoplectinae have only a moderately long soft dorsal fin base and a moderate number of rays (14 to 17), with an indication that the number of rays is in the process of being reduced posteriorly in the series, and the Triodontidae a short-based

dorsal fin with a low number of rays (modally 11), the

generalized tetraodontid condition can be considered to be a relatively short-based dorsal fin and lowered number of rays (approximately 10 to 12). Thus, the great increase in the length of the base and

in the number of rays in the dorsal fin of Chonerhinos and Xenopterus must be considered specializations for stronger more sustained swimming, perhaps associated with their invasion of fluviatile fresh waters, although

they are also found in coastal marine waters, with the

possible exception that the problematical C. africanus may be confined to the Congo. Similarly, the elaborate open cup nasal apparatus and increased number of

lateral lines in these two genera are specializations. Chonerhinos and Xenopterus also have specialized skulls (lacking prefrontals in both genera, and with enor- mously enlarged frontals in Xenopterus). Chonerhinos and Xenopterus are highly specialized

genera. Chonerhinos, which has lengthened the base of the dorsal and anal fins and increased the number of

rays to a lesser extent than Xenopterus, and which has a

less specialized skull than Xenopterus, obviously is the more generalized of the two. Fraser-Brunner (1943:4)

also considered these two closely related genera as highly

specialized, with the increased numbers of vertebrae and

fin rays "a secondary development." The contention of Le Danois (1959:248) that these two genera are the most

primitive of the tetraodontids and ancestral to the diodontids cannot be taken seriously. While Chonerhinos and Xenopterus are highly

specialized, in my opinion they are not sufficiently differ- entiated anatomically from the other tetraodontids to be

recognized as even subfamilially distinct (much less as a separate family). However, one genus of tetraodontids, Canthigaster, is usually recognized as a distinct family both in the general ichthyological literature and in that more specifically devoted to plectognaths, a practice that I have previously followed. Since about two dozen

species of Canthigaster are usually recognized as a separate family, and it is being suggested here that this
be changed, a detailed osteological description of C. rostrata is given here for the sake of comparison with that

of another, less specialized, tetraodontid, Lagocephalus

laevigatas. Following below is first a discussion of the differences between Canthigaster and the other tetraodontids, and

then of the anatomical diversity of the Tetraodontinae. The species of Canthigaster are distinguished from one

another externally primarily by coloration, with slight aid from the number of dorsal fin rays, one species (amboinensis) usually having 11 or 12 rather than 9 or 10, and perhaps from the caudal peduncle length versus depth (differences between species not yet well worked

out). The species are as similar internally as externally, there being an unrelieved sameness in the osteological configuration: 1) the vertebral column is always highly

arched; 2) the haemal arches of the first three vertebrae

are relatively well developed although they do not usually completely enclose the haemal canal (first arch sometimes complete); 3) the haemal spines of the other abdominal vertebrae are well developed and have a characteristic rounded and flattened posterior lobe; 4) the haemal spines of the caudal vertebrae are also well developed and of similar shape in all the species; 5) the

neural spines of the first three vertebrae are bifid and

that of the fourth is bifurcate anteriorly; 6) the neural

spine of the seventh abdominal vertebra is always a long

shaft lying along the anterior edge of the first basal pterygiophore of the dorsal fin, while the neural spines of the successive vertebrae until the antipenultimate are also elongate shafts; 7) the neural spine of the antipenultimate vertebra is slightly expanded anteroposteriorly and that of the penultimate even more so; 8) the caudal fin supporting skeleton is essentially similar

in all species; 9) the basal pterygiophores of the dorsal fin are all placed between the neural spines of the seventh abdominal to the third caudal vertebrae; 10) the basal pterygiophores of the anal fin are supported mostly by

the haemal spines of the first to third caudal vertebrae but sometimes with assistance of the fourth; 11) the first basal pterygiophores of the dorsal and anal fins are always much larger than the others; 12) the supraneural

is similarly well developed and usually arched; 13) the snout is relatively long and narrow; 14) there is always

only one hypohyal; 15) there is never an interhyal; 16) there is only a slight trace of the dorsal roof of the myodome; 17) there are never trituration teeth; 18) the parasphenoid never has a dorsal flange in the orbit to the

frontals; 19) the pharyngobranchial of the first arch always bears small teeth; 20) the supraoccipital is always

high crested; 21) the ethmoid is extremely long and Tshaped; 22) the frontal has a pair of posterolateral wings meeting or closely approaching one another distally; 23) the prefrontal is flattened dorsally and gently downcurved anterolaterally and is always placed in about the middle of the skull; 24) the sphenotics are not much ex- posed on the dorsal surface of the skull; 25) the vomer is always well developed and relatively well compressed

laterally and well removed from the prefrontals; and 26) the parasphenoid always has a deep keel.
'S S

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In general, there is such skeletal similarity between the

•pecies that for most practical purposes it can be truly said that to see the skeleton of one species of Canthigaster is to have seen them all, which is decidedly not the

case with other genera of tetraodontids with similar numbers of species. Until recently I had thought that a goodly number of these monotonously similar features of the species of Canthigaster were not shared by any tetraodontids and

that Canthigaster could with good justification be recog- nized as familially distinct from the Tetraodontidae. But

the skeletal structure of one relatively specialized tetra- odontid examined recently, and, to a lesser extent, that

of a few other species related to it, shows so many

similarities to Canthigaster that I am forced to the conclusion that they share a close common ancestry. From

this point of view, Canthigaster seems to me to merit only subfamilial recognition on the basis of the anatomical differences between it and the other tetra- odontids which remain after consideration of the struc- ture of Carinotetraodon lorteti, and its relatives. Recently described as Tetraodon somphongsi

(Klausewitz, April 1957a and 1957b) and immediately

thereafter as Carinotetraodon chlupatyi (Benl, July

1957; Benl and Chlupaty 1957), based on specimens from

fresh water in Thailand, Dekkers (1975) has shown that

the proper specific name is lorteti Tirant 1885. Benl

(1959) suggested that the species be retained in the genus

Carinotetraodon since it differed from all other tetra- odontids {Canthigaster being considered familially distinct) in being able to raise up a large fold of skin in the midline both dorsally and ventrally, just as in Canthigaster. It was believed that such behavioral and

anatomical skin changes would probably indicate other, more internal, differences between somphongsi and the other tetraodontids. Tyler (1978) has reviewed the growing aquarium literature on lorteti and the history of its name.

Because of its moderate tubelike nasal apparatus with

a single rounded nostril, Carinotetraodon lorteti otherwise would have to be accommodated in Monotreta. In fact, on the basis of its coloration and external morphometries, lorteti seems to be most closely related

to M. caria (Hamilton-Buchanan), but lorteti is suffi- ciently distinct from the four species of Monotreta ex- amined (cutcutia, which is the type-species, palembangensis, leiurus, and gularis) to warrant its retention

in Carinotetraodon. Regardless of its nomenclature, C. lorteti shares with

Canthigaster not only the ability to lift up a ridge of skin

dorsally and ventrally along the midline, but a number of internal features as well. The vertebral column in Carinotetraodon is highly arched and almost exactly

similar in configuration to that of Canthigaster. The first three vertebrae have bifid neural spines and well- developed haemal spines which do not completely

enclose the haemal canal, while the fourth vertebra has

the neural spine bifurcate anteriorly, and a large haemal

spine, although the flattened region of the spine does not form a distinctive posterior lobe as in Canthigaster. The

haemal spines of the fifth and subsequent vertebrae are

as well developed as in Canthigaster, but again they do

not have distinctive posterior lobes. The neural spine of the fourth vertebra is shorter than in Canthigaster, that

of the fifth similar to Canthigaster and that of the sixth

longer. The long neural spine of the seventh vertebra, supporting the anterior edge of the first basal pterygio- phore, and the succeeding neural spines until the anti- penultimate, are also long shafts, just as in Canthigaster, and the basal pterygiophores of the dorsal fin are accommodated between the neural spines of the 7th to 11th vertebrae in both genera. However, even though

both genera possess a specialized reduced number of 17 vertebrae, there are eight abdominal in Canthigaster and

only seven in Carinotetraodon. In both genera there are seven vertebrae with neural spines anterior to the first basal pterygiophore of the dorsal fin and seven with

neural spines posterior to the last basal pterygiophore. The caudal fin supporting skeleton, and, in general, the

last three vertebrae, are highly similar in both genera. The anal fin basal pterygiophores are closely supported

basally primarily by the haemal spines of the first three caudal vertebrae, with secondary assistance from that of the fourth, in both genera. Although the number of basal pterygiophores in the dorsal (12) and anal (9) fins of Carinotetraodon is greater than in Canthigaster (usually 8 or 9 dorsal and 5 anal), the first basal pterygiophores of both fins in Canthigaster are enormously larger than the

others and could represent fusion products of what are

the first few pterygiophores in these fins in Carinotetraodon. The similarities between Carinotetraodon and Canthigaster in the skull are less extensive than in the vertebral column, but are of phylogenetic interest. In Carino- tetraodon the frontal does not have a pair of posterolateral processes whose distal ends meet or closely ap- proach one another to partially enclose the muscle to the operculum, one of the most characteristic features of Canthigaster, but a perhaps functionally somewhat

similar arrangement is formed by the sphenotic of Carinotetraodon. The sphenotic in Carinotetraodon is broadly present on the dorsal surface of the skull, with an

anterolateral wing excluding the posterolateral edge of the frontal from the upper rear margin of the orbit, and, more importantly to the present discussion, a posterolateral wing prominently projecting out from the lateral surface of the skull, a feature found in none of the other

tetraodontids examined. The space between the anterolateral and posterolateral wings of the sphenotic of Carinotetraodon would seem to correspond to that

enclosed by the posterolateral wings of the frontal of Canthigaster. It is suggested here that the condition such

as found in Carinotetraodon could have given rise to than

in Canthigaster by the gradual posterolateral expansion

of the frontals overlying first the anterolateral wing of the

sphenotic, which would become reduced in size and

eliminated eventually, and then overlying the posterolateral wing of the sphenotic, which likewise would be

eliminated eventually as the frontal took over its supportive function, leaving only a small portion of the
sphenotic visible on the dorsal surface of the skull. Completion of the process would require only the coming

together in close proximity of the distal ends of the two

posterolateral wings of the frontal (those that had replac- ed the two wings of the sphenotic) to form a more complete well around the muscle to the operculum.

In Carinotetraodon the supraoccipital crest is not as high and laterally compressed as in Canthigaster, but it

is higher than in most other tetraodontids, and such a

condition could easily give rise to that of Canthigaster. The parasphenoid of Carinotetraodon has a well- developed ventral flange and is arched dbrsally in front of the orbit much as in Canthigaster. In Carinotetraodon

the prefrontal is relatively posterior in position, being

only slightly forward of about the middle of the skull, and while it does not have the characteristic smooth flat dorsal surface gently curved downward anterolaterally as found in Canthigaster, it is in contact anteriorly with the vomer only by a thin but wide anterior prolongation. If this anterior prolongation was reduced in size and then

lost, the prefrontal of Carinotetraodon would have the Canthigaster condition of being far removed from the vomer. The ethmoid of Carinotetraodon is not especially long in comparison to many other tetraodontids, but it is long enough for one to envision its elongation in the

process of lengthening the snout in Canthigaster and the conversion into a T-shaped cross section. A few other

features that would be necessary to the conversion of a Carinotetraodon-\ike fish into a Canthigaster-Vike one

are the development of a high anterodorsal wing on the suboperculum and a straightening of the dorsal edge of the operculum. One of the important distinguishing features of Canthigaster is the single nostril at the end of a very small short tube, and it is reasonable to suppose that Canthigaster was derived from a tetraodontid line with a

single nostril at the end of a better developed nasal tube. Among tetraodontids a nasal tube with a single nostril is found only in a few species of Monotreta (a few other

species of the genus have the opening bilobed) and in the

closely related Carinotetraodon. Only Carinotetraodon and Canthigaster are known to have the ability to lift up a ridge of skin along the

midline, and the osteology of Carinotetraodon shows

striking similarities to that of Canthigaster, more so than

does that of any other tetraodontid. It seems highly likely that Carinotetraodon and Canthigaster share a close common ancestry, from which Carinotetraodon has

diverged little but from which Canthigaster has become

highly enough modified to warrant subfamilial recognition. It would be of interest to know if the common

ancestral group was marine, fresh water, or euryhaline. Monotreta and Chelonodon, closely related to Carinotetraodon, contain species which show a few of the same

features (arched vertebral column, well-developed haemal spines on the abdominal vertebrae) of similarity between Carinotetraodon and Canthigaster, but, to a much lesser degree, than in Carinotetraodon. Nevertheparasphenoid

prefrontal

Figure 245.—Spfcoeroide* mat

(atturlateral view of head,

97.5 mm SL, Virginia.
x^^^-ff
Figuit24&.—Fuguchrytop8: lateral view of head, 98.6 mm SL, India.

Figure 249.—fu^ oblongus: lateral view of head, 46.2 mm SL, India.

and while they are primarily shallow-water coastal forms, one deepwater species (pachygaster) occurs on

both sides of the Atlantic as well as in the Indo-Pacific. Lagocephalus is world wide in distribution and tends to be found further offshore than Sphoeroides, with at least one of its species {lagocephalus) relatively oceanic and

circumtropical in distribution. The basic structure of the vertebral column does not

vary greatly among the species of Sphoeroides, there always being eight abdominal vertebrae modally, with most species {angusticeps, dorsalis, greeleyi, tricho- cephalus, lobatus, sechurae, spengleri) having a total of

17 vertebrae, with others {annulatus, nephelus, pachygaster, testudineus) a total of 18, one (maculatus) a total of 19, and another (marmoratus) a total of 20 (all figures modal). Lowered numbers of vertebrae can be considered

a specialization. In contrast to the vertebral column, the range in skull structure in Sphoeroides is so diverse that if only the two

species at the extremes of the osteological range were

studied one would receive the definite impression that they were not at all closely related and could not be con- tained in the same genus. To contrast the two extremes, S. dorsalis has: 1) a narrow skull £ind long slender snout region; 2) the

palatines are not widely divergent and the jaws are rela-
interoperculum mesopterygoic

Figure 250.—Arothron

atellatus : lateral view of head, 292 mm SL. India.

hyomandibulor

proolk

I pterotic sphenottc /|

Figure 251. —Tctroodonm6u: lateral view of head, 47.7 mm SL, Congo.

nteroperculum

ectoplerygoi

lively narrow; 3) the ethmoid and vomer are extremely

elongate; 4) the prefrontals are placed in about the middle of the skull; 5) the sphenotics form only the rear margin of the orbit; and 6) the frontals are wide posteriorly over the skull but very narrow interorbitally and of constantly decreasing width anteriorly. By comparison,

S. annuiatus has: 1) a broad skull and short wide snout

region; 2) the palatines are widely divergent and the jaws

are relatively wide; 3) the ethmoid is of moderate length and the dorsal surface of the vomer is exceptionally

short; 4) the prefrontals are placed anteriorly well in front of the middle of the skull; 5) the sphenotics are prolonged anterodorsally to form not only the rear but

also part of the dorsal margin of the orbit; 6) the frontals are laterally expanded anteriorly to the extent that they

are wider anteriorly than posteriorly.
Figure 252.—Chelonodon

fluviatilia: lateral view of head,

84.7 mm SL. Thailand.

metapterygoid mesopterygoid

Between these two extremes of dorsalis and annulatus, however, are other species of Sphoeroides which form an

almost continuous series of intermediate conditions. Thus, S. lobatus, angusticeps, and nephelus have only

slightly wider skulls and slightly less elongate snout

regions than S. dorsalis and otherwise are similar to it, while a number of other species (S. spengleri, maculatus, and greeleyi) have progressively wider skulls and less elongate snout regions, leading to species such as S. trichocephalus and pachygaster with wider frontals, progressively less slender or tapering anteriorly, and

eventually to S. testudineus in which the frontals are only slightly tapered anteriorly above the orbit, not being

greatly narrower there than posteriorly, and only taper- ing to a point far anteriorly and abruptly at the rear edge

of the prefrontals. The above series of progressively wider

skulls does not necessarily indicate precisely similar

specific relationships. Among the species of Sphoeroides the condition of the

skull in testudineus is that which most closely ap- proaches that of annulatus. In fact, these two species are usually considered to be closely related geminates to each side of the Central American isthmus {annulatus in the eastern Pacific and testudineus in the Gulf of Mexico

and the Caribbean) which have retained relatively similar color patterns of pale circles and reticulations unique

in the genus. One would suspect that the extremes of dorsalis and

annulatus both represent specializations, and that a

generalized skull structure in tetraodontids would
prerosphenoid hyomandibular

parasphenoid

frontal

Figure 254.—Chonerhinos

modestus: lateral view of head,

31.0 mm SL, Borneo.

Figure 255.—Xenopterug

naritua: lateral view of head,

143 mm SL, Bay of Bengal.

feature a moderate skull width and snout region length, with the frontals wide posteriorly but gradually and

evenly narrowed anteriorly, and the sphenotics not prolonged anterodorsally to form more than the rear margin of the orbit, these being conditions as found in the ancestral triodontids. In this view, species such as S. maculatus, trichocephalus, and pachygaster have

relatively generalized skulls in which the frontals are of moderate width and taper gradually anteriorly, while, going in one direction, greeleyi is perhaps very slightly

specialized in at least this one respect by the slightly abrupt narrowing of the frontals at the level of the

prefrontals, while testudineus is more specialized by the

lesser anterior tapering of the frontals and the more

abrupt narrowing at the level of the prefrontals. The

testudineus-Uke condition could be ancestral to that of annulatus through an increased expansion of the anterior region of the frontals and an anterodorsal expansion

of the sphenotics. The monotypic Guentheridia in the eastern Pacific
Figure 256.—Carinotetraodon lorteti: lateral view of head, 35.9 nun SL, locality i

differs externally from Sphoeroides only in having the in- ternal epithelium of the nasal sac deeply pitted rather than smooth or with ridges, and the gill rakers anteriorly on the fourth arch less well developed. The single

species, formosa, is often placed in Sphoeroides (as by

Fraser-Brunner 1943). The skull structure of formosa is remarkably similar to that of annulatus, being an even more specialized version of it, with the frontals more

laterally expanded anteriorly and the sphenotics even more anterodorsally expanded to form at least half of the

dorsal margin of the orbit. Only in annulatus among the

species of Sphoeroides does the parasphenoid have a dorsal flange in the interorbital septum which meets the

frontal, and formosa also has a similar flange. The color pattern of formosa can be considered a variation on that

of annulatus, with more numerous light reticulations and

circles and larger dark spots. It is obvious that annulatus

is a specialized derivative of a testudineus-Vike stock, and

that formosa is a specialized derivative of an annulatuslike stock. Thus, formosa should be included in Sphoeroides as the most extreme example of frontal widening and sphenotic anterior prolongation, for the pitted epithelium of its nasal sac and smaller gill rakers on the

fourth arch certainly are not sufficiently distinctive features to warrant even subgeneric recognition of for- mosa within Sphoeroides. Two of the examined species of Sphoeroides in which

the skull is only slightly less wide and the snout region only slightly less elongate than in the extreme condition

of dorsalis share with dorsalis one external peculiarity not otherwise found among the tetraodontids. In the western Atlantic S. dorsalis and in the eastern Pacific S. lobatus and angusticeps there are a pair of dark dermal

flaps which are relatively constant in position on the dorsum (sometimes absent as an intraspecific variation), while Shipp (1974:59) reported that this pair of flaps is also present in the eastern Atlantic S. marmoratus, not

studied here. These three species (four including marmoratus) undoubtedly share a close common ancestry, with the ancestral species becoming divided into two

isolated populations with the emergence of the Central American isthmus. The Atlantic population evolved into the highly specialized (in narrowness of skull) dorsalis (and probably marmoratus), while the eastern Pacific population diverged into lobatus and angusticeps with a

slightly lesser narrowing of the skull, differing from one

another mainly in angusticeps having a plainer coloration and having lost all the spines. Sphoeroides nephelus, which also has a relatively narrow skull, is probably also related to the line which

gave rise to dorsalis, lobatus, and angusticeps, while its closest relative is maculatus (see Shipp and Yerger

1969a, b, who show that parvus, not studied here, nephelus, and maculatus constitute a closely related

species complex). On the basis of its skull structure,

spengleri, with a moderate skull width, is not far removed from that complex, while pachygaster, with a somewhat wider skull, may be derived from a spenglerilike form. The deepwater S. pachygaster, with its thick, flabby

spineless skin, seems externally to be one of the most dis- tinctive and specialized species of Sphoeroides. However,

internally pachygaster is only moderately specialized by

a slightly more than moderate width of the skull, a slight anterodorsal prolongation of the sphenotics, a less firm

ossification of the skull, and an unusually great amount

of sculpturing on the dorsal surface of the skull, especially on the frontals, and by the loss of teeth on the first
pharyngobranchial, pachygaster being the only species of Sphoeroides examined lacking at least minute teeth on

this pharyngobranchial. The characteristics of the skull of pachygaster were first well described and illustrated by Kuronuma (1943). The possible relationships of S. pachygaster to Lagocephalus is discussed subsequently.

In addition to the anatomical diversity of Sphoeroides

discussed above (number of vertebrae, skull shape, rare presence of a dorsal flange of the parasphenoid, rare loss of teeth on the first pharyngobranchial), a few other items can be mentioned. A dorsal and ventral hypohyal

are present in most species, but only a single hypohyal is present in S. greeleyi and trichocephalus (and

Guentheridia formosa). An interhyal is absent in most

species, but it is present in greeleyi, maculatus, and

pachygaster. All species have two or more (most numerous in annulatus, in a disorganized plate) tritura- tion teeth to either side of the midline in the upper jaw, but most species do not have trituration teeth in the lower jaw, these being present only in S. angusticeps, annulatus, dorsalis, and greeleyi (and Guentheridia for- mosa) as three or more units, often tending to form a

platelike structure (especially with increasing specimen

size?) to either side of the midline. Remnants of the dorsal roof of the myodome are present in a few species. In S. dorsalis medial prongs of the prootics are well de- veloped, almost as well as described and illustrated here for Lagocephalus laevigatus, while smaller prongs

are present in S. angusticeps and greeleyi. In S. maculatus most specimens have only a very weak indication of a medial projection from the prootics, but lome

have moderately developed prongs about as large ..s in angusticeps and greeleyi. The amount of variation in the structure of the dorsal surface of the skull that is correlated with specimen size can be judged from the illustration of four specimens of

S. maculatus ranging from 12.4 to 201 mm.

While the above gives an idea of the anatomical diversity to be expected within a speciose genus and at least a broad view of the species relationships with one another,

a far more detailed analysis based on numerous external

features of all of the Atlantic species is given by Shipp

(1974), including several newly described species not

studied here.

All of the six species of Lagocephalus have been ex- amined to provide an additional survey of the anatomical

diversity to be expected within a genus. The variation in skull structure in Lagocephalus is only slightly less than

that found in the far more numerous species of Sphoeroides examined. Three of the six species of Lagocephalus have relatively deep chunky bodies and drab coloration and seem to be closely related on the basis of external features alone,

differing mainly in scale pattern on the dorsum; lunaris having scales from the snout to the dorsal fin, spadiceus from the rear of the snout to no more than half way back

the distance between the head and dorsal fin, and iner- mis with spmes totally absent. These three species have

the olfactory epithelium folded over the entire inner sur- face of the sac, usually with two of the folds on the rear

wall much larger than the others and themselves bearing

additional smaller folds. Two other species are somewhat

more elongate and conspicuously patterned and seem

closely related, laevigatus with a pattern of crossbars on

the dorsum and lagocephalus, slightly more elongate than laevigatus, with a dark dorsum, often with black

spotting, and gradually paler ventrum. Both of these

species lack spines on the back but have them well developed on the abdomen, and both tend to have only one of the folds on the rear wall of the nasal sac much

larger than the others and itself bearing smaller folds. The most distinctive species of Lagocephalus is scler- atus, with an elongate and depressed body and distinctly depressed caudal peduncle, and a color pattern of a dark dorsum with pale and dark spots and reticulations

Figure 257 .Sphoeroidet maculatus: dorsal views of skulls to show changes in shape, amounts

of cartilage viaible, and degree of auturing with

increasing specimen sizes, as indicated,

12.4-201 mm SL, New Jersey and Virginia.
abruptly changing on the middle of the side of the body

to plain pale below. It also has the olfactory epithelium

less folded than in the other species, the folds confined to the rear wall of the sac and the enlarged folds not themselves bearing elaborate folds, and fewer dorsal and anal

fin rays. In scleratus the dorsal rays are usually 10 to 12 and in the other species 13 to 15, while the anal fin usually has one less ray than the dorsal in all of the species. While the depressed body and caudal peduncle are

specializations in some way associated with its probably

rapid swimming, and its color pattern unique in the genus, the less elaborate folding of the olfactory epithelium is probably a more generalized condition than

in the other species. Since the majority of tetraodontids have relatively short-based fins with relatively few rays, as does Triodon, I would think that the moderate number

of rays in scleratus is more generalized than the larger number in the other species. There are more numerous internal differences between

the species of Lagocephalus. A specialized dorsal flange

of the parasphenoid in the interorbital septum that meets and sutures with the ventral surface of the frontals

is present in laevigatas, lagocephalus, lunaris, and

spadiceus but is absent in inermis and scleratus. In laevigatus and lagocephalus the pteroaphenoid is in conFigure 258.—Dorsal views of skulls of: A, Sphoeroidet dortalit, 155 mm SL, Florida; B,S. nepheliu, 128 mm SL, Bahamas:

C, 5. lobattu, 67.5 mm SL, Panama (Pacific).

tact with the dorsal flange of the parasphenoid, but not

in the other two species with a dorsal flange. A single hypohyal is present in all species except laevigatus, which retains the more generalized condition of both a

dorsal and ventral hypohyal. The first pharyngobranchial is toothless in laevigatus, lagocephalus, and

spadiceus, but in lunaris it bears a few minute teeth (much smaller than those on the second and third pharyngobranchials) and in inermis and scleratus numerous minute teeth, the retention of numerous teeth being the most generalized condition. A feature of the skull unique to Lagocephalus among

the tetraodontids is the development of a posterolateral wing of the frontal which meets or closely approaches the

posterodorsal surface of the pterotic to completely or partially roof over a temporal fossa. These specialized wings

are best developed in lunaris, laevigatus, spadiceus, and

lagocephalus (in respective increasing order of greatest

size and length of the wing), in which their wings usually make direct contact with the pterotic to completely roof
over the fossa, but the wings are relatively shorter in iner- mis and scleratus and do not meet the posterodorsal sur- face of the pterotic and thus only incompletely roof over the fossa. The lesser development of the wings in mermis and scleratus would seem to be the most generaliz- ed condition. The posterolateral region of the pterotic is directed more or less laterally in laevigatas, lunaris, scleratus, and spadiceus, but it is prolonged posterolaterally in inermis and, especially greatly so, in lago- cephalus. The ventral flange along the middle of each

side of the rear of the skull formed by the pterotic and exoccipital is much longer in lagocephalus than in the other

species. A larger portion of this flange in Lagocephalus is formed by the exoccipital than in most, but not all, other

tetraodontids (see, for example, illustration of Tetraodon

lineatus). The shape of the anterior portion of the frontals in Lagocephalus is probably of as much phylogenetic in- terest as is that of the posterolateral wing development.

In scleratus the frontal tapers gradually and evenly toward the front and is of moderate width, this being

similar to the condition in the more generalized species of Sphoeroides. In inermis the frontal is somewhat broader

over the orbit than in scleratus and abruptly begins to taper to a point at the rear of the prefrontals. In lunaris the configuration is much the same as in inermis, except

Figure 259.—Dorsal views of skulls of: A, Sphoeroides anguaticepa, 172 mm SL. Galapagos;

B, S. epengleri, 92.8 mm SL, Nicaragua;

C, S. maculattu, 179 mm SL, Virginia.

that there is greater abruptness in the tapering, the

length of the broad region of the frontal above the orbit is shorter, and the lateral edge of the prefrontal forms a

proportionally greater amount of the edge of the orbit. In

laevigatus, lagocephalus, and spadiceus the frontal is even wider over the orbit than in lunaris, and is similarly abruptly tapered, with the prefrontal forming a large part of the relatively straight edge of the orbit. Since a gradually tapered frontal of moderate width, as found in the ancestral triodontids, can be considered the

generalized condition, the above series is one of in- creasing specialization. The most generalized species in

this respect, scleratus, is also one of the two species with

the most generalized condition of the posterolateral wing

of the frontal, while the other species {inermis) with a

generalized posterolateral wing has the next most

generalized condition of anterior tapering. The extreme posterolateral region of the dorsal surface

of the pterotic in most species of Lagocephalus is uprais- ed into a flange, with which the posterolateral wing of the

frontal articulates in lunaris, spadiceus, and laevigatus.
or is directed toward in scleratus and inermis. No such

flange is present in lagocephalus, but the area of contact between the especially long posterolateral prolongations

of both the frontal and pterotic is much greater than in the other species. The ethmoid in Lagocephalus is relatively long in all six species, but its width varies from moderate in scleratus and lunaris to wide (the other four species). Anteriorly the ethmoid always broadly sutures with the

dorsal surface of the vomer, and, as explained for laevigatas in the detailed osteological description, this articulation sometimes becomes fully fused in large specimens. In laevigatas the ethmoid and the haemal

spines of the sixth and seventh, and, to a lesser extent, of the eighth, caudal vertebrae become swollen or hyperostotic in large adults. The only other species studied here

as a large adult specimen, a 214 mm lagocephalus, does

not show any hyperostosis, but the specimens oi inermis,

lunaris, scleratus, and spadiceas studied are all too small

to have hyperostotic parts even if that should be the norm for large adults. The supraneural element is relatively long in most

species of Lagocephalus, while it is extremely long in lagocephalus and only moderately long in inermis. Medial prongs from the prootic in the rear of the orbit, representing the remains of the dorsal roof of the myodome, are well developed in scleratus and

laevigatus, reaching almost to the midline, and are moderately developed in lunaris and spadiceus, while

Figure 260.—Dorsal views of skulls of: A, Sphoeroides greeteyi, 60.8 mm SL, locality unknown: B, S. trichocephalus, 57.1 mm SL, Panama (Pacific); C, S. pachygaster. 117 mm SL, Mozambique.

they are absent in inermis and lagocephalus. The

amount of surface sculpturing (not fully shown in the il- lustrations) of the top of the skull varies from slight in scleratus to moderate or well developed in the other

species. This, however, may be subject to intraspecific variation or change with increasing specimen size, for Kuronuma (1943) reported that lunaris and spadiceus, in contrast to inermis, had little surface sculpturing, mostly

confined to the ethmoid. The modal number of vertebrae in Lagocephalus is 17

{lunaris, scleratus, spadiceus), 18 (inermis, lago- cephalus), and 19 (laevigatus), with the lower numbers

more specialized. Neural prezygapophyses, especially on

the caudal and more posterior abdominal vertebrae, are extremely well developed as anterolaterally directed prongs in lagocephalus and scleratus, the two most

streamlined and probably rapid swimming species, but

are only moderately developed in the other four species. Likewise associated with muscle attachment are keels or ridges along the dorsolateral region of the neural arches

(and, to a lesser extent, along the ventrolateral region of the haemal arches of the caudal vertebrae). These keels are well developed in lagocephalus and scleratus, moderately developed in laevigatus and spadiceus, and
scarcely developed at all in inermis and lunaris. The

neural and haemal spines of the last few caudal vertebrae

are shorter in scleratus than in the other species, associated with the depressed caudal peduncle. A feature unique to Lagocephalus among the tetra- odontids is the posterior prolongation of the distal ends of the last basal pterygiophores of the dorsal and anal fins as prongs above and below the neural and haemal spines

of the vertebrae just behind the bases of these fins. The

prongs are moderately developed in inermis and lago- cephalus, slightly longer in laevigatas and lunaris, and of

greatest length in spadiceus (dorsal basal pterygiophore

only, the anal basal pterygiophore having a prong of only moderate length) and in scleratus.

All of the species of Lagocephalus have two or three rounded trituration teeth in a single series to each side of the midline of the upper jaw but none in the lower jaw, and all possess an interhyal, while none of the abdominal

vertebrae possess complete haemal arches. The first ray

in both the dorsal and anal fins of Lagocephalus is exceptionally short (slightly longer in young than adults) and

sometimes lacks cross-striations, and it is shorter than

the first ray of any of the other tetraodontids examined.

In all of the species of Lagocephalus the form of the epural is characteristic. In other tetraodontids the epural

varies from a more or less square block of bone to an

elongate rod, but the orientation of the bone is more or

less vertical or obliquely anteroventral to posterodorsal,

Figure 261 .—Dorsal views of skulls of:

left, Sphoeroides testudineua, 68.5 mm SL, Venezuela;

right, S. annulatus, 174 mm SL. locality unknown.

while in Lagocephalus the epural is dorsoventrally flat- tened and prolonged anteroposteriorly, in which direction it is oriented, an apparently specialized condition unlike that of any other gymnodont. The presence of two lateral lines on the body in Lagocephalus can also be

considered a specialization, since only a single lateral

line is present in triodontids and the basal triacan- thodids. Fraser-Brunner (1943) believed that Lagocephalus is the most primitive tetraodontid and that Canthigaster was derived from it, but he gave no reasons for so thinking. As discussed earlier, Canthigaster probably evolved from a Carinotetraodon-like line. I find no particular

similarities between Canthigaster and Lagocephalus. Fraser-Brunner thought that the skull of molids was

"almost exactly similar to that of Lagocephalus, even

possessing the postero-lateral limbs of the frontals characteristic of that genus." In fact, the frontals of molids do not have prominent posterolateral wings and

to my eyes the skulls of molids show no particular

similarities to those oi Lagocephalus, but, rather, as dis- cussed under the Molidae, they do show similarities to that of Triodon. One of the few similarities that at least a few species of Lagocephalus have to Triodon not found in
other tetraodontids are the exceptionally well-developed

neural prezygapophyses as anterolaterally projecting prongs found in lagocephalus and scleratus, which, while

not as large as in Triodon, at least approach those of Triodon in size. However, these prongs and the keels on

the neural arches seem to be specialized structures

associated with the musculature of a strongly powered

caudal peduncle for rapid swimming and are probably

independently evolved in Triodon and in a few of the

species of Lagocephalus. Lagocephalus cannot be reasonably considered as an

especially generalized tetraodontid. It possesses many

unique features not found elsewhere among the tetra- odontids or the ancestral triodontids and triacanthodids (most importantly the posterolateral wings of the frontals partially or completely enclosing a temporal fossa, the horizontal epural, especially short first dorsal and

anal fin rays, posterior prolongation of the distal ends of the last dorsal and anal fin basal pterygiophores) and

other features that, while not unique to it, can still be considered specialized (highly folded olfactory

epithelium, two lateral lines).

It seems more reasonable to me to consider LagoFifcure 262.—Dorsal views of skulls of:

left, Guentheridia formoaa, 175mmSL, Panama

(Pacific); right, Colomeeus peittacus, 179 mm SL, Surinam.

cephalus a specialized derivative of a Sp/ioerotdes-like group, for the following reasons. Lagocephalus scleratus must be considered, overall, the most generalized species

of the genus, because, in spite of a few specializations probably mostly associated with its mode of swimming

(depressed body and caudal peduncle, 17 vertebrae,

single hypohyal, exceptionally well-developed neural prezygapophyses and last basal pterygiophore prongs) it has a lesser degree of development of the specialized

features that characterize the genus (especially the evenly tapered frontals of moderate width and the relatively poorly developed posterolateral wings which do not meet

the pterotic and thus only partially enclose the temporal

fossa) as well as many other generalized features (first pharyngobranchials with numerous teeth, no dorsal flange on the parasphenoid contacting the frontals in the

orbit, well-developed prootic prongs representing the remains of the dorsal roof of the myodome, moderate

325
number of dorsal and anal fin rays, least highly folded

olfactory epithelium, minimal surface sculpturing on

top of the skull, spines on the back as well as the belly), a greater combination of generalized features than

any of the other species. A scleratus-like stock, minus its specializations, probably gave rise to inermis, which alone among Lagocephalus shares a few of the generalized features of

scleratus (first pharyngobranchial with numerous teeth, no dorsal flange on parasphenoid) and has the second most generalized configuration of the cranium, with the

posterolateral wing of the frontal similar to scleratus and

the anterior region of the frontal only slightly more

specialized than in scleratus by its greater width and

more abrupt tapering. It is probable that this line leading

to inermis also gave rise, by further specializations and

before the scales were totally lost, to lunaris, and that a

lunaris-like stock is ancestral to spadiceus, laevigatus, and lagocephalus. I would guess that in general

spadiceus has remained closer to this ancestral line than

have laevigatus and lagocephalus, with lagocephalus a

specialized more open water derivative of a laevigatuslike stock.

If scleratus can be accepted as the most generalized

species of Lagocephalus, then it is probable that Lagocephalus is an originally deepwater derivative of a

Sp/ioeroides-like ancestral group, for the cranium of

Figure 263.—Dorsal views of skulls of: A, Lagocephalus inermis, 52.2 mm SL, Bay of Bengal;

B, L. scleratus, 80.9 mm SL, Philippines;

C, L. lunaris, 62.3 mm SL, Bay of Bengal.

scleratus is not markedly different from that of several species of Sphoeroides, including that of pachygaster, which alone among Sphoeroides has a deepwater habitat, a highly folded olfactory epithelium, and a general countenance similar to that of the deep, chunky bodied

species of Lagocephalus, such as inermis, the closest

relative of scleratus and a species which may have

retained the general appearance of the ancestral line leading to it and scleratus, which scleratus lost as it became specialized for more rapid swimming. In S. pachygaster the frontals are about as wide as in L. scleratus, and they are similarly evenly tapered anteriorly, and the ethmoid-vomerine regions are remarkably

similar. Moreover, while not prolonged posterolaterally, the broad posterior end of the frontal projects out over

the underlying epiotic and pterotic as a short roof over

this region. In many other species of Sphoeroides, both specialized (e.g., dorsalis and testudineus) and

generalized (e.g., spengleri and maculatus) the posterior end of the frontal is slightly prolonged posterolaterally over the underlying epiotic and pterotic as a short roof. An only slightly increased posterolateral prolongation of
Figure 264.—Dorsal views of skulls of:

left, Lagocephalu» apadiceus,

98.2 mm SL, Mozambique;

right, L. lagocephalus,

214 mm SL, Malpelo Islands.

the frontal in pachygaster or any of the other species of Sphoeroides with a moderately wide, evenly tapered

frontal would lead to exactly the condition of the frontal found in L. scleratus. These species of Sphoeroides also share with L. scleratus the generalized features of the absence of a dorsal flange of the parasphenoid in the orbit, while most of them have numerous small to minute teeth on the first pharyngobranchial, except for S. pachygaster in which it is a toothless plate similar to that of most Lagocephalus. Most of these species of Sphoeroides have several small rounded trituration teeth in a single row to either side of the midline and none in the lower jaw, just as in Lagocephalus, and most also have both a dorsal and ventral hypohyal, a probable condition of the ancestral stock of Lagocephalus since L. laevigatus retains two hypohyals. A few of these species of Sphoeroides have moderately to well -developed prootic prongs in the rear of the orbit representing the remains of the dorsal roof of the myodome, and a few have interhyals, all conditions to be

expected in the ancestral stock of Lagocephalus.

In short, Lagocephalus seems relatively clearly to have

been derived from a Sp/ioeroides-like ancestral group,

the connection between the two being most clearly seen

in L. scleratus and in any number of relatively generalized species of Sphoeroides, as well as particularly in S. pachygaster. I would suspect that it was the same line of

Sphoeroides radiation leading to the deepwater pachygaster that gave rise to Lagocephalus, at a time before the few specializations of pachygaster (loss of teeth on

first pharyngobranchial, loss of spines, complete loss of remnants of the dorsal roof of the myodome) had become

established, this line leading to a form with two lateral

lines, moderately folded olfactory epithelium, and the

skeletal structure of scleratus and external characteristics ofinermis (except with spines on the belly and dor- sum), with the scleratus -like line diverging in external and a few internal features associated with its more rapid swimming and the inermis-like line developing a more

specialized skull structure, this latter line being

ancestral to most of the other species of Lagocephalus. Perhaps Sphoeroides was more widespread in the IndoPacific than at present, and has subsequently become

confined to the Atlantic and eastern Pacific as it met

superior competition in shallow Indo-Pacific waters from

the plethora of genera of tetraodontids evolving there, and was able to remain in the Indo-Pacific only in the form of a single deepwater species. Fraser-Brunner (1943) associated Amblyrhynchotes

and Torquigener (including Fugu) with Sphoeroides (as the Sphoeroidinae) and Lagocephalus (the Lagocephalinae, together with the Sphoeroidinae comprising

the Lagocephalidae), on the basis of their having the sphenotics small and separated from the prefrontals by

327
the frontals, in contrast to Colomesus (family

Colomesidae), another genus with two nostrils, in which

the sphenotics are large and prolonged anteriorly to meet

the prefrontals, excluding the frontals from the orbital margin.

I agree that the generalized condition of the nasal sac with two nostrils probably does link the "Lagocephalidae" and "Colomesidae" in a natural group as ap- posed to the "Tetraodontidae," and that Sphoeroides is distinctive among them in retaining the generalized condition of the lateral line. However, when numerous

species are examined the osteological differences between the groups are not as clear cut as previously thought, and they scarcely merit familial recognition. For example, Colomesus does have the sphenotics prolonged anteriorly further than in any other tetra- odontid, and the posterior recurving of its anterolateral region is also distinctive. However, the sphenotics become fully prolonged anteriorly to meet or very nearly meet the prefrontals and exclude the frontals from the margin of the orbit only in specimens of about 100 mm

and larger (see Tyler 1964 for illustrations of the skull at various sizes). At sizes of about 50 mm the skulls of the two species of Colomesus bear a strong resemblance to those of Sphoeroides annulatus and formosa, both of which, like Colomesus, have the frontal narrower posteFigure 265.—Dorsal views of skulls of: left, Amblyrhynchotes honckenii, 97.4 mm SL, Mozambique;

right, A. richei, 59.4 mm SL, New Zealand.

riorly than anteriorly and the sphenotics prolonged anteriorly, although not as far forward in adults of S. an- nulatus and formosa as in adults of Colomesus. In both

S. annulatus and formosa the anterior region of the sphenotics is laterally expanded, although the expansion

is not recurved as in Colomesus. Among Sphoeroides

(including Guentheridia) only annulatus and formosa

have a dorsal flange of the parasphenoid meeting the

frontals in the interorbital septum, and one (psittacus, along the coast of northern South America) of the two

species of Colomesus also has a dorsal flange of the para- sphenoid while the other (asellus, fresh water of northern South America) does not. Both species of Colomesus have two hypohyals, as does

S. annulatus, while formosa has only one. In Colomesus

there are numerous trituration teeth in both jaws, sometimes consolidated into paired plates, and both S. an- nulatus and formosa have the same arrangement, somewhat unusual among Sphoeroides. Colomesus has minute teeth on the first pharyngobranchial and lacks an

interhyal, as do S. annulatus and formosa, along with
most other Sphoeroides . Colomesus has 19 vertebrae, as does S. annulatus, while formosa has a more specialized reduced number of 17. In Colomesus medial prongs of the

prootic are present representing the remains of the dorsal

roof of the myodome, although these are less well- developed in psittacus than asellus, while neither S. an- nulatus nor formosa retain these remnants, a slightly more specialized condition. In both S. annulatus and for- mosa there are eight dorsal rays and seven anal rays, while Colomesus has a perhaps slightly more generalized number of 10 or 11 rays in these fins. In short, there are striking similarities between the os- teological makeup of Colomesus, S. annulatus and for- mosa, and the conversion of an annulatus-formosa-\ike

fish into one like a Colomesus would require only the

retention of remnants of the myodome and a few more

dorsal and anal fin rays along with the further anterior prolongation and recurving of the sphenotics and the development of a second lateral line, short segments of which are present in some specimens of many species of Sphoeroides, including S. annulatus and formosa. It seems likely to me that Colomesus arose from the same

line of Sphoeroides radiation as that which gave rise to annulatus and formosa from a testudineus-\ike ancestry. Perhaps this happened somewhere between the an- nulatus and formosa levels of organization, with Colomesus becoming far more specialized than either an- nulatus or formosa. Fraser-Brunner (1943) also conFigure 266.—Dorsal views of skulls of:

left, Torquigener pleurogramma, 113 mm S

Australia; right, Amblyrhynchotes piosae,

33.8 mm SL, Australia.

sidered Colomesus to be a derivative of a Sphoeroideslike stock, but for unstated reasons, which I would guess were zoogeographic. While Lagocephalus and Colomesus are relatively easily distinguished from the ancestral Sphoeroides-

( including Guentheridia here and following) -like stock, the relationships of the Indo-Pacific Amblyrhynchotes,

Torquigener, and Fugu are less clear. Fraser-Brunner

(1943) said that Sphoeroides has a long ethmoid, with

the frontals well removed from the premaxillary pedicels, 17 vertebrae, and no lower lateral line, while Amblyrhynchotes, Torquigener, and Fugu have the ethmoid

shorter, the frontals reaching far forward, close to the premaxillary pedicels, 20 to 21 vertebrae, and a lower

lateral line. Sphoeroides does tend to have a longer ethmoid, a

longer ethmoid-vomerine region, and the frontal further removed from the anterior end of the ethmoid-vomerine

region than in Amblyrhynchotes, Torquigener, and

Fugu, in most species of which the portion of the ethmoid-vomerine region that is exposed dorsally is rela- tively short so that the frontals do closely approach the

anterior end of the ethmoid-vomerine region. However,
in Torquigener pleurogramma, for example, the ethmoid

is no longer than in, for example, Sphoeroides greeleyi, nor is the entire ethmoid-vomerine region of T. pleuro- gramma shorter than in S. greeleyi, and the frontals are about equally far removed from the anterior end of the ethmoid-vomerine region. Fugu rubripes and Amblyrhynchotes honckenii likewise have relatively long ethmoid-vomerine regions in contrast to the other species

of those genera examined, while these regions are still shorter than in any species of Sphoeroides. The usually

greater length of the ethmoid-vomerine region in Sphoeroides helps to distinguish that genus from the other

three, and this moderate length in Sphoeroides can be

considered more generalized, for it more closely cor- responds to that of triodontids and triacanthodids than

does the usually foreshortened ethmoid-vomerine region

oi Amblyrhynchotes, Torquigener, and Fugu. While the modal number of vertebrae in Sphoeroides

ranges from 17 to 20, only two species have 19 or 20. In Amblyrhynchotes the modal number in the three species studied is 19, and using Fraser-Brunner's (1943) figure of

20, the range is 19 to 20. In Torquigener the modal number in the three species studied ranges from 19 to 21. In Fugu the modal number ranges from 20 to 23. Thus,

the number of vertebrae tend to be one to several units higher in most species of Amblyrhynchotes, Torquigener, and Fugu than in most species of Sphoeroides.

Figure 267.—Dorsal views of skulls of: left, Torquigener pleuroatictus, 87.1 mm SL, Australia:

right, Fugu ehrysope, 98.6 mm SL, Japan.

Fraser-Brunner (1943) said that Amblyrhynchotes had

the frontal evenly narrowed anteriorly, 20 vertebrae,

prickles on the side of the body at least behind the pectoral fin and no ridge along the lower lateral line, while Torquigener (including the species assigned to Fugu) had

the frontals much wider behind the prefrontals than between them, 21 vertebrae, no prickles on the side of the body and a ridge along the lower lateral line. As previously discussed, the ridge along the lower lateral line is pre- sent in some species of Amblyrhynchotes as well as in Torquigener and Fugu, although perhaps more commonly in Torquigener and Fugu. The modal vertebral numbers do not significantly differ, except that Fugu has

proportionally more species with more than 20 vertebrae than does Torquigener. At least the species of Amblyrhynchotes studied here have prickles on the side of the body which are absent in all of the species of Torqui- gener and Fugu studied.

In the three species of Amblyrhynchotes studied the

frontals are of moderate width and gradually taper anteriorly in honckenii and piosae, very much as in the species oi Sphoeroides with moderately wide frontals, except
that the ethmoid-vomerine region is at least somewhat

shorter, while in richei the frontals over the rear of the or- bit are very wide, at least as wide as more posteriorly, and evenly taper anteriorly to bluntly rounded ends, in front of which is an extremely short ethmoid-vomerine

region. The two species of Torquigener studied are about

as different in cranial configuration as A. richei is in comparison to A. honckenii and piosae. In T. pleurogramma

the frontal over the orbit evenly tapers to the posterior edge of the prefrontal, and then more abruptly tapers medial to the prefrontal, with a general configuration not much different than that of, for example, Sphoeroides

testudineus, except for having a wider ethmoid. In T. pleurostictus the frontal is laterally expanded over the

orbit, much wider there than more posteriorly, and only

begins to taper abruptly to a point at the posterior edge

of the prefrontal. The sphenotic in pleurostictus is more

anterodorsally expanded than in pleurogramma. The

major features of the skull in 10 species of Fugu has been

described and illustrated by Kuronuma (1943), who compared their configuration to that of three species oiLagocephalus and one of Sphoeroides (pachygaster) . The

structure of three of the species of Fugu studied here

(rubripes, oblongus, and chrysops) more or less encompasses the diversity found by Kuronuma. In rubripes and

oblongus the sphenotic is somewhat anterolaterally ex- panded; the frontal is laterally expanded over the orbit,

Figure 268.—Dorsal views of skulls of:

left, Fugu oblongus, 46.2 mm SL, India;

right. F. rubripes, 151 mm SL, Japan.

usually gently tapers to the posterior edge of the prefrontal, and then abruptly tapers medial to the prefrontal. The skull of chrysops differs from the others by being ex- ceptionally wide and having relatively straight lateral margins, the frontal being especially wide.

In all of the species oi Amblyrhynchotes, Torquigener, and Fugu studied the parasphenoid has a dorsal flange in the orbit meeting the frontals, there are small to minute

teeth on the first pharyngobranchial, a supraneural is present but the interhyal is absent and there are essentially no prootic medial prongs representing the remains

of the dorsal roof of the myodome. In all of the species of these three genera studied there are one to three small rounded trituration teeth in a single row to either side of the midline of the upper jaw but none in the lower jaw, except for A. richei, which had no trituration teeth in either jaw. Amblyrhynchotes piosae has both dorsal and

ventral hypohyals, while the other two species (honckenii and richei) of that genus have only the ventral hypohyal. Torquigener pleurogramma has both hypohyals but

pleurostictus has only one. In Fugu all three species studied {chrysops, oblongus, rubripes) had a single hypohyal. Amblyrhynchotes richei is unique among the 331
^L\'<^i.j^.:'^i

tetraodontids studied in lacking even a trace of a mesopterygoid. On the basis of the material examined, I am unable to distinguish Fugu from Torquigener, and I suspect that when more species of Torquigener are examined the dis- tinction would be even more difficult to make. Amblyrhynchotes is obviously closely related to Torquigener and Fugu, differing from them by the tendency to have

the frontal evenly narrowed anteriorly and to have

prickles on the side of the body. Much more remains to be done on the external and internal morphology of these

Indo-Pacific genera with two nostrils and, most usually, two lateral lines.

It is pure surmise, but I would guess that an early Sp/ioeroides-like stock with a generalized moderately wide skull and evenly tapered frontals in the Indo-Pacific gave rise to Amblyrhynchotes, Torquigener, and Fugu,

with the major changes from the ancestral type being the usual development of a lower lateral line, the usual shor- tening of the ethmoid-vomerine region, the constant development of the dorsal flange of the parasphenoid, and the frequent anterodorsal prolongation of the sphenotics. If this hypothesis is correct, the ancestral Sphoeroides-like group has subsequently become extinct in the shallow waters of the Indo-Pacific, and is represented

there only by a single deepwater species. All of the genera discussed above with two nostrils (the "Lagocephalidae" and "Colomesidae") were said by

Figure 269.-Dorsal views of skulls of: left, Arothron atellatus, ca. 420 mm SL, Seychelles;

right, A. armilla, 61.3 mm SL, Australia.

Fraser-Brunner (1943) to have the prefrontals separated on the dorsal surface of the skull mainly by the frontals, while in Ephippion, Arothron, Monotreta, Chelonodon,

Carinotetraodon, and Tetraodon (the "Tetraodontidae"), all with a single nostril, the prefrontals were said

to be separated mainly by the ethmoid (and the sphenotics separated from the prefrontals by the frontals, as in the "Lagocephalidae"). Whether one considers the ethmoid or the frontal to be

the main element separating the prefrontals is often a

highly subjective decision. In only a minority of species

of both groups can it be said clearly that the prefrontals on the dorsal surface of the skull are nearly exclusively separated by either the frontals or the ethmoid. In the

great majority of species of both groups the ethmoid ex- tends posteriorly approximately to the level of the posterior end of at least the main body of the prefrontals, although much of this posterior region of the ethmoid is often overlaid by the frontals and thus cannot be seen in dorsal view. In Sphoeroides, Lagocephalus, and Colomesus, for example, the prefrontals are separated about half by the ethmoid and half by the frontals, and there is much variation between species. In Amblyrhynchotes

332
the prefrontals tend to be separated mainly by the frontals, while in Fugu it is variously mostly by the frontals

or about half by the ethmoid and half by the frontals. In Torquigener the two species examined have the prefrontals separated about half by the ethmoid and half by the

frontals. Again, however, this is more a simple matter of how broadly the frontals cover the dorsal surface of the ethmoid rather than a characteristic of fundamental importance.

In Ephippion, Arothron, Monotreta, Chelonodon, Carinotetraodon, and Tetraodon the ethmoid tends to form

a greater proportion of the prefrontal separation than

does the frontal, and a greater proportion than in most

(but not all) species of the genera with two nostrils. In Arothron, for example, most species have the prefrontals separated almost entirely by the ethmoid, but in one

species {armilla) the prefrontals are separated almost ex- actly half and half by the ethmoid and frontals. In Tetraodon, Carinotetraodon, and Chelonodon the separation

is mostly if not entirely by the ethmoid, while in Monotreta the separation in most species is about half and half by the ethmoid and frontals, but almost exclusively by

the frontals in one species (gularis). Fraser-Brunner said that Arothron (as the Arothroninae) had the sphenotics not laterally expanded beyond

the rest of the orbital roof formed by the frontals, the

orbital roof strongly arched, the prefrontal curved down

Figure 270.—Dorsal views of skulls of: left, Tetraodon lineatiu, 222 mm SL, French Equitorial Africa; right, T. mbu, 47.7 mm SL, Congo.

before the eye and enclosing the olfactory foramen, the ethmoid relatively narrow and compressed, and a single

lateral line, while in Ephippion, Monotreta, Chelonodon, Carinotetraodon, and Tetraodon (the Tetraodontinae) the sphenotics are laterally expanded beyond the

frontal as a prominent lobe, the orbital roof is not much

arched, the prefrontal not curved down before the eye and not enclosing the olfactory foramen, the ethmoid

broad and a lower lateral line present which joins the upper.

It is true that the approximately six species of Arothron form a distinctive subgroup of Indo-Pacific puffers that is recognizable by external features alone: by a cer- tain difficult to describe sameness in configuration

(short, heavy bodies), as well as by the normally bifid tentacle with pitted inner surfaces and the single lateral

line. In the relatively normal members of Arothron

(represented in species studied here by hispidus, nigro- punctatus, stellatus) the sphenotics are only slightly if at

all expanded beyond the edge of the frontal, primarily because the frontal is exceptionally wide at the posterior region of the orbit (about 3 times as wide as more posteriorly in front of the supraoccipital), and the orbital roof
Figure 271 .—Dorsal view of skull o( Ephippion

guttifer, 101 mm SL, Guinea.

is at least moderately arched, with the anterolateral end

of the prefrontals curved down in front of the eye, more so

in adults than in the young, and enclosing the olfactory foramen, and the ethmoid of moderate to narrow width

(less wide than in Tetraodon and Ephippion but no less wide than in Chelonodon, Carinotetraodon, and most

species of Monotreta). Not all of these typical features are confined to Arothron, for the prefrontal entirely encloses the olfactory fo- ramen in the related Ephippion and in Chelonodon

patoca (but not C. fluviatilis), while in the related Tetra- odon lineatus (but not T. mbu) the prefrontal encloses all but the medial edge of a large olfactory foramen. The fo- ramen completely encloses the prefrontal in several species of the more distantly related genera Amblyrhynchotes, Torquigener, and Fugu, although in none of these do the prefrontals have such large downcurved anterolateral regions as found in most adult Arothron. The

sphenotics are not laterally expanded beyond the frontals in Monotreta gularis, and are only slightly to moderately expanded beyond them in the other species of Monotreta.

Moreover, one species, originally described as Tetrao- don armilla McCuUoch, that has the general external configuration and look of an Arothron, including a single

lateral line, differs greatly from the typical Arothron

skull plan. Externally, armilla differs from Arothron in having the nasal apparatus represented by a single flap of skin on each side of the head, the outer surface smooth

and the inner only very slightly irregular, while in Arothron there is always a bifid tentacle whose inner surfaces

are pitted by circular olfactory organs.

In the three typical species of Arothron studied {hispi- dus, nigropunctatus, stellatus), the parasphenoid either does not have a dorsal flange in the orbit, or does not have it well enough developed to reach dorsally far enough to contact the frontals, while in armilla the dorsal flange is well developed and contacts the prefrontals

as well as the frontals. While the typical species of Arothron have minute teeth on the first pharyngobranchial, in armilla they are relatively well developed, being only

slightly smaller than those of the second and third pharyngobranchials. In typical Arothron there is little or no evidence of prootic prongs in the rear of the orbit representing the remains of the dorsal roof of the myodome, while the prootic prongs are well developed in ar- milla, reaching almost to the midline. In typical Arothron several trituration teeth are present in a single series to either side of the midline of the upper jaw, but none

are present in the lower jaw, while in armilla, even at the small size of the examined individual, the numerous tri- turation teeth in both the upper and lower jaws are consolidated into large composite plates to either side of the

midline. Like the typical species o( Arothron, armilla has

only a ventral hypohyal and no interhyal. The most dramatic and perhaps phylogenetically in- teresting way, however, in which armilla differs from

typical Arothron is in the shape of the frontals and prefrontals. Instead of having the frontals greatly laterally expanded above the orbit, as in typical Arothron, the

frontals of armilla are only slightly wider over the rear of the orbit than more posteriorly, and gradually and evenly

taper to bluntly rounded ends anteriorly, much as in most of the more generalized species of genera with two

nostrils. The prefrontals of armilla are not enlarged and

laterally expanded to the same degree as the frontals at the rear of the orbit, and, although they do completely

enclose the olfactory foramen, they are only slightly downcurved anterolaterally. The prefrontals in armilla

are separated from one another about half and half by

the ethmoid and frontals, a probably more generalized

condition than having them separated mostly by the eth- moid as in typical Arothron. Although in two features (a single nasal flap and a dorsal flange of the parasphenoid meeting the frontals) ar- milla is more specialized than the typical species of Arothron, it has a far more generalized condition of skull configuration, especially of the frontals and prefrontals.

In fact, if the several species of Arothron not examined

for this work have skull structures similar to that of the

three typical species examined here and not intermediate between them and armilla, then armilla may be con-
sidered sufficiently distinct from Arothron to merit ge- neric recognition, the name Omegophora Whitley being

available for it (by monotypy and original designation, even though not sufficiently diagnosed). More importantly, it seems likely to me that a form

like armilla which still retained a bifid nasal tentacle and

the dorsal flange of the parasphenoid not yet fully devel- oped, could represent the ancestral group from which the

typical Arothron arose, for armilla has the most generalized condition of the frontals (moderate width, evenly and gradually tapering anteriorly), sphenotics (not es- pecially laterally expanded and not expanded anterodorsally) and prefrontals (moderate size, not greatly downcurved before eye) found among the ArothronAike

species.

It is possible that the pitted cup inner olfactory epi- thelium, as found in typical Arothron, indicates a rela- tionship with Chelonodon, one of whose species {fluviatilis) is the only other one among these related genera

(Fraser-Brunner's "Tetraodontidae") to have a pitted cup epithelium. However, the skull structure in typical Arothron and Chelonodon is not especially similar and

the partial similarly in olfactory epithelium may be for- tuitous, as is, I would guess, the slight similarity in skull structure between C. patoca and A. armilla.

Figure 272.—Dorsal views of skulls of: left, Chelonodon patoca, 70.6 mm SL, New Guinea;

right, C. fluviatilia, 84.7 mm SL, Thailand.

The monotypic Ephippion of the west coast of Africa is tolerant to fresh and brackish water when young, but

adults seem to be found primarily in marine coastal habitats. Since Ephippion has a decidedly bifid nasal tentacle, as do many species of Tetraodon, several of which

live in African fresh waters, and both genera have an upper lateral line which, usually, is joined by a lower lat- eral line, it has usually been thought that Ephippion is a

close relative of Tetraodon with specialized scales. As

previously described, the scales of Ephippion even in juvenile stages are larger than those of any other tetrao- dontids except Xenopterus and Chonerhinos, while with

increasing specimen size the scales oi Ephippion become

enlarged into a partial carapace over the body (except

ventrally and to some extent dorsally) between the head and the dorsal and anal fins, the scales of adults being far larger there than in any other plectognaths except ostracioids. The skull of Ephippion differs from that in the two

species of Tetraodon studied mostly by having the anterolateral wings of the sphenotics heavier and thicker, and
less dorsoventrally compressed into a plate. The frontal

in Ephippion is about as laterally expanded over the middle of the orbit as in Tetraodon, but it tapers some- what more evenly and gradually to a point anteriorly than in Tetraodon. In Ephippion the prefrontals are separated about half and half by the ethmoid and frontals, while in Tetraodon they are mostly separated by the ethmoid. The ethmoid of Ephippion is slightly less wide

than in Tetraodon. The vertebrae in Ephippion are 8 +

12 = 20, while in the three species of Tetraodon for which

vertebral counts are presented the range is 8 + 9 = 17

to 8 + 11 = 19. In £p/iippion there are several tritura- tion teeth in a single row to either side of the midline in the upper jaw, but none in the lower; while in the two

species of Tetraodon cleared and stained, there are no

trituration teeth in either jaw. In both Ephippion and

Tetraodon there are minute teeth on the first pharyngobranchial and the dorsal flange of the parasphenoid in the orbit meets the frontals, but there are no remnants of the dorsal roof of the myodome, no interhyal, and only a

single hypohyal.

Until recently, the categories Monotreta, Chelonodon, and Tetraodon were badly in need of revision. They are defined, as subgenera of Tetraodon, by Fraser-Brunner

(1943) entirely on nasal and scale pattern characteristics

Figure 273.—Dorsal views of skulls of: 1 Monotreta gularis, 46.8 mm SL, Burma;

right. M. leiurus. 61.5 mm SL, Thailand.

that are less than adequate. These categories have nearly always been used at the generic level, for failure to do so

leaves Tetraodon an unmanageable assemblage of numerous species, some obviously far more closely related than others. The use of these three categories also presents problems, which will probably only be solved when each of the species not discussed here has had its external and internal features compared with those described here. Dekkers (1975) has provided an excellent

revision of these Asiatic and mainly freshwater puffers based on external characters, placing them all in one

genus, with five unnamed subcategories for 15 species, two of which (erythrotaenia and waandersii) contain sin

gle species not studied here. For purposes of compara

five discussion in this monograph, Tetraodon, Chelonodon, and Monotreta are recognized at the generic level In Monotreta (nasal apparatus a tube with a single

nostril, the aperture of the tube with or without lips or

flaps) three of the four species studied are rather similar

to one another, and possess one feature unique to the
tetraodontids, while the other species does not share

these similarities. All four species studied are rather similar externally, with the nasal apparatus about the same

in all and varying only in the length of the tube, the upper lateral line joining the lower, at least a few prickles on the side of the body, and a color pattern featuring at

least one large black spot on the side of the body.

In M. gularis (Dekkers 1975:95, considered gularis a synonym of cutcutia, but the single specimen I have

identified and studied as gularis is not conspecific with

cutcutia), the sphenotic does not extend laterally beyond

the edge of the frontal, the frontal is much expanded lat- erally over the middle of the orbit, the posterolateral

region of the jjrefrontal is not much less wide than the average width of the interorbital region, the lateral edge

of the prefrontal is gently curved, the ethmoid is very

short and relatively wide, the palatine-vomerine strut supporting the upper jaw is relatively short, and the pre- maxillary pedicel is of moderate length (as in most other

tetraodontids). However, in the other three (leiurus, cutcutia, palembangensis) species of Monotreta studied the sphenotics extend laterally beyond the edge of the frontal (at least as much as illustrated for leiurus; in palembangensis the

sphenotic is even wider and further extended laterally), the frontal is only moderately laterally expanded over

Figure 274.—Dorsal views of skulls of: left, Chonerhinos modestus, .54.5 mm SL, Borneo;

right. Xenoplerus naritus, 143 mm SL, Bay of Bengal, with the barred band representing the

cut surface of the thickened frontal, removed

to expose the portions of the sphenotic and

pterotic which it overlies (dashed line marks

lateral edge of removed portion of frontal).

the middle of the orbit and is strongly tapered anteriorly

to the posterolateral region of the prefrontal, which is much less wide than the average width of the interorbital region, the lateral edge of the prefrontal is rela- tively straight and produced anterolaterally to a point, the ethmoid is very long and of moderate width, the pal- atine-vomerine strut supporting the upper jaw is long

relative to gularis (but not relative to a large number of other tetraodontids), and the premaxillary pedicel is of

relatively great length. The open space enclosed between the dorsomedial

edges of the two premaxillaries in M. leiurus, cutcutia, and palembangensis is much greater than in gularis or any other tetraodontid, partially because of the rela- tively great length of the premaxillary pedicels, but

equally important because the open space extends far further forward beyond the level of the anterior ends of 337
y^m^.:

Figure 275.—Dorsal view of skull of Carinotetra- odon lorteti, 33.1 mm SL, locality unknown.

the palatines than in any other tetraodontids, i.e., the medial edges of the premaxillaries in leiurus, cutcutia, and palembangensis have a much longer concave region than in any other tetraodontids. The four species of Monotreta studied are alike in that

there are small to minute teeth on the first pharyngobranchial, no trituration teeth in either jaw, no evidence

of prootic prongs representing remnants of the dorsal roof

of the myodome, no interhyal, a single hypohyal (one specimen of leiurus with two on one side and one on the

other), and no supraneural element. The only other

tetraodontids in which the supraneural is absent are members of the closely related genera Tetraodon (in which it is absent in mbu but present in Uneatus), Chelonodon (absent in fluuiatilis but present in patoca), and Carinotetraodon (absent in the single species

studied). In one of the species oi Monotreta (leiurus) the

first five abdominal vertebrae have bifid neural spines, and the neural spine of the sixth abdominal vertebra is bifid anteriorly but single posteriorly, while in the other

three species the neural spines of only the first four verte- brae are bifid. In most other tetraodontids the first three abdominal vertebrae have bifid neural spines, and the

neural spine of the fourth vertebra is bifid anteriorly but

single posteriorly. In Arothron, however, the neural

spines of the first four abdominal vertebrae are bifid, and

at least a short portion of the anterior end of the neural

spine of the fifth vertebra is bifid. Thus, Arothron and

Monotreta tend to have a slightly greater development of

bifid neural spines than do the other genera of tetraodontids, a specialization. In Monotreta the vertebrae are 18 in cutcutia and

gularis, but 20 or 21 in leiurus and palembangensis. Even though the ensemble of subsidiary characters, in- ternal and external, does not serve to separate gularis from the other three species of Monotreta studied, the

differential shapes and sizes of the frontal, prefrontal, ethmoid, vomer, palatine, and, especially, premaxillary

clearly indicate that there are two lines of diversification within the species of Monotreta studied. If additional

species of Monotreta not studied here are eventually shown not to bridge the gap between the two groups, they

should be recognized as at least subgenerically distinct (the identification of the specimen here studied as

gularis needs verification). One suspects that the ex- amination of additional species will bridge the gap. For

example, Carinotetraodon lorteti, otherwise assignable

to Monotreta because of the nasal tube with a single nostril (but with the upper and lower lateral lines not joining and both reaching the tail), has the length of the eth- moid about intermediate between gularis and the other

three species of Monotreta, the palatine-vomerine shaft about as long as in the three specialized species, the

length of the premaxillary pedicel intermediate between

gularis and the other three species, and the size of the space between the concave posteromedial regions of the two premaxillaries very similar to that of gularis. The

anterolateral wing of the sphenotic in Carinotetraodon is about like that of one of the three specialized species (palembangensis) of Monotreta, but there is no struc- ture in any of the four species of Monotreta similar to the

posterolateral wing of Carinotetraodon.

It seems obvious that Carinotetraodon and thus

Canthigaster, as discussed earlier in this section, have

their closest relationships among the Afom)tre(a-like

tetraodontids, but that a clearer understanding of the

relationships of these fishes awaits the time when the

critical internal and external features can be compared

for a larger number of species than it has been possible to do here. Such a further study must also obviously in- clude Chelonodon and Tetraodon, the generic limits of neither of which are presently clear. For example, in Tetraodon the lateral line system is highly variable, but it is probably basically represented by a lower line which joins the upper and continues to the

tail, this being modified in some species by the loss of the connection between the upper and lower lines, or even

the loss of the lower line, and perhaps of much of the upper line as well. The bifid nasal tentacle tends to be deeply split, almost to the base, and the inner epithelium smooth. The skulls of the two species studied are

relatively similar, differing mainly that in Uneatus the sphenotics are more anteriorly expanded than in mbu

(probably partially attributable to the much greater size of the study individual of Uneatus) and that the postero-
Figure 276.—Ventral views of

skulls of: left, Sphoeroides

/atus, 179 mm SL, Virginia

right, Arothron stellatus. ca. 420 mm SL, Seychelles.

branchiostegal rays

Figure 277. —Dorsal views of terus naritus, lOS mm SL, Bay

branchial arches (extended on of Bengal: (right) lower side) and lateral views Arothron nigropunctatua,

of hyoid arch of: (left) Xenop- .i6.8 mm SL, Solomon Islands.
ventral flange of the pterotic in lineatus has a goodly contribution from the exoccipital but in mbu next to none. Tetraodon mbu is unique among the tetraodontids studied in completely lacking a pterosphenoid. The eth- moid-vomer-palatine region is essentially similar in both

lineatus and mbu, and the prefrontals differ mainly in that of lineatus having an anteromedial arm helping to enclose the olfactory foramen. The skull shape of Ephippion is not far removed from that of Tetraodon and both

probably have a close common ancestral group, perhaps

as close as that which unites Tetraodon with Monotreta and Chelonodon. The only two species usually assigned to Chelonodon

differ slightly more than do the two of Tetraodon ex- amined. In C. fluviatilis, which has a deeply pitted ol- factory epithelium, the frontals abruptly end anteriorly

in a more or less straight transverse line at the rear edge

of the prefrontals, the latter being relatively thin and entirely separated by the ethmoid. In C. patoca the frontals become narrower anteriorly over the orbit, but they do

not stop abruptly at the level of the posterior edge of the

prefrontals, continuing anteriorly as rapidly tapering

points between the prefrontals, the latter being relatively thick and separated by both the ethmoid and frontals. The sphenotics in patoca are less anterodorsally ex- tended than in fluviatilis. The skull condition in patoca

is slightly more generalized than that of fluviatilis, and

patoca retains a supraneural which is lost by fluviatilis. Both species lack any remnants of the dorsal roof of the myodome, and there is no interhyal and only one hypohyal. The parasphenoid has a dorsal flange in the orbit meeting the frontals and there are minute teeth on the

first pharyngobranchial, while fluviatilis has numerous

trituration teeth to either side of the midline in both the upper and lower jaws, and patoca has only two or three

teeth in each series in the upper jaw and none in the lower jaw. The vertebrae are modally 18 in fluviatilis and

19 in patoca. On the basis of the differences in the olfactory epithe- lium, and of fluviatilis having the lobes of the olfactory apparatus oriented parallel to the body versus at a right angle to it in patoca, Le Danois (1959) generically separated fluviatilis (as Dichotomycterus) from patoca

(Chelonodon). The validity of such minor nasal dif- ferences alone in distinguishing genera is highly questionable, but should other species assignable to Chelonodon other than the commonly collected

fluviatilis and patoca come to light (a few valid species probably lurk among the numerous synonyms usually

listed for each of these names) and fall into one or the

other of the fluviatilis or patoca skull plans and not into intermediate types, there may be justification for es- tablishing two genera for what is now Chelonodon. The precise relationship of Chelonodon to Tetraodon and Monotreta is not clear on the basis of the present

data. As previously discussed, Chonerhinos and Xenopterus

are highly specialized tetraodontids which have secondarily increased the number of vertebrae and of dorsal and

anal fin rays, elaborated the lateral line system until

there are approximately three lines on the body, in- creased the size and amount of folding of the olfactory epithelium in the open cup nasal apparatus, and in- creased the size of at least some of the spines, mostly

those of the belly. The greater increase in numbers of vertebrae and dorsal and anal fin rays in Xenopterus in- dicates that it is the more specialized of the two, and this

is also borne out in the structure of the skull. While both

species are unique among the tetraodontids in the loss of the prefrontals (Fraser-Brunner 1943 said that the prefrontals are very small, but I find no trace of them at all), the skull of Chonerhinos otherwise is not markedly dif- ferent from that of many of the species of the Monotreta-Chelonodon-Tetraodon group. The frontals of Chonerhinos are slightly wider over the middle of the or- bit than more posteriorly and are tapered gradually and

evenly to gently rounded points anteriorly that broadly

overlie the relatively broad ethmoid, which is of moderate length, while the sphenotics are well extended

anteroventrally, projecting out beyond the edges of the

frontals and forming about the rear half of the upper edge

of the orbit. In Xenopterus the frontals are much more laterally ex- panded and thickened than in Chonerhinos, forming a

large plate over most of the dorsal surface of the skull. In the two smaller specimens studied the frontals are nor- mally articulated by interdigitation in the midline, but

in the largest specimen the two frontals are indis- tinguishably fused to one another in about the middle

third of their lengths. While the sphenotic oi Xenopterus

is about as anterolaterally extended as in Chonerhinos, it

is nearly entirely overlain by the frontal and only its ex- treme distal end appears in dorsal view, projecting

slightly beyond the edge of the frontal in about the middle of the upper edge of the orbit. The main body of the

supraoccipital in Xenopterus is less wide than in Chonerhinos, but the supraoccipital crest is wider and heavier

in the former than in the latter. In Xenopterus the neural and haemal spines of the penultimate vertebra become

hyperostotic, but this does not occur in Chonerhinos. The ethmoid in Xenopterus is shorter but broader than

in Chonerhinos and in both genera the anterodorsal end

of the vomer tends to fully fuse with the anteroventral end of the ethmoid. Both genera are also similar in having the pterosphenoids in contact with the parasphenoid

in the rear of the orbit, the pterosphenoid, para- sphenoid, and prootic forming a more elaborate and massive structure there than in any other tetraodontids. This

is perhaps functionally similar to the bracing strut of a dorsal flange from the parasphenoid in the middle of the

orbit to the under surface of the frontals as found in many other tetraodontids, but not in Chonerhinos and

Xenopterus. The only other tetraodontids in which the pterosphenoid meets the parasphenoid are several species of Lagocephalus, but this is associated with the

dorsal flange of the parasphenoid in the middle of the or- bit and thus is not analogous to that in Chonerhinos and

Xenopterus. In Xenopterus the supraneural is larger and

deeper bodied than in Chonerhinos. Both genera lack any remnants of the dorsal roof of the myodome, there is no
interhyal and only one hypohyal, the first pharyngobranchial has small to minute teeth and there are no

trituration teeth in either jaw. A sesamoid articular was

not found in the lower jaw of any of the specimens of Chonerhinos and Xenopterus examined, and these genera may be at least unusual, if not unique, among the

tetraodontids in the loss of this element.

In short, the skull in the more generalized of these two

specialized genera bears its greatest similarity to that of some of the species of Monotreta, Chelonodon, and

Tetraodon, perhaps especially to the latter, but the precise relationship of Chonerhinos to any of them is unclear. One would expect Chonerhinos to have arisen from

a line having a nasal sac with a single nostril, a well- developed lateral line system with at least one and a half

or two lines on the body, a tendency to increase the number of dorsal and anal fin rays above the perhaps

generalized number of about 10 to 12 and a tendency to increase the number of vertebrae above the generalized number of 20, all of which features are found in varying degrees among one or the other of Monotreta,

Chelonodon, and Tetraodon, and the ancestry of Chonerhinos is probably shared at one point with that of one or more of those three closely related genera.

Chonerhinos and, progressively more so, Xenopterus are probably derived from the ancestry of the Monotreta- Chelonodon-Tetraodon group, but their more precise relationships remain unknown.

Canthigaster is deemed to be sufficiently anatomically distinct from the other tetraodontids to be recog- nized as subfamilially distinct (Canthigasterinae) from them (Tetraodontinae), although the author is biased toward the conservative approach of only subfamilial

recognition for Canthigaster, since recently it usually is given full familial rank. Almost as much anatomical dis- tinctiveness is present between Chonerhinos-Xenopterus and the other tetraodontins as there is between the

canthigasterins and tetraodontins. Moreover, there is no genus known as closely intermediate between

Chonerhinos-Xenopterus and the other tetraodontins as Carinotetraodon is between the canthigasterins and the

other tetraodontins. Thus, there is no compelling reason

to recognize Canthigaster as even subfamilially distinct, and it is done here more as a matter of personal

preference than on the basis of persuasive anatomical

evidence. The argument against subfamilial recognition of Canthigaster could also take into account the situation Summary of generic relationships and intrafamilial classiflcation.—Because of the complexity of the external and osteological diversity of the tetraodontids, most of the analyses of the generic relationships within the family are given in the preceding section on

anatomical diversity, which need be only summarized

here. The genera having a nasal sac with two nostrils seem to form a natural group whose more generalized representatives are more generalized than most of those genera in which a single nostril is present at the end of a tube or in which there is a tentacle or an open cup nasal ap- paratus. Among the genera with two nostrils, Sphoeroides is the only one with a single lateral line, and

its osteology seems to be overall the most generalized, with Lagocephalus and Colomesus derived from a

Sp/ioeroides-like ancestral group, but from rather dif- ferent lines of radiation within that group. Amblyrhynchotes, Fugu, and Torquigener may also have been

derived from an early Sphoeroides-like group, and are probably more closely related to one another than to any

of the other genera with two nostrils, but their more

precise relationships are not clear on the basis of the pre- sent work. The genera in which the nasal sac has opened up by

the loss of the separation between the two nostrils are probably derived from an ancestral group with two nostrils and a single lateral line. A Carinotetraodon-Vike form is probably ancestral to Canthigaster, and

Carinotetraodon itself is probably most closely related to Monotreta. Ephippion is probably a close derivative of a Tetraodon-like form, and the relationship between

Monotreta, Chelonodon, and Tetraodon undoubtedly is close but the details of those relationships are not clear on the basis of the present work. The highly specialized

Canthigaster

Carinotetraodon

Ephippion

Figure 278.—Hypothesized

phylogenetic relationships of the genera of Tetraodontidae. 341
in the Monacanthidae and in the triacanthodid subfamily Triacanthodinae. In the monacanthids the highly

specialized genus Psilocephalus could be considered as subfamilially distinct (as it sometimes has been in the

past) from the monacanthids, and is not so recognized

here mainly because some of the intermediates between

its structure and that of more generalized monacanthids

are found in some of the Alutera-Vike fishes. Similarly, the highly specialized monacanthid Pseudaluteres could be considered subfamilially distinct, and is not so recog- nized here mainly because it is clear that Oxymonacanthus is intermediate between it and the more

generalized monacanthids, and an Oxymonacanthus-\ike

form gave rise to it. In the triacanthodids, the two long- snouted highly specialized genera of the Recent subfamily Triacanthodinae could each be recognized as a

distinct subgroup (tribe) and are not so recognized here mainly because a different genus is intermediate between each of the two long-snouted genera and the more generalized triacanthodins, i.e., a Bathyphylax-like

line is ancestral to Halimochirurgus and one like Tyde- mania to Macrorhamphosodes.

Relationships to the Diodontidae and to the Other

Tetraodontoidei. —The ways by which a triodontidlike ancestral group probably gave rise to two major lines of

radiation, one leading to the tetraodontids and dio- dontids and the other to the molids, are discussed under

the Triodontidae. The molids undoubtedly branched off the common ancestral line at a more generalized level of triodontidlike organization than did the tetraodontoids,

for molids retain a significant number of important

generalized features found in triodontids but not in tetra- odontoids, even though molids superficially seem far removed from triodontids and almost totally specialized. In fact, the tetraodontoids are at least as highly specializ- ed and as anatomically far removed from the ancestral

triodontidlike fishes as are the molids, as further discuss- ed under the Triodontidae.

In the vast majority of ways that tetraodontids differ from diodontids, tetraodontids retain more generalized,

triodontidlike, conditions than do diodontids. But there

are important exceptions in which diodontids have the more generalized conditions, indicating that the division

of the ancestral line into tetraodontids and diodontids

took place early in the evolution of the superfamily

(Eocene, on the basis of the fossil record), with diodontids retaining a few generalized features while overall becoming far more specialized than the tetraodontids. As previously discussed, it seems reasonable to assume

that the ancestral eoplectins that gave rise to the trio- dontids and other gymnodont lines did so at a time when

the premaxillaries and dentaries were not yet fused to

their opposite members, but only interdigitated to them, and with the teeth in the biting edge of the jaws small rounded units incorporated into the matrix of the bone

but retaining much of their individual identity. It is here assumed that the line of triodontidlike fishes which gave

rise to the tetraodontoids had the premaxillaries and

dentaries unfused and that the fusion of these bones to

their opposite members in diodontids and molids has been independent. It is possible that the triodontidlike

fishes which gave rise to the molids already had the dentaries fused, as in Triodon and at least Zignoichthys of the eoplectins, and that molids became further specializ- ed by having the premaxillaries fused as well (along with numerous other specializations, including the loss of dis- tinct teeth in the biting edge of the jaws). While diodontids have the more specialized condition

of fused premaxillaries and dentaries in relation to tetra- odontids having both of these bones articulated to their opposite members by interlocking emarginations, the fu- sion of these two jaw bones is a relatively uncomplex

event in comparison to the changes in the dental units in- corporated into the matrix of the bone. Diodontids retain the generalized condition of small rounded dental units

in the biting edge, just as in triodontids and eoplectins, while tetraodontids have extremely specialized teeth, perhaps the most specialized among teleosts, these being

long, slender rods lying obliquely transverse to the body

axis, parallel to the biting edge and incorporated into the

matrix. The large trituration plates present in the upper and lower jaws of diodontids are of about the same size as those of Triodon, even though there are usually fewer

series of teeth involved in the formation of the composite

plates (see discussion under the diodontid Chilomycterus orbicularis). However, the form of the trituration teeth and plates has probably been highly variable in most groups of gymnodonts, correlated with changes of

diet in newly occupied habitats, and not too much importance can be attached to the at least superficial similarity of the trituration plates in Triodon and

diodontids, i.e., the trituration plates of diodontids are not necessarily to be considered generalized. Other than the form of the teeth of the biting edge of the jaws, diodontids are more generalized and Triodonlike than tetraodontids only by: 1) the more frequent presence of both a dorsal and ventral hypohyal; 2) the presence of a prominent anteriorly directed prong on the suboperculum attached by ligament to the interoper- culum; 3) having none of the basal pterygiophores of the

dorsal and anal fin interdigitated to one another distally; and 4) the presence of a prominent lateral flange on the fused hypural plate, if this is homologous with the hypurapophysis of Triodon, which is debatable.

In all of the other far more numerous characters listed here in the comparative diagnoses of the tetraodontids and diodontids, the conditions found in the tetra- odontids are the more generalized and the least far removed from those in the ancestral triodontids (pre- Recent Triodon level of organization). The diodontids must thus be considered an early Eocene offshoot of the basal tetraodontids, with most of the diodontid specializations centering around a more

highly defensively armoured exoskeleton variously of long erectile quills or short nonerectile spines with massive bases forming an open quilted carapace around

a relatively slow swimming body with a reduced caudal

region and usually relatively more massive jaws with a

greater crushing and grinding function.
Family Diodontidae Comparative diagnosis (contrast with that of the Tetraodontidae). —Teeth incorporated into the matrix

of the biting edge of the jaws as small and more or less rounded units; premaxillaries and dentaries fully fused

to their opposite members in the midline; lateral surface

of the maxillary with a deeply indented or laterally flang- ed surface, the thickened ridges increasing its strength; the jaws massive; a large trituration plate always present

in the upper and lower jaws; first and second pharyngobranchials with minute teeth, third pharyngobranchial

with minute teeth or toothless, and sometimes absent;

dorsal and ventral hypohyal usually both present; inter- hyal never present; anterior edge of ectopterygoid rela- tively straight and only slightly concave; ethmoid and vomer greatly reduced in size and fused together into a

relatively thin and functionless plate; palatine not notched posteriorly, but broadly sutured thereto, and

taking its main support from, the frontal; prefrontal small or absent; frontals exceptionally wide and massive;

anterior end of parasphenoid exceptionally wide and

deeply concave, the concavity not being a place of ar- ticulation for other bones; rear margin of the orbit form- ed by the frontal alone; sphenotic with a long, slender,

laterally directed sturdy prong from its anterolateral

edge; frontal broadly in contact posteroventrally in the

rear of the orbit with the prootic, and, to a lesser extent, with the pterosphenoid, but not in contact with the

sphenotic; suboperculum with a prominent anteriorly directed prong attached by a short ligament to the posterior end of the interoperculum, the latter not articulating with the operculum; supracleithrum positioned

horizontally almost in the same line as the axis of the body; postcleithrum a single short piece, no longer than

about the distance along the scapula to the lowest actinost; supraoccipital crest dorsoventrally compressed and entirely in a horizontal plane, wider than deep

throughout its length; exoccipital condyles poorly developed; all of the vertebrae anterior to the first basal pterygiophore of the dorsal fin and a few of those posterior to the last basal pterygiophore of the dorsal fin with

bifid divergent neural spines; many of the more posterior abdominal vertebrae and several of the more anterior caudal vertebrae with prominent lateral flanges from

the ventrolateral surfaces of the centra; neural spines of the vertebrae supporting the basal pterygiophores of the

dorsal fin short and broad, not slender shafts and not

penetrating deeply the interspaces between the pterygiophores; a supraneural element never present; none of the basal pterygiophores of the dorsal and anal fins inter- digitated with one another; none of the abdominal

vertebrae with haemal arches, complete or incomplete;

several of the vertebrae posterior to the bases of the last basal pterygiophores of the dorsal and anal fins anteroposteriorly compressed, much shorter in centrum length than those more anteriorly; abdominal vertebrae always

greater in number than the caudal vertebrae; dorsal and

anal fins more posterior in position; only two vertebrae

fully posterior to that whose haemal spine is the last support of the last anal fin basal pterygiophore; caudal fin supporting skeleton with no free epural, no free hypurals, and no free parhypural, and with the haemal spine of the penultimate vertebra fused to its centrum; a prominent

lateral flange present on the fused hypural-centrum

plate; haemal canal not penetrating the last vertebral complex; caudal fin rays modally either 9 or 10, in the

ventral region of the fin only the single lowermost ray un- branched, perhaps 11 caudal rays in the Eocene

Prodiodon; scales always relative massive, whether long

erectile quills or shorter spines borne on a large triradiate

plate, or some combination of erectile and fixed spines. Detailed description of Diodon holocanthus. Material examined:—Five cleared and stained

specimens, 12.3-113 mm; one dry partially disarticu- lated skeleton, 124 mm.

SKULL.

Occipital Region.

Basioccipital. —A short column, expanded anterolaterally; cartilage filled at its anterior and anterolateral edges; articulates by interdigitation posterolaterally with

the exoccipitals, anterolaterally with the prootics, and

anteriorly with the overlying parasphenoid. In all of the specimens examined a certain amount of externally visi- ble cartilage persists at the region of junction of the

basioccipital, exoccipitals, and prootics, as it also does at the junction of the exoccipital, prootic, and pterotic and

at the junction of the posterior portions of the para- sphenoid and prootics. Extremely large specimens can be

expected to have more extensive interdigitation and less cartilage visible in these areas than shown in the illus- trations. The rim of the round concave posterior end of the basioccipital articulates by fibrous tissue with the rim of the concave anterior face of the first vertebra. The

posterodorsal surface of the basioccipital forms the lower

wall of the foramen magnum.

Exoccipital. —Cartilage filled at all of its edges of articulation with the other cranial bones; articulates by

interdigitation anterodorsally with the epiotic, laterally with the pterotic, anteroventrally with the prootic, and

Figure 279.— Range of diversity in body form

in the Diodontidae: Diodon holocanthus (left) and Chilomycterua achoepfi (right). 343
Figure 280.—Dtodon holocanthus (center), with Chilomycterus schoepfi (above)

for comparison : lower left, nasal

region as seen externally and scales from upper middle region of body of

C. schoepfi, and, lower right, nasal

region as seen externally and scales from upper middle region of body of D. holocanthus; dotted line on Figure

of C. schoepfi shows the course of the

lateral line canals and their major

pores, as deciphered by placing drops of ink on each pore found by microscopic search of a partially drying specimen.

Otic Region.

Pterotic. —Expanded posterolaterally into a

flattened, almost vertical, supporting strut for the pectoral girdle; broadly cartilage filled along its medial

edges; articulates by interdigitation anterodorsally with

the sphenotic, anteroventrally with the prootic, posteroventrally with the exoccipital, and dorsomedially with

the epiotic. At a concavity on the posterior surface of its posterolaterally expanded portion, the pterotic articulates by fibrous tissue with the anterior end of the supracleithrum. Along the anterolateral edge of its ventral sur- face the pterotic supports the hyomandibular. This

articulation between the pterotic and hyomandibular is by fibrous tissue anteriorly, but posteriorly the two bones become extensively interdigitated with one another

Sphenotic. —Confined to the dorsal and lateral portions of the skull and not entering into the formation

of the wall of the orbit; cartilage filled along all. of its edges of articulation with the other cranial bones; ar- ticulates by interdigitation anteriorly with the frontal, medially with the supraoccipital, posteromedially with

the epiotic, posterolaterally with the pterotic, and ventrolaterally with the prootic. The region of articulation between the sphenotic and prootic forms a concave sur- face to which the anterior half of the dorsal edge of the hyomandibular is held by fibrous tissue. The dorsolateral edge of the sphenotic possesses a stout, pronglike,

lateral process which serves as the place of origin for muscles which insert on the operculum. Epiotic—A thin, more or less squarish plate; cartilage filled along all of its edges of articulation with

the other cranial bones; articulates by interdigitation anteriorly with the sphenotic, medially with the supraoccipital, posteriorly with the exoccipital, and laterally with the pterotic.

ventromedially with the basioccipital. Posteromedially

the dorsal edges of the exoccipitals interdigitate with one

another so that the dorsal as well as the lateral walls of the foramen magnum are formed by the exoccipitals. From the posterior end of its ventrolateral edge the exoccipital possesses a pair of short but sturdy processes which overlie and articulate by fibrous tissue with the

anterolateral region of the first vertebra, these processes being the modified exoccipital condyle.

Supraoccipital. —A flat plate anteriorly, but drawn

out posteriorly into a much depressed spine which

reaches to about the level of the end of the first vertebral centrum; articulates by interdigitation anteriorly with

the frontals, anterolaterally with the sphenotics, and

posterolaterally with the epiotics and exoccipitals. The

ventral surface of the anterior half of the supraoccipital

spine interdigitates with the dorsomedial surfaces of the

exoccipitals.

Prootic. —Cartilage filled along all of its edges of

articulation with the other cranial bones, except anteriorly; articulates by interdigitation anterodorsally with the frontal, anteromedially with the ptero- sphenoid, anteroventrally with the parasphenoid,

posteromedially with the basioccipital, posteriorly with

the exoccipital, posterolaterally with the pterotic, and

laterally with the sphenotic. Medially on its ventral sur- face the prootic articulates with the lateral edge of the

posterior end of the parasphenoid. This articulation is usually through cartilage, and only in large specimens do

the two bones become interdigitated to any appreciable

extent. Cartilage persists in this region long after it has

at least mostly disappeared from external view between

the region of junction of the basioccipital, exoccipital, and prootic and the region of junction of the prootic, exoccipital, and pterotic. There is no evidence of a myodome. Along the concave area at the region of ar- ticulation between the prootic and sphenotic, the hyomandibular is supported through fibrous tissue. This

support is strengthened, however, by the extensive inter-
digitation of the anterolateral edge of the prootic with the

anterodorsal edge of the hyomandibular.

Orbital Region.

Frontal. —Extremely large and laterally ex- panded; articulates by interdigitation posteromedially

with the supraoccipital, which it slightly overlies, and

posterolaterally with the sphenotic. Medially along its ventral surface in the region of the orbital cavity the frontal interdigitates with the pterosphenoid. At its anterior end the frontal is extensively interdigitated medially

with the palatine and laterally with the prefrontal, the

latter bone being broadly overlain by the frontal. Along

the posterior half of its medial edge the frontal interdigi- tates with its opposite member, but more anteriorly the medial edges of the two frontals articulate with one

another only by fibrous tissue. Between the regions where

the medial edge of the frontal is in close contact with its opposite member and where it interdigitates with the

palatine, the frontal overlies the ethmoid cartilage.

Prefrontal. —A thin plate of extremely variable

size, but always broadly overlain by the frontal and

hence apparently very small as seen dorsally. The prefrontal articulates by extensive interdigitation medially

with the palatine and posteriorly and laterally with the

frontal.

Parasphenoid. —More or less in the form of a cross, with the longer shaft becoming increasingly deeper and

wider toward its anterior end. The anterior end of the parasphenoid is so deeply concave that the cavity ex- tends back posteriorly almost to the level of the shorter

transverse arms of the parasphenoid. The parasphenoid

articulates by interdigitation posterolaterally along the

dorsal surface of its transverse arms with the prootics, while at its extreme posterior end the parasphenoid overlies and interdigitates with the basioccipital. Between its regions of interdigitation with the basioccipital and with

the prootic, the parasphenoid has its lateral edges in contact with the cartilage that is present along the medial

edges of the prootics. Anterolaterally the parasphenoid

interdigitates with the medial edge of the palatine. The

highly concave anterior end of the parasphenoid has its dorsal surface held to the ventral surface of the ethmoid

cartilage. The posterior end of the platelike ossification that occurs between the ethmoid cartilage and the dorsal surface of the parasphenoid, to be described below as the ethmoid-vomer, is slightly overlain by and interdigi- tated with the anterior concave end of the parasphenoid. A very shallow ventral flange or keel is present along the medial portion of the ventral surface of the para- sphenoid in the region under the orbital cavity.

Ethmoid Region. Ethmoid-vomer. —All that remains of the ossifica- tions of the ethmoid region is a plate of bone which is very thin throughout its length, except at its anterior edge where it becomes substantially thicker. The plate of bone lies between the ventral surface of the ethmoid cartilage and the anterodorsal portion of the parasphenoid. The posterior end of the plate fits under and interdigi- tates with the inner surface of the dorsal half of the deeply concave anterior end of the parasphenoid, while the

anterior edge of the plate lies anterior to the ethmoid cartilage. There is no evidence in any of the specimens ex- amined that any of the edges of the plate are cartilage

filled, but even if the plate were entirely an endochondral ossification the bone is so thin that one would not expect to find cartilage filled edges. Only by histological examination of the developing bone would it be possible

to state whether the bone is of dermal or endochondral

origin or of a combination of the two. From the position

of the anterior portion of the plate (between the frontals and in at least close apposition with the ethmoid cartilage) one would suspect that the bone is the ethmoid. However, the posterior end of the bone fits into the concavity of the parasphenoid, a characteristic of the vomer

in most plectognaths. Until histological examination of the development of the bone sheds light on its nature, I presume that it probably represents the fused rudiments

of both the ethmoid and vomer.

Mandibular Region. Hyomandibular. —Expanded dorsally, tapering to a stout shaft anteroventrally; cartilage filled at its anteroventral edge and along the middle of its dorsal edge; ar- ticulates dorsally by fibrous tissue with the concavity

along the ventrolateral edges of the prootic and sphenotic and along the anterior half of the anteroventral edge of the pterotic. The support of the hyomandibular is fur- ther strengthened by the extensive interdigitation of its anterodorsal end with the anterolateral edge of the

prootic and of its posterodorsal end with the ventrolateral edge of the pterotic. Anteriorly the hyomandibular articulates by fibrous tissue with the posterior ends of the metapterygoid and symplectic. In large specimens the articulation between the hyomandibular

and the metapterygoid becomes slightly interdigitated. Along the ventral half of its posterior edge the hyomandibular articulates by fibrous tissue with the preoper- culum. Immediately behind its uppermost point of contact with the preoperculum, the hyomandibular

possesses an upraised region whose posterior surface is hollowed out to receive and hold by fibrous tissue the anterior rounded articular facet of the operculum.

Pterosphenoid. —Relatively elongate dorsoventrally; much wider dorsally than ventrally; cartilage

filled along all of its edges, except medially; articulates by interdigitation dorsally with the frontal and ventrally with the prootic.

Quadrate. —Wide posteriorly, tapering to a knob

anteriorly for articulation with the articular in the lower

jaw; only a very short posterior process present from its ventral edge between the symplectic and preoperculum;

cartilage filled at its posterior edge; articulates by inter-
digitation anterodorsally with the ectopterygoid and

posteroventrally with the symplectic, which it broadly

overlies; articulates by fibrous tissue ventrally with the preoperculum and through cartilage posteriorly with the metapterygoid. The anterior knoblike end of the quadrate articulates against the groove on the posterior edge

of the articular in the lower jaw, with the fibrous tissue articulation strengthened by a short anteromedially

directed process from the anterior edge of the quadrate

just above its knoblike anteroventral end.

Metapterygoid. —A large plate of bone; cartilage

filled along its anteroventral edge; articulates by inter- digitation anterodorsally with the ectopterygoid and

mesopterygoid and anteroventrally with the symplectic,

all three of which bones the metapterygoid broadly overlies; articulates posteroventrally by fibrous tissue and

slight interdigitation with the hyomandibular, while anteriorly it articulates through cartilage with the quadrate.

Opercular Region. Operculum. —A large flat plate with a high, well- developed, lateral flange which ends dorsally by project- ing over the hyomandibular to serve as a place of attach- ment for muscles originating on the lateral wing of the

sphenotic; articulates by fibrous tissue ventrally with the suboperculum. The upper anterior edge of the oper- culum is laterally expanded into a stout facet for fibrous

tissue articulation with the concave surface of the upraised area on the posterior edge of the hyomandibular.

Suboperculum. —A relatively flat plate, except for a

lateral thickening along its edge of fibrous tissue ar- ticulation with the anterior edge of the operculum. From

its anterodorsal region the suboperculum is prolonged

anteriorly as a narrow shaft to a level slightly forward of the posterior edge of the preoperculum. The anterior end

of this shaftlike process connects by a short ligament

with the posterior end of the interoperculum.

Symplectic. —Large; broadly overlain by both the metapterygoid and quadrate; cartilage filled at its posterior end; articulates through cartilage with the anterior end of the hyomandibular, and by interdigitation dorsally with the metapterygoid and anteriorly with the quadrate. Ventrally the symplectic articulates by fi- brous tissue with the preoperculum.

Palato-Pterygoid Region.

Palatine. —Expanded dorsally into a horizontal

plate; articulates by interdigitation dorsally with the

frontal, ventrally with the ectopterygoid, and posterodorsally with the parasphenoid. Posteroventrally the

palatine broadly overlies and articulates by slight inter- digitation with the mesopterygoid. The anterior edge of the portion of the palatine which overlies the mesopterygoid is cartilage filled in all but the larger study

specimens. Anterodorsally the rounded edge of the

palatine articulates by fibrous tissue with the concave ar- ticular facet of the maxillary, while a medially directed prong from the anterior edge of the palatine articulates by fibrous tissue with the posteromedial edge of the pre- maxillary.

Ectopterygoid. —An almost straight shaft of bone, except for a thin posterodorsally expanded portion that

interdigitates with the palatine, mesopterygoid, and

metapterygoid; articulates by extensive interdigitation dorsally with the palatine and ventrally with the quadrate.

Mesopterygoid. —Somewhat variable in shape, but

always broadly overlain by the palatine and metapterygoid; articulates anterodorsally by slight interdigitation with the palatine, while anteroventrally and posteroventrally it articulates by more extensive interdigitation

with, respectively, the ectopterygoid and metapteryInteroperculum. —A stout rod, with a large ventral

flange in about the middle of its length; articulates by

ligaments anteriorly with the angular in the lower jaw and posteriorly with the anterior end of the suboper- culum. The medial surface of the ventral flange of the in- teroperculum articulates by fibrous tissue with the

lateral surface of the epihyal and the posterolateral sur- face of the ceratohyal. Preoperculum. —Large; expanded posteroventrally; its dorsal edge somewhat laterally expanded to form a broad surface of fibrous tissue articulation with

the ventral edges of the quadrate, symplectic, and

hyomandibular.

Upper Jaw.

Premaxillary. —The two premaxillaries are indis- tinguishable fused in the midline and together with the fused teeth form a massive crushing plate; anterior edge

of premaxillary forming the border of the upper jaw for about the dorsal two-thirds of that border, ventral to which the maxillary forms the anterior edge of the upper

jaw. In the middorsal line the fused premaxillaries form a

short posteromedial process which articulates by fibrous

tissue with the palatines and the ethmoid-vomer.

Posterolaterally the premaxillaries are broadly overlain by and extensively interdigitated with the maxillaries. The fused teeth of the premaxillary are closely similar to those described for Triodon. They are small, discrete, in- dividual pieces formed in the relatively small pulp cavity

of the premaxillaries. They move forward toward the edge of the jaw and become closely packed against one

another in the bony matrix that surrounds them. By the time they reach the leading edge of the jaw they are so densely packed together that they have lost much of their individuality, at least in large specimens. Whether the

teeth at the edge of the jaw ever truly fuse indistinguish- ably with themselves and the premaxillary is again a
matter for histological study. The remains of approxi- mately 20 of the formerly separate dental units can be

seen along the edge of the premaxillary to either side of the midline and to a depth of 5 to 10 units posteriorly from the edge. At the posterior end of the tooth bearing

region, the sockets surrounding the individual pri- mordia open to the exterior on the outer surface of the

premaxillaries by small pores, similar to those described

for Triodon. A large trituration plate is present in the dorsomedial region of the inner surface of the fused premaxillaries. The trituration plate is divided into right and left halves whose medial edges are in close contact. Each plate has its relatively flat surface marked by ap- proximately five parallel grooves which show the limits of the originally separate dental plates that are now fused

together in a solid mass. These dental plates are formed

in a large pulp cavity, above the trituration plate, which

is separated from the pulp cavity in which the teeth of the jaws are formed by a thin bony partition and which is broadly open to the exterior posteriorly to either side of the midline. The newly developed platelike trituration teeth are obliquely placed in an anterodorsal to postero- ventral plane at about a 45° angle to the surface of the

trituration plate. At first, only the posteroventral edge of the new tooth plate is exposed at the surface of the

trituration plate, but as the tooth is moved forward and

downward, its whole substance is gradually worn away. As the tooth plates are moved forward they become more

and more closely packed together, until they lose most of

their individual identity, at least in larger specimens.

Maxillary. —Expanded ventrally where it forms the lower one-third of the anterior margin of the upper jaw; broadly overlies and extensively interdigitates with the

premaxillary. The medial surface of its free ventral end

articulates by fibrous tissue with the dorsolateral surface

of the dentary. Posterodorsally the maxillary possesses a medially directed process which runs under the anterior end of the palatine to make fibrous tissue contact with

the lateral edge of the posteromedial projection of the

fused premaxillaries. The concavity on the posterodorsal edge of the maxillary articulates by fibrous tissue with the anterior end of the palatine. In about the middle

of its length the maxillary is laterally expanded into a heavy flange which serves as a place for muscle at- tachment.

Lower Jaw.

Dentary. —The two dentaries are indistin- guishably fused in the midline, and, like the premaxillaries, form a huge crushing beak in conjunction with the

fused teeth. The concave posteromedial surface of the dentary interdigitates with the lateral surface of the articular. Posteroventrally the dentary interdigitates with

the angular. A large trituration plate, divided into right and left halves in close contact with one another, is pre- sent in the medial region of the inner surface of the fused

dentaries. The structure and development of the dental

units of the trituration plate and biting edge of the lower

jaw are exactly like that described for the premaxillary, except that the internal cavity for the dental pulp is somewhat smaller. The dorsolateral surface of the dentary articulates by fibrous tissue with the ventromedial

surface of the maxillary.

Articular. —More or less triangular in shape; its posterior edge laterally expanded basally and bearing a groove for fibrous tissue articulation with the quadrate;

cartilage filled for only a short distance anteriorly where

it is continuous with the remains of Meckel's cartilage; articulates by extensive interdigitation anteriorly with

the dentary and posteroventrally with the angular. The

sesamoid articular is a nubbin of bone, of variable size, which is usually interdigitated with the articular just above and posterior to the remains of Meckel's cartilage. Angular. —A small bone interdigitated anteriorly with the dentary and dorsally with the eu'ticular. Posteriorly the angular attaches by ligament to the inter- operculum. BRANCHIAL APPARATUS.

Hyoid Arch and Branchiostegal Rays. Hypohyals. —Dorsal and ventral hypohyals

present; the ventral hypohyal about twice as large as the

dorsal hypohyal; dorsal hypohyal cartilage filled at its ventral edge, ventral hypohyal cartilage filled at its posterior edge; articulate through cartilage with one another and with the anterior end of the ceratohyal; ar- ticulate by fibrous tissue medially with their opposite members.

Ceratohyal. —Somewhat expanded posteriorly; cartilage filled at its anterior and posterior edges; ar- ticulates through cartilage anteriorly with the hypohyals, and through cartilage and slight interdigitation

posteriorly with the epihyal, which it overlies. All six branchiostegal rays articulate by fibrous tissue with the

ceratohyal, the platelike first ray with a vertical groove on the medial surface in about the middle of its length, as explained below.

Epihyal. —Round and broadly overlain by the posterior end of the ceratohyal, with which it articulates through cartilage and slight interdigitation. The lateral surface of the epihyal articulates by fibrous tissue with

the medial surface of the ventral flange of the inter- operculum.

Branchiostegal rays. —Six in number; the first branchiostegal ray a large plate, of increasing width posteriorly, whose lateral edge is sharply downturned and

whose medial edge is more gradually upturned. Anteriorly the downturned lateral edge of the first branchiostegal becomes thickened into a vertical articular face which fits against the vertical groove on the medial sur- face of the ceratohyal. The second branchiostegal ray is a 347
normally tapering shaft, articulating with a slight indentation on the ventromedial surface of the ceratohyal just posterior to the articulation of the first branchiostegal. The third to sixth branchiostegal rays articulate one just behind the other with the lower half of the posterolateral surface of the ceratohyal. The third branchiostegal is more laterally expanded in the anterior third of its length than are the other rays.

Branchial Arches. —All the elements are cartilage

filled at their edges of articulation with the other elements of the series, and the articulations are usually through cartilage and fibrous tissue. The branchial

arches are composed of three basibranchials, three pairs of hypobranchials, five pairs of ceratobranchials, four

pairs of epibranchials, and three pairs of pharyngobranchials. Three gills are present; the fourth arch has no

gill and there is no slit between the fourth arch and the lower pharyngeal.

First arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. First basi- branchial the largest of the basibranchial elements; dis- placed forward so that it articulates posteriorly with the second basibranchial and posterolaterally with the first hypobranchials. First hypobranchial the longest of the hypobranchial elements; articulates ventrally with the

region of articulation between the first and second basi- branchials and dorsally with the first ceratobranchial.

First ceratobranchial the shortest of the ceratobranchial

elements, which, except for the first ceratobranchial, in- crease in length posteriorly in the series; possesses weakly developed flanges from its anteroventral and postero- ventral edges, similar flanges being increasingly well developed on the second and third ceratobranchials but

not present on the fourth or fifth ceratobranchials; ar- ticulates ventrally with the first hypobranchial and dorsally with the first epibranchial. First epibranchial a

slender rod; articulates dorsally with an upraised area on

the anterodorsal surface of the first pharyngobranchial.

First pharyngobranchial a relatively flat plate; wider

laterally than medially; bearing over all of its ventral

surface innumerable, small, villiform teeth, slightly

larger in the posterior region than anteriorly; articulates

at an upraised area on its anterodorsal surface with the

first epibranchial and at an upraised area on its posterodorsal surface with the second epibranchial.

Second arch. —Basi-, hypo-, cerate-, epi-, and

pharyngobranchial elements present. Second basi- branchial the smallest of the basibranchial elements; ar- ticulates anteriorly with the first basibranchial, anterolaterally with the first hypobranchials, posteriorly with

the third basibranchial, and posterolaterally with the second hypobranchials. Second hypobranchial the shortest of the hypobranchial elements; articulates ventrally

at the region of articulation between the second and third basibranchials and dorsally with the second cerato- branchial. Second ceratobranchial articulated dorsally with the second epibranchial. Second epibranchial a long

slender rod; like the first epibranchial, but with a slight expansion on its posterior edge for fibrous tissue articulation with the third epibranchial; articulates dorsally

principally to the upraised area on the second pharyngobranchial, only secondarily with the upraised area on the

posterodorsal surface of the first pharyngobranchial. Sec- ond pharyngobranchial the longest of the pharyngobranchial elements; its toothed surface narrower but

longer than that of the first pharyngobranchial; in- numerable villiform teeth present, like those on the first pharyngobranchial, but with those along the posterior edge distinctly larger than more anteriorly; articulates at an upraised area on its dorsal surface principally with the second epibranchial but also with the anterodorsal end of the third epibranchial.

Third arch. —Basi-, hypo-, cerato-, epi-, and

pharyngobranchial elements present. Third basi- branchial somewhat wider posteriorly than anteriorly; articulates anteriorly with the second basibranchial,

anterolaterally with the second hypobranchials, posterolaterally with the third hypobranchials, and posteriorly with the fourth ceratobranchials. Third hypobranchial almost as long as the first hypobranchied;

directed anteroventrally under the second hypobranchial, with its narrow anterior end articulated by fi- brous tissue with the region of the first basibranchial and

dorsal hypohyals. Third ceratobranchial articulated ventrally with the third hypobranchial and dorsally with the

third epibranchial. Third epibranchial thicker than

those anterior to it; expanded dorsally into two short

flanges, the more anterior of which articulates with the upraised area on the second pharyngobranchial, while

the more posterior flange articulates with the anterior edge of the fourth epibranchial. Third pharyngobranchial an elongate, thin, flat plate; toothless; held

in place primarily by fibrous tissue to the posterior edge of the second pharyngobranchial, without any

special connection with any of the other branchial elements.

Fourth arch. —Cerato- and epibranchial elements

only. Fourth ceratobranchial a stout shaft; without ventral flanges; the longest of the ceratobranchial elements;

articulates ventrally with the third basibranchial and

dorsally with the fourth epibranchial. Fourth epi- branchial by far the longest and stoutest of the epi- branchial elements; somewhat produced into a thin

flange posteriorly along the lower two-thirds of its length;

articulates ventrally with the fourth ceratobranchial, while dorsally it ends in the general fibrous tissue that binds the dorsal surfaces of the pharyngobranchial

elements to the ventral surfaces of the parasphenoid and

prootics.

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial large; slightly ex- panded laterally along most of its length; toothless; ar- ticulates ventrally with the base of the fourth cerato- branchial.
PAIRED FIN GIRDLES.

Pectoral Fin.

Supracleithrum. —In position almost parallel to the

axis of the body; a round shaft anteriorly, but becoming

wider and dorsoventrally depressed posteriorly; articulates at its rounded anterior end by fibrous tissue with

the concavity on the posterior surface of the laterally directed wings of the pterotic. The posterior portion of the supracleithrum overlies and articulates by fibrous

tissue with the dorsolateral surface of the cleithrum and

postcleithrum.

Cleithrum. —Wide dorsally, but tapering to a narrow shaft in the lower third of its length; much ex- panded posterolaterally throughout the middle of its length. The cleithrum articulates by fibrous tissue dorsally with the overlying supracleithrum and with the

anterior half of the ventral edge of the postcleithrum, which it overlies. Posterodorsally the cleithrum articulates by fibrous tissue and slight interdigitation with the

anterior edge of the scapula. Along its posterior edge, in about the middle of its length, the cleithrum articulates by fibrous tissue with the anterodorsal and anteroventral edges of the coracoid. The anterior ends of the two cleithra articulate with each other by fibrous tissue

in the midventral line of the body between the medial

edges of the platelike portions of the first branchiostegal

rays at the level of the end of the ceratohyal.

Postcleithrum. —A rounded shaft anteriorly, but becoming compressed posteriorly into a thin sheet whose

outline is highly irregular from specimen to specimen. In none of the specimens is there any evidence of two

separate elements making up the postcleithrum, for the

dorsal and ventral postcleithra apparently have fused

into one piece. The postcleithrum articulates by fibrous tissue anteriorly with the cleithrum and supracleithrum.

Coracoid. —Constricted in the middle, but expanded dorsally and even more expanded ventrally;

cartilage filled along its dorsal and anteroventral edges;

articulates by fibrous tissue anterodorsal ly and anteroventrally with the cleithrum, while dorsally it articulates through cartilage with the base of the scapula and

bases of the second to fourth actinosts.

Scapula. —Scapular foramen not entirely enclosed by the scapula, but, rather, with the lower half of its anterior edge closed by the cleithrum; cartilage filled at

its dorsal and ventral edges; articulates by interdigi- tation anteriorly with the cleithrum, posterodorsally with the anterior edge of the first actinost and posteroventrally with the anteroventral edge of the second actinost. Ventrally the scapula is supported through cartilage by the coracoid.

Actinosts. —Four elements; all cartilage filled at both ends, except for the reduced first actinost, which is cartilage filled only dorsally; first actinost a triangular wedge interdigitating with the dorsal half of the posterior edge of the scapula and the anterodorsal edge of the second actinost; second, third, and fourth actinosts more

or less constricted in the middle, but with decreasing amounts of constriction from the second to the fourth. The second, third, and fourth actinosts interdigitate with one another at their ventral edges of contact, and the anteroventral edge of the second actinDst interdigitates with the posteroventral edge of the scapula. Dorsally the

first, second, and third actinosts interdigitate with one

another. The fourth actinost articulates anterodorsally with the third actinost by fibrous tissue in some

specimens but by interdigitation in others. The second to fourth actinosts are supported basally through cartilage by the coracoid. Distally the actinosts and scapula support by fibrous tissue most of the fin rays.

Fin rays. —Twenty-two to twenty-four fin rays present in most specimens; the first ray very small and

divided into two halves throughout its length, the medial

half much larger than the lateral half. The first ray ar- ticulates by fibrous tissue with the scapula, whereas the

other rays articulate with the actinosts. The first two

rays and the last ray are unbranched; all the others are branched. Fiist ray without cross-striations, the others

cross-striated. VERTEBRAL COLUMN. —All vertebrae with

biconcave centra, except for the last, which ends posteriorly in fusion with the parhypural and hypurals.

Abdominal Vertebrae.

First vertebra. —Neural spine bifid; neural arch

with a bony roof over the neural canal, the shelflike medial processes from each side of the neural arch meeting and interdigitating in the midline; articulates by fibrous tissue over the upper half of the anterolateral surface of its centrum with the short exoccipital condyles, while the rim of the concave anterior end of the centrum rests against the rim of the concave posterior end of the basioccipital. The deeply concave posterolateral edge of the neural arch articulates by fibrous tis- sue with the anteriorly projecting neural prezygapophysis of the second vertebra. Other abdominal vertebrae. —Twelve abdominal

vertebrae in 10 specimens. The 1st to the Uth ab- dominal vertebrae have bifid and divergent neural

spines. The bifid neural spines are of about the same

height on all the vertebrae, but the anteroposterior length of the spines increases from the 1st to about the

4th abdominal vertebra and then decreases from the 5th

to the 11th abdominal vertebra. Shelflike medial projections from each side of the neural arch meet and inter- digitate (or even fuse) in the midline to form the bony
roof over the neural canal on the first to ninth ab

dominal vertebrae. The 10th and Uth abdominal verte brae have no such bony roof over the neural canal, the canal being roofed over between the divergent neura

spines of these two vertebrae only by fibrous tissue. The

dorsomedial region of the bony roof over the neural cana becomes upraised into what is, in effect, a third neura

spine on some of the abdominal vertebrae. There is only

a trace of such a dorsomedial flange on the third ab dominal vertebra but on the fourth abdominal vertebra it

is distinctly present, and by the fifth and sixth ab dominal vertebrae it reaches its maximum develop ment, then becomes progressively less well developed on

the seventh and eighth abdominal vertebrae until by the ninth abdominal vertebra it is no longer present. At its greatest development, on the fifth and sixth abdominal

vertebrae, this dorsomedial flange is prolonged anteriorly to such an extent that it protrudes over the posterior region of the neural arch of the preceding verte- bra, with fibrous tissue attaching it to the bony roof over

the neural canal. Neural prezygapophyses are well developed on all of the abdominal vertebrae and ar- ticulate by fibrous tissue with the posterodorsal regions

of the lateral surfaces of the centrum just anterior to them. Haemal arches are not present on any of the ab- dominal vertebrae, but from the 9th to 12th abdominal

vertebrae progressively larger ventrolateral flanges are present from the ventrolateral edges of the centra. These

flanges are the place of attachment of large muscle

masses. The 12th abdominal vertebra differs from the

other abdominal vertebrae in that its neural arch does

not possess a bifid and divergent neural spine. From the base of its neural arch area two broad plates project dorsally and slightly medially to meet the bases of the first two dorsal fin basal pterygiophores. There is no distinct bony roof over the neural canal of the 12th abdominal

vertebra, the functional roof being formed by the fibrous

tissue articulation of the ventral ends of the basal pteryg- iophores with the dorsal ends of the lateral walls of the neural arches.

Caudal Vertebrae. —Nine caudal vertebrae in 10 specimens; the first six caudal vertebrae variously supporting the dorsal and anal fin basal pterygiophores. The

first three caudal vertebrae are structurally similar to the

last abdominal vertebra, but their ventrolateral flanges become progressively shorter, and delicate posteroventrally directed processes from the ventrolateral surfaces

of their centra are present which articulate by fibrous tis- sue with the dorsal ends of the anal fin basal pterygio- phores. As is the case with the last abdominal vertebra, the lateral walls of the neural arches of the first three caudal vertebrae articulate by fibrous tissue dorsally with the ventral ends of the dorsal fin basal pterygiophores. The fourth caudal vertebra differs from the preceding caudal vertebrae by the only slight develop- ment of its ventrolateral flange, and by the presence

along the posterior half of the dorsal surface of its neural arch of a bifid and divergent neural spine. The anterior

half of the dorsal surface of this neural arch possesses the

dorsomedially directed bony plates which articulate by

fibrous tissue with the bases of the last two dorsal fin basal pterygiophores, in the same way as described for the preceding caudal vertebrae. From its posteroventral edge the fourth caudal vertebra possesses a short posterior process which articulates by fibrous tissue with an

anteriorly directed prong from the haemal process of the

fifth caudal vertebra. The fifth caudal vertebra possesses

a bifid and divergent neural spine between which is supported by fibrous tissue the last dorsal fin basal ptery- giophore, with no bony roof present over the neural canal between the medial edges of its divergent neural spine. Delicate ventral processes are present from the ventrolateral edges of the fifth caudal vertebra which support

the dorsal end of the last anal fin basal pterygiophore, while a bifid and divergent haemal process is present

ventrally to either side of the upper end of the last anal

fin basal pterygiophore. There is no special bony roof over the haemal canal, except the functional one formed by the ventral processes of the fifth caudal vertebra meeting with the dorsal end of the last anal fin basal

pterygiophore. The anterior edge of the bifid haemal

process is produced into a short prong which articulates by fibrous tissue with the posterior process from the

fourth caudal vertebra. The sixth and seventh caudal

vertebrae are similar to one another, their centra being

relatively short anteroposteriorly and both possessing

bifid neural and haemal spines. No bony roofs are present between these bifid neural and haemal spines, so that the neural and haemal canals are roofed over only by fibrous

tissue. The anterior edges of the neural and haemal

spines of the sixth caudal vertebra support by fibrous tis- sue, respectively, the last dorsal fin basal pterygiophore and the last anal fin basal pterygiophore. The eighth caudal vertebra has its neural and haemal spines bifid and divergent anteriorly, but as single medial plates posteriorly. The undivided posterior portions of the neural and haemal spines of this vertebra are posteriorly ex- panded, and they interdigitate with the anterior edge of the plate formed by the last vertebra and associated caudal fin supporting elements. From the lateral surface

of the haemal spine of the eighth abdominal vertebra, a

posteriorly directed process is present which articulates by fibrous tissue with the anteriorly directed process from the last vertebral segment.

Caudal Skeleton. —The caudal fin supporting struc- tures are consolidated into a single plate which in adults shows only meager traces of areas of suturing or fusion of the originally separate elements. In specimens smaller than about 100 mm, however, at least one of the elements

retains its individuality, this being the epural. The

elongate epural is interdigitated with the posterior edge

of the neural spine of the eighth caudal vertebra and with

the anterodorsal edge of the main portion of the plate supporting the caudal fin. In larger specimens the suturing between these two elements becomes obscure and

true fusion may take place. Anteroventrally on the caudal plate in the smaller study specimens there is some

indication of an originally separate parhypural having
fused with the main body of the plate, but even in the

12.3 mm specimen this thinner parhypural region is con- tinuous with the main body of the plate. The rest of the

plate is composed of the last vertebral centrum fused with all of the hypural elements. In about the anterior two-thirds of its length the caudal plate possesses a lateral flange whose depth increases anteriorly. The anterior end

of the lateral flange articulates by fibrous tissue with the

posterolateral process from the haemal spine of the penultimate vertebra. The posterior edge of the caudal

plate supports the caudal fin rays. Caudal fin rays. —Nine in number; the uppermost

ray and the lowermost ray unbranched, the other rays becoming increasingly branched toward the middle rays, which are branched in triple dichotomies. The bifid bases of the rays articulate by fibrous tissue with the posterior edge of the caudal plate. DORSAL A^^D ANAL FINS.

Fin rays and pterygiophores. —Fifteen fin rays

usually present, the first two rays and the last ray un- branched, the others branched in single or double dichotomies. Distal pterygiophores either absent or unossified. The fin rays are supported through fibrous tissue

at their bifid bases by 12 basal pterygiophores. The

pterygiophores are cartilage filled at both ends, and all of them, with the exception of the last, are stout rods which

decrease in width posteriorly in the series. The last pterygiophore is rodlike anteriorly, but posteriorly it is expanded into a flat plate. The ventral edge of the last pterygiophore articulates by fibrous tissue with the bony

roofs over the neural canal of the fourth and fifth caudal

vertebrae. The other pterygiophores articulate ventrally by fibrous tissue with the irregular dorsal edges of the neural arch plates of the 12th abdominal to 4th caudal

vertebrae. The pterygiophores articulate by fibrous tis- sue dorsally with one another and with the dorsal fin rays.Anal Fin. Fin rays and pterygiophores. —Thirteen or fourteen

fin rays usually present; the first two rays and the last ray unbranched, the others branched in single or double

dichotomies. Distal pterygiophores either absent or unossified. The fin rays are supported through fibrous tissue

at their bifid bases by nine basal pterygiophores. The

basal pterygiophores decrease slightly in length posteriorly in the series and are all, with the exception of the

last pterygiophore, stout rods. The last pterygiophore is rodlike anteriorly, but slightly expanded posteriorly into

a flat plate. The amount of expansion of the last anal fin pterygiophore is not equal to that of the last dorsal fin pterygiophore, but in large specimens the difference is not great. The pterygiophores are cartilage filled at both

ends. The dorsal ends of the pterygiophores articulate by

fibrous tissue with the irregular ventral edges of the

haemal processes of the first to fifth caudal vertebrae. At

their distal ends the pterygiophores articulate with one

another by fibrous tissue. Anatomical diversity.—The few genera of Recent

diodontids form an anatomically compact family of gymnodonts that has probably changed little in overall configuration since the Eocene, with the exception of an

increase in the size of the scales and in certain rearrange- ments of the dentition and jaw supporting structures. The few relatively complete fossil diodontids are from

the Eocene of Monte Bolca, Italy, and are referable to Diodon tenuispinus Agassiz and D. erinaceus Agassiz. Agassiz (1844b) simply said that D. erinaceus was larger and rounder, and had shorter and heavier spines, than in the more fully described D. tenuispinus. The types of D. tenuispinus are in Paris, and Le Danois (1955, 1959) proposed the new generic name Prodiodon for tenuispinus on the basis of the supposedly anteriorly elongate sphenotics broadly entering the edge of the orbit above and of the supposedly sutured (rather than ful- ly fused) premaxillaries which would distinguish

tenuispinus from all Recent species. The three type-specimens of P. tenuispinus (see Material Examined) have been examined for this work. None of the three show much detail of the jaws, skull structure, vertebral column, and armament. A dorsal view illustration of the only one of these three specimens

that is in counterpart, and considered at the Paris museum to be the holotype, is presented by Le Danois

(1959:215, fig. 184). The illustration, in my opinion, is wildly inaccurate and impressionistic, being rendered

with heights of artistic license. I find it difficult to decipher any pertinent details in the dorsoventrally compressed and probably fractured cranium, but Le Danois showed the shapes and sizes of most of the bones there, with the sphenotic being quite unlike that of any Recent

species, lacking a lateral prong and being prolonged anteriorly to form much of the lateral edge of the upper orbit, much as in the tetraodontid Colomesus. I seriously doubt that the degree of detail shown in the illustration by Le Danois is actually present. Le Danois described and showed the upper jaws with

the premaxillaries sutured as in tetraodontids, with in- terlocking emarginations, while saying that the dentaries

are either fused to one another or at least closely at- tached. To my eyes the jaws that are exposed in the three specimens seem to be fully fused medially without any

evidence of sutured right and left halves. Several transversely elongate trituration teeth are present to either

side of the midline on what is apparently the inner sur- face of the lower jaw in the specimen in counterpart. Le

Danois showed the pectoral and dorsal fins far more

clearly than they exist on the specimen. What vague in- dication remains of the dorsal fin in the fossil is far shorter based than illustrated by Le Danois, with the

true fin corresponding only to the posterior half of the il- lustrated fin. The illustration clearly shows 23 verte- brae, but I would estimate that the much vaguer outlines represent about 18 to 20 vertebrae. 351
The extremely long spine shown in the illustration by Le Danois of P. tenuispinus behind the pectoral fin base

is hinted at in the specimen in counterpart, but it is not

as definite as shown, and could represent either a large spine or the postcleithrum. Most of the spines that are apparent seem to have been relatively short and without massive three-rooted bases, perhaps having been mostly

erectile and like those of the Recent Diodon except

shorter. The spines just behind the pectoral fin base seem to have been somewhat longer than the others. The

placement of the branchiostegals is clear, but the first, presumedly platelike, branchiostegal is not evident.

In the specimen in counterpart there seems to have

been 11 caudal fin rays, one more than in any Recent

species, although some of the rays are displaced and the count is not certain. In two of the three specimens there

</.-{/

•<///
prefrontal cartilage pterosphenoid sphenotic epiotic ethmoid-vomer

palatine premaxillary

supraoccipital

^- exoccipital

pterotic basioccipital hyomandibular

interoperculun^ quadrate metapterygoid parasphenoid

is some indication that the hypurals were not as fully fus- ed together as in Recent species, with it being possible that there were two more or less separate plates of about

equal size, one above and one below, but, again, it is only

clear in this regard that there was some sort of groove or

less ossified narrow horizontal region in the middle of the caudal plate posterior to the region of the last vertebral centrum. Four additional specimens (see Material Examined)

that are identified as P. tenuispinus in European collec- tions add little to what is known on the basis of the type- specimens. In MCSNV B.18, 31.5 mm SL, the only items

of interest to the present discussion are that, as in the type-specimens, there seem to be 11 caudal fin rays and

the trituration teeth are paired, at least one transversely elongate tooth being placed to each side of the midline, and that the spines just behind the pectoral fin base (up

to 1.1 mm long) are a little more than twice the length of the spines elsewhere (0.3-0.4 mm long), while the basal

plate of the spine has up to six radiations, these being

relatively small, about one-half the length of the projecting spine. The scales are similar to this in MCSNV

B.19, 40.5 mm SL.

In the type-specimen of D. erinaceus some of the

scales, especially posteriorly on the body, do seem to be

three rooted and thus unerectile, although the roots are

relatively short and do not approach the massiveness of those found in Chilomycterus. It is possible, however,

that the larger size of the roots in the type of P. erina- ceus (77.5 mm SL) in comparison to those of the types of

P. tenuispinus (12.6-46.5 mm SL) is at least partially ac- counted for by the differential specimen sizes. The spines

just behind the region of the pectoral fin (which is not

clear) base are longer (3.3 mm) than those elsewhere (up

Figure 282.—Diodon holocanthus:

lateral view of head, composite based c several specimens, 12. .3-124 mm SL,

Gulf of Mexico and Caribbean.

to L6 mm) on the body of the type of P. erinaceus and may have been two rooted and erectile, although their impressions are so poor that this is difficult to tell for sure. Other specimens labeled P. erinaceus in European col- lections (see Material Examined) variously show the

transversely elongate trituration teeth in a single series of one or two units to each side of the midline, just as in P. tenuispinus, and spines slightly longer behind the pectoral fin base than elsewhere and of a small size similar

to that of P. tenuispinus, some seeming to have short multiradiate bases and others only biradiate bases, and

thus probably some combination of small erectile and

nonerectile spines. The number of caudal fin rays and

the structure of the last few caudal vertebrae are not

clear in any of the specimens assigned to P. erinaceus, but in one of them (IGUP 8670-71) there is a strong indi- cation that the first branchiostegal ray is an enlarged

horizontal plate just as in Recent species. Since there is the possibility that the Eocene diodontids assigned to P. tenuispinus, and by implication to the

at least closely related P. erinaceus, differ from the Recent species by having 11 caudal fin rays and the hypurals not fully fused to one another, the generic term

Prodiodon is retained for them, especially in light of the

fact that the numerous diodontid jaws known from the Eocene onward have been given generic nomenclatural

status separate from that of the Recent species, as ex- plained below. 353
* i S_•- Q i » O

I 2 S|

nil

1 1 1

1 1 1 1

5lf r &1|J

354
Being especially strong and massive, isolated diodontid jaws and fragments have been widely found in every

period from the Eocene onward, and the confused nomenclature given to these parts has been extensively and astutely reviewed by Tavani (1955), who recognized

several new genera on the basis of dental structure, as only briefly summarized here. Tavani found that Eodiodon, from the middle and upper Eocene of Europe, dif- fered from all other diodontid jaws by having a uniform bony mass not differentiated into small teeth at the bit- ing edge and larger elements in an internal trituration

plate, as well as a difference in the place of articulation with the palatine. Tavani (1955) recognized Eodiodon as the family Eodiodontidae, in contrast to four genera with distinct and differentially formed teeth in the biting and tritura- tion regions. Of the latter four genera, Tavani differenti- ated Progymnodon (see Dames 1883), from the middle and upper Eocene of Europe, and Kyrtogymnodon, from

the Pliocene of Europe, from the remaining two genera, Oligodiodon from the Oligocene and Miocene of Europe and North America, and Diodon, from the Miocene of Europe to Recent, on the basis of the depth of the osse- ous jaw tissue separating the small teeth in the biting edge from the large teeth in the trituration plate. Pro- gymnodon and Kyrtogymnodon, as the subfamily Pro- gymnodontinae, have only a thin band of bony tissue separating the two, and Oligodiodon and Diodon, as the Diodontinae, have a broad band. The difference between the Progymnodon and Oligo- diodon type spatial arrangement as so carefully de- scribed by Tavani (1955) undoubtedly represents the evolutionary change that took place leading to the arrangement as found in the Recent species, in which the

biting edge and trituration teeth are well separated by a deep layer of bone, although less so in young specimens

than adults. However, I am skeptical about the reported

dental condition in Eodiodon, of it not having any teeth

differentiated from the osseous tissue of the jaws. My

skepticism is primarily because in the two groups most

basal in the ancestry of the gymnodonts, the eoplectin triacanthodids and triodontids, the teeth are clearly dif- ferentiated from the bone, as they are in all diodontids from the Eocene to Recent, with the possible exception of Eodiodon.

I suspect that the apparent lack of discrete teeth in Eodiodon alone is some artifact of preservation of the few known jaw fragments assigned to Eodiodon, or that the

biting edge teeth and those of the trituration plate were

lost sometime between the process of preservation and

the eventual recovery of the abraded fragments. With the

true nature of the dental units of Eodiodon perhaps still unknown, and with no knowledge of what the structure of the fish behind the jaws was like in Eodiodon, Progymnodon, Kyrtogymnodon, and Oligodiodon, and only the

slightest knowledge of the body of Prodiodon, I feel no

compulsion for recognizing Eodiodon as familially dis- tinct from the other diodontids, and none for recogniz- ing subfamilies on the basis alone of the width of the os- seous tissue separating the biting and trituration teeth, while still being keenly aware of the great value of Tavani's work. With the exception of Tavani's (1955) careful analysis

of the dental structure in fossil diodontid jaws, and of the few hints about the general configuration of the body in Prodiodon, our knowledge of the anatomical diversity of the family rests essentially on that of the Recent species. The diodontids differ externally mainly in the form of the nasal apparatus (two nostrils or one) and spines

(erectile or nonerectile). In times past, only two genera of diodontids were usually recognized, Chilomycterus for
ceratobranchials

epibranchials

pharyngobranchials

CDQ C=~> basibranchials

hypobranchials

Figure 285.—Diodon holocanthua:

dorsal view of branchial arches

(extended on lower side); lateral (above) and medial (below, upside down)

views of hyoid arch; composite based on several specimens 12.3-124 mm SL, Gulf of Mexico and Caribbean.

those species in which all of the spines have massive tri- or quadriradiate bases and are nonerectile and Diodon

for those species in which at least some of the spines have

less massive and only biradiate bases and are erectile. However, in the two most recent revisions of diodontid

systematics, three genera have been recognized by

Fraser-Brunner (1943) and Le Danois (1959), entirely on

the basis of the nasal apparatus and spines, and none of the three genera are entirely comparable between the two

works. Fraser-Bruner ( 1943) recognized Diodon for those species with two nostrils and with at least some of the spines

erectile (principally hystrix, holocanthus, jaculiferus,

calori), Dicotylichthys for those with a bifid nasal tentacle and with at least some of the spines erectile (princi- pally nicthemerus, pilatus, punctulatus, and diuersispinis), and Chilomycterus for those with two nostrils (the division between which might be fragile and easily broken) and with all of the spines three rooted and nonerectile (numerous species). Two or three subgenera were recognized by Fraser- Brunner (1943) in each of the three genera but these have

not been used by subsequent workers. The three subgenera of Diodon and Dicotylichthys have exactly the same

characters, one subgenus in each for those species all of whose spines are two rooted and erectile and two sub-
Figure 286.—Diodon holocanthus

lateral view of pectoral girdle, composite based

specimens, 12.3-124 mm SL, Gulf

of Mexico and Caribbean.

Figure 2H7.—Diodon holocanthus:

lateral view of caudal fin supporting

structures, composite based on several specimens, 12.3-124 mm SL, Gulf of Mexico and Caribbean.

genera in each for those species which have most of the

spines three rooted and nonerectile, differing in whether

the few erectile spines are behind the pectoral fin or on

the head. This seems too fine a splitting, especially on

the basis of one character. The division of Chilomycterus by Fraser-Brunner into two subgenera was on the

basis of having two spines above the eye, one on the middle of the forehead, and a nasal tube with two nostrils (Cyclichthys for antennatus, antillarum, echinatus, orbicularis, schoepfi, spinosus) versus three spines above the

eye, none on the forehead and "nasal papilla adpressed,

division between nostrils feeble, easily broken" (Chilo- mycterus for affinis, atinga, tigrinus = reticulatus, and

californiensis, a synonym oi affinis). As discussed subsequently, the nasal differences between the subgenera Cyclichthys and Chilomycterus

are valid, as modified, and those species with an open

pitted cup do lack a spine in the middle of the forehead

while those with two nostrils always have a spine there. The number of spines above the eye is not consistently

different between the two groups, and much depends on how one interprets the position of the third spine in the
series over the upper edge of the orbit. In most species of the subgenus CycUchthys the third spine has its exter- nal process placed distinctly behind the eye, but in orbi- cularis it is placed just above the rear margin of the eye, while in the subgenus Chilumycterus, only affinis has the

external process just above the rear margin of the eye, while in atinga and tigrinus it is placed just behind the

rear margin of the eye and in reticulatus distinctly behind the rear margin of the eye. Some of the difficulties in this arrangement of genera

are that: 1) Diodon contains species such as jaculiferus

in which most of the spines have massive triradiate bases and only a few just behind the pectoral fin base are es- pecially elongate and erectile, the bases of these spines being only biradiate, or with a triradiate base in which

one of the radiations (that normally directed anteriorly when there is a triradiate base and nonerectile spine) is shortened and directed strongly dorsally or ventrally toward one of the two well-developed radiations; 2) Dio- don contains species such as calori in which only the

spines on the forehead are two rooted and erectile;

3) those species of Diodon such as hystrix and holocanthus that have all or most of the spines essentially two

rooted and erectile in young stages have most of the

spines nonerectile in large adults, the base of the spine tending to become massive and triradiate with the devel- opment of an anteriorly directed root; 4) in Diodon at

least two species, jaculiferus and calori, sometimes do

not have two nostrils, the septum between the nostrils in a minority of specimens (about lO'^^c in jaculiferus) ap- parently being resorbed (and not damaged by tearing);

5) in Dicotylichthys, just as in Diodon, there are species such as pilatus and punctulatus in which most of the

spines are triradiate and nonerectile, those that are es- sentially biradiate and erectile being, respectively, just behind the pectoral fin base and on the head and belly;

6) in Dicotylichthys at least one species, nicthemerus,

usually has a nasal tube with two nostrils in young spec- imens, the partition between the two nostrils apparently

usually being resorbed in adults to produce a bilobed tube or tentacle, and Le Danois (1959:227) reported a specimen with both conditions, one on either side; 7) in Chilomycterus there are two types of nasal apparatuses, most species having two nostrils and a relatively smooth

or only slightly folded epithelium on the inner surface of the tube, but three species, reticulatus, tigrinus, and af- finis having the nasal apparatus as an open low cup (i.e., one large nostril) with a pitted epithelium, perhaps at all sizes, and another species, atinga, in which the nasal apparatus is tubular with two nostrils and a relatively smooth inner epithelium in young specimens, but with

the great majority of large specimens having converted

this into an open cup with a pitted surface by the resorption of the partition originally separating the two nostrils, the remains of the partition apparent even in large adults as an unpitted ridge across the middle of the

pitted cup. Le Danois (1959) recognized Diodon for those species with either two nostrils or a bifid tentacle and with at

least some of the spines two rooted and erectile, this being the combination of Fraser-Brunner's (1943) Diodon

and Dicotylichthys, while Fraser-Brunner's Chilomycterus, containing all the species in which all the spines

are three rooted and nonerectile, in Le Danois' system is split into Chilomycterus for reticulatus (and tigrinus), with the nasal apparatus an open cup with a pitted surface, and Atinga for all the other species, supposedly all with two nostrils and an unpitted inner epithelium. Le

Danois' system has all of the drawbacks of Fraser- Brunner's in that Diodon contains species with a covering of almost as fully nonerectile, triradiate spines as in Fraser-Brunner's Chilomycterus, and of two different types of nasal tentacles, while Le Danois' Chilomycterus

contains a single species (she considered tigrinus and

reticulatus synonymous) with a pitted cup nasal apparatus (as well as one poorly preserved Miocene species, acanthodes, which seems to have had some two-rooted

erectile spines and an unknown nasal apparatus, and

would thus be assignable by her own system to Diodon) and her Atinga contains species having a nasal tube with two nostrils except for two species, affinis, which has a pitted cup at all stages as far as known, and atinga, in which adults develop a pitted cup nasal apparatus exactly as found in Chilomycterus reticulatus, tigrinus, and

affinus. Neither of the above two systems are tenable, but

internal characters do little to clarify the situation, even though a large number of species were examined for this work. For purposes of discussion, the generic categories

of Fraser-Brunner are used below. The nomenclature and

diagnostic characters of many of the species of Chilo- mycterus are confused, and one or two of the names used

here may be synonymous. For example, C. reticulatus, the type-species of Chilomycterus, is known only from

very large adults (300 to over 600 mm), and C. tigrinus may be the younger adult of it, since both are extremely

similar osteologically. They differ mainly in tigrinus having fewer but larger dark spots and few if any larger dark

blotches. Before passing on to the osteological diversity of the

diodontids, one additional external feature is of syste- matic significance. As outlined by Tyler (1970b:25), the

great majority of diodontids have 9 caudal fin rays, while

a few species of Chilomycterus (sensu Fraser-Brunner) have 10. The four species presently known with 10 rays

are affinis, atinga, reticulatus, and tigrinus, all four of which have the nasal apparatus as a pitted cup, at least

in adults. Since the ancestral tetraodontids and at least some of the Eocene diodontids have 11 caudal rays, the

four species of Chilomycterus with 10 caudal rays are more generalized in this respect than are the other species of diodontids, all of which have the caudal rays fur- ther reduced to 9, at least modally. Conversely, these

four species are more specialized than other diodontids in their nasal apparatus, for at least the more generalized of the ancestral tetraodontids, as well as the triodontids and triacanthodids, have two nostrils to each side. One unusual internal feature is shared by the four species of Chilomycterus with the combination of 10 caudal

rays, no spines on the forehead, and a pitted cup nasal
apparatus. All four have the specialized condition of the absence of the prefrontal. However, the absence of a prefrontal is not entirely confined to these four species, for C. orbicularis lacks the prefrontal but has nine caudal

rays, a spine on the forehead, and a nasal tube with two

nostrils. In C. orbicularis the palatines are more elon- and less widely spaced than in the other species of Chilomycterus, and the frontals are deeply indented in the region where prefrontals ordinarily occur. The minor variation in the caudal fin supporting struc- tures in diodontids is discussed by Tyler (1970b), this in- volving the degree of fusion between the epural and the neural spine of the penultimate vertebra and between

the parhypural variously to the fused hypural-centrum

plate or to the haemal spine of the penultimate vertebra. These regions are so difficult to interpret in the spec- imens examined that no information of diagnostic or phylogenetic usefulness was found.

In many diodontids, as in all other gymnodonts except

Triodon, the fifth ceratobranchial is toothless. However,

in C. affinis, orbicularis, and tigrinus the fifth cerato- branchial bears a small patch of minute teeth. In the sin- gle large specimen of C. reticulatus examined a small patch of minute teeth is present on the fifth ceratobranchial on one side but not on the other. The two species of Dicotylichthys examined (nicthemerus and punctulatus) both have a well-developed elongate patch of minute

teeth on the fifth ceratobranchials. These small teeth could either be remnants of those that probably occurred on the fifth ceratobranchial of the ancestral tetraodontid line, retained from its triodontid ancestry before the

fourth gill was lost, or a de novo acquisition in a few dio- dontids from an immediate ancestry lacking teeth on the

fifth ceratobranchial. The latter seems more reasonable,

for the loss of teeth on the fifth ceratobranchial is un- doubtedly associated with the loss of the fourth gill and

of the gill slit between the fourth and fifth arches, which

event occurred in the ancestral line common to both the tetraodontids and diodontids, and both families prob- ably have a long history of lacking teeth on the fifth cer- atobranchial while still retaining the ability to occasionally develop teeth there as dietary changes took place in various evolutionary lines making use of slightly differ- ing foods.
Figure 289.—Dorsal views of skulls of: left, Chilomycterus schoepfi,

60.1 mm SL, Louisiana; right, C. affinis, 310 mm SL, Galapagos.

Figure 290.— Dorsal views of skulls of: left, DiodonjacuUferus,

5.3.4 mm SL, Australia; right, Chilomycterua orbicularia, 72.9 mm SL, Somalia.
Figure 291.—Dorsal view of skull of Dicotylichthya punctulatus, 226 mm SL,

Australia.

pharyngobranchials

epihyal

branchiostegal rays

basibranchials hypobranchials

ceratobranchials

dorsal hypohyal

ventral hypohyal

ceratohyal

Figure 292.—Chi/omyctcnts achoepfi: dorsal view of branchial arches (extended oi lower side) and lateral view of hyoid arch,

168 mm SL, Florida.

Figure 293.—Nasal apparatuses of representative

diodontids: A, Chilomycterus mauretanicus;

B, C. orbicularis; C, C. schoepfi; D, C. antennatus,

1 being the normal condition of two nostrils

in each tube and a ridge along the inner

surface, while 2 and 3 are variations of abnormal conditions, 2 having a single nostril on one side but the normal two nostrils on the other side (USNM 249592, 75.2 mm), and 3 having

a single nostril on both sides (USNM 249592,

85.7 mm); E, C. reticulatus; F. C. atinga.

1 being the normal condition of an open nasal

sac (one nostril) on each side and 2 being an abnormal condition of a closed sac with two

nostrils on one side but an open sac on the other (ANSP 103900, 278 mm); G, Diodon hystrix; H. D. holocanthus, 1 being the normal condition

of two nostrils in each nasal sac and 2 being an abnormal condition of a single nostril on

one side but two nostrils on the other (ANSP

105586, 186 mm); l.D.jaculiferus, 1 being

the normal condition of two nostrils in each nasal sac and 2 being an abnormal

condition of a single nostril on one side but two nostrils on the other (USNM 176952,

42.2 mm): J, Dicotylichthys punctulatus; K, D. nicthemerus, a bifid tentacle in adults but two nostrils in a tube in young specimens.

fIP '^7 ^"a
1/:^:^

Figure 294. —Ventral viewsof upper jaws to show trituration tooth plates: A, Chilomycterus

orbicularis, 77.0 mm SL, Somalia, and 158 mm SL,

Philippines: B, C. schoepfi, 62..'j mm SL, Texas, and 168 mm SL,

Florida, the latter species with trituration plates more or less typical of all diodontids except C. orbicularis.

Figure 29.5.

Chilomycterus schoepfi: upper

left, lateral view of upper jaw, with inset showing detail of lateral edge of crushing beak with its individual dental units incorporated into but distinct from the bony matrix of the premaxillary; lower

left, cross section through middle of one

of the individual flattened disklike

trituration teeth; right, outline of about

one-half of a trituration tooth, with the

detail showing the irregular surface;

ie8 mm SL, Florida.

The dentition of the pharyngobranchials is also slightly variable in diodontids. The pharyngobranchials of the

first and second arches always bear small to minute

teeth, while the pharyngobranchial of the third arch, when present, is always smaller than those preceding it and is nearly always toothless. The pharyngobranchial of the third arch is absent in Chilomycterus affinis, atinga,

reticulatus, and tigrinus, and it is especially small and

toothless in C. antillarum, mauretanicus, orbicularis, spinosus, and Dicotylichthys nicthemerus . In C. schoepfi

this pharyngobranchial is as small as in the preceding

species, but it sometimes bears minute teeth even though

usually it is toothless. In D. punctulatus this pharyngobranchial is toothless but of moderate size. In Diodon

this pharyngobranchial is toothless and of moderate

(hystrix, jaculiferus) to relatively large (holocanthus)

size. Gill rakers along the anterior edge of the fourth cer- atobranchial are present in Chilomycterus affinis, atinga, reticulatus, tigrinus, orbicularis, Diodon holo- canthus, hystrix, jaculiferus, and in Dicotylichthys nic- themerus and punctulatus, while they are absent in C. antennatus, antillarum, mauretanicus, schoepfi, and

spinosus. The loss of gill rakers along the anterior edge of the fourth arch must be considered a specialization, since

in the only other family without a fourth gill, the tetrao- dontids, rakers are always present here. Both the dorsal and ventral hypohyals are present in

all of the diodontids examined except for Chilomycterus

atinga, reticulatus, and tigrinus, which lack (in the

single specimen examined of each species) the dorsal ele- ment. The trituration teeth internal to the biting edge of the upper and lower jaws always form a large plate divided

into right and left halves, each half formed by a single

series of large wide flattened tooth plates whose medial
edges are straight and the other edges rounded, in all species examined except for C. orbicularis. In C. orbicularis the trituration plate is smaller than in the other species, the division into right and left halves is less distinct, and

there are two or more series of far smaller and less wide

teeth in each half of the plate. In fact, the individual

teeth in the trituration plate of C. orbicularis are not much larger than those of the biting edge, at least in adults, in which the number of series of teeth increases

greatly over the two or three to each side found in young

specimens, while at the same time the width of the rows,

especially of the innermost row, is greatly decreased. Having numerous series of trituration teeth to each

side of the midline and not greatly different in size from

those in the biting edge would seem to be a more

generalized condition than that of a single series of large wide plates to each side of the midline and greatly dif- ferent from the teeth of the biting edge. Such numerous

series of small trituration teeth are also found in the

triodontids, the most generalized gymnodonts. However,

C. orbicularis is highly specialized in certain other

features of the skull, and tetraodontids, the closest

relatives of the diodontids, are more generalized than

diodontids and usually have only a single series of small

trituration teeth to each side of the midline, when they occur at all. Moreover, the trituration teeth in the

earliest known diodontids, in the Eocene, are large transversely elongate units that occur in a single series to each side of the midline, just as in all Recent species ex- cept C. orbicularis. I suspect that the numerous tritura- tion teeth of C. orbicularis are a de novo acquisition of

this single specialized diodontid and thus not the retention of an ancestral condition such as found in triodontids. The numerous small trituration teeth of C. orbicularis can be considered just as specialized in their own way as the far larger trituration teeth in a single series to either

side of the midline found in all other diodontids. The jaws of C. orbicularis tend to be less massive and

to have a sharper biting edge than in other diodontids, and this, in conjunction with the differences in the tri- turation plates, probably indicates that C. orbicularis has a diet of less hard bodied food than do the other dio- dontids.

In the large trituration plates as found in the great majority of diodontids, the wide individual tooth plates

are formed at the base of the pulp cavity and have a

slightly concave smooth upper surface and a slightly con- vex papillate lower surface. The individual plates migrate toward the exposed surface of the trituration plate

to replace those worn away through use as new plates are continuously being formed at the edge of the pulp cavity. As they move toward the exposed trituration surface the

individual plates become increasingly flattened and

more closely cemented together. The number of individual plates in the single series to each side of the midline

usually increases greatly with increasing specimen size,

Figure 296.—Diodon hystrix: cross section of upper (above in each set) and lower jaws just

to one side of the midline, showing the numbers

of dental units in the biting edges of the jaws and in the trituration plates, increasing greatly

in number with increasing specimen size: A, 88.3 mm SL, B, 228 mm SL, and C, 505 mm S
Figure 297 .—Diodon holocanthus: cross sectioi of upper (above in each set) and lower jaws

just to one side of the midline, showing

the numbers of dental units in the biting edges of the jaws and in the trituration

plates, increasing greatly in number with

increasing specimen size: A, 63.4 mm SL;

B, 122 mm SL; C, 183 mm SL; D. 375 mm SL.

but there is little difference between species in the number of plates at any given size, based on the limited sur- vey made (Fig. 302). However, the largest specimen of a diodontid examined for internal trituration teeth, a single 545 mm spec- imen of C. reticulatus, had only about 18 plates, ap- proximately the number to be expected from the other

species examined at sizes between about 200 and 220 mm.

The total number of plates in the series carmot be counted

externally because only about a third to a half or fewer have any of their surfaces exposed, and the total number

can only be seen by carefully sawing through the jaw just

to one side of the midline, a laborious procedure. The

trituration surface is somewhat oblique to the broad plane

of the individual plates, and the exposed surface is covered by several overlapping plates. In most diodontids there are a large pair of apertures posteromedially on the dorsal surface of the premaxillaries just to either side of the midline which open into the large posterior edge of the pulp cavity, but in Chilo- mycterus affinis and orbicularis the apertures on the dorsal surface of the premaxillaries are smaller, more

numerous, and less precisely arranged than in the other

diodontids. This character may be particularly prone to change with increasing specimen size. The numbers of vertebrae in the diodontids examined

show no differences useful in recognizing natural groups.

In Chilomycterus the total number varies modally from

18 to 23, with 10 to 13 abdominal and 8 to 10 caudal, while in Diodon there are 19 to 21 total, with 10 to 12 ab- dominal and usually 9 caudal. In the single specimens of 364
Figure 29S.—Chilomycterus schoepfi: cross section of upper (above in each set) and

lower jaws just to one side of the midline, showing the numbers of dental units in the biting edges of the jaws and in the

trituration plates, increasing greatly

in number with increasing specimen size: A, 97.6 mm SL and B, 166 mm SL.

the two species of Dicotylichthys examined, both had 9 caudal vertebrae, one with 11 abdominal and the other with 12. The uppermost pectoral fin ray in diodontids is usually

relatively short and formed of two approximately equal unsegmented halves, but in the single specimen of Chi- lomycterus affinis examined, a large adult of 310 mm,

this ray is a single piece of bone, the two halves that can

be expected to be found in smaller specimens apparently having completely fused, or one of the halves having been

resorbed. Generic relationships. —It is difficult to discuss ge- neric relationships without first establishing a natural

division of the family into genera, and as pointed out in the preceding section, the two most recent revisions recognized three noncomparable genera on the basis of

nostril and spine characteristics, with each of the revi- sions having serious limitations. The osteology of the species examined here helps to some extent, but leaves much left to be done.

Figure 299.—ChUomycterug antillarum: cross

section of upper (above) and lower jaws just

to one side of the midline, showing the numbers of dental units in the biting edges of the jaws and in the trituration plates, 116 mm SL.

Figure 300.—Chilomycterus atinga: cross

section of upper (above) and lower jaws just one side of the midline, showing the numbers

of dental units in the biting edges of the jaws and in the trituration plates, 173 mm SL.

Within Chilomycterus, by far the most speciose genus

of diodontids, three groups are recognizable. Chilomycterus affinis, atinga, reticulatus, and tigrinus are unique among the diodontids by having the third pharyngobranchial absent, a pitted open cup nasal apparatus (at least as adults), no spines on the forehead and 10 caudal

fin rays. Three of these four species are also unique by

the presence of only a single hypohyal. All four species have the prefrontal absent and similar skull shapes, the

prefrontal otherwise being absent in diodontids only in
5201 O a • D. DC.

c. VC

c, Oc

holocanthus

Figure 301.Chitomycterus mauretanicus: cross

section of upper (above) and lower jaws just to one side of the midline, showing the numbers of dental units in the biting edges of the jaws and in the trituration plates, 92.2 mm SL.

C. orbicularis, which has a much different skull shape and arrangement of the trituration teeth. All four species have gill rakers along the anterior edge of the fourth

arch, as does C. orbicularis (as well as Diodon tind Dicotylichthys), all of these species being from the IndoPacific with the exception of C. affinis, from the Atlantic, while the other species of Chilomycterus {anten- natus, antillarum, mauretanicus, schoepfi, and

spinosus), all from the Atlantic, do not have gill rakers along the anterior edge of the fourth arch. The only

species of Chilomycterus with teeth on the fifth ceratobranchial are orbicularis and three {affinis, reticulatus, tigrinus) of the four species with a pitted cup

nasal apparatus, no spines on the forehead and 10 caudal

rays. The evidence indicates that C. affinis, atinga, reticulatus, and tigrinus are all closely related, and that C. antennatus, antillarum, mauretanicus, schoepfi, and

spinosus are a distinct subgroup of equally closely related

species. The Indo-Pacific C. orbicularis would seem to have its closest relatives among the primarily Indo-Pacific former group than to the latter Atlantic group, for it shares a few

differential characters (prefrontal absent, gill rakers present on anterior edge of fourth arch, teeth on fifth cer- atobranchial) with them and none with the Atlantic group. Most of the differential features of C. affinis, atinga, reticulatus, and tigrinus are specializations

(pitted open cup nostril, loss of prefrontal and pharyngobranchial of third arch, usual presence of teeth on the

fifth ceratobranchial, and usual loss of the dorsal hypohyal), and their retention of 10 caudal fin rays is the only way in which they are more generalized than C. orbicularis and the other speciose subgroup of Chilomycterus

(and other diodontids). The presence in C. orbicularis of a toothless small pharyngobranchial of the third arch, two hypohyals, and a nasal apparatus of a tube with two

nostrils is less specialized than in C. affinis, atinga, retic- ulatus, and tigrinus, but its other features that distin- guish it from them are specialized (narrowness of the

region around the palatine and anterior end of the frontal, numerous rows of trituration teeth, nine caudal fin rays), while it shares with them the specialized features

of the loss of the prefrontal and the presence of teeth on

the fifth ceratobranchial. The exclusively Atlantic subgroup of Chilomycterus

is specialized only in the loss of gill rakers on the anterior

10 15 20 2! Number of tritufation tooth plates i

Figure 302.—Chart showing the increased number of trituration plates in the upper jaw with increasing specimen size, with

the same relationship holding for the lower jaw also, in Diodon holocanthus, D. hyslrix, Chilomycterus schoepfi, C. mauretanicus,

C. atinga, C. antillarum, and C. reticulatus.
edge of the fourth arch and in having nine caudal fin rays, while being more generalized than either of the

other two subgroups by always retaining a prefrontal, and more generalized than the C. affinis, atinga, reticulatus. and tigrinus subgroup by the constant presence of two hypohyals and a pharyngobranchial on the third arch, the constant absence of teeth on the fifth ceratobranchial, and the normal presence of a nasal tube

with two nostrils. The only specialized feature that the

exclusively Atlantic subgroup shares with C. orbicularis

is the presence of nine caudal fin rays, but otherwise the

Atlantic subgroup is far more generalized than C. orbicularis. Whether the three subgroups within Chilomycterus

should be recognized subgenerically is a matter of opinion, but on a practical level I doubt that such categories would be generally used and none are here proposed.

In summary, C. orbicularis is most closely related to the C. affinis, atinga, reticulatus, and tigrinus subgroup and in its own way is about as specialized as them,

probably having diverged from a common ancestral line

at a time when the nasal apparatus was still a tube with two nostrils. The C. antennatus, antillarum, mauretanicus, schoepfi, and spinosus subgroup is more distantly related to the other two and in most ways is more

generalized than them, probably having diverged from

the line leading to the other two subgroups at a time when there were still 10 caudal fin rays and gill rakers on

the anterior edge of the fourth arch, with the subse- quent loss of one of the caudal rays and of those gill rakers while in general becoming less differentiated from

the basal stock than did the other two subgroups. The three species of Diodon studied, two of which

(holocanthus and hystrix) have all of the spines erectile and the other (jaculiferus) with only a few behind the

pectoral fin erectile, scarcely differ osteologically, the

prefrontal in jaculiferus being slightly smaller than in the

other two. The two species oi Dicotylichthys studied, one

(nicthemerus) with all the spines erectile and the other (punctulatus) with only those on the head erectile, are equally similar osteologically and can be distinguished from Diodon internally only by the presence of a specialized well-developed band of teeth on the fifth cera- tobranchial, this being entirely toothless in Diodon,

while externally they differ only by Diodon having a

nasal tube with two nostrils versus the specialized bi- lobed tentacle of Dicotylichthys. I do not think that this combination of two characters is of sufficient magnitude

to warrant generic recognition, it being no greater, and in actuality less, than that between the three unnamed sub- groups of Chilomycterus. It is suggested that Dicotylichthys be placed in the synonymy of Diodon. Moreover, the skeletal structure of Diodon and Dicotylichthys is nearly indistinguishable from that of the entirely Atlantic subgroup of Chilomycterus. Both Diodon

and Dicotylichthys differ from it only by the presence of

at least a few erectile spines and of gill rakers on the

anterior edge of the fourth arch, and Dicotylichthys additionally by the presence of teeth on the fifth cerato- branchial, a rather unimpressive array of differences. Diodon, Dicotylichthys, and the entirely Atlantic sub- group of Chilomycterus have apparently diverged little from the generalized ancestral stock. The presence of a

full covering of erectile spines without massive radiating bases would seem to be the most generalized condition in diodontids, as it is the closest to the normal condition in tetraodontids. In this view the development of a huge

triradiate base to the scale, which makes it nonerectile, is a specialization, and the species of Diodon and Dicotylichthys with all of the spines erectile are more generaliz- ed than those with only a minority of them erectile, while by the same token Chilomycterus, all of whose species have all of the spines with huge triradiate bases, is the most specialized of all. In short, Diodon and Dicotylichthys do not seem

anatomically different enough to warrant separate

generic recognition, and while they are more generalized and easily distinguishable osteologically from the two

Chilomycterus : orbicularis

Chilomycterus: affinis, atinga,

reticulatus, tigrinus

Figure 303.—Hypothesized

phylogenetic relationships of the genera of Diodontidae.

Dicotylichthys

Chilomycterus : antennatus, antillarum, mauretanicus, schoepfi, spinosus

Prodiodon
more specialized subgroups of Chilomycterus (the affinis, atinga, reticulatus, (igrinuA- subgroup, and the or- bicularis subgroup) they differ from the more generalized subgroup of Chilomycterus {antennatus, antillarum, mauretanicus, schoepfi, spinosus) only slightly, pri- marily by retaining at least some erectile spines without huge triradiate bases. Relationship to the other Tetraodontoidei.—The

relationship of the Diodontidae as a specialized offshoot

of the line of gymnodonts leading to the Tetraodontidae

is discussed under the latter and under the Trio- dontidae, with additional remarks under the Molidae.

SUPERFAMILY MOLOIDEA

Comparative diagnosis (contrast with that of the Tetraodontoidea), which is also that of its only contained family, the Molidae.—No inflatable diver- ticulum of the gut; first branchiostegal ray without an

inturned and enlarged dorsal edge, articulated to the

ventral edge of the ceratohyal and not forming a pumping plate; air bladder absent, at least in adults; four gills, greatly expanded dorsally above and beyond the supporting arches; a gill slit present between the gill bearing

fourth arch and the gill-less fifth arch, with gill rakers present along both the posterior edge of the fourth arch and the anterior edge of the fifth arch; gill rakers present

along the anterior edge of the first gill slit; pharyngobranchials with extremely large teeth, the three ele- ments being those of the second to fourth arches; cera- tohyal and epihyal not sutured to one another; interhyal and dorsal hypohyal always present; teeth in biting edge

of jaws apparently indistinguishably incorporated into the bony matrix of the preraaxillary and dentary; basisphenoid present; caudal fin aborted, either absent

altogether or represented by only a few rays in the central region of the pseudocaudal fin formed by posteriorly migrated soft dorsal and anal fin rays and supported

mostly by equally posteriorly migrated basal pterygio- phores from the soft dorsal and anal fins; dorsal, anal, caudal, and pectoral fin rays often extensively branched

but with extremely few cross-striations, those present

only at the extreme distal ends of the rays; sesamoid ar- ticular absent; postcleithrum with an anteriorly di- rected process toward or over the actinosts; three acti- nosts; supracleithrum extremely elongate, broadly ar- ticulated over the anterior one-third to one-half of its length with the pterotic; coracoid long and slender, without a posterodorsal prong below the lower actinost; operculum and suboperculum of greatly simplified struc- ture and reduced lateral surface area; interoperculum

absent as an ossification or present as a simple slender

rod of bone not extending posteriorly beyond the level of the epihyal; basioccipital greatly prolonged dorsally behind the exoccipitals to border the foramen magnum

to the exclusion of the exoccipitals; exoccipitals without

Figure 304.—Range of diversity in body

form in the Molidae: Mola mola (left) and Romania laevis (right).

condyles and not in contact with the first vertebra, which

articulates anteriorly only with the basioccipital; epiotic with a high dome or ribbonlike posterodorsal prolongation; pterotic greatly prolonged posteriorly, well past the

level of the end of the basioccipital; bony canal for the

nerves and blood vessels running from the orbit to the

nasal region complete, entirely surrounded by the prefrontal; palatine receiving its main support dorsally by a broad articulation with the ethmoid, vomer (if present),

prefrontal, and parasphenoid; no vertebrae with bifid neural spines projecting dorsally or dorsolaterally on

each side of the neural arch; centra of the abdominal

vertebrae without any ventral or ventrolateral processes, the ventral and ventrolateral surfaces of the centra

perfectly smooth; dorsal and anal fin rays widely

separated from their basal pterygial supports by a large block of cartilage; scales small but the basal plates in more or less close contact and forming a continuous

covering over the entire body, with none of the scales in the form of prominent prickles or spines; two minute

nostrils flush with the surface of the skin; lateral line either absent or extremely inconspicuous (not discerni- ble to me on either cleared and stained or intact alcohol preserved specimens at 30 magnifications).

Detailed description of Mola mola. Material examined. —Two cleared and stained speci- mens, 306 mm and 310 mm; two sets of jaws from large specimens of unknown length, one dry and one alcohol preserved.

Occipital Region.

Basioccipital. —A short column, expanded at the

anterior end and prolonged anterodorsally into a pair of sturdy prongs much like those of the first vertebra; broadly cartilage filled along the expanded anterior edge
Figure 305.—Mota mola: upper left, nasal

region as seen externally: lower left, scales from upper middle region of body.

of the columnar portion; articulates through cartilage anteroventrally with the prootics and anterodorsally with

the exoccipitals. The posterior end of the parasphenoid

overlies the anterior half of the midventral surface of the

basioccipital and is held to it by fibrous tissue, the

basioccipital remaining largely cartilaginous in the re- gion overlain by the parasphenoid. The anterodorsally

directed prongs of the basioccipital articulate by fibrous

tissue anteriorly with the exoccipitals and posteriorly with the bifid neural spine of the first vertebra. The

medial edges of the anterodorsally directed prongs form

the lateral walls of the foramen magnum, while the dorsal wall is formed by cartilage and the ventral wall by the

dorsal surface of the columnar portion of the basioccipital. The rim of the round concave posterior end of the

basioccipital articulates by fibrous tissue with the rim of the concave anterior end of the first vertebra.

Exoccipital. —A large, nearly flat plate; cartilage

filled along all of its edges of articulation with the other

cranial bones; articulates through cartilage dorsomedial

with the supraoccipital, dorsolaterally with the epiotic,

laterally with the sphenotic and pterotic, ventrally with

the prootic, and medially with the basioccipital. Along

the middle region of its medial edge the exoccipital ar- ticulates by fibrous tissue with the anterodorsal prong of the basioccipital. The exoccipital does not articulate

with the first vertebra, nor does it enter into the formation of the walls of the foramen magnum.

Supraoccipital. —A rounded plate ventrally, but produced dorsally into a high and stout supraoccipital

crest; cartilage filled along all of its ventral edges; ar- ticulates through cartilage laterally with the epiotics and

posteriorly with the exoccipitals. Anteriorly the base of the supraoccipital is overlain by the frontals, with which

it articulates by fibrous tissue.

Otic Region.

Pterotic. —Broadly cartilage filled along its anterior edge; articulates through cartilage anterolaterally with the sphenotic, anteromedially on its dorsal

surface with the epiotic and exoccipital and antero- medially on its ventral surface with the prootic. Along most of the length of its dorsal surface the pterotic possesses an upraised flange just lateral to which the supra- cleithrum articulates by fibrous tissue. Along most of the

length of its lateral surface a similar flange is present just

lateral to which the hyomandibular articulates by

fibrous tissue.

Sphenotic. —Cartilage filled along its medial and

anterior edges; articulates through cartilage posteriorly with the pterotic, dorsomedially with the epiotic and exoccipital, and ventromedially with the prootic and

pterosphenoid. Anteriorly the sphenotic articulates by

fibrous tissue with the overlying frontal. At its posterodorsal edge the sphenotic possesses a posterior process which articulates closely by fibrous tissue with the dorsal surface of the pterotic and which supports the antero- medial edge of the supracleithrum. Posteriorly along its ventral surface the sphenotic articulates by fibrous tissue with the anterior edge of the hyomandibular.

Epiotic. —A more or less rounded plate ventrally, but prolonged posterodorsally into a spine which connects by a tendon to the muscle mass of the dorsal fin; cartilage filled along all of its ventral edges; articulates through cartilage medially with the supraoccipital, posteriorly with the exoccipital and laterally with the

sphenotic. Anteriorly the epiotic articulates by fibrous

tissue with the overlying frontal.

Prootic. —Cartilage filled along all of its edges of

articulation with the other cranial bones; articulates through cartilage anterodorsally with the pterosphenoid,

anterolaterally with the sphenotic, posterolaterally with

the pterotic, and posteriorly with the exoccipital and

basioccipital. The anteroventral edge of the prootic ar- ticulates by fibrous tissue with the posterodorsal wing of the parasphenoid, while more posteriorly the medial edge

of the prootic similarly articulates with the lateral edge

of the parasphenoid. Along its anteroventral edge the

prootic is produced into a laterally expanded wing which

articulates by fibrous tissue with the anteromedial edge

of the dorsal end of the hyomandibular.
Orbital Region.

Frontal. —A relatively flat plate; expanded posterolaterally to overlie and articulate by fibrous tissue with the supraoccipital, epiotic, and sphenotic. The

medial edges of the two frontals are broadly concave and

enclose between themselves the anterior portion of the

cartilaginous tissue of the otic and occipital regions. The

dorsomedial edges of the two frontals articulate with one

another by fibrous tissue. Along its posteroventral edge

the frontal overlies and articulates by fibrous tissue with the pterosphenoid and sphenotic. Anteriorly the rounded end of the frontal broadly overlies and artic- ulates by fibrous tissue with the ethmoid and prefrontal.

Prefrontal. —A more or less vertical column posterolaterally, but expanded into a thin vertical sheet

anteriorly; cartilage filled along the middle region of its medial surface; articulates by fibrous tissue posterodorsally with the overlying frontal, anteromedially with the ethmoid, and anterolaterally with the palatine. A canal

for the olfactory nei-ve and vessels is present through the substance of the prefrontal, rather than being present at the interface of the prefrontal, frontal, and ethmoid carBasisphenoid. —A large rounded plate anteriorly, but laterally expanded posteriorly into a process whose

concave posterior surface articulates by fibrous tissue with the medial edge of the anteroventral region of the

prootic. The ventral edge of the basisphenoid articulates by fibrous tissue with the longitudinal concavity on the

dorsal surface of the parasphenoid. The anterior and dorsal edges of the upper half of the basisphenoid are carti- lage filled. Dorsally the basisphenoid articulates by

fibrous tissue with the ventral edge of the ptero- sphenoid. A small gap is present between the otherwise

closely apposed edges of the pterosphenoid and basi- sphenoid which serves as a foramen for the exit of vessels from the cranial cavity.

Ethmoid Region.

Ethmoid.—Thick and squarish; continuous posteroventrally with the remains of the ethmoid cartilage; articulates by fibrous tissue along the anterior half of its ventral surface with the vomer and along the posterior

half of its ventral surface with the dorsal surface of the concave anterior end of the parasphenoid. The lateral surfaces of the ethmoid articulate by fibrous tissue anteriorly with the palatines and posteriorly with the prefrontals. Parasphenoid. —Elongate; expanded ventrally along most of its length into a stout, but not particularly deep, flange. About two-thirds the way back its length the parasphenoid gives rise to a pair of short posterodorsally directed wings which articulate by fibrous tissue with the anteroventral edges of the prootics. Posterior to these dorsal wings, the parasphenoid articulates by fi- brous tissue laterally with the posteromedial edges of the

prootics and posteriorly with the anteromedial surface of the basioccipital. Just anterior to its dorsal wings, the

dorsal surface of the parasphenoid becomes concave for a short distance to receive and hold by fibrous tissue the

ventral edge of the basisphenoid. Along the lateral sur- face of about the anterior one-fourth of its length the parasphenoid articulates by fibrous tissue with the thin

posterior portion of the palatine. The anterior end of the parasphenoid is deeply concave and filled with gela- tinous tissue. The posterior end of the vomer does not fit into this concavity; rather, the ventral edge of the con- cave anterior end of the parasphenoid supports by

fibrous tissue the posterior edge of the vomer. The dorsal portion of the concave anterior edge of the parasphenoid

articulates by fibrous tissue with the ventral surface of the ethmoid.

Pterosphenoid. —A relatively flat plate; cartilage

filled along all of its edges, except medially; articulates through cartilage posteroventrally with the prootic and

posterodorsally with the sphenotic. Dorsally the

pterosphenoid is overlain by the frontal, with which it ar- ticulates by fibrous tissue. The ventral edge of the pterosphenoid articulates by fibrous tissue with the dorsal edge of the basisphenoid.

Vomer.—A small squarish bone articulated by

fibrous tissue dorsally with the anterior half of the ventral surface of the ethmoid, laterally with the medial

edges of the palatines and posteriorly with the ventral edge of the concave anterior end of the parasphenoid. The anterior edges of both the vomer and ethmoid ar- ticulate by fibrous tissue with the posteromedial edge of the upper jaw. Mandibular Region. Hyomandibular. —Expanded posterodorsally, but

tapering anteroventrally to a thick rounded shaft; carti- lage filled at its anteroventral edge and along the anterior one-third of its dorsal edge. The hyomandibular ar- ticulates by fibrous tissue along most of the length of its dorsal edge with the ventrolateral surface of the pterotic, but anterodorsally it is also supported by the medial portion of the posteroventral edge of the sphenotic and by

the ventrolateral flange of the prootic. Along the ventral

half of its posterior edge the hyomandibular articulates by fibrous tissue with the posterior half of the dorsal edge

of the preoperculum. Dorsally along its anteroventral end

the hyomandibular articulates by fibrous tissue with the

posteroventral edge of the metapterygoid. Just above the

posterodorsal end of the preoperculum, the hyomandibular possesses a thickened area whose concave posterior face articulates by fibrous tissue with the concave

anterior end of the operculum.

Quadrate. —Wide posteriorly, but tapering to a knob anteriorly for articulation with the articular in the lower jaw; a short posteriorly directed process present 370
from its posteroventral region; slightly cartilage filled along its posterior edge; articulates by fibrous tissue anterodorsally with the ectopterygoid and ventrally with

the preoperculum. Posteriorly the quadrate articulates through cartilage with the metapterygoid. The inner sur- face of the posteroventral portion of the quadrate that

overlies the symplectic forms a concave groove in which

the symplectic is held by fibrous tissue. The articulation

of the knoblike anterior end of the quadrate with the ar- ticular in the lower jaw is strengthened by the fibrous tis- sue attachment of an anteromedial projection from the

anterior edge of the quadrate with the posteromedial

edge of the articular.

Metapterygoid. —Broad anteriorly, but tapering to a point posteriorly; cartilage filled along its anterior and

anteroventral edges; articulates through cartilage anteriorly with the quadrate and by fibrous tissue anteroventrally with the symplectic and posteroventrally with the hyomandibular. The cartilaginous region between the hyomandibular, metapterygoid, and symplectic is the

place of fibrous tissue articulation of the dorsal end of the

interhyal. The anterodorsal edge of the metapterygoid

articulates by fibrous tissue with the posterior end of the mesopterygoid.

Symplectic. —A long rod, slightly wider posteriorly than anteriorly; cartilage filled at its posterior and anterior edges; articulates by fibrous tissue dorsally with the metapterygoid and anteroventrally with the concavity on

the inner surface of the quadrate.

Palato-Pterygoid Region.

Palatine. —Wide anteriorly, but becoming a flat vertical plate posteriorly; articulates by fibrous tissue anteromedially with the ethmoid and vomer, postero- medially with the parasphenoid, ventrally with the ec- topterygoid and mesopterygoid, and posterodorsally with

the prefrontal. The anterodorsal edge of the palatine, which is produced medially as a slender prong, articulates by fibrous tissue with the posterodorsal edge of the

maxillary.

Ectopterygoid. —Only slightly V-shaped, with the apex directed posteriorly; articulates by fibrous tissue dorsally with the slightly overlying palatine, ventrally with the quadrate, and posteriorly with the mesopterygoid, which it slightly overlies.

Mesopterygoid. —More or less squarish; articulates by fibrous tissue anteriorly with the slightly overly- ing palatine and ventrally with the cartilaginous region between the metapterygoid and quadrate. Opercular Region. Operculum. —A straight shaft of bone, becoming

laterally compressed posteriorly; articulates at its con- cave anterior edge by fibrous tissue with the concave

facet on the posterior edge of the hyomandibular, while

ventrally it overlies and articulates by fibrous tissue with

the suboperculum.

Suboperculum. —Lx)ng and flat; widest in about the middle of its length and becoming much thinner both

anteriorly and posteriorly; articulates by fibrous tissue posteriorly with the overlying operculum and anteriorly with the long ligament in which the interoperculum is embedded.

Interoperculum. —A long delicate needle of bone

entirely embedded within the ligament which runs between the angular in the lower jaw and the anterior end of the suboperculum. At the level of the posterior end

of the interoperculum, the ligament is particularly firmly held to the general connective tissue around the lat- eral surface of the epihyal.

Preoperculum.—More or less flat throughout its length, except along its dorsal edge where it is slightly ex- panded to form a broadened surface for fibrous tissue ar- ticulation posteriorly with the hyomandibular and anteriorly with the quadrate. In about the middle of its length

the dorsal edge of the preoperculum articulates by

fibrous tissue with the cartilaginous region between the hyomandibular, metapterygoid, and symplectic.

Upper Jaw.

Premaxillary. —The two premaxillaries ars indis- tinguishably fused in the midline and together with the fused teeth form a large nibbling plate; anterior edge of premaxillary forming about the dorsal two-thirds of the border of the upper jaw, the lower third of the border being formed by the anterior edge of the maxillary. The

premaxillaries articulate laterally by fibrous tissue with

the broadly overlying maxillaries. Dorsally, however, the expanded upper ends of the maxillaries fit into deep concavities in the surface of the premaxillaries and are held

there by fibrous tissue. The premaxillaries thus broadly

overlie the dorsal ends of the maxillaries. The posterior edge of the fused premaxillaries is overlain by the maxillaries along all of its length, except for a very short dis- tance medially. The pulp cavity of the fused premaxillaries is small, shallow, and confined to the dorsal region

of the bone. The dorsal roof over the pulp cavity is thin and smooth internally, but the ventral floor of the cavity

is thick and highly irregular. The pulp material extends

into and between the innumerable bony lamellae and

spikes rising from the floor of the eavity. No discrete teeth or dental units of any kind are visible there in either of the two cleared and stained study specimens, or

in the two additional sets of much larger jaws, nor can any such structures be distinguished in the hard substance of the biting edge of the fused premaxillaries. A

large trituration plate is present on the medial third of the under surface of the fused premaxillaries. In the two

relatively small cleared and stained specimens, the tri- turation plate is distinctly divided into closely apposed
right and left halves, each of which contains four or five elongate teeth. The teeth are set in deep sockets and re- main distinct and separate from one another but become

increasingly intimately held to the bony matrix anteriorly. As an old tooth at the anterior end of the tritura- tion plate is worn away or resorbed, a new tooth devel- ops in a new socket at the posterior end of the plate. In the two sets of jaws from specimens apparently at least several times as large as the two cleared and stained specimens, the teeth of the trituration plate are far more

numerous, less regularly arranged, relatively smaller and

placed more anteriorly on the undersurface of the premaxillaries. The trituration teeth apparently undergo ex- tensive change with increasing size.

Maxillary. —Straight and rather flattened, except

dorsally where it becomes expanded into a large rounded

head which fits into the deep concavity on the dorsal sur- face of the premaxillary. Below the latter region the maxillary broadly overlies and articulates by fibrous tissue with the dorsal surface of the premaxillary. Posterodorsally the medial ends of the two maxillaries and the medial edge of the fused premaxillaries articulate by a

fibrous tissue sheet with the anterior edges of the eth- moid and vomer. The ventromedial surface of the maxillary articulates by fibrous tissue with the dorsolateral surface of the dentary.

medial surface of the dentary. Posteroventrally the medial surface of the articular is concave and forms a groove in which the dorsal end of the angular is held by

fibrous tissue. In about the middle of its posterior edge

the articular possesses a transverse groove which articulates by fibrous tissue with the quadrate. A sesamoid ar- ticular is absent. Angular. —A short rod; cartilage filled at its dorsal edge; articulates by fibi-ous tissue anteriorly with the dentary and dorsally with the groove on the medial sur- face of the articular. Posteriorly the angular connects

with the ligament that encloses the interoperculum. BRANCHIAL APPARATUS.

Hyoid Arch and Branchiostegal Rays. Hypohyals. —Dorsal and ventral hypohyals

present, the ventral slightly larger than the dorsal; the

ventral and posterior edges of the dorsal hypohyal and

the dorsal and posterior edges of the ventral hypohyal

cartilage filled; articulate through cartilage with one

another and with the anterior edge of the ceratohyal. The

anterodorsal end of the dorsal hypohyal articulates by

fibrous tissue with the middle of the lateral surface of the

basibranchial. The anteromedial edges of the hypohyals

articulate by fibrous tissue with their opposite members.

Dentary. —The two dentaries are indistinguish- ably fused in the midline and, with the fused teeth, form

a large nibbling plate like that of the upper jaw. The pos- teromedial surfaces of the fused dentaries are deeply con- cave to receive and articulate by fibrous tissue with the

anterior ends of the articulars. Posteroventrally the dentary articulates by fibrous tissue with the anterior end of the angular. Posterodorsally along its lateral surface the dentary articulates by fibrous tissue with the medial sur- face of the maxillary. The biting edge of the dentary is a hard and apparently completely homogenous substance,

like that of the upper jaw. A trituration plate composed

of separate, but closely apposed, right and left halves is present on the medial third of the inner surface of the fused dentaries in the two relatively small cleared and

stained specimens. Each side contains two series of separate and distinct teeth set in deep sockets. The inner

series contains four elongate teeth, while the other series contains three somewhat rounded teeth. The pulp cavity and replacement of the teeth of the trituration plate

are the same as described for the fused premaxillaries, and the two sets of jaws from much larger specimens similarly have far more numerous and smaller teeth placed more anteriorly on the bone.

Articular. —More or less triangular in shape; cartilage filled for a short distance anteriorly on its medial

surface where it is continuous with the remains of Meckel's cartilage. The tapering anterior portion of the

articular articulates by fibrous tissue with the concave

Ceratohyal. —Short, but wide; more expanded

anteriorly than posteriorly; cartilage filled at its anterior knd posterior edges; articulates through cartilage anteriorly with the hypohyals and posterodorsally with the

epihyal. The posterior half of the ventral edge of the cera- tohyal possesses two successive indentations separated by a ventrally directed prong. The ceratohyal supports

the first three branchiostegal rays. Epihyal.—Small; cartilage filled along its anterior and ventral edges; articulates anteriorly and ventrally through cartilage with the ceratohyal, while posterodorsally it articulates by fibrous tissue with the base of the

interhyal, and laterally supports the last few branchiostegal rays. The lateral surface of the epihyal articulates by fibrous tissue with the ligament enclosing the inter- operculum at the level of the posterior end of the latter.

Interhyal. —A short, thick column; deeply carti- lage filled at both ends; articulates by fibrous tissue ventrally with the epihyal and dorsally with the cartilagi- nous area between the hyomandibular, ectopterygoid, sympletic, and preoperculum.

Branchiostegal rays. —Six in number; the first five rays long, flat, and relatively straight; the sixth branchiostegal wide for a short distance anteriorly, but rapidly tapering posteriorly to a long, thin, slender shaft. The

branchiostegal rays articulate by fibrous tissue with the hyoid arch elements as follows: first and second branchiostegals with the successive concavities on the ventral
edge of the ceratohyal; third branchiostegal with a slight concavity on the posterior edge of the ceratohyal; fourth branchiostegal with the cartilage between the epihyal and ceratohyal; fifth and sixth branchiostegals with the

lateral surface of the epihyal.

Branchial Arches. —The elements are cartilage filled at their edges of articulation with the other elements of the series, and the articulations are usually through cartilage and fibrous tissue. The branchial arches are composed of three basibranchials, three pairs of hypobranchials, five pairs of ceratobranchials, four pairs of epi- branchials, and three pairs of pharyngobranchials. Four

gills are present, with a large slit between the fourth arch and the lower pharyngeal. The gills are enormously

enlarged and only about the lower third of their lengths

are supported by the branchial arches; these were de- scribed long ago by Alessandrini (1839) and most recently, in great detail, by Adeney and Hughes (1977). The

anterior edges of the upper two-thirds of their lengths are held by fibrous tissue to the ventral surfaces of the posterior end of the cranium and the first several vertebrae.

First arch. —Basi-, hypo-, cerato-, and epibranchial elements present. First basibranchial laterally compressed anteriorly; about the same length as the

third basibranchial and somewhat shorter than the sec- ond basibranchial; with a ventral keel medially on its ventral surface; displaced forward so that it articulates

posteriorly with the second basibranchial and posterolaterally with the first hypobranchials. First hypobranchial the longest of the hypobranchial elements, which

decrease in length posteriorly in the series; articulates

dorsally with the first ceratobranchial, ventrally with the second basibranchials and anteroventrally with the first basibranchial. First ceratobranchial slightly longer and

deeper than the other ceratobranchials, which are about

equal in length but which decrease in depth posteriorly

in the series; articulates ventrally with the first hypobranchial and dorsally with the first epibranchial. First epibranchial a slender rod articulating dorsally with the

fibrous tissue sheet between the dorsal edges of the metapterygoid and hyomandibular and the ventral edge

of the parasphenoid.

Second arch. —Basi-, hypo-, cerato-, epi-, and pharyngobranchial elements present. Second basibranchial

the longest and widest of the basibranchial elements; with a ventral keel medially on its ventral surface; artic- ulates anteriorly with the first basibranchial, anterolaterally with the first hypobranchials, posterolaterally with

the second hypobranchials, and posteriorly with the

third basibranchial. Second hypobranchial only slightly shorter and narrower than the first hypobranchial; artic- ulates ventrally with the anterolateral edge of the third basibranchial and posterolateral edge of the second basi- branchial, while dorsally it articulates with the second

ceratobranchial. Second ceratobranchial articulated dorsally with the second epibranchial. Second epibranchial

a very narrow rod articulating dorsally with the middle of

the toothless edge of the second pharyngobranchial. Sec- ond pharyngobranchial a rounded plate bearing about

four long teeth set in sockets along its ventral edge. The

bases of the teeth are expanded and articulate with their sockets by fibrous tissue. Third arch. —Basi-, hypo-, cerato-, epi-, and pharyngobranchial elements present. Third basibranchial

rectangular in shape; its ventral surface without a keel; articulates anteriorly with the second basibranchial,

anterolaterally with the second hypobranchials, and posterolaterally with the dorsal ends of the third hypobranchials and the ventral ends of the third ceratobranchials, while posteriorly it supports the cartilaginous area to which are attached the fourth and fifth cerato- branchials. Third hypobranchial a short column of bone, almost vertical in position and sunken below the general connective tissue that lies between the rest of the basi- branchials and hypobranchials; articulates dorsally with

the ventral surface of the cartilage between the posterolateral end of the third basibranchial and the ventral end

of the third ceratobranchial, while its ventral end connects by a band of fibrous tissue with the ventral keel of the second basibranchial and, continuing anteriorly, with the ventral keel of the first basibranchial. Third

ceratobranchial articulated dorsally with the third epi- branchial. Third epibranchial a stout rod; articulates dorsally with the third pharyngobranchial. Third pharyngobranchial the largest of the pharyngobranchial ele- ments; bears about six long, sharp-pointed teeth whose expanded bases articulate by fibrous tissue with their sockets on the ventral edge of the pharyngobranchial; ar- ticulates ventrally with the third epibranchial and anteriorly and posteriorly with, respectively, the second and

fourth pharyngobranchials.

Fourth arch. —Cerato-, epi-, and pharyngobranchial elements present. Fourth ceratobranchial articu- lated ventrally with the third basibranchial and dorsally with the fourth epibranchial. Fourth epibranchial a large flattened plate, wider ventrally than dorsally; articulates ventrally with the dorsal ends of the fourth and fifth ceratobranchials and dorsally with the fourth pharyngobranchial. Fourth pharyngobranchial similar to the sec- ond pharyngobranchial; bearing four teeth in a single

Fifth arch. —Ceratobranchial (lower pharyngeal) element only. Fifth ceratobranchial like the others in the

series, but not as deep; toothless; articulates ventrally with the base of the fourth ceratobranchial. PAIRED FIN GIRDLES.

Pectoral Fin. Supracleithrum. —Long and flat, somewhat

expanded ventrally where it overlies the cleithrum; in position more or less parallel to the posterior end of the

skull; articulates by fibrous tissue posteromedially with 373
the cleithrum and posterodoreally with the postcleith- rum. Anteriorly the medial edge of the supracleithrum

articulates by fibrous tissue with the entire length of the

dorsolateral surface of the pterotic and with the posterolateral edge of the sphenotic.

Cleithrum. —Widest dorsally, constricted at the

level of the scapula and becoming a thin flat plate ventrally. Above the level of the scapula, the posterior region

of the medial surface of the cleithrum articulates by

fibrous tissue dorsolaterally with the broadly overlying supracleithrum, while the dorsal edge of the portion of the cleithrum overlain by the supracleithrum articulates with the anteroventral edge of the postcleithrum. Along its posterior edge the cleithrum possesses a broad

but shallow concavity in which the anterodorsal edge of the scapula is held by fibrous tissue. The posterior edge

of the cleithrum below the scapula articulates by fibrous

tissue with the anterior edge of the coracoid. The ventro- medial surfaces of the two cleithra articulate with one

another by fibrous tissue.

Postcleithrum. —Approximately Y-shaped; with

the bifurcate portion at the level of the actinosts and the

long arm articulated by fibrous tissue anterolaterally with the supracleithrum and anteroventrally with the

cleithrum. In neither of the two cleared and stained spec- imens is there any evidence of the postcleithrum being composed of two elements, the dorsal and ventral postcleithra apparently having fused into a single piece. The

lateral surface of the portion of the postcleithrum that

lies posterior to the cleithrum is embedded in the thick, firmly collagenous subdermal tissue of the skin. The

medial surface of the anterior fork of the inverted Y overlies and articulates by fibrous tissue with the bases of the

three actinosts.

Coracoid. —A flattened plate throughout its length, except ventrally where it becomes more rounded and

shaftlike; slightly expanded anteriorly in the middle

region of its length and more expanded anteriorly at its dorsal end; cartilage filled at its anterodorsal edge; artic- ulates anterodorsally through cartilage with the base of the scapula, while its dorsal edge articulates through cartilage and fibrous tissue with the bases of the three actinosts. The anterior edge of the coracoid articulates by

fibrous tissue with the posterior edge of the cleithrum.

Scapula. —Widest dorsally, constricted in the middle and only becoming slightly expanded ventrally; scapular foramen not entirely enclosed by bone, for the

anteroventral edge of the scapula is well separated from

the posterior edge of the cleithrum. A sheet of fibrous tis- sue, bearing a small pore representing the scapular fora- men, connects these edges of the scapula and cleithrum. The scapula is deeply cartilage filled at its dorsal and

ventral edges. The posterodorsal edge of the scapula is somewhat expanded posteriorly and overlies the anterodorsal edge of the anteriormost actinost, with which it ar- ticulates by fibrous tissue. The posteroventral edge of the

scapula articulates by fibrous tissue with the anteroventral edge of the anteriormost actinost, while ventrally the scapula articulates through cartilage with the coracoid.

Actinosts. —Three actinosts present; decreasing in

size and degree of central constriction posteriorly in the

series. The reduced first actinost of other plectognaths is not present as a separate piece, although it is possible that the posterodorsal portion of the scapula represents

the remains of this actinost indistinguishably fused to the scapula. The three actinosts articulate with one

another dorsally and ventrally by fibrous tissue and with

the coracoid through cartilage and fibrous tissue. The actinosts are cartilage filled at their dorsal and ventral

Fin rays. —Twelve fin rays present, the first three

rays and the last ray unbranched, the others so extensively branched distally that up to 20 terminal segments

(incomplete quintuple dichotomies) are present on some

fin rays. The medial and lateral halves of each fin ray are not closely apposed to one another except distally, a large amount of connective tissue otherwise separating the two

halves for most of their lengths. For the vast majority of

their lengths the rays lack cross-striations, which are only present extremely distally on some of the branches

as poorly defined articulations. The first ray differs from

the others by possessing a slender anteroventral process from the anterior edge of the medial half of the fin ray. The deeply bifurcate bases of the rays surround plugs of

cartilage whose ventral regions are calcified either as a

single piece or as a pair (lateral and medial) of calcifica- tions (not shown in the figures). VERTEBRAL COLUMN. —All vertebrae with bicon- cave centra, except for the last, which ends posteriorly with a relatively flat surface.

Abdominal Vertebrae.

First vertebra. —Neural spine bifid; no bony roof over the neural canal. The rim of the concave anterior

face of the centrum articulates by fibrous tissue with the rim of the concave posterior end of the basioccipital. The

anterolateral edges of the bifid neural spine articulate by

fibrous tissue with the medial surfaces of the anterodorsal wings of the basioccipital. The dorsal edges of the

bifid neural spine are overlain by the anterior edge of the neural spine of the second vertebra, while its posterolateral edges are indented to accommodate the short prongs from the anterolateral edges of the neural spine of the second vertebra. Other abdominal vertebrae. —Eight abdominal ver- tebrae in two specimens; neural spines increasing in length from the second to the fifth abdominal vertebrae; neural spines of the fifth to eighth abdominal vertebrae about equal in length; second to eighth abdominal ver- tebrae with bony roofs over the neural canal. The neural arches from either side of the second abdominal verte-
bra do not fuse with one another above the neural canal,

but, rather, have their medial surfaces closely apposed and articulated with one another by fibrous tissue. This

dorsomedial region of apposition is thickened and pro- longed anteriorly and posteriorly into a neural spine whose right and left halves are likewise closely apposed

medially and held together by fibrous tissue. The ventral surface of the anterior prolongation of the neural

spine of the second vertebra overlies the dorsal edge of the bifid neural spine of the first vertebra and effectively

roofs over the neural canal in this area. The posterior pro- longation of the neural spine of the second vertebra overlies the anterior edge of the neural arch and base of the

neural spine of the third vertebra. The neural arches and

spines of the third and fourth abdominal vertebrae are

likewise only closely apposed, with fibrous tissue holding the right and left halves closely together. The neural

spines of the third and fourth abdominal vertebrae are prolonged only posteriorly, and overlie the neural arch and spine of the vertebra just posterior to them. The posterodorsal end of the neural spine of the fourth abdominal vertebra articulates by fibrous tissue with the ventral edge of the first dorsal fin basal pterygiophore. The

right and left sides of the neural arches of the fifth to eighth abdominal vertebrae fuse to one another in the midline above the neural canal and are prolonged posterodorsally into long, stout, undivided neural spines. The lower posterior edges of these neural spines overlie the anterior edges of the neural arches of the vertebra

just posterior to them. More distally the neural spines of the fifth to eighth abdominal vertebrae articulate by

fibrous tissue between the more anterior of the dorsal fin basal pterygiophores.

Caudal Vertebrae. —Nine caudal vertebrae in two

specimens. With the exception of the last two vertebrae,

all of the caudal vertebrae have well-developed and undivided neural and haemal spines. The neural and hae- mal spines decrease slightly in stoutness, but not partic- ularly in length, posteriorly in the series. The degree of anteroposterior expansion of the neural arch and base of the neural spine decreases from the first to the sixth caudal vertebrae so that the neural spines of the sixth and

seventh caudal vertebrae are slender shafts throughout

their entire lengths. The neural spines of the first to sev- enth caudal vertebrae support by fibrous tissue the more

posterior of the dorsal fin basal pterygiophores. The distal three-fourths of the haemal spines of the first and sec- ond caudal vertebrae articulate with one another by fi- brous tissue and the thick shaft thus formed is overlain

laterally and anteriorly by the deeply concave posterior surface of the enlarged first anal fin basal pterygiophore. The posterior edge of the haemal spine of the second caudal vertebra articulates with the anterior edge of the sec- ond anal fin basal pterygiophore. The haemal spines of the third to seventh caudal vertebrae support the other

anal fin basal pterygiophores. The size of the neural and

haemal canals through the neural and haemal arches of the caudal vertebrae decreases posteriorly in the series until these canals are very narrow in the seventh caudal

vertebra. The short neural spine of the eighth caudal ver- tebra arises directly from the centrum and contains no

canal whatsoever. The haemal process, however, of the eighth caudal vertebra contains an extremely narrow

canal through its substance in one of the specimens but

not in the other. The neural and haemal spines of the

eighth caudal vertebra curve anteriorly and their distal ends articulate with, respectively, the posterior edges of the neural spine and of the haemal spine of the seventh

caudal vertebra. The ninth caudal vertebra is a simple

shaft which ends posteriorly with a flat surface abutting

against a calcified cartilage, explained below. DORSAL. ANAL, AND PSEUDOCAUDAL FINS. —

While a larval caudal fin fold without rays is present in at

least the molids Masturus and Ranzania, this is lost in development and the adult pseudocaudal fin in molids is apparently a secondary formation from dorsal and anal

fin rays (Gudger 1937a, b; Raven 1939a; Tyler 1970b). The fin rays of the pseudocaudal fin are continuous with

those of the dorsal and anal fin series and are supported

basally by modified basal pterygiophores of the dorsal and anal fins. Only an arbitrary distinction can be made

between the dorsal, pseudocaudal, and anal fins, but

such a distinction is perhaps advisable for the sake of dis- cussion. The pseudocaudal fin, composed of postero- medially migrated dorsal and anal fin rays, is here considered to include all those fin rays supported by the modified basal pterygiophores posterior to the neural and

haemal spines of the seventh caudal vertebra. The 15 dorsal fin basal pterygiophores and the 9 anal

fin basal pterygiophores anterior to the seventh caudal

vertebra have a normal relationship with the neural and

haemal spines of the vertebrae to which they articulate. The ventral ends of these dorsal fin basal pterygiophores

are cartilage filled while the distal ends of all but the first dorsal fin basal pterygiophore are irregularly cartilage

filled and closely apposed to the ventral surface of the

large cartilaginous plate that intervenes between them

and the dorsal fin rays. The first dorsal fin basal pteryg- iophore tapers to a point distally and articulates by fi- brous tissue posteriorly with the neural spine of the fifth abdominal vertebra and with the anterior edge of the sec- ond basal pterygiophore. Along the dorsal third of its anterior edge the first basal pterygiophore articulates by

fibrous tissue, and possibly slight interdigitation, with

the posteroventral edge of the supraneural. The supra- neural tapers to a blunt point anteriorly and is embedded

between the right and left muscle masses of the dorsal

fin. The large cartilaginous plate that intervenes between

the basal pterygiophores and the dorsal fin rays is calci- fied irregularly in the two cleared and stained specimens. The posterior one-third of the plate is the best calcified portion, but calcareous areas are also present at the anterior end and along much of the ventral portion of the

plate. The plate is homogenous posteriorly, but shows some evidence anteriorly of being composed of successive cartilaginous blocks closely applied to one another. The lateral surface of the plate possesses upraised areas between which run the ligaments from the fin rays to the
dorsal fin muscle mass. There are 18 dorsal fin rays pres- ent anterior to the first dorsal fin ray supported by a modified dorsal fin basal pterygiophore posterior to the

neural spine of the seventh caudal vertebra. The first five dorsal fin rays are unbranched, and the sixth ray is only

slightly branched at its extreme distal end. The 7th to 16th fin rays are extensively branched distally, so much

so that some of the rays have over 50 terminal segments

(incomplete sextuple dichotomies). The right and left halves of each of the rays are well-separated by fibrous

tissue from one another medially throughout their lengths, except distally where they begin to branch. As

with the pectoral fin rays, cross-striations are only pres- ent extremely distally on some of the branches as poorly defined articulations. The bifurcate bases of the dorsal

fin rays enclose plugs of calcified cartilage which articulate by fibrous tissue with the cartilaginous plate below

them. There are thus three series of pterygial elements

supptorting the dorsal fin rays: 1) the ossified basal pterygiophores; 2) the partially calcified cartilaginous

plate representing the closely apposed or confluent medial pterygiophores; and 3) the calcified cartilagi- nous plugs or distal pterygiophores at the bifurcate bases

of the fin rays. Except for the anteriormost pterygiophore, the nine

anal fin basal pterygiophores are like those of the dorsal

fin, except longer. They have concave proximal ends which are cartilage filled and they articulate by fibrous

tissue with the haemal spines of the caudal vertebrae and

with one another. Their distal ends are irregularly carti- lage filled and closely apposed or continuous with the

partially calcified cartilaginous plate that intervenes between them and the anal fin rays. The first anal fin basal pterygiophore is deeply concave along the posterior surface of the upper two-thirds of its length where it overlies and articulates by fibrous tissue with the hae- mal spines of the first two caudal vertebrae. Distally the

first basal pterygiophore is bifurcate into two parts which

fit against the medial pterygial plate. The medial pterygial plate is, like the dorsal fin medial pterygial plate, irregularly calcified. Sixteen anal fin rays are present

anterior to the first anal fin ray supported by a modified

basal pterygiophore posterior to the haemal spine of the seventh caudal vertebra. The first five anal fin rays are unbranched, and the sixth is only slightly branched distally. The 7th to 15th anal fin rays are branched in the same extensive manner as the corresponding rays of the

dorsal fin. The 16th anal fin ray is much less branched

than those anterior to it. The anal fin rays have the same

structure as those of the dorsal fin and likewise have

plugs of calcified cartilage, or distal pterygiophores, embedded between their bifurcate bases. Posterior to the neural spine of the seventh caudal ver- tebra there are seven modified dorsal fin basal pterygio- phores which distally support the seven dorsal fin rays of the upper half of the pseudocaudal fin. The uppermost,

or first, modified basal pterygiophore is placed at about a

right angle to the vertebral column, but the second to seventh modified basal pterygiophores are progressively more obliquely placed, until the seventh is almost

parallel to the vertebral column. Except for the first, these modified basal pterygiophores are cartilage filled at both ends and articulate by fibrous tissue proximally

with the neural spines of the seventh or eighth caudal

vertebrae and distally with the blocks of calcified carti- lage that form the medial pterygiophores of the pseudocaudal fin. The proximal ends of the second to fifth modified basal pterygiophores articulate with the posterior edge of the neural spine of the seventh caudal vertebra, while the proximal ends of the sixth and seventh modified basal pterygiophores articulate with the posterior edge of the neural spine of the eighth caudal vertebra. The proximal end of the first modified basal pterygio- phore tapers to a narrow shaft articulated by fibrous tis- sue with the posterior edge of the last unmodified dorsal

fin basal pterygiophore. The distal end of the first modified basal pterygiophore articulates with the postero- ventral edge of the large, partially calcified, cartilagi- nous mass that makes up the medial pterygiophore of the

dorsal fin. The medial pterygiophore above the second

modified basal pterygiophore is also continuous with the medial pterygiophore of the dorsal fin, being delimited from it only by a constricted region of cartilage. The cal- cified cartilages of the medial pterygiophores at the distal ends of the third to sixth modified basal pterygio- phores remain separate from one another in the two

cleared and stained specimens. The medial pterygio- phore of the modified seventh basal pterygiophore is con- nected with the cartilage at the end of the ninth caudal

vertebra and with the medial pterygiophore of the eighth modified anal fin basal pterygiophore. It is to be expect- ed that in larger specimens more of the medial pterygio- phores of the pseudocaudal fin become continuous with one another, because even in the two relatively small study specimens, the short, thin processes of the fifth and sixth medial pterygiophores almost make contact with the medial pterygiophores below them. The distal pterygiophores of the pseudocaudal fin, whose posterolateral surfaces are overlain by the bifurcate bases of the

fin rays, are blocks of calcified cartilage which increase in size in the series from that distal to the first to that distal to the seventh modified basal pterygiophore. The distal pterygiophores are thickest at their ends which artic- ulate by fibrous tissue with the medial pterygiophores. The seven fin rays supported by the distal pterygio- phores increase slightly in length in the series from that attached to the first to that attached to the seventh

pterygiophore. The fin ray above the first modified basal pterygiophore is branched in a double dichotomy, but

the other rays of the pseudocaudal fin are simply divided

into two terminal segments. None of the fin rays are

cross-striated. In the two study specimens, bony ossicles are just beginning to be evident around the bifurcate distal ends of a few of the more medial rays of the pseudocaudal fin, these ossicles being well developed in adults. The anal fin portion of the pseudocaudal fin has basically the same structure as the dorsal fin portion. However, since eight modified anal fin basal pterygiophores

are present, rather than seven modified basal pterygio- phores as in the dorsal portion, there are eight anal fin
rays that can be assigned to the anal portion of the pseu- docaudal fin. The lowermost, or first, modified anal fin basal pterygiophore is placed at about a right angle to the vertebral column, but the second to eighth modified

basal pterygiophores are progressively more obliquely placed so that the eighth is placed about parallel to the

vertebral column. The first modified basal pterygio- phore articulates distally with the inner edge of the car- tilaginous plate that forms the medial pterygiophore of the anal fin, while proximally it articulates by fibrous tis- sue with the posterior edge of the last unmodified anal fin basal pterygiophore. The second modified basal pteryg- iophore ends distally at its medial pterygiophore, which

is continuous with the medial pterygiophore of the anal

fin and is delimited from it only by a slightly constricted

region of cartilage. The anterior edge of the second modified basal pterygiophore articulates proximally by

fibrous tissue with the posterior edge of the first modified basal pterygiophore. The third to fifth modified

basal pterygiophores articulate proximally by fibrous tis- sue with the posterior edge of the haemal spine of the seventh caudal vertebra, while the sixth to ninth modified basal pterygiophores articulate with the posterior edge of the haemal spine of the eighth caudal vertebra.

Distally the modified basal pterygiophores connect with

the calcified cartilage of their medial pterygiophores. The medial pterygiophores distal to the third to the sev- enth modified basal pterygiophores are separate from

one another, but that distal to the eighth modified basal pterygiophore is continuous with the calcified cartilage

at the end of the ninth caudal vertebra and with the medial pterygiophore distal to the seventh modified

basal pterygiophore of the dorsal portion of the pseudocaudal fin. The distal pterygiophores of calcified carti- lage in the anal portion of the pseudocaudal fin have the same structure as those of the dorsal portion. The lower- most fin ray of the anal portion of the pseudocaudal fin is branched in a double dichotomy, but the other seven fin rays of the anal portion are simply divided distally into two terminal segments. None of the rays are crossstriated, and bony ossicles have just begun to form, just as in the dorsal portion, in the two study specimens. The pseudocaudal fin, as here defined, thus consists of

15 fin rays, the uppermost ray and lowermost ray of which are branched in double dichotomies, while the

other 13 rays are simply bifurcate distally. The upper

seven rays belong to the dorsal fin and are supported by

seven bony modified dorsal fin basal pterygiophores, as

well as by calcified cartilages which form a medial and a

distal series. The lower eight rays belong to the anal fin and are supported by eight bony modified anal fin basal

pterygiophores, as well as by calcified cartilages which

form a medial and a distal series. The dorsal and anal fin rays form a continuous series around the posterior end of the body, with those dorsal to the ninth caudal vertebra being considered as dorsal fin rays and those ventral to that vertebra being considered as anal fin rays. The divi- sion of the dorsal and anal fin rays into those of the dorsal and anal fins proper and those of the pseudocaudal

fin is arbitrary, but convenient.

Anatomical diversity. —While three genera of molids

are presently recognized, there is some doubt regarding

the number of species in two of them, as most recently

revised (Fraser-Brunner 1951). Ranzania is monotypic

{laevis = truncatus). Masturus is probably monotypic,

Fraser-Brunner stating that the two forms he tentatively recognized as specifically distinct were probably

only the sexes of a single species (lanceolatus =oxyuropterus). Fraser-Brunner believed that Mola was repre- sented by two species, the worldwide M. mola being

largely replaced in the south Pacific by M. ramsayi, the

latter differing from M. mola mainly in having several more fin rays in the pseudocaudal fin, larger bony ossi- cles at the distal ends of these rays, and no band of smaller scales along the base of the pseudocaudal fin. Subsequent to Fraser-Brunner's (1951) revision, a new

genus and species of molid has been described, Pseudomola lassarati Cadenat (1959), based on a single specimen from west Africa. The specimen was thought to be unusual by the presence of a large white abdominal

region and additional white spots and reticulations. It otherwise was said to differ from Mola only in lacking, at

its large size (1,090 mm total length), bony ossicles at the

distal ends of at least some of the rays of the pseudocaudal fin and to differ from Masturus only by lacking

the posteriorly prolonged lobe of the pseudocaudal fin. This lobe is often lost (bitten off?) in Masturus and evenly healed over, while little is known about variation in the time of development of the ossicles in Mola. Pseudomola lassarati could easily be a Mola mola that has not yet developed the bony ossicles along the edge of the pseudocaudal fin or a Masturus lanceolatus that has

lost the posterior lobe of the pseudocaudal fin. However, some specimens of M. lanceolatus are known to have a white abdominal region and additional white spots or blotches (see photographs in Gudger 1937a, b) very similar to those of P. lassarati, and it is probably with M.

lanceolatus that P. lassarati is synonymous. A fossil species of molid, Mola pileatus (Beneden), is known from the Miocene on the basis of the bony ossicles that are present in the skin above and below the mouth,

just as in the Recent species of Mola (these being the remains of the postlarval skin spines, according to Fraser-Brunner 1951:110) and of a few fused premaxillaries and dentaries that are more molidlike than diodontidlike (see Leriche 1907 and 1926, and contained refer- ences, and Deinse 1953). Fraser-Brunner (1951) distinguished Ranzania (as the Ranzaniinae) from Mola and Masturus (Molinae) as

follows: Ranzania more elongate; vertebrae 8 -I- 10 or 11

(vs. 9 -(• 8); carapace of hexagonal plates (vs. a colla- genous carapace); lips produced and funnellike (vs. lips normal); gill rakers free (vs. concealed in thick skin); 5 branchiostegal rays (vs. 6); no secondary postlarval meta- morphosis (vs. the development of prominent spiny processes from the body during a Molacanthus stage). Masturus was distinguished from Mola by having the middle

fin rays of the pseudocaudal fin not supported basally by basal pterygiophores and none of the pseudocaudal

fin rays developing bony ossicles at their distal ends. 377
^^v
supraoccipital epiotic pterosphenoid frontal basisphenoid

exoccipital

cartilage

prefrontal ethmoid

palatine ectopterygoid

interopercuiuin

operculum suboperculum

, . , V preoperculum ^ symplectic \ \ "^ "^ quadrate metapterygold parasphenoid / mesopterygoid

I would slightly modify some of the above statements. The body depth in Ramania is about 3 times in the stan- dard length in the young, but large adults are deeper

bodied, the depth being only twice, or slightly less than

twice, in the standard length. In Mola and Masturus the depth is usually between one and one and a half in the standard length, with the young slightly less deep bodied

than large adults. The individual scale plates in Ranzania are thicker and more angular (often being hexagonal) than in Mola and Masturus, whose scale plates are more or less circular. However, the carapace of Ranzania

is relatively thin, for in Mola and Masturus the thinner

scale plates rest upon a thick layer of collagenous connective tissue. The funnellike mouth in Ramania, which when closed forms a vertical slit, is unique among the

plectognaths. The gill rakers in the specimens of Mola

and Masturus examined here, none of which are large

adults, do not have the gill rakers concealed in thick

skin, although a flap of skin from the leading edge of the

raker to the gill arch strengthens their articulation to the

arch, more so than in Ramania. It is apparently only in large adults of Mola and Masturus that the gill rakers become more concealed. In the four specimens of Ranzania either cleared and stained or radiographed, the

vertebrae were 8 -(- 10 = 18, while in two specimens of Mola they were 8 + 9 = 17 and in two oi Masturus 8-1-8 = 16, and it would appear that eight is the normal

Figure 307.—MoJa mola: lateral view of head, composite based on two specimens,

306 and 310 mm SL, California.

number of abdominal vertebrae in molids and that there

is a modal difference of one caudal vertebra between the

three genera. It is possible that Fraser-Brunner's counts

of nine abdominal vertebrae in Mola and Masturus were made from radiographs and that the anterodorsal prongs

of the basioccipital were mistaken for the first vertebra. A few additional external characters distinguish Ranzania from Mola and Masturus. In Ramania the pectoral

fin is relatively longer and more falcate, and fits into a

shallow concavity on the carapace when folded back,

while in Mola and Masturus the pectoral fin is shorter and more rounded, and there is no concavity for it on the carapace. In Ramania the rays of the pseudocaudal fin are highly branched distally, while in Mola and

Masturus they are usually not branched in more than

single to triple dichotomies. In young Ranzania the distal edge of the pseudocaudal fin is relatively rounded and

not set off distinctly from the dorsal and anal fins, much

as in both young and adult Mola and Masturus. In adult Ranzania, however, the distal edge of the pseudocaudal

fin becomes relatively straight and slightly oblique, and

is distinctly set off from the dorsal and anal fins. 379
Ill

i! .-S U III

s ^ ;;

380
Mi

5 I 2 •= : > o S S S S= f £ i|.|rH|s

I- iSc«t"
liii
i .2 » » f

-^
Most of the internal differences between the three genera of molids clearly indicate that Mola and

Masturus are much more closely related to one another than either is to Ranzania, as widely supposed in the

past, mostly on the basis of external appearances.

In Mola and Masturus the mesopterygoid is a small

squarish bone which does not make contact posteriorly with the metapterygoid, while in Ranzania it is larger and more elongate, and contacts the metapterygoid. In Mola and Masturus the epiotics are dome-shaped and

only moderately prolonged posterodorsally, while in Ranzania they are greatly elongate posterodorsally as thin but wide bands of bone. In Mola and Masturus the

supraoccipital crest is short and broad, while in Ranzania it is long and narrow, extending back as far beyond

the head to contact the anterior prolongation of the first basal pterygiophore of the dorsal fin. In Mola and Masturus the sphenotic only slightly overlies the anterolateral surface of the pterotic, while in Ranzania it broadly

overlies it. In Mola and Masturus the vomer is ossified, while it is unossified in Ranzania. In Mola and Masturus the basisphenoid is placed in the posterior half

of the orbit and articulates with the prootic and ptero- sphenoid as well as with the parasphenoid, while in Ranzania the basisphenoid is placed in the middle of the orbit and articulates with the frontals above and the palatines and parasphenoid below. In Mola and Masturus the

anterodorsal prolongations from either side of the basioccipital do not meet one another in the midline above the neural canal, being separated there by the long anterior extension of the neural spine of the first vertebra, while

in Ranzania the anterodorsal prolongations of the basioccipital meet and fuse or suture in the midline above the

neural canal, being only slightly separated from one

another posteriorly by the short anterior extension of the

neural spine of the first vertebra. In Mola and Masturus

there are six branchiostegal rays, the fifth about the same size as the fourth and the sixth much more slender than any of the others, while in Ranzania there are only

five branchiostegals, the sixth either being lost or fused with the fifth, which is much larger than any of the other

branchiostegals. In Mola and Masturus the cerato- branchials are exceptionally deep bodied, but in Ranzania they are not. In Mola and Masturus the operculum

is shorter and wider than in Ranzania. In Mola and

Masturus the suboperculum retains a posterior prolongation behind or below the operculum as well as an anterior portion directed internal to the rear of the preoper- culum, while the suboperculum of Ranzania is repre- sented only by the anterior portion, which is longer than

in Mola and Masturus. In Masturus the interoperculum

is unossified and in Mola it is a short rod well separated from the suboperculum, while in Ranzania it is a long rod which contacts the suboperculum. In Mola and Masturus

none of the actinosts are sutured to one another, while in Ranzania all of them are sutured or interdigitated to one

another to some extent. In Mola and Masturus the post- cleithrum is not greatly expanded posteriorly as a

flattened plate, while it is in Ranzania. In Mola and

Masturus the parasphenoid is about as wide anteriorly as

it is toward the rear of the orbit, while in Ranzania it is narrower anteriorly than more posteriorly. In Mola and

Masturus the posterior portion of the palatine articulates broadly to the lateral surface of the parasphenoid,

while in Ranzania it articulates more to the dorsal sur- face of the parasphenoid. In Mola and Masturus the symplectic is of moderate length, extending back posteriorly only about half the length of the ventral edge of the metapterygoid, while in Ranzania it is elongate and ex- tends back nearly the whole length of the ventral edge of the metapterygoid. In Mola and Masturus the neural

arch and spine of the second vertebra is prolonged anteriorly and posteriorly well beyond the levels of the anterior and posterior edges of the centrum, while in Ranzania they are not prolonged. In Mola and Masturus the

neural arches of the abdominal vertebrae are not inter- digitated with one another, while in Ranzania they are broadly and deeply interdigitated. In association with

their deeper bodies, the basal pterygiophores of the dorsal and anal fins in Mola and Masturus are less elongate, and the neural and haemal spines and the pterygio- phores they support are less obliquely placed than in Ranzania. In Mola and Masturus only the first two haemal spines of the caudal vertebrae are decidedly

oriented toward one another, while in Ranzania most of the successive sets of two haemal spines from the caudal

vertebrae are decidedly oriented toward one another. The first basal pterygiophore of the dorsal fin is a rela- tively simple shaft in Mola and Masturus, and it is broadly in contact with the second basal pterygiophore, while in Ranzania the first basal pterygiophore is a complex element obviously representing the fusion of two

basal pterygiophores, and it is not in contact with the se- cond basal pterygiophore. A short but deep supraneural

is present in Mola, but the similarly shaped region anterodorsally on the first basal pterygiophore of the dorsal fin in the single specimen of Masturus studied is fully fused to the pterygiophore. In Ranzania the long anterior extension from the complex first basal pterygio- phore may represent a supraneural fully fused to the

pterygiophore. In Mola and Masturus the posterior sur- face of the proximal end of the first basal pterygiophore

of the anal fin is deeply concave and encloses the distal end of the haemal spines of the first two caudal

vertebrae, while in Ranzania this pterygiophore is not concave proximally and articulates along the anterior edge of the haemal spine of the first caudal vertebra. In Mola and Masturus most of the basal pterygiophores of the dorsal and anal fins are anteroposteriorly expanded

and platelike, while in Ranzania they are mostly long

slender rods. In Mola and Masturus the bases of the first dorsal and anal fin rays are only slightly, if at all, larger than those just behind them, while in Ranzania these bases are greatly enlarged anteriorly. In Mola and

Masturus the ossification of the skeleton is less complete

than in Ranzania.

In only a few ways are either Mola or Masturus more

like Ranzania than one another. The trituration teeth in the upper jaw of all three genera occur as a single series of elongate teeth to either side of the midline. In the lower


$»-4th abdominal vertebrae

Figure 317.Maaturus lanceolatus: ventral

(left) and dorsal (right) views of skull, 127 mm SL. Flonda.
Figure 318.— Ra

laevU: dorsal (left) and

ventral (right) views of skull.

65.1 mm SL, Hawaii.

Figure 3\9.—Masturus lanceolatua: lateral view of head, 127 mm SL, Florida. Figure 320.—Ranzania laevi*: lateral view of head, 65.1 mm SL, Hawaii.
basibranchials hypobranchials

ceratobranchials

pharyngobranchials '^^^ epibranchials i,i9^

Figure 322.Masturus lanceolatus: dorsal view of lower jaw, 127 mm SL, Florida.

Figure 321.— Dorsal views of branchial arches

(extended on lower side) and lateral views of hyoid arch of: left, Ramania laevis, 66.9 mm SL, Hawaii;

right, Masturus lanceolatus, 127 mm SL, Florida.

Figure 323.—Ramania laevis: A, dorsal view (left) of lower jaw and ventral view (right) of upper jaw,

493 mm SL, Hawaii, to show the more numerous

trituration teeth in a larger specimen,

in comparison to; B, dorsal view of lower jaw,

65.1 mm SL, Hawaii.
Figure 32i.—Ranzania laevis: diagrammatic

representation of the relationships between

the basal pterygiophores of the dorsal, anal.

and pseudocaudal fins and the neural and

haemal spines of the supporting vertebrae,

65.1 mm SL, Hawaii.

Figure 325.—iJonzonia laevu: scales from upper middle region of body, to show the approximately hexagonal scale

plates, articulated to one another by

extensive minute interdigitations along all of their edges of contact

(greatest length of largest scale

plate 6.0 mm), 493 mm SL, Hawaii.

jaw of Mola and Ranzania the trituration teeth are less elongate than in the upper jaw and occur in a major

series to either side of the midline as well as in a series of smaller teeth to either side lateral to the major series. In Masturus the trituration teeth in the lower jaw are not

divided into right and left sets, but rather has a single major series placed medially, lateral to which are two

series of smaller teeth on each side. In general configuration the pseudocaudal fin and its supporting elements are much more similar in Mola and

Masturufi than in Ranzania. While a normally shaped and placed larval caudal fin fold without rays is known to be present in at least Masturus and Ranzania, this is lost

in development and the adult pseudocaudal fin in molids

is a secondary formation from posteromedially migrated

dorsal and anal fin rays and their basal pterygial supports, although it is possible that the rays in the central nipple of the pseudocaudal fin of Masturus are remnants

of true caudal fin rays (as believed by Fraser-Brunner

1951; see Tyler 1970b for discussion).

In Ranzania the pseudocaudal fin is supported by the

last two caudal vertebrae. The last vertebra is a simple

rod seemingly representing a single centrum, which Leis

(1977) has shown to be a fusion product of two anlagen in larval stages. The penultimate vertebra has relatively well-developed neural and haemal spines which anteriorly support the last basal pterygiophores of the dorsal and anal fins and which posteriorly support the radial elements of the pseudocaudal fin. Most of the radials probably are posteromedially migrated basal pterygio- phores (Tyler 1970b:27). There are seven radials above and eight below in two of the three specimens of Ranzania examined, but only six above and seven below in the other (as also illustrated by Leis 1977:fig. 11), and a total of 19 or 20 fin rays in the pseudocaudal lobe, while Fraser-Brunner (1951) recorded 22 rays as the norm.
Contrary to Tyler (1970b:29), at least the more extensively branched dorsal, anal, and pectoral fin rays of all molids, and in Ranzania the pseudocaudal rays as well, often bear cross-striations distally, the number of cross- striations probably increasing with increasing specimen

size. The molid cross-striations, however, are fewer in number and more distally placed than in the fins of other

plectognaths.

In Mola the pseudocaudal fin is supported by the last three caudal vertebrae, of which the last is a simple rod

representing only a centrum. The penultimate vertebra has short neural and haemal spines which curve anteriorly to be supported at their distal ends by the fully developed neural and haemal spines of the antipenul- timate vertebra, while their posterior edges support the more medially placed radial elements. But it is the neural and haemal spines of the antipenultimate

vertebra which support most of the radial elements. There are seven radial elements above and eight below, and 15 pseudocaudal fin rays, in both specimens examined. Fraser-Brunner (1951) gave 16 rays as the norm for the south Pacific M. ramsayi and 12 for the worldwide M.

mola, with which distinction the two California specimens of M. mola examined here are not in agree- ment. Masturus has one less caudal vertebra than Mola, and

it is obvious that Masturus has lost what is the last vertebra oi Mola, the simple rod representing a centrum. With the exception of Masturus lacking this rodlike cen- trum the pseudocaudal supports of Mola and Masturus

are rather similar, the ultimate vertebra oi Masturus being homologous and functionally corresponding to the penultimate of Mola, and the penultimate of Masturus

to the antipenultimate of Mola. The most diagnostically important difference between Masturus and Mola in this region is that Masturus has more (20 or more) rays in the pseudocaudal fin than does Mola, the additional rays mostly being accounted for by

those in the medial lobe that is present in Masturus but

absent in Mola, and that bony ossicles do not develop

distally on any of the pseudocaudal rays in Masturus but do in Mola. Whereas at least most of the rays in the upper and lower halves of the pseudocaudal fin of both Masturus (exclusive of the medial lobe) and Mola are in- dividually supported by radial elements, at least most of the rays of the medial lobe of Masturus are not supported by radial elements but rather take support from the last vertebral centrum. In the single specimen of Masturus

examined there are about (it being difficult to decide where the pseudocaudal rays begin) 7 rays in the upper

half of the pseudocaudal, 10 below, and 6 in the medial

lobe, with the dorsal fin having 20 rays and the anal fin

19, a total dorsal, pseudocaudal, and anal count of 62. Fraser-Brunner (1951) gave a total count of 60 to 62, with

eight (rarely seven or nine) rays in the medial lobe for M.

lanceolatus, and a total of 55 to 57, with four (rarely three

or five) in the medial lobe for M. oxyuropterus. Obviously, more extensive data is needed for these various fin counts in both Mola and Masturus, and such can be easily ascertained only from cleared and stained specimens,

or from very finely radiographed specimens.

In short, Mola and Masturus differ primarily mainly in the details of the pseudocaudal fin and its supports: 1) Mola has a ninth caudal vertebral centrum

that is lost by Masturus; 2) Masturus has a group of rays

in a medial lobe of the pseudocaudal fin that are sup- ported by the last vertebral centrum rather than by

radials, this medial lobe not being present in Mola and

perhaps being the remnants of true caudal fin rays;

3) Mola develops bony ossicles at the distal end of many

of the pseudocaudal rays while Masturus never does; and

4) Mola has a better developed neural spine on the eighth caudal vertebra than does Masturus. Other differences

are: 1) Mola has a supraneural that appears in Masturus to be fully fused to the first basal pterygio- phore of the dorsal fin; 2) Mola has the interoperculum

ossified, while it is unossified in the single small specimen of Masturus examined; 3) the trituration teeth

in the lower jaw of Mola are divided into right and left series, while Masturus has a major medial series. The above differences between Mola and Masturus

seem to justify the retention of them as distinct genera, even if they should be found to be represented by a single species each. The far more numerous differences listed between Ranzania and Mola-Masturus reflect in part the

ease of distinguishing between subgroups composed of only a few species. In the present case each of the three genera either has only a single species or only a single species was examined for this work, so there is, in es- sence, no intrageneric variation and the comparisons made are only between three units. Thus, it seems to me

that the extensive differences listed between Ranzania and Mola-Masturus do not necessarily justify the recognition of two subfamilies within the family Molidae, and,

as a personal opinion, I do not think the differences between the two groups are of sufficient magnitude for subfamilial recognition. Generic relationships.—With it being clear that Mola and Masturus are far more closely related to one

another than to Ranzania, the most pertinent remaining

question is whether one or the other of these two lines of molid evolution is more generalized than the other and

anatomically closer to the triodontidlike ancestral group. The only other question of consequence is whether Mola

or Masturus is the more generalized within its line of

radiation. To address the last question first. Mola is more

generalized than Masturus by: 1) the retention of the ninth caudal vertebra, separate supremeural, and ossified interoperculum; 2) by the better development of the neural spine of the eighth caudal vertebra; 3) by the

retention of the trituration teeth in right and left series to

either side of the midline in the lower jaw. Conversely, Masturus is more generalized than Mola by: 1) the

possible retention of true caudal fin rays in the medial

lobe of the pseudocaudal fin; and 2) the lack of ossicles at the ends of any of the pseudocaudal fin rays. Overall, it would seem that Mola has remained slightly more generalized than Masturus. Many of the differences between Ranzania and Mola- Masturus indicate that Ranzania is more specialized
Ranzania

Figure 326.—Hypothesized phylogenelic

relationships of the genera of Molidae.

than the other two genera, these specializations often associated with the streamlining of the body for what is probably more rapid and sustained swimming. The specialized features of Ranzania (i.e., the features

further removed in comparison to Mola-Masturus from

those of the hypothetical pre-Triodon ancestral group, discussed under Triodon) are: 1) the funnellike lips, closing to a vertical groove; 2) the falcate pectoral fins, resting in an indented region on the carapace; 3) the thickened, angular scale plates of the carapace; 4) the pseudocaudal fin distinctly set off from the dorsal and

anal fins in adults; 5) the great posterior prolongation of the epiotics and of the supraoccipital crest; 6) the unossified vomer; 7) the anterior displacement of the basi- sphenoid; 8) the greater anterodorsal prolongations of the basioccipital, meeting in the midline over the neural

canal; 9) the strong interdigitation of the neural arches and spines of the abdominal and more anterior caudal

vertebrae leading to greater rigidity of the vertebral column within a slightly less flexible carapace; 10) the

loss of the sixth branchiostegal and great enlargement of the fifth; 11) the loss of the posterior portion of the sub- operculum; 12) the elongate, rodlike operculum; 13) the

interdigitation of the actinosts to one another; 14) the

great platelike expansion of the postcleithrum beneath

the carapace in the region of the pectoral fin; 15) the decreased width of the anterior end of the parasphenoid;

16) the articulation of the posterior region of the palatine with the dorsal surface of the parasphenoid; 17) the elongation of the basal pterygiophores, and the greater obliqueness of them and their neural and haemal spine

supports; 18) the grouping in pairs of most of the

successive sets of two haemal spines of the caudal

vertebrae; 19) the complexity of the first basal pterygio- phore of the dorsal fin; and 20) the anterior expansion of the bases of the first dorsal and anal fin rays. Conversely, a lesser number of features of Romania

can be considered more generalized than in MolaMasturus, these being: 1) the lesser reduction in the number of caudal vertebrae, the centrum of the 10th be- ing retained; 2) the branching of the rays of the pseudocaudal fin not much less than that of the dorsal and anal

fins; 3) the better development of the interoperculum and mesopterygoid; 4) the lack of a secondary larval

stage; 5) the lack of a deep collagenous layer under the

scales, probably associated with the better ossification of the skeleton; 6) the gill rakers perhaps less concealed in adults; 7) ceratobranchials not as deep bodied; and

8) the second abdominal vertebra without prominent

anterior and posterior extensions of its neural arch and

spine. On the whole, Ranzania has far more specializations than do Mola and Masturus, and Ranzania must be considered to be the more specialized of the two lines of molid diversification. The fewer specializations of MoUx

and Masturus (the opposite of the generalized conditions of Ranzania discussed above) can be assumed to have arisen after the divergence of the early molids into the two lines leading on the one hand to Mola and the

slightly more specialized Masturus and, on the other hand, through even greater specialization, to Ranzania. Raven (1939b), on the basis of the musculature and

skeleton, also concluded that Ranzania was more

specialized than Mola and Masturus, while Fraser- Brunner (1951), on more superficial and fewer characters, believed Ranzania, in spite of certain specializations, to be the most generalized of the molids, and

Masturus to be slightly more generalized than Mola,

primarily because of the reputed retention of true caudal

fin rays in the medial lobe of the pseudocaudal fin.

Relationships to the other Tetraodontoidei.—As dis- cussed under the Triodontidae, molids have their closest anatomical affinity among the gymnodonts with the trio- dontids, retaining a number of generalized features (e.g., fourth gill and gill slit; basisphenoid; unmodified first branchiostegal ray; uninflatable gut; general configuration of the bones of the snout) from their triodontid ancestry while at the same time becoming remarkably

specialized with the abortion of the rear end of the body

and the encasement of the relatively slow swimming

body in a firm or thickened skin. While molids are most

closely related to triodontids, they undoubtedly evolved from them at a level of organization somewhat less specialized than that of the Recent Triodon, as discussed more fully under the latter. Molids have sometimes been thought to be closely related to diodontids, since both the premaxillaries and

dentaries are fully fused to their opposite members only

in these two families of gymnodonts. However, as dis- cussed under Triodon, the fusion of the premaxillaries and dentaries is not that complex an event and the phylogenetic usefulness of it is meager within the gymnodonts. While it is true that the generalized biting edge

dentition of diodontids (with numerous small units) could have given rise to that of molids (discrete units es- sentially absent), the structure of the rest of the head and

body of diodontids is extremely unlike that of molids,

there being no similarities such as are found between

molids and triodontids. In one other superficial respect

there is a minor similarity between molids and diodontids. Diodontids have a short caudal peduncle and a reduced number of caudal vertebrae, especially of those

posterior to the dorsal and anal fin bases, while in molids 392
this latter region is even more reduced. In light of the fact that molids have their closest anatomical affinity with

triodontids and that diodontids and molids are anatomically extremely different, there is every reason to believe that the reduction in the bony structure in the caudal region of diodontids has taken place independently of that in molids, and that it in no way indicates

that the diodontid caudal peduncle was a precursor to the abortion of the rear end of the body in molids. The

diodontid caudal peduncle has probably become reduced from that found in most of the ancestral tetraodontoids concomitant with the development of the huge spines

that guard the body in diodontids as a slow swimming

highly defensive mode of life was evolved.

Material Examined

Length in millimeters is always standard length, and,

unless otherwise stated, the Recent specimens listed below are cleared and alizarin stained preparations. In- stitutional abbreviations are as follows: ANSP,

Academy of Natural Sciences of Philadelphia; BMNH,

British Museum (Natural History), London; GVF,

George Vanderbilt Foundation, fishes now at the Cali- fornia Academy of Sciences, San Francisco; JLBSII,

J.L.B. Smith Institute of Ichthyology, Grahamstown,

South Africa; SU, Stanford University, Calif, (now at the

California Academy of Sciences, San Francisco); TABL,

Tropical Atlantic Biological Laboratory, U.S. Bureau of Commerical Fisheries (now National Marine Fisheries

Ser\'ice), Miami, Fla.; USNM, United States National Museum (National Museum of Natural History), Washington, D.C.; WAM, Western Australian Museum,

Perth. Recent Species PLECTOGNATHI

Triacanthodidae

Atrophacanthus japonicus (Kamohara): ANSP 102138,

2, 9.1-10.4 mm, Celebes; ANSP 102139, 5, 35.6-43.1 mm, Celebes; BMNH 1960. 5.4.1, 1, 34.7 mm, Celebes. Halimochirurgus alcocki Weber: USNM 93474, 1, 124 mm, Philippines. Halimochirurgus centriscoides Alcock: ANSP 100828,

2, 99.2-113 mm, Bay of Bengal.

Hollardia hoUardi Poey: ANSP 103303, 1, 84.7 mm,

Puerto Rico; ANSP 100867, 2, 62.7-95.5 mm, Honduras, ANSP 103299, 3, 72.0-129 mm, Nicaragua; ANSP 97654, 1, 174 mm, Venezuela.

Hollardia meadi Tyler: ANSP 97396, 1, 64.5 mm.

Johnsonina eriomma Myers: ANSP 97750, 2, 75.5-85.5 mm, Panama; ANSP 103149, 2, 60.1-66.3 mm,

Panama; ANSP 103300, 2, 67.0-68.0 mm, Puerto Rico. Macrorhamphosodes platycheilus Fowler: ANSP

100862, 1, ca. 85 mm (posterior part of body absent), Bay of Bengal; ANSP 100865, 2, 80.3-85.3 mm. Bay of Bengal; USNM 93482, 1, too disintegrated to measure,

Philippines. Macrorhamphosodes uradoi (Kamohara): ANSP

101254, 2, 69.9-114 mm, Japan.

Parahollardia lineata (Longley): ANSP 100473, 1, 45.7 mm, Florida; ANSP 93375, 1, 62.2 mm, Florida; ANSP

102144, 1, 82.0 mm, Florida; ANSP 102145, 1, 86.1 mm. South Carolina; ANSP 97637, 3, 79.4-84.4 mm,

Louisiana. Parahollardia schmidti Woods: ANSP 100866, 5, 48.7- 62.5 mm, Honduras; ANSP 103302, 2, 62.0-74.0 mm,

Nicaragua; ANSP 100128, 4, 56.8-77.8 mm, Nicaragua. Paratriacanthodes retrospinis Fowler: ANSP 103285, 1, 85.3 mm, Mozambique.

Triacanthodes anomalus (Schlegel): ANSP 101257, 4, 50.6-59.7 mm, Japan; ANSP 101256, 1, 71.5 mm,

Japan; SU 49435, 1, 91.0 mm, Formosa.

Triacanthodes ethiops Alcock: USNM 93486, 2, 55.3- 63.7 mm, Philippines; ANSP 103286, 1, 76.1 mm,

Kenya. Tydemania navigatoris Weber: ANSP 100861, 6, 58.8- 67.0 mm. Bay of Bengal; ANSP 100863, 2, 60.1-62.2 mm, Bay of Bengal; ANSP 102137, 1, 63.3 mm. Bay of Bengal; USNM 93471, 1, ca. 95 mm, dry skeleton, Philippines.

Triacanthidae

Pseudotriacanthus strigilifer (Cantor): SU 41732, 1, 79.0 mm, India; ANSP 89387, 4, 119-145 mm,

Thailand. Triacanthus biaculeatus (Bloch): SU 27746, 2, 113-118 mm, Borneo; ANSP 76585, 1, 124 mm, China; SU

41730, 1, 25.6 mm, India; GVF reg. no. 2655, 3, 10.9-

19.1 mm, Thailand.

Triacanthus nieuhofi Bleeker: ANSP 102982, 1, 108 mm, possibly Australia. Tripodichthys angustifrons (Hollard): ANSP 98719, 1, 137 mm, Australia. Tripodichthys blochi (Bleeker): ANSP 103298, 3, 55.1- 88.9 mm, locality unknown; ANSP 103301, 3, 69.4-97.3 mm, locality unknown; ANSP 63429-54, 11, 18.4-50.9 mm, Philippines; ANSP 63476, 1, 81.0 mm, Philippines; ANSP 63421-25, 5, 24.3-105 mm, Philippines; SU 26930, 2, 92.0-107 mm, Philippines. Tripodichthys oxycephalus (Bleeker): ANSP 102325, 1, 125 mm. Bay of Bengal.

Trixiphichthys weberi (Chaudhuri): ANSP 102136, 1, 29.6 mm. Bay of Bengal; ANSP 101389, 3, 101-119 mm, Bay of Bengal.
Balistidae

Abalistes stetlatus (Lacepede): ANSP 111538, 1, 87.6 mm, India. Balistapus undulatus Mungo Park: ANSP 102146, 1, 124 mm, unknown western Pacific locality; ANSP

102147, 1, 122 mm, unknown western Pacific locality; ANSP 102152, 3, ca. 120 mm, unknown western Pacific

locality, wet partially disarticulated skeletons. Batistes capriscus Gmelin: ANSP 109437, 2, 38.4-46.1 mm, Texas; ANSP 109438, 1, 44.7 mm, Texas; ANSP

109534, 1, 127 mm, Mexico, dry partially disarticu- lated skeleton; ANSP 109535, 1, 93.7 mm, Louisiana, dry partially disarticulated skeleton; USNM 12983, 1, ca. 360 mm, Gulf of Mexico.

Balistes forcipatus Gmelin: ANSP 103217, 1, 164 mm,

Guinea.

Batistes potytepis Steindachner: ANSP 88972, 1, 56.1 mm, Galapagos; ANSP 109530, 1, ca. 390 mm, Mexico.

Balistes vetuta Linnaeus: ANSP 109439, 1, 59.8 mm,

Colombia.

Balistoides conspiciltum (Bloch and Schneider): ANSP

105836, 1, 214 mm, locality unknown.

Balistoides viridescens (Bloch and Schneider): ANSP

106793, 1, 87.8 ram, Borneo. Canthidermis maculatus (Bloch): ANSP 100085, 1, 80.1 mm, Alabama; ANSP 101364, 1, 217 mm, Mexico.

Hemibatistes bursa (Bloch and Schneider): ANSP

109441, 2, 141-160 mm, locality unknown.

Hemibalistes chrysopterus (Bloch and Schneider): ANSP 68600, 1,90.1 mm. New Hebrides. Melichthys niger (Bloch): ANSP 109440, 2, 147-168 mm, locality unknown.

Melichthys vidua (Solander): ANSP 109442, 1, 202 mm, locality unknown. Odonus niger (Ruppell): ANSP 100991, 1, 173 mm.

New Guinea. Rhinecanthus aculeatus (Linnaeus): ANSP 97373, 1, 72.8 mm, Samoa; ANSP 109443, 2, 172-207 mm, locali- ty unknown. Rhinecanthus rectangulus (Bloch and Schneider): ANSP 101777, 1, 37.4 mm. Phoenix Islands; ANSP

113259, 1, 70.4 mm, Chagos Archipelago. Rhinecanthus verrucosus (Linnaeus): ANSP 72220, 1, 98.2 mm, Borneo. Sufflamen frenatus (Latreille): ANSP 106816, 1, 74.3 mm, Somalia; ANSP 109436, 1, 180 mm, locality un- known.

Sufflamen verres (Gilbert and Starks): ANSP 100279,

2, 30.9-39.5 mm, Panama.

Xanthichthys lineopunctatus (Hollard): ANSP 91806,

1, 181 mm, Hawaii. Xanthichthys ringens (Linnaeus): ANSP 74895, 1, 40.7 mm. Lesser Antilles; ANSP 113814, 2, 57.6-62.2 mm,

Bahamas. Monacanthidae Acanthaluteres spilomelanurus (Quoy and

Gaimard): ANSP 109810, 1, 63.7 mm, Australia.

Alutera heudetotii Hollard: ANSP 109455, 2, 107-114 mm, Florida; ANSP 109536, 2, ca. 190 mm, Florida, wet completely disarticulated skeletons. Alutera monoceros (Linnaeus): ANSP 111505, 2, 111- 136 mm, India. Alutera schoepfi (Walbaum): ANSP 105131, 1, 82.8 mm, Colombia; ANSP 109454, 1, ca. 200 mm, Florida, wet partially disarticulated skeleton. Alutera scripta (Osbeck): ANSP 100109, 2, 46.2-73.3 mm, Florida. Amanses scopas (Cuvier): ANSP 109739, 1, 167 mm,

Saipan. Brachaluteres trossulus (Richardson): SU 20566, 2, 43.2-55.5 mm, Australia. Cantherhines pardalis (Ruppell): ANSP 104784, 1, 79.4 mm, Madagascar.

Cantherhines putlus (Ranzani): ANSP 109444, 1, 56.2 mm, Bahamas; ANSP 101613, 3, 35.1-42.6 mm,

Bahamas; ANSP 97383, 1, 45.9 mm. Lesser Antilles; ANSP 109445, 2, 68.7-83.2 mra; Louisiana. Cantherhines sandwichiensis (Quoy and

Gaimard): ANSP 10032, 1, 92.5 mm, Hawaii. Chaetoderma spinosissimus (Quoy and

Gaimard): ANSP 109812, 1, 33.0 ram, Malaya. Laputa cingalensis Fraser-Brunner: ANSP 100831, 1, 51.9 mm. Bay of Bengal. Monacanthus chinensis (Bloch): ANSP 90145, 1, 79.4 mm, Moluccas; ANSP 89557, 2, 84.4-101 mm,

Thailand. Monacanthus ciliatus (Mitchill): ANSP 109446, 2, 51.3-58.2 mm, Colombia; ANSP 109447, 2, 75.7-81.3 mm, Florida; ANSP 109448, 2, 52.5-78.4 mm, Florida; ANSP 109449, 3, 57.2-88.1 mm, Florida; TABL un- catalogued {Silver Bay station 1268), 1, 74.5 mm.

North Carolina; TABL uncatalogued (Oregon station

5402), 1, 38.3 mm, Jamaica; TABL uncatalogued

(Oregon station 3589), 1, 119 mm, Panama.

Monacanthus mylii (B. de Saint-Vincent): ANSP

117147, 1, 60.8 mm. New Guinea. Monacanthus tuckeri Bean: ANSP 84488, 3, 28.4-31.9 mm, Bahamas; ANSP 110521, 1, 70.4 mra, Baharaas. Navodon setosus (Waite): ANSP 97904, 1, 31.0 mm. New Zealand; ANSP 96426, 1, 69.2 mm. New Zealand. Oxy monacanthus tongirostris (Bloch and

Schneider): ANSP 109434, 1, 26.5 mm, Seychelles; ANSP 104808, 5, 18.0-56.7 ram, Seychelles; SU 8884, 2, 63.5-73.2 mm, Samoa.

Paraluteres prionurus (Bleeker): ANSP 102875, 1, 46.4 mm, Seychelles. Paramonacanthus barnardi Fraser-Brunner: ANSP

109808, 1, 42.5 mm. South Africa. Paramonacanthus cryptodon (Bleeker): ANSP 96729,

1, 40.3 mm, Philippines; ANSP 63130, 1, 68.5 mm,

Siam; USNM 169045, 2, 64.1-68.9 mm, Philippines. Paramonacanthus curtorhynchus (Bleeker): ANSP

100821, 3, 44.7-47.4 mm. Bay of Bengal. Pervagor metanocephalus (Bleeker): ANSP 104788, 2, 57.4-74.4 mm, Mauritius. Pervagor spilosomus (Lay and Bennett) : ANSP 109451,

1, 103 mm, locality unknown; ANSP 109450, 3, 67.7-
83.2 mm, Hawaii; ANSP 112743, 1, 54.4 mm, Hawaii; ANSP 84774, 4, all ca. 65 mm, Hawaii, dry partially disarticulated skeletons. Pseudaluteres nasicornis (Schlegel): SU 26926, 2, 50.8- 108 mm, Philippines. Psilocephalus barbatus (Gray): ANSP 109648, 1, 142 mm, Australia; SU 35714, 2, 137-139 mm, Singapore. Rudarius ercodes Jordan and Fowler: ANSP 29477-85,

3, 37.7-44.9 mm, Japan. Rudarius minutus Tyler: ANSP 109788, 1, 17.9 mm,

Borneo. Stephanolepis auratus (Castelnau): ANSP 106265, 1, 112 mm, Ghana.

Stephanolepis cirrhifer (Schlegel): ANSP 76598, 1, 50.2 mm, Hong Kong.

Stephanolepis hispidus (Linnaeus): ANSP 109452, 2, 42.8-50.4 mm, Florida; ANSP 109543, 1, 80.2 mm,

Florida. Stephanolepis setifer (Bennett): ANSP 94610, 1, 113 mm, Bahamas. Aracanidae

Aracana aurita (Shaw): ANSP 109572, 1, 87.3 mm,

Tasmania; ANSP 98627, 1, ca. 110 mm, Australia, dry

partially disarticulated skeleton. Aracana flavigaster Gray: ANSP 33169, 2, 45.0-70.0 mm, Australia, dry partially disarticulated skeletons; perhaps the female of A. ornata. Aracana ornata Gray: ANSP 109570, 1, 70.5 mm,

Australia; ANSP 33173, 1, 67.5 mm, Australia. Caprichthys gymnura McCulloch and Waite: WAM

P7711, 1, 74.1 mm, Australia. Capropygia unistriata Kaup: ANSP 109575, 1, 87.9 mm, Australia. Kentrocapros aculeatus (Houttuyn): SU 53434, 2, 90.0- 90.7 mm, Japan. Strophiurichthys robustus Fraser-Brunner: ANSP

109569, 1, 150 mm, Australia.

89.9-107 mm, Panama; ANSP 98626, 4, 105-193 mm,

locality unknown, dry partially disarticulated

skeletons. Lactoria cornuta (Linnaeus): ANSP 91662, 1, 43.0 mm,

Guam; ANSP 98621, 1, 114 mm, Philippines; ANSP

98622, 1, 88.2 mm, Philippines; ANSP 98623, 1, 104 mm, Philippines; ANSP 98620, 1, 119 mm, China Sea. Lactoria fornasinii (Bianconi): ANSP 89016, 2, 12.5- 18.0 mm, Hawaii; ANSP 83863, 1, 65.2 mm, Hawaii; ANSP 104837, 1, 15.4 mm, Madagascar; ANSP

104866, 2, 50.3-66.2 mm, Seychelles. Ostracion lentiginosum Bloch and Schneider: ANSP

112738, 2, 24.4-33.2 mm, Hawaii; ANSP 98624, 1, 88.8 mm, Hawaii; ANSP 106667, 1, 68.2 mm, southwest

Pacific; ANSP 104875, 2, 95.9-115 mm, Mauritius.

Ostracion tuberculatus Linnaeus: ANSP 104830, 1, 29.8 mm, Seychelles; ANSP 112942, 1, 54.5 mm,

Aldabra Atoll; ANSP 112881, 1, 38.7 mm, Australia; ANSP 112904, 2, 96.7-122 mm, Australia. Rhinesomus bicaudalis (Linnaeus): ANSP 85199, 1, 83.7 mm, Haiti; ANSP 70147, 1, 77.4 mm, Honduras. Rhinesomus triqueter (Linnaeus): ANSP 74890, 3, 15.5-36.9 mm, Florida; ANSP 98625, 2, 88.7-136 mm,

Puerto Rico; ANSP 91385, 1, 134 mm, Colombia. Rhynchostracion rhinorhynchus (Bleeker): ANSP

90158, 1, 88.2 mm, Java; ANSP 95825, 1, 133 mm,

Java. Tetrosomus concatenatus (Bloch): ANSP 104755, 1, 43.4 mm, Thailand. Tetrosomus gibbosus (Linnaeus): ANSP 10081, 1, 96.3 mm, Burma.

Triodontidae

Triodon macropterus Lesson: SU 13747, 1, 391 mm,

Philippines; ANSP 98917, 1, 463 mm, Japan.

Tetraodontidae

Ostraciidae

Acanthostracion guineensis Bleeker: ANSP 102874, 1, 178 mm, Ivory Coast. Acanthostracion notacanthus (Bleeker): ANSP 102909,

1, 148 mm, St. Helena. Acanthostracion polygonius Poey: ANSP 83840, 1, 117 mm, Bahamas; ANSP 80008, 1, 92.5 mm. Lesser Antilles. Acanthostracion quadricornis (Linnaeus): ANSP

98614, 1, 67.1 mm, Florida; ANSP 98616, 1, 58.2 mm,

Mexico; ANSP 98615, 1, 77.7 mm, Florida; ANSP

98617, 2, 8.2-15.3 mm, Louisiana; ANSP 98618, 1, 73.0 mm, Texas; SU 51172, 3, 17.5-25.0 mm, Guiana; ANSP 98843, 2, 121-152 mm, Surinam; ANSP 102749,

1, 254 mm, Colombia; ANSP 103506, 1, 350 mm,

Venezuela; ANSP 98619, 3, 130-163 mm, locality un- known, dry partially disarticulated skeletons. Lactophrys trigonus (Linnaeus): ANSP 49179-80, 2,

Amblyrhynchotes honckenii (Bloch): ANSP 11507, 1, 70.7 mm, India; ANSP 104778, 1, 97.4 mm, Mozambique. Amblyrhynchotes piosae (Whitley): ANSP 113990, 1, 33.8 mm, Australia. Amblyrhynchotes richei (Freminville): USNM ace. no. 244693, 1, 59.4 mm. New Zealand; ANSP 109916, 1, 50.8 mm, Australia. Arothron armilla (Waite and McCulloch): ANSP

109790, 1, 61.3 mm, Australia. Arothron hispidus (Linnaeus): ANSP 104798, 1, 40.8 mm, Seychelles. Arothron nigropunctatus (Bloch and

Schneider): ANSP 106817, 1, 56.8 mm, Solomon

Islands; ANSP 104737, 1, 182 mm, Thailand. Arothron stellatus (Bloch and Schneider): ANSP

109529, 1, ca. 420 mm, Seychelles, dry partially disarticulated skull; ANSP 78242, 1, 292 mm, India. Canthigaster amboinensis (Bleeker): ANSP 82355, 1, 80.3 mm, Hawaii.
Canthigaster bennetti (Bleeker): ANSP 104825, 1, 58.3 mm, Seychelles. Canthigaster jactator Jenkins: ANSP 89255, 1, 54.2 mm, Hawaii.

Canthigaster janthinoptera (Bleeker): ANSP 104806, 2, 42.6-45.5 mm, Seychelles. Canthigaster margaritata (Ruppell): ANSP 104829, 1, 46.0 mm, Seychelles; ANSP 109471, 1, 76.6 mm,

locality unknown.

Canthigaster punctatissima (Gunther): ANSP 109472,

2, 13.1-20.2 mm, Costa Rica; ANSP 109473, 2, 19.6- 46.1 mm, Costa Rica; ANSP 81467, 3, 42.5-49.5 mm,

Mexico.

Canthigaster rivulata (Schlegel): ANSP 84675, 1, 101 mm, Hawaii.

Canthigaster rostrata (Bloch): ANSP 113827, 3, 10.0- 18.2 mm, Virgin Islands; ANSP 102141, 1, 59.6 mm,

Texas; ANSP 102142, 1, 55.2 mm, Texas; ANSP

102143, 1, 96.5 mm, Texas, dry partially disartic- ulated skeleton. Canthigaster ualentini (Bleeker): ANSP 99975, 4, 33.9- 72.9 mm, Seychelles; ANSP 99948, 9, 30.5-72.8 mm,

Seychelles; ANSP 99962, 10, 18.1-70.7 mm, Seychelles; ANSP 104790, 1, 80.3 mm, Mauritius. Carinotetraodon lorteti (Tirant): ANSP 109469, 1, 25.1 mm, locality unknown; ANSP 109470, 2, 33.1-35.9 mm, locality unknown.

Chelonodon fluviatilis (Hamilton-Buchanan): ANSP

109456, 4, 21.1-30.2 mm, locality unknown; ANSP

109457, 3, 70.1-84.7 mm, Thailand. Chelonodon patoca (Hamilton-Buchanan): ANSP

117140, 1, 70.6 mm. New Guinea. Chonerhinos modestus (Bleeker): SU 33563, 3, 31.0- 54.5 mm, Borneo. Colomesus asellus (MuUer and Troschel): ANSP 98840,

3, 27.3-33.6 mm, Peru; ANSP 98908, 2, 50.6-50.8 mm,

Brazil; ANSP 76254, 1, 113 mm, Venezuela; ANSP

37899, 1, 128 mm, Venezuela. Colomesus psittacus (Bloch and Schneider): ANSP

75845, 2, 49.7-52.3 mm, Trinidad; ANSP 98869, 2, 76.9-112 mm, Surinam; ANSP 98907, 1, 179 mm,

Surinam; ANSP 97658, 2, 178-180 mm, Surinam, dry

skeletons. Ephippion guttifer (Bennett): ANSP 103236, 1, 101 mm, Guinea; ANSP 103245, 1, 108 mm, Guinea. Fugu chrysops (Hilgendorf): ANSP 97548, 1, 98.6 mm,

Japan. Fugu oblongus (Bloch): ANSP 77245, 1, 46.2 mm, India. Fugu rubripes (Temminck and Schlegel): ANSP 95480,

1, 83.2 mm, Japan; USNM 26455, 1, 151 mm, Japan.

Guentheridia formosa (Gunther): ANSP 95552, 1, 175 mm, Panama. Lagocephalus inermis (Temminck and

Schlegel): ANSP 100832, 1, 52.2 mm, Bay of Bengal. Lagocephalus laevigatus (Linnaeus): ANSP 103120, 1, 61.4 mm, Alabama; ANSP 102155, 2, 143-166 mm,

Florida; ANSP 102153, ca. 290 mm, Uruguay, wet

disarticulated skeleton; ANSP 102154, 1, ca. 290 mm,

Uruguay, dry skeleton.

Lagocephalus lagocephalus (Linnaeus): ANSP 70299,

1, 214 mm, Malpelo Islands, eastern Pacific. Lagocephalus lunaris (Bloch and Schneider): ANSP

111509, 1, 62.3 mm. Bay of Bengal. Lagocephalus scleratus (Gmelin): ANSP 96685, 1, 80.9 mm, Philippines. Lagocephalus spadiceus (Richardson): ANSP 104787,

1, 98.2 mm, Mozambique.

Monotreta cutcutia (Hamilton-Buchanan): ANSP

63132, 1, 45.4 mm, Thailand; ANSP 59928-37, 1, 73.9 mm, Thailand. Monotreta gularis (Hamilton-Buchanan): USNM

44811, 2, 46.8-47.1 mm, Burma.

Monotreta leiurus (Bleeker): ANSP 59928-37, 2, 61.5- 66.3 mm, Thailand. Monotreta palembangensis (Bleeker): ANSP 27770, 1, 103 mm, Sumatra.

Sphoeroides angusticeps (Jenyns): ANSP 95841, 1, 172 mm, Galapagos.

Sphoeroides annulatus (Jenyns): ANSP 109459, 3, 15.0-21.4 mm, California; ANSP 109461, 3, 10.9-15.8 mm, California; ANSP 109460, 1, 13.5 mm, California; ANSP 109458, 1, 174 mm, locality unknown.

Sphoeroides dorsalis Longley: ANSP 109462, 1, 131 mm, Florida; ANSP 109519, 1, 139 mm, Georgia, dry

skeleton; ANSP 109520, 1, 155 mm, Florida, dry

skeleton. Sphoeroides greeleyi Gilbert: ANSP 109463, 3, 24.2- 60.8 mm, locality unknown.

Sphoeroides lobatus (Steindachner): ANSP 97332, 1, 67.5 mm, Panama.

Sphoeroides maculatus (Bloch and Schneider): ANSP

109466, 1, 126 mm, Virginia; ANSP 109465, 3, 31.0- 57.8 mm, Virginia; ANSP 109464, 2, 97.5-106 mm,

Virginia; ANSP 84307, 3, 9.2-10.2 mm. New Jersey; ANSP 102043, 1, 12.4 mm. New Jersey; ANSP 109467,

1, 201 mm, Florida; all the following 11 specimens are dry and partially to completely disarticulated

skeletons from Virginia of between ca. 50 and 2(X) mm, ANSP 109516-18, 109521-28. Sphoeroides nephelus (Goode and Bean): ANSP

105222, 1, 48.5 mm, Mississippi; ANSP 110533, 1, 128 Sphoeroides pachygaster (Ranzani): ANSP 109468, 2, 134-137 mm, Florida; ANSP 101322, 1, 80.6 mm,

Nigeria; ANSP 104781, 1, 117 mm, Mozambique.

Sphoeroides spengleri (Bloch): ANSP 10531, 1, ca. 90 mm, Florida, dry skeleton; ANSP 10532, 1, 92.8 mm,

Nicaragua, dry skeleton. Sphoeroides testudineus (Linnaeus): ANSP 107328, 1, 68.5 mm, Venezuela. Sphoeroides trichocephalus (Cope): ANSP 109742, 1, 57.1 mm, Panama.

Tetraodon lineatus Linnaeus: ANSP 77913, 1, 222 mm,

French Equitorial Africa. Tetraodon mbu Boulenger: ANSP 112236, 1, 47.7 mm,

Belgian Congo.

Torquigener pleurogramma (Regan): ANSP 98690, 1, 113 mm, Australia.
Torquigener pleurostictus (Giinther): ANSP 89848

87.1 mm, Australia. Xenopterus naritus (Richardson): ANSP 100814, 108-143 mm. Bay of Bengal.

jaws only, from a large specimen of unknown length from Massachusetts. Ramania laeuis (Pennant): ANSP 109435, 2, 65.1-66.9 mm, Hawaii; ANSP 109561, 1, 493 mm, Hawaii.

Diodontidae

Chilomycterus affinis Gunther: ANSP 103806, 1, 310 mm, Galapagos. Chilomycterus antennatus (Cuvier): ANSP 76412, 1, 70.5 mm, Trinidad. Chilomycterus antillarum Jordan and Rutter: ANSP

97512, 1, 66.4 mm, Surinam.

Chilomycterus atinga (Linnaeus): ANSP 103900, 1, 278 mm, Florida. Chilomycterus mauritanicus Le Danois: ANSP 103209,

1, 82.1 mm, Guinea. Chilomycterus orbicularis (Bloch): ANSP 108827, 2, 72.9-77.0 mm, Somalia; ANSP 98008, 1, 158 mm,

Philippines. Chilomycterus reticulatus (Liimaeus): ANSP 102574,

1, 545 mm, Sierra Leone. Chilomycterus schoepfi (Walbaum): ANSP 109476, 2, 20.3-22.6 mm, Louisiana; ANSP 109477, 1, 60.1 mm,

Louisiana; ANSP 109478, 1, 62.5 mm, Texas; ANSP

109474, 1, 159 mm, Louisiana; ANSP 109479, 1, 35.2 mm, Louisiana; ANSP 109475, 1, 168 mm, Florida; ANSP 109513, 1, ca. 80 mm, Texas, dry partially disar- ticulated skeleton; ANSP 109514, 1, ca. 125 mm,

Florida, dry partially disarticulated skeleton. Chilomycterus spinosus (Linnaeus): ANSP 109669, 1, 51.0 mm, Brazil. Chilomycterus tigrinus (Cuvier): ANSP 101341, 1, 165 mm, Somalia.

Dicotylichthys nicthemerus (Cuvier): USNM 201630,

1, 51.8 mm, Australia. Dicotylichthys punctulatus Kaup: USNM 47923, 1, 226 mm, Australia. Diodon holocanthus Linnaeus: ANSP 102151, 1, 12.3 mm, Louisiana; ANSP 109480, 1, 53.5 mm, Texas; ANSP 102149, 1, 108 mm, Florida; ANSP 102148, 1, 81.8 mm, Florida; ANSP 102150, 1, 113 mm, Florida; ANSP 102162, 1, 124 mm. Virgin Islands, dry partially disarticulated skeleton. Diodon hystrix Linnaeus: ANSP 104740, 2, 80.6-84.4 mm, Somalia; ANSP 106756, 2, 45.1-42.2 mm, Florida; ANSP 109515, 1, ca. 200 mm, Florida, dry partially disarticulated skull. Diodon jaculiferus Cuvier: ANSP 98272, 1, 53.4 mm,

Australia.

Molidae

Masturus lanceolatus (Li6nard): USNM 117330, 1, 127 mm, Florida. Mola mola (Linnaeus): SU 16438, 1, 306 mm, California; SU 16441, 1, 310 mm, California; USNM 27238, dry jaws only from a large specimen of unknown length from Massachusetts; USNM 102086, alcohol preserved

NONPLECTOGNATHS

Acanthuridae

Acanthurus sp. (acronurus stage): ANSP 86416, 1, 53.6 mm. Society Islands, Acanthurus gahhm (Forskal): ANSP 109483, 2, 155-158 mm, unknown western Pacific locality. Acanthurus leucosternon Bennett: ANSP 108204, 1, 114 mm, Seychelles. Acanthurus lineatus (Linnaeus): ANSP 109484, 2, 103- 118 mm, unknown western Pacific locality; ANSP

109482, 1, ca. 150 mm, unknown western Pacific

locality, dry partially disarticulated skeleton; ANSP

109481, 1, ca. 160 mm, unknown western Pacific

locality, dry partially disarticulated skeleton. Acanthurus nigoris Cuvier: ANSP 109487, 1, 127 mm,

locality unknown.

Acanthurus nigrofuscus (Forskal): ANSP 109485, 4, 62.3-73.3 mm, unknown, western Pacific locality; ANSP 109486, 3, 77.3-131 mm, locality unknown.

Acanthurus olivaceus Bloch and Schneider: ANSP

109488, 1, 109 mm, locality unknown; ANSP 109480, 1, 152 mm, locality unknown.

Acanthurus sandvicensis Streets: ANSP 109490, 1, 69.0 mm, Hawaii. Acanthurus triostegus (Linnaeus): ANSP 83246, 2, 29.1-29.8 mm, Marquesas Islands; ANSP 87546, 3, 27.9-35.1 mm, Marquesas Islands; ANSP 109491, 6, 40.6-68.9 mm, locality unknown.

Ctenochaetus striatus (Quoy and Gaimard): ANSP

109492, 4, 74.8-123 mm, locality unknown.

Ctenochaetus strigosus (Bennett): ANSP 108208, 1, 93.0 mm, Seychelles. Naso sp.: ANSP 108416, 1, 107 mm, Seychelles; ANSP

108419, 1, 72.0 mm, Seychelles. Naso sp., probably N. annulatus (Quoy and

Gaimard): MCZ uncatalogued, 1, ca. 370 mm,

locality unknown, dry skull. Naso breuirostris (Cuvier and Valenciennes): ANSP

109493, 1, 209 mm, locality unknown; ANSP 88537, 1, 228 mm, Tuamotus. Naso fageni Morrow: ANSP 103532, 1, 515 mm,

Seychelles. Naso hexacanthus (Bleeker): ANSP 109495, 1, 158 mm,

locality unknown; ANSP 109494, 1, 188 mm, locality unknown. Naso literatus (Bloch and Schneider) : ANSP 109497, 2, 111-209 mm, unknown western Pacific locality; ANSP

109496, 1, 191 mm, locality unknown. Naso thynnoides (Cuvier and Valenciennes): JLBSII

616d, 1, 191 mm, Tanganyika. Naso unicornis (Forskal): ANSP 89114, 1, 267 mm,

Hawaii.
Paracanthwus hepatus (Linnaeus): ANSP 108441, 1, 21.2 mm, Seychelles; ANSP 108444, 1, 31.6 mm,

Seychelles; ANSP 90446, 1, 179 mm, Java. Prionurus punctatus Gill: ANSP 81238, 3, 35.0-47.9 mm, Galapagos.

Prionurus scalprum Cuvier and Valenciennes: ANSP

109779, 1, 44.3 mm, Japan; ANSP 109553, 1, 111 mm.

Japan. Zebrasoma flavescens (Bennett): ANSP 109498, 1, 60.0 mm, unknown western Pacific locality; ANSP 109499,

2, both 101 mm, locality unknown. Zebrasoma rostratus (Gunther): ANSP 108278, 1, 94.7 mm, Seychelles. Zebrasoma veliferum (Bloch): ANSP 109500, 1, 156 mm, locality unknown.

Zanclidae

Zanclus cornutus (Linnaeus): ANSP 109504, 1, ca. 70 mm, locality unknown; ANSP 109501, 1, 58.0 mm,

locality unknown; ANSP 109502, 1, 66.4 mm, locality unknown; ANSP 109503, 1, 70.4 mm, locality un- known. Chaetodontidae

Chaetodon citrinellus Broussonet: ANSP 109506, 1, 81.6 mm, unknown western Pacific locality. Chaetodon octofasciatus Bloch: ANSP 109508, 1, 67.1 mm, unknown western Pacific locality. Chaetodon striatus Linnaeus: ANSP 91118, 1, 44.6 mm, Bahamas; ANSP 91611, 1, 57.4 mm. Virgin

Islands. Chaetodon triangulum Cuvier and Valenciennes: ANSP 73227, 1, 87.2 mm, Philippines. Chelmon rostratus (Linnaeus): ANSP 109511, 3, 48.7- 93.4 mm, unknown western Pacific locality. Chaetodontoplus mesoleucus (Bloch): ANSP 109510, 3, 59.2-76.3 mm, unknown western Pacific locality. Centropyge multispinis (Playfair): ANSP 108469, 3, 19.0-69.0 mm, Seychelles. Centropyge vrolicki (Bleeker): ANSP 109505, 1, 90.4 mm, unknown western Pacific locality. Forcipiger longirostris (Broussonet): ANSP 109512, 1, 114 mm, locality unknown; ANSP 108393, 2, 139-140.0 mm, Seychelles. Holacanthus ciliaris (Linnaeus): ANSP 91094, 2, 35.7- 54.4 mm, Bahamas; ANSP 104989, 1, 26.0 mm.

Cayman Islands. Holacanthus tricolor (Bloch): ANSP 104970, 2, 40.2- 68.4 mm, Cayman Islands. Pomacanthodes imperator (Bloch): ANSP 108461, 1, 27.2 mm, Seychelles. Pomacanthus aureus (Bloch): ANSP 91609, 1, 56.6 mm, Florida.

Fossil Species

Institutional abbreviations for the repositories of the

fossils examined are as follows: AMNH, American Museum of Natural History, New York; BMNH, British Museum (Natural History), London; IGPUB, Istituto di Geologia e Paleontologia della University di Bologna; IGPUP, Istituto di Geologia e Paleontologia della Universita di Pisa; IGPUR, Istituto di Geologia e Paleontologia della University di Roma; IGUN, Institute de

Geologie, Universite de Neuchatel; IGUP, Istituto di Geologia della Universita di Padova; MCSNV, Museo

Civico di Storia Naturale, Verona; MNHN (IP), Museum National d'Histoire Naturelle, Institute de

Paleontologie, Paris; NSKG, Naturwissenschaftliche Sammlungen des Kantons Glarus, Switzerland. PLECTOGNATHI

Triacanthodidae

Eoplectus bloti Tyler: MCSNV NS 52-53, in counterpart, 65.2 mm, Eocene of Monte Bolca, Italy, holotype. Protobalistum imperiale (Massalongo): MCSNV T9-

10, in counterpart, 522 mm. Eocene of Monte Bolca,

Italy, holotype of Ostracion imperialis. Spinacanthus cuneiformis (de Blainville): MNHN (IP) 10918, single plate, 104 mm. Eocene of Monte Bolca,

Italy, holotype of Blennius cuneiformis. Zignoichthys oblongus (Zigno): IGUP 6789, single

plate, ca. 161 mm. Eocene of Monte Bolca, Italy, holotype of Ostracion oblongus.

Triacanthidae Acanthopleurus collettei Tyler, new species: all specimens from the Oligocene of Canton Claris, Switzerland; NSKG 2689, single plate, 110 mm,

holotype; NSKG 146, single plate, 96.2 mm, paratype; NSKG 56, single plate, ca. 120 mm, paratype; NSKG 6b, single plate, 82.7 mm, paratype; NSKG

uncatalogued, single plate, last few vertebrae missing and length unmeasurable, paratype; BMNH P 524, single plate, ca. 82 mm, paratype; IGUN uncatalogued, single plate, 108 mm, paratype. Acanthopleurus serratus (Agassiz): all specimens from

the Oligocene of Canton Claris, Switzerland; BMNH P

454, single plate, ca. 91 mm, cotype of Pleuracanthus

serratus; BMNH P 3974, single plate, front of head

missing and length unmeasurable, cotype of Pleura- canthus serratus; BMNH P 1892, single plate, ca. 78 mm; NSKG 222 a-b, in counterpart, 114 mm; NSKG

7, single plate, 93.3 mm; NSKG 158 b, single plate, 153 mm; NSKG 8, single plate, 109 mm; NSKG uncatalogued, single plate, 120 mm; NSKG uncatalogued,

single plate, 117 mm; NSKG uncatalogued, single

plate, 127 mm; IGUN uncatalogued, single plate, last few vertebrae missing and length unmeasurable. Acanthopleurus sp.: three plates representing poor

impressions or distorted and incomplete specimens

unidentifiable to species, all from the Oligocene of
Canton Glarus, Switzerland; BMNH uncatalogued,

ca. 135 mm; BMNH P 4522, ca. 120 mm; BMNH P

1893, unmeasurable.

Protacanthodes ombonii (Zigno): IGUP 10.901-902, in counterpart, 112 mm. Eocene of Monte Bolca, Italy, holotype of Protobalistum ombonii.

Balistidae Balistomorphus orbiculatus (Heer): NSKG 2688, single plate, 65.6 mm, Oligocene of Canton Glarus,

Switzerland, holotype of Acanthoderma orbicula- tum. Balistomorphus ovalis (Agassiz): both specimens from

the Oligocene of Canton Glarus, Switzerland; IGUN

228, single plate, 121 mm, holotype of Acanthoderma

ovale; NSKG 178b, single plate, 119 mm.

Balistomorphus spinosus (Agassiz); both specimens

from the Oligocene of Canton Glarus, Switzerland; BMNH P. 3973, single plate, ca. 90 mm, holotype of Acanthoderma spinosum; NSKG 189 a-b, in counterpart, too indistinct to measure.

Aracanidae

Proaracana dubia (de Blainville): all three specimens

from the Eocene of Monte Bolca, Italy; MNHN (IP) 10974-75, in counterpart, 54.5 mm, holotype oiBalistes dubius; MCSNV T8 and T63, in counterpart, 31.4 mm; IGPUP uncatalogued, single plate, ca. 52 mm.

Ostraciidae

Eolactoria sorbinii Tyler: MCSNV T6-7, in counterpart, 15.5 mm, Eocene of Monte Bolca, Italy, holotype. Triodontidae

Triodon antiquus Leriche: BMNH P 12629, large frag- ment of right premaxillary, Eocene of Barton, Hants., England; BMNH P 15193, large fragment of right premaxillary. Eocene of Barton, Hants., England; BMNH P 15726, large fragment of fused dentaries, Eocene of Schaerbeek, Belgium; BMNH P 46696, frag- ment of middle of fused dentaries. Eocene of the London Clay, England; BMNH P 28899, small frag- ment of teeth from edge of jaw. Eocene of the London

Clay, England; BMNH P 25776-81, five fragments of fused dentaries and one right premaxillary. Eocene of Barton Hants., England. Tetraodontidae

"Tetraodon" lecointrae Leriche: IGPUP Miocene of Piromafo, Italy, no. 13, three fragments of the elongate

dental lamellae at edge of jaw. Eotetraodon pygmaeus Zigno: IGUP 6890-91, in counterpart, 18.2 mm. Eocene of Monte Bolca, Italy.

Diodon scillae Agassiz: IGPUP Miocene of Terra Rossa, Italy, no. 1, one complete trituration plate with

right and left halves; IGPUP Miocene of Livello ad

Aturia, Italy, no. 3, one half of a trituration plate; IGPUP Miocene of Terreno Agrario, Italy, no. 27, one

half of a trituration plate. Diodon tenuispinus Agassiz: seven specimens from the Eocene of Monte Bolca, Italy; MNHN (IP) 10976-77,

in counterpart (dorsoventral), 19.7 mm, holotype; MNHN (IP) 10978, single plate (dorsoventral), 12.6 mm; MNHN (IP) 10979, single plate (dorsoventral),

46.5 mm; MCSNV B. 18, single plate (dorsoventral),

31.5 mm; MCSNV B. 19, single plate (dorsoventral),

40.5 mm; BMNH P 11168, in counterpart (dorsoventral), 22.9 mm; BMNH P 12360, single plate

(dorsoventral), 13.5 mm.

"Diodon" sp.: eight specimens from the Eocene of Monte Bolca, Italy; MCSNV T 10, single plate (dorsoventral), 11.8 mm, Italy; MCSNV T 11, single plate

(dorsoventral), 35.1 mm; IGUP 12810-11, in counterpart (dorsoventral), 27.3 mm; IGUP 6894, single plate

(dorsoventral), 17.4 mm; IGUP 6861, single plate

(dorsoventral), 11.8 mm; MCSNV MS 50-51, in counterpart (dorsoventral), 68.9 mm; MCSNV T2,

single plate (dorsoventral), 18.4 mm; BMNH P 10735,

in counterpart (dorsoventral), 25.8 mm.

Eodiodon erinaceus (Agassiz): five specimens from the Eocene of Monte Bolca, Italy; BMNH P 3873, single plate (dorsoventral), 77.5 mm, holotype of Diodon

erinaceus; BMNH P 10426, single plate (dorsoventral), 96.5 mm; IGUP 8855-56, in counterpart

(dorsoventral), 50.3 mm; IGUP 8853-54, in counterpart

(dorsoventral), 68.8 mm; IGUP 8670-71, in counterpart

(dorsoventral), ca. 64 mm.

Kyrtogymnodon capellinii (de Stefano): IGPUP

Miocene of Livello ad Aturia, Italy, no. 4, right and left halves of a trituration plate; IGPUP Miocene of Terrene Agrario, Italy, no. 28, fragment of a large tritura- tion plate. Oligodiodon acanthodes (Sauvage): IGPUP uncatalogued, most of left premaxillary and top of maxillary, Oligocene of Monti Livomesi, Italy. Oligodiodon platyodus (Portis): IGPUR uncatalogued, one half of a trituration plate, 15.4 mm greatest length, Oligocene of Montecchio Maggiore, Italy, type specimen of Diodon platyodus. Progymnodon hilgendorfi Damea: BMNH P 11089,

large fragment of jaw with teeth and trituration plate. Eocene of Fayum, Egypt. Progymnodon gigantodus (Portis): IGPUR uncatalogued, right and left halves of a trituration plate, 41.8 mm greatest length of entire plate. Eocene of Castel Madama, Italy, type specimen of Diodon gigantodus; IGPUP Miocene of Terra Rossa, Italy, no. 1, two

separate halves of the same trituration plate; IGPUP

Miocene of Livello ad Aturia, Italy, no. 3, half of a

large trituration plate; IGPUP Miocene of Terreno

Agrario, Italy, no. 27, two halves of a trituration plate.
NONPLECTOGNATHS

Acanthuridae

(Identifications under revision) Acanthurus sp.: three specimens from the Eocene of Monte Bolca, Italy; BMNH P 16130 and P 17020, in counterpart, the two halves separately catalogued, 120 mm; MCSNV T 3, single plate, 25.6 mm; MCSNV T 1, single plate, 18.8 mm, possibly a young Naseus

nuchalis. Acanthurus ovalis Agassiz: both specimens from the Eocene of Monte Bolca, Italy; MCSNV T 4-5, in counterpart, 127 mm; IGUP 6874, single plate, 76.1 mm.

Acanthurus tenuis Agassiz: BMNH P 11176, single

plate, 86.6 mm. Eocene of Monte Bolca, Italy. Naseus intermedius Zigno: IGUP 6917-18, in counterpart, 105 mm. Eocene of Monte Bolca, Italy, holotype. Naseus nuchalis Agassiz: eight specimens from the Eocene of Monte Bolca, Italy; MNHN (IP) 10910-11,

in counterpart, 155 mm, holotype; BMNH P 19059,

single plate, 212 mm; BMNH P 11174, in counterpart,

151 mm; BMNH P 11098, in counterpart, 177 mm;

IGUP 12062-63, in counterpart, 190 mm; IGUP 11609-

10, in counterpart, 152 mm; MCSNV T 12, single

plate, 109 mm; MCSNV B 1965.13, single plate, 106 mm.

Naseus rectifrons Agassiz: 18 specimens from the Eocene of Monte Bolca, Italy; MNHN (IP) 10908-09,

in counterpart, 189 mm, holotype; BMNH P 10427,

single plate, 205 mm; BMNH P 11173, in counterpart, 112 mm; BMNH P 41890, single plate, 171 mm; BMNH P 9831, single plate, 67.5 mm; BMNH P 21393,

single plate, ca. 200 mm, incomplete; BMNH P 43490,

in counterpart, 38.4 mm; IGUP 11895, single plate, 83.0 mm; IGUP 25103, single plate, 160 mm; IGUP

25101, single plate, 189 mm; IGUP 8701-02, in counterpart, 185 mm; IGUP 8698-99, in counterpart, 97.0 mm; MCSNV Vin C 58-59, two specimens with the same

catalogue number, both in counterpart, 92.4 and 195 mm; MCSNV Vm C 56-57, in counterpart, 88.8 mm; MCSNV MS. C 50, single plate, 144 mm; MCSNV VHI C 70, single plate, 108 mm; MCSNV Vm C 68, single

plate, 187 mm; AMNH 9531 A-B, in counterpart, 212 mm.

Naso deani (Hussakof): AMNH 7483, single plate, 231 mm, Antigua, West Indies, uncertain age, holotype of Zebrasoma deani.Acanthonemidae

Acanthonemus subaureus (de Blainville): 10 speci- mens from the Eocene of Monte Bolca, Italy; MNHN (IP) 10904-05, in counterpart, 192 mm,

holotype of Chaetodon subaureus; MNHN (IP) 10906-

07, in counterpart, 99.5 mm; BMNH P 16201, single

plate, 126 mm; BMNH P 9940, single plate, 165 mm; BMNH P 16200-01, in counterpart, 126 mm; IGUP

25100, single plate, ca. 123 mm; IGUP 25102, single

plate, 167 mm; IGUP 11606-07, in counterpart, 126 mm; IGUP 6884, single plate, 62.8 mm; MCSNV VD

108-109, ca. 72 mm.

Zanclidae

Eozanclus brevirostris (Agassiz): MNHN (IP) 10740-

41, in counterpart, 101 mm. Eocene of Monte Bolca,

Italy, holotype of Zanclus brevirostris.

Teleostei Incertae Sedis

Protriacanthus gortanii d'Erasmo: IGPUB uncatalogued, single plate, 20.5 mm. Lower Cenomanian of Comen, near Trieste, Italy, holotype.

EPILOGUE

Remaining Problems

The more outstanding remaining problems on the anatomy, classification, and phylogeny of the plectog- naths of which I am aware are the need for: 1) systematic surveys of other anatomical systems to complement

that on the myology by Winterbottom (1974) and on the

osteology and external features presented here; 2) systematic worldwide familial revisions of the balistoids, ostracioids, tetraodontoids, and molids, to expand

the coverage of groups begun by Tyler (1968) for triacanthoids; 3) future diggings to increase the number of perti- nent fossils available and tell us more about the

phylogeny and anatomical diversity of the order and its relatives; 4) rigorous comparisons between the fossil and

Recent acanthurids and their chaetodontoidlike rela- tives with the fossil and Recent plectognaths to definitively determine if these groups share a late Cretaceous

or early Eocene ancestral stock; 5) a reconciliation of any conflicting classificatory schemes for plectognaths based on similar hypothesized phylogenies; and 6) clari- fication of specific identifications and nomenclature of many Indo-Pacific tetraodontids, diodontids, and monacanthids.
ACKNOWLEDGMENTS

This monograph is a much revised and expanded out- growth of a work begun at Stanford University in 1958 as a doctoral dissertation under the. guidance of George S. Myers; his instructive and encouraging influences prevailed over so many aspects of the germinal

stages of this monograph that it would be impossible to

list them, and I will simply express my lasting appreciation for his help and innumerable kindnesses devoted to my education. Stanley H. Weitzman, then also of Stanford University, was equally helpful to the early formative aspects of

this work, and he has continued to the present to freely make available on many occasions his osteological, systematic, and phylogenetic expertise. The late Margaret H. Storey of Stanford's Natural

History Museum was of constant curatorial and biblio- graphic assistance, while the interchange of ideas, tech- niques, and data with my fellow students was most in- valuable and is here gratefully acknowledged, these then

student friends being Warren C. Freihofer, Hugh H.

DeWitt, and Tyson R. Roberts. The majority of this work was done while a member of the curatorial staff of the Academy of Natural Sciences

of Philadelphia, and I am especially grateful to H.

Radclyffe Roberts, until 1973 its Director, for encouraging this research during my time there. His under- standing of the vagaries of research is much appreciated. My associates there in the Department of Ichthy- ology and Herpetology constantly assisted in the

preparation of this monograph, these coworkers being Jane H. Baker, Ann L. Berkes, Warren N. Berkes, Eugenia B. Bohlke, James E. Bohlke, Charles C. G.

Chaplin, Kathy Depolito, Lynn Keane, Mark D. Lange, and Judith Silver; I would like to especially single out Judith Silver and Lynn Keane, successive secretary- major domos of the department, for unstinting cooperation in every aspect of this work, from typing to proof- reading, and from bibliographic searching to the

considerate care of the researcher. I have been blessed by a succession of equally cooperative Eind artistic scientific illustrators whose skillful techniques form

a major portion of any merit to this monograph and who were exceptionally pleasant to work closely with: Gail Costanzo, Mary H. Fuges, Olivia B. Hall, Helga

0. Kumpera, and Joanne R. Schatz. Additionally, Stephen P. Gigliotti generously gave his advice on il- lustrative matters and James E. Bohlke did so on

systematic questions. Other members of the Academy of Natural Sciences of Philadelphia were immeasurably helpful in a variety of ways. C. Willard Hart, then editor of Academy publications, provided many helpful suggestions in coordinating the manuscript and illustrations, as did the Academy's engraver, Hal Talman, president of Phototype of Philadelphia. Larry Herbert, the late Oliver

Bradley, and Joseph Green of the Academy engineering department were always on call to build or repair, often on short notice, the mechanical and electrical contrivances essential to this project. Beverly Mowbray and Nancy Steele of the publications staff at the Academy

could always see a lighter side to a heavy scientific tale. Jesse J. Freese and Mary E. Sink kept the convolutions

of budgetary and administrative rules and reports to the

efficient minimum. Charles Sibre, and his sons John and

Michael Sibre, of the photographic department, gracefully as well as proficiently provided the 35 mm negatives of the cleared and stained specimens that formed

the basis for the initial traced outlines for most of the os- teological illustrations presented here. Their good humor

in the face of messy containers of glycerine scattered about their studio was remarkable. The introductory and concluding portions of this monograph, and of the updating and revisions of the entire manuscript, were written while serving as the Director of the Lerner Marine Laboratory, Bimini, Bahamas,

of the American Museum of Natural History, and while on the staff of the Office of Resource Research of the National Marine Fisheries Service, Washington, D.C., where Lamarr B. Trott, Chief of the then Division of Research Management, provided many kindnesses, and

then as a member of the Southeast Fisheries Center of that service, Miami, Fla., where the support of Harvey R.

Bullis, Jr., the then Center Director, and William J. Richards, Miami Laboratory Director, and Laurie Smith, secretary to the Atlantic Bluefin Tuna Program,

were especially helpful. Most of the 10 years of research at the Academy of Natural Sciences of Philadelphia leading to the major

portion of this monograph were supported in large part by the National Science Foundation through grants GB-1248, GB-5102, GB-6859X, and GB-16190. J. Frances Allen, Richard F. Johnston, William Sievers, and J. T. Spencer, the officers of the National Science Foundation then administering these grants, are sincerely thanked for their support, and for doing so with a minimal amount of bureaucratic paper work. The

thoughtfulness and trust of the National Science Foundation and of their advisory boards and ad hoc committees of colleagues mostly unknown to me is a true pleasure to acknowledge. The success of any osteological survey of a speciose worldwide group of fishes such as the plectognaths is dependent on obtaining for dissection specimens repre- senting as many species as possible. The great majority

of specimens studied here were either loaned or donated

to Stanford University and the Academy of Natural

Sciences of Philadelphia by the following cooperative

colleagues: Tokiharu Abe, Frederick H. Berry, Harvey

R. Bullis, Jr., Daniel M. Cohen, H. Adair Fehlmann,

Leslie W. Knapp, Giles W. Mead, George S. Myers, and

Robert R. Rofen. Without the specimens from them, my

coverage of the plectognaths would be so meager as not to warrant publication. Photographic prints of many of the illustrations, used

in preference to constant handling for over a decade of the final ink drawings, generously were provided by Vic-
tor Kumpera and Vlastimil Wagner, of Sao Paulo,

Brazil. The cross sections of the jaws of diodontids, showing

the trituration plates and teeth of the biting edge, all were skillfully cut and polished by Edgar R. Lawrence,

dental surgeon of West Chester, Pa. More generally, Helga 0. Kumpera was a mainspring

in the laborious mechanism leading to the completion of

this monograph, as the culmination of a 20-year study. Her help ran the gamut from the typing of hundreds of pages of manuscript to translating into English numerous articles in several foreign languages, and from thou- sands of hours spent in stippling illustrations to equally numerous hours spent in proofreading. The following colleagues have generously provided specimens for examination or made available data about

or assistance with specimens in their care, and their vital help is greatly appreciated (affiliations listed as of the time the help was rendered, and therefore sometimes

outdated at this time): Tokiharu Abe, Tokaiku Fisheries Research Laboratory, Tokyo; B. Accordi, Istituto di Geologia e Paleontologia dell'Universita di Roma; Gerald

R. Allen and John E. Randall, Bernice P. Bishop Museum, Honolulu; Roberto D. Andreucci, Escola

Paulista de Medicina, Sao Paulo; James E. and Ethyl H.

Atz, Gareth J. Nelson, Donn E. Rosen, Bobb Schaeffer, and C. Lavett Smith, American Museum of Natural

History, New York; Reeve M. Bailey and Teruyo Uyeno,

University of Michigan, Ann Arbor; Keith E. Banister,

P. Humphrey Greenwood, Alison Longbottom, Rosemary

McConnell, G. Palmer, Colin Patterson, Ethelwynn

Trewavas, Charlotte Welch, and Peter J. Whitehead,

British Museum (Natural History), London; M. L. Bauchot, M. Blanc, Jacques Blot, and J. Guibe, Museum National d'Histoire Naturelle, Paris; Frederick H. Berry, National Marine Fisheries Service, Miami; E.

Bertelsen, Marinebiologisk Laboratorium, Charlotten- lund Slot; M. Boeseman and G.F. Mees, Rijksmuseum

van Natuurlijke Historic, Leiden; James E. Bohlke,

Charles C. G. Chaplin, and Neal R. Foster, Academy of Natural Sciences of Philadelphia; Niels Bonde, Mineralogisk-Geologisk Institut, K(/benhavn; Margaret G. Bradbury, San Francisco State College; Heraldo A. Britski, Museu de Zoologia da Universidade de Sao Paulo; Harvey R. Bullis, Jr., and Richard A. Waller, National Marine Fisheries Service, Miami and Washington, D.C.; Vernon E. Brock, Warren E. Burgess, and William A.

Gosline, University of Hawaii, Honolulu; Jean Cadenat,

Institute Frangais d'Afrique Noire, Gofee, Senegal; David K. Caldwell, University of Florida, St. Augustine; Edgar Casier, Institut Royal des Sciences Naturelles de

Belgiques, Brusselles; William Chan, Fisheries Research

Station, Aberdeen, Hong Kong; Edward Chin, Richard

L. Haedrich, and Andrew Konnerth, Woods Hole

Oceanographic Institution, Woods Hole, Mass.; Eugenie

Clark, University of Maryland, College Park; Glenn H. Clemmer and Royal D. Suttkus, Tulane University, New

Orleans; Daniel M. Cohen and Bruce B. Collette, National Systematics Laboratory, National Marine

Fisheries Service, Washington, D.C.; Walter R.

Courtenay, Florida Atlantic University, Boca Raton; Giambattista Dal Piaz, Istituto di Geologia, Paleontologia e Geologia Applicata dell'Universita di Padova;

William P. Davis, Aquatic Sciences, Inc., Boca Raton;

L. F. de Beaufort, H. Nijssen, and P. J. H. van Bree, Zoologisches Museum, Amsterdam; KurtDeckert, Humboldt Universitat, Berlin; Thomas Devany, C. Richard

Robins, and David G. Smith, University of Miami; Hugh

H. DeWitt, University of Maine, Walpole; Myvanwy M.

Dick, Alfred S. Romer, and Tyson R. Roberts, Museum

of Comparative Zoology, Cambridge; Pedro Duarte

Bello, Universidad de La Habana; Alfred W. Ebeling,

University of California, Santa Barbara; Paul R. Ehrlich and Donald Kennedy, Stanford University; Donald S. Erdman, Department of Agriculture, San Juan, Puerto

Rico; William N. Eschmeyer, W. I. FoUett, Warren C.

Freihofer, George S. Myers, and Pearl M. Sonoda,

California Academy of Sciences, San Francisco; H. Adair Fehlmann and Leslie W. Knapp, Smithsonian Oceanographic Sorting Center, Washington, D.C.; P. Fourmanoir. Centre Office de la Recherche Scientifique et Technique Outre-Mer, Paris; A. J. Fraser and R. J. McKay, Western Australian Museum, Perth; A. Fraser- Brunner and John C. Marr, Food and Agriculture Organization of the United Nations, Rome; K. C. George, Central Marine Fisheries Research Substation,

Kerala; Robert R. Gibbs, Edgar N. Gramblin, Robert H. Kanazawa, Ernest A. Lachner, Leonard P. Schultz, Victor G. Springer, William R. Taylor, and Stanley H. Weitzman, National Museum of Natural History, Washington, D.C.; Carter R. Gilbert, University of

Florida, Gainesville; J. R. Grindley, South African Museum, Cape Town; Bruce W. Halstead, World Life Research Institute, Colton, Calif.; Carl L. Hubbs, John

E. McCosker, and Richard H. Rosenblatt, Scripps

Institution of Oceanography; J. Jenny, Naturwissenschaftliche Sammlungen des Kantons Glarus; Robert S. Jones, College of Guam, Agana; S. Jones, Central Marine Fisheries Research Institute, Mandapam Camp,

India; Paul Kahsbauer, Naturhistorisches Museum,

Wien; Toshiji Kamohara, Kochi University; Wolfgang

Klausewitz, Natur-Museum und Forschungs-Institute, Frankfurt; Adolf Kotthaus, Biologische Anstalt

Helgoland, Hamburg; Richard J. Kresja, California State Polytechnic College, San Louis Obispo; Louis A. Krumholz, University of Louisville; V. M. Makushok

and T. S. Rass, Institute of Oceanology, Academy of Sciences of the U.S.S.R., Moscow; E. Marchal, Centre de Recherches Oceanographiques, Abidjan; G. E. Maul, Museu Municipal do Funchal; Giles W. Mead, Los

Angeles County Museum of Natural History; A. G. K. Menon, Zoological Survey of India, Calcutta; Robert V.

Miller, National Marine Fisheries Service, Washington,

D.C.; Martin A. Moe, Oceanographic Mariculture In- dustries, Riviera Beach, Fla.; Donald Moore, National Marine Fisheries Service, Galveston; Basil Nafpaktitis, University of California, Los Angeles; J(/rgen Nielsen,

Universitetets Zoologiske Museum, K<rt)enhavn; Ross F.

Nigrelli, New York Zoological Society, Brooklyn; John R. Paxton, Frank H. Talbot, and Gilbert P. Whitley,
Australian Museum, Sydney; Michael J. Penrith, State Museum, Windhoek; Craig Phillips, U.S. National Aquarium, Washington, D.C.; E. Postel, Faculte des

Sciences, Rennes; Jiirgen Remane and J. P. Schaer,

Universite de Neuchatel; Robert R. Rofen, Aquatic

Research Institute, Hayward, Calif.; Robert L. Shipp,

University of South Alabama, Mobile; J. L. B. and

Margaret M. Smith, Rhodes University, Grahamstown;

Lorenzo Sorbini, Museo Civico di Storia Naturale, Verona; Walter A. Starck, Chino, Calif.; F. Strauch,

Universitat Koln; Guido Tavani, Licio Giannelli, and

Andrea Cerrina Feroni, Museo di Paleontologia dell 'Universita di Pisa; Donald A. Thompson, University of Arizona, Tucson; Luiz R. Tommasi, Institute

Oceanografico da Universidade de Sao Paulo; E. Tortonese, Museo Civico di Storia Naturale, Genoa; Vittorio

Vialli, Istituto di Geologia e Paleontologia dell'Univer

sita di Bologna; Vlastimil Wagner, Sao Paulo, Brazil Frank Williams, Guinean Trawling Survey, Lagos

Richard Winterbottom, Queen's University, Kingston,

Ontario; Donald Wohlschlag, University of Texas, Port

Aransas; Loren P. Woods, Field Museum of Natural

History, Chicago; Ralph W. Yerger, Florida State

University, Tallahassee. Preliminary arrangements toward the publication of

this monograph were facilitated by a special grant from

the Lerner Fund for Marine Research of the American Museum of Natural History. The manuscript for this work has benefited greatly from the helpful criticism of several colleagues who

volunteered their valuable time to peruse it: first, Richard Winterbottom and Bruce B. Collette, and then

C. Lavett Smith and Stanley H. Weitzman. Their

generosity is much appreciated and their suggestions mostly accepted and used. Richard Winterbottom, while at Queens University, Kingston, Ontario, and at both the Academy of Natural

Sciences of Philadelphia and the U.S. National Museum

of Natural History, Washington, D.C., provided many

highly valuable hours of discussion on the anatomy,

classification, and phylogeny of plectognath fishes and

freely shared his research data with me. His interest in, and information given toward furthering, the work

leading to this monograph has been invaluable, even though he is not necessarily in agreement with all of the phylogenetic conclusions set forth here and probably

does not approve of the style of classification adopted

here. He is an esteemed colleague of impeccable credentials and more than proven worth in the study of myology and of plectognaths, as well as being a dear friend with whom I happen to disagree on some points of how to divide and group the supra- and subfamilial (but not

familial, on which we are mostly in agreement)

categories of Tetraodontiformes. The errors of omission and commission that remain in

this monograph, after eluding my strenuous efforts to eliminate them, are entirely my own and are not at all at- tributable even in part to any of my so freely cooperating

colleagues acknowledged above. This monograph is dedicated to the four friends most

intimately associated at the personal level with its preparation: Helga Olga Schrader, Milan Kumpera

Tyler, Marisa Alenna Tyler, and Antoinette Carmela De

Fazio.

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seinen Schiilem, p. 73-84. Leipzig. 1887b. Ueber rudimentare Fischnasen. Anat. Anz. 2:652-657.

1888. On the degeneration of the olfactory organ of certain fishes. Rep. 57th Meet. Br. Assoc. Adv. Sci., Manchester, 1887, Sect. D - Biol., p. 736-738. WILLEM, V.

1941. Le mode respiratoire de Balistes et d'Ostracion. Acad. R.

Belg., Bull. CI. Sci. (Brussels), Ser. 5, 27:288-294.

1942. Contribution a I'etude des organes respiratories chez les teleosteens Plectognathes. K^ Partie: Les Balistes. Bull. Mus.

R. Hist. Nat. Belg. (Brussels) 18(35):l-24. 1944. Contribution a I'etude des organes respiratories chez les teleosteens Plectognathes. 2^ Partie: Les Chaetodontiformes.

Bull. Mus. R. Hist. Nat. Belg. (Brussels) 20(6):1-21. 1945. Contribution a I'etude des organes respiratories chez les teleosteens Plectognathes. 3^ Partie: Les Ostracionidis. 4e Partie: Le role de I'interoperculaire dans la manoeuvre respiratoire chez

les teleosteens. Bull. Mus. R. Hist. Nat. Belg. (Brussels) 21(23):

1-16. 1947. Contribution a I'etude des organes respiratories ches les teleosteens Plectognathes. 5^ Partie: Tetrodontes et Dmdon.

Bull. Mus. R. Hist. Nat. Belg. (Brussels) 23(17):1-17.

1949. Contribution a I'etude des organes respiratories chez les teleosteens Plectognathes. 6« Partie: Mola. Bull. Mus. R. Hist. Nat. Belg. (Brussels) 25(24):l-4. WILLL\MSON, W. C.

1851. Investigations into the structure and development of the

scales and bones of fishes. Philos. Trans. R. Soc. Lond., 1851

(pt. n):643-702. WILLUGHBY, F. 1686. Historia piscium libri quatuor, Oxford. 343 p. WINTERBOTTOM, R.

1970. Evolution of the pelvic fin ray musculature of some triacan- thoid fishes (Plectognathi). Copeia 1970:453-456.

1971. A reinterpretation of the mechanism of extension of the tetra- odontid pufferfish postcleithral apparatus, with notes on the oblique eye muscles of the diodontids (Plectognathi). Not. Nat.

(Phila.) 440:1-7. 1974. The familial phytogeny of the Tetraodontiformes (Acanthopterygii: Pisces) as evidenced by their comparative myology. Smithson. Contrib. Zool. 155:1-201.
V\TNTHEk I. . 1877. Fiskene^ a.ioitri; en comparativ-anatomisk under80gelse. Tredie afsnii. Xaturh. Tids. (Copenhagen), Ser. 3, 11:267-478. WOODWARD, A. S. 1901. Catalogue of the fossil fishes in the British Museum (Natural History). Part IV. Br. Mus. Nat. Hist., 636 p. WORTMAN, J. L.

1886. The comparative anatomy of the teeth of the Vertebrata.

In Litch, W. F. (editor), The American system of dentistry, p. 351-504. Lea Brothers & Co., Philadelphia. ZIGNO, A. DE.

1874a. Annotazioni paleontologiche. Pesci fossili nuovi del calcare

Eoceno dei Monti Bolca

Lett. Arti (Venice) 18:287

! Postale. Mem. R. 1st. Veneto

301. 1874b. Catalogo ragionato dei pesci fossili del calcare Eoceno di M. Bolca et M. Postale disposti secondo il metodo dell' Agassiz modificato dal Pictet (continua). Atti R. 1st. Veneto Sci., Lett. Arti (Venice), Ser. 4, 3(Nov. 1873-Oct. 1874):1897-1929.

1887a. Due nuovi pesci fossili della famiglia dei Balistini scoperti

nel terreno Eoceno del Veronese. Soc. Ital. Sci. |Soc. XL (dei quaranta)], Mem. Mat. Fis. (Venice), Ser. 3, 6:1-8. 1887b. Nuove aggiunte alia ittiofauna dell'epoca Eocena. Mem.

R. 1st. Veneto Sci., Lett. Arti (Venice) 23:9-33.
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Table 2.—Total number of vertebrae and vertebral formulas of Recent plectognath flshes examined radio^aphed and as cleared and stained specimens.

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Triacanthodidae

Hollardiinae HollardiagosUnei 8+12 1 Hollardia hoUardi 8+ 12 20 HoUardia meadi 8+ 12 3

Parahollardia lineata 8+12 17 ParahollardiaschmidtiS+ 12 17 Triacanthodinae Atrophacanthus japonicus S+12 38 Bathyphyiax bom bifrons 8+12 1 Bathyphylax omen 8+ 12 1 Halimochirurgus alcocki &+12 8

Halimochirurgus centriscoides 8+ 12 7 Johnsonina eriomma 8+12 15 Macrorhamphosodes platycheilus 8+12 13 Macrorhamphosodes uradoi 8+ 12 6 Mephisto fraserbrunneri 8+ 12 1 Paratriacanthodes herrei 8+ 12 3 Paratriacanthodes retrospinis 8+ 12 6 Tnacantfwdesanomalus 8+ 12 19 Triacanthodes ethiops 8+ 12 7 Tydemania navigatoris 8+12 16 Triacanthidae

Pseudotriacanthus strigUifer 8+ 12 21 Triacanthus btaculeatus 8+12 31 Triacanthusmeuhofi 8+ 12 2 Tripodichthys angustifrons 8+12 1 Tripodichthys blochi 8+ 12 36

Tripodichthys oxycephalus 8+ 12 2

7>iiip/jic/i«hysu)e<)?ri8+12 8

Balistidae Abalistesstellatus 1+11 1 Balistapus undulatus 1 +11 2

Batistes capriscus 7+11 32

Batistes forcipatus 7+11 1 Batistes polytepis 7+ U 30

Batistes uetuta 1+11 6

Batistoides conspicitium 7+11 2

Balistoides viridescens 7+11 1 Canthidermismaculatusl+ 11 10 Hemibalistes bursal + 11 2

Hemibalistes chrysopterus 1 + 11 1 Me/ichfhysmger 7+11 in 3 '1 3 7+10 in 1 Melichthysvidual+U 1 Odonus niger 1 + 11 2 Pseudobalistes flavimarginata 7+11 1 Rhinecanthusacuteatusl + 11 4 Rhinecanthus rectangulus 7+11 in 5 5 1 7+12 in 1 Rhinecanthus verrucosus 7+11 l Sufflamenfrenatusl + 11 1 Sufflamen verres 7+11 2 Xanthichthys lineopunctatus 7+11 1 Xant/iic/if/iysringefw7+ll 4 Monacanthidae

Acanthaluteres spilomelanurus 6+ 14 1 Atuteraheudetotiil +13 8

v4/u(erQ monoceros 7+16 1 i4;u£cra sc^cp/i 7+16 in 11 1 11 7+15 in 1
Table 2.—Total number of vertebrae and vertebral formulas of Recent plectognath fishes examined as radiographed and as cleared and stained specimens.—Continued.

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Alutera scripta 7+ liin 3 3 1 7+16 in 1 Amansesscopas 1+12 * Brachaluteres trossulus 7 + 13 22 Brachaluteres uivarum 7 + 13 2 Cantherhinespardalisl+ 12 11 CantherhinespuUusl+ 12 H

Cantherhines sandwichiensis 7 + 12 8 Cantherhines trachylepis 7 + 13 2 Chaetoderma spinosissimus 7+ 13 2 Laputa cingalensis 7+12 1 Monacanthus chinensis 7 + 12 3 Monacanthus ciliatus 6+ 13 in 49 49 1 6+14 in 1 Monacanthus mylii 7+12 1 Monacanthus tuckeri &+!% 6 Navodon setosus 7+13 1 Oiymonacant/ius longirostris S+ 17 in 6 16

8+ 16 in 1 Paraluteres prionurus 1 + IZ in 1 1 1 7 + 14 in 1 Paramonacanthus bamardi 7+12 1 Paramonacanthus cryptodon 7+ 12 in 3 3 1 7+ 13 in 1 Paramonacanthus curtorhynchus 7+12 3 Paramonacanthus oblongus 7+ 12 2 Pervagor melanocephalus 7+ 12 in 1 2 6+13 inl

Pervagor spilosomus 7 + 12 4 Peroagortomentosus 7+13 in 4 2 4

7 + 12 in 2 Pseudaluteres nasicomis 8+18

Psilocephalus barbatus 1+22 in 3

^

^ 7+23 inl 8+22 inl Rudarius ercodes 7+13 in 17 17 2

7 + 14in2

fludanasminutiis7+12 4 Stephanolepis auratus 7+12 1 Step/iano/epis cirrhi/er 7+ 13 in 1 1 1 7+ 12 inl

Stephanolepis hispidus 1 + 12 in 33 1 33 1 7 + 13 inl

7 + Uinl

Stephanolepis setiferl + 12 14 Aracanidae Aracanaaunta (2 fused) 9+9 2

/Iracana ornafa (2 fused) 10+8 2 Caprichthys gymnura (2 fused) 10+8 1 Capropygia unistriata (2 fused) 10+8 1 Kentrocapros aculeatus (2 fused) 9+9 2 Strophiurichthys robustus (2 fused) 9+9 1 Ostraciidae

Ostraciinae

Lactoria comuta (4 fused) 9+9 5 Lactona/omasmii (5 fused?) 9+9 5

Ostracion lentiginosum (2+2 or 4 fused) 9+9 4 Ostracion tuberculatus (2 + 2 fused) 9+9 4 Rhynchostracion rhinorhynchus (4 fused) 9+9 1 Tetrosomusconcatenatus {4 (used) 9+9 1 Tetrosomusgibbosus (4 (used) 9+9 1

415
Table 2.—Total number of vertebrae and vertebral formulas of Recent plectognath fishes examined as radiographed and as cleared and stained specimens.—Continued.

Lactophrysinae

Acanthostracion guineensis (5 fused) 9+9

Acanthostracion notacanthus (5 fused) 9+9

Acanthostracion polygonius (5 fused) 9+9

Acanthostracion quadricornis (5 fused) 9+10

Lactophrys trigonus (5 fused) 9+9

Rhinesomus bicaudalis (5 fused) 9+9

Rhinesomus triqueter (5 fused) 9+9

Triodontidae Triodon macropterus 9+11

Tetraodontidae: figures followed by (A) are simplified from Abe's ( 1942) extensive analysis of vertebral variation in Japanese puffers Tetraodontinae Amblyrhynchotes honckenii 8+11 in 5 8+ 12 in 3 Amblyrhynchotes hypselogenion 8+11 in 5 8+ 12 in 2 7+12 in 1 Amblyrhynchotes piosae 8+11

Arothron armilla 8+11

Arothron hispidus 8+ 10 in 12 8+9 in 2 9+ 10 in 1 Arothron immaculatus 8+10 in 59 8+9 in!

8 + 11 in 1 Arothron meleagris 8+10 in 2 9+ 10 in 5 9+11 in 1 Arothron nigropunctatus 9+9 in 6 8+9 in 1 8+ 10 in 1 Arothron reticulatus 8+10 (A) Arothron setosus 9+ 10 in 6 9+9 in 1 8+9 in 1 Arothron stellatus 8+10

Carinotetraodon lorteti 7+10 in 2 7+9 in 1 Chelonodon fluuiatilis 8+ 10 in 38 8+llin9 8+9 in 4 Chelonodon patoca 8+11 in 25 8+ 10 in 1 Chonerhinos modestus 10+ 16 in 6 10+ 15 in 3 10+ 17 in 1 9+ 16 in 1 9+ 17 in 1 Colomesus asellus 8+ 11 in 8 8+ 12 in 1 8+ 10 in 1 Colomesus psittacus 8+ 11 in 5 8+ 10 in 1 Ephippion guttifer 8+ 12 Fugu chrysops 9+13 in 11 9+ 12 in 6 Fugu niphobles 8+ 13 in

8+ 12 in i 8+11 in 8+14 in
Table 2.—Total number of vertebrae and vertebral formulas of Recent plectognath radiographed and as cleared and stained specimens.—Continued.

8+ 12 in 1 9+13 inl Fugu rubnpes 9+ 12 in 2 9+ 13 in 3 9+14inl

Fugu stictonotus 8+14 in 65 8+ 15 in 12 8+ 13 in 1 Fugu vermiculans 8+ 14 in 225 \ 8+ 13 in 15 / 8+ 15 in 14 ( . 9+13in 1 }

"^ 9+14 in 1 i 7+15in 1 /

Fugu xantkopterus 8+13 (A) Guentheridia formosa 8+9

Lagocephalus inermis 8+ 10 Lagocephalus laevigatus 8+11 in 10 8+ 10 in 2 Lagocephalus lagocephalus 8+ 10 Lagocephalus lunaris 8+9 in 9 8+11 inl Lagocephalus scleratus 8+9 in 8 8+llin2

8+ 12 in 2

7 + 12inl

Lagocephalus spadiceus 8+9

Monotreta cutcutia 8+10

Monotreta gularis 8+10

Monotreta leiurus 9+11 in 2 10+11 in 2 10+ 10 inl Monotreta palembangensis 10+11

Sphoeroides angusticeps 8+9

Sphoeroides annulatus 8+10 in 19 8+9 in 2 9+ 10 inl Sphoeroides dorsalis 8+9 in 20 8+8 inl

Sphoeroides lobatus 8+9

5 143 173 21 1

2 10

2

1 20

7 5

2

417
Table 2.—Total number of vertebrae and vertebral formulas of Recent plectognath fishes examined as radiographed and as cleared and stained specimens.—Continued^

Sphoeroides maculatus 8+11 in 26 8+ 10 in 8 Sphoeroides marmoratus 8+ 12 in 7 8+11 in 2 Sphoeroides nephelus 8+10 in 32 8+llin2 8+9 in 1 7+ 10 in 2 9+10 in 1 Sphoeroides pachygaster 8+10

Sphoeroides sechurae 8+9 in 35 8+ 10 in 1 Sphoeroides spengleri 8+9 in 34 8+10 in 1 Sphoeroides testudineus 8+ 10 in 74 8+9 in 32 8+8 in 1 8+11 in 1 7+9 in 2 Sphoeroides tnchocephalus 8+ 9 in 5 8+ 10 in 2 Tetraodon Uneatus 8+10 in 1 8+11 in 1 Tetraodon mbu 8+9

Tetraodon miurus 8+11

Torquigener hamiltoni 8+ U in 2 9+11 in 1 9+12 in 2 Torquigener pleurogramma 8+ 12 Torquigener pleurostictus 8+ 11 Xenopterus naritus 11 + 18 in 1 11 + 19 in 1 10+ 19 in 1 Canthigasterinae Canthigaster amboinensis 8+9

Canthigaster bennetti 8+9 in 4 9+9 in 1 Canthigaster compressa 8+9 in 30 8+ 10 in 1 Canthigaster coronata 8+9

Canthigaster jactator 8+9 in 8 8+10 in 1 Canthigasterjanthinoptera 8+9

Canthigaster margaritata 8+9

Canthigaster papua 8+9

Canthigaster punctatisstma 8+9 in 23 8+8 in 1 Canthigaster rivulata 8+9

Canthigaster rostrata 8+9

Canthigaster solandri 8+9 in 19 8+ 10 in 2 Canthigaster ualentini 8+9

Diodontidae Chilomycterus affinis 13+10

Chilomycterus antennatus 12+8

Chilomycterus antillarum 10+9

Chilomycterus atinga 13 + 8 Chilomycterus mauretamcus 12+8

Chilomycterus orbicularis 11 + 8 Chilomycterus reticulatus 12+10

Chilomycterus schoepfi 11+8 in 3 12+8 in 2 10+8 in 1
-Total number of vertebrae and vertebral formulas of Recent plectognath fishes examined radio^aphed and as cleared and stained specimens. —Continued.

Chilomycterusspinosus 10+S 1 Chilomycterus tigrinus 12+ 10 Dicotylichthys nicthemerus 11 + 9 1 Dicotylichthys punctulatus 12+9 1 Diodon holocanthus 12+9 10 Diodonhystrixn+9in2 3 1 11+10 inl 12+8 in 1 Diodon jaculiferas 10+9 1 Molidae Masturus lanceolatus 8+8 2 Moia mola 8+9 2 Ranzanialaevis%+W 4

'A vertebra with bifid neural and haemal spines but centrum of normal si:

419
Table 3.—Numbers of teeth in the upper and lower jawg of ostracioids.

12 13 14 15 16 17 ARACANIDAE

Aracana aurita Aracana flavigaster

Caprichthys gymnura

Capropygia

Kentrocapros

aculeatus

Strophiurichthys inermis

Strophiurichthys robustus OSTRACIIDAE

Acanthostracion

guineensis Acanthostracion notacanthus

Acanthostracion

polygonius Acanthostracion

quadricornis Lactophrys tngonus

cornuta Lactona

diaphana

Lactoria

fornasinii Ostracion cubicus

Ostracion lentiginosum

Ostracion

tuberculatus Rhinesomus

bicaudalis Rhinesomus

triqueter Rhyncho

Rhynchostracion

rhinorhynchus Tetrosomus

concatenatus Tetrosomus

gibbosus

upper

lower upper

lower pper

upper

lower upper

lower pper

lower

pper

lower upper

upper ower

ower

ower

upper ower

upper

5 7 15 9 7

4 1 25

3 4 10 6

1
Index of Discussions of Genera

Abalistes 123, 128, 179 Acanthaluteres 146, 154, 167, 173-174, 176, 178, 180, 182 Acanthopleurus 4, 79, 88, 96-98, 118, 134 Acanthostacion . . 184, 218, 220-223, 228-229, 236-238,

239-240, 241, 242 Acreichthys 180 Alaterta . . .123, 136, 146, 153, 154, 167, 174, 178, 180-183, 344 Amanses 143, 146, 154, 167, 172, 173, 176,

178, 180, 182, 183 Amblyrhynchotes .... 290-291, 297-298, 329, 331-334,

336, 343 Anoplocapros 195, 198, 199, 205-206 Aracana 195-199, 203, 205, 206, 243 Arothron 290, 291, 297, 334-337, 340

Arotrolepis 146, 154, 175, 183 Atinga 358 Atrophacanthus 56, 66, 68, 70

Balistapus 109, 110, 120, 122-123, 128, 179

Balistoides HO, 123, 128, 179

Batistes 120, 123, 128, 130, 179 Balistomorphus 98, 110, 118, 120-121 Bathyphylax 56, 66-68, 70, 73, 344

Blandou'skius 154, 183 Brachaluteres 136, 144, 146, 153, 154, 167,

173, 174, 178, 181, 182, 183 Cantherhines 136, 146, 154, 167, 176, 178, 180, 182-183 Canthidermis 77, 99, 101, 110, 120, 122-123,

128, 129, 130, 133 Canthigaster 144, 153, 181, 290, 298-299,

314-316, 326, 340, 343 Caprichthys 195, 198-199, 204, 205-206, 243 Capropygia 195, 198-199, 204, 205-206, 243 Carinotetraodon 4, 144, 290, 297, 298, 314-316,

326, 334-336, 340, 342, 343 Chaetoderma . . . 136, 144, 146, 153, 154, 167, 174-175,

176, 178, 180-181, 183 Chelonodon 290, 291, 297, 315, 334-338,

340, 342, 343 Chilomycterus .... 344, 355, 357-359, 360-361, 364-370 Chonerhinos 265, 287, 290, 298, 337, 342-343 Colomesus . . 290-291, 297, 298, 330-331, 334, 343, 353

Cryptobalistes 78, 79, 98, 132, 133, 134 Dicotylichthys 358, 360, 361, 364, 367, 368, 369 Diodon 353, 354, 357, 358-360, 364, 368, 369 Eodiodon 357

Eolactoria 5, 207, 222, 223, 240, 242-243 Eoplectus .4, 7, 56, 64-65, 74-76, 77, 131, 134, 206, 261 Eotetraodon 287 Ephippion 77, 265, 290, 297, 298, 334, 335, 337-338, 342, 343 Eubalichthys 154, 178, 183 Fugu 290-291, 297-298, 329, 331-334,

335, 336, 343 Guenthendia . . . .290-291, 297, 298, 320, 322, 330, 331

Halimochirurgus

Hemibalistes . . . Holtardia Johnsonina ....

56, 66-68, 70, 344

128

. . . .56, 57, 66, 69

.... 56, 66-69, 70 Kentrocapros 193, 195, 198-199, 203-204, 205 Kyrtogymnodon 353 Lactophrys 220, 222, 223, 228, 229, 236, 237, 238, 239-240, 241, 242

Lactoria 222-223, 228, 229, 236-238, 240-243 Lagocephalus 277, 282, 290-291, 297, 298, 299, 316-317, 322-329, 331, 332, 334, 342, 343 Laputa 146, 154, 167, 176-178, 180, 181, 183 Leprogaster 173 Liosaccus 297 Macrorhamphosodes 56, 66-68, 70, 342 Marosichthys 79, 88, 98, 123, 134 Masturus 77, 377, 379, 381, 386, 392, 393-394 Melichthys 101, 110, 120-121, 123, 128-129, 179 Mephisto 56, 66-68, 70 Meuschenia 154, 178, 182 Mola 77, 123, 379, 381, 386, 392, 393-395 Moiacanthus 377 Monacanthus 143, 153, 154, 167, 172, 173,

174, 176, 178-181, 182, 183 Monotreta 290, 291, 297, 298, 314, 315, 334, 335-336, 338-340, 342, 343 Navodon 136, 154, 167, 176, 178, 180, 182, 183 Nematobalistes 123 Odonus 110, 120, 122, 123, 128, 133, 179

Oligobalistes 120, 121 Oligodiodon 355 Omegophora 335

Ostracion 221, 222, 223, 228-229, 236,

237, 240-241, 242, 243 Oxvmonacanthus 154, 167, 173-174, 176, 178, 181-182, 183, 342 ParahoUardia 56, 66, 69

Paraluteres 99, 146, 153, 154, 167, 173, 174-175, 176, 181, 182, 183 Paramonacanthus 153, 154, 167, 174, 176, 178-179, 180-181, 182, 183 Paratriacanthodes 56, 66-68, 70 Peruagor . . . 154, 167, 176, 178, 179-180, 181, 182, 183 Proaracana 5, 185, 195, 198, 204-205, 206 Prodiodon 260, 343, 352-355, 357 Progymnodon 260, 357 Protacanthodes . . .4, 75, 76, 77, 78, 79, 88, 93, 95, 98, 131-132, 134, 207, 210 Protobalistum 56, 57, 59, 63-64, 76, 206

Protriacanthus 98

Pseudaluteres 100, 144, 146, 154, 167, 172, 173-174, 176, 181, 182, 183, 344

Pseudobalistes 110, 123 Pseudomola 377 Pseudomonacanthus 88, 92-93, 97, 98 PsUocephalus 100, 135, 144, 146-147, 153, 154,

167, 172-173, 174, 175, 176, 178, 181, 182 183, 344

421
Ramania 77, 123, 262, 375, 377, 379,

384, 390-392 Rhinecanthus 101, 110, 120, 121, 122, 123, 128, 167, 179

Hhtne.somu.s 220, 222-223, 228, 229, 236, 237, 239-240, 241, 242 Rhvnchostracion 222, 223, 228, 229, 236, 237, 240-241, 242, 243 Rudarius 136, 143, 154, 167, 172, 173, 174, 176, 181, 182-183 Scobinichthys 154, 182 Sphoeroides 290, 291, 297, 298, 316-322,

324, 327, 328-333, 335, 343 Spinacanthus 56, 63-64, 76, 206 Stephanolepis 153, 154, 167, 176, 178-179,

180, 181, 182, 183 Strophiurichthys .... 195, 198, 199, 203, 204, 205, 206 Sufflamen 123, 128, 130, 179 Tetraodon 286-287, 290, 291, 297, 298, 314,

324, 335, 336, 337-338, 340, 342, 343

Tetro.somus 220, 222, 223, 228, 229, 236,

237, 238, 240-242, 243 Torquigener 265, 290-291, 297, 298, 329, 331-334, 336, 343 Triacanthodes 56, 66-70 Triacanthus 57, 88, 92, 93, 95, 98 Triodon 6, 65, 74-75, 167, 210, 243, 244,

253, 254, 255, 260, 261-263, 273, 323,

326, 344, 348, 349, 361, 394 Tripodichthys 88, 92, 93, 98

Tnxiphicht'hys 78, 79, 82, 88, 92-93, 98, 134 Tydemania 56, 66, 68, 70, 344 Verrunculus 123 Xanthichthys\Q\, 110, 120-121, 122, 123, 128, 133, 179 Xenopterus 265, 287, 290, 298, 337, 342-343 Zignoichthys 56, 65, 74, 77, 261, 344
WHSE

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