EXOGYRA OLISIPONENSIS SHARPE AND EXOGYRA COSTATA SAY IN THE 


CRETACEOUS OF THE WESTERN INTERIOR 


By JOHN B. REESIDE, Jr. 

INTRODUCTION 

This paper records the occurrence in the Upper 

Cretaceous of the Western Interior of Exogyra oZisiponensis Sharpe, not hitherto noted in the United States, 

and of Exogyra costata Say, not previously known outside of the Atlantic and Gulf coastal region. Notes 

on the genus and both species are included, and representative specilnens are figures. 

GENUS EXOGYRA 

The genus Exogyra has been discussed at length by 

many writers since its establishment in 1820 by Say.! 

Among the later descriptions that of Pervinquiere 2 is 

particularly useful for Cretaceous species. The extensive treatise of Jourdy 3 is the most comprehensive 

general discussion and affords a compact history of the 

vicissitudes the genus has undergone since its establishment, a statement of its present scope, range, and other 

details of highest interest to the student of Exogyra. 

No better characterization is available than that given 

by Jourdy,4 which may be translated as follows: 

General form.-"':'-Arcuate, in a sort of crescent in the narrow, 

elongated species. The oldest species are unornamented, small, 

even dwarfed; the later species are often large and ornamented 

to various degrees. 

Upper (right) valve.-Generally flat, thin, operculiform, 

marked by ooncentric growth lines disposed in spirals whose 

center is at the beak, placed at the posterio.r summit of the 

shell.. Sometimes radial ribs, rarely tubercles. 

Lowe?' (left) valve.-Deep, carinate, and with helicoid beak in 

proportion as the area of attachment is less extended; absolutely fiat in the case of maximum area of attachment. Sometimes winglike expansions beneath the hinge. The ornamentation consists of concentric striae, more or less lamellose, or of 

radial ribs, more or less fine, rarely tuberculated or spinose. 

Hinge.-The hinge of the lower valve, in youth and in small 

species, reduced to a ligamental groove, twisted and without 

thickened lateral ridges; that of heavier species is at first 

anodont but beoomes monodont in the most differentiated 

species, the latter arrangement characterized by a blunt tooth 

in the upper valve corresponding to a shallow groove or dimple 

in the lower valve. 

As understood by the above characterization, Exogyra 

ranges frOln the upper Liassic (Toarcian) to the end of 

the Cretaceous and possibly into the Tertiary, changing, in general, from small, rather flattened, unsculptured species to large, deep-shelled, sculptured species. 

I Say, Thomas, Observations on some species of zoophytes, shells, etc., principally fossil: Am. Jour. ScL, vol. 2, p. ~, 1820. . 

J Pl'rvinquiere, LOon, Etudes de paJOontologie tunisienne, pt. 2, Gastropodes et 

lamellibrallches des terrains crOtac6s, pp. 172-193, Paris, 1912. 

8 Jourdy, Edmond, llistoire uaturello des Exogyres: Annales de palOontologie, 

vol. 13, pts. I, 2, 1924. 

• Idem, p. 97. 


100874: 0 -20--18 


Pervinquiere,5 dealing chiefly with Cretaceous forms, 

divided Exogyra into groups whose limits, he says, "are 

often difficult to define" and which are possibly to be 

viewed as subgenera. These groups are: 

1. Group of E. costata Say. 

2. 	 Group of E. tatissima Lamarck (co'l.tloni-aquila) (= Aetostreon 

Bayle). 

3. Group of E. columba Lamarck (=RhynchostTeon Bayle). 

4. Group of E. africana Coqtland. 

5. Group of E. haliotidea Sowerby. 

6. Group of E. flabellata Goldfuss (=Ceratostreon Bayle). 

Jourdy 6 considered Pervinquiere's grouping not sufficiently comprehensive and lacking the phylogenetic 

viewpoint and proposed another, as follows: 

A. 	 Gibbous and smooth line derived from E. monoptera Deslongchamps; several species show a suggestion of excrescences, E. arduennensis D'Orbigny, E. larteti Coquand. 

B. 	Shallow, .smooth line derived from E. lingulata (Walton) 

Lycett, contiimed by E. rauliniana D'Orbigny, E. haliotidea Sowerby, E. bourgeoisi Coquand, E. auricularis 

Goldfuss. 

C. 	Smooth line carried to the end of the Jurassic by E. nana 

Sowerby and branching in the Cretaceous into two lines: 

CI . An entirely unsculptured line including E. tombeckiana D'Orbigny; large forms like E. aquila Goldfuss; E. conica Sowerby; E. langloisi Coquand; a 

few forms inclined to become spinose, E. couloni 

Defrance, E. plicifera Dujardin. 

C2• A lamellose line apparently beginning with E. 

polygona Von Buch, continued by E. africana 

Lamarck, E. deletrei Coquand, E. subfimbriata 

Coquand, etc. Through E. ponderosa Roemer it 

produced E. costata Say, and through other lamel-. 

lose forms, E. overwegi Von Buch, E. texana 

Roemer,7 E. fourneti Coquand. 

D. 	Sculptured Jurassic line, derived from the line of E. nana 

through E. praevirgula Douville and Jourdy, the source of 

the ornate species which are the most numerous and most 

beautiful of the genus. There are two lines: 

DI . Line of E. virgula Defrance, with very fine, regular 

costation, including E. larteti Coquand, E. suborbiculata Lamarck, E. decussata Goldfuss, E. 

columba Lamarck. 

D2• Line of E. catalonica Loriol with strong ribs, derived 

from E. virgula through E. welschi jourdy. It 

reaches the Cretaceous through E. minos Coquand 

and continues by E. callimorphe Coquand, E. 

boussingaulti D'Orbigny, E. harpa Forbes, E. 

olisiponensis Sharpe, E. flabellata Goldfuss, E. 

matheroniana D'Orbigny, E. laciniata Nilsson, E. 

lemeslei J ourdy. 

6 Pervinquiere, LOon, op. cit., p. 172. 

6 Jourdy, Ed~ond, op. cit., p. 91. 

7 E. texa71a has been placed by many authors under E. flabellata and surely belongs 

to the same group. Jourdy must have placed the species here by error instead of in 

the group D? . 

267 
268 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

Jourdy notes the lack of important variations in the 

sculpture of the upper (right). valve. It shows from. 

the earliest species the well-defined spiral trace of the 

beak and only in a few species any but concentric 

sculpture. The helix of the beak of the lower (left) 

valve also enters but little into the evolution of either 

genus or species. The very earliest forms are so 

strongly attached that they do not show a helix, 

though it is present in the oldest forms of E. nana 

(Callovian). Slender beaks are the more numerous 

and persist almost to the end of the Cretaceous, though 

the best-developed helices appear in the Upper Cretaceous. In a general way the forms that end the 

several' genetic lines have the best development of 

dentate hinge, ornamented surface, and helicoid beaks, 

and there is a progression from simpler early types to 

more complex later types. 

Exogyra olisiponensis Sharpe 


Plates 65-68; Plate 69, Figures 1-4'. 


1850. Exogyra olisiponensis Sharpe, Geol. Soc. London Quart. 


Jour., vol. 6, p. 185, pI. 19, figs, 1, 2. 

1862. Ostrea overwegi Coquand (not Von Buch), Soc. emulation 

Provence Mem., vol. 2, p. 226, pI. 19, figs. 1-6. 

'1862. Ostrea coquandi Julien. Coquand, op. cit., p. 324, pI. 33, 

figs. 10-12. 

1864. Ostrea (Exogyra) cornuarietis Meneghini (not Goldfuss), 

Soc. itaI. sci. nat. Atti, vol. 6, p. 412, pI. 4, figs. 1 a-c. 

1869. Ostrea olisiponensis Sharpe. Coquand, Monographie du 

genre Ostrea, terrain cretace, p. ~25, pI. 45, figs. 1-7. 

1869. Ostrea overwegi Coquand (not Von Buch), op. cit., p. 140, 

pI. 44, figs, 1-7 (8-9?); pI. 46, figs. 14-15. 

1872. Ostrea olisiponensis Sharpe. Lartet, Ann~Jes sci. geol., 

vol. 3, p. 59, pI. 11, figs. 1-2. 

.1875. Exogyra ponderosa White (not Roemer), U. S. Geog. 

Surveys W. 100th Mer.. Rept., vol. 4, pt. 1, p. 172, 

pI. 14, figs. 1 a-c. 

1877. Ostrea olisiponensis Sharpe. Lartet, Exploration geolo­


gique de la Mer Morte, p. 138, pI. 9, figs. 1-3. 


1880. Ostrea oxyntas Coquand, Acad. Hippone Bull. 15, p. 170. 


1882. Exogyra oxyntas Coquand. Seguenza, R. accad. Lincei 


Atti, ser. 13, vol. 12, p. 178, pI. 18, figs. 1 a-c. 


1882. Exogyra olisoponensis Sharpe. Seguenza, op. cit., p. 180. 


pI. 17, figs. 2 a-b. 

1886. Exogyra pseudoafricana (part) Choffat, Faune cretacique 

du Portugal, vol. 1, ser. 1, p. 38 (not Ostreidae, pI. 4, 

figs. 1-4); ser. 4, Ostreidae, pI. 6, fig. 14 [1902J. 

1891. Ostrea olisiponensis Sharpe. Peron, Exploration scientifique de la Tunisie, pt. 4, lnvertCbres fossiles des 

terrains cretaces, p. 114, pI. 23, figs. 14-18. ' 

1902. Ostrea (Exogyra) olisiponensis Sharpe. Choffat, Faune 

cretacique du Portugal, vol. 1, ser. 4, p. 166, Ostreidae, 

pI. 6, figs. 17-19. . 

1903. Exogyra olisiponensis Sharpe. Fourtau, lnst. egyptien 

Bull., ser. 4, vol. 4, p. 283, text figs. 3-5. 

1903. Exogyra olisiponensis Sharpe var. d'uplex, Paulcke, Neues 

Jahrb., Beilage-Band 17, p. 269, pI. 15, figs. 7, 8. 

1905. Ostrea (Exogyra) olisiponensis Sharpe. Choffat, Contributions a la connaissance geologique des colonies 

portugaises d'Afrique, pt. 2, Nouvelles donnees sur la 

zone littorale d'Angola, p. 44, pI. 1, figs. 4, 5. 

1911. Ostrea (Exogyra) olisipon,ensis Sharpe. Woods, in Falconer, The geology and geography of northern Nigeria, 

app. 2, p. 277, pI. 20, figs. 1-3. 

1912. Exogyra olisiponensis Sharpe. Pervinquiere, Etudes de 

paleontologie tUllisienne, pt. 2, Gastropodes et lamellibranches des terrains cretaces, p. 174, pI. 13, figs. 4, 5, 9. 

1918. Exogyra olisiponensis Sharpe? Bose, Texas Univ. Bull. 

1856, p. 230, pI. 20, fig. 4. 

1927. Exogyra olisiponensis Sharpe. Reeside, in Wasson and 

Sinclair, Am. Assoc. Petroleum Geologists Bull., vol. 

11, p. 1268, pI. 11, figs. 1-3. 

Sharpe's original description of the species, based 

on material from the" Hippurite limestone" at Lisbon, 

Portugal, is as follows: 

Shell nearly hemispherical; upper valve thick, slightly 

gibbose, covered with regularly concentric scales, the beak 

incurved in the plane of the valve; lower valve very thick and 

very gibbose, regularly rounded on the anterior margin and 

somewhat pr9duced posteriorly; the surface squamose, with the 

edges of the scales raised up into short ribs, of which there are 

10 or 12 near the margin of an old shell; in some specimens the 

ribs are nearly continuous; in others they only occur near the 

margin of the scales, while in others they are hardly visible; 

the surface of the valve between the ribs is nearly smooth;' 

beak of the lower valve laterally involute; the surface of attachment usually small. 

Cot}uand in his earlier work 8 assigned to E. olisiponensis only distantly ribbed, somewhat spinose, 

keeled shells, assigning to E. overwegi Von Buch the 

finer-ribbed, rather evenly sculptured, well-rounded 

forms. Under E. overwegi he distinguished five 

varieties-costulata, scabra, rugosa, reticulata, and 

laevigata. Coquand later 9 noted that the real E. 

overwegi was a different and much later type and 

renamed his material E. oxyntas. Coquand cited 

E. olisiponensis from southern France, Spain, Portugal, 

Algeria, and Palestine. He cited his E. overwegi 

(=oxyntas) from Sicily, Tripoli, Tunisia, Palestine, 

southern France, and Spain. 

Meneghini 10 assigned to E. cornuarietis' Goldfuss 

nearly smooth forms of E. olisiponensis fronl Sicily. 

Lartet 11 followed Coquand in his use of the names 

E. overwegi and E. olisiponensis as applied to specimens 

from Palestine, putting the relatively fine-ribbed 

forms into the first and the more coarsely ribbed 

forms into the second species. 

Seguenza 12 al&o ,followed Coquand in distinguishing 

E. olisiponensis from E. oxyntas. Under E. olisiponensis he named three varieties-the typical form, 

var. ecostata, 'and var. prominens. Under E. oxyntas 

he accepted Coqvand's five varieties and added four 

more---ecostata, italica, asperrima, and brancaleonensis. 

8 Coquand, Henri, G~ologie et paleontologie de la r~gion sud de la province de 

Constantine: Soc. emulation Provence M~m., vol. 2, p. 226, pI. 19, figs. 1-{), 1862; 

'Monographie du genre Ostrea, terrain cr~tac~, pp. 125, 140, pI. 44, figs. 1-7; pI. 4.5, 

figs. 1-7, Marseille, 1869. 

9 Coquand, Henri, Etudes supplementaires sur la paleontologie algerienne: Acad. 

Hippone Bull. 15, p. 170, 1880. 

10 Menegbini, Giuseppe, Studii paleontologici sulle ostriche cretacee di Sicilia: 

Soc. ita!. sci. nat. Atti, vol. 6, p. 412, pI. 4,·figs. 1 a-c, 1864. 

11 Lartet, Louis, Essai sur la geologie de la Palestine: Annales sci. geol., vol. 3, 

p. 59, pI. 11, figs. 1-2, 1872. 

12 Seguenza, Giuseppe, Studt geologici e paleontologici suI cretaceo medio dell, 

Italia meridionale: R. accad. f.incei Atti, ser. 3, vol. 12, pp. 178-180, pI. 17, figs. 2...:2b; 

pI. 18, figs. I-Ie, 1882. 
EXOGYRA IN CRETACEOUS 

The variety brancaleonensis, so far as one may judge 

fr0111 figures, has the broad rounded ribs of the costata 

group rather than the narrow ribs of the earlier group 

to which E. olisiponensis belongs. ~eguenza's speci111enS canle frOl11 Sicily. 

Choffat 13 seems to have included in his E. pseudoafricana feebly costate shells that belong to E. olisiponensis, believing that the second species were derived 

fronl the first. Choffat also called attention to the 

radinl ribs on the upper valves of nlany individuals of 

E. olisilJOnensis, a feature that had escaped record by 

the previous students of the species. 

Peron 14 united E. oxyntas and parts of certain other 

species, as conceived by Coquand, with E. olisiponensis. 

He showed that the presence of a keel on the shell is a 

very variable feature: in Sharpe's type its prominence 

is accidental and due to the large size of the area of 

attachment, and it is not the important character 

which Coquand thought it to be. Peron noted the 

great range of variability in size, form, and both concentric and radial sculpture that may be met in a large 

collection and was inclined to consider E. pseudoafri-· 

cana Choffat as belonging to E. olisiponensis and also 

part of E. trigeri Coquand. Peron dealt with material 

from Tunisia and assigned it to the Cenomanian. 

Choffat 15 in a later paper did not accept Peron's 

assimilation of E. oxyntas and E. olisiponensis. He 

also recanted his earlier opinion of relationship between E. pseudoafricana and E. olisiponensis and gave 

the range of E. olisiponensis as from upper Cenomanian 

to upper Turonian, assigning the type locality to the 

upper Turonian. On the basis of about 100 specimens from the type locality (Alcantara, near Lisbon, 

Portugal), he gave an emended diagnosis of the species 

which lllay be translated· as follows: 

Shell inequivalve, higher than wide in youth; in adult age 

the dimensions are equal, or the width is greater than the 

height. Outline ov.al or subcircular, anterior border rectilinear, 

forming generally a rounded angle with the pallial border. 

Upper valve oval, thick, lightly and irregularly convex, with 

beak recurved in the plane of the shell, smooth or nearly smooth 

in the earliest stages, then .acquiring growth lamellae that are 

vel·tical, sharp, crowded closely together, bifurcating and uniting 

again in a short distance. Besides the concentric lamellae 

there are radial swellings irregular, generally narrow, raised (as 

much as 3 millimeters), hardly any wider at base than at summit; they are irregularly spaced and seem sometimes to bifurcate. They rarely appear at a diameter of 10 millimeters, but 

generally at that of 20 millimeters, but I know only two specimens in which they appear as late as in the specimen figured 

by Sharpe. Their number ranges from 7 to 12. 

Lower valve very thick, very gibbous, the anterior third 

more or less flattened and the rest of the shell regularly rounded 

with beak generally more -or less flattened, as in Sharpe's figure 

and in my Figure 19; very rarely free, as in my Figure 17. 

IS Choffllt, Paul, Faune cr6taclque du Portugal, vol. 1, ser. 1, p. 38, 1886; vol. 1, 

ser. 4, Ostreldae, pI. 6, fig. 14, 1902. . 

H Peron, Alphonse, Exploration scientifique de la Tunlsle, pt. 4, Invert~brGs 

fossiles dcs terrains cr6tac6s de la r~gion sud des hauts plateaux de la Tunisie, pp. 

114-119, pI. 23, figs. 14-18, Paris, 1891. 

16 Choffat, Paul, Faune cr6tacique du Portugal, vol. 1, ser. 4, p. 166, Ostreidae, 

pI. 6, figs. 17-19, 1902. 

OF WESTERN INTERIOR 269 

Scar of attachment generally small. The exterior surface is 

ornamented by growth lamellae, often raised along radial lines, 

forming sometimes continuous ribs, lamellose, spinose when 

well preserved, more or less widely spaced, reaching to the beak 

when attachment does not prevent. Some disappear before 

reaching the pallial border; others appear on the middle of the 

shell. Their distance apart and consequently their number is 

variable; the original of Sharpe and that of my Figure 17 may 

be considered to have distant ribs, but others have them much 

nearer. Ligamental groove deep in young individuals and 

shallow in the older ones. Muscular impression of medium 

size, near the anterior border. 

Paulcke 16 described from Peru E. olisiponensis var. 

duplex, founding it on shells with a broad fluTow extending from the beak on the posterior side of the 

lower valve and especially strong radial ribs on the 

upper valve e~tending almost from the beak instead 

of leaving a central area smooth or with only concentric sculpture. With this variety he said he found 

the typical form of the species. 

Fourtau 17 included under E. olisiponensis E. oxyntas and E. pseudoafricana, believing that he had 

theIn all together in the Cenomanian of Egypt. 

Choffat 18 described from Angola typical E. olisiponensis and reiterated his stand of 1902 that E. pseudoafricana is distinct. 

Schlagintweit 19 recorded E. olisiponensis from Peru, 

suggesting that possibly E. polygona Von Buch as figured by Von Buch and Gabb is to be considered identical with E. olisiponensis, though he allowed the question 

to remain open until the originals could be compkred. 

Woods 20 described from Nigeria specimens of E. 

olisiponensis marked by only a few radial ribs. Woods 

considered the two Nigerian localities as Turonian, 

though only one furnished associated species. 

Pervinquiere 21 described from the middle and upper 

Cenomanian of Tunisia both typical and varietal forms 

of E. olisiponensis. He united with it E. oxyntas Coquand and part of E. pseudoafricana Choffat. Pervinquiere mentioned six variants (see p. 270), though he 

saw no advantage in naming them.. He believed 

E. olisiponensis to be exclusively Cenomanian. 

Bose 22 reported from Coahuila, Mexico, a single 

specim~n which he referred with doubt to E. olisiponens'is and to the Cenomanian. It is not well preserved 

but seems to the writer, so far as the figure may indicate, to belong to the species. 

16 Paulcke, Wilhelm, Ueber die Kreideformation in Siidamerika und ihre Beziehungen zu anderen Gebieten: Neues Jahrb., Beilage-Band 17, p. 269, pI. 15, figs. 7, 

8,1903. 

17 Fourtau, R., Contribution 11 l'~tude de ~a faune crlltacique d'Egypte: Inst. 

Egyptien Bull., ser. 4, vol. 4, p. 283, text figs. 3-5, 1903. 

18 Choffat, Paul, Contributions 11 la connaissance g~ologique des colonies portugaises d'Afrique, pt. 2, Nouvelles donn~es sur la zone littorale d'Angola, p. 44, pI. 1, 

figs. 4, 5, Lisbon, 1905. 

1D Schlagintweit, Otto, Die fauna des Vracon und Cenoman in Peru: Neues 

Jahrb., Beilage-Band 33, p. 109, 1911. 

• %0 Woods, Henry, The paleontology of the Upper Cretaceous despoits of northern 

Nigeria, in Falconer, J. D., Th~) geology and geography of northern Nigeria, appendix 2, p. 277, pI. 20, figs. 1-3, London, 1911. 

II Pervinquiere, L~on, Etudes de pal~ontologie tunisienne, pt. 2, Gastropodes et 

lamellibranches des terrains cr~tac~s, p. 174, pI. 13, figs. 4, 5, 9, Paris, 1912. 

22 Bose, Emil, On a new ammonite fauna of the lower Turonian of Mexico: Texas 

Univ. Bull. 1850, p. 230, pI. 20, fig. 4, 1918. 
270 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

It appears to the writer, after examination of the 

many published figures and of the specimens noted 

below, that there is no really essential difference 

between E. oxyntas and E. olisipone~sis and that they 

may be considered one species with variable sculpture. 

E. olisiponensis may then be thought of as including a 

series of forms ranging in radial sculpture of the left 

valve from nearly smooth forms through forms with 

discontinuous irregular ribs w forms with strong 

widely spaced ribs and forms with closer-set weaker 

ribs. The ribs are always narrow and the interspaces 

relatively wide, concave. In concentric sculpture it 

ranges from nearly smooth forms to forms with conspicuous lamellae raised into high spinose flutings. In 

size it is usually 50 to 80 millimeters in maximum 

dimension, though it may reach 165 millimeters. In 

form it varies less than in sculpture: The outline is 

usually oval to subcircular; the upper valve is nearly 

flat; the lower valve is gibbous, regularly rounded. 

The degree of coiling varies, being dependent on .the 

size of the area of attachment. In large collections 

all the extreme variants are connected by series of intermediate forms, and no chronologic value appears 

to attach to individual variants. . 

Pervinquiere's grouping of the variants is perhaps 

as good as any: 

1. Typical form. Upper valve with central part ribless; 

lower valve with ribs distant, discontinuous, rising into spines. 

2. iVar. oxyntas Coquand. Lower valve with ribs relatively 

fine, numerous, continuous, not spinose. 

3. Var. duplex Paulcke. Upper valve with strong radial ribs 

reaching almost to the nucleus of the shell; iower valve with 

strong, distant, spinose ribs and with a deep sulcus on posterior 

side bordered by high ribs. ' 

4. Var. unnamed C= cornuarietis Meneghini, not Goldfnss). 

Lower valve ribbed on only third or haIT of shell nearest the 

beak, remainder nearly smooth. 

5. Var. unnamed C=pseudoafricana Coqu~nd, part). Lower 

valve nearly smooth or lamellose; ribs very few or weak. 

6. Var. unnamed C=trigeri Coquand of Peron). Lower 

valve with lamellae only, raised here and there in flutings; 

no ribs. ' 

From southern Utah the writer has some 19 specimens assignable' to E. olisiponensis. To these may 

be added that figured by C. A. White 23 as E. ponderosa Roemer. Sixteen of the specimens came from 

a locality 2 miles northeast of N otom, Wayne County, 

Utah, on the road from N otom to Caineville, collected 

in part by E. M. Spieker and the writer, in part by 

the late Robert Forrester, of Salt Lake City CU. S. 

Geoi. Survey localities.. 6942 and 12248). Eight of 

these specimens are right'valves and eight are left 

valves. A single large specimen was collected by 

H. B. Waters at a locality 2 miles west of Escalante, 

Garfield County (U. S. Geoi. Survey locality 10401). 

Two other large specinlens were collected years ago 

in southern Utah by members of the Powell Survey 

23 White, O. A., Report upon the invertebrate fossils collected in portions of 

Nevada, Utah, Oolorado, New Mexico, and Arizona: U. S. Geog. ,Surveys W. 

100th Mer. Rept., vol. 4, pt. 1, p. 172, pI. 14, figs. 1 a-c, 1875. 

of Colorado River. One of these is marked "Black 

Bluff," but the second is unlabeled. White's figured 

specimen came fronl Impracticable Ridge. 

For comparison the writer has three specimens from 

Colombia collected by Dr. M. A. Rollot; half a dozen 

specimens from eastern Ecuador collected by J. H,' 

Sinclair and Theron \Vasson; and three specnnens, 

from Angola collected by C. W. vVashburne. Chief 

dependence was necessarily placed on published figures., 

The stratigraphic position of the ,collection from the, 

locality 2 miles northeast of N otom is at the base of 

the Mancos shale. The only fossil directly associated 

with E. olisiponensis here is Gryphaea, newberryi 

Stanton, which occurs in great abundance, though one 

of the valves of E,. olisiponensis was attached w a shell 

of Plicatula hydrotheca White and bears a fairly clear 

mold of it. Over a large area in Utah, Colorado, 

and New Mexico Gryphaea newberryi marks a zone 

in which occur lower Turonian species such as Metoicoceras whitei Hyatt, and there is every reason to 

believe that the age at the locality near Nowm is the 

same. The locality 2 miles west of Escalante is near 

the base of the beds of Colorado age, a horizon definitely lower Turonian. The specimen from Black 

Bluff grew upon a shell of Anchura? jorresteri Reeside 24, 

closely akin to A. olisiponensis Choffat, assigned ta 

the lower Turonian. 

The following notes on the specimens from Gtah 

will be of service: 

Right valves unassigned to varieties (pI. 65, figs. 1-7; 

pI. 66, fig. 3).-These are very close to various figured 

right valves. They do not show the ribs extending as 

close to the p.ucleus as in Paulcke's specimen,26 but are 

much like those figured by Choffat 26 and Peron.27 

Typical variety (pI. 65, figs.' 8-11; pI. 66, figs'. 1-2).­

Some of the specimens from Utah fit very well Sharpe's 

figure. 28 They also resemble closely the specinlens 

figured by Choffat 29 and by Peron,30. though the ribs 

on the latter are nearly continuous. The forms 

figured by Woods 31 and Fourtau 32 are closest perhaps to the forms here considered typical though having fewer and weaker ribs and inclining toward the 

ribless variants. Bose's specimen 33 seems to be closest 

to those placed here. 

Variety duplex Paulcke (pI. 66, figs. 4-11).-One 

~pecimen from Utah (pI. 66, figs. 6-8) is very close to 

Paulcke's type.34 A second (pI. 66, figs. 4, 5) has 

U Reeside, J. B., jr., Five new species of Oretaceous mollusks from Oolorado and 

Utah: Washington Acad. Sci. Jour., vol. 18, pp. 1928. ' 

26 Paulcke, Wilhelm, op. cit., pI. 15, fig. 8. 

26 OhofIat, Paul, Faune crlltacique du Portugai, vol. 1, ser. 4, Ostreidae, pI. 6, 

fig. 17 b, 1902; Contributions a la connaissance gllologique des colonies portugaises 

d'Afrique, pt. 2, Nouvelles donnees sur la zone littorale d'Angola, pt. 1, fig. 5, 1903. 

'II Peron, Alphonse, op. cit., pI. 23, fig. 15. 

28 Sharpe. Daniel, op. cit., pI. 19, fig. 1. 

29 OhofIat, Paul, Faune crlltacique du Portugal, vol. 1, ser. 4, Ostreidae, pI. 6,. 

fig. 17 a, 1902. 

30 Peron, Alphonse, op. cit., pI. 23, fig. 16. 

81 Woods, Henry, op. cit., pI. 20, figs. 1-3. 

82 Fourtau, R., op. cit., fig. 5. 

83 Bose, Emil, op. cit., pI. 20, fig. 4. 

a. Paulcke, Wilhelm, op. cit., pI. 15, figs. 7-8. 
EXOGYRA IN CRETACEOUS 

weaker ribs. Choffat's specil11en from Angola 35 is 

very like those from Utah. A fine specimen of the 

variety dU1Jlex from ColO1nbia, collected by Dr. M. A. 

Rollot, of Bogotft, is figured for comparison (pI. 66, 

figs. 9-11). It is a little stronger in sculpture than 

those from Utah but otherwise is nluch like them. 

Variety oxyntas Coquand (pI. 67; pI. 68, figs. 1-2).­

The specinlens from Utah referred to the variety 

oxyntas are not as finely and as evenly ribbed as those 

figured by Coquand 36 and have l110re inclination toward 

.a spinose ornanlentation but are nevertheless c~ose 

enough to be placed with them. A specimen figured 

by Lartet 37 as E. overwegi val'. scabra is much like 

those fronl Utah, as is also one figured by Peron. 3S 

Two specilnens fr0111 Angola are figured for comparison (pI. 68, figs. 1-2). 

Variety forresteri Reeside, n. var. (pI. 68, figs .. 3-5; 

p1. 69, figs. 1-4).-Several large shells from southern 

Utah, one preserving both valves, seem to differ 

·enough to deserve a new varietal name. The right 

valve shows an ul11bonal smooth area bordered by a 

:zone of fine radial striations; the remainder of the 

:surface shows concentric laInellae interrupted by areas 

of indistinct fine radial striation. The left valve has 

dose-set regular ribs, like those of the variety oxyntas, 

in the ulnbonal region, but these pass into irregular 

·flutings on the middle of the shell and the latest stages 

·of growth show chiefly the concentric lamellae. 

E. ponderosa White (not Roemer) 39 belongs here 

(pI. 69, figs. 1-2). One of Coquand's figures of 

E. oVe1'wegi' (= oxyntas) 40 suggests the form also. Other 

conlparisons with published figures might be nlade-but 

seenl of rather doubtful value. 

Exogyra costata Say 

Plate 69, Figures 5-8 

1820. Exogy1'a costata Say, Am. Jour. Sci., vol. 2, p. 43. 

1828. Exogym, costata Say. Morton, Acad. Nat. Sci. Philadelphia Jour., ser. 1, vol. 6, p. 85, pI. 6, figs. 1-4. 

[For complete synonymy for years 1828-1926 see Wade, 

U. S. Geol. Survey Prof. Paper 137, p. 56, 1926.] 

'1 1927. Exogy1'a cf. E. overwegi Von Buch. Trechmann, Geol. 

Mag., vol. 64, p. 53..' . 

Not 1871. Exogy1'a costata Say. Stoliczka, Palaeontologia 

indica, Cretaceous fauna of southern India, vol. 

3, p. 461, pI. 40, figs. 1-3; pI. 41, fig. 1. 

Exogyra costata Say has recently been described in 

great detail by Stephenson,41 an~ there is no need of 

86 ChofTat, Poul, Contributions 11 la connoissonce g6010gique des colonies portugaisos d' Afrique, pt. 2, Nouvollos dOllllllcs sur In zone littorale d'Angola, pI. 1, figs. 

4-5, HJ03. 

86 Coquond, Honri, Monographie du genre Ostrea, terrain cr()tac(), pI. 44, figs. 1-7, 

lSGIl. 

B7 Lartot, LOllis, op. cit., pI. 11, fig. 2. 

8.!1 Poron, Alphonso, op. cit., pI. 23, fig. 14. 

811 White. C. A., op. cit., pI. 14, figs. 1 a-c. 

40 Coqnnnd, Henri. Monographie du genre Ostrea, terrain crlltacll, pI. 44, fig. 5, 

ISGIl. 

41 Stopliellson, L. W., Species of Ezogyra from the eastern Oulf region and the 

Carolinns: U. S. Oeol. Survey Prof. Poper SI, pp. 50-53, pI. lG, figs. 3-4; pI. 17, figs. 

]-2; pI. 18; pI. lll, figs. 1-4; pI. 20, fig. 1, llllG; '1'he Cretaceous formations of North 

Carolina: North Carolina Oeol. and Econ. Survey, vol. 5, pt. 1, pp. 173-179, pI. 47, 

jigs. 2-5; pI. 48, 11l23. 

OF WESTERN INTERIOR 271 

repeating the discussion here. The species is characterized by attaining a large size; by the well-rounded 

form of the lower valve; by the sculpture of the lower 

valve-regularly arranged, simple or bifurcating, 

broad, flattened ribs ·separated by very narrow interspaces; by the sculpture of the upper valve-prominent concentric lamellae with rarely radial costae on 

the posterior portion. . 

To judge from sca~tered citations and figures in the 

literature E. overwegi Von Buch is of nearly the same 

age and very much like E. costata in form and sculpture. Whether it is identical can be decided only by 

comparison of authentic material of E. overwegi with 

E. costata. The identity of E. overwegi was for long 

obscured by confusion with E. olisiponensis Sharpe 

(see pp. 268-270), and only in later works has it been 

correctly interpreted. 

The writer has in hand two mutually attached 

shells of E. costata coll~cted by W. T. Lee in the SE. 

U sec. 11, T. 6. N., R. 69 W., about 5 miles south of 

Fort Collins, Colo., and just south of Fossil Creek. 

The horizon is in the sandstone constituting the 

exposures long known as Fossil Ridge, which has 

yielded a large fauna listed by Henderson. 42 Stratigraphically the sandstone of Fossil Ridge is near the 

top of a series of five sandstones which in early work 

were interpreted as one and named the IIygiene 

sandstone. Later work by several geologists, especially those examining the region for oil companies, 

has shown t"p'~ series to include' an interval of some 

1,500 feet. The five sandstones are now called, in 

ascending order, the Hygiene, Terry, Rocky Ridge, 

Larimer, and Richard sandstone members of the 

Pierre shale. 43 The' Rocky Ridge and Larimer sandstones make Fossil Ridge. The Milliken sandstone 

member of the Fox Hills s'andstone, containing 

Sphenodiscus lenticularis Owen, lies 5,000 to 6,000 feet 

higher in the section than the sandstones of Fossil 

Ridge, and the Niobrara formation about 3,000 feet 

below them. The fossils reported from the sandstones of Fossil Ridge show that they are of upper 

Campanian age; these include such species as Baculites 

ovatus Say, Baculites compressus Say, Acanthoscaphites? nodosus Owen, Placenticeras intercalare Meek, 

and Ptychoceras sp. An element in the fauna of Fossil 

Ridge of great interest as joining with Exogyra costata 

in indicating a connection with that of the Gulf series 

consists of the species Capulus spangleri IIenderson, 

GY1'Odes abyssfna (Morton), Gyrodes crenata (Conrad), 

Anchura haydeni White, and Volutoderma clatworthyi 

Henderson. In the Gulf series Exogyra costata is not 

usually associated with fauna containing the genus 

Placenticeras, its normal range being higher, but it 

does at some places so occur. 

42 Henderson, Junius, The Cretaceous formations of northeastern Colorado: 

Colorado Oeol. Survey Bull. 19, pp. 31-32, 1920. 

43 Mather, K. F., Oilluly, James, and Lusk, R. D., Geology and oil and gas prospects of northeastern Colorado: U. S. Oeol. Survey Bull. 796, PP. 65-124, 1925. 
( 
• 


PLATES 65-69 


273 
• 

PLATE 65 

Page 

FIGURES 1-7. Exogyra olisiponensis Sharpe. Three right valves from the base of the Mancos shale on the road from Notom 

to Caineville, 2" miles northeast of Notom, Wayne County, Utah. U. S. Nat.. Mus. catalogue No. 73613__ 270 

8-11. Exogyra olisiponensis Sharpe, typical variety. Left valve from same locality. U. S. Nat. Mus. catalogue 

No. 73612 _______________ ~~--------------------------------__________________________________ 270 

274 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 65 

4 

3 

5 

10 

6 

7 

1 
 2 


9 


EXOGYRA OLISIPONENSIS SHARPE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 66 


6 

7 

EXOGYRA OLISIPONENSIS SHARPE 
, . 

• 

PLATE 66 


\ Page 

FIGURES 1-2. Exogyra olisiponensis Sharpe, typical variety. Left valve from the base of the Mancos sha.le on the road 

from Notoll1 to Caineville, 2 miles northeast of Notom, Wayne County, Utah. U. S. Nat. Mus. catalogue No. 73613______________________________________________________________________________ 270 


3. Exogyra olisiponensis Sharpe. Right valve from same locality. U. S. Nat. Mus. catalogue No. 73613__ 270 


4-5. Exogyra olisiponensis Sharpe var. duplex Paulcke. Left valve from same locality. U. S. Nat. Mus. catalogue No. 73609______________________________________________________________________________ 270 


6-8. 	Exogyra olisiponensis Sharpe var. duplex Paulcke. Left valve from same locality. U. S. Nat. Mus. catalogue No. 73609 __________________________________ --------------- _________________ ~___________ 270 


9-11. Exogyra olisiponensis Sharpe var. d~tplex Paulcke. Complete shell from Rio Villaviejo near La Union, 


HuHa, Colombia, shown for comparison. U. S. Nat. Mus. catalogue No. 73607______________________ 270 


275 

• 

PLATE 67 

Page 

FIGURES 1-3. Exogyra olisiponensia Sharpe var. oxyntas Coquand. Left valve from base of Mancos shale on road from 

Notom to Caineville, 2 miles northeast of Notom, Wayne County, Utah. U. S. Nat.. Mus. catalogue

No. 73610____________________________________________________________________________________ 271 

4. Exogyra olisiponensis Sharpe, ar. oxyntas Coquand. Left valve from same locality. U. S. Nat. Mus. catalogue No. 73610_______________________________________________________________________________ 271 

5-6. Exogyra olisiponensis Sharpe var. oxyntas Coquand. Complete shell, somewhat weathered, from locality 4 

kilometers east of Novo Redondo, Angola, shown for comparison. U. S. Nat. Mus. catalogue No. 73604_ 271 

7-8. Exogyra olisiponensis Sharpe var. oxyntas Coquand. Left valve from Black Bluff, Utah. U. S. Nat. Mus. 

catalogue No. 7361L__ ..: ____________________________________________________________ . _ _____ __ __ _ 271 

276 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 67 

1 
 3
 2 


5 
 4 


6 


7 8 


EXOGYU."- OLTSIPONENSTS SHARPE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 68 


EXOGYRA OLISIPONENSIS SHARPE 
PLATE 68 

FIGURES 1-2. Exogyra olisiponensis Sharpe var. oxyntas Coquand. Left valve from locality 4 kilometers east of Novo 

Redondo, Angola, shown for comparison. U. S. Nat. Mus. catalogue No. 73604 ______________________ _ 

3-5. Exogyra olisiponensis Sharpe var. forresteri Reeside, n. var. Type specimen from base of beds of Colorado 

age, 2 miles west of Escalante, Garfield County, Utah. ·U. S. Nat. Mus. catalogue No. 73605 __________ _ 

Page 

271 

271 

• I 

277 

, "\\" 
PLATE 69 

FIGURES 1-2. Exogyra olisiponensis Sharpe val,". forresteri Reeside, n. var. Left valve figured by C. A. White as E. ponderosa Roemer. Impracticable Ridge, Utah. U. S. Nat. Mus. catalogue No. 13417 __________________ _ 

3-4. Exogyra olisiponensis Sharpe var. forresteri Reeside, n. var. Left valve from southern Utah, exact locality 

unknown. U. S. Nat. Mus. catalogue No. 73608_________________________________________________ _ 

Pag~ 

271 

271 

5-7. Exogyra costata Say. Two mutually attached shells from Fossil Ridge, 5 miles south of Fort Collins, Colo. 

U. S. Nat. Mus. catalogue No. ,73606 ____________________________________________________________ _ 271 

278 

I, I· il 
U . S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 69 

1 

5 

3 

6 

2 7

EXOGYRA OLISIPONENSIS SHARPE AND EXOGYRA COSTATA SAY