Review of 

Ordovician Pelecypods 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 

Review of 

Ordovician Pelecypods 

By JOHN POJETA, JR. 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 

Summary of morphological, taxonomic, 

phylogenetic, and paleoecological data 

for Ordovician pelecypods 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1971 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director 

Library of Congress catalog-card No. 72-168736 

For sale by the Superintendent of Documents1 U.S. Government Printing Office 

Washington, D.C. 20402 - Price $1.50 (paper cover) 
CONTENTS 

Page 

Abstract __________________________________________ _ 1 Ordovician pe~ecypods-Continued 

Introduction ______________________________________ _ 1 Modiomorphidae [Modiolopsidae] ________________ _ 

Acknowledgments __________________________________ _ 2 Less well known Ordovician pelecypod groups _____ _ 

Materials and methods _____________________________ _ 2 Conocardiidae _____________________________ _ 

Historical resume __________________________________ _ 4 Vlastidae _________________________________ _ 

Cambrian bivalves _________________________________ _ 8 Anomalodesmata __________________________ _ 

Ordovician pelecypods ______________________________ _ 9 Ordovician pelecypods of uncertain higher taxoActinodontoida ________________________________ _ 9 nomic position ______________________________ _ 

Cycloconchidae ____________________________ _ 10 Phylogenetic summary _____________________________ _ 

Lyrodesmatidae ___________________________ _ 10 Ordovician lineages and higher level pelecypod taxonomy_ 

Redoniidae _______________________________ _ 11 Lile habils ________________________________________ _ 

Babinkidae ___________________________________ _ 12 Ordovician epifauna ____________________________ _ 

N uculoids ____________________________________ _ 15 Ordovician infauna _____________________________ _ 

Pteriomorphians _______________________________ _ 17 Cyrtodontidae _________________________________ _ 

Cyrtodontidae _____________________________ _ 17 References cited ___________________________________ _ 

Ambonychiidae ____________________________ _ 18 Index ____________________________________________ _ 

Pterineidae _______________________________ _ 19 

PLATE 1. 

2. 

3. 

4. 

. 5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

1.-, .:>. 

14. 

15. 

ILLUSTRATIONS 

[Plates follow index] 

Astarte, Actinoclonta, Ischyrodonta, Redonia, Palaeoneilo, and Bab£nka. 

Allodesma and Cycloconcha. 

Cycloconcha and Lyrodesma. 

Ctenodonta. 

Similodonta and Deceptrix . 

Nuculites, JJi yopl usia, Palaeoconcha, Tancrediopsis, and Cyrtodonta. 

Cyrtodonta, Cyrtodontula, and Yanuxemia. 

Fanuxemia. 

Yanuxemia and Septijer. 

Opisthoptera, Ambonychia, Allonychia, Anomalodonta, and Pterinea. 

Pterinea, Palaeopteria, Aristerella, Afodiolus, and Arcuatula. 

Colpomya, JJfodiolopsis, Pholadomorpha, Saffordia, and Sphenoliwn. 

A!odiolodon, JJJodiolops£s, Mytilus, Arcuatula, and Perna . 

JJ[odiolopsis and Plethucardia. 

1Jfod£olopsis and Cuneamya.' 

16. JJfodiolopsis, JJfatheria, and Rhytimya. 

17. TVhiteavesia. 

18. Psiloconcha, Orthodesma, and Cymatonota. 

19. Eopteria, TVhiteaves1·a, and Conocanlium. 

20. Conocanliwn, Euchasma, Eopteria, and Vlasta. 

III 

Page 

20 

22 

22 

23 

23 

24 

25 

30 

30 

32 

34 

35 

37 

43 
IV CONTENTS 

Pa~re 

FIGURE 1. Reproductions of Lyrodesma, Allodesma, Plethocardia, and Ambonychia_ _ _ 11 

2. Reproductions of Redonia_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 12 

3. Reproductions of monoplacophorans_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 14 

4. Reproductions of Ahtioconcha_ _ _ _ __ _______ __ _ _ __ ____ _____ __ _______ _ 19 

5. Chart of phylogenetic relationships of Paleozoic pelecypods____________ 26 

6. Chart of range and abundance of Ordovician pelecypods_______________ 27 

7. Life-habit reconstructions of late Early Ordovician pelecypods__________ 31 

8. Life-habit reconstructions of late Middle Ordovician pelecypods________ 32 

9. Life-habit reconstructions of Late Ordovician pelecypods______________ 33 

TABLES 

Page 

TABLJ<; 1. Alphabetical listing of generic names used for Ordovician pelecypods_____ 6 

2. Generic names that have been applied to Cambrian animals which at one 

time or another were thought to be pelecypods____________________ 9 
REVIEW OF ORDOVICIAN PELECYPODS 

BY JoHN PoJETA, JR. 

ABSTRACT 

T'he study of Ordovician peleeypods has lagged because of 

the impre·ssion that adequate material for deta<iled investigations was not available. Silicified specimens rf·rom the Cincinnati 

arch area have provid'('d much of the material for the present 

sttuly. These specimens show the entire shell morphology of 

many Ordovician species and have he,lped resolve a number 

of morphological and sy·stematic questions which have previously 

hindered the understanding of early pelecypod phyl·ogeny and 

modes of life. 

Ordovician pelecypods are taxonomically and morphologically 

more diverse than has heretofore been generally recognized. 

The hard-part morphology of each of the major families of 

Ordovician ,pelecypods is described herein, and the families are 

united into six major phy·logenetic groups ; almost all other 

Paleozoic pelecypods can be derived from one or another o'f 

these six groups. Because the groups ·represent the primary 

radiation of the class, it is proposed that the Pelecypoda 'be 

divided into six subclasses: (1) Rostroconchida Oox (Conocardiaeea), (2) Palaeotaxodonta Korobkov (Nuculoidea and 

Solemyoida), ( 3) Isofilibranchia Iredale (MytHacea), ( 4) 

Pteriomorphia Beurlen (Cyrtodontaeea. Arcacea, Limopsacea, 

P·teriacea, Pinnacea, Ambonychiacea. Pectinacea, Anomiacea, 

Limacea, and 03treacea), ( 5) Heteroconehia Hertwig ( Actinodontoida, Babinkidae, Unionoida, Tri.gonioida, Veneroida, 

Myoida, and Hippuritoida), and ( 6) Anomalodesmata Dall 

( Edmondiidae, Sanguinolitidae= Solenomorphidae, Pholadomya-. 

cea, Pandoraeea, l\Iegadesmatidae, and '?Septibranehoidea). Five 

of the six subclasses continue to the present, with only the 

problematic Rostro:conchida becoming extinct. 

Mode of life reconstructions for the various epochs of the 

Ordovician suggest that pelecJ'IpOds were originally in'faunal 

and point up the diversifieation of epifaunal foruns through 

Ordovician time. 

INTRODUCTION 

Ordovician pelecypods are the first undoubted representatives of an important biological group, and of 

necessity are the forms upon which the phylogenetic 

speculations of the origin of younger pelecypod taxa 

are based. Early Paleozoic pelecypods in general, and 

Ordovician pelecypods in particular, are heirs to several 

generalizations which at best are only partly correct. 

Chief among these misunderstandings are the belief 

that adequate material for detailed studies is not available and the belief that Ordovician pelecypods are a 

homogeneous group showing little morphologic, ecoIogie, and phyletic variation. Mainly because of these 

generalizations, the study of Ordovician pelecypods has 

lagged far behind that of other Ordovieian invertebrates. In the 19th century there was a great deal 

of descriptive work dealing with Ordovician pelecypods. 

Hmvever, since that time, taxonomic studies have continued on a diminished scale, ·and little has been added 

to the knowledge of the detailed stratigraphic distribution o'f these animals. 

In recent years there has been renewed interest in 

the study of early Paleozoic peleeypods. The silicified 

specimens that are being dbtained from the Ordovician 

deposits of North America show that adequate material 

for detailed study is available and that Ordovician 

pelecypods are not a homogeneous group. It is now possible to document each of the major groups of Ordovician pelecypods morphologica1ly and to use these data 

to draw ecologic and phylogenetic conclusions. 

Phylogenetically, I have grouped Ordovician pelecypods into six major lineages from which almost all other 

Paleozoic pelecypod groups can be derived. Because 

the six lineages represent the primary radiation of 

the class, I propose that the Pelecypoda (Bivalvia) 

be divided into six subclasses: (1) Rostroconchida 

Cox ( Conoeardiacea), Early Ordovician-Permian; 

(2) Palaeotaxodonta l{orobkov (Nuculoidea and 

Solemyoida), Early Ordovician-Holocene; (3) Isofilibranchia Iredale (Mytilacea), Early OrdovicianHoloeene; (4:) Pterimnorphia Beurleri (Cyrtodontacea, 

Arcacea, Limopsacea, Pteriacea, Pinnacea, Ambonychiacea, Pectinacea, Anomiacea, Li1naeea, and Ostreacea), 

Middle Ordovieian-Holocene; ( 5) Heteroconchia 

Hertwig (Actinodmitoida, Babinkidae, Unionoida, 

Trigonioida, Veneroida, Myoida, and Hippuritoida), 

Early Ordovician-Holocene; ( 6) Anomalodesmata 

Da 11 ( Edmoncliidae,, Sanguinolitidae= Solenom.orphiclae, Pholadomyacea, Pandoracea, Megadesrnatidae, and 

?Septibranchoidea), Middle Ordovician-Holocene. 

Early Ordovieian pelecypod faunas are dominated by 

in faunal deposit (nuculoid) and suspension ( conocardiids, babinkids, redoniids, cycloconchids, and lyrodesmatids) feeders; at this time probably only some 

1 
2 REVIEW OF ORDOVICIAN PELECYPODS 

of the n1odiomorphids (and perhaps some conoeardiids) 

were epifaunal suspension feeders. The fact that the 

earliest pelecypod faunas are dominated by infaunal 

forms suggests that the aneestral mode of life of the 

class is infaunal. In the l\iiddle Ordovician there was 

a diversification of epifaunal suspension feeders with 

the appearance of the pteriaceans and ambonychiids. 

However, infaunal forms remain prominent, and are 

supplemented by the appearance of the edmoncliids, 

sanguinolitids, and some eyrtodontids; other cyrtodontids probably \vere semi-infaunal in their mode 

of life. 

ACKNOWLEDGMENTS 

I would like to thank the following individuals for 

plaeing specimens and type material at my disposal: 

C. Babin, Laboratoire de Geologie, Brest; R. L. Batten, 

American Museum of Nat ural History; Mme. Bau-

'douin-Bodin, Museum d'Histoire N aturelle, Nantes; 

1{. E. Caster, University of Cincinnati; l\L J. Cope·-

land, Geological Survey of Canada; vV. T. Dean, British Museum (Natural History); R. H. Flo\ver, New 

l\fexieo Institute of l\Iining and Technology ; L. F. 

Hintze, Brigham Young University; C. F. l{ilfoyle, 

New York State l\fuseum; J. IC Pope, Miami University, Oxford, Ohio; and E. S. Richardson, Jr., 

Field :Museum of Natural History, Chicago. 

For helpful conversations, eorrespondenee, and for 

reading some or all of the manuscript I would like to 

thank: K. J. Boss, Museum of Comparative Zoology, 

Harvard University; Peter Bretsky, Northwestern University; E. G. l{auffman, Joseph Rosewater, and T. R. 

Waller, U.S. Na1tiona:l Museum; .Jifi l{Hz, Czechoslovak Geologieal Survey; A. L. l\IeAlester, Yale University; N. D. Newell, American l\Iuseum of Natural 

History; David Nieol, lTniversity of Florida, Gainesville; Bruce Runnegar, University of New England, 

~ ew South vVales, Australia; Howard Sanders, 'Voocls 

Hole Oceanographic Institution; and S. l\L Stanley, 

.fohns Hopkins lJniversity. 

Colleagues on the U.S. Geological Survey staff were 

helpful throughout the study. Thanks are extended to 

D. F. B. Black, E. R. Cressman, A. B. Gibbons, R. C. 

Kcpferle, S. J. Luft, J. H. Peck, ,V. L. Peterson, J. S. 

Pomeroy, ,V. C. s,vadley, G. ,V. 'Vier, and D. E. 

'Volcott, for their help with the lithostratigraphy of 

the Ordovician roeks in the State of l{entucky, and 

the collecting of Cincinnati arch silicified blocks; David 

Oldham for his help in collecting in the field, in etching clown, pieking, and sorting silicified specimens, 

and for his fine dra\vings of figures 5-9; R. H. MciGnney and II. E. l\Iochizuki for taking some of the photographs; and R. J. Ross for providing specimens from 

the Antelope Valley Limestone. 

MATERIALS AND METHODS 

Many museum specimens of Ordovician pelecypods 

are poor molds and easts. This is partly an artifact of 

eollecting, partly because previous workers did not 

take advantage of silieifiecl material, partly the result 

of no one having a long continuing interest in working with these animals, and only partly the result of 

poor preservation. 

Molds and easts preserved on the exposed surfaees 

of limestone ledges are generally weathered and show 

little morphologieal detail other than shell shape (pl. 

15, fig. 4). However, "crack-out" speeimens frmn limestone blocks commonly preserve some n1uscle sears (pl. 

14, fig. 6; pl. 15, fig. 7). Such speci1nens may be internal 

or composite molds, although in some specimens the 

reerystallizecl shell is preserved (pl. 18, fig. 9). Speeimens obtained from the splitting of shales cmnmonly 

preserve the shell seulpture whieh is commonly superimposed on the internal n1old (pl. 13, figs. 16, 17). 

Unfortunately many of the early workers, on whose 

reconnaissanee studies a large part of our knowledge 

of Ordovician peleeypods rests, described speci1nens 

preserved on the exposed surfaces of limestone ledges 

or else described inferior molds and casts of various 

sorts. This approach is understandable in an historical 

context, as these men were interested in describing 

large unknown faunas as fast as possible. However, 

it has created difficulties for later systematists who 

attempt to use these early names, as well as for workers 

who wish to summarize data dealing with Ordovician 

pelecypods. 

There is a great deal of silicified Ordovician fossil 

material in North Ameriea. My work since 1965 on the 

Ordovieian faunas of the tristate area of Ohio, Indiana, 

and l{entucky has resulted in the collecting of 17 tons 

of roek, which is yielding an abundant and varied 

silicified pelecypod fauna. In addition, I have smaller 

collections of silicified Ordovician pelecypods from 10 

other Ameriean States and one Canadian province. 

Silicified material is unrivaled in the information it 

provides about early Paleozoic pelecypods in that it 

allows one to observe most of the hard-part morphology 

of the species concerned (pl. 13, fig. 6). These species 

are generally preserved as various types of molds and 

casts (pl. 13, fig. 15) which seldon1 show hinge-line 

features, although it is not uncommon for them to show 

some of the muscle scars. One must crack a great deal 

of limestone to obtain a relatively few reasonably wellpresetTed specimens which usually do not provide as 

much information as does silicified material. Thus, 

when available, silicified material is preferable for 

observing shell morphology in Ordovician pelecypods. 
MATERIALS AND METHODS 3 

The early describers of Ordovician pelecypods 

seldom took advantage of silicified specimens; when 

they did use such material it generally consisted of 

individual specimens weathered free of the matrix and 

stained a red-brown color. No concentrated efforts were 

made to etch large quantities of this material in hydrochloric acid. For many years, Dr. G. A. Cooper, U.S. 

National ~iuseum, has been etching large quantities 

of Permian limestone and assembling an exquisite collection of silicified Pennian invertebrates. I am now 

attempting to do the same with North American Ordovician faunas, be.ginning with the classic Cincinnati 

arch section. 

The belief that Ordovician pelecypods show little 

nwrphologic variation has been expressed to n1e on 

several occasions by eolleagues working with younger 

mollusean faunas. This is categorically not so. From 

the Middle Ordovician onward, pelecypods form a 

highly varied and highly successful group that is 

abundantly represented in the Ordovician platform 

deposits of North America. Furthermore, most of the 

higher level Ordovician pelecypod taxa are known from 

the Early Ordovician onward (figs. 5, 6). 

The variability and abundance of Ordovieian pelecypods have been masked by several historical and 

fortuitous factors in eluding: ( 1) The widespread use 

of a few common generic names sueh as Otenodonta for 

most Ordovician nuculoids and 111 od-iolopsis for most 

modioliform shells. These names have become nearly 

synonymous with family-level taxa and convey such 

broad coneepts that they hide the fact the animals 

themselves are much more varied. (2) The literature 

is highly seattered in a large number of faunal studies 

and small monographs which have been published in 

a great many periodicals; until someone compiled this 

literature no adequate idea of the morphological diversity of the group could be formed. ( 3) The fact that 

most describers of Ordovician pelecypods dealt with 

them as side issues has resulted in a series of confusing, 

contradictory, and generally vague taxon concepts, 

which in turn has resulted either in indiscriminate use 

of generic names or in the lumping of all more or less 

similar shapes under a few broadly defined names. 

~iany workers have been involved in the description 

of Ordovician pelecypod species. Most species were 

described as a part of more general faunal studies, or 

monographs on the group were prepared between other 

studies; no one developed a long-term continuing 

interest in working with these animals, and workers 

interested in comparing younger pelecypod faunas to 

Ordovician ones can develop only vague concepts about 

Ordovician faunas from the available literature. In 

general the concepts of Ordovician pelecypod taxa are 

at a stage where the family-level and generic-level 

categories are poorly defined or are mere lumpings of 

species under one heading, and most species-level taxa 

are defined on slight differences in the shape of n10lds 

or on geographic or stratigraphic bases. 

The seemingly ,widespread opinion that Ordovician 

pelecypods were rare faunal elements is again an 

example of overgeneralization. There is, of course, no 

comparison between the variety of Ordovician brachiopods and pelecypods when the sum total of genera 

and species are compared. However, in some areas, 

peleeypods are known to be as varied as brachiopods. 

Identified in the Cincinnati arch area, on the basis of 

specimens obtained from 4 tons of etched limestone 

in a stratigraphic interval about 400 feet thick (upper 

Camp Nelson Li1nestone through Devils Hollow Member of Lexington Limestone) were : 29 species of pelecypods placed in 17 genera, 23 species of brachiopods 

placed in 21 genera (identified by R. B. Neuman), and 

32 species of gastropods placed in 19 genera (identified 

by E. L. Y ochelson). These identifications are all prelimiilary pending further study and the obtaining of 

additional specimens; nonetheless, the figures show the 

order of 1nagnitude of the species present in the three 

groups studied. 

In the Middle Ordovician rocks of central l(entucky 

(where my collecting has been the most extensive), 

pelecypods and brachiopods are not necessarily InutuaHy 

exelusive. They oceur together in all eombinations from 

approximately equal numbers of individuals of each 

group to eom'binations where one group oeeurs aJmost 

to the total exclusion of the other. I have many collections that have yielded hundreds of individuals of 

various species of pelecypods. My single largest collection (lTSGS 6034:-CO) is from the Tyrone Limestone. It 

consisted of 1,4:68 pounds of li1nestone, which yielded 

about 12,500 silieified specimens. Of these about 10,000 

were mollusks, whereas only six were brachiopods; 2,200 

of the mollusks were pelecypods, 3,200 were gastropods, 

4,300 were cephalopods, and there \Yere 95 chiton plates. 

USGS collection 6134-CO from the Curdsville Limestone Member of the Lexington Limestone consisted of 

632 pounds of limestone. Upon etehing, this yielded a 

silicified fauna having 779 pelecypods and 92'7 brachiopods. lJSGS eollection 6145-CO from the Point Pleasant 

Limestone eonsisted of 11-! pounds of limestone. lTpon 

etching, this yielded a silicified fauna having 18 pelecypods and 500 brachiopods. ~iany n1ore exa1nples could 

be given, but those given above show that in these Middle 

Orclovieian rocks, brachiopods and pelecypods occur 

together in varying proportions. lTSGS eollection 6034-

CO illustrates another point, that at least in the Cincinnati arch area, Ordovician pelecypod species 1nay be 
4 REVIEW OF ORDOVICIAN PELECYPODS 

represented by large numbers of individuals that 1nay 

form a significant part of the rock in which they occur. 

As the first undoubted representatives of their class, 

Ordovician pelecypods are often referred to by persons 

,working on younger faunas and are smnetimes incorporated into elaborate phylogenetic diagrams. For 

much of their data, these \YOrkers 1nust refer to 19th 

century authors whose works are subject to the inherent 

difficulties of the period, especially to the highly interpretive hand-drawn figures which they often published 

(Allodes1na, fig. 1F, G; pl. 2, figs. 1-5; Plethocardia, fig. 

1H; pl. 14, fig. 9). Many of these early drawings are 

really reconstructions and the specimens from which 

they were 1nade show various features in an equivocal 

1nanner or not at all (Pojeta, 1966, pl. 46, figs. 1-5). 

Many of the phylogenetic diagrams of pelecypods 

show a broad Ordovician base from which a number of 

branches arise. These diagrams give the general appearance of a bush and imply that in Ordovician time there 

was some sort of broad, homogeneous, but "plastic" 

ancestral pelecypod stock. I do not think that this picture 

is a reasonable approximation of early pelecypod phylogeny. Rather it is a picture that is produced because 

of a lack of knowledge of many of these early forms. I 

think that it is possible to document at least six distinct 

Ordovician pelecypod lineages (figs. 5, 6) ; four of these 

lineages are distinct from the Early Ordovician on\vard, 

and two are known from the Middle Ordovician onward. 

In addition there are probably a few 1nore lineages 

which at present are too poorly known to document 

adequately. Already by the Early Ordovician, pelecypods had differentiated into several stocks, which suggests that the ancestors of these stocks should be sought 

in the Cambrian. 

Because so much of the knowledge of Ordovician 

pelecypods still rests upon early reconnaissance studies, 

the stratigraphic occurrences of generic.- and specifielevel taxa are known only in a general way, and the 

group has not been used for the biostratigrahie zonation 

of the Ordovician. The Cincinnati arch material is providing a beginning for an evaluation of the usefulness 

of pelecypods for detailed Ordovician biostratigraphic 

studies; once the vertieal succession of the pelecypods 

is understood in this area it can then be used as a standard of cmnparison for other late Middle and Late Ordovician sequenees. 

In the subdivision of the Ordovician into Lo,ver, Middle, and Upper units I have followed Cooper (1956) in 

placing the Whiterock Stage at the base of the Middle 

Ordovician, in a position older than the Chazy. Also I 

have used the traditional l\1iddle-lTpper Ordovician 

boundary as drawn in the Ohio Valley, which places 

Eden age rocks in the Upper Ordovician. Bergstrom 

and Sweet ( 1966) presented evidence suggesting that 

Eden age rocks in the Ohio Valley overla,p with Barneveld (Trenton) age rocks in New York and that the 

Eden is not younger but partly or wholly of the same 

age as the Barneveld. This latter stratigraphic consideration has little effeet in figures 5 and 6 as there are only 

a few pelecypods known from Eden age rocks, and no 

new higher taxa or phylogenetic groups originate in 

these rocks. 

This report has required the acemnulation of specimens from a number of n1useums, the nan1es of whieh 

are subsequently abbreviated as follows: AM, American 

Museum of Natural History; GSC, Geological Survey 

of Canada; LGB, Laboratoire de. Geologie, Brest; MU, 

Miami University, Oxford, Ohio; NYSM, New York 

State l\1usemn; UCM, University of Cincinnati Museum; USGS, U.S. Geological Survey; USNM, U.S. 

National Museum, Department of Paleobiology; 

USNMDl\1, U.S. Na,tional Museum, Division of Mollusks; vVM, W a.lker Museum collection at the Field lfuseum of Natural History, Chicago; YPM, Y a.le Peabody 

Museum. 

HISTORICAL RESUME 

The study of Ordovician pelecypods began with Goldfuss' 1836 description of Pterinea car in ala (fig. 1/) from 

the Ordovieian rocks of New York. This species is now 

recognized as an ambonychiid, probably some species of 

Am_bonyclda Hall. North American descriptive studies 

were continued by Conrad, Hall, and a few others in the 

early reports of the New York Survey, so that hy 1850 

a few dozen names had been proposed for Ordovician 

pelecypods. In 1868, Bigsby listed about 300 species 

names that had been proposed for this group; his compilation was on a worldwide basis, but \vas largely made 

up of names proposed for western European and eastern 

North American for1ns. In the latter part of the 19th 

century, a large number of species names were proposed 

for North American species in many different journals; 

fortunately this scattered literature was brought together by l\1iller (1877, 1889-97) and Bassler (1915) 

in their bibliographies. Bassler (1915) listed about 550 

nan1es that had been proposed for North American species to that date. 

Miller (187±) was the first worker to attempt anything like a monograph of the group, when he treated 

all Ordovician pelecypods that had been described from 

the Cincinnati, Ohio, area. However, it was not until 

Ulrich began a systematic study of the group in the 

1890's that Ordovician pe.leeypods received any intensive monographic treatment. Behveen 1890 and 189·5 

lTlrieh published a series of s1naller papers (1890a, b, 
HISTORICAL RESUME 5 

c, 1892a, b) and two lengthy n1onographs (1893 [1895], 

1894) ; these papers are still the standard references for 

A1nerican species. 

Ulrich revised the nomenclature of the group to his 

satisfaction, although some of his nomenclatural decisions are unusual by 1970 standards. He published his 

last 1najor paper about Ordovician pelecypods in 1895, 

although an earlier paper was reprinted in 1897. Occasionally thereafter, Ulrich deseribed a few nmv species 

in the works of other authors, but published nothing else 

dealing with Ordovician pelecypods. Ho·wever, he was 

not inactive in the fie,Id as his opinion ·was often solicited 

by others when they had to deal with these animals, 

and he was responsible for many of the pe,lecypod identifications appearing in American Ordovician fa.m1al 

lists between 1900-40. Toward the end of his life he apparently planned a major paper or papers dealing with 

Ordovician pelecypods as there are bits and pieces of 

1nanuscripts written in a shaky hand and elated in the 

late 1930's scattered throughout the Ordovician collections of the lT.S. Geological Survey and the U.S. N ationa! Museum. These manuscripts contain many new 

names whieh also often appear on muse.mn labels; however, to my knowledge none of these names were ever 

published. 

Twentieth century American literature dealing with 

Ordovician pelecypods is not extensive; a number of 

new names have been proposed, however, as in the 19th 

century, pelecypods 1vere usually deseribed in more general faunal studies, and only a few papers deal mainly 

with pelecypods. 

Most of the knowledge of North American Ordovician pelecypods is based upon faunas described from 

the northeastern part of the United States and adjacent parts of Canada. Forms from the southeastern 

United States are poorly known as are Appalaehian 

and Arctic species; western North A1neriean pelecypod 

faunas are almost unknmvn, although we are now beginning to accumulate materials from the Ordovician 

of Nevada and lTtah. 

In Europe, Ordovician pelecypod studies have been 

carried out by a ntrmbe,r of \Yorkers in a series of regional papers which deal with most of the important 

Ordovician outcrop areas. Here too, many of these 

studies are now old and many of them were parts of 

more general faunal studies. Some of the more important works inelude: Barrande ( 1881) and Pfab 

( 1934) in Bohemia; Barrois ( 1891), Thoral ( 1935), 

and Babin (1966) in France; Hind (1910), Reed (1944, 

1946, and 1952), Lamont ( 1946) , and Harper ( 194 7) 

in the British Isles; Maillieux (1939) in Belgium; 

Isberg (193-4), Soot-Ryen (1969) and Soot-Ryen and 

Soot-Ryen (1960) in Scandinavia; Sharpe (1853), 

421-895 0- 71 - 2 

Verneuil and Barrande ( 1855), and Born ( 1918) in 

Iberia; Vinassa de Reg11y (1927) in Sardinia; and 

Eichwald (1860), Bekker (19121), and Opik (1'9'30) in 

Estonia. 

Exeept for a relatively recent monograph on the 

l\1iddle Ordovician pelecypods of l{azakhstan ( l{halfin, 

1958) ~ Orclovioian pelecypods from other parts of the 

world have been described as incidental to n1ore general faunal studies, and only a handful of species is 

known. In Asia, Reed (1912, 1915) described a few 

species from the Himalayas and Burma, l{obayashi 

( 1934) and En do ( 1935) described some species from 

Korea and Manchuria, and Reed (1917) and Grabau 

( 1922) made some of the Chinese forms 1._·.-:nown. What 

little is known about South American Ordovician 

pelecypods is largely based upon the works of l{obayashi (1937), Harrington (1938), and Rusconi (1954, 

1955). Termier and Termier (1950) and Gigout (1951) 

have described a few shells from the North African 

Ordovieian. Little has been published about Australian, 

Tasmanian, and New Zealand Ordovician pelecypods, 

but a few species were described by Johnston (1888), 

Tate (1896), and Hill, Playford, and Woods (1969). 

Since the first Ordovician pelecypod was described 

in the middle 1830's, about 200 different generic names 

have been used for pelecypods of this period. About 125 

of these names are based upon Ordovician type species; 

approximately 100 of these latter names are use,ful or 

potentially useful, the other 25 being objective synonyms, obvious subjective synonyms, or based upon such 

poor material that their concepts may never be tied 

clown. As an estimate, based on what is presently known 

about Ordovician pelecypods, about 150 generic-level 

taxa would accommodate the morphological variability. 

This estimate is largely based on North American and 

western European faunas; how the extensive Ordovician faunas of Asia, South America, and Australia will 

alter this number when they become better known is 

of course uncertain. As a basis of comparison, Branson 

(1948) listed about 160 generic names which had been 

used for Permian pelecypods; in the past 20 years, 

Permian mollusks have been investigated far more, intensively than Ordovician ones, and a number of new 

generie names have been proposed for the pelecypods. 

On the species level, I know of about 1,400 names 

which have been used for Ordovician pelecypods (table 

1). lTnfortunately, most of these names are based upon 

n1olds and casts which have been little studied since 

the names 1-vere proposed, and there is no way to predict 

how many of them will prove to be meaningful conceptual designations. The general impression one obtains from the literature is that Ordovician pelecypods 

have been split too finely at the species level. Variation 
6 REVIEW OF ORDOVICIAN PELECYPODS 

studies on Ordovician pelecypods are in their infancy 

(~IcAlester, 19,63a), but on the basis of the Cincinnati 

arch silicified material such studies ean now be carried 

out for several species. Branson ( 1948) Ested about 

1,500 species level names which had been used for 

Permian pelecypods; there may be as many as 10,000 

names available for Cretaceous pelecypods (E. G. 

Kauffman, oral eon1mnn., 1968), and the estimates of 

the number of Holocene species are frmn 10,000 to 

20,000. 

Of the 1,400 Ordovician species names which I have 

indexed so far, aln1ost one-third of these are placed in 

only three genera: Otenodonta, 183 spec,ies; Oyrtodonta, 

116 species; and Al odiolopsis, 163 species; more than 

half of all the species names are placed in only 16 

generic-level taxa (table 1). 

At one time or another, Orclovieian pe1eeypods have 

been placed in at least 50 different family-level taxa, 

although all 50 names were not applied to the group at 

any one time. Recent \York suggests that about 15-20 

would be sufficient, with approximately half of these 

families having Ordovieian type genera. Vokes' (1967) 

classification included Ordovician peleeypods in 15 of 

51 superfamilies, 10 of 15 orders, and five of six 

subclasses. 

TABLE 1.-Alphabetic listing of the 228 generic names used for 

Ordovician pelecypods with the approximate number of species 

presently assigned to each genus 

[Author names for each genus can be found in Vokes (1967). The generic names listed 

include all those in which anyone has ever placed an Ordovician species. The 

species counts per ge-rms are based on the most recent work(s) which deals with the 

species concerned; as some species have not been revised for a long time, some are still assigned to genera which obviously do not occur in the Ordovician. Of the 

223 generic names listed, 18 belong to bivalved animals which also have been placed 

in the Conocardiacea, Ribeiriidae, or Conchostraca; some of these may be pelecypods, whereas others may be arthropods or distinct bivalved mollusks. Six of the 

223 generic names are Ulrich's (1894) informal taxonomic groups of the genus Cten- donta. If these 24 generic names are deleted there remain 199 generic names which 

have been used for Ordov:cian pelecypods. Of the l 43 genera whieh have Ordovieian 

type speeies, 18 belong to bivalved animals which may not be pelecypods and 

13 are objective synonyms. Of the 1,487 species, 68 belong to bivalves which may not be pelecypods leaving 1,419 names that have been applied to pelecypods] 

Genus Type species Ordovician in age 

Actinodonta_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ 

Actinomya_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Objective 

synonym 

Whiteavesia. 

Actinopterella_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ No _____________ _ Actinopteria_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ No _____________ _ Actinopterinia _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ Adranaria__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ Ahtioconcha _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ Allodesma_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ AllonycMa_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ Alnifia_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ Ambonych£a __________________ Yes _____________ _ Ambonychinia ________________ Yes _____________ _ Ambonychiopsis ___ ____________ Yes _____________ _ Amita _______________________ Objective 

synonym 

Tetinka. 

Amphicoelia __________________ , No _____________ _ 

Approximate 

number of Ordovician 

species 

presently 

assigned to each genus 

12 

1 

1 

1 

2 

1 

3 

5 

1 

40 

30 

14 

1 

Genus 

Ancilla _____________________ _ 

Anderkenia __________________ _ Angellum ___________________ _ 

Anodontopsis ________________ _ Anomalocoelia _______________ _ Anomalodonta _______________ _ Anoptera ____________________ _ Anuscula ____________________ _ 

Area _______________________ _ 

Aristerella ___________________ _ Astarte _____________________ _ 

Avicula ___ __________________ _ Aviculopecten ________________ _ Babinka ____________________ _ 

Bodmania ___________________ _ Boucekia ____________________ _ 

Byssodesma _________________ _ Byssonychia __ _______________ _ 

Cadomia ____________________ _ 

Callodonta __________________ _ Card£ola ____________________ _ Cardiolaria _____ _____________ _ Cardiomorpha _______________ _ Cardium ____________________ _ 

Caritodens __________________ _ 

Ceromyopsis __ _______________ _ Chaenodomus _________________ _ 

Cl eidophorus [ Clidophorus ] _____ _ Cleionychia [ Clionychia] __ _____ _ Clionopistha _________________ _ Colpomya ___________________ _ 

Conocardium ________________ _ Corallidomus _ _______________ _ Cornellites ___ ________________ _ 

Cosmogoniophorina ___________ _ Coxiconchia _________________ _ Ctenodonta __________________ _ nasuta group ____________ _ 

gibberula group __________ _ 

levata group _____________ _ 

pectunculoides group ______ _ recurva group ____________ _ logani group _____________ _ Cucullea ____________________ _ CucuZZella ___________________ _ 

Cuneamya ___ ________________ _ Cycloconcha _________________ _ Cymatonota __________________ _ Cypricardia _________________ _ Cypricardinia _______________ _ Cypricardites ________________ _ Cyrtodonta __________________ _ Cyrtodontula ________________ _ Davidia _____________________ _ Dcemska ___ _________________ _ 

D~pley.rodonta _______________ _ D~ste~ra ___ __________________ _ Dolabra __ __________________ -- Dualina _ ___________________ _ 

Ectenocardiomorpha __________ _ Ectenoptera _ ________________ _ 

Edmondia ___________________ _ 

Elasmodophora ______________ _ Endodesma __________________ _ Eoasmussia _________________ _ 

Type species Ordovician in age 

Objective 

synonym 

Sluzka. 

Approximate 

number of Ordovician 

species 

presently 

assigned to each genus 

Yes______________ 3 

Yes______________ 1 

No_ _ _ _ _ _ _ _ _ _ _ _ _ _ None 

Yes______________ 1 

Yes______________ 2 

Yes______________ 2 

Objective synonym _________ _ 

Babz'nka. 

No______________ 4 

Yes_ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

No______________ 2 

No______________ 11 

No______________ 1 

Yes _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

Yes_ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

Yes_ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 

Yes______________ 1 

Objective synonym _________ _ 

Ambonychia. Yes _____ ~________ 2 

Yes______________ 1 

No______________ 11 

Yes______________ 1 

No______________ 1 

No______________ None 

Yes_ _ _ _ _ _ _ _ _ _ _ _ _ 1 

Yes______________ 1 

Objective synonym _________ _ 

Cymatonota. Yes______________ 26 

Yes______________ 24 

No______________ 1 

Yes____ _ _ _ _ _ _ _ _ _ _ 7 

No______________ 13 

Yes______________ l 

No______________ None 

Yes______________ 3 

Yes______________ 2 

Yes______________ 183 

Yes _______________________ _ Yes _______________________ _ 

Yes _______________________ _ Yes _______________________ _ Yes _______________________ _ Yes _____________________ · __ _ 

No______________ 1 

Yes______________ 3 

Yes______________ 22 

Yes______________ 4 

Yes______________ 10 

No______________ 4 

No______________ 4 

Yes______________ 5 

Yes______________ 116 

Yes______________ 49 

Yes___ _ _ _ _ _ _ _ _ _ _ _ 2 

Yes______________ 2 

Yes______________ 2 

Yes______________ 1 

No______________ 1 

No______________ 1 

Yes______________ !J 

Objective syno- _________ _ 

nym Opisthoptera. No _____________ _ Yes _____________ _ 

Yes ____ ---------- Yes _____________ _ 

10 

1 

11 

1 
Genus 

Eoischyrina _________________ _ Eopteria ____________________ _ 

Eridonychia _________________ _ Euchasma ___ ________________ _ 

Euchasmella _________________ _ 

Eurymya _ _________________ -- Eurymyella _____ _____________ _ 

FiZ1:oza _________________ - __ ---

Filius _______________ - ____ ---

Gloria __________ -- ___ ----_---

Glyptarca ___________________ _ 

Goniophora __________________ _ 

Goniophorina ________________ _ 

Gosseletia ___________________ _ 

Grammysia _____ _____________ _ Heikea _____ _________________ _ 

H emicardium ________________ _ Hippomya _ _________________ _ Ischyrinia ___________________ _ 

Ischyrodonta _________________ _ Isoarca _____________________ _ 

Isocardia ___________________ _ Leda _______________________ _ 

Leptodesma _________________ _ 

Lithobia ____________________ _ 

Lunulacardium ______________ _ Lyonsia ___ __________________ _ 

Lyrodesma __________________ _ Lyronucula __________________ _ 

M acrodesma _________________ _ Maminka ___________________ _ 

Maryonychia ________________ _ 

M atercula ___________________ _ 

M atheria __ __________________ _ Megalodus __________________ _ 

~1egan~bonia _________________ _ 

M egaptera _ _________________ _ 

M odiodesma _________________ _ 

Modiola ____________________ _ 

~~ odiolodon _________________ _ 

111 odiolopsis _________________ _ M odiomorpha ________________ _ M yalina ____________________ _ 

M yophoria __________________ _ Myoplusia __________________ _ 

M ytilarca ___________________ _ 

M ytilops ____________________ _ 

M ytilus _____________________ _ ffucula _____________________ _ 

ffuculana ___________________ _ 

}{ uculites ___________________ _ 

Opistholoba __________________ _ 

Opisthoptera _________________ _ 

Orthodesma __________________ _ 

Orthodontiscus _______________ _ Orihon~a ___________________ _ 

Orthonotella _ ________________ _ Ortonella ____________________ _ J>alaearca ___________________ _ 

Palaeoconcha ________________ _ 

J>alaeoneilo __________________ _ 

J>alaeopteria _________________ _ J>alaeosolen _____ _____________ _ 

J>aracyclas __________________ _ 

J>arallelodon _________________ _ 

J>arallelodus __ _______________ _ 

J>aramodiola ____ _____________ _ 

J>aramytilarca _ ______________ _ 

HISTORICAL RESUME 

Type species Ordovician in age 

Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ 

No ____ ---------- Objective synonym Dceruska. 

Objective synonym Synek. 

Objective synonym Slava. 

Approximate 

number of Ordovician 

species 

presently 

assigned to each genus 

1 

7 

None 

2 

1 

4 

2 

Yes______________ 3 

No______________ 7 

Yes______________ .5 

No______________ 1 

No______________ 3 

Yes______________ 26 

No______________ None 

Yes______________ 2 

Yes______________ 2 

Yes______________ 10 

No______________ 8 

No______________ 2 

No______________ 4 

No______________ 3 

Yes______________ 1 

No______________ 3 

No_ _ _ _ _ _ _ _ _ _ _ _ _ _ None 

Yes______________ 26 

Yes______________ 1 

Yes______________ 2 

No______________ 2 

Yes______________ 1 

Objective synonym _________ _ 

11faminka. Yes______________ .5 

No______________ 1 

No_ _ _ _ _ _ _ _ _ _ _ _ _ _ None 

Objective synonym _________ _ 

Opisthoptera. Objective synonym _________ _ 

111 odiolops is. No _____________ _ 

Yes _____________ _ Yes _____________ _ No _____________ _ No _____________ _ 

No _____________ _ Yes _____________ _ No _____________ _ No _____________ _ No _____________ _ No _____________ _ 

No _____________ _ No _____________ _ 

Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ No _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ No _____________ _ Yes _____________ _ No _____________ _ No _____________ _ No _____________ _ 

Yes _____________ _ Yes _____________ _ Yes _____________ _ 

None 

19 

163 

6 

5 

1 

9 

13 

1 

3 

35 

5 

6 

None 

.5 

32 

None 

9 

1 

3 

9 

2 

9 

1 

3 

1 

2 

1 

2 

7 

Genus 

J>araphtonia _________________ _ 

J>atrocardia _ ________________ _ 

J>eriploma _____ ______________ _ 

J>holadornorpha ______________ _ J>hysetomya _ ________________ _ 

J>lethocardia __ _______________ _ 

J>lethom ytilus ________________ _ 

Pleurorhynchus ______________ _ 

J>osidonomya ________________ _ 

J>raeanomalodonta ____________ _ J>raearca ____________________ _ 

J>raecard Z:um _________________ _ J>raeleda ____________________ _ 

J>raeluc£na __________________ _ 

Praem yophoria _______________ _ J>raenucula __________________ _ 

J>rolobella ___________________ _ 

Prothyris ___________________ _ 

J>seudarca ___________________ _ 

J>seudaxinus ________________ _ 

J>seudocyrtodonta ___ __________ _ 

J>seudoeuchasma _____________ _ 

J>seudotechnophorus __________ _ J>siloconcha _________________ _ 

J>s ilonychia _________________ _ J>teria ______________________ _ 

J>terinea _ ___________________ _ 

Pteron ites ___________________ _ 

J>teronitina __________________ _ 

J>tychopterinia _______________ _ J>yanomya __________________ _ 

J>yrenomoeus ________________ _ Redonia ____________________ _ 

Rhombopteria __ ______________ _ 

Rhynchotropsis __ _____________ _ Rhytimya ___________________ _ 

Ribeirella ___________________ _ 

Ribeiria _ ___________________ _ 

Ribeirina ___________________ _ 

Saifordia _ __________________ _ 

Sanguinol~es ________________ _ 

Sedgwickia __________________ _ 

Serm:corallidomus _____________ _ Serv~or _____________________ _ 

Shanina ____________________ _ 

Shaninopsis _________________ _ 

Siliquarca __ _________________ _ 

8-imilodonta _________________ _ Slava _______________________ _ 

Sluha ______________________ _ 

Sluzka ______________________ _ 

Solen _______________________ _ 

Solerwmorpha ___ _____________ _ So~non~ya __________________ _ 

Sowteria ____________________ _ 

S pathella ____________________ _ Sphenolium _________________ - Synek ______________________ _ 

Tancrediopsis ___ _____________ _ 

T echnophorus ________________ _ 

T ellinites __________ - _------ --

Tellinomya __ ____________ - ----

Tenka ______________________ _ 

Tenuis _____________________ _ 

T etinka _________________ - - __ -

Thorslundia _________________ _ 

T olmachov ia _________________ _ 

Type species 

Ordovician in age 

Yes _____________ _ Yes _____________ _ 

No _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ No _____________ _ No _____________ _ No _____________ _ Yes _____________ _ Yes _____________ _ No _____________ _ Yes _____________ _ No _____________ _ 

Yes _____________ _ Yes _____________ _ Yes _____________ _ No _____________ _ Yes _____________ _ 

Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ 

Yes _____________ _ No _____________ _ No _____________ _ No _____________ _ Yes _____________ _ Yes ____________ _ Yes _____________ _ 

No _____________ _ Yes ____________ _ No _____________ _ Yes _____________ _ 

Yes _____________ _ No _____________ _ No _____________ _ Yes _____________ _ 

Yes ____________ _ No _____________ _ No _____________ _ Yes _____________ _ 

Objective 

synonym 

Sluha. Yes _____________ _ 

Yes ____________ --

Yes _______ ------- Yes _____________ _ No _____________ _ 

Yes ____________ -- No _____________ _ No _____________ _ 

No _____________ _ No _____________ _ 

Yes _____________ _ No _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ Yes _____________ _ 

No _____________ _ 

Objective 

synonym 

Ctenodonta. No _____________ _ 

Objective 

synonym 

Tenka. 

No _____________ _ Yes _____________ _ 

Yes _____________ _ 

7 

Approximate 

number of Ordovician 

species 

presently 

assigned to each genus 

4 

2 

None 

8 

1 

5 

1 

None 

4 

3 

3 

1 

4 

2 

1 

2 

8 

None 

3 

1 

2 

1 

1 

13 

2 

None 

31 

1 

2 

1 

2 

1 

7 

1 

1 

23 

1 

1.5 

1 

6 

2 

2 

3 

1 

18 

1 

1 

7 

1 

2 

1 

1 

1 

1 

1 

.5 

3 

2 

15 

1 

1 

1 

1 

1 
8 REVIEW OF ORDOVICIAN PELECYPODS 

Genus 

Type species 

Ordovician in age 

Vanuxernia_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ 

Vlasta_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ No _____________ _ 

TVanwanella_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ 

TVanwania ___________________ No ______________ _ 

TVanwanoiclea ________________ Yes _____________ _ 

TV arburgia_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Yes _____________ _ 

Whiteavesia __________________ Yes _____________ _ 

TVhitella _____________________ Objective synonym Cyrtodontula. 

CAMBRIAN BIVALVES 

Approximate 

n·umber of Ordovician 

species 

presently 

assigned to each genus 

50 

1 

1 

2 

2 

5 

20 

lTndonbted pelecypods are documented in the fossil 

record from the beginning of the Ordovician mnvard 

(Tremadoc-Holocene; figs. 5, 6) . Early Ordovicia11 

pelecypods have been identified from France (Barrois, 

1891; Thoral, 1935; Babin, 1966), Malaysia (Pojeta, 

herein), :.Manchuria (ICobayashi, 1933), North America 

(Billings, 1865: Butts, 19-±1: Cloud and Barnes, 19-1:8), 

South America (Harrington, 1938), S·weclen (SootRyen, 1969), and "'\Vales (Hicks, 1873). 

Because pelec.ypods are \Yell represented in the Early 

Ordovician, it is reasonable to infer that there must 

have been some Cambrian (pre-Tremadoc) ancestor ( s) 

of the group. However, the problem of what Cambrian 

animals can reasonably be assigned to the Pelecypoda 

is still a vexing one. The various Ca1nbrian bivalves 

\vhieh have been placed in the Pelecypoda are all suspect 

for one reason or another, and there have been long 

debates as to whether these Cambrian bivalves are 

pelecypods, arthropods, or unique bivalved animals. 

A group of Cambrian (pre-Tremadoc) bivalves which 

has sometimes been placed in the Pelecypoda (but which 

may be a unique group of bivalved animals), is rep'-

resented by the genera Bagenovia, Oambridium, 

(Horn}7 , 1957; Sytchev, 1960), and .8tenothecoides 

(Rasetti, 1954; Robison, 1964). These three genera have 

a peculiar muscle pattern and are not known to have 

had a ligament. Yochelson ( 1969) has described bivalved 

articulated speci1nens of Stenothecoides frmn the Lower 

Cambrian of Alaska and Siberia; his reconstruction of 

the soft tissues of this genus is not pelecypodlike, and he 

proposed a new elass of mollusks, the Stenothecoida, for 

the three genera. 

Of the various Cambrian bivalves the Early to Middle 

Cambrian genus F ordilla Barrande is probably the 

most pelecypodlike in external appearance (Barrande, 

1881; Lochman, 1956). Ulrich and Bassler ( 1931) 

placed Fonlilla in the Conchostraca: Raymond (19-1:6) 

regarded Fordilla as nn arthropod of uncertain position; Kobayashi (195-l:) felt it to be an open question as 

to "·hether F ordilla is a pelecypod or a couchostracan; 

and Poulsen (1932, 1967) regarded Fordilla as a. pelecypod. Arguments as to whether or not Fordilla is a 

pelecypod are based largely upon shell shape, thickness, 

and composition; little is knmvn about the internal 

features of the genus, although Barrande ( 1881) figured 

a specimen showing some n1usele scars and a structure 

resembling a pallial line. 

Morris (1967) placed the Early Cambrian-Late Ordovician group Ribeirioida in the Pelecypoda. However, 

he documents this phlcement only with the follo,ving 

statement ( 1967, p. 469) : 

The Bivalvia [Peleeypoda] may have separated as a distinct 

group of l\Iollusea by lateral compression as an adaptation to 

burrowing or ploughing through a soft substrate, i.e., originally 

infaunal. Primitive forms including the Ribeiroida [sic] attain 

this having a simple folded shell with a gape along the anterior, 

ventral and posterior margins; but more advanced groups develop an elastic ligament dorsally joining two calcified shells. 

It \Yould seem likely that early bivalved arthropods 

\Youlcl also have a simple folded shell. Kobayashi ( 1933, 

195-l:) in his studies of the ribeirids was impressed by 

their lack of pelecypod features and considered them to 

be arthropods. Both Morris and ICobayashi included 

some Ordovician genera in the ribeirioids which I feel 

are better allied to the concardiids, for example, 

EopteJ•ia Billings and Eu.chasma Billings; these genera 

arc :further discussed on page 22. 

Vogel ( 1962) described the species Lamellodonta 

simple.v from the ~1iddle Cambrian of Spain~ he classified the species as a pelecypod. The specimens upon 

which L. simpleJ.~ is based are deformed and all the 

features which Vogel indieated on his reconstructions 

are not readily seen on his plate figures. However, some 

of the figures do shmv \vhat appear to be elongate teeth; 

the presence of these apparent teeth suggest that the 

form may be a pelecypod. Better illustrations and more 

specimens of L. si1nplex are needed before its pelecypod 

nature. can be unequivocally established. 

At one time or another, about 34 species of Cambrian 

animals have been placed in the Pel~cypoda (table 2). 

In my opinion, none of these species can be unequivoeally regarded as a Cambrian pelecypod, although some 

them sh:ow s01ne features found in pelecypods. 
ACTINODONTOIDA 9 

TABLE 2.-The 17 generic names that have been applied to Cambrian animals which at one time or another were thought to be 

pelecypods 

Genus 

Ambonychia ___________________________________ _ Bagenovia _____________________________________ _ 

Cambridium ___________________________________ - Ctenodonta ____________________________________ _ Cypricardia ___________________________________ _ Davidia _______________________________________ _ FordiUa _______________________________________ _ 

Lamellodonta _________________________________ -- M odioloides _ _: ________________________________ --

~~i!~~s~~~===========================~======= Palaeoneilo ___________________________ - - - - - - - - - -

Stenothecoides ~it~t:i~~~~~================================== _________________________________ - -

~:~~~~i~===================================== 

ORDOVICIAN PELECYPODS 

ACTINODONTOIDA 

Approximate 

number of Cambrian 

species which 

have been 

placed in 

each genus 

1 

3 

2 

5 

1 

3 

2 

1 

1 

4 

1 

1 

1 

1 

5 

1 

1 

Three Ordovician families ( Cycloconchidae, Lyrodesmatidae, and Redoniidae) seem to be related to one 

another on the basis of a common dental pattern and 

can be united in an upper level taxon. There is a serious problem as to what to call this taxon. Douville 

(1912, 1913) placed Actinodonta, Lyrodesma, JI,J odiolopsi,s, Redonl~a, and others in his higher taxon Actinodonta, based on what he regarded as a common 

dental pattern among these genera. Dechaseaux (1952) 

placed Actinodonta, Lyrodes1na, and the families Ambonychiidae, Anthracosiidae, and. Cyrtodontidae in a 

suborder Actinodonta of the order Taxodonta. These 

groupings are extremely broad, and unite diverse 

stocks under one heading on a pre~umed relationship 

between diverse dental patterns. 

Newell (1965) placed the Carydiidae, Cycloconchidae, Lamellodontidae, and Modiomorphidae in the 

order Actinodontoida ; at the same time he allied the 

Lyrodesmatidae questionably to the order Trigonioida, 

and placed the Actinodontoida, Trigonioida, and Unionoida in the subclass Palaeoheterodonta.. 

As an ordinal-level taxon, the Actinodontoida 

( Actinodonta) has at one time or another included n1ost 

Ordovician, nonnuculoid, dentate pelecypods. It has 

been a convenient wastebasket grouping thalt was either 

vaguely defined or else defined on the basis of features 

which were equivocally possessed by a number of forms 

placed in the order. 

Cox ( 1960) proposed that Dall's ( 1900) name 

Pantodontida be used for a taxon which included: 

Actinodonta, Allodesnw, Oycloconcha., I schyrodonta, 

Lyrodes1na, and Redonia. This proposal has the advantages of eliminating the confusing term Antinodonta 

( Actinodontoida) as an ordinal-level taxon and of not 

allying the modiomorphids to the other included 

groups. However, Cox's concept of the Pantodontida 

was significantly broader than Dall's which included 

only Allodesma and Oyclocmwha, and the na1ne Pantodontida is little known. 

Further, Allodesma is founded on poor material (pl. 

2, figs. 1-5). Ulrich's ( 1894) reconstruction of the hinge 

needs to be corroborated (fig. 1F, G) and based on 

wha,t is presently known of the genus it ca1mot be 

allied to Actinodonta, Oycloconclw, Lyrodes1na, and 

Redonia. lschyrodonta is a problematic form, some 

species of which may possess a duplivincular ligament 

(pl. 1, fig. 6) ; if this is so, these species might better be 

allied to the Cyrtodontidae as suggested by Ulrich 

(1893 [1895]). 

In spite of its obvious drawbacks, it seems best to 

use the name Actinodonta, as Actinodontoida, for a 

grouping including the Cycloconchidae, Lyrodesina.tidae, and Redoniidae. Actinodontoicla is widespread in 

the literature, and at one time or another has included 

all of the groups which I would place in it. Short of proposing a new name it is a matter of redefining Pantodontida which has not been widely used or redefining 

Actinodontoida which often appears in the literature. 

What the latter has lacked is an adequate conceptual 

base; my definition of Actinodontoida follows. 

Phylum MOLLUSCA Cuvier, 1797 

Class PEL.ECYPODA Goldfuss, 1820 

Subclass HETEROCONCHIA Hertwig, 189.5 

Order ACTINODONTOIDA Douville, 1912 

Shell equivalved, inequilaterwl; beaks prosogyral or 

opisthogyral; nonbyssate ~ scmlpture usually of concentric growth lines, sometimes with a few radial ribs; 

liga1nent opisthodetic, elongated, and parivincular. 

Pallial line continuous in attachment, integropalliate 

or sinupalliate; dimyarian, adductors subequal, anterior 

adductor supported by a n1yophoric buttress on its 

posterior face; pedal muscles, two or 1nore pairs; dentition flaring, ventrally divergent, with all of the teeth 

reaching or nearly reaching the beaks; at least primitively, the posterior teeth extend the full length of the 

dorsal margin posterior to the beaks and extend under 

the ligament. 
10 REVIEW OF ORDOVICIAN PELECYPODS 

The Ordovician range of the Actinodontoida is 

Arenig-Richmond (late Early Ordovician-late Late 

Ordovician) . 

This definition is sufficiently broad to include nonOrdovician for1ns such as the Carydiidae Haffer ( 1959) 

which may be late surviving actinodontoids; it is framed 

so as to exclude forms with a duplivincular ligament 

and all byssate groups. 

Babin ( 1966) used the ordinal name Pantodontida for 

essentially what I have called Actinodontoida. He defined the Pantodontida as being inequivalved; this is 

probably a misprint as each of the genera concerned is 

equivalved, and Babin defined them as such. 

CYCLOCONCHIDAE 

Two genera are herein included in the Cycloconchidae. Oycloconcha Miller (pl. 2, figs. 6-21; pl. 3, figs. 

1-4) is known from about 200 specimens from Middle 

and Upper Ordovician rocks from the tristate area of 

Ohio, Indiana, and Kentucky. The genus presently includes four named species all of which are small, the 

largest known specimen being 30 mm long. Oycloconcha 

possesses well-defined cardinal, anterior lateral, and 

posterior lateral teeth (pl. 2, figs. 14-17) ; the teeth are 

nmnerous and all reach or nearly reach the beaks. In 

addition, the genus is elongate in an anterior-posterior 

direction (pl. 2, figs. 6, 7) and has an external, elongate 

liga1nent posterior to the prosogyral beaks (pl. 2, figs. 

12, 18, 21), an integropalliate pallial line (pl. 3, figs. 1, 

2), and multiple pedal scars extending between the adductors (pl. 2, figs. 8, 9; pl. 3, fig. 3). 

Actinodonta Phillips (pl. 1, figs. 3-5) has been reported frmn the lower Middle Ordovician rocks of Great 

Britain and Morocco (Lla1ivirn and Llandeilo), but it 

is best known from the Armoricain Sandstone of Arenig 

age (Early Ordovician) of Brittany. It too is a small 

shell, generally less than 50 1n1n long. Although the 

details of the morphology of Actinodonta are poorly 

known, many of the published figures of speeies of the 

genus show a hinge line with numerous well-developed 

diverging teeth all of which reach or almost reach the 

beaks (pl. 1, fig. 3). Commonly the teeth can be divided 

into cardinal, anterior lateral, and posterior lateral eleInents; as in Oycloconcha the posterior lateral teeth run 

the length of the hinge line posterior to the beaks (pl. 

1, fig. 5). Babin ( 1966, p. 230) illustrated the hinge lines 

of several speeies of Actinodonta. 

Based upon the similarity of dentition a close phylogenetic relationship is indicated between Oycloconcha 

and A ctinodonta. 

L YRODESMATIDAE 

The Lyrodesmatidae is presently regarded as a 

monotypic family~ although Ly1'odes1na Conrad will 

probably be. subdivided when it is studied in1nore detail; 

Fischer ( 1886) and Stewart ( 1920) suggested bases for 

subdividing the genus. Babin (1966) placed Siliquarca 

Tromelin and Lebesconte [Pseudarca Tromelin and 

Lebesconte] in the family. Siliquarca is usually considered to be a nuculoid (McAlester, 1968) ; however, 

it is so poorly known that its affinities are uncertain. 

Lyrodesnw as presently recognized is primarily a 

Middle and Late Ordovician genus occurring in North 

America and Great Britain (pl. 3, figs. 5-23); it may 

range into the Silurian as noted by Ziegler, Cocks, and 

Bambach (1968). However, at least two species of 

similar animals ( L. a1'moricana Tromelin and Lebesconte and L. ac1uniTwta (Barrois)) are known from 

the Lower Ordovician (Arenig) rocks of Brittany 

(pl. 3, fig. 11; fig. 1A -E). L. acurnin.)ata was originally 

placed in N1wulites by Barrois (1891), however, as 

figured by him and by Babin ( 1966) it is most probably 

a species of Lyrodesrna. 

The Middle and Late Ordovician species of 

Lyrodesnw have a prominent dentition which flares 

outward from~ but is concentrated immediately below, 

the beaks (pl. 3, figs. 10, 15, 20, 23). At first glance this 

appears to be distinct from the dentition of the Cycloconchidae. However, in some species of Middle and Late 

Ordovician Lyrodesmas the posterior teeth are significantly longer than the other ,teeth (pl. 3, figs. 9, 23); 

further, Barrois ( 1891) figured specimens of L. arrnoricana (Early Ordovician) which have prominent posterior lateral teeth that extend the length of the dorsal 

margin posterior to the beaks (fig. lA-O). I have made 

a very serious attempt to locate Barrois' specimens of 

L. arnwricana but have been unable to find them. However, Dr. Claude Babin has sent me a specimen of this 

species '" hich shows the dentition (pl. 3, fig. 11). It 

is a shell with Lyrodesma shape and prominent posterior lateral teeth and sockets which run the length 

of the posterior dorsal margin. 

Thus~ the oldest known members of the Lyrodesmatidae h.ave a dentition similar to that of the Cycloconchidae. In some of the Middle and Late Ordovician 

Lyrodesmas the posterior teeth are still significantly 

longer than the other teeth (pl. 3, figs. 9, 23), although 

they no longer occupy the entire dorsal margin posterior to the beaks; in other Middle and Late Ordovician Lyrodesmas (pl. 3, figs. 10, 15, 20) the posterior 

teeth are not appreciably different in size fron1 the other 

teeth. This reduction in the length of the posterior 
ACTINODONTOIDA 11 

lateral teeth is the most obvious trend in the evolution 

of lyrodesmatids; it is a trend not seen in the Ordovician cycloconchids. 

Lyrodesrna is unique in that it is the earliest known 

siphonate pelecypod which possesses a pallial sinus 

(pl. 3, figs. 16-18 ). This feature must be strongly 

emphasized for it indicates that infaunal siphonate 

pelecypods originated early in the history of the class 

and not in the middle or late Paleozoic as is sometimes 

suggested. 

REDONIIDAE 

Babin (1966) proposed the family Redoniidae for the 

Early and Middle Ordovician genus Redonia Rouault. 

Redonia is not known to occur in North America, and 

I have seen few specimens of the genus; therefore, the 

following discussion is based largely upon the literature, 

especially upon the recent review of the group by Babin. 

The dentition of Reclonia (pl. 1, fig. 7; fig. 2A- O) 

differs from that of other actinodontoids in that the 

number of teeth per valve is reduced. In lyroclesmatids 

A B 

H 

(pl. 3, figs. 10, 15, 20, 23) and cycloconchicls (pl. 2, figs. 

14, 15) it is common to have five or six teeth per valve, 

and there may be as many as seven or eight (pl. 3, fig. 

12); rarely there are as few as four teeth per valve 

(Babin, 1966, p. 230, fig. 1). According to Babin ( 1966, 

p. 243), redoniids have one or two long posterior lateral 

teeth and one or tv,;o short anterior teeth (pl. 1, fig. 7; 

fig. 2A -0). Especially important in relating the 

redoniids to the cycloconchids andlyrodesmatids are the 

observations that all the teeth reach or nearly reach the 

beaks, and that the posterior lateral teeth extend the 

length of the dorsal margin posterior to the beaks. 

Reclonia shows such other actinoclontoid features as a 

myophoric buttress supporting the posterior face of the 

anterior adductor muscle and an external ligament. 

At one time or another, Redonia has been allied to 

several other pelecypod groups. Most recently Chavan 

(1954, 1966a, b, 1967) regarded it as being a carclitacean 

belonging to the family Permophoridae [Kalenteridae] 

c 

E I 

FIGURE 1.-Lyrodesrna, Allodesrna, Plethocardia, and 1imbonychia from various: authors. A- 0, Lyr·odesrna arnoriccma from Barro•is (18!)11). D , E, Lyrodesma acum·inata from HarTO·is (1891). Ji', G. 

Allodesma subeltiptic·urn, reconstruction of hinge line from Ulrich (1894) . 8-ee also plate 2, figures 2 

and 5; H, Plethocardia mnbonata, reconstruction of hinge line from Ulrich (1894). See also 

plate 14, figm'e 9. I , Ambonychia carinata from Goldfuss (1836). A-Hare X 2; I is natural Slize. 
12 REVIEW OF ORDOVICIAN PELECYPODS 

A 

B 

c FIGURE 2.-Redonia cleshayesi Rouault. 

Drawings o.f casts from Babin ( 19GG). 

A, X 5. B, 0, X 3. Reproduced with 

permission 00: the author. 

on the basis of his interpretation of the homologies of 

the teeth of Redonia using Bernard's notation. 

Newell (195'7) included Redonia in the mytiliform 

family Modiomorphidae [.Modiolopsidae] on the basis 

that at least some modiomorphids have posterior lateral 

teeth extending backward from the beaks under the 

ligament. This does not seem to be the so among Ordovician modiomorphids; species in which the hinge line 

is "·ell known are either edentulous (pl. 17, figs. 1, 3, 

11, 13, 15) or possess only cardinal teeth (pl. 13, figs. 6, 

8) . This topic will be further discussed below in the 

section entitled Modiomorphidae. 

The oldest known specimens of Redonia arc from the 

Arenig rocks of Brittany (Barrois, 1891; Ba:bin, 1D66) 

and south -central France ( Thoral, 1935). 

BABINKIDAE 

The Babinkidae is a monotypic taxon represented by 

the now well-known genus Babinka Barrande which 

contains the two species B. prin'ba Barranda, 1881 (pl. 1, 

figs. 12- 14) and B. oelandensis Soot-Ryen, 196D. 

At the time the concept of the .Monoplacophora was 

being constructed, in the early and middle 1950's, 

Vokes (1954) briefly reviewed a few species of early 

Paleozoic pelecypods which possess multiple pedal scars. 

The species reviewed included B. prima, and Vokes felt 

that the multiple pedal scars indicated a phylogenetic 

relationship between monoplacophorans and early 

pelecypods. 

Horny (1D60) considered monoplacophorans and 

multiple-muscled hypothetical pelecypods as having 

arisen indeipe.udently :from an annelid ancestor. He regarded B abinka as being the closest known pelecypod 

to the hypothetical diplacophoran pelecypod ancestor. 

He placed Babinka in a separate order of pelecypodsthe Diplacophora-and felt that all pelecypods were 

descended from this type of ancestor. 

McAlester (1964, 1D65, 1966) described the shell 

morphology of Babinka in detail, discussed its taxonomic position within the Pelecypoda, and speculated on 

its relationship to the Monoplacophora. 

Babinka znima is known from about 136 specimens 

from rocks which range in age from late Tremadoc to 

about Llanvirn (early Early Ordovician to early Middle 

Ordovician) in south-central France (Thoral, 1935·; 

Dean, 1966) and Bohemia (McAlester, 1964,1965, 1966), 

and thus it is one of the earliest known undoubted 

pelecypods. McAlester did not regard Babinlca as the 

stem stock from which all other pelecypods arose. Rather 

he presented convincing documentation that Babinka is 

the earliest known lucinoid pelecypod; previously 

lucinoids had not been reported from rocks older than 

Middle Silurian, and none are presently known between 

the early Middle Ordovician and the Middle Silurian. 

Lncinoids are in faunal suspension feeders; they eli ffer 

from other pelecypods having this mode of life by 

lack of a posterior inhalcnt siphon, although they have 

both anterior and posterior inhalent currents and some 

have a posterior exhalent siphon (Allen, 1958). In 

all lucinoids, the anterior inhalent current is the main 

feeding and respiratory current. Such an anterior inhalent current is regarded as a phylogenetically 

primitive feature in various taxodonts and solemyids. 

However, Allen (1958, p. 480) considered the anterior 

inhalcnt current of lucinoids to be a secondary specialization on the basis of the observation that living forms 

have the posterior inhalent and exhalent apertures of 

typical pelecypods. 

Lucinoids use the foot for burrowing and locomotion 

and also for the construction of a mucous-lined anterior 

inhalent tube which connects the front edge of the mantle cavity with the water-sediment interface. The pos-
BABINKIDAE 13 

terior exhalent current discharges either directly into 

the sediment or to the surface through a retractable posterior siphon. Correlated with this specialized mode of 

life is a characteristically elongated anterior adductor 

muscle which has a complex ciliary sorting mechanism 

for direct.ing food to the mouth. Commonly, especially 

in the family Lucinidae, the anterior end of the shell 

is prominently expanded. 

Babinka has an anteriorly expanded shell; the anterior adductor muscle scar is somewhat larger than 

the posterior one, but it is not nearly so elongated as 

in later lucinoids (pl. 1, fig. 14). McAlester (1965) 

also described a vague elongated impression below the 

anterior adductor scar in Babinka which he felt suggested that the ciliary sorting mechanism might have 

been developing. In general external physiognomy, 

Babinka is lucinoid, and the bulk of its other shell features fall within the range of variation expressed by 

later lucinoids. One would not expect the earliest members of a group to exhibit all the complex of characters which the later members of the group possess. At 

the very least, Babinka shows some lucinoid features, 

it is the only Ordovician form known to exhibit these 

tendencies, and it is a fair appraisal of our present 

knowledge to regard Babinka as the earliest lucinoid 

related to members of the group which became prominent in Silurian time. 

The chief critic of the lucinoid assignment of B abinka 

is Chavan ( 1966a). He has pointed out that B abinka 

is morphologically further removed from Silurian 

lucinoids than the latter are from post-Paleozoic members of the group. This is especially true in the elongation and digitation of the anterior adductor scar which 

is prominent in the Silurian lucinoid Ilionia Billings 

but almost absent in Babinka. Chavan felt that the 

dentition of Babinka is not comparable to lucinoids, and 

that such features as anterior shell elon~gation and lack 

of a pallial sinus are too widespread among many 

groups to have significance in placing Babinka in the 

lucinoids. 

Chavan did not derive the lucinoids from Babinka 

a,nd he placed the genus in the Actinodontoida. Babinka 

docs not have actinodontoid dentition, as least not in 

the sense that I have defined this feature (p. 9). Unfortwlately, the dentition of Babinlca is known only from 

the youngest (early Middle Ordovician) representatives 

of the genus. If the older representatives of the genus 

n,re found t·o have the elongate posterior teeth of 

actinodontoids, then Babinka can he placed in the Actinodontoida. If B abinka never had such teeth, then it 

and the younger lucinoids probahly form a linea.ge 

distinct from the other heteroconchians and should 

be placed in a separate subclass. 

421 - 895 0- 71 - 3 

At the same time that McAlester related Babinka 

to the lucinoids, he postulated that Babinka was a 

direct descendant of monoplacophoran (or monoplacophoranlike) mollusks and that B abinka (and therefore the lucinoids) arose independently of other pelecypods indicating that the pelecypods are "polyphyletic" 

and that for these reasons the lucinoids should be taxonomically separated from other pelecypods at a high 

taxon level. His arguments on these latter points are 

based upon a series of comparisons of the muscle scars 

of Babinka prirna to the musculature of Neopilina 

galatheae Lemche. McAlester rightly placed only secondary emphasis on the multiple pedal scars of Babinka 

as indicating a relationship to the Monoplacophora; 

rather he based his arguments on a set of small accessory muscle scars and the total muscle scar pattern of 

Babinka which he regarded as being close to that of 

N eopilina galatheae. 

Many groups of pelecypods, both living and fossil, 

are known to possess multiple pedal or multiple byssal 

muscles; these muscles are used for movements of the 

foot or for adjustment on the byssal anchorage. Two 

pairs of pedal muscles are the common situation in 

living heteroconchian pelecypods. However, some living nuculoids, cardiids, pteriids, and mactrids have 

from three to five pairs of pedal muscles (McAlester, 

1965, p. 234; Newell, 1937 [1938], p. 21). Among Paleozoic pelecypods, multiple pedal or byssal scars are 

known in several groups including: nuculoids (Driscoll, 

1964, p. 62), modiomorphids (pl.13, figs. 7, 11), ambonychiids (pl. 10, fig. 17), myalinids (Newell, 1942, p. 30), 

cycloconchids (pl. 2, figs. 8, 9; pl. 3, fig. 3), and babinkids (pl. 1, figs.12-14); if anything, the condition seems 

to be more widespread in the Paleozoic. Because multiple pedal or byssal scars occur in a number of unrelated and variously specialized recent and fossil pelecypods, this feature by itself does not indicate an especial 

relationship of any one stock to the l\fonoplacophora. 

B abinka has eight pairs of pedal scars nmning between and over the adductor scars, and ventral to the 

pedal scars are numerous pairs of smaller accessory 

scars (pl. 1, figs. 12-14). Neopilina galatheae also has 

eight pairs of pedal muscles and has numerous pairs 

of smaller muscles laterad the pedal muscles (fig. 3A); 

these smaller muscles serve as pallial, ctenidial, and 

visceral muscles. 

Neopilina galatheae has five pairs of ctenidial retractors on each side of the body, and these are situated 

between the third and seventh pedn.l muscles (fig. 3A); 

the numerous smaller accessory muscle scars of Babinka 

are situated approximately between the third and seventh pairs of pedal muscles (although they almost 

reach the second pair of pedal muscles) and have been 
14 REVIEW OF ORDOVICIAN PELECYPODS 

FIGURE 3.-Monoplacophorans. A, Reconstruction of body musculature of Neopilina galatheae modified 

from Lemche and Wingstrand (1959, pl. 35, fig. 121). X % of their figure. Lettered muscles 

are the pedal r etractors, and blackened muscles are the ctenidial retra~tors. Repr()lducecl with 

permission of the authors. B, Pedal retractor muscle scars of PiUna from Knight and Yochelson 

(1960). a, Pedal retractor musde s~ars orf A1·chacophiala from Knight and Yochelson (1960). 

B and a are natural size and are from the Treatise on Invertebrate Paleontology, courtesy of 

The Geological Society of Ameri-ca and The University of Kansas. 

called ctenidial retractors (pl. 1, figs. 12- 14). The proposed rela.tionship of Babinlca to the Monoplacophora 

is based upon the similarity in the number of pedal 

scars and, ·more importantly, upon the lJositioning of 

the smaller gill retractors of N eopilina galatheae and 

more or Jess similar scars of Babinka prima between the 

third and seventh pedal scars in the former species, and 

approximately between the third and seventh pedal 

scars in the latter species. 

McAlester (1965) also pointed out that the Silurian 

monoplacophoran Pilina Koken has eight pairs of pedal 

retractors, and he showed that this number also occurs 

in early Paleozoic forms. However, the distribution of 

the pedal retractors in Pilina (fig. 3B) is quite different 

from that of N eopilina galatlwae (fig. 3A). The three 

anteriormost scars of Pilina may represent multiple 

origins of only one muscle; this is the interpretation 

given by Knight and Yochelson (1960) for a more or 

less similar arrangement of pedal scars in the Ordovician monopla.cophoran Archaeophiala Perner (fig. 30). 

The number of pedal retractors in early Paleozoic monoplacophorans ranges widely from the possible eight 

pairs in Pilina to two pairs in Oyrtonella Hall. Eight 

pairs of linearly arranged pedal retractors, which represent the known maximum for monoplacophorans, occurs unequivocally only in one species of the Holocene 

genus N eopilina and at best is not a common condition 

in early Paleozoic monoplacophorans. Thus, to extrapolate from a living monoplacophoran to an Ordovician 

pelecypod on this basis le~Lves a strong element of uncertainty. 

The numerous smaller scars of Babinka are known 
NUCULOIDS 15 

from only one specimen of that genus; their positioning 

approximately between the third and seventh pedal retractors, though similar to the positioning of c~enidial 

retractors in N eopilina galatheae, may be forttntous as 

the variation or lack of variation of this positioning in 

Bablnka cannot be established at the present time. 

Furthermore, additional living species of N eopilina 

have been described which have a different number of 

gills than N. galatheae. N. Moingi Clarke and Menzies 

( 1959) is known to have six pairs of gills; although the 

details of the anatomy of this species a.re not yet available, it presumably has six pairs of gill retrae~o~rs on 

each side. It is not known if all of these are positiOned 

between the third and seventh pair of pedal retractors. 

In some groups of pelecypods, such as the astartids, 

a variable number of small muscles originate high in 

the umbonal cavity (pl. 1, figs. 1, 2) and insert into 

various organs in the visceral n1ass. In some of the Miocene Astartes from Chesapeake Bay there a.re frmn one 

to seven pairs of such muscle sears in a single species. 

These Inuscles, rather than the branchial retractors of 

Neop.ZZina galatheae, may be the homologues of the 

numerous small accessory n1uscles of B abinka. 

Proponents of the monoplacophoran-Ba:binka, relationship feel that the muscle patterns in Babinka prima 

and N eopilina galatlzeae are too similar to be entirely 

the result of chance and that it is reasonable to in·fer 

that the pedal and small accessory sears of Babinka 

represent and inheritance frmn some sort of monoplacophoran ancestor. I feel that the gaps in knowledge 

of the variation in the small accessory scars of B abinka 

and the gill retractors of Neopilina, the lack of demonstration of the occurrence of eight linearly arranged 

pairs of pedal retractors in early Paleozoic monoplacophorans, and the presence of possible homologues 

of the small accessory muscles o~f Bablnka in other 

groups of pelecypods weigh heavily against the probability of a Babinh~a-Inonoplaeop1l0ran relationship exelusive of all other pelecypods. At the present time 

there is no need to separate the lucinoids from all other 

pelecypods at the subclass level for reason of a possible 

relationship of this group to the Monoplacophora. However, as discussed above, Ba'binka and the lucinoids 

should perhaps be separated at the subclass level for 

other reasons. 

The probable lucinoid relationship of Babinka is one 

of the links in the chain which points up the diverse 

origins of various later pelecypod taxa in Ordovician 

ancestors. Ordovician pelecypods do not form some sort 

of undiffe·rell'tiated "plastic" stock w hieh frorm tilne to 

tim,e gave rise to later groups; a.l.ready by Ordovician 

time, pelecypods had differentiated into several ma.jor 

phyletic lines which are not readily related to one another, or to another molluscan group, on tJhe basis of the 

known fossils. 

NUCULOIDS 

Until reeently, most Ordovician nueuloids were placed 

in the single family Ctenodontidae; t~1is arrangemen~ 

is now being questioned, and the family-level taxa of 

the group are in a state of flux. . . 

To date no Ordovician nuculoids with a reslllfer have 

been discovered; all have a continuous tooth row with 

no ligament pit interrupting it (pl. 4, figs. 13, 17, 18, 

20 ; pl. 5, figs. 3, 20; pl. 6, fig. 9). Ulrich (1894) noted 

that Late Ordovician species of what he called the 

Otenodonta levata group ha.ve a sn1all undefined pit 

beneath the beak, whereas Middle Ordovician species 

of this group do not, I have examined Ulrich's Late 

Ordovician specimens of the species eoncerned (pl. 5, 

figs. 14-16), and in my opinion the material is not 

well enough preserved to establish the presenee of such 

a. pit. In most Ordovician nuculoids the teeth 'below the 

beaks are very small, and it is only on the best df 

specimens that they can be seen. Pfab ( 1934) indica~ed 

the presenee of a ligament pit in some of the Bohemian 

Ordovician nuculoids; this structure is clearly indicated 

on his text figures but is not obvious on his photographs. 

Thus, on the basis of what is presently known, the 

evolution of a resilifer in nuculoids seems to have !been 

a post-Ordovician development. 

Ordovician nueuloids are a highly varied and successful group, although this fact has been hidden to 

a large extent by the plaeement of most of them in one 

of two genera. Oleidophorns Hall has been used for 

those speeies having a prominent anterior myophoric 

buttress (pl. 6, figs. 1, 2) which leaves a slit-like impression in n1olds, and Otenodonta Salter has been used 

for those forms supposedly lacking a prominent anterior 

buttress. It is now generally felt that Oleidopho·ru.s is 

a synony1n of Nuculites Conrad, a name long used for 

similar Silurian-Devonian shells, and indeed there is 

relatively little morphologic. diversity in this stock. 

On the other hand, Otenodonta means many things 

to many people; the name has been used so widely for 

so many different nuculoids that the only information 

it now conveys is that a nuculoid is being described. 

Smail lV ucul a-like shells (pi. 5, figs. 1-6) , large 

Numtlana-like shells (pl. 4, figs. 6, 7), and a host of 

intermediate shell shapes (pl. 1, figs. 8-11; pl. 5, figs. 

7, 8; pl. 6, figs. 9-15) have all been placed in Otenodonta. 

At least 180 Ordovician nuculoid species have been 

placed in Otenodonta, and the name has been used for 

some nueuloids in every Paleozoic system. 

Ulrich (1'894) divided Otenodonta into a series of 

informal taxa, each of which was named after a "typical" species and called a group. His informal nomen-
16 REVIEW OF ORDOVICIAN PELECYPODS 

clature has been used by a few workers but has not 

gained widespread acceptance; son1e of his groups are 

clearly generic-level taxa. A few workers have proposed 

additional generic-level taxa for Ordovician nuculoids; 

however, for the most part these names have not been 

widely used. In some taxa this was due to poor initial 

conceptualization; a few names were consciously 

avoided (for example, Palaeoconcha Milier; Ulrich, 

1894, p. 580), and in North America in particular almost all na'mes except Ctenodonta and Cleidoplwr"l.t8 

were simply neglected. 

North American Ordovician nuculoids as known at 

the present time belong to a minimum of eight genericlevel taxa: Ctenodonta Salter (pl. 4, figs. 1-24), 

Deceptriw Fuchs (pl. 5, figs. 7 -20), Jl,f yoplusia N eumayr 

(pl. 6, figs. 3-5), Nuculites Conrad (pl. 6, figs. 1, 2), 

Palaeoconchct ::Miller pl. 6, figs. 6-8), Palaeoneilo HaU 

and Whitfield (pl. 1, figs. 8-11), Shnilodonta Soot-Ryen 

(pl. 5, figs. 1-6), and Tancrediopsis Beuhausen (pl. 6, 

figs. 9-15). Further, some authors recognize Praenucula 

Pfab as being distinct from Deceptriw, and the known 

material suggests that at least three new genera have 

not been named. There may be as many as 112 genera 

of North American nuculoids where previously only 

two genera were usually recognized. In Europe at least 

two additional Ordovician genera are recognized : 

Cardiolaria M1mier-Chalmas and Cadmnia TrmneEn; 

Pseudarca Tromelin and Lebesconte is a European 

genus which is usually classified as a nuculoid, however, 

its affinities are uncertain. 

The na1ne Ctenodonta was originally proposed for 

large opisthogyrate N'lwuiana-form shells, Tellin.omya 

nasnta Hall being the type species (pl. 4, figs. 1-3). 

The name should be restricted to this general type of 

shell. In eastern North America this type of shell is 

known to range from the Murfreesboro Limestone (Porterfield Age) (pl. 4, figs. 11, 12) to the Waynesville 

Shale and Kaga wong beds ( Rich1nond Age) (pl. 4, 

figs. 8, 9). In western North America, shells assignable 

to Ctenodonta are known from the Antelope Valley 

Limestone of Nevada (pl. 4, figs. 16, 17) and from the 

Ordovician of the Seward Peninsula of Alaska (pl. 4, 

figs. 14, 15). Elsewhere in the world, Ctenodonta s. s. 

has been reported from the Ordovician Gordon Limestone of Tasmania (Johnston, 1888, pl.. 5). Recently 

acquired shells frortn the Ordovician part of the Setul 

Formation of Malaya (probably latest Early Ordovician, Y ochelson and Jones, 1968) are the oldest known 

specimens of the genus (pl. 4, figs. 20~22). 

The name Tancrediopsi.s, proposed about 70 years ago, 

was little used for Ordovician shells until recently 

(McAlester, 1963a). It is used for small triangular 

shells whose stratigraphic distribution is not well kno\vn 

(pl. 6, figs. 9-15), but "'hich are found in the ~fiddle 

and Upper Ordovician rocks of North America. Among 

the oldest specimens assignable to this genus are those 

from the Antelope Valley Limestone of N eyada (pl. 6, 

fig. 14). Some of the shells figured by En do ( 1935) 

under the name Ctenodonta takalzashii from the J(nngyao Formation of Manchuria may belong to 

Tancredio psi:s. 

Many posteriorly auriculate and 'anteriorly elongate 

North American nuculoids haye long been referred to 

Ctenodonta (pl. 5, figs. 7-22). Ulrich (1894) assigned 

these shells to his Ctenodonta leNda group and subsequent to his work at least three generic names \Yere proposed for shells of this .general character: Deceptriw 

Fuchs (1919), Pradeda Pfab (1934), and Praenucula 

Pfab (1934). (See McAlester, 1968, for figures of the 

type specimens of the type species of each of the genera.) 

''Then shell shape is used as the major generic criterion, 

these names appear to be synonyms. Because Deceptriw 

is the oldest of the three names, it is used herein; 

Praenucula is sometimes distinguished from Decept1'iw 

on the basis of the number and size of the teeth in the 

tooth rmvs anterior and posterior to the beaks. The 

teeth in each tooth row of Praenncula are of approximately the same size and number, whereas, in Deceptriw 

the teeth in the posterior tooth row are similar and more 

numerous than those in the anterior tooth row. 

Shells of the Deceptriw type are kno,vn from rocks as 

old as the Antelope Valley Limestone of Nevada (pl. 5, 

figs. 11, 12) and range up"'ard into rocks of Devonian 

age. Deceptriw is 'videly distributed in the Ordovicim1 

rocks of North America being known from the Arctic 

(pl. 5, fig. 21) to Tennessee (pl. 5, fig. 13) and from 

Nevada (pl. 5, figs.11, 12) to New York (pl. 5, fig. 22'). 

The names Palaeoconclza (pl. 6, figs. 6-8) and Shnilodonta ( pL 5, figs. 1-6) are applied to n1ore or less similar 

small shells which are triangular dorsally, rounded 

ventrally, and Nucula-like in general aspect. Hmvever, 

Palaeoconcha is used for extremely small shells which 

possess a posterodorsal auricle that is lacking in Sirnilodon.ta. The oldest Ordovician shells of the Similoclonta 

type known to me are vVilderness Age and they range 

upward into the Silurian. Endo (1935) described shells 

which may belong to Shnilodonta under the name 

Ctenodonta manclzurien.'!i8 from the J(angyao Formation of Manchuria. 

Small nuculoids which are probably best placed in 

the genus Palaeoneilo are known from many parts of 

the Ordovician and are at least as old as late vVilderness 

(pl. 1, figs. 8-11); they range upward into the Jurassic 

(Cox, 1937) . 

Although lllyoplu8/ia is not well known in the American Ordovician, at least one arctic species, Ctenodonta 
PTERIOMORPHIANS 17 

carpender·i Sch uchert ( 1900) , seems to belong here (pl. 

6, figs. 3-5) ; several spe.cies from European rocks have 

been placed in the genus (Neumayr, 1884). 

The oldest known nuculoids a.re those reported by 

Thoral (1935) from the lower Arenig and perhaps 

upper Tremadoc rocks of south-central France. Harrington ( 1938) reported some nuculoids from the lower 

Tremadoc of Argentina ; based on external features 

these forms see.m to be properly assigned; however, they 

have not yet been shown to have taxodont dentition. One 

of the specimens Harrington assigned to Oosn-wgoniophorma tenu:icostata (1938, pl. 3, fig. 4) seems to show 

taxodont dentition; it is from the lower Tremadoc of 

Argentina and may be the oldest known nuculoid pelecypod. Other Early Ordovician nuculoids have been 

reported from the Arenig rocks of Argentina (Harrington, 19'38), France (Barrois, 189'1; Babin, 19·66), 

Wales (Hicks, 1873), and Malaysia (herein, pl. 4, figs. 

20-22). 

In the past, the divers,ity of Ordoviciannuculoids has 

been masked by an extremely conservative taxonomic 

approach which resulted in excessive lumping at the 

generic level. This was especi,ally true in North America 

where even as ne\v names became available they were 

not used. Generic-level splitting of Otenodonta is constructive fron1 the biological point of view as it is a 

means of indicating the diversity of Ordovician nuculoids and frmn the stratigraphic point of view as the 

restricted taxa are more useful age indicators than was 

the older more broadly defined Otenodonta. 

PTERIOMORPHIANS 

Ordovician <Species of three families Cyrtodontidae, 

Ambonychiida.e, and Pterineidae poBsess the highly 

characteristic and distinctive duplivincular ligament 

(pl. 7, fig. 10; pl. 10, figs. 6, 8; pl. 11, fig .. 11), a primitive 

feature among pteriomorphian pelecypods. This type 

of ligament leaves a series of paralle,l grooves and 

ridges on the ligament area. (See Newell, 1937 [1938] 

and 1942, for detailed discus,sions of this ligament type.) 

In living forms the duplivincular ligament is present 

only in arcoids; however, in the Paleozoic it was more 

widespread. In addition to the Ordovician groups mentioned above, the duplivincular ligament is found in 

Paleozoic areaceans, myalinids, the older pteriaceans 

and pectinaceans, and perhaps in the limaceans. Thus, 

the duplivincular type of ligament is a primitive feature among 1nost groups of anisomyarian pelecypods. 

I think of these various groups as being phylogenetically related ( 1) on the basis of the common possession of the morphologically and physiologically complex duplivincular ligament, (2) on the tendency of 

most members of the group to reduce the anterior end 

through byssal a.ttachment, and ( 3) on the maintenance 

of the byssus during the adult stage with a consequent 

epifaunal life habit as the m'ain mode of life. Newell 

( 1954) on the basis of his studies of late Paleozoic 

pelecypods felt that this duplivincular ligament group 

probably gave rise to the Mytilacea, a widespread byssally attached superfamily. He (1965) united the mytilaceans and duplivincular liga.ment forms in the 

subclass Pteriomorphia, but placed Ordovician Inytilaceanlike shells in the subclass Palaeoheterodonta as 

part of the order Actinodontoida: 

Ordovician mytilaceanlike shells lack a duplivincula.r 

ligament (pl. 15, figs. 5, 6; pl. 13, figs. 6, 8), have a 

distinctive shell shape (pl. 12, figs. 5, 13; pl. 15, figs. 

2, 3) often much like living species of Arcuatula Lamy 

(pl. 11, fig. 32), 111 odiolu.s Lamarck (pl. 11, fig. 31; 

Soot-Ryen, 1955, pl. 7), and llfytella Soot-Ryen (1955, 

pl. 5, fig. 22), and probably should be classified with 

the Mytilacea and not the Actinodontoida. Paleozoic 

modioliform shells do not seem to be allied to forms 

having a duplhnineular ligament, and the two groups 

are distinctive throughout their stratigraphic range,. 

I feerl that Ordovician Inodioliform shells were probably 

ancestral to the later 1nytilaceans, and I think that 

the Mytilacea should form a separate high -level taxon 

equal in rank to, and distinct from, the other byssally 

attached anisomyarian groups; Ordoviean modioliforin mytilaeeans are further discussed on page 20. 

CYRTODONTIDAE 

Kobayashi ( 1934), Hicks ( 1873), and Barrois ( 1891) 

placed several Arenig· (Early Ordovician) species in 

genera assigned to the Cyrtodontidae. l{obayashi's 

placement of a species frmn l{orea in Oyrtodon.ta was 

cited as a questionable identification by him. Hicks' 

figures are generalized, but the specimens he illustrated 

do not seem to be cyrtodontids. Barrois' figure.s o:f 0. 

lata (1891, pl. 3, figs. 5a-b) and one of his figures of 0. 

obt,usa (1891, pl. 3, fig. 4a.) resermble younger cyrtodontids in general outline, however, Babin (1966) felt that 

these species might belong to Actinodonta and questionably placed thmn in that genus. 

Barrois (1891) illustrated two other possible arcoids, 

Area? na.ranjoana? and Parallelodon antiquus. Babin 

(1966) illustrated the hinge of the former species and 

showed that it has aetinodont dentition and that in 

shell shape it is similar to Oyrtodonta lata. Parallelodon 

antiquus is an enigmatic form whose generic placement 

can only be .correctly established when additional specimens of the species are found. As figured by Barrois 

( 1891), this species has a dentition similar to that of 

1niddle and late Paleozoic parallelodontids which are 

gener~lly regarded as descended from early Paleozoic 
18 REVIEW OF ORDOVICIAN PELECYPODS 

cyrtodontids. It was Barrois' figure of P. antiqufu8 which 

led Cox (1960) to suggest that Oyrtodo~ta and Parallelodon arose from some common Ordovician ance<Stor. 

In 1966, when Babin restudied P. antiquus he could 

locate only one specimen of the species, and he felt that 

this was probably the one used by Barrois to illustrate 

the dentition. Babin noted that the speci1nen showed 

the dentition illustrated by Barrois in an equivocal 

manner (1966, p. 146) : "* * *; cette denture est 

d'ailleur.s d'analyse delicate et beaucoup moins demonstrative que ne laisse supposer 'la figure donnee par Ba,rrois." Babin regarded a second specimen which he 

thought Barrois might have had as probably being 

lost. Babin did not figure P. af/~tiqu~us / however, based 

on Barrois' figures of the species the shape is highly 

reminescent of Pseudm'ca [ Slliquarca J a11;d therefore, 

Pa1'allelodon antiqutts may belong to this genus. 

Be that as it may, the point is obvious that few, if 

any, cyrtodontids or other arcoids are known from 

Lower Ordovic,ian rocks. In North America, cyrtodontids probably occur in the Chazy Limestone of New 

York (Raymond, 1916) and are probably the oldest 

known representative's of the group. Somewhat younge~r 

are possible species of cyrtodontids from the St. Peter 

Sandstone of Minnesota (Sardeson, 1896) and the Llandeilo of Scotland (Hind, 1910). However, cyrtodontids 

are not well represented in the Ordovician record until 

Wilderness-Barneveld time (late Middle Ordovician) 

when they are among the most varied, abundant, and 

geographically widespread pelecypods (fig. 6). The 

family continued on into Devonian time. 

Cyrtodontids are especially conspicuous elements of 

later Midclie Ordovic,ian pelecypod faunas, and it is 

on the basis of shells of this age that the group is best 

known. Cyrtodontids have a prominent duplivincular 

ligament (pl. 7, fig. 10; pl. 9, fig. 1), are equivalved 

(pl. 6, figs. 16, 17, 21-23; pl. 8, figs. 3, 12), and have 

well-developed dentition of cardinal and posterior 

lateral teeth (pl. 7, figs. 1-4, 7-10; pl. 8, figs. 1, 5, 6, 

8, 13; pl. 9, figs. 1-3). They show a great deal of variation in the number, position, shape, and direction of 

growth of the cardinal teeth (pl. 7, figs. 1-4, 7, 8, 10; 

pl. 8, figs. 1, 5, 6, 8) ; on .some specimens these teeth 

do not reach the beaks but are positioned n1ore like 

anterior lateral than cardinal teeth (pl. 7, figs. 1, 2, 7). 

The posterior lateral teeth are all confined to the 

posterior end of the hinge area, never cross the ligaInent area, and never reach the beaks (pl. 7, figs. 2, 10; 

pl. 8, fig. 8). 

It is generally agreed that crytodontids are1 the most 

probable ancestors of the arcaceans (Douville, 1913; 

Newell, 1954 and 19165; .Cox, 19,60) on the basis of comparisons of the dentition of ea,rly Paleozoic crytodontids 

and younger arcace,ans. However, the 1node of life of 

cyrtodontids is difficult to evaluate. Some cyrtodontids 

are Glycymeris-like in their shell form (pl. 6, figs. 21-

23) and probably lived as shaUow infauna. However, 

most show son1e reduction of the anterior end of the shell 

(pl. 7, fig. 3; pl. 9, figs. 4-7), a feature of hyssally ruttached pelecypods, and some show the anterior aductor 

muscle mom1ted on an umbonal shelf or shell thickening 

(pl. 7, fig. 10; pl. 8, figs. 1, 2, 5), a feature known only 

in byssaUy attached pelecypods. Cyrtodontid phylogenetic relationships and the modes of life of 1nembers 

of the group are discussed further on pa;ge '35. 

In the Middle Ordovician rocks of the Jessamine dome 

area of central Kentucky, cyrtodontids are common elements of the Tyrone Limestone and the lower Lexington Limestone; here the group is most abundant in 

biogenic calcarenites and comes and goes up the section as this lithofacies comes and goes. In this type of 

rock, cyrtodontid species are represented by large numbers of individuals of varied sizes, and probably lived 

in this habitat. The robust nature of the shells of most 

cyrtodontids suggests that they could have lived in 

higher energy zones where sands were being deposited. 

The Tyrone Limestone is largely a fine-grained (sublithographic) unit which contains a few small biogenic 

calcarenite bodies. Numerous cyrtodontids occur in these 

sands; they also occur in the enclosing cryptograined 

lin1estone, but are smaller, much less numerous, and not 

as well silicified. 

AMBONYCHIIDAE 

Ambonychiids are the best known of the three Ordo-

~vician prteriomorphian families (Pojeta, 1962, 1966, 

1968). They are equivalved (pl. 10, fig. 17), strongly 

inequilateral shells (pl. 10, fig. 1), which have a highly 

variable dentition (pl. 10, figs. 6-11) and are known 

to have had a prominent byssus (pl. 10, figs. 4, 12). 

Where posterior lateral teeth are present in ambonychiids, they are confined to the posterior part of the 

hinge line and do not cross the ligament area or reach 

the beaks (pl. 10, figs. 7, 9-11); cardinal teeth, where 

present, are ventral to the cluplivincular ligament in 

the region of the beaks (pl. 10, fig. 8). 

For the most part, ambonychiids are relatively large 

animals that lived epifaunally. Some species were obviously gregarious, and large numbers' of articulated 

shells are found together in some places on a bedding 

plane or forming the bulk of a single thin bed. Forms 

which are herein interpreted as nestling are found surrounded by erect branching bryozoans. 

The entire hard-part n1orphology of several Ordovician ambonychiid genera is known. These are ribbed 

monomyarian forms that had lost the entire anterior 

end of the shell and had already undergone a recurring 
PTE.RIOMORPHIANS 19 

theme of pelecypod phylogeny. The oldest knowninembers of the family have been found in Chazy Limestone 

of New York (Raymond, 1916); the family ranges into 

the late Late Devonian and probably gave rise to the late 

Paleozoic and early Mesozoic Myalinidae. 

An interesting sidelight about Ordovician ambonychiids is that some individuals served as attachment 

sites for edrioasteroids (pl. 10, figs. 13, 16). The few 

specimens I have seen with edrioasteroids attached have 

them near the ventral and posterior edges-or those 

parts of the shell closest to the inhalent and exhalent 

currents. Attacl1ment is also on the broadest part of the 

shell, and it may be that attachment on this site was 

related more to the space available than to currents 

set up by the pelecypod. 

PTERINEIDAE 

Paleozoic pteriaceans have been little studied and are 

poorly known. Ahtioconcha Opik from the Baltic 

J{ukruse stage ( C2-early Caradoc) is the oldest known 

probable pteriacean (fig. 4). In North America a few 

undoubted pteriaceans are known from upper Middle 

Ordovician (Barneveld) rocks (pl.11, fig. 9); the group 

underwent a slight expansion in the Late Ordovician 

(fig. 6), but its evolution is primarily 1a post-Ordovician 

one. 

Ordovician pteriaceans are largely placed in the single 

family Pterineidae, and most undoubted pteriacean 

species are placed in the single genus Pte1·inea Goldfuss. 

In the Ordovician, this genus is most abundant in rocks 

of Cincinnati age (Late Ordovician), and as known 

from Ohio Valley and New York species is strongly 

inequilateral (pl.11, figs. 7, 14) and inequivalved (pl. 11, 

figs. 3-6). The left valve is convex, and the right valve 

is almost flat to concave (pl. 11, figs. 4, 6); the sculpture 

of the two valves differs, with that of the left valve being 

more accentuated (pl. 11, figs. 1, 7) than that of the right 

valve (pl. 11, figs. 2, 8). The shell is strongly dentate 

and has both cardinal and posterior lateral teeth which 

do not cross the ligament nor reach the beaks (pl. 11, 

figs. 10, 11), the ligament is duplivincular (pl. 11, fig. 

11), and there are anterior and posterior alations of the 

dorsal margin (pl. 11, figs. 10-13). Commonly in Ohio 

Valley specimens the outer ostracum is preserved 

whereas the inner ostracum is dissolved away (pl. 11, 

fig. 12) ; this suggests that the inner ostracum was 

aragonitic whereas the outer was calcitic. Pterinea was 

an epifaunal element and probably was similar to the 

living genera Pteria and Pinctada in its mode of life. 

The ·oldest known undoubted North American 

pterineids are from the upper Lexington Limestone 

(upper Middle Ordovician) of Kentucky; they are 

known only from left valves which are convex (pl. 11, 

FIGURE 4.-A.hUoconcha auris. A, dorsal view. B, right valve. 

Reproduced from Opik (1930). X 2/3. 

fig. 9) and are probably assignable to the genus 

PalaeopteTia Whiteaves on the basis of the teeth being 

nearly parallel to the dorsal margin and being arranged 

as anterior and posterior laterals. Whiteaves (1897) 

figured a right valve of Palaeopte1ia which was also 

convex, but less convex than the left valve. 

Except for Ahtioconcha Opik (1930), older species 

placed in the Pteriacea are not well documented and 

some such as Thoral's (1935) ?Pterinea crassa belong 

to other taxa (in this example, Eopteria). Ahtioconcha 

(fig. 4) is an inequivalved shell from the Middle Ordovician of Estonia; it has a convex left valve and a flat 

to concave right valve, it is strongly anisomyarian, but 

lacks a posterior alation. Eberzin (1960) placed the 

genus in a separate family Ahtioconchidae. 

Several other pteriacean generic names usually 

applied to younger species have been used for Ordovician fonns including: "Avicula" (Barrande, 1881), 

R hmnbopteria (Jackson, 1890), and Leptodesma (SootRyen and Soot-Ryen, 1960); a few Ordovician genera 

ineluding Alnifia Termier and Termier and Ande'rkenia Khalfin have been questionably placed in the 

Pteriacea. 

Other Ordovician pelecypods which have been described as being inequivalved are A1isterella Ulrich 

(pl. 11, figs. 15-24) and Heikea Isberg. Ulrich (1894) 

described ATisterella as having the left valve smaller 

than the right (pl. 11, fig. 20). IIis specimeills of the 

type species of the genus (A. nitidula Ulrich) include 

individuals which are right convex (pl. 11, fig. 20), left 

convex (pl. 11, fig. 23), and equivalved (pl. 11, fig. 15). 

The specimens are all small molds and could easily 
20 REVIEW OF ORDOVICIAN PELECYPODS 

have been distorted; Aristerella 1nay be a distinct 

generic-level taxon, but it is doubtful that it was 

inequivalved. 

As pointed out by Nicol (1958), right-convex inequival ved shells are known from the Ordovician. Two 

fairly large specimens in the U.S. National Museum 

collections from the Ordovician of Estonia are Inarkedly right convex (pl. 11, figs. 25-30). These 1nolds are 

labeled Arristerella, but it is doubtful that they can be 

assigned to that genus, and it is uncertain to what 

higher level taxon they belong. 

He·ikea Isberg (1934) was described as being inequivalved. Based on Isberg's figures this inequality is at 

best slight and may be the result of distortion during 

preservation. 

Some Ordovician pterineids, like ambonychiids, 

served as attachment sites for eclrioasteroids (pl. 10, 

figs. 14, 15). 

MODIOMORPHIDAE [MODIOLOPSIDAE] 

The family J\iodiomorphidae is perhaps the 1nost perplexing of Ordovician pelecypod groups. Pelecypods 

which range in age from Early Ordovician to Late 

Permian have been placed in the Modiomorphidae, but 

the concept summed up by the name is vague and uncertain, and probably more than one family-level taxon 

is included in the Modiomorphidae as presently recognized. Many of the genera in the family have a modioliform shape (pl. 12, figs. 5, 9; pl. 13, figs. 1-6; pl. 15, 

figs. 1-3,6; pl. 17, figs. 2, 4, 6-9); however, other aspects 

of the hard-part n1orphology, especially the hinge-line 

features, are unknown in the majority of genera. 

Because of this situation the phylogenetic position of 

these animals has long been moot, and they have been 

allied to the mytilaceans (Cox, 1960; Soot-Ryen, 1955), 

carditaceans (Newell, 1957), and actinodontoids 

(Douville, 1913; Newell, 1965). 

In the Ordovician, 111 odiolopsis Hall is the most 

widely used modion1orphid generic name. In the years 

before family-level priority, the fa1nily name for this 

group of shells was Modiolopsidae; Modiomorphidae 

Miller (1877) has 10 years priority over Modiolopsidae 

Fischer (1887). As the modern study of these animals 

develops, it may prove useful to resurrect the name 

Modiolopsidae. 111 odiolopsis was proposed by Hall 

(1847) with the type species being Pteri:nea rnwdiolaris 

Conrad (1838) by original designation. Ulrich (1924) 

using a tortured nomenclatural and taxonomic logic 

removed P. 1nodiolari.s from the genus 111 odiolopsis, 

substituted Oypricardites ovata Conrad ( 1841) as the 

type species of 111 odiolopsis, and made Pterinea modiolaris the type species of a new genus Jl./ odiodesma 

Ulrich. This procedure made ll/ odiolopsis and 111 odiodesma objective synonyms as both names have the same 

type species. 

Fortunately, Conrad's holotype of 111 odiolopsis nwdiolari.s has been preserved (fide Hall, 1'847, p. 295 and 

Ulrich, 1924, pl. 32 explanation), and it is figured herein on plate 15, figures 1-3. It is a composite mold of 

a distinctly modioliform shell with anisomyarian Inusculature and concentric sculpture. The musemn label 

accompanying the holotype gives the locality as 

"Pulaski beds [Late Ordovicinn], Rome, N.Y." (this 

differs somewhat from the locality as given by Conrad, 

1838). In general form and musculature, 111. modiolaris 

is distinctly mytilacean. Nothing definite is known about 

the dentition of this species, although Ulrich ( 1924) 

regarded 111 odiodesnw. (type species 111 odiolopsis nwdiolaris) as being edentulous. Specimens similar to llf. 

nwdiolaris from the Pulaski Shale of New York and 

elsewhere show that the species has multiple accessory 

muscle scars anterior to the beaks (probably anterior 

pedal-byssal retractors) (pl. 16, figs. 1, 2), an integropalliate pallial line (pl. 16, figs. 1, 2), and an 

elongate opisthodetic ligament (pl. 15, figs. 5, 6). The 

ligament is only rarely preserved and then only as a 

dark stain connecting the two valves. 

Based on the type species, the name 111 odiolopsis is 

applicable to modioliforn1 shells which expand noticeably posteriorly so that the 1naximum height of the 

shell is significantly more than the height measured 

down from the beaks and which also have concentric 

sculpture, an entire pallial line, anisomyarian musculature, and multiple accessory muscle scars in front of 

the beaks. 

Ulrich ( 1894, p. 521) illustrated the hinge lines of 

two species of ltf odiolopsis which generally fit the definition of the genus based on the type species. Although 

the hinges of Ulrich's specimen's are not so well preserved as indicated on his figures, they do suggest that 

the genus was edentulous (pi .14, fig. 1). Other specimens not previously figured (pl. 14, figs. 2-5) also suggest that 111 odiolopsis was edentulous. 

The hinges of three species of Ordovician pelecypods 

which are placed in the Modiomorphidae in most classifications are now reasonably well known on the basis 

of silicified specimens from the Lexington Limestone 

of central l{entncky.11/ odiolodon oviforntis Ulrich possesses only cardinal teeth (pl. 13, :fi.gs. 6, 8, 9), Whiteavesia cincinnatiensis (Hall and Whitfield) is entirely 

edentulous (pl. 17, figs. 1, 3, 5, 11, 13, 15; pl. 19, figs. 

16-18), and Oolpmnya con8tricta Ulrich possesses a 

Jta,rge bosslike cardinal tooth below the beak of each 

valve (pl.12, figs. 2, 3). 

Jl,f odiolodon ovifornds possesses multiple byssal retractor muscle scars posterior to the beaks (pl. 13, figs. 
MODIOMORPHIDAE [ MODIOLOPSIDAE] 21 

7, 11) and has the shell shape, pallial line, and anisomyarian musculature of byssally attached mytilaceans 

(pl. 13, figs. 1-6). Details of the shell musculature are 

not so well known in lVhiteavesia and Oolpomya, however, in shell shape they suggest byssally attached 

mytilaceans. 

Based on shell shape and general hard-part morphology such Ordovician modiomorphids as 111 odiolopsis 

(pl. 15, figs. 1-6), 11/odiolodon (pl. 13, figs. 1-15), 

lVhitea-oesia (pl. 17), and less well known genera such 

as Pholadomorpha Foerste (pl.12, figs. 5-9) are strongly reminiscent of the geologically younger modioliform 

mytilaceans. Soot-Ryen (1955) in his summary paper 

on American west coast Mytilacea regarded this group 

as having descended from middle Paleozoic modiomorphids. Indeed, Ordovican modiomorphids are so 

mytilaceanlike in shell shape that it is difficult to entertain thoughts of other possible relationships for the 

group. 

In comparing the hinge of mytilaceans and Ordovician Inodiomorphids, little is known of tl1e modiomorphid ligament. As mentioned above, on son1e molds 

it is preserved as a dark stain connecting the two valves 

(pl. 15, figs. 5, 6), and it is opisthodetic and elongate. 

Trueman ( 1950) and Soot-Ryen ( 1955) discussed 

the opisthodetic elongate mytilid ligament. Trueman 

noted that the inner fibrous part of the ligament of 

llf ytilus edulis Linne is attached to the flat surfaces 

(nymphae) of ligamenta! ridges composed of nacreous 

vacuolated shell material (pl. 13, fig. 18). To the unaided eye these ligamenta! ridges are white and of an 

obviously different consistency fron1 the rest of the 

shell (pl. 13, figs. 18-20). Because these ridges support 

the ventral, fibrous, compressional ( resilial) part of 

the ligament, Soot-Ryen named the1n the resilial 

ridges, and he regarded them as one of the most characteristic features of the family ~fytilidae (pl. 13, figs. 

18-20). No such resilial ridges have been observed on 

any of the silicified Ordovician modiomorphid shells 

discussed above (pl. 12, fig. 2; pl. 13, figs. 6-8; pl. 17, 

figs. 1, 3, 11, 13). 

The modiomorphid ligament may not have been entirely composed of tensional elements acting only in 

C-spring fashion. It is normal in pelecypods for the 

ligament to contain both tensional and compressional 

parts although these are developed to differing degrees 

in different taxa. Ulrich ( 1924) described the ligament 

of 111 odiolopsis [ 111 odiodesma J as having both inner and 

outer parts, the inner part being supported by a longitudinal rib which left a slitlike mark on molds (pl. 12, 

fig. 4). The ventron1edial edge of the resilial ridge of 

some living mytilaceans leaves a more or less similar 

mark on rubber molds. However, as the silicified speci421-895 0- 71 - 4 

mens of Ordovician modiomorphids show no sign of 

an internal longitudinal rib supporting the ligament, 

it is doubtful that such a structure was present. Probably Ulrich's "longitudinal slit" was made by the dorsal margin of the shell. 

As far as known, American Ordovician modiomorphids either are edentulous (pl. 14, figs. 1-5; pl. 17, 

figs. 1, 3, 5, 10, 11, 13, 15; pl. 19, figs. 16-18) or have 

only cardinal teeth (pl. 12, figs. 2, 3; pl. 13, figs. 6, 8, 9). 

The latter when present are mounted on a hinge plate 

and are strong obvious teeth (pl. 12, fig. 3; pl. 13, fig. 8). 

Mytilids, too, either are edentulous (pl. 13, fig. 19) 

or have only cardinal teeth (pl. 13, figs. 18, 20). In the 

latter, the teeth may be derived from provincular teeth, 

or they 1nay be related to shell sculpture ( dysodont). 

Cardinal teeth in the Mytilidae may be sn1all and not 

mounted on a hinge plate as in 111 ytilus edulis (pl. 13, 

fig. 18), or they may be large and supported on a hinge 

plate as in some species of Perna (pl. 13, fig. 20). It is 

not possible to draw an absolute homologous parallel 

between mytilid dentition and that of the Ordovician 

modioliform modiomorphids. However, the two groups 

are similar in showing several dental types \vhich vary 

in more or less the same way. 

The various phylogenetic relationships postulated for 

the Modiomorphidae result, at least in part, from the 

uncertainty of the concept implied by the name. Several 

distinct groups of Ordovician shells have been united 

in the Modiomorphidae including: ( 1) the modioliform 

byssate forms discussed above, (2) Redonia (pl. 1, fig. 

7) which is herein regarded as an actinodontoid ( p. 

11) and (3) burrorwing forms such as Oymatonota 

(pl.18, figs.10-13). 

Newell (1942, 1954) in his work on late Paleozoic 

mytilaceans felt that it was most likely that they came 

from cyrtodontids through an ambonychiacean intermediary rather than from the Modimnorphidae. He also 

based much of his interpretation on shell shape and 

musculature, some of the late Paleozoic myalinids being 

remarkably like mytilaceans in these respects. However~ 

mytilacean shell shape is known from the Early Ordovician on ward, and if for no other reason than the 

principle of parsimony it would seem best to regard late 

Paleozoic undoubted mytilaceans as having descended 

from similarly shaped early Paleozoic forms. The reasons advanced for not coming to this conelusion a.re 

to me less likely than those given for regarding mytilaceans as descended frmn 1nodiomorphids. 

Ordovician modioliform modiomorphids are like late 

Paleozoic mytilaceans in shell shape, musculature, byssal attaclunent, and, in a more general way, ligament 

type and dentition. They differ by specifics of dentition 

and by lack of a resilial ridge. My interpretation of 
22 REVIEW OF ORDOVICIAN PELECYPODS 

these data is that the early Paleozoic modioliforn1 

modiomorphids are ancestral mytilaceans. I regard the 

late Paleozoic n1odioliform myalinids as being convergent to the Mytilacea. The myalinids have a duplivincular ligament which is unknown in either the 

mytilaceans or the 1nodimnorphids. I am a ware that the 

duplivincular ligament was lost in the phylogeny of 

the pectinaceans and pteriaceans and there is no reason 

why it could not be lost in the phylogeny of other 

groups. However, both the pectinaceans and the pteriaceans are regarded as having descended from the first 

occurring similarly shaped Paleozoic shells, and none of 

the 1nodioliform early Paleozoic she1ls are known to 

have had a duplivincular ligament. 

Newell (1957) a1lied the modioliform modiomorphids 

and Redonia to the Carditacea on the basis that these 

were the earliest known forms to have posterior lateral 

teeth extending under the ligament to the beaks and on 

general body form. Redo,nia does have such teeth, but 

as noted above is probably better classified with the 

actinodontoids than with the modiomorphids. Redonia 

was considered to be the ancestral carditacean by Chavan 

( 1966a, b). None of the Ordovician modioli form modiomorphids in which the hinge line is known have 

posterior lateral teeth (although younger forms placed 

in the same group have been described as having such 

teeth). As noted previously, they are either edentulous 

or possess only cardinal teeth, and on this basis their 

pogtulated relationship to the Ca,rditae&'t is weakened. 

N eweU ( 1965) placed the Modiomorphidae in the order Actinodontoida along with the Cycloconchidae, 

Lamellodontidae, and Carydiidae. For reasons simila,r 

to those cited above that deal with a. possible modioInorphid-carditacean relationship, it seems doubtful 

thalt the modioliform modiomorphids can be allied to 

the actinodontoids. Modioliforn1 modiomorphids have 

a complex of characters similar to those of the l\fytilacea, and the former are herein rega.rded as the ancestors of the latter. 

The earliest 1nodioliform modiomorphids seem to be 

Arenig Age (fig. 6) and were figured by Hicks ( 1873, pl. 

5, fig. 18), Ba,rrois ( 1891, pl. 3, fig. 9), and Babin ( 1966, 

pl. 7, fig. 13). The specimens placed in the Modiomorphidae by Harrington ( 1938) from the lower Tremadoc 

and lower Arenig of Argentina cannot be readily allied 

to the modioliforn1 modiomorphids. In North America, 

modioliform modiomorphids are known from rocks as 

old as the lower Lehman Formation of Utah (pl. 15, 

fig. 8) and the upper Pogonip Group of Nevada (Walcott, 1884). 

The Mytilacea has long been recognized as a distinctive high-level taxon, and Iredale (1939), Cox (1960), 

and Newell (1965) have placed the group in its own 

order. For the most part, however, the Mytilacea have 

consistently been classified with the other Anisomyaria. 

The concept of the Anisomyaria is an old one to which 

in recent years the arcoids have been added and for 

which the name Pteriomorphia Beurlen (1944) has 

been adopted. As long as the early history of the Mytilacea was not well known, their placement with the anisomyarians was acceptable on the basis of the musculature 

and the byssal mode of life of the adults. However, 

mytilaceans from the Early Ordovician onward are not 

known to have had a duplivineular ligament, and they 

are distinct from the pteriomorphians from the begining of the known fossil record of the two groups. If 

the two groups have had a separate history from the 

Ordovician onward this should be reflected in their 

taxonomy; I think that this can best be done by treating them as separate subclasses. Cox ( 1960, p. 78) briefly 

summarized the malacological data indicating that the 

Mytilacea are distinct from the other anisomyarians; 

although he did not place the mytilaceans in a separate 

subclass he was thinking along these lines : "Their 

[ mytilaceans] recognition as a distinct order seems 

justified, but at present I hesitate to place them in a different subclass from that to which the remaining dysodonts of N eumayr belong, and so include them in the 

Pteriomorphia." 

LESS WELL KNOWN ORDOVICIAN PELECYPOD GROUPS 

The remaining groups of Ordovician pelecypods are 

not well known largely because of the lack of wellpreserved specimens. So far my etching program has 

shed little light on these families; it is hoped that expansion of the program into geographic areas other than 

the tristate area of Ohio, Indiana, and Kentucky will 

improve knowledge of these animals. 

CONOCARDIIDAE 

About three-dozen species names are presently available for Ordovician Oonocardi~wn-like animals. These 

species are distributed among several genera, the best 

known being: Eopteria Billings (pl. 19, figs. 1-14), 

Euchasrna Billings (pl. 20, figs. 6-21), and Oonocardiun~; 

Bronn (pl. 20, figs. 1-5). At one time or another 1nost 

of these forms have been allied to the Crustacea, although their calcareous shells with growth lines suggest 

they are mollusks. Animals with conocardiid shell shape 

are persistent Paleozoic faunal elements and range in 

age from Early Ordovician to Late Permian; they are 

an enigmatic group and their pelecypod affinities are 

not well established. 

The oldest known possible conocardiids are species 

placed in Eopteria and Eucha8rna by Kobayashi (1933) 

from the Wanwaukou Dolomite (lower Canadian) of 
VLASTIDAE 23 

Manchuria; the species which Thoral ( 1935) called 

~ Pterinea crass a from the Arenig rocks of south-central 

France probably belongs to Eopteria)· and species of 

Erzwhasma (pl. 20, figs. 18_:21) a.re known from the Setul 

Formation of Malaysia in rocks which are probably 

latest Canadian in age ( Y ochelson and Jones, 1968). In 

North America, E opterhr, and E,ncha.rsrna are known 

from rocks of Canadian age (Early Ordovician) in 

Newfoundland (Schuchert and Dunbar, 1934), the 

Ozarks (pl. 19, figs. 5-14), Quebec (pl. 19, figs. 1-3; pl. 

20, figs. 6-11) , Texas (Cloud and Barnes, 1948) , Vermont (pl. 20, figs. 16, 17), Virginia (pl. 20, figs. 12, 13), 

and elsewhere (pis. 19, 2q). In Canadian (Lower Ordovician) rocks, conocardiids are widely distributed. In 

post-Canadian Ordovician rocks, conocardiids a.re 

known from fewer speeimens and pla.ces. However, 

conocardiids are as distinct from other pelecypods in 

the Ordovician as they are in the Permian. 

Ordovician representatives of the Conoeardiidae are 

known fron1 a relatively few specimens which show 

little beyond exten1al features. They are small, are 

known from a variety of rock types, do not have so pronounced a posterior ( ~) tube as do later for1ns, and probably had a burrowing mode of life. Reeently, silieified 

specimens of Erztcha.rsnw have been obtained whieh promise to provide some data on the internal features of the 

group (pl. 20, figs. 18-21). 

During the Paleozoic, the conocardiids underwent 

a eomplex radiation which is not well doemnented in 

the available literature. The biological diversity of the 

group is not at present well understood because of the 

inclusion of all species within a relatively few genera 

and families, and the group is badly in need of modern 

monographic treatment. 

VLASTIDAE 

In the Ordovician of North America the fa1nily 

Vlastidae is represented by the single species Vlasta 

arnericana Fritz, 1951, (pl. 20, fig. 2'2) from the Dundas 

Forn1ation (Upper Ordovician) of Ontario; this is a 

large species with prmninent concentric m1dulations, 

but about which little else is known. 

The Vlastidae is largely a Silurian family known 

primarily from material described hy Barrande ( 1881) 

from Bohemia. Reed (1915) placed the genus Shanina 

from the Middle Ordovician of Bunna in this family, 

Isberg (1934) placed Shaninopsis from the Upper Ordovician of Sweden in the Vla:stidae, and Vokes ( 1967) 

added H ippornya Salter to the Vlastidae. The last three 

mentioned genera are all diagramed as having unusually 

large shell (byssal ~) grupes. 

ANOMALODESMA T A 

This section deals with a series of fonns which are 

or have been regarded as burrowing pelecypods ("desmodonts") and which cannot be assigned to any of the 

infaunal groups discussed previously. 

Douville (1907, 1912, 1913) using Neumayr's terminology (1884, 1891) developed the concept of a primary radiation of pelecypods into three major modes 

of life: ( 1) normal infaunal form&-taxodonts, preheterodonts, and heterodonts; (2) epifaunal forms fixed 

in some manner to the substrater---dysodonts; and ( 3) 

burrowing or boring infauna:l form-desmoclonts. The 

phylogenetic validity of Douville's burrowing braneh 

has not been generally accepted, although Cox ( 1960) 

and Runnegar (1966) felt that there was probably a 

core group among his desn1odonts which had an early 

Paleozoic origin and continues to the present. 

For various reasons, several Ordovician genera have 

been considered to be burrowing forn1s including: 

Oymatonota Ulrich (pl. 18, figs. 10-13), Psiloconcha 

Ulrich (pl. 18, figs. 1-6), Orthodesrna Hall and Whitfield (pl. 18, figs. 7-9), Rhytirnya lJlrich (pl. 16, figs. 

10, 11), and Ouneamya Hall and Whitfield (pl. 15, figs. 

9-14). Vokes (1967) listed these genera in five different 

families : Modiomorphidae, Solemyidae, Orthonotidae, 

Pholadellidae, and Edmondiidae, respectively. Four of 

the five families concerned are plaeed by Newell (1965) 

and Vokes (1967) in the subclass Cryptodonta. This 

taxon is a sort of pelecypods imperfecti and is admittedly one of convenience for poorly understood Paleozoic pelecypods. 

Of the genera listed above, Oyn1atonota is the best 

documented as an undoubted burrower. Nothing is 

known of the hinge or pallial line of this genus, and 

little is known of its musculature. However, it has a 

distinctly solenifonn shape, with subparallel dorsal and 

ventral ~1argins (pl. 18, figs. 12, 13) and it has both 

anterior and posterior shell gapes (pl. 18, figs. 10, 11). 

In shell shape and gapes, Oymatonota is much like the 

later Paleozoic genera Palaeosolen Hall, Pr'othyris 

Meek, and Solen01norpha Cockerell (see Driscoll, 1965, 

for figures of the latter genera) and should probably be 

allied to these forms. Oymatonota has traditionally been 

placed in the Modiomorphidae; however,_its shell shape 

and gapes make it distinct from the byssate 1nodioliform 

modiomorphids. Shells of the Oyn~>atonotal type seen1 to 

form a separate pelecypod lineage distinct frmn the 

Ordovician on ward throughout the Paleozoic. 

Psiloconcha (pl. 18, figs. 1~6) is another burrowing 

Ordovician form which is probably related to Oymatonota. The former genus is not so strongly soleniform 
24 REVIEW OF ORDOVICIAN PELECYPODS 

as Oy1naton.ota; however, it does have anterior and 

posterior shell gapes (pl. 18, figs. 5, 6) and a general 

burrowing aspect to the shell. Unfortunately in preparing the best preserved of the known speci1nens of 

Psiloconcha, Ulrich accentuated the posterior gape unduly (pl. 18, fig. 5). Nothing is known of the hinge or 

pallial line of Psiloconclw_; however, on one specimen 

the adductor 1nuscle scars are known (pl. 18, fig. 1). 

Orthodesma (pl. 18, figs. 7-9) as defined by Ulrich 

( 1894) was supposed to have anterior and posterior shell 

gapes. None of the specimens of this genus seen by me 

show this in an unequivocal manner, and some species 

placed in the genus have a modioliform aspect. However, 

most species of Orthodesnw have a general soleniform 

shell shape, and Bayer (1967, p. 420) noted having 

found : "One hundred and fifty pelecypods of the burrowing type ( Orthodes11w.) * * * in growth position." 

It may be that Orthodesma as presently defined includes 

both burrowing and nonburrowing fonns. 

Runnegar ( 1966) felt that pholadomyids and eclInondiids constitute a major division of the class Pelecypoda; a division which has been distinct since the 

Ordovician, having descended frmn such genera as 

Rhytin~ya (pl. 16, figs. 10, 11). I:Iis sugg·ested rela~tionship of Rhytim.ya to the pholadomyaceans is based 

largely upon shell sculpture, the Ordovician genus having the radially arranged granules and concentric undulations of many younger members of the group (pl. 

16, fig. 11). Unfortunately nothing is known of the hinge 

or pallial line of Rhyti'lnya. Runnegar placed a number of genera in this lineage including such widely used 

names as Ednw~ndiaJ l(oninck (Wilson, 1959, 1960), 

Ohaenmnya Meek, llfyonia Dana, and tentatively 

vVilkingia Wilson [Alloris1na].lTlrich (1894) suggested 

that Rhytintya. was related to 1Vilkingia on the basis of 

criteria similar to those suggested by Runnegar (1966). 

Cox (1960L Dickens (1963), and Runnegar (1966) considered the Devonian genus Gra:nv1nysia as being related 

to the pholadomyacean lineage. Also probably allied to 

this complex is the genus o~meam_.ya (pl. 15, figs. 9-14)' 

a primarily Middle and Late Ordovician fonn which 

has a shell sculpture, consisting of concentric undulations. As early as 1894, Ulrich related Ounea.m.ya to 

Gran1.11nysia. 

Ulrich (1893 [1895], 1894), allied Sphenoliu:m Miller, 

Physet01nya Ulrich, and Saff'oPdia Ulrich to either 

Rhythnya or Ou,newnya. Of the species of Sphenolium 

illustrated by Ulrich, only S. palallel~wn was figured 

with concentric undulations; I have not been able to 

locate his material of this species nor his specimens of 

Physetmnya. Sphenoli~Mn stTiatu1n (pl. 12, fig. 14) was 

also illustrated by Ulrich, but it does not show concentric undulations. Ulrich's specimens of Saffordia 

ventralis (pl. 12, figs. 10-12), the type species of the 

genus, show a shell with a prominent escutcheon (pl. 12, 

fig. 10) and a single cardinal tooth in the left valve 

(pl. 12, fig. 11). Saffm'dia is in most respects similar to 

H elkea Is berg ( 1934), and the two names may be 

synonyms. 

As a working hypothesis I propose that Ordovician 

anomalodesmatans be divided into two groups: ( 1) 

those fonns with gaping soleniform shells such as Oymatonota and Psiloconcha, which are probably related to 

such younger genera as Solenmnorpha, Prothyris, and 

Palaeosolen, and (2) those forms which have a shell 

sculpture of prominent concentric undulations such as 

Rhytin1,.ya and Ott/JWam.ya and which are probably related to such younger genera as Gramnty8ia, Edm.ondia, 

and lV ilkingia. How these two groups are related to 

each other is not clear although Cox ( 1960, p. 80) placed 

both of then1 in the order Eudesmodontida. It should 

be mentioned that Ordovician infaunal pelecypods also 

occur in the following groups: nuculoids, actinodontoicls, 

abinkids, conocardiids, and probably smne cyrtodontids. 

ORDOVICIAN PELECYPODS OF UNCERTAIN HIGHER 

TAXONOMIC POSITION 

There remain a few problematic Ordovician genera 

which have been allied to groups that are "\Yell represented in younger rocks: Plethocanlia. Ulrich (pl. 14, 

figs. tl-12) has been placed in the Megalodontidae 

(Ulrich, 1894; Vokes, 1967), jJJ ather,ia Billings (pl. 16, 

figs. 6-9) has been placed in the Astartidae ( Cha van, 

1966a, b; Vokes, 1967), and Tenka Barrancle, Tetin!t~a 

Barrancle, and Pa:trocardia Fischer have been placed in 

the Lunulacardiidae (Fischer, 1887; Vokes, 1967). 

Ulrich ( 1894) questionably placed Plethocardia. in 

the family Megalodontidae, and in his discussion was 

hesitant about including the genus in that fa:Inily. lTlrioh 

had two speeimens of Plethoca,rrdia on whieh he based 

his analysis of the hinge line. A figured syntype of 

P. umbo1wta Ulrieh (pl. 14, figs. 9-12) , type species of 

the genus, does not preserve the dentition nearly so well 

as indicated in Ulrich's drawing (fig. 1A); there are 

remnants of eardinal and lateral teeth that suggest a 

cyrtodontid hinge (pl. 14, fig. 9), and the general shell 

shape and enrolled beaks are also suggestive of tlw 

Cyrtodontidae (pl. 14, figs. 11, 12). Ulrich ( 189-1) also 

discussed the dentition of a specimen of P. w1nbonata 

from Kentucky (pl. 14, figs. 7, 8) which he did not 

figure. Much of the hinge line of this shell has been 

weathered away, and the rest is covered with adventitious 

silica (pl. 14, fig. 8), and little can be determined of the 

teeth. 
PHYLOGENETIC SUMMARY 25 

Based on what is presently known of Plethocm'dia it 

"·onld be better to ally the genus to the Cyrtoclontidae 

than to the l\1egalodontidae. There is a resemblance of 

the shell shape of Plethocardia to lJfegalodon and, 

cyrtodontids, but Plethoca.rd·ia does not show the large 

hinge plate and complex dentition of 1negalodontids. 

Chavan (1966a, b) felt that he could establish the 

presence of three heterodont groups in the Ordovician. 

Using Bernard's method of tooth notation he regarded 

Redonia as a carditacean, and felt that he could relate 

the bvo crassatellacean families Cardiniidae and Astartidae to the genera Oypricm'dinia and 111 atheria, 

respectively. 

Redonia has been discussed above in the sections dealing \vith the actinodontoids and modiomorphicls. Oypricm'dinia is a generic name little used for Ordovician 

pelecypods, and it \Yould be necessary to know to which 

species Cha van was referring before discussing any 

possible relationships. 111 at he ria is a small shell with 

cardinal teeth (pl. 16, figs. 6, 9) and a duplivincular 

ligament; the latter structure is unknown in heterodonts. On general morphological grounds it would seem 

that the la,te Paleozoic crass:atellaceans (Newell, 1958; 

Boyd and Newell, 1968) should be rela,ted to such forms 

as Oycloco·ncha rather than ffif ather·ia. 

Barrande (1881) described four Ordovician species 

placed in the genera Tenka,, Tetinka, and Patrocard,ia 

(originally placed in H emicardiurrn). These genera are 

usually placed in the Lunulacardiidae, a fa1nily allied 

to the Ambonychiacea in most classifications (Clarke, 

1904; Newell, 1965; Vokes, 1967). Clarke (1904) discussed Lu.nulacardiu1n Muenster at son1e length, but the 

genera placed in the family are all poorly understood, 

and at best the family is not well represented in the 

Ordovician. 

PHYLOGENETIC SUMMARY 

Based on the preceding interpretations, Ordovician 

pelecypods can be arranged in six major lineages: (1) 

Rostroconchida ( Conocardiacea) ; ( 2) Palaeotaxodonta 

( N uculoidea and Solemyoida) ; ( 3) Isofilibranchia 

( Mytilacea) ; ( 4) Pteriomorphia ( Cyrtodontacea, 

Areacea, L1

imopsacea, Pteriacea, Pinnacea, Anlbonyehiacea, Pectinacea, Anomiacea, Limacea, and Ostreacea) ; ( 5) Heteroconchia ( Actinodontoida, Babinkidae, Unionoida, Trigonioida, V eneroida, Myoida, and 

Hippuritoida); and (6) Anomalodesmata (Edmondiidae, Sanguino1litidae= Solenomorphidae, Pholadomyacea, Pandoraeea, Megadesmatidae, and ?Septibranchoidea). These lineages are distinct from the Early 

Ordovician or eady Middle Ordovician onward; eventually it may prove necessary to add additional 

lineages when such groups as the vlastids and older 

babinkids become better known and to divide the anomalodesmatans into two evolutionary lines. At the 

present time it is possible to relate most post-Ordovician 

pelecypod stocks to one or another of the, six Ordovician 

linea:ges recognized herein (fig. 5). 

ROSTROCONCHIDA 

Conocardiaceans (pls. 19, 20) are a highly distinctive 

Paleozoic group. There has long beeh a lingering doubt 

a:bont their pelecypod nature; ho·wever, they seem to be 

mollusks, and they a,re generally regarded as aherrent 

Paleozoic pelecypods which gave rise to no other stock. 

The gr•oup appea.rs in the Early Ordovician and continues to the Late Permian. 

PALAEOTAXODONTA 

Frmn the Early Ordovician onward, nuculoids are 

important constituents of pelecypod faunas, and by Middle Ordovician time they are highly diversified (fig. 

6). The major features of their post-Ordovician evolution seem to have been the development of a resilife,r 

and in s:on1e groups a pallial sin us. Like the conoca,rdiids, 

nucnloids are as distinctive in the Ordovician as in 

younger rocks and are not readily related to other 

Ordovician pelecypod stocks. 

ISOFILIBRANCHIA 

The modioliform 1nodiomorphids form a third distinctive Ordovician pe,lecypod stock. As mentioned p·reviously, it is doubtful if all the genera placed in the 

Modiomorphidae form a single fmnily unit, but the 

modioliform genera form a eompaet unit from the Early 

Ordovician onward, and I regard them as ancestral to 

t:he Mytilidae. The mytilids cannot be readily related 

to the rest of the anisomyarians, all of which have a 

duplivineular ligan1ent smnewhm'B in their aneestry, 

and it would be best to place the mytilaeeans in a 

subclass of their own, separate frmn the rest of the 

Anisomyaria. 

PTERIOMORPHIA 

A fourth Ordovician pelecypod lineage is fonned 

by the three families which possess a duplivincular 

ligament : Ambonyehiidae, Cyrtodontidae, and Pterineidae. As interpreted herein, this group gave rise to 

the arcoids and to all later anisomyarians except the 

Mytilaeea. This general viewpoint was suggested by 

Newell ( 19.54), except that he regarded 1nytilaceans 

as having descended from fonns possessing a duplivincular ligament. 
26 

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REVIEW OF ORDOVICIAN PELECYPODS 

ROSTROCONCHIDA ISOFILIBRANCHIA PTERIOMORPHIA 

PALAEOTAXODONTA HETEROCONCHIA 

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FIGURE 5.-Proposed phylogenetic relationsihips of most groups orf Paleozoic pelecypods!. Black lineages are thosrer which originate 

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PHYLOGENETIC SUMMARY 

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0 60 I I I I I 

NUMBER OF SPECI 

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27 

FIGURE 6.-Chart showing range and relative abundance of various Ordovician pelecypod groups. Figures are biased on approximately 1,000 species which could be assigned both to the taxon and stratigraphic 'interval concerned. Spedes in any one orf 

the ·stratigraphic interv-als used are treated as though they occur throughout that inte•rval, hence the effect of a histogram. 
28 REVIEW OF ORDOVICIAN PELECYPODS 

The descent of arcaceans from cyrtodontids has been 

widely accepted for many years and was documented 

by Douville (1913), Newell (1954), and Cox (1959). 

These authors showed how in successive stages the 

cyrtodontid type of dentition could give rise to the 

parallelodont dentition of middle and late Paleozoic 

arcaceans, and how this in turn could give rise to the 

arcacean dentition typical of l\1esozoic and Cenozoic 

forms. In this process, the horizontal and oblique teeth 

of cyrtodontids and parallelodontids eventually came 

to be almost at right angles to the dorsal margin, which 

makes the arcaceans secondarily taxodont. In their 

dentition, arcaceans are convergent to the nuculoids, 

but as indicated by the stratigraphie succession and 

the presence of the duplivincular ligament in living 

arcoids, they are related to the pteriomorphians and 

not to the nuculoids. This line of reasoning is also supported by ontogenetic data (,Jackson, 1890, p. 365) 

which show that in at least some living arcaceans the 

earliest teeth are oblique to the dorsal1nargin and perpendicular teeth fonn later in the growth of the animal. 

Duplivincular-ligament forms first appear in the 

fossil record somewhat later in Ordovician time than 

the first three lineages discussed above, and relationships among the three duplivincular-ligament families 

are difficult to evaluate. The pterineids are the most 

specialized in that they have an inequivalved shell, a 

feature unknown in any Early Ordovician pelecypods. 

The ambonychiids and the cyrtodontids have retained 

the primitive equivalved shell. The ambonychiids show 

a tendency toward the loss of the anterior end of the 

shell and the development of a 1nonomyarian condition, 

although some ambonychiids retain an anterior lobe 

and maintain a heteromyarian condition. The cyrtodontids are the most generalized of the three families 

in that as a group they show the least reduction of 

the anterior end, some species being almost Glycymeri8-

1ike in shell shape (pl. 6, figs. 21-23). Most cyrtodontids 

show some reduction of the anterior end (pl. 7, fig. 3; 

pl. 9, figs. 4-7) ; however, this is usually not as pronounced as in the ambonychiids (pl. 10, figs. 1, 3, 6, 8). 

Even in the cyrtodontid genus Va:JI/UXe7nia where the 

beaks are almost terminal (pl. 7, fig. 10; pl. 8, fig. 1), 

the anterior adductor is not lost, rather it is raised and 

originates on an umbonal shelf. 

As a working hypothesis it is suggested that the 

cyrtodontids are the most primitive of the duplivincular-ligament forms and that this family gave rise 

independently to the pterineids and ambonychiids; 

presumably the pterineids arose first as they are the 

most specialized (fig. 5). Later in the Paleozoic the 

eyrtodontids gave rise to the arcaceans, the ambonychiids gave rise to the myalinids, and the pterineids 

gave rise to the rest of the pteriaceans, the pectinaceans, 

and the pinnids. 

HETEROCONCHIA 

The actinodontoids form a fifth Ordovician peleeypod lineage. As herein defined, three, possibly four, 

Ordovician families belong to this stock : Cyeloconchidae, Lyrodesmatidae, Redoniidae, and possibly 

Babinkidae. It seems probable that 1nost of the later 

heterodont and palaeoheterodont groups are descended 

frmn the actinodontoids. On the basis of what is 

presently known, only the aetinodontoids have a dentition which could have given rise to various heterodont 

and palaeoheterodont dental types. This general viewpoint has previously been suggested by Douville (1913) 

and Cox ( 1960) . 

Cox ( 1960) placed the heterodonts and the palaeoheterodonts ( actinodontoids, unionoids, and trigonioids) in a single subclass-the Heteroconchia Hertwig. 

If the aetinodontoids did give rise to the other palaeoheterodonts and to the heterodonts, it would seem that 

the taxonomy would better reflect the phylogeny of the 

groups if they were placed in a single subclass (Heteroeonchia) ; there seems to be no need for a subclass 

Palaeoheterodonta. In Ordovician time, heteroconchians ( aetinodontoicls) were subordinate pelecypod 

faunal elements (fig. 6) ; it was in the post-Ordovician 

that this group became so important and eventually in 

the l\:fesozoic and Cenozoic became the dominant pelecypod group. 

In spite of some morphologieal differences from 

younger lucinoids, Babinka shows more lucinoid 

features than any other known pre-Silurian pelecypod, 

and it probably should be classified as a lucinoid. 

Lucinoids form an ancient pelecypod lineage which 

solved the problems of infaunal living in an unique 

way. If Babinka cannot be related to the actinodontoids 

then the lucinoids have an ancestry different from that 

of the hete.roconchians and should be placed in a subclass of their own. Herein Babinka is tentatively allied 

to the actinodontoids. 

Oycloconcha is similar in general morphology and 

especially in hinge features to such late Paleozoic crassatellaceans as 0-riomla88atella (Newell, 1958; Boyd and 

Newell, 1968), and it seems likely that the erassatellaceans are descended 'frmn the cyeloconchids. Likewise, 

Lyrodesma in its general morphology, but especially in 

its hinge features is so similar to younger trigoniaeeans 

that it seems likely the Lyrodesmatidae gave rise to the 

T'rigoniacea. 

Cha van ( 1966a, b) felt that by using Bernard's 

mEt \ocl of establishing tooth homologies he could relate 

Redonia to what he considered to be 1niddle and late 
PHYLOGENETIC SUMMARY 29 

Paleozoic carditaceans. However, Cox (1960, p. 69) and 

Boyd and Newell ( 1969) cautioned that care should be 

taken in the application of Bernard's system. The 

hinge similarities between Redonia and the PerInophoridae [Kalenteridae] are not as striking as those 

between other actinodontoids and their presumed 

descendants. 

ANOMALODESMATA 

Anomalodesmatans, the sixth lineage, became prominent in the latter part of the Ordovician (fig. 6), and 

most species plaeed in the genera Ouneamrya, Oyrmatonota, Psiloconcha, and Rhytinz,ya are Late Ordovician in age. The soleniform anomalodesmatans may 

date from the lower Middle Ordovician rocks of Europe 

(Llandeilo) where species now placed in the genus 

0 oxiconchia (Babin, 1966) were rega,rded as desmoclonlts 

by Douville ( 1913). The earliest known anomalodesInatans with concentric undulations are early Wilderness Age and have been placed in the genus o~mea:rnya 

(Wilson, 1956). It may be that the seemingly late appearance of the anomalodesmatans is based upon the 

difficulty of identifying such structures as shell gapes 

and concentric undulations in inadequately preserved 

molds and casts; as the group becomes better known its 

range may be extended downward. 

RELATIONSHIPS OF THE VARIOUS LINEAGES TO ONE 

ANOTHER 

The fact that the six lineages are so distinct from 

the time when pelecypods first became abundant in the 

fossil record makes it exceptionally diffieult to relate 

then1 to one another; it also suggests a more or less 

long pre-Ordovician evolution of the group, or alternatively, an exceedingly rapid Early Ordovician 

evolution similar to that of 1nammals in the Paleocene. 

Presumably all pelecypods had a common preOrdovician ancestor, and Vogel (1962) has postulated 

that the Middle Cambrian animal Lanwllodonta fulfilled this role. Horny ( 1960) proposed that some 

B abinka-like pelecypod would be most suitable as the 

co nun on ancestor of all pelecypods, and that B abinka 

was the least modified descendant of this common ancestor. Neither of these proposals is entirely satisfactory; Lamellodonta needs to be better documented before it can be cast in the role of the ancestral pelecypod, 

and Babinka seems to be no more or less primitive 

morphologically than Oycloconcha or various of the 

nuculoids which also show multiple accessory muscle 

scars and a more or less generalized type of shell. 

The concept that all pelecypods are descended from 

nuculoid taxodonts (Jackson, 1890) is not well sup421-895 0- 71 - 5 

ported by the stratigraphic sequence which shows that 

conocardiids, babinkids, nuculoids, modioliform modiomorphids, and actinodontoids all appear in the fossil 

record at about the same time (figs. 5, 6) ; in addition, 

it is cliffieult to see how taxodont dentition could have 

given rise to the other Ordovician dental types. Allen 

and Sanders ( 1969) described the solemyid protobranch 

N'ltcinella serrei Lamy which has a dentition that they 

regarded as reminiscent of Ordovician actinodontoids. 

If Nucinella can be shown to possess actinodontoid dentition this raises the attractive possibility that the 

earliest pelecypods were all protobranch, but not taxodont. However, if Allen and Sander's interpretation 

is correct, Nucinella is unique among pelecypods in 

t1hat it is a monomyarian which 1naintains the anterior 

adductor muscle and not the posterior one; normally 

this is a characteristic of early ontogenetic stages in 

pelecypods. 

In the past few years a number of authors, both 

paleontologists and malacologists, have speculated on 

the early phylogeny of the Pelecypoda including: Balbin 

( 1966), Cox ( 19·60), Dechasea ux · ( 1952), Newell (1966), 

Purcheon ( 1959, 1960, 1963), Stasek ( 1963), and Vogel 

( 1962). These speculations generally fall into one of 

two categories : ( 1) Those which place the nuculoid taxodonts at the base of pelecypod phylogeny, and (2) 

those which treat actinodontoids as the ancestral stock. 

This is a serious difference, although if Allen and 

Sanders ( 1969) are correct, many of the diffieulties presented by this diehotomy will be obviated. However, 

even among those who regard actinodontoids as the basal 

stock there is strong disagreement as to how the other 

groups are related to the actinodontoids. For example, 

Vogel suggested that taxodonts were derived from 

eyrtodontids, ·whereas, Babin suggested that they were 

derived from a hypothetical archetypic pelecypod ancestor. Add these conclusions to those of persons who 

would place taxodonts at the base of the pelecypod 

phylogenetic tree and one quickly sees that speculations 

on the interrelationships of early pelecypod groups are 

based on exceedingly scanty data which can be interpreted in various logical ways with one interpretation 

being as likely as another. 

The question of the relationships of the various Ordovician pelecypod lineages to one another is still wide 

open; because of the scantiness of the available data 

on this point I have made n.o attempt herein to relate 

these lineages to one another (fig. 5) ; presumably they 

are related somewhere in the pre-Ordovician. Only the 

finding of additional specimens which provide documentation that one proposed phylogeny is more likely 

than another will resolve the difficulties. 
30 REVIEW OF ORDOVICIAN PELECYPODS 

ORDOVICIAN LINEAGES AND HIGHER LEVEL 

PELECYPOD TAXONOMY 

If the Ordovician pelecypod lineages documented 

above reasonably approximate pelecypod phyletic lines, 

as I believe they do, then this information should be 

reflected in the taxonomic hiera.rchy of the class at the 

subclass level. 

Both Cox (1960) and Newell (1965) regarded the 

nuculoids and the duplivincular-ligament forms and 

their descendants as pelecypod subclasses, and this much 

of the picture drawn above is already incorporated into 

the formal taxonomy of the class. The rest of this picture should be reflected in the pelecypod taxonomic hierarchy and the conocardiids, mytilaceans, heteroconchians, and anomalodesmatans should also be placed 

in separate subclasses. Ordovician pelecypods show what 

the primary radiation of the group was like, and they 

are the ancestors of all later forms. If phylogen~tic data 

should be incorporated into classification, then the 

taxonomy of pelecypods should be revised along the 

lines suggested below. 

Based on the relationships postulated herein I propose that the subclass level taxonomy of the Pelecypoda 

should be arranged as follows: 

Stttbclass Rostroconchida Oox.-The conocardiids are 

an enigmatic, highly distinctive, Paleozoic, bivalved 

group which is usually allied to the Pelecypoda; they 

originated in the Early Ordovician and died out in the 

Late Permian. For this subclass the name Rostroconchida Cox (1960) is available. 

Subclass Palaeotaxodonta [{orobkov.-Nuculoids are 

a distinct pelecypod lineage from the Early Ordovician 

to the present and already in Ordovician time they were 

a highly varied and highly successful group. Most recent authors have placed nuculoids in a separate highlevel taxon for which the name Palaeotaxodonta l{orobkov is available. 

Subclass Isofilibranchia /redale.-Mytilacean-like 

shells are known from the Early Ordovician to the present; the older species all have a more or less M odioltts 

shape and are probably ancestral to the younger 

Mytilidae. Mytilaceans are like the pteriomorphians in 

being byssally attached anisomyarians; however, 

throughout their stratigraphic ranges the two groups 

are distinct from each other, and the mytilaceans never 

possessed the duplivincular type of ligament. These 

data suggest that the two groups are separate lineages 

of about equal antiquity which should have ·the same 

taxonomic· rank. For this subclass the name Isofilibranchia Iredale (1939) is available. 

Subclass Pterimnorphia Beurlen.-Duplivincular 

ligament forms are a distinctive pelecypod stock from 

the early Middle Ordovician onward, although the 

primitive duplivincular ligament was eventually lost 

in all members of the group except the arcoids. The 

taxon includes most of the living anisomyarians as well 

as the arcoids and the ambonychiaceans. For this subclass the name Pteriomorphia Beurlen ( 1944) is 

available. 

Subclass H eteroconchia H ertttoig.-Ordovician actinodontoids are probably ancestral to the heterodonts, 

unionaceans, and trigoniaceans. For this group, Hertwig's (1895; Cox, 1960) name Heteroconchia is available. Cox included the forms here called anomalodesmatans in this subclass; I think that this group forms 

a subclass of its own. 

Subclass Anornalodesm.~ata Dall.-Certain Ordovician 

burrowing forms and their probable descendants, such 

as Edmondia, Solenonwrpha, Wilkingia, and Pholadmnya, are herein placed . in a separate subclass; two 

distinct stoc.ks may at present be combined in this taxon. 

Newell ( 1965) placed the Paleozoic members of this 

subclass in the subclass Cryptodonta, and the younger 

forms in the subclass Anomalodesmata. Runnegar 

( 1966) placed both the Paleozoic and younger forms 

in the Anomalodesmata; this procedure is followed 

herein. For this taxon the name Anomalodesmata Dall 

( 1889) is available. 

LIFE HABITS 

By La1te Ordovician time, pelecypods had undergone 

an adaptive radiation by which they had already explored most of the major modes of life utilized by 

younger forms except for the cementing of the shell 

to the substrate and swimming, although the degree of 

exploration of some of the modes of life was not as 

advanced as it was to become. 

Ordovician infaunal burrowing pelecypods are 

represented by babinkids, cycloconchids, ano!lnalodesmatans, lyrodesmatids, nuculoids, probably some cyrtodontids and modioliform modiomorphids, and possibly 

some ambonychiids. Epifaunal forms include the pterineids, most ambonychiids, and some Inodioliform modiomorphids and cyrtodontids. Epifaunal nestlers on 

bryozoan colonies are found among the modioliform 

modiomorphids, probably among the ambonychiids, and 

perhaps among the pterineids. Boring infaunal pelecypods are not undoubtedly known in the Ordovician; 

however, Whitfield (1893 [1895]) deseribed the boring 

modiolifor1n modiomorphid Oorallidomus and figured 

(pl. 13) specimens of this genus embedded in burrows 

on the underside of a coral; unfortunately I have not 

been able to locate his material. Although conocardiids 

bear at least superficiaJ resemblances to some ymm~r 

boring pelecypods there is to date nothing to suggest 

that they lived like them. 
LIFE HABITS 31 

A review of the introduction of the various ecological 

types into the known fossil record is instructive. At approximately the same time in the early Early Ordovicim1 

(Tremadoc), two pelecypod lineages appear: babinkids 

and conocardiids (fig. 6). These are in faunal forms, and 

their almost simultaneous appearance near the base of 

the Ordovician suggests that this mode of life is the 

primitive one for pelecypods. This reenforces Yonge's 

(1962) conclusion that the presence of a byssus in the 

adult represents the persistence of a postlarval organ 

and that pelecypods having an adult byssus are neotonous (paedomorphic) in this respect. By the end of 

Early Ordovician time (Arenig), seven pelecypod 

groups are represented in the known record : babinkids, 

conocardiids, cycloconchids, lyrodesmatids, modioli form 

modiomorphids, nuculoids, and redoniids (figs. 6, 7). 

Of these only the modioliform modiomorphids and 

perhaps some of the conocardiids are likely to include 

110presentatives which were infaunal. Perhaps at this 

stage of the development of the class, epifaunal pelecypods would have had to compete for living space with 

tho epifaunal articulate brachiopods. It may be that 

pelecypods met less competition as part of the infauna, 

although lmowledge of t'ho soft-bodied Ordovician infauna is poor at best. 

As far as pelecypods are concerned, the early Middle 

Ordovici•an ("Whiterock-Porterfield) is especially noteworthy beoause of the introduction of undoubted epifaunal groups. It was at this time that the first ambonychiids, cyrtodontids, ·and pterineids appeared; these 

three groups initiate the known fossil record of the 

subclass Pteriomorphia which has been predominantly 

epifaunal throughout its history. Ambonychiids were a 

highly successful early Paleozoic group (Pojeta, 1006), 

many members of which are mytiliform in shape and 

probably had a life habit sim il ar to that displayed by 

11/ytilus. The remaining early Middle Ordovician pelecypod fauna is ma.de up of the same groups as are found 

in the late Early Ordovician (fig. 6). 

The late Middle Ordovician (Wilderness-Barneveld) 

was a time of diversification for the pelecypod groups 

which had originated previously, especially for t he 

cyrtodontids, modioliforn1 modiomorphids, and nuculoids. It was also at this time that undoubted infaunal 

anomalodesmatans appear in the fossil record. Of groups 

which originated earlier the redoniids and babinkids 

are not known from these or younger rocks (fig. 8) . 

With the exception of the vlastids and possibly the 

lunulacardiids, no new family -level taxa appear in the 

Late Ordovician (Cincinnatia.n) . There is some expanFIGURE 7.- Life-habit r econstructions of late Early Ordovician pelecypod f auna. This composite diagram shows representative 

genera od' pelecypods in their probable life positions. Specimens a r e not drawn to relative or actual scale. Note the liack od' 

diverSiification of the ·epifauna. Idealized algae are inclm:led in the fliagram. Aol'inodonta drawn from Phillips and Salter 

(1848), Babinlca drawn from McAlester (1965), Ly1·odesm.a drawn from Barroii.s (1891) and Babin (1966), Modi()lopsis 

dmwn from Barrois (18\}1) and Babin (1966), Redonia drawn from Born (1918) and Babin (1966). 
32 REVIEW OF ORDOVICIAN PELECYPODS 

FIGURE 8.- Life-habit reconstructions of late Middle Or,dovician pelecypod fauna. This composite diagram shows• representative 

genera of pelecypods in their probable life positions. Spe·cimens not drawn to relative or actual seale. Drawings are based 

on specimens figured on the plates. Note the diversification of the epifauna. Idealized algae are included in the diagram. 

sion o:f a :few groups and contraction of others in the 

number of known species, and there are some changes at 

the generic level, but overall the Late Ordovician is 

similar to the late Middle Ordovician in having about 

the same number of known species and the same composition at the higher taxonomic levels. Ho,vever, 

ecologically the oldest well-documented nestling modioliform modiomorphids (fig. 9) are fotmd in Richmond 

Age rocks (late Late Ordovician; pl. 16, figs. 4, 5) ; some 

of the Richmond ambonychiids also seem to have been 

nestlers, although :for these the evidence is not as direct 

as for the modioliform modiomorphids. The probable 

boring clam Oorallidmnus is known only from Richmond Age rocks. 

Both suspension feeders ( Lyrode81na) and deposit 

feeders (Otenodonta) are known :from the late Early 

Ordovician onward. 

ORDOVICIAN EPIFAUNA 

Ordovician byssate epifaunal groups are: ahtioconchids, most ambonychiids, proba·bly some cyrtodontids 

of the V amtmernia type, some modioliform modiomorphids, and pterineids. Cyrtodontids underwent a complex radiation of their own which seems to have resulted 

in epifaunal, semi-infauna.l, and infaunal forms, and 

this group is discussed separately after the section on 

the Ordovician infauna. 

Modioliform modiomorphids probably were similar 

in mode of life to those living mytilaceans which have 

an anterior lobe and nonterminal beaks (for example, 

Arcu.attlla, llf odiolu.s, and Mytella). These animals can 

live on or in a variety of substrates including hard bottoms where they are raised above the substrate, although 

often nestled in nooks and crannies (Kauffman, 1969, p. 

N144) ; soft bottoms where they are partly buried in the 

substrate up to about the depth of the posterior part of 

the umbonal ridge (I have seen some individuals of 

Arctlatula dernissus (Dillwyn) living in this fashion, 

both in aquaria and in nature); and in many populations of A. dernissus embedded in peat mats where they 

are often completely buried and almost vertical in position with the posterior end uppermost (personal observation and S.M. Stanley, oral commun., 1968) . Thus, 

pelecypods with a llf odiolu.s shape can be epifaunal, 

semi-infaunal, or infaunal. As I could not distinguish 

these different modes of life in the Ordovician on the 

basis of data currently available to me, I have dra,Yn 

all the Ordovician :forms on hard bottoms raised above 

the substrate (figs. 7-9) whi ch seems to be a reasonably 

common life position in Holocene species. In one Ordovician species of llf odiolopsis it was possible to document 
LIFE HABITS 33 

FIGURE 9.-Life-habit reconstructions of Late Or•do·vician pelecypod fauna. This cornposrite diagram shows representative genera 

of pelecypods in their probable life positions. Note the further diver,sification of the epifauna. Specimens not drawn to relative or actual scale. Drawings are based on specimens figured on the plate& 

that it was a nestler on trepostome bryozoan colonies 

(pl. 16, figs. 4, 5). The trepostome was identified as probably a species of H allopora by 0. L. Karklins, U.S. 

Geological Survey. 

In some places, Ordovician modioliform modiomorphids are found crowded on single bedding planes or 

forming single thin beds with many of the shells being 

articulated and varying in size. These facts suggest that 

at least some species were gregarious like some living 

mytilaceans. Oorallid01nus, the one probable Ordovician borer, looks much like a modioliform modiomorphid. (See Whitfield, 1893 [1895], p. 493, pl. 13.) 

The first ambonychiids to appear in the fossil record 

already show a marked reduction of the anterior end 

of the she11. This reduction indicates that the group was 

already specialized and had already undergone a more 

or less long period of evolution. From nearly the beginning of their known history, ambonychiids can be divided into two groups: those which possess an anterior 

lobe (pl. 10, fig. 5) and those which lack such a lobe (pl. 

10, figs. 1, 12). Ambonychiids arc both ecological and 

morphological homeomorphs of the recent mytilids. 

Those ambonychiids which have lost the anterior lobe 

(such as Ambonychia, figs. 8, 9) are much like living 

species of ll!ytilus in shape and body construction and 

probably lived in an epifaunal fashion like members 

of llfytil1ts. This genus projected above the bottom and 

was attached to hard substrates. Ambonychiids which 

have an anterior lobe are often deeper bodied than 

mytilids with a similar lobe; however, it seems likely 

that these ambonychiids showed the same variations in 

life habits as JJ! odiol·us-like mytilaceans. 

Some late Late Ordovician (Richmond) Ambonychias are occasionally found in beds which contain large 

numbers of branching trepostome bryozoans that seem 

to surround "crack-out" specimens of the clams. This 

occurrence suggests that these Ambonychias were nestling on the bryozoans. Although the evidence for 

nestling among ambonychiids is not as direct as the 

evidence for nestling of modioliform modiomorphids, 

it seems likely that the ambonychiids also would have 

exploited this mode of life. 

The peculiar ambonychiid genus Opisthoptera (pl. 

10, figs. 1, 2) is also found in Richmond Age rocks. 

Opistlwptera is an equivalved, markedly alate form 

which may have lived much like modern species of 

Pteria attached to various erect substrates and using 

the wing as a rudder to orient itself to the currents 
34 REVIEW OF ORDOVICIAN PELECYPODS 

(Kauffman, 1969, p. N132, N144). No specimens of 

Opisthoptera have been found in this position, and they 

may have been attached to hard horizontal substrates 

as shown in figure 9. 

Some Ambonychiids, like modioliform modiomorphids, are found in large numbers on single bedding 

planes or forming a single thin bed with many of the 

shells still articulated and varying in size. These features suggest that some species were gregarious like 

some living mytilids. Some Ordovician ambonychiids 

are found with edrioasteroids attached to them (fig. 9). 

Ordovician pteriaceans are placed in two families. 

The Ahtioconchidae is poorly known and is represented 

by the single species Ahtioconcha auris Opik. It is 

markedly inequivalved and left convex and was presumably attached by a byssus. 

Ordovician pteriaceans placed in the genus Pterinea 

have both a well-developed anterior lobe and a posterior wing. In shell shape they are pteriaform; however, their pronounced valve inequality is more like 

Pinctada. Like their living counterparts, Ordovician 

forms were probably entirely epifaunal. The known 

specimens of Pterinea to which edrioasteroids are 

attached always have the latter on the ieft valve. This 

placement suggests that this valve was uppermost and 

that the commissure of the shell was never at right 

angles to the substrate the way it is in some living 

species of Pteria which are pendant on alcyonarians. 

All Ordovician pterineids may not have had the right 

valve flat against the substrate as shown in figure 9; they 

may have also been attached with the commissure at 

some acute angle to the substrate as shown for Palaeopteria in figure 8. Palaeopteria is far less inequivalved 

than Pterinea and may have been attached to trepostome 

bryozoans the way Pteria attaches to alcyonarians, 

although there is no direct evidence for this. 

ORDOVICIAN INFAUNA 

The Ordovician infauna is highly varied and, as 

mentioned previously, includes babinkids, most conocardiids, cycloconchids, cyrtodontids of the Oyrtodonta 

type (p. 37), anomalodesmatans, lyrodesmatids, 

nuculoids, redoniids, probably some modioliform 

modiomorphids, and possibly some ambonychiids. The 

possible infaunal and semi-infaunal representatives of 

the last two groups are discussed in the preceding section on Ordovician epifauna. 

Lyrodesma and Babinka were infaunal siphonate 

suspension feeders. Lyrodesma is sinupalliate and elongate and therefore was probably a "normal" siphonate 

pelecypod (figs. 7-9). B abinka lacks a pallial sinus and 

was probably a mucous tube feeder like the later 

lucinoids (fig. 7). Among the anomalodesmatans with 

elongate gaping shells a pallial sinus is unknown; however, at least some of them probably were sinupalliate. 

As far as known the remaining Ordovician infaunal 

forms were integropalliate, and the shell was probably 

in contact (or nearly in contact) with the sedimentwater interface at the point of origin of the inhalant 

current. 

Lyrodesma is the oldest known siphonate pelecypod 

which has a pallial sinus; this feature combined with 

the anteriorly-posteriorly elongated shell strongly suggests that the genus was infaunal with only the siphons 

reaching the sediment-water interface (figs. 7- 9). The 

rostrate nature of the posterior end of the shell is 

similar to such living forms as Anomalocardia and 

suggests a vertical life position. The oldest known specimens of Lyrodesma which sho~ a pallial sinus are 

early Late Ordovician in age (Eden and Maysville); 

however, Middle and Early Ordovician shells with the 

same shape and dentition as the Late Ordovician 

species of Lyrodesma probably had the same mode of 

life. 

Paleozoic pelecypods in which an undoubted pallial 

sinus is present are not known to be numerous; however, the structure is known to occur in three subclasses 

and has an early origin. In addition to Lyrodesma, 

sinupalliate pelecypods include the palaeotaxodont 

genera Palaeoneilo and A ntraconeilo (McAlester, 1963h, 

1968); the trigonicean Scaphellina (Newell and Ciriacks, 1962) ; and the anomalodesmatan genera Wilkingia (Wilson, 1959), Pymm~ts (Newell, 1956), Orassiconcha (Netschajew, 1894), Oasterella (Mendes, 

1952), Vacunella, Ohaenomya, and perhaps Oblicarina 

(\iVaterhouse, 1967). The structure is probably more 

widespread than the above list indicates, although it 

has not been documented because the pallial line is unknown in many Paleozoic genera. The fact that the 

pallial sinus occurs in Ordovician pelecypods indicates 

that siphonate suspension feeding was an early adaptation of the group, although the possibilities opened up 

by this mode of life \\ere not fully exploited w1til the 

post-Paleozoic (Stanley, 1968). 

McAlester's reconstruction of the mode of life of 

Babinlca as a shallow infaunal element is highly probable, and his figure of that genus is copied here in 

figure 7. 

Ordovician nuculoids like their living counterparts 

were probably deposit-feeding infauna. In general, they 

can be divided into two groups: nuculiform shells such 

as Deceptrix and nuculaniform shells such as Otenodonta s.s. Reconstructions of Ordovician nuculoids in 

figures 7-9 are largely based on the studies of the habits 

of living species by Yonge (1939), Drew (189.9), and 

Stanley (1968, 1970). No Ordovician solemyids !lire 
LIFE HABITS 35 

known, although the name S olent.ya (as S olenemya) has 

occasionally been used for Ordovician clan1s (Ruedemann, 1912). 

Yonge's studies of N~wula indicate that the animal 

positions itseif in the sediment with the anterior end 

uppermost, whereas Yoldl~a positions itself with the 

posterior end uppermost. Although Drew and Y onge 

figured Y oldia in an almost vertical position with the 

posterior end above the sediment-water interface, 

Stanley ( 1968) has shown that it burrows diagonally 

and does not expose the posterior end of the shell. However, an equally important point is that the life position 

of nuculaniform shells such as Y oldia is the reverse of 

n uculiform shells such as N ucula. 

Y onge noted that in its life position in the substrate, 

._IV ucula nucleu8 has an anterior inhalent current and 

is shallowly buried with the anterior end approximately 

parallel to the sediment-water interface, and this end 

is covered with a thin veneer of sediment. It is assumed 

herein that Ordovician N ueula-like shells such as Deceptrix and Similodonta lived in a similar fashion 

(figs. 8, 9). 

The burrowing habits of such nuculaniform shells 

as lJJ alletia, N1.tculana-, and Yoldia are varied; in addition, these animals have posterior in current and excurrent siphons which may insert into a prominent 

pallial sinus. Because of-these characteristics it is difficult to compare these living forms to such integropalliate nuculaniform shells as Otenodonta. s.s. Still it seems 

likely, based on shell shape, that Otenodonta s.s.lived in 

a manner similar to one or another of the living nuculaniform species. 

111 alletia, a deeper water form having a thin transparent shell, burrows parellel to the sediment-water 

interface and not at some angle to it. According to 

Y onge ( 1939), this species is unlike othe,r nuculaniform 

shells he examined in that it tends to move about more 

or less continuously; probably this 1node of life has 

little significance for interpreting the life habit of such 

thick -shelled forms as 0 tenodonta. 

The species of LmnubulU8 and Y oldia studied by 

Yonge and Stanley burrow diagonally, completely 

burying the shell. It seems likely that Otenodonta lived 

in a manner similar to one of these genera (figs. 7-9) . 

Ordovician solenif0rm anomalodesmatans such as 

Oymatonota are interpreted as burrowing forms based 

on their elongate shell shape, subparallel dorsal and 

ventral margins, reduced mnbos, and anterior and 

posterior shell gapes. These features reoccur in various 

distantly related pelecypod groups which have become 

relatively deep burrowers, such as myids, solemyids, 

and solenids. Nothing is known of the hinge line or 

pallial line of Ordovician solenifonn shells and little is 

known of their musculature; however, their general shell 

shape points up their infaunal habits. The depth to 

which these forms could burrow is uncertain; it would 

depend upon the extensihiiity of the siphons, but nothing is known of the pallial line. 

The general morphology and shell sha.pe of the equivalved, elongated telliniform genus Oycloeoncha suggests that it was a shallow infaunal form. There is 

nothing to suggest that Oyeloeoncha is closely related 

to Tellinacea, rather it see1ns to be related to the late 

Paleozoic crassatellaceans (Newell, 1958; Boyd and 

Newell, 1968). Redoniids also were probably infaunal 

elements; based on Babin's figures (1966, p. 246) of 

this group, they probably lived in a manner similar to 

Oyeloconcha (figs. 7-9). 

Mos't conoca,rdiids were probably infaunal elements, 

although such forms as Eucha81na fron1 the Early 

Ordovician (pl. 20, figs. 18-21) may have been epifaunat Conocardiids a.re not included in any of the 

reconstructions shown here as there is still much debate 

about such basic morphological interpretations as which 

end is anterior in this group. 

CYRTODONTIDAE 

Cyrtodontids present 'a perplexing melange of forms 

wl1ich are diffieult to evaluate as there is nothing quite 

like them in modern seas. They are abundant in the 

upper Middle and Upper Ordovician rocks of North 

America (fig. 6) and are known to range upward into 

the Devonian rocks of Europe (Frech, 1891; Maillieux, 

1937). In ·Ordovician time the group underwent an 

obvious adaptive radiation which produced Glycymerislike shells (pl. 6, figs. 21-23), N oetia-like shells (pl. 7, 

fig. 6), Orenella-like shells (pl. 8, fig.11), and Septiferlike shells (pl. 8, fig. 1). Some of the cyrtodontids show 

a pronounced reduction of the anterior end, all of them 

have the umbos displaced anteriorly, and all are robust 

shells. The range of variation of Ordovician cyrtodontid 

shell form suggests that they were adapted to ·a variety 

of niches and probably habita;ts. 

By Devonian time, cyrtodontids were no longer as 

varied or as large as in Ordovician time, and as noted by 

Douville (1913) some of them had begun to approach 

Carboniferous ·and Mesozoic parallelodontids and arcids 

in shell shape and dentition. 

Cyrtodontids of the Y anuxenda type (pl. 8) show 

some features, which are usually found in byssally attached pelecypods, including some reduction of the 

anterior end of the shell (pl. 9, fig. 7), some reduction 

in the size of the anterior adductor muscle (pl. 8, fig. 8), 

anterior displace~ment of the beaks (pl. 8, fig. 5), and the 

elevation of the anterior ~adductor muscle on either a 

shell thickening (pl. 8, fig. 6) or an umbonal septum 
36 REVIEW OF ORDOVICIAN PELECYPODS 

(pl. 8, fig. 1). They show no byssa.l gape (pl. 8, fig. 3); 

however, some specimens show a slight deflection of 

the anterodorsal margin forming abyssal sinus (pl. 9, 

fig. 7). 

Cyrtodontids of the V anu.xe1nia type are characterized 

by having the anterior teeth i1nmediately below the 

beaks (pl. 8, figs. 1, 5, 6, 8, 13) and by having the anterior adductor muscle displaced medially and originating on a raised shell thickening (pl. 8, fig. 5) or on an 

umbonal shelf or septum (pl. 8, fig. 1) which :floors the 

anterodorsal part of the 1shell. The anterior end of the 

pallial line terminates at the mnbonal shelf (pl. 9, fig. 7) 

or thickening (pl. 8, fig. 9), and in forms in which the 

shelf is well developed there is usually some development 

of a myophoric notch on its posteroventral surfaee (pl. 

8, figs. 1, 2; pl. 9, figs. 5-7). The myophoric notch probably served as the seat and passageway of an accessory 

n1uscle. In forms which lack an umbonal septum, but 

have a shell thickening, an accessory n1uscle scar is 

present on the lateral-posterior face of the anterior adductor scar (pl. 8, figs. 6-9); this scar is in a position 

homologous with the myophoric notch. 

A notched umbonal septum, similar to the septum of 

Vanuwemia, is found in living species of the b~ssally 

attached mytilid genus SelJ'tifeJ' (pl. 9, figs. 14-17). In 

Septifer, as in Van'~.t.;r:emia, the umbonal septum. serves 

as the sea:t of the anterior adductor muscle., and in both 

genera the depth of the myophoric notch shows individual variation (pl. 9, figs. 4-7, 11-14) and species 

variation (pl. 8, fig. 1; pl. 9, figs. 5-17). The notch is 

a,lways deep in some species and always shallow in 

others, but it is not developed to the same depth in a.U 

individuals of a species. 

In Septifer bilomdarri8 the myophoric notch is either 

undeveloped or only shallowly developed (pl. 9, figs. 

8-13), whereas, in S. exciBus it is always deep (pl. 9, 

figs. 14-17). In attempting to determine what structure 

forms the notch, I only had specimens of S. bilooularis 

for dissection, and as noted above in this species, the 

notch is at best only shallowly developed. When present, 

the notch is equally developed in the mnbonal septa of 

each valve of an individual, and it extends along the 

lateral face of each septum as a groove, thus the notches 

must be formed by paired structures (pl. 9, figs. 16, 17). 

The most likely paired structures to have formed the 

myophoric notches in Septijer are the anterior byssal 

retractor 1nuscles. InS. biloC1..lla.ris, these muscles insert 

into the byssal apparatus imn1ediately posterior to the 

umbonal septum and probably would be in contact with 

the septmn only when contracted. Although I did not 

have preserved specimens of S. exoisus to dissect, the 

large size of the myophoric notches and the grooves on 

the lateral faces of the shelves suggest that in this species 

the anterior byssal retractors are in more or less continuous linear contact with the septum. 

To the best of my knowledge, it is only in byssate 

pelecypods that an umbonal shelf is present. Among 

living forms it is found in the mytilid genus Septifer 

and in the dreissenid genera Dreissenia and 0 ongeria. In 

fossil forms it is h.'11own in smne myalinids such as 

SeptimyaZina (Newell, 1942) and Atonwdes1na: 

(Dickens, 1963), and perhaps in the ambonychiid 

genera Ambonyohiopsis and Oongerimnorpha (Pojeta, 

1966). 

Because the umbonal septmn is known only in byssally 

attached pelecypods, its presence suggests that cyrtodontids of the V anu.xe1ni.a type were byssate. Also 

these cyrtodontids show the additional features of 

byssally attached pelecypods cited above, as well as some 

:flattening of the anterior face of the shell (pl. 8, fig. 3), 

and an articulated specin1en will often balance on this 

face. However, the anterior edge of the shell remains 

rounded (pl. 8, fig. 8) , and a specimen balanced on it 

is definitely unstable. A byssus would help stabilize the 

shell, but it semns unlikely that cyrtodontids of the 

V antt&xe'lnia type were epifaunal after the fashion of 

llfytil!U8 or An&bonych:ia. They may have been semiinfaunal in the sense of being partly buried in the sediment as are some pinnicls, burrowing arcs (Lim, 1966), 

and modioliform mytilids, or they may have dwelt in 

depressions and conea vi ties as do many of the byssally 

attached arcs. Supporting the view that cyrtodon.tids 

with an umbonal shelf or thickening were not entirely 

epifaunal are rare specimens in which the posterior end 

is encrusted with epibionts (pl. 8, fig. 14), whereas, the 

anterior end is free of epibionts; to date all specimens 

of this type seen by me have been single valves. The 

byssus, as in some of the burrowing arcs, may have been 

used to maintain the position of the partly buried shell 

in the sediment (fig. 8). 

Sardeson ( 1939) thought that shells of the V a;nuwemia 

type did not crawl about or burrow in the sea bottom, 

but rather that they were anchored to solid objects either 

pennanently or temporarily or that they rolled about 

with the storms and currents. He regarded them as 

anchored by the foot. 

Cyrtodontids with an umbonal septum were evolving 

in a manner of their own, and although they may have 

nestled in concavities on the sea bottom like the younger 

byssally attached ares, they do not seem to be on the 

direct line of descent leading to the arcaceans. Shells 

of the Y anuxem.ia type were showing a stabilization in 

position of the dental elements, whereas, shells of the 

Oyrtodon.ta type are highly variable in this regard 

especially in the nmnber and placement of the anterior 

teeth. Also cyrtodonticls with an mnbonal septum show 
LIFE HABITS 37 

more or less typical features of byssally attached 

anisomyarian duplivincular pelecypods, whereas, byssally attached arcaceans do not; the latter retain the 

anterior end of the shell, the beaks are displaced far 

back from the anterior margin, and they possess a midventral byssus. 

Cyrtodontids of the Oyrtodonta type lack an umbonal 

shelf or shell thickening (pl. 7, fig. 2), and some or all of 

the anterior teeth are not placed immediately below the 

beaks (pl. 7, figs. 1-4, 7, 8). In this group, an accessory 

n1uscle scar is present on the lateral surface of the hinge 

plate opposite the anterior teeth (pl. 6, figs. 18-20) ; one 

specimen I have seen may have an accessory scar in a 

position homologous to that of the accessory scar of 

cyrtodontids of the Vanuxen~;ia type (pl. 7, fig. 2). 

Some of the cyrtodontids which lack an umbonal shelf 

may have been byssally attached because of the presence of such features as reduction of the anterior part 

of the shell and significant anterior displacement of 

the beaks (pl. 7, figs. 2--4). However, others seem to 

have been infaunal including the Glycymeris-like and 

Noetia-like shells (pl. 6, figs. 21-23; pl. 7, figs. 5, 6). 

The N oetia-like shells are primarily a Late Ordovician development and are placed in the genus Oyrtodontula [Whitella J (pl. 7, figs. 5, 6 ; fig. 9). Living 

Noet,ia (S. M. Stanley, oral cmnmun., 1968) burrow 

in sandy bottoms often to the depth of the posterior margin of the shell, but some only to the depth of the umbonal ridge with the posterior end of the shell remaining 

exposed. Lim ( 1966) has shown that son1e species of living A nadara live in a similar position and substrate. 

Some of the Anadaras burrow 6-10 em below the surface with the posterior end of the shell totally out of 

contact with the sediment surface. It cannot yet be 

determined whether or not some of the Ordovician 

N oetia-like shells lived in the latter fashion; however, 

it seems likely that they were burrowing forms having 

a mode of life similar to burrowing arcs like N oetia 

and Anadara. 

The Glycymeris-like cyrtodontids are placed in the 

genus Oyrtodonta and 'vere probably shallow burrowers 

based on their general shell form. They may have burrowed like Oyrtodontu.Za, leaving the posterior end of 

the shell sticking up out of the sediment (fig. 8) ; Glycyrneris is known to adopt such a life position at times 

( Vles, 1906). 

Sardeson (1924) suggested that Oyrtodonta Tnegambona was probably epifaunal or semi-infaunal; he 

thought it could have lived on any shell edge except 

the posterior and that it probably anchored itself to the 

substrate by its foot. 

The most variation in shell shape and anterior dentition is among cyrtodontids of the Oyrtodonta type, and 

421-895 0- 71 - 6 

it is probably frmn this group that arcaceans arose in 

Devonian time. The fact that cyrtodontids were so 

varied and actively radiating in Ordovician time suggests that they are ancestral to the other duplivincular 

ligament forms. 

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A 

Page 

Abbreviations of names of museums__________ 4 

Abundance of Ordovician pelecypods_________ 3 

Actinodonta ________________________________ 9, 10, 17 

Actinodonta___________________________________ 6, 9 

cuneata___ _ _ __ _ _ __ _ __ _ ___ _ __ _ ___ _ ___ _ ___ _ _ pl. 1 

Actinodontoida ________________________ 1, 9, 17, 22,25 

Actinodontoids ______________________ 20, 24, 28, 29,30 

Actinomy'L----------------------------------- 6 Actinopterella __ ______________________________ _ 

Actinopteria _________________________________ _ 

Actinopterinia _______________________________ _ 

acuminata, Lyrodesma_________________________ 10 

acuminatum, Lyrodesma_______________________ pl. 3 

Adranaria ___ ----------------------- __________ 6 Ahtioconcha ___________________________________ 6,19 

auris ____ -------- ____ _ __ _ ___ ____ _ __ _ ___ _ __ 34 

Ahtioconchidae _______________________________ 19, 34 

Ahtioconchids_ --------- ____ ____________ ______ 32 

alata, Ambonychia _____________________________ pl.10 

albertina, IJeceptrix _ _ _ _ _ ____ __ __ ___ _ ___ _ ___ _ __ pl. 5 

Alcyonarians___ ____ ____ ____ __ __ ___ _ _ __ _ _ __ _ _ _ 34 

Allodesma __ -------------------------------- __ 4, 6 subellipticum ______________________________ pl. 2 

Allonychia __ ---- _ __ _ ___ _ ___ ____ _ _ ___ _ __ _ _ _ __ _ _ 6 

fianaganensis _____________________________ pl. 10 

Allorisma ------------------------------------ 24 Alnijia ____ --------- _____ ---- __________ -- _ __ _ _ 6, 19 

Ambonychia _____________________________ 4, 6, 9, 33,36 

alata ______________________________________ pl.10 

casterL __ -- _ ---- ________ -------- ___ ------- pl. 10 

obesa ____ ------ ___________________________ pl. 10 

radiata ___ ______________ --------- __________ pl. 10 

ulrichL---------------------------------- pl.10 

SP---------------------------------------- pl.10 

Ambonychiacea______________________________ 1, 25 

AmbonYchiaceans______________________ ____ __ 30 

Ambonychias ____ ---------------------------- 33 Ambonychiidae _________________________ 9, 17,18,25 

Ambonychiids __ -- __ 2, 4, 13, 18, 20, 28, 30, 31, 32, 33, 34 

Ambonychinia_________________________________ 6 

Ambonychiopsis_____________________________ __ 6, 36 

americana, Vlasta __ ------------------------ 23; pl. 20 americanus, Modiolus _________________________ pl.11 

Am ita ___ -----------------------------________ 6 Amphicoelia _________________________________ _ Anadara __ ________ -- _ __ _ ___ _ ______ _ _ __ ____ ___ _ 37 

Ancilla _________ ------ _______________________ _ 

Anderkenia_ _ _____ _ ______ ____ _____ ___ ________ _ 6, 19 

Angellum___ ___ _ ___ _______ ___ ________ _ ___ _ __ _ _ 6 

Anisomyaria __ --------------------- __________ 22,25 

Anisomyarianpelecypods------------------ 17, 25,30 A.nodontopsis_ _ _ _________ _ _____ _ _ ___ _ ___ _ __ _ __ 6 

Anomalocardia______ ___ __ _ ______ ____ _ ___ _ ___ _ _ 34 

Anomalocoelia _______________________________ _ 

Anomalodesmata _____________________ 1, 23, 25, 29,30 

Anomalodesmatans _____________________ 29, 30, 31, 34 

Anomalocionta ____ ---------- ________ __________ 6 

gigantea __________________________________ pl. 10 

Anomiacea___________________________________ 1, 25 

Anoptera __ ------------------------- ____ ______ 6 

Antelope Valley Limestone___________________ 16 

antiquus, Parallelodon ________________________ 17,18 

Antraconeilo_ -- __ --- ____ ___ _ __ _ __ __ _ _ _ _ __ _ __ _ _ 34 

Anuscula ___ ______ -- __ ------ _ _ _ ____ _ _ __ _ _ _ _ _ __ 6 

INDEX 

[Italic numbers indicate major references] 

Page 

Area _____________ ---__________________________ 6 

naranjoana_ _ _ _ ___ _ __ _ _ ___ _ _ ____ __ __ _ __ _ __ 17 

Arcacea_ _ _ _________ ____________ ____________ __ 1, 25 

Arcaceans __ ----------- _______ ------------- 18, 28,37 

Archaeophiala___ _ ___ _ ___ _ ___ _ ____ _ ____ ___ _ ___ _ 14 

Arcids___ ____ _ ___ _ ___ ___ _ _ ___ _ ___ ____ ____ _ _ ___ 35 

Arcoids ______________ ------------------- 18, 22, 25,30 

Arcuatula ____________________________________ 17, 32 

demissa ______________________________ pls.11, 13 

demissus____ ____ _ ___ _ ___ _ ___ _ ______ _ _ __ _ _ _ 32 

Aristerella __ -------------------------- 6, 19, 20; pl.11 nitidula _______________________________ 19; pl. 11 

armoricana, Lyrodesma _____________________ 10; pl. 3 

A.starte ____________________________________ --- 6 

wneiformis _______________________________ pl.1 

Astartes, Miocene____________________________ 15 

Astartidae ____________________________________ 24, 25 

Atomodesma_ _ _ ___ _ __ _ _ __ _ _ __ _ ___ _ ___ _ __ ____ _ _ 36 

auris, Ahtioconcha ________________ ------------ 34 

Avicula_ ____ _ _ __ _ ___ ___ _ _ __ _ ___ _ __ ___ __ __ _ ___ _ 6, 19 

Aviculopecten_ __ _ ___ ___ _ ___ _ ___ _ __ _ ___ _ __ ____ _ 6 

B 

Babinka _____________________ 6, 12, 13, 14, 15, 28, 29,34 

oelandensis _ _ _ _ _ _ _ ___ _ __ _ _ ______ _ ___ _ __ _ __ 12 

prima----------------------- 12, 13, 14, 15; pl. 1 

Babinka-like pelecypod_______________________ 29 

Babinkidae ______________________________ 1, 12, 25,28 

Babinkids. __________________ 1, 13, 24, 25, 29, 30, 31,34 

bafji.nense, IJeceptrix ______ ------------------ __ pl. 5 

Bagenovia __________ -------------- ____ ______ __ 8, 9 

beckneri, Cyrtodonta ___________________________ pl. 7 

bilocularis, Septifer ___________ -------------- 36; pl. 9 

blumenbachii, Euchasma ______________________ pl.20 

Bodmania _________ __________ ------------------ 6 

Boucekia ____________________ ----------------- Byssodesma __ ________________________________ _ 

Byssonychia _________________________________ _ 

c 

Cadomia___ _ _ _ _ __ _ __ _ __ _ ___ _ __ _ __ _ __ _ _ __ _ __ _ __ 6, 16 

caelata, Lyrodesma ___ ---------------- _________ pl. 3 

Callodont z__ ___ __ _ __ _ _ _ _ ___ _ __ _ _ __ _ __ _ _ _ _ _ __ _ _ 6 

Cambrian bivalves __________________________ _ 

Cambridium_ _ _ __ _ ___ _ ____ _ _ __ _ _ __ _ _ _ _ _ __ _ ___ _ 8, 9 

Camp Nelson Limestone_____________________ 3 

Cardiids _______ -------------------- ___ ____ ____ 13 

Cardiniidae_ _ _ __ _ __ __ __ ____ __ _ _ __ _ __ _ _ __ _ __ _ _ 25 

Cardiola_ __ _ __ _ __ _ __ _ _ __ ____ _______ _ __ _ _ _ _ __ _ _ 6 

Cardiolaria ____ --------------------- ____ ______ 6,16 

Cardiomorpha_____ _ ___ ___ ___ ___ _ _ __ _ ___ _ ___ _ __ 6 

Carditacea_ _ _ _ _ _ ___ __ _ __ _____ _ __ __ ___ __ _ _ __ _ _ 22 

Carditaceans ___________________________ 11, 20, 22,25 

Cardium _____ ------___________________________ 6 

carinata, Pterinea__ _ _ ___ ___ _ _ _ __ _ _ __ __ ___ _ __ _ _ 4 

Caritodens _________ --- ____ ___ _ __ _ ___ _ _ __ _ ___ _ _ 6 

carpenderi, Myoplusia ___ ---------------------- pl. 6 

carpenderi, Ctenodonta_________________________ 17 

Carydiidae ___ ------------------------------ 9, 10,22 casei, Opisthoptera ____________________________ pl.lO 

Caster ella _________ ----________________________ 34 

casteri, Ambonychia ___________________________ pl.10 

Ceromyopsis _________________ ------------ ____ _ 6 

Chaenodomus ________________________________ _ 

Chaenomya __ --------------------------------- 24,34 

Chazy Limestone of New York _____________ 4, 18,19 

Page 

Cincinnati arch area fossils___________________ 3 

cincinnatiensis, Pterinea _______________________ pl.11· 

TVhiteavesia ____ --------- ___________ 20; pls.17, 19 

Cleidophorus _____ ------ ________ ------ _- --- __ 6, 15, 16 

[Cleidophorus] planulata, Nuculites ____________ pl.6 

Cleionychia __ --------- ____ -------------------- 6 

Clidoz>horus ___ __ ------ ________ -- ___ --- _ ------- 6 

Clinopistha ___ -------- _____ ----------- _ ------- 6 Clionychia ___ -_______ -_______________________ _ 

Colpomya_____________________________________ 6, 21 

constricta _______________________ --- ___ 20; pl. 12 

concentrica, Modiolopsis __ __ ------------------- 13 

Conchostraca _________ ------------------ ____ __ 8 

Congeneria ______ ------------------------------ 36 

Congeriomorpha ____ --- _________ ------- _____ --- 36 

Conocardiacea _______ --- _ _ _ _ _ __ _ ___ _ _ __ ___ __ __ 1, 25 

Conocardiidae ___ - ___ - ___________ --- _________ - 22 

Conocardiids _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1, 2, 23, 24, 25, 29, 30, 31, 34 

Conocardium__________________________________ 6, 22 

immaturum __ _____________________________ pl. 19 

sp ________ -------------------------- ______ pl. 20 

Conocardium-m-e animals_____________________ 22 

conradi, Lyrodesma ____ _______________________ - pl. 3 

constricta, Colpomya _______________________ 20; pl.12 

Corallidomus _____ ------ ___ -------------- 6, 30, 32,33 

Cornellites __________ -- _ _ _ _ _ __ _ _ __ _ __ ___ _ _ ___ _ _ 6 

Cosmogoniophorina ____ -------------- _______ __ 6 tenuicostata_ __ _ __ _ __ _ _ _ __ _ ____ __ _ ___ _ __ _ __ 17 

Coxiconchia _______ -------------------------- __ 6, 29 crassa, Pterinea __ _____________________________ 19, 23 

Crassatellaceans __ ---------------------------- 25,35 Crassiconcha______ __ __ __ _ ___ _ ___ _ _ __ ___ _ ___ _ __ 34 

Crenella-like shells____________________________ 35 

Cretaceous pelecypods________________________ 6 

Crustacea ___________ -________________________ 22 

Cryptodonta _________________________________ 23,30 

Ctenodonta _______________ 3, 6, 7, 9, 15, 16, 17, 32, 34,35 

carpenderL ___ _ ___ _ ___ _ _ ___ _ __ _ _ _ __ __ __ _ _ _ 17 

gibberula group __ ----------- _______ ------- 6 

iphigenia_ -------------------------------- pl. 4 

levata group _____ ----------------------- 6, 15,16 

log ani group ______ ------------------------ 6 

manchuriensis _______________________ -___ - 16 

nasuta __ ___________________________ -___ _ __ pl. 4 

group ________ --------------__________ 6 

pectunculoides group _____________________ _ 

recurva group _______ ---------------------- 6 

takahashiL--- ______ ---------------------- 16 sp __________________ ----------- ___ ____ ____ pl. 4 

Ctenodontidae _____ -------------------------- 15 Cucullea ___ ________ --- _________ -- ________ -__ -- 6 

Cucullella ___________ --- _______ --- _______ -___ - 6 

Cuneamya _______________________________ 6, 23, 24,29 

miamiensis ________________________________ pl.15 

scapha ____________________________________ pl.15 

cuneata, Actiwdonta__________________________ pl.1 

Tancrediopsis ___________________________ -- pl. 6 

cuneiformis, Astarte___________________________ pl. 1 

Cycloconcha ____________ ---------- 6, 9, 10, 25, 28, 29,35 

mediocardinalis _________________________ pis. 2, 3 

millerL ----------------------------------- pl. 2 oblong a _____________________________________ pl. 3 

ovata_ _ _ _ _ _ _ ___ _ __ _ ___ _ _ _ _ ___ _ __ ___ _ _ __ _ __ pl. 2 

sp_ ___ _ __ _ _ __ _ __ _ __ _ ___ _ __ _ __ _ __ _ __ _ _ ___ __ pl. 2 

Cycloconchidae ____ --------------------- 9, 10, 22,28 

43 
44 

Page 

Cycloconchids ______ -------------- 1, 11, 13, 30, 31, 34 

Cymatonota ________________________ 6, 21, 23, 24, 29,35 

recta ______________________________________ pl. 18 

typicalis_ --------------------------------- pl.18 Cypricardia_ _ __ _ __ _ ___ _ __ _ _ ___ _ ___ _ _ _ _ _ _ _ _ __ _ _ 6, 9 

Cypricardinia_______________ ___ ___________ ____ 6, 25 

Cypricardites ___________________ -------------- 6 

ovata ________________ ____ ------------------ 20 

Cyrtodonta __________________________ 6, 8, 17, 18, 34,37 

becknerL _________________________________ pl. 7 

grandis___________________________________ pl. 6 

luculcntus ___ ------------------------- pl. 6 huronesis _________________________________ pl. 7 

lata_______________________________________ 17 

megambona_ _ _ _ _ __ _ _ ___ _ _ _ _ __ _ __ _ __ _ __ _ _ __ 37 

obtusa __________________________ ---------- 17 

sajJordi_ _ __ _ __ _ __ _ _ __ _ _ __ _ ___ _ __ _ __ _ _ _ _ _ _ _ pl. 7 

sp ______________________________________ pls. 6, 7 

Cyrtodontacea ______________ ----------------- 1, 25 

Cyrtonella ______ -------------- ____ ----------- _ 14 

Cyrtodontid type of dentition________________ 28 

Cyrtodontidae _____ ---------- ________ 9, 17, 24, 25,35 

Cyrtodontids ____ 2, 18, 24, 25, 28, 30, 31, 32, 34, 35, 36,37 

Cyrtodontula___ _ __ ___________ _______ _______ __ _ 6, 37 

rugatina _______ ----------- _______ ___ _____ _ pl. 7 

scofieldL _ __ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _ _ __ _ _ _ _ _ __ _ _ _ pl. 7 

D 

Davidia___ _ __ _ __ _ _ __ ____ _ _ __ _ _ _ _ __ _ _ __ _ _ __ _ _ _ _ 6, 9 

Dceruska_ _ _ _______ ___________ ___ ___ ____ ____ __ 6, 7 

Deceptrix _____________________________ 16, 34, 35; pl. 2 

albertina____ _______ ____ _____ __ ___ ___ ____ _ _ pl. 5 

baffinense_____________________ ___ _ ___ _ ____ pl. 5 

jilistriata_____________ ____ _ ______ _______ ___ pl. 5 

hartsvillensis_ _ ____ ___________ ____ ____ _____ pl. 5 

levata_______ ______ _____ ____ _ __________ ____ pl. 5 

sp ________________________________________ pl.5 

decipiens, Ischyrodonta ________________________ pl.1 

demissa, Arcuatula ____________________ ____ pls. 11,13 

Pterinea __________________________________ pl.11 

demissus, Arcuatula_____ _ ___ _ _ __ _ __ _ _ _ _ _ __ _ _ _ _ 32 

deshayesiana duvaliana, Redonia _______________ pl.1 

Desmodonts _________________________________ 23, 29 

Devils Hollow Member of Lexington Limestone_____________________________ 3 

Diplacophora _________________ ---------- ____ __ 12 

Dipleurodonta ____ ____________________________ _ 

Disteira __ ____________________________________ _ 

Dolabra______ ____ ___ ___ _____ ___ ___ _ __ _ ___ _____ .6 

Dreissenia_ _ _ ___ ____ _______ _ ___ ____ ___ ____ ____ 36 

Dualina _____________________________________ _ 

Dundas Formation___________________________ 23 

dnvaliana, Redonia deshaytsiana_______________ pl.1 

Dysodonts_ _ _ _ ___ ____ ___ ____ ____ ___ ___ _ ___ ___ 23 

E 

Ectenocardiomorpha ____ ___________________ --~- 6 

Ectenoptera__ _ __ _ _ __ _ _ _ _ _ ___ _ __ _ _ __ _ __ _ ___ _ _ __ 6 

Edmondia __________________________________ 6, 24, 30 

Edmondiidae _______________________________ 1, 23,25 

Edmondiids__________________________________ 2, 2·1 

Edrioasteroids _____________________________ 19, 20,34 

edulis, Mytilus ____________________________ 21; pl.13 

Elasmodophora_ _ _ _ _ _ _ _ _ _ _ _ _ __ _ __ _ __ _ _ _ _ __ _ _ __ 6 

Endodesma __________________________________ _ 

Eoasmussia ___ _______________________________ _ 

Eoischyrina __ ________________________________ _ 

Eopteria _______________________________ 7, 8, 19, 22,23 

richardsoni__ ______________________________ pl.19 

sp ___________________________________ pls. 19,20 

Epifaunal suspension feeders_________________ 2 

Eridonychia___________ ___ ____ ___ _________ _____ 7 

E~whasma _____________________________ 7, 8, 22, 23,35 

blumenbachiL _____________________________ pl. 20 

sp ________________________________________ pl. 20 

Euchasmella_ __ _ __ _ _ __ _ __ __ __ _ __ _ _ _ _ _ _ _ _ __ _ _ __ 7 

Eudesmodontida ____________________________ _ 24 

European pelecypod studies _________________ _ 

INDEX 

Eurymya __________________________________ ---

Enrymyella __________________________________ _ 

Page 

7 

ewingi, Neopilina_____________________________ 15 

excisus, Septifer ---------------------------- 36; pl. 9 

F 

faberi, Palaeoconcha______ ___ ___ _______ ____ ___ _ pl. 6 

fecunda, Palaeoneilo ___________________________ pl.1 

Filiola________________________________________ 7 

jilistriata, Dcceptrix _____ ___________ --------- __ pl. 5 

jlanaganensis, Allonychia ______________________ pl.lO 

Fordilla __ ___ ------------------------------- __ 8, 9 

G 

galatheae, Neopilina ________________________ 13, 14,15 

gibberula, Ctcnodonta, group _________ ----- ___ - 6 

Tancrediopsis ___ __________________ -- __ -- __ pl. 6 

gibbosa, Vanuxemia ______________________ pls. 7, 8, 9 

gigantea, Anomalodonta __ --------------------- pl.10 Gloria ___________________________________ --___ 7 

Glycymeris-like cyrtodontids _______________ 18, 28,37 

Glycymeris-like shells _______________ -------- __ 35,37 

Glyptarca __ _______________________________ -_ _ _ 7 

Goniophora ___________________ ----------------

Goniophorina _____________________ -- _ ---------

Gordon Limestone of 'l'asmania______________ 16 

Gosseletia _______ ---------- ____ ---------- ____ __ 7 

Grammysia___________________________________ 7, 24 

grand is, Cyrtodonta _____________ ----------- ___ pl. 6 

lnculentus, Cyrtodonta ___________ c ________ pl.6 

Psiloconcha _______________________________ pl.18 

II 

Hallopora_____________________________________ 33 

hartsvillmsis, Deceptrix________________________ pl. 5 

Heikea ___________________________________ 7, 19, 20,24 

Hemicardium_ -------------------------------- 7, 25 Heteroconehia _________________________ 1, 9, 25, ~8, 30 

Heterodonts _________ ---------------------- 23, 28,30 

Hippomya____________________________________ 7, 23 

Hippuritoida_________________________________ 1, 25 

Historieal resume ____ ---------------__________ 4 

huronensis, Cyrtodonta ________________________ pl. 7 

immaturum, Conocardium _____________________ pl.19 

inconstans, Vanuxemia ________________________ pl.8 

Infaunal deposit feeders______________________ 1 

inornatum, Lyrodesma ________________________ pl.3 

iphigenia, Ctenodonta ___ ---------------------- pl. 4 

Ischyrinia_____ __ __ ___ ____ ____ ________ ____ _ ___ _ 7 

Ischyrodonta_ ___ __ _ ___ _ _ __ _ _ _ _ __ _ ____ ___ _ _ ___ _ 7, 9 

decipiens __________________________________ pl.1 

Isoarca_ _ _ _ __ ___ ___ __ ___ ___ ___ _ ___ __ _ _ __ __ ___ _ 7 

Isocardia ________ _______________ ---------------

Isofilibranehia ______________________________ 1, ~5, 30 

J 

Jessamine dome area of Kentucky------------ 18 

K 

Kagawong beds______________________________ 1U 

Kalenteridae _________________________________ 11,29 

Kangyao Formation of Manehuria____________ 16 

L 

Lamellodonta_________________________________ 9, 29 

simplex___________________________________ 8 

Lamellodontidae_ ---------------------------- 9, 22 

lata, Cyrtodonta_______________________________ 17 

Leda _________________________________________ _ 

Lehman Formation__________________________ 22 

Lemubulus_ _ _ _ ____ _____ ________ _ ___ _ _____ ___ _ 35 

Leptodesma_ _ _ __ _ _ _ _ _ ___ _ _ _ _ _ _ __ _ _ ___ _ _ __ _ _ _ _ _ 7, 19 

levata, Ctenodonta, group~------------------- 6, 15,16 

Deceptrix_ _ __ _________ ___ ____ _ ___ ________ _ pl. 5 

Page 

Lexington Limestone _________________________ 19,20 

Life habits___________________________________ 30 

Limacea______ __ ____ ___ _ ___ ___ ____ __ __ __ __ _ ___ 1, 25 

Limopsaeea ____________ ---------------------- 1, 25 

Lithobia_ _ _ _ __ _ ___ ___ ___ ___ _ __ ____ ____ ____ ___ _ 7 

Llandeilo of Scotland_________________________ 18 

logani, Ctcnodonta, group_____________________ 6 

Lucinoids_ ----------------------------- ___ 13, 28,34 

luculentus, Cyrtodontagrandis _________________ pl.6 

Lunulacardiidae ______________________________ 24,25 

Lunulaeardiids_____ __ _ _____ _ ___ _ ___ ____ ____ __ 31 

Lunulacardium_______________________________ 7, 25 

Lyonsia _______ ____________ -------------------- 7 

Lyrodesma __________________ 7, 9, 10, 11, 28, 32, 34; pl. 2 

acuminata ___ ----------------------------- 1o 

acuminatum ______________ ---------------- pl. 3 

armoricana _____________________________ 10; pl.3 

caelata _____________ -___ ------------------- pl. 3 

conradi _____________ ---------------------- pl. 3 

inurnatum ________________ ---------------- pl. 3 

major ____________ --- ____ ------------------ pl. 3 

poststriatum_ ----------------------------- pl. 3 

sub planum ___ ---------------------------- pl. 3 Lyrodesmatidae ____________________________ 9, 10,28 

Lyrodesmatids _______________________ 1, 11, 30, 31,34 

Lyronucula ___________ ________ ---------------- 7 

M 

Macrodesma ______ ____________________________ _ 

Mactrids_ _ _ _ ___ ____ __ _ _ _ _ __ __ __ __ __ ___ _ ___ ___ 13 

major, Lyrodesma_ _ _ __ __ _ ___ __ __ __ _ _ __ _ _ ____ __ pl. 3 

Malletia _____________________ -______ __ _ _ ___ _ __ 35 

Maminka ____________________________________ _ 

manchuriensis, Ctenodonta_ _ _ _ __ ___ _ ____ ____ _ _ 16 

Maryonychia ______ __________ ------------------ 7 

Matercula______ _ ___ _ ___ ___ ___ _ __ ____ ____ _ __ _ _ _ 7 

Matelials and methods ____ ------------------- 2 Matheria ____ ________________________________ 7, 24,25 

rugosa ____________________________________ pl.16 

tener ______________________________________ pl.16 

mediocardinali~, Oycloconcha ________________ pls. 2, 3 

Megadesmatidae_____ _ __ __ __ __ ___ ___ _ ____ _ __ _ _ 1, 25 

Megalodon_ __ ___ _ _ __ __ _ ___ __ __ ___ ___ ____ _ ___ __ 25 

Megalodontidae ______________________________ 24,25 

Megalodontids____ _ _ __ ____ ___ ___ _ __ _ ____ ____ _ _ 25 

Megalodus_ _ _ __ _ __ __ __ ___ ___ ___ ____ ____ _ ___ _ _ _ 7 

megambona, Cyrtodonta __ _ ---------------------- 37 Mcgambonia _________________________________ _ 

Mcgaptera ___________________________________ _ 

miamiensis, Ouneamya ________________________ pl.15 

mickelboronghi, Rhytimya ______________________ pl.16 

milleri, Cycloconcha ___________________________ pl.2 

modiolaris, Mrdiolopsis ____________ 20; pls.12, 15,16 

Modiodesma ____________ --------------------- 7, 20,21 

Modiola__ __ ___ __ _ _ __ __ _ _ _ ___ __ _ ___ _ _ ___ _ _ __ _ _ _ 7 

modiolaris, Pterinca_ _ __ _____ ___ _ ___ _ ___ _ ___ _ _ _ 20 

Modioliform modiomorphids____________________ 21, 

22, 25, 29, 30, 31, 32, 33, 34 

Modioliform mytilids__ _ __ _ _ _ ___ ___ _ ___ _ ___ _ _ _ 36 

Modiolodon_ _ _ _ ___ __ ___ ___ _ ___ ___ _ _ __ _ _ __ ___ _ _ 7, 21 

nviformis _______________________________ 20; pl. 13 

Modioloides ___________________ ._ ___ ____ _ __ _ ___ _ 9 

Modiolopsidae__ ____ __ _ ___ __ _ ___ ___ ___ _ ___ _ _ __ 12 

Modiolopsis ________________________ 3, 6, 7, 9, 20, 21,32 

concentrica____ _ ___ __ __ __ __ __ _ _ _ ____ ___ _ ___ 13 

modiolaris _____________________ 20; pls.12, 15,16 

pogonipensis ______________________________ pl.15 

rogersensis ________________________________ pl.12 

simnlatrix ________________________________ pl.14 

valida _____________________________________ pl.14 

versaillensis _______________________________ pl. H 

sp ___________________________________ pls. 15, 16 

Modiolus ___________________________________ 17, 30,32 

americanus _______________________________ pl.11 

lt.lodiomorvha_ _ _____ _______ ___ ___ _ ___ _ ____ ___ _ 7 

Modiomorphidoo [Modiolopsidae]_ ____ 9, 12, 20, 23,25 

Modiomorphids __________________________ 2, 12, 13,21 

Molds and casts of Ordovician peleeypods ___ _ 
Page 

Mollusca______________________________________ 9 

Monoplacophora ___________________________ 12, 13,14 

Morphologic variation of Ordovician pelecypods _____________________________ _ 

Murfreesboro Limestone______________________ 16 

Myalina__________________________ ______ ______ 7 

Myalinidae _ _ _ _ __ ___ ___ _ __ ___ _ __ ___ _ _ _ _ _ _ _ _ _ _ _ 19 

Myalinids _________________________________ 13, 21, 36 

Myids_ --- _ __ _ __ _ _ __ ___ _ __ ___ ___ _ _ _ _ _ __ ___ ___ _ 35 

Myoid a_______________________________________ 1, 25 

!llyonia_ __ _ _ _ _ _ __ _ __ _ ___ __ _ _ _ _ _ ___ _ ___ _ ___ __ _ _ 24 

llfyophoria ___________________________________ _ 

lllyoplusia_ _ __ _ _ _ _ _ __ _ __ _ __ _ _ __ ___ _ _ _ __ ___ __ _ _ 7, 16 

carpcndcri_ _ _ __ _ _ _ _ _ _ _ __ _ __ _ ____ _ _ _ _ _ __ ___ pl. 6 

Mytclla _______________________________________ 17, 32 

Mytilacea _____________________________ 1, 17, 21, 22,25 

Mytilaceans ____________________________ 20, 21, 30,32 

!llytilarca_ _ __ __ __ _ _ _ __ ___ _ _ _ _ __ _ __ _ _ _ __ ____ ___ 7 

Mytilidae __________________________________ 21, 25, 30 

Mytilids ___________________________________ 21, 25, 33 

!11 yt ilo ps _____________________________________ _ 

Illytilus ____ ______________________________ 7, 31, 33, 36 

cdulis __________________________________ 21; pl.13 

naranjoana, Area_____________________________ 17 

nasuta, Ctcnodonta ____________________________ pl.4 

Ctcnodonta, group________________________ 6 

Tellinomya________ ___ __ _ _ ___ _ ___ _ _ _ _ _ __ ___ 16 

Ncopilina____ ___ _ ___ ___ _ __ ___ _ __ ____ _ _ _ _ ___ _ _ _ 15 

cwingi_ __ _ _ _ ___ ___ ___ _ _ __ ___ ____ _ __ _ ___ ___ 15 

galatheae ___ ____________________________ 13, H, 15 

nitidula, Aristcrclla ________________________ 19; pl.ll 

NoetiL ____ -------------------------- _________ 37 

Noctia-Iike shells ______________________________ 35,37 

Nucinella__ ___ __ _ _ __ _ _ _ _ __ _ __ _ _ _ _ _ ___ _ __ __ _ _ __ 29 

scrrei_ _ __ ____ _ _ _ _ _ _ _ _ _ _ ___ _ __ _ ___ _ __ _ _ __ _ _ 29 

nucleus, Nucula ________ ------------- _________ 35 

Nucula _______________________________________ 7, 35 

nucleus___________________________________ 35 

Nuculana ____ _______________________________ 7, 15, 35 

Nuculitcs __ ______________________________ 7, 10, 15, 16 

[ Clcidophcrus] planulata__ __ _ _ _ _____ __ _ ___ _ pl. 6 

Nuculoidea _____________ ---------------------- 1, 25 

Nuculoids _____________ 1, 13, 15, 24, 25, 28, 29, 30, 31,34 

0 

oucsa, Ambonychia ____________________________ pl.10 

Oblicarina_ _ _ _ _ _ __ __ _ _ _ _ _ __ ___ __ _ ___ _ _ _ _ __ _ __ _ 34 

oblong a, Cycloconcha_ _ _ _ _ _ _ __ _ __ _ __ __ _ _ _ __ ___ _ pl. 3 

obtusa, Ctcnodonta_ _ _ _ _ __ _ __ _____ _ _ _ __ _ ___ __ _ _ 17 

oclandensis, Babinka_ _ _ __ _ ___ ___ __ _ _ _ __ ___ _ __ _ 12 

Opistholoba __________________________________ _ 

Opisthoptaa __ ____________________________ 6, 7, 33, 34 

easeL ____________________________________ pl. 10 

Ordovician epifauna_______ _ ____ __ ___ _ _______ _ 32 

Ordovician infauna__ _ __ ___ ___ __ ____ __ _ __ ___ _ _ 34 

Ordovician lineages and higher level pelecypod 

taxonomy_----------------------_________ 30 

Ordovician pelecypod groups, less well known_ 22 

Ordovician pelecypods ___ -------------------- 9 

Ordovician pelecypods of uncertain higher taxonomic position __ ------------------------ 24 

OriocrasSftella______ _ _ _ _ ___ _ _ _ _ _ _ ___ _ _ _ _ _ _ _ _ _ __ 28 

Orthodcsma _________________________________ 7, 23, 24 

sp ________________________________________ pl. 18 

Orthodontiscus_ ___ __ _ __ _ ___ ___ _ __ ____ __ _ __ _ _ _ _ 7 

Orthonota ___ _________________________________ _ 

Orthonotclla ___ _______________________________ _ 

Orthonotidae__ __ _ __ ___ ___ ___ _ _ _ ____ __ _ ___ __ _ _ 23 

Ortonclla ____________________________________ _ 

ovata, Cycloconcha _____________________________ pl. 2 

Cypricarditcs________ ___ _ __ _ __ _ __ __ _ __ _ __ _ _ 20 

Ostreacea______ __ _ ___ _ __ ___ _ ___ __ _ ___ _ __ _ __ _ __ 1, 25 

oviform is, Modiolodon ______________________ 20;.pl.13 

Ozomia_ _ __ _ ___ _ ___ _ ___ ___ _ __ _ ___ _ _ __ _ ___ _ __ __ 9 

INDEX 

p 

Palaearca__ __ _ ___ ___ ___ _ ___ ________ _______ ___ _ 7 

Palaeoconcha_ _ _ _____ __ _____ ___ _ ___ ____ _______ 7, 16 

Palaeoheterodonta __________________________ 9, 17, 28 

Palaeoheterodonts___ _______ ____ _ ___ ___ ___ ____ 28 

Palaeoconcha fabcrL______ ___________ ___ ____ ___ pl. 6 

Palaconcilo _______________________________ 7, 9, 16, 34 

fewnda__ ___ ____ ______ __ __ ____ ___ ___ ___ _ __ pl. 1 

Palaeoptcria __________________________ 7, 19, 34; pl. 11 

Palacosolcn __ ________________ ---- ___________ 7, 23,24 

Pabeotaxodonta ____________________________ 1, 25,30 

Pandorace.a_____ ___ _ __ __ _ ________ ___ ____ __ _ ___ 1, 25 

Pantodontida_ _ _ _ ____ __ _ __ __ ____ ___ __ _ _ __ _ _ _ _ 9, 10 

Paracyclas_ _ _ ___ ___ _ __ ___ _ ______ _ ___ ___ ___ _ _ _ _ 7 

ParallelodoiL __ _ __ _ _ __ _ __ __ _ ____ _ _ _ _ ___ ___ _ __ _ 7, 18 

antiquus _________________ ---- _____________ 17, 18 

Parallelodont type of dentition_______________ 28 

Parallelodontids_ _ ___ _ __ _ ___ _____ __ ___ _ ___ ___ _ 35 

Parallelodus _ __ ___ ___ _ ___ ___ ___ _ __ ____ ___ _ __ _ _ 7 

parallclum, Sphcnolium_______________________ 24 

Paramodiola _________________________________ _ 

Paramytilarca ____ ____________________________ _ 

Paraphtonia _________________________________ _ 

Patrocardia _________________________________ 7, 24,25 

Pectinacea_____ ___ ____ ___ ___ __ __ _ _ _ _ ___ ___ ___ _ 1, 25 

pcctunculoidcs, Ctcnodonta, group_____________ 6 

Pelecypoda _________________________________ 9, 24,30 

Pcriploma____________________________________ 7 

Pennophoridae _______________________________ 11,29 

Perna________________________________________ 21 

pincta ___________________________ -_- ______ pl.13 

pholadiformis, Pholadomorpha_ ---------------- pl.12 

Pholadellidae ______________ - _- --- ____ --- _ _ __ __ 23 

Pholadomor ph a_______________________________ 7, 21 

pholadiformis ____ ---------------------- ___ pl.12 

Pholadomya _______________ -_- ---- ___ -____ _ _ _ _ 30 

Pholadomyacea ___ __ -_ _ __ _ _ _ ___ __ _ _ _ _ _ ___ _ _ _ _ _ _ 1, 25 

Pholadomyids ______ -_ ___ _ __ ___ __ _ _ _ _ _ _ _ _ ___ _ __ 24 

Phylogenetic summary_______________________ 25 

Physetomya __ _________________ -- _ _ _ __ __ _ __ _ _ __ 7, 24 

Pilina ________________ ________ ---------------- 14 

pincta, Perna ____ -------------------------- ___ pl.13 Pinctada _____ _________________________________ 19, 34 

Pinnacea__ ___ _ ___ __ ___ _ __ __ __ __ _ _ __ _ _ _ _ ___ _ _ _ 1, 25 

planulata, Nuculitcs [Cleidophorus] ____________ pl.6 

Plcthocardia ______________________________ 4, 7, 24,25 

umbonata _____________________________ 24; pl.14 

Plcthomytilus ________________________________ _ 

Plcurorhynchus ______________________________ _ 

Pogonip Group of Nevada____________________ 22 

pogonipcnsis, Modiolopsis ____ ----------------- pl.15 

Posidonomya _____________ -------------- __ ____ 7, 9 

poststriatum, Lyrodesma ____ ------------------- pl. 3 Prawnomalodonta_ _ _ _____________ __________ __ 7 

Pracarca ___ __________________________________ _ 

Praecardium __ _______________________________ _ 

Praeleda___ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ __ _ _ _ __ _ _ _ _ _ _ _ 7, 16 

Praelncina ____ _______________________________ _ 

Pracmyophoria ___ ____________________________ _ 

Pracnucnla__ _ _ _ _ _ _ _ __ __ _ _ _ _ _ ____ _ _ _ ___ _ _ _ _ ___ 7, 16 

Preheterodonts__ _ _ _ _ _ _ ___ _ __ __ _ _ _ _ _ _ __ _ __ __ _ _ 23 

prima, Babinka __________________ 12, 13, 14, 15; pl.1 

Prolobella ___ _________________________________ _ 

Prothyris ___________________________________ 7, 23, 24 

Pseudarca _______________________________ 7, 10, 16,18 

Pswdaxinus_______ ___ __ _____________ _________ 7 

Pswdocyrtodonta ____________________________ _ 

Pswdowchasma _____________________________ _ 

Pswdotcchnophorus ____ ______________________ _ 

Psiloconcha __ ____________________________ 7, 23, 24,29 

grand is ___________________________________ pl. 18 

Psilonychia___ ___ __ _ __ _ _ __ __ _ ___ ___ ___ ___ _ __ __ 7 

Pteria ___________________________________ 7, 19, 33,34 

Pteriacea _____________________________________ 19,25 

Pteriaceans _______________________________ 1, 2, 19,34 

Pteriids_ _ _ __ ___ __ _ _ __ __ _ ___ ___ ___ ___ ___ ___ ___ 13 

Pterinca ____________________________________ 7, 19, 34 

carinata_ _ _ _ _ _ ___ ___ ___ ___ ____ ___ ___ ___ ___ 4 

45 

Page 

Pterinea-Continuecl 

cincinnatiensis ____________________________ pl.ll 

crassa ____ _________________________________ 19,23 

demissa ________ --------------------------- pl.ll modiolaris____ __ ___ ___ _ ___ _ ___ ___ ____ ____ __ 20 

wclchi_ ___________________________________ pl. 11 

SP------------------------------------ pls. 10,11 Pterineidae ________________________________ 17, 19,25 

Pterineids ________________________ 1\l, 20, 30, 31, 32,34 

Ptetiomorphia _____________________ 1, 17,21, 25, 30,31 

Pteriomorphians _______________ -------------- 17,30 

Pteronifes____ ___ ___ ____ _______ _ _ __ ___ _ ___ ____ _ 7 

Pteronitina_ _ ___ __ __ ___ ___ _ ___ _ _ __ ___ ____ ___ _ _ 7 

Ptychoptcrinia_ _ __ _ ___ ____ ____ __ __ ___ _ ___ ___ _ _ 7 

Pulaski beds ____ ----------------------------- 20 

Pulaski Shale_________________________________ 20 

Pyanomya__ _ ___ _ __ ___ ____ ___ _ ___ _______ ___ _ _ _ 7 

Pyramus ____________________ ----------------- 34 

Pyrenomoeus ___ ------------------------------ 7 

R 

radiata, Ambonychia _______________________ ____ pl.10 

recta, Cymatonota _____________________________ pl.18 

rccnn'a, Ctenodonta, group____________________ 6 

Rcdonia_ ------------------ 7, 9, 11, 13, 21, 22, 25, 28,29 

deshaycsiana du.valiana ____________________ pl.1 

Redoniidae _________________________________ 9, 11, 28 

Redoniids ____________________________ 1, 11, 31, 34,35 

Relationships of the various lineages to one 

another__________________________________ 29 

Resume, historicaL__________________________ 4 

Rhombopteria_ _ __ _ __ __ _ ___ __ _ _ __ _ _ _ _ __ _ _ _ _ __ __ 7, 19 

Rhynchotropsis___ _ _ _ _ _ __ __ _ _ __ ___ ___ __ _ ___ __ __ 7 

Rhytimya _________________ _______________ 7, 23, 24, 2\l 

mickclborou.gh i ____________________________ pl. 16 

sp ________________________________________ pl.16 

Ribeirella_ _ _ _ _ __ _ __ _ ___ ___ __ _ __ _ ___ __ _ _ __ ___ __ 7 

Ribeiria_____ _ _ _ _ __ _ _ _ _ __ _ _ __ __ _ ___ ___ _ _ _ _ __ _ _ _ 7, 9 

Ribeirina_ _ _ __ ___ _ __ __ _ _ _ _ ____ __ _ _ _ _ _ ___ _ _ _ ___ 7 

Ribe.irioida___ __ __ _ ___ _ _ _ _ ___ _ ___ ___ __ _ _ ___ ___ 8 

richardsoni, Eopteria __________________________ pl.19 

rogascnsis, Modiolopsis ______ __________________ pl.12 

Rostroconchida _____________________________ 1, 25, 30 

rugatina, Cyrtodontu.la __ ---------------------- pl. 7 rugosa, lllatheria _______________________________ pl. 16 

s sajfordi, Cyrtodonta ___________________________ pl. 7 

Sajfordia_ _ _ _ __ ___ _ _ _ _ _ _ _ __ _ _ _ __ _ _ __ __ __ __ _ __ _ 7, 24 

ventralis _______________________________ 24; pl.12 

St. Peter Sandstone__________________________ 18 

Sangu.inolitcs _ _ _ __ _ _ _ ___ _ _ __ __ ___ _ __ __ _ __ _ _ _ _ _ 7 

Sanguinolitidae=Solenomorphidae_ ____ ______ 1, 25 

Sanguinolitids _______________________________ _ 

scapha, Cuneamya _______________________ ______ pl.15 

Scaphellina_ _____ ___ __ _ _ _ _ __ _ ___ _ __ __ _ ___ __ _ __ 34 

scofieldi, Cyrtodontula _________________________ pl. 7 

Scdgwickia___ _ __ _ _ _ _ __ __ _ _ __ _ _ _ _ _ _ ___ _ _ _ __ _ _ _ _ 7 

Scmicorallidomus __ --- _________ -- _____ ----- ___ _ 

Septibrancho:dea_ _ _ _ _ _ __ _ __ _ ____ __ ___ _ __ ___ _ _ 1, 25 

Scptifcr _________________________________ -- ___ - 36 

bilowlaris __ _________________________ - __ 36; pl. 9 

e.rcisus __________________________________ 36; pl.9 

Septija-like shells _______________________ -____ 35 

Scptimyalina __ ____________ ------------------- 36 

scrrei, Nne in ella______________________________ 29 

Servitor_______________________________________ 7 

Setul Formation of Malaya __ ----------------- 16,23 

Shanina_ ________ _ _________ __________ _________ 7, 23 

Shaninopsis _____ ----------------------------- 7, 23 

Silicified Ordovieian fossil n1aterial_ _ _ _ _ _ _ _ _ _ _ 2 

Sili(,jU&'Ca_--- ------------------------------ 7, 10, 18 similis, Similodonta ___________________________ pl.5 

Similodonta _________________________________ 7, 16,35 

similis_ ___ __ _ ___ ___ _ __ _ ___ ___ _ __ _ _ _ _ __ _ __ _ pl. 5 

simplex, Lamcllodonta_________________________ 8 

simulatrix, Modiolopsis ________________________ pl.14 

Slava _________________________ ------ ______ -- _ _ 7 

b7uha ____ ____________________________________ _ 
46 

Page 

Sluzka ________________ ------------ __ ---------- 6, 7 

Solemya ___ -------------------------- _ -------- 35 Solemyidae________ _____ ____ _ ___ ___ _ _ __ _ ______ 23 

Solemyids ___ ---- _____ ------------ _ _ _ _ __ _ _____ 35 

Solemyoida________________________ ___ ________ 1, 25 

Solen. ____ -----------_________________________ 7 

Solenomorpha ____ ------------------------ 7, 23, 24,30 

Solenomya __ _________________ ------------ ____ _ 7 

Sowteria __ ___ -- _____________ ---------- ___ ___ __ 7 

Spathella _________ ------ __ __ ___ _ _ __ ___ _ __ ___ __ 7 

Sphenolium___________________________________ 7, 24 

parallelum_ ----- ____________ --------- _____ 24 striatum _______________________________ 24; pl.12 

Stenothecoida. ___ ---------------------------- 8 

Stenothecoides________ ___ __ __ ____ __ _ __ _ _____ ___ 8, 9 

striatum, Sphenolium ______________________ 24; pl. 12 

Subdivision of the Ordovician_________________ 4 

subellipticum, Allodesma______________________ pl. 2 

subplanum, Lyrodesma________________________ pl. 3 

Suspension feeders____________________________ 1 

Synek. _________ ---- _ _____ _ ___ ____ __ _ ___ _ __ _ _ _ 7, 9 

T 

takahashii, Ctenodonta_________________________ 16 

Tancrediopsis________________________________ _ 7,16 

cuneata___________________________________ pl. 6 

gibberula ________ ------- _ ___ _____ __ _ ___ ____ pl. 6 

Taxodont dentition___________________________ 29 

Taxodonta_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9 

Taxodonts ____________________________________ 23,29 

INDEX 

Technophorus •• ______________________________ _ 

Tellinacea. __________________________________ _ 

Tellinites ____________________________________ _ 

Page 

7 

35 

7 

Tellinomya ___ ------------------------------- _ 7 

nasuta ______ ---- _ ------------- ____ -------- 16 

tener, Matheria ______ ------~------------------- pl.16 

Tenka .•• ----------------------------------- 7, 24,25 

tenuicostata, Cosmogoniophorina_______________ 17 

Tenuis ____ --- __ ---- ____ ------ _ --- _ ___ __ __ _ ___ 7 

Tetinka----------------------------------- 6, 7, 24,25 

Thorslundia __ _ ------------------------------- 7 

Tolmac· ovia.--------------------------------- 7 Trepostome bryozoans________________________ 33 

Trigoniacea _____________ -------- _____ --------- 28 

Trigoniaceans ___ ----------------------------- 30 

Trigonioida.--------------------------------- 1, 9, 25 

Trigonioids. _______ -------------------------- 28 typicalis, Cymatonota __________________________ pl.18 

Tyrone Limestone____________________________ 18 

Tyrone Limestone collection offossils_________ 3 

u 

ulrichi,Ambonychia. __________________________ pl.lO 

umbonata, Plethocardia _____________________ 24; pl.14 

Unionaceans ____ ----------------------------- 30 Unionoida ___________________________________ 1, 9, 25 

Unionoids___ __ _ __ _ ____ _ ___ _ _______ __ ___ _ __ _ __ 28 

v 

Vacunella ___________ ________________ ------- _ -- 34 

valida, Modiolopsis ____________________________ pl. 14 

Page 

Vanuxemia __ _ --------------------- 8, 28, 32, 35, 36,37 

gibbosa.------------------------------- pls. 7, 8, 9 

inconstans. ----------------- __ --- __ __ _ __ _ _ pl. 8 

sp_ --------- ____ ---------- ___ ------- __ _ _ _ _ pl. 8 

Variability of Ordovician pelecypods_________ 3 

Veneroida •• ---------------------------------- 1, 25 ventralis, SajJordia _________________________ 24; pl.12 

versaillensis, Modiolopsis ______________________ pl.14 

Vlasta ______ --- _ ---- ___ ------------ ________ -- _ 8 

americana ______________________________ 23; pl. 20 

Vlastidae _______________ ------- _ __ ____ __ ____ _ _ 23 

Vlastids ________ ------------------------------ 25 

w 

Wanwanella ___ ------------------------------- 8 

Wanwania____________________________________ 8, 9 

Wanwanoidea. ____ ____ ---------- __ _ _ ___ _____ __ 8 

Wanwaukou Dolmite of Manchuria.__________ 23 Wa · burgia. _ ____ __ _ _ _ _ __ _ __ _ __ _ ___ _ ___ ___ _ __ _ _ 8 

Waynesville Shale.___________________________ 16 

welchi, Pterinea ____________________________ --- pl.ll 

Whiteavesia __ _ ------------------------------- 6, 8, 21 cincinnatiensis _____________________ 20; pis. 17,19 

Whitella ____ ------- ___ _ __ _ __ _ __ _ __ _ ____ __ __ _ ___ 8 

Whiterock Stage______________________________ 4 

Wilkingia __________________________________ 24, 30, 34 

y 

Yoldia. ______ --- _ ----------------------------- 3 
PLATES 1-20 

Contact photographs of the plates in this report are available, at cost, from U.S. Geological Survey Library, Federal 

Center, Denver, Colorado 80225. 
PLATE 1 

FIGURES 1, 2. Astarte cunezjormis Conrad; oblique interior views of right and left valves showing multiple small accessory muscle 

scars in apex of umbonal cavity, X 3. Collected by C. Buddenhagen from zone 10 of the Calvert Formation 

(Miocene), 3 feet above beach level, 1.25 miles south of wharf at Plum Point, Md. USNM 162676 and 162677. 

3-5. Actinodonta cuneata Phillips; 3, right valve exterior; 4, left valve internal mold; .5, right valve, internal mold showing 

musculature and dentition, X 1. All figures from Phillips and Salter (1848, pl. 21). 

6. Ischyrodonta decipiens Ulrich; syntype; left valve showing cardinal teeth and possible remnants of duplivinicular 

ligament, X 2. The museum label lists the horizon and locality as: "Richmond (Whitewater), Oxford, Ohio." 

USNM 46205. 

7. Redonia deshayesiana duvaliana Rouault; right valve internal mold showing posterior teeth and adductor muscle scar, 

X 1. Figure from Born, 1918, pl. 25. 

8-11. Palaeoneilo fecunda (Hall); Ulrich hypotype; 8, left valve, X 3.5; 9, right valve, X 3.5; 10, right valve, X 1; 11, 

dorsal view, X 3.5. The museum label lists the horizon and locality as: "Maquoketa (Richmond), near Dubuque, 

Iowa." USNM 46130. 

12-14. Bab£nka prima Barrande; three views of a right valve internal mold showing the musculature and dentition of the 

species; 12, X 5; 13, X 5; 14, X 3. Sarka Beds (approximately Llanvirn), Prague, Czechoslovakia. All figures 

from McAlester (1965). Copied with the permission of the Palaeontological Association from the original figures 

in "Palaeontology." 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 1 

4 

' . \ .. : ' 

12 

9 7 

10 

ASTARTE, ACTINODONTA, JSCHYRODONTA, REDONIA, PALAEONEILO, AND BABINKA 
PLATE 2 

FIGURES 1- 3. Alludesma subellipticum Ulrich; syntype; 1, loft valve, X 1; 2, left valve internal mold, X 4; 3, dorsal view showing 

imprints of cardinal teeth, X 10. The museum label lists the horizon and locality as: "Trenton, near Cannon 

Falls, Minnesota." See fig. 1F, G, page for Ulrich's reconstruction of the hinge line of this species. USNM 162678. 

4, 5. Allodesma subellipticum Ulrich; syntype; 4, right valve, X 4; 5, dorsal view showing imprints of cardinal teeth, X 10. 

Horizon and locality the same as in fig. 1 above. USN~VI 46078. 

6. Cycloconcha milleri (Meek); Ulrich hypotype; left valve, X 1. The museum label lists the horizon and locality as: 

"Richmond (Waynesville), Versailles, Indiana." USNM 70464. 

7. Cycloconcha rnilleri (Meek); Ulrich hypotype; right valve, X 1. Horizon and locality t he same as in fig. 6 above. USNM 

46162. 

8, 9. Cycloconcha sp.; right and left valves showing dentition and multiple accessory muscle scars, X 3. Horizon and locality 

unknown. USNM 162680-162681. 

10, 11. Cycloconcha rni/leri (Meek); Ulrich hypotype; 10, anterior view, X 2; 11, ventral view, X 2. Horizon and locality the 

same as in fig. 6 above. USNM 162679. 

12, 13. Cycloconcha rnilleri (Meek); 12, dorsal view showing ligament, X 2; 13, anterior end of right valve showing growth 

lines, X 3. Horizon and locality the same as in fig. 6 above. UCM 3507. 

14. Cycloconcha ovata Ulrich; left valve showing dentition, X 3. The museum label lists the horizon and locality as: "Eden, 

Covington, Kentucky." MU 129T. 

15. Cydoconcha ovata Ulrich; left valve showing dentition, X 4. Tho museum label lists the horizon and locality as: "Cincinnatian (Utica), Covington, Kentucky." USNM 33472. 

16. Cycloconcha rnediocardinalis Miller; syntype; right valve showing dentition, X 3. The museum label lists the horizon 

and locality as: "Cincinnatian, Cincinnati, Ohio." WM 8893. 

17. Cycloconcha milleri (Meek); Ulrich hypotypo; left valve showing lateral teeth, X 2. The museum label lists the horizon and locality as: "Richmond (Waynesville), Hanover, Ohio." USNM 47344. 

18, 19. Cycloconcha milleri (Meek); previously unfigurod syntype;18, dorsal view showing ligament, X 2; 19, anterior view, 

X 2. The museum label lists the horizon and locality as: "Cincinnati Group, 40 miles west of Cincinnati, Ohio." 

USNM 26409. 

20. Cycloconcha ovata Ulrich; X 1 view of a specimen showing dentition. On the same slab occur Lyrodesrna (above) and 

Deceptrix (below). The museum label lists the horizon and locality as: "Cincinnatian (Utica), Covington, Kentucky." USNM 162682. 

21. Cycloconcha milleri (Meek); dorsal view showing ligament, X 2. The museum label lists the horizon and locality as: 

"Richmond (Waynesville), Aurora, Indiana." USNM 100766. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 2 

ALLODESMA AND CYCLOCONCHA 
PLATE 3 

FIGURES 1-3. Cycloconcha cf. C. mediocardinalis Miller; 1, right valve, internal mold showing musculature and pallial line, X 3; 2, 

natural cast of fig. 1 preserving shell material, X 3; 3, dorsal view of fig. 1 showing multiple accessory muscle scars 

X 3. The museum label lists the horizon and locality as: "Eden (Southgate), Covington, Kentucky." USNM 49972. 

4. Cycloconcha cf. C. oblonga Foerstc; left valve, X 2. Point Pleasant Limestone, near intersection of U.S. Route 52 and 

Ohio Route 133 along the Ohio River. USGS locality 6146-CO. USNM 162683. 

5-8. Lyrodesma subplanum Ulrich; 5, left valve, X 1; 6, right valve, X 1; 7, anterior view, X 3; 8, dorsal view, X 3. The 

museum label lists the horizon and locality as: "Cynthi ana section [probably upper Lexington Limestone], 7f mile 

so uth of Cynthiana, Kentucky. " USNM 162684. 

9. Lyrodesma subplanum Ulrich; specimen showing dentition with elongate posterior teeth, X 3. Upper .Lexington Limestone, on Kentucky Route 982 0.4 of a mile south of Cynthiana, Ky. USGS locality 6146- CO. USNM 162685. 

10. Lyrodesma acuminatum Ulrich; syntype showing dentition, X 3. The museum label lists the horizon and locality as: 

"Black River, six mile" south Cannon Falls, Minnesota." USNM 46215 . 

11. Lyrodesma armuricana Tromelin and Lebesconte; mold, left valve showing elongate posterior lateral teeth, X 3. The 

museum label accompanying the specimen contains the following information: "Malroche, Pont-Rean, 35. Arenie 

superieur. Stratut & No. 735." LGB. 

12. Lyrudesma inornatum Ulrich; syntype; right valve showing seven cardinal teeth, X 3. The museum label lists the 

horizon and locality as: "Middle Beds [probably Maysville] Cincinnati Group, Covington, Kentucky." USN M 46222. 

13- 15. Lyrodesma major (Ulrich) ; syntype; 13, right valve, exterior, X 1; 14, dorsal view, X 2; 15, hinge line view, X 3. The 

museum label lists the horizon and loc:J.lity as: "Cincinnati Group, Clarksville, Ohio." USNM 46223. 

16. Lyrodesma poststriatum (Emmons); right valve, internal mold showing the pallial sinus, X 2. The museum label lists the 

horizon and locality as: "Pulaski drift, near Trenton Falls, New York." USNM 162686. 

17. Lyrodesma conradi Ulrich; syntype; left valve, internal mold showing the pallial sinus, X 2. The museum label lists the 

horizon and locality as: "Eden (Southgate), Covington, Kentucky." USNM 46220. 

18, 19. Lyrodesma poststriatum (Emmons); 18, right valve, internal mold showing pallial line, pallial sinus, a nd adductor 

and pedal muscle scars, X 3; 19, oblique dorsal view showing impressions of teeth and pedal and adductor muscle 

scars, X 2. Horizon and locality the same as in fig. 16 above . ·usNM 10197. 

20. Lyrodesma conradi Ulrich; shelled specimen showing teeth with denticlcs and pedal a nd adductor muscle scars, 

X 5. The museum label lists the horizon and locality as: " Cincinnatian (Utica), Covington, Kentucky." USNM 

33473. 

21, 22. Lyrodesma major (Ulrich); syntype; 21, dorsal view, internal mold showing adductor and pedal scars and umbonal 

apices and impressions of teeth, X 3. 22, left valve internal mold showing adductor and pedal scars and anterior 

buttress, X 3. The museum label lists the horizon and locality as: "Richmond (Waynesville), Clarksville, Ohio ." 

USNM 46224. 

23. Lyrodesma caelata Salter; rubber mold of holotypc showing the elongated posterior teeth, X 3. USNM 162687. 

Original from the Budleigh Saltcrton Pebble Bed (?lower Caradoc), British Museum (Natural History) W. Vicary 

collection L. 15690. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 3 

CYCLOCONCHA AND LYRODESMA 
PLATE 4 

FIGURE 1. Ctenodonta nasuta (Hall); lectotype (McAlester, 1968); right valve, X I. The museum label lists t he horizon and locality 

as: "Trenton Limestone, Middleville, New York." AM 723/la. 

2, 3. Ctenodonta nas:uta (Hall); paratype; 2, right valve, X I ; 3, dorsal view, X I. Horizon and locality the same as in fig. 1 

above. AM 723/lb. 

4. Ctenodonta nasuta (Hall); dorsal view showing external ligament insertion groove, X 1.5. East bank Ottawa River, half a 

mile below Pauquette Rapids. USNM locality 9253. USNM 162688. 

5-7. Ctenodonta nasuta (Hall); 5, dorsal view showing external ligament insertion groove, X 1.1; 6, interior of right valve, 

X l.l; 7, exterior of right valve, X 1.1. The museum label lists th~ horizon and locality as: "Black River, Pauquctte 

Rapids, Ottawa, Canada." USNM 14718. 

8, 9. Ctenodonta cf. C. iphigenia Billings; 8, hinge line view, X 2; 9, exterior view right valve, X I. The museum label lists the 

horizon and locality as: "Richmond (Waynesville), Hano-ver, Ohio." USNM 40501. 

10. Ctenodonta nasuta (Hall); interior view of right value showing teeth, anterior buttress, adductor muscle scars, and pallial 

line, X 1.4. The museum label lists the horizon and locality as: "Upper Black River, Pauquette Rapids, Ottawa River, 

Canada." USNM 162689. 

11, 12. Ctenodonta sp.; 11, dorsal view showing ligament insertion grooves, X 1; 12, left exterior ~iew, X 1. The museum label 

lists the horizon and locality as: "Stones River (Murfreesboro), 1.5 miles north Murfreesboro, Tennessee." USNM 

47065. 

13. Ctenodonta nasuta (Hall); hinge line view showing continuous tooth rows and the lack of .an internal ligament, X 2. Ottawa 

Formation, near Braeside, Ontario, Canada. USNM locality 9254. USNM 162690. 

14, 15. Ctenodonta sp.; 14, dorsal view showing ligament insertion groove, X 3; 15, right interior showing teeth, X 1. Collected 

by C. L. Sainsbury. Ordovician, Seward Peninsula, Alaska. USGS collection 6027-CO. USNM 162691. 

16, 17. Ctenodonta sp.; 16, exterior right valve, X 1; 17, interior right valve showing continuous tooth rows, X 2. Antelope Valley 

Limestone, southeast end Groom Range, Nevada. USGS locality D-1571- CO. USNM 162692. 

18, 19. Ctenodonta nasuta (Hall); 18, interior view of left valve showing teeth, anterior buttress, and adductor muscle scars, 

X 1.4; 19, interior umbonal view showing features seen in fig. 18 and pedal retractor muscle scars, X 2.5. The museum 

label lists the horizon and locality as: "Trenton, Ottawa, Canada." USNM 18034. 

20-22. Ctenodonta sp.; 20, interior right valve view showing teeth and adductor muscle scars, X 2; 21, exterior right valve view, 

X 1; 22, dorsal view showing ligament insertion groove, X 2. Lower shelly facies of the Setul Formation, off south 

point of Pulau Langgun, Langkawi Islands, Malaysia. Gastropods and brachiopods from this collection suggest a late 

Canadian (Early Ordovician) age, Yochelson and Jones (1968). USNM 162693. 

23, 24. Ctenodonta nasuta (Hall); 23, exterior view left valve, X 1.1; 24, interior view left valve showing anterior buttress, adductor muscle scars, and integropalliate pallial line, X 1.1. The museum label lists the horizon and locality as: "Upper 

Black River, Pauquette Rapids, Ottawa River, Canada." USNM 92269. 
GEOLOGICAL SURVEY PROF'ESSIONAL PAPER 695 PLATE 4 

.,.... ._ .. _ 13 

7 

CTENODONTA 
FIGURE 1. 

2. 

3. 

4, 5. 

6. 

7. 

B. 

9, 10. 

11. 

12. 

13. 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

PLATE 5 

Similodonta similis (Ulrich); left valve, X 4. The museum label lists the horizon and locality as: "Richmond (Maquoketa), 

Bristol, Minnesota." USNM 25021. 

Similodonta similis (Ulrich) ; para type; right valve, X 3.5. The museum label lists the horizon and locality as: "Richmond 

(Maquoketa), Spring Valley, Minnesota." USNM 163508=USNM 145663, McAlester (1968). 

Similodonta simi/is (Ulrich); interior view right valve showing tooth rows and adductor muscle scars, X 3.5. Horizon 

and locality the same as in fig. 1 above. USNM 47037. 

Similodonta similis (Ulrich) ; 4, anterior view showing lunule, X 3; 5, dorsal view showing escutcheon, X 3. Horizon and 

locality the same as in fig. 1 above. USNM 162694. 

Similodonta similis (Ulrich); interior view right valve, X 1. Horizon and locality the same as in fig. 1 above. USNM 

162695. 

Deceptrix aff. D. hartsvillensis (Safford); left valve, X 3.5. Grier Limestone Member, Lexington Limestone, YMCA 

Camp, Jessamine County, Ky. USGS locality 5096-CO. USNM 162696. 

Deceptrix aff. D. hartsvillensis (Safford); right valve, X 3.5. Horizon and locality the same as in fig. 7 above. USNM 

162697. 

Deceptrix aff. D. hartsvillensis (Safford); 9, dorsal view showing ligament space posterior to the beaks, X 3.5; 10, anterior 

view, X 3.5. Grier Limestone Member, Lexington Limestone, west side of U.S. Route 227, north of Fqrd, Ky. USGS 

locality 5067-CO. USNM 162698. 

Deceptrix sp.; right valve interior, X 3. Antelope Valley Limestone, Ike's Canyon section, Toquima Range, Nev. USGS 

locality D-1519-CO. USNM 162699. 

Deceptrix sp.; right valve exterior, X 3. Horizon and locality the same as in fig. 11 above. USGS locality D-1520-CO. 

USNM 162700. 

Deceptrix cf. D. hartsvillensis (Safford); left valve, X 1. The museum label gives the horizon and locality as: "Trenton, 

Hartsville, Tennessee." USNM 47017. 

Deceptrix albert ina (Ulrich); syntype; hinge line view, X 3. The museum label lists the horizon and locality as: "Richmond 

(Waynesville), Clarksville, Ohio." USNM 162701. 

Deceptrix filistriata (Ulrich); syntype; left valve showing dentition, X 3. The museum label lists the horizon and locality as: 

"Eden (Economy), Covington, Kentucky." USNM 46131. 

Deceptrix albertina (Ulrich); syntype; left valve showing dentition, X 3. Horizon and locality the same as in fig. 14 above. 

USNM 46122. 

Deceptrix aff. D. hartsvillensis (Safford); dorsal view showing ligament space posterior to beaks, X 3. Horizon and locality 

the same as in fig. 9 above. USNM 162702. 

Deceptrix albertina (Ulrich) ; syntype; X 1. Horizon and locality the same as in fig. 14 above. USNM 162703. 

Deceptrix aff. D. hartsvillensis (Safford); oblique interior view showing adductor and pedal muscle scars, X 3.5. Horizon 

and locality the same as in fig. 9 above. USNM 162704. 

Deceptrix aff. D. hartsvillensis (Safford); right valve showing continuous tooth rows, X 3.5. Grier Limestone Member, 

Lexington Limestone, Antioch Church Road section, Jessamine County, Ky. USGS locality 4879-CO. USNM 162705. 

Deceptrix baffinense (Ulrich); left valve, X 2. The museum label lists the horizon and locality as: "Shale Member, Putnam 

Highland Formation, northwest segment Silliman's Fossil Mount, Baffin Island." USNM 124612. 

Deceptrix levata (Hall) ; right valve, X 1. The museum label lists the horizon and locality as: "Trenton, Sacketts Harbor, 

New York." USNM 4707. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 5 

SIMILODONT A AND DECEPTRIX 
PLATE 6 

FIGURE 1. Nuculites [Cleidophorus] planulata Conrad; mold right valve showing slitlike impression of buttress, X 3. The museum label lists the horizon and locality as: "Pulaski drift, ncar Trenton Falls, New York." USNM 162706. 

2. Nuculites [Cleidophorus] planulata Conrad; mold right valve showing slitlikc impression of buttress, X 3. Horizon and 

locality the same as in fig. 1 above. USNM 162707. 

3- 5. M yoplusia carpenderi (Schuchert); 3, dorsal view, X 1; 4, right valve, X 1; 5, left valve, X 1. The museum label lists 

the horizon and locality as: "Trenton, head of Frobisher Bay, Baffin Land." USNM 28164. 

6- 8. Palaeoconchafaberi Miller; syntype; 6, anterior view, X 5; 7, dorsal view, X 5; 8, right valve, X 5. The museum label 

lists the horizon and locality as: "Cincinnatian, Versailles, Indiana." WM 8870. 

9. Tancrediopsis cuneata (Hall); interior left valve showing tooth rows and adductor muscle scars, X 4. Ottawa Formation, 

about half a mile below Pauquctte Rapids, Ontario, Canada. USNM locality 9253. USNM 162708. 

10. Tancrediopsis cuneata (Hall); exterior left valve, X 4. The museum label lists the horizon and locality as: "Upper Black 

River, Pauquette Rapids, Ottawa River, Canada." USNM 72265. 

11. Tancrediopsis gibberula (Salter); left valve internal mold, X I. The museum label lists the horizon and locality as: "Black 

River (Platteville), Beloit, Wisconsin." USNM 15881. 

12. Tancrediopsis gibberula (Salter); dorsal view, internal mold showing adductor and pedal muscle scar impressions, X 1. 

Horizon and locality the same as in fig. 11 above. USNM 162709. 

13. Tancrediopsis gibberula (Salter); right valve, internal mold showing impressions of adductor muscle scars and pallial line, 

X 4. Horizon and locality the same as in fig. 11 above. USNM 15662. 

14. Tancrediopsis aff. T. cuneata (Hall); right valve, X 1. Antelope Valley Limestone, Central Pahranagat Range, Nev. 

USGS locality D-1374-CO. USNM 162710. 

15. Tancrediopsis cuneata (Hall); oblique interior view showing adductor and pedal muscle scars, X 4. Horizon and locality 

the same as in fig. 9 above. USNM 162711. 

16, 17. Cyrtodonta grandis luwlentus (Sardeson); 16, anterior view, X I; 17, posterior view, X 1. The muse um label lists the horizon 

and locality as: "Richmond, Bristol, Minnesota." USNM 25060. 

18. Cyrtodonta sp.; dorsal interior of articulated valves showing accessory muscle scars (horizontal arrows) and anterior 

adductor muscle scar (oblique arrow), X 3.5. Ottawa Formation, near Braeside Ontario, Canada. USNM locality 

9254. USNM 162712. 

19. Cyrtodonta sp.; dorsal interior view of right valve showing accessory muscle scar (vertical arrow) on lateral face of hinge 

plate, anterior adductor muscle scar to left (horizontal arrow), X 10. Horizon and locality the same as in fig. 18 above. 

USNM 162713. 

20. Cyrtodonla sp.; dorsal interior view of left valve showing accessory muscle scar on lateral face of hinge plate (short arrow) 

and anterior adductor muscle scar (long arrow), X 4. Horizon and locality the same as in fig . 18 above. USNM 162714. 

21- 23. Cyrtodonta grandis (Ulrich); syntype; 21, right valve, X 1; 22, dorsal view, X 1; 23, left valve, X 1. The museum label 

gives the horizon and locality as: "Trenton, 1);. miles south Burgin, Kentucky." USNM 46182. 
GEOLOGI CAL SURVEY PROFESSIONAL PAPER 695 PLATE 6 

6 7 

2 3 

10 

13 

18 

16 14 

15 

19 20 

NUCULITES, MYOPLUSIA, PALAEOCONCHA, TANCREDIOPSIS, AND CYRTODONTA 
PLATE 7 

FrounE 1. Cyrtodonta saffordi (Hall); Safford hypotype, X 2. Note the peculiar anterior dentition. The museum label lists the horizon 

and locality as: "Trenton (Catheys), Nashville, Tennessee." USNM 46191. 

2. Cyrtodonta cf. C. huronensis Billings; right valve showing dentition, anterior adductor muscle scar, and what may be an 

accessory muscle scar (arrow), X 3.5. Ottawa Formation, ncar Braeside, Ontario, Canada. USNM locality 9254. 

USNM 162715. 

3. Cyrtodonta cf. C. huronensis Billings; right interior, X 2. Horizon and locality the same as in fig. 2 above. USNM 162716. 

4. Cyrtodonta cf. C. huronensis Billings; left valve, X 2. Horizon and locality the same as in fig. 2 above. USNM 162717. 

5. Cyrtodontula rugatina (Ulrich); left valve, X 1. The museum label lists t he horizon and locality as: "Black River (Decorah), Minneapolis, Minnesota." USNM 46357. 

6. Cyrtodontula scofieldi (Ulrich) ; left valve, Ulrich hypotype, X 1. Note the bryozoan incrustation on the posterior umbonal 

slope which suggests that this part of the shell projected above the sediment-water interface. The museum label lists the 

horizon and locality as: "Black River (Decorah), St. Paul, Minnesota ." USNM 46358. 

7. Cyrtodonta beckneri Conkin; right value interior, X 1. Liberty Formation (upper Dillsboro Formation), upstream from 

Oidenburg-Enochsburg Road crossing of Salt Creek, Ind. USGS locality 6139-CO. USNM 162718. 

8. Cyrtodonta sp .; left valve interior, note t he ligamenta! grooves and ridges, X 2. The museum label lists the horizon and 

locality as: "Richmond, Gore Bay, Manitoulin Island." USNM 100850. 

9, 10. Vanuxemia gibbosa Ulrich ; 9, oblique interior view showing the myophoric notch (arrow), X 3; 10, left valve showing 

dentition, anterior adductor muscle scar, myophoric notch, and ligamenta! grooves and ridges, X 5. The museum label 

lists the horizon and locality as: " Trenton, Haynies, Tennessee." Also see pl. 9, fig. 7. USNM 46942. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 7 

10 

CYRTODONT A, CYRTODONTULA, AND V ANUXEMIA 
PLATE 8 

FIGURES 1, 2. Vanuxemia sp.; 1, right valve showing umbonal septum and dentieles on anterior teeth, X 3.5; 2, oblique interior view 

showing myophoric notch (white a rrow), umbonal septum (left, black arrow), and hinge plate (right, black arrow), 

X 3.5. The museum label lists the horizon and locality as: "Lorraine (Upper), Bristol, Minnesota." USNM 25033. 

3. Vanuxemia gibbosa Ulrich; anterior view, X 1. Basal part of the Curdsville Limestone Member, Lexington Limestone, 

behind Old Crow Distillery, Woodford County, Ky. USGS locality 5072-CO. USNM 162719. 

4, 5. Vanuxemia cf. V. inconstans Billings; 4, right exterior, X 1.2; 5, right interior, X 4. Ottawa Formation, near Braeside, 

Ontario, Canada. USNM locality 9254. USNM 162720. 

6, 7. Vanuxemia cf. V. inconstans Billings; 6, left valve, X 3; 7, oblique interior view showing accessory scar (arrow), X 3. 

Horizon and locality the same as in fig. 4 above. USNM 162721. 

8-10. Vanuxemia cf. V. inconstans Billings; 8, left interior, X 2; 9, oblique interior view showing accessory scar (arrow), 

X 2.5; 10, exterior view, X 3. Horizon and locality the same as in fig. 4 above. USNM 162722. 

11. Vanuxemia cf. V. inconstans Billings; left exterior, X 2.2. Horizon and locality the same as in fig. 4 above. USNM 

162723. 

12. Vanuxemia gibbosa Ulrich; dorsal view of articulated specimen, X 2. The museum label lists the horizon and locality 

as: "Trenton, Haynies, Tennessee." USNM 162724. 

13. Vanuxemia cf. V. inconstans Billings; right valve showing ligament grooves and ridges and denticles on posterior 

teeth, X 4. Horizon and locality the same as in fig. 4 above. USNM 162725. 

14. Vanuxemia gibbosa Ulrich; left exterior showing incrustation of trepostome bryozoans on the posterior half of the 

shell, X 3. Horizon and locality the same as in fig. 12 above. Also see pl. 9, fig. 6. USNM 162726. 
I 

PROFESSION A L PAPER 695 PLATE 8 

9 

.. 

'· .. 

'- ~. ~ ~· -~.,. ... ;/' 
PLATE 9 

FIGURE 1. Vanuxcmia gibbosa Ulrich; hinge line view showing the dentition and ligament grooves and ridges, X 4. The museum 

label lists the horizon and locality as: "Trenton, Haynies, Tennessee." USNM 162727. 

2. Vanuxemia cf. V. inconstans Billings; left valve showing denticles on anterior teeth, X 3. Ottawa Formation, near Braeside, Ontario, Canada. USNM locality 9254. USNM 162728. 

3. Vanuxemia cf. V. inconstans Billings; left valve showing denticles on anterior teeth, X 3. Horizon and locality the same 

as in fig. 2 above. USNM 162729. · 

4-7. Vanuxemia gibbosa Ulrich; four specimens of the same species showing how the myophoric notch is developed to differing degrees in different individuals, X 2. Horizon and locality the same as in fig. 1 above. USNM 46942, 162726, 

162730, 162731. 

8-13. Septij er bilocularis (Linne); paired valves of three individuals of the species showing varying degrees of myophoric 

no tch development, X 2. 8, 9, little or no notch; 10, 11, slight development of notch; 12, 13, notch well developed. 

Semporna Reef, North Borneo. USNMDM. 658045a-c. 

14- 17. Septijer excisus Wiegm; paired valves of two individuals showing varying degrees of myophoric notch development, 

in this species the notch is always well developed, X 2. 14, 15, notch of moderate depth; 16, 17, notch exceptionally 

deep. Kashiwajima, Tosa, Japan. USNMDM 304298a, b . 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 9 

V ANUXEMIA AND SEPT I FER 
FIGURE 1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

PLATE 10 

Opisthoptera casei (Meek and Worthen); left valve internal mold, X 2. Whitewater Formation, Richmond, Ind. USNM 

46265. 

Opisthoptera casei (Meek and Worthen); rubber mold of right valve showing sculpture, X 1. Waynesville Shale, Claksville, Ohio. USNM 46267. 

Ambonychia cf. A. ulrichi (Pojeta); right valve, X 1. Perryville Limestone Member, Lexington Limestone, near Perryville, Ky. USGS collection 5015-CO. USNM 162733. 

Ambonychia ulrichi (Pojeta); anterior view showing byssal gape, X 1. "Hudson River Group," Lindleys' Hirl, Tenn. 

AM 1124/4. 

Allonychia jlanaganensis Foerste; anterior view showing anterior lobe, X 1. Millersburg Member, Lexington Limestone, 

nca r Winchester, K y . USGS locality 5066-CO. UCM 35906. 

Anomalodonta gigantea Miller; hinge line view showing ligament grooves and ridges, X 1. "Hudson River Group," Versailles, Ind. YPM 23324. 

Ambanychia alata Meek; rubber mold of left valve showing posterior muscle scars, pallial line, and remnants of posterior 

teeth, X 1. Locality and horizon unknown. UCM 35923. 

Ambanychia alata Meek; hinge line showing ligament grooves and ridges and anterior teeth, X 5. Oregonia Member, 

Arnheim Formation of Stout and others (1943) , excavation at intersection of Westwood-Northern Boulevard and 

Boudinot Avenue, Cincinnati, Ohio . UCM 35913. 

9. Ambonychia alata Meek; rubber mold of left valve showing posterior teeth, X 1. Arnheim Formation, near Morrow, Ohio. 

USNM 46087. 

10. Ambonychia radiata Hall; internal mold, right valve showing posterior dentition, posterior muscle scars, and pallial line, 

X 1.5. "Hudson River Group," Pulaski, N.Y. AM 928/2. 

11. Ambonychia radiata Hall; right valve showing posterior teeth, X 1.5. Eden Formation of former usage, Covington, Ky. 

MU2. 

12. Ambonychia casteri (Pojeta); anterior view of composite mold showing pallial line and byssal gape, X 1. Fort Ancient 

Member, Waynesville Formation of Stout and others (1943), Bull Run Creek, south of Oxford, Ohio. MU 1. 

13. Ambonychia sp.; a specimen showing an entire attached edrioasteroid, X 1. The museum label gives the horizon and locality 

as: "Maysville, Cincinnati, Ohio." USNM 53900. 

14. Pterinea sp.; left valve with attached edrioasteroids and bryozoans, X 1. The museum label gives the horizon and locality 

as: "Maysville Group (Corryville beds), Cincinnati, Ohio." USNM 40741. 

15. Pterinea sp.; left valve with attached edrioasteroid and bryozoans, X 2. Corryville Shale Member, McMillan Formation, 

Stonelick Creek, downstream from crossing of Ohio Route 131, near Modest, Ohio. USNM 162734. 

16. Ambonychia sp. undet.; left valve showing remains of an edrioasteroid, X 1. Bellevue Limestone Member, McMillan 

Formation, excavation for Liberal supermarket across from Frisch's drive-in, Hamilton Avenue, North College Hill, 

Ohio. USNM 162735. 

17. Ambonychia obesa (Ulrich); dorsal view showing multiple anterior byssal retractor scars, X 1.5. Whitewater Formation, 

2 miles south Richmond, Ind. on Route 27. UCM 35921. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 10 

1 

/ 

L 

9 

PTERINEA 
PLATE 11 

FIGURES 1-4. Pterinea demissa (Conrad); 1, left valve, X 1.1; 2, right valve, X 1.1; 3, dorsal view, X 2 ; 4, anterior view, X 2. 

The museum label lists the horizon and locality as: "Arnheim Formation, Waynesville, Ohio. " USNM 40525. 

5-8. Pterinea cincinnatiensis Miller and Faber; 5, dorsal view, X 4; 6, anterior view, X 4; 7, left valve, X 1.5; 8, right 

valve, X 1.5. The museum label lists the horizon and locality as: "Maysville, Cincinnati, Ohio." USNM 162736. 

9. Palaeopteria sp.; interior left valve sho\ving the teeth, X 4. Perryville Limestone Member, Lexington Limestone, 

near Perryville, Ky. USGS locality 5015-CO. USNM 162737. 

10, 11. Pterinea demissa (Conrad); 10, left valve internal mold, X 1; 11, enlargement of dorsal part of fig. 10 showing anterior 

and posterior teeth, anterior muscle scars, and ligamenta! grooves and ridges, X 3. The museum label lists the 

horizon and locality as: "Pulaski drift, Thorold, Ontario. " USNM 34598. 

12. Pterinea sp.; left valve showing the inner surface of the outer shell layer, X 1.5. The museum label lists the horizon 

and locality as: "Richmond (Waynesville), Versailles, Indiana." USNM 46487. 

13. Ptcrinca u:clchi (James); left valve showing prominent wing and growth lines, X 2. The museum label lists the horizon and locality as: "Richmond (upper Liberty), near Springfield Church, Todd's Fork, Ohio." USNM 70089. 

14. Pterinea demissa (Conrad); left valve showing anterior adductor scar, X I. The museum label lists the horizon and locality as: "Pulaski, near Trenton Falls, New York." USNM 23606. 

15, 16. Aristerella nitidula Ulrich; syntype; 15, dorsal view showing that t he specimen is nearly equivalved, X 5; 16, right valve, 

X 5. The museum label lists the horizon and locality as: ''Black River, Chatfield, Minnesota." USNM 46092. 

17. Aristerella nitidula Ulrich; syntype; right valve, X 5. Horizon and locality the same as in fig. 15 above. USNM 162738. 

18. Aristerella nitidula Ulrich; syntype ; left valve, X 5. Horizon and locality the same as in fig. 15 above. USNM 162739. 

19, 20. Aristerella nitidula Ulrich; 19, left valve, X 5; 20, dorsal view, X 5. The museum label lists the horizon and locality 

as: "Black River, St. Paul, Minnesota." USNM 46647. 

21. Aristerella nitidula Ulrich; syntype; right valve, X 5. Horizon and locality the same as in fig. 15 above. USNM 162740. 

22. Aristerella nitidula Ulrich; syntype; left valve, X 5. Horizon and locality the same as in fig.19 above. USNM46093. 

23. Aristertlla nitidula Ulrich; syntype; dorsal view, X 5. Horizon and locality the same as in fig. 15 above. USNM 162741. 

24. Aristerella nitidula Ulrich ; syntype; right valve, X 5. Horizon and locality the same as in fig. 15 above. USNM 162742. 

25, 26. "Aristerella"; 25, left valve showing adductor muscle scars, X 1; 26, right valve, X 1. The museum label lists the 

horizon and locality as: "Ord. (Jerve, D1) , B;uon Toll's Estate, near Jerve, Esthonia." USNM 162743. 

27-30. "Aristerella"; 27, right valve, X 1; 28, left valve showing adductor muscle scars, X 1; 29, dorsal view, X 1; 30, anterior 

view, X 1. Horizon and locality the same as in fig. 25 above. USNM 99198. 

31. Modiolus american us Leach; Holocene mytilid showing shell shape, X 1. Open surf beach, south shore Sanibel Island, 

Florida, near the " rocks." USNM 16744. 

32. Arcuatula demissa (Dillwyn) ; Holocene mytilid showing shell shape, X 1. Woodmere golf course, Nassau County, Long 

Island, N .Y. USNM 162745. 
GEOLOGICAL SURVEY 

/ ').=;-: 

/( 

J 

J 

PROFESSIONAL PAPER 695 PLATE 11 

f. .. .... 

PTERINEA, PALAEOPTERIA, ARISTERELLA, MODIOLUS, AND ARCUATULA 
PLATE 12 

FIGURES 1,2. Colpomya constricta U lrich; 1, exterior left valve, X 3.5; 2, interior left valve showing anterior dentition, X 3.5. Devils 

Hollow Member, Lexington Limestone, Franklin County, Ky. USGS locality 5087-CO. USNM 162746. 

3. Colpomya constricta Ulrich ; syntype; right valve showing anterior dentition, X 4. The museum label lists the horizon and 

loca lity as: "Trenton (Perryville), Frankfort, Kentucky." USNM 46120. 

4. iHod'iolop;i;; modiolaris (Conrad); Ulrich hypotype showing dorsal longitudinal groove, X 2. The museum label lists the 

horizon and locality as: "Upper Pulaski, 1 mile above Pulaski, New York." USNM 101 314. 

5. Pholadornorpha pholadiforrnis (Hall); articulated specimen showin g divaricating sculpture, X 1. The museum label lists 

the horizon and locality as: "Richmond (Waynesville), Clarksville, Ohio." USNl\'l 70414. 

6,7. Phuladomorpha pholadiforrnis (Ha ll); U lrich hypotypes showing some aspects of the hinge line; 6, right valve, X 3; 

7, left valve, X 3. The museum label lists ihc horizon and locality as: "Richmond (Wa~·nesv ill e), Clarksville, Ohio." 

USNM 46342 and 162747. 

8. Pholadornorpha pholadiformis (Hall); left valve showing sculpture, X 1. The museum label lists the horizon and lo calit~­

as: "Richmond Group (Waynesville Formation), Waynesville, Ohio. " USN.M 40578. 

9. Pholadornorpha pholadiforrnis (Hall); left valve, X 1. Horiwn and locality the same as in fig. 8 above. USNlVI 162748. 

10-12. Saffordia ventralis Ulrich; syntype; 10, dorsal view showing tooth and escutcheon, X 1; 11, view of hinge line showing 

cardinal tooth, X 2; 12, left valve exterior, X l. The museum label lists t he horizon and locnlity as: "Richmond 

(Maquoketa), Spring Valley, Minnesota." USNl\1 46309. 

13. Modiulopsis aff. M. rogersensis Foerste; left valve, X 1. The museum label lisls the horizon and locality as: "Eden 

Group, So uthgate Member, Warner St., central Covington, Kentucky." USNl\I 101443. 

14. Sphenoliurn striatum U lrich; holotypc; right valve, X 1. The museum label lists the horizon and localit~- as: "Trenton 

(Prosser), 13 miles south Cannon Falls, Minnesota." USNl\I 46311. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 12 

COLPOMY A, MODIOLOPSIS, PHOLADOMORPHA, SAFFORD! A, AND SPHENOLIUM 
PLATE 13 

FIGURES 1-14. Modiolodon oviformis (Ulrich); 1, right valve, X 1, USNM 162749; 2, left valve, X 1, USNM 162750 ; 3, left valve, 

X 1, USNM 162751 ; 4, left valve, X 1, "CSNM 162752; 5, left valve, X 1, USNM 162753; 6, 7-6, interior left 

valve showing adductor muscle ~ca , teeth, and pallial line, X 2, 7-dorsal interior view showing multiple byssal 

retractor muscle scars, arrow points to most posterior scar, X 3, USNM 162754 ; 8, right valve showing teeth, X 3, 

USNM 162755; 9, right valve showing teeth, X 2, USNM 162756 ; 10, view of posterior end of broken shell showing 

two shell layers, X 3, USNM 162757; 11, dorsal interior view showing multiple byssal retractor muscle scars, arrow 

points to the most posterior scar, X 3, USNM 162758; 12, dorsal view, X 2, USNM 162759 ; 13, 14-13, anterior 

view, X 3, 14-ventra.J view, X 3, USNM 162760. Logana Member, Lexington Limestone, U.S. Highway 62 crossing 

of Kentucky River. USGS locality 5092- CO. 

15. M odiolodon oviform is (ulrich); syntype; internal mold showing some of the pallial line and the anterior adductor 

muscle scar, X 1. The museum label lists the horizon and locality as: "Trenton (Hermitage), Curdsville, Mercer 

County, Kentucky." U SNM 46231. 

16. M odiolopsis concentrica Hall and Whitfield; left valve composite mold, X 1. Clarksville Member, Waynesville Formation of Stout and others (1943), Sewell's ltun nort heast of Clarksville, Ohio. USN:\'I 162761. 

17. M odiolopsis concentrica Hall and Whitfield; right valve composite mold, X 1. Horizon and locality the same as in 

fig. 16 above. USN:\-I 1()2762. 

18. M ytil1ts edulis Linne; Holocene mytilid showing teeth just below the beak and the white resilial ridge, X 1.5. Locality 

unknown. USNM 162763. 

19. Arcuatula demissa (Dillwy n); Holocene myti!id showing edentulous hinge and the white rcsilial ridge with a piece of 

the ligament still attached, X 1.5. Woodmere golf course, Nassau Co~mt , Long Island, N .Y. USN:\11 162764. 

20. Perna pincta (Born); Holocene mytilid showing the ligament, white resilial ridge, and hinge plate with a single tooth, 

X 1. Algiers. USNMDM 199369. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 13 

19 

MODIOLODON, MODIOLOPSIS, MYTILUS, ARCUATULA, AND PERNA 
PLATE 14 

FIGURE 1. Modiolcpsis valida Ulrich; syntype; right valve showing absence of cardinal teeth, X 2. The museum label lists the 

horizon and locality as: "Richmond (Waynesville), Waynesville, Ohio." USNM 46260. 

2. 1\Iodiolopsis aff. M. simulatrix Ulrich; left valve showing absence of cardinal teeth, X 4. The museum label lists the 

horizon and locality as: "Eden Group, Southgate Member, Warner St., central Covington, Kentucky." USNM 101330. 

3. Modiclopsis aff llf. simulatrix Ulrich; right valve showing absence of cardinal teeth, X 4. The museum label lists the 

horizon and locality as: "Eden Group, Southga te Member, Newport, Kentucky." USNM 101440. 

4. Modiolopsis aff. 1\I. simulatrix Ulrich; right valve showing the edentulous hinge area, X 4. Horizon and locality the 

same as in fig. 2 above. USNM 162765. 

,>. Jvl odiolopsis versaillensis l\1iller; Ulrich hopotype showing absence of cardinal teeth, X 5. The museum label lists the 

horizon and localitr as: "Richmond (Waynesville) , Versailles, Indiana and 2 miles southeast of Weisburg, Indiana." 

USNl\'I 46261. 

6. 1\Iodiolopsis aff. 1\1!. simulatrix Ulrich; internal mold showing adductor muscle scars and pallial line, X 2. The muse um 

label lists the horlzon and locality as : "Eden Group, Southgate Member, creeks in southwest side of Covington, 

Kentucky." USNM 101449. 

7, 8. Plethocardia umbonata Ulrich; previously unf'gured syntype; 7, right exterior view, X 1; 8, view of hinge line, X 2. 

The museum label lists the horizon and locality as: "Black River, Mercer County, Kentucky." USNM 47359. 

9- 12. Plethocm·dia umbonata Ulrich; syntype; 9, hinge line view (compare to reconsLruction in fig. 1 H, p . 11), X 2; 10, dorsal 

view, X 1; 11, anterior view, X 1; 12, left exterior view, X 1. The museum label lists the horizon and locality as 

"Black River, 6 miles south Cannon Falls, Minnesota." USNM 46279. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 14 

MODIOLOPSIS AND PLETHOCARDIA 
PLATE 15 

FIGURES 1-3. M odiolopsis modiolaris (Conrad); hclotype; 1, view of entire specimen showing articulated valves, X 1; 2, left valve, 

X 1; 3, right valve, X 1. The museum label lists the ho"rizon and locality as: "Pulaski beds, Rome, New York." 

This specimen was figured by Hall, 1847, pl. 81, fig . 1a and Ulrich, 1924, pl. 32, fig. 1. NYSM 2758. 

4, 5. Mc;diolopsis modiolaris (Conrad); holotype M. angust-ijrons (Conra d); 4, right valve composite mold, X 1; 5, dorsal 

view showing dark stain remnant of the ligament between the two valves, photographed unwhitened, X 3. The 

museum label lists the horizon and locality as: "Pulaski beds, Rome, New York." This specimen was figured by 

Hall, 1847, pl. 81, fig. 1b and Ulrich, 1924, pl. 32, figs. 4, 5. NYSM 2759. 

6. Modiolopsis cf. M. modiolaris (Conrad); articulated specimen showing dark organic film covering valves and remains 

of the ligament, X 1, photographed unwhitened. The museum label lists the horizon and locality as: "Maysville 

(Fairmount), Covington, Kentucky." USNM 46230. 

7. Modiolopsis sp.; internal mold left valve showing adductor muscle scars and pallial line, X 1. The museum label lists 

the horizon and locality as: "Maysville (Fairview), Newport, Kentucky." USNM 46707. 

8. j\1 odiolopsis cf. M. pogonipensis Walcott; internal mold right valve, X 1. Collected by L. Hintze. Lehman Formation, 

from the K-north section of Hintze, Ibex area, Utah. USNM 162766. 

9, 10. C1meamya miamiensis Hall and Whitfield ; 9, left valve, X 1; 10, right valve, X 1. Horizon and locality unknown. 

USNM 162767. 

11. Cuneamya cf. C. scapha Hall and Whitfield ; anterior view showing lunule, X 1. The museum label lists the horizon 

and locality as: "Richmond (Waynesville), Richmond, Indiana and Waynesville, Ohio." USNM 47217. 

12. Cuneamya miamiensis Hall and Whitfield; dorsal view showing ligament space, X 1. Horizon and locality unknown 

USNM 162768. 

13, 14. Cuneamya cf. C. scapha Hall and Whitfield; 13, posterior view, X 1; 14, ventral view, X 1. Horizon and locality 

same as in fig. 11 above. USNM 162769. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 15 

9 

4 

5 

MODIOLOPSIS AND CUNEAMY A 
PLATE 16 

FraunEs 1-3. Modiolopsis modiolaris (Conrad); 1, enlargement of anterior end of internal mold showing adductor muscle scar, 

pallial line, and multiple accessory scars anterior to the beak (arrow), X 3; 2, entire specimen shown in fig. 1, X 1; 

3, rubber mold of the specimen shown in fig. 2, X 1. The museum label lists the horizon and locality as: "Pulaski 

drift, Trenton Falls, New York." USNM 101464. 

4, 5. M odiolopsis sp.; 4, enlargement of upper right hand part of fig. 5 showing nestling modioliform modiomorphid pelecypod 

and trematid inarticulate brachiopod, X 2; .5, entire trepostome bryozoan colony showing two nestling modioliform 

modiomorphids (right-hand facing arrow and longer left-hand facing arrow) and trematid brachipod (shorter lefthand facing arrow), X 1. The museum label lists the horizon and locality as: "Richmond (Waynesville), Clarksville, 

Ohio." USNM 70458. 

6. M atheria rugosa Ulrich; syntype; right valve showing cardinal teeth and ligament grooves and ridges, X 2. The museum 

label lists t he horizon and locality as: "Trenton (Prosser), 6 miles south Cannon Fa\Js, Minnesota ." USNM 46226. 

7- 9. Mathe1·ia tener Billings; syntype; 7, exterior left valve, X 2; 8, exterior left valve, X 1; 9, interior left valve showing 

cardinal teeth and ligament grooves and ridges, X 4. The museum label lists the horizon and locality as: "Trenton, 

Blue Point, Lake St. John, Quebec." GSC 1670. 

10. Rhytimya rnickelboroughi (Whitfield); Ulrich hypotype; left valve, X 1. The museum label lists the horizon and locality 

as: "Maysville (Fairmount) , Cincinnati, Ohio." USNM 4.6301. 

11. Rhytimya sp.; right valve showing shell sculpture of concentric undulations and radiating granules, X 3. The museum 

label lists the horizon and locality as: "Lorraine or Eden, Rome, New York." USNM 102037. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 16 

MODIOLOPSIS, MATHERIA, AND RHYTIMYA 
PLATE 17 

FraU RES 1, 2. Whiteavesia cincinnatiensis (Hall and Whitfield); 1, left valve showing lack of posterior teeth, X 2; 2, exterior left valve 

showing numerous fine growth lines, X I. Lagana Member, Lexington Limestone, on hill above Old Crow distillery, 

Woodford County, Ky. USGS locality 5073-CO. USNM 162770. 

3, 4. Whiteavesia cincinnatimsis (Hall and Whitfield); 3, right valve interior showing lack of posterior teeth, X 2; 4, right 

valve exterior, X I. Lagana Member, Lexington Limestone, U.S. Route 62 crossing of Kentucky River. USGS 

locality 4865- CO. USNM 162771. 

.'i. Whitcavesia cf. W. cincinnatwnsis (Hall an d Whitfield); left valve showing Jack of cardinal teeth, X 3.5. Perryville 

Limestone Member, Lexington Limestone, quarry south of Perryville, Ky. USGS locality 5015-CO. USNM 162772. 

6. Whiteavesia cincinnatiensis (Hall and Whitfield); right valve composite mold, X I. The museum label lists the horizon 

and locality as: "Trenton (Cynthiana), West Covington, Kentucky." USNM 162773. 

7. Whiteavesia cincinnatiensis (Hall and Whitfield); Ulrich hypo type; horizon and locality the same as in fig. 6 above. 

USNM 46339. 

8. Whiteavesia cincinnatiensis (Hall and Whitfield); right valve composite mold, X l. Horizon and locality the same as in 

fig. 6 above. USNM 92317. 

9. Whiteavesia cincinnatiensis (Hall and Whitfield); right valve exterior, X 3. Horizon and locality the same as in fig. 3 

above. USNM 162776. 

10. Whiteavesia cincinnatiensis (Hall and Whitfield); Ulrich hypotype; this is the specimen upon which Ulrich based the 

analysis of the hinge line of the species, X 3. Horizon and locality the same as in fig. 6 above. USNM 162777. 

11, 12. Whiteavesia cf. W. cincinnatiensis (Hall and Whitfield); 11, left valve interior showing lack of cardinal teeth, X 2; 

12, left valve exterior, X 1. Horizon and locality the same as in fig. 5 above. USNM 162774. 

13, 14. Whiteaves1·a cf. W. cincinnatiensis (Hall and Whitfield); 13, right valve interior showing lack of cardinal teeth, X 2; 

14, right valve exterior, X 1. Horizon and locality the same as in fig. 5 above. USNM 162775. 

15. Whiteavesia cf. W. cincinnatiensis (Hall and Whitfield); left valve interior, X 2. Horizon and locality the same as in 

fig. 5 above. USNM 162778. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 17 

WHITEA VESIA 
PLATE 18 

FIGURES 1-6. Psiloconcha grand is Ulrich; syntype; 1, left valve showing adductor muscle scars, X 2; 2, right valve, X 2; 3, ventral 

view showing shell gapes (arrows), X 2; 4, dorsal view showing shell gapes (arrows), X 2; 5, posterior view showing 

gape, X 3; 6, anterior view showing gape, X 3. The museum label lists the horizon and locality as: "Richmond 

(Waynesville), Waynesville, Ohio." USNM 46283. 

7. Orthodesma sp.; right valve, X 1. The museum label lists the horizon and locality as: "Maysville (Orthorhynchula Bed), 

Tuscarora Mt., ~ miles southeast of McConnellsburg, Pennsylvania." USNM 66172. 

8, 9. Orthodesma sp.; right valve internal mold showing adductor muscle scars and pitted pallial line, X 2; 9, natural cas, 

of fig. 8, X 2. The museum label lists the horizon and locality as: "Eden (Southgate) ,north end of Arnsterdamt 

Covington, Kentucky ." USNM 101634. 

10, 11. Cymatonota typicalis Ulrich; syntype; 10, posterior view showing shell gape, X 2; 11, anterior view showing shell gape, 

X 2. The museum label lists the horizon and locality as: "Richmond (Waynesville), Waynesville, Ohio." USNM 

46170. 

12. Cymatonota recta Ulrich; syntype ; left valve, X 1.5. The museum label lists the horizon and locality as: "Maysville 

(Bellevue), Cincinnati, Ohio." USNM 46168. 

13. Cymatonota recta Ulrich; syntype ; left valve, X 1.5. Horizon and locality the same as in fig. 12 above. USNM162779. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 18 

PSILOCONCHA, ORTHODESMA, AND CYMATONOTA 
PLATE 19 

FIGURES 1-3. Eopteria richardsoni Billings; holotype; 1, left(?) valve, X 1; 2, left(?) valve, X 3; 3, dorsal view, X 3. The museum 

label lists the horizon and locality as: "Beekmantown, St. Antoine de Tilly, Quebec." GSC 756. 

4. Eopteria sp.; left(?) valve, X 2. Specimen from the bioherm at the :Yieiklejohn Peak section, Nevada (Ross, 1967). 

USGS locality D- 1966- CO. USN.M 162780. 

5-9. Eopteria sp.; 5, right(?) valve, X 5; 6, left(?) valve, X 5 ; 7, dorsal view, X 5; 8, ventral view, X 5; !J, anterior(?) 

view, X 5. The museum label lists the horizon and locality as: "Smit hville Formation, 1Y:;l miles north Smithville, 

Arkansas." USNM 162781. 

10-14. Eopteria sp.; 10, ventral view, X 5; 11, dorsal view, X 5; 12, right(?) valve, X 5; 13, left (?) valve, X.~; 14, anterior 

(?) view, X 5. Horizon and locality t he same as in fig. 5 above. USNM 162782. 

15. Conocarclium cf. C. immaturwn Billings; left(?) valve, X 5. The museum label lists the horizon and locality as: "Upper 

Black R ive r, Pauquette Rapids, Ottawa River, Canada." USNM 92270. 

16. Whiteavesia cf. W. cincinnatiensis (Hall and Whitfield); right in terior view, X 2. Perryville Limestone Member, 

Lexingt on Limestone, quarry south of Perryville, Ky. USGS locality 5015-CO. USNM 162783. 

17. Whiteavesia cincinnatiensis (Hall and Whitfield) ; right valve shmYin g lack of cardinal teeth, X 3.5. Lagana Member, 

Lexington Limestone, Interstate Route 64 crossing of Kentucky H.ivcr. USGS collection D-1196-CO. USN M 

162784. 

18. Whiteavesia cf. W. cinC'innatiensis (Hall and Whitfield); right valve showing lack of cardinal t eeth, X 10. Horizon and 

localit y the same as in fig. 16 above. USNM 162785. 
·GEOLOGICAL SURVEY PROFESSIONAL PAPER 695 PLATE 19 

EOPTERIA, WHITEAVESIA, AND CONOCARDIUM