A Detailed Taxonomy of Upper Cretaceous 

and Lower Tertiary Crassatellidae in the 

Eastern United States— 

An Example of the Nature of Extinction 

at the Boundary

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535
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A Detailed Taxonomy of Upper Cretaceous 

and Lower Tertiary Crassatellidae in the 

Eastern United States— 

An Example of the Nature of Extinction 

at the Boundary

By G. LYNN WINGARD

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535

A detailed qualitative and quantitative 

taxonomic analysis of the Crassatellidae 

(Mollusca, Bivalvia) at the Cretaceous-Tertiary 

boundary demonstrates the inaccuracy of the 

published fossil record

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1993
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director

Any use of trade, product, or firm names in this publication is for

descriptive purposes only and does not imply endorsement by the

U.S. Government

Library of Congress Cataloging in Publication Data

Wingard, G. Lynn.

A detailed taxonomy of Upper Cretaceous and Lower Tertiary Crassatellidae in the eastern United States ; an example of the

nature of extinction at the boundary / by G. Lynn Wingard. 

p. cm. — (U.S. Geological Survey professional paper ; 1535) 

Includes bibliographical references. 

Supt. of Docs, no.: I 19.16:1535 

1. Crassatellidae—United States. 2. Paleontology—Cretaceous. 3. Paleontology—Tertiary. 4. Cretaceous/Tertiary boundary.

5. Paleontology-United States. I. Title. II. Series. 

QE812.V45W56 1993

564'.ll-dc20 92-43207

CIP

For sale by U.S. Geological Survey, Map Distribution

Box 25286, MS 306, Federal Center

Denver, CO 80225
CONTENTS

Abstract.................................................................................................................. 1

Introduction............................................................................................................. 1

Acknowledgments................................................................................................ 3

Summary of previous work on the Crassatellidae...................................................... 5

Statistical methods .................................................................................................... 10

Statistical analysis..................................................................................................... 15

Subspecies of Crassatella vadosa........................................................................... 15

Species of Crassatella .......................................................................................... 22

Species of Bathytormus...................................... .................................................. 35

Genera of Crassatellidae....................................................................................... 40

Summary of statistical analyses ............................................................................. 49

Systematic paleontology ............................................................................................. 50

Family Crassatellidae........................................................................................... 50

Subfamily Crassatellinae................................................................................. 51

Genus Crassatella ................................................................................... 51

Crassatella vadosa ............................................................................ 63

Crassatella tumidula......................................................................... 68

Crassatella carolinensis ..................................................................... 72

Crassatella aquiana. .......................................................................... 74

Crassatella kodgei........................... .................................................. 76

Genus Bathytormus................................................................................. 79

Bathytormus alaeformis..................................................................... 82

Bathytormus pteropsis ....................................................................... 84

Subfamily Scambulinae................................................................................... 88

Genus Scambula ..................................................................................... 88

Scambula perplana............................................................................ 89

Patterns and trends among the Crassatellidae................................................................ 92

Conclusions.............................................................................................................. 94

References cited........................................................................................................ 96

Additional references................................................................................................. 100

Stratigraphy and fossil distribution......................................................................... 100

Evolution and extinction....................................................................................... 103

Other................................................................................................................ 103

Index to taxonomic names........................................................................................... 105

APPENDIXES

Page

APPENDIX 1. Data on specimens included in the analysis of subspecies of Crassatella vadosa, comprising adult whole specimens only...... 108

2. Data on specimens included in the analysis of subspecies of Crassatella vadosa, comprising adults, juveniles, broken

specimens, and internal molds......................................................................................................................... 109

3. Data on specimens included in the analysis of species of Crassatella, comprising adult whole named abundant specimens

only............................................................................................................................................................110

4. Data on specimens included in the analysis of species of Crassatella, comprising adults, juveniles, broken specimens,

internal molds, unnamed specimens, and rare species..........................................................................................Ill

5. Data on specimens included in the analysis of species of Bathytormus, comprising adult whole named specimens only .........114

6. Data on specimens included in the analysis of species of Bathytormus, comprising adults, juveniles, broken specimens,

and unnamed specimens .................................................................................................................................115

in
IV CONTENTS

7. Data on specimens included in the analysis of the genera of Crassatellidae, comprising adult whole specimens only............. 117

8. Data on specimens included in the analysis of the genera of Crassatellidae, comprising all adults, juveniles, broken

specimens, and internal molds......................................................................................................................... 120

9. Description of collection localities........................................................................................................................... 125

ILLUSTRATIONS

PLATE 1. Type specimens of Crassatella vadosa Morton, 1834.

2. Type specimens of Cretaceous Crassatellidae.

3. Type specimens of Tertiary Crassatellidae.

4. Morphologic variation within Crassatella hodgei (Stephenson), 1923.

5. Morphologic variation within Crassatella carolinensis Conrad, 1875 and comparison to other Cretaceous Crassatella.

6. Juvenile Crassatella hodgei (Stephenson), 1923.

7. Growth series for Crassatella vadosa Morton, 1834.

8. Morphologic variation within Crassatella vadosa Morton, 1834.

9. Morphologic variation within Crassatella vadosa Morton, 1834.

10. Juvenile characters and internal molds of Crassatella vadosa Morton, 1834.

11. Geographic variation of Crassatella vadosa Morton, 1834.

12. Juvenile Crassatella vadosa Morton, 1834.

13. Genus and species unknown.

14. Morphologic variation within Crassatella aquiana Clark, 1895.

15. Morphologic variation and ontogenetic sequence within Crassatella tumidula Whitfield, 1865.

16. Tertiary juvenile Crassatella.

17. Morphologic variation and ontogenetic sequence within Bathytormus pteropsis (Conrad), 1860.

18. Morphologic variation and ontogenetic sequence within Bathytormus alaeformis (Conrad), 1830.

19. Morphologic variation within Bathytormus alaeformis (Conrad), 1830.

20. Comparison of juvenile Bathytormus and Scambula.

21. Variation of hinge form, sculpture, and morphology in the Crassatellidae.

22. Type specimens of questionable generic or familial assignment.

FIGURE 1. Correlation chart showing the stratigraphic units within the Gulf and Mid-Atlantic Coastal Plains ........................................ 4

2. Map showing the outcrop pattern of the Cretaceous-Tertiary contact, limits of the sedimentary cover of the Coastal

Plain, and localities ............................................................................................................................................ 6

3. Chart showing the ranges of the genera of the two subfamilies of Crassatellidae, Crassatellinae and Scambulinae, as recorded

in the Treatise of Invertebrate Paleontology ........................................................................................................... 10

4. Chart showing the ranges of the published Crassatellidae names of the Upper Cretaceous and lower Tertiary of the Gulf

and Mid-Atlantic Coastal Plains............................................................................................................................ 11

5. Schematic diagram showing the digitized points on a typical crassatellid shell.................................................................... 12

6. Photograph showing device used to measure valve width ............................................................................................... 13

7-12. Plots showing:

7. Canonical variables 1 and 2 for the first canonical variate analysis of the subspecies of Crassatella vadosa........................ 18

8. Canonical variables 1 and 2 for the second canonical variate analysis of the subspecies of Crassatella vadosa .................... 20

9. Canonical variables 1 and 2 for the first canonical variate analysis of the species of Crassatella. ...................................... 27

10. Canonical variables 2 and 3 for the first canonical variate analysis of the species of Crassatella. ...................................... 29

11. Canonical variables 1 and 2 for the second canonical variate analysis of the species of Crassatella ................................... 31

12. Canonical variables 2 and 3 for the second canonical variate analysis of the species of Crassatella ................................... 33

13. Histogram showing canonical variable 1 for the first canonical variate analysis of the species of Bathytormus......................... 37

14-17. Plots showing:

14. Canonical variables 1 and 2 for the second canonical variate analysis of the species of Bathytormus................................. 38

15. Canonical variables 1 and 2 for the first canonical variate analysis of the genera of Crassatellidae ................................... 43

16. Canonical variables 1 and 2 for the second canonical variate analysis of the genera of Crassatellidae................................ 45

17. Pattern of species distribution within the genera for Crassatella and Bathytormus.. ..................................................... 48

18. Schematic diagram showing hinge characters and musculature of Crassatella .................................................................... 53

19. Range chart showing comparison of the ranges of the published Crassatellidae species with ranges determined in this study .... 57

20. Schematic diagram showing hinge characters and musculature of Bathytormus.... .............................................................. 81

21. Schematic diagram showing hinge characters and musculature of Scambula ...................................................................... 90
CONTENTS V

Page

22. Graph showing evolutionary rates based on the published fossil record compared to data obtained in this study...................... 95

23. Spindle diagram showing diversity patterns from the published record of Crassatellidae compared to the diversity

patterns illustrated in this study .......................................................................................................................... 95

TABLES

Page

TABLE 1. Published generic and specific names of the Upper Cretaceous and lower Tertiary Crassatellidae of the Gulf Coast and

Mid-Atlantic Coastal Plains ................................................................................................................................... 8

2. Thirty-four morphological variables constructed for the statistical analysis.......................................................................... 14

3. Class means and grand means for subspecies of Crassatella vadosa ................................................................................... 16

4. Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the subspecies of

Crassatella vadosa.. ............................................................................................................................................. 16

5. Mahalanobis' distances between classes for the first canonical discriminant analysis of the adult whole specimens of the

subspecies of Crassatella vadosa............................................................................................................................ 17

6. Standardized canonical coefficients for the first canonical discriminant analysis of the adult whole specimens of the

subspecies of Crassatella vadosa............................................................................................................................ 17

7. Results of the classificatory discriminant analysis of the adult whole specimens of the subspecies of Crassatella vadosa............. 17

8. Results of the classificatory discriminant analysis of the juveniles, broken specimens, and internal molds of the

subspecies of Crassatella vadosa............................................................................................................................ 19

9. Mahalanobis' distances between classes for the second canonical discriminant analysis of all the specimens of the

subspecies of Crassatella vadosa............................................................................................................................ 19

10. Standardized canonical coefficients for the second canonical discriminant analysis of all the specimens of the subspecies of

Crassatella vadosa............................................................................................................................................... 21

11. Class means and grand means for species of Crassatella .................................................................................................. 24

12. Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the species of

Crassatella......................................................................................................................................................... 26

13. Mahalanobis' distances between classes for the first canonical discriminant analysis of the adult whole named specimens of

the species of Crassatella...................................................................................................................................... 26

14. Standardized canonical coefficients for the first canonical discriminant analysis of the adult whole named specimens of the

species of Crassatella.......... ................................................................................................................................. 28

15. Results of the classificatory discriminant analysis of the abundant adult whole named specimens of the species of Crassatella..... 28

16. Mahalanobis' distances between classes for the second canonical discriminant analysis of all the specimens of the species of

Crassatella......................................................................................................................................................... 30

17. Standardized canonical coefficients for the second canonical discriminant analysis of all the specimens of the species of

Crassatella......................................................................................................................................................... 32

18. Results of the classificatory discriminant analysis of the juveniles, broken specimens, and internal molds of the species of

Crassatella ......................................................................................................................................................... 32

19. Results of the classificatory discriminant analysis of all the specimens of the species of Crassatella, except internal molds ......... 34

20. Class means and grand means for species of Bathytormus................................................................................................ 36

21. Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the species of

Bathytormus....................................................................................................................................................... 36

22. Standardized canonical coefficients for the first canonical discriminant analysis of the adult whole named specimens of the

species of Bathytormus......................................................................................................................................... 37

23. Results of the classificatory discriminant analysis of the adult whole named specimens of the species of Bathytormus................ 37

24. Mahalanobis' distances between classes for the second canonical discriminant analysis of all of the specimens of the

species of Bathytomius......................................................................................................................................... 37

25. Standardized canonical coefficients for the second canonical discriminant analysis of all the specimens of the species of

Bathytormus....................................................................................................................................................... 39

26. Results of the classificatory discriminant analysis of the juveniles, broken specimens, and unnamed specimens of the

species of Bathytormus......................................................................................................................................... 39

27. Results of the classificatory discriminant analysis of all the specimens of the species of Bathytonnus ...................................... 39

28. Class means and grand means for the genera of Crassatellidae.......................................................................................... 41

29. Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the genera of

Crassatellidae ..................................................................................................................................................... 42

30. Mahalanobis' distances between classes for the first canonical discriminant analysis of the adult whole specimens of the

genera of Crassatellidae........................................................................................................................................ 42

31. Standardized canonical coefficients for the first canonical discriminant analysis of the adult whole specimens of the

genera of Crassatellidae........................................................................................................................................ 44
VI CONTENTS

	Page

32. Results of the classificatory discriminant analysis of the adult whole specimens of the genera of Crassatellidae......................... 44

33. Mahalanobis' distances between classes for the second canonical discriminant analysis of all the specimens of the

	genera of Crassatellidae........................................................................................................................................ 44

34. Standardized canonical coefficients for the second canonical discriminant analysis of all the specimens of the genera of

	Crassatellidae ..................................................................................................................................................... 46

35. Results of the classificatory discriminant analysis of the juveniles, broken specimens, and internal molds of the genera of

	Crassatellidae ..................................................................................................................................................... 46

36. Results of the classificatory discriminant analysis of all the specimens of the species of Crassatellidae ..................................... 47

37. Specific names relevant to Lamarck's original designation of Crassatella ............................................................................ 54

38. Minimum, maximum, and mean values for characters of Crassatella vadosa........................................................................ 67

39. Crassatella vadosa—Occurrence and collections studied................................................................................................... 69

40. Minimum, maximum, and mean values for characters of Crassatella tumidula........... .......................................................... 71

41. Crassatella tumidula—Occurrence and collections studied................................................................................................ 72

42. Crassatella carolinensis—Occurrence and collections studied............................................................................................ 74

43. Minimum, maximum, and mean values for characters of Crassatella aquiana...................................................................... 75

44. Crassatella aquiana—Occurrence and collections studied ................................................................................................. 77

45. Minimum, maximum, and mean values for characters of Crassatella hodgei.. ....................................................................... 78

46. Crassatella hodgei—Occurrence and collections studied.................................................................................................... 80

47. Minimum, maximum, and mean values for characters of Bathytormus alaeformis ................................................................ 83

48. Bathytormus alaeformis—Occurrence and collections studied ........................................................................................... 85

49. Minimum, maximum, and mean values for characters of Bathytormus pteropsis.. ................................................................. 87

50. Bathytormus pteropsis—Occurrence and collections studied.............................................................................................. 89

51. Minimum, maximum, and mean values for characters of Scambula perplana... .................................................................... 92

52. Scambula perplana—Occurrence and collections studied.................................................................................................. 93

CONVERSION FACTORS

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A DETAILED TAXONOMY OF UPPER CRETACEOUS

AND LOWER TERTIARY CRASSATELLIDAE IN THE

EASTERN UNITED STATES-AN EXAMPLE OF THE NATURE

OF EXTINCTION AT THE BOUNDARY

By G. LYNN WINGARD

ABSTRACT

Current theories on the causes of extinction at the CretaceousTertiary boundary have been based on previously published data; 

however, few workers have stopped to ask the question, "How good is 

the basic data set?" To test the accuracy of the published record, a 

quantitative and qualitative analysis of the Crassatellidae (Mollusca, 

Bivalvia) of the Gulf and Mid-Atlantic Coastal Plains of the United 

States for the Upper Cretaceous and lower Tertiary was conducted. 

Thirty-eight species names and four generic names are used in publications for the Crassatellidae within the geographic and stratigraphic 

constraints of this analysis. Fourteen of the 38 species names are 

represented by statistically valid numbers of specimens and were 

tested by using canonical discriminant analysis. All 38 names, with the 

exception of 1 invalid name and 4 names for which no representative 

specimen could be located, were evaluated qualitatively. The results 

show that the published fossil record is highly inaccurate. Only 8 valid, 

recognizable species exist in the Crassatellidae within the limits of this 

study, 14 names are synonymized, and 11 names are represented by 

indeterminate molds or poorly preserved specimens. Three of the four 

genera are well founded; the fourth is based on the juvenile of another 

genus and therefore synonymized. This detailed taxonomic analysis of 

the Crassatellidae illustrates that the published fossil record is not 

reliable. Calculations of evolutionary and paleobiologic significance 

based on poorly defined, overly split fossil groups, such as the 

Crassatellidae, are biased in the following ways:

• Rates of evolution and extinction are higher,

• Faunal turnover at mass extinctions appears more catastrophic,

• Species diversity is high,

• Average species durations are shortened, and

• Geographic ranges are restricted.

The data on the taxonomically standardized Crassatellidae show evolutionary rates one-quarter to one-half that of the published fossil 

record; fauna! change at the Cretaceous-Tertiary boundary that was 

not catastrophic; a constant number of species on each side of the 

Cretaceous-Tertiary boundary; a decrease in abundance in the Tertiary; and lower species diversity, longer average species durations, and 

expanded geographic ranges. Similar detailed taxonomic studies need 

to be conducted on other groups of organisms to test the patterns 

illustrated for the Crassatellidae and to determine the extent and 

direction of the bias in the published fossil record. Answers to our 

questions about evolutionary change cannot be found in the literature 

but rather with the fossils themselves. Evolution and extinction occur

Manuscript approved for publication September 23, 1992.

within small populations of species groups, and it is only through 

detailed analysis of these groups that we can achieve an understanding 

of the causes and effects of evolution and extinction.

INTRODUCTION

Evolutionary rates of organisms have received a great 

deal of attention in the last decade, particularly in 

discussions of the causes of mass extinction at the 

Cretaceous-Tertiary boundary. Two major factions have 

formed: (1) those who support a catastrophic extraterrestrial cause for the extinctions (for example, Alvarez 

and others, 1980; Emiliani, 1980; Davis and others, 1984; 

Alvarez and Muller, 1984; and Hut and others, 1987) and 

(2) those who look to terrestrial causes, whether catastrophic or gradual, to explain the extinctions (for example, Officer and Drake, 1983; Hallam, 1984; Lutz, 1987; 

and Crocket and others, 1988). Proponents of each side of 

this debate have relied on calculations of evolutionary 

rates that are based on plots of compiled faunal lists of 

species, genera, or families through time (for example, 

Raup and Sepkoski, 1982; Kitchell and Penna, 1984), yet 

very few authors have asked, "How reliable are these 

data?"

Perhaps the most notable use of compiled faunal lists is 

in Raup and Sepkoski (1982; 1984; 1986; for a complete 

list of the sources for the compiled data see Sepkoski, 

1982a). Raup and Sepkoski (1982) concluded from their 

plots of families through the Phanerozoic that two types 

of extinction rates were operating: (1) normal background extinction and (2) mass extinctions. They also 

concluded that the total rate of background extinction 

has declined since the Early Cambrian. Subsequently, on 

the basis of the same set of compiled data, Raup and 

Sepkoski (1984; 1986) determined that a periodicity 

existed in the rate of mass extinctions.

Raup and Sepkoski are aware of the constraints of 

their data set. Sepkoski (1982b, p. 285) stated,
CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

Several major problems are encountered when using global 

taxonomic data to identify and delimit mass extinctions. It is 

generally impossible to determine how abrupt an event was 

because of the long and unequal durations of the stratigraphic intervals used to tabulate the data. This problem is 

further aggravated by inherent sampling errors which push 

the apparent ends of stratigraphic ranges backward in time, 

blurring the effects of mass extinctions .... Distortion is 

also introduced by the use of genera and higher taxonomic 

units in global data. Adequate data on global species' ranges 

have never been compiled, partly because of inconsistencies 

in defining fossil species from country to country and from 

generation to generation and partly because of the sheer 

magnitude of such a task ....

Raup made several references to the problems of the 

data set; he discussed the need for "complete data" that 

has "as tight a time resolution as possible" (Raup, 1984, 

p. 12) and described the data as "noisy and uncertain" 

(Raup, 1987, p. 3). Raup and Boyajian (1988, p. 112), in 

a paper on the patterns of extinction, devoted a section to 

the "variable quality of taxonomy" in which they stated,

The products of taxonomic research contain many problems 

and uncertainties familiar to all systematic biologists and 

paleobiologists. Some groups are over- or under-split, and 

concepts of the genus and family vary greatly. A genus in one 

group may be equivalent to a family in another group.

The limitations of the data were enunciated most clearly 

by Sepkoski (1982b, p. 288), who stated,

And even with the best available data sets, questions remain 

about the temporal duration, taxonomic universality, and 

geographic distribution of the various events. Clearly, these 

questions must be answered, at least in part, before any 

comprehensive theory of the general causes of mass extinction can be formulated.

The revelation of possible periodicity of extinction 

caused a surge of reports by astronomers, astrophysicists, and geologists contemplating probable theories to 

explain the periodicity, including oscillations in the galactic plane (Swartz and James, 1984), a companion star 

(Davis and others, 1984), and comet showers (Hut and 

others, 1987). These authors paid little attention to the 

reservations expressed by Raup and Sepkoski. Hallam 

(1984, p. 686) advocated caution when he stated, "In 

assessing the value of these speculative papers it is 

clearly necessary first to scrutinize the Raup and Sepkoski analysis on which they are based," and in closing he 

commented that "Before astronomers indulge in further 

speculations about the cause of mass extinctions they 

would do well to learn something about the rich stratigraphical record of their own planet" (Hallam, 1984, p. 

687). Other authors (Quinn, 1987, p. 475; Stanley, 1984, 

p. 69, for example) expressed criticism of the conclusions 

of Raup and Sepkoski (1984; 1986) and of the basic data 

set (Signer and Lipps, 1982; Newell, 1982, p. 260), but 

the debate about the causes of mass extinctions rages on 

with little regard for these concerns. Few steps are being

taken, other than by Raup and Sepkoski themselves (see 

comment by Raup and Boyajian, 1988, p. 110-111), to 

rectify the inherent problems of the compiled faunal lists.

Rates of evolution based on compilations of data have 

been applied to other paleontological problems in addition to discussions of mass extinction. They have been 

used to describe the Phanerozoic marine diversity in 

general (Fischer and Arthur, 1977; Sepkoski, 1981) and 

bivalve diversity in particular (Miller and Sepkoski, 

1988). Survivorship of Bivalvia was analyzed by Gilinsky 

(1988). Phanerozoic background extinction (Boyajian, 

1986) and rates of origination and extinction in higher 

taxa (Gilinsky and Bambach, 1987) also were studied 

using previously published faunal lists.

With all of this attention paid to counts of taxa through 

time, it is surprising that so few researchers have 

investigated the question raised by Raup and Sepkoski 

and their critics, "How accurate are previously published 

faunal lists?" Koch (1978) compared the published fossil 

record to the actual fossil record for the molluscan fauna 

of the Upper Cretaceous of the Western Interior; he 

found that the published record underestimated species 

diversity by a factor of approximately three to four. In 

addition, he noted that there is "no readily available 

'correction factor'" to compensate for the "deficiencies in 

the published record" (Koch, 1978, p. 371). An extensive 

comparison of compiled taxonomic data from the literature and taxonomically standardized museum collections 

of living benthic Foraminifera led Culver, Buzas, and 

Collins (1987, p. 169) to conclude that

Evolutionary generalizations based on data generated from 

the literature only are often unreliable and may be directly in 

opposition to reality. Extensive attempts at taxonomic 

standardization should be the norm in paleobiological investigations.

Wingard and Sohl (1990) attempted taxonomic standardization of the Upper Cretaceous genus Nucula and 

concluded that the genus had been split on the basis of 

assumptions of geographic and stratigraphic separation 

of species; this splitting led to an overestimate of species 

diversity for the Nucula and an underestimate of species 

duration. Presumably, paleontologists and stratigraphers working within a limited time frame and a 

restricted geographic region are aware of each other's 

taxonomic contributions. The degree of splitting 

recorded for Nucula within these narrowly defined stratigraphic and geographic limits, however, suggests that 

this is not the case. In fact, the degree of splitting seen 

for the Nucula would suggest that when a major system 

boundary, such as the Cretaceous-Tertiary, is crossed, 

the problem of splitting will be intensified. In the past, 

paleontologists and stratigraphers often worked exclusively in the Cretaceous or in the Tertiary and were not 

concerned with constructing unified taxonomies through
INTRODUCTION

both periods. Yin (1985, p. 590) addressed this issue for 

the bivalves at the Permian-Triassic boundary and found 

that the two groups were not as dissimilar as previously 

described, nor were the differences concentrated at the 

boundary; he stated,

To these evidences of gradual changes and replacements 

should be added the consideration that the disparity between 

Permian and Triassic bivalves may have been artificially 

accentuated for supposed biostratigraphic convenience by 

authors specializing below or above the erathem boundary. 

Furthermore some genera may be synonymous ... or even 

certain species .... In short, the replacement of pectinaceans from the Paleozoic to the Mesozoic occurs step by 

step over a period of at least 10 million years. The erathem 

boundary can hardly be selected on pectinacean or bivalve 

evidence alone.

In recent years more authors have begun to examine 

fossils across the Cretaceous-Tertiary boundary in an 

attempt to gain a better understanding of the nature of 

extinction at the boundary (Heinberg, 1979; Hansen and 

others, 1987; Jones and others, 1987; Hansen, 1988). 

Still, we lack detailed taxonomic analyses of individual 

groups of organisms, particularly the macrofossils. 

Hansen (1982, p. 231) pointed out that

The literature is top-heavy, however, in that a great deal 

more speculation has been published concerning the time 

than actual detailed stratigraphic studies of the interval. 

Nowhere is this lack more evident than with studies of latest 

Cretaceous and earliest Tertiary macrofauna. In this regard, 

macropaleontology lags far behind micropaleontology. 

Numerous studies exist documenting the detailed stratigraphic ranges of microfossil taxa up to and across the K/T 

[Cretaceous-Tertiary] boundary, but it is surprisingly difficult to find a similar treatment of the macrofossils.

The purpose of this investigation is to develop a 

standardized taxonomy for one family of molluscs, the 

Crassatellidae, across the Cretaceous-Tertiary boundary 

to examine the issues raised above. First, how reliable is 

the basic data set? Second, are calculations of evolutionary rates based on previously published faunal lists 

accurate? If not, then by how much do these calculated 

rates differ from the picture obtained from the fossil 

record? Examining the evolution, extinction, and migration that have occurred within one family across the 

Cretaceous-Tertiary boundary should shed some light on 

the nature of extinction at the boundary. The analysis of 

this one family serves as an example of the type of 

studies that could be done with other groups of organisms to evaluate theories concerning evolution and 

extinction.

The primary taxonomic unit under investigation in the 

Crassatellidae is the species. As Raup and Boyajian 

(1988, p. 112) state, "The ultimate objective of any study 

of extinction should probably be to assess mortality at 

the level of species." Newell (1982, p. 260) pointed out,

"Evolutionary biologists are agreed that the species is 

the only taxon with objective reality and it is at this level 

that both evolution and extinction take place." Both of 

these papers go on to state that the species unfortunately 

cannot be used because of problems in the species record. 

But if species are the basic units of evolution, then 

paleontologists should clarify and quantify the problems 

in the species record so that it can be put to use in 

evolutionary studies; that is the intent of this analysis of 

the Crassatellidae.

Species and genera of the family Crassatellidae are 

here examined from the lower Campanian through the 

Wilcox Stages in the eastern Gulf Coastal Plain and the 

Mid-Atlantic Coastal Plain of the United States (figs. 1, 

2). This geographic area was selected because of the 

author's knowledge of the stratigraphy of that region and 

because the detailed attention this area has received in 

the literature provides tight time-stratigraphic control. 

In addition, many of the Crassatellidae described in 

North America for this time period occur in this geographic region. The northern part of the Mid-Atlantic 

region was included particularly to observe any possible 

migrations due to changing climatic regimes.

The Crassatellidae were selected because they occur 

on both sides of the Cretaceous-Tertiary boundary, are 

fairly well preserved (often in their original aragonitic 

state), and exhibit an interesting evolutionary history 

according to the published literature. Figure 3 illustrates 

the subfamilies and genera for the Crassatellidae as 

recorded in the Treatise of Invertebrate Paleontology 

(Chavan, 1969, p. N573-N578). A rapid radiation of the 

Crassatellidae appears to have occurred in the Cretaceous, but of the seven genera found prior to the 

Cretaceous-Tertiary boundary, only three survived into 

the Cenozoic. The recorded pattern of evolution and 

extinction of the Crassatellidae make this family an 

interesting test case for the evaluation of previously 

published taxonomic data.

ACKNOWLEDGMENTS

I express my utmost gratitude to Norman F. Sohl, 

U.S. Geological Survey, for his guidance at every phase 

of this research project and for his review of this 

manuscript. The bulk of my knowledge of molluscan 

taxonomy, evolution, and systematics I owe to our 

discussions over the last 10 years. Norm did not live to 

see this manuscript in print. The loss of his vast knowledge and enthusiasm for our profession is immeasurable; 

personally, I miss our daily discussions filled with his 

wit, wisdom, and encouragement. Thank you, Norm.

The contributions of Carl Koch, Old Dominion University, as a reviewer and in our many discussions on 

statistical analyses, are greatly appreciated. John
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FIGURE 1.—Stratigraphic units within the Gulf and Mid-Atlantic Coastal Plains for the time frame of this study. (Data were compiled from the following 

others, 1982; Gibson and others, 1982; Harland and others, 1982; Owens and others, 1970; Sohl and Owens, 1991; and L.M. Bybell, T.G. Gibson, N.F. Soh

oral commun., 1989.)
INTRODUCTION

Pojeta, U.S. Geological Survey, Anthony G. Coates and 

Philip W. Wirtz, George Washington University, and 

Martin A. Buzas, U.S. National Museum of Natural 

History, provided advice and suggestions at different 

phases of the research. Ralph Chapman, U.S. National 

Museum of Natural History, wrote the digitizing program used in this analysis and provided instruction and 

resources to aid in its application. Linda Gosnell, Robert 

Wingard, and Robin Espenschade provided technical 

assistance. L. Gosnell drafted the canonical variable 

plots; without her assistance, these plots would not be 

interpretable. Linda Jacobsen's (U.S. Geological Survey) 

contributions as editor have been invaluable and deserve 

special thanks.

I thank the following individuals for making their 

collections available: Norman F. Sohl, U.S. Geological 

Survey, Lauck W. Ward, Virginia Museum of Natural 

History, Peter Hoover, Paleontological Research Institution, George Davis, Academy of Natural Sciences of 

Philadelphia, and Thomas Waller, U.S. National 

Museum of Natural History. Warren Blow facilitated my 

study of the U.S. National Museum collections.

This research was funded in part by grants from Sigma 

Delta Epsilon, Graduate Women in Science; Achievement Rewards for College Scientists; and Sigma Xi. This 

paper is an updated and expanded version of my Ph.D. 

dissertation, 1990, George Washington University, 

Washington, D.C.

SUMMARY OF PREVIOUS WORK ON THE CRASSATELLIDAE

Crassatella Lamarck, 1799 was first recognized in the 

United States in 1824 (Say, 1824, p. 49) in the middle 

Tertiary deposits of Maryland. Starting in 1830 and 

continuing for the next 45 years, Conrad named and 

described 12 species of crassatellids in the Upper Cretaceous and lower Tertiary beds of the Gulf and MidAtlantic Coastal Plains (table 1; fig. 4). Only 4 of these 12 

species are represented by well-preserved specimens 

and are present in significant numbers in the sediments 

of this region. Three of the five crassatellid names 

contributed by Gabb (table 1) also were named from 

poorly preserved specimens. Other workers who named 

crassatellids in the 1800's include Morton (1834), Rogers 

and Rogers (1839), d'Orbigny (1850), Safford (1864), 

Whitfield (1865; 1885), and Heilprin (1880).

Whitfield's (1885) monograph on the Cretaceous and 

Tertiary paleontology of New Jersey marked a turning 

point in the taxonomic literature on the crassatellids in 

North America. Unlike the cursory information provided 

by his predecessors, Whitfield's discussions on 11 crassatellid species (2 of them new) contained detailed 

descriptions and comparisons to other species. Dall 

(1903), in an account of the Tertiary fauna of Florida,

extensively discussed the Crassatellidae and particularly 

emphasized the evolutionary significance of the hinge 

and resilifer.

Continuing the trend of providing detailed species 

descriptions into the 20th century, Gardner (1916) 

reported on the crassatellids of the Upper Cretaceous 

deposits of Maryland. Stephenson (1914) included many 

occurrence charts of species at various localities in the 

eastern Gulf region, including crassatellids. It was not 

until 1923, however, that Stephenson began his detailed 

taxonomic descriptions of the crassatellids. During the 

remainder of his career, Stephenson named two subspecies, five species, and one genus of Crassatellidae within 

the eastern Gulf and Mid-Atlantic Coastal Plains alone 

(table 1; fig. 4).

Stewart's (1930) comprehensive analysis of the genera 

of Crassatellidae clarified many taxonomic questions. He 

named and described the genus Bathytormus and identified Crassatella protexta Conrad as the type species 

(see pi. 21, figs. 11 and 13 for an example); C. alaeformis 

Conrad was recognized as a member of this genus. 

Bathytormus Stewart is distinguished from Crassatella 

Lamarck by a ligamental cavity that extends to the 

ventral border of the hinge plate in all ontogenetic stages 

(Stewart, 1930, p. 137). Stewart (1930, p. 138) noted that 

the diagnostic character of the hinge is often not developed and therefore not apparent on juveniles of the 

family. He stated, "The restricted ligamental cavity [of 

Crassatella] is not always shown on small specimens, 

particularly on those less than 15 mm in length. In fact, 

one might easily place the immature form in Bathytormus while the adult would be a typical Crassatella."

In 1965, Palmer and Brann prepared a Catalogue of the 

Paleocene and Eocene Mollusca of the Southern and 

Eastern United States. Four species of Bathytormus, 23 

species of Crassatella, and 12 Crassatella sp. remain at 

the conclusion of their synonymizations of the Crassatellidae; 12 of these 39 species fall within the geographic and 

stratigraphic limits of this study.

Chavan (1939; 1952; 1969) and Yokes (1946; 1973; 1988) 

conducted the most extensive research on the Crassatellidae in recent years. In 1952, Chavan erected two 

subfamilies within the Crassatellidae, Crassatellinae and 

Scambulinae. Crassatellinae contains 11 genera and 8 

subgenera (Chavan, 1969, p. N573-N577), and Scambulinae contains 4 genera and 2 subgenera (Chavan, 1969, 

p. N577-N578) (fig. 3). As did Dall (1903) and Stewart 

(1930), Chavan considered the characters of the hinge to 

be of primary importance in distinguishing genera.

Table 1 is a summary of all the published generic and 

specific names used for the Crassatellidae within the 

Upper Cretaceous and lower Tertiary of the Gulf and 

Mid-Atlantic Coastal Plains from 1830 to the present. 

Stratigraphic ranges are illustrated on figure 4. A glance
6 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

New Jersey

40°

35°

30C

85° 80

FIGURE 2.— Outcrop pattern of the Cretaceous-Tertiary contact place names. B, enlargement of Washington, D.C., and Potomac 

(dotted line), limits of the sedimentary cover of the Coastal River region, Fairfax, Arlington, Prince William, Stafford, and 

Plain (bold solid line), and localities (numbered open circles) (see King George Counties in Virginia, and Montgomery, Prince 

app. 9 for locality descriptions). A, enlargement of Chatta- George's, Charles, and St. Mary's Counties in Maryland, 

hoochee River region, Alabama and Georgia. Solid squares are
INTRODUCTION

Chattahoochee 

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FIGURE 2.—Continued.

at table 1 gives some indication of the proliferation of 

names in the Crassatellidae, even within the narrow 

geographic and stratigraphic limits of this study. Several 

problems are evident throughout the published record of 

the Crassatellidae. First is the prevalence of names 

assigned to poorly preserved material; it is impossible to 

statistically or morphologically evaluate these specific 

names. Second, and less apparent, is the failure to 

recognize different stages in the ontogenetic sequence of 

a single species. Finally, the early workers often had 

limited sample sizes and did not have the benefit of 

comparing large suites of specimens. Consequently, 

intraspecific variation often was not recognized, and end

members of a single species were split into separate 

taxa. Statistical evaluation can help resolve these latter 

problems.

To answer the question "How good is the basic data 

set?" all species names represented by well-preserved 

material were statistically analyzed. Diagnostic characters used by the original authors or subsequent workers 

were combined to form the basis for the discriminating 

variables selected for the statistical analysis. These 

diagnostic characters include features of the shell's general outline, such as the shape of the posterior extremity, 

posterior-dorsal margin, anterior margin, and ventral 

margin; the convexity; and the height and orientation of
10 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

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FIGURE 3.—Ranges of the genera of the two subfamilies of Crassatellidae, Crassatellinae 

and Scambulinae, as recorded in the Treatise of Invertebrate Paleontology (Chavan, 1969, 

p. N573-N578). Number of subgenera indicated in brackets.

the beaks. Other authors used length, height, and thickness of the shell to distinguish taxa. The superficial 

characters of the ornament and the posterior ridge were 

significant identifiers to still other workers. Internally, 

the musculature, hinge characters, and presence or 

absence of marginal crenulations were deemed diagnostic. At the generic level, the characters of the hinge were 

the primary diagnostic features; orientation of the beaks 

also was important at this level. I used the characters 

selected by the original authors to test the validity of the 

specific and generic names they erected.

STATISTICAL METHODS

The statistical analysis of the Crassatellidae was 

divided into four phases:

1. Compiling historical data,

2. Collecting specimens from the field and assembling 

specimens from established collections for analysis,

3. Creating a morphometric data base through a digitization process, and

4. Statistically testing four subsets of the data. Each of 

the four subsets were put through two canonical 

discriminant analyses: the first tested only adult 

whole abundant named specimens; the second tested 

all the specimens. The four subsets are

• Subspecies of Crassatella vadosa,

• Species of Crassatella,

• Species of Bathytormus, and

• Genera of Crassatellidae.

In the first phase, references to the genera and species of 

Crassatellidae were compiled, and their geographic and 

stratigraphic positions were identified. The bulk of these 

data came from the U.S. Geological Survey Mesozoic 

invertebrate species card file, the U.S. Geological Survey Tertiary invertebrate species card file, Sherborn 

(1902; 1922-1933), Ruhoff (1980), the Zoological Record 

of the Zoological Society of London (1869-1983), Palmer 

and Brann (1965), Sohl and Koch (1983; 1984), Boyle 

(1893), and from numerous individual articles. Although 

taxonomic analyses are usually based only on information 

from other taxonomic papers, for the Crassatellidae, 

biostratigraphic papers listing species occurrences offer
STATISTICAL METHODS 11

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FIGURE 4. —Ranges of the published Crassatellidae names of the 

Upper Cretaceous and lower Tertiary of the Gulf and Mid-Atlantic 

Coastal Plains. Generic abbreviations: C., Crassatella (incorporates 

Crassatellites, junior synonym of Crassatella); G., Gouldia; U.,

valuable information on distribution; thus, data from 

such papers are included in the compilation. The data 

files were assembled using SAS (SAS Institute, 1982) on 

the George Washington University (GWU) IBM-4341 

mainframe computer.

In the second phase of the analysis, type specimens 

and suites of crassatellids were assembled from the U.S. 

Geological Survey Mesozoic (USGS) and Cenozoic collections (USGS-CENO), the U.S. National Museum of 

Natural History (USNM) Mesozoic and Cenozoic collections, the Paleontological Research Institution (PRI), 

and the Academy of Natural Sciences of Philadelphia 

(ANSP). An attempt was made to obtain material from 

all stratigraphic and geographic occurrences indicated by 

the literature search in phase one.

In phase three of the analysis, the morphometric data 

base was created by using a series of 14 points digitized 

from selected specimens assembled in phase two. Since 

the purpose of this study is to test the accuracy of 

previous specific and generic classifications of the Crassatellidae, I selected the diagnostic characters as close as

Uddenia; S., Scambula. Species are arranged in alphabetical order. 

Four species names were omitted due to lack of stratigraphic information. See table 1 for complete listing of species.

possible to those identified by the authors of the original 

species descriptions as discussed in the preceding chapter. The digitization process was based on six homologous characters (fig. 5, points 1-6), following the recommendations of Bookstein and others (1985). These 

characters are closely tied to the biology of the animal 

and can be readily identified; thus, the results obtained in 

digitizing are reproducible. Pelecypods, however, lack 

any fixed points along the anterior, posterior, and ventral margins of their shells, yet general outline was the 

character most often cited as diagnostic by previous 

authors. In order to include marginal points and still 

keep the results reproducible, I constructed eight lines 

formed by the intersection of two homologous character 

points. Where these lines crossed the margin of the shell, 

a projected point was digitized (fig. 5, points 7-14).

Any specimens missing one or more of the six homologous points (with the exception of internal molds, as 

discussed below, p. IS) were eliminated from consideration. In collections containing more than 30 individuals, 

30 specimens were selected randomly for digitization. In
12 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

10 11

12

FIGURE 5. —Digitized points on a typical crassatellid shell; these points were used to construct the character 

variables defined in table 2. Points 1 to 6 represent homologous characters on the individual specimens: 

1, the beak; 2, the base of the resilifer; 3, the ventral end of the posterior lateral ridge; 4, the ventral 

end of the anterior lateral ridge; 5, the point on the base of the posterior adductor where it intersects 

the pallial line; and 6, the point on the base of the anterior adductor where it intersects the pallial line. 

Points 7 to 14 represent the projected points on the perimeter of the shell, formed by constructing a line 

through two homologous characters (modified from Wingard, 1991).

collections of 30 or fewer individuals, all specimens were 

retained for digitization if all six of their homologous 

points were present. Digitization was done from 

photographs or photocopies of the selected specimens. 

Shells less than 1 cm in length, internal molds, and 

type specimens were photographed; all others were 

photocopied.

Each fossil was assigned eight labels: (1) genus, (2) 

species, (3) locality number, (4) specimen number, (5) left 

versus right valve, (6) preservation, (7) juvenile versus 

adult, and (8) measure of width in millimeters. The 

purpose of the statistical analyses was to test the accuracy of previously defined taxonomic categories; to make 

the statistical analysis as unbiased as possible, I 

refrained from critically examining the specimens and 

imposing my own concepts of genera and species (labels 

1 and 2). Instead, I identified the generic and specific 

categories from a cursory examination of the diagnostic 

characters mentioned by the previous authors and the 

locality and the stratigraphic unit in which the specimen 

was found. For distinguishing between the genera

Bathytormus and Crassatella, I followed Stewart's 

(1930, p. 137) diagnosis, and for Scambula I used Conrad's (1872, p. 51) description. Categorizing Uddenia 

proved to be difficult (discussed in detail in the "Systematic Paleontology" section). To statistically test the validity of the genus, however, specimens labeled as Uddenia 

were classified as such if they came from localities where, 

according to the published literature, Uddenia occurred. 

In the process of selecting the Uddenia, I recognized a 

fifth unnamed group (genus and species unknown) that 

was also included in the analysis. Scambula, Uddenia, 

and the unnamed group were included only in the generic 

level tests because, within the confines of this study, 

these are monotypic taxa in my opinion. Specimens were 

assigned a specific name only if their characters matched 

the original species description and only if they came 

either from the type locality and stratigraphic unit of the 

species or from a locality and stratigraphic unit where 

there was a published account of the species occurrence. 

If a specimen did not meet both of these criteria then 

it was classified as an unnamed species (C. sp., for
STATISTICAL METHODS 13

example) within a given genus. 1 If a specimen's generic 

identity could not be determined, it was classified as 

genus and species unknown.

Specimens were assigned to one of three categories of 

preservation (label 6): (1) the shell has all homologous 

and projected points and intact margins, (2) the shell has 

all six homologous points but, due to a broken shell 

margin, one or two projected points may be extrapolated, or (3) the specimen is an internal mold so the 

resilifer point and the measurement of width are missing 

entirely and the other points are compromised. Internal 

molds were retained in the digitized collection for localities if original shell material was absent or extremely 

rare or if the molds were the original types.

The decision to designate any fossil shell as a juvenile 

or as an adult specimen (label 7) is arbitrary because by 

definition this transition is marked by the development of 

gametes, and this event is not ordinarily recorded in the 

hard parts of the fossil. For Bathytormus and Crassatella, arbitrary limits were established at lengths of 15 

and 30 mm; specimens less than 15 mm in length were 

identified as juveniles2; specimens greater than 30 mm in 

length were identified as adults. Specimens having 

lengths between 15 and 30 mm were analyzed according 

to their characters: (1) a well-developed hinge, a change 

in surface ornamentation, or a change in posterior shape 

were considered adult characters or (2) the absence of 

these characters caused a specimen to be identified as a 

juvenile.

The measure of the width of the specimen (label 8) is a 

measure of the convexity of the shell. 3 This third dimension of the specimens (not reflected in the digitized 

measurements) is included because some of the original 

authors discussed this aspect of shell shape in their 

diagnoses. A device designed specifically for this study 

measures what, on a perfectly equivalved specimen, 

would be one-half of the width, to the nearest 100th 

millimeter (±0.05 mm) (fig. 6).

The specimens were digitized on a Summagraphics 

digitizing pad linked to a personal computer, using 

"Measure," a digitization program (written in Turbo 

Basic by Ralph Chapman, U.S. National Museum of

1 A few exceptions were made to this rule in the case of the subspecies of 

Crassatella vadosa. At two outcrops in the type are (Iocs. 51, 52) for C. vadosa 

ripleyana, the collections contain a mixture of specimens that fit the descriptions 

of C. vadosa vadosa and C. vadosa ripleyana. Although C. vadosa vadosa is the 

only species present at these two localities according to the published accounts, 

the specimens were categorized into either subspecies according to their morphologic features.

2 The lower limit was based on a statement by Stewart (1930, p. 138) in a 

discussion of the differences in hinges between Bathytormus and Crassatella in 

which he commented that, for specimens less than 15 mm, the hinges do not serve 

well as a diagnostic character.

3 Width for pelecypods is defined as the distance between two planes parallel to 

the commissural plane that are tangent to the outermost parts of the two valves 

(Pojeta, 1987, p. 411).

FIGURE 6.—Device used to measure valve width. The fossil rests on its 

plane of commissure, and any protruding parts of the hinge drop into 

a depression on the lower platform; the upper platform is lowered, 

and the micrometer indicates the width of one valve to the nearest 

100th millimeter (± 0.05 mm). (Device patent pending; designed by 

R. Wingard.)

Natural History, Smithsonian Institution, Washington, 

B.C., 1987). The six homologous points and eight projected points (fig. 5) were digitized for all specimens 

(excluding internal molds, which do not retain the resilifer character), and the eight labels were entered from 

the keyboard. The coordinate file created by these 

procedures serves as the main data base. From a variable template file, actual measurements were calculated 

as the distance or angle between two or three of the 

coordinate points (table 2). Simple distance measurements were used as much as possible because they are 

the most independent type of data. However, the angular data contribute valuable discriminating information4 

and are the best linear expression of hinge, posterior, 

and anterior shapes, all characters mentioned as diagnostic by original authors of crassatellid species. The 

final data file contains close to 1,000 digitized specimens 

from 28 species categories and 5 generic categories, with 

7 categorical variables and 34 continuous variables 

recorded for each specimen.

4 Wingard and Sohl (1990) found the angles to be of primary importance in 

discriminating between species of Nucula.
14 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 2. — Thirty-four morphological variables constructed for the statistical analysis

[D, distance measurement. A, angle. Variable points, digitized points on figure 5 used to construct each variable; *, convex values not digitized. 

Discriminant analysis columns 1-4 indicate which variables were used (X) in the analysis of the four subsets of the data: (1) subspecies of Crassatella 

vadosa, (2) species of Crassatella, (3) species of Bathytormus, and (4) genera of Crassatellidae. N, nonnormal variable, deleted from the data set 

for all four analyses. Totals at bottom reflect runs in which no internal molds were used]

Description of variable

One-half the measure of shell width. ..............

Length ...........................................

Distance from the beak to the posterior ..........

Distance from the beak to the anterior ...........

Hinge angle. ......................................

Posterior angle ...................................

Height of the posterior region ....................

Anterior angle ....................................

Height of the anterior region .....................

Length of the ventral margin .....................

First increment of posterior height ...............

Second increment of posterior height .............

Third increment of posterior height. ..............

First increment of anterior height ................

Second increment of anterior height ..............

Third increment of anterior height. ...............

Length of the posterior dorsal margin ............

Length of the anterior dorsal margin .............

Height of the anterior margin ....................

Height of the posterior margin ...................

Length of the resilifer ............................

Length of the posterior lateral ridge. .............

Length of the anterior lateral ridge. ..............

Width of the hinge plate ..........................

Angle from anterior lateral to resilifer ............

Distance from posterior lateral to margin. ........

Distance from anterior lateral to margin ..........

Height of the posterior adductor. .................

Height of the anterior adductor. ..................

Width of the mantle cavity .......................

Internal posterior angle. ..........................

Internal anterior angle. ...........................

Distance from posterior adductor to ventral ......

Distance from anterior adductor to ventral .......

Total number of variables included. ..........

Variable abbreviation

. . . CONVEX

... LENGTH

. . . POSTHT

. . . ANTHT

. . . HINGE

. . . POST

. . . POSTWID

. . . ANTER

. . . ANTWID

. . . VENTRAL

. . . POSTWID1

. . . POSTWID2

. . . POSTWID3

. . . ANTWID1

. . . ANTWID2

. . . ANTWID3

. . . POSTDOR

. . . ANTDOR

. . . ANTVERHT

. . . POSVERHT

. . . RESILIF

. . . POSTLAT

. . . ANTLAT

. . . HINGEPL

. . . RESILANG

. . . POSTLAT2

. . . ANTLAT2

. . . POSTADHT

. . . ANTADHT

. . . MANTCAV

. . . INTPOST

. . . INTANT

. . . POSADDST

. . . ANTADDST

Variable

Type

D

D

D

D

A

A

D

A

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

D

A

D

D

D

D

D

D

D

D

D

Points

*

8-13

1-9

1-12

3-1-4

7-9-10

7-10

11-12-14

11-14

10-11

7-^8

8-9

9-10

13-14

12-13

11-12

1^8

1-13

4-11

3-10

1-2

1-3

1-4

3-4

1^-2

3-^8

4-13

3-5

4-6

5-6

1-5-6

1-6-5

5-10

6-11

1

X

-

-

X

N

N

X

X

X

X

-

-

N

-

X

N

X

X

-

X

N

X

-

X

X

-

X

-

X

-

-

X

X

X

18

Discriminant 

analysis

2

X

X

X

X

-

-

-

X

-

X

X

X

-

X

X

-

X

X

X

-

-

X

X

X

X

X

X

X

-

-

X

X

X

X

24

3

_

X

-

_

-

-

-

-

X

-

-

-

-

X

-

-

X

X

-

X

-

X

X

X

X

-

X

-

-

X

X

-

X

X

15

4

_

X

X

X

-

-

-

X

-

-

X

X

-

X

-

-

-

X

X

X

-

X

X

X

X

-

X

X

-

X

X

X

X

X

21

In phase four, the morphometric data base assembled 

in phase three was used to quantitatively evaluate the 

discrete species and generic categories. The first step in 

the statistical analysis phase was to "clean" and reduce 

the original morphometric data base (created in phase 

three). To clean the data, outliers, miscodes, and nonnormal variables were identified and removed. Outliers 

and miscodes were detected by running the entire data 

set through the discriminant analysis procedure. Once 

these were removed, univariate tests uncovered five 

nonnormal variables, which were also eliminated from 

the data set (see table 2, discriminant analysis column 1). 

Next, the clean data set was separated into four subsets

representing the four taxonomic categories of Crassatellidae being studied: (1) the subspecies of Crassatella, (2) 

the species of Crassatella, (3) the species of Bathytormus, and (4) the genera of Crassatellidae. Four separate 

stepwise discriminant analyses were done on the subsets 

of the data to further reduce the data set by identifying 

those variables that contributed significantly (to a level 

of 0.1) to the differences among the categories; the 

remainder of the variables were eliminated for each 

subset (see table 2 for a list of variables included in each 

analysis).

The second and last step in phase four was to test the 

four refined subsets of data using canonical discriminant
STATISTICAL ANALYSIS 15

analysis and classificatory discriminant analysis to quantitatively evaluate the primary question being asked, 

"How accurate is the published fossil record?" Are the 

genera and species cited in the literature statistically 

distinct and well defined, or is there a significant degree 

of overlap between the categories? Discriminant analysis 

is an excellent statistical procedure for testing a priori 

groups because it forces maximum separation among the 

groups and minimum separation within groups; any 

overlap seen between categories is therefore significant 

because the statistical bias is towards separation. Two 

separate canonical discriminant analyses were executed 

on each of the four subsets of the data. The first excluded 

the unnamed species categories, the broken specimens, 

the internal molds, and the juveniles. The second analysis for each subset included all of the data. Classificatory 

discriminant analyses were done to test the model developed by each canonical discriminant analysis and to test 

the unknown species categories. All of the statistical 

computer analyses in phase four were done using SAS on 

the GWU IBM mainframe. The results of the multivariate statistical analyses of the refined data set are discussed in the following section.

STATISTICAL ANALYSIS

Several aspects of canonical discriminant variable 

analysis and classificatory discriminant analysis must be 

understood before the results of the subspecies and 

subsequent analyses are considered. First, the maximum 

possible separation between the defined classes is found 

along each canonical variable; consequently, any overlap 

between groups is significant. Second, narrowly defined 

groups (for example, small local populations) by their 

very nature show higher classification results than 

broadly defined groups. Finally, in the classificatory 

discriminant analysis, classification results are always 

high when the calibration data set itself is classified 

because these are the data upon which the model is 

based.

SUBSPECIES OF CRASSATELLA VADOSA

Before proceeding with an evaluation of the species of 

Crassatellidae, two questions need to be answered: (1) 

are the proposed subspecies valid and (2), if valid, are 

any subspecies worthy of being raised to specific rank. 

Crassatella vadosa Morton, 1834 has been split into 

three subspecies: (1) Crassatella vadosa ripleyana Conrad, 1858, originally described as a species from the Owl 

Creek Formation in Tippah County, Miss. (loc. 52), (2) 

Crassatella vadosa wadei Stephenson, 1941, described 

from the Coon Creek Formation, at Coon Creek, Tenn. 

(loc. 27), and (3) Crassatella vadosa vadosa represented 

by replaced specimens and internal molds from the

Prairie Bluff Chalk, Prairie Bluff, Ala. (loc. 56). In 

addition, numerous other localities of C. vadosa have 

been reported (see apps. 1, 2), but none of these specimens have been assigned to a subspecies.

To test whether Crassatella vadosa ripleyana and C. 

vadosa wadei should be raised to specific rank, the initial 

assumption is that the two described subspecies, C. 

vadosa ripleyana and C. vadosa wadei, do represent 

valid species categories for the statistical analysis. The 

category Crassatella vadosa includes the type Prairie 

Bluff specimens (C. vadosa vadosa} as well as all other 

reported C. vadosa specimens. The null hypothesis5 is 

that no statistically significant differences exist between 

"C. ripleyana" C. wadei" and C. vadosa. If the null 

hypothesis cannot be rejected, this would indicate that 

"C. wadei" "C. ripleyana," and C. vadosa are members 

of the same species, as previous authors have indicated. 

The alternative hypothesis is that distinctive differences 

exist between "C. ripleyana," "C. wadei," and C. 

vadosa; therefore, the subspecies should be raised to 

specific rank. If the degree of overlap seen between 

the categories is substantial, this would indicate that 

even the validity of the subspecies categories should be 

questioned.

Analysis.— First, 145 well-preserved adult specimens6 were divided into 3 categories and treated as 

distinct taxonomic units or "species": (1) Crassatella 

vadosa (21 specimens), (2) "C. ripleyana" (33 specimens), and (3) "C. wadei" (91 specimens). The specimens 

are from seven localities in the Upper Cretaceous units of 

the Gulf Coast and Mid-Atlantic regions (app. 1). Eighteen morphologic measurements (table 2) were used to 

discriminate the three "species" categories.

An examination of the univariate statistics for the 

analysis (table 3, first analysis) shows that the mean 

values of the distance measurements are fairly close 

together for each of the three categories. The group 

means on each variable for "Crassatella wadei," however, are generally larger than the grand means for all 

three classes combined, whereas the group means for C. 

vadosa and "C. ripleyana" are closer together and 

smaller than the grand means. An examination of the 

standard deviations (table 4, first analysis) reveals that

5 This is the general hypothesis comprising different hypotheses that are tested 

at different stages of each discriminant analysis. The F test of the Mahalanobis' 

distances tests the null hypothesis that the group means of each class are equal. 

If this null hypothesis cannot be rejected, then the means of the two groups will 

be close together on the canonical discriminant variables. During the canonical 

discriminant procedure, the null hypothesis being tested is that the canonical 

correlation for each canonical variable and all correlations that follow equal 0. If 

this null hypothesis cannot be rejected, then the canonical variables do not 

correlate to the original data, and the whole procedure is invalid. For more 

detailed information, refer to Davis (1973, p. 442^456) and SAS User's Guide: 

Statistics (SAS Institute, 1982, p. 369-380).

6 The criteria for classifying specimens into ontogenetic and preservational 

categories are discussed in the section on "Statistical Methods," page 13.
16 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 3. — Class means and grand means for subspecies o/Crassatella vadosa on each variable used in both canonical

discriminant analyses

[For the purpose of the analysis, each subspecies was treated as a "species" category. See table 2 for an explanation of the morphological 

variables. 1, the means from the first canonical discriminant analysis, including adult whole specimens only; 2, the means from the second 

canonical discriminant analysis of all specimens, including juveniles, broken specimens, and internal molds; *, in the second analysis, 

CONVEX and RESILANG were removed because these values are not available for internal molds]

Class mean

Morphological variable

CONVEX ..........

ANTHT ............

POSTWID..........

ANTER ............

ANTWID...........

VENTRAL.........

ANTWID2. .........

POSTDOR..........

ANTDOR. ..........

POSVERHT. .......

POSTLAT..........

HINGEPL. .........

RESILANG ........

ANTLAT2..........

ANTADHT.........

INTANT ...........

POSADDST ........

ANTADDST. .......

C. vadosa

1

10.62

25.15

12.78

147.70

13.56

25.23

8.83

28.22

19.90

18.10

16.50

20.41

21.06

9.82

7.97

72.19

9.73

10.42

2

*

25.88 

14.60 

144.27 

14.81 

28.62

8.24 

29.68 

21.11 

18.83 

17.97 

23.10 

*

10.43 

8.89 

68.39 

9.67 

10.02

"C. ripleyana"

1

12.17 

26.18 

12.09

145.89 

13.68 

25.61

9.90 

28.75 

20.33 

18.50 

16.91 

20.15

22.43 

10.09 

8.15 

74.43 

10.03 

10.83

2

*

26.19 

12.09 

145.73 

13.86 

25.60

9.97 

28.84 

20.34 

18.50 

16.93 

20.22 

*

10.10 

8.18 

74.22 

10.06 

10.87

"C. wadei"

1

13.02 

32.05 

18.78 

145.39 

19.51 

34.94

11.71 

35.51 

25.56 

23.81 

20.88 

27.15

22.30 

13.46 

10.52 

68.32 

12.93 

14.34

2

*

31.87 

18.68 

145.35 

19.42 

34.73

11.64 

35.29 

25.42 

23.68

20.78 

27.00 

*

13.39 

10.46 

68.33 

12.85 

14.26

Grand mean

1

12.48 

29.71 

16.39 

145.84 

17.32 

31.41

10.88 

32.92 

23.55 

21.77 

19.34 

24.58

22.15 

12.16 

9.61

70.27 

11.81 

12.97

2

*

28.40 

15.83 

144.97 

16.54 

30.60

9.95 

31.84 

22.74 

20.76 

18.94 

24.19 

*

11.59 

9.41 

69.40 

11.05 

11.91

TABLE 4. — Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the 

subspecies of Crassatella vadosa on each variable used in the analyses

[For the purpose of the analysis, each subspecies was treated as a "species" category. See table 2 for an explanation of the morphological 

variables. Total, total sample standard deviations of the data from all "species" categories combined. Within class, pooled within-class 

standard deviations for the "species" categories. Between class , between-class standard deviations for the "species" categories. 1, data 

from the first canonical discriminant analysis, including adult whole specimens only; 2, data from the second canonical discriminant 

analysis of all specimens, including juveniles, broken specimens, and internal molds; *, in the second analysis, CONVEX and RESILANG 

were removed because these values are not available for internal molds]

Standard deviation

Morphological variable

CONVEX .........

ANTHT ...........

POSTWID.........

ANTER ...........

ANTWID..........

VENTRAL........

ANTWID2. ........

POSTDOR.........

ANTDOR. .........

POSVERHT. ......

POSTLAT.........

HINGEPL. ........

RESILANG .......

ANTLAT2.........

ANTADHT........

INTANT ..........

POSADDST .......

ANTADDST. ......

Total

2

4

. . . . 3

. . . . 6

.... 3

. . . . 6,

. . . . 2

. . . . 5

. . . . 3

. . . . 3,

. . . . 3

4

. . . . 3,

. . . . 2,

.... 1,

. . . . 4,

. . . . 2,

. . . . 2.

i

.16 

.64 

.90 

.36 

.93 

.79

.21 

.41 

.76 

.59 

.26 

.37

,14 

,34 

,67 

,26 

,16 

,65

2

*

5.13 

3.71 

9.28 

4.20 

6.89

2.80 

6.10 

3.99 

3.76 

3.65 

4.52 

*

2.37 

1.79 

5.91 

2.40 

3.12

Within class

1

2.00 

3.51 

2.36 

6.35 

2.72 

5.04

1.91 

4.25 

2.71 

2.44 

2.59 

2.83

3.13 

1.62 

1.19 

3.37 

1.60 

1.98

2

*

4.24 

2.71 

9.31 

3.44 

5.89

2.35 

5.39 

3.31

2.87 

3.30 

3.74

*

1.84 

1.55 

5.50

1.87 

2.41

Between class

1

1.03 

3.73 

3.81 

.97 

3.48 

5.61

1.38 

4.13 

3.20 

3.24 

2.45 

4.09

.55 

2.06 

1.44 

3.21 

1.79 

2.18

2

*

3.55 

3.11 

.73 

2.98 

4.42

1.89 

3.56 

2.76 

2.99 

1.93 

3.13 

*

1.85 

1.12 

2.74 

1.86 

2.43

F

1

12.81 

54.53 

126.31 

1.13 

79.26 

60.05

25.01 

45.66 

67.41 

85.16 

43.37 

101.07

1.51 

77.69 

70.86 

43.71 

60.57 

58.44

2

*

54.13 

101.64

.48 

57.68 

43.45

49.87 

33.56 

53.41 

83.31 

26.41 

53.88 

*

77.92 

40.13 

19.18 

76.04

77.70

Probability F

1

0.0001 

.0001 

.0001 

.3277 

.0001 

.0001

.0001 

.0001 

.0001 

.0001 

.0001 

.0001

.2247 

.0001 

.0001 

.0001 

.0001 

.0001

2

*

0.0001 

.0001 

.6202 

.0001 

.0001

.0001 

.0001 

.0001 

.0001 

.0001 

.0001 

*

.0001 

.0001 

.0001 

.0001 

.0001
STATISTICAL ANALYSIS 17

TABLE 5.—Mahalanobis' distances between classes for the first 

canonical discriminant analysis of the adult whole specimens of the 

subspecies of Crassatella vadosa

[For the purpose of the analysis, each subspecies was treated as a "species"

category]

"Species"

Mahalanobis' distance 1 between classes 

C. vadosa "C. ripleyana" "C. wadei''

C. vadosa......

"C. ripleyana". 

"C. wadei".....

2.1486

4.7413 >.7794

1 Mahalanobis' distances are a measure of the separation of the multivariate 

means of two classes (Davis, 1973, p. 450-451).

all but two of the variables, anterior angle and resilifer 

angle (ANTER, RESILANG, see table 2 for an explanation of all variables), show statistically significant 

differences among the three "species," but just over half 

of the variables have higher between-class standard 

deviations as compared to within-class standard deviations. On the basis of the univariate statistics, the 

following predictions can be made: (1) "C. ripleyana" will 

fall closer to the group mean for C. vadosa along the 

canonical variables than "C. wadei," (2) the variables 

with the higher between-class standard deviations may 

be the primary discriminating variables, and (3) anterior 

angle and resilifer angle will contribute the least to the 

discrimination of the three classes.

The Mahalanobis' distances computed between classes 

(table 5) support the initial conclusions drawn from the 

univariate statistics; the distance between Crassatella 

vadosa and "C. ripleyana" is less than the distance 

between C. vadosa and "C. wadei." An F test on the 

Mahalanobis' distances shows all values to be greater 

than the critical value for F at the 5 percent level of 

significance, so the null hypothesis of equal class means is 

rejected.

The plot of canonical variables 1 and 2 (fig. 7) illustrates the predicted separation of "Crassatella wadei" 

from C. vadosa and "C. ripleyana," and the overlap of C. 

vadosa and "C. ripleyana," to the point that the group 

mean for "C. ripleyana" falls within the zone of overlap 

of the two classes. "C. wadei" is isolated primarily along 

canonical variable 1, which accounts for 95.83 percent of 

the variance between the classes and has a canonical 

correlation value of 0.93. The standardized canonical 

coefficients (table 6) reveal which variables are contributing significantly to the discrimination of the classes; 

the most significant discriminator (highest absolute 

value of standardized canonical coefficients) along 

canonical variable 1 is the height of the posterior 

margin (POSVERHT). Along canonical variable 2, 

which accounts for 4.17 percent of the variance and 

has a canonical correlation value of 0.48, "C. wadei" 

falls between C. vadosa and "C. ripleyana." The most

TABLE 6. —Standardized canonical coefficients for the first canonical 

discriminant analysis of the adult whole specimens of the subspecies 

of Crassatella vadosa

[See table 2 for an explanation of the morphological variables. Canonical variables 

1 and 2 are plotted on figure 7]

Morphological Standardized canonical coefficient 

variable Canonical variable 1 Canonical variable 2

CONVEX ............

ANTHT ..............

POSTWID............

ANTER ..............

ANTWID.............

VENTRAL...........

ANTWID2. ...........

POSTDOR............

ANTDOR. ............

POSVERHT. .........

POSTLAT............

HINGEPL. ...........

RESILANG ..........

ANTLAT2. ...........

ANTADHT...........

INTANT .............

POSADDST ..........

ANTADDST. .........

-0.7050

.3260

.6271

.4720

1.0136

.3015

-0.4572

-0.9133

-1.9750

2.1341

.3319

1.3759

.2966

.8279

.1379

-0.6542

-1.3466

.4989

-0.9580

11.6356

-0.8973

1.2720

1.7628

-1.6285

-3.0255

3.1803

-9.8455

-1.7142

-6.0909

6.2692

-0.0772

2.6150

-1.1625

.4028

.9122

-2.4066

TABLE 7.—Results of the classificatory discriminant analysis of the 

adult whole specimens of the subspecies of Crassatella vadosa; 

calibration data set tested against itself

[For the purpose of the analysis, each subspecies was treated as a "species" 

category. Of the total number of specimens (145), 93.8 percent classify into the 

predicted "species" categories]

Original "species" 

category1

Total

no. of

specimens

Number of specimens

(percentage of specimens) within the

"species" category determined by analysis

C. vadosa "C. ripleyana" "C. wadei"

C. vadosa .......

"C. ripleyana" . . 

"C. wadei" ......

21

33 

91

15 (71.43)

3 (9.09) 

0(0)

6 (28.57)

30 (90.91) 

0(0)

0(0)

0(0) 

91 (100.0)

Total. 145 18 36 91

1 "Species" category assigned prior to analysis.

significant discriminator along canonical variable 2 is the 

distance from the beak to the anterior margin (ANTHT) 

(table 6). The length of the anterior dorsal margin 

(ANTDOR) and the width of the hinge plate (HINGEPL) 

are important discriminators on both canonical variables 

1 and 2.

A discriminant analysis was conducted to obtain classification results for the adult whole specimens of Crassatella vadosa, "C. ripleyana," and "C. wadei" (table 7). 

The variables that measure shell width and resilifer 

angle (WIDTH, RESILIF) were deleted from this subset of the data so that internal molds, which lack measurements on these two variables, could be tested against 

the data set consisting of the adult whole specimens. An 

intermingling of C. vadosa, which covers a wide
18 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES ^EXTINCTION AT THE BOUNDARY

6-

4-

<M

CO

"co 

"c o

o

c

CO

o

o-

-2-

-4-

-6 -4

Q Crassatella vadosa

-202 

Canonical variable 1

EXPLANATION

* "Crassatella ripleyana " i "Crassatella wadei'

FIGURE 7.—Canonical variables 1 and 2 for the first canonical variate analysis of the 

subspecies of Crassatella vadosa. For the purpose of the analysis, each subspecies was 

treated as a "species" category. Data for the analysis include adult whole specimens 

only. Large symbols for the "species" categories represent the midpoints of those 

categories. Canonical variable 1 accounts for 95.83 percent of the variance between 

"species" categories and has a canonical correlation of 0.93. Canonical variable 2 accounts 

for 4.17 percent of the variance between "species" categories and has a canonical 

correlation of 0.48. See table 6 for standardized canonical coefficients.

geographic range, with the isolated population of "C. 

ripleyana" (71.43 percent of C. vadosa classify correctly7 

is seen in the classification results (table 7), but "C. 

ripleyana" was fairly discrete (90.91 percent classify 

correctly). C. vadosa occurs over a broad geographic 

range, whereas "C. ripleyana" and "C. wadei" are from 

discrete populations, so it is expected, due to the nature 

of discriminant analysis, that the category for C. vadosa 

would have lower classification results than either

7 Classify correctly, in the discussion of discriminant analysis results, refers to 

classification in the statistical sense only and does not refer to taxonomic 

classification.

either "C. ripleyana" or "C. wadei." "C. wadei" classify 

correctly 100 percent of the time. Next, only the juveniles, broken specimens, and internal molds were tested 

against the model established by the discrimination of 

the adult whole specimens (table 8). Only 34.9 percent of 

all the specimens classify correctly. In this analysis of the 

juveniles, broken specimens, and internal molds, 50 

percent of the specimens representing C. vadosa classify 

as "C. wadei," whereas none of the adult whole specimens of C. vadosa had classified as "C. wadei," and 25 

percent of "C. wadei" specimens classify into C. vadosa. 

In the final step in the examination of the subspecies of 

Crassatella vadosa all the adult whole specimens,
STATISTICAL ANALYSIS 19

TABLE 8.—Results of the classificatory discriminant analysis of the 

juveniles, broken specimens, and internal molds of the subspecies of 

Crassatella vadosa, tested against the calibration data set of the 

adult whole specimens

[For the purpose of the analysis, each subspecies was treated as a "species" 

category. Of the total number of specimens (86), 34.9 percent classify into the 

predicted "species" categories]

Original "species" 

category1

C. vadosa. ......

"C. ripleyana" . . 

"C. wadei"......

Total .........

Total 

no. of 

specimen!

74 

8 

4

86

Number of specimens 

(percentage of specimens) within the 

"species" category determined by analysis

C. vadosa

22 (29.73) 

3 (37.50) 

1 (25.00)

26

"C. ripleyana"

15 (20.27) 

5 (62.50) 

_0(0)

20

"C. wadei"

37 (50.00) 

0(0) 

3 (75.00)

40

1 "Species" category assigned prior to analysis.

juveniles, broken specimens, and internal molds were 

included in the same analysis. The data set consists of 231 

specimens from 13 localities (app. 2) distributed among 

the three classes as follows: (1) C. vadosa (95 specimens) 

spread over the reported geographic range of the species, including C. vadosa vadosa, (2) "C. ripleyana" (41 

specimens), and (3) "C. wadei" (95 specimens). The 

classes were analyzed by using 16 of the morphologic 

variables (table 2); width and resilifer angle were deleted 

from the data set in order to include internal molds.

The univariate analysis of the class means (table 3, 

second analysis) on each variable shows very little 

change for "Crassatella ripleyana" and "C. wadei" from 

the first analysis of the adult whole specimens, as would 

be expected since very few specimens have been added 

to these classes for this analysis. The inclusion of internal 

molds is significant to the class of C. vadosa, however, 

because the topotype specimens of C. vadosa Morton are 

internal molds from Prairie Bluff, Ala., and these specimens represent C. vadosa vadosa. In addition, the size of 

this class more than quadrupled with the addition of the 

juveniles, broken specimens, and internal molds. The 

individual class means on each variable for C. vadosa 

moved closer to the grand mean on most variables (table 

3) as a result of these additions to the category. A 

comparison of standard deviations (table 4, second analysis), shows the height of the posterior region (POSTWID) to be the only variable having significant differences in between-class versus within-class standard 

deviation. Anterior angle (ANTER) fails the F test at 

the 5 percent level of significance. The univariate statistics therefore indicate that there is more overlap 

between C. vadosa and "C. wadei" than in the previous 

analysis, and that the height of the posterior region 

(POSTWID) contributes significantly to the discrimination of the classes.

The Mahalanobis' distances again support the initial 

conclusions drawn from an examination of the univariate

TABLE 9.— Mahalanobis' distances between classes for the second 

canonical discriminant analysis of all the specimens of the subspecies 

of Crassatella vadosa, including juveniles, broken specimens, and 

internal molds, measured for this analysis

[For the purpose of the analysis, each subspecies was treated as a "species"

category]

"Species"

Mahalanobis' distance1 between classes 

C. vadosa "C. ripleyana" "C. wadei"

C. vadosa......

"C. ripleyana". 

"C. wadei".....

2.2226

2.8438 3.6007

1 Mahalanobis' distances are a measure of the separation of the multivariate 

means of two classes (Davis, 1973, p. 450-451).

data. The distances between "Crassatella wadei" and 

"C. ripleyana" and "C. wadei" and C. vadosa decrease 

when the full data set is examined (table 9). All Mahalanobis' distances pass the F test at the 5 percent level of 

significance, so the null hypothesis of equal means among 

the classes is rejected.

The plot of canonical variables 1 and 2 (fig. 8) illustrates overlap between all three classes when all of the 

specimens are included in the data set. The class means 

for "Crassatella ripleyana" and "C. wadei" fall within 

the region of overlap with C. vadosa. Canonical variable 

1, which contributes more to the separation of "C. wadei" 

from C. vadosa and "C. ripleyana," accounts for 78.70 

percent of the variance seen between the classes and has 

a canonical correlation value of 0.83. Characters of the 

dorsal margin (POSTDOR, POSTLAT, ANTLAT2, 

HINGEPL) and the anterior adductor (ANTADHT, 

ANTADDST) seem to contribute the most to the discrimination of the classes along canonical variable 1, 

although none of the standardized canonical coefficient 

values are particularly large (table 10). Canonical variable 2, which accounts for 21.30 percent of the variance 

seen between the classes and has a canonical correlation 

value of 0.60, causes the separation of C. vadosa from the 

other two classes. The standardized canonical coefficients (table 10) indicate that most of the separation 

along canonical variable 2 can be attributed to characters 

on the anterior portion of the shell (ANTDOR, ANTHT).

Discussion. —The analysis of the adult whole specimens of "Crassatella ripleyana," "C. wadei," and C. 

vadosa reveals that measurable differences do exist 

between the three groups of specimens. Evidence of the 

separation is seen in the results of the F tests on the 

univariate class means, the results of the F test on the 

Mahalanobis' distances, the separation visible on the plot 

of the canonical variables (fig. 7), and the classification 

results (table 7). These differences are evident on the 

figured specimens as well, particularly when C. vadosa 

vadosa and C. vadosa ripleyana are compared to C. 

vadosa wadei (compare pi. 1, figs. 2-4, 16 to pi. 7, fig. 

15). The null hypothesis being examined in this portion of
20 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

CM

CO

75 

_o"c 

o

CO

O

3-

1-

-1-

-3.

-5

-5 -3 -1 1

Canonical variable 1

EXPLANATION

H Crassatella vadosa * "Crassatella ripleyana' "Crassatella wadei"

FIGURE 8.—Canonical variables 1 and 2 for the second canonical variate analysis of the 

subspecies of Crassatella vadosa. For the purpose of the analysis, each subspecies was 

treated as a "species" category. Data for the analysis include all adults, juveniles, broken 

specimens, and internal molds. Large symbols for the "species" categories represent the 

midpoints of those categories. Canonical variable 1 accounts for 78.70 percent of the 

variance between "species" categories and has a canonical correlation of 0.83. Canonical 

variable 2 accounts for 21.30 percent of the variance between "species" categories and 

has a canonical correlation of 0.60. See table 10 for standardized canonical coefficients.

the analysis therefore can be rejected; statistically significant differences do exist between "C. ripleyana" "C. 

wadei," and C. vadosa. The degree of overlap seen on the 

plot of the entire data set (fig. 8), however, indicates that 

these differences are not of specific rank. The question 

remains, however, are the subspecies divisions valid?

The answer to this question does not lie in statistics 

and may be impossible to ascertain given the present 

state of disagreement among taxonomists on the concept 

of subspecies. According to Blackwelder (1967, p. 172), a

valid subspecies occupies a distinct geographical area and 

has "structural features partially setting" it apart as a 

subspecies. He further states that "species can be distinguished because of gaps in the variation of their features. 

Subspecies as usually defined cannot be so distinguished, 

except in some percentage of cases, a figure often placed 

at 75 percent" (Blackwelder, 1967, p. 172-173).

Blackwelder's criteria for a valid subspecies initially 

seem to be met for the adult whole specimens of Crassatella vadosa wadei included in this analysis. All of the
STATISTICAL ANALYSIS 21

TABLE 10.— Standardized canonical coefficients for the second 

canonical discriminant analysis of all the specimens of the subspecies 

o/Crassatella vadosa, including juveniles, broken specimens, and 

internal molds measured for this analysis

[See table 2 for an explanation of the morphological variables. Canonical variables 

1 and 2 are plotted on figure 8]

. , . . Standardized canonical coefficient

ANTHT .............

POSTWID...........

ANTER .............

ANTWID............

VENTRAL..........

ANTWID2. ..........

POSTDOR...........

ANTDOR. ...........

POSVERHT. ........

POSTLAT...........

HINGEPL. ..........

ANTLAT2...........

ANTADHT..........

INTANT ............

POSADDST .........

ANTADDST. ........

Canonical variable 1

-0.6401

.5945

.2725

-0.0030

.2622

-0.0356

-1.0591

-0.6537

.7326

-0.7357

1.5190

1.8134

-0.7790

.1063

-0.4112

1.1318

Canonical variable 2

2.1524

-0.1776

.1222

.3559

-1.3210

-1.4529

1.2989

-3.5760

1.9542

.7061

.6126

.0839

.2839

-1.3712

-1.3354

-0.1538

specimens of C. vadosa wadei come from a single locality (app. 1) and presumably a single population. 8 The 

complete separation of "C. wadei" along canonical variable 1 (fig. 7) and the classification results of 100 percent 

correctly classified (table 7) certainly meet the requirements of partially setting "C. wadei" apart from C. 

vadosa; however, such high classification values are to be 

expected when the calibration data set itself is classified. 

The separation of "C. wadei" also can be explained 

partially by its stratigraphic isolation from "C. ripleyana" and C. vadosa. As the groups are defined for this 

analysis, "C. wadei" occurs in the Coon Creek Formation 

in Tennessee (loc. 27), upper Campanian to lower Maastrichtian, whereas the specimens of C. vadosa and of "C. 

ripleyana" occur in the middle and upper stratigraphic 

units of the Maastrichtian. Nevertheless, there are some 

real morphologic differences between "C. wadei," "C. 

ripleyana," and C. vadosa.

In contrast, the adult whole specimens of Crassatella 

vadosa ripleyana do not clearly meet Blackwelder's 

criteria for subspecies. For example, "C. ripleyana" and 

C. vadosa occur in the middle and upper Maastrichtian, 

and the type locality for C. vadosa ripleyana is Owl 

Creek, in Tippah County, Miss. (loc. 52), but C. vadosa 

ripleyana also has been reported from Owl Creek beds at

8 In the case of fossils, the concept of population is not equivalent to a biologic 

population representing a single point in time. Even if all the specimens come 

from one locality and one stratigraphic unit, they still represent a span of time. 

The population therefore consists of generations of descendants.

Providence School, in Tippah County, Miss. (loc. 51). An 

examination of both collections from the Providence 

School and Owl Creek localities reveals a combination of 

typical C. vadosa and C. vadosa ripleyana forms, yet 

surprisingly Providence School is predominantly C. 

vadosa ripleyana and Owl Creek is predominantly C. 

vadosa. The classification results (table 7) also illustrate 

a blending of "C. ripleyana" and C. vadosa forms; the 

relatively poor (71.43 percent) classification results for 

C. vadosa can be explained, at least in part, by the wide 

geographic spread of the group.

The true nature of the relationship between Crassatella vadosa ripleyana, C. vadosa wadei, and C. 

vadosa is revealed in the analysis that includes the 

internal molds (all of which are C. vadosa vadosa), 

broken specimens, and juveniles. Although the juveniles 

are not discussed by the authors of the original descriptions, they are members of the population and must be 

considered. The general overlap seen on the canonical 

variable plots for C. vadosa, "C. ripleyana," and "C. 

wadei," and the occurrence of the group means of "C. 

ripleyana" and "C. wadei" in the region of overlap, is 

significant because canonical discriminant analysis tends 

to maximize separation. Notably, the Prairie Bluff topotype specimens of C. vadosa vadosa occur in the entire 

area of the plot for C. vadosa, except in the region of 

overlap with "C. ripleyana." This area of the plot is 

occupied by the Tippah County, Miss., specimens of C. 

vadosa. Also, the juveniles of all three categories occur 

clustered around the group mean for C. vadosa. The 

classification results from the discriminant analysis of the 

juveniles, broken specimens, and internal molds (table 8) 

also reveal this intermingling; only 34.9 percent of all of 

the specimens classify correctly (all less than or equal to 

the 75 percent limit of Blackwelder, 1967, p. 173). 

Specimens of C. vadosa classify as C. vadosa, "C. 

ripleyana," or "C. wadei." The misclassified specimens 

of "C. ripleyana" are three broken specimens from the 

type locality (loc. 52), so their misclassification may 

simply be a result of the damage to the specimens. The 

misclassified specimen of "C. wadei" is a juvenile.

The results of the analysis that includes broken and 

juvenile specimens indicate from the following evidence 

that Crassatella vadosa ripleyana and C. vadosa wadei 

are two end members of the C. vadosa species: (1) the 

close proximity of the univariate means, (2) the deficiency of variables having higher between-class standard 

deviations than within-class standard deviations, (3) the 

overlap of groups on the plot of canonical variables 1 and 

2, and (4) the classification results less than or equal to 75 

percent. Whether or not C. vadosa ripleyana and C. 

vadosa wadei are valid subspecies of C. vadosa depends 

on how a subspecies is defined. If the term subspecies is 

simply a convenient way to acknowledge morphologic
22 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

variation within a species, then C. vadosa ripleyana and 

C. vadosa wadei are valid terms because they do possess 

distinctive differences in overall shape among the adult 

specimens. If, however, subspecies must be completely 

isolated geographically from one another to be valid then 

C. vadosa ripleyana and C. vadosa wadei are not valid 

subspecies. Although C. vadosa wadei and C. vadosa 

ripleyana have never been reported outside the area of 

their type localities, a close examination of the collections 

from the Gulf Coast and Mid-Atlantic regions reveals C. 

vadosa ripleyana-like specimens (pi. 9, fig. 3, and pi. 11, 

fig. 3) and C. vadosa wadei-like specimens (pi. 11, figs. 

8-10) do occur in other areas. In the Gulf Coast and 

Maryland the forms appear intermixed with specimens of 

the typical C. vadosa vadosa-like form. The North 

Carolina and New Jersey forms tend to be similar to C. 

vadosa wadei. The close proximity of the juveniles of all 

three categories to the group mean for C. vadosa on the 

plot (fig. 8) raises the possibility that environmental 

influences acted on the individuals of the populations as 

they matured and caused the variations seen; the specimens of C. vadosa and C. vadosa ripleyana from the 

Owl Creek Formation in Tippah County, Miss., may 

indicate an area undergoing environmental fluctuation. 

Another possibility is that the variations in form are the 

result of sexual dimorphism, but the patterns of distribution illustrated in this analysis do not support this 

interpretation.

Blackwelder (1967, p. 174) summarized the difficulties 

in dealing with subspecies:

The problems involved here are (1) whether there is in 

nature enough diversity within some species to be usefully 

studied; (2) if so, whether this diversity can be treated in the 

taxonomic system; and (3) if so, whether the segregates can 

or should be named in the formal system of nomenclature. 

The first question is generally answered in the affirmative. 

The second question has scarcely ever been faced; it is the 

crux of the present problem and is here believed to be likely 

to be eventually answered in the negative. The third question has clouded the second and is answered either negatively 

or affirmatively according to the experience of the speakers. 

The Rules of Nomenclature have for a half-century permitted 

such naming.

In the case of the subspecies of Crassatella vadosa, there 

is indeed enough diversity to be examined and discussed, 

but I do not believe the differences are significant enough 

to warrant isolation into formal subspecies categories. 

This issue is discussed further in the "Systematic Paleontology" section. The most important question is 

whether or not either of the subspecies under discussion 

should be raised to species rank; that question has 

definitely been answered in the negative.

SPECIES OF CRASSATELLA

The purpose of this analysis is to test the validity of the 

many species names that have been proposed for the 

genus Crassatella within the stratigraphic and geographic limits of this study (table 1). The null hypothesis5 

is that no statistically significant differences exist 

between the species categories of Crassatella. If the null 

hypothesis cannot be rejected for any pair of species 

categories, this would indicate the existence of synonyms. The alternative hypothesis is that the species 

names are all valid. A comparison of the species of 

Crassatella across the Cretaceous-Tertiary boundary is 

of particular importance to this study because the bulk of 

the species names (32 of 38, table 1) examined herein 

occur within this genus.

Analysis. — In the first part of the analysis, 239 adult 

whole specimens were tested from the following species 

categories9 (see app. 3 for geographic and stratigraphic 

distribution):

Species9 No. of 

specimens

Crassatella vadosa Morton, 1834.................... 145

C. gardnerae Harbison, 1945........................ 53

"C. hodgei (Stephenson), 1923" (and C. carolinensis 8

Conrad, 1875). 

C. lintea Conrad, 1860.............................. 13

C. tumidula Whitfield, 1865 ........................ 14

"C. halei Harris, 1897a" (= C. tumidula) ...........____6_

Species categories having five or fewer specimens measured for the group were excluded from this first analysis; 

all unnamed specimens also were excluded. The specimens are distributed among 18 localities in the Upper 

Cretaceous and lower Tertiary units of the Gulf and 

Mid-Atlantic Coastal Plains (app. 3). The species of 

Crassatella were discriminated on the basis of 24 morphologic measurements (table 2).

An examination of the univariate class means (table 11, 

first analysis) on each distance measurement reveals 

that, in general, "Crassatella hodgei" (and C. carolinensis), "C. halei" (= C. tumidula), and C. lintea have 

values lower than the grand mean of all species categories combined. C. vadosa, C. gardnerae, and C. tumidula 

tend to have univariate class mean values larger than the

9 The criteria for assigning specimens to species categories are discussed in the 

"Statistical Methods" section (p. 12-13). Critical evaluation of specimens was 

deliberately avoided for the statistical analysis. Consequently, when the specimens were later evaluated, the following incorrect assignments were detected:

(1) all specimens initially assigned to Crassatella halei are actually C. tumidula,

(2) 1 specimen assigned to C. tumidula is a C. halei, (3) 2 specimens assigned to 

C. sp. C belong to a species different from the other 123 specimens of the total 

measured, (4) 3 of the specimens assigned to C. sp. A belong to a species different 

from the other 211 specimens of the total measured, and (5) the category C. 

hodgei actually contains 2 species, C. hodgei (9 specimens total measured) and C. 

carolinensis (4 specimens total measured). Items 1 and 5 above are significant in 

that they lead to a misrepresentation in the statistical analysis.
STATISTICAL ANALYSIS 23

on each variable (table 12, first analysis) show that only 

the variable that measures the internal posterior angle 

(INTPOST, see table 2 for an explanation of all variables) 

has a higher standard deviation between classes than 

that within classes. The lack of clear patterns emerging 

from the univariate statistics, and the lack of variables 

having high standard deviations between classes, leads 

to the prediction that a plot of the canonical variables will 

grand mean on most variables. The standard deviations 

show a great deal of overlap among species categories. In 

addition, classification results are not expected to be 

high.

The Mahalanobis' distances computed between classes 

(table 13) reveal patterns that are more distinctive than 

those of the univariate statistics, particularly if their 

ranked order is examined. The seven largest distances 

are between Cretaceous and Tertiary species of Crassatella. The smallest distances are between C. vadosa, 

C. gardnerae, and C. lintea. From these patterns, it is 

expected that Cretaceous and Tertiary species will be 

separated on the plot of the canonical variables and that 

at least three of the four Cretaceous species will occur in 

proximity to each other. All of the values for the Mahalanobis' distances are greater than the critical value for F 

at the 5 percent level of significance, so the null hypothesis of equal means is rejected.

The plot of canonical variables 1 and 2 (fig. 9) illustrates the separation of Crassatella tumidula (both 

divisions), the Tertiary species, from C. vadosa, C. 

gardnerae, and C. lintea, three of the Cretaceous species, along canonical variable 1. "C. hodgei" (and C. 

carolinensis), a Cretaceous form, falls closer to the plot 

of the Tertiary species than to other Cretaceous species 

categories. Canonical variable 1 accounts for 61.61 percent of the variance between the groups and has a 

canonical correlation of 0.90. The standardized canonical 

coefficients (table 14) reveal that the variables pertaining 

to the dorsal region of the shell and the hinge characters 

(POSTDOR, ANTDOR, ANTLAT, ANTLAT2) contribute the most to the discrimination of the classes along 

canonical variable 1. Along canonical variable 2, which 

accounts for 14.70 percent of the variance between the 

groups and has a canonical correlation of 0.71, only "C. 

hodgei" (and C. carolinensis) is clearly separated. The 

discriminating variables (POSTDOR, ANTDOR, ANTLAT, ANTLAT2) remain the same for canonical variable 

2 as for canonical variable 1. The plot of canonical 

variables 2 and 3 (fig. 10) shows overlap of all species 

areas; "C. hodgei" (and C. carolinensis) is the most 

isolated, and C. vadosa, the least isolated, falls in the 

central region of the plot. Canonical variable 3 accounts 

for 12.20 percent of the variance between the categories 

and has a canonical correlation of 0.68; the primary

discriminating variables are characters of the dorsal 

region (POSTDOR, POSTLAT)

A discriminant analysis was executed to obtain classification results (table 15) on the adult whole named 

specimens of Crassatella having more than five specimens measured per species category. The variables that 

measure shell width and resilifer angle (CONVEX, 

RESILIF) were eliminated from this subset of the data 

so that internal molds could be tested against the calibration set of adult whole specimens. C. vadosa, C. 

gardnerae, and C. lintea show a tendency to intermix in 

the classification process, as would be expected from the 

results of the canonical discriminant analysis; significantly, none of these specimens classify as Tertiary 

forms. One Cretaceous Crassatella specimen, a "C. 

hodgei" (and C. carolinensis), does classify as a Tertiary 

form, and likewise the two Tertiary species categories, 

C. tumidula and "C. halei" (= C. tumidula), show a 

tendency to combine with "C. hodgei" (and C. carolinensis) in the classification process.

A second canonical discriminant analysis was conducted, including the adult whole specimens tested in the 

first analysis, unnamed specimens (Crassatella sp.), 

juveniles, broken specimens, internal molds, and species 

having five or fewer specimens measured. The unnamed 

specimens are those Crassatella from localities that do 

not have a published citation of an occurrence of a 

particular species of Crassatella. The additional species 

of Crassatella tested in this portion of the analysis are 

the Cretaceous species (1) C. prora, (2) C. monmouthensis, (3) C. transversa, (4) C. subplana, and (5) C. 

carolinana and the Tertiary species (6) C. gabbi and (7) 

C. sepulcollis. These specimens were excluded from the 

initial analysis because they do not include statistically 

significant numbers and because some occur only as 

internal molds. They are included here, however, to 

reveal any relationship to the well-represented categories. For this portion of the analysis, 710 specimens were 

included from 16 species categories (including 3 separate 

categories of Crassatella sp. groups). The specimens 

come from 51 localities of Upper Cretaceous and lower 

Tertiary units of the Gulf Coast and Mid-Atlantic regions 

(app. 4).

In comparison to the analysis of the abundant whole 

adult specimens, the univariate statistics for the analysis 

of all of the specimens of the Crassatella species show 

more variables having greater values for between-class 

standard deviation than for within-class standard deviation (table 12, second analysis). The individual class 

means (table 11, second analysis) for each category on 

each variable show change primarily in the means of 

Crassatella tumidula, compared to the earlier results. 

C. carolinana has the largest average size of all 

of the species categories being tested, followed by
24 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 11. — Class means and grand means for species of Crassatella on each variable used in both canonical discriminant analyses

[See table 2 for an explanation of the morphological variables. 1, the means from the first canonical discriminant analysis, including adult whole named specimens only 

(excluding species categories with s5 specimens); 2, the means from the second canonical discriminant analysis of all specimens, including juveniles, broken 

specimens, internal molds, unnamed specimens, and species categories with s5 specimens; —, species excluded from the first analysis; *, in the second analysis, 

CONVEX and RESILANG were removed because these values are not available for internal molds]

Class mean

Morphological variable

CONVEX .......

LENGTH. .......

POSTHT ........

ANTHT .........

ANTER .........

VENTRAL......

POSTWID1......

POSTWID2......

ANTWID1. ......

ANTWID2. ......

POSTDOR.......

ANTDOR. .......

ANTVERHT .... 

POSTLAT .......

ANTLAT........

HINGEPL. ......

RESILANG .....

POSTLAT2......

ANTLAT2. ......

POSTADHT .....

INTPOST .......

INTANT ........

POSADDST .....

ANTADDST. ....

C. vadosa

1

12.48

42.67 

37.42 

29.71 

145.84 

31.41

6.56 

6.46 

2.34 

10.88 

32.92 

23.55

22.58 

19.34 

11.43 

24.58 

22.15 

13.82

12.17 

9.98 

41.00 

70.27 

11.81 

12.97

2

*

41.00 

35.94 

28.40 

144.97 

30.60

6.57 

5.92

2.85 

9.95

31.84 

22.74

21.31 

18.94 

11.24

24.19 

*

13.20

11.59 

9.73 

40.95 

69.40 

11.05 

11.91

C. gardnerae

1

13.15 

44.45 

38.25 

29.19 

147.25 

34.96

4.98 

6.28 

3.17 

9.35 

34.03 

24.12

21.79 

19.63 

11.81 

25.49 

22.63 

14.53

12.40 

10.20 

40.10 

66.83 

11.37 

11.73

2

*

44.08 

37.88 

29.03 

147.00 

34.61

4.95 

6.22 

3.13 

9.33 

33.71 

23.95

21.68 

19.41 

11.69

25.21

*

14.43

12.34 

10.13 

40.27 

66.73 

11.31 

11.68

C. hodgei 

(and C. carolinensis)

1

7.19

31.96 

27.57 

22.20 

142.13

24.86

4.35 

5.49 

5.25

5.78 

23.64 

19.12

16.47 

14.41 

9.46 

19.95 

14.69 

9.38

10.01 

6.98

45.46 

60.54 

8.66

7.78

2

*

31.98 

26.83 

21.69 

140.64 

25.19

4.45 

4.91 

4.74 

5.62 

23.50 

18.67

15.66 

14.32 

9.31

19.88

*

9.36

9.64 

7.03 

43.76 

60.12

7.81 

7.40

C. prom

1

—

2

*

24.14 

19.42 

14.37 

139.29 

21.79

4.25 

2.52 

3.48 

1.86 

18.32 

13.19

6.86 

9.66 

9.21

16.25

*

8.95

4.45 

7.13 

40.15 

53.78 

4.16 

2.38

C. monmouthensis

1 2

_ *

- 26.73 

- 22.12 

- 16.57 

- 149.65

- 24.18

- 4.85 

- 3.49 

- 3.21 

- 2.73 

- 19.68 

- 15.15

- 10.29

- 12.04 

- 7.93

- 17.12 

_ *

- 7.97

- 7.44 

- 6.39 

- 41.57 

- 56.17 

- 6.67 

- 3.66

Class mean

Morphological variable

CONVEX .......

LENGTH. .......

POSTHT ........

ANTHT .........

ANTER .........

VENTRAL......

POSTWID1......

POSTWID2. .....

ANTWID1. ......

ANTWID2. ......

POSTDOR.......

ANTDOR. .......

ANTVERHT .... 

POSTLAT.......

ANTLAT........

HINGEPL. ......

RESILANG ..... 

POSTLAT2......

ANTLAT2. ......

POSTADHT ..... 

INTPOST .......

INTANT ........

POSADDST ..... 

ANTADDST. ....

C. transversa

1

—

2

*

47.74 

38.45 

28.13 

147.25 

43.52

.59 

5.04 

7.65 

5.31 

35.34 

25.23

19.35 

18.39 

12.54

26.44 

*

16.96

13.30

11.85 

37.36 

55.80

9.41 

8.01

C. sp.

1

—

A

2

*

37.33 

32.61 

25.35

145.78 

28.29

5.61 

5.65 

3.11 

8.29 

28.69 

20.67

19.24 

17.03 

10.26

22.19

*

11.83

10.51 

8.56 

41.44 

67.64 

10.24 

10.54

C.

i

12.81 

44.29 

36.01 

34.51 

140.80 

30.75

5.60 

7.23 

5.90 

9.10 

32.90 

29.91

24.76 

20.08 

13.26 

25.94 

24.42 

13.03

16.92 

10.03 

52.72 

61.89 

9.51 

10.64

tumidula

2

*

35.60 

29.15

27.88 

136.90 

24.53

4.40 

5.91 

5.31 

7.32 

26.47 

24.15

19.98 

16.21 

11.05

91 9fi £L.£o

*

10.44

13.39 

8.18 

51.92 

62.62 

7.63 

8.70

C. halei 

(=C. tumidula)1

1

10.78 

35.06 

30.98 

27.25 

137.92 

22.59

6.33 

6.34

7.07 

7.74 

27.50 

23.54

20.53 

16.56 

10.86 

22.16 

21.02 

11.29

13.22 

9.08 

51.19 

65.73 

8.26 

8.83

2

*

35.06 

30.98 

27.25 

137.92 

22.59

6.33 

6.34 

7.07 

7.74 

27.50 

23.54

20.53 

16.56 

10.86

22.16

*

11.29

13.22 

9.08 

51.19 

65.73 

8.26 

8.83

C. gabbi

1 2

_ *

- 42.90 

- 36.57 

- 26.72 

- 139.67 

- 33.45

- 7.79 

- 6.75 

- 6.23 

- 5.77 

- 31.95 

- 22.98

- 18.59 

- 21.04 

- 10.73

- 27.47

_ *

- 11.27

- 12.45

- 7.45 

- 40.24 

- 58.63 

- 12.52 

- 8.60
STATISTICAL ANALYSIS 25

TABLE 11. — Class means and grand means for species of Crassatella on each variable used in both canonical

discriminant analyses— Continued

Morphological variable

Class mean

C. sepulcollis C. sp. C C. subplana

1

C. carolinana

CONVEX ....... - * - *

LENGTH........ - 25.39 - 17.61

POSTHT ........ - 21.39 - 15.11

ANTHT......... - 17.40 - 12.01

ANTER......... - 139.51 - 143.50

VENTRAL...... - 17.70 - 11.72

POSTWID1...... - 4.95 - 2.73

POSTWID2...... - 3.78 - 2.79

ANTWID1....... - 3.25 - 2.54

ANTWID2....... - 4.73 - 3.16

POSTDOR....... - 19.11 - 13.41

ANTDOR........ - 15.18 - 10.32

ANTVERHT.... - 12.39 - 8.59

POSTLAT....... - 12.31 - 9.38

ANTLAT........ - 7.02 - 5.67

HINGEPL....... - 16.39 - 12.46

RESILANG..... - * - *

POSTLAT2...... - 7.14 - 4.28

ANTLAT2....... - 8.39 - 4.80

POSTADHT..... - 5.98 - 3.61

INTPOST ....... - 45.52 - 45.00

INTANT........ - 64.23 - 63.45

POSADDST..... - 6.84 - 5.31

ANTADDST..... -_____5.20 - 4.26

	__________Class mean__________

Morphological variable ____C. lintea C. sp. B 

___________________1________2______1______2

CONVEX ....... 6.20 * - *

LENGTH........ 28.35 25.23 - 39.99

POSTHT ........ 24.36 21.51 - 32.59

ANTHT......... 19.69 17.69 - 27.49

ANTER ......... 140.30 141.46 - 139.68

VENTRAL...... 17.06 15.77 - 27.43

POSTWID1...... 6.14 5.38 - 7.03

POSTWID2...... 4.96 4.27 - 6.21

ANTWID1....... 2.85 2.79 - 5.38

ANTWID2....... 7.22 6.15 - 9.52

POSTDOR....... 21.33 18.89 - 29.01

ANTDOR........ 15.87 14.45 - 23.10

ANTVERHT.... 15.94 13.95 - 20.93

POSTLAT....... 12.61 11.39 - 15.89

ANTLAT........ 7.96 7.33 - 10.97

HINGEPL....... 17.13 15.63 - 22.44

RESILANG..... 17.94 * - *

POSTLAT2...... 9.07 7.86 - 13.31

ANTLAT2....... 7.98 7.21 - 12.27

POSTADHT..... 6.76 6.05 - 9.53

INTPOST ....... 43.26 44.03 - 45.07

INTANT ........ 69.46 67.30 - 64.00

POSADDST..... 8.91 8.04 - 8.88

ANTADDST..... 9.48 8.10 - 11.10

43.42

34.33

34.57

137.46

31.62

5.74

5.37

3.37

11.51

30.85

27.33

25.98

21.31

13.92

28.89 

*

10.25

13.47

9.38

45.56

62.55

10.14

15.30

63.60

49.91

46.50

140.37

47.97

8.56

8.14

6.94

15.01

44.58

39.74

34.52

23.95

18.35

34.97

*

21.08

21.67

16.72

46.58

62.76

13.46

17.52

Grand mean

12.09

41.83

36.32

29.02

145.23

30.94

6.05

6.34

2.98

9.99

32.08

23.48

21.91

18.85

11.35

24.24

21.88

13.46

12.22

9.73

42.01

68.53

11.22

12.09

35.09

30.43

24.12

144.53

26.08

5.29

5.23

3.11

7.82

26.94

19.77

18.03

16.23

9.84

21.13

*

10.95

10.05

8.10

42.45

66.84

9.46

9.71

1 Data set for analyses 1 and 2 is identical.
26 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 12. — Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the species of Crassatella

on each variable used in the analyses

[See table 2 for an explanation of the morphological variables. Total, total sample standard deviations of the data from all species categories combined. Within class, 

pooled within-class standard deviations for the species categories. Between class, between-class standard deviations for the species categories. 1, data from the 

first canonical discriminant analysis, including adult whole named specimens only (excluding species categories with s5 specimens); 2, data from the second 

canonical discriminant analysis of all specimens, including juveniles, broken specimens, internal molds, unnamed specimens, and species categories with s5 

specimens; *, in the second analysis, CONVEX and RESILANG were removed because these values are not available for internal molds]

Morphological variable

CONVEX .............

LENGTH. .............

POSTHT ..............

ANTHT ...............

ANTER ...............

VENTRAL............

POSTWID1............

POSTWID2. ...........

ANTWID1. ............

ANTWID2. ............

POSTDOR.............

ANTDOR. .............

ANTVERHT ..........

POSTLAT.............

ANTLAT..............

HINGEPL. ............

RESILANG ...........

POSTLAT2............

ANTLAT2. ............

POSTADHT ...........

INTPOST .............

INTANT ..............

POSADDST ...........

ANTADDST. ..........

Standard deviation

Total

...... 2

...... 9

...... 7

...... 6

...... 7

...... 8

...... 2

...... 1

...... 1

...... 2

...... 6

...... 5

...... 4

...... 4

...... 2

...... 5

...... 3

...... 3

...... 3

...... 2

...... 4

...... 4

...... 2

...... 2

i

.94 

.12 

.67 

.41 

.21 

.35

.61 

.44 

.97 

.62 

.95 

.37

.76 

.13 

.47 

.03 

.84 

.09

.28 

.11 

.49 

.73 

.47 

.89

2

*

12.22 

10.67 

8.58 

8.50 

10.36

2.52 

1.96 

1.91 

3.43 

9.49 

6.91

6.59

5.28 

3.21

6.54

*

4.44

3.93 

3.07 

4.14 

5.30 

3.16 

3.92

Within class

1

2.37

8.24 

6.86 

5.77 

6.91 

7.32

2.54 

1.39 

1.61

2.28 

6.21 

4.80

4.40 

3.75 

2.28 

4.66 

3.44 

2.76

2.91 

1.92 

3.10 

3.90 

2.25 

2.57

2

*

8.35 

7.25 

5.93

8.29 

7.20

2.13 

1.56 

1.76 

2.38 

6.48 

4.91

4.52 

3.91 

2.40

4.81

*

2.87

2.84 

2.04 

3.23 

4.58 

2.31 

2.70

Between class

1

1.93 

4.46 

3.89 

3.18 

2.52 

4.54

.79 

.47 

1.27 

1.45 

3.55 

2.75

2.11 

1.98 

1.10 

2.21 

1.94 

1.58

1.72 

1.00 

3.59 

2.99 

1.16 

1.50

2

*

9.30 

8.15 

6.45 

2.29

7.77

1.43 

1.25 

.80 

2.58 

7.22 

5.06

5.00 

3.72 

2.23

4.63

*

3.53

2.84 

2.39 

2.72 

2.84 

2.25 

2.97

F

1

26.35 

11.69 

12.82 

12.09 

5.28 

15.33

3.87 

4.51 

24.99 

16.10 

13.01 

13.09

9.19 

11.16 

9.32 

8.96 

12.66 

12.97

13.93 

10.82 

53.64 

23.40 

10.51 

13.60

2

*

55.04 

56.06 

52.51 

3.38 

51.70

19.84 

28.65 

9.15 

52.37 

55.02 

47.16

54.35 

40.13 

38.57

41.14

*

67.08

44.53 

61.04 

31.59 

17.05 

41.96 

53.52

Probability F

1

0.0001 

.0001 

.0001 

.0001 

.0001 

.0001

.0022 

.0006 

.0001 

.0001 

.0001 

.0001

.0001 

.0001 

.0001 

.0001 

.0001 

.0001

.0001 

.0001 

.0001 

.0001 

.0001 

.0001

2

*

0.0 

.0 

.0 

.0001 

.0

.0001 

.0001 

.0001 

.0 

.0 

.0

.0 

.0 

.0

.0

*

.0

.0 

.0 

.0001 

.0001 

.0 

.0

TABLE 13.—Mahalanobis' distances between classes for the first canonical discriminant analysis of the adult whole named specimens of the

species of Crassatella, excluding species categories with five or fewer specimens

Species

C. vadosa. ............................

C. gardnerae .........................

"C. hodgei" (and C. carolinensis) ..... 

C. tumidula ..........................

"C. halei" (=C. tumidula) ............

C. lintea ..............................

C. vadosa

2.2441

6.2539 

7.6723

7.5436

3.4546

C. gardnerae

_

5.9276 

7.2716

7.3763

4.0800

Mahalanobis' distanci

"C. hodgei" (and 

C. carolinensis)

_

6.9087

5.3784

5.5032

a1 between classes

C. tumidula

_

_

—

5.6798

7.4944

"C. kalei" 

(=C. tumidula)

_

_

—

_

7.8419

C. lintea

_

_

—

_

_

1 Mahalanobis' distances are a measure of the separation of the multivariate means of two classes (Davis, 1973, p. 450^151).

C. transversa and then by the group composed of C. 

vadosa, C. gardnerae, and C. subplana. C. sp. C has the 

smallest mean size for the majority of the linear distance 

measurements.

The Mahalanobis' distances (table 16) between classes 

show very low values for the group of Cretaceous 

Crassatella, C. vadosa, C. gardnerae, and C. lintea and 

C. sp. A as well (similar results were obtained in the 

analysis of the adult whole specimens, table 13). Note

that the category for C. sepulcollis, consisting of a single 

specimen being tested, fails the F test of the Mahalanobis' distances at the 5 percent level of significance when 

paired with "C. hodgei" (and C. carolinensis), C. monmouthensis, C. lintea, and C. sp. C. The null hypothesis 

of equal means between these pairs cannot be rejected, 

but, because the category C. sepulcollis is represented 

by only two specimens, failure of the F test is not 

surprising.
STATISTICAL ANALYSIS 27

CM

8

5-

3-

_ 

JD

5 1

CO

E -1 

o

c

CO 0

-5-

-7

-4-20246 

Canonical variable 1

8 10

EXPLANATION

Cretaceous species

D Crassatella gardnerae 

o"Crassatella hodgei" (and C. carolinensis) 

o Crassatella lintea 

0 Crassatella vadosa

Tertiary species

+ "Crassatella halei" (= C. tumidula) 

IE Crassatella tumidula

FIGURE 9.—Canonical variables 1 and 2 for the first canonical variate analysis of the species 

of Crassatella. Data for the analysis include adult whole specimens from named species 

categories only (excluding species categories with five or fewer specimens). Large symbols 

for the species categories represent the midpoints of those categories. Canonical variable 1 

accounts for 61.61 percent of the variance between species categories and has a canonical 

correlation of 0.90. Canonical variable 2 accounts for 14.70 percent of the variance between 

species categories and has a canonical correlation of 0.71. See table 14 for standardized 

canonical coefficients.

The plot of canonical variables 1 and 2 (fig. 11) illustrates the nearly complete overlap of the Cretaceous 

species Crassatella vadosa, C. gardnerae, C. lintea, and 

C. sp. A; even the group means of the four categories fall 

within the region of overlap. The Tertiary forms, C. 

tumidula and "C. halei" (= C. tumidula), are partially 

separated from the Cretaceous cluster of the C. vadosa

group; "C. halei" (= C. tumidula) falls almost completely 

within the area of C. tumidula on the plot, and the group 

means fall close together. "C. hodgei" (and C. carolinensis) and C. sp. C fall between and partially overlap the 

Cretaceous and the Tertiary groups on the plot. The 

remaining points are the individuals from the categories 

represented by five or fewer specimens. Both canonical
28 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 14. —Standardized canonical coefficients for the first canonical discriminant analysis of the 

adult whole named specimens of the species of Crassatella, excluding species categories with five 

or fewer specimens

[See table 2 for an explanation of the morphological variables. Canonical variables 1, 2, and 3 are plotted on figures

9 and 10]

Morphological variable Standardized canonical coefficient

Canonical variable 1 Canonical variable 2 Canonical variable 3

CONVEX ......................... -0.4800 1.7845 -0.4576

LENGTH.......................... -0.3832 4.3320 6.2305

POSTHT .......................... -8.4422 -9.0325 -4.5286

ANTHT........................... -5.2809 1.3375 .7294

ANTER........................... -0.3508 -0.0216 -0.2975

VENTRAL ....................... .1531 .9370 1.5889

POSTWID1........................ .3921 -0.0093 .7650

POSTWID2........................ 1.5642 1.3739 .8153

ANTWID1......................... -0.2364 .1103 -0.1385

ANTWID2......................... 1.6373 -0.6230 .0488

POSTDOR......................... 20.2462 -12.2669 -14.6049

ANTDOR ......................... -33.1656 23.8356 -5.1876

ANTVERHT...................... 1.1318 1.0139 -1.7285

POSTLAT......................... -3.4113 8.3909 10.9802

ANTLAT ......................... 17.8982 -11.0322 2.6541

HINGEPL......................... -4.0296 .6731 -4.0325

RESILANG....................... -0.0123 .5736 -0.2303

POSTLAT2........................ -5.8452 7.2593 5.3419

ANTLAT2......................... 22.3020 -16.4472 2.8537

POSTADHT....................... .1264 -1.0203 -0.5526

INTPOST ......................... .1582 .1763 1.0047

INTANT .......................... -1.2863 .6965 1.2254

POSADDST....................... -0.8206 -0.4561 -0.3214

ANTADDST....................... -0.5879 -0.6163 1.4400

TABLE 15.— Results of the classificatory discriminant analysis of the abundant adult whole named specimens of the species of Crassatella;

calibration data set tested against itself 

[Of the total number of specimens (239), 84.9 percent classify into the predicted species categories]

Original species category1 Total no. 

of specimens

Number of specimens (percentage of specimens) 

within the species category determined by analysis

C. vadosa C. gardnerae "C. hodgei" (and 

C. carolinensis) C. tumidula

"C. halei" 

(=C. tumidula) C. lintea

C. vadosa........................

C. gardnerae ....................

"C. hodgei" (and C. carolinensis) 

C. tumidula .....................

"C. halei" (=C. tumidula).......

C. lintea .........................

Total

145

53

8

14

6

13

239

134 (92.41) 

13 (24.53) 

0 (0) 

0 (0) 

0 (0) 

2 (15.38)

149

9 (6.21) 

38 (71.70)

1 (12.50)

0(0)

0(0) 

_2 (15.38)

50

1 (0.69)

I (1.89) 

6 (75.00)

1 (7.14)

2 (33.33) 

_0(0)

II

0(0)

0(0)

0(0) 

12 (85.71)

0(0) 

_0(0)

12

0(0) 

0(0) 

1 (12.50) 

1(7.14) 

4 (66.67) 

0(0)

1 (0.69)

I (1.89) 

0(0) 

0(0) 

0(0) 

_9 (69.23)

II

1 Species category assigned prior to analysis.

variables 1 and 2 seem to contribute to the partial 

separation of the Cretaceous and Tertiary clusters. 

Canonical variable 1 accounts for 48.05 percent of the 

variance and has a canonical correlation of 0.84; canonical 

variable 2 accounts for 22.59 percent of the variance and 

has a canonical correlation value of 0.72. The primary 

discriminating variables on canonical variable 1 are characters of the hinge and dorsal regions (POSTDOR, 

ANTDOR, POSTHT) (table 17). The plot of canonical

variables 2 and 3 (fig. 12) shows only two distinctive 

differences from the plot of canonical variables 1 and 2; 

C. transversa is isolated on the plot, and C. carolinana 

falls within the region of the plot defined by C. tumidula. 

Canonical variable 3 accounts for 9.91 percent of 

the variance between the groups and has a canonical 

correlation of 0.57; the variables that measure attributes of the dorsal margin (POSTDOR, ANTDOR, 

POSTLAT, ANTLAT2) (table 17) again contribute to
STATISTICAL ANALYSIS 29

4-

2- co

JD 

-Q 

03

03

> 0

03 

"cO

O

c

O 03 -2o

-4-

-6

-6 -4-20 2 

Canonical variable 2

EXPLANATION

Cretaceous species

a Crassatella gardnerae 

o"Crassatella hodgei" (and C. carolinensis) 

o Crassatella lintea 

H Crassatella vadosa

Tertiary species

+ "Crassatella halei" (= C. tumidula) 

E Crassatella tumidula

FIGURE 10.— Canonical variables 2 and 3 for the first canonical variate analysis of the 

species of Crassatella. Data for the analysis include adult whole specimens from named 

species categories only (excluding species categories with five or fewer specimens). 

Large symbols for the species categories represent the midpoints of those categories. 

Canonical variable 2 accounts for 14.70 percent of the variance between species 

categories and has a canonical correlation of 0.71. Canonical variable 3 accounts for 

12.20 percent of the variance between species categories and has a canonical correlation 

of 0.68. See table 14 for standardized canonical coefficients.

the discrimination of the groups, as they do on canonical 

variables 1 and 2.

The last step of the analysis was to classify the 

juveniles, broken specimens, internal molds, and 

unnamed specimens. The juveniles, broken specimens, 

and internal molds of all the species categories were 

tested against the calibration data set of the adult whole 

specimens (excluding the variables for shell width and

resilifer angle; table 2). An intermingling of Cretaceous 

and Tertiary specimens can be seen on table 18, but all of 

the Cretaceous forms that classify as Tertiary are either 

internal molds or damaged specimens. In contrast, many 

of the Tertiary forms classify as Cretaceous, and the 

majority of these are juveniles. A strong bias is introduced in this classification process by forcing Crassatella 

prora, C. monmouthensis, C. transversa, C. subplana,
30 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 16.—Mahalanobis' distances between classes for the second canonical discriminant analysis of all the specimens of the species of 

Crassatella, including juveniles, broken specimens, internal molds, unnamed specimens, and species categories with five or fewer 

specimens, measured for this analysis

Mahalanobis' distance1 between classes

Species

C. vadosa C. gardnerae r ' Ca Vnens^s) ' Prora ^. monmouthensis C. transversa C. sp. A C. tumidula

C. vadosa ................... 

C. gardnerae ................ 

"C. hodgei" (and C. 

carolinensis). 

C. prora .....................

C. monmouthensis ..........

C. transversa. ...............

C. sp. A .....................

C. tumidula .................

"C. halei" (=C. tumidula)...

C. gabbi .....................

C. sepulcollis. ...............

C. sp. C .....................

C. subplana .................

C. carolinana ...............

C. lintea. ....................

C. sp. B .....................

Species

C. gabbi .....................

C. sepulcollis ................

C. sp. C .....................

C. subplana .................

C. carolinana ...............

C. lintea. ....................

C. sp. B .....................

1.9305 

3.4722

7.9647 

4.4165

8.0443

1.4569

5.9406

5.8055

6.8753

3.6551

3.8867

7.3230

7.4486

2.5513

4.6523

"C. halei" 

(=C. tumidula)

9.1522

4.9632

5.6142

9.1523

8.7397

5.7025

5.3963

3.2328

7.8076 

4.1834

6.8900

1.4620

5.9602

6.2065

6.5786

3.8835

4.0081

7.9185

7.4730

3.1172

4.4632

C. gabbi

—

6.9743

7.1824

10.0712

10.8616

7.2253

7.4589

6.4822

2.8867

7.0203

2.8307

4.6777

4.7792

6.1239

3.0798

2.9857

7.7201

8.0443

3.5768

3.9604

C. sepulcollis

—

—

2.3241

8.1448

8.4403

3.0444

5.2331

5.4848

8.0550

7.8722

8.6545

8.2005

10.0480

7.2060

7.2103

11.0466

10.7847

7.9953

8.1558

C. sp. C

—

—

—

7.8491

9.4071

2.7290

5.4708

—

7.1475

3.9693

6.3767

6.5100

6.6685

3.7238

3.5324

8.7533

9.0966

4.4351

5.7214

C. subplana

—

—

—

—

8.4184

7.5618

8.6646

—

—

7.6407

9.5181

9.6258

8.6420

8.0120

8.2454

11.3130

9.4030

8.4654

8.5268

C. carolinana

—

—

—

—

—

7.9922

6.7387

—

—

—

5.7276

5.7786

6.4906

3.4231

3.3918

7.6424

7.7568

2.3080

4.4404

C. lintea

—

—

—

—

—

—

4.6710

—

—

—

—

4.0999

8.7731

4.9323

5.2485

7.9509

8.4179

5.5580

5.0930

C. sp. B

—

—

—

—

—

—

—

1 Mahalanobis' distances are a measure of the separation of the multivariate means of two classes (Davis, 1973, p. 450-451).

and C. carolinana (the poorly preserved or rare species 

categories), and C. sp. A (the unnamed species category) 

to classify as one of the species categories from the 

original calibration data set (the abundant adult whole 

named specimens).

The final discriminant analysis tested all specimens 

(except internal molds) against a calibration data set 

based on all specimens except unnamed forms and internal molds (table 19); the purpose was to establish how the 

unnamed specimens would classify into the existing 

categories. Categories containing only one specimen 

were not considered valid for the calibration data set by 

the requirements of the discriminant analysis program. 

The results show that the two unnamed categories of 

Cretaceous Crassatella, C. sp. A, and C. sp. B fall 

almost exclusively into the group composed of C. vadosa, 

C. gardnerae, and C. lintea; 1.46 percent are categorized 

as "C. hodgei" (and C. carolinensis). C. sp. C, in 

contrast, has at least some members that classify as 

almost every other species category; 56 percent, the 

largest percent, classify as C. lintea.

Discussion.—The results of the analysis of Crassatella species in the Upper Cretaceous and lower Tertiary reveal several interesting points. First, taxonomic 

splitting occurs within the Cretaceous and Tertiary 

individually but not across the boundary. Second, there 

is some separation between the Cretaceous and the 

Tertiary species groups that have good representation. 

These two points imply that a faunal change actually 

occurred at the boundary. Third, this data set may 

provide some clues to the nature of evolution and extinction among the Crassatella.

Statistically, there is no doubt that Crassatella 

vadosa, C. gardnerae, C. lintea, C. sp. A, and C. sp. B 

are all members of the same species. Prior to the 

statistical analysis, a cursory examination of the specimens indicated that this was indeed the case (compare pi. 

1, figs. 3, 4, 10, 12; pi. 8, figs. 4, 6; pi. 9, figs. 1, 9). C. 

lintea is in fact the juvenile of C. vadosa (discussed in 

detail in the "Systematic Paleontology" section). Many 

lines of statistical evidence support this synonymy: (1) 

the proximity of the univariate means, even if the
STATISTICAL ANALYSIS 31

10

CM

25 4'

.CO 

CO

± 2

CO

o

I oCO

O

-2H

-4-

-6"

-8 -6-4-2024 

Canonical variable 1

8

Cretaceous species

a Crassatella carolinana

D Crassatella gardnerae

o "Crassatella hodgei" (and C. carolinensis)

O Crassatella lintea

® Crassatella monmouthensis

H Crassatella prora

© Crassatella subplana

i Crassatella transversa

EXPLANATION

B Crassatella vadosa 

D Crassatella sp. A 

i Crassatella sp. B 

	Tertiary species 

41 Crassatella gabbi 

+ "Crassatella halei" (= C. tumidula) 

i> Crassatella sepulcollis 

Kl Crassatella tumidula 

x Crassatella sp. C

FIGURE 11.—Canonical variables 1 and 2 for the second canonical variate analysis of the 

species of Crassatella. Data for the analysis include all adults, juveniles, broken specimens, 

internal molds, unnamed specimens, and species categories with five or fewer specimens. 

Large symbols for the species categories represent the midpoints of those categories. 

Species categories represented on the plots by a single digit number contain only one or two 

specimens. Canonical variable 1 accounts for 48.05 percent of the variance between species 

categories and has a canonical correlation of 0.84. Canonical variable 2 accounts for 22.59 

percent of the variance between species categories and has a canonical correlation of 0.72. 

See table 17 for standardized canonical coefficients.
32 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 17.— Standardized canonical coefficients for the second canonical discriminant analysis of 

all the specimens of the species of Crassatella, including juveniles, broken specimens, internal 

molds, unnamed specimens, and species categories with five or fewer specimens, measured for this 

analysis

[See table 2 for an explanation of the morphological variables. Canonical variables 1, 2, and 3 are plotted on figures

11 and 12]

Morphological variable

Standardized canonical coefficient

Canonical variable 1 Canonical variable 2 Canonical variable 3

LENGTH.......................... 1.7503 -2.6327 -4.4273

POSTHT .......................... 10.2151 -12.5081 -5.3438

ANTHT........................... 3.0475 -3.0141 -7.6214

ANTER........................... .1173 -0.1927 -0.2621

VENTRAL........................ .3287 2.6223 2.0052

POSTWID1........................ .1658 .4616 .4428

POSTWID2........................ -1.7893 2.2949 .6471

ANTWID1......................... .2125 .0257 -0.1808

ANTWID2......................... -0.8272 1.6498 2.8317

POSTDOR......................... -20.8921 7.4673 -14.5584

ANTDOR.......................... 11.0329 -11.4191 -12.0118

ANTVERHT...................... .0388 -0.2743 -2.2727

POSTLAT......................... 3.5808 2.0018 16.4662

ANTLAT.......................... -5.9259 7.7648 9.2925

HINGEPL......................... 1.2267 -1.3658 -5.9064

POSTLAT2........................ 6.5912 1.9237 6.9561

ANTLAT2......................... -7.6462 9.3645 10.4175

POSTADHT....................... -0.8584 -1.5754 1.9501

INTPOST ......................... -0.1648 .1802 .2937

INTANT.......................... .8757 .1320 -0.2924

POSADDST....................... .7728 -1.2541 .8585

ANTADDST....................... -0.2562 .7090 2.6425

TABLE 18.—Results of the classificatory discriminant analysis of the juveniles, broken specimens, and internal molds of the species of 

Crassatella, tested against the calibration data set of the adult whole named specimens

Original species category1 Total no. 

of specimens

Number of specimens (percentage of specimens) 

within the species category determined by analysis

C. vadosa C. gardnerae "C. hodgei" (and 

C. carolinensis) C. tumidula

"C. halei" 

(=C. tumidula) C. lintea

C. vadosa. .......................

C. gardnerae ....................

"C. hodgei" (and C. carolinensis) 

C. prora .........................

C. monmouthensis. ..............

C. transversa. 

C. sp. A......

C. tumidula .. 

C. sp. C......

C. subplana'..

C. carolinana. 

C. hodgei ..... 

C. lintea ......

Total

86

3

4

1

5

2

33

13

58

1

1

1

7

215

39 (45.35)

I (33.33)

0(0) 

0(0) 

0(0)

0(0)

II (33.33) 

0(0) 

0(0) 

1 (100.00)

1 (100.00) 

0(0) 

_0(0)

53

24 (27.91)

1 (33.33)

2 (50.00)

0(0)

0(0)

0(0)

6(18.18)

0(0)

0(0)

0(0)

0(0)

1 (100.00) 

_0(0)

34

11 (12.79) 

0(0) 

2 (50.00) 

1 (100.00) 

5 (100.00)

2 (100.00) 

7 (21.21) 

4 (30.77) 

27 (46.55) 

0(0)

0(0) 

0(0) 

__3 (42.86)

62

1 (1.16)

0(0)

0(0)

0(0)

0(0)

0(0) 

1 (3.03) 

6(46.15) 

0(0) 

0(0)

0(0) 

0(0) 

0(0)

3 (3.49)

0(0)

0(0)

0(0)

0(0)

0(0) 

1 (3.03)

1 (7.69)

2 (3.45) 

0(0)

0(0) 

0(0) 

0(0)

8 (9.30) 

1 (33.33) 

0(0) 

0(0) 

0(0)

0(0) 

7 (21.21) 

2 (15.38) 

29 (50.00) 

0(0)

0(0) 

0(0) 

_4(57.14)

51

1 Species category assigned prior to analysis.
STATISTICAL ANALYSIS

CO

.0 

.Q

cd

>

"cc 

"c g

o

c

CO

O

4- 

2- 

0-

-2-

-4-

-6-

-8

-4-20246 

Canonical variable 2

8 10

Cretaceous species

n Crassatella carolinana

D Crassatella gardnerae

o "Crassatella hodgei" (and C. carolinensis)

o Crassatella lintea

® Crassatella monmouthensis

1 Crassatella prora

i Crassatella subplana

3 Crassatella transversa

EXPLANATION

H Crassatella vadosa 

D Crassatella sp. A 

I Crassatella sp. B 

Tertiary species 

4 Crassatella gabbi 

+ "Crassatella halei" (= C. tumidula) 

i> Crassatella sepulcollis 

El Crassatella tumidula 

x Crassatella sp. C

FIGURE 12.—Canonical variables 2 and 3 for the second canonical variate analysis of the 

species of Crassatella. Data for the analysis include all adults, juveniles, broken specimens, 

internal molds, unnamed specimens, and species categories with five or fewer specimens. 

Large symbols for the species categories represent the midpoints of those categories. 

Species categories represented on the plots by a single digit number contain only one or two 

specimens. Canonical variable 2 accounts for 22.59 percent of the variance between species 

categories and has a canonical correlation of 0.72. Canonical variable 3 accounts for 9.91 

percent of the variance between species categories and has a canonical correlation of 0.57. 

See table 17 for standardized canonical coefficients.
34 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 19.—Results of the classificatory discriminant analysis of all the specimens of the species of Crassatella, except internal molds, measured 

for this analysis, tested against the calibration data set of all specimens of Crassatella measured for the analysis, except unnamed specimens 

and internal molds

Original species Total 

«*W spedml

"C. hodgei" (and 

C. carolinensis). 

C. sp. A ..........

C. tumidula. ......

"C. halei" (and 

C. tumidula).

C. sepulcollis. .....

C. sp. C ..........

C. subplana. ......

C. carolinana .....

C. hodgei .........

C. sp. B ..........

Total .........

188 

56 

12

206

27

6

1 

2 

125 

1

2 

2 

20 

2

650

Number of specimens (percentage of specimens) within the species category determined by analysis

ls C. vadosa

176 (93.62) 

19 (33.93) 

0(0)

137 (66.50) 

0(0)

0(0)

0(0) 

0(0) 

6 (4.80) 

1 (100.00)

0(0) 

0(0) 

2 (10.00) 

1 (50.00)

342

C. gardnerae

10 (5.32) 

35 (62.50) 

0(0)

50 (24.27) 

0(0)

0(0)

1 (100.00) 

0(0) 

4 (3.20) 

0(0)

0(0) 

0(0) 

0(0) 

_0(0)

100

"C. hodgei" 

(and C. 

carolinensis)

0(0) 

0(0) 

12 (100.00)

3 (1.46) 

1 (3.70)

1 (16.67)

0(0) 

0(0) 

14 (11.20) 

0(0)

0(0) 

0(0) 

1 (5.00) 

_0(0)

32

C. tumidula

0(0) 

0(0) 

0(0)

0(0) 

23 (85.19)

1 (16.67)

0(0) 

0(0) 

9 (7.20) 

0(0)

0(0) 

0(0) 

0(0) 

_0(0)

33

"C. halei" 

(=C. 

tumidula)

0(0) 

0(0) 

0(0)

0(0) 

2 (7.41)

4 (66.67)

0(0) 

0(0) 

4 (3.20) 

0(0)

0(0) 

0(0) 

0(0) 

_0(0)

10

C. sepulcollis

0 

0 

0

0 

0

0

0 

1 

15 

0

0 

0 

0 

0

16

(0) 

(0) 

(0)

(0) 

(0)

(0)

(0) 

(50.00) 

(12.00) 

(0)

(0) 

(0) 

(0) 

(0)

C. carolinana

0(0) 

0(0) 

0(0)

0(0) 

1 (3.70)

0(0)

0(0) 

0(0) 

0(0) 

0(0)

2 (100.00) 

0(0) 

0(0) 

_0(0)

3

C. hodgei

0(0) 

0(0) 

0(0)

0(0) 

0(0)

0(0)

0(0) 

0(0) 

3 (2.40) 

0(0)

0(0) 

2 (100.00) 

0(0) 

0(0)

5

C. lintea

2 (1.06) 

2 (3.57) 

0(0)

16 (7.77) 

0(0)

0(0)

0(0) 

1 (50.00) 

70 (56.00) 

0(0)

0(0) 

0(0) 

17 (85.00) 

1 (50.00)

109

1 Species category assigned prior to analysis.

juveniles, broken specimens, and internal molds are 

included (table 11), indicates similarity along each variable, (2) the low values for the Mahalanobis' distances 

between the classes (tables 13, 16) show the lack of 

multivariate separation between the species categories, 

(3) the nearly complete overlap of the areas for each 

species category on the plots of canonical variables 1 and 

2 (figs. 9, 11) is indicative of a single species, especially 

since canonical discriminant analysis tends to maximize 

differences between groups, (4) the occurrence of the 

group means in the area of overlap (especially on fig. 11) 

illustrates the similarity of the populations as a whole, 

and (5) the classification results (tables 15, 18, 19) 

generally are low for C. gardnerae, C. lintea, and 

C. sp. A but show that the majority of the misclassified 

species fall within one of the species categories of this 

group. The low classification values for C. gardnerae are 

especially surprising considering that all specimens come 

from a single locality, which usually causes higher classification values than expected; this is further evidence 

that C. gardnerae is a junior synonym of C. vadosa.

The results from the other Cretaceous Crassatella 

species categories are more difficult to interpret, primarily because of the small numbers of individuals included 

in these categories. "C. hodgei" (and C. carolinensis) is 

of particular interest because it occupies a position on the 

plots (figs. 9-12) midway between the other Cretaceous 

species and the Tertiary species. In addition, C. tumidula and "C. hodgei" intermix in the classification results 

(tables 15, 18,19). These patterns indicate a morphologic

similarity of "C. hodgei" (and C. carolinensis) to the 

Tertiary species categories and may imply an evolutionary link that cannot be explained readily. The misassigned specimens9 probably did not contribute to this 

unexpected pattern because superficially the C. hodgei 

measured appear to be very similar to the C. carolinensis measured (compare pi. 4, fig. 13 and pi. 5, fig. 12 to pi. 

5, figs. 13, 15-20). The diagnostic characters of the two 

species are discussed in the "Systematic Paleontology" 

section.

Twelve of the 14 individuals from both species categorized as "C. hodgei" come from a single locality, Blufftown, Ga. (loc. 4). Their identification as C. hodgei was 

based on Stephenson's (1923, p. 273) and Cooke's (1943, 

p. 22) citations of the species at that locality, and in 

addition, the specimens seem consistent with the type 

description for C. hodgei. The other two specimens of C. 

hodgei are from Stephenson's (1923, p. 272) type locality 

at Snow Hill, N.C. (loc. 8). Given the low stratigraphic 

position of the Blufftown specimens, it is not surprising 

that they are isolated partially from the C. vadosa group 

on the plots (figs. 9, 10). The remainder of the Cretaceous species are not present in statistically significant 

numbers to draw any conclusions about their relationships to the well-defined species categories.

The statistical analysis of the Tertiary forms indicates 

that Crassatella tumidula and "C. halei" are synonymous, which is the expected result considering that all 

the specimens in the category "C. halei" are in fact 

C. tumidula. 9 The individuals assigned to C. sp. C
STATISTICAL ANALYSIS 35

demonstrate a fair degree of overlap with the Cretaceous 

forms on figures 11 and 12. This overlap can be attributed to the smaller than average size of C. sp. C (table 

11); 45 percent of the specimens assigned to this category 

are juveniles. Qualitative evaluation proved that the 

majority of the specimens (117 of 125) assigned to this 

category belong to the species C. sepulcollis (herein = C. 

aquiana Clark). The juveniles of this species have a 

general outline similar to the juveniles of C. vadosa and 

the measured specimens of C. hodgei and C. carolinensis 

(compare pi. 3, figs. 2, 5 to pi. 5, figs. 6-10); this 

similarity probably causes the overlap seen on the 

plots. The categories of C. gabbi and C. sepulcollis are 

not represented by statistically significant numbers of 

individuals.

A separation of the Tertiary and Cretaceous forms 

does exist, as an examination of the ranked Mahalanobis' 

distances (table 13) shows and as the partial separation 

along canonical variables 1 and 2 on the plots illustrates 

(figs. 9, 11). The classification results exhibit a curious 

pattern; in general, Cretaceous forms classify as other 

Cretaceous categories when they do not classify correctly. The Tertiary species categories, however, classify as either Cretaceous or Tertiary forms. Specimens of 

Crassatella tumidula and specimens of "C. halei" (and 

C. tumidula), each come from a small geographic area 

(app. 4) and thus would be expected to have high 

classification results (>90 percent) and occupy limited 

areas on the plots. The plots of the individuals on the 

canonical variables, however, reveal a wide scatter. For 

comparison, examine the areas of the plot covered by C. 

vadosa versus C. tumidula (fig. 11); the area for C. 

vadosa is the result of plotting 231 individual specimens 

from 13 localities, whereas the area for C. tumidula is a 

plot of only 27 specimens from 4 localities. Apparently, a 

large degree of intragroup diversity exists in the Tertiary forms, especially in C. tumidula; this diversity may 

explain the low classification results (<90 percent).

Finally, in a simple examination of the statistical 

results presented here, several ideas emerge concerning 

the nature of evolution and extinction at the CretaceousTertiary boundary for the genus Crassatella. The members of the genus were fairly abundant but had low 

diversity just below the Cretaceous-Tertiary boundary 

in the upper Maastrichtian beds. In the lower Tertiary, 

abundance was very low, but intragroup diversity 

appears to have been high. These Tertiary individuals 

seem to bear more resemblance to their Campanian 

ancestors than to the adult Maastrichtian Crassatella, 

but they do show a degree of morphological overlap with 

the juveniles of the Maastrichtian group. Perhaps this is 

a case of different environmental influences acting upon 

the adults of the Cretaceous and Tertiary groups, or

perhaps the Tertiary forms are exhibiting neoteny (see 

Raup and Stanley, 1978, p. 353 for explanation).

SPECIES OF BATHYTORMUS

Only two species of Bathytormus Stewart, 1930 have 

been identified within the geographic and stratigraphic 

constraints of this study: (1) B. pteropsis (Conrad), 1860, 

a Cretaceous species, and (2) B. alaeformis (Conrad), 

1830, a Tertiary species. The purpose of this analysis is 

to determine if the Upper Cretaceous form is continuous 

across the Cretaceous-Tertiary boundary and to determine if numerous specimens from localities that have no 

published record of Bathytormus occurrence are synonymous with the established species. The null hypothesis5 

is that no statistically significant differences exist 

between the two species categories and the two categories of unnamed specimens (Bathytormus sp.). Failure to 

reject the null hypothesis for any pair of species categories would indicate the existence of synonyms. The alternative hypothesis is that the species names are valid and 

that the unnamed specimens represent new species.

Analysis. — The first segment of the analysis tested 

111 adult whole specimens divided between the two 

named species: (1) Bathytormus pteropsis (13 specimens) 

and (2) B. alaeformis (98 specimens). The individuals of 

B. pteropsis included in this analysis come from the Gulf 

Coast region exclusively, whereas the B. alaeformis 

specimens are limited to the Mid-Atlantic region; a total 

of 28 localities were examined (app. 5). The Bathytormus 

species were discriminated on the basis of 15 morphologic 

measurements (table 2).

An examination of the univariate class means (table 20, 

first analysis) reveals some differences in shape between 

Bathytormus pteropsis and B. alaeformis. The variables 

measuring the height and shape of the anterior margin 

(ANTWID, ANTWID1, ANTLAT, ANTADDST, see 

table 2 for an explanation of all variables) show very 

similar class means between the two groups, so similar in 

fact that they fail the F test for equality of variance 

(tables 20, 21, first analysis). The variables measuring 

length and the shape of the posterior margin, however, 

are considerably different. No significance should be 

placed on the proximity of the univariate means of B. 

alaeformis to the grand mean of both classes combined; 

the similarity is the result of a disproportionate number 

of B. alaeformis included in the analysis. Despite the 

differences seen in the univariate class means, all of the 

variables show greater within-class variation than 

between-class variation as measured by standard deviation (table 21, first analysis). Nevertheless, the univariate statistics show that some separation of the two 

classes is indicated for the multivariate analysis.
36 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 20. — Class means and grand means for species o/Bathytormus on each variable used in both canonical discriminant analyses

[See table 2 for an explanation of the morphological variables. 1, the means from the first canonical discriminant analysis, including adult whole named specimens only; 

2, the means from the second canonical discriminant analysis of all specimens, including juveniles, broken specimens, and unnamed specimens; —, species excluded 

from the first analysis]

Class mean

Morphological variable

LENGTH. .............

ANTWID..............

ANTWID1. ............

POSTDOR.............

ANTDOR. .............

POSVERHT. ..........

POSTLAT.............

ANTLAT..............

HINGEPL. ............

RESILANG ...........

ANTLAT2.............

MANTCAV. ...........

INTPOST .............

POSADDST ...........

ANTADDST. ..........

B.

1

28.37 

12.07 

4.42 

20.54

14.51

10.65 

10.36

8.55 

16.08 

19.65

6.34

18.43 

39.40 

4.62 

6.86

pteropsis

2

27.23 

11.66

4.18 

19.75 

13.92

10.38 

9.94 

8.19 

15.37 

19.39

6.08 

17.52 

39.64 

4.55 

6.70

B. sp. A

1 2

- 25.58 

- 10.12 

- 3.73 

- 18.27 

- 13.03

- 10.16 

- 9.35 

- 7.31 

- 14.21

- 21.73

- 5.95 

- 16.70 

- 39.97

- 4.87 

- 5.85

B. alaeformis

1

37.41

12.77 

4.97 

27.65

17.44

13.08 

16.79 

9.71 

23.41 

21.32

8.16 

25.84 

33.69 

7.03 

6.86

2

37.59

12.83 

5.18 

27.61 

17.76

12.96 

16.98 

9.92 

23.81 

21.11

8.31 

26.22 

33.94 

6.92 

6.79

B. sp. B

1 2

- 37.01

- 12.76 

- 5.14

- 27.27 

- 17.73

- 12.73 

- 17.48 

- 9.90 

- 24.19 

- 20.58

- 8.29 

- 26.14 

- 34.27 

- 6.96 

- 6.86

Grand mean

1

36.35 

12.69 

4.91 

26.81

17.10

12.79 

16.04 

9.57 

22.56 

21.12

7.95 

24.97 

34.36 

6.75 

6.86

2

35.30 

12.40 

4.92 

25.86 

16.90

12.40 

15.60 

9.47 

22.07 

21.00

7.86 

24.42 

35.13 

6.50 

6.67

TABLE 21. — Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the species of

Bathytormus on each variable used in the analyses

[See table 2 for an explanation of the morphological variables. Total, total sample standard deviations of the data from all species categories combined. Within class, 

pooled within-class standard deviations for the species categories. Between class, between-class standard deviations for the species categories. 1, data from the 

first canonical discriminant analysis, including adult whole named specimens only; 2, data from the second canonical discriminant analysis of all specimens, 

including juveniles, broken specimens, and unnamed specimens]

Standard deviation

Morphological variable

LENGTH. ..........

ANTWID...........

ANTWID1. .........

POSTDOR...........

ANTDOR. ..........

POSVERHT. .......

POSTLAT..........

ANTLAT...........

HINGEPL. .........

RESILANG ........

ANTLAT2..........

MANTCAV. ........

INTPOST ..........

POSADDST ........

ANTADDST. .......

Total

1

8.51

3.20

1.54

6.12

4.49

3.03

4.11

2.37

5.43

3.09

2.39

6.19

3.20

1.83

1 88

2

9.58 

3.49 

1.76 

6.93 

4.93

3.06

4.77 

2.70 

6.40 

3.48

2.52

7.10 

3.64 

1.85 

1.97

Within class

1

8.03 

3.20 

1.53 

5.70 

4.40

2.94 

3.56 

2.35 

4.91 

3.06

2.32 

5.73 

2.62 

1.66 

1.89

2

8.51 

3.39 

1.69 

6.02 

4.64

2.88 

3.75 

2.56 

5.28 

3.47

2.36 

6.13 

2.82 

1.65 

1.96

Between class

1

4.11 

.32 

.25 

3.23 

1.33

1.10 

2.93 

.52 

3.33 

.76

.83 

3.37 

2.59 

1.10 

.00

2

5.20 

1.05 

.60 

4.02 

2.02

1.23 

3.43 

1.07 

4.24 

.61

1.06 

4.22

2.68 

1.00 

.36

P

1

14.53 

.56 

1.50

17.83 

5.09

7.78 

37.42 

2.74

25.58 

3.40

7.10 

19.16 

54.24 

24.21 

.00

2

20.17 

5.20 

6.70 

24.09

10.27

9.85 

45.33 

9.40 

34.81 

1.65

10.81 

25.61 

49.04 

19.73 

1.82

Probability P

1

0.0002 

.4568 

.2235 

.0001 

.0261

.0062 

.0001 

.1005 

.0001 

.0679

.0089 

.0001 

.0001 

.0001 

.9960

2

0.0001 

.0017 

.0002 

.0001 

.0001

.0001 

.0001 

.0001 

.0001

.1786

.0001 

.0001 

.0001 

.0001

.1448

The division of the data into just two species classes 

requires that only one Mahalanobis' distance and only 

one canonical variable be calculated. The value of 5.23 for 

the Mahalanobis' distance passes the F test at the 5 

percent level of significance, so the null hypothesis of 

equal means is rejected. The histogram (fig. 13) shows 

the frequency distribution of each category along canonical variable 1, which accounts for 100 percent of the 

variance and has a canonical correlation of 0.86. The

means of the two species categories are clearly separated 

on the histogram, and the only overlap is from a single 

specimen of Bathytormus pteropsis. An examination of 

the specimen does not reveal an explanation for the 

overlap. The standardized canonical coefficients (table 

22) reflect the role of elongation of B. alaeformis in 

separating the two species categories. All of the variables that contribute significantly to the discrimination of 

the two classes are measurements of length: (1) the
STATISTICAL ANALYSIS 37

40

o" 30 

CD

|20

uZ 

10

t$$$$| B. pteropsis 

H B. alaeformis

'

^^^ ~

• ^ pfH ^

1.2 2.4 3.6 4.8 6.0 

Canonical variable 1

40 

30

20

10

TABLE 23.— Results of the classificatory discriminant analysis of the 

adult whole named specimens of the species of Bathytormus; 

calibration data set tested against itself

[Of the total number of specimens (111), 99.1 percent classify into the predicted 

species categories]

Number of specimens 

Original species Total (percentage of specimens) within the 

patpowv1 no: species category determined by analysis

B. pteropsis B. alaeformis

B. pteropsis. ..... 13 12 (92.31) 1 (7.69)

B. alaeformis.... 98 0(0) 98(100.00) 

Total.......... Ill 12 99

-1.2

FIGURE 13. —Canonical variable 1 for the first canonical variate analysis 

of the species of Bathytormus. The number of individual specimens 

occurring along the canonical variable is recorded on the y axis. Data 

for the analysis include adult whole specimens from the two named 

species categories only: Bathytormus pteropsis and Bathytormm 

alaeformis. The P marks the midpoint for the Bathytormus pteropsis 

category, and the A marks the midpoint for the Bathytormus alaeformis category. Canonical variable 1 accounts for 100 percent of the 

variance between species categories and has a canonical correlation of 

0.86. See table 22 for standardized canonical coefficients.

TABLE 22.—Standardized canonical coefficients for the first 

canonical discriminant analysis of the adult whole named specimens 

of the species of Bathytormus

[See table 2 for an explanation of the morphological variables. Canonical variable 

1 is plotted on figure 13]

LENGTH.................

ANTWID .................

ANTWID1................

POSTDOR ................

ANTDOR.................

POSVERHT..............

POSTLAT ................

ANTLAT .................

HINGEPL................

RESILANG ..............

ANTL AT2 ................

MANTCAV...............

INTPOST.................

POSADDST ..............

ANTADDST..............

Standardized canonical coefficient

Canonical variable 1

........ 15.1993

........ -0.2318

........ -0.1643

........ -10.2462

........ -33.3512

........ .4992

........ 12.5984

........ 17.7743

........ -18.7929

........ .0150

........ 13.1903

........ 3.8122

........ 2.1238

........ -1.3739

........ 1.6371

length of the anterior and posterior dorsal margins 

(ANTDOR, POSTDOR), (2) the width of the hinge plate 

(HINGEPL), (3) the length of the anterior and posterior 

lateral ridges (ANTLAT, POSTLAT), (4) the length of 

the shell (LENGTH), and (5) the distance between the 

end of the anterior lateral ridges and the anterior margin 

(ANTLAT2).

A discriminant analysis of the adult whole specimens of 

Bathytormus produced the classification results seen in 

table 23. A total of 99 percent of all the specimens classify 

correctly7; again the only incorrectly classified specimen 

was a single B. pteropsis.

1 Species category assigned prior to analysis.

TABLE 2.4.—Mahalanobis' distances between classes for the second 

canonical discriminant analysis of all the specimens of the species of 

Bathytormus, including juveniles, broken specimens, and 

unnamed specimens measured for this analysis

Species

Mahalanobis' distance1 between classes 

B. pteropsis B. sp. A B. alaeformis B. sp. B

B. pteropsis.. 

B. sp. A ..... 

B. alaeformis 

B. sp. B......

1.6712 -

4.6454 4.7555

4.9681 4.9921 0.9161

1 Mahalanobis' distances are a measure of the separation of the multivariate 

means of two classes (Davis, 1973, p. 450-451).

A second canonical discriminant analysis was conducted to include the unnamed specimens (Bathytormus 

sp.), the juveniles, and the broken specimens, in addition 

to the adult whole specimens. For this portion of the 

analysis, 216 specimens from 4 species categories were 

tested: (1) B. pteropsis (15 specimens), (2) B. sp. A (27 

specimens), (3) B. alaeformis (148 specimens); and (4) B. 

sp. B (26 specimens). These specimens were distributed 

over 42 localities (app. 6), and the inclusion of B. sp. A 

brings a few Mid-Atlantic specimens from the Cretaceous into the analysis.

An examination of the univariate class means indicates 

a similarity of Bathytormus pteropsis and B. sp. A on 

most variables (table 20, second analysis); B. alaeformis 

and B. sp. B have nearly identical class means on all 

variables. The standard deviations again show higher 

values for within-class variation than for between-class 

variation (table 21, second analysis). The results of the 

univariate analyses indicate that B. pteropsis and B. sp. 

A will overlap at least partially on the plots and that B. 

alaeformis and B. sp. B will have class means in proximity to each other but that there will be at least some 

separation between the Tertiary and Cretaceous forms.

An examination of the Mahalanobis' distances (table 

24) supports the univariate conclusions. The F test of the 

Mahalanobis' distances between Bathytormus alaeformis and B. sp. B, and between B. pteropsis and B. sp. 

A, fails at the 5 percent level of significance, so the null
CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

3-

CM

•2 1

.0 I

CO

O

c -1

O

c: CC 

O

-3-

-5

-6 -4 -2 0

Canonical variable 1

EXPLANATION

Cretaceous species

A Bathytormus pteropsis 

A Bathytormus sp. A

Tertiary species

x Bathytormus alaeformis 

H Bathytormus sp. B

FIGURE 14. —Canonical variables 1 and 2 for the second canonical variate analysis of the 

species of Bathytormus. Data for the analysis include all adults, juveniles, broken 

specimens, and unnamed specimens. Large symbols for the species categories represent 

the midpoints of those categories. Canonical variable 1 accounts for 94.39 percent of the 

variance between species categories and has a canonical correlation of 0.88. Canonical 

variable 2 accounts for 3.81 percent of the variance between species categories and has 

a canonical correlation of 0.35. See table 25 for standardized canonical coefficients.

hypothesis of equal means between the two pairs of 

species categories cannot be rejected. The species are 

maintained as discrete categories for the remainder of 

the analysis, however, to test their relationship further. 

The plot of canonical variables 1 and 2 (fig. 14) reinforces the initial conclusions. Bathytormus alaeformis 

and B. sp. B overlap, as do B. pteropsis and B. sp. A, and 

the group means of the two pairs fall within the region 

of overlap for the pairs. The overlap on the plots (fig. 

14) between the Cretaceous and Tertiary groups of

Bathytormus is the result of three specimens; one B. 

alaeformis is broken, one B. pteropsis is the same 

specimen responsible for the overlap seen on figure 13, 

and one specimen is an unremarkable B. sp. A. The 

separation of the Cretaceous from the Tertiary forms 

occurs along canonical variable 1, which accounts for 

94.39 percent of the variance between groups and has a 

canonical correlation of 0.88; the discriminating variables 

along canonical variable 1 (table 25) are length, anterior 

dorsal, anterior lateral, and hinge plate (LENGTH,
STATISTICAL ANALYSIS 39

TABLE 25. — Standardized canonical coefficients for the second 

canonical discriminant analysis of all the specimens of the species of 

Bathytormus, including juveniles, broken specimens, and 

unnamed specimens, measured for the analysis

[See table 2 for an explanation of the morphological variables. Canonical variables 

1 and 2 are plotted on figure 14]

LENGTH. ............

ANTWID.............

ANTWID1. ...........

POSTDOR............

ANTDOR. ............

POSVERHT. .........

POSTLAT ............

ANTLAT.............

HINGEPL. ...........

RESILANG ..........

ANTLAT2. ...........

MANTCAV. ..........

INTPOST ............

POSADDST ..........

ANTADDST. .........

Standardized canonical coefficient

Canonical variable 1

-10.9961

.6148

-0.2231

7.0707

20.6716

.1440

-7.1878

-11.5272

13.2149

-0.3030

-7.3407

-3.2927

-1.6815

.6263

-1.5308

Canonical variable 2

9.2503

-3.7702

1.5982

-11.0292

.5176

3.2492

5.1676

-3.7458

.5377

.4489

-3.2960

.6239

1.3196

-1.0838

2.1979

TABLE 26.—Results of the classificatory discriminant analysis of the 

juveniles, broken specimens, and unnamed specimens of the species 

of Bathytormus, tested against the calibration data set of the adult 

whole named specimens

Original species category1

B. pteropsis. .........

B. sp. A .............

B. alaeformis ........

B. sp. B .............

Total ..............

Total 

no. of 

specimens

2

11

50

13

76

Number of specimens 

(percentage of specimens) 

within the species category 

determined by analysis

B. pteropsis

2 (100.00) 

10 (90.91) 

1 (2.00) 

1 (7.69)

14

B. alaeformis

0(0) 

1 (9.09) 

49 (98.00) 

12 (93.31)

62

1 Species category assigned prior to analysis.

ANTDOR, ANTLAT, HINGEPL), all measurements of 

length as in the first analysis. Canonical variable 2 

accounts for only 3.81 percent of the variance between 

groups and has a canonical correlation of 0.35. Along this 

axis, the length of the valve (LENGTH), and the length 

of the posterior dorsal regions (POSTDOR) contribute to 

the discrimination of the specimens.

A discriminant analysis of the juvenile, broken, and 

unnamed specimens was done using the calibration data 

set of the adult whole specimens (table 26). Ninety-six 

percent of the specimens classify as expected; the majority of Bathytormus sp. A classify as B. pteropsis, and the 

majority of B. sp. B classify as B. alaeformis. Of the 

three specimens that do not classify as expected, two are 

broken and one is a juvenile. A final discriminant analysis 

tested all specimens of Bathytormus against a calibration 

data set based on all specimens of B. pteropsis and B.

TABLE 27.—Results of the classificatory discriminant analysis of all 

the specimens of the species of Bathytormus, including juveniles, 

broken specimens, and unnamed specimens, measured for this 

analysis, tested against the calibration data set of all the named 

specimens of Bathytormus measured for the analysis, including 

juveniles and broken specimens

Original species category1

Total

no. of

specimens

Number of specimens

(percentage of specimens)

within the species category

determined by analysis

B. pteropsis B. alaeformis

B. pteropsis. .........

B. sp. A .............

B. alaeformis ........

B. SD. B .............

15

27

148

26

14 (93.33)

24 (88.89)

1 (0.68)

1 (3.85)

1 (6.67)

3 (11.11)

147 (99.32)

25 (96.15)

Total 216 40 176

1 Species category assigned prior to analysis.

alaeformis to determine how the unnamed specimens 

would classify (table 27). Only three specimens of B. sp. 

A classify as the Tertiary B. alaeformis; two of these 

specimens are broken, and the third is one of the three 

specimens responsible for the overlap seen on figure 14. 

The single specimen of B. sp. B, which classifies as the 

Cretaceous B. pteropsis, is a juvenile.

Discussion. — The results of the analysis of the species 

of Bathytormus illustrate that two species existed within 

the stratigraphic and geographic ranges of this study, 

the Upper Cretaceous B. pteropsis and the lower Tertiary B. alaeformis. The geographic and stratigraphic 

ranges of B. pteropsis and B. alaeformis are expanded 

by the inclusion of the unnamed specimens into the 

established species categories. The patterns seen in the 

genus Bathytormus differ substantially from those 

exhibited by Crassatella. The taxonomic splitting demonstrated in the analysis of Crassatella has not occurred 

with Bathytormus. In addition, the statistical separation 

between the Cretaceous and Tertiary Bathytormus species is more clear-cut than that illustrated by the Crassatella species.

An examination of the specimens assigned to Bathytormus sp. A, prior to the analysis, indicated that they 

were members of B. pteropsis (compare pi. 17, figs. 3^1 

to pi. 17, figs. 12, 17, juvenile portion of shell); and, 

likewise, that specimens assigned to B. sp. B were 

members of B. alaeformis', these observations were 

confirmed by the statistical tests. Several lines of statistical evidence point to the synonymy of Bathytormus sp. 

A with B. pteropsis, and of B. sp. B with B. alaeformis: 

(1) the similarity of the univariate means for each pair of 

species (table 20), (2) the failure of the Mahalanobis' 

distances for the two pairs to pass the F test, (3) the 

conterminous boundaries of the two pairs on the plot of 

canonical variables 1 and 2 (fig. 14), (4) the proximity of 

the class means of the two pairs on the plot, and (5) the
40 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

percentage of B. sp. A classified as B. pteropsis, and of 

B. sp. B classified as B. alaeformis, in the discriminant 

analysis (table 27).

The Cretaceous and Tertiary species of Bathytormus 

are fairly discrete (compare pi. 2, fig. 3 to pi. 3, fig. 14). 

Only a few specimens overlap on the plots (figs. 13, 14), 

and the classification results are in the 90-percent range 

for most of the species categories (tables 23, 26, 27). An 

examination of the standardized canonical coefficients 

(tables 22, 25) indicates that changes in the length and in 

the posterior region separate the Tertiary from the 

Cretaceous forms. Intraspecific diversity appears to 

have been about the same on either side of the 

Cretaceous-Tertiary boundary, but abundance appears 

to have increased dramatically. This pattern differs from 

that seen in the Crassatella, in which intraspecific diversity increased in the Tertiary and abundance decreased.

GENERA OF CRASSATELLIDAE

The purpose of this portion of the statistical analysis is 

to determine the validity of the generic names used for 

the family Crassatellidae within the geographic and 

stratigraphic limits of this study. A few specimens from 

the Astartidae family are included for comparison. The 

null hypothesis is that no statistically significant differences exist between the generic categories being tested. 

If the null hypothesis cannot be rejected for any pair of 

generic categories, this would indicate the existence of 

synonyms. The alternative hypothesis is that all the 

generic names are valid. In addition, the distribution of 

species categories within the genera are examined for 

Bathytormus and Crassatella, and the validity of the 

generic assignments for all the species of Crassatellidae 

included in this analysis are tested.

Analysis.— In the first part of the analysis, 700 adult 

whole specimens from 6 generic categories were tested: 

(1) Crassatella Lamarck, 1799 (495 specimens), (2) 

Bathytormus Stewart, 1930 (140 specimens), (3) Scambula Conrad, 1869a (32 specimens), (4) Uddenia 

Stephenson, 1941 10 (19 specimens), (5) the unnamed 

group (genus and species unknown; 7 specimens), and (6) 

astartids (7 specimens). Appendix 7 lists the 72 localities 

for the specimens included in this analysis from the 

Upper Cretaceous and lower Tertiary units of the Gulf 

Coast and Mid-Atlantic regions. The genera were discriminated on the basis of 21 morphologic measurements11 (table 2).

10 The method for identifying specimens as Uddenia is discussed in the section 

"Statistical Methods" on page 12. Unlike the other categories, Uddenia specimens were not categorized on the basis of morphologic characters.

11 The stepwise discriminant analysis (see "Statistical Methods," p. 14, for a 

complete explanation) determined that 22 morphologic measurements were

The univariate class means (table 28, first analysis) are 

fairly distinct for each variable in the six generic categories. The means for Uddenia and the astartids show 

the greatest correspondence, in part due to their similar 

overall size. Most of the variables have higher values for 

between-class standard deviation than those for withinclass standard deviation (table 29, first analysis). The 

univariate results indicate that the genera will occupy 

fairly discrete areas on the plots of the canonical variables, but that some overlap between Uddenia and the 

astartids is likely. Apparently, at least some of the 

separation of the generic categories can be attributed to 

the average size of the individuals assigned to each 

genus.

All of the Mahalanobis' distances (table 30) computed 

between the generic categories are greater than the 

critical value for F at the 5 percent level of significance, 

so the null hypothesis of equal group means is rejected. 

An examination of the ranked order of the Mahalanobis' 

distances reveals the multivariate relationship of the 

generic categories. The smallest distance measurement 

is between Scambula and the astartids. The next three 

closest values are pairs that include Uddenia: the astartids and Uddenia, Crassatella and Uddenia, Scambula 

and Uddenia. The three pairs of generic categories that 

have the greatest Mahalanobis' distances are pairs that 

include the unnamed group: Uddenia and the unnamed 

group, Crassatella and the unnamed group, Bathytormus and the unnamed group.

The plot of canonical variables 1 and 2 (fig. 15) illustrates the isolation of Bathytormus along canonical variable 1, which accounts for 66.16 percent of the variance 

between all the groups and has a canonical correlation of 

0.94. The remaining generic categories all overlap along 

canonical variable 1. Canonical variable 2, which 

accounts for 27.80 percent of the variance between 

groups and has a canonical correlation of 0.87, separates 

Scambula from Crassatella and Bathytormus. The 

remaining three categories, Uddenia, the unnamed 

group, and the astartids, all overlap on both canonical 

variables 1 and 2. Uddenia and the astartids were 

expected to show a fair amount of overlap on the basis of 

their ranked Mahalanobis' distances, but the unnamed 

group was expected to be more discrete. Close examination of the plots, however, reveals that only one individual of Scambula falls within the area of the unnamed 

group on the plot. The standardized canonical coefficients 

(table 31) show that overall length and the characters

important discriminators for the generic analysis. No measurements of shell 

width were taken on Uddenia specimens, however, due to their diminutive size, 

so this variable was deleted. Only the classification results for Scambula were 

affected by the exclusion of the variable for shell width.
STATISTICAL ANALYSIS 41

TABLE 28. — Class means and grand means for the genera of Crassatellidae (and related groups) on each variable used in both canonical

discriminant analyses

[See table 2 for an explanation of the morphological variables. 1, the means from the first canonical discriminant analysis, including adult whole specimens only; 2, the 

means from the second canonical discriminant analysis of all specimens, including juveniles, broken specimens, and internal molds; —, generic category excluded 

from the first analysis; all specimens in category are internal molds]

Class mean

Morphological variable

LENGTH. ..............

POSTHT ...............

ANTHT ................

ANTER ................

POSTWID1.............

POSTWID2. ............

ANTWID1. .............

ANTDOR. ..............

ANTVERHT ...........

POSVERHT. ...........

POSTLAT ..............

ANTLAT...............

HINGEPL. .............

RESILANG ............

ANTLAT2. .............

POSTADHT ............

MANTCAV. ............

INTPOST ..............

INTANT ...............

POSADDST ............

ANTADDST. ...........

Crassatella

1

37.99

33.02

26.09

145.24

5.59

5.77

3.06

21.29

10 «A

19.02

17.40

10.47

22.55

20.50

10.92

8.67

24 99

42.12

67.47

10.35

10.71

2

35.09 

30.43 

24.12 

144.53 

5.29 

5.23

3.11 

19.77 

18.03 

17.55 

16.23 

9.84 

21.13 

18.45

10.05 

8.10 

23.33 

42.45 

66.84 

9.46 

9.71

Bathytornms

1

35.80 

28.30 

19.01 

133.89 

1.82 

4.43

4.92 

16.96 

13.70 

12.64 

15.67 

9.51 

22.15 

21.35

7.88 

5.96 

24.51

34.88 

58.28 

6.70 

6.86

2

35.30 

27.70 

18.88 

134.51 

1.94 

4.18

4.92 

16.90 

13.51 

12.40 

15.60 

9.47 

22.07 

21.00

7.86 

5.91 

24.42 

35.13 

58.08 

6.50 

6.67

Scambula

1

8.04 

6.40 

5.42 

144.76 

.84 

1.73

1.29 

4.69 

3.40 

3.50 

4.04 

3.58 

5.53 

19.45

1.13 

.99 

4.91 

51.32 

59.22 

2.51 

2.47

2

8.34 

6.66 

5.63 

144.62 

.83 

1.79

1.23 

4.87 

3.51 

3.62 

4.19 

3.68 

5.71 

19.39

1.21 

1.03 

5.12 

51.28 

59.16 

2.60 

2.52

Uddenia

1

4.88 

4.18 

3.39 

150.42 

.69 

.73

.73 

2.79 

2.36 

2.89 

2.56 

1.70 

3.43 

15.46

1.10 

1.04 

3.46 

43.45 

62.55 

1.85 

1.38

2

5.06 

4.29 

3.52 

150.16 

.68 

.76

.73 

2.91 

2.48 

2.93 

2.64 

1.77 

3.57 

15.52

1.15 

1.05

3.58 

43.62 

62.04 

1.88 

1.46

Class mean

Morphological variable

LENGTH. ..............

POSTHT ...............

ANTHT ................

ANTER ................

POSTWID1.............

POSTWID2. ............

ANTWID1. .............

ANTDOR. ..............

ANTVERHT ...........

POSVERHT. ...........

POSTLAT ..............

ANTLAT...............

HINGEPL. .............

RESILANG ............

ANTLAT2. .............

POSTADHT............

MANTCAV. ............

INTPOST ..............

INTANT ...............

POSADDST ............

ANTADDST. ...........

Unnamed group1

1

2.05

i «r;

1 64

132.71

2.55

.32

4.04

1.44

i 29

1.35

1.22

1.16

1.78

6.65

.30

.34

1 44

53.93

58.27

1.01

.96

2

2.05 

1.65 

1.64 

132.71 

2.55 

.32 

4.04

1.44 

1.29 

1.35 

1.22 

1.16 

1.78 

6.65

.30 

.34 

1.44 

53.93

58.27 

1.01 

.96

Indeterminant 

crassatellid molds

1

—

2

41.35 

33.38 

25.21 

138.57 

4.29 

4.36 

6.22

22.37

17.72 

19.12 

16.63 

10.62

23.48 

3.21

12.07 

10.37 

31.10 

38.06 

57.02 

8.76 

7.62

Astartids1

1

4.31 

3.73

3.28 

140.82 

.48 

.73 

.27

2.75 

2.05 

2.43 

2.68 

2.03 

3.50 

18.76

.73 

.75 

2.95 

50.20 

63.47 

1.69 

1.35

2

4.31 

3.73

3.28 

140.82 

.48 

.73 

.27

2.75 

2.05 

2.43

2.68 

2.03 

3.50 

18.76

.73 

.75 

2.95 

50.20 

63.47 

1.69 

1.35

Grand mean

1

34.59 

29.47 

22.64 

142.92 

4.40 

5.08 

3.27

18.78 

16.88 

16.25 

15.73 

9.55 

20.77 

20.33

9.39 

7.41 

22.93 

41.33 

64.98 

8.85 

9.12

2

33.14 

28.08 

21.61 

142.36 

4.26 

4.72 

3.38

18.03 

15.99 

15.43 

15.19 

9.26 

20.17 

18.84

8.95 

7.13 

22.24 

41.32 

64.46 

8.30 

8.50

1 Data set for analyses 1 and 2 is identical.
42 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 29. — Standard deviations, the value for F, and the probability of F for the canonical discriminant analyses of the genera of

Crassatellidae (and related groups) on each variable used in the analyses

[See table 2 for an explanation of the morphological variables. Total, total sample standard deviations of the data from all generic categories combined. Within class, 

pooled within-class standard deviations for the generic categories. Between class, between-class standard deviations for the generic categories. 1, data from the 

first canonical discriminant analysis, including adult whole specimens only; 2, data from the second canonical discriminant analysis of all specimens, including 

juveniles, broken specimens, and internal molds]

Standard deviation

Morphological variable

LENGTH. ..........

POSTHT ...........

ANTHT ............

ANTER ............

POSTWID1.........

POSTWID2. ........

ANTWID1. .........

ANTDOR. ..........

ANTVERHT .......

POSVERHT........

POSTLAT ..........

ANTLAT...........

HINGEPL. .........

RESILANG ........

ANTLAT2. .........

POSTADHT ........

MANTCAV. ........

INTPOST ..........

INTANT ...........

POSADDST ........

ANTADDST. .......

Total

1

13.03

11.27

9.07

8.93

2.80

1.99

2.04

7.26

7.02

6.54

5.72

3.27

7.24

4.16

4.20

3.23

8.73

5.56

5.73

3.51

4.04

2

13.45 

11.58 

9.26 

9.65 

2.81 

2.06 

2.15

7.50 

7.11 

6.54 

5.97 

3.51 

7.63 

6.08

4.23 

3.32 

9.17 

5.55 

6.21 

3.50 

4.08

Within class

1

9.27

7.89 

6.30 

7.57 

2.09 

1.46 

1.78

5.12

4.83 

4.29 

4.00 

2.35 

4.95 

3.82

3.00 

2.23 

6.26 

3.90 

4.18 

2.35 

2.94

2

11.27 

9.67

7.67 

8.64 

2.28 

1.77 

1.91

6.28 

5.85 

5.19 

5.00 

3.00 

6.29 

5.83

3.53 

2.71

7.68 

4.06 

4.92 

2.82 

3.45

Between class

1

10.06 

8.85 

7.17 

5.24 

2.04 

1.50 

1.11

5.66 

5.59 

5.41

4.48 

2.49 

5.80 

1.83

3.23 

2.56 

6.68 

4.36 

4.31 

2.86 

3.05

2

7.98 

6.92 

5.62 

4.69 

1.78 

1.14 

1.06

4.44 

4.38 

4.31 

3.55 

1.98 

4.70 

1.91

2.54 

2.08 

5.44 

4.11 

4.10 

2.25 

2.37

F

1

137.44 

146.72 

151.05 

55.99 

110.91 

123.32 

45.44

142.52 

156.08 

186.06 

146.41 

130.85 

159.85 

26.87

134.80 

154.90 

132.92 

145.51 

124.48 

172.63 

125.18

2

71.60 

73.09 

76.67 

42.02

87.41 

60.00 

44.13

71.41 

80.05 

98.49 

72.22 

62.03 

79.60 

15.36

73.81 

84.12 

71.46 

146.32 

98.91 

90.86 

67.39

Probability F

1

0.0 

.0 

.0 

.0001 

.0 

.0 

.0001

.0 

.0 

.0 

.0 

.0 

.0 

.0001

.0 

.0 

.0 

.0 

.0 

.0 

.0

2

0.0001 

.0001 

.0001 

.0001 

.0 

.0001 

.0001

.0001 

.0 

.0 

.0001 

.0001 

.0 

.0001

.0001 

.0 

.0001 

.0 

.0 

.0 

.0001

TABLE ?>§.—Mahalanobis' distances between classes for the first canonical discriminant analysis of 

the adult whole specimens of the genera of Crassatellidae (and related groups)

Generic category

Crassatella .......

Bathytormus ..... 

Scambula ........

Uddenia ..........

Unnamed group . . 

Astartids .........

Mahalanobis' distance1

Crassatella

6.8839 

6.9111 

4.9761 

10.1253 

6.2193

Bathytormus

8.4885 

7.5138 

12.2380 

8.7321

Scambula

5.3996 

6.3019 

3.0862

between classes

Uddenia

8.7428 

4.2505

Unnamed 

group

7.0025

Astartids

—

1 Mahalanobis' distances are a measure of the separation of the multivariate means of two classes (Davis, 1973, p. 

450-451).

of the anterior dorsal region are the primary discriminating variables along canonical variable 1 (LENGTH, 

ANTDOR, ANTLAT, ANTLAT2, see table 2 for an 

explanation of all the variables). The separation seen 

along canonical variable 2 is due primarily to the variables that measure the height of the posterior region 

(POSTVERHT, POSTADHT, POSADDST).

A discriminant analysis of the adult whole specimens of 

Crassatellidae produced the classification results seen in 

table 32. The variable for resilifer angle was deleted from 

the analysis so that the internal molds, which lack this 

measurement, could be tested against the calibration

data set of the adult whole specimens. Crassatella, 

Bathytormus, and the unnamed group show very high 

classification results (>99 percent) and little or no overlap with the other generic categories. Scambula, Uddenia, and the astartids, however, show a tendency to 

intermingle in the classification process, as expected 

from the results of the canonical discriminant analysis 

plot. Notably, Scambula produced much higher classification results (90.63 percent) when the variables measuring shell width and resilifer angle were included, but 

the inclusion of shell width excludes the unnamed group 

from the analysis.
STATISTICAL ANALYSIS 43

5-

3-

CM

.Q

I

.2 -3H 

o

CO _f

O v

-7-

-9-

-11

-11 -9 -7 -5 -3 -1 1 

Canonical variable 1

EXPLANATION

* Bathytormus 

H Crassatella 

n Scambula

o Uddenia

8 astartids

• unnamed group

FIGURE 15.—Canonical variables 1 and 2 for the first canonical variate analysis of the genera 

of Crassatellidae (and related groups). Data for the analysis include adult whole specimens 

only. Large symbols for the generic categories represent the midpoints of those categories. Canonical variable 1 accounts for 66.16 percent of the variance between generic 

categories and has a canonical correlation of 0.94. Canonical variable 2 accounts for 27.80 

percent of the variance between generic categories and has a canonical correlation of 0.87. 

See table 31 for standardized canonical coefficients.

Juvenile specimens, broken specimens, and internal 

molds were added to the data set for a second canonical 

discriminant analysis. A total of 999 specimens from 7 

generic categories was tested: (1) Crassatella (710 specimens), (2) Bathytormus (216 specimens), (3) Scambula 

(35 specimens), (4) Uddenia (21 specimens), (5) the 

unnamed group (7 specimens), (6) the astartids (7 specimens), and (7) internal molds of unknown generic identity (3 specimens). Twenty-one morphologic variables 

were used to test the generic categories11 (table 2). 

Resilifer angle was not excluded here, as it was during

previous analyses that included internal molds, because 

the position of the resilifer is a diagnostic character in 

distinguishing the genera of Crassatellidae. 12 The data 

were distributed among 91 localities in the Upper Cretaceous and lower Tertiary of the Gulf Coast and MidAtlantic regions (app. 8).

12 On all internal molds, the digitized point for the resilifer was identical to the 

point for the beak. Any variable that incorporates the resilifer point on internal 

molds is therefore not a real measurement. The number of internal molds in this 

analysis, however, is so small (6 percent) that the benefits of including the 

variable for resilifer angle outweigh the disadvantages.
44 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 31. — Standardized canonical coefficients for the first 

canonical discriminant analysis of the adult whole specimens of the 

genera of Crassatellidae (and related groups)

[See table 2 for an explanation of the morphological variables. Canonical variables 

1 and 2 are plotted on figure 15]

The inclusion of the additional specimens caused only 

slight changes in the values of the univariate class 

means, most notably on Crassatella (table 28). A very 

different pattern is seen, however, for the standard 

deviation values. In the first analysis of the adult whole 

specimens, the majority of the variables have higher 

values for between-class standard deviation than those 

for within-class standard deviation (table 29); in contrast, 

all but one of the variables have higher values for 

within-class standard deviation than those for betweenclass standard deviation in the second analysis. The 

Mahalanobis' distances (table 33) calculated between the 

generic categories all pass the F test at the 5 percent 

level of significance, so the null hypothesis of equal 

means is rejected. Patterns similar to those seen in the 

analysis of the adult whole specimens emerge when the 

ranked Mahalanobis' distances are examined. Scambula 

and the astartids show the shortest distance value, and 

the four greatest distance values are categories paired 

with the unnamed group.

The configuration of the plot of canonical variables 1 

and 2 (fig. 16) resembles the plot for the adult whole 

specimens (fig. 15), but the presence of the juveniles in 

this analysis can be seen in the central portion of the plot

TABLE 32.—Results of the classificatory discriminant analysis of the adult whole specimens of the genera of Crassatellidae (and related groups);

calibration data set tested against itself 

[Of the total number of specimens (700), 97.6 percent classify into the predicted generic categories]

LENGTH. ............

POSTHT .............

ANTHT ..............

ANTER ..............

POSTWID1...........

POSTWID2...........

ANTWID1. ...........

ANTDOR. ............

ANTVERHT .........

POSVERHT. .........

POSTLAT............

ANTLAT.............

HINGEPL. ...........

RESILANG ..........

ANTLAT2. ...........

POSTADHT..........

MANTCAV. ..........

INTPOST ............

INTANT .............

POSADDST ..........

ANTADDST. .........

Standardized canonical coefficient

Canonical variable 1

-8.4739

-0.7869

.8653

.3753

-0.0925

-0.3063

.0690

18.1394

-1.0260

-0.4580

.1109

-9.5596

2.3137

-0.3443

-9.3746

1.9207

3.7714

1.1069

.5773

2.2493

1.3019

Canonical variable 2

-2.3855

-4.4664

3.2726

.0621

-0.2824

.7440

-0.1317

-0.4294

3.8146

-83.1007

-2.5836

1.1067

4.9093

.0512

.2454

42.0158

-1.6972

-2.1768

.7930

46.2336

-4.3411

Original generic category1

Crassatella ................

Bathytormus ..............

Scambula. .................

Uddenia ...................

Unnamed group ...........

Astartids ..................

Total ....................

Total 

no. of 

specimens

........ 495

........ 140

........ 32

1Q

........ 7

........ 7

........ 700

Number of specimens (percentage of specimens) 

within the generic category determined oy analysis

Crassatella

493 (99.60)

0(0) 

0(0) 

0(0) 

0(0) 

_0(0)

493

Bathytormus

1 (0.20) 

140 (100.00) 

0(0) 

0(0) 

0(0) 

_0(0)

141

Scambula

1 (0.20) 

0(0) 

24 (75.00) 

1 (5.26) 

0(0) 

2 (28.57)

28

Uddenia

0(0) 

0(0) 

3 (9.38) 

15 (78.95) 

0(0) 

1 (14.29)

19

Unnamed group

0(0) 

0(0) 

4 (12.50) 

0(0) 

7 (100.00) 

_0(0)

11

Astartids

0(0) 

0(0) 

1 (3.13) 

3 (15.79) 

0(0) 

4 (57.14)

8

1 Generic category assigned prior to analysis.

TABLE 33.—Mahalanobis' distances between classes for the second canonical discriminant analysis of all the specimens of the genera of 

Crassatellidae (and related groups), including juveniles, broken specimens, and internal molds measured for this analysis

Mahalanobis' distance1 between classes

Generic category

Crassatella Bathytormus Scambula Uddenia Unnamed group cralsateUi^molds Astartids

Crassatella .............................

Bathytormus ...........................

Scambula. ..............................

Uddenia ................................

Unnamed group ........................

Indeterminant crassatellid molds .......

Astartids ...............................

.... 5.6403

.... 5.3830

.... 3.6027

.... 8.0383

.... 4.4980

.... 4.5563

7.1883

5.9556

10.1542

6.3256

7.2805

4.6916

4.7753

7.3949

2.8095

7.4593

5.7263

3.7752

_ _ _

_ _ _

_ _ _

_ _ _

_ _ _

8.5243 - -

5.6473 6.6917 -

1 Mahalanobis' distances are a measure of the separation of the multivariate means of two classes (Davis, 1973, p. 450-451).
STATISTICAL ANALYSIS 45

4_ 

2.

CM 0-

•- 

co -'

CO

o

c -4. 

o

c

CO

° -6.

-8-

-10

-10 -8 -6 -4 -2 0 

Canonical variable 1

EXPLANATION

* Bathytormus 

m Crassatella 

D Scambula 

o Uddenia

8 astartids

D indeterminant crassatellids

• unnamed group

FIGURE 16.—Canonical variables 1 and 2 for the second canonical variate analysis of the 

genera of Crassatellidae. Data for the analysis include all adult and juvenile specimens 

measured for the statistical analysis, including broken specimens and internal molds. 

Large symbols for the generic categories represent the midpoints of those categories. 

Canonical variable 1 accounts for 74.83 percent of the variance between generic 

categories and has a canonical correlation of 0.92. Canonical variable 2 accounts for 

19.95 percent of the variance between generic categories and has a canonical correlation 

of 0.77. See table 34 for standardized canonical coefficients.

where most of the areas impinge upon one another. 

Canonical variable 1, which accounts for 74.83 percent of 

the variance between the generic categories and has a 

canonical correlation of 0.92, is again primarily responsible for separating Bathytormus from the other generic 

categories. Crassatella and Bathytormus overlap, but 

they are separated at least partially from the other 

generic categories along canonical variable 2, which 

accounts for 19.95 percent of the variance between

categories and has a canonical correlation of 0.77. The 

primary discriminating variables along canonical variable 1 are the length of the anterior dorsal margin 

(ANTDOR) and the variables that measure the height of 

the posterior region of the shell (POSVERHT, POSTADHT, POSADDST) (table 34). The primary discriminating variables along canonical variable 2 are the same 

three variables that measure the height of the posterior 

region of the shell.
46 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

A discriminant analysis, using the adult whole specimens as a calibration data set, classified the juveniles, 

broken specimens, and internal molds of the Crassatellidae genera (table 35). Excluding the three indeterminant internal molds, the majority (83.5 percent) of the 

individuals classify correctly. 7 Although only 2 specimens of Uddenia are included in this analysis, 27 specimens classify as Uddenia, including at least 1 specimen 

from the other 3 described generic categories, Crassatella, Bathytormus, and Scambula. All of the specimens of Crassatella and Bathytormus that classify as 

Uddenia are juveniles; the one specimen of Scambula 

that classifies as Uddenia is a broken specimen. The

TABLE 34.—Standardized canonical coefficients for the second 

canonical discriminant analysis of all the specimens of the genera of 

Crassatellidae (and related groups), including juveniles, broken 

specimens, and internal molds, measured for this analysis

[See table 2 for an explanation of the morphological variables. Canonical variables 

1 and 2 are plotted on figure 16]

internal molds of uncertain generic identity classify as 

Crassatella.

The purpose of the final portion of the analysis was to 

determine if correct generic assignments had been made 

for each species in this study. A discriminant analysis 

was conducted using as a calibration data set all 999 

specimens digitized. The same 999 specimens were classified into the calibration data set using their specific 

assignments. The results (table 36) show that the majority, 94.98 percent, of the specimens in each species 

category classify into the correct generic category. Species categories having fewer than 10 specimens tend to 

have few individuals that classify correctly, but these 

results are not statistically significant. The low classification results for the species of Scambula may appear to 

be problematic, but, when the variables for shell width 

and resilifer angle are included in the data set, 91.1 

percent of the specimens classify correctly. Specimens of 

Uddenia classify as Bathytormus, Scambula, and the 

astartids, as an examination of the canonical variable 

plots (figs. 15, 16) indicates.

Finally, to determine the pattern of species distribution within the genera for Crassatella and Bathytormus, 

the data points for the individual species were plotted 

within the area of the genus on the plot of canonical 

variable 1 and canonical variable 2 for the adult whole 

specimens (fig. 17). For Bathytormus, the Cretaceous 

species B. pteropsis and B. sp. A, and the Tertiary 

species B. alaeformis and B. sp. B, occupy distinct 

regions of the generic area plot, with some overlap 

occurring in the central region around the group mean 

for the genus. The picture is quite different, however, for 

the Crassatella; all the species categories, Tertiary and 

Cretaceous, are centered around the group mean for this 

genus.

Discussion.— The results of the generic analysis 

reveal that as a whole the genera of Crassatellidae are 

well defined and that the species categories are properly 

assigned to them. Although overall size appears to be 

responsible for at least some of the separation of the 

generic categories, this is a valid attribute of a genus and

TABLE 35.—Results of the classificatory discriminant analysis of the juveniles, broken specimens, and internal molds of the genera of

Crassatellidae (and related groups), tested against the calibration data set of the adult whole specimens

[Excluding the indeterminant molds, 83.5 percent of the specimens classify into the predicted generic categories]

Morphological variable

LENGTH. ............

POSTHT .............

ANTHT ..............

ANTER ..............

POSTWID1...........

POSTWID2. ..........

ANTWID1. ...........

ANTDOR. ............

ANTVERHT .........

POSVERHT. .........

POSTLAT............

ANTLAT.............

HINGEPL. ...........

RESILANG ..........

ANTLAT2. ...........

POSTADHT..........

MANTCAV. ..........

INTPOST ............

INTANT .............

POSADDST ..........

ANTADDST. .........

Standardized canonical coefficient

Canonical variable 1

-5.6640

-1.6533

.6003

.2798

-0.0373

-0.1286

.0405

12.1673

-1.4645

24.4325

.4775

-7.2886

1.2537

-0.3119

-6.2436

-10.9092

3.7634

1.2940

.6483

-11.3798

1.4818

Canonical variable 2

-3.0648

-3.6660

3.9756

.0375

-0.3753

.7292

-0.2489

4.5711

3.4238

-28.5845

-4.1009

-2.1722

6.3376

.0091

-2.4344

15.1830

-1.1582

-1.9351

1.0135

16.5807

-4.0842

Original generic category1

Crassatella ...........................

Bathytormus .........................

Scambula. ............................

Uddenia ..............................

Indeterminant crassatellid molds ..... 

Total ...............................

Total no. 

of specimens

215 

76 

3 

2 

3

299

Crassatella

175 (81.40) 

3 (3.95) 

0(0) 

0(0) 

3 (100.00)

181

Number of specimens (percentage of specimens) 

within the generic category determined by analysis

Bathytormus

3 (1.40) 

69 (90.79) 

0(0) 

0(0) 

_0(0)

72

Scambula

1 (3.26) 

0(0) 

2 (66.67) 

1 (50.00) 

_0(0)

10

Uddenia

21 (9.77) 

4 (5.26) 

1 (33.33) 

1 (50.00) 

_0(0)

27

Unnamed group

0(0) 

0(0) 

0(0) 

0(0) 

0(0)

0

Astartids

9(4.19) 

0(0) 

0(0) 

0(0) 

0(0)

9

1 Generic category assigned prior to analysis.
STATISTICAL ANALYSIS 47

TABLE 36.— Results of the classificatory discriminant analysis of all the specimens of the species of Crassatellidae measured for this analysis,

tested against the calibration data set consisting of the same specimens, but classified into the genera of Crassatellidae

[Excluding the two categories of indeterminant crassatellids, 94.98 percent of the specimens classify into the predicted generic categories]

TWnl

Number of specimens (percentage of specimens) within the generic category determined by analysis

Original species category1 no. of

Crassatella

Crassatella carolinana ............

C. gabbi ...........................

C. gardnerae ......................

"C. halei" (=C. tumidula) ........

C. hodgei ..........................

"C. hodgei" (and C. carolinensis) . .

C. lintea ...........................

C. monmouthensis. ................

C. prora ...........................

C. sepulcollis ......................

C. subplana .......................

C. transversa ......................

C. tumidula .......................

C. vadosa. .........................

C. vadosa ripleyana ...............

C. vadosa wadei ...................

C. sp. A ...........................

C. sp. B ...........................

C. sp. C ...........................

Bathytormus alaeformis ...........

B. pteropsis. .......................

B. sp. A ...........................

B. sp. B ...........................

Scambula perplana ................

S. sp. ..............................

Uddenia sp. A .....................

U. sp. B ...........................

Unnamed group ...................

Cretaceous indeterminant

crassatellid molds.

Tertiary indeterminant crassatellid

molds.

Astartids ..........................

Total ............................

3

1

56

6

2

12

20

5

1

2

1

2

27

95

41

95

214

2

125

148

10

32

26

15

20

16

5

7

2

1

7

999

3 (100.00)

1 (100.00)

56 (100.00)

6 (100.00)

2 (100.00)

12 (100.00)

20 (100.00)

5 (100.00)

0(0)

2 (100.00)

1 (100.00)

0(0)

27 (100.00)

92 (96.84)

41 (100.00)

95 (100.00)

205 (95.79)

2 (100.00)

117 (93.60)

0(0)

0(0)

4 (12.50)

2 (7.69)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

1 (100.00)

1 (14.29)

695

Bathytormus

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

1 (100.00)

0(0)

0(0)

0(0)

0(0)

1 (1.05)

0(0)

0(0)

0(0)

0(0)

0(0)

147 (99.32)

10 (100.00)

27 (84.38)

24 (92.31)

0(0)

0(0)

1 (6.25)

0(0)

0(0)

0(0)

0(0)

0(0)

211

Scambula

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

O.(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

3 (2.40)

0(0)

0(0)

0(0)

0(0)

11 (73.33)

15 (75.00)

1 (6.25)

1 (20.00)

1 (14.29)

0(0)

0(0)

2 (28.57)

34

Uddenia

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

4 (1.87)

0(0)

4 (3.20)

1 (0.68)

0(0)

1 (3.13)

0(0)

2 (13.33)

2 (10.00)

12 (75.00)

4 (80.00)

0(0)

0(0)

0(0)

1 (14.29)

35

Indeterminant 

Unnamed crassatellid

group

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

1 (6.67)

3 (15.00)

0(0)

0(0)

6 (85.71)

0(0)

0(0)

0(0)

4

molds

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

2 (100.00)

0(0)

2 (2.11)

0(0)

0(0)

2 (0.93)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

2 (100.00)

0(0)

0(0)

8

Astartids

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

0(0)

3 (1.40)

0(0)

1 (0.80)

0(0)

0(0)

0(0)

0(0)

1 (6.67)

0(0)

2 (12.50)

0(0)

0(0)

0(0)

0(0)

3 (42.86)

10

1 Species category assigned prior to analysis.

should not cause concern about the legitimacy of the 

results. Characters of the hinge are most often cited as 

diagnostic features of the genera of Crassatellidae, but 

these characters do not prove to be primary discriminating variables within the confines of this statistical analysis. Rather, the characters of the posterior region of the 

shell prove to be the primary discriminators between 

generic categories.

All of the evidence presented, the univariate class 

means, the plots of the canonical variables, and the 

classification results, illustrate statistically that Crassatella and Bathytormus are valid, well-defined genera. 

This is not surprising considering the vast amount of 

attention they, particularly Crassatella, have received in

the scientific literature. This extensive coverage, however, has contributed to the problem of taxonomic splitting illustrated earlier in the analysis of the species of 

Crassatella. A comparison of the species distribution 

within the areas defined for Crassatella and Bathytormus (fig. 17) is revealing. The species categories within 

Crassatella overlap one another as rings of various 

diameters centered around the group mean for the 

genus. This pattern (1) may be indicative of the oversplitting which has occurred within the Crassatella, (2) 

may illustrate a pattern of gradual evolution within the 

genus, or (3) may simply be an artifact of the analytical 

techniques, particularly the variables selected for inclusion at this stage of the analysis. The species that
48 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

CM

. 

.a

5 

g

CO -1

O 

CO

5-

3-

-H

-3H

-5-

-7

-9 -7 -5 -3 -1

Canonical variable 1

EXPLANATION

Cretaceous species

A Bathytormus pteropsis

A Bathytormus sp. A

D Crassatella gardnerae

o"Crassatella hodgei" (and C. carolinensis)

o Crassatella lintea

H Crassatella vadosa

* Crassatella vadosa ripleyana

• Crassatella vadosa wadei 

D Crassatella sp. A 

Tertiary species 

x Bathytormus alaeformis 

N Bathytormus sp. B 

+ "Crassatella halei" (= C. tumidula) 

Kl Crassatella tumidula 

x Crassatella sp. C

FIGURE 17.—Pattern of species distribution within the genera for Crassatella and 

Bathytormus. Plot of canonical variables 1 and 2 is a magnification of the figure 15 plot. 

The heavy lines define the areas for the genera Crassatella and Bathytormus as they 

appear on figure 15. Large symbols for the generic categories represent midpoints of the 

genera. The distribution of the species categories within the plots for the genera are 

illustrated. Species categories with only one or two specimens have been left off the plot, 

although they were included in the analysis.
STATISTICAL ANALYSIS 49

compose a genus define the characters of the genus, but 

it is reasonable to expect each species to contribute a 

unique attribute to that genus. Unique contribution of 

species to the genus is not the picture seen in Crassatella 

but is illustrated by Bathytormus. The two species 13 of 

Bathytormus occupy distinct morphological areas of the 

genus but overlap in the central portion where their 

common generic characters link them. The internal 

molds of indeterminant generic origin prove to be members of the genus Crassatella as well; the position of 

these unknown specimens on the canonical variable plots 

and the classification results are evidence of the generic 

affinity.

The results for Scambula, Uddenia, and the unnamed 

group require close scrutiny to determine whether or not 

they are legitimate generic categories. Scambula 

appears distinct from all other genera of Crassatellidae 

(compare pi. 21, figs. 1-5, 7, 9 to pi. 21, figs. 6, 8, 10-17), 

and this distinction is corroborated by the univariate 

class means. The multivariate analyses, however, do not 

substantiate the initial conclusions. The lowest Mahalanobis' distances both with and without the juveniles and 

broken specimens are between Scambula and the astartids. On the canonical variable plots (figs. 15, 16), Scambula is overlapped by the unnamed group, Uddenia, and 

the astartids; in the classification results, only 71 percent 

of the specimens classify correctly on an average. If the 

Uddenia, the astartids, and the unnamed group are 

ignored, however, Scambula occupies a discrete area on 

the plot. The percent of Scambula that classify correctly 

rises to the 90 percent range when the variables for shell 

width and resilifer angle remain in the classification 

analysis. These variables are obviously important in 

discriminating the genus Scambula, and their inclusion 

illustrates that Scambula is statistically distinct, just as 

initial observations suggest.

The statistical results for Uddenia indicate it is a 

poorly defined generic category. In the process of conducting this study, I discovered that the name Uddenia 

is a junior synonym of Crassatella; the type specimen is 

a juvenile C. vadosa (see the "Systematic Paleontology" 

section for a complete explanation). The ambiguity surrounding Uddenia explains the overlap of Uddenia with 

Crassatella, Bathytormus, and Scambula, particularly 

on figure 16, which includes the juveniles. The intermingling of Uddenia and the juveniles of other genera in the 

classification results further illustrates the invalid nature 

of the generic category Uddenia.

The unnamed group forms a distinct category composed of individuals that superficially appear to match

13 The analysis of the Bathytormus species illustrates that B. sp. A is 

synonymous with B. pteropsis and that B. sp. B is synonymous with B. 

alaeformis.

Stephenson's (1941, p. 181) original description for Uddenia texana. The distinctive univariate class means, the 

high values for Mahalanobis' distances, and the high 

classification results, as well as the distinctive appearance indicate that the unnamed group is a separate 

taxonomic category. The overlap with Scambula seen on 

the plots is the result of a single specimen of Scambula 

falling in the area for the unnamed group. Further 

examination reveals that this group is not a member of 

the Crassatellidae; thus, statistical separation is 

expected (see "Systematic Paleontology," p. 57-58 for 

full explanation).

The astartids were included in this analysis for several 

reasons. First, many specimens of the astartids were 

found in museum collections labeled as Uddenia. Second, 

I wanted to examine the possibility that the genus 

Scambula may actually be a member of the family 

Astartidae. A strong similarity between Scambula and 

the Astartidae is indicated, and the juvenile specimens of 

all the genera of Crassatellidae analyzed here bear a 

resemblance to the specimens of Astartidae included in 

this study. Finally, the Astartidae and the Crassatellidae 

are thought to share a common ancestor. The small 

number of Astartidae included here are not enough to 

reach any conclusions, but the results warrant further 

study.

SUMMARY OF STATISTICAL ANALYSES

The purpose of the statistical analysis was to test the 

previously defined species and genera of the family 

Crassatellidae for the Gulf and Mid-Atlantic Coastal 

Plains (table 1), in order to quantitatively evaluate the 

validity of the taxa. The following issues have been 

resolved. The subspecies of Crassatella vadosa represent end members of the species when the full spectrum 

of individuals assigned to C. vadosa is evaluated. C. 

gardnerae and C. lintea are synonyms of C. vadosa. The 

lower Campanian forms, C. hodgei and C. carolinensis 

are quantitatively different from the younger species of 

Crassatella, and likewise the Tertiary species C. tumidula is statistically distinct from the older species of 

Crassatella. Two well-defined species of Bathytormus 

exist, B. pteropsis and B. alaeformis. At the generic 

level, Crassatella, Bathytormus, Scambula, and the 

unnamed group (genus and species unknown), are quantitatively recognizable genera, whereas Uddenia 

appears to be poorly defined statistically. Consequently, 

questions about 10 of the 38 species names, the 2 

subspecies names and all of the generic names listed in 

table 1 have been quantitatively resolved.

The statistical analysis has failed, however, to resolve 

the validity of the majority of the names applied to 

Crassatellidae within the geographic and stratigraphic
50 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

limits of this study. This failure can be primarily attributed to the lack of specimens representing many of the 

names presented in table 1. In some cases only single 

type specimens exist, and often the types are in such a 

poor state of preservation that their morphologic characters cannot be digitized. These names can only be 

evaluated qualitatively, not quantitatively, and their 

validity is discussed in the following section on "Systematic Paleontology."

Additionally, the statistical methods I employed for 

evaluating the taxonomic categories limited the effectiveness of this analysis in answering the initial question, 

"How accurate is the published fossil record for the 

Crassatellidae?" First, there is the problem of reducing a 

three dimensional form to two dimensions. I attempted 

to overcome this limitation by including the measurement of shell width, but this variable only provides a 

value for the distance to the widest point on the shell's 

surface. It does not impart any information about where 

the widest point lies, if it is a single point or a broad area 

of the shell, and if there are any fluctuations in width on 

the shell's surface; these characters proved to be important diagnostic features in the qualitative analysis of the 

taxa that follows. Other characters that proved to be 

important in diagnosing taxa but were excluded from 

consideration in the statistical analysis were characters 

of the ornament, the posterior ridge, and the height and 

curvature of the beak.

Many avenues for future quantitative analysis of this 

data set need to be explored, for example elimination or 

addition of variables and the effects on the results, but 

for now the purpose has been served. The majority of the 

taxa are evaluated in the following section by the qualitative examination of large suites of Crassatellidae.

SYSTEMATIC PALEONTOLOGY

The following diagnoses and descriptions are 

restricted to the genera and species of Crassatellidae 

that are found in the Upper Cretaceous and lower 

Tertiary deposits of the Mid-Atlantic and Gulf Coastal 

Plains of the United States. The synonymies include 

references that contain pertinent discussions, descriptions, or illustrations; they are by no means complete. 

Papers using a generic or specific name in faunal lists 

only are excluded below, unless the paper contains the 

first documented use of that name. The following abbreviations indicate depositories:

AMNH American Museum of Natural History, New 

York, N.Y.

ANSP Academy of Natural Sciences of Philadelphia, Philadelphia, Pa.

CNHM Chicago Field Museum of Natural History, 

Chicago, 111.

PRI Paleontological Research Institution, Ithaca, 

N.Y.

USGS U.S. Geological Survey, Reston, Va.

Mesozoic locality numbers, the majority of 

these samples are housed at the U.S. Geological Survey in Reston, Va. Cenozoic locality numbers, the majority of these samples 

are housed at the U.S. National Museum of 

Natural History in Washington, B.C.

USNM U.S. National Museum of Natural History, 

Smithsonian Institution, Washington, B.C.

The dental formulas given in the descriptions follow the 

system outlined by Boyd and Newell (1968, p. 7-10; 1969, 

p. N908-N910); a "1" indicates an elevated portion of the 

hinge (either a tooth or a ridge); a "0" indicates a 

recessed area (either a socket or a simple depression); 

parentheses enclose indicators of ambiguous teeth and 

their corresponding depressions; horizontal lines separate the cardinal and lateral series; an "R" indicates the 

position of the resilifer.

Phylum MOLLUSCA

Class BIVALVIA

Subclass HETERODONTA Neumayr, 1884

Order VENEROIDA H. Adams & A. Adams, 1856

Superfamily CRASSATELLACEA Ferussac, 1822

Family CRASSATELLIDAE Ferussac, 1822

The origin of the concept of the family Crassatellidae 

can be traced to Lamarck (1799); he differentiated the 

crassatellids from the mactrids on the basis of differences 

in the hinge structure and whether or not the valves 

closed. Deshayes (1824, p. 32-33) further outlined these 

differences, stating that crassatellids can be distinguished from mactrids by having (1) margins that close 

completely [that is, no shell gape], (2) the absence of 

lateral teeth [lateral ridges, however, are present], and 

(3) the absence of a pallial sinus. Deshayes described the 

latter as being "without contradiction the best of all 

characters for separating the two genera, and probably 

to distance this genus [Crassatella] from the family of 

the mactras" (translated from French, Deshayes, 1824, 

p. 33).

The astartids and the crassatellids were formally 

united in the family Crassatellidae by Ferussac (1822). 

D'Orbigny (1844, 1845, 1853) agreed that, on the basis of 

similarities in their "organic functions," a closer relationship existed between the astartids and the crassatellids 

than between the mactrids and the crassatellids. He 

considered the absence of a pallial sinus and the absence 

of shell gape, both features characteristic of the astartids 

and the crassatellids, to represent a similarity in "organic 

functions," whereas the similarity of the ligament seen in 

both the mactrids and the crassatellids is a "mechanical 

function." Gray (1847), however, limited the family Crassatellidae to the single genus Crassatella. Deshayes
SYSTEMATIC PALEONTOLOGY 51

(1860, p. 734) agreed with Gray and discussed his "repugnance" at placing a genus with an external ligament (the 

astartids) in the same family as a genus with an internal 

ligament (the crassatellids). Stoliczka (1871, p. 292) 

further pointed out distinctive differences in the soft 

anatomy of the rectum between astartids and crassatellids. Since 1847, the majority of workers have maintained 

two separate families, the Crassatellidae and the Astartidae, currently united under the superfamily Crassatellacea (Chavan, 1969). 14

Chavan (1952) divided the Crassatellidae into two 

subfamilies, the Crassatellinae and the Scambulinae. The 

Scambulinae are distinguished by the following characters (Chavan 1952, p. 120; 1969, p. N577): (1) "stretched" 

teeth, (2) long lamellar teeth, extending down from near 

the beak, (3) a narrow resilifer, and (4) strongly opisthogyrous or orthogyrous beaks. In contrast, the Crassatellinae illustrate these characters (Chavan, 1969, p. 

N473): (1) lamellar teeth that do not extend the length of 

the dorsal margin and that begin below the cardinals, (2) 

a well-developed resilifer, and (3) prosogyrous or orthogyrous beaks.

Numerous detailed discussions of the morphology and 

anatomy of the crassatellids have been completed since 

Lamarck's (1799, p. 85) definition of the genus Crassatella. The most comprehensive were written by d'Orbigny (1844, p. 72-74), 15 Deshayes (1860, p. 735-737), 

Fischer (1887, p. 1020-1022), 16 and Lamy (1916, p. 

197-205). The three genera and eight species of Crassatellidae examined within the geographic and stratigraphic limits of this study are united by the morphologic 

characteristics of the family. All are equivalved and do 

not have gaping valves. The shells are inequilateral with 

varying degrees of posterior elongation. Exteriorly, a 

lunule and escutcheon and posterior ridge are apparent; 

the ornament is comarginal. The musculature consists of 

anterior and posterior adductors and anterior and posterior pedal retractors. The pallial line is entire. The hinge 

structure is composed of an internal resilifer that originates at the beak and is posterior to the cardinals; one 

true cardinal is present in the right valve, and two are in

14 Boyd and Newell (1968), in a paper on Paleozoic Crassatellacea, indicate that 

the resemblance of the Astartidae and the Crassatellidae is due to convergence. 

Consequently, Bernard (1983) proposed erecting a superfamily Astartellacea to 

further separate the Astartidae and the Crassatellidae. For the present, I follow 

Chavan's (1969) usage until these larger questions can be resolved.

15 D'Orbigny's (1844; 1845; 1853) discussion indicates he has inverted the left 

and right valves on the crassatellids. For the right valve, he mentions two 

divergent teeth and three fossettes of which the anteriormost fossette is the 

largest; d'Orbigny says that the ligament is situated in this anterior fossette. He 

is clearly speaking of the left valve because the widest and posterior-most section 

of the hinge platform contains the resilifer in the Crassatellidae.

16 The illustration in Fischer (1887, fig. 768) is incorrectly labeled as a right 

valve; it is a left valve. His discussion and the labels on the diagram indicate that 

this was simply a typographical error.

the left valve; the laterals are not true teeth but are 

simple raised ridges.

The statistical analysis supports the conclusion that 

three valid, well-defined genera exist in the family 

Crassatellidae within the constraints of this study: Crassatella Lamarck, 1799, Bathytormus Stewart, 1930, and 

Scambula Conrad, 1869a. These genera are statistically 

discriminated by characters measuring length, the anterior dorsal region, and the height of the posterior region. 

A high degree of intrageneric diversity is quantitatively 

illustrated for the Crassatellidae.

Subfamily CRASSATELLINAE Ferussac, 1822 

Genus Crassatella Lamarck, 1799

Crassatella LAMARCK, 1799, p. 85. LAMARCK, 1801, p. 119. 

LAMARCK, 1805, p. 407^08. DESHAYES, 1824, p. 32-33. CONRAD, 1838, p. 20-21. REEVE, 1842, p. 42. NYST, 1843, p. 83. 

D'ORBIGNY, 1844, p. 72-74. D'ORBIGNY, 1845, p. 577-578 [modified copy d'Orbigny, 1844]. CONRAD, 1846, p. 395. D'ORBIGNY, 

1853, p. 287-288 [modified copy d'Orbigny, 1844]. DESHAYES, 

1860, p. 735-737. STOLICZKA, 1871, p. 293-294. MARTENS, 

1880, p. 22. TRYON, 1884, p. 224 [partim]. WHITFIELD, 1885, p. 

115 [partim; not = Etea Conrad]. FISCHER, 1887, p. 1020-1022 

[partim]. LAMY, 1916, p. 197 [partim]. STEWART, 1930, p. 

134-137. CHAVAN, 1939, p. 27. STEPHENSON, 1941, p. 176-177. 

CHAVAN, 1952, p. 119. DARTEVELLE and FRENEIX, 1957, p. 

136. CHAVAN, 1969, p. N573-N574. FRENEIX, 1972, p. 135-149. 

VOKES, 1973, p. 48-52.

Crassatellites KRUEGER, 1823, p. 465-466. DALL, 1903, p. 

1468-1469 [partim]. GARDNER, 1916, p. 648-649. IREDALE, 

1921, p. 207-208. SHIMER and SHROCK, 1944, p. 419. GARDNER, 1945, p. 90.

Pachythaerus CONRAD, 1869a, p. 47. VOKES, 1946, p. 177.

Crassatella (Pachythaerus) CONRAD, 1872, p. 50. STEWART, 1930, 

p. 137. CHAVAN, 1939, p. 27. CHAVAN, 1952, p. 119. CHAVAN, 

1969, p. N574. FRENEIX, 1972, p. 146.

Crassatellites (Crassatellites) Krueger. WOODRING, 1925, p. 93-94.

Uddenia STEPHENSON, 1941, p. 180. CHAVAN, 1952, p. 119, 120. 

CHAVAN, 1969, p. N577.

Crassatella (Landinia) CHAVAN, 1952, p. 119. CHAVAN, 1969, p. 

N574.

[non] Crassatella (Scambula) TRYON, 1884, p. 224. FISCHER, 1887, 

p. 1022. DALL, 1903, p. 1467.

[non] Crassatella (Crassinella) DALL, 1903, p. 1468. LAMY, 1916, p. 

244-251. COSSMANN, 1921, p. 135-136.

Additional subgenera proposed but not considered herein:

Crassatella (Rochella) FRENEIX, 1972, p. 135-136 [Upper Cretaceous; Morocco].

Crassatella (Sublandinia) FRENEIX, 1972, p. 142 [Lower Cretaceous; Morocco].

Crassatella (Riosatella) VOKES, 1973, p. 48-59 [Holocene; offshore, 

Rio Grande, Southern Brazil].

Type species. —Crassatella tumida Lamarck, 1805 = 

Crassatella gibba Lamarck, 1801 = Venus ponderosa 

Gmelin, 1791 [non Mactra cygnea Chemnitz, 1782].

Characters of Coastal Plain Crassatella. —The species 

of Crassatella included in this analysis are all equivalved, 

inequilateral, and prosogyrous and have no shell gape;
52 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

outlines vary from ovate, to trigonal, to quadrilateral; 

anterior margins are always rounded; posterior margins 

are highly variable; a lunule and an escutcheon are 

present, but the lunule is usually better defined on the 

left valve, and the escutcheon is usually better defined on 

the right valve; a posterior ridge is always present, but 

has varying degrees of strength. The shell ornament is 

comarginal and highly variable, even within species, but 

juveniles within a given species show fairly consistent 

patterns of ornamentation; an underlying radial element 

may be visible on worn shells. The typical pattern for the 

dentition of this genus, moving from posterior lateral 

ridges across the hinge plate to the anterior lateral 

ridges, is as follows (see fig. 18):

Right Valve 0 1 O-R(l) 0 1 0 (1)-1 0 1 

Left Valve 1 0 l-R(O) 1 0 1 (0)-0 1 0

The right valve dentition consists of one posterior lateral 

ridge17 separated from the resilifer (R) by an edentulous 

space. The resilifer originates at the beak on a platform 

formed by the rear wall of the trigonal socket, below and 

slightly anterior to the resilifer. The rear wall of this 

socket may form a small narrow raised ridge, which has 

been identified as a cardinal tooth by some authors18 but 

which I consider, at best, a pseudocardinal even when 

maximally developed. One large cardinal tooth lies anterior to the beak and is preceded anteriorly by a socket. 

The anterior edge of the hinge plate may be raised in a 

thin narrow ridge; this anterior-most ridge has been 

identified also as a cardinal (Fischer, 1887, p. 1021; Ball, 

1903, p. 1465) but it also is a pseudocardinal at best. Two 

anterior lateral ridges are present17 (Fischer, 1887, p. 

1021, mentions only one), separated by a groove. The left 

valve dentition consists of two posterior lateral ridges17 

(Fischer, 1887, p. 1021, mentions only one), separated by 

a groove. The resilifer originates at the beak on an 

edentulous space posterior to the beak. A small receptor 

pit occurs at the flared base of the posterior cardinal; two 

well-defined cardinals are separated by a socket. Forward of the anterior-most cardinal is a narrow groove 

that functions as a receptor for the anterior-most raised 

ridge of the opposite valve. One anterior lateral ridge17 is 

present. The ligament of Crassatella is internal, originates at the beak, and extends part way across the hinge 

plate. Interiorly, two well-developed, deeply incised 

adductors can be found (fig. 18); although the existence of 

quick and catch muscles among the Crassatellidae has

17 Dall (1903, p. 1465) stated that "there are nowhere any developed laterals at 

all." He believed the "bevelled" dorsal margins are obsolete laterals. Deshayes 

(1824, p. 33) referred to the lateral teeth as "absent."

18 Fischer (1887, p. 1021) termed the ridge a rudimentary posterior cardinal. 

Dall (1903, p. 1465) stated that three cardinals exist in the right valve but that the 

posteriormost is "more or less smothered and obliterated by the descending 

resilium." The Lamy (1916, p. 199-200) description is consistent with that of Dall.

been reported (Boss, 1982, p. 1136), there is no evidence 

of such division among the species of Crassatella herein 

studied. In addition, a small discrete anterior pedal 

retractor is located above the anterior adductor and near 

the end of the anterior lateral ridge (fig. 18; pi. 4, fig. 14; 

pi. 7, fig. 14; and pi. 14, fig. 17). A posterior pedal 

retractor occurs as a small notch continuous with the 

dorsal-most corner of the posterior adductor scar (fig. 18; 

pi. 7, fig. 14; and pi. 14, fig. 17). The pallial line is distinct 

and entire (pi. 7, fig. 14), and the ventral margin is at 

least partially crenate on all well-preserved adults. 

These characters are all consistent with Lamarck's 

(1799, p. 85) original definition.

Discussion of Type Designation.—Lamarck first recognized the genus Crassatella in 1799 from specimens 

collected in the Eocene of the Paris basin. He described 

it simply as an inequilateral shell, subtransverse, having 

closing valves, sunken lunule and escutcheon, and having 

the resilifer located under the beak and above the hinge 

teeth (Lamarck, 1799, p. 85). The type species was 

designated as Mactra cygnea Chemnitz, 1782; this designation has led to questions concerning Lamarck's intentions, identification of subsequent types (see table 37 for 

a partial listing), and the correct name for the genus.

Fischer (1887) was the first author to raise the issue of 

the correct assignment for Mactra cygnea Chemnitz. He 

believed that the shell for which Lamarck proposed the 

genus Crassatella probably belonged to the genus Mactra (Fischer, 1887, p. 1021). Crassatella plumbea (Chemnitz), 1783 is the species Fischer cites as the type for the 

genus (table 37). He indicated that Crassatella plumbea 

(Chemnitz), 1783 was the next specific name used by 

Lamarck in 1801; in actuality, Lamarck (1801, p. 119) had 

used the name Crassatella gibba, but he referred to 

Chemnitz (1783, Conchylien Cabinet, plate 69, figs. A-D) 

illustration of C. plumbea. Fischer seems to have correctly recognized C. gibba as a junior synonym of C. 

plumbea.

Dall (1903, p. 1468) concurred that Lamarck's original 

type was a Mactra, so he accepted Crassatellites 

Krueger, 1823, as the next valid name. Krueger's (1823, 

p. 466) description of Crassatellites lacked any significant details, but his reference to Lamarck's original 

description of the genus indicates he was not erecting a 

new generic name. Instead, Krueger added the suffix 

-ites to indicate a fossil species, following a common 

practice of his time (fide Iredale, 1921, p. 207-208). 

Crassatellites sinuatus Krueger is listed as the type for 

the genus (Krueger, 1823, p. 466).

Stewart (1930, p. 134-137) and Vokes (1973, p. 48-52) 

provided the most thorough examinations of the problem 

of the type designation for Crassatella. They both concluded that Mactra cygnea Chemnitz was indeed a 

Mactra but that it clearly was not the specimen that
SYSTEMATIC PALEONTOLOGY 53

Crassatella

PL

RV: 01 0-R(1) 01 0 (1)-1 01 

LV: 1 01-R(0) 1 01 (0)-01 0

FIGURE 18.—Hinge characters and musculature of Crassatella. Dental formulas read from the posterior 

lateral ridges to the anterior lateral ridges. RV, right valve; LV, left valve. AA, anterior adductor; 

AR, anterior pedal retractor; PA, posterior adductor; PL, pallial line; PR, posterior pedal retractor; 

R, resilifer.

Lamarck described. Vokes (1973, p. 49) described Chemnitz's figure (Chemnitz, 1782, pi. 21, fig. 207) as "a rather 

poorly executed oblique view of paired valves of a 

shell marked by apparently well-defined and depressed 

lunule and escutcheon. No illustration is given of the 

hinge structure and the description of the species 

(p. 217) [presumably Chemnitz, 1782] mentions it only in

generalized and non-definitive terms." "Obviously Lamarck was basing his description of the genus upon some 

source other than the Chemnitz figure and had mistakenly identified the form there shown with the material 

before him" (Vokes, 1973, p. 49). Stewart (1930) and 

Vokes (1973) concluded that the name Crassatella Lamarck is valid (although both state that the International
54 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 37. — Specific names relevant to Lamarck's original designation of Crassatella that have been used as type species for the genus

*, objective synonyms based on the author's references to the same set of figures. These names are discussed on p. 52-55, this paper. For a complete discussion of

subsequent type designations see Stewart (1930, p. 134-136)]

Species Author Date Reference Comment

Unknown.............. Chemnitz

Mactra cygnea... 

Venus plumbea*.

Venus ponderosa* 

Mactra cygnea...

Chemnitz 

Chemnitz

Gmelin 

Lamarck

Crassatella gibba* ..... Lamarck

Crassatella tumida*... Lamarck

? "Naturf. 19, t. 8, f. 

a-d".

1782 Conchylien Cabinet, v.

6. pi. 21, fig. 207.

1783 Conchylien Cabinet, v.

7. p. 5, pi. 69, figs. A,

B. 

1791 Systema Naturae, v. 1,

pt. 6, p. 3280. 

1799 Memoire Societe

d'Histoire Naturelle,

v. 1, p. 85.

1801 Systema Animaux Sans 

Vertebres, p. 119.

1805 Annales du Museum 

d'Histoire Naturelle, 

v. 6, p. 408-409.

This reference is cited by Chemnitz (1783) and Gmelin 

(1791), but the publication referred to and species illustrated are unknown.

Refers to Chemnitz, "Naturf. 19, t. 8, f. a-d."

Refers to Chemnitz, "Naturf. 19, t. 8, f. a-d et Conch. 7, t.

69, f. A-D." 

Lamarck lists species as type for new genus. Refers to

"Chemn. 6, t. 21, f. 207," which subsequent authors

attribute to Chemnitz (1782), but description does not

match Chemnitz figure (fide Yokes, 1973). 

Lamarck refers to Chemnitz, "Conch. 7, Supp. t. 7, Supp.

69, litt. A, B, C, D. Mactra. Encycl. pi. 259, f. 3, a. b."

The first part of this reference corresponds to Chemnitz

(1783); the second is unknown.

Lamarck refers to Chemnitz, "Conch, vol. 7, tab. 69, litt. 

A, B. Mactra. Encyclop. pi. 259, f. 3, a, b. An mactra 

Cygnus. [sic] Gmel. syst. nat. 5, p. 3060?" First part 

of reference corresponds to Chemnitz (1783).

Commission on Zoological Nomenclature should rule on 

the generic name and its type species) on the basis that 

(1) Lamarck was naming and describing a distinct group 

and (2) Lamarck (1805, p. 408-409) stated that he "established" Crassatella tumida as characteristic of the 

genus. Vokes (1973, p. 52) further pointed out that "the 

name Crassatellites is not available under the provisions 

of articles 20 and 56(b) of the International Code." 

Article 56(c) of the most recent code (International 

Commission on Zoological Nomenclature, 1985, p. 105) 

states, "A genus-group name formed for use in palaeontology by substituting -ites, -ytes, or -ithes for the 

original termination of a generic name, and applied only 

to fossils, enters into homonymy."

The confusion about Lamarck's original designation 

has led to the use of numerous specific names as types for 

the genus Crassatella', the names relevant to Lamarck's 

original designation are listed in table 37. As stated 

above, when Lamarck (1799, p. 85) identified Mactra 

cygnea Chemnitz as the type species for Crassatella, he 

was examining a Crassatella. A comparison of the 

generic descriptions for Mactra (Lamarck, 1799, p. 85) 

and Crassatella (Lamarck, 1799, p. 85) resolves any 

doubts; Crassatella is described as having closed valves, 

whereas Mactra has gaping valves. Two species of 

Crassatella were listed by Lamarck in 1801. Crassatella 

gibba (Lamarck, 1801, p. 119) refers to a specimen 

illustrated by Chemnitz "Chemn. Conch. 7, Supp. t. 69, 

litt. A, B, C, D; [Conchylien Cabinet, 1783] Mactra.

Encycl. pi. 259, f. 3, a. b. 19). Subsequently, Lamarck 

(1805, p. 408^109) named and described Crassatella 

tumida (figured by Lamarck, 1807, pi. 20, figs. 7a, 7b); it 

is this species that he identified as being characteristic of 

the genus. Lamarck gave the same citation for Crassatella tumida in 1805, as he had given for C. gibba in 

1801: Chemnitz, "Conch, vol. 7, tab. 69, litt. A, B. 

Mactra. Encyclop. pi. 259, f. 3, a, b.," adding "An 

mactra Cygnus. [sic] Gmel. syst. nat. 5, p. 3060?" 

Crassatella tumida is therefore a synonym of C. gibba. 

Complicating matters further, Gmelin (1791, p. 3280) 

cited the same Chemnitz illustrations "Naturf. 19, t. 8. f. 

a-d et Conch. 7. t. 69. f. A-D" under the name Venus 

ponderosa. Finally, Chemnitz (1783, p. 5) referred to his 

own illustration (Conch. Cab., Supp. v. 7, pi. 69, figs. 

A-D) as Venus plumbea.

All of these names—"Mactra cygnea Chemnitz" 

Lamarck, 1799 [non M. cygnea Chemnitz, 1782], Crassatella gibba Lamarck, Crassatella tumida Lamarck, 

Venus ponderosa Gmelin, and Venus plumbea Chemnitz—have been considered synonymous by some 

authors and therefore used as types for the genus 

Crassatella (table 37). Vokes (1973, p. 50) pointed out 

that V. plumbea, however, is not available because the 

International Commission on Zoological Nomenclature 

ruled that new specific names published in Neues Systematiches Conchylien Cabinet by Martini and Chemnitz

19 I have been unable to identify what text Lamarck is referring to when he 

cites "Encycl." Vokes (1973) and Stewart (1930) do not discuss this.
SYSTEMATIC PALEONTOLOGY 55

are rejected because the rules of binomial nomenclature 

were inconsistently applied.

Chavan (1969, p. N573) and Yokes (1973, p. 50) retain 

Mactra cygnea Lamarck, 1799 [non M. cygnea Chemnitz, 1782], 20 along with Cmssatella tumida, Cmssatella 

gibba, and Venus ponderosa, as synonyms and the type 

species for Cmssatella. I prefer Stewards (1930, p. 135) 

type designation, which omits M. cygnea] I agree with 

Yokes20 that M. cygnea Lamarck does not exist, but I 

also believe it is too presumptuous to assume the specimen Lamarck saw in 1799 was the same species he cites 

in 1801 and again in 1805. Crassatella tumida Lamarck, 

1805 is clearly identified as characteristic of the genus by 

Lamarck, so this species, and any which are synonymous 

with it, should be considered the type species of Crassatella. I therefore follow Stewart; the type species for 

Crassatella Lamarck should be cited as Crassatella 

tumida Lamarck, 1805 = Crassatella gibba Lamarck, 

1801 = Venus ponderosa Gmelin, 1791 [non Mactra 

cygnea Chemnitz, 1782].

Subdivision of Crassatella.—The name Crassatella 

historically has been applied to many diverse species no 

longer considered part of the genus. Since Lamarck's 

original description of the genus in 1799, numerous 

subdivisions have been proposed. Conrad (1869a, p. 47) 

was the first to attempt such subdivision, believing he 

detected a generic level difference in the hinge structure 

of the Cretaceous through Eocene Crassatella, versus 

the Miocene and younger Crassatella. He erected a new 

genus Pachythaerus for the older species and designated 

Crassatella Vindiemensis d'Orbigny [sic, Conrad; = C. 

Vindinnensis d'Orbigny, 1844] as the type species. The 

following key points in general were noted correctly by 

Conrad21 : (1) the triangular receptor pit behind the 

cardinal tooth, and below the resilifer on the right valve, 

is wider in species older than Miocene, (2) a small pit at 

the base of the posterior cardinal, below the resilifer, on 

the left valve is present in species older than Miocene but 

is absent in many younger species, (3) the interior 

ventral margins of the older species are always crenulated [in well-preserved adult specimens], whereas the 

Miocene or younger species may or may not be crenulated, and (4) the resilifer of the Cretaceous species is 

much smaller than that of Miocene and younger species, 

but the difference in early Tertiary species is not as 

distinctive (compare pi. 21, fig. 15 to pi. 21, figs. 8, 10,

20 Yokes (1973, p. 50) uses the form "Mactra cygnea Chemnitz' Lamarck, 1799 

[non M. cygnea Chemnitz, 1782]" and correctly states, "It is to be noted that 

Lamarck did not describe any species in 1799 and technically there is no such 

species as 'Mactra cygnaea [sic] Lamarck.' " The latter is the form used by 

Chavan (1969, p. N573).

21 There are exceptions to any generalization. Crassatellids fitting Conrad's 

description of the Late Cretaceous and early Tertiary group have been found in 

recent oceans (Vokes, 1973), but the majority of prevalent species reflect the 

characters noted in Conrad's observations.

and pi. 21, fig. 17). Despite these correct observations, 

Conrad should have retained the name Crassatella for 

the older group because the type for the genus Crassatella tumida [= C. gibba = Venus ponderosa] (Eocene, 

Paris basin) falls in this category.

In 1872, Conrad (1872, p. 50) reduced Pachythaerus to 

subgeneric rank; he included three unrelated species in 

the subgenus: Crassatella Pteropsis [sic] Conrad [herein 

= Bathytormus pteropsis (Conrad)]; C. Ripleyana [sic] 

Conrad [herein = C. vadosa Morton]; and C. ligeriensis 

d'Orbigny, 1844. The inclusion of B. pteropsis in the 

subgenus Pachythaerus blurs Conrad's (1869a, p. 47) 

original distinction of the group because the hinge of 

Bathytormus does not fit the character of the hinge of 

Pachythaerus as described by Conrad (1869a, p. 47). In 

fact, the hinge of Bathytormus bears a striking resemblance to many of the Miocene and younger forms, and 

Bathytormus may very well have been the ancestor to 

the more recent forms of crassatellids as discussed in the 

section "Patterns and Trends Among the Crassatellidae," 

page 92 (compare pi. 21, figs. 13 to 15). Since 1869, 

Pachythaerus has been alternately synonymized with 

Crassatella (Tryon, 1884, p. 224; Whitfield, 1885, p. 115; 

Fischer, 1887, p. 1022; Ball, 1903, p. 1467, 1468), maintained as a distinct subgenus (Stewart, 1930, p. 137; 

Chavan, 1952, p. 119; Chavan, 1969, p. N574), and 

maintained as a distinct genus (Vokes, 1946, p. 177).

Scambula Conrad, 1869a, has been included in Crassatella as a subgenus or section by several authors 

(Tryon, 1884, p. 224; Fischer, 1887, p. 1022; Ball, 1903, p. 

1467), but it is clearly a distinct genus (compare pi. 21, 

figs. 5 to 8), as the statistical analysis in this paper 

verifies, and is discussed under its own heading (p. 88).

The subgenus Landinia was described by Chavan 

(1952, p. 119; 1969, p. N574) as a "Narrow form, elongated in back, with persistent lamellous cords; hinge 

with two more oblique, anterior lamellars longer than 

Crassatella', strong furrow and ridge, fPII, PHI, elongated" (translated from French, Chavan, 1952, p. 119, 

footnote 3). Crassatella landinensis Nyst, 1843 is the 

type species. Chavan included Crassatella vadosa Morton, among other species, in Landinia.

The genus Crassatella was clarified and refined by 

Stewart (1930, p. 137-140); he evaluated the crassatellids 

and identified one new genus, Bathytormus, and discussed in detail Eucrassatella Iredale, 1924. Species 

having unrestricted resilifers extending to the border of 

the hinge plate were separated into the genus Bathytormus. Gardner (1916, p. 649) was the first to note 

distinctive differences between individuals herein 

assigned to Bathytormus and typical Crassatella. It was, 

however, the differences in shape of the posterior margin 

between C. vadosa Morton and C. pteropsis Conrad 

[herein = Bathytormus pteropsis] that she recognized,
56 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

not the generic level differences seen in the hinge 

(compare pi. 21, fig. 8, to figs. 10, 17). Following the 

publication of Stewart's revision, Stephenson (1941, p. 

176) recognized two subgroups within the Cretaceous 

species of Crassatella on the basis of the same differences in the hinge noted by Stewart, but he did not 

recognized or discuss Bathytormus. Although the position and extent of the resilifer is the key diagnostic 

character of Bathytormus, this genus proved to be 

distinct from Crassatella during the statistical analysis 

portion of this study, even when variables related to the 

resilifer were not included.

The genus Eucrassatella, as defined by Iredale (1924, 

p. 202) and recognized by Stewart (1930, p. 139-141), 

contains Neogene species having a large ligamental 

cavity and smooth internal margin (pi. 21, figs. 15,16, for 

example). The characters cited as distinctive of Eucrassatella parallel those differences discussed by Conrad 

when he separated the Cretaceous and lower Tertiary 

species into Pachythaerus (Conrad, 1869a, p. 47). 

Despite Stewart's recognition and discussion of the characters originally used by Conrad in the separation of 

Pachythaerus from Crassatella, he did not synonymize 

Pachythaerus with Crassatella. Stewart allowed the 

subgenus to stand for the Upper Cretaceous species on 

the basis of the presence '-of higher beaks and steeper 

umbonal slopes, characters not originally mentioned by 

Conrad.

The genus Crassatella, as herein defined, encompasses those species having a restricted ligamental cavity and crenulated margin in their adult stages. Any 

further subdivision of the genus obfuscates the natural 

variability seen within the species, populations, and 

individuals of Crassatella and imposes a false order. 

Using the characters that Chavan (1969, p. N573-N574) 

considered diagnostic of the three subgenera, Landinia, 

Pachythaerus, and Crassatella s.s., it is impossible to 

assign the individual species herein studied to a subgenus. The characters cited, such as "obliquely truncate 

posteriorly; compressed" (Chavan, 1969, p. N574) for 

Landinia, or "prominent dorsal slope" (Chavan, 1969, p. 

N574) for Pachythaerus, vary within single individuals 

during their ontogeny. Furthermore, Chavan (1952, p. 

119) assigns C. vadosa Morton to the subgenus Landinia, whereas C. ripleyana Conrad was assigned by 

Conrad (1872, p. 50) to the subgenus Pachythaerus', 

these two species are herein demonstrated to be synonymous. Finally, such species as C. tumidula (pi. 15, figs. 

1-17) do not fit in any subgeneric category as currently 

defined, so either revision of the subgenera or the 

erection of a new subgenus would be necessary to 

accommodate them. I believe the subgeneric divisions 

Landinia and Pachythaerus should be suppressed. The 

genus Crassatella should be allowed to stand by itself,

including its full range of variation; false subdivisions 

lacking diagnostic characters should not be imposed.

In addition to the subgenera relevant to this study and 

discussed above, the following subgenera have been 

proposed for Crassatella: Crassatella (Rochella) Freneix (1972, p. 135-136); Crassatella (Sublandinia) Freneix (1972, p. 142); and Crassatella (Riosatella) Vokes 

(1973, p. 48-59). I have not examined the validity of 

these names, but if they are based on continuously 

variable characters, as are the subgenera examined 

above, instead of clearly diagnostic characters, then 

these names should also be suppressed.

Distribution and validity of species.—One of the early 

discoveries of Crassatella (as herein defined) in North 

America was by Conrad (described by Morton, 1834, p. 

66) in the Prairie Bluff Chalk in Alabama (pi. 1, figs. 2, 

3). Conrad (1838, p. 20; 1846, p. 395) also recognized the 

genus in Tertiary deposits of New Jersey, Maryland, 

Virginia, North Carolina, and Alabama and in Cretaceous deposits of New Jersey (figs. 2, 19). Numerous 

species names have been proposed over the years since 

Conrad's first recognition of the genus in 1834 (table 1). 

Dall (1903, p. 1469) correctly pointed out that many of 

the names that exist in the literature for North American 

crassatellids are "nominal." However, many of the 12 

species, such as C. sepulcollis [herein = C. aquiana 

Clark], that Dall (1903, p. 1469) stated were nominal and 

"ill-defined or doubtful Eocene forms described from 

fragments or internal casts," are species that are abundant and represented by extremely well preserved material. Furthermore, C. carolinensis Conrad, 1875, a Cretaceous form, is included in Ball's (1903, p. 1469) list of 

Eocene crassatellids.

Three valid species in the Cretaceous, and two valid 

species in the lower Tertiary, are herein recognized for 

the eastern Gulf Coast and Mid-Atlantic regions of the 

United States (fig. 19). The statistical analysis herein 

demonstrates that, within this group of Crassatella, 

there is a large degree of intraspecific variation that 

contributes to the difficulty of isolating species characters. The five Crassatella species described below can be 

distinguished visually by the characters of the juvenile, 

the details of the ornament, the position and height of the 

beak, and the characters of the posterior margin. The 

best statistical discriminators of the species are the 

characters of the dorsal margin and the height of the 

posterior margin.

One problem prevalent in the taxonomic literature of 

the Crassatellidae is the failure to recognize juvenile 

members of the fauna. Immature specimens often are 

identified as separate species, or even separate genera, 

which contributes to the proliferation of taxonomic 

names. This problem was first acknowledged for the 

crassatellids by Smith (1881, p. 489^191). Specific names
SYSTEMATIC PALEONTOLOGY 57

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FIGURE 19.— Comparison of the ranges of the published Crassatellidae 

species (see fig. 4) with ranges determined in this study. Generic 

abbreviations: C., Crassatella (incorporates Crassatellites, junior 

synonym of Crassatella); G., Gouldia; U., Uddenia; S., Scambula;

based on juveniles are synonymized herein and are 

discussed under the heading of their new assignments.

Uddenia Stephenson is the one genus, within the 

Crassatellidae studied herein, that was founded on a 

juvenile specimen. Stephenson (1941, p. 180) designated 

Gouldia conradi Whitfield [non Crassatella conradi 

Whitfield] as the type species for his new genus; the 

description of Uddenia is as follows:

This tiny member of the Crassatellidae has heretofore been 

referred by different authors to Crassatellites, Gouldia, and 

Eriphyla (of the Astartidae), though it obviously forms a 

group different from any of these genera. It is apparently 

nearest to Crassatella, from which it differs in its diminutive 

size, its shorter and higher outline, its straight, long steeply 

descending dorsal margins, its relatively long, narrow lateral 

teeth and sockets, and the high position of its adductor scars.

With the exception of the steeply sloping dorsal margins, 

these characters are compatible with the description of a 

juvenile Crassatella, and I believe this inconsistency can 

be attributed to the incomplete preservation of the type 

specimens of G. conradi Whitfield (ANSP 18735; pi. 22, 

figs. 1-4). Stewart (1930, p. 147) indicated Gouldia was a 

juvenile Crassatella, and an examination of the type 

specimens of G. conradi Whitfield confirms this. The

B., Bathytormus. Species are arranged in alphabetical order. Four 

species names were omitted due to lack of stratigraphic information. 

See table 1 for complete listing of species.

genus Uddenia is therefore considered a junior synonym 

of Crassatella.

Many additional small specimens have been assigned 

to Uddenia since its inception. Where possible, these are 

synonymized below, but the poor preservational state of 

many of the shells (pi. 22, figs. 5, 6, for example) makes 

reassignment impossible in all cases. The hinge of U. 

texana Stephenson (1941, p. 181) is not visible on the 

type material, but the exterior characters resemble a 

small triangulate form (pi. 13, figs. 1-5) found with 

Crassatella vadosa Morton in the Gulf Coast and MidAtlantic deposits. U. texana and the unnamed group 

(genus and species unknown) have the general appearance of a Crassinella, but an examination of the hinge of 

the unnamed group reveals that it is not a member of the 

Crassatellidae (compare pi. 13, figs. 1-3 to pi. 12, figs. 2, 

4 and pi. 6, fig. 2). Unlike Crassatellidae, the resilifer of 

the triangulate form is located centrally below the beak 

and between the cardinals. The lack of any knowledge 

about the internal characters of U. texana makes it 

impossible to determine whether it is a juvenile crassatellid, like Gouldia conradi, or whether it belongs in a 

different family. The statistical analysis of the genera of 

Crassatellidae supports the conclusions drawn here;
58 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

Uddenia was statistically a poorly defined genus that 

intermingled with other Crassatellidae on the plots and 

classification results. The unnamed group was statistically distinct from the other genera.

Many names exist in the literature that cannot be 

resolved (table 1; fig. 19). The following are species 

assigned to Crassatella within the geographic and stratigraphic ranges of this study but are based on specifically 

indeterminable internal molds or poorly preserved specimens:

1. Crassatella alta CONRAD, 1835, p. 335-336 [mentioned in a discussion of the stratigraphy; contains no description or illustration of species]. 

Crassatellites alta CLARK and MARTIN, 1901, 

p. 182-183, pi. 42, fig. 3. PALMER and 

BRANN, 1965, p. 98 (= C. sp., p. 107). 

[non] Crassatella alta CONRAD, 1832, p. 21, 

pi. 7.

Conrad originally named and described Crassatella alta in 1832 from the bluffs at Claiborne, Ala. 

(Conrad, 1832, p. 21); thus, the reported range of C. 

alta in general falls outside the stratigraphic limits of 

this study. The synonymy given above is incomplete 

and, besides the original citation, only includes the 

specimens that fall within the stratigraphic and 

geographic ranges herein considered. Clark and 

Martin (1901, p. 182) found an imperfect specimen, 

having exterior characters preserved, in beds of the 

Aquia Formation at Hardesty, Prince George's 

County, Md. 22 They based their specific determination on a notation made by Conrad (1835, p. 335) 

stating that he had found a cast of C. alta in a stream 

bed in Upper Marlboro, Prince George's County, 

Md., an area where the Aquia Formation is known to 

crop out. The lack of complete preservation of Clark 

and Martin's specimen, the fact that Conrad's specimen was only a cast, and the fact that no such 

specimens have since been found in the well studied 

Aquia make this specific determination tenuous at 

best.

2. Crassatella palmula CONRAD, 1846, p. 396, pi. IV,

fig. 1. CLARK, 1896, p. 93. 

[non] Bathytormus alaeformis (Conrad) 

PALMER and BRANN, 1965, p. 49.

22 Presumably the Hardesty referred to by Clark and Martin (1901) is located 

in Prince George's County, 0.8 km west of the Patuxent Kiver, off Queen Anne 

Bridge Road, below Route 214, and 11.25 km northeast of Upper Marlboro; this 

location can be found on the 1913 map of Prince George's County (Maryland 

Geological Survey, 1911). In addition to the Hardesty in Prince George's County, 

present-day maps show a Hardesty in Anne Arundel County on Route 2 between 

the intersections of Route 2 with Route 214 and Route 424, south of Edgewater, 

approximately 9.5 km east-northeast of the Hardesty in Prince George's County; 

this locality cannot be found on the 1907 Maryland Geological Survey Atlas map 

of Anne Arundel County (Maryland Geological Survey, 1917).

Crassatella palmula was named and described by 

Conrad (1846, p. 396) from deposits near Upper 

Marlboro, Prince George's County, Md. After giving 

a complete description of the species, Conrad (1846, 

p. 396) states, "A single imperfect valve is all I have 

found of this species." This specimen (ANSP 30580; 

pi. 3, figs. 11, 13) appears to be a crassatellid, but it 

is in such a poor state of preservation that few 

diagnostic characters can be derived from it. Clark 

(1896, p. 93) arrived at the same conclusion; he states 

the name should be "debarred from the list of Eocene 

fossils of the Middle Atlantic slope." Although the 

name cannot be "debarred," it should be restricted to 

the type specimen. Palmer and Brann (1965, p. 49) 

have synonymized C. palmula with Bathytormus 

pteropsis (Conrad), a species that occurs in the type 

area of C. palmula, but I believe synonymization of 

such a poorly preserved specimen is impossible.

3. Crassatella monmouthensis GABB, 1860a, p. 302, 

pi. 48, fig. 19 [text lists as fig. 20]. WHITFIELD, 1885, p. 119, pi. 17, figs. 21, 22.

Etea monmouthensis (Gabb). CONRAD, 1877, p. 

275.

Crassatellites monmouthensis (Gabb). JOHNSON, 1905, p. 14.

Etea trapezoidea (Conrad). WELLER, 1907, p. 

543-546, pi. 58, figs. 20, 21, pi. 59, fig. 7 (C. 

monmouthensis Gabb junior synonym of 

Venilia [sic] trapezoidea Conrad, 1860, p. 282, 

pi. 47, fig. 7).

Veniella (Etea) trapezoidea Conrad. RICHARDS, 

1958, p. 175, pi. 28, figs. 8, 9, pi. 29, figs. 7, 

15.

The type collection contains four internal molds 

from Monmouth County, N.J. (ANSP 18738; pi. 22, 

figs. 7-9), the smallest of which is labeled "type." I 

agree with Welter's (1907, p. 545) comments that the 

smallest specimen appears different from the other 

three and that the smaller specimen is probably not 

the one that Gabb (1860a, pi. 48, fig. 19) illustrated; 

the quality of the original illustration, however, 

makes an absolute determination impossible. On the 

basis of the strong angulation of the posterior ridge 

and the low profile of the adductors on the internal 

molds, I believe the three larger molds are specimens of Etea (Arcticidae). The state of preservation 

of the smallest specimen makes a familial as well as 

generic determination difficult. Since Gabb's description and illustration correspond more closely to Etea 

than to Crassatella, the name Crassatella monmouthensis is not discussed further in this study of 

the Crassatellidae.
SYSTEMATIC PALEONTOLOGY 59

4. Crassatella delawarensis GABB, 1860a, p. 303, pi.

48, fig. 20 [text lists as fig. 21]. 

Etea delawarensis (Gabb). CONRAD, 1877, p.

275.

Crassatellites delawarensis (Gabb). JOHNSON, 

1905, p. 14.

Additional descriptions of specimens that have 

been synonymized with Crassatella delawarensis 

Gabb:

Crassatella delawarensis Gabb. WHITFIELD,

1885, p. 119, p. 210, pi. 27, figs. 14, 15.

PALMER and BRANN, 1965, p. 106 (C.

delawarensis Whitfield non Gabb = C. sp.). 

Etea delawarensis (Gabb). WELLER, 1907, p.

546, pi. 59, figs. 8, 9. RICHARDS, 1958, p.

177, pi. 28, fig. 4, pi. 29, fig. 11, pi. 31, fig. 1.

Named from a single internal mold having a portion of replaced shell material adhering to the mold, 

this specimen (ANSP 18733; pi. 22, figs. 10-12) is of 

dubious locality and stratigraphic position. A label in 

Gabb's handwriting found with the specimen lists the 

locality as Crosswicks, N.J., but the text states the 

type locality is a "deep cut, Delaware and Chesapeake Canal" (Gabb, 1860a, p. 303). The age of the 

specimen is therefore questionable; the Delaware 

and Chesapeake Canal locality is Cretaceous, and the 

present-day Crosswicks Creek locality is Cretaceous, but since Crosswicks Creek drains both Cretaceous and Tertiary strata, a specimen from Crosswicks Creek could be from either period. Whitfield 

(1885, p. 210) and, later, Weller (1907, p. 546) 

believed that they found individuals of this species in 

the Manasquan Formation (late Paleocene and early 

Eocene). Richards (1958) figures three specimens of 

Etea delawarensis; the first (Richards, 1958, pi 31, 

fig. 1) is the type specimen; the second (Richards, 

1958, pi. 29, fig. 11) is similar in form to the type and, 

like the type, appears extremely worn; the third 

(Richards, 1958, pi. 28, fig. 4) appears similar to 

Crassatella transversa Gabb. The type specimen 

resembles a Bathytormus because of its elongate 

posterior, oblique posterior adductor, and strong 

posterior ridge. The questionable locality information and the poor preservational state of the specimen, however, make it necessary to restrict the 

name C. delawarensis Gabb to the type specimen.

5. Crassatella cuneata GABB, 1861a, p. 168-169 [new

assignment for Crassatella pteropsis GABB,

1860b, p. 395, pi. 68, fig. 28, non Conrad, I860].

Crassatella gabbi SAFFORD, 1864, p. 368 [new

assignment for Crassatella pteropsis GABB,

1860b, p. 395, pi. 68, fig. 28, non Conrad,

I860].

The following citations have been synonymized 

with Crassatella pteropsis Gabb non Conrad, but a 

direct relationship to the type cannot be confirmed:

Crassatella cuneata Gabb. WHITFIELD, 1885, 

p. 118, pi. 17, figs. 18-20.

Crassatella gabbi Safford. HARRIS, 1896, p. 63,

pi. 5, figs. 7-11 [Palmer and Brann, 1965 say,

"in part, pi. 5, figs. 7, 7a type, 8, 9, not figs.

10, 11"]. PALMER and BRANN, 1965, p.

100-101. TOULMIN, 1977, p. 147-148, pi. 2,

figs. 1, 2. 

Crassatellites cuneatus (Gabb). WELLER, 1907,

p. 556, pi. 61, figs. 11, 12. RICHARDS, 1958,

p. 185, pi. 31, fig. 2. 

Crassatellites gabbi (Safford). GARDNER, 1933,

p. 151-152.

Gabb's original description of Crassatella pteropsis [non Conrad] in 1860 gives the following locality 

information: "Ripley Group, Hardeman Co., Tenn., 

Prof. Safford; and from the same formation at 

Eufaula, Ala. Collection of the Smithsonian Institution, No. 553" (Gabb, 1860b, p. 395). USNM specimen 553 is extremely damaged, but no notation with 

the specimen indicates that this damage occurred 

since it was designated as Gabb's type, nor is there 

any indication of provenance. The figure presented 

by Gabb (1860b, pi. 68, fig. 28) and the measurements given in the text (Gabb, 1860b, p. 395) do not 

seem to correspond to USNM 553, although the 

damage to the specimen leaves room for doubt. The 

type locality for C. pteropsis Gabb [non Conrad] 

remains questionable, although subsequent authors 

have presumed (probably correctly) that it was 

Hardeman County, Tenn.

The age and formation of the species also have 

been questioned by various authors. Gabb placed the 

species in the Cretaceous Ripley "Group," but the 

Ripley, as previously defined in Tennessee, has 

included lower Tertiary beds. In addition, an examination of the other species Gabb included in the 

Cretaceous Ripley "Group" contains some distinctly 

Tertiary fauna such as the Turritella species (Gabb, 

1860b, p. 392, pi. 68, fig. 13). Confounding the 

problem of stratigraphic position, both Cretaceous 

and Tertiary beds crop out in Hardeman County, 

Tenn.

In 1861, Gabb (1861a) recognized his name Crassatella pteropsis as a junior homonym of Conrad's 

species and renamed it C. cuneata. Subsequently, 

Safford (1864, p. 368), apparently oblivious to Gabb's 

reassignment, himself reassigned Crassatella 

pteropsis to C. gabbi Safford. From this point on, not
60 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

a single author acknowledged that Crassatella 

cuneata Gabb and C. gabbi Safford were based on 

the same original species description and type, C. 

pteropsis Gabb non Conrad, and are therefore synonyms. Gardner (1933, p. 151) states, "The Cretaceous species was later renamed C. cuneata by Gabb 

(1861a), the Midway species, C. gabbi by Safford/' 

but there is no indication that either Safford or Gabb 

intended a division of the species by age; both 

authors cite the occurrence of the species as the 

Cretaceous, Ripley Group. The name Crassatella 

cuneata [=Crassatellites cuneatus (Gabb)] has been 

applied to several Cretaceous internal molds and 

casts from New Jersey (Whitfield, 1885; Weller, 

1907; Richards, 1958). These subsequent designations cannot be confidently synonymized with Gabb's 

type because they are far removed from the type 

locality and are poorly preserved. In the Gulf Coast, 

Crassatella gabbi [=Crassatellites gabbi (Safford)] 

has been applied to Tertiary specimens of varying 

description (Harris, 1896; Gardner, 1933; Toulmin, 

1977). Although the Gulf Coast specimens are closer 

geographically to Gabb's presumed type, the state of 

preservation of the type specimen and the brief 

description do not permit confident synonymization 

here either. Harris (1896, p. 63, pi. 5, figs. 7, 7a) 

examined and figured Safford's "type," which can no 

longer be located (fide Palmer and Brann, 1965), but 

Safford never published a description or illustration 

of C. gabbi.

The name Crassatella cuneata Gabb is the senior 

synonym of C. gabbi Safford, and this name resides 

with the USNM specimen 553 by Gabb's (1860b, p. 

392) original designation; in my opinion, the name 

should be restricted to this specimen. The poor 

condition of the type makes it impossible to determine the validity of the assignments made by subsequent authors. The specimens that have been synonymized with C. cuneata Gabb and its junior synonym 

C. gabbi Safford need to be reevaluated. The New 

Jersey specimens assigned to C. cuneata are specifically indeterminable molds and casts. The Gulf 

Coast specimens assigned to C. gabbi may prove to 

be synonymous with other species, or an examination of the material may illustrate the need to erect a 

new species.

6. Crassatella transversa GABB, 1861b, p. 364-365.

WHITFIELD, 1885, p. 122, pi. 17, figs. 16, 17.

Etea transversa (Gabb). CONRAD, 1877, p.

275.

Crassatellites transversus (Gabb). JOHNSON, 

1905, p. 14. RICHARDS, 1958, pi. 61, fig. 5 

[figure of type but description taken from 

Weller, 1907].

Additional descriptions of specimens that have 

been synonymized with Crassatella transversa 

Gabb but that cannot be directly related to the 

type:

Crassatellites transversus (Gabb). WELLER, 

1907, p. 555, p. 61, fig. 5. RICHARDS, 1958, 

p. 185 [description only; figure is of the type 

specimen].

The species description was based upon a single 

phosphatic internal mold in the collection of the 

Burlington County Lyceum of Natural History (now 

ANSP 18744; pi. 22, figs. 13-15); the locality and 

formation are listed simply as "Cretaceous, New 

Jersey." Many stratigraphic units later described as 

Tertiary were included originally in the Upper Cretaceous, so it is possible that this was not even a 

Cretaceous specimen. The specimen illustrated and 

described by Weller (1907, p. 555, pi. 61, fig. 5) and 

the description repeated by Richards (1958, p. 185) 

cannot be related to the type Crassatella transversa 

by locality or stratigraphic position since no details of 

provenance were given with the type. Weller's 

(1907, pi. 61, fig. 5) specimen is also an internal mold, 

as is the type, but the poor state of preservation of 

this specimen makes a specific determination impossible. The shape of the posterior margin, the oblique 

position of the posterior adductor, the ratio of height 

to length, and the strong posterior ridge of the type 

C. transversa, all bear a striking resemblance to the 

Tertiary Bathytormus alaeformis (Conrad), a fact 

noted by Whitfield when he stated "in form it presents many features in common with C. protexta 

Conrad" [= Bathytormus alaeformis (Conrad)] 

(Whitfield, 1885, p. 122). Without more specific 

locality information and additional specimens, however, it is impossible to relate the type C. transversa 

Gabb to other species; the name should therefore be 

restricted to the type specimen.

7. Crassatella planata CONRAD, 1866, p. 104, pi. 8, 

fig. 4. CONRAD, 1867, p. 270.

Conrad based this name on an incomplete internal 

mold; no locality or stratigraphic position were designated in the original description. In 1867, he stated 

that he found the species in "the Cretaceous marl 

near Barnsboro," N.J. The type specimen is apparently missing (it does not appear in Johnson's (1905, 

p. 14) catalogue of ANSP Cretaceous types), but 

doubtless if it was available it would provide no 

further clues as to its specific identity.
SYSTEMATIC PALEONTOLOGY 61

8. Crassatella peralta CONRAD, 1866, p. 104, pi. 8, 

fig. 1 [plate citation as given in text, but pi. 8, 

fig. 1 caption reads Crassatella alta Conrad]. 

CONRAD, 1867, p. 270.

Conrad (1866, p. 104) originally described this 

species from an internal mold found at Goshen, Cape 

May County, N.J., which is a Tertiary locality. He 

also mentions finding "A very perfect ferruginous 

cast of this species from a new locality," but where 

the new locality is, and whether the figured specimen is from the "new locality" or from Goshen, 

remains in doubt. I believe the specimen Conrad 

figured on plate 8, figure 1 is the specimen he 

intended to call Crassatella peralta (despite the 

caption reading C. alta) because his description of C. 

peralta matches this figure. In 1867, Conrad (1867, 

p. 270) stated that he found this species in "the 

Cretaceous marl near Barnsboro. They are not found 

in the Miocene, as I supposed from the locality 

named on the specimens in the collection of the 

Academy." It is unclear whether Conrad believed 

the original locality label to be wrong or whether he 

believes he was mistaken in designating the Cape 

May County locality as Tertiary. This confusion over 

stratigraphic and geographic position of the species, 

the poor preservation of the originally figured specimen, and the fact that the type appears to be 

missing (Moore, 1962, p. 84; not in Johnson's (1905, 

p. 14) catalogue) makes it impossible to determine 

the validity of this species.

9. Crassatella prora CONRAD, 1869b, p. 43, pi. 1, fig. 

8. WHITFIELD, 1885, p. 120, pi. 18, figs. 10, 

11.

Etea prora (Conrad). CONRAD, 1877, p. 275. 

Crassatellites prorus (Conrad). JOHNSON, 1905, 

p. 14. WELLER, 1907, p. 558, pi. 61, figs. 6, 

7. RICHARDS, 1958, p. 186, pi. 29, fig. 6, pi. 

30, figs. 13, 14 [pi. 29, fig. 6 is a photograph of 

Conrad's type from ANSP; pi. 30, figs. 13, 14, 

is a reproduction of Whitfield's drawing of the 

same ANSP type].

Conrad's type specimen of Crassatella prora is an 

internal mold (ANSP 18739; pi. 22, figs. 16, 17). 

Another internal mold (pi. 22, figs. 18, 19) is present 

in the same box as the type specimen figured by 

Conrad (1869b), Whitfield (1885), Weller (1907), and 

Richards (1958). As far as I can determine, this 

second specimen has never been figured nor are 

there any notations on the labels to indicate where it 

came from, but it definitely belongs in the genus 

Etea (Arcticidae). Whitfield (1885, p. 121) indicated 

that a second smaller specimen "of the same form" 

was found with Conrad's type, but since the second

specimen now residing with the type is larger than 

the type specimen, it would seem this is not the 

specimen to which Whitfield referred. No additional 

specimens from the type locality of Crosswicks, 

N.J., have been illustrated, although Richards (1958) 

indicates he found specimens of this species in the 

Merchantville Formation at Matawan, Monmouth 

County, N.J. The worn condition of Conrad's type 

specimen (pi. 22, figs. 16,17) makes specific and even 

generic determination difficult, but it does appear to 

be a crassatellid. In the absence of determinant 

characters, the name Crassatella prora Conrad [= 

Crassatellites prorus (Conrad)] should be restricted 

to the type specimen illustrated by Conrad (1869b, 

pi. 1, fig. 8).

10. Crassatellites newkirkensis STEPHENSON, 1923, 

p. 268, pi. 67, figs. 17-19.

The holotype of Crassatellites newkirkensis is a 

compressed articulated calcite-replaced specimen 

(USNM 31744), and the paratype is an internal mold 

(USNM 31745). Three (herein = Iocs. 12, 19A, 20) of 

the six localities listed by Stephenson (1923, p. 269) 

for Crassatellites newkirkensis are also localities for 

Crassatellites hodgei Stephenson (1923, p. 272-273) 

[herein = Crassatella hodgei (Stephenson)]. The 

compressed nature of the holotype makes any 

detailed comparisons of shape between Crassatellites newkirkensis and other species impossible, but 

the preserved characters of the ornamentation are 

consistent with those of Crassatella hodgei. The 

relationship of the internal mold to the holotype is 

difficult to establish. Further, Stephenson's study 

collection from North Carolina was examined, and 

the majority of specimens he had labeled as Crassatellites newkirkensis were internal molds, most of 

which could easily have been assigned to either 

Crassatella carolinensis Conrad or Crassatella 

hodgei. In fact, Stephenson had originally labeled 

some of these specimens Crassatellites carolinensis 

[herein = Crassatella carolinensis Conrad] then 

later crossed this out and wrote Crassatellites 

newkirkensis. It is therefore recommended that the 

name Crassatellites newkirkensis reside only with 

the holotype specimen.

11. Crassatellites neusensis STEPHENSON, 1923, p. 

270, pi. 67, figs. 1-3.

The holotype of Crassatellites neusensis (USNM 

31735) has been destroyed,23 and the two remaining

23 Several specimens of North Carolina types are lost or destroyed, probably 

due to an accident in the 1950's when a drawer of North Carolina types was 

dropped at the Smithsonian Institution (N.F. Sohl, U.S. Geological Survey, oral 

commun., 1987).
62 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

paratypes (USNM 31736 and USNM 31737, pi. 2, 

figs. 4, 5) are both worn left valves, with original 

shell material preserved, but encased in matrix so 

that the internal features are not visible. For erassatellites neusensis, Stephenson (1923, p. 271) lists 

three localities, two of which are also localities for 

Crassatellites hodgei Stephenson [herein = Crassatella hodgei (Stephenson)]. Crassatellites neusensis could easily be a juvenile of Crassatella hodgei 

(compare pi. 2, figs. 4, 5 to pi. 2, figs. 8, 11 and pi. 5, 

fig. 9); the characters of general shape and the 

ornamentation remaining on the specimens are consistent with such a designation, and the largest 

specimen observed among the types and Stephenson's study collection was approximately 2.5 cm in 

length. The poor condition of the paratypes and the 

specimens in the study collection, however, prevents 

examination of such key characters as the hinge 

structure, the orientation of the muscle scars, and 

the details of the juvenile ornamentation, which 

would allow confident synonymization with Crassatella hodgei. Therefore, it is recommended that 

the name Crassatellites neusensis be restricted to 

the paratype specimens.

The following species names exist in the literature, but 

their validity cannot be confirmed due to the lack (or 

unavailability) of a type specimen and the lack of any 

specimen (topotype or otherwise) in existing collections 

that fits the original description:

1. Crassatella alabamensis D'ORBIGNY, 1850, p. 239.

The type locality is Prairie Bluff, Ala., but d'Orbigny stated that the specimen had a different form 

from Crassatella vadosa Morton. Yet, he compared 

Crassatella alabamensis to C. marrotiana d'Orbigny, 1844, which bears a strong resemblance to C. 

vadosa Morton. The type Prairie Bluff Chalk has 

been studied extensively for the last 140 years, and 

no additional reports of Crassatella alabamensis 

have emerged.

2. Crassatella littoralis CONRAD [nomen nudum], 

1868, p. 731. CONRAD, 1869b, p. 41, pi. 1, fig. 

3. WHITFIELD, 1885, p. 212, pi. 28, figs. 6, 7. 

PALMER and BRANN, 1965, p. 102. 

Crassatellites littoralis (Conrad). WELLER, 

1907, p. 559, pi. 61, figs. 9, 10.

Conrad (1868, p. 731) included Crassatella littoralis in a list of fossils from the "blue marl layer" of the 

Shark River Formation of New Jersey; this places 

Crassatella littoralis in the Eocene, Claibornian 

Stage, and therefore out of the range of this study. 

Weller (1907, p. 559), however, extended the range 

of Crassatellites littoralis (Conrad) [= Crassatella

littoralis Conrad] down into the Manasquan Formation, Wilcox Stage of the Paleocene, which is 

included in this study. The type specimen, an internal mold from Shark River, N.J., has apparently 

been lost from the collections of ANSP (Moore, 1962, 

p. 72), and the figure and description provided 

by Conrad do not distinguish this species from 

many similar forms of Crassatella. The question of 

the validity of this species must therefore remain 

unresolved.

3. Crassatella rhombea WHITFIELD, 1885, p. 

213-214, pi. 27, figs. 16-19. PALMER and 

BRANN, 1965, p. 103.

Crassatellites rhombea (Whitfield). WELLER, 

1907, p. 561, pi. 61, fig. 8.

Whitfield (1885, pi. 27, figs. 18-19) figured two 

specimens with his original description, one an internal mold from Squankum, N.J., and the other "preserving the shell" from near New Egypt, N. J. (Whitfield, 1885, pi. 27, figs. 16-17). Judging from Weller's 

(1907, pi. 61, fig. 8) photograph, the New Egypt 

specimen is little more than an internal mold that has 

some shell material adhering to the matrix. Whitfield 

(1885, p. 214) states that "The shell differs in its 

general form and outline from any American species 

hitherto described .... The internal cast differs 

from all American species in its transverse form and 

broad posterior end." Yet the illustrations for Crassatella rhombea display a striking resemblance to 

Whitfield's (1885, pi. 18, figs. 4-16) figures of Crassatella subplana Conrad in the same volume. Since 

Whitfield's designation of Crassatella rhombea as a 

Tertiary species is in agreement with current New 

Jersey stratigraphy, it is possible that C. rhombea is 

related to the Cretaceous form Crassatella vadosa 

Morton [herein = C. subplana Conrad]. On the other 

hand, Crassatella rhombea may be the internal mold 

of a common Tertiary form seen in the Gulf Coast, or 

it may be a separate species, but without better 

preservation and additional material none of these 

possibilities can be confirmed.

4. Crassatella conradi WHITFIELD, 1885, p. 209, pi. 

28, figs. 1-5 [plate caption says Crassatella 

curia ?]. WELLER, 1907, pi. 61, figs. 9, 10 

[figures illustrate Whitfield's type specimens; 

text synonymizes with Crassatellites littoralis 

(Conrad)]. PALMER and BRANN, 1965, p. 

99-100.

Crassatella conradi was named by Whitfield 

(1885, p. 209) from internal molds from Squankum 

and New Egypt, N.J. Three specimens are figured 

with the caption "Crassatella curta Conrad ?"; Whitfield discussed these individual specimens under C.
SYSTEMATIC PALEONTOLOGY 63

conradi, however, and mentioned that he "at first 

thought these casts might be the same specifically as 

that described by Conrad as C. curta" (Whitfield, 

1885, p. 210). I believe the plate caption is in error 

and perhaps was prepared prior to the text. One 

specimen illustrated by Whitfield (1885, pi. 28, fig. 3) 

(AMNH 9015/1) is not a crassatellid (it may be 

a Cucullea). The other two specimens may be 

crassatellids, but since they are lost (fide Palmer 

and Brann, 1965, p. 100) no assignment, including 

Weller's (1907, p. 559) synonymization of Crassatella 

conradi under Crassatellites littoralis, can be 

validated.

The following species name is invalid:

Crassatella eufalensis [sic] Gabb. BOYLE, 1893, p. 

101.

Boyle (1893, p. 101) lists Gabb (1860b, p. 394, pi. 

68, fig. 26) as the author of the species, but this 

citation refers to Corbula eufalensis [sic] Gabb. The 

confusion may have resulted because Gabb cited 

Corbula eufalensis as C. eufalensis under the heading Corbula, but the facing page (Gabb, 1860b, p. 

395) contains the Crassatella descriptions. Subsequent authors have included Crassatella eufaulensis 

[the modern spelling of Eufaula, Ala.] in faunal lists, 

but no description or illustration of Crassatella 

eufalensis [= Crassatella eufaulensis] exists in the 

literature. The name Crassatella eufalensis [= 

Crassatella eufaulensis] is not based on a specimen 

and is therefore unfounded.

The specific names presented below (p. 63-92) are 

herein considered valid species of Crassatellidae in the 

Upper Cretaceous and lower Tertiary strata of the Gulf 

Coast and Mid-Atlantic regions of the United States.

Crassatella vadosa Morton, 1834

Plate 1, figures 1-17; plate 5, figures 1, 3, 4, 6;

plate 7, figures 1-15; plate 8, figures 1-16;

plate 9, figures 1-13; plate 10, figures 1-17;

plate 11, figures 1-13; plate 12, figures 1-5;

plate 21, figures 6, 8

Crassatella vadosa MORTON, 1834, p. 66, pi. 13, fig. 12. GABB, 1877, 

p. 310-311. WHITFIELD, 1885, p. 116-117, pi. 17, figs. 12-15. 

HARBISON, 1945, p. 80, pi. 1, fig. 2.

Crassatella subplana CONRAD, 1853, p. 274, pi. 24, fig. 9. WHITFIELD, 1885, p. 121, pi. 18, figs. 14-16 [incorrectly cites Conrad, 

1853, as p. 247].

Crassatella ripleyana CONRAD, 1858, p. 327, pi. 35, fig. 3.

Crassatella (Pachythaerus) ripleyana CONRAD, 1872, p. 50, pi. 1, 

fig. 7.

Crassatella lintea CONRAD, 1860, p. 279, pi. 46, fig. 5.

Crassatellites linteus (Conrad). JOHNSON, 1905, p. 14. GARDNER, 

1916, p. 653, pi. 39, figs. 6, 7. WADE, 1926, p. 80. RICHARDS, 

1958, p. 190, pi. 30, figs. 1, 2.

Crassatellites vadosus (Morton). JOHNSON, 1905, p. 14. GARDNER, 

1916, p. 649, pi. 39, figs. 1-4. WADE, 1926, p. 79, pi. 25, figs. 6-8. 

SHIMER and SHROCK, 1944, p. 419, pi. 167, figs. 1-3. RICHARDS, 1958, p. 189, pi. 29, fig. 10.

Crassatellites subplanus JOHNSON, 1905, p. 14. WELLER, 1907, p. 

553, pi. 61, figs. 1-4. GARDNER, 1916, p. 651 [quotes Conrad (1853, 

p. 274) and Weller (1907, p. 553-554)]. RICHARDS 1958, p. 187, pi. 

29, figs. 9, 12, 13 [quotes Weller (1907, p. 553-554; figs. 12, 13 

previously figured as Whitfield's (1885) pi. 18, figs. 14, 15].

Crassatellites ripleyanus JOHNSON, 1905, p. 14.

Crassatellites sp. STEPHENSON, 1923, p. 277, pi. 68, figs. 5-7.

Crassatellites carolinana STEPHENSON, 1927, p. 17, pi. 7, figs. 1, 

la, 2, pi. 8, figs. 1-3.

Crassatella vadosa ripleyana (Conrad). STEPHENSON, 1941, p. 177. 

STEPHENSON, 1955, p. 117, pi. 19, figs. 11-16.

Crassatella vadosa wadei STEPHENSON, 1941, p. 177.

Uddenia conradi (Whitfield). STEPHENSON, 1941, p. 180. RICHARDS, 1958, p. 191 [partim; description is copy of Whitfield (1885, 

p. 125); pi. 29, fig. 2 = Crassatella ? sp.]

Crassatella gardnerae HARBISON, 1945, p. 79, pi. 1, figs. 3, 4.

Uddenia fragilis HARBISON, 1945, p. 80, pi. 2, figs. 8, 9.

Crassatella (Landinia) vadosa Morton. CHAVAN, 1952, p. 119.

[?] Gouldia conradi WHITFIELD, 1885, p. 125, pi. 18, figs. 1-3.

[?] Eriphyla conradi (Whitfield). JOHNSON, 1905, p. 14. WELLER, 

1907, p. 550, pi. 60, figs. 6-8 [partim; figs. 6-8 reproduction of 

Whitfield's (1885, pi. 18, figs. 1-3) types; non pi. 60, figs. 4, 5 = 

familial assignment unknown].

[non] Crassatellites (?) conradi (Whitfield). STEPHENSON, 1923, p. 

274, pi. 67, figs. 10-16 [name preoccupied by Crassatella conradi 

Whitfield, 1885, p. 209, not = Gouldia conradi Whitfield, 1885, p. 

125].

Diagnosis.— Ornamentation shifts gradually from 

sharp, fine regular comarginal lineations of juvenile to 

coarser more irregular comarginal lineations of adult. 

Subdued posterior ridge. Beak usually positioned at 

anterior one-third of shell length on adults. Resilifer 

restricted on right valve by broad triangular socket at 

edge of hinge plate, on left valve by flared posterior 

cardinal and by well-defined pit at base of cardinal. 

Height and length of valve nearly equal on early stages of 

juvenile.

Description.—Shell equivalve, inflation shallow to 

ventricose; maximum convexity one-third to one-half of 

height from beak; shell smoothly convex to slightly 

flattened across umbo when viewed from dorsal or 

ventral margin parallel to plane of commissure; exterior 

outline of adult varies from triangular to trigonally 

suboval to nearly subquadrate; nepionic outline quadrate, height and length nearly equal; juvenile gradually 

shifts from more quadrate to more trigonal form during 

ontogeny. Inequilateral; beak position of adults at anterior one-third of shell length, juveniles at anterior twofifths; prosogyrous, beak strongly curved and pointed on 

juveniles, becoming less so on adults. Anterior dorsal 

margin straight to slightly concave; point of incurving 

varies from position just anterior to beak, to position 

opposite maximum width of lunule; slope of margin fairly 

steep; lunule well developed on left valve of adults with 

sharp ridge defining area, less well defined on right valve
64 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

with no distinct ridge; anterior margin smoothly 

rounded. Posterior dorsal margin typically straight to 

slightly concave at end of escutcheon on adults, juveniles 

convex at point where escutcheon forming; slope of 

margin varies from nearly flat on juveniles to steep on 

adults with trigonal outline; escutcheon elongate, well 

defined on right valve with area defined by ridge, less 

well defined on left valve with ridge absent; shape of 

posterior margin delineated by presence of subdued 

posterior ridge; posterior area arcuately truncate. Ventral margin smoothly rounded anteriorly, varies posteriorly from slightly convex to flattened to slightly concave 

below adductor. Nepionic shell ornamented by distinct 

high comarginal ridges, comarginal threads may be visible in interspaces; approximately first third of adult 

shell has regular raised sealer or sharp comarginal 

ridges; spacing of comarginal threads remains constant 

throughout ontogeny and is continuous across interspaces and ridges; interspaces exhibit variation in topography; comarginal ridges gradually become more and 

more pronounced, rounded, and less regular over second 

third of adult shell, forming ribs; undulations may appear 

on final third of adult shell, comarginal threads and ribs 

intact; ribs and undulations rarely cross posterior ridge 

into posterior area; ornament of posterior area primarily 

ridges and comarginal threads; radial element underlies 

exterior shell surface and may be exposed when surface 

worn. Hinge angle variable, average 104.91 degrees on 

adults; juvenile hinge more obtuse, average 109.91; 

moving from posterior lateral ridges across hinge plate to 

anterior lateral ridges, dentition may be noted as follows:

Right Valve 0 1 0-R 010 -101 

Left Valve 1 0 l-R(O) 1010 (1)-0 1 0

Right valve dentition consists of one posterior lateral 

ridge, separated by edentulous space from resilifer (R); 

resilifer originates at beak on platform formed by rear 

wall of trigonal socket below and slightly anterior to 

resilifer; opening of resilial platform to umbonal cavity is 

obstructed by position of small trigonal socket; trigonal 

socket may have vertical grooves on rear wall; one large 

cardinal tooth with transverse grooves on sides lies 

anterior to beak; anterior socket may exhibit transverse 

grooves on anterior wall; two anterior lateral ridges 

present, separated by groove. Left valve dentition consists of two posterior lateral ridges, separated by groove; 

resilifer originates at beak; opening of resilial area to 

umbonal cavity is impeded by flared base of posterior 

cardinal and well-defined pit at base of posterior slope of 

cardinal; two well-defined cardinals with transverse 

grooves on sides separated by socket; forward of 

anterior-most cardinal is narrow groove followed by 

short ridge; one anterior lateral ridge present. Resilifer 

subcircular to suboval. Dentition of juveniles evident,

resilifer may be discernible. Isomyarian adductor muscle 

scars; anterior immediately below ventral edge of anterior lateral ridge, on anterior margin, reniform, deep on 

adults; posterior immediately below ventral edge of 

posterior lateral ridge, on posterior margin, subcircular 

to suboval, may be less deep than anterior. Crescentshaped anterior pedal retractor present underneath ventral end of anterior lateral and above anterior adductor; 

posterior pedal retractor occurs as notch in dorsal most 

corner of posterior adductor. Pallial line distinct, entire. 

Crenulations present from end of anterior lateral ridge 

ventrally to posterior lateral ridge on adults; development begins anteriorly so juveniles may display various 

stages of marginal crenulation. Prodissoconch subcircular and free of ornamentation.

Discussion. — Crassatella vadosa was first named and 

described by Morton (1834, p. 66) for a single specimen 

found by Conrad at the type locality of the Prairie Bluff 

Chalk (uppermost Maastrichtian) in Alabama. The preservation in the Prairie Bluff is either as molds or as 

calcite replaced shells; the type specimen (ANSP 19593; 

pi. 1, figs. 2, 3) is replaced by calcite, which preserves 

the fine details of ornament and internal characters. 

Morton acknowledged that this species was also found in 

New Jersey, thus establishing it as a wide-ranging form. 

Yet, over the next 150 years C. vadosa Morton, as herein 

defined, was assigned to six different species and two 

subspecies within the geographic and stratigraphic limits 

of this study. The authors of the junior synonyms of C. 

vadosa did not recognize the various stages in the 

ontogenetic sequence, nor did they recognize the degree 

of intraspecific variation of the species.

Crassatella subplana, a broad, flat subquadrate form, 

as the name implies (ANSP 18743; pi. 1, fig. 14; pi. 11, 

fig. 13), was described by Conrad (1853, p. 274) from 

imperfectly preserved material from Arneytown, N.J. 

Gabb (1861a, p. 169, list only) extended the range of 

Crassatella subplana to the Alabama Cretaceous "chalk 

formation." Whitfield (1885, p. 121) described and figured Conrad's specimens and cited the "elevated form" of 

the species as its distinguishing feature. Despite the 

overlap in ranges with Crassatella vadosa, no one 

attempted to directly compare the two species until 

Weller (1907, p. 554-555):

These common casts of the Navesink marl were apparently 

identified as C. vadosa by Whitfield, at least in part, but 

after a study of the types of that species as well as numerous 

other examples from the South, it has not seemed possible to 

identify any of the New Jersey specimens with that species. 

C. subplana differs from C. vadosa in its much more 

depressed-convex valves, those of C. vadosa being quite 

ventricose, especially towards the umbo, although in their 

general outline and surface markings the two species are 

much alike.
SYSTEMATIC PALEONTOLOGY 65

Gardner (1916) expanded the range of Crassatellites 

subplanus [= Crassatella subplana] into Maryland. She 

(Gardner, 1916, p. 652-653) quoted Weller's (1907, p. 

553-554) description of Crassatellites subplanus exactly, 

yet she reassigned all of his figures to either Crassatellites vadosus [= Crassatella vadosa] or Crassatellites 

linteus [= Crassatella lintea]', she disagreed with 

Weller's inclusion of Crassatellites linteus in the synonymy of Crassatellites subplanus but agreed with his 

distinction between Crassatellites subplanus and Crassatellites vadosus.

Crassatella ripleyana was diagnosed by Conrad (1858) 

from beds of the Owl Creek Formation24 in Tippah 

County, Miss. The species, as Conrad described it, is 

"Triangular, very inequilateral, thick, . . .; umbonal 

slope angulated, subcarinated; ..." (Conrad, 1858, p. 

327) and also ventricose (ANSP 18741; pi. 1, figs. 1, 4, 9, 

11, 16). In 1872, Conrad (1872, p. 50) included C. 

ripleyana in the subgenus Pachythaerus. For the next 

68 years, authors of taxonomies disagreed with Conrad's 

contention that C. ripleyana was "very distinct from all 

others of this country" (Conrad, 1858, p. 327). Gabb 

(1877, p. 310) listed C. ripleyana as a junior synonym of 

C. vadosa; Whitfield (1885), Gardner (1916), and Wade 

(1926) concurred. Gardner (1916, p. 651) compared the 

typical representatives of Crassatellites vadosus and C. 

ripleyana:

Conrad's C. ripleyana is doubtless a synonym [of C. vadosa], 

which includes the larger and heavier individuals. The young 

are quite uniform in outline and sculpture, but after the form 

has passed the typical C. vadosus stage there is a strong 

tendency for it to become produced posteriorly and to 

develop a rather heavy carina with the concomitant medial 

depression stage represented by the C. ripleyana.

The name C. ripleyana did not appear again until 1940, 

when it was included in faunal lists for the Owl Creek 

Formation (Stephenson and Monroe, 1940, p. 230, 247) as 

a subspecies of C. vadosa. Stephenson (1941, p. 176-177) 

discussed the "varietal forms" of C. vadosa, including C. 

vadosa ripleyana, and justified the division of the species 

into numerous subspecies by stating that "the fairly 

consistent differences" are "recognizable in collections 

from different horizons and localities" (Stephenson, 1941, 

p. 176).

Conrad (1860, p. 279) assigned the name Crassatella 

lintea to a moderately sized, flat subquadrate form with 

concentric ridges and fine striations (ANSP 19594; pi. 1, 

figs. 5-8, 10) from Eufaula Bluffs, Barbour County, Ala. 

In his discussion of Crassatella lintea, Conrad (1860) 

states "Accompanies C. vadosa, and nearly related to it, 

but numerous specimens of each compared showed a

24 See Sohl (1960, p. 5-6) for a discussion of the stratigraphic position of 

Conrad's collections.

specific difference. It is thinner, less cuneiform posteriorly, and differs in the fine raised concentric lines. ..." 

Crassatellites linteus [= Crassatella lintea] was identified as a juvenile of C. vadosa by Gabb (1877, p. 310-311) 

and Johnson (1905, p. 14); Whitfield remarks that C. 

lintea "appears to be the same species" as C. vadosa 

(Whitfield, 1885, p. 117). Weller (1907, p. 553), apparently noting the similarity in form, lists Crassatella 

lintea [= Crassatellites linteus] as a junior synonym of 

C. subplana. The species range was extended to Maryland in 1916 by Gardner (1916, p. 653-655). Gardner 

(1916, p. 654) expressed her disagreement with 

Johnson's and Weller's synonymies:

C. linteus Conrad has been considered, without justification, 

as the young of some of the clearly allied and larger forms, 

such as C. vadosus and C. subplanus. Aside from the fact 

that it shows no evidence of immaturity, the shell is thinner 

and more compressed and much less strongly carinated 

posteriorly than C. vadosus of the same size. The resemblance to C. subplanus is more striking, but the concentric 

sculpture is finer and more sharply impressed in the former, 

and as a rule, the umbones are set farther forward and are 

more strongly prosogyrate.

She concluded by stating that Crassatella vadosa and C. 

lintea have a similar distribution in Maryland but that C. 

lintea is not as abundant. Wade (1926, p. 80-81) repeats 

Gardner's synonymy and description and extends the 

distribution of Crassatella lintea into Tennessee, where 

it also occurs with C. vadosa. The problems of identifying 

juvenile members of species within the Crassatellidae 

was addressed by Stewart (1930, p. 138). He discussed 

the slow development of the characters of the ligamental 

cavity and concluded that these characters fail as diagnostic features in very young Crassatellidae. Crassatella 

lintea is cited as an example of an immature specimen 

that has been improperly assigned due to the poor 

development of hinge characters (Stewart, 1930, p. 138). 

Shimer and Shrock (1944, p. 419) indicate Crassatella 

lintea is "probably" the juvenile of C. vadosa, but 

Richards (1958, p. 190) maintained Crassatella lintea as 

a separate species and expanded the range to New 

Jersey.

Gouldia conradi Whitfield (1885, p. 125) is a juvenile 

specimen of Crassatella that has alternately been placed 

in Gouldia (Astartidae), Eriphyla (Astartidae), and 

Uddenia25 (Crassatellidae). Although the type specimens 

are imperfectly preserved (ANSP 18735; pi. 22, figs. 

1-4), a comparison of Whitfield's shells with juvenile 

Crassatella vadosa (pi. 12, figs. 1-4) and juvenile Crassatella hodgei (pi. 5, fig. 9) reveals affinities to both 

species. However, the type Gouldia conradi more

25 The problems of Uddenia are discussed in the section "Distribution and 

validity of species" on pages 57-58.
66 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

closely resembles Crassatella vadosa; therefore, they 

have been questionably synonymized. The other specimens assigned to Gouldia conradi cannot be synonymized with any crassatellid species due to their poor 

preservational state. Stephenson's (1923, p. 274) specimens, which he initially identified as Crassatellites ? 

conradi (Whitfield),26 came from Snow Hill, N.C., in 

lower Campanian units. This locality is below the known 

stratigraphic range for Crassatella vadosa but falls 

within the range of Crassatella carolinensis Conrad and 

Crasatella hodgei (Stephenson) (fig. 19). Only two 

(USNM 31932; pi. 22, figs. 5, 6; USNM 31902, broken) of 

the six specimens that Stephenson (1941, pi. 67, figs. 

10-16) figured are still present in the collections of the 

USNM; the rest have been lost or destroyed. Even these 

two specimens are so damaged that it is impossible to 

make a specific assignment. Uddenia fragilis Harbison 

(1945, p. 80) (ANSP 16216) is a juvenile Crassatella 

vadosa.

Internal molds of Crassatellites carolinana were originally described by Stephenson (1923, p. 277, pi. 68, figs. 

5-7) as Crassatellites sp.; when additional specimens 

preserving characters of the exterior were located, 

Stephenson (1927, p. 17) named the specimens. Crassatellites carolinana has a large flattened subquadrate form 

with abroad hinge angle (USNM 73438, 73439; pi. 1, figs. 

15, 17; pi. 10, fig. 16; pi. 11, figs. 11, 12). Stephenson 

recognized the similarities between Crassatellites subplanus and Crassatellites carolinana (compare pi. 1, fig. 

14 to fig. 15), but stated that Crassatellites subplanus 

was "relatively shorter" (Stephenson, 1927, p. 18). He 

believed Crassatellites vadosus differed from Crassatellites carolinana by being "more convex and more sharply 

pointed posteriorly" and by having "a more sharply 

defined umbonal [posterior] ridge" and in the detailed 

characters of the hinge (Stephenson, 1927, p. 18-19).

Stephenson (1941, p. 177) separated the specimens 

originally identified by Wade (1926, p. 79) as Crassatellites vadosus from Coon Creek, McNairy County, Tenn., 

into the new subspecies C. vadosus wadei. The subspecies is distinguished from the typical form of the species 

in being "higher and flatter" and having "the beak more 

distantly removed from the anterior extremity" 

(Stephenson, 1941, p. 177) (USNM 32784; see pi. 9, figs. 

7, 8, 11 for topotype examples).

The last name to be introduced for the group of 

specimens herein identified as junior synonyms of Crassatella vadosa was C. gardnerae (holotype, ANSP 16200; 

paratype, USNM 103753, see pi. 1, figs. 12, 13), named 

by Harbison (1945, p. 79) from deposits at Pleasant

26 This assignment is in error because the name was already occupied by 

Crassatella conradi Whitfield (1885, p. 209). Stephenson was not synonymizing 

Gouldia conradi Whitfield (1885, p. 125) with Crassatella conradi Whitfield.

Ridge Lake, Union County, Miss. She distinguished this 

species from typical forms of C. vadosa on the basis of "a 

more prominent umbo; the umbonal [posterior] ridge is 

heavier, and especially the shell is more elongated" 

(Harbison, 1945, p. 80). C. gardnerae varies from the 

"Owl Creek form," presumably C. vadosa ripleyana 

(Harbison does not specify) in having more shallow 

muscle scars, a less triangular cardinal, and a longer, 

flatter valve, and less "prominent umbo" (Harbison, 

1945, p. 80). In addition, she lists the occurrence of C. 

vadosa at Pleasant Ridge Lake in Union County, Miss., 

in the text (Harbison, 1945, p. 80) but does not include C. 

vadosa in the table entitled "Distribution and range of 

species found at Pleasant Ridge Lake, Mississippi" (Harbison, 1945, table I, p. 90). The specimen illustrated as C. 

vadosa (Harbison, 1945, pi. 1, fig. 2) is from the type 

locality of the Owl Creek Formation, Tippah County, 

Miss., as noted by Stephenson (1955, p. 117).

The species names Crassatella subplana, C. ripleyana, C. lintea, C. gardnerae, and Crassatellites carolinana and the subspecies names Crassatella vadosa 

ripleyana and C. vadosa wadei are junior synonyms of 

Crassatella vadosa Morton. The statistical analysis supports this conclusion; although the data for Crassatella 

subplana and Crassatellites carolinana are inconclusive, 

the results were not incompatible with synonymy. In the 

course of this study, I measured 520 individuals within 

this group and visually and microscopically examined 

hundreds more. Characters such as convexity, general 

outline, shape of the posterior margin, accentuation of 

the posterior ridge, and height and length, used by the 

original authors to justify separation into species and 

subspecies, do not persist as diagnostic characters when 

entire suites of specimens are examined. The range of 

variation of the species covers the complete spectrum 

encompassed by all the junior synonyms of Crassatella 

vadosa; it is impossible to maintain the individual species 

concepts represented by the junior synonyms. These 

separate species concepts can be united under Crassatella vadosa by the characters of the juveniles, the 

pattern and sequence of ornamentation, and the detailed 

characters of the hinge. Although some of the authors 

discussed herein claim to distinguish differences in even 

these features, I find the characters to be consistent 

within their normal range of variation and diagnostic on 

all well-preserved individuals.

Two morphotypes exist among the adult Crassatella 

vadosa. One is represented by the original concepts of 

Crassatella subplana, C. vadosa wadei, and Crassatellites carolinana. These individuals retain the juvenile 

characters of a subquadrate outline, broad hinge angle, 

reduced convexity, and subdued posterior ridge into 

adulthood (pi. 1, figs. 14, 15; pi. 7, figs. 1-15; pi. 8, fig. 15; 

pi. 9, fig. 8; pi. 10, figs. 14, 16). The other morphotype is
SYSTEMATIC PALEONTOLOGY 67

TABLE 38.—Minimum, maximum, and mean values for characters of Crassatella vadosa 

[See table 2 for an explanation of the morphological variables. Data source: digitized data set; excludes broken specimens and internal molds]

Morphological variable

CONVEX ........

LENGTH. ........

HINGE...........

POST.............

ANTER ..........

ANTVERHT

POSVERHT. . . . . .

Adults (382 specimens)

Minimum

6.45

23.20

78.35

99.23

129.10

13.31

12.09

Maximum

18.82 

67.45 

125.13 

174.09 

168.66 

36.96 

34.34

Mean

12.33

41.18 

105.08 

130.84 

145.97 

21.29 

20.72

Juveniles (31 specimens) Combined (413 specimens)

Minimum

1.04 

4.84 

100.09 

112.84 

127.76 

2.18 

2.75

Maximum

7.73 

29.73 

125.65

162.74 

168.77 

17.72 

16.98

Mean

4.37 

19.34 

110.16 

130.16 

144.09 

10.65 

11.01

Mean

11.73 

39.55 

105.46 

130.79 

145.83 

20.49 

19.99

illustrated by the type concepts of Crassatella vadosa 

and C. ripleyana. A triangular outline, reduced hinge 

angle, inflated valve, and sharp posterior ridge defining 

a steeply sloped posterior area are characteristic of this 

second group of Crassatella vadosa (pi. 1, figs. 1^, 16; 

pi. 8, figs. 11, 14; pi. 9, fig. 3; pi. 11, figs. 3, 4, 6). I do not 

believe, however, that these two morphotypes can be 

isolated into discrete species, or even subspecies, 

because a full range of variation exists between the two 

types (for example, pi. 5, fig. 1; pi. 8, fig. 7; pi. 9, fig. 9). 

Furthermore, both morphotypes can be found distributed throughout the range of Crassatella vadosa. The 

triangulate form can be found in Mississippi (pi. 1, figs. 1, 

4, 16), Alabama (pi. 1, fig. 3), Georgia (pi. 9, fig. 3), and 

Maryland (pi. 11, fig. 3). The quadrate flattened form is 

also found in Mississippi (p. 10, fig. 14), Alabama (pi. 11, 

fig. 10), and Maryland, in addition to Tennessee (pi. 7, 

fig. 15), New Jersey, (pi. 1, fig. 14; pi. 10, fig. 17), and 

North Carolina (pi. 11, figs. 11, 12). Elongate shells 

(represented by the type concept of Crassatella gardnerae) are intermediate between the other two forms and 

occur with them in deposits in Tennessee, Mississippi, 

Alabama, and Georgia (pi. 8, figs. 4, 7; pi. 9, figs. 6, 12, 

13; pi. 10, fig. 11; pi. 11, fig. 7). A large degree of 

variation can be seen even within a single population (pi. 

8, figs. 6, 12, 15; pi. 9, figs. 7, 8, 10; pi. 11, fig. 7). At one 

point, I considered that these morphotypes illustrate 

sexual dimorphism, but their distribution, and the presence of intermediate forms, does not support this hypothesis. The variation seen within Crassatella vadosa is 

probably a reflection of environmental pressures on the 

individuals during growth.

Crassatella vadosa is a morphologically variable species that encompasses the two subgroups discussed 

above and the intermediate forms. The average values 

for the genus are presented in table 38. The most obvious 

variation is seen in the shape of the posterior margin and 

the resulting effects on the overall outline of the individual. The contribution of the posterior margin to the 

intraspecific variation was demonstrated during the statistical analysis of the described subspecies categories of 

Crassatella vadosa; height of the posterior region was

the most significant discriminating variable (table 6). The 

extremes of variation in posterior elongation can be seen 

by comparing plate 9, figure 13, a trigonally suboval 

posteriorly elongate form in which length is much 

greater than height, to plate 8, figure 15, a subquadrate 

specimen in which height and length are more nearly 

equal. Intermediate to these forms is the typical form of 

C. vadosa (pi. 8, fig. 3), a triangular shell having a 

pointed posterior margin. The characters of the hinge 

angle and the slope of the posterior dorsal margin are 

linked to the shape of the posterior margin; posteriorly 

elongate and subquadrate forms (pi. 9, figs. 5, 12) have 

broad hinge angles and gently sloping posterior dorsal 

margins; triangular forms (pi. 11, figs. 2, 6) have narrower hinge angles and more steeply sloping posterior 

dorsal margins. Convexity of the adults of the species can 

vary from gently curved (pi. 8, figs. 6, 8, 12, 13) to 

ventricose (pi. 11, figs. 4, 5). Individuals with ventricose 

valves have well-defined posterior ridges and steeply 

inclined posterior areas (pi. 11, fig. 4), whereas specimens with reduced convexity tend to have subdued 

posterior ridges and flattened posterior areas (pi. 11, fig. 

10). The position of the beak is fairly constant for the 

adults of the species at the anterior one-third of shell 

length (pi. 8, figs. 4, 9, 14), but a few adults retain the 

juvenile position at the anterior two-fifths of shell length 

(pi. 8, fig. 15; pi. 9, fig. 8). The posterior portion of the 

ventral margin varies from convex (pi. 9, fig. 8) to flat 

(pi. 9, fig. 7) to concave (pi. 9, fig. 13). The sequence of 

development of the ornamentation is consistent for the 

species, although some individuals may never develop 

the undulations seen on the lower third of other shells 

(compare pi. 8, fig. 9 to fig. 11). Interspaces between 

ridges may exhibit some variation in topography; a flat 

interspace having only the comarginal growth threads 

may be present, or small raised areas in between the 

dominant ridges may be seen. Some ridges are sharp and 

pointed (pi. 10, fig. 4), others scaled (pi. 10, figs. 9, 12; pi. 

12, fig. 3), and still others slightly rounded (pi. 8, fig. 3), 

but these differences can be attributed to wear on the 

shell surface.
68 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

The ontogeny of Crassatella vadosa shows consistency 

in the sequence of events but variation in the size at 

which the adult characters are fully developed (compare 

pi. 10, fig. 5 to fig. 6). The prodissoconch of C. vadosa is 

rarely preserved, but when visible it is clearly distinguished from the nepionic portion of the shell (pi. 12, fig. 

5). The nepionic portion of the shell is quadratic, with 

height and length being nearly equal (pi. 7, fig. 4; pi. 8, 

fig. 10); this shape results in a very broad hinge angle (pi. 

7, fig. 8; pi. 10, figs. 6, 8). The juvenile portion of the 

shell is more strongly prosogyrous than the adult; the 

concave anterior dorsal margin at the point where the 

lunule is developing contributes to the prosogyrous 

appearance. At this stage, the primary pattern of ornamentation is already visible, with comarginal threads 

occurring in interspaces between the more pronounced 

comarginal ridges (pi. 12, figs. 1, 3). The posterior ridge 

is discernible, both internally and externally, but is 

subdued. The hinge platform displays the most obvious 

juvenile characters; here, the resilifer is not developed, 

and the resilial platform not yet defined; the cardinals 

and their corresponding sockets are small and narrow; 

only the lateral ridges are as well defined as they are on 

adult individuals (compare pi. 7, fig. 2 to fig. 14). The 

adductor muscle scars are shallow, as is the pedal 

retractor. An examination of plate 7, figures 1 to 15 

illustrates a growth series for C. vadosa. As the shell 

matures, the shape gradually shifts from quadrate to 

more mature subquadrate to subtrigonal, along with 

concomitant changes in hinge angle, slope of the posterior dorsal margin, and development of the posterior 

ridge. The ornamentation gradually shifts from the very 

fine, well-defined ridges on the juvenile portion (which 

give C. lintea its name) to the more rounded ribs on the 

adult (compare ornament of umbo to ventral portion of 

shell on pi. 7, figs. 5, 7 and pi. 8, figs. 10, 14, 16); 

eventually, as the shell approaches old age, undulations 

may appear on the lower third of the shell causing the 

ventral margin to curve inward (pi. 11, fig. 4). Internally, 

the hinge characters gradually mature, as the resilifer 

becomes well defined and as the resilial platform 

becomes isolated from the edge of the hinge plate (compare pi. 7, fig. 2 to fig. 14). The muscle scars become 

more distinctive as the shell material thickens.

The shift from the more juvenile characters to the 

more adult characters most commonly occurs at onethird the size of the adult, but tremendous variation in 

size can be seen at the phase where the shift occurs. 

Some individuals acquire fully adult characters at a very 

small size and presumably young stage (pi. 8, figs. 1, 2; 

pi. 10, figs. 1, 5), whereas others retain the juvenile 

characters at a relatively large size and presumably older 

stage (pi. 10, figs. 13, 14). I believe some ecologic or 

environmental constraints are acting on the individuals

that retain the juvenile characters at later stages; this 

subgroup is represented by the original concepts of 

Crassatella vadosa wadei, C. subplana, and Crassatellites carolinana.

Comparisons of Crassatella vadosa with the other 

members of the genus are made under the discussions of 

each of those species.

Occurrence. — See table 39 for C. vadosa localities, 

stratigraphic units, and collections studied. Refer 

to figure 2 and appendix 9 for locality positions and 

descriptions.

Stratigraphic range. — Lower(?) Campanian; upper 

Campanian through upper Maastrichtian (fig. 19).

Type material examined.— ANSP 19593; holotype 

Crassatella vadosa Morton. ANSP 19594; holotype 

Crassatella lintea Conrad. ANSP 18741; syntypes Crassatella ripleyana Conrad. ANSP 18743; syntypes Crassatella subplana Conrad. ANSP 18735; holotype Gouldia conradi Whitfield. USNM 73438; holotype 

Crassatellites carolinana Stephenson. USNM 73439; 

paratype Crassatellites carolinana Stephenson. USNM 

103753; paratype Crassatella gardnerae Harbison.

Crassatella tumidula Whitfield, 1865 

Plate 15, figures 1-17; plate 16, figures 4, 6.

Crassatella tumidula WHITFIELD, 1865, p. 267, pi. 27, fig. 16. DE 

GREGORIO, 1890, p. 198-199, pi. 26, fig. 11. HARRIS, 1897, p. 56, 

pi. 11, figs. 3, 4. PALMER and BRANN, 1965, p. 105 [partim]. 

TOULMIN, 1977, p. 186, pi. 13, figs. 7-9.

Crassatellites tumidulus GARDNER, 1945, p. 91, pi. 6, figs. 4, 6 

[discussed under C. antestriatus; figure reproduction of holotype].

[?] Crassatella alta Conrad. TUOMEY, 1858, p. 271 [list only].

[?] Crassatella tiimidula Whitfield. ALDRICH, 1894, p. 242 [list only; 

assigned to C. gabbi Safford by Palmer and Brann (1965)].

Diagnosis. —Valves ovate trigonal in outline; unevenly 

convex, anterior ventricose, posterior attenuated; valve 

flat to slightly concave anterior to posterior ridge; posterior area narrow; posterior margin pointed; lunule well 

developed on both valves; escutcheon poorly developed 

on both valves. Ornamentation begins at beak as strong 

comarginal ridges, fading rapidly in ventral direction; 

comarginal growth threads continuous over entire surface. Elongate narrow resilifer descends half way across 

resilial platform; resilial platform open to umbonal cavity; anterior lateral ridges short.

Description.— Shell equivalve; inflation ventricose 

anteriorly, attenuated posteriorly; shell smoothly convex 

over anterior two-thirds, flattening or becoming slightly 

concave on posterior third as viewed from dorsal or 

ventral margin parallel to plane of commissure; adults 

ovate trigonal in outline, height nearly equals length; 

nepionic outline subcircular, posteriorly truncate; juveniles rapidly assume ovate trigonal outline; height-tolength ratio increases during ontogeny. Inequilateral, to
SYSTEMATIC PALEONTOLOGY 69

TABLE 39. —Crassatella vadosa— Occurrence and collections studied

[Fm, Formation. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of Natural Sciences

of Philadelphia]

Locality 

number

27. ...

28. ...

29. ...

30A..

30B..

31....

32. ...

34B..

35. ...

36A..

36B..

37. ...

38 A..

38B..

40. ...

41....

42. ...

43. ...

44. ...

45. ...

47. ...

48. ...

49. ...

51....

52. ...

53. ...

54. ...

56. ...

57. ...

58. ...

59A..

59B..

63. ...

64. ...

69 A..

69B..

69C..

70. ...

71. ...

72. ...

73 A..

73B..

75. ...

State

Tennessee

Mississippi

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Alabama

....do........

Georgia

....do........

....do........

Alabama

....do........

Georgia

Alabama

Georgia

....do........

New Jersey

....do........

Mississippi

....do........

....do........

Tennessee

Mississippi

Alabama

....do........

....do........

....do........

....do........

Georgia

....do........

North Carolina

....do........

South Carolina

Maryland

....do........

....do........

....do........

....do........

....do........

County

McNairy

Union

....do........

Tippah

....do........

Union

....do........

....do........

....do........

Barbour

....do........

Quitman

....do........

....do........

Barbour

....do........

Quitman

Barbour

Quitman

....do........

Burlington

Monmouth

Tippah

....do........

....do........

Hardeman

Kemper

Wilcox

....do........

....do........

....do........

Lowndes

Clay

....do........

Fender

New Hanover

Georgetown

Prince George's

....do........

....do........

....do........

....do........

....do........

Stratigraphic unit

Coon Creek Fm

Ripley Fm, Coon

Creek Tongue

....do........

....do........

....do........

....do........

....do........

Ripley Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Mount Laurel Sand

and (or) Navesink Fm

....do........

Owl Creek Fm

....do........

....do........

....do........

Prairie Bluff Chalk

....do........

....do........

....do........

....do........

....do........

Providence Sand

....do........

Peedee Fm

....do........

....do........

Severn Fm

....do........

....do........

....do........

....do........

....do........

Collection number

32784, 450436-450442, 450449-450451, 450455-450457,

450465, 450475, 450481, 451056, 451057, 451062, 451096,

453896.

103753, 103754, 450447, 450448, 450460, 451060, 451061,

451067, 453873.

453881.

450453, 450454, 450478, 451063.

20820.

451058, 451064, 451065, 453870.

450461, 450462, 451066.

453872.

453868.

21125.

503, 505, 12670, 453878, 453882, 453886.

ANSP: CONRAD (unnumbered collection), 19594.

451081.

451093.

451079.

450417, 450464, 450477, 450551.

451103.

451077.

450459, 450466-450469, 451086, 451088, 451089, 451092.

450807, 451084, 451090, 453876, 453885.

450452, 450458, 451091.

ANSP 18743.

450472, 453890, 453891.

20804.

451068.

20608, 128139, 450418, 450443-450446, 450474, 450509,

450510, 450851, 451052, 451054, 451069, 453867.

ANSP 18741.

453875.

459095.

450471, 450500, 450853. ANSP 19593.

450502.

450820.

451071, 451080.

453887.

451075.

450554.

73438, 73439, 453871.

450511.

453892.

450463, 450473, 451099, 451100.

451095.

450476, 451055.

131763, 131764, 131766, 450416, 450470, 450479, 450480,

450520, 451098, 453893.

453874.

32291.

Questionable C. vadosa collections

14. ...

63. ...

74. ...

New Jersey

Georgia

Maryland

Camden

Clay

Anne Arundel

Woodbury Clay

Providence Sand

Severn Fm

ANSP 18735.

450816.

451104.
70 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

nearly equilateral; beak position varies from anterior 

one-third length on juveniles to just anterior of one-half 

length on large adults; prosogyrous, beak strongly 

curved and pointed on juveniles, becomes less so on 

adults. Anterior dorsal margin generally straight, with 

slight indentation at maximum width of lunule; slope of 

margin steep; lunule broad, well developed on both 

valves of adults with sharp ridge defining area; anterior 

margin smoothly rounded. Posterior dorsal margin 

straight to slightly concave; slope of margin varies from 

moderate on juveniles to steep on adults; escutcheon 

narrow, poorly developed on both valves; posterior ridge 

subdued, preceded anteriorly by shallow depression or 

flattened area; posterior area very narrow on adults, 

broader on early stages of juvenile; posterior margin 

pointed. Ventral margin smoothly rounded anteriorly, 

ascending posteriorly to intersect dorsal margin. Ornamentation of nepionic portion of shell and of early juvenile stages distinct high comarginal ridges, descending 

into V-shaped interspaces, covered with comarginal 

growth threads; only first few comarginal ridges are 

continuous across shell surface from anterior to posterior, remainder fade anterior to posterior ridge; comarginal ridges rapidly disappear in ventral direction as 

well; remainder of shell surface covered with comarginal 

growth threads, and occasional undulations in shell surface. Hinge angle averages 102 degrees on adults, 118 

degrees on juveniles; moving from posterior lateral 

ridges across hinge plate to anterior lateral ridges, 

dentition noted as follows:

Right Valve 0 1 0-R 010 -101 

Left Valve 1 0 l-R(O) 1010 (1)-0 1 0

Right valve dentition consists of one posterior lateral 

ridge, separated by edentulous space from resilifer (R); 

resilifer originates at beak and descends about half way 

across resilial platform; resilial platform open to umbonal 

cavity; narrow elongate trigonal socket lies anterior to 

resilial platform and just below beak; one large cardinal 

tooth, with transverse grooves on sides, lies anterior to 

beak; two short anterior lateral ridges present, separated by groove. Left valve dentition consists of two 

posterior lateral ridges, separated by groove; resilifer 

originates at beak and descends about half way down 

resilial area, leaving broad flat edentulous space below; 

resilial area open to umbonal cavity; small pit at base of 

posterior slope of cardinal; two well-defined cardinals 

with transverse grooves on sides separated by socket; 

forward of anterior-most cardinal is narrow groove followed by short ridge; one short anterior lateral ridge 

present. Resilifer elongate, narrow. Dentition defined at 

early stages of juvenile, resilifer may be discernible. 

Isomyarian adductor muscle scars, shallow on juveniles, 

deeper on adults; anterior reniform, posterior

subcircular. Crescent shaped anterior pedal retractor 

present below anterior lateral ridge and hinge platform. 

Pallial line distinct, entire. Crenulations present from 

end of anterior lateral ridge ventrally to posterior lateral 

ridge on well-preserved adults; development begins 

anteriorly so juveniles may display various stages of 

marginal crenulation. Prodissoconch not seen.

Discussion, — Whitfield (1865, p. 267) first named and 

described Crassatella tumidula from a locality "six miles 

above, Claiborne, Ala., west side of the [Alabama] 

river." Harris (1897, p. 56) repeated Whitfield's original 

description and stated that the type locality was "doubtless Greggs Landing." In addition, Harris found the 

species at two other localities on the Alabama River: 

Bell's Landing and Yellow Bluff. For the next 80 years, 

C. tumidula appeared in faunal lists and discussions of 

the genus, but no other authors contributed to the 

understanding of the species. Palmer and Brann (1965, p. 

101) synonymized C. tumidula Whitfield, Aldrich (1894, 

p. 242) with C. gabbi Safford. Since Aldrich's publication 

is only a list, there is no way to determine which species 

he was examining, but C. tumidula are known from the 

locality he cited ("the vicinity of Prairie Creek and Mr. 

McConnico's plantation," Aldrich, 1894, p. 242); therefore, it is reasonable to assume that Aldrich was correct. 

Based on locality, Palmer and Brann (1965, p. 105) 

synonymized C. alta Conrad, Tuomey (1858, p. 271) with 

C. tumidula. Again, this is only a list, so there is no way 

to determine what species Tuomey actually had, but C. 

tumidula is known to occur at Bell's Landing, whereas 

C. alta has never been reported from that locality since 

1858. The possibility exists that Tuomey's specimen was 

a Crassatella tumidula. Toulmin (1977, p. 186) found the 

species at seven additional localities, all confined to the 

outcropping Tertiary sediments of southern Alabama. It 

appears that C. tumidula may have a fairly limited 

geographical distribution since examinations of museum, 

survey, and field collections have not revealed any 

localities outside Alabama.

The low degree of intraspecific variation displayed by 

Crassatella tumidula, when evaluated qualitatively, 

may be attributable in part to the limited extent of the 

species' geographic range. The consistency of characters 

seen is contrary to the results of the statistical analysis, 

which illustrate a high degree of intraspecific variation 

and a wide scatter on the plots. This statistical scatter 

can be explained in part by the ontogenetic changes as 

discussed below. Particularly unusual for this genus is 

the consistency of the exterior outline; although ontogenetic changes occur, adults at similar stages in their life 

history, generally look the same (compare pi. 15, fig. 14 

to fig. 12 and to fig. 15). As with other species of 

Crassatella, the largest degree of variation in C. tumidula is seen in the degree of posterior elongation (compare
SYSTEMATIC PALEONTOLOGY 71

TABLE 40.— Minimum, maximum, and mean values for characters of Crassatella tumidula 

[See table 2 for an explanation of the morphological variables. Data source: digitized data set; excludes broken specimens and internal molds]

Morphological variable

CONVEX ........

LENGTH. ........

HINGE...........

POST.............

ANTER ..........

ANTVERHT

POSVERHT.

Adults (17 specimens)

Minimum

5.52

18.92

82.02

91.33

126.84

9.87

7.93

Maximum

18.65 

66.53 

121.22 

163.32 

156.90 

40.66 

29.74

Mean

12.12 

40.08 

103.34 

126.84 

139.73 

23.36 

18.14

Juveniles (15 specimens) Combined (32 specimens)

Minimum

2.11 

8.61 

110.34 

91.32 

116.61 

4.03 

3.94

Maximum

7.27 

19.11 

126.40 

147.15 

163.89 

10.50 

8.53

Mean

4.30 

14.62 

116.86 

114.54 

134.16 

7.32 

6.48

Mean

8.46 

28.15 

109.68 

121.08 

137.12 

15.84 

12.68

pi. 15, fig. 6 to fig. 7). The area anterior to the posterior 

ridge varies from deeply compressed to flattened (compare pi. 15, fig. 12 to fig. 15). Many of the differences 

seen between individuals can be ascribed to wear. For 

example, the presence or absence of crenulations is one 

of the primary criteria cited by the original authors for 

distinguishing C. tumidula from other species of Tertiary Crassatella, but a little abrasion can remove this 

diagnostic character (examine the intact anterior ventral 

portion versus the worn posterior portion of the specimen illustrated on pi. 15, fig. 17). Ornamentation may 

also be affected by erosion; the comarginal ridges usually 

seen across the umbo (pi. 15, figs. 3, 5, 6, 9) may be 

reduced, or the usually relatively smooth lower portions 

of the valve may appear to be more strongly ribbed and 

(or) have radial sculpture when the outer layer of shell 

material is removed (pi. 15, fig. 16). The summary of 

statistical measures for the species is found in table 40. 

The nepionic stage of Crassatella tumidula begins as a 

subcircular form with prominent comarginal ridges (pi. 

16, figs. 4, 6). Next, the juvenile passes through a 

suboval stage (pi. 15, figs. 9, 11); the posterior ridge is 

evident, and the depression anterior to the ridge may be 

formed, although the shell is still relatively flat; the 

posterior area at this phase is much broader than on the 

adults; the ornament is already past the stage of forming 

strong comarginal ridges, so only comarginal growth 

threads are present near the ventral margin (pi. 15, fig. 

3) and the beak is strongly prosogyrous. The muscle 

scars and general character of the dentition are visible at 

these early stages, but the resilifer has not yet formed 

(pi. 15, figs. 2, 11). As C. tumidula matures, the shell 

becomes more inflated anteriorly, while the posterior 

remains flat, the posterior area becomes increasingly 

narrow, and the posterior margin more pointed (pi. 15, 

figs. 3, 6). The height-to-length ratio increases during 

ontogeny, causing the relative position of the beak to 

move closer to the midline of the shell and causing the 

hinge angle to become more acute. Faint crenulations 

begin to appear at about the same time the resilifer 

becomes discernable (pi. 15, fig. 7). An examination of

plate 15, figures 1 to 17, reveals the various stages in the 

development of C. tumidula.

The species Crassatella tumidula has several unique 

features among the members of the genus herein considered. Unfortunately, these features are difficult to discern in previously published illustrations of the species 

and has led, I believe, to confusion of the species, 

primarily with the adult form of C. halei Harris [herein 

= C. aquiana Harris]. The ornamentation of C. tumidula and C. halei is similar (compare pi. 3, fig. 6 to pi. 15, 

fig. 1), and in addition the internal features of large adult 

C. tumidula are nearly identical to those of C. halei 

(compare pi. 3, fig. 9 to pi. 15, fig. 10). The similarity of 

internal features led to problems in the discrimination of 

these two species from the digitized specimens in the 

analysis portion of this study. No other species of Crassatellidae considered in this study exhibits the characteristic inflated anterior and attenuated posterior of C. 

tumidula; this feature, very obvious when viewed from 

the dorsal margin (pi. 15, figs. 5, 8), is difficult to detect 

on a conventionally illustrated specimen. In addition, the 

characters of the lunule and escutcheon are unique within 

the context of this study. All other members of the genus 

included here have a well-developed lunule on the left 

valve and a well-developed escutcheon on the right valve; 

the lunule on the right valve and the escutcheon on the 

left valve are less well defined (see pi. 8, fig. 13 for one 

example). C. tumidula, however, have a well-developed 

lunule on both valves and a poorly developed escutcheon 

on both valves; the left valve escutcheon is less well 

developed than the right (pi. 15, figs. 5, 8). This lack of 

development of the escutcheon is probably due to (or the 

cause of) the morphological constraints of an attenuated 

posterior. Finally, the posterior area of the adult C. 

tumidula is narrower than other members of the genus. 

Identification of these external features of C. tumidula 

distinguishes this species from all other members of the 

genus.

Occurrence.—See table 41 for C. tumidula localities, 

stratigraphic units, and collections studied. Refer 

to figure 2 and appendix 9 for locality positions and 

descriptions.
72 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 41. —Crassatella tumidula— Occurrence and collections studied 

[Fm, Formation; Mbr, Member. Collection number, USNM (U.S. National Museum) collection or specimen numbers]

Locality 

number

114 ......

115A.....

115B.....

116 ......

117 ......

118 ......

119 ......

120 ......

State

. . Alabama

.. ....do........

.. ....do........

.. ....do........

.. ....do........

.. ....do........

.. ....do........

.. ....do........

County

Marengo

Pike

Dale

Moni*oe

....do........

AA/ilpnv

Monroe

Stratigraphic unit

Nanafalia Fm

....do........

Nanafalia(?) Fm

Tuscahoma Fm

Tuscahoma Fm, Bells Landing

Mbr 

Tuscahoma Fm, Greggs

Landing Mbr 

Tuscahoma Fm

Tuscahoma Fm, Bells Landing

Mbr

Collection number

129898, 450516, 450553,

450560, 450846, 450861 

450522, 450847.

450848.

450813, 450842.

90968, 137064, 155060, 4

450521, 450558, 450561 

450559, 450812, 450814.

453918, 459096.

453917.

450555, 450556,

150517-450519,

, 450817, 450843.

Stratigraphic rcmge.—Wilcox (fig. 19). 

Type specimen.— CNHM UC-24476; holotype Crassatella tumidula Whitfield.

Crassatella carolinensis Conrad, 1875 

Plate 2, figure 9; plate 5, figures 5, 8, 11, 13, 15-20.

Crassatella carolinensis CONRAD, 1875, p. 6, pi. 2, fig 24. GROOT, 

ORGANIST, and RICHARDS, 1954, p. 46 [list only].

Crassatellites carolinensis STEPHENSON, 1923, p. 269, pi. 66, figs. 

16, 17. RICHARDS, 1958, p. 184, pi. 30, fig. 12.

Diagnosis.— Evenly spaced comarginal ridges cover 

entire shell surface; no line of demarcation from juvenile 

to adult ornamentation. Fairly unobstructed area 

between resilifer and edge of hinge platform; right valve 

reduced triangular socket below resilifer; left valve 

reduced pit at base of posterior slope of cardinal. Exterior evenly convex as viewed from any margin parallel to 

plane of commissure. Posterior ventral edge of juvenile 

slightly rounded.

Description. — Shell equivalve, inflation somewhat 

reduced for genus; evenly convex as viewed from any 

margin parallel to plane of commissure; varying from 

subquadrate juveniles to trigonally suboval adults in 

outline; inequilateral, posteriorly elongate, with beak 

lying at approximately anterior two-fifths; prosogyrous, 

beak most strongly curved on juvenile portion, less 

obvious at later stages. Anterior dorsal margin moderately sloping, slightly concave at maximum width of 

lunule; lunule well developed on left valve of adults with 

sharp ridge defining area, less well defined on right valve 

with no distinct ridge; anterior margin smoothly 

rounded. Posterior dorsal margin generally straight, 

with occasional indentation corresponding to middle of 

escutcheon; escutcheon well developed on right valve of 

adults with ridge defining area, less well defined on left 

valve with no distinct ridge; slope of posterior dorsal 

margin increases with shell growth; posterior delineated

by presence of posterior ridge, forming slightly curved 

truncate margin. Ventral margin smoothly curved anteriorly, flattening posteriorly below posterior adductor. 

Ornamentation consists of fairly evenly spaced, narrow, 

sharp, comarginal ridges covering entire shell surface, 

with faint comarginal threads occurring in interspaces; 

lower portion of adult shell may show undulations. Hinge 

angle variable, average 116 degrees; hinge platform 

normal for genus; moving from posterior lateral ridges 

across hinge plate to anterior lateral ridges, dentition 

noted as follows:

Right Valve 0 1 0-R 010 -101 

Left Valve 1 0 l-R(O) 1010 (1)-0 1 0

Right valve dentition consists of one posterior lateral 

ridge, separated by edentulous space from resilifer (R); 

resilifer originates at beak on platform formed by rear 

wall of small socket below and slightly anterior to 

resilifer; opening of resilial platform to umbonal cavity is 

partially obstructed by position of small socket; one large 

cardinal tooth lies anterior to beak; two anterior lateral 

ridges present, separated by groove. Left valve dentition consists of two posterior lateral ridges, separated by 

groove; resilifer originates at beak; opening of resilial 

area to umbonal cavity only slightly impeded by small 

depression at base of posterior slope of cardinal; two 

well-defined cardinals separated by socket; forward of 

anterior-most cardinal is narrow groove followed by 

short ridge; one anterior lateral ridge present. Resilifer 

spoon shaped. Juveniles display only partially developed 

hinge characters; resilifer poorly defined. Isomyarian 

adductor scars; anterior reniform; posterior subcircular. 

Anterior pedal retractor present. Pallial line distinct, 

entire. Crenulations present from end of anterior lateral 

ridge ventrally to posterior lateral ridge on adults; 

development begins anteriorly so juveniles exhibit various stages of marginal crenulation. Prodissoconch not 

seen.
SYSTEMATIC PALEONTOLOGY 73

Discussion.— Conrad's (1875, appendix, p. 6) original 

description of Crassatella carolinensis was based on two 

specimens, one from New Jersey and one from Snow 

Hill, N.C. The small shell figured by Conrad (1875, pi. 2, 

fig. 24) is probably the New Jersey specimen (fide 

Stephenson, 1923, p. 269) and represents a juvenile of 

the species as herein defined. Stephenson (1914) included 

Crassatellites carolinensis (Conrad) in faunal lists from 

various localities in Mississippi, Alabama, and Georgia, 

including the type locality of the Blufftown Formation on 

the Chattahoochee River, but these specimens were 

never illustrated or described. Labels on Stephenson's 

study collections indicate that many of the specimens he 

initially believed were C. carolinensis, he later reassigned to other species of Crassatella. Subsequently, 

Stephenson (1923, p. 269) discussed and figured Conrad's 

North Carolina specimen (USNM 31929; pi. 2, fig. 9). 

Groot, Organist, and Richards (1954, p. 46) did not 

describe or illustrate Crassatella carolinensis but 

included it in a list of fossils found in the Merchantville 

Formation at the Chesapeake and Delaware Canal, Del. 

Richards (1958, p. 184) simply repeated Conrad's original 

description and figure. Consequently, until now only two 

specimens of C. carolinensis have ever been figured, and 

a suite of specimens has never been examined.

Crassatella carolinensis displays less intraspecific 

variation than most species of Crassatella examined, but 

only one population of C. carolinensis was found. 27 

Homogeneity is common for this genus within a single 

population; no doubt, if populations from additional localities had been observed, more variation in characters 

could be reported. Nevertheless, the Blufftown specimens do exhibit some dissimilarities, primarily in 

attributes of shape. The inflation of the shell ranges from 

relatively flat to fairly convex for the genus (compare pi. 

5, figs. 11, 13 to fig. 17). The range of overall shape 

variation can be seen by comparing plate 5, figure 13 to 

figure 17; plate 5, figure 13 represents a posteriorly 

elongate, suboval individual in which the height-tolength ratio is two to three; the height-to-length ratio of 

figure 17 is four to five, forming a trigonal outline. The 

posterior ventral margin may be flattened below the 

posterior adductor (pi. 5, fig. 16) or slightly sulcate (pi. 5, 

fig. 18). The hinge characters and other internal features 

are generally consistent.

The ontogenetic sequence of Crassatella carolinensis 

is notable for this genus in its lack of clearly delineated 

stages. Adult characters are expressed fairly early in the 

ontogeny of the species; before the specimens have 

reached 10 percent of their adult size, the subcircular 

outline (illustrated on pi. 2, fig. 9; pi. 5, fig. 8) has given

27 Minimum, maximum, and mean values were not calculated for Crassatella 

carolinensis characters because of the limited number of specimens available.

way to the more suboval form. On these earliest stages, 

the comarginal ridges are present, but the comarginal 

threads are not yet visible, and the posterior dorsal 

margin slopes away from the beak at a very low angle. 

The adult ornamentation is present by the time the 

specimens reach 20 percent of their adult size; the slope 

of the posterior dorsal margin increases gradually as the 

shell matures. The hinge characters are distinguishable 

by the time the specimens attain 25 percent of their adult 

size and are well developed by the time they reach 50 

percent of their adult size.

Crassatella carolinensis Conrad differs from all other 

species of Crassatella examined for this paper in the 

regularity and continuity of its ornamentation across 

various growth stages (pi. 5, figs. 8, 13, 15, 17-20). 

Although juvenile C. vadosa display regular growth 

lines, they differ from C. carolinensis in several key 

features. Unlike C. carolinensis, C. vadosa undergo 

changes in their patterns of ornamentation as they 

mature (compare pi. 8, figs. 10, 11, 16 to pi. 5, figs. 17, 

18). Another character applicable to all but the very 

young specimens is the shape of the anterior dorsal 

margin; when C. carolinensis are reaching full maturity, 

C. vadosa are usually still in their juvenile stages; at this 

point C. vadosa have noticeably concave anterior dorsal 

margins, whereas C. carolinensis have fairly straight to 

only slightly concave anterior dorsal margins (compare 

pi. 7, fig. 5 to pi. 5, fig. 19). C. vadosa retains the 

subcircular shape of the prodissoconch during the early 

stages of growth, but C. carolinensis passes almost 

immediately into a suboval outline. Finally, the minute 

details of the ornamentation can be used to distinguish 

juvenile C. vadosa from C. carolinensis. The comarginal 

growth threads of C. carolinensis are barely visible at 

the earliest stages of development, but quickly become 

distinctive and remain so throughout the growth stages 

of the shell; only two orders of ornamentation can be 

seen, the comarginal ridges and the comarginal threads. 

In contrast, the comarginal growth threads of juvenile C. 

vadosa are more readily apparent in the early stages (pi. 

7, figs. 4, 10) and become less distinctive later on; a third 

order of ornamentation, more prominent than the 

threads, but less prominent than the ridges, develops 

approximately half way through the juvenile stage in the 

interspaces between the ridges. Adult C. vadosa are 

easily distinguished from C. carolinensis by their ontogenetic changes in ornamentation. C. hodgei (Stephenson), which coexists with C. carolinensis in the Blufftown Formation along the Chattahoochee River, is the 

other species most likely to be confused with C. carolinensis; these species are contrasted in the discussion of 

C. hodgei.

Occurrence. —See table 42 for C. carolinensis localities, stratigraphic units, and collections studied. Refer
74 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 42. —Crassatella carolinensis — Occurrence and collections studied 

[Fm, Formation. Collection number, USNM (U.S. National Museum) collection or specimen numbers]

Locality 

number State County Stratigraphic unit Collection number

4. ..... .Georgia Stewart

8....... North Carolina Greene

Blufftown Fm 450423-450430, 450805, 450815, 453880. 

Tar Heel Fm 31929.

to figure 2 and appendix 9 for locality positions and 

descriptions.

Stratigraphic Range. —Lower Campanian (fig. 19).

Type material examined.—USNM. 31929; hypotype 

Crassatellites carolinensis (Conrad) Stephenson.

Crassatella aquiana Clark, 1895

Plate 3, figures 1-10; plate 14, figures 1-18; 

plate 16, figures 1-3, 5.

Crassatella aquiana CLARK, 1895, p. 5. CLARK, 1896, p. 82, pi. 26,

figs. 2a-2c. 

Crassatella sepulcollis HARRIS, 1896, p. 64, pi. 6, figs. 1, la.

PALMER and BRANN, 1965, p. 104. TOULMIN, 1977, p. 148, pi.

2, figs. 3, 4. 

Crassatella halei HARRIS, 1897, p. 57, pi. 11, fig. 5. SHIMER and

SHROCK, 1944, p. 419, pi. 167, fig. 12 [reproduction of Harris'

figure]. PALMER and BRANN, 1965, p. 101 [partim]. 

Crassatellites aquianus (Clark). CLARK and MARTIN, 1901, p.

181-182, pi. 42, figs. 1, 2a, 2b. 

[non] Crassatella mississippiensis Conrad. TUOMEY, 1858, p. 269,

271 [included in Palmer and Brann's (1965, p. 101) synonymy of C.

halei]. 

[non] Crassatella sp. ALDRICH, 1886, p. 57 [questionably included in

Palmer and Brann's (1965, p. 101) synonymy of C. halei].

Diagnosis.— Valves trigonally subquadrate; beaks 

high; significantly and evenly convex, with slight flattening anterior to posterior ridge on large adults. Ornament 

begins at beak as sharp high comarginal ridges, fading 

rapidly posteriorly and ventrally to comarginal growth 

threads alone.

Description.— Shell equivalve; adults and juveniles 

significantly convex, with maximum width close to beaks 

at approximately one-quarter of shell height; generally 

evenly convex as viewed from any side, although adults 

may show slight flattening anterior to posterior ridge; 

adults trigonally subquadrate in outline; juveniles suboval to subquadrate. Inequilateral; beaks high, position 

ranges from anterior one-quarter length on juveniles to 

anterior two-fifths length on adults; prosogyrous, beak 

strongly curved and pointed on juveniles, becoming less 

so on adults. Anterior dorsal margin straight to slightly 

concave at maximum width of lunule; slope of margin 

steep; lunule broad, well developed on left valve with 

ridge defining area, less well defined on right valve; 

anterior margin smoothly rounded on adults, elliptical on 

juveniles. Posterior dorsal margin straight, steeply 

inclined; escutcheon narrow, well developed on right 

valve with sharp ridge defining area, less well defined on

left valve; posterior ridge subdued, preceded anteriorly 

on adults by slightly flattened area; posterior area broad; 

posterior margin truncate. Ventral margin rounded 

anteriorly to below beak; posteriorly margin varies from 

rounded to slightly concave below posterior adductor. 

Ornamentation of nepionic and early juvenile stages of 

shell consists of sharp high comarginal ridges with deep 

V-shaped interspaces; only first few comarginal ridges 

are continuous across shell surface from anterior to 

posterior, remainder fade anterior to posterior ridge, 

then rapidly disappear in ventral direction as well; 

comarginal growth threads are continuous across entire 

shell surface; later stages of adult shells may show 

undulations on surface. Hinge angle averages 110 

degrees for adults; 109 degrees for juveniles; moving 

from posterior lateral ridges across hinge plate to anterior lateral ridges, dentition noted as follows:

Right Valve 0 1 0-R 010 -101 

Left Valve 1 0 l-R(O) 1010 (1)-0 1 0

Right valve dentition consists of one long posterior 

lateral ridge, separated by edentulous space from resilifer (R); resilifer originates at beak on platform formed by 

rear wall of socket below and slightly anterior to resilifer; 

socket relatively large obtuse triangular shape on juveniles, small acute triangular shape on adults; opening of 

resilial platform to umbonal cavity is partially obstructed 

by position of small socket; one large cardinal tooth lies 

anterior to beak; two short anterior lateral ridges 

present, separated by groove. Left valve dentition consists of two long posterior lateral ridges, separated by 

groove; resilifer originates at beak; small depression 

present on basal side of posterior slope of cardinal; two 

well-defined cardinals separated by socket; forward of 

anterior-most cardinal is narrow groove followed by 

short ridge; one short anterior lateral ridge present. 

Resilifer elongate, triangular, extends to near edge of 

hinge platform on large adults. Dentition defined at early 

stages of juvenile, resilifer may be visible. Isomyarian 

adductor muscle scars, anterior reniform, posterior subcircular. Crescent-shaped anterior pedal retractor 

present above anterior adductor and below anterior 

lateral ridge, tangent to edge of hinge platform. Pallial 

line distinct on adults, entire. Crenulations present on 

mature individuals, from anterior lateral ridge ventrally 

to below posterior adductor; very faint crenulations may
SYSTEMATIC PALEONTOLOGY 75

TABLE 43.— Minimum, maximum, and mean values for characters of Crassatella aquiana 

[See table 2 for an explanation of the morphological variables. Data source: digitized data set; excludes broken specimens and internal molds]

Morphological variable

CONVEX ........

LENGTH. ........

HINGE...........

POST.............

ANTER..........

ANTVERHT

POSVERHT......

Adults (72 specimens)

Minimum

4.70

16.31

93.48

99.03

128.28

6.78

7.16

Maximum

20.04 

73.90 

120.44 

152.06 

163.49 

37.81 

32.78

Mean

6.87 

22.28 

109.84 

123.34 

144.33 

10.81 

11.09

Juveniles (47 specimens) Combined (119 specimens)

Minimum

2.49 

8.70 

94.66 

105.33 

123.39 

3.93 

4.66

Maximum

7.50 

22.02 

121.05 

150.12 

172.13 

11.66 

10.83

Mean

4.12 

12.98 

107.92 

126.44 

143.00 

6.43 

6.89

Mean

5.78 

18.60 

109.08 

124.56 

143.80 

9.08 

9.43

be present on late stages of juveniles. Prodissoconch not 

seen.

Discussion.— Clark (1895, p. 5) named Crassatella 

aquiana from a single articulated specimen found in the 

Aquia Formation, at Aquia Creek, Va. The original 

description was brief and limited to the exterior features 

of the shell: "Shell moderately large, attenuated posteriorly; surface with a few broad, shallow, concentric lines, 

often obscure; lunules broad, deeply depressed" (Clark, 

1895, p. 5). In comparing C. aquiana to C. alaeformis [= 

Bathytormus alaeformis], an abundant fossil in the 

Aquia Formation, Clark (1895, p. 5) also mentioned the 

high umbones of C. aquiana. Clark (1896, pi. 26, figs. 

2a-2c) figured the holotype the following year (USNM 

207155; pi. 3, figs. 3, 8, 10), and in 1901 Clark and Martin 

(1901, p. 182) listed additional localities of Crassatellites 

aquianus [= Crassatella aquiana] in the Piscataway 

Member of the Aquia Formation from the Potomac River 

region.

Crassatella sepulcollis was named and described by 

Harris (1896, p. 64) from deposits in Wilcox County, Ala. 

(holotype, PRI 64, see pi. 3, figs. 1, 2, 5; paratype, PRI 

65, see pi. 3, figs. 4, 7). Harris (1896, p. 65) stated, "Its 

high, anteriorly located and curving beaks, its broad 

post-umbonal slope, its hinge characters, and size and 

general outline distinguish it from any other known 

form." In 1897, Harris (1897, p. 57) named and described 

C. halei from deposits at Greggs Landing on the Alabama River, Monroe County, Ala. (PRI 140; pi. 3, figs. 6, 

9).

A comparison of the descriptions for Crassatella halei 

and C. sepulcollis reveals only two significant differences: (1) C. halei is described as having a "faint longitudinal medial depression" on the "post-umbonal slope" 

(Harris, 1897, p. 57) and (2) C. halei has an oblique 

cardinal tooth in the right valve (Harris, 1897, p. 57). 

These differences can be attributed to ontogenetic 

change; C. halei, therefore, is the adult form of C. 

sepulcollis. Although Clark's description of C. aquiana 

is meager, nothing in the description is incompatible with 

Harris' description of C. sepulcollis. Furthermore, a 

comparison of the type specimen of C. aquiana (pi. 3,

figs. 3, 8, 10) and additional specimens in the collection of 

the USNM (pi. 14, figs. 3, 8, 10) to the type specimens of 

C. sepulcollis (pi. 3, figs. 1, 2, 4, 5, 7) reveals that C. 

aquiana and C. sepulcollis are synonyms. Although no 

internal features are preserved on the Mid-Atlantic 

forms, both C. aquiana and C. sepulcollis possess the 

diagnostic high beaks, trigonally subquadrate outlines, 

and strong ornament near the beaks that fades ventrally 

and posteriorly (pi. 3, figs. 2, 3, 5; pi. 14, figs. 2, 5, 9-11). 

C. aquiana is therefore accepted as the senior synonym. 

The species is rare and poorly preserved in the type area, 

but abundant and better preserved in the Gulf Coast 

region, where C. sepulcollis and C. halei were originally 

described. Consequently, the description and diagnosis 

herein included are based primarily on the Gulf Coast 

forms. C. aquiana is probably an element of a warm 

water fauna, which occasionally migrated northward 

along the Atlantic coast during the Paleocene.

The species has received little consideration in the 

literature since the early 1900's. Palmer and Brann 

(1965, p. 101) included two names, Crassatella mississippiensis Conrad, Tuomey, 1858 (non Conrad, 1848) and 

? C. sp. Aldrich, 1886, in their synonymy of C. halei. 

Both of these names originally appeared in list form only, 

so there was no means by which Palmer and Brann could 

establish what species the original authors were examining. Based on the localities cited for these two names, 

they should more likely be synonymized with C. tumidula. Since C. tumidula and C. aquiana overlap in 

occurrence in the Gulf Coast region, however, there is no 

way to verify assignments made in list form without 

examining the specimens.

The largest degree of intraspecific variation within 

Crassatella aquiana occurs between the various growth 

stages. There is, however, a range in variation of shape 

and posterior elongation, affected by the differences in 

height-to-length ratio. An examination of plate 14, figures 4, 6, 11, and 15 shows this range of differences; as 

height increases relative to length, the individual has a 

steeper posterior dorsal slope and shortened posterior 

compared to individuals having lower height-to-length 

ratios (see table 43 for the average measurements for the
76 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

species). The posterior margin can range from rounded 

(pi. 3, fig. 8) to squarely truncate (pi. 14, fig. 7). 

Variation can also be seen in the extent of the "faint 

depression" anterior to the posterior ridge; the more 

depressed this area is, the more concave the posterior 

ventral margin is (see pi. 14, figs. 12, 15, 18). Abrasion of 

some individuals may remove or reduce the characteristically high comarginal ridges near the beak, as seen on 

two of the type specimens (pi. 3, figs. 6, 7).

The nepionic stage of Crassatella aquiana begins as a 

subcircular valve having coarse, high, comarginal ridges 

covering the surface (pi. 16, fig. 5). The early juvenile 

stage maintains this distinctive ornament, but the external outline becomes quadrate and has a broad flat posterior margin delineated by a distinct posterior ridge (pi. 

16, figs. 1, 2). In these early stages, the beak is strongly 

prosogyrous, and the valves show a high degree of 

convexity for such small individuals. Internally the dentition is already defined (pi. 16, fig. 2), and the resilifer 

usually is visible; the adductor muscle scars are distinct 

but shallow (pi. 14, fig. 1); the anterior pedal retractor 

may not be apparent. Gradually, as the shell matures, 

the height-to-length ratio increases, and the beak 

migrates closer to the midline of the shell, giving the 

external outline a more triangular appearance and causing a decrease in the hinge angle and an increase in the 

slope of the posterior dorsal margin. These external 

changes are reflected internally in changes in the character of the dentition. In the younger stages, the right 

valve cardinal is nearly vertical and fairly broad for the 

size of the hinge plate, and the triangular receptor pit 

below the resilifer covers half of the posterior area of the 

hinge plate (pi. 14, fig. 4). As the hinge angle becomes 

more acute, the right valve cardinal no longer increases 

in breadth but becomes obliquely angled anteriorly (as 

noted by Harris (1897, p. 57) in his description of C. 

halei, and the triangular receptor pit below the resilifer 

becomes increasingly narrow, opening up the resilifer 

platform to the umbonal cavity (pi. 3, fig. 9). Concomitant changes can be noted in the left valve, although they 

are not as obvious as in the right valve. The later stages 

of the juvenile shell and the adult shell are covered only 

with comarginal growth threads; in the late stages of a 

mature adult, undulations may appear on the surface of 

the shell. Faint crenulations do not appear until very late 

in the juvenile stage (usually when length equals 20-25 

mm) and gradually become more pronounced with maturity (pi. 14, fig. 14).

Crassatella aquiana occur with C. tumidula at many 

outcrops in Alabama, but the evenly convex nature of the 

valves of C. aquiana, as opposed to the attenuated 

posterior of C. tumidula, should serve to distinguish 

these two species (compare pi. 14, fig. 13 to pi. 15, 

fig. 5). The lack of any ornamental pattern other than

comarginal growth threads on the adult C. aquiana, will 

set this species apart from all Cretaceous members of the 

genus. The absence of any character for ornament in the 

statistical analysis explains the quantitative overlap of C. 

aquiana juveniles with C. vadosa. Finally, the 

extremely large adult specimens of C. aquiana, which 

have relatively open resilial platforms, may resemble 

large adult members of Bathytormus, particularly B. 

alaeformis, which is found in abundance at the type 

locality of C. aquiana. The lack of extreme posterior 

elongation and an examination of the juvenile portions of 

the shell should differentiate C. aquiana from Bathytormus (compare pi. 14, figs. 17, 18 to pi. 18, fig. 22 and pi. 

19, fig. 11).

Occurrence.—See table 44 for C. aquiana localities, 

stratigraphic units, and collections studied. Refer 

to figure 2 and appendix 9 for locality positions and 

descriptions.

Stratigraphic Range.—Midway and Wilcox (fig. 19).

Type material examined. — USNM 207155; holotype 

Crassatella aquiana Clark. PRI 64; holotype Crassatella sepulcollis Harris. PRI 65; paratype Crassatella 

sepulcollis Harris. PRI 140; Crassatella halei Harris.

Crassatella hodgei (Stephenson), 1923

Plate 2, figures 7, 8, 10, 11; plate 4, figures 1-19; 

plate 5, figures 2, 7, 9, 10, 12, 14; plate 6, figures 1-6.

Crassatellites hodgei STEPHENSON, 1923, p. 271, pi. 67, figs. 4-9.

RICHARDS, 1958, p. 187, pi. 31, figs. 3-4 [incorrect citation of type

locality and of type specimen as USNM 31847]. 

Crassatellites roodensis STEPHENSON, 1923, p. 273, pi. 68, figs. 1-4.

STEPHENSON, 1926, p. 246, pi. 90, fig. 5. 

Crassatella hodgei (Stephenson). RICHARDS, 1954, p. 2, text figs. 1,

2. 

[?] Crassatella pteropsis ? CONRAD, 1875, appendix, p. 6, pi. 1, fig.

25. 

[?] Crassatellites pteropsis (Conrad). RICHARDS, 1950, p. 74, figs.

61b, 61c.

Diagnosis.—Indentation of posterior ventral margin 

and (or) sharply pointed posterior margin when present; 

prominent posterior ridge when present. Sharp, high, 

widely spaced comarginal ridges on early portions of 

shell; sharp angulation of posterior ventral edge of 

juvenile; early expression of adult form during ontogeny, 

including posterior ridge, indentation of posterior ventral margin, and crenulations. Flattening of umbo region 

as viewed from dorsal or ventral margins parallel to 

plane of commissure.

Description.— Shell equivalve, inflation shallow to 

fairly convex; maximum convexity at midpoint of height; 

shell flattens across umbo region as viewed from ventral 

or dorsal margins parallel to plane of commissure; adults 

vary from trigonally suboval to obtusely trigonal in 

outline; nepionic outline subcircular; juveniles rapidly
SYSTEMATIC PALEONTOLOGY 77

TABLE 44. —Crassatella aquiana— Occurrence and collections studied

[Fm, Formation; Mbr, Member. Collection number: USNM, (U.S. National Museum) collection or specimen numbers, unless otherwise noted; PRI, Paleontological

Research Institution]

Locality 

number

77A. .......

78 .........

79 .........

80 .........

81 .........

86 .........

87 .........

88 .........

91 .........

92 .........

102 .........

104 .........

105 .........

106 .........

118 .........

119 .........

Questionable C.

77A. .......

80 .........

82A. .......

State

..... Alabama

..... ....do........

..... ....do........

..... ....do........

...... ....do........

..... Maryland

..... ....do........

..... Virginia

..... ....do........

..... ....do........

..... Maryland

..... ....do........

..... ....do........

..... ....do........

..... Alabama

..... ....do........

aquiana collections

..... Alabama

..... ....do........

..... Maryland

County

Wilcox

....do........

....do........

....do........

....do........

Prince George's

....do........

Stafford

....do........

King George

Charles

....do........

Prince George's

Prince George's/

Charles

Monroe

Wilcox

Wilcox

....do........

Prince George's

Stratigraphic unit

Clayton Fm, Pine Barren Mbr

Porters Creek Clay

Naheola Fm

Porters Creek Clay

....do........

Aquia Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Tuscahoma Fm,

Greggs Landing Mbr

Tuscahoma Fm

Clayton Fm, Pine Barren Mbr

Porters Creek Clay

Aquia Fm

Collection number

129744.

154914, 450552, PRI 64.

PRI 65.

129745, 129749, 129750, 129754, 129756,

450543-450550, 450562-450565.

129753, 129755.

450839.

450850.

207155

450830, 450832.

450833.

450512, 450864.

136177, 450513, 450863.

450841, 450845.

450514, 450862.

450515. PRI 140.

450818.

129748.

129747.

450858.

assume adult shape; inequilateral; beak position highly 

variable, ranging from anterior one-quarter to near 

midlength of shell; early stages of shell prosogyrous; 

adult appears weakly prosogyrate to nearly orthogyrate 

as viewed perpendicular to plane of commissure. Anterior dorsal margin slightly concave to slightly convex at 

maximum width of lunule; margin slopes steeply away 

from beak; lunule well developed on left valve of adults 

with sharp ridge defining area, less well defined on right 

valve with no distinct ridge; anterior margin smoothly 

rounded. Posterior dorsal margin straight to slightly 

concave near end of escutcheon; slope of margin varies 

from steep to gentle depending on posterior elongation; 

escutcheon elongate, well defined on right valve with 

area defined by ridge, less well defined on left valve with 

ridge absent; posterior ridge varies from sharp raised 

carinate forms preceded by depression in shell surface to 

forms with simple ridge marked by bend in growth lines; 

posterior margin varies from pointed to quadrilaterally 

truncate on adults. Ventral margin gently curved anteriorly, flattened to rounded below beak, strongly 

incurved to flattened below posterior adductor. Ornamentation begins at beak as evenly spaced coarse raised 

ribs with broad interspaces reduced to raised sharp lines 

in posterior area, gradually shifts to closely spaced finer 

ribs at later stages, and in some cases fades entirely; 

comarginal threads begin near beak and continue across

entire shell surface, including ribs, interspaces, and 

posterior area; lower portions of shell may show deep 

broad undulations of surface; stage at which shift in 

ornamentation occurs is highly variable. Hinge angle 

variable, average 113 degrees; moving from posterior 

lateral ridges across hinge plate to anterior lateral 

ridges, dentition noted as follows:

Right Valve 0 1 0-R 010 -101 

Left Valve 1 0 l-R(O) 1010 (1)-0 1 0

Right valve dentition consists of one posterior lateral 

ridge, separated by edentulous space from resilifer (R); 

resilifer originates at beak on platform formed by rear 

wall of a trigonal socket below and slightly anterior to 

resilifer; opening of resilial platform to umbonal cavity is 

incompletely obstructed by position of trigonal socket; 

trigonal socket may have vertical grooves on rear wall of 

socket; one large cardinal tooth lies anterior to beak, 

some with transverse grooves on sides of tooth; two 

anterior lateral ridges present, separated by groove. 

Left valve dentition consists of two posterior lateral 

ridges, separated by groove; resilifer originates at beak; 

opening of resilial area to umbonal cavity restricted by 

depression at base of posterior slope of cardinal; two well 

defined cardinals separated by socket, some with transverse grooves on sides of cardinals; forward of anteriormost cardinal is narrow groove followed by short ridge;
78 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

one anterior lateral ridge present. Resilifer shaped like 

elongate teardrop. Juveniles display well-developed 

hinge characters at early stages. Isomyarian adductor 

muscle scars; anterior reniform; posterior subcircular to 

suboval. Anterior pedal retractor present. Pallial line 

distinct, entire. Crenulations present from end of anterior lateral ridge ventrally to posterior lateral ridge on 

adults; development begins anteriorly early in ontogeny 

so young specimens may have complete marginal crenulations. Prodissoconch not known.

Discussion.—The concepts of Crassatellites hodgei 

Stephenson [= Crassatella hodgei] and Crassatellites 

roodensis Stephenson have been intertwined since their 

original description (Stephenson, 1923, p. 271-274). An 

examination of the type specimens selected by Stephenson illustrates the problem. The holotype of Crassatella 

hodgei (USNM 31930; pi. 2, figs. 7, 8) shows a prominent 

posterior ridge and an accompanying indentation of the 

posterior ventral margin, but the paratype (USNM 

31931; pi. 2, figs. 10, 11) has only a smoothly rounded 

posterior ridge and a nearly flat posterior ventral margin. The holotype of Crassatellites roodensis is lost,23 

but two paratypes (USNM 31748 and 31749; pi. 4, figs. 

10, 18) exhibit the same range of variation seen in the 

types of Crassatella hodgei. Plate 4, figure 10 illustrates 

a smoothly rounded posterior ridge and a flat posterior 

ventral margin; the specimen on plate 4, figure 18 shows 

a prominent posterior ridge and indented posterior ventral margin. The confusion is compounded by the state of 

preservation of the specimens; the exteriors of many of 

the shells have deteriorated (see pi. 4, figs. 9, 10, 17-19 

for examples), and the internal characters of most of the 

specimens are not visible. It seems that Stephenson's 

(1923, p. 272) primary criterion for splitting the two 

species was one of size; he stated,

The species [Crassatellites hodgei] is also closely allied to C. 

roodensis, from which it differs chiefly in size, being on the 

average about half as large. The many small individuals of 

the species found at several localities in North Carolina seem 

to justify separating it from C. roodensis, the many individuals of which are all large. Future studies may show the 

necessity for combining the two forms.

Crassatellites roodensis Stephenson is herein considered 

to be a junior synonym of Crassatella hodgei (Stephenson). The name Crassatella hodgei is retained as the 

senior synonym because it has page priority; in addition, 

the holotype of C. hodgei still exists, and Stephenson's 

original description of C. hodgei is thorough, incorporating the attributes he ascribed to Crassatellites roodensis. Other than Stephenson's original description of Crassatella hodgei and Crassatellites roodensis from North 

Carolina, South Carolina, and the Chattahoochee River 

region of Georgia and Alabama, no subsequent evaluation of the species has been made. Faunal lists have

TABLE 45.—Minimum, maximum, and mean values for characters of 

Crassatella hodgei

[See table 2 for an explanation of the morphological variables. Data source: 

digitized data set supplemented by data from specimens not included in 

discriminant analysis]

Morphological variable

Adults (13 specimens)

Minimum Maximum Mean

CONVEX ... 

LENGTH....

HINGE......

POST........

ANTER .....

ANTVERHT 

POSVERHT.

5.91

28.12

91.71

96.00

131.00

14.87

13.56

14.42

55.00

116.50

145.88

147.92

26.50

28.00

9.44

38.88

110.54

117.55

140.68

19.02

18.58

expanded the provenance of the species to New Jersey 

(Richards, 1954, p. 2)28 and Mississippi (Sohl, 1964, p. 

353; "affinities to roodensis"}.

Crassatella hodgei, as originally defined by Stephenson (1923) and as herein expanded, is a highly variable 

species. My attempts to separate morphotypes into 

distinct species groups met with failure; the range of 

variation is continuous and gradational. Specimens that 

could be grouped one way on the basis of the characters 

of the posterior ridge and posterior ventral margin had to 

be regrouped when characters of the hinge or of the 

juvenile were considered. The largest and most obvious 

variation is seen in the characters of the posterior region 

of the shell. A comparison of plate 2, figure 11; plate 4, 

figures 11, 15, 16; and plate 5, figures 2, 12, 14 illustrates 

the extremes in overall form; plate 5, figure 12 is a 

trigonal form having a quadrilaterally truncate posterior, a moderately developed posterior ridge, and a slight 

indentation of the posterior ventral margin; plate 2, 

figure 11, the paratype, illustrates the obtusely trigonal, 

posteriorly elongate form, which has a diminished posterior ridge and flattened posterior ventral margin; plate 4, 

figures 11 and 16 illustrate the extent of development of 

the posterior ridge and the accompanying indentation of 

the posterior ventral margin. The hinge angle varies 

from obtuse (pi. 4, fig. 15) to a nearly right angle (pi. 5, 

fig. 2) depending on the degree of posterior elongation 

(see table 45 for the range of values); the slope of the 

posterior dorsal margin is fairly gentle on the obtuse 

forms and fairly steep on the forms approaching a right

28 Richards (1954, p. 2; 1958, p. 187) seems to have confused Crassatella hodgei 

and Crassatellites roodensis as defined by Stephenson (1923, p. 271-274), yet he 

did not synonomize the two species or even acknowledge that C. roodensis 

existed. He listed the known localities of Crassatella hodgei as being South 

Carolina, Georgia, and Alabama (Richards, 1954, p. 2); these were the localities 

Stephenson identified for Crassatellites roodensis. The type locality listed in the 

1958 publication (Richards, 1958, p. 187) for Crassatella hodgei, Roods Bend, 

Chattahoochee River, Ala., is the type locality for Crassatellites roodensis. The 

USNM specimen number 31847 does not correspond to either Crassatella hodgei 

(USNM 31930) as Richards (1958, p. 187) indicated or to Crassatellites roodensis 

(USNM 31747).
SYSTEMATIC PALEONTOLOGY 79

angle. A comparison of figures 5, 10, 14, and 15 on plate 

4 illustrates the variation in the ventral margin from 

rounded below the beak and posteriorly indented (pi. 4, 

figs. 14, 15) to rounded below the beak and flattened 

posteriorly (pi. 4, figs. 5, 10). The position of the beak can 

vary from the anterior one-third of shell length (pi. 4, 

figs. 5, 10) to near the midpoint of the shell (pi. 4, fig. 4; 

pi. 5, fig. 2). Convexity ranges from inflated (pi. 4, fig. 

16) to depressed (pi. 5, fig. 12) (table 45). A considerable 

amount of variation is seen in the size of the shell at the 

point where the ornamentation shifts from the juvenile to 

the adult expression. The widely spaced prominent 

ridges of the early stages of the shell are clearly visible 

on plate 6, figures 1, 3, and 5 and plate 4, figures 3, 4, and 

13. Plate 4, figure 13 shows the shift from the juvenile 

ornament to the broad closely spaced ridges of the adult 

form. Eventually, on some individuals (plate 4, fig. 16), 

the ridges begin to fade, and comarginal growth threads 

remain as the only form of ornament in the final stages of 

shell growth.

The ontogenetic sequence of Crassatella hodgei shows 

rapid development of many adult characters. The subcircular prosogyrous outline of the earliest stages of the 

shell (pi. 6, figs. 1, 3) rapidly gives way to the adult shape 

(pi. 5, figs. 7, 9; pi. 6, fig. 5). Internally, the muscle scars, 

pallial sinus, hinge characters, and marginal crenulations 

are well developed at very early stages for this genus (pi. 

6, fig. 4). Changes in ornamentation occur at various 

stages as discussed above.

The species Crassatella hodgei is distinctive from all 

other members of the genus, and family, by the sum of its 

diagnostic characters. The extreme range of intraspecific 

variation, however, may cause confusion and result in 

some individuals being assigned to other species. Some 

specimens that lack a prominent posterior ridge may be 

confused with C. vadosa (compare pi. 5, fig. 1 to fig. 12), 

but the ornamentation of the juvenile portion of the 

shells quickly distinguishes the two species. The ornamentation of juvenile C. vadosa consists of fine ridges 

and comarginal lines that become coarser in later stages; 

the inverse is true for C. hodgei, which begins with 

coarse ornamentation that becomes finer as the shell 

matures (compare pi. 5, fig. 4 to fig. 9; pi. 4, fig. 11 to pi. 

8, figs. 11, 16). In addition, the juvenile shells of C. 

hodgei rapidly assume the more trigonal form of the 

adults, whereas C. vadosa retains a subquadrate outline 

into advanced stages of the ontogenetic sequence (compare pi. 5, figs. 4, 6 to figs. 7, 10; pi. 6, fig. 4 to pi. 12, fig. 

4).

Crassatella hodgei and Crassatellites carolinensis 

(Conrad) Stephenson [= Crassatella carolinensis Conrad] coexist in the Blufftown Formation along the Chattahoochee River; their similarity in general form at these 

localities may cause the two species to be confused.

Differences in ornamentation clearly distinguish the two 

species (compare pi. 5, fig. 10 to fig. 17; fig. 12 to fig. 18); 

Crassatella hodgei displays shifts in ornamentation during maturation, whereas C. carolinensis does not. 

Although the adult specimens show similar outlines, the 

juveniles of the two species are distinctive. In the early 

stages, Crassatella hodgei have already developed a 

posterior ridge and an adult trigonal shape, with a 

sharply angled posterior region (pi. 5, fig. 9). Crassatella 

carolinensis juveniles are subquadrate with a rounded 

posterior and a nearly flat posterior dorsal slope (pi. 5, 

fig. 8). The convexity of the valves as viewed from the 

dorsal or ventral margins perpendicular to the plane of 

commissure is flattened across the umbo region for 

Crassatella hodgei and gently rounded for C. carolinensis (pi. 5, fig. 11). In addition, although some members of 

Crassatella hodgei share similar hinge characters with 

C. carolinensis, the average form for C. hodgei is 

distinctly different, primarily in the more complete 

obstruction of the resilial platform. The differences 

between the resilial platforms of Crassatella carolinensis and C. hodgei can be seen by comparing plate 5, 

figure 5 to figure 14; plate 4, figure 15 to plate 5, figure 

16.

In the past, specimens of Crassatella hodgei have been 

assigned to Crassatella pteropsis [= Bathytormus 

pteropsis as herein defined] (Conrad, 1875; Richards, 

1950). These specimens are discussed in detail under the 

Bathytormus pteropsis section, and they are considered 

synonyms of C. hodgei.

Occurrence.—See table 46 for C. hodgei localities, 

stratigraphic units, and collections studied. Refer 

to figure 2 and appendix 9 for locality positions and 

descriptions.

Stratigraphic range.—Lower through upper? Campanian (fig. 19).

Type material examined.—USNM 31930; holotype 

Crassatella hodgei (Stephenson). USNM 31931; paratype Crassatella hodgei (Stephenson). USNM 31748, 

31749; paratype Crassatellites roodensis Stephenson.

Genus Bathytormus Stewart, 1930

Bathytorm-us STEWART, 1930, p. 137-138. CHAVAN, 1939, p. 27-30.

CHAVAN, 1952, p. 120. CHAVAN, 1969, p. N574. 

Crenocmssatella HABE, 1951, p. 105. 

Crassatella (Bathytormus) Stewart, GLIBERT and VAN DE POEL,

1970, p. 92.

Type Species. —Crassatella protexta Conrad, 1832.

Characters of Coastal Plain Bathytormus.—The two 

species of Bathytormus included in this analysis are 

equivalved, inequilateral, and posteriorly elongate and 

have no shell gape; species may be orthogyrous or 

weakly prosogyrous; shell outlines are subelliptical or 

transversely trigonal; posterior margins are narrow;
80 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 46. —Crassatella hodgei — Occurrence and collections studied 

[Fm, Formation; Mbr, Member. Collection number, USNM (U.S. National Museum) collection or specimen numbers]

Locality 

number

1..........

2. .........

3. .........

4. .........

5. .........

6. .........

8. .........

9. .........

10. .........

11..........

13A........

13B ........

16. .........

17. .........

18. .........

19A........

19C ........

19D........

20. .........

21..........

22. .........

25A........

25B ........

26. .........

Questionable C.

State

Mississippi

....do........

....do........

Georgia

....do........

....do........

North Carolina

....do........

....do........

....do........

Delaware

....do........

South Carolina

North Carolina

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Alabama

....do........

Georgia o

hodgei collection

County

....do........

Lee

Stewart

....do........

....do........

Greene

Wayne

Lenoir

Pitt

New Castle

....do........

Lenoir

....do........

Sampson

....do........

....do........

....do........

....do........

Bladen

B arbour

....do........

Stewart

Stratigraphic unit

Coffee Sand

....do........

....do........

Blufftown Fm

....do........

....do........

Tar Heel Fm

....do........

....do........

....do........

Merchantville Fm

....do........

Bladen Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Ripley Fm,

Cusseta Sand Mbr

....do........

Cusseta Sand

Collection number

450408, 451059.

450419, 451053.

450409-450411, 453894.

450402-450406, 450421, 450422, 450431-

450435, 450501, 450815, 453880.

453862.

450407, 451094, 453879.

31930, 31931, 451097.

453864.

451101.

459093.

450420.

450412.

31748, 31749, 453861.

450852.

451102.

451106.

453856.

453857.

453858.

453859.

453860.

453863.

453866.

450413-450415, 453865, 453884.

19B North Carolina Sampson Bladen Fm 453855.

anterior margins rounded. Anterior dorsal margins are 

moderately steep; a lunule is present but is usually 

narrow and poorly defined. Posterior dorsal margins are 

straight to slightly concave; the escutcheon is elongate, 

narrow, and fairly well defined on both valves, but the 

right valve is slightly broader. The posterior area is 

narrow and is delineated by a posterior ridge. The 

ventral margin is rounded from the anterior margin to 

below the posterior adductor; it may be straight to 

slightly concave just anterior to the posterior ridge. The 

characteristic ornament for the genus consists of distinct, 

raised evenly spaced comarginal ridges on the umbo 

region and comarginal growth threads continuous across 

the entire shell surface. The typical pattern for the 

dentition of this genus, moving from the posterior lateral 

ridges across the hinge plate to the anterior lateral 

ridges, is as follows (see fig. 20):

Right Valve 010- R(l) 0 1 0 (1) -1 0 1 

Left Valve 101- R(0) 1 0 1 (0) -0 1 0

The right valve dentition consists of one sharp posterior 

lateral ridge. An elongate triangular resilifer originates

at the beak and extends to the edge of the hinge 

platform. Anteriorly a narrow trigonal socket is separated from the resilifer by a low, sharp narrow ridge; the 

ridge is almost a bifurcation of the posterior dorsal edge 

of the cardinal. One cardinal tooth lies anterior to the 

beak and is preceded anteriorly by a narrow socket. The 

anterior edge of the hinge plate may form a thin narrow 

ridge. Two anterior lateral ridges are present and are 

separated by a groove. The left valve dentition consists 

of two posterior lateral ridges, separated by a groove. 

The triangular resilifer originates at the beak and 

extends to the edge of the hinge platform. Two narrow 

cardinals are separated by a socket; the posterior-most 

cardinal is broader and may have a small pit at the 

posterior base of the tooth on large adults; a narrow 

groove forward of the anterior-most cardinal functions as 

a receptor for the anterior-most raised ridge of the 

opposite valve. One anterior lateral ridge is present. The 

ligament of Bathytormus is internal, originates at the 

beak, and extends all the way across the hinge plate. The 

musculature of Bathytormus consists of two subequal 

adductor muscle scars; the anterior is reniform, and the
SYSTEMATIC PALEONTOLOGY 81

Bathytormus

PL

RV: 01 0-R(1) 01 0 (1)-1 01 

LV: 1 01-R(0) 1 01 (0)-01 0

FIGURE 20.— Hinge characters and musculature of Bathytormus. Dental formulas read from the 

posterior lateral ridges to the anterior lateral ridges. RV, right valve; LV, left valve. AA, anterior 

adductor; AR, anterior pedal retractor; PA, posterior adductor; PL, pallial line; PR, posterior pedal 

retractor; R, resilifer.

posterior is parabolic. In addition, two pedal retractors 

are present; the anterior pedal retractor is crescentshaped and distinct and is located above the anterior 

adductor and below the edge of the hinge plate; the 

posterior pedal retractor is continuous with the posterior 

adductor and forms a notch in the anterior-dorsal corner 

of the scar. The pallial line is distinct and entire, and the 

ventral border may be faintly crenulated on wellpreserved, mature adults. These characters are consistent with Stewart's original designation and with the 

characters of the type species Crassatella protexta 

Conrad.

Discussion.— Stewart (1930, p. 137) erected Bathytormus and removed to this new genus the species originally classified as Crassatella that possess a "ligamental 

cavity extending to the ventral border of the hinge." The 

failure, however, of the ligamental cavity as a diagnostic 

character for juvenile Bathytormus versus juvenile 

Crassatella was discussed by Stewart (1930, p. 138). A 

comparison of plate 7, figures 1, 2, 6, and 8 to plate 17, 

figures 14, 16, 18, and 21 illustrates the problem;

Crassatella do not develop their characteristic restricted 

resilifers until fairly late in ontogeny, thus juvenile 

Crassatella appear to possess a typical Bathytormus 

hinge. The failure of the resilifer as a diagnostic character for all ontogenetic stages, in addition to the doubtful 

assignment of some species to Bathytormus, led Glibert 

and Van de Poel (1970, p. 92-93) to reduce Bathytormus 

to subgeneric rank.

Chavan (1939, 1952, 1969) maintained Bathytormus as 

a valid genus. In a discussion of the genus Crassatina, 

Chavan notes similarities between Bathytormus and 

Crassatina and states that they are "two related genera 

probably issuing from a common origin" (Chavan, 1939, 

p. 29; translated from French). Both Bathytormus and 

Crassatina can be divided into two groups (Chavan, 

1939, p. 28): the first having inflated orthogyrous beaks, 

elongate rostrated posterior, convex shell, and ornamentation of concentrically rounded cords and the second 

having small prosogyrous beaks, enlarged dilated (but 

not rostrate) posterior, flat shell, and ornamentation of 

lamellose spaced cords. Chavan (1939, p. 28) assigned
82 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

Crassatella protexta, the type species of the genus to the 

first group (pi. 21, figs. 11, 13) and Bathytormus alaeformis (pi. 21, figs. 14, 17), discussed below, to the 

second group (Chavan, 1939, p. 29) on the basis of its 

ornament. Crenocrassatella Habe (type species Crassatella foveolata Sowerby, 1870) was recognized as a 

junior synonym of Bathytormus by Chavan (1952, p. 

120).

Bathytormus Stewart is herein recognized as a valid 

genus. In the Upper Cretaceous deposits of the Gulf 

Coast and Mid-Atlantic regions, Bathytormus is a rare 

but distinctive component of the fauna. The distribution 

of Bathytormus in the lower Tertiary deposits is 

restricted to the Mid-Atlantic region, but there it is 

relatively common. Bathytormus can be distinguished 

from adult Crassatella by the resilifer, which extends 

from the beak to the ventral edge of the hinge plate, and 

from all growth stages of Crassatella by the extreme 

posterior elongation and the narrow lunule. The shape of 

the posterior and characters of the dorsal margin were 

the primary discriminators between Crassatella and 

Bathytormus during the statistical analysis. Despite the 

statistical separation of the two species, B. alaeformis 

and B. pteropsis show a large degree of intraspecific 

variation.

Bathytormus alaeformis (Conrad), 1830

Plate 3, figures 12, 14-19; plate 18, figures 1-22;

plate 19, figures 1-13; plate 20, figures 5, 7;

plate 21, figures 14, 17.

Crassatella alaeformis CONRAD, 1830, p. 228, pi. 10, fig. 1. CONRAD, 1846, p. 396, pi. 3, fig. 2 [not fig. 3 (= ? Crassatella protexta) 

as indicated in text and plate caption]. CLARK, 1895, p. 5. CLARK, 

1896, p. 81-82, pi. 27, fig. la-Ik. YOKES, 1961, p. 50, pi. 10, figs. 

5, 6.

Crassatella capri-cranium ROGERS and ROGERS, 1839, p. 375-376, 

pi. 30, fig. 2 (two illustrations) [= ROGERS, 1884, p. 672, pi. 5, fig. 

2 (reprint)].

Crassatella declivis HEILPRIN, 1880, p. 151-152, plate on p. 150, fig. 

9. ALDRICH, 1897, p. 170, pi. 3, figs. 1, la.

Crassatella protexta Conrad. DE GREGORIO, 1890, pi. 25, fig. 12 

[reproduction of Conrad, 1846, pi. 3, fig. 2 = C. alaeformis Conrad].

Crassatellites alaeformis (Conrad). CLARK and MARTIN, 1901, p. 

180-181, pi. 41, figs. 1-8 [partim; not C. palmula Conrad]. WARD, 

1985, pi. 2, fig. 7.

Bathytormus alaeformis (Conrad). STEWART, 1930, p. 137. CHAVAN, 1939, p. 29. PALMER and BRANN, 1965, p. 48-49 [partim; 

not = C. palmula Conrad].

Crassatella (Bathytormus) alaeformis Conrad. GLIBERT and VAN 

DE POEL, 1970, p. 92-93.

Crassatellites capricranium (Rogers and Rogers). WARD, 1985, pi. 1, 

fig. 9.

[non] Crassatella. palmula CONRAD, 1846, p. 396, pi. 4, fig. 1.

Diagnosis. — Subelliptical; extreme posterior elongation; weakly prosogyrous adults; subdued posterior 

ridge; posterior area flattened to gently sloping. Ornament across umbone sharp, high comarginal ridges,

gradually becomes rounded and less prominent ventrally 

and posteriorly; ventral portion of large adults lacks 

distinctive ornament in contrast to umbone. Resilifer 

extends to edge of hinge platform; posterior cardinal in 

right valve situated vertically. Crenulations faint, form 

late in ontogeny.

Description.— Shell equivalve, inflation shallow to 

moderately convex, anterior wider than posterior; adults 

subelliptical in outline, juveniles shift from quadrate to 

suboval during ontogeny. Inequilateral; extreme posterior elongation, beak position ranges from anterior onequarter to two-fifths of shell length, average threetenths; adults weakly prosogyrous, juveniles strongly 

prosogyrous; beak sharply pointed on juveniles, less so 

on adults. Anterior dorsal margin straight to slightly 

concave, moderately sloping; lunule very narrow, faint 

ridge defines area on left valve of juveniles and young 

adults, broader, more well defined on large, mature 

specimens; anterior margin evenly rounded. Posterior 

dorsal margin straight to slightly concave on adults; 

juveniles slightly concave at maximum width of escutcheon; margin gently sloping; escutcheon elongate, narrow, 

fairly well defined on both valves, right valve slightly 

broader; posterior margin elongate, narrow, truncates in 

gentle arc; posterior area narrow, gently sloping, delineated by subdued posterior ridge. Ventral margin 

rounded from anterior margin to below posterior adductor; straight to slightly concave just anterior to posterior 

ridge. Predominant ornamentation of juvenile portion of 

shell sharp, high evenly spaced comarginal ridges, with 

deep V-shaped interspaces; relief of ornament decreases 

ventrally and posteriorly; spacing becomes increasingly 

irregular, and ornament shifts to more rounded, broader 

comarginal ribs, then fades entirely leaving only comarginal growth threads, which are continuous across entire 

shell surface; ornament of posterior area subdued; faint 

radial lines may be seen under high magnification on 

young individuals or on ventral portion of large adults. 

Hinge angle variable, average 123 degrees for adults, 121 

degrees for juveniles; moving from posterior lateral 

ridges across hinge plate to anterior lateral ridges, 

dentition noted as follows:

Right Valve 0 1 O-R(l) 0 1 0 (1)-1 0 1 

Left Valve 1 0 l-R(O) 1 0 1 (0)-0 1 0

Right valve dentition consists of one sharp posterior 

lateral ridge; elongate triangular resilifer originates at 

beak, extends to edge of hinge platform; anteriorly very 

narrow trigonal socket separated from resilifer by low, 

sharp, narrow ridge; ridge almost bifurcation of posterior 

dorsal edge of cardinal; one cardinal tooth anterior to 

beak, preceded anteriorly by narrow socket; anterior 

edge of hinge plate may form thin narrow ridge; two 

anterior lateral ridges separated by groove. Left valve
SYSTEMATIC PALEONTOLOGY

dentition consists of two posterior lateral ridges separated by groove; triangular resilifer originates at beak, 

extends to edge of hinge platform; two narrow cardinals 

separated by socket; posterior-most cardinal broader, 

vertical, may have small pit at posterior base of large 

adults; anterior-most cardinal angled forward; narrow 

groove forward of anterior-most cardinal functions as 

receptor for anterior-most raised ridge of opposite valve; 

one anterior lateral ridge is present. Dentition forms 

early in ontogeny, resilifer somewhat later. Two subequal adductor muscle scars, anterior reniform, posterior 

parabolic. Anterior pedal retractor crescent shaped, 

distinct, located above anterior adductor, below edge of 

hinge plate; posterior pedal retractor continuous with 

posterior adductor, forms notch in anterior-dorsal corner 

of scar. Pallial line distinct, entire. Crenulations appear 

very late in ontogeny, faint, extending from anterior 

lateral ridges around to below posterior adductor. Prodissoconch circular, free of ornament.

Discussion. —Crassatella alaeformis was named by 

Conrad (1830, p. 228) from a single specimen found in the 

lower Tertiary deposits at Piscataway Creek, Prince 

George's County, Md. (holotype, ANSP 30498, see pi. 3, 

figs. 14, 17). In his original description of the species 

Conrad inverted the anterior and posterior portions of 

the valve; he described the anterior portion as "rostrate" 

and the posterior portion as "short and rounded" (Conrad, 1830, p. 228). Subsequently, Conrad (1846, p. 396) 

corrected this error, noting that the posterior side of C. 

alaeformis was "produced, cuneiform, obliquely truncated at the extremity."

Since Conrad's original description, Bathytormus 

alaeformis (Conrad) has been recognized by many workers in the well-studied Aquia Formation (late Paleocene) 

of the Mid-Atlantic (Clark, 1895, p. 5; 1896, p. 81; Clark 

and Martin, 1901, p. 180; Yokes, 1961, p. 50; Ward, 

1985). Clark (1895, p. 5) was the first author to recognize 

that Crassatella capri-cranium Rogers and Rogers and 

C. declivis Heilprin (USNM 2490; pi. 3, figs. 16, 18, 19) 

were junior synonyms of C. alaeformis. Some authors 

(Clark and Martin, 1901, p. 180; Palmer and Brann, 1965, 

p. 49) have questionably synonymized C. palmula Conrad with C. alaeformis. I believe the extremely poor 

preservation of the type specimen of C. palmula (ANSP 

30580; pi. 3, figs. 11, 13) prevents even questionable 

synonymization. 29 Stewart (1930, p. 137) assigned C. 

alaeformis Conrad to his new genus Bathytormus on the 

basis of the hinge characters.

The large degree of intraspecific variation seen in 

Bathytormus alaeformis was first discussed and illustrated by Clark and Martin (1901, p. 180-181, pi. 41).

29 For a complete discussion of Crassatella palmula Conrad see section 

"Distribution and validity of species" on page 58.

TABLE 47.—Minimum, maximum, and mean values for characters of 

Bathytormus alaeformis

[See table 2 for an explanation of the morphological variables. Data source: 

digitized data set; excludes broken specimens and internal molds]

Morphological variable Adults (112 specimens)

Minimum Maximum Mean

CONVEX ... 

LENGTH....

HINGE......

POST........

ANTER .....

ANTVERHT 

POSVERHT.

1.15

9.83

110.40

82.42

118.16

3.82

4.72

21.32

59.99

135.30

172.72

161.15

23.98

23.40

7.07

37.47

122.59

115.85

134.64

13.94

13.03

While most of these differences can be attributed to 

ontogenetic change, variations in the degree of posterior 

elongation, height-to-length ratio, prominence of the 

beak, and inflation can be noted in individuals at the 

same stage in their life cycle (see table 47 for range of 

values). An examination of plate 18 illustrates different 

configurations of the posterior region; plate 18, figures 17 

and 18 represent extremely elongate individuals, 

whereas plate 18, figure 20 shows a comparatively short 

specimen. The mixed distribution of posteriorly elongate 

forms with the shorter higher forms indicates the possibility that these variances in shape may be due to sexual 

dimorphism, but a conclusive determination has not been 

reached. Greater height-to-length ratios than average 

for the species can give specimens an oval appearance 

(pi. 19, figs. 3, 4). Degree of inflation can vary for 

similarly sized individuals (compare pi. 19, figs. 7, 8), but 

this is more commonly a function of ontogenetic stage. 

Variations also are noted in the degree of concavity of the 

posterior dorsal margin (compare pi. 18, fig. 14 to fig. 

18), and in the posterior ventral margin (compare pi. 18, 

figs. 15, 17 to figs. 18, 20). The prominence of the beak 

varies somewhat (compare pi. 18, fig. 14 to fig. 22), but 

care must be taken to determine that this is not a 

function of wear; a few specimens illustrated by Clark 

and Martin (1901, pi. 41, fig. 2, for example) appear to be 

worn. In fact, abrasion can account for many differences 

seen in the ornament, the marginal crenulations, the 

prominence of the beak, and the shape of the posterior 

extremity.

Ontogenetic changes account for the largest degree of 

intraspecific variation. The nepionic stage of Bathytormus alaeformis is subquadrate (pi. 20, figs. 5, 7), but the 

juvenile rapidly passes through a suboval form and 

assumes a truncated subelliptical outline (pi. 18, figs. 1, 

2). At these early stages, the beak is highly pointed and 

strongly prosogyrous, and the ornament consists of high, 

sharp evenly spaced ridges with deep V-shaped interspaces; the interspaces are covered with sharp comarginal growth threads, and faint radial lines may be visible 

on specimens at high magnifications (pi. 20, fig. 5). The
84 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

dentition, pallial line, and muscle scars are fully developed on young juveniles of B. alaeformis, although the 

resilifer may not be well defined (pi. 18, figs. 2, 5). The 

valves are shallow, and the posterior ventral margin is 

gently curved at this stage. As an individual matures, 

the resilifer becomes distinct, the inflation of the valve 

increases, and the posterior ventral margin becomes 

straight, then concave (pi. 18, fig. 13); the ornament 

gradually begins to shift to more rounded ribs, and, as 

the juvenile passes into the adult stage, faint marginal 

crenulations appear on the anterior ventral border (pi. 

18, figs. 7, 12). Plate 18, figures 12 and 15, show the 

transition between juvenile and adult stages.

The continued maturation of the adult Bathytormus 

alaeformis is marked by an apparent increase in height 

relative to length (although this is difficult to confirm 

because very few large adult specimens have intact 

posterior margins) and increased convexity (examine the 

sequence of pi. 18, figs. 19, 21, 22). The increase in 

convexity is accompanied by the development of a 

broader, more well-defined lunule (pi. 19, figs. 6, 9), a 

less prominent configuration of the beaks, and a steeper 

posterior area. Ornamentation of the ventral portion of 

these large, mature adults consists of comarginal growth 

threads alone, in marked contrast to the distinctive 

ridges seen on the umbo. Plate 18, figures 21 and 22, 

illustrates the characteristics of a mature adult B. alaeformis. Finally, in the very largest individuals, the hinge 

assumes some characteristics seen on Crassatella 

throughout their life cycle: (1) a small pit appears at the 

base of the posterior cardinal of the left valve (pi. 19, fig.

13) and (2) the resilifer may no longer extend completely 

to the edge of the hinge plate, particularly in the right 

valve.

The comparison of a juvenile Bathytormus alaeformis 

(pi. 18, fig. 3, 8, or 11) to a large, mature adult member 

of the species (pi. 18, fig. 21 or fig. 22), without considering the intervening forms, may suggest that two 

species are present. Crassatella capri-cranium Rogers 

and Rogers, for example, represents the very mature 

members of B. alaeformis, which have well-developed 

lunules. The type specimen of B. alaeformis (pi. 3, fig.

14) is itself a fairly large adult, but it has not yet 

developed the broad, well-defined lunules. C. declivis 

Heilprin (USNM 2490; pi. 3, figs. 18, 19) illustrates the 

characteristic ornament of a young adult specimen of B. 

alaeformis. Careful examination of the sequence illustrated on plate 18, however, reveals that all these 

individuals are members of the same species, B. alaeformis (Conrad).

Bathytormus alaeformis can be distinguished from all 

Crassatella species by the generic differences in the 

hinge characters and by its extreme posterior elongation. 

Even on the largest members of B. alaeformis, the hinge

can still be separated from the typical form of Crassatella. The pit on the back side of the posterior cardinal 

of the left valve of B. alaeformis is shallow, small, and 

occurs on the side of the tooth, whereas the typical pit of 

Crassatella is deeper, larger, and occurs at the base of 

the tooth and spreads onto the hinge platform itself 

(compare pi. 21, fig. 17 to fig. 8). Although the resilifer of 

the large, mature B. alaeformis does not extend to the 

very edge of the hinge platform, it is still more open and 

elongate than the resilifer of Crassatella. When internal 

features cannot be seen, the large specimens of B. 

alaeformis may be confused with C. aquiana where they 

co-occur in Maryland and Virginia. The posterior elongation, the gentle slope of the posterior dorsal margins, 

and the low, weakly prosogyrous beaks of B. alaeformis 

should be distinguishable from the posteriorly truncate, 

steeply sloping dorsal margins and high strongly prosogyrous beaks of C. aquiana (compare pi. 14, figs. 3, 8, 10 

to pi. 19, figs. 6, 11 and pi. 18, fig. 21). The specific 

differences between B. alaeformis and B. pteropsis are 

discussed in the section on B. pteropsis.

Occurrence. —See table 48 for B. alaeformis localities, 

stratigraphic units, and collections studied. Refer 

to figure 2 and appendix 9 for locality positions and 

descriptions.

Stratigraphic Range. —Upper Midway through Wilcox 

(fig. 19).

Type material examined. — ANSP 30498; holotype and 

paratype Crassatella alaeformis Conrad. USNM 2490; 

holotype and paratype Crassatella declivis Heilprin.

Bathytormus pteropsis (Conrad), 1860

Plate 2, figures 1-3; plate 17, figures 1-21; 

plate 20, figures 1, 3, 4, 6; plate 21, figures 10, 12.

Crassatella pteropsis CONRAD, 1860, p. 279, pi. 46, fig. 9. GABB,

1877, p. 310. STEPHENSON and MONROE, 1940, pi. 9, figs. 4, 5. 

Crassatella (Pachythaerus) pteropsis CONRAD, 1872, p. 50 [non pi. 1,

fig. 1 = ? Crassatella sp.]. 

Crassatellites pteropsis (Conrad). GARDNER, 1916, p. 655, pi. 39, fig.

5 [partim; includes C. pteropsis Gabb in synonymy; incorrectly cites

type locality as Owl Creek, Tippah Co., Miss.]. SHIMER and

SHROCK, 1944, p. 419, pi. 167, fig. 4. 

[?] Crassatella pteropsis Conrad. GABB, 1877, p. 310. 

[non] Crassatella pteropsis GABB, 1860b, p. 395, pi. 68, fig. 28.

CONRAD, 1869a, p. 47-48. 

[non] Crassatella pteropsis ? CONRAD, 1875, appendix, p. 6, pi. 1, fig.

25 [= ? Crassatella hodgei (Stephenson)]. 

[non] Crassatellites pteropsis (Conrad). RICHARDS, 1950, p. 74, figs.

61b, 61c [= ? Crassatella hodgei (Stephenson)].

Diagnosis.— Transversely trigonal, rostrate adults; 

orthogyrous adults; uppermost portion of beak sharply 

pointed; narrow, poorly defined lunule; prominent posterior ridge, steeply sloping posterior area in adults. 

Comarginal ornament continuous across shell surface, 

gradually becomes rounded and less prominent, but
SYSTEMATIC PALEONTOLOGY 85

TABLE 48. —Bathytormus alaeformis — Occurrence and collections studied

[Fm, Formation; Mbr, Member. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of

Natural Sciences of Philadelphia]

Locality 

number

82A ........

82B ........

83 ..........

84 ..........

85 ..........

86 ..........

87 ..........

88

89 ..........

90 ..........

91..........

92 ..........

93 ..........

94 ..........

95 ..........

96..........

97..........

98..........

99 ..........

100..........

101 ..........

102 ..........

103 ..........

104 ..........

105 ..........

107 ..........

108 ..........

112..........

113A........

113B ........

State

Maryland

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

Virginia

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

Maryland

... ....do........

... ....do........

... ....do........

... ....do........

... ....do........

Virginia

... ....do........

... ....do........

County

Prince George's

....do........

....do........

....do........

....do........

....do........

....do........

Stafford

....do........

....do........

....do........

King George

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Stafford

Charles

....do........

....do........

Prince George's

Anne Arundel

Charles

King George

Hanover

....do........

Stratigraphic unit

Aquia Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Aquia Fm,

Paspotansa Mbr

....do........

....do........

Aquia Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Collection number

450823.

450860.

450536.

450856.

115796, 450523, 450531-450533,

450808. ANSP 30498.

450839.

207153, 450857, 450859, 450865.

450572,

2490, 155549, 450526-450530, 450809,

450822, 450824, 450834.

136215, 450573.

450810.

450524, 450525, 450537, 450806,

450828, 450830, 450832.

450534, 450833.

453904.

450826,

366485, 450838, 450840, 453913-453915.

453910.

450811.

450539, 450829, 450837.

450540, 453906, 453909, 453911,

450825.

450827.

450821.

450538, 450831.

450535, 450835.

136177, 450569, 450570, 450571,

450841.

450819.

450836.

453908.

366477, 453905, 453907, 453919,

453921.

453912.

453922.

453920.

remains distinctive, in later stages of shell growth. 

Resilifer elongate, narrow, extends to edge of hinge 

platform; cardinals in right valve angled anteriorly.

Description.— Shell equivalve, inflation moderate to 

fairly convex; exterior outline of adults transversely 

trigonal, rostrate; juvenile outline shifts from subcircular, to quadrate, to subtrigonal during ontogeny. Inequilateral; beak position of adults at approximately anterior 

one-third of shell length, early stages of juveniles 

approximately anterior two-fifths shell length; uppermost portion of beak sharply pointed; adults orthogyrous, juveniles slightly prosogyrous. Anterior dorsal 

margin varies from convex to straight to slightly concave; slope of margin fairly steep on adults; lunule very 

narrow and poorly defined on both valves, left valve 

slightly longer with faint ridge defining area; anterior 

margin smoothly rounded. Posterior dorsal margin

slightly concave near end of escutcheon; slope of margin 

moderately steep on adults, gentle on juveniles; escutcheon elongate, narrow, slightly broader and better 

defined on right valve with sharp ridge delineating area; 

posterior margin rostrate on adults, trapezoidal on juveniles; posterior area delineated by presence of posterior 

ridge; ridge straight or arcuate, subdued on juveniles, 

becomes more prominent on adults; posterior area broad, 

flattened on juveniles, narrow, steeply sloping on adults. 

Ventral margin smoothly rounded anteriorly, flat to 

slightly concave posterior to beak. Ornamentation of 

juvenile stages sharp, high, evenly spaced, comarginal 

ridges, becomes more rounded and less distinctive in 

adult stages; ridges continue on posterior area only on 

earliest portions of shell, ornament subdued in posterior 

area in later stages; comarginal growth threads present 

over entire shell surface; later stages of adults may show
CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

undulations and faint radial lines on ventral margin. 

Hinge angle variable, average 117 degrees for adults, 114 

for juveniles; moving from posterior lateral ridges across 

hinge plate to anterior lateral ridges, dentition noted as

follows:

Right Valve 0 1 O-R(l) 0 1 0 (1)-1 0 1 

Left Valve 1 0 1-R 101 (0)-0 1 0

Right valve dentition consists of one sharp posterior 

lateral ridge; elongate triangular resilifer originates at 

beak, extends to edge of hinge platform; anteriorly very 

narrow trigonal socket separated from resilifer by low 

narrow ridge; ridge almost bifurcation of posterior dorsal 

edge of cardinal; one narrow cardinal tooth anterior to 

beak, angled forward, preceded anteriorly by narrow 

socket; anterior edge of hinge plate may form thin 

narrow ridge; two anterior lateral ridges, separated by 

groove. Left valve dentition consists of two posterior 

lateral ridges, separated by deep groove; elongate triangular resilifer originates at beak, extends to edge of 

hinge platform; two narrow anteriorly angled cardinals 

separated by socket, posterior-most cardinal broader; 

narrow groove forward of anterior-most cardinal functions as receptor for anterior-most raised ridge of opposite valve; one anterior lateral ridge is present. Cardinal 

teeth transversely striated on sides, except posterior 

side of rear cardinal in left valve smooth. Dentition and 

resilifer fully developed at fairly young stages. Two 

subequal adductor muscle scars; anterior reniform; posterior parabolic, more deeply incised than anterior. 

Crescent-shaped anterior pedal retractor distinct, 

located above anterior adductor and below anterior lateral ridge, posterior pedal retractor indistinct, anteriordorsal notch of posterior adductor. Pallial line distinct, 

entire. Crenulations distinct, fine, extend from anterior 

lateral ridge, ventrally to posterior lateral ridge, posterior portion may be faint; formation begins fairly late 

in ontogenetic sequence. Prodissoconch oval, free of 

ornament.

Discussion. — Conrad (1860, p. 279) named Crassatella 

pteropsis from elongate, posteriorly rostrate, specimens 

found in Union or Tippah County, Miss., probably from 

the Ripley Formation (see Sohl, 1960, p. 6, for a discussion of Conrad's localities). The absence of C. pteropsis 

Conrad from Johnson's (1905, p. 14) list of ANSP Cretaceous types indicates that it was probably among the 

specimens sent to Alabama and lost during the Civil War 

(N.F. Sohl, U.S. Geological Survey, oral commun., 

1989). Fundamental topotype material is illustrated on 

plate 17, figure 5, 10, and 18, and hypotypes are shown 

on plate 2, figures 1, 2, and 3. Conrad noted the 

similarity in form between C. pteropsis and C. alaeformis Conrad, 1830 but concluded that differences in

ornamentation could be used to distinguish the two 

species.

Gabb (1860b, p. 395) applied the name Crassatella 

pteropsis to a different species in the same year and in 

the same publication as Conrad's original description of 

C. pteropsis; C. pteropsis Gabb30 is a junior homonym of 

C. pteropsis Conrad by page priority. Subsequently, 

Conrad (1869a, p. 47^8) believed C. pteropsis Gabb was 

a juvenile of C. pteropsis Conrad, but an examination of 

the type specimen of C. pteropsis Gabb (USNM 553) does 

not support this hypothesis. In 1872, Conrad (1872, p. 50) 

included C. pteropsis in the subgenus Pachythaerus; the 

problems with this assignment are discussed in the 

section "Subdivision of Crasatella" (p. 55).

Only a few individuals have recognized Crassatella 

pteropsis Conrad in the Cretaceous Coastal Plain sediments since Conrad's work. Gardner (1916, p. 649) 

separated C. pteropsis from typical Crassatella on the 

basis of the outline and posterior keel and provided the 

first detailed description of the species (Gardner, 1916, p. 

655-656) (pi. 2, fig. 1 is Gardner's hypotype, USNM 

32291). She does, however, include C. pteropsis Gabb in 

her synonymy of C. pteropsis Conrad, and she incorrectly lists Owl Creek, Tippah County, Miss., as the type 

locality for the species. Stephenson (1941, p. 176) recognized a subgroup of Crassatella within the Navarro 

Group of Texas, where "the resilifer descends in each 

valve to the inner hinge margin, and opens freely to the 

interior of the shell." This group was represented in 

Texas by C. quinlanensis Stephenson, 1941 and in the 

eastern Gulf by C. pteropsis. Although C. quinlanensis 

is outside the geographic limits of this study, future 

investigations will probably demonstrate it to be a synonym of C. pteropsis Conrad. Stephenson's subgroup 

comprises the Cretaceous members of Bathytormus, but 

this generic name has never been formally applied to any 

Cretaceous species. Chavan (1969, p. N574) lists the 

range of Bathytormus as Upper Cretaceous to Holocene 

(fig. 3), but the basis for his extension of the genus into 

the Cretaceous is not documented. Sohl and Koch (1983, 

1984) were the first to recognize B. pteropsis in the 

Cretaceous, and applied the generic name in faunal lists 

of the Upper Cretaceous, Maastrichtian, Haustator 

bilira Assemblage Zone.

Bathytormus pteropsis is like most other crassatellids 

in that it exhibits the largest degree of intraspecific 

variation in characters of the posterior margin and in the 

ratio of height to length. The summary statistics for the 

species are given in table 49. The extremes of posterior 

elongation can be seen by comparing plate 17, figures 12 

and 14, a highly elongate form, to plate 17, figures 20 and

30 For a discussion of Crassatella pteropsis Gabb see the section "Distribution 

and validity of species" on pages 59-60.
SYSTEMATIC PALEONTOLOGY 87

TABLE 49.— Minimum, maximum, and mean values for characters of Bathytormus pteropsis 

[See table 2 for an explanation of the morphological variables. Data source: digitized data set; excludes broken specimens and internal molds]

Morphological variable

CONVEX ........

LENGTH. ........

HINGE...........

POST.............

ANTER ..........

ANTVERHT

POSVERHT.

Adults (29 specimens)

Minimum

3.52

22.59

109.00

88.99

113.77

7.69

6.71

Maximum

7.90 

33.29 

131.37 

179.28 

145.69 

15.30 

13.55

Mean

5.63 

28.96 

116.51 

139.25 

131.61 

12.56 

10.93

Juveniles (8 specimens) Combined (37 specimens)

Minimum

1.71 

10.43 

108.29 

82.87 

122.86 

5.48 

6.21

Maximum

4.42 

20.41 

126.48 

131.08 

139.53 

9.56 

8.81

Mean

3.21 

17.24 

114.84 

105.98 

127.99 

7.87 

7.82

Mean

5.11 

26.43 

116.15 

132.06 

130.82 

11.54 

10.26

21, an abbreviated form; plate 17, figure 9 illustrates an 

unusually high form for the species. The degree of 

posterior elongation causes concomitant changes in the 

slope of the posterior-dorsal margin. The posterior ridge 

of B. pteropsis is fairly prominent in mature adults (pi. 

17, figs. 12, 15, 19), but the degree of prominence varies 

(compare pi. 17, figs. 12, 17). Variations in the posterior 

ridge cause slight differences in the posterior-ventral 

margin; some specimens have slight indentations anterior to the posterior ridge (pi. 17, fig. 12), and others 

have a straight posterior-ventral margin (pi. 17, fig. 20). 

The anterior dorsal margin varies from slightly convex 

(pi. 2, figs. 1, 3; pi. 17, figs. 12, 15) to straight (pi. 17, 

figs. 10, 21) immediately anterior to the beak. Inflation of 

the valves can range from flattened (pi. 2, fig. 2) to fairly 

convex (pi. 17, fig. 13).

The majority of the intraspecific variation in Bathytormus pteropsis is seen between individuals at various 

stages in their ontogeny. The nepionic stage of the shell 

is subcircular (pi. 20, fig. 6) but rapidly passes into 

suboval then to trapezoidal stages (pi. 20, fig. 1; pi. 17, 

figs. 1^1). The beak is sharply pointed, as in the adults, 

but is slightly prosogyrous and located closer to the 

midline of the shell than on adults. The posterior ridge 

becomes visible in very early stages (pi. 17, figs. 3, 4) but 

is not prominent. The broad and flattened posterior area 

on the juveniles gives the shell its trapezoidal appearance 

and forms a gently sloping posterior-dorsal margin. 

Hinge characters develop at very young stages (pi. 20, 

figs. 3, 4); the pallial line, muscle scars, and marginal 

crenulations do not appear until later (pi. 17, fig. 1). 

Ornamentation on the juveniles consists of very strong, 

evenly spaced ribs and faint, barely visible comarginal 

threads (pi. 20, fig. 6; pi. 17, figs. 3, 4). As B. pteropsis 

mature, the convexity of the valves increases, the slope 

of the posterior-dorsal margin increases, the posterior 

ridge becomes more prominent, the slope of the posterior 

area increases, the shell becomes orthogyrous, and the 

beak position shifts anteriorly (pi. 17, figs. 5, 7, 8). The 

sharpness of the ornamental ridges on the shell surface 

decreases with maturity, and in later stages the shell 

surface may show undulations (pi. 17, fig. 15). The

ontogenetic changes of B. pteropsis are primarily gradual, and variations can be seen in the size at which the 

changes occur.

Bathytormus pteropsis can be distinguished from the 

early Tertiary B. alaeformis on the basis of detailed 

characters of dentition and ornament and of overall 

shape. Statistically, the characters of length and shape of 

the posterior margin were the primary discriminating 

variables between the two species. The cardinal tooth in 

the right valve of B. pteropsis is angled anteriorly, 

whereas the corresponding tooth in B. alaeformis is 

nearly vertical (compare pi. 17, figs. 9, 16 to pi. 18, fig. 12 

and pi. 19, fig. 2). Although not diagnostic on young 

individuals, the ornament of large adult B. alaeformis 

fades ventrally in contrast to the umbonal ornament. The 

ornament of adult specimens of B. pteropsis is less 

prominent than that of the juvenile stages but is still 

distinctive. Adult B. alaeformis appear more prosogyrous, whereas adult B. pteropsis appear orthogyrous 

(compare pi. 17, fig. 13 to pi. 19, figs. 6-9). The posterior 

regions of the two species are distinctive: B. alaeformis 

has an extremely elongate, arcuate truncate posterior, 

with a subdued posterior ridge and flattened posterior 

area (pi. 21, figs. 14, 17); B. pteropsis is proportionately 

less elongate with a pointed posterior margin, prominent 

posterior ridge, and steeply sloping posterior area (pi. 

21, figs. 10, 12). The juveniles of the two species can be 

distinguished by their outline: B. pteropsis juveniles are 

trapezoidal and B. alaeformis juveniles are subelliptical 

(compare pi. 20, figs. 1, 7).

Bathytormus pteropsis can be distinguished from all 

Crassatella by the generic differences in hinge structure 

(compare pi. 21, figs. 8 to fig. 10). C. vadosa occurs with 

B. pteropsis in the Upper Cretaceous sediments of the 

Gulf and Mid-Atlantic Coastal Plains. In addition to the 

differences in hinge structure, C. vadosa and B. pteropsis can be distinguished by the extent of posterior 

elongation compared to height, the pointed posterior, the 

convex posterior-dorsal margin, and the pointed beak of 

B. pteropsis. The hinge characters fail as diagnostic 

characters on the juveniles, but immature B. pteropsis 

are posteriorly elongate trapezoidal and have highly
CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

pointed slightly prosogyrous beaks, whereas immature 

C. vadosa are quadrate and have strongly prosogyrous 

beaks (compare pi. 20, fig. 1 to pi. 12, figs. 1^4). The 

hinge of C. carolinensis is more like that of a Bathytormus than any other Crassatella, but the fine ornament of 

C. carolinensis distinguishes it from B. pteropsis.

Historically, Bathytormus pteropsis has been confused 

most often with the highly variable Crassatella hodgei. 

Triangulate, posteriorly elongate forms of Crassatella 

hodgei lacking a produced posterior ridge can bear a 

striking resemblance to B. pteropsis (compare pi. 2, figs. 

1, 3 to figs. 8, 11). I believe Conrad (1875, p. 6) may have 

found a Crassatella hodgei at Snow Hill, N.C. He 

questionably identified it as a juvenile Crassatella 

pteropsis, but he did not discuss the specimen, and the 

figure is so poor that it does not provide any further 

information. During the extensive search of USGS and 

USNM collections for this study, no specimens of B. 

pteropsis were found from beds equivalent to the lower 

Campanian deposits found at Snow Hill; Crassatella 

hodgei, however, is relatively abundant in the lower 

Campanian. Gabb (1877, p. 310) also may have confused 

the two species when, in referring to Crassatella pteropsis, he stated, "A rare shell at Pataula Creek, Georgia, 

though very common in North Carolina." No B. pteropsis 

have been identified in North Carolina, although they are 

a rare component of the sediments at Pataula Creek; 

Crassatella hodgei, however, are abundant in North 

Carolina. Finally, Richards (1950, figs. 61b, 61c) illustrates two specimens identified as Crassatellites pteropsis from Snow Hill, N.C., that appear to be Crassatella 

hodgei. As with other members of their genera, Crassatella hodgei and B. pteropsis can be distinguished on 

the basis of their hinge characteristics (compare pi. 4, 

figs. 14, 15 to pi. 17, figs. 16, 18). If details of the hinge 

cannot be seen on a specimen, however, B. pteropsis may 

be distinguished from Crassatella hodgei by its narrower 

posterior area, more concave posterior-dorsal margin, 

and more pointed beak.

Occurrence. —See table 50 for B. pteropsis localities, 

stratigraphic units, and collections studied. Refer 

to figure 2 and appendix 9 for locality positions and 

descriptions.

Stratigraphic Range. — Maastrichtian (fig. 19).

Type maternal examined. — USNM 20845; hypotype 

Crassatella pteropsis Conrad, Stephenson and Monroe. 

USNM 32291; hypotype Crassatella pteropsis Conrad, 

Gardner.

Subfamily SCAMBULINAE Chavan, 1952 

Genus Scambula Conrad, 1869

Scambula CONRAD, 1869a, p. 48. CONRAD, 1872, p. 51. WHITFIELD, 1885, p. 123. WELLER, 1907, p. 562-563. WOODRING, 

1925, p. 94 [in discussion of Crassatellites]. CHAVAN, 1939, p. 

31-33.

STEPHENSON, 1941, p. 182. SHIMER and SHROCK, 1944, p.

419. CHAVAN, 1952, p. 120. CHAVAN, 1969, p. N577. 

[non] Anthonya GABB, 1877, p. 311. 

[non] Anthonya (Scambula) STEWART, 1930, p. 147-148 [discussed

under Gouldiidae]. 

[non] Crassatella TRYON, 1884, p. 224. FISCHER, 1887, p. 1020-

1022 [incorrectly lists C. perplexa Conrad as type species], 

[non] Crassatellites (Scambula) DALL, 1903, p. 1468. 

[non] Crassatella (Scambula) LAMY, 1916, p. 202-203.

Type Species.—Scambula perplana Conrad, 1869[a].

Conrad (1869a, p. 48) first identified the genus Scambula from a single, rather poorly preserved specimen 

from the Upper Cretaceous deposits in Haddonfield, 

N.J. His initial description gives little indication of the 

unique characters of the genus and simply states, "Hinge 

with two approximate teeth in the right valve, the 

posterior one direct and ending at the apex; a long 

anterior double tooth parallel with the straight cardinal 

line; anterior muscular impression small, rounded" (Conrad, 1869a, p. 48). A subsequent discussion of the genus 

and species (Conrad, 1872, p. 51) provides more detail, 

including the compressed character of the valve and the 

unique nature of the hinge.

Considering the rare occurrence of Scambula, it has 

received considerable attention in the literature. Scambula has alternately been recognized as a distinct genus, 

as a synonym of other genera, or as a subgenus. Gabb 

(1877) considered Scambula a junior synonym of Anthonya Gabb; he stated that the hinges agree perfectly and 

that the only significant difference is that Scambula 

occurs in one plane, while Anthonya is twisted. Stewart 

(1930, p. 147) agreed with Gabb, and he included Scambula as a subgenus of Anthonya in the family Gouldiidae. 

Scambula was listed as a synonym of Crassatella by 

Tryon (1884, p. 224) and Fischer (1887, p. 1022). Ball 

(1903, p. 1464-1465) believed Conrad's species represented a juvenile of Crassatellites. He discusses Scambula as a section of Crassatellites, describing it as 

"Valves with the nepionic shell flattened, the adult 

usually elongated, the third right cardinal obsolete or 

absent, the resilium large; the inner margins of the 

valves rarely crenate but usually smooth" (Ball, 1903, p. 

1467). Many of the species included in Ball's Crassatellites (Scambula) have later been reassigned to Bathytormus or Eucrassatella; these species do not possess the 

generic characters identified by Conrad (1869a; 1872) in 

his original description of Scambula. Lamy (1916, p. 202) 

agreed with Ball, whereas Woodring (1925, p. 94) points 

out the errors in Ball's assignment.

Whitfield (1885), Weller (1907), and Stephenson (1941) 

were among the authors who maintained Scambula as a 

distinct genus. Stephenson (1941, p. 182) stated, 

"although this genus [Scambula] differs considerably in 

form and proportions from Crassatella, it appears to be 

more closely allied to that genus than to the Gouldiidae in
SYSTEMATIC PALEONTOLOGY 89

TABLE 50. —Bathytormus pteropsis — Occurrence and collections studied 

[Fm, Formation. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; USGS, U.S. Geological Survey]

Locality 

number

30A..........

31............

32. ...........

33. ...........

34A..........

37. ...........

39. ...........

43. ...........

44. ...........

45. ...........

46. ...........

60. ..........

61............

62A..........

63. ...........

64. ...........

65. ...........

67. ...........

70. ..........

71...........

75. ..........

State

. . . . . Mississippi

..... ....do........

..... ....do........

..... ....do........

..... ....do........

. . . . . Georgia

. . . . . Alabama

..... ....do........

. . . . . Georgia

..... ....do........

..... ....do........

. . . . . Alabama

..... ....do........

..... ....do........

, . . . . Georgia

..... ....do........

..... ....do........

..... ....do........

. . . . . Maryland

..... ....do........

..... ....do........

County

Tippah

Union

....do........

....do........

....do........

Quitman

Barbour

....do........

Quitman

....do........

....do........

Barbour

Barbour/Henry

....do........

Clay

....do........

Quitman

Clay

Prince George's

....do........

....do........

Stratigraphic unit

Ripley Fm,

Coon Creek Tongue

....do........

....do........

Ripley Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Providence Sand

....do........

.. ..do.. ......

....do........

....do........

....do........

....do........

Severn Fm

....do........

....do........

Collection number

450493, 451063.

451064, 451065.

451066.

450492, 451070.

20845, 450566-450568.

451081.

450487, 450488, 451082.

450496, 450498, 451086-451089, 451092.

450495, 451073, 451084, 451090.

450494, 451091.

USGS 25998.

451085, 459094.

451074.

450489, 453877.

450490, 450491, 450499, 450816, 451072,

451075.

451076.

451078.

451083.

451099.

451095.

32291, 450497.

which Stewart places it." Chavan not only maintained 

Scambula as a distinct genus (Chavan, 1939), but also 

used the genus as the type for the subfamily of Crassatellidae, Scambulinae (Chavan, 1952, 1969). The relationship between Bathytormus and Scambula is discussed by Chavan (1939, p. 32); he believes Scambula 

"represents an evolved condition which is less 

advanced."

Within the Upper Cretaceous of North America only 

one species of Scambula is known (fig. 19). Only two 

other species names have been proposed for the genus 

since the definition of Scambula and S. perplana by 

Conrad (1869a, p. 48). S. widmeri was proposed by 

Richards (1962, p. 204) but is herein synonymized with S. 

perplana. S. gilleti was proposed by Chavan (1939, p. 

32-33) for a specimen discussed and figured by Gillet 

(1921, p. 13-14, pi. 1, figs. 13-14) as Astarte sinuata from 

the Barremian (Lower Cretaceous) of Wassy, France. 

An examination of Gillet's figures indicates that Chavan 

is correct in assigning these specimens to the genus 

Scambula] however, Chavan's schematic drawing of S. 

gilleti is an inaccurate reproduction of Gillet's original 

figures. Her specimens bear a resemblance to S. perplana, but the posterior margins are broken; Chavan 

illustrated whole specimens having a quadrate posterior. 

Additionally, it seems likely that Scambula existed in 

the Cenomanian (lowermost Upper Cretaceous) of North 

Africa. Newton (1916, p. 572, pi. I, figs. 15, 16) illustrated and described a specimen identified as Anthonya 

cf. baudeti Coquand from Angola, which I believe is 

actually a Scambula. I have not examined any specimens 

of Scambula from the Cretaceous deposits of Europe or 

Africa, but it is unlikely that the range of S. perplana 

would extend down into the Lower Cretaceous. The 

genus Scambula, therefore, seems to have at least two 

or three species worldwide, restricted to the Cretaceous. 

Scambula is recognized herein as a unique, rare genus 

of Crassatellidae within the geographic and stratigraphic 

ranges of this study,

Scambula perplana Conrad, 1869

Plate 2, figure 6; plate 20, figure 2; 

plate 21, figures 1-5, 7, 9.

Scambula perplana CONRAD, 1869a, p. 47, pi. 9, figs. 7, 8. CONRAD, 1872, p. 51, pi. 1, fig. 2. WHITFIELD, 1885, p. 123-124, pi. 

18, figs. 8-10. WELLER, 1907, p. 562-563, pi. figs. 13, 14. WADE, 

1926, p. 82, pi. 25, figs. 11, 12, 15, 16. CHAVAN, 1939, p. 32 [in 

discussion of Cmssinella and related genera]. STEPHENSON, 

1941, p. 183, pi. 26, figs. 11, 12. SHIMER and SHROCK, 1944, p. 

419, pi. 167, figs. 6, 7. STEPHENSON, 1955, p. 118, pi. 18, figs. 

3-5. RICHARDS, 1958, p. 192, pi. 32, fig. 9.

Crassatella perplana (Conrad). STOLICZKA, 1871, p. 294, 295.

CrassateHites (Scambula) perplanus (Conrad). JOHNSON, 1905, p. 

14.

Anthonya (Scambula) perplana (Conrad). STEWART, 1930, p. 147, 

148.

Scambula widmeri RICHARDS, 1962, pt. 2, p. 204, pi. 93, figs. 19, 20.
90 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

Scambula

LV: 0 1 (0) (1)-(0) 1 0 1 R-(0) 1 0 1 

RV: 1 0 (1) (0)-(1) 0 1 0 (1) R-(1) 0 1 0

FIGURE 21.—Hinge characters and musculature of Scambula. Dental formulas are the reverse of the 

text and figures 18 and 20 and are read from the anterior lateral ridges to the posterior lateral 

ridges. LV, left valve; RV, right valve. AA, anterior adductor; AR, anterior pedal retractor; PA, 

posterior adductor; PL, pallial line; PR, posterior pedal retractor; R, resilifer.

Diagnosis. — Shell flat, triangular, opisthogyrous, 

with high pointed beaks. Raised posterior ridge absent. 

Anterior dorsal margin steeply sloping; anterior margin 

turns abruptly to ventral margin. Posterior dorsal margin concave. Ornament fine comarginal growth threads 

overlying broad rounded ribs, separated by incised fine 

lines. Cardinal teeth and resilifer narrow and posteriorly 

curved. Two independent pedal retractors present above 

the adductors and underneath the ventral edge of the 

lateral ridges (see fig. 21 for position of muscle scars).

Description.— Shell equivalve, flat; outline of shell 

triangular, adults posteriorly elongate, juveniles 

approaching equilateral. Inequilateral; beak position of 

adults at approximately anterior two-fifths shell length, 

juveniles closer to midlength of shell; beak high, pointed, 

opisthogyrous. Anterior dorsal margin straight to 

slightly convex, slopes steeply down to ventral margin; 

lunule extremely narrow, elongate; anterior margin 

turns abruptly to ventral margin. Posterior dorsal margin concave, slopes steeply away from beak, levels out
SYSTEMATIC PALEONTOLOGY 91

above anterior termination of posterior adductor; 

escutcheon elongate, narrow, flattened; raised posterior 

ridge absent, posterior area demarcated by bend in 

ornament alone; posterior margin truncate. Ventral margin broadly rounded, shell material thickened at edge. 

Ornament consistent across shell surface; fine ornament 

of comarginal growth threads overlies dominant ornament of rounded raised ribs, separated by incised fine 

lines; lamellae of ribs may extend past dorsal margins 

giving rugose appearance. Hinge angle approaches right 

angle; moving from posterior lateral ridges across hinge 

plate to anterior lateral ridges, dentition noted as 

follows:

Right Valve 010 (l)-R(l) 010 (l)-(O) (1) 0 1 

Left Valve 1 0 1 (0)-R 101 (O)-(l) (0) 1 0

Right valve dentition consists of one sharp raised posterior lateral ridge extending from beak to above posterior 

adductor, separated by shallow furrow from second faint 

posterior lateral ridge that fades into resilial area; elongate, narrow, triangular resilifer originates at beak, 

extends to edge of hinge platform, curves posteriorly; 

anteriorly very narrow trigonal socket separated from 

resilifer by low, sharp, narrow ridge; ridge almost bifurcation of posterior edge of cardinal; one strong medial 

cardinal tooth anterior to beak, curves posteriorly, vertical striations present on sides of tooth; deep, narrow, 

elongate socket separates strong medial cardinal from 

faint, narrow, low anterior ridge, which blends ventrally 

into hinge platform; one short anterior lateral ridge, 

separated by groove from long anterior lateral ridge, 

extpnjis length of anterior dorsal margin to above anterior adductor. Left valve dentition consists of two sharp 

posterior lateral ridges, separated by deep groove; both 

posterior lateral ridges extend from above posterior 

adductor to beak but interior-most ridge fades slightly 

near beak; elongate, narrow, triangular resilifer originates at beak, extends to edge of hinge platform; two 

narrow cardinals separated by deep narrow socket, all 

curve posteriorly; anterior-most cardinal slightly 

broader; anterior-side of posterior cardinal and both 

sides of anterior cardinal covered with vertical striations; 

faint anterior lateral ridges continuous with edge of 

hinge platform, separated by groove from sharp anterior 

lateral ridge extending from beak along anterior dorsal 

margin to above anterior adductor. Edge of hinge platform continuous with umbonal cavity; cavity beneath 

hinge platform absent. Two subequal shallow adductor 

muscle scars, anterior oval, posterior subelliptical. Anterior and posterior pedal retractor scars independent, 

small, subcircular, located above adductor scars. Pallial 

line faint, entire. Fine, sharp marginal crenulations 

present from anterior lateral ridges ventrally to posterior lateral ridges. Prodissoconch not seen.

Discussion.— Conrad (1869a, p. 47) named Scambula 

perplana from a single specimen recovered from Cretaceous units in Haddonfield, N.J. Richards (1958, p. 192) 

identified ANSP 18740 (see pi. 2, fig. 6) as Conrad's type 

specimen, but this specimen is a left valve and is imbedded in matrix so that the exterior is not visible. Conrad, 

however, figures the exterior as well as the interior of a 

right valve of S. perplana (Conrad, 1869a, pi. 9, figs. 7, 

8), so ANSP 18740 is clearly not the holotype specimen. 

Stephenson (1941, p. 183) mentions the existence of three 

left valves and two right valves at ANSP; presumably, if 

these specimens still exist, one of the right valves is the 

holotype.

Conrad (1872, p. 51) points out, "The hinge of this shell 

[Scambula perplana] is very distinct from that of Crassatella." On the basis of these fundamental differences in 

hinge structure, in addition to other distinctive characteristics of the species, most subsequent authors have 

maintained S. perplana in a separate genus. The exceptions are Stoliczka (1871, p. 295) and Johnson (1905, p. 

14). Stoliczka believes S. perplana is similar to the 

Recent species Crassatella radiata and therefore should 

remain in the genus Crassatella. Weller (1907, p. 562, 

563) is the first worker to find the species outside of the 

type locality; his collections are from the Woodbury Clay, 

Lorillard, N.J., and the Wenonah Formation, near Marlboro, N.J. The first recognition of S. perplana in the Gulf 

Coast Cretaceous deposits came in faunal lists of 

Stephenson (1914, p. 24, tables 2, 8), and the first 

illustration of S. perplana from the South was in Wade 

(1926, p. 82). Stephenson later expanded the range of S. 

perplana to Texas (Stephenson, 1941, p. 183) and Missouri (Stephenson, 1955, p. 118). In 1962, Richards 

identified a new species of Scambula, S. widmeri, from 

the Woodbury Clay of New Jersey and distinguished it 

from S. perplana on the basis of its small size and coarser 

sculpture. From the Richards (1962, p. 204, pi. 93, figs. 

19, 20) illustration and description of the ornament and 

shape of S. widmeri, I believe it to be a juvenile of S. 

perplana, although the type specimen (ANSP 30750) has 

not yet been examined.

Variations in the shape of the posterior margin account 

for the largest degree of intraspecific diversity seen in 

Scambula perplana (see table 51 for the summary statistics for the species). The degree of posterior elongation is primarily a result of ontogeny, but differences can 

be seen among similarly sized individuals (compare pi. 

21, fig. 1 to fig. 5). The typical posterior margin for S. 

perplana is truncate and flattened, as seen in plate 21, 

figure 5, but occasionally the posterior is almost pointed 

(pi. 21, fig. 1) or rounded. The more elongate the 

specimen, the flatter the ventral margin becomes
92 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

TABLE 51.—Minimum, maximum, and mean values for characters of 

Scambula perplana

[See table 2 for an explanation of the morphological variables. Data source: 

digitized data set; excludes broken specimens and internal molds]

Morphological variable Adults (32 specimens)

Minimum Maximum Mean

CONVEX... 

LENGTH....

HINGE......

POST........

ANTER .....

ANTVERHT 

POSVERHT.

0.34

3.28

83.29

119.25

118.00

1.44

1.37

1.00

16.37

103.73

163.05

173.65

5.90

5.69

0.62

8.04

92.38

145.23

144.76

3.40

3.50

compare pi. 21, figs. 3, 5), but the ventral margins of 

specimens of the same length can vary from flattened to 

rounded. Variations in the anterior dorsal margin range 

from straight (pi. 21, fig. 5) to slightly convex (pi. 21, fig. 

7). Internally, the configuration of the hinge and the 

adductor muscle scars is fairly constant within the species (fig. 21) (pi. 21, figs. 3, 5). The pedal retractors, 

however, can be obvious and well defined or absent.

It is rare to find unabraded specimens of Scambula 

perplana, so few individuals preserve the fine details of 

the ornament (compare pi. 20, fig. 2 and pi. 21, fig. 7 to 

pi. 21, figs. 1, 2, 4). The ornament seen on well-preserved 

specimens, however, is consistent with the remnants 

seen on abraded shells, with the exception of the laminae, which extend past the dorsal margins of the shell 

(pi. 21, figs. 1, 4) giving a rugose appearance to those 

edges. The laminae have not been observed on wellpreserved individuals, leaving some doubt as to whether 

this is a preservational or ontogenetic character or if it 

truly is a specific difference. All of the specimens found 

to preserve the details of ornament in this study were 

juveniles, and I believe it was this preservational bias 

that led Richards (1962, p. 204) to assign the name S. 

widmeri to small specimens of S. perplana with the 

ornament intact. Abrasion of shells can also affect the 

appearance of the beak (pi. 21, fig. 1) and the marginal 

crenulations.

The nepionic portion of Scambula perplana begins as a 

nearly equilateral triangular specimen, having virtually 

no posterior area and a steeply sloping, straight posterior dorsal margin (pi. 20, fig. 2). As the shell matures, 

the posterior becomes more and more elongate. Elongation causes the beak to shift anteriorly, so the shell 

becomes increasingly inequilateral. At these intermediate juvenile stages, the ventral margin is usually 

rounded, the hinge structure fully developed, and the 

posterior dorsal margin is concave; the muscle scars, 

pallial line, and marginal crenulations are faint or absent. 

Continued growth in the posterior direction produces an 

inequilateral adult, typically having a slightly flattened 

ventral margin, truncate posterior margin, strongly

concave posterior dorsal margin, and fully developed 

muscle scars, pallial line, and marginal crenulations.

Scambula perplana can be distinguished from all other 

crassatellids considered in this study by the following 

generic characteristics. The opisthogyrous beaks and 

strongly concave posterior dorsal margin are unique and 

immediately apparent upon examination (compare pi. 21, 

figs. 4, 5 to figs. 6, 8 and to figs. 10, 12). The extremely 

flat shell also distinguishes Scambula', even juveniles of 

the other crassatellids studied have a higher degree of 

convexity. This distinction proved to be the key discriminating variable in the statistical analysis. Finally, the 

primary distinguishing characteristic is the hinge. The 

hinge structure of Bathytormus bears the most resemblance to that of Scambula, as Chavan (1939, p. 32) 

pointed out; both genera have a resilifer that extends 

from the beak to the edge of the hinge plate (compare 

figs. 20, 21; compare pi. 21, figs, 5, 10). The hinge 

platform of Scambula, however, is very narrow, as are 

the teeth and the resilifer, and the ventral margin of the 

hinge platform slopes posteriorly. The right valve of 

Scambula exhibits two posterior lateral ridges, and the 

left valve, two anterior lateral ridges; all other crassatellids studied have one ridge. The right valve of Scambula 

has a low ridge, anterior to the cardinal tooth, that fades 

into the hinge platform; on Bathytormus this anterior 

ridge is the dorsal edge of the hinge. The teeth and 

sockets of Scambula are curved posteriorly, and the 

sides of the teeth are covered with distinctive vertical 

ridges, as opposed to the transverse ridges seen on some 

Crassatella and Bathytormus.

Occurrence.—See table 52 for S. perplana localities, 

stratigraphic units, and collections studied. Refer 

to figure 2 and appendix 9 for locality positions and 

descriptions.

Stratigraphic Range.—Lower Campanian through 

Maastrichtian.

Type material examined. — ANSP 18740; supposed holotype Scambula perplana Conrad.

PATTERNS AND TRENDS AMONG THE 

CRASSATELLIDAE

The quantitative and qualitative analysis of the Crassatellidae resolves the initial question of the validity of 

the generic and specific names presented in table 1. More 

questions are raised than answered, however, about the 

evolutionary history and biogeographic patterns of the 

Crassatellidae.

The crassatellids of the Gulf and Mid-Atlantic Coastal 

Plains appear in the lowermost Campanian in the form of 

two species, Crassatella hodgei, an extremely variable 

species, and C. carolinensis, an extremely conservative
PATTERNS AND TRENDS AMONG THE CRASSATELLIDAE 93

TABLE 52. —Scambula perplana — Occurrence and collections studied

[Fm, Formation. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of Natural Sciences

of Philadelphia]

Locality 

number

4...........

14. ..........

15. ..........

27. ..........

31...........

33

37. ..........

38A.........

41...........

42. ..........

43. ..........

44. ..........

45. ..........

50. ..........

55. ..........

63

State

Georgia

New Jersey

....do........

Tennessee

Mississippi

....do........

Georgia

....do........

Alabama

Georgia

Alabama

Georgia

....do........

Mississippi

Alabama

Georgia

County

Stewart

Camden

....do........

McNairy

Union

....do........

Quitman

....do........

Barbour

Quitman

Barbour

Quitman

....do........

Union

Montgomery

Clay

Stratigraphic unit

Blufftown

Woodbury Clay

....do........

Coon Creek Fm

Ripley Fm,

Coon Creek Tongue

Ripley Fm

....do........

....do........

....do........

....do........

....do........

....do........

. ...do.. ......

Owl Creek Fm

Prairie Bluff Chalk

Providence Sand

Collection number

453880.

ANSP 18740.

450505, 453889.

450508, 451062, 451096.

451064.

450503, 451070.

450504, 451081.

451093.

451103.

451077.

450506, 450507, 451086, 451092, 454609.

451090.

451091.

453869.

453883.

453897.

species (fig. 19). Both of these forms are rare, and which, 

if either of them, was the ancestor to the upper Campanian and Maastrichtian crassatellids is uncertain. The 

more open resilifer of C. carolinensis indicates that C. 

carolinensis may have given rise to Bathytormus pteropsis, but the juvenile C. carolinensis resembles the 

juvenile of C. vadosa. On the other hand, the more 

restricted resilifer of C. hodgei implies that C. hodgei is 

the ancestral C. vadosa, yet, in its posteriorly elongate 

form, it resembles B. pteropsis exteriorly. Consequently, either species could have been the precursor to 

B. pteropsis or to C. vadosa. Alternately, the C. hodgei 

and C. carolinensis lineages may have died out, but an 

ancestral Crassatella may have survived and spawned 

the younger forms. The concurrent ranges of C. vadosa 

and C. hodgei are based on the identification of a single 

specimen, the type Gouldia conradi Whitfield, as a 

juvenile C. vadosa. The condition of this specimen makes 

the determination questionable as discussed in the "Systematic Paleontology" section (p. 65-66). Whether the 

range of C. vadosa extends from the Maastrichtian into 

the lower Campanian or not, the pattern of stratigraphic 

occurrence of C. hodgei and C. vadosa suggests gradual 

evolutionary change from C. hodgei to C. vadosa.

In the Maastrichtian, three species representing three 

genera occur throughout the geographic range of this 

study: Crassatella vadosa, Bathytormus pteropsis, and 

Scambula perplana. C. vadosa is an abundant and 

morphologically varied species; B. pteropsis and S. perplana are rare species having low intraspecific variation. 

As stated above, the origin of C. vadosa and B. pteropsis 

is uncertain, but they seem to have arisen during the

Campanian. Scambula probably arose during the Early 

Cretaceous (see discussion, p. 89), but it does not cross 

the Cretaceous-Tertiary boundary.

Paleocene sediments in the study area contain two 

species of Crassatella, C. aquiana and C. tumidula, and 

one species of Bathytormus, B. alaeformis. C. vadosa 

may be the predecessor of C. aquiana and C. tumidula, 

or C. aquiana and C. tumidula may be descended from 

a species outside the region of study. Certainly there is a 

strong resemblance between C. aquiana and C. vadosa. 

B. pteropsis, the only known Cretaceous member of that 

genus identified to date, is logically the ancestor of B. 

alaeformis.

No ancestral-descendent relationships can be proven 

for this group of crassatellids, but a phylogenetic analysis 

incorporating fauna from other regions and stratigraphic 

levels should be conducted. At present, the pattern 

appears to be one of gradual evolutionary change. All of 

the fauna studied herein can be united through the 

characters of their juveniles, and it may be the juveniles 

that provide the best clues to the patterns of evolution 

among the Crassatellidae. Dall (1903, p. 1464) implied 

that the crassatellid resilifer has progressively 

descended across the hinge plate through time. The 

pattern is not quite that simple; the lower Campanian 

forms of Crassatella hodgei and C. carolinensis possess 

less restricted resilifers than do the younger C. vadosa. 

One explanation for the open resilifers characteristic of 

Bathytormus and Eucrassatella may be the neotenous 

retention of juvenile hinge characters. Juvenile Crassatella have resilifers that open to the edge of the hinge 

platform; these juveniles may be confused with adult
94 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

Bathytormus. Possibly, the retention of the open resilifer later and later into adulthood produced a progressive 

phylogenetic trend from Crassatella to Bathytormus and 

from Bathytormus to Eucrassatella (compare pi. 21, 

figs. 8, 10, 15, 17). One piece of evidence supports this 

theory; on very large B. alaeformis the resilifer no 

longer extends entirely to the hinge plate (pi. 21, fig. 17, 

for example), indicating that a retracted resilifer, the 

adult condition for Crassatella, is a geriatric character 

for Bathytormus. Scambula, however, may play an 

important role in the development of the resilifer that is 

not yet understood. Perhaps Scambula, which first 

appears in the Lower Cretaceous, is the precursor to 

Bathytormus, and Crassatella represents the evolved 

condition.

Another question, which requires more data to be 

answered, is whether iterative evolution occurs within 

the Crassatellidae. There is some evidence in this data 

set to suggest that certain morphologic shapes are 

repeated at different intervals in time. Compare, for 

example, Crassatella hodgei (pi. 5, fig. 12), C. vadosa 

(pi. 10, fig. 10), and C. aquiana (pi. 14, fig. 15). \yhether 

this similarity in form is the result of respog§e to the 

environment, limitations of the basic bauplan, or a little 

of both is unknown at present.

The biogeographic distribution of Bathytormus and 

Crassatella before and after the Cretaceous-Tertiary 

boundary reveals an interesting pattern. Bathytormus is 

rare in the Upper Cretaceous, but it is found from 

Maryland to the Gulf Coast. Crassatella is an abundant 

member of the Upper Cretaceous fauna, and its distribution pattern is similar to that of Bathytormus. On the 

Tertiary side of the boundary, a very different pattern is 

seen. Bathytormus, restricted to the Mid-Atlantic 

region, is the abundant crassatellid, whereas Crassatella 

is a sparse component of the fauna. A few individuals of 

C. aquiana occur in the Mid-Atlantic Coastal Plain 

Paleocene deposits, but it is far more abundant in the 

Gulf Coast sediments. The implication is that Bathytormus is a cool water form, and Crassatella, a warm 

water form, but many other factors could explain this 

distribution.

The evolutionary and biogeographic patterns illustrated through a quantitative and qualitative analysis of 

the Crassatellidae provide some insight into the natural 

history of this family of molluscs and present many 

avenues for future research. Through such detailed 

analyses of other individual families, we can better 

understand the patterns of faunal change through time.

CONCLUSIONS

Through quantitative and qualitative analyses, this 

study demonstrates the high degree of inaccuracy of the

published faunal record for one family of molluscs, the 

Crassatellidae, within the limited geographic and stratigraphic region of the Upper Cretaceous and lower Tertiary deposits of the Gulf and Mid-Atlantic Coastal Plains 

of the United States. Previous authors applied 38 specific 

names and 4 generic names to crassatellids within the 

limits of this study (table 1). Of the 38 original specific 

names, only 8 are valid recognizable species (fig. 19). Of 

the remaining 30 specific names, 14 were synonymized 

with the valid species, 11 are assigned tq indeterminant 

internal molds or poorly preserved specjjj}e,|||, | was 

invalid, and no representative specimeji c.gu]^ ^g located 

for 4 of the names. Three of the four genera were well 

founded; the fourth was based on the juvenile of another 

genus and therefore synonymized.

Crassatellidae at the Cretaceous-Tertiary fyoundary. — In addition to demonstrating the inaccuracy of the 

published fossil record, this analysis illustrates the following points for the Crassatellidae within the geographic and stratigraphic limits of this study:

• Rates of evolution and extinction based on previously published data are biased toward higher rates 

(fig. 22),

• Faunal change did occur at the boundary, but it was 

not catastrophic (compare published data to data 

from this paper, fig. 19),

• The number of species remained constant on each 

side of the boundary (fig. 23),

• A decrease in faunal abundance occurred in the early 

Tertiary, and

• The published data is biased toward higher species 

diversity, shorter average species durations, and 

restricted geographic ranges.

Rates of evolution and extinction calculated by using 

the published faunal record are two to four times too high 

(fig. 22). Averaging the 38 published specific names 

(table 1) over the 30-million-year time span covered by 

this study, the published record gives a rate of evolution 

of 1 new species every 790,000 years. On the basis of the 

eight valid species presented in this paper, this rate 

decreases to one species every 3.75 million years (fig. 

22). Even if the 11 indeterminant species are added into 

this equation, the rate is only 1 species every 1.57 million 

years.

If the data are evaluated separately for each side of the 

Cretaceous-Tertiary boundary, the published faunal 

record for the Crassatellidae gives the appearance of 

dramatic turnover. Twenty-five of these 38 published 

species names are cited for the Upper Cretaceous, and 13 

are cited for the Tertiary; a tremendous number of 

crassatellids seem to have gone extinct at the 

Cretaceous-Tertiary boundary and apparently were 

replaced during a period of rapid rebounding evolution in
CONCLUSIONS 95

CD "o

CD 

Q. 

CO

CD 

.Q

40

30

20

10

10 20 

Time in millions of years

30

FIGURE 22.—Evolutionary rates based on the published fossil record 

compared to data obtained in this study. The published fossil record 

lists 38 species for the 30 million years covered by this study; the rate 

for the published record is illustrated on the upper line. Only eight of 

these species proved to be valid and are described in this paper; the 

rate for the described species is shown on the lower line. Even if the 

11 indeterminate internal molds and poorly preserved specimens are 

included, the rate is still one-half that of the published record; the 

rate for the combined data set of described and indeterminant species 

is shown on the middle line. Rates illustrated are taxonomic frequency rates, which measure the number of species per million 

years. This diagram is a simplistic illustration of the contrast in rates 

between the published fossil record and the data contained here; it is 

not intended as an example of the way rates should be calculated.

the Paleocene. If rates of extinction are averaged over 

the 18-million-year span of the Upper Cretaceous, the 

published record indicates that one species went extinct 

every 720,000 years; the data presented here indicate 

that only one species went extinct every 3.6 million years 

on an average. For the Paleocene, the rate of evolution 

based on the published record would appear to be one 

new species every 920,000 years; however, the data in 

this analysis show a rate of only one new species every 4 

million years.

In contrast to the catastrophic turnover illustrated in 

the published fossil record, this analysis illustrates an 

even faunal exchange, in terms of the number of species, 

for the Crassatellidae at the Cretaceous-Tertiary boundary. Five well-founded species went extinct during the 

Upper Cretaceous, three of these just below the boundary, and three well founded species appear in the Paleocene (figs. 19, 23). The genera of Crassatellidae show a 

decrease in diversity from three in the Upper Cretaceous

o

>» 

CO

CO "tr

CD

CO 

3 

O 

CD 

CJ

CO •i—•

CD

6

O)

CD "i_

CD 

CO

CD 

C 

CD 

CJ 

O 

_Q

CO

CD 

Q. 

Q.

CD

c? 

CO

CO

a.

co 

O

a

-55

-60

65

-70

-75

-80

This paper

10 5 0 5 

Number of species

FIGURE 23.—Diversity patterns from the published record of Crassatellidae compared to the diversity patterns illustrated in this 

study. Information is restricted to the Campanian through Wilcox 

Stages of the eastern Gulf and Mid-Atlantic Coastal Plains.

to two in the Paleocene; the genus Scambula became 

extinct at the end of the Mesozoic.

Although diversity did not change much across the 

boundary, abundance of individuals seems to decrease 

dramatically in the Tertiary; 642 specimens of Cretaceous crassatellids were located for the quantitative 

analysis, but only 342 Tertiary crassatellids were 

located. This disparity in numbers may be the result of 

sampling bias, but I believe it is probably a reflection of 

a true decrease in numbers during the Tertiary. Every 

collection studied contains a larger number of Cretaceous 

individuals, and in addition the literature contains references to crassatellid occurrences in approximately the 

same proportions. I therefore conclude that Crassatellidae abundance truly did decrease in the Paleocene.

The net result of the splitting of the Crassatellidae 

demonstrated in this analysis, or of any group of organisms, is that basic paleobiologic information is compromised. Figures 19 and 23 illustrate the extent to which
96 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

splitting can inflate measurements of species diversity. 

Intuitively, species durations are expected to be shortened by splitting, but averaging reduces any dramatic 

differences. The average species duration for the published fossil record of the Crassatellidae is 6.9 Ma; for the 

data presented here it is 8.4 Ma. When evaluating 

individual species durations, however, the stratigraphic 

ranges may increase, decrease, or remain the same 

following taxonomic standardization. Crassatella vadosa 

and C. aquiana display the expected increase in species 

duration (fig. 19) following synonymization, but the 

range of C. hodgei remains the same (or is shorter if you 

discount the questionable portion of the range). Species 

that were not synonymized (C. tumidula and C. carolinensis for example, fig. 19), tend to have shorter ranges 

after evaluation, due to revised stratigraphic information. Splitting also affects the geographic ranges of 

species. The published fossil record for the Crassatellidae contains many geographic isolates, for example C. 

carolinana, that have been synonymized with other 

species, thus broadening the geographic range.

Significance to evolutionary studies.—The high 

degree of inaccuracy of the published fossil record demonstrated for the Crassatellidae in this analysis raises 

questions about the use of published fossil data. If other 

groups of molluscs, and other organisms in general, 

exhibit the same degree of splitting illustrated here for 

the Crassatellidae, then studies based on the published 

fossil record are biased in the following ways:

• Rates of evolution and extinction are higher,

• Faunal turnover at mass extinctions appears more 

catastrophic,

• Species diversity is high,

• Average species durations are shortened, and

• Geographic ranges are restricted. 

It may be that the Crassatellidae are the exception, not 

the rule; perhaps lumping of species is more common in 

the published fossil record, in which case the opposite 

bias would be seen. However, preliminary examination 

indicates that the problems illustrated here for the 

Crassatellidae are representative of the problems seen in 

the published literature for other groups of molluscs. 

Either way, it is important to do similar detailed taxonomic studies on other families of molluscs and other 

organisms in general in order to test the patterns illustrated for the Crassatellidae. The fossils themselves 

should be the source of data, not the literature, when we 

examine questions of paleobiologic significance. Evolution and extinction occur within small populations of 

species groups, and it is only through detailed analysis of 

those groups that we will achieve an understanding of 

the causes and effects of evolution and extinction.

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ADDITIONAL REFERENCES 103

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EVOLUTION AND EXTINCTION

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OTHER

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Paleontology, v. 36, no. 3, p. 592-610.
104 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

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no. 2, p. 76-92. 

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Hallam, A., Patterns of evolution as illustrated by the fossil 

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Chicago Press, p. 69-118.

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Geology, v. 12, p. 205-208.
INDEX TO TAXONOMIC NAMES 105

INDEX TO TAXONOMIC NAMES

[Italic numbers indicate primary discussion]

Anthonya................................................... 88

cf. baudeti............................................... 89

perplana ................................................. 89

(Scambula). ............................................. 88

Astarte sinuata........................................... 89

Bathytormus. ............ 5, 12, 13, 40-49, 51, 55-56,

59, 79-82, 88-89, 92, 93, 94;

apps. 7, 8

alaeformis. ................. 5, 35^0, 46, 49, 58, 60,

75, 76, 8"2-84, 86, 87, 94;

apps. 5, 6, 9; pis. 3, 18-21

protextus.. ........................ 5, 79, 81, 82; pi. 21

pteropsis ............................ 35-40, 46, 49, 55,

58, 79, 82, 84-88, 93; 

apps. 5, 6; pis. 2, 17, 20, 21

Crassatella [=Crassatellites]...... 5, 12, 13, 40-49,

50, 51-63, 81-82,

84, 87-88, 92, 93-94;

apps. 7, 8

alabamensis ............................................ 62

alaeformis (See also

Bathytormus alaeformis)............. 5, 82; pi. 3

alia ......................................... 58, 61, 68, 70

aquiana [= C. aquianus]...... 35, 71, 74-76, 84,

93, 94, 96; app. 9, 

pis. 3, 14, 16

capri-cranium [=C. capricranium] ... 82, 83, 84 

carolinana.. ................... 23, 28, 30, 63, 66, 68,

96; app. 4; pis. 1, 10, 11 

carolinensis......... 22, 23, 26, 27, 30, 34, 35, 49,

56, 61, 66, 72-74, 79, 88, 92, 

93, 96; apps. 3, 4; pis. 2, 5

conradi............................... 57, 62-63, 63, 66

cuneata [=C. cuneatus]. ....................... 59-60

curia ................................................. 62-63

declivis ................................. 82, 83, 84; pi. 3

delawarensis................................... 59; pi. 22

e ufa le n s is................................................ 63

eufaidensis.............................................. 63

foveolata ................................................. 82

gabbi ................... 23, 35, 59-60, 68, 70; app. 4

gardnerae................. 22, 23, 27, 30, 34, 49, 63,

66, 68; apps. 3, 4;

pis. 1, 8, 9

gibba ....................................... 51, 52, 54, 55

halei. ................................. 34, 71, 74, 75, 76;

pi. 3 

hodgei............ 22, 23, 26, 27, 30, 34-35, 49, 61,

62, 66, 73, 76-79, 84, 88, 92-94,

96; apps. 3, 4, 9; pis. 2, 4-6

landinensis.............................................. 55

Page 

ligeriensis................................................ 55

lintea [=C. linteus].. ............ 22, 23, 27, 30, 34,

49, 63, 65, 66, 68;

apps. 3, 4; pi. 1

littoralis. ............................................ 62, 63

ma rrotia n a.............................................. 62

mississippiensis .................................. 74, 75

monmouthensis........................ 23, 26, 29, 58;

app. 4; pi. 22 

neusensis .................................... 61-62; pi. 2

newkirkensis.................................. 61; app. 9

palmula................................ 58, 82, 83; pi. 3

pe ralta.................................................... 61

perplana [=C. perplanus],......................... 89

planata................................................... 60

plumbea.................................................. 52

prora [=C. prorus]..... 23, 29, 61; app. 4; pi. 22

protexta [=B. protextus]......... 5, 60, 79, 81, 82

pteropsis Conrad (See

Bathytormus pteropsis} ........... 55, 76, 84, 86

pteropsis Gabb .......................... 59-60. 84, 86

quinlanensis............................................ 86

radiata ................................................... 91

rhombea.................................................. 62

ripleyana [=C. ripleyanus] (See

C. vadosa ripleyana)................... 15, 55, 56,

63, 65, 66, 68;

pis. 1, 8

roodensis..................................... 76-79; pi. 4

sepulcollis. ......................... 23, 26, 35, 56, 74,

7.5, 76; app. 4; pi. 3 

sinuatus.................................................. 52

subplana [=C. subplanus]......... 23, 29, 62, 63,

64-65, 65, 66, 68; 

app. 4; pis. 1, 11

transversa [=C. transversus]. 23, 28, 29, 59, 60;

app. 4; pi. 22 

tumida.......................................... 51, 54, 55

tumidida [=C. tumidulus]......... 22, 23, 27, 28,

34, 34-35, 49, 56,

68-72, 75, 76, 93, 96;

apps. 3, 4; pis. 15, 16

vadosa [=C. vadosus]....... 13, 15-22, 23, 26-27,

30-35, 49, 55, 56, 62,

63-68, 69, 73, 76, 79,

87, 94, 96; apps. l^t;

pis. 1, 5, 7-12, 21,

22 (questionable)

vadosa ripleyana................. 13, 15-22, 63, 65,

67; apps. 1, 2;

pis. 1, 8

vadosa wadei.................. 15-22, 63, 66, 66, 68;

apps. 1, 2; pis. 8, 9, 11

vindie mensis. ............................................ 55

vindin nensis ............................................. 55

(Bathytormus) .......................................... 79

(Crassinella)................. ............................ 51

(Landinia) .......................................... 51, 55

vadosa .................................................. 63

(Pachythaerus) ............................... 51, 55, 56

ripleyana .............................................. 63

(Riosatella) ......................................... 51, 56

(Rochella) ........................................... 51, 56

(Scambula). .................................... 51, 55, 88

(Sublandinia) ...................................... 51, 56

Crassatellites (See Crassatella).................. 51, 53

(Cmssatellites).. ........... ............................. 51

Crassat ma... ................................................ 81

Crassinella .................................................. 57

Cren-ocrassatella. ..................................... 79, 82

Eriphyla con radi .......................................... 63

de/a M>a re ns is ............................................. 59

monmouthensis......................................... 58

jcwwa................................. ...................... 61

transversa ................................................ 60

trapezoidea ............................................... 58

Eucrassatella.... ........................ 55-56, 88, 93-94

?/ ndulata .............................................. pi. 21

Gouldia conradi ......... 57, 63, 65-66, 68, 93; pi. 22

Mactra cygnea .................................... 51, 52-55

Pachythaerus........ ............................. 51, 55, 56

Scambula............ 12, 40^3, 44, 46, 42^4, 49, 51,

55, 88-89, 92, 94, 95; apps. 7, 8 

gilleti.. ..................................................... 89

perplana ................. 88, 59-92, 93; pis. 2, 20, 21

widmeri. ........................................ 89, 9i, 92

Uddenia.. ................................ 12, 40^3, 46, 49,

51, 57-55; apps. 7, 8 

conradi. ................................ 63, 65-66; pi. 22

fragilis. ...................................... 63, 66; pi. 13

texana ............................................ 57; pi. 13

Venus 

plumbea.... ............................................... 54

ponderosa. ........................................... 51, 55

V<? n ;e Ma trapezo idea ...................................... 58

APPENDIXES 1-9

Appendixes 1 to 8 summarize the data provided for each discriminant analysis described in the chapter "Statistical 

Analysis." These data indicate how samples were classified for the statistical analysis only. In some cases, published 

species were incorrectly identified, as discussed in the text; therefore, these tables should not be used as indicators 

of species occurrence. Species occurrence tables are in the section "Systematic Paleontology."

Appendix 9 is the locality register.
108 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

APPENDIX 1

Data on specimens included in the analysis of subspecies of Crassatella vadosa, comprising adult whole specimens only

[For the purpose of the analysis, each subspecies was treated as a "species" category. Collections listed according to sequence of statistical analysis. Fm, Formation. 

Locality number corresponds to numbers on figure 2 and in appendix 9. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless 

otherwise noted; ANSP, Academy of Natural Sciences of Philadelphia]

"Species"1 Number of 

specimens2

Stratigraphic unit State County Locality 

number3

Collection 

number

Crassatella vadosa ...... 10

1

1

4

_5

Total 21

Owl Creek Fm 

Providence Sand 

Severn Fm 

....do........

....do........

Mississippi 

Georgia 

Maryland 

....do........

....do........

Tippah

Clay

Prince George's

....do........

....do........

52

63

72 

73A

75

451069

451075

451055

450520

32291

Crassatella "ripleyana". ........

Total

Crassatella "wadei". ............

Total

3

2

14

1

4

2

7

33

30

31

29

1

91

Owl Creek Fm

....do........

....do........

....do........

....do........

....do........

....do........

Coon Creek Fm

....do........

....do........

....do........

Mississippi

....do........

....do........

....do........

....do........

....do........

....do........

Tennessee

....do........

....do........

....do........

Tippah

....do........

....do........

....do........

....do........

....do........

....do........

McNairy

....do........

....do........

....do........

52

52

52

52

52

52

51

27

27

27

27

ANSP 18741

128139

450851

451052

450510

451054

451068

451056

451057

451062

32784

1 Total "species": 3.

2 Total specimens: 145.

3 Total localities: 7.
APPENDIXES 109

APPENDIX 2

Data on specimens included in the analysis of subspecies of Crassatella vadosa, comprising adults, juveniles, broken specimens,

and internal molds

[For the purpose of the analysis, each subspecies was treated as a "species" category. Collections listed according to sequence of statistical analysis. Fm, Formation. 

Locality number corresponds to numbers on figure 2 and in appendix 9. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless 

otherwise noted; ANSP, Academy of Natural Sciences of Philadelphia. —, no specimen for column]

"Species" 1 s^edmen? Stratigraphic unit

Crassatella vadosa ....... 12

2

4

12

4

1

10

16

1

5

3

2

1

1

9

10

2

Total 95

Crassatella "ripleyana". . . 3

2

18

2

5

4

7

Total 41

Crassatella "wadei". ...... 31

31

32

1

Total 95

Owl Creek Fm

Prairie Bluff Chalk

....do........

....do........

....do........

....do........

....do........

....do........

Providence Sand

Severn Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Owl Creek Fm

....do........

....do........

....do.. ......

....do........

....do........

....do........

Coon Creek Fm

....do........

....do........

....do........

State

Mississippi

Alabama

....do........

....do........

....do........

....do........

....do........

....do.. ......

Georgia

Maryland

....do........

....do........

....do........

....do........

....do........

....do........

....do.. ......

Mississippi

....do........

....do........

....do........

....do........

....do........

....do........

Tennessee

....do........

....do........

....do........

County

Tippah

Wilcox

....do........

....do........

....do........

....do........

....do........

....do........

Clay

Prince George's

....do........

....do........

....do........

....do........

....do........

....do........

Anne Arundel

Tippah

....do........

....do........

....do........

....do........

....do........

....do........

McNairy

....do........

....do........

....do........

Locality 

number3

52

57

58

56

56

56

59A

59A

63

70

70

72

73A

73A

73A

75

74

52

52

52

52

52

52

51

27

27

27

27

Number of 

Collection ^ken 

number and internal

451069

450502

450820

450500

450853

ANSP 19593

451071

451080

451075

451099

451099

451055

131763

131764

450520

32291

451104

ANSP 18741

128139

450851

451052

450510

451054

451068

451056

451057

451062

32784

molds

2

2

4

12

4

1

10

16—

5

3

1

1

1

5

4

1

_

—

4

1

1

1—

1—

1—

Number 

of 

juveniles

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

2—

—

—

—

—

—

1—

—

—

2—

1 Total "species": 3.

2 Total specimens: 231.

3 Total localities: 13.
110 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

APPENDIX 3

Data on specimens included in the analysis of species of Crassatella, comprising adult whole named abundant specimens only

[Collections listed according to sequence of statistical analysis. Fm, Formation; Mbr, Member. Locality number corresponds to numbers on figure 2 and in appendix 

9. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of Natural Sciences of 

Philadelphia; PRI, Paleontological Research Institution]

Species 1 g.

C. vadosa ..............

Total

C. gardnerae ...........

Total

"C. hodgei"

(and C. carolinensis).

Total

C. tumidula ............

Total

"C. halei"

(= C. tumidula).

Total

C. lintea. ...............

Total

lumber o 

pecimens

3

2

30

31

29

14

1

4

2

7

10

1

1

1

4

5

145

5

4

7

37

53

2

6

8

2

3

1

1

4

2

1

14

1

4

1

6

1

1

1

3

1

5

1

13

e

z Stratigraphic unit

Owl Creek Fm

....do........

Coon Creek Fm

....do........

....do........

Owl Creek Fm

....do........

....do.. ......

....do........

....do........

....do........

Coon Creek Fm

Providence Sand

Severn Fm

....do........

....do........

Ripley Fm, Coon Creek Tongue

....do........

....do........

....do........

Blufftown Fm

....do........

Tuscahoma Fm, Bells Landing Mbr

Tuscahoma Fm

Tuscahoma Fm, Bells Landing Mbr

Tuscahoma Fm

Tuscahoma Fm, Bells Landing Mbr

....do........

Tuscahoma Fm, Greggs Landing Mbr

Tuscahoma Fm, Greggs Landing Mbr

Nanafalia Fm

....do........

Ripley Fm

Severn Fm

Ripley Fm

....do........

....do........

Severn Fm

....do........

State

Mississippi

....do........

Tennessee

....do........

....do........

Mississippi

....do........

....do........

....do........

....do........

....do........

Tennessee

Georgia

Maryland

....do........

....do........

Mississippi

....do........

....do........

....do........

Georgia

....do........

Alabama

....do........

....do........

....do........

....do........

....do........

....do........

Alabama

....do........

....do........

Alabama

Maryland

Alabama

Georgia

....do........

Maryland

....do........

County

Tippah

....do........

McNairy

....do........

....do........

Tippah

....do........

....do........

....do........

....do........

....do........

McNairy

Clay

Prince George's

....do........

....do........

Union

....do........

....do........

.. ..do.. ......

Stewart

....do........

Monroe

Wilcox

Monroe

Wilcox

Monroe

....do........

....do........

Monroe

Marengo

....do........

Barbour

Prince George's

Barbour

Quitman

....do........

Prince George's

....do........

Locality 

number3

52

52

27

27

27

52

52

52

52

51

52

27

63

72

73A

75

28

28

28

28

4

4

117

116

117

116

111

111

118

118

114

114

36B

73A

43

45

38A

73A

70

Collection 

number

ANSP 18741

128139

451056

451057

451062

450851

451052

450510

451054

451008

45,1069

32784

451075

451055

450520

32291

103753

451061

451060

451067

450805

450815

453916

450813

90968

450842

155060

450843

450515

PRI 140

129898

450846

ANSP 19594

131766

451089

451091

451093

451098

451100

1 Total species: 6.

2 Total specimens: 239.

3 Total localities: 18.
APPENDIXES 111

APPENDIX 4

Data on specimens included in the analysis of species o/Crassatella, comprising adults, juveniles, broken specimens, internal molds, unnamed

specimens, and rare species (fewer than five specimens)

[Collections listed according to sequence of statistical analysis. Fm, Formation; Mbr, Member. Locality number corresponds to numbers on figure 2 and in appendix 

9. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of Natural Sciences of 

Philadelphia; PRI, Paleontological Research Institution; USGS-CENO, U.S. Geological Survey, Cenozoic. —, no specimen for column]

Species1

C. vadosa ........

C. gardnerae .....

"C. hodgei" (and

C. carolinensis) .

Number of 

specimens2

...... 3

1

2

2

1

1

31

31

32

18

2

5

4

7

12

2

4

12

4

10

16

1

1

5

3

2

9

10

Total 231

...... 5

6

7

38

Total 56

3

9

1

1

Stratigraphic unit

Owl Creek Fm

Prairie Bluff Chalk

Severn Fm

Owl Creek Fm

Severn Fm

....do........

Coon Creek Fm

....do........

....do........

Owl Creek Fm

....do........

....do........

....do........

....do........

....do........

Prairie Bluff Chalk

....do........

....do........

....do........

....do........

....do........

Coon Creek Fm

Providence Sand

Severn Fm

....do........

....do........

....do........

....do........

Ripley Fm, Coon

Creek Tongue

....do........

....do........

....do........

Blufftown Fm

....do........

Tar Heel Fm

....do........

State

Mississippi

Alabama

Maryland

Mississippi

Maryland

....do........

Tennessee

....do........

....do........

Mississippi

....do........

....do........

....do........

....do........

....do........

Alabama

....do........

....do........

....do........

....do........

....do........

Tennessee

Georgia

Maryland

....do........

....do........

....do........

....do........

Mississippi

....do........

....do........

....do........

Georgia

....do........

North Carolina

....do........

County n

Tippah

Wilcox

Anne Arundel

Tippah

Prince George's

....do........

McNairy

....do........

....do........

Tippah

....do........

....do........

....do........

....do........

....do........

Wilcox

....do........

....do........

....do........

....do........

....do........

McNairy

Clay

Prince George's

....do........

....do........

....do........

....do........

Union

....do........

....do........

....do........

Stewart

....do........

Greene

....do........

jocality 

umber

52

56

74

52

73A

73A

27

27

27

52

52

52

52

51

52

57

58

56

56

59A

59A

27

63

70

70

72

73A

75

28

28

28

28

4

4

8

8

I

number *

cU

ANSP 18741

ANSP 19593

451104

128139

131763

131764

451056

451057

451062

450851

451052

450510

451054

451068

451069

450502

450820

450500

450853

451071

451080

32784

451075

451099

451099

451055

450520

32291

103753

451061

451060

451067

450805

450815

31930

31931

lumber of

specimens 

nd internal

molds

—

1

2—

1

1

1—

1

4

1

1

1—

2

2

4

12

4

10

16—

—

5

3

1

5

4

—

2—

1

1

3

1—

Number 

of 

juveniles

—

—

—

—

—

—

—

—

2—

—

—

1—

—

—

—

—

—

—

—

—

—

—

—

—

—

2

—

1—

—

—

—

—

—

C. prora.

Total 14

...... 1 Mount Laurel

_ Sand

Total 1

C. monmouthensis ..... 5 Unknown 

Total ~~5

New Jersey Monmouth 48 ANSP 18739 1

C.transversa ...... 2 Unknown

Total ~2

New Jersey Monmouth Unknown ANSP 18738 5

New Jersey Unknown Unknown ANSP 18744 2
112 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

APPENDIX 4-CONTINUED

Species 1

C. sp. A ...............

Total 

C. tumidula ...........

Total

"C. halei" 

(= C. tumidula).

Total 

C. gabbi ...............

Total 

C. sepulcollis ..........

Total

SS Stratigraphic unit

2

1 

2 

1 

5 

2 

2 

1 

2 

10 

15 

16 

19 

10 

17 

11 

12 

14 

1 

32

4 

30 

5 

214

2

1 

2

4 

2

1

4 

6

4 

1

~27 

1

4 

1 ~6

~i1

1 

1 ~~2

Ripley Fm 

....do........

....do........

....do........

....do........

Peedee Fm 

Coffee Sand 

....do........

Prairie Bluff Chalk 

Ripley Fm 

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Ripley Fm, Coon Creek 

Tongue 

....do........

....do........

Severn Fm

Tuscahoma Fm, 

Landing Mbr 

....do........

Tuscahoma Fm, 

Landing Mbr 

Tuscahoma Fm 

Tuscahoma Fm, 

Landing Mbr 

Tuscahoma Fm, 

Landing Mbr 

Tuscahoma Fm 

Tuscahoma Fm, 

Landing Mbr 

....do.. ......

Tuscahoma Fm, 

Landing Mbr

Tuscahoma Fm, 

Landing Mbr 

Nanafalia Fm 

....do........

Bells 

Greggs

Greggs 

Bells

Bells 

Greggs

Greggs

Clayton Fm (basal)

Porters Creek Clay 

....do........

State

Alabama 

....do........

Mississippi 

Alabama 

....do........

North Carolina 

Mississippi 

....do........

....do........

Georgia 

Alabama 

....do........

....do........

....do........

....do........

Georgia 

.. ..do.. ......

....do........

....do........

Mississippi 

....do........

....do........

Maryland

Alabama 

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Alabama 

....do........

....do........

Tennessee

Alabama 

....do........

County

Barbour 

....do........

Union 

Barbour 

....do........

New Hanover 

Prentiss 

....do........

Kemper 

Quitman 

Barbour 

....do........

....do........

....do........

....do........

Quitman 

....do........

....do........

....do........

Tippah

Union 

....do........

Prince George's

Monroe 

....do........

....do........

Wilcox 

Monroe

....do........

Wilcox 

Monroe

....do........

....do........

Monroe

Marengo 

....do........

Hardeman

Wilcox 

....do........

Number of 

Locality Collection »J°J^ 

number3 number .gfgJSSl 

molds

36B

36B 

30B 

36A 

36B 

69B 

2 

1 

54 

38B 

43 

43 

40 

41 

36A 

37 

42 

38A 

44 

30A

31 

31

70

117

120 

118

116 

118

117

116 

117

117 

118

118

114 

114

76

78 

79

ANSP 

CONRAD 

12670 

20820 

21125 

505 

450511 

451053 

451059 

459095 

451079 

451086 

451089 

450551 

451103 

21125 

451081 

451077 

451093 

450807 

451063

451058 

451065 

451100

453916

453917

450812

450813 

450814

90968

450842 

155060

450843 

450515

PRI 140

129898 

450846

450854

PRI 64 

PRI 65

2

1 

2 

1 

1 

2

2 

2

5 

1

2 

1

3 

1

Number 

of 

juveniles

1

1 

1

3 

1

5

2

1 

2

1 

2

1
APPENDIXES 113

APPENDIX 4-CONTINUED

Species1

C. sp. C . . . . ,

Number of c , ,. , . ., specimens2 Stratigraphic unit

........... 1

2 

1

58

4 

39

6 

14 

Total 125

Tuscahoma Fm 

....do........

Nanafalia Fm 

Porters Creek Clay

....do........

Clayton Fm, Pine 

Barren Mbr 

Nanafalia Fm 

Porters Creek Clay

State

Alabama 

....do........

....do........

....do........

....do........

....do........

....do........

....do........

County

Wilcox 

....do........

Dale

Wilcox

....do........

....do........

Pike 

Wilcox

Locality 

number3

119 

119 

115B

80

81

77A

115A

78

Collection 

number

459096 

450818 

450848 

USGS-CENO 

264 

USGS-CENO 

283 

129744

450847 

154914

Number of 

broken 

specimens 

and internal 

molds

1 

1

Number 

of 

juveniles

2 

1 

22

3

22 

6

C. subplana

Total

1 Mount Laurel Sand New Jersey 

T

Monmouth/ 

Burlington

47 ANSP 18743

C. carolinana .

C. lintea .......

C. sp. B .......

........ 1

2

Total 3 

........ 1

1 

3 

6

1

5 

3

Total 20 

........ 2

Total 2

Pgg(jgg Fm

....do........

Ripley Fm

Severn Fm 

Ripley Fm 

....do........

....do........

Severn Fm 

....do........

Providence Sand

North Carolina

....do........

Alabama

Maryland 

Alabama 

Georgia

....do........

Maryland 

....do........

(T-pnyorja

Pender

....do........

B arbour

Prince George's 

Barbour 

Quitman

....do........

Prince George's 

....do........

Clay

69A

69A

36B

73A

43 

45

38A

73A

70

63

73438 -

73439 1

ANSP 19594 -

131766 - 

451089 - 

451091 -

451093 -

451098 - 

451100 2

450816 -

_

2 

3

—

1 Total species: 16.

2 Total specimens: 710.

3 Total localities: 51.
114 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

APPENDIX 5

Data on specimens included in. the analysis of species of Bathytormus, comprising adult whole named specimens only

[Collections listed according to sequence of statistical analysis. Fm, Formation; Mbr, Member. Locality number corresponds to numbers on figure 2 and in appendix 

9. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of Natural Sciences of Philadelphia]

o • i Number of 

SPecies specimens2

B. pteropsis. .............. 1

2

1

1

1

2

1

1

3

Total 13

B. alaeformis ............. 1

4

5

1

3

4

1

2

1

13

2

1

3

3

1

1

1

1

1

3

1

4

1

2

1

1

3

3

2

6

2

2

1

1

2

4

5

1

4

Total 98

Stratigraphic unit

Providence Sand

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Ripley Fm

Aquia Fm

Aquia Fm, Paspotansa Mbr

Aquia Fm

....do........

Aquia Fm, Paspotansa Mbr

Aquia Fm

....do........

....do........

Aquia Fm, Paspotansa Mbr

....do........

....do........

....do........

Aquia Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Aquia Fm, Paspotansa Mbr

Aquia Fm

....do........

....do........

Aquia Fm, Paspotansa Mbr

Aquia Fm

....do........

....do........

....do........

....do........

State

Alabama

....do........

Georgia

....do........

....do........

....do........

....do........

.. ..do.. ......

Mississippi

Maryland

Virginia

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Maryland

Virginia

....do........

....do........

Maryland

Virginia

. ...do.. ......

....do........

....do........

....do........

....do........

Maryland

Virginia

....do........

Maryland

Virginia

....do........

Maryland

....do........

Virginia

....do........

Maryland

....do........

....do........

Virginia

....do........

County

Barbour

Barbour/Henry

Clay

....do........

....do........

....do........

....do........

Quitman

Union

Prince George's

King George

....do........

....do........

....do........

....do........

Stafford

King George

....do........

....do........

....do........

Stafford

King George

Anne Arundel

Stafford

....do........

....do........

Prince George's

Stafford

King George

Stafford

King George

....do........

Stafford

Charles

Stafford

....do........

Charles

King George

....do........

Prince George's

....do........

Stafford

King George

Charles

Prince George's

Prince George's

Stafford

....do........

Locality 

number3

60

61

67

64

63

63

63

65

34A

85

93

98

98

95

98

88

98

94

94

94

90

96

107

91

101

88

82A

88

99

91

100

97

91

102

91

88

103

97

94

86

85

88

94

104

85

87

88

89

Collection 

number

451085

451074

451083

451076

451072

451075

450490

451078

20845

ANSP 30498

453904

453906

453909

453910

453911

450809

453912

453914

453915

453913

450810

450811

450819

450537

450821

450822

450823

450824

450825

450826

450827

450829

450830

450831

450832

450834

450835

450837

450838

450839

450808

2490

366485

136177

115796

450859

450526

450573

1 Total species: 2.

2 Total specimens: 111.

3 Total localities: 28.
APPENDIXES 115

APPENDIX 6

Data on specimens included in the analysis of species o/Bathytormus, comprising adults, juveniles, broken specimens, and unnamed specimens

[Collections listed according to sequence of statistical analysis. Fm, Formation; Mbr, Member. Locality number corresponds to numbers on figure 2 and in appendix 

9. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of Natural Sciences of 

Philadelphia; USGS-CENO, U.S. Geological Survey, Cenozoic. —, no specimen for column]

Species 1

B. pteropsis .......

Total

B. sp. A. ..........

Total

B. alaeformis .....

Number of 

specimens2

1

2

1

1

1

2

1

1

5

15

2

3

1

1

1

1

1

1

6

2

1

5

2

27

2

7

7

1

2

3

6

1

3

2

1

24

2

1

3

3

1

2

1

1

2

3

4

5

2

2

Stratigraphic unit

Providence Sand

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Ripley Fm

Ripley Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Ripley Fm, Coon Creek

Tongue

....do........

Severn Fm

Aquia Fm

Aquia Fm, Paspotansa Mbr

Aquia Fm

....do........

....do........

Aquia Fm, Paspotansa Mbr

Aquia Fm

....do........

....do........

Aquia Fm, Paspotansa Mbr

....do........

....do........

....do........

Aquia Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

State

Alabama

....do........

Georgia

....do........

....do........

....do........

....do........

....do........

Mississippi

Alabama

....do........

....do........

....do........

....do........

....do........

Georgia

....do........

....do........

Mississippi

....do........

....do........

Maryland

Maryland

Virginia

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Virginia

....do........

Maryland

Virginia

....do........

....do........

Maryland

Virginia

....do........

....do........

....do........

....do........

....do........

County

Barbour

Barbour/Henry

Clay

....do........

....do........

....do........

....do........

Quitman

Union

Barbour

....do........

....do........

....do........

....do........

....do........

Quitman

....do........

....do........

Union

Tippah

Union

Prince George's

Prince George's

King George

....do........

....do........

....do........

....do........

....do........

Stafford

King George

....do........

....do........

....do........

....do........

Stafford

King George

Anne Arundel

Stafford

....do........

....do........

Prince George's

Stafford

King George

Stafford

King George

Stafford

King George

Locality 

number^

60

61

67

64

63

63

63

65

34A

43

43

43

43

43

39

45

44

44

33

30A

31

70

85

93

98

112

98

95

98

88

98

94

94

94

94

90

96

107

91

101

88

82A

88

99

91

100

91

97

j

Collection 

number "

cu

451085

451074

451083

451076

451072

451075

450490

451078

20845

451086

451087

451088

451089

451092

451082

451091

451073

451084

451070

451063

451065

451100

ANSP 30498

453904

453906

453908

453909

453910

453911

450809

453912

453913

453914

453915

453913

450810

450811

450819

450537

450821

450822

450823

450824

450825

450826

450827

450828

450829

lumber of

specimens 

id interna

molds

—

—

—

—

—

—

—

—

—

—

1

—

—

—

—

—

—

2

—

—

1

1

1

3

1

1 —

—

—

—

—

2—

11—

—

—

—

—

1 —

—

1 —

3

1

2

1

Number 

of 

1 juveniles

—

—

—

—

—

—

—

—

2

—

—

—

—

—

1—

—

2—

1

1

2

—

—

1

1

1—

2—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—
116 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

APPENDIX 6-CONTINUED

Species 1

B. alaeformis—

Continued.

Total

B. sp. B. ..........

Total

Number of 

specimens2

3

1

1

3

3

2

9

2

2

3

1

1

7

6

10

1

2

148

1

10

2

3

5

1

4

26

Stratigraphic unit

Aquia Fm

....do........

....do........

....do.. ......

....do........

....do........

Aquia Fm, Paspotansa

Mbr

Aquia Fm

....do........

....do........

....do........

Aquia Fm, Paspotansa

Mbr

Aquia Fm

....do........

....do........

....do........

....do........

Aquia Fm

....do........

....do........

....do........

....do........

....do........

....do........

State

Virginia

Maryland

Virginia

....do........

Maryland

Virginia

....do........

Maryland

....do........

Virginia

....do........

....do........

Maryland

....do........

....do........

Virginia

....do........

Maryland

Virginia

Maryland

....do........

....do........

Virginia

....do........

County

Stafford

Charles

Stafford

....do........

Charles

King George

....do........

Prince George's

....do........

Stafford

....do........

King George

Charles

Prince George's

....do........

Stafford

.. ..do.. ......

Prince George's

King George

Charles

Prince George's

....do........

Hanover

....do........

Locality 

number^

91

102

91

88

103

97

94

86

85

89

88

94

104

85

87

88

89

105

92

108

84

87

113 A

113A

I

Collection 

number !

<J]

450830

450831

450832

450834

450835

450837

450838

450839

450808

136215

2490

366485

136177

115796

450859

450526

450573

450841

450833

450836

450856

450857

366477

USGS-CENO

26337

lumber of

specimens 

nd interna

molds

1

—

—

—

—

—

3

—

—

—

—

—

5

2

5—

1

—

—

1

2

4

1

4

Number 

of 

1 juveniles

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

1

—

—

—

1 Total species: 4.

2 Total specimens: 216.

3 Total localities: 42.
APPENDIXES 117

APPENDIX 7

Data on specimens included in the analysis of the genera of Crassatellidae, comprising adult whole specimens only

[Collections listed according to sequence of statistical analysis. Fm, Formation; Mbr, Member. Locality number corresponds to numbers on figure 2 and in appendix 

9. Collection number: USNM (U.S. National Museum) collection or specimen numbers, unless otherwise noted; ANSP, Academy of Natural Sciences of 

Philadelphia; PRI, Paleontological Research Institution; USGS-CENO, U.S. Geological Survey, Cenozoic]

n Qr,TM.ni Number of 

Genera specimens2

Crassatella ... 3

2

30

31

29

14

1

4

2

7

10

1

1

1

4

5

5

4

7

37

1

2

1

3

1

10

15

16

17

7

17

10

7

11

31

2

30

2

3

1

1

4

2

1

1

4

1

1

1

1

1

35

1

17

13

Stratigraphic unit

Owl Creek Fm

....do........

Coon Creek Fm

....do........

....do........

Owl Creek Fm

....do........

....do........

....do........

....do........

....do........

Coon Creek Fm

Providence Sand

Severn Fm

....do........

....do........

Ripley Fm, Coon Creek Tongue

....do........

....do........

.. ..do.. ......

Ripley Fm

Ripley Fm, Coon Creek Tongue

Ripley Fm

....do........

Coffee Sand

Ripley Fm

....do........

....do........

....do........

....do........

....do........

....do........

....do........

....do........

Ripley Fm, Coon Creek Tongue

....do........

....do........

Tuscahoma Fm, Bells Landing Mbr

Tuscahoma Fm

Tuscahoma Fm, Bells Landing Mbr

Tuscahoma Fm

Tuscahoma Fm, Bells Landing Mbr

....do........

Tuscahoma Fm, Greggs Landing Mbr

....do........

Nanafalia Fm

.. ..do.. ......

Clayton Fm (basal)

Porters Creek Clay

....do........

Tuscahoma Fm

Porters Creek Clay

....do........

Clayton Fm, Pine Barren Mbr

Porters Creek Clay

State

Mississippi

....do........

Tennessee

....do........

....do........

Mississippi

....do........

....do........

....do........

....do........

....do........

Tennessee

Georgia

Maryland

....do........

....do........

Mississippi

....do........

....do........

....do........

Alabama

Mississippi

Alabama

....do........

Mississippi

Georgia

Alabama

....do........

....do........

....do........

....do........

Georgia

....do........

....do........

Mississippi

....do........

....do........

Alabama

....do........

....do........

....do........

....do........

....do........

....do........

....do........

.. ..do.. ......

....do........

Tennessee

Alabama

....do........

....do........

....do........

....do........

....do........

....do........

County

Tippah

....do........

McNairy

....do........

....do........

Tippah

....do........

....do........

....do........

....do........

....do........

McNairy

Clay

Prince George's

....do........

....do........

Union

....do........

....do........

....do........

B arbour

Union

B arbour

....do........

Prentiss

Quitman

Barbour

....do........

....do........

....do........

....do........

Quitman

....do........

....do........

Tippah

Union

....do........

Monroe

Wilcox

Monroe

Wilcox

Monroe

....do........

....do........

... .do.. ......

Marengo

....do........

Hardeman

Wilcox

....do........

....do........

....do........

....do........

....do........

....do........

Locality Collection 

number3 number

52 ANSP 18741

52 128139

27 451056

27 451057

27 451062

52 450851

52 451052

52 450510

52 451054

51 451068

52 451069

27 32784

63 451075

72 451055

73A 450520

75 32291

28 103753

28 451061

28 451060

28 451067

36B 12670

30B 20820

36A 21125

36B 505

2 451053

38B 451079

43 451086

43 451089

40 450551

41 451103

36 A 21125

37 451081

42 451077

38A 451093

30A 451063

31 451058

31 451065

117 453916

116 450813

117 90968

116 450842

117 155060

117 450843

118 450515

118 PRI 140

114 129898

114 450846

76 450854

78 PRI 64

79 PRI 65

119 459096

80 USGS-CENO 264

81 USGS-CENO 283

77A 129744

78 154914
124 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

APPENDIX 8-CONTINUED

Number of

Genera1

Unnamed

group.

Total

Indeterminant

crassatellids.

Total

Number of 

specimens2

1

3

2

1 ~^j

1

2 ~~3

Stratigraphic unit

Woodbury

Providence

....do........

Severn Fm

Clay

Sand

Clayton Fm (basal)

Aquia Fm

State

New Jersey

Georgia

....do........

Maryland

Alabama

Maryland

County

Camden

Clay

Quitman

Prince George's

Lowndes

Prince George's

Locality 

number3

14

62B

65

71

77B

82A

Collection 

number

451105

450091

451078

451095

459092

450858

broken 

specimens 

and

internal

molds

—

—

_

—

1

2

Number 

of 

juveniles

—

—

_

—

—

—

Astartids....... _7

Total ~~7

1 Total genera: 7.

2 Total specimens: 999.

3 Total localities: 91.

Ripley Fm Georgia Quitman 44 451090
APPENDIXES 

APPENDIX 9

125

DESCRIPTION OF COLLECTION LOCALITIES

All of the specimens used in this study came from collections of the U.S. Geological Survey (USGS), the U.S. 

National Museum of Natural History, Smithsonian Institution (USNM), the Academy of Natural Sciences of 

Philadelphia (ANSP), and the Paleontological Research Institution (PRI). The following locality descriptions contain 

all of the information available for each collection; in some cases this information is vague; in other cases, precise. 

Author comments and ancillary information are in square brackets.

UPPER CRETACEOUS

CAMPANIAN

Coffee Sand

USGS Mesozoic locality 17783. USNM 450408, 

451059. Roadcut on the northeast-facing slope of 

Young's Creek Valley, Prentiss County, Miss, 

(sec. 9, T. 6 S., R. 8 E.). Collection comes from 

2.4 to 3.1 m (8 to 10 feet) above the contact of the 

Coffee Sand with the underlying Eutaw Fm. 

USGS Mesozoic locality 6909. USNM 450419, 

451053. 10 km (6 miles) east of Booneville on road 

to Hare's old mill site on Big Brown Creek, 

Prentiss County, Miss.

USNM 450409-450411, 453894. Roadcut of northfacing slope of Mantachie Creek Valley, just 

north of county school, and 3.2 km (2 miles) due 

west of Ratliff, Lee County, Miss. (SV2 sec. 9, T. 

8S., R. 7E.).

Blufftown Formation

6,7

USGS Mesozoic localities 844, 5392, 6405, 26033. 

USNM 450402-450406, 450421-450435, 450501, 

450805, 450815, 453880. Bluffs on the left bank of 

the Chattahoochee River at Blufftown, 49.8 km 

(31 miles) below Columbus, Stewart County, Ga. 

(32°11' N., 84°57'45" W.). This is the type locality for the Blufftown Formation. 

USGS Mesozoic locality 5395. USNM 453862. 

Chattahoochee River, 66 km (41 miles) below 

Columbus, near Florence, Stewart County, Ga. 

USGS Mesozoic localities 25563, 26023. USNM 

450407, 451094, 453879. Bluffs at Florence, on 

the Chattahoochee River, 28.2 km (17.5 miles) 

above Eufaula Landing, Stewart County, Ga. 

(32°05' N., 85°03' W.).

Tar Heel Formation

USGS Mesozoic locality 5348. USNM 31929- 

31932, 451097. Small exposure in ravine near a 

schoolhouse in scarp bordering swamp west of 

town of Snow Hill, Greene County, N.C.

9 USGS Mesozoic locality 5418. USNM 453864. 

Right bank of the Neuse River, 127.9 km (79.5 

miles) above New Bern, Wayne County, N.C.

10 USGS Mesozoic locality 5353. USNM 451101. 

Left bank of the Neuse River, at Auger Hole 

Landing, 116.8 km (73 miles) above New Bern, 

Lenoir County, N.C.

11 USGS Mesozoic locality 5347. USNM 459093. 

Right bank of the Tar River, at Blue Banks 

Landing, 11.3 km (7 miles) above Greenville and 

downstream from Tyson Creek, Pitt County, 

N.C.

12 USGS Mesozoic locality 5357. Black River, 

Mossy Log Landing, 115 km (71.5 miles) above 

Wilmington, Sampson County, N.C. The Tar 

Heel Formation is overlain by the Bladen Formation at this outcrop. [Specimens identified as 

Crassatella newkirkensis by Stephenson (1923) 

were examined from this locality. The poor preservational state of the specimens makes it impossible to determine if they should be reassigned to 

C. hodgei Stephenson (1923). For discussion, see 

Wingard, this paper, p. 61.]

Merchantville Formation

13A USNM 450420. Deep cut on the south side of the 

Chesapeake and Delaware Canal, just east of the 

Summit Bridge (Route 301), New Castle County, 

Del.

13B USGS Mesozoic locality 17698. USNM 450412. 

Old dump on road to Kirkwood, 0.8 km (0.5 mile) 

east of Summit Bridge over the Chesapeake and 

Delaware Canal, New Castle County, Del.

Woodbury Clay

14 USNM 451105. ANSP 18740, 18735. Haddonfield, Camden County, N.J.

15 USGS Mesozoic localities 16293, 31091. USNM 

450505, 453889. Small east-flowing branch of 

Cooper Creek, south of Maple Avenue, small 

exposures 107 to 183 m (350-600 feet) east of
126 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

intersection of Maple Avenue with Grove Street, 

1.6 km (1 mile) north of Haddonfield, Camden 

County, N.J.

Bladen Formation

16 USGS Mesozoic locality 5372. USNM 31748, 

31749, 453861. Hodge's old mill site, 5.6 km (3.5 

miles) southeast of Mullins, Marion County, S.C.

17 USGS Mesozoic locality 4135. USNM 450852. 

Small exposure on the left bank of the Neuse 

River, 20.1 km (12.5 miles) above Kinston and 

100.6 km (62.5 miles) above New Bern, Lenoir 

County, N.C.

18 USGS Mesozoic locality 5354. USNM 31736, 

31737, 451102. Right bank of the Neuse River at 

Whiteley Creek Landing, just above milepost 60 

(96.5 km above New Bern), Lenoir County, N.C.

19A USGS Mesozoic locality 5358. USNM 451106. 

Right bank of the Black River, at Bryant 

Newkirks Marl Hole, 106.2 km (66 miles) above 

Wilmington, Sampson County, N.C.

19B USGS Mesozoic locality 5359. USNM 453855. 

Left bank of the Black River, 102.9 km (64 miles) 

above Wilmington, Sampson County, N.C.

19C USGS Mesozoic locality 5360. USNM 453856. 

Left bank of the Black River at Corbit's Landing, 

101.8 km (63.25 miles) above Wilmington, Sampson County, N.C.

19D USGS Mesozoic locality 5361. USNM 453857. 

Right bank of the Black River, 100.5 km (62.5 

miles) above Wilmington, Sampson County, N.C.

20 USGS Mesozoic locality 5362. USNM 453858. 

Left bank of the Black River, at Kerrs Cove, 

100.1 km (62.25 miles) above Wilmington, Sampson County, N.C.

21 USGS Mesozoic locality 5365. USNM 453859. 

Left bank of the Black River at Hatchers 

Reaches, 87.7 km (54.5 miles) above Wilmington, 

Sampson County, N.C.

22 USGS Mesozoic locality 5368. USNM 453860. 

Right bank of the Cape Fear River at Walker's 

Bluff, just below 60-mile marker (96.5 km) and 

20.9 km (13 miles) below Elizabethtown, Bladen 

County, N.C.

Wenonah Formation

23 USGS Mesozoic locality 31101. South bank of Big 

Brook, just west of Hillsdale Road and approximately 3.2 km (2 miles) east of Marlboro, Monmouth County, N.J. [Two casts of Crassatella 

sp. aff. hodgei were examined from this locality. 

These could not be confidently assigned to a 

species.]

24 USGS Mesozoic locality 16289. North-facing bluff 

on Big Brook, 121.9 m (400 feet) east of northsouth road and 1.9 km (1.2 miles) east of Marlboro, Monmouth County, N.J. [Faint external 

impressions and poorly preserved internal molds 

of Crassatella sp.? were examined from this 

locality; no confident assignment can be made 

due to the poor preservation.]

UPPER CAMPANIAN AND LOWER MAASTRICHTIAN 

Ripley Formation (Cusseta Sand Member)

25A USGS Mesozoic locality 5396. USNM 453863. 

Roanoke Bluff, just below Woolridge Landing, 

right bank of the Chattahoochee River, Barbour 

County, Ala.

25B USGS Mesozoic locality 6402. USNM 453866. 

Woolridge Landing, Upper Rood's Bend, right 

bank of the Chattahoochee River, 21.7 km (13.5 

miles) above Eufaula Landing, Barbour County, 

Ala.

Cusseta Sand

26 USGS Mesozoic localities 6401, 27544. USNM 

450413-450415, 453865, 453884. Lower Rood's 

Bend, left bank of the Chattahoochee River, just 

below the mouth of Soapstone Creek, 20.4 km 

(12.7 miles) above Eufaula Landing, Stewart 

County, Ga.

Coon Creek Formation

27 USGS Mesozoic localities 10198, 16951, 25406, 

30762. USNM 32784, 450436-450442, 450449- 

450451, 450455-450457, 450465, 450475, 450481, 

450508, 451056, 451057, 451062, 451096, 453896. 

Bluffs and bed of Coon Creek on the former 

Dave Week's place, 5.6 km (3.5 miles) south of 

Enville, 12 km (7.5 miles) north of Adamsville, 

and 198 m (0.125 mile) east of the main 

Henderson-Adamsville road in the northeastern 

part of McNairy County, Tenn. Type locality of 

the Coon Creek Formation. [The Coon Creek 

Science Center of the Memphis Museum System 

now exists at the site.]

Ripley Formation (Coon Creek Tongue)

28 USGS Mesozoic localities 18078, 18616, 18629, 

25411. USNM 103753, 103754, 450447, 450448, 

450460, 451060, 451061, 451067, 453873. Scraped 

area along the north side of the dam at Union 

County Lake, 1.8 km (1.1 miles) northeast of 

Pleasant Ridge, Union County, Miss. (NWV4 

NEV4NEV4 sec. 11, T. 6 S., R. 4 E.).
APPENDIXES 127

29 USGS Mesozoic locality 26340. USNM 453881. 

Roadcut on secondary road about 4.2 km (2.6 

miles, airline) south of Pleasant Ridge intersection, Union County, Miss. (NWV4SWV4NWV4 sec. 

26, T. 6S., R. 4E.).

30A USGS Mesozoic locality 25407. USNM 450453, 

450454, 450478, 450493, 451063. Roadcut on 

northeast-facing slope of Hall Creek, a tributary 

of the Tallahatchie River, 4.6 km (2.9 miles) due 

southwest of Dumas, Tippah County, Miss, (center SV2NWV4 sec. 34, T. 5 S., R. 4 E.).

30B USNM 20820. 4 km (2.5 miles) south of Dumas, 

Tippah County, Miss.

31 USGS Mesozoic localities 6873, 17277, 25408, 

25409. USNM 451058, 451064, 451065, 453870. 

Lee's old mill site, roadcut on northeast-facing 

slope of Tallahatchie River valley, 3.2 km (2 

miles) north-northeast of Keownville on the road 

to Molino, Union County, Miss. (NWV4NEV4 sec. 

17, T. 6S., R. 4E.).

32 USGS Mesozoic locality 25410. USNM 450461, 

450462, 451066. Roadcut in east-facing slope of 

Hall Branch, 1.45 km (0.9 mile) west of Molino, 

Union County, Miss. (SWV4NEV4 sec. 8, T. 6 S., 

R. 4E.).

Ripley Formation

33 USGS Mesozoic locality 25485. USNM 450492, 

450503, 451070. Roadcuts on Mississippi Route 

30 on the north-facing slope of Wilhite Creek 

valley from 1.1 to 2.7 km (0.7 to 1.7 miles) south 

of Keownville, Union County, Miss. (SEV4 sec. 

30, T. 6S., R. 4E.).

34A USGS Mesozoic locality 711. USNM 20845, 

450566-450568. Bed of Hall Branch of Tallahatchie River on the old C.R. Hall's farm near 

Molino, Union County, Miss. (sec. 5, T. 6 S., R. 

4E.).

34B USGS Mesozoic locality 13122. USNM 453872. 

12.9 km (8 miles) northeast of New Albany near 

top of four-way divide, Union County, Miss. 

(SEV4?sec. 23, T. 6 S., R. 4 E.).

35 USGS Mesozoic locality 6468. USNM 453868. 

New Albany-Pontotoc Road, 4.8 km (3 miles) 

south of New Albany, south side of Kings Creek 

in Union County, Miss.

36A USGS Mesozoic locality 279. USNM 21125. Various localities within a 24.1- to 32.2-km (15-20 

mile) radius of Eufaula, Barbour County, Ala.

36B USGS Mesozoic localities 26013, 27518, 28433. 

USNM 503, 505, 12670, 453878, 453882, 453886. 

ANSP 19594 and an unnumbered specimen from 

Conrad's collections. Bluffs at Eufaula, below

Eufaula Landing, right bank of the Chattahoochee River, Barbour County, Ala. [Note: The 

label on collection 503 says simply "Eufaula, 

Alabama." Presumably this collection by F.B. 

Meek was made from the Bluffs at Eufaula.]

37, 45 USGS Mesozoic localities 27542, 28431. USNM 

450452, 450458, 450494, 450504, 451081, 451091. 

Bluffs on the left bank of the Chattahoochee 

River, about 3.2 km (2 miles) below the Central 

of Georgia railroad crossing, Quitman County, 

Ga. [Locality 45 determined to be equivalent to 

locality 37.]

38A USGS Mesozoic locality 28438. USNM 451093. 

Left bank of the Chattahoochee River, 4.2 to 4.3 

km (2.6-2.7 miles) south of Eufaula Landing, 

Quitman County, Ga.

38B USGS Mesozoic locality 26014. USNM 451079. 

Bluff on left bank of the Chattahoochee River, 

4.5 km (2.8 miles) below Eufaula Landing, Quitman County, Ga.

39 USGS Mesozoic locality 27552. USNM 450487, 

450488, 451082. Right bank of the Chattahoochee 

River, 7.9 km (4.9 miles) below Eufaula Landing 

and 0.24 km (0.15 mile) above mouth of Cool 

Branch, Barbour County, Ala. (NEV4 sec. 18, T. 

10 N., R. 29 E.).

40 USGS Mesozoic locality 857. USNM 450417, 

450464, 450477, 450551. Chattahoochee River, 

between Eufaula and Barbour Creek, 3.2 km (2 

miles) below Eufaula Landing, Barbour County, 

Ala.

41 USGS Mesozoic locality 33305. USNM 451103. 

Bluffs on right bank of the Chattahoochee River, 

just above mouth of Barbour Creek, Barbour 

County, Ala. (SV2SWV4 sec. 9, T. 10 N., R. 29 E.).

42 USGS Mesozoic locality 25991. USNM 451077. 

Bluffs of Chattahoochee River, left side about 

396 m (0.25 mile) above the mouth of Barbour 

Creek and 6.4 km (4 miles) south of Eufaula in 

Quitman County, Ga.

43 USGS Mesozoic localities 27919, 27923, 27924, 

28409, 28434. USNM 450459, 450466-450469, 

450496, 450498, 450506, 450507, 451086-451089, 

451092, 454609. Bluffs along right and left sides 

of Barbour Creek, between the first bend above 

and the first bend below the U.S. Route 431 

bridge, Barbour County, Ala. (SEV4 , sec. 7, T. 10 

N., R. 29 E.).

44 USGS Mesozoic localities 5417, 25557, 25923, 

27878, 27894, 28417. USNM 450495, 450807, 

451073, 451084, 451090, 453876, 453885. Mercers 

Mill, between the old Central Georgia railroad 

bridge and the dam, 1.2 km (0.75 mile) due south
128 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

of Georgetown Courthouse, Tobanee Creek, 

Quitman County, Ga.

45 Locality 45 determined to be equivalent to locality 37.

46 USGS Mesozoic locality 25998. Left bank of the 

Chattahoochee River, 1.9 km (1.2 miles) below 

the mouth of Barbour Creek and 0.8 km (0.5 mile) 

above the mouth of Cheyneyhatchee Creek, just 

below mouth of Cool Branch and 8.7 km (5.4 

miles) below Eufaula Landing, Quitman County, 

Ga.

MIDDLE AND UPPER MAASTRICHTIAN 

Mount Laurel(?) Sand and (or) Navesink(P) Formation

47 ANSP 18743. Arneytown, Monmouth-Burlington 

County line, New Jersey.

48 USGS Mesozoic localities 31111, 31112. USNM 

450472, 453890, 453891. ANSP 18739. Eastnortheast flowing tributary of Crosswicks Creek, 

3.5 km (2.2 miles) west-northwest of Hornerstown and 1.9 km (1.2 miles) northeast of Arneytown, Monmouth County, N.J. [Note: ANSP 

18739 is labeled simply "Crosswicks, New Jersey," but N.F. Sohl (USGS, oral commun., 1989) 

believes this is most likely the same locality as 

USGS Mesozoic localities 31111 and 31112.]

Owl Creek Formation

49 USGS Mesozoic locality 713. USNM 20804. 

Exposures in Walnut Creek bed, Braddock's 

farm on south-facing slope of Walnut Creek valley, 6 km (3.75 miles) east-southeast of Falkner 

and 11.3 km (7 miles) northeast of Ripley, Tippah 

County, Miss. (NEV4SEV4SEV4 sec. 16, R. 3 S., T. 

4E.).

50 USGS Mesozoic locality 6872. USNM 453869. 

Roadcut on route from New Albany to Ecru 

Road, about 3.2 km (2 miles) east of the main 

New Albany-Ecru road and 4.8 km (3 miles) 

south of New Albany on north-facing slope of 

King's Creek valley, Union County, Miss.

51 USGS Mesozoic locality 25422. USNM 451068. 

Roadcut on north-facing slope of a tributary to 

Fourth Creek, 1.4 km (0.9 mile) north of Providence School, Tippah County, Miss. (NEV4NWV4 

sec. 27, T. 2 S., R. 4 E.).

52 USGS Mesozoic localities 707, 6464, 6876, 8309, 

25423. USNM 20608, 128139, 450418, 450443- 

450446, 450474, 450485, 450486, 450509, 450510, 

450851, 451052, 451054, 451069, 453867. ANSP 

18741. Bluffs on south side of Owl Creek, 4 km 

(2.5 miles) northeast of Ripley, Tippah County,

Miss. (NV2SEV4 sec. 7, T. 4 S., R. 3 E.). This is 

the type locality for the Owl Creek Formation.

53 USGS Mesozoic locality 25420. USNM 453875. 

Roadcut on Tennessee State Route 57 on westfacing slope of Muddy Creek valley near old 

Trimm's mill, 5.3 km (3.3 miles) east of the 

junction that is 2.4 km (1.5 miles) south of 

Middleton, Hardeman County, Tenn. The Owl 

Creek Formation (loc. 53) is overlain by the 

Clayton Formation (loc. 76) at this locality.

Prairie Bluff Chalk

54 USGS Mesozoic locality 6480. USNM 459095. 

Roadcut on old U.S. Highway 45 at top of northfacing slope of Wahalak Creek valley, 9.7 km (6 

miles) north of Scooba, Kemper County, Miss. 

(sec. 9, T. 12 N., R. 18 E.).

55 USGS Mesozoic locality 27530. USNM 453883. 

Roadcut on U.S. Highway 231, about 1.9 km (1.2 

miles) north of road intersection in Orion and 

182.9 m (200 yards) north of junction with Alabama State Route 94, Montgomery County, Ala. 

(NWV4 sec. 36, T. 12 N., R. 20 E.).

56 USGS Mesozoic localities 270, 6793. USNM 

450471, 450500, 450853. ANSP 19593. Prairie 

Bluff, Alabama River, Wilcox County, Ala. This 

is the type locality for the Prairie Bluff Chalk.

57 USGS Mesozoic locality 310. USNM 450502. 

Dawson Bluff, just above mouth of Tear Up 

Creek, Alabama River, Wilcox County, Ala.

58 USGS Mesozoic locality 6439. USNM 450820. Old 

Canton Landing, about 22.5 km (14 miles) below 

mouth of Pine Barren Creek, Alabama River, 

Wilcox County, Ala.

59A USGS Mesozoic localities 25498, 26989. USNM 

451071, 451080. Shell Bluff on Shell Creek, 

Wilcox County, Ala. (sec. 36, T. 14 N., R. 6 E.).

59B USGS Mesozoic locality 30660. USNM 453887. 

Roadcuts on Alabama State Highway 263, about 

6.8 km (4.2 miles) southeast of intersection with 

county Route 7 and State Route 21, southeast of 

Braggs, Lowndes County, Ala. (sec. 22, T. 12 N., 

R. 13 E.).

Providence Sand

60 USGS Mesozoic localities 27906, 32935. USNM 

451085, 459094. Left bank of White Oak Creek on 

bend about half way between county Route 47 

bridge and powerline crossing, Barbour County, 

Ala. (SWV4SWV4 sec. 9, T. 9 N., R. 29 E.).

61 USGS Mesozoic locality 25921. USNM 451074. 

Bluffs of White Oak Creek at bridge of Barbour 

County Route 47 and Alabama State Route 95,
APPENDIXES 129

old Alexanders Mill site, at Barbour-Henry 

County line, Ala. (SEV4SWV4 sec. 8, T. 9 N., R. 

29 E.).

62A USGS Mesozoic locality 25993. USNM 450489, 

453877. White Oak Creek, 960 m (0.6 mile) above 

mouth and 160 m (0.1 mile) below powerline 

crossing over creek, Barbour-Henry County line, 

Ala. (NEV4 sec. 16, T. 9 N., R. 29 E.).

62B USGS Mesozoic locality 32250. USNM 450484, 

459091. Fort Gaines Northeast No. 1 Well, depth 

108 ft, Sandy Branch Public Use Area, eastern 

bank of the Walter F. George Reservoir, along 

the left bank of the Chattahoochee River valley, 

about 7.6 km (4.7 miles) northwest of Fort Gaines 

and 3.7 km (2.3 miles) south of Pataula Creek, 

Clay County, Ga.

63 USGS Mesozoic localities 6412, 25556, 25935, 

28442. USNM 450490, 450491, 450499, 450816, 

451072, 451075, 453897. 1.4 km (0.9 mile) above 

the mouth of Pataula Creek at the Narrows, 

right bank below the waterfalls, Clay County, 

Ga.

64 USGS Mesozoic localities 855, 25988. USNM 

450554, 451076. Chattahoochee River at mouth of 

Pataula Creek, 20.8 km (12.9 miles) below 

Eufaula, Clay County, Ga.

65 USGS Mesozoic locality 25992. USNM 450482, 

450483, 451078. Roadcut and drainage ditch of 

the north-northwest-facing slope of Pataula 

Creek valley, just southeast of bridge of U.S. 

Route 82 over Pataula Creek, 4.0 km (2.5 miles, 

airline) northwest of Morris, and 3.2 km (2 miles) 

northwest of junction with Georgia Route 29, 

Quitman County, Ga.

66 No locality assigned.

67 USGS Mesozoic locality 27560. USNM 451083. 

Left side of Chattahoochee River, about 91.4 m 

(100 yards) below mouth of Pataula Creek and 

20.3 km (12.9 miles) south of Eufaula, Clay 

County, Ga.

68 No locality assigned.

Peedee Formation

69A USGS Mesozoic localities 12262, 13585. USNM 

73438, 73439, 453871. New Rocky Point Quarry, 

Pender County, N.C.

69B USGS Mesozoic locality 780. USNM 450511. Castle Hayne Quarry, New Hanover County, N.C.

69C USGS Mesozoic locality 32344. USNM 453892. 

Allisons Landing, right bank of the Pee Dee 

River, 104.4 km (64.9 miles) above Georgetown, 

Georgetown County, S.C.

Severn Formation

70 USGS Mesozoic localities 32774, 32775. USNM 

450463, 450473, 451099, 451100. Excavations for 

Landover Mall shopping center near intersection 

of Maryland Route 202, Interstate 95, and 

Brightseat Road, Prince George's County, Md. 

[USGS 32774 is from the concretion zone; USGS 

32775 is from the loose sands associated with the 

concretion layer.]

71 USGS Mesozoic locality 28858. USNM 451095. 

Excavations immediately west of bridge of Interstate 95 and just north of Central Avenue (Route 

214), within cloverleaf approach and exit 15 of 

capital beltway, Interstate 495/95 Prince 

George's County, Md.

72 USGS Mesozoic locality 9592. USNM 450476, 

451055. Near head of small ravine about 1.4 km 

(0.9 mile) southwest of Brightseat, Prince 

George's County, Md. [Probably the same as 

locality 73A.]

73A USGS Mesozoic localities 851, 32772, 32773. 

USNM 131763, 131764, 131766, 450416, 450470, 

450479, 450480, 450520, 451098, 453893. Exposures in small drainage ditch on the Wilson Dairy 

Farm south of Sheriff Road, Prince George's 

County, Md. Gardner's (1916) Brightseat locality.

73B USGS Mesozoic locality 21067. USNM 453874. 

Excavations for Oxon Hill High School, east of 

Indian Head Highway, Prince George's County, 

Md.

74 USNM 451104. Millersville, Anne Arundel 

County, Md.

75 USGS Mesozoic locality 852. USNM 32291, 

450497. Near Oakland, about 11.3 km (7 miles) 

from Washington, D.C., Prince George's County, 

Md. [Oakland is west of District Heights in the 

triangle formed by Marlboro Pike, Walker Mill 

Road, and Silver Hill Road. This is 7 miles from 

the heart of Washington, D.C. (the Capitol building) but only 1.5 miles from the District line.]

PALEOCENE 

Clayton Formation

76 USGS Cenozoic locality 18396. USNM 450854. 

See locality 53 for a complete description. [This 

collection is from the base of the Clayton and 

probably contains reworked Owl Creek Formation fossils.]

77A USGS Cenozoic locality 284. USNM 129744, 

129748. Prairie Creek, Wilcox County, Ala. Pine 

Barren Member.
130 CRETACEOUS AND TERTIARY CRASSATELLIDAE, EASTERN UNITED STATES-EXTINCTION AT THE BOUNDARY

77B USNM 459092. Creek bottom in SEV4 sec. 28, T. 

12 N., R. 14 E., Lowndes County, Ala. [This 

collection is from the basal Clayton and probably 

contains reworked Prairie Bluff fossils.]

Porters Creek Clay and (or) Naheola Formation

78 USGS Cenozoic locality 3102. USNM 154914, 

450552. PRI 64. Graveyard Hill, west of Oak 

Hill, Wilcox County, Ala.

79 PRI 65. 1.6 km (1 mile) north of Allenton, Wilcox 

County, Ala.

80 USGS Cenozoic locality 264. USNM 129745, 

129747, 129749, 129750, 129754, 129756, 137256, 

137257, 450543^50550, 450562^50565. Prairie 

Creek, east of Rosebud, Wilcox County, Ala.

81 USGS Cenozoic locality 283. USNM 129753, 

129755. Block Creek Branch of Prairie Creek, 

Wilcox County, Ala.

Aquia Formation

82A USGS Cenozoic locality 17126. USNM 450823, 

450858. The former Brook's Estate; tributary of 

Cabin Branch stream at end of cul-de-sac of 

Gappy Avenue off Central Avenue, 1.2 km (0.75 

mile) southeast of Central Avenue and Addison 

Road intersection, Prince George's County, Md.

82B USGS Cenozoic locality 17124. USNM 450860. 

0.8 km (0.5 mile) east of Phelps Corner, in branch 

of Henson Creek, crossing Ernshaw Road, 

Prince George's County, Md. [Phelps Corner is 

just south of the capital beltway (1-95) interchange 37A, at the intersection of Oxon Hill 

Road, Brinkley Road, and St. Barnabus Road. 

Ernshaw Road was renamed Brinkley Road, 

probably in the 1950's.]

83 USNM 450536. Indian Head Highway, 12.9 km (8 

miles) south of Washington, B.C., Prince 

George's County, Md. [Distance south of Washington probably refers to distance south of the 

heart of the city.]

84 USNM 450856. Vicinity of Brightseat, Prince 

George's County, Md.

85 USGS Cenozoic locality 2489. USNM 115796, 

450523, 450531^50533, 450572, 450808. ANSP 

30498. Piscataway Creek, Prince George's 

County, Md.

86 USNM 450839. 1.6 km (1 mile) northeast of 

Piscataway Creek, Prince George's County, Md.

87 USGS Cenozoic localities 17100, 17104. USNM 

207153, 450850, 450857, 450859, 450865. North 

side of Piscataway Creek at Indian Head Highway crossing, Prince George's County, Md.

88 USGS Cenozoic locality 2508. USNM 2490, 

155549, 207155, 450526^50530, 450809, 450822, 

450824, 450834. Aquia Creek, Stafford County, 

Va.

89 USGS Cenozoic locality 2030. USNM 136215, 

450573. Mouth of Aquia Creek, Potomac River, 

Stafford County, Va.

90 USNM 450810. North bank of Potomac Creek, 4 

km (2.5 miles) above the mouth, Stafford County, 

Va.

91 USNM 450524, 450525, 450537, 450806, 450826, 

450828, 450830, 450832. Potomac Creek, Stafford 

County, Va.

92 USNM 450534, 450833. Potomac River, 800 m 

(0.5 mile) below Potomac Creek, King George 

County, Va.

93 USNM 453904. Potomac River, above Belvedere 

Beach, King George County, Va. Paspotansa 

Member.

94 USGS 26359. USNM 366485, 450838, 450840, 

453913^53915. Potomac River, 0.5 km (0.3 mile) 

above Belvedere Beach, King George County, 

Va. Paspotansa Member.

95 USNM 453910. Potomac River, below Belvedere 

Beach, King George County, Va. Paspotansa 

Member.

96 USNM 450811. Potomac River, 800 m (0.5 mile) 

below Belvedere Beach, King George County, 

Va.

97 USNM 450539, 450829, 450837. Paspotansa 

Creek, King George County, Va.

98 USNM 450540, 453906, 453909, 453911, 453912. 

Potomac River below Paspotansa Creek, King 

George County, Va.

99 USNM 450825. Potomac River, 3.2 km (2 miles) 

below Potomac Creek, King George County, Va.

100 USNM 450827. Potomac River, Fairview Beach, 

King George County, Va.

101 USNM 450821. South bank of Potomac River 

near Marlboro Point, above mouth of Potomac 

Creek, Stafford County, Va.

102 USNM 450512, 450538, 450831, 450864. Liverpool Point, Potomac River, Charles County, Md. 

[This is probably the collection site described by 

Dryden and Overbeck (1948, p. 78, loc. 5) as 

"Shore of Potomac River, 2150 feet south of 

wharf at Liverpool Point, about 17 miles W.S.W. 

of La Plata," although the note with the collection reads simply "Liverpool Point."]

103 USNM 450535, 450835. Mill, 1.6 km (1 mile) 

southeast of Mason Springs, Charles County, 

Md.

104 USGS Cenozoic locality 2243. USNM 136177, 

450513, 450569-450571, 450863, 453922.
APPENDIXES 131

Glymont, Potomac River, Charles County, Md. 

[This is probably the collection site described by 

Dryden and Overbeck (1948, p. 78, loc. 2) as 

"Bluff about 1500 feet above (northeast of) Glymont wharf, Potomac River. Locality about 10V2 

miles N.W. of La Plata," although the note with 

the collection reads simply "Glymont, Potomac 

River."]

105 USNM 450841, 450845. Reedy Run, south branch 

of Chickawupen Creek near Posey's, Seat Pleasant, Prince George's County, Md.

106 USNM 450514, 450862. Near mouth of Mattawoman Creek, Prince George's-Charles County 

line, Md.

107 USNM 450819. South River Bridge, Anne Arundel County, Md.

108 USNM 450836. 4 km (2.5 miles) above Pope's 

Creek, Charles County, Md.

109 USGS Cenozoic locality 2349. USNM 148893. 

Clifton Beach, Charles County, Md. [Dryden and 

Overbeck (1948, p. 79, loc. 6) mention outcrops 

occurring "6880 to 1180 feet above Clifton Beach 

wharf." I examined specimens of Bathytormus 

alaeformis from this locality, but these specimens could not be located at the USNM when 

formal identification and numbering of specimens 

were conducted.]

110 Between Buena Vista and Collington, Prince 

George's County, Md. [I examined specimens of 

Bathytormus alaeformis from this locality, but 

these specimens could not be located at the 

USNM when formal identification and numbering of specimens were conducted. Because B. 

alaeformis and Crassatella aquiana co-occur in 

the Aquia deposits, this collection may have 

contained one, or the other, or a mixture of these 

two species.]

111 ANSP 30580. Upper Marlboro, Prince George's 

County, Md.

112 USNM 453908. Rappahanock River, north of 

Hop Yard, King George County, Va. [Hop Yard 

Landing is located 4 miles west of the intersection of U.S. Route 301 and State Route 3 at 

Office Hall, King George County, Va. (Port 

Royal, Va. 7.5-min quadrangle).]

113A USGS Cenozoic locality 26337. USNM 366477, 

453907, 453919, 453920, 453905. 0.8 km (0.5 mile) 

east of Wickham Crossing, right bank of the 

Pamunkey River, Hanover County, Va. Piscataway Member.

113B USGS Cenozoic locality 26362. Right bank of the 

Pamunkey River, 1.5 km (0.95 mile) above the 

Route 301 bridge (airline miles), Hanover 

County, Va.

Nanafalia Formation

114 USGS Cenozoic localities 271, 5641. USNM 

129898, 450516, 450553, 450555, 450556, 450560,

450846. 450849, 450861. Nanafalia Bluff, Tombigbee River, Marengo County, Ala. 

115A USGS Cenozoic locality 10765. USNM 450522,

450847. 400 m (0.25 mile) northeast of Henderson 

on Natch Road, Pike County, Ala. 

115B USGS Cenozoic locality 10769. USNM 450848. 

Becks Mill, 16.1 km (10 miles) from Brundridge, 

on the Pea River, Dale County, Ala. [Questionably assigned to Nanafalia Formation.]

Tuscahoma Formation

116 USGS Cenozoic locality 10782. USNM 450813, 

450842. Yellow Bluff, Alabama River, Wilcox 

County, Ala.

117 USGS Cenozoic localities 2669, 3098, 5594. 

USNM 90968, 137064, 155060, 450517-450519, 

450521, 450558, 450561, 450817, 450843, 453916. 

Bells Landing, Alabama River, Monroe County, 

Ala. Bells Landing Member.

118 USGS Cenozoic locality 9498. USNM 450515, 

450559, 450812, 450814. PRI 140. Greggs Landing, Alabama River, Monroe County, Ala. 

Greggs Landing Member.

119 USGS Cenozoic localities 5601, 10779. USNM 

450818, 450844, 453918, 459096. Lower Peach 

Tree, Alabama River, Wilcox County, Ala. 

[USNM 453918 was taken from a roadcut along 

the access to the ferry and is from the Bells 

Landing Member.]

120 USNM 453917. Cliffs below Blacks Bluff, Alabama River, Wilcox County, Ala. Bells Landing 

Member.

PLATES 1-22

Contact photographs of the plates in this report are available, at cost, 

from the U.S. Geological Survey Photographic Library, Federal Center, Denver, CO 80225
PLATE 1

Type specimens of Crassatella vadosa Morton, 1834

FIGURES 1-17. Crassatella vadosa Morton, 1834.

1, 4, 9, 11, 16. Syntypes of Crassatella ripleyana Conrad, 1858 from the Owl Creek Formation at locality 52,

Mississippi. ANSP 18741. 

1, 9. Exterior and interior right valve (xl). 

4. Exterior left valve (xl). 

11. Interior right valve of broken specimen (xl). 

16. Exterior right valve (xl). 

2, 3. Interior and exterior left valve (x 1) holotype Crassatella vadosa Morton, 1834 from the Prairie

Bluff Chalk at locality 56, Alabama. ANSP 19593.

5-8, 10. Syntypes of Crassatella lintea Conrad, 1860 from the Ripley Formation at locality 36B, Eufaula, 

Alabama. ANSP 19594.

5. 8. Exterior and interior right valve (xl.5).

6. 7. Exterior and interior right valve (xl.5).

10. Exterior left valve of articulated specimen (xl.5).

12, 13. Exterior and interior right valve (xl) paratype Crassatella gardnerae Harbison, 1945 from the 

Coon Creek Tongue of the Ripley Formation at locality 28, Mississippi. USNM 103753 

(USGS 18629).

14. Partially preserved exterior right valve (xl) syntype Crassatella subplana Conrad, 1853 from 

the Mount Laurel Sand and (or) Navesink Formation at locality 47, New Jersey. ANSP 

18743.

15, 17. Exterior and interior right valve (x 1) paratype Crassatellites carolinana Stephenson, 1927 from 

the Peedee Formation at locality 69A, North Carolina. USNM 73439.
U.S. GEOLOGICAL SURVEY

CRASSATELLA
PLATE 2

Type specimens of Cretaceous Crassatellidae

FIGURES 1-3. Bathytormus pteropsis (Conrad), 1860.

1. Exterior right valve in matrix (xl.5), hypotype (Gardner, 1916, pi. 39, fig. 5), from the Severn

Formation at locality 75, Maryland. USNM 32291.

2, 3. Articulated specimen, hypotype (Stephenson and Monroe, 1940, pi. 9, figs. 4, 5) from the Ripley 

Formation at locality 34A, Mississippi. USNM 20845.

2. Dorsal view (xl.5).

3. Exterior left valve (xl.5).

FIGURES 4, 5. Crassatellites neusensis Stephenson, 1923. Paratypes from the Bladen Formation at locality 18, North 

Carolina.

4. Exterior left valve (xl.5). USNM 31737.

5. Exterior left valve (xl.5). USNM 31736.

FIGURE 6. Scambula perplana Conrad, 1869. Interior left valve in matrix (x5), supposed holotype (according to 

Richards, 1958, p. 192; see discussion p. 90), from the Conrad collection from the Woodbury Clay 

at locality 14, New Jersey. ANSP 18740. 

FIGURES 7, 8, 10, 11. Crassatellites hodgei Stephenson, 1923. Holotype and paratype from the Tar Heel Formation at locality

8, North Carolina.

7, 8. Interior and exterior left valve (xl.5) holotype. USNM 31930. 

10, 11. Interior and exterior left valve (xl.5) paratype. USNM 31931.

FIGURE 9. Crassatella carolinensis Conrad, 1875. Exterior left valve in matrix (x2), hypotype (Stephenson, 1923, 

pi. 66, fig. 17), from the Tar Heel Formation at locality 8, North Carolina. USNM 31929.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 2

BATHYTORMUS, CRASSATELLA, AND SCAMBULA
PLATE 3 

Type specimens of Tertiary Crassatellidae

FIGURES 1-10. Crassatella aquiana Clark, 1895.

1, 2, 5. Left valve holotype Crassatella sepulcollis Harris, 1896 from the Porters Creek(?) Clay at 

locality 78, Alabama. PRI 64.

1. Interior (xl.5).

2. Specimen tilted to reveal characters of the umbo (xl.5). 

5. Exterior (xl.5).

3, 8, 10. Articulated specimen, holotype Crassatella aquiana Clark, 1895 from the Aquia Formation 

at locality 88, Virginia. USNM 207155. 

3. Dorsal view (xl). 

8. Exterior right valve (xl). 

10. Exterior left valve (xl). 

4, 7. Interior and exterior right valve (xl.5) paratype Crassatella sepulcollis Harris, 1896 from

the Naheola(?) Formation at locality 79, Alabama. PRI 65.

6, 9. Exterior and interior right valve (xl) holotype Crassatella halei Harris, 1897 from the 

Greggs Landing Member of the Tuscahoma Formation at locality 118, Alabama. PRI 

140. 

FIGURES 11, 13. Crassatella palmula Conrad, 1846. Interior (hinge visible) and exterior left valve (xl) holotype from the

Aquia Formation at locality 111, Maryland. ANSP 30580. 

FIGURES 12,14-19. Bathytormus alaeformis (Conrad), 1830.

12, 14, 15, 17. Holotype and paratype Crassatella alaeformis Conrad, 1830 from the Aquia Formation at

locality 85, Maryland. ANSP 30498. 

12, 15. Left valve paratype. 

12. Interior (xl).

15. Specimen tilted to reveal ornament of umbo (xl). 

14, 17. Exterior and interior right valve (xl) holotype. 

16, 18, 19. Holotype and paratype of Crassatella declivis Heilprin, 1880 from the Aquia Formation at

locality 88, Virginia. USNM 2490. 

16,19. Exterior and interior left valve (xl.5) paratype. 

18. Exterior right valve (xl.5) holotype.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 3

CRASSATELLA AND BATHYTORMUS
PLATE 4 

Morphologic variation within Crassatella hodgei (Stephenson), 1923

FIGURES 1-19. Crassatella hodgei (Stephenson), 1923.

1, 3, 5, 12, 13. Specimens from the Blufftown Formation at locality 4, Georgia. 

1. Exterior left valve (x2). USNM 450402 (USGS 6405). 

3. Exterior left valve (xl.5). USNM 450403 (USGS 844). 

5. Exterior left valve (xl). USNM 450404 (USGS 844).

12. Interior left valve (xl.5). USNM 450405 (USGS 6405).

13. Exterior left valve (xl.5). USNM 450406 (USGS 6405). 

2. Exterior right valve (xl) of specimen from the Blufftown Formation at locality 6, Georgia.

USNM 450407 (USGS 25563). 

4. Exterior left valve (xl) of specimen from the Coffee Sand at locality 1, Mississippi. USNM

450408 (USGS 17783). 

6, 7, 11, 14-16. Specimens from the Coffee Sand at locality 3, Mississippi.

6, 7. Exterior and interior right valve (xl). USNM 450409. 

11, 14. Exterior and interior right valve (xl). AA, anterior adductor; AR, anterior pedal

retractor; PA, posterior adductor; PR, posterior pedal retractor. USNM 450410. 

15, 16. Exterior and interior left valve (xl). USNM 450411. 

8. Latex cast of exterior left valve (xl.5) of specimen from the Merchantville Formation at

locality 13B, Delaware. USNM 450412 (USGS 17698).

9, 17, 19. Poorly preserved specimens from the Cusseta Sand at locality 26, Georgia (the type locality 

for Crassatellites roodensis Stephenson, 1923). 

9. Exterior left valve (xl). USNM 450413 (USGS 6401). 

17. Exterior left valve (xl). USNM 450414 (USGS 27544). 

19. Exterior right valve (xl). USNM 450415 (USGS 6401).

10, 18. Poorly preserved paratypes of Crassatellites roodensis Stephenson, 1923 from the Bladen 

Formation at locality 16, South Carolina. USGS 5372. 

10. Exterior right valve in matrix (xl). USNM 31748. 

18. Exterior left valve in matrix (xl). USNM 31749.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 4

CRASSATELLA
PLATE 5 

Morphologic variation within Crassatella carolinensis Conrad, 1875 and comparison to other Cretaceous Crassatella

FIGURES 1, 3, 4, 6. Crassatella vadosa Morton, 1834.

1, 3. Exterior and interior right valve (xl.5) of specimen from the Severn Formation at

locality 73A, Maryland. USNM 450416 (USGS 32772).

4. Exterior left valve (xl.5) of specimen from the Ripley Formation at locality 40, 

Alabama. USNM 450417 (USGS 857).

6. Exterior left valve (xl.5) of specimen from the Owl Creek Formation at locality 52,

Mississippi. USNM 450418 (USGS 6464). 

FIGURES 2, 7, 9, 10, 12, 14. Crassatella hodgei (Stephenson), 1923.

2, 10. Interior and exterior right valve (xl) of specimen from the Coffee Sand at locality 2, 

Mississippi. USNM 450419 (USGS 6909).

7. Latex cast of exterior left valve (x2) of specimen from the Merchantville Formation at

locality 13A, Delaware. USNM 450420.

9, 12, 14. Specimens from the Blufftown Formation at locality 4, Georgia. USGS 6405. 

9. Exterior left valve (x3). USNM 450421.

12. 14. Exterior and interior right valve (xl.5). USNM 450422.

FIGURES 5, 8, 11, 13, 15-20. Crassatella carolinensis Conrad, 1875. Specimens from the Blufftown Formation at locality 4,

Georgia.

5. Enlargement of right valve hinge (xl.5). USNM 450423 (USGS 6405). 

8. Exterior left valve (x3). USNM 450424 (USGS 5392). 

11, 13, 16. Left valve. USNM 450425 (USGS 6405). 

11. Dorsal view (xl.5).

13. 16. Exterior and interior (xl.5). AA, anterior adductor; PA, posterior adductor;

R, resilifer. 

15. Exterior right valve (xl.5). USNM 450426 (USGS 5392).

17. Exterior left valve (xl.5). USNM 450427 (USGS 5392).

18. Exterior left valve (xl.5). USNM 450428 (USGS 5392).

19. Exterior right valve (xl.5). USNM 450429 (USGS 5392).

20. Exterior right valves in matrix (xl.5). USNM 450430 (USGS 26033).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 5

CRASSATELLA
PLATE 6 

Juvenile Crassatella hodgei (Stephenson), 1923

FIGURES 1-6. Crassatella hodgei (Stephenson), 1923. Specimens from the Blufftown Formation at locality 4, Georgia. USGS

26033.

1. Exterior left valve (SEM X25.8). USNM 450431. 

2, 6. Right valve. USNM 450432. 

2. Interior (SEM x31.7). 

6. Partially preserved prodissoconch and nepionic portions of shell (SEM x!22).

3. Exterior right valve (SEM X41.7). USNM 450433.

4. Interior right valve (SEM x9.11). USNM 450434.

5. Exterior right valve (SEM X16.9). USNM 450435.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 6

CRASSATELLA
PLATE 7 

Growth series for Crassatella vadosa Morton, 1834 '

FIGURES 1-15. Crassatella vadosa Morton, 1834. Specimens from the Coon Creek Formation at locality 27, Tennessee. USGS

16951.

1, 5. Interior and exterior left valve (xl.5). USNM 450436. 

2, 3, 4. Left valve. USNM 450437.

2. Enlargement of hinge (x4).

3, 4. Interior and exterior (xl.5). I 

6, 7. Interior and exterior left valve (xl.5). USNM 450438.

8. 10. Interior and exterior left valve (xl.5). USNM 450439.

9. 11. Interior and exterior left valve (xl.5). USNM 450440. 

12, 13. Interior and exterior left valve (xl.5). USNM 450441.

14, 15. Interior and exterior left valve (xl.5). USNM 450442. AA, anterior adductor; AR, anterior pedal 

retractor; PA, posterior adductor; PL, pallial line; PR, posterior pedal retractor; R, resilifer.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 

7

5
PLATE 8 

Morphologic variation within Crassatella vadosa Morton, 1834

FIGURES 1-16. Crassatella vadosa Morton, 1834.

1-3, 11, 14, 16. Specimens, classified as "Crassatella ripleyana" (Conrad), 1858 for the canonical discriminant 

analysis of subspecies, from the Owl Creek Formation at locality 52, Mississippi. USGS 

6464.

1, 2. Interior and exterior left valve (xl.5). USNM 450443. 

3. Exterior left valve (xl). USNM 450444. 

11. Exterior left valve (xl.5). USNM 450445. 

14, 16. Left valve. USNM 450446. 

14. Exterior (xl).

16. Specimen tilted and enlarged (xl.5) to reveal details of juvenile stage.

4, 5, 9. Specimens, classified as Crassatella gardnerae Harbison, 1945 for the canonical discriminant 

analyses of Crassatella species, from the Coon Creek Tongue of the Ripley Formation at 

locality 28, Mississippi. USGS 25411. 

4, 5. Interior and exterior right valve (xl). USNM 450447.

9. Exterior right valve (xl). USNM 450448. 

6, 8, 12, 13, 15. Specimens, classified as "Crassatella wadei" Stephenson, 1941 for the canonical discriminant

analysis of subspecies, from the Coon Creek Formation at locality 27, Tennessee. 

6, 8. Articulated specimen. USNM 450449 (USGS 30762). 

6. Exterior right valve (xl).

8. Dorsal view (x 1.5). (Note character of nepionic portion of shell.) 

12, 13. Articulated specimen. USNM 450450 (USGS 30762).

12. Exterior right valve (xl).

13. Dorsal view (xl.5). E, escutcheon; L, lunule. 

15. Exterior left valve (xl). USNM 450451 (USGS 16951).

7, 10. Specimens from the Ripley Formation at locality 45, Georgia. USGS 28431. 

7. Exterior right valve (xl). USNM 450452. 

10. Dorsal view left valve (xl.5). USNM 450458.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 8

CRASSATELLA
PLATE 9

Morphologic variation within Crassatella vadosa Morton, 1834

FIGURES 1-13. Crassatella vadosa Morton, 1834.

1, 9. Specimens, classified as Crassatella sp. A for the statistical analysis, from the Coon Creek 

Tongue of the Ripley Formation at locality 30A, Mississippi. USGS 25407. 

1. Exterior right valve (xl). USNM 450453. 

9. Exterior left valve (xl). USNM 450454. 

2, 4, 5, 7, 8, 10, 11. Specimens from the Coon Creek Formation at locality 27, Tennessee (type locality for

Crassatella vadosa wadei Stephenson, 1941). 

2, 5, 8. Left valve. USNM 450455 (USGS 25406).

2. Enlargement of hinge (x2). 

5, 8. Interior and exterior (xl).

4, 7. Interior and exterior right valve (xl). USNM 450456 (USGS 16951). 

10, 11. Interior and exterior left valve (xl). USNM 450457 (USGS 16951). 

3. Exterior left valve (xl) of specimen from the Ripley Formation at locality 45, Georgia.

USNM 450458 (USGS 28431). 

6. Interior right valve (xl) of specimen from the Ripley Formation at locality 43, Alabama.

USNM 450459 (USGS 28409).

12, 13. Interior and exterior left valve (xl) of specimen from the Coon Creek Tongue of the 

Ripley Formation at locality 28, Mississippi (type locality of Crassatella gardnerae 

Harbison, 1945). USNM 450460 (USGS 25411).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 9

3

1 '•* j * i m
PLATE 10

Juvenile characters and internal molds of Crassatella vadosa Morton, 1834

FIGURES 1-17. Crassatella vadosa Morton, 1834.

1, 5, 13, 14. Specimens from the Coon Creek Tongue of the Ripley Formation at locality 32, Mississippi.

USGS 25410.

1, 5. Exterior and interior right valve (xl.5). USNM 450461. 

13, 14. Interior and exterior left valve (xl.5). USNM 450462. 

2. Dorsal portion of exterior left valve (x 1) in shelly matrix from the Severn Formation at locality

70, Maryland. USNM 450463 (USGS 32774).

3, 12. Articulated specimen from the Ripley Formation at locality 40, Alabama. USNM 450464 (USGS 

857).

3. Dorsal view (xl.5). 

12. Exterior left valve (xl.5). 

4. Exterior left valve (x3) of specimen from the Coon Creek Formation at locality 27, Tennessee.

USNM 450,465 (USGS 16951).

6-8, 10, 11. Specimens from the Ripley Formation at locality 43, Alabama. USGS 27919. 

6, 7. Interior and exterior right valve (xl.5). USNM 450466. 

8. Interior left valve (xl.5). USNM 450467.

10. Exterior right valve (xl.5). USNM 450468.

11. Exterior left valve (xl.5). USNM 450469.

9. Exterior right valve (xl.5) of specimen from the Severn Formation at locality 73A, Maryland. 

USNM 450470 (USGS 32772).

15. Left side of internal mold (xl) topotype from the Prairie Bluff Chalk at locality 56, Alabama. 

USNM 450471 (USGS 270).

16. Right side of internal mold (xl) paratype Crassatellites carolinana Stephenson, 1927 from the 

Peedee Formation at locality 69A, North Carolina. USNM 73439 (USGS 12262).

17. Left side of internal mold (xl) from the Mount Laurel Sand and (or) Navesink Formation at 

locality 48, New Jersey. USNM 450472 (USGS 31111).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 10

CRASSATELLA
PLATE 11

Geographic variation of Crassatella vadosa Morton, 1834

FIGURES 1-13. Crassatella vadosa Morton, 1834.

1. Exterior left valve in matrix (x 1), specimen from the Severn Formation at locality 70, Maryland. USNM

450473 (USGS 32774). 

2, 3. Specimens from the Severn Formation at locality 73A, Maryland. USNM 131764.

2. Interior right valve (xl).

3. Exterior left valve (xl). 

4-6. Right valve of specimen from the Owl Creek Formation at locality 52, Mississippi. USNM 450474 (USGS

25423). 

4, 6. Exterior and interior (xl).

5. Dorsal view (xl). 

7. Exterior right valve (xl) of specimen from the Coon Creek Formation at locality 27, Tennessee (type

locality of Crassatella vadosa wadei Stephenson, 1941). USNM 450475 (USGS 16951). 

8, 9. Exterior and interior right valve (x 1.5) of specimen from the Severn Formation at locality 72, Maryland.

USNM 450476. 

10. Exterior left valve (x 1.5) of specimen from the Ripley Formation at locality 40, Alabama. USNM 450477

(USGS 857). 

11, 12. Interior and exterior left valve (xl) holotype Crassatellites carolinana Stephenson, 1927 from the

Peedee Formation at locality 69A, North Carolina. USNM 73438 (USGS 12262).

13. Exterior left valve (xl) syntype Crassatella subplana Conrad, 1853 from the Mount Laurel Sand and 

(or) Navesink Formation at locality 47, New Jersey. ANSP 18743.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 11

CRASSATELLA
PLATE 13

Genus and species unknown

FIGURES 1-5. Specimens originally thought to be Uddenia texana Stephenson, 1941; however, hinge characters as illustrated 

here show that this unnamed group is not a member of the Crassatellidae (see discussion on p. 57-58 of text). 

1, 3. Specimens from the Providence Sand at locality 65, Georgia. USGS 25992. 

1. Interior right valve (SEM x25). USNM 450482.

3. Interior left valve (SEM X40.5). USNM 450483. 

2. Interior left valve (SEM x60) of specimen from the Providence Sand at locality 62B, Georgia. USNM

450484 (USGS 32250). 

4, 5. Specimens from the Owl Creek Formation at locality 52, Mississippi. USGS 25423.

4. Exterior right valve (SEM x54). USNM 450485.

5. Enlargement of beak of articulated specimen (SEM x200). USNM 450486.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 13
PLATE 15

Morphologic variation and ontogenetic sequence within Crassatella tumidula Whitfield, 1865

FIGURES 1-17. Crassatella tumidula Whitfield, 1865.

1, 4-8, 10, 16. Specimens from the Nanafalia Formation at locality 114, Alabama.

1, 4, 8, 10, 16. Two valves (probably from the same individual). USGS-CENO 271.

1, 10. Exterior and interior right valve (xl). USNM 450553. AA, anterior

adductor; PA, posterior adductor; R, resilifer. 

4, 16. Interior and exterior left valve (xl). USNM 450560.

8. Dorsal view of paired valves (xl.5). USNM 450553, 450560. L, lunule.

5. Dorsal view (xl.5) of articulated specimen. USNM 450555.

6. Exterior right valve (x2). USNM 450556.

7. Interior right valve (x2). USNM 450516 (USGS-CENO 5641).

2, 3, 9, 12-15, 17. Specimens from the Bells Landing Member of the Tuscahoma Formation at locality 117, 

Alabama.

2. Interior left valve (x2). USNM 450517.

3. Exterior left valve (x2). USNM 450558. 

9, 13. Exterior (x2) and interior (x3) left valve. USNM 450519 (USGS-CENO

5594).

12. Exterior left valve (xl). USNM 450561. 

14. Interior right valve (xl). USNM 450518.

15, 17. Exterior and interior left valve (xl). USNM 450521 (USGS-CENO 5594). 

11. Interior left valve (x2) of specimen from the Greggs Landing Member of the Tuscahoma 

Formation at locality 118, Alabama. USNM 450559.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 15

CRASSATELLA
PLATE 16

Tertiary juvenile Crassatella

FIGURES 1-3, 5. Crassatella aquiana Clark, 1895. Specimens from the Porters Creek(?) Clay at locality 80, Alabama. 

USGS-CENO 264.

1. Exterior left valve (SEM xll.9). USNM 450562.

2. Interior left valve (SEM X14.6). USNM 450563.

3. Exterior left valve (SEM X21.6). USNM 450564.

5. Partially preserved prodissoconch and nepionic portions of shell (SEM x 122). USNM 450565. 

FIGURES 4, 6. Crassatella tumidula Whitfield, 1865. Right valve of specimen from the Nanafalia Formation at locality

115A, Alabama. USNM 450522 (USGS-CENO 10765). 

4. Exterior (SEM X9.31). 

6. Enlargement of nepionic portion of shell (SEM x21).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 16

CRASSATELLA
PLATE 17

Morphologic variation and ontogenetic sequence within Bathytormus pteropsis (Conrad), 1860

FIGURES 1-21. Bathytormus pteropsis (Conrad), 1860.

1^4. Specimens, classified as Bathytormus sp. A for the statistical analysis, from the Ripley Formation at 

locality 39, Alabama. USGS 27552.

1. 4. Interior and exterior left valve (x3). USNM 450487.

2. 3. Interior and exterior left valve (x3). USNM 450488.

5, 10, 18. Specimens from the Ripley Formation at locality 34A, Mississippi. USGS 711. 

5. Exterior left valve (x2). USNM 450566. 

10. Exterior right valve (xl.5). USNM 450567. 

18. Interior left valve (xl.5). USNM 450568. 

6, 7. Interior and exterior left valve (x2.5) of specimen from the Providence Sand at locality 62A, Alabama.

USNM 450489 (USGS 25993). 

8, 12, 14. Specimens from the Providence Sand at locality 63, Georgia.

8. Exterior right valve (x2). USNM 450490 (USGS 28442). 

12, 14. Exterior and interior left valve (xl.5). USNM 450491 (USGS 25935).

9. Interior right valve (x 1.5) of specimen from the Ripley Formation at locality 33, Mississippi. USNM 

450492 (USGS 25485). AA, anterior adductor; AR, anterior pedal retractor; PA, posterior 

adductor; PR, posterior pedal retractor; R, resilifer. 

11. Interior right valve (x2) of specimen from the Coon Creek Tongue of the Ripley Formation at locality

30A, Mississippi. USNM 450493 (USGS 25407).

13,19. Articulated specimen from the Ripley Formation at locality 45, Georgia. USNM 450494 (USGS 28431). 

13. Dorsal view (x2). E, escutcheon; L, lunule. 

19. Exterior right valve (x2).

15. Exterior right valve (x2) of specimen from the Ripley Formation at locality 44, Georgia. USNM

450495 (USGS 27878).

16. Interior right valve (xl.5) of specimen from the Ripley Formation at locality 43, Alabama. USNM

450496 (USGS 27919).

17. Exterior right valve (xl.5) of specimen from the Severn Formation at locality 75, Maryland. USNM

450497 (USGS 852).

20, 21. Exterior and interior right valve (xl.5) of specimen from the Ripley Formation at locality 43, 

Alabama. USNM 450498 (USGS 27924).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 17

BATHYTORMUS
PLATE 18 

Morphologic variation and ontogenetic sequence within Bathytormus alaeformis (Conrad), 1830

FIGURES 1-22. Bathytormus alaeformis (Conrad), 1830.

1, 2. Exterior and interior right valve (x2) of specimen from the Aquia Formation at locality 85,

Maryland. USNM 450523.

3, 5, 18. Specimens from the Aquia Formation at locality 91, Virginia. 

3, 5. Exterior and interior left valve (xl.5). USNM 450524.

18. Exterior left valve (xl). USNM 450525.

4, 6, 7, 14, 20-22. Specimens from the Aquia Formation at locality 88, Virginia. 

4, 6, 7. Right valve. USNM 450526 (USGS-CENO 2508).

4. Valve tilted to reveal characters of juvenile portion on umbo (xl). 

6, 7. Exterior and interior (xl). 

14. Exterior right valve (xl.5). USNM 450527.

20. Exterior right valve (xl). USNM 450528.

21. Exterior left valve (xl). USNM 450529.

22. Exterior right valve (xl). USNM 450530. 

8-10. Specimens from the Aquia Formation at locality 85, Maryland. USGS-CENO 2489.

8. Exterior right valve (xl.5). USNM 450531.

9. Exterior right valve (xl.5). USNM 450532.

10. Exterior right valve (xl.5). USNM 450533.

11, 13, 16, 19. Specimens from the Aquia Formation at locality 104, Maryland. USGS-CENO 2243. 

11, 13. Exterior and interior left valve (xl). USNM 450569. 

16. Exterior right valve (xl). USNM 450570. 

19. Exterior left valve (xl). USNM 450571. 

12, 15. Interior and exterior right valve (xl) of specimen from the Aquia Formation at locality 92,

Virginia. USNM 450534.

17. Exterior left valve (xl) hypotype (Clark and Martin, 1901, pi. 41, fig. 7a) from the Aquia 

Formation at locality 87, Maryland. USNM 207153.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 18

19

BATHYTORMUS
PLATE 19

Morphologic variation within Bathytormus alaeformis (Conrad), 1830

FIGURES 1-13. Bathytormus alaeformis (Conrad), 1830.

1-5, 8. Paired valves of specimen from the Aquia Formation at locality 103, Maryland. USNM 450535.

1. 3. Interior and exterior left valve (xl.5).

2. 4. Interior and exterior right valve (xl.5).

5. Interior view through the ventral shell gape of the muscle scars and dentition of paired valves 

(xl.5). AA, anterior adductor; AR, anterior pedal retractor; PA, posterior adductor; R, 

resilifer.

8. Dorsal view of paired valves (xl.5).

6. Dorsal view (xl.5) of articulated specimen from the Aquia Formation at locality 83, Maryland. USNM

450536.

7. Dorsal view (xl.5) of articulated specimen from the Aquia Formation at locality 91, Virginia. USNM

450537. 

9, 10. Articulated specimen from the Aquia Formation at locality 102, Maryland. USNM 450538.

9. Dorsal view (xl).

10. Exterior right valve (xl).

11, 13. Exterior and interior left valve (xl.5) of specimen from the Aquia Formation at locality 97, Virginia. 

USNM 450539. AA, anterior adductor; AR, anterior pedal retractor; PA, posterior adductor; PR, 

posterior pedal retractor.

12. Exterior right valve (xl.5) of specimen from the Aquia Formation at locality 85, Maryland. USNM 

450572 (USGS-CENO 2489).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 19

AA

BATHYTORMUS
PLATE 20

Comparison of juvenile Bathytormus and Scambula

FIGURES 1, 3, 4, 6. Bathytormus pteropsis (Conrad), 1860. Right valve of specimen from the Providence Sand at locality 63,

Georgia. USNM 450499 (USGS 25935). 

1. Exterior (SEM X14.9).

3. Enlargement of hinge platform (SEM x34.3).

4. Interior (SEM X15.9).

6. Detail of nepionic portion of shell (SEM x48.7). 

FIGURE 2. Scambula perplana Conrad, 1869. Exterior right valve (SEM x21.2) of specimen from the Ripley Formation

at locality 33, Mississippi. USNM 450503 (USGS 25485). 

FIGURES 5, 7. Bathytormus alaeformis (Conrad), 1830. Left valve of specimen from the Aquia Formation at locality 98,

Virginia. USNM 450540.

5. Detail of nepionic portion of shell (SEM x26). 

7. Exterior (SEM x8.9).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 20

BATHYTORMUS AND SCAMBULA
PLATE 21

Variation of hinge form, sculpture, and morphology in the Crassatellidae

FIGURES 1-5, 7, 9. Scambula perplana Conrad, 1869.

1. Exterior left valve (x4) of specimen from the Ripley Formation at locality 37, Georgia. USNM 450504 

(USGS 27542).

2. Exterior right valve (x3) of specimen from the Woodbury Clay at locality 15, New Jersey. USNM

450505 (USGS 16293). 

3-5. Specimens from the Ripley Formation at locality 43, Alabama. USGS 27919.

3. Interior left valve (x4). USNM 450506.

4, 5. Exterior and interior right valve (x4). USNM 450507. AA, anterior adductor. 

7. Exterior left valve (x6) of specimen from the Ripley Formation at locality 43, Alabama. USNM 454609 

(USGS 28434).

9. Enlargement of right valve hinge (x3) of specimen from the Coon Creek Formation at locality 27,

Tennessee. USNM 450508 (USGS 25406). R, resilifer. 

FIGURES 6, 8. Crassatella vadosa Morton, 1834. Exterior and interior left valve (xl) of specimen from the Owl Creek

Formation at locality 52, Mississippi. USNM 450509 (USGS 25423). R, resilifer. 

FIGURES 10, 12. Bathytormus pteropsis (Conrad), 1860.

10. Interior right valve (xl.5) of specimen from the Ripley Formation at locality 44, Georgia. USNM

450495 (USGS 27878). 

12. Exterior right valve (xl.5) of specimen from the Ripley formation at locality 43, Alabama. USNM

450496 (USGS 27919).

FIGURES 11, 13. Bathytormus protextus (Conrad), 1832. Exterior and interior right valve (x 1) of specimen from the Eocene 

at Bells Landing, Alabama. USNM 450541 (USGS-CENO 1416).

FIGURES 14, 17. Bathytormus alaeformis (Conrad), 1830. Exterior and interior left valve (xl) of specimen from the Aquia 

Formation at locality 89, Virginia. USNM 450573 (USGS-CENO 2030). AR, anterior pedal retractor; 

PR, posterior pedal retractor; R, resilifer.

FIGURES 15, 16. Eucrassatella undulata (Say), 1824. Interior and exterior right valve (xl) of specimen from the Miocene at 

the West Branch of the Nansemond River, 7 miles below Suffolk, Virginia. USNM 450542 (USGSCENO 2836). AR, anterior pedal retractor; PA, posterior adductor; R, resilifer. (Note the wide resilifer 

that projects down into the umbonal cavity.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 21

SCAMBULA, CRASSATELLA, BATHYTORMUS, AND EUCRASSATELLA
PLATE 22

Type specimens of questionable generic or familial assignment

FIGURES 1-4. Gouldia conradi Whitfield, 1885 [herein = Crassatella vadosa ? Morton, 1834]. Syntypes from the

Woodbury Clay at locality 14, New Jersey. ANSP 18735. 

1, 2. Exterior and interior right valve (x6).

3. Exterior right valve (x5).

4. Exterior right valve (x5). 

FIGURES 5, 6. Uddenia conradi (Whitfield) Stephenson, 1923 (pi. 67, fig. 16). Exterior and interior right valve (x5)

hypotype from the Tar Heel Formation at locality 8, North Carolina. USNM 31932. 

FIGURES 7-9. Crassatella monmouthensis Gabb, 1860. Holotype and paratype from Monmouth County, New Jersey.

ANSP 18738. 

7, 8. Holotype, internal mold with adhering shell material.

7. Right side of mold (x 2.5).

8. Dorsal view of mold (x2.5).

9. Paratype, right side of internal mold (xl.5), probable Etea (Arcticidae).

FIGURES 10-12. Crassatella delawarensis Gabb, 1860. Holotype, internal mold with adhering shell material from Monmouth 

County, New Jersey. ANSP 18733.

10. Right side (xl. 5).

11. Left side (xl.5).

12. Dorsal view (xl.5).

FIGURES 13-15. Crassatella transversa Gabb, 1861. Holotype, internal mold from an unknown stratigraphic position and 

locality (listed simply as "Cretaceous, New Jersey"). ANSP 18744.

13. Dorsal view (xl).

14. Right side (xl).

15. Left side (xl). 

FIGURES 16-19. Crassatella prora Conrad, 1869. Holotype and paratypes from the Mount Laurel Sand and (or) Navesink

Formation at locality 48, New Jersey. ANSP 18739. 

16, 17. Holotype, left side and dorsal view of partial internal mold (x2). 

18, 19. Paratype(?), dorsal view and left side of internal mold (x2), probable Etea (Arcticidae).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1535 PLATE 22

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