Giant Upper Cretaceous 

Oysters from the Gulf 

Coast and Caribbean

GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-H

FILE COPY

Biological Survey

Giant Upper Cretaceous 

Oysters from the Gulf 

Coast and Caribbean

By NORMAN F. SOHL and ERLE G. KAUFFMAN 

CONTRIBUTIONS TO PALEONTOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-H

These exceptionally massive species are among the 

most unusual Cretaceous ostreids^ are stratigraphically restricted^ and provide a basis for rejined 

correlation

Geological Survey

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

The U.S. Geological Survey Library has cataloged this publication as follows :

Sohl, Norman Frederick, 1924-

Giant Upper Cretaceous oysters from the Gulf Coast and 

Caribbean, by Norman F. Sohl and Erie G. Kauffman. 

Washington, U.S. Govt. Print. Off., 1964.

iv, 31 p. 5 plates, map. diagrs., tables. 30 cm. (U.S. Geological 

Survey. Professional Paper 483-H) 

Contributions to paleontology. 

Bibliography: p. 18-19.

1. Mollusks, Fossil. 2. Paleontology Cretaceous. 3. Paleontology Gulf Coastal Plain. 4. Paleontology Caribbean area. I. Kauffman, Erie Galen joint author. II. Title. (Series)

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

Washington, D.C., 20402 - Price 40 cents (paper cover)
CONTENTS

Abstract-___________________________________

Introduction ________________________________

Morphologic terminology and measurements___ 

Systematic paleontology-. ___________--_-____-

Crassostrea cusseta Sohl and Kauffman n. sp_ 

Arctostrea aguilerae (Bose)____-_______-_.

References. __________________________________

Index_______________________________________

Page

HI

1

6

6

7

14

19

21

ILLUSTRATIONS

[Plates follow index]

PLATE 1-3. Arctostrea aguilerae (Bose)

4. Arctostrea aguilerae (Bose) and Crassostrea cusseta Sohl and Kauffman n. sp.

5. Crassostrea cusseta Sohl and Kauffman n. sp.

FIGURE 1. Correlation chart of the Upper Cretaceous rocks bearing Crassostrea cusseta Sohl and Kauffman n. sp. and Arctostrea aguilerae (B6se)_________________________________________

2. Geographic occurrence of Crassostrea cusseta Sohl and Kauffman n. sp. and Arctostrea aguilerae (Bose) ___-________-_______-_________-.__-___----__-----_-------_----------_

3. Morphology of the Ostreidae_ ____________________________-__--__-_--_-----__-__---

Page 

H2

3

5

TABLES

TABLE 1. Summary of measurements for Crassostrea cusseta Sohl and Kauffman n. sp. from Georgia 

and Alabama._-_-_______________-___-__-_________-____-___---_-______-____----

2. Summary of measurements for Arctostrea aguilerae (Bose)._____________________________

Page

H8 

14

in

CONTRIBUTIONS TO PALEONTOLOGY

GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN

By NORMAN F. SOHL and ERLE G. KAUFFMAN

ABSTRACT

Two unusually massive ostreid species, representing the 

largest and youngest Mesozoic members of their respective 

lineages, occur in Upper Cretaceous sediment of the gulf coast 

and Caribbean areas. Their characteristics and significance, 

as well as the morphologic terminology of ostreids in general, 

are discussed.

Crassostrea cusseta Sohl and Kauffman n. sp. is the largest 

known ostreid from Mesozoic rocks of North America; it occurs 

sporadically in the Cusseta Sand and rarely in the Blufftown 

Formation of the Chattahoochee River region in Georgia and 

Alabama. It is especially notable in that it lacks a detectable 

posterior adductor muscle scar on large adult shells. C. 

cusseta is the terminal Cretaceous member of the C. soleniscus 

lineage in gulf coast sediments; the lineage continues, however, 

with little basic modification, throughout the Cenozoic, being 

represented in the Eocene by C. gigantissima (Finch) and 

probably, in modern times, by C. virginica (Gmelin). The C. 

soleniscus lineage is the first typically modern crassostreid group 

recognized in the Mesozoic.

Arctostrea aguilerae (Bose) occurs in Late Campanian and 

Early Maestrichtian sediments of Alabama, Mississippi, 

Texas(?), Mexico, and Cuba. The mature shell of this species 

is larger and more massive than that of any other known arctostreid. Arctostrea is well represented throughout the Upper 

Jurassic and Cretaceous of Europe, but in North America, 

despite the great numbers and diversity of Cretaceous oysters, 

only A. aguilerae and the Albian form A. carinata are known. 

The presence of A. aquiierae in both the Caribbean and gulf 

coast faunas is exceptional, as the Late Cretaceous faunas of 

these provinces are generally distinct and originated in different faunal realms.

INTRODUCTION

An unusually diverse assemblage of ostreid species 

and a great abundance of individuals have always been 

hallmarks of Upper Cretaceous deposits in the Gulf 

Coastal Plain province. Even at present, careful 

collecting by paleontologists continues to turn up new 

and frequently bizarre species, adding to an already 

impressive list of oysters available for biostratigraphic, 

taxonomic, and evolutionary studies. The giant species described here are among the most unusual ostreids 

to be discovered in modern times. Both are exceptionally massive, representing the largest and final 

development of their respective species groups in the

gulf coast Upper Cretaceous. Despite their rare and 

scattered occurrence, both species are stratigraphically 

restricted and provide a good basis for refined correlation (fig. 1).

Crassostrea cusseta is unique in many ways. Its 

great size and massive shell are unequaled among 

American Mesozoic oysters. It is the youngest as 

well as the largest known member of the C. soleniscus 

lineage in Cretaceous rocks; this lineage, the first 

typically modern crassostreid group known from the 

Mesozoic, appears to transgress the Mesozoic-Cenozoic 

boundary with little modification other than loss of 

marginal denticles and gives rise to large modern 

crassostreid types typified by the Eocene C. gigantissima 

(Finch) ( = C. georgiana Conrad) and the Recent C. 

virginica (Gmelin). A gradual increase in size and 

massiveness characterizes the lineage from its Cretaceous origin to the development of C. gigantissima. 

Subsequent Crassostrea are smaller and more varied. 

A second significant evolutionary trend seems to involve a gradual reduction of the marginal denticles, 

which are well developed over the commissure in 

C. soleniscus and gradually disappear in younger species 

of the lineage. On large adult valves of C. cusseta, a 

posterior adductor muscle scar is not visible, a rare 

phenomenon among oysters, possibly indicating atrophy 

of the muscle in old age.

Arctostrea aguilerae (Bose), equally impressive because of its great size and massive shell, is the largest 

known member of the genus. Its distribution is equally 

significant. Few species of invertebrates are found in 

both the Upper Cretaceous deposits of the Caribbean 

and those of the Gulf Coastal Plain province. Arctostrea 

aguilerae is one of these, exhibiting an extensive gulf 

coast-Caribbean dispersal that transcends the faunal 

provinciality of the two areas. This species exhibits a 

nearly continuous distribution on the Gulf Coastal 

Plain and is known from Alabama, Mississippi, Texas(?), 

and Mexico (fig. 2). In addition, it is represented at six 

localities in Cuba.

Hi
Stage

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FIGURE 1. Correlation chart of Upper Cretaceous rocks bearing Crassostrea cusseta Sohl ajd Kauflman n. sp. and Arctostrea aguilerae (Bose). 1, Stratigraphic ran

range of A. aguilerae.
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H3
H4 CONTRIBUTIONS TO PALEONTOLOGY

EXPLANATION OF LETTER SYMBOLS

Di. Inclination angle of the dorsal part of the valve (above the 

point of posterior curvature) to the hinge line; measured between the plane of the hinge line and the average inclination 

of the dorsal part of the midline.

H. Height of the shell or valve, measured perpendicular to the 

plane of the hinge line.

HA. Height of the auricle, measured perpendicular to the plane 

of the hinge line.

HCA. Height of the cardinal area, measured perpendicular to 

the plane of the hinge line, between the dorsal margin and 

the ventral edge of the cardinal area.

HD. Height of that part of the shell possessing denticulate 

margins, measured perpendicular to the plane of the hinge 

line.

HL. Hinge line: a straight line connecting the ventrolateral 

margins of the cardinal area and delineating a plane of 

horizontal reference for all measurements. The hypothetical plane of the hinge line is perpendicular to the plane 

of the commissure.

HMS. Height of the muscle scar, or insertion area, measured 

perpendicular to the plane of the hinge line. This is not 

the longest diameter of the scar.

HPC. Height of that part of the shell dorsal to the point of 

abrupt posterior curvature, measured perpendicular to the 

plane of the hinge line.

L. Length of the valve, measured parallel to the plane of the 

hinge line, between the anteriormost and posteriormost projections of the valve when it is oriented with the hinge line 

horizontal.

LA. Length of the auricle, measured between the commissure 

and the lateral edge of the valve, parallel to the plane of 

the hinge line.

LCF. Lateral cardinal folds (new term): arched folds of the 

cardinal area on either side of the resilifer, bounded laterally 

in many species by shallow marginal cardinal troughs and 

(or) by raised lateral valve margins. The lateral part of 

the ligament attaches to part or all of each fold.

LCT. Lateral cardinal troughs (new term): concave troughs 

lying on either side of the midcardianl fold in the right 

valve, between the arched midcardinal fold and upturned 

lateral edges of the valve. The lateral part of the ligament 

attaches to these surfaces.

LHL. Length of the hinge line, measured along a line between 

the junctions of the ventral edge of the cardinal area and 

the lateral margins of the valve (commissure).

LM. Length of the midline of the valve, measured between the 

middorsal and midventral margins.

LMS. Length of the muscle scar, or area of muscle insertion, 

exposed on the interior surface of the valve; measured 

parallel to the plane of the hinge line.

MCT. Marginal cardinal troughs (new term): shallow, narrow 

troughs or grooves just inside the lateral margins of the 

valve on either side of the cardinal area. The troughs are 

bounded medially by the lateral cardinal folds and laterally 

by the raised outer margin of the cardinal area and (or) by 

overlapping calcite lamellae from the lateral edge of the 

shell. This structure is present in many ostreid species, 

being characteristic of some, merely a rare variant of others. 

MDMS. Maximum diameter of the muscle scar, or insertion

area.

MF. Midcardinal fold (new term): a shallow to highly arched, 

axially elongate fold situated centrally on the cardinal area 

of the right valve in some ostreid groups (in place of a 

resilifer). The midcardinal fold extends from the dorsal 

margin to the midventral edge of the cardinal area and fits 

into the resilifer of the left valve when the valves are 

articulated. The resilium attaches to part or all of this 

fold.

MLMF. Maximum length of midcardinal fold along its axis. 

R. Resilifer: a triangular to rectangular, concave fossette situated centrally to subcentrally in the cardinal area. It 

extends from near the middorsal margin of the valve to the 

midventral edge of the cardinal area and is bounded laterally 

by flat to convex areas (lateral cardinal folds or plates) for 

attachment of the lateral ligament. The resilifer contains 

the resilium in living oysters. A resilifer is typically present 

on the left valve in the Ostreidae and also occurs on the 

right valve of many species groups. Where present on the 

right valve, it is commonly shallower than the corresponding 

structure on the left valve and is bounded ventrally by a 

raised lip. In species which have a resilifer only on the 

left valve, the right valve possesses a flat plate (midcardinal 

plate) or arched fold (midcardinal fold) in the central part 

of the cardinal area.

SC. Subcardinal cavities (new term): shallow to moderately 

deep reentrants of the floor of the valve beneath various 

structures of the cardinal area. Subcardinal cavities most 

commonly underlie the midcardinal and lateral cardinal 

folds and rarely occur below the resilifer or lateral cardinal 

troughs. These cavities are formed predominantly in species having a massive cardinal area. The terms "middle" 

and "lateral subcardinal cavity" may be applied to indicate 

the relative position of the cavities below the cardinal area. 

IT. Total angle of inclination of the valve, measured between 

the plane of the hinge line (horizontal) and a straight line 

joining the beak with the midventral margin of the valve. 

WR. Maximum width of the resilifer, measured perpendicular 

to the axis of this structure. The width of the midcardinal 

fold or plate is similarly measured.
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H5

MCT

c

FIGURE 3. Morphology of the Ostreidae: terminology and measurements. Explanation of symbols in text. A, Cardinal area, right valve of Crassostrea cusseta; 

B, dorsal half of interior, left valve of Arctostrea aguilerae; C, interior view, right valve, of Crassostrea cusseta; D, interior view, left valve of Arctostrea 

aguilerae.
H6 CONTRIBUTIONS TO PALEONTOLOGY

The shell form Arctostrea is not known among Cenozoic and Recent oysters, and this unique group is here 

recognized as a distinct genus. Arctostrea is characterized by its massive narrow curved shell, crosslaminated shell structure, quadrate to triangular valve 

cross section, surface sculpture, and its deep muscle 

scar.

The genus Arctostrea is well represented in Europe 

throughout the Cretaceous bv a relatively continuous 

sequence of forms. Its stratigraphic distribution, 

however, is very discontinuous in North America, 

where it is represented by only two species: A. carinata 

(Lamarck) from the Albian (Fredericksburg and 

Washita Groups) and A. aguilerae (Bose) from the 

Upper Campanian and Lower Maestrichtian. No 

explanation can be offered for the absence of Arctostrea 

throughout the lower part of the Upper Cretaceous in 

an area so rich in ostreid elements. Cenomanian, 

Turonian, and Santonian faunas of North America and 

western Europe are very similar, yet arctostreids, 

which characterize the lower part of the European 

Upper Cretaceous sequence [A. pectinata or columbrina 

from the Santonian; A. carinata, ricordeana, and 

diluviana (in part) from the Turonian], are not known 

from corresponding North American sedimentary rocks. 

This is unusual, because ostreids are among the most 

cosmopolitan of Cretaceous pelecypods.

The present study is one of the first in a continuing 

investigation of American Cretaceous oysters by the 

authors. In an effort to standardize morphologic terminology in the ostreids, a brief review of existing 

nomenclature and some pertinent new terms are presented. The amended descriptions of Crassostrea and 

Arctostrea used in this study include paleontological 

and malacological concepts in use at present and define 

more restricted and more natural boundaries for the 

taxa. They are considerably expanded over previous 

attempts and provide data for a much greater number 

of shell characters than were used in the past as a 

basis for supraspecific classification.

We express our appreciation to R. W. Imlay, of the 

U.S. Geological Survey, and to R. S. Boardman and 

P. M. Kier, of the U.S. National Museum, for their 

criticism of the manuscript. Discussions with Dr. H. B. 

Stenzel of the Shell Development Co. regarding generic 

taxonomy were very helpful. Photography was done 

by Jack Scott and his staff, and drawings were done 

by Larry B. Isham, all of the U.S. National Museum. 

To them we express our thanks. Members of the MidSouth Earth Science Club generously donated specimens of Arctostrea aguilerae for study.

MORPHOLOGIC TERMINOLOGY AND MEASUREMENTS

The proper interpretation of ostreid species and subspecies depends upon an intimate knowledge of morphologic features that are useful in the differentiation 

of taxa, the normal variation limits of populations, and 

the effect of environment on morphological variation. 

To achieve this, many modern workers have applied 

population systematics to this group and have found 

it necessary to reevaluate the importance of various 

shell structures in delineating taxa. This need has led 

to a search for features to use as a basis for ostreid 

taxonomy that are less affected by environment than 

are shape, ornamentation, and convexity. Structures 

of the cardinal area, muscle scar, denticles, and shell 

structure hold great promise in this respect. The value 

and of other features is yet untested.

Wherever possible, standard pelecypod terminology 

has been used in this study (after Newell, 1937, 1942; 

Shrock and Twenhofel, 1953), but there are structures, 

particularly those of the cardinal area, for which there 

is no standardized terminology. Inasmuch as these 

structures play a leading role in modern ostreid taxonomy, it is desirable that they be defined. New or 

revised terms used in this paper are defined on page H4 

and are illustrated in figures 3A and 3B.

Similarly, measurements and ratios not commonly 

used in studies dealing with the Ostreidae are presented for the species described. These measurements 

and ratios, in addition to the standard measurements, 

are in part illustrated in figures 3(7 and 3D and are 

summarized in tables 1 and 2. The unusual structure 

of the ostreid species described herein necessitates 

many of these additional measurements. Other structures are investigated simply as possible criteria for 

the recognition and differentiation of taxa. Proper 

evaluation of their utility must await broader studies 

of the species groups to which Crassostrea cusseta and 

A. aguilerae belong. For all measurements the specimens 

were oriented so that the hinge line delineated a horizontal plane of reference perpendicular to the plane of 

the commissure.

The symbols used in figure 3 are given in alphabetical 

order on page H4.

SYSTEMATIC PALEONTOLOGY

Genus CRASSOSTREA Sacco : emended

1897. Sacco, Federico, I molluschi dei terreni terziarii del 

Piemonte e della Liguria: Clausen, Torino, v. 23, p. 15.

1941. McLean, R. A., The oysters of the western Atlantic: 

Acad. Nat. Sci. Philadelphia, Notulae naturae, no. 

67, p. 8, pi. 1, figs. 1-4.
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H7

1950. Gunter, Gordon, The generic status of living oysters and 

the scientific name of the common American species: 

Am. Midland Naturalist, v. 43, no. 2, p. 438-449.

1954. Thomson, J. M., The genera of oysters and the Australian 

species: Australian Jour. Marine and Freshwater 

Research, v. 5, no. 1, p. 141, 142.

Type species. Ostrea virginica Gmelin, by original 

designation.

DIAGNOSIS

Prodissoconch inequivalve, inequilateral; anterior 

ligament outside cardinal area; short hinge bears two 

toothlike denticles at each end. Adult shell variable 

in form, large in size, elongate along midline, straight 

to curved; left valve larger and more massive than 

right. Radial ornament unequally developed on left 

and right valves. Surface of left valve smooth to 

finely and irregularly plicate or costate. Right valve 

smooth to faintly plicate, flat. Left valve deeply 

cupped dorsally and centrally; valves normally show 

subcardinal cavities. Cardinal area of left valve composed of well-defined central triangular resilifer and 

subequal triangular lateral cardinal folds or plates. 

Cardinal area of right valve composed of midcardinal 

fold or central plate and subequal lateral cardinal 

troughs or plates. Adductor muscle scar ventroposterior, normally colored, large, shallow, semicircular 

to semielliptical; flat side dorsal and nearly perpendicular to midline. Mesozoic forms have simple 

ovoid to elongate denticles; Cenozoic forms have 

nondenticulate adult valves. Shell lamellate.

REMARKS

Numerous modern species of oysters have been 

extensively studied biologically, owing to their commercial importance. This work, though not done 

primarily for taxonomic purposes, has greatly aided 

neontologists in forming a natural classification of 

modern ostreids based primarily on the anatomy and 

reproductive habits of the animal. The majority of 

contemporary ostreid workers dealing with living 

species do not regard shell form or ornamentation as a 

good basis for classification because they are cognizant 

of the great variation of ostreid shell growth in response 

to different environments. The work of these men is 

of great interest to the paleontologist, who has relied 

upon shell morphology in classification and who now 

finds himself with little basis for the largely artificial 

divisions that he has recognized in the past.

It is significant that certain structures of the shell, 

many of them not previously used by paleontologists, 

are consistent with the natural divisions of the 

neontologists. The prodissoconch features are primary 

among these. The position of the posterior adductor 

muscle scar varies with the presence or absence of a

promyal chamber. Subcardinal cavities also reflect 

the presence of this structure. The identification 

of modern crassostreid types in Cretaceous sediments 

is based on the neontological concept of the genus, 

as put forth by Ranson (1948, 1950: he used the term 

Gryphaea, later rejected), Gunter (1950), Thomson 

(1954), and others.

Modern Crassostrea are dioecious, and the eggs are 

deposited, fertilized, and developed in the water outside the shell. This is the main characteristic used to 

separate the genus from Ostrea, which contains wholly 

monoecious, larviparous species. Correspondingly, species of Crassostrea produce a much greater number of 

eggs than do species of Ostrea about 50 million in 

studied species and the eggs are smaller. Small gill 

ostia and the presence of a promyal chamber further 

differentiate Crassostrea from Ostrea. To accommodate 

the promyal chamber, the dorsal part of the left valve 

is deeply cupped, and the posterior adductor muscle 

scar is displaced ventrally and posteriorly, occurring 

well down toward the feeding margin of the shell. 

Both shell features characterize the Crassostrea soleniscus lineage of the Upper Cretaceous. Many Crassostrea have well developed subcardinal cavities, and 

these again reflect the presence of the promyal chamber 

and the displacement of the viscera. This feature is 

well defined in C. cusseta and in some specimens of 

C. soleniscus.

Denticles are present on the commissure and are 

reflected on the lateral margins of the valves in all 

members of the Crassostrea soleniscus lineage. All other 

Mesozoic Crassostrea that we have examined in detail 

seem to have them as well. On the other hand, the 

Ceno/oic Crassostrea, even within this same lineage, 

lack denticles. Of the American Cenozoic Crassostrea 

examined, only the Early Tertiary representatives of 

C. gigantissima exhibit denticles, and in this species 

they are restricted to the juvenile shell and probably 

reflect an ancestry in the denticulate Mesozoic lineage 

of C. soleniscus.

Further examination of most Mesozoic and Cenozoic 

Crassostrea will be required to determine whether this 

difference is as consistent as it seems to be in the 

American species. If the distinction proves consistent, 

division of Crassostrea into two subgenera seems warranted. Such a study is unfortunately beyond the 

scope of the present paper.

Crassostrea cusseta Sohl and Kauffman n sp.

Plate 4, figures 5, 9, 10; plate 5, figures 1-4

MATERIAL

Fifteen well-preserved specimens from the base of 

the Cusseta Sand (Upper Cretaceous) at six localities
H8 CONTRIBUTIONS TO PALEONTOLOGY

in Georgia and Alabama. One specimen from the 

upper Blufftown Formation of Alabama. Six specimens nearly complete, lack only ventral extremity; 

remainder retain dorsal one-third of valve, including 

cardinal structures. Numerous additional fragments.

DESCRIPTION

General form. Summary of measurements presented 

in table 1. Shell exceptionally large and massive, 

moderately inequivalve. Left (lower, attached) valve 

much more convex, slightly larger than right (upper, 

free) valve. Valves close fitting, of similar shape, 

highly inequilateral, and strongly curved posteriorly 

(pi. 4, fig. 10). Valve inclination typically opisthocline 

to nearly acline; average angle 95°. Height of shell 

greater than length: average ratio 1:0.577; average 

measurements of adult specimens: height, 377 mm; 

length, 211 mm; thickness of left valve, 65.6 mm; 

thickness of right valve, 59.4 mm.

Marginal outline relatively uniform for members of 

Ostrea. Some valves elongate, spatulate, and slightly 

curved toward posterior; valves more commonly subcrescentic and strongly curved posteriorly. Posterior 

curvature abrupt on most specimens (pi. 5, fig. 4), 

gradual on rare individuals. Point of initial posterior 

curvature is %-% the total height from the dorsal 

margin (pi. 5, fig. 4). Dorsal margin blunt, straight 

to slightly curved, not parallel to hinge line; dorsolateral margins narrowly and unevenly rounded, 

lateral margins straight to slightly curved and subparallel dorsally in absence of well-defined posterior 

auricle, slightly to moderately curved medially at point 

of posterior bend (anterior margin convex, posterior 

concave in outline), straight and subparallel ventrally; 

ventral margin unknown. On valves having posterior 

auricle, dorsoposterior margin moderately rounded 

(convex outward) at auricle, recessed (concave) below 

it (pi. 5, fig. 1).

Right valve uniformly slightly convex; left valve 

moderately to highly arched, convexity unevenly distributed. Umbonal area flattened on all right and on 

some left valves. Greatest convexity of left valve just 

anterior to midline along a narrow, sharp, irregular 

ridge bordering attachment scar (pi. 5, fig. 4) and ventral to this, along a moderately rounded subcentral fold 

Large gently rounded irregular folds, undulations, and 

constrictions superimposed on normal form of valves 

in many specimens. Point of greatest convexity of 

either valve dorsocentral. Anterior slope of left valve 

moderate to steep on most specimens, vertical or overhung on a few specimens; posterior slope moderately 

inclined; dorsal and ventral slopes gentle. Lateral edge 

of valves thick, steeply inclined (predominantly vertical) to plane of commissure.

TABLE 1. Summary of measurements for Crassostrea cusseta Sohl 

and Kauffman n. sp. from Georgia and Alabama

Character

Valve length (L) ____ . _ . ___ do_ ,

Ratio length rheight (L:H)-_. ____ - _ .

Curvature of beak: 

Left valve:

Right valve:

Curvature of shell: 

Left valve:

Right valve:

Height (beak to point) of shell curvature

Number of concentric lamellae in 10 mm distance (along midline height) :

At 100mm height. . __-- _ _ __ . _ __

At 350mm height.-.. -----------------

Posterior auricle: 

Height (HA) - - . ----- ----- millimeters _ _

Ratio height of auricle to height of cardinal 

area (HA:HCA)_-__- _ __--____degrees_- 

Angle of inclination (Ti) :

Angle between hinge line and dorsal margin 

degrees- - 

Length, hinge line (LHL)---_-millimeters .

Ratio length of hinge line to height of cardinal area (LHL:HCA)_- 

Midcardinal fold (MF) (right valve): 

Maximum length along axis (MLMF) 

millimeters 

Maximum width perpendicular to axis 

millimeters 

Terminal elevation above floor of cardiRatio terminal elevation to maximum

Resilifer (left valve) : Maximum width (WR) _ millimetersDenticles: 

Valves having denticles.-- __ percent-- 

Height of denticulate lateral margins 

(HD),_ __-_ _ . ..millimetersTotal margin denticulate (in terms of 

total height) . __ _____ percent--

Muscle scar: 

Maximum diameter (MDMS) 

millimeters-- 

Height (HMS) __.. do. 

Length (LMS) (width) ..........do.. ..

Height, beak to dorsal margin of scar 

millimeters- - 

Attachment scar: 

Height. _____________ ...do ....

Number 

of specimens

3

4 

4 

3 

4 

10

1 

3

6 

5

0 

4

1 

6

7

1 

1 

1 

6 

6 

4 

4 

2 

1

4 

4

4

3 

3

6 

13 

13

13

14 

10 

9 

9

3 

3 

3

13 

6

2 

9

2 

2 

2

2

3 

3

Range

331-420 

406. 4-508 

187-250 

0.54:1-0.60:1 

60-78. 8 

42-79

110-210

2^7 

2-6 

2-3 

1-5 

1-5

57. 3-146 

36-69

0. 55:1-1. 5:1

68-114 

29-73

5-67 

48-153 

74-158

0.30:1-1.35:1

74-158 

30-65 

11-32 

0.20:1-0.7:1

38-58 

23-29 

0.5:1-0.72:1

112-305

38.2-72.9 6-12

67.2-85 

58-85 

31-57

98-186

70-170 

57-98

Average

377 

435 

211 

0. 57:1 

65.6 

59.4

25

75

54.5 

45.5

00.0 

100.0

14.3 

85.7

143

3 

3

1 

3.2 

4.3 

2.8 

3.0 

3.0 

2.0

89.5 

48.1

0. 95:1

95 

51.7

36 

99 

112.4

0.91:1

118 

47 

21 

0.47:1

45 

27 

0.61:1

85 

172.5

55 

9.3

76 

71 

44

142

126 

82

Beaks and umbos. Beak blunt, indistinct, worn on 

most specimens. Umbo flat, poorly defined, obscured 

on left valve by attachment scar. Beak and umbo 

in left valves, suborthogyre and straight to opisthogyre 

and moderately curved, attaining one-quarter or rarely 

one-half of a volution. Prosogyre and opisthogyre 

beaks and umbos equally represented in right valves.

Posterior auricle. Most specimens have slight dorsoposterior emargination. Well-developed posterior au-
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H9

ricle present on 25 percent of specimens examined. 

Auricle semicircular in outline, moderately rounded, 

typically small; vertical diameter normally less, rarely 

more, than that of midcardinal fold or resilifer (pi. 5, 

fig. 1, typical of species). Auricle of right valve formed 

by dorsolateral emargination of posterior lateral cardinal trough (pi. 5, fig. 1); trough broader, shallower, 

and margin thicker at auricle than over rest of cardinal 

area. Auricle of left valve formed by expansion of 

posterior lateral cardinal fold and acute infolding of 

dorsoposterior margin (pi. 5, fig. 2); rarely, a shallow 

trough separates these two parts of auricle. Lateral 

margins of auricles on both valves typically notched 

or infolded, producing bend in plane of commissure (pi. 

5, fig. 1). All gradations noted between faint emargination of dorsoposterior border and prominent auricles 

such as those illustrated. Average measurements of 

well-developed auricles on adult specimens: height, 

89.5 mm; length, 48.1 mm; average ratio of auricle 

height to cardinal area height, 0.95:1.

Attachment area. Attachment area or scar, medium 

to large (average dimensions: height, 125.7 mm; length, 

81.7 mm), situated dorsoposteriorly on posterior flank 

of subcentral ridge (pi. 5, fig. 4), and subrounded to 

ovate in outline. Area slightly concave, obscuring 

normal ornamentation but not well defined or associated 

with secondary calcareous deposits. Animal apparently 

attached throughout life.

Ornamentation. Ornamentation of both valves consists of coarse, crowded, irregular, overlapping concentric lamellae of several sizes (pi. 4, fig. 10; pi. 5, 

fig. 4). Lamellae flat, totally in contact with preceding 

surfaces, unevenly spaced, more crowded lateraUy 

than centrally. Beaks and umbos worn; early ornamentation unknown.

Cardinal area. Cardinal area elongate, subtriangular 

in specimens that have short dorsal margin (pi. 5, fig. 

2), grading to subrectangular (pi. 5, fig. 1); height 

greater than length. Hinge line moderately long, 

slightly curved (concave ventrally), not parallel to 

dorsal margin; angle between them acute (pi. 5, fig. 3), 

averaging 36°. Hinge line rarely perpendicular to 

axis of midcardinal fold or resilifer; angle between 

them acute (pi. 5, fig. 1). Apically, cardinal area 

curved posteriorly to varying degrees, depending on 

curvature of umbone and beak (pi. 5, fig. 2). Average 

measurements, cardinal area: height, 112.4 mm; 

length, 99 mm.

Cardinal area of right valve includes prominent 

midcardinal fold bounded by deep, narrow lateral 

cardinal troughs (pi. 4, fig. 9). Midcardinal fold 

elongate, narrow, subtriangular to rectangular; height 

two to three times width, sides typically straight and 

subparallel to gently diverging (pi. 4, fig. 9; pi. 5,

fig. 1). Fold highly arched and has greatest convexity 

ventrally; top flattened to slightly convex; sides steeply 

reclined to vertical; ventral termination irregularly 

rounded; vertical to moderately inclined ventral flank. 

Lateral cardinal troughs narrow, deep, steep sided, 

elongate; bounded medially by flanks of midcardinal 

fold, laterally by raised, thickened marginal rim of 

valve. Anterior cardinal trough broader than posterior 

(pi. 4, fig. 9); individual trough width variable from 

place to place and from specimen to specimen. Anterior trough narrowest dorsally, broadest medially, 

becoming narrow again ventrally (pi. 4, fig. 9). Ventral one-half of posterior trough exceptionally narrow; 

dorsal one-half somewhat flared and shallower on 

individuals lacking well-defined auricle (pi. 4, fig. 9), 

abruptly flared and much shallower, with gently inclined lateral margin, on individuals having \v elldeveloped posterior auricle (pi. 5, fig. 1). Both troughs 

narrow abruptly and become shallow at dorsal extremity. Posterior trough somewhat deeper than anterior 

trough on majority of specimens, and continuous with 

slightly depressed area in dorsoposterior valve floor 

marking position of concealed muscle attachment area 

(pi. 4, fig. 9).

Cardinal area of left valve includes central resilifer 

and narrow lateral cardinal folds or platforms (pi. 5, 

fig. 2). Resilifer deep, elongate; height two to three 

times width; outline subtriangular, slightly flared 

ventrally (pi. 5, fig. 2). Depth of resilifer and convexity of lateral cardinal folds increase ventrally. 

Floor of resilifer broadly rounded; sides steep to vertical, overhanging at contact with lateral cardinal 

folds (pi. 5, fig. 2). Average measurements of resilifer: 

maximum width (ventral), 45 mm; terminal (ventral) 

depth, 27 mm; ratio of depth to width 0.61:1. Lateral 

cardinal folds narrow, equalling not more than one-half 

the width of the resilifer (pi. 5, figs. 2, 3); posterior 

fold broadest. Folds slightly to moderately and 

asymmetrically arched, rarely flattened; steepest flank 

of lateral cardinal folds adjacent to resilifer. Anterior 

fold bounded laterally by overlapping lamellar calcite 

plates which protrude from thick lateral edge of valve 

(pi. 5, fig. 3). Posterior lateral cardinal fold bounded 

ventrally at its outer edge by similar lamellae (pi. 5, 

fig. 3), but, in presence of well defined auricle, is expanded and merges dorsoposteriorly with infolded shell 

surface of auricle; rarely, posterior lateral cardinal 

fold is separated from infolded shell surface of auricle 

by a shallow sulcus (pi. 5, fig. 2). Both lateral cardinal 

folds terminating ventrally in a shelf overhanging floor 

of valve, forming shallow to moderately deep subcardinal cavities on either side of resilifer.

Surface markings on cardinal area of both valves 

consist of moderately prominent unequal widely and

729-809 O - 64 - 2
H10 CONTRIBUTIONS TO PALEONTOLOGY

irregularly spaced incised horizontal lines and raised 

ridges, commonly associated with faint color banding. 

Horizontal structures transgressed at right angles by 

very fine crowded subequal raised vertical lines that 

are continuous across the fine horizontal ornament and 

discontinuous across major elements (pi. 5, fig. 3). 

Rest of shell interior smooth.

Denticles. Denticles present on 85 percent of valves 

examined. On majority of specimens, denticles situated on dorsolateral margins of shell adjacent to, but 

outside of, commissure (pi. 4, fig. 5); rarely present on 

commissure or internally (pi. 5, fig. 3). Denticles faint 

to moderately prominent on lateral valve margins, 

medium sized, crowded (averaging 9.3 in 10 mm), 

narrow, elongate perpendicular to plane of commissure, 

more numerous on lateral edges of some calcite lamellae 

than on others, and commonly discontinuous across 

major sets of lamellae (pi. 4, fig. 5). Where present on 

internal surface of valve, denticles limited to a shallow 

trough just inside or on commissure (pi. 5, fig. 3), 

moderately prominent, subequally spaced, crowded, 

elongate perpendicular to margin of shell. Extent of 

denticulate lateral valve margin variable, typically 

about one-half total height of valve (averaging 55 

percent of margin denticulate); denticles become 

fainter and more irregularly spaced ventrally.

Muscle scar. Monomyarian. Terminal adult posterior adductor muscle scar not discernible on interior 

surface of any observed valve, probably posteroventral 

in position. Abandoned scar observed on two specimens in posterodorsal quadrant of valve, just below 

posterior one-half of resilifer and posterior lateral 

cardinal fold (pi. 5, fig. 2); scar originally obscured by 

covering of innermost calcite lamellae of subnacreous 

layer (pi. 5, fig. 2: peeled off for observation). Open 

lamellar structure underlies muscle scar in many shells, 

but somewhat caved on a few specimens (pi. 4, fig. 9). 

Scar, or insertion area, large, subovate, flat to very 

slightly concave; surface of area covered with fine to 

medium, thin, flat, overlapping calcite lamellae; 

lamellae irregularly spaced, crowded to sparse; their 

traces parallel those of exterior growth lines and 

lamellae. Attachment scars of Quenstedt's muscle 

just ventral from resilium or midcardinal fold, slightly 

posterior to midline. Attachment to small elevated 

knob in left valve, to small axially elongate trough in 

right valve.

Shell structure. Nacreous layer and periostracum 

not preserved. Hypostracum confined to area of muscle 

attachment, not well preserved, and not studied in 

detail. Thick shell composed predominantly of subnacreous layer consisting of numerous subparallel 

horizontal sheets of calcite, tightly packed throughout 

most of shell; open lamellar structure common in area

of muscle attachment. Subnaoreous layer composed 

of two types of calcite layers, generally alternating; 

thick lamellae of coarsely crystalline calcite (average 

thickness 0.8 mm) separated by thin chalky layers, 

possibly remnants of former nacreous layers.

REMARKS

This remarkable species is the largest known ostreid 

from Mesozoic rocks of North America, as well as one 

of the earliest known modern types of Crassostrea. It 

is further unique in the massive development of the 

cardinal structures and, particularly, in the nature and 

position of the muscle scar.

It is difficult to interpret the absence of a muscle 

scar on large valves. The area of muscle insertion is 

visible on only 2 of 16 specimens. In both specimens, 

the area is large and shallow and is situated dorsally 

just below the posterior cardinal area, and was at one 

time covered by a few thin plates of lamellar calcite 

(pi. 5, fig. 2). On some specimens, the inner surface 

of the valve is caved over the covered scar (pi. 4, fig 9), 

and this caving indicates an open lamellar structure in 

the underlying shell layers. This structure in the area 

of muscle insertion is typical of many Ostreidae.

The observed muscle scars probably do not represent 

the last formed attachment area on the adult shell, 

but rather are remant scars on the muscle track. The 

normal position of the terminal adult attachment area 

in Crassostrea, including soleniscus, is in the posteroventral quadrant of the shell, near the posterior margin. On large, nearly complete specimens of C. cusseta, 

there is no discernible insertion area anywhere on the 

inner valve surface (pi. 4, fig. 9, pi. 5, fig. 3); the absence of a discernible insertion area denotes either 

that the terminal scar left no impression or that it is 

covered by the innermost calcite lamellae of the valve 

interior. On all specimens on which the position of 

the scar could be determined, either by peeling away 

shell layers or by noting a caved zone in the floor of 

the valve, the position of the scar was dorsoposterior; 

this is atypical of its final position in Crassostrea.

The lack of any discernible muscle scar on the interior surface of large Crassostrea cusseta valves can be 

explained in two ways. Either large old shells lacked 

a functional posterior adductor muscle, perhaps owing 

to atrophy, or the stress on the posterior adductor was 

so limited while it was performing its function that the 

muscle did not require a normal type of attachment 

area and inserted without leaving a trace on the smooth 

interior valve surface. An atrophied muscle seems a 

more practical explanation. Even the largest individuals of other giant oysters we have examined from 

Cretaceous, Tertiary, and Recent deposits have a welldefined insertion area, generally marked by prominent
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN Hll

lines, grooves, or overlapping lamellae. Although the 

insertion area decreases in prominence with age on 

many species, we can find no examples of it becoming 

so faint as to be indistinguishable on the valve floor. 

On the largest and most complete valves of C. cusseta, 

only the ventral tip of the valve is missing, and the 

floor of the valve is completely exposed. Even the 

faintest trace of an insertion area should be evident, 

were it present. There is little possibility that the 

insertion area was limited to the most ventral part of 

the valve; no known oysters have an insertion area so 

situated.

We therefore assume that the absence of a muscle 

scar on the interior surface of large adult valves indicates atrophy of the adductor muscle and subsequent 

covering of the last formed scar by additional layers of 

calcite during late maturity and old age. Unfortunately, small adult specimens of this species are not yet 

known, and we cannot ascertain precisely at what 

point the scar disappeared. The thin covering over the 

insertion area on the two large valves in which the 

muscle scar was observed indicate that it was obscured 

late in the developmental history of the oyster. It is 

probable that this is a gerontic feature of the species. 

Unless the mantle margins became modified at this 

time, it is douotful whether the oyster lived long after 

atrophy of the adductor muscle. Inactivation of the 

muscle would probably produce continual gaping of the 

shell, considerable inflow of clastic detritus, especially 

in turbid waters, and eventual clogging of the gills.

Crassostrea cusseta n. sp. belongs to a generalized 

and conservative lineage of oysters characterized by 

relatively smooth elongate massive shells, strong 

development of the cardinal structures, large shallow 

posteroventrally situated muscle scars, and deeply 

cupped left valve. The lineage had its beginnings in 

the early forms of C. soleniscus (Meek) and is probably 

represented today by C. virginica (Gmelin) on the 

Atlantic Coast. C. cusseta is the culmination of the 

lineage in Cretaceous rocks of North America. Another 

crassostreid stock, represented by C. subtrigonalis 

(Evans and Shumard) and C. glabra (Meek and Hayden), occurs in even younger Cretaceous rocks of the 

northern Western Interior (Upper Santonian and 

Maestrichtian). Both crassostreid lines transgress the 

Cretaceous-Tertiary boundary with little basic change 

and have modern counterparts.

The known representatives of the C. soleniscus lineage 

are characterized in their evolution by a gradual increase in size from their origin to the development of 

C. gigantissima of the Eocene. Younger crassostreids 

which apparently belong to the same lineage are smaller 

and more variable and have somewhat less massive

shells. A gradual loss of denticles in adult shells of 

successively younger species is another notable trend. 

Denticles are well developed on young and adult 

valves of C. soleniscus and cover much of the dorsolateral and lateral margins. In C. cusseta the denticles 

are more restricted on the dorsolateral margins and 

migrate to the lateral edge of the valves on most large 

adults. The young of C. gigantissima are sparsely 

denticulate, whereas the adults lack denticles. Modern 

massive crassostreids, like C. virginica, rarely have 

denticles on the dorsolateral margins of the immature 

valve and completely lack them on the adult valve.

On the basis of shell characters which modern 

neontologists consider significant to ostreid classification, C. cusseta and other members of the lineage must 

be placed in Crassostrea. They possess the elongate 

large, massive shell typical of the genus; a deeply 

cupped left valve between the muscle scar and the 

cardinal area; a posteroventrally situated muscle scar 

(this is the assumed position of the terminal scar in 

C. cusseta}; subcardinal cavities; a thick elongated 

cardinal area; and a shell composed predominantly 

of superimposed nonvesicular, nonchalky layers of 

lamellar calcite (subnacreous layer).

COMPARISON WITH OTHER SPECIES

Crassostrea cusseta most closely resembles the youngest representatives of C. soleniscus Meek, an older 

species from which it was probably derived. The two 

are very similar in general shape, convexity, and 

development of the cardinal structures.

Crassostrea cusseta can be readily distinguished from 

C. soleniscus. It attains a larger size, has a relatively 

broader shell, and is much less variable in form than 

the older species. The average form and the range of 

variation of each species is distinct. C. soleniscus 

is characteristically very narrow, elongate, and straight, 

ranging to somewhat arcuate or broad and rounded, 

and has an exogyroid beak (Stephenson, 1952, pi. 16, 

figs. 1-4; pi. 17, figs. 7-10); C. cusseta is predominantly 

strongly curved posteriorly, or is subcrescentic, and 

does not attain the rounded form. Its beaks and umbos 

are blunt, broad, and flat and do not develop exogyroid 

coiling. C. soleniscus commonly has a narrow, attenuated, or sharply rounded dorsal margin. A small 

posterior auricle is rarely developed in C. soleniscus 

and, where present, is usually confined to rounded 

exogyroid variants. The auricle is formed in this 

species by outward and upward flaring of the posterior 

lateral cardinal margin. C. cusseta commonly develops a larger and more prominent posterior auricle. 

On the left valve, the auricle is formed by acute inbending of the lateral shell margin; on the right valve, 

by lateral expansion of the posterior lateral cardinal
H12 CONTRIBUTIONS TO PALEONTOLOGY

trough and infolding of the lateral rim of the trough. 

Concentric lamellae are more numerous and more 

crowded on C. soleniscus than on C. cusseta and are 

transgressed on the umbos of small to moderate size 

individuals by fine costae. Costae have not been 

observed on C. cusseta.

Comparison of shell interiors reveals other distinctions 

between the two species. The most conspicuous difference is in the nature and position of the posterior 

adductor muscle scar central to posterocentral and 

not covered in C. soleniscus, dorsoposterior and covered 

with lamellae on large valves of C. cusseta. The right 

and left cardinal areas of C. soleniscus are shorter and 

more curved than those of C. cusseta, and the midcardinal fold is relatively larger, diverging at a greater 

angle, and is less convex. Lateral cardinal troughs 

are very shallow or are commonly not developed in 

C. soleniscus; there is no well-defined lateral brim 

bordering the troughs or the central cavity of the shell. 

The right valves of C. soleniscus are, consequently, 

much shallower than those of C. cusseta, and, in some 

specimens, have a flat or . convex interior surface.

The left valve of C. soleniscus has a larger, broader, 

shallower, and more rapidly expanding resilifer than 

does the equivalent valve of C. cusseta. In addition, 

the resilifer of C. soleniscus is not well delineated from 

the lateral cardinal folds, and the folds themselves are 

narrower and flatter than those of C. cusseta. The 

folds slope into, rather than away from, the resilifer. 

The lateral edges of overlapping surface lamellae do 

not form a marginal brim for the cardinal area in C. 

soleniscus, and there is no sulcus or groove separating 

the posterior lateral cardinal fold from the outer part of 

the auricle. Subcardinal cavities are rarely developed 

in C. soleniscus.

Denticles occur in both species, but they are smaller, 

more crowded, more commonly situated on the valve 

interiors or commissure, and less extensive on the 

dorsolateral margins of C. soleniscus.

Large massive oysters apparently related to C. cusseta 

also occur in the European Cretaceous. One of the 

most closely comparable species is Crassostrea^. pantagruelis (Coquand) (1869, pi. 68, figs. 1, 2), which has a 

similar massive elongate shell, a dorsally situated 

muscle scar, and even greater development of the 

cardinal structures than has C. cusseta. Numerous 

details of the cardinal area, the exposed muscle scar 

of large adult shells, and the more curved, attenuated 

beak and umbo of the European species easily distinguish the two forms.

Crassostrea gigantissima (Finch) can be distinguished 

from C. cusseta by its well-defined, more ventrally 

situated muscle scar, less massive cardinal area, lack 

of denticles in the adult valve, lack or poor development of auricles, and fine radial sculpture on the dorsal 

part of many shells. Lateral cardinal troughs are not 

well defined in C. gigantissima.

OCCURRENCE

Localities for Crassostrea cusseta:

USGS Mesozoic loc. 25563: Upper Cretaceous, upper part of 

the Blufftowri Formation, Chattahoochee River, bluff at 

Florence, Stewart County, Ga. First concretionary 

layer and b?low. Collected by L. W. Stephenson and 

N. F. Sohl, Mar. 17, 1955.

USGS Mesozoic loc. 5902: Upper Cretaceous, Cusseta Sand, 

Chattahoochee River, opposite Woolridge landing, about 

15 miles above Eufaula, Ala., on the Georgia side of the 

river. Collected by L. W. Stephenson, 1909. 

USGS Mesozoic loc. 26027: Upper Cretaceous, Cusseta Sand 

(S-351), Chattahoochee River, west bank, below old 

Woolridge landing, 13.6 miles above Eufaula, Ala., 1 mile 

below the mouth of Roods Creek, sec. 18, T. 12 N., R. 

30 E., Harbour County, Ala. Collected by N. F. Sohl 

and H. I. Saunders, Nov. 7, 1955.

USGS Mesozoic loc. 28541: Upper Cretaceous, Cusseta Sand 

(S-95S), near old Woolridge landing, bluffs on west side 

of Chattahoochee River about 13.6-13.7 miles above 

Eufaula landing in Barbour County, Ala. Collected by 

N. F. Sohl, R. L. Rieke, and H. R. Bergquist, Oct. 26, 1961. 

USGS Mesozoic loc. 5396: Upper Cretaceous, Cusseta Sand, 

Chattahoochee River, Roanoke Bluff, just below Woolridge landing, west bank, about 15 miles above Eufaula, 

Ala. Collected by L. W. Stephenson, July 22, 1907. 

USGS Mesozoic loc. 26029: Upper Cretaceous, Cusseta Sand 

(S-327), Old Seale-Eufaula Road bridge over the Middle 

Fork of Cowickee Creek, 8.05 miles north of intersection 

of U.S. 241 and first bend of the creek upstream from 

the bridge, sec. 18, T. 12 N., R. 29 E., Barbour County, 

Ala. Collected by N. F. Sohl and H. I. Saunders, 

Oct. 30, 1955.

Crassostrea cusseta is most commonly found in Upper 

Cretaceous rocks of the Chattahoochee River region in 

Georgia and Alabama. With the exception of one 

fragmentary specimen (USGS Mesozoic loc. 25563) 

from the upper part of the Blufftown Formation, the 

species is restricted to the basal beds of the Cusseta 

Sand (fig. 1). C. cusseta occurs throughout 60 feet of 

sand and silt in this sequence.

The Blufftown specimen (USGS Mesozoic loc. 25563) 

came from beds in the lowermost part of unit 2 of 

Veatch and Stephenson's Florence Bluff section (1911, 

p. 155-156). Stephenson considered these beds as the 

lowest part of an expanded Ripley Formation that 

included the Cusseta Sand Member at its base. Subsequently this unit was placed first at the base of the 

Cusseta Sand (Cooke, 1943, p. 25) and then, later, in 

the upper part of the Blufftown Formation (Eargle, 

1955, p. 36, 47). Disagreement as to the placement 

of this unit was the result of miscorrelation by Stephenson and Veatch of unit 2 with the fossiliferous units 

near Woolridge landing, several miles downstream on 

the Chattahoochee River.
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H13

Crassostrea cusseta is most abundant near Woolridge 

landing in Barbour County, Ala. (USGS 5902, 26027, 

28451). Here it is concentrated in a 1-foot-thick zone 

in the middle of a 4-foot poorly sorted gray clayey, 

silty sand unit containing abundant worn shells and 

bone fragments. This unit is the basal bed of the 

Cusseta Sand and here overlies a clean unfossiliferous 

buff-colored crossbedded medium-grained sand. The 

contact of the two beds is undulatory, the undulations 

having a vertical magnitude of about 1 foot in a 

lateral distance of 15 feet. Specimens collected by 

Stephenson at Roanoke Bluff (USGS 5396) are from 

the same zone.

Crassostrea cusseta also occurs in the basal bed of 

the Cusseta Sand exposed on the Middle Fork of 

Cowickee Creek (USGS 26029), a tributary of the 

Chattahoochee River, Barbour County, Ala. As noted 

by Monroe (1941, p. 92), this bed contains worn shells, 

bones, and shark teeth.

The species is questionably represented in the Black 

Creek Formation of North Carolina by a large incomplete specimen figured by Stephenson (1923, pi. 37). 

Apparently Stephenson (1923, p. 141, pi. 36) regarded 

this and several other incomplete figured specimens as 

C. cusseta:

A large species of oyster which I regard as identical with an 

undescribed species from the Ripley Formation (upper part of 

the Exogyra ponderosa zone) on [the] Chattahoochee River 

(Ga.-Ala.), at Woolridge landing (5396, 5902), and at Florence 

(5395), has been found at two localities in North Carolina.

The large specimen illustrated by Stephenson 

(1923, pi. 37) is comparable to C. cusseta in size, shell 

thickness, and inferred valve curvature but is too 

incomplete to allow definite identification. The smaller 

specimens illustrated by Stephenson (1923, pi. 36, figs. 

1-4) from the Snow Hill Marl Member of the Black 

Creek Formation differ from C. cusseta by having 

strongly curved and more attenuated beaks and umbos 

and by having narrower cardinal areas; the two forms 

also differ in the development of various cardinal structures and in the position and exposed nature of the 

muscle attachment area. In these respects, the Snow 

Hill specimens are more nearly like C. soleniscus Meek, 

a species ancestral to C. cusseta.

TYPES

Holotype, a large, nearly complete left valve (pi. 5, 

figs. 3, 4) characteristic of the species, from the Cusseta 

Sand along the Chattahoochee River, below old Woolridge landing, Barbour County, Ala. (USGS Mesozoic 

loc. 26027); USNM 132057. Illustrated paratypes 

from the Cusseta Sand, USNM 132058-132061 inclusive. Measured, unillustrated paratypes from the 

Cusseta Sand, USNM 132062a, b; 132063 a-c; 132064

a-d. Unmeasured, unfigured paratypes used in description of species, from the Cusseta Sand, USNM 

132065a, b; 132066 a-c: from the Blufftown Formation, 

USNM 132067.

Genus ARCTOSTREA Pervinquiere: emended

1910a. Pervinquiere, Leon, Observations sur la nomenclature 

des Ostraces: Soc. geol. France Bull., ser. 4, v. 10, p. 

645, 646.

1910b. Pervinquiere, Leon, Ostrea carinata: Paleontologia Universalis, ser. 3, p. 197.

Type species. Ostrea carinata Lamarck, by original 

designation.

DIAGNOSIS

Shell normally small to moderate, elongate, narrow, 

falciform, highly inequilateral, strongly recurved medially or ventrally, subequivalved; left valve slightly 

larger and more convex than right valve; valves highly 

convex and have diamond to quadrate cross section. 

Small anterior and posterior auricles commonly developed dorsolaterally. Narrow crest (midline) of 

valves flat to narrowly rounded; lateral flanks steep, 

intersecting plane of commissure at 45°-90°. Adult 

ornament equally developed in both valves. Ornament 

along crest consists either of a sinuous central plication 

or of a complex of bifurcating sinuous plicae and costae 

arising from the midline, from which originate subequally developed, evenly spaced, moderate-size plicae 

that extend from the flanks to margin. Commissure 

trace zig-zag to sharply undulating; margin deeply incised at intersection with each plication. Beak small, 

opisthogyre, moderately curved. Cardinal area consists of well-defined triangular central resilifer and 

subequally to unequally developed lateral cardinal 

plates. Lateral margins have simple ovoid to elongate denticles. Muscle scar dorsoposterior, comma 

shaped, commonly incised, conspicuous, bordered by 

prominent lip. Shell lamellate, having individual 

lamellae composed of reticulate pattern of prominent 

vertical and very thin horizontal calcite plates.

REMARKS

Arctostrea, which was proposed as a subgenus and 

which has since been used as a genus, subgenus, or 

section of Ostrea and Lopha (=Alectryonia), appears to 

deserve generic ranking on the basis of its shell form, 

cross section, and unique ornamentation pattern, and 

on the basis of the development and the dorsal position 

of its posterior adductor muscle scar. No other superspecific taxa approach this genus in all these respects, 

and the genus is not represented among modern oysters. 

Eastellum Schrbter, in the sense of Faujas-Saint-Fond
H14 CONTRIBUTIONS TO PALEONTOLOGY

(1799, pi. 28, fig. 7), is most closely related to Arctostrea. It differs by having a relatively flat posterior 

flank, a rounded crest, and a greatly expanded posterior 

auricle; it also differs in details of the ornamentation 

pattern. Further, the validity of Rastellum is in doubt. 

The problem is currently being investigated by Dr. 

H. B. Stenzel.

We are restricting the use of Arctostrea in this study to 

forms resembling the type species Arctostrea carinata 

(Lamarck). We do not include within the genus 

oysters like Rastellum of Fauj as-Saint-Fond or palmate 

forms such as Ostrea travisana Stephenson and Ostrea 

subovata Shumard. These species have marginal 

variants which externally attain the general ornamentation pattern and narrow curved form of Arctostrea, 

but they lack the wide thick shells, with their diamondshaped or subquadrate cross section, so typical of 

Arctostrea; further, the detail of the ornamentation 

and internal characteristics differ considerably. Rare 

varieties of Arctostrea attain a palmate form externally, 

owing to flaring of the posterior margin (pi. 4, fig. 3); 

but even these forms retain the narrow, closely spaced, 

typically curved internal shell margins of Arctostrea 

(pi. 4, fig. 4). Similarly shaped forms, such as 0. 

travisana, are equally as broad internally as externally. 

The palmate form in Arctostrea is probably produced 

by crushing and overturning of the normally vertical 

posterior margin or in crowded growth situations that 

limit convex growth of the shell. Arctostrea, and forms 

closely related to it (Rastellum, the 0. travisana lineage), 

appear to have had a common ancestry in the Jurassic. 

During the Cretaceous the two branches evolved concurrently and separately; rarely they produced somewhat 

similar forms that reflected their common ancestry; 

they never merged, however, through an intermediate 

morphologic series of forms.

Arctostrea aguilerae (Bose)

Plate 1, figures 1, 2; plate 2, figures 1-4; plate 3, figures 1-7; 

plate 4, figures 1-4, 6-8

1906. Ostrea (Alectryonia) Aguilerae Bose, Mexico Inst. Geol. 

Bol. 24, p. 47; pi. 2, fig. 2; pi. 4, fig. 5; pi. 6, figs. 1, 2.

1925. Arctostrea atkinsi Raymond, Boston Soc. Nat. History 

Occasional papers, v. 5, p. 183-185, pi. 7, figs. 1, 2.

MATERIAL

Thirty complete and fragmentary specimens from 

11 localities in Mexico, Cuba, Alabama, Mississippi, 

and Texas (Upper Cretaceous: Upper Campanian, 

Lower Maestrichtian). Three specimens consist of 

articulated complete valves. The remainder are about

equally divided between well-preserved to fragmentary 

right and left valves.

GENERAL FORM

Summary of measurements presented in table 2. 

Shell exceptionally large and massive, somewhat 

inequivalved; left (lower, attached) valve commonly 

thicker and more massive than right (upper, free) 

valve; valves close fitting, interlocking along strongly 

plicate margin; valves inequilateral, moderately to very 

strongly curved posteriorly; dorsal inclination typically 

opisthocline, average angle 52°. Length somewhat 

greater than height: average ratio 1.08:1; average 

measurements of adult specimens: height, 161 mm; 

length, 151 mm; thickness of left valve, 51 mm; 

thickness of right valve, 47 mm.

TABLE 2. Summary of measurements for Arctostrea aguilerae

(Bose)

Character

Valve length, actual, along midline (LM) 

millimeters.. 

Valve height (H)_ ... _ do_ 

Ratio H:LM. _________ _ __ do __

Ratio L:H____ _-. ... 

Maximum thickness:

Maximum width:

Number of ribs, on anterior margin __ ...

On posterior margin. _ . . _ . _ ..

Number of millimeters per rib:

Posterior auricle: 

Height (HA)...... ......do - 

Length (LA) ___________ do . 

Angle of inclination (Ti) :

Dorsal half of shell (Di)___. ... do . 

Length of hinge line (LHL) _ millimeters..

Ratio length of hinge line to height of 

cardinal area (LHL:HOA) _ __ ... .....

Width of resilifer (WR):

Left valve _ ., _ ___ _ .do. ..

Muscle scar: 

Height (HMS). .do 

Length (LMS).. .... do 

Number 

of specimens

10 

10

10

10

10

6

6

5

5

10

10

8

8 

5

9

12 

12

10

6

6

 7 

7

11

Range

196-352 

116-186

0.57-0.90:1

119-200

30-71

33-76

71-115

66-87

23-49

16-31

4.4-8.3

5 0 Q 7

26-46 

12-34

25-92

94-142 

34-63 

20-58

0.93-2.0:1

12. 8-28. 3

13. 2-29. 6

25-46 

17-22

28-47

Average

250 

161

0.66:1

151

1.08:1

51

47

87

77

30.2

21.8

6.5

8.0

33

22

52°

118° 

52 

39

1.43:1

21

19

36 

20

33

Valves elongate, generally curved toward posterior, 

crescentic to fishhook shaped in outline. Point of 

maximum curvature usually %-% midline length from 

dorsal margin. Dorsal margin straight to subcentrally 

angulate, not parallel to hinge line; dorsolateral margins 

narrowly rounded; dorsoanterior margin straight to 

somewhat rounded; dorsoposterior margin roundly to 

irregularly convex at auricle, concavely recessed below 

auricle. Lateral margins moderately to strongly curved 

medially, subparallel to decidedly convergent toward 

point of greatest curvature (anterior convex; posterior 

straight to somewhat concave), usually well curved and
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H15

subparallel ventrally; ventral margin narrowly rounded 

to subangulate.

Right and left valves highly convex; greatest convexity near point of maximum curvature, sloping to 

plane of commissure more gently dorsally than ventrally. 

Crest broadly arched; anterior slope usually vertical 

to steeply inclined outward; posterior slope overhanging to steeply inclined outward. Well-defined umbonal 

ridge bisects umbone, continues ventrally posterior to 

midline as axis of origin for primary plicae.

DESCRIPTION

Beaks and umbo. Beak worn or obscured on all 

specimens. Umbo, if not obscured by attachment 

scar, bears median, curved, round-topped ridge; umbo 

opisthogyre, moderately curved for approximately 

one-half whorl.

Posterior auricle. Posterior auricle well formed on 

majority of specimens. Auricle irregularly semicircular, small to proportionally large. Auricle of right 

valve formed by expansion of posterior cardinal trough 

margin, in some specimens in conjunction with moderate upfolding of dorsolateral shell margin; auricle 

bounded laterally by shell margin and medially by 

lateral cardinal trough. Auricle of left valve formed by 

lateral expansion of posterior marginal cardinal trough 

and corresponding moderate to strong infolding of 

dorsolateral shell margin. Variation in size of auricle 

great. Average measurements of auricles on adult 

specimens: height, 33 mm; length, 22 mm.

Attachment area. Attachment area small to medium 

size (maximum size noted; height, 24 mm; length, 72.4 

mm), situated dorsoposteriorly, in some specimens 

extending onto auricle. Outline irregularly oviform; 

area not normally well defined.

Ornamentation. Ornamentation of both valves consists of numerous round-crested narrow chevronshaped plicae that are irregularly accentuated to 

spinose projections or flutings at their intersection with 

lamellar growth rugae. Plicae arise by bifurcation and 

intercalation from a discontinuous subcentral plica 

that originates as an umbonal ridge, at midlength and 

toward the ventral margin, medial plica commonly 

forms high point of broadly arched upper valve surface 

and is close to steep posterior slope. Plicae finest 

dorsally, increasing in prominence ventrally over arched 

upper surface. Plicae of dorsolateral flank closely 

spaced and low, terminating at commissure in narrow, 

shallow alternating sulci and plicae. As shell thickens 

toward point of maximum valve curvature, plicae become more prominant, and valve flanks steepen, 

becoming vertical, continuation of plicae on vertical 

or highly inclined flanks forms low undulations, exposing chevron-shaped lamellar calcite plates; plicae 

gently arcuate ventrally, directed over flanks to commissure; Chevron-shaped terminations of imbricate 

plicae tightly interlock with corresponding V-shaped 

sulci of interplical area of opposite valve. Concentric 

sculpture consists of growth lines and overlapping 

lamellae. Average number of plicae: anterior margin, 

30.2; posterior margin, 21.8. Average width of plicae 

at shell margin: anterior margin, 6.5; posterior margin, 

8.0.

Internal impression of sculpture restricted to large 

crenulations on narrow raised valve margin. Plications narrowest, lowest, and most closely spaced on 

dorsolateral margin and at posterior margin at point of 

greatest valve curvature.

Cardinal area. Cardinal area longer than high 

(average ratio 1.43 :1), sub triangular to subrectangular. 

Length of hinge line variable, from about % to % midline 

valve length. Hinge line not parallel to dorsal margin; 

angle between them acute, from 20° to 45°; angle between hinge line and axis of resilifer acute, from 35° to 

68°. Apically, resilifer curves posteriorly, curvature 

increasing dorsally. Average measurements, cardinal 

area: height, 39 mm; length, 52 mm.

Cardinal area of right valve comprises posteriorly 

curving triangular central resilifer, higher than wide, 

bordered by low, raised, flat-topped, equally to subequally broad, lateral cardinal platforms. Resilifer 

shallow; base very broadly rounded; sides steepest 

dorsally, more gently sloping ventrally. Average 

measurements of resilifer: maximum width, 21 mm; 

depth seldom exceeds 2 mm. Lateral cardinal folds 

quadrate in cross section and almost as wide to wider 

than resilifer; posterior fold usually broadest. Folds 

normally flat topped, less commonly gently arched; 

steepest margin borders resilifer. Anterior margin of 

lateral cardinal fold bounded by upturned lamellar 

plates of the lateral valve margin. Posterior lateral 

cardinal fold separated from auricle dorsoposteriorly 

by narrow, shallow to moderately deep incised sulcus. 

Ventral terminations of cardinal folds merge with 

valve floor or are raised moderately above it; subcardinal cavities poorly developed.

Cardinal area of left valve consists of posteriorly 

curved triangular resilifer, higher than wide, bordered 

by broad lateral cardinal folds or platforms. Resilifer 

shallow and broadly rounded to moderately deep and 

narrowly rounded. Sides of resilifer steepest dorsally, 

overhung slightly (pi. 1, fig. 2), gently sloping at ventral 

margin. Resilifer narrow dorsally, regularly expanding 

and becoming shallower ventrally. Average measurements of resilifer: width, 19 mm; depth, less than 5 

mm. Lateral cardinal folds quadrate in cross section, 

flat topped to broadly arched, narrower than resilifer;

729-809 O - 64 - 3
H16 CONTRIBUTIONS TO PALEONTOLOGY

taper dorsally. Medial flank of folds steepest anteriorly 

where sides may overhang resilifer. Lateral margin of 

anterior fold bounded by a narrow, deep to shallow, 

marginal cardinal trough (pi. 4, fig. 8); trough anteriorly 

bounded by upturned lamellae of shell margin. Posterior lateral cardinal fold broader than anterior fold on 

majority of specimens and bounded posteriorly by a 

narrow to moderately narrow steep sided marginal 

cardinal trough separating auricle from lateral cardinal 

fold (pi. 1, fig. 2; pi. 3, fig. 6; pi. 4, fig. 8). Lateral 

cardinal folds terminate ventrally in a shelf overhanging floor of valve in some specimens; form shallow 

to rather deep (pi. 3, fig. 6) subcardinal cavities.

Surface markings on cardinal area consist of unequal 

irregularly but closely spaced fine incised horizontal 

lines and coarser raised lamellar ridges; ridges coarsen 

on resilifer. Vertical cardinal sculpture consists of fine 

discontinuous microscopic lines. Remainder of shell 

interior smooth except for muscle attachment area.

Denticles. Most mature thick-shelled individuals 

lack denticles. Denticles present on only one adult left 

valve (pi. 2, fig. 3). Denticles raised, subulate in outline, elongate normal to the valve margin; extend along 

posterior margin from dorsal part of auricle to a point 

about midheight of muscle scar; denticles longest and 

most prominent over auricular area, dimmish in 

prominence ventrally; average number about 15 in 10 

mm on auricular margin, 20 in 10 mm in latitude of 

muscle scar.

Muscle scar. Monomyarian: posterior adductor scar 

situated dorsoposteriorly, almost entirely behind midline, near posterior margin. Scar large, lunulate; expands ventrally. Posterior, ventral, and anteroventral 

margins of scar raised above valve floor; form sharpedged ridge that on some specimens overhangs valve 

floor toward posterior valve margin and develops a 

trough between valve margin and muscle scar. Dorsoanterior margin of muscle scar broken on most specimens, broadly arcuate, continuous with valve floor; 

overhangs deep oblique incised muscle insertion area. 

Scar floor longitudinally ridged by edges of lamellar 

shell layers; ridges crossed obliquely or at right angles 

by raised overriding threads and cords having variable 

strength and spacing; cords strongest ventrally (pi. 4, 

fig. 7). Average measurements, muscle scar: height, 

36 mm; length, 20 mm; maximum diameter, 33 mm.

Shell structure. Periostracum not preserved; hypostracum not observed. Main body of shell composed 

of thick calcite plates separated by nacreous (?) lamellae; plates rather uniform in thickness at medial part 

of shell but alternately taper to a thin edge marginally 

(pi. 4, fig. 6). On weathered surface (pi. 4, fig. 2), 

plates form a cross-hatched pattern suggestive of a

vertical prismatic structure crosscut by secondary 

lamellae.

REMARKS

Like most ostreids, Arctostrea aguilerae (Bose) exhibits a wide variation in shape and outline. Insofar 

as is known, this variability is not due to crowding. 

The studied available specimens evidently lived as discrete individuals. Variation is most noticeable in the 

amount of valve curvature. The narrowest and least 

curved variety is well typified by Raymond's (1925, 

pi. 7) holotype of the synonymous Cuban species 

Arctostrea atkinsi and by another specimen from Cuba 

here figured on plate 3, figure 5. Bose's (1906, pi. 6, 

figs. 1, 2) syntype of Arctostrea aguilerae displays 

moderate curvature. The greatest curvature is in 

gulf coast representatives of the species (pi. 2, fig. 6; 

pi. 1, figs. 1, 2), in which the ventral extremity is so 

strongly recurved that it almost extends to the plane 

of the hinge line.

Transverse cross sections through the center of the 

shell of Arctostrea aguilerae are quadrate (pi. 4, fig. 6) 

and have vertical sides and a broadly arched upper 

surface. This growth form normally produces a 

slender ventral valve outline. However, several specimens have a flared ventral flank caused by skewed 

growth along a posteriorly inclined midline plane (pi. 

4, fig. 3; pi. 3, fig. 3), thus producing an overhung anterior slope and gentle posterior flank and giving a 

palmate appearance to the valve exterior. On such 

distorted shells, however, the interior margins of the 

commissure are subparallel and closely spaced, and 

they do not flare (pi. 4, fig. 4).

General surface sculpture is fairly constant, although 

some variation from the mean presented in our description was noted. Spines are present on all specimens 

but are erratically developed, ranging from low nodes 

on some specimens to elongate spinose projections extending 8 or 9 mm above the surface of the plicae on 

others. The surface of most specimens is partly worn, 

and the spines are not well preserved. The syntype 

figured by Bose (1906, pi. 6, fig. 2) has well developed 

spines, as do the specimens here figured on plate 1, 

figure 1; plate 2, figure 2. The plicae pattern varies 

primarily as a function of the shell shape. Rare shells 

that have a palmate posterior flank also have elongate 

continuous extensively bifurcating plicae. A similar 

pattern develops on thin-shelled specimens (Bose, 1906, 

pi. 2, fig. 2; pi. 2, fig. 2 herein).

COMPARISONS

Ostrea carinata Lamarck from the Cenomanian of 

France, the type species of Arctostrea, is smaller than 

A. aguilerae (Bose), rarely exceeding its holotype
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H17

(Pervinquiere, 1910b, p. 197, figs, a, b) in size (height 

about 73 mm). Like Arctostrea aguilerae, some specimens of A. carinata have a quadrate whorl cross section, and the plicae arise from a medial ridge by 

bifurcation. More commonly, the cross section is subquadrate, the upper surface narrowly subcarinate and 

the lateral slopes subparallel. The plicae are fairly 

uniform over the entire length of the shell and are 

raised, sharp crested, and continuous along the anterior 

slope, whereas they are lamellarly truncate in A. 

aguilerae. The amplitude of the commissure plications is proportionally greater on A. carinata than on 

A. aguilerae, but the rib spacing is proportionately 

narrower. Ribs on the type species range between 

3.5 and 4.8 mm in width on the anterior margin, 

whereas the same measurement ranges between 5.9 

and 8.7 (average 8.0 mm per rib) on A. aguilerae. 

Finally, the muscle scar of A. carinata is relatively 

closer to the hinge line than is that of A. aguilerae. 

Arctostrea columbrina, as figured by Pervinquiere 

(1910b, p. 198), closely resembles A. carinata and 

differs from A. aguilerae in essentially the same respects. 

Other common Upper Cretaceous European Arctostrea such as A. pectinata (Lamarck) (in part, of Woods, 

1913, p. 342) are all smaller and less massive than A. 

aguilerae. Some specimens of A. pectinata from the 

Santonian approach A. aguilerae in size but in cross 

section have a narrower upper valve surface with more 

inclined lateral flanks (Coquand, 1869, pi. 29, fig. 7). 

The surface ornamentation of A. pectinata consists of 

widely spaced sharp-crested plicae extending without 

lateral truncation to the commissure. Arctostrea serrata 

(Defrance) (Coquand, 1869, pi. 30, fig. 5) and A. 

zeitteri (Bayle) (Bayle, 1878, pi. 146, figs. 1, 2) have a 

carinate upper valve surface, subovate whorl cross 

section, and plicae which are not truncated on the 

flanks of the valves.

OCCURRENCE 

Localities in Mexico:

USGS Mesozoie loc. 28181 (7039): Northeast edge of town of

Cdrdenas, San Luis Potosi, Mexico. Orbitoides zone of

Wade's Canon Canada section. 

USGS Mesozoie loe. 38323 (FE 251): Rio Monte Bello, San Luis

Potosi, Mexico. Collected by Ing. Felipe Mendes

Munguia, May 31, 1961.

Bose (1906, p. 49) cited the type locality of Arctostrea 

aguilarae as "Cuesta de Nahual (Hacienda de la 

Palma, Distrito de Hildalgo, San Luis Potosi)," which 

lies about 20 km south of the village of Canoas on the 

Tampico-Cardenas railroad. Bose also noted that the 

species occurs in the vicinity of Canoas. The type 

specimens come from what he called the lower beds, 

which contain Exogyra costata, at the "Gryphaea

vesicularis horizon" (= Cardenas Formation, Lower 

Senonian). Bose was in error in assigning this zone 

to the Lower Senonian, as Exogyra costata is restricted 

to the Late Campanian and Early Maestrichtian.

Imlay (1944a, p. 1084, 1106) correlated the Cardenas 

Formation with the Maestrichtian and, in the same 

paper (p. 1138), reproduced a 5570-foot stratigraphic 

section of the Cardenas Formation as measured by 

Bruce Wade in Canon Canada, about 3.22 km southeast 

of Cardenas. The specimens of Arctostrea from the 

Cardenas area studied for the present paper can be 

fitted into Wade's section, and all come from above his 

"Coon Creek horizon" of unit 9.

Collection 28181 comes from rocks equivalent to the 

Orbitoides zone of Wade's section, a unit about 650 feet 

thick (units 11-28 of Imlay's 1944a reproduction). 

This zone occurs above beds that contain a lower 

Exogyra costata zone fauna and appears to be a correlative of the Nacatoch Sand of Texas or of the Ripley 

Formation of the east Gulf Coastal Plain.

Fossils associated with A. aguilerae from USGS 

Mesozoie loc. 38323, such as Veniella conradi (Morton) 

and Idonearca cf. /. deatsvillensis Stephenson, are also 

typical of the Exogyra costata zone. The exact level, 

in terms of Wade's section, from which the type specimens were collected is not known. The associated 

fossils, however, tend to indicate a stratigraphic position somewhat higher (units 32-56) than that at the 

preceding two localities but still within the E. costata 

zone.

As here interpreted, in the type area in San Luis 

Potosi, Arctostrea aguilerae ranges through beds that 

are no older than Latest Campanian and are as young 

as Early Maestrichtian.

Localities in Cuba (all collections by R. H. Palmer, 

1929-33): 

USGS Mesozoie loc. 27127 (Palmer loc. 51): Finca de Guanajita,

9 km west of Santa Clara and crossing 3 km south of

Carratera, Santa Clara Province, Cuba. 

USGS Mesozoie loc. 27126 (Palmer loc. 51a): La Lomita near

Guanajita, Santa Clara Province, Cuba. 

USGS Mesozoie loc. 27173 (Palmer loc. 907): Batey Jesus Maria

and continuation of same hill, 2 km to west and 1.29 km

southwest of Matanzas, Matanzas Province, Cuba. 

USGS Mesozoie loc. 27175 (Palmer loc. 911): 1 km southwest of

central Jesus Maria, Matanzas Province, Cuba. 

USGS Mesozoie loc. 27198 (Palmer loc. 1145): Northwest of

Dos Hermandos, 1 km on road to Abreus, Santa Clara

Province, Cuba.

The occurrence of A. aguilerae in Cuba was first 

noted by Raymond (1925), who described it as a new 

species, Arctostrea atkinsi. Raymond's description was 

based on three fragmentary right valves from well 

spoils. The well was on the Santa Rosalia property, 

near the Harvard University Botanical Gardens, 

southeast of Cienfuegos in Santa Clara Province.
HIS CONTRIBUTIONS TO PALEONTOLOGY

Plaster casts of the holotype are available in the collections of the U.S. National Museum. These collections also contain specimens from the Habana Formation at five additional localities in Matanzas and Santa 

Clara Provinces.

The age of the Habana Formation has been a matter 

of some dispute. Keijzer (1945, p. 150-156) summarized 

the problems involved in dating the formation. MacGillavry (1937) and Imlay (1944b) presented good 

faunal evidence for the Maestrichtian age of the 

formation.

The fossils associated with Arctostrea aguilerae from 

this area substantiate such an age assignment. Listed 

below are some of the more diagnostic associated species 

and their occurrence. All rudists marked by an asterisk 

occur in the Titanosarcolites limestone of Jamaica, 

accepted as of Maestrichtian age for many years 

(Chubb, 1956).

*Bournonia cancellata (Whitfield), USGS Mesozoic loc. 

27127, 27126.

*Plagioptychus jamaicaensis (Whitfield), USGS Mesozoic 

loc. 27127, 27126.

* Titanosarcolites giganteus (Whitfield), USGS Mesozoic 

loc. 27127. - '

*Praebarrettia sparcilirata (Whitfield), USGS Mesozoic

loc. 27127, 27126, 27173, 27175. 

Parastroma guitarti Palmer, USGS Mesozoic loc. 27127,

27126.

Parastroma sanchezi Douville', USGS Mesozoic loc. 27127. 

Antillocaprina annulata Palmer, USGS Mesozoic loc.

27175.

* Antillocaprina quadrangularis (Whitfield), USGS Mesozoic loc. 27127. 

Exogyra costata Say, USGS Mesozoic loc. 27173, 27175.

In addition to the above fossils, an abundance of 

other pelecypods, both rudists and representatives of 

such genera as Neithea, Idonearca, and Alectryonia are 

associated with A. aguilerae. Gastropods and corals 

are locally common.

Exogyra costata Say is a common fossil on the Gulf 

Coastal Plain and occurs with Titanosarcolites both in 

Mexico and in the Southeastern United States. It 

ranges through the Late Campanian into the Maestrichtian. Titanosarcolites occurs with Sphenodiscus at 

several localities on the gulf coast.

The Cuban occurrences of A. aguilerae can therefore 

be ascribed to the Maestrichtian.

Locality in Texas:

USGS Mesozoic loc. 587: Cretaceous. Ford of the Medina 

River at Castroville, Texas. Collected by C. A. White,

1888.

The ventral one-half of an Arctostrea aguilerae is 

present in a collection containing a mixture of fossils 

from both the Exogyra costata and E. ponderosa zones. 

Faults in this area involve the Anacacho Limestone, 

Austin Chalk, Corsicana Marl, and Escondido Formation. Owing to these structural conditions, the vague 

nature of the locality data, and the obvious mixing of 

the collection, assignment of the specimen to a stratigraphic level is impossible. In spite of this, the occurrence of the species in the Upper Cretaceous of Texas is 

worthy of note.

Localities in Mississippi and Alabama:

USGS Mesozoic loc. 25509: Upper Cretaceous. Ripley Formation, 

Chiwapa Member. Roadcuts of Mississippi Route 30 

in north-facing slope of Wilhite Creek valley from 0.7 to 

1.7 miles south of Keownville, Union County, Miss., from 

SE}£SW>iNEtf to SEtf of sec. 30, T. 6 S., R. 4 E. Collected by L. W. Stephenson and N. F. Sohl, 1955.

USGS Mesozoic loc. 28712: Upper Cretaceous. Ripley Formation, Chiwapa Member. Bluffs south of Okanatie Creek 

a,bout 50 yards above bridge on secondary road, near 

center west edge sec. 16, T. 8 S., R. 3 E., Union County, 

Miss. Collected by Mid-South Earth Science Club, 

1962.

USGS Mesozoic loc. 25498: Upper Cretaceous. Prairie Bluff 

Chalk. Shell Bluff on Shell Creek, sec. 36, T. 14 N., 

R. 6 E., Wilcox County, Ala. Collected by L. W. Stephenson, N. F. Sohl, and W. H. Monroe, 1955.

In Mississippi, Arctostrea aguilerae (Bose) occurs in 

the Chiwapa Sandstone Member of the Ripley Formation at two localities. Its occurrence at USGS 

Mesozoic locality 25009 has been noted in a measured 

section by Sohl (1960, p. 35, unit 13). Here it occurs 

abundantly in a 5-foot unit that also contains 

Sphenodiscus lobatus (Tuomey) of Hyatt, Exogyra 

costata Say, and other typical Ripley Formation invertebrates. One specimen assigned to Titanosarcolites sp. was also found in this section at a level 39 

feet higher than A. aguilerae, near the top of the formation.

Specimens of A. aguilerae from USGS Mesozoic 

locality 28712 are embedded in the same sandy limestone matrix and are assumed to have come from about 

the same position.

The occurrence of Sphenodiscus alone is sufficient 

to indicate a probable Maestrichtian age. Its proximity 

to the species of Titanosarcolites further strengthens the 

assignment.

The Alabama specimens occur near the type section 

of the Prairie Bluff Chalk at Shell Bluff on Shell Creek 

Here the formation is only about 12 feet thick. Arctostrea occurs near the base of the formation. The 

associated molluscan fauna (USGS Mesozoic loc. 

25498) is as follows:

Pelecypocla:

Idonearca capax (Conrad) 

Inoceramus sp. 

Ostrea tecticosta Gabb 

Gryphaea mutabilis Mortou 

Exogyra costata Say 

Trigonia thoracica Morton?
GIANT UPPER CRETACEOUS OYSTERS FROM THE GULF COAST AND CARIBBEAN H19

Pelecypoda Continued

Plicatula urticosa Morton

Lima reticulata Forbes

Anomia argentaria Morton

Paranomia scabra (Morton)

Liopistha protexta (Conrad)

Veniella conradi (Morton)

Crassatella vadosa Morton

Legumen ellipticum Conrad 

Gastropoda:

Turritella vertebroides Morton

Xenophora leprosa (Morton)

Anchura cf. A. abrupta Conrad

Pugnellus densatus Conrad

Euspira rectilabrum (Conrad)

Gyrodes abyssimis (Morton)

Gyrodes petrosus (Morton)

Sargana stantoni (Weller)

Pyrifusus sp.

Napulus octoliratus (Conrad)

Pyropsis sp.

Volutomorpha cf. V. retifera Dall

Longoconcha sp.

Anisomyon cf. A. centrale Meek

Anisomyon sp. 

Cephalopoda:

Eutrephoceras perlatus Morton

Baculites columna Morton

Baculites carinatus Morton

Baculites cf. B. ovatus Morton

Discoscaphites conradi petichiolus Morton

Discoscaphites conradi qulosus Morton?

Discoscaphites cf. D. roanensis Stephenson

Coahuilites sp.

In addition to the above, various species of echinoids, 

bryozoa, serpulid worms, boring sponges, corals, and 

the brachiopod Terebratulina floridana (Morton) also 

are present.

The fauna is typical of the chalk facies and of the 

Prairie Bluff Chalk. The ammonites indicate a high 

Maestrichtian level. Baculites columna occurs only 

in the highest part of the Cretaceous section, in beds 

above the first occurrence of Spheno&scus from New 

Jersey to Texas, and has recently been found in the 

Fox Hills Sandstone of South Dakota (W. A. Cobban, 

written communication, March 1963). Coahuilites is 

common in the Maestrichtian of Mexico. The remainder of the ammonites are similarly restricted to 

the highest Cretaceous formations.

SUMMARY OF STRATIGRAPHIC RANGE

All the known specimens of Arctostrea aguilerae are 

associated with fossils indicating latest Cretaceous 

age (fig. 2). In the type area in Mexico, the species 

may occur as low as the uppermost Campanian; 

but in Cuba, Mississippi, and Alabama, it seems to be 

restricted to beds of Maestrichtian age.

TYPES

Illustrated hypotypes from Cuba, USNM 132075,

132076. 132078, 132079, 132080. Illustrated hypotype from Mexico, USNM 132072. Illustrated hypotypes from Mississippi, USNM 132069-132071, 132074,

132077. Illustrated hypotypes from Alabama, USNM 

132073, 132081, 132082. Mentioned hypotype from 

Texas, USNM 132341. Measured unfigured hypotypes 

from Mississippi, USNM 132068 (four specimens).

REFERENCES

Bayle, E., 1878, Explication de la Carte Geologique de la France,

pt. 1, Fossiles principaux des terrains: Paris, Atlas, pi. 146,

figs. 1, 2. 

Bose, Emil, 1906, La fauna de moluscos de senoniano de Cardenas,

San Luis Potosi: Mexico Inst. Geol. Bol. 24, 95 p., 17 pi. 

Chubb, L. J., 1956, Rudist assemblages of the Antillean Upper

Cretaceous: Am. Paleontology Bull., v. 37, no. 161, p.

1-23. 

Cooke, C. W., 1943, Geology of the Coastal Plain of Georgia:

U.S. Geol. Survey Bull. 941, 121 p. 

Coquand, Henri, 1869, Monographic du genre Ostrea; terrain

cretace: Marseille, H. Seran, 215 p., atlas of 75 pi. 

Eargle, D. H., 1955, Stratigraphy of the outcropping Cretaceous

rocks of Georgia: U.S. Geol. Survey Bull. 1014, 101 p.,

map. 

Faujas-Saint-Fond, B., 1799, Histoire naturelle de la montagiie

de Saint-Pierre de Maestricht: Paris, H. J. Jansen, p.

166, 167, pi. 28, fig. 7. 

Gunter, Gordon, 1950, The generic status of living oysters and

the scientific name of the common American species:

Am. Midland Naturalist, v. 43, no. 2, p. 438-449. 

Imlay, R. W., 1944a, Cretaceous formations of Central America

and Mexico: Am. Assoc. Petroleum Geologists Bull.,

v. 28, no. 8, p. 1077-1195.

 1944b, Correlation of the Cretaceous formations of the

Greater Antilles, Central America and Mexico: Geol.

Soc. America Bull., v. 55, p. 1005-1046, 3 pi. 

Keijzer, F. G., 1945, Outline of the geology of the eastern par,

of the Province of Oriente, Cuba: Geog. geol. Mededeel.

Physiog.-geol. Reeks, ser. 2, no. 6, 206 p., 11 pi. 

MacGillavry, H. J., 1937, Geology of the Province of Camaguey,

Cuba, with revisional studies in rudist paleontology: Geog.

geol. Mededeel., Physiog.-geol. Reeks, v. 14, 169 p., 3 pi. 

McLean, R. A., 1941, The oysters of the western Atlantic: Acad.

Nat. Sci. Philadelphia, Notulae naturae, no. 67, p. 1-14. 

Monroe, W. H., 1941, Notes on deposits of Selma and Ripley

age in Alabama: Alabama Geol. Survey Bull. 48, 150 p.,

1 map. 

Newell, N. D., 1937, Late Paleozoic pelecypods, Pectinacea:

Kansas Geol. Survey [Rpt.], v. 10, pt. 1, p. 15-35.

 1942, Late Paleozoic pelecypods, Mytilacea: Kansas

Geol. Survey [Rpt.], v. 10, pt. 2, p. 22-34. 

Pervinquiere, Leon, 1910a, Observations sur la nomenclature des

Ostraces: Soc. geol. France Bull., ser. 4, v. 10, p. 645, 646.

 1910b, Ostrea carinata: Paleontologia Universalis, ser. 3,

pt. 2, p. 197, 197a-c, 198. 

Ranson, Gilbert, 1948, Prodissoconques et classification des

Ostreicles vivants: Mus. royal histoire nat. Belgique Bull.,

v. 24. no. 42, p. 1-12.
H20 CONTRIBUTIONS TO PALEONTOLOGY

Ranson, Gilbert, 1950, La chambre promyaire et la classification 

zoologique des Ostreides: Jour. Conchyliologie, v. 90, p. 195-200.

Raymond, P. E., 1925, A new oyster from the Cretaceous of 

Cuba: Boston Soc. Nat. History Occasional Papers, v. 5, 

p. 183-185, pi. 7, figs. 1, 2.

Sacco, Federico, 1897, I molluschi dei terreni terziarii del Piemonte e della Liguria: Clausen, Torino, v. 23, p. 15.

Shrock, R. R., and Twenhofel, W. H., 1953, Principles of invertebrate paleontology: New York, McGraw-Hill Book 

Co., 816 p.

Sohl, N. F., 1960, Archeogastropoda, Mesogastropoda and 

stratigraphy of the Ripley, Owl Creek, and Prairie Bluff 

Formations: U.S. Geol. Survey Prof. Paper 331-A, 151 p., 

18 pi., [1961].

Stephenson, L. W., 1923, Cretaceous formations of North 

Carolina: North Carolina Geol. and Econ. Survey, v. 5, 

p. 604, 104 pi.

 1952, Larger invertebrate fossils of the Woodbine Formation (Cenonamian) of Texas: U.S. Geol. Survey Prof. 

Paper 242, pi. 16, figs. 1-4; pi. 17, figs. 7-10.

Thomson, J. M., 1954, The genera of oysters and the Australian 

species: Australian Jour. Marine and Freshwater Research, 

v. 5, no. 1, p. 132-168.

Veatch, Otto, and Stephenson, L. W., 1911, Geology of the 

Coastal Plain of Georgia: Georgia Geol. Survey Bull. 26, 

466 p., 1 map.

Woods, Henry, 1913, A monograph of the Cretaceous Lamellibranchia of England: London, v. 2, pt. 9, p. 341-355.
INDEX

[Italic page numbers indicate major references]

abrupta, Anchura--..._____--_______________-___---.

abyssinus, Gyrodes,,----------.........-_.-_--------__-.-________

aguilerae, Arctrostrea- ...........................__ 1,4,^3,15,16,17,18; pis. 1,

Aguilerae, Ostrea (Alectryonia) __. ...__-_________._...

(Alectryonia) Aguilerae, Ostrea-.-------... ______-____________

Anacacho Limestone....__..___..__._________________

Anchura abrupta _____-- -- .--.___---____________..,

Anisomyon centrale...______..-___-___-_________..

SP_ --- . .. . .............

annulata, Antillocaprina--- ...-- --___..__________.-_____ 

Anomia argentaria--.-...--.--------------- -- -----.--.-.----.--.-.--------

Antillocaprina annulata.-----.-.-------.._---------________._...

guadrangularis_________._______-__._____......_

Arctostrea.......---___________-________ __._.. 4, 18,13, 15

aguilerae..-...................................... 1,4, 13, 15,16,17,18; pis. 1

atkinsi -------------------- _--_--------.-----.----..-----.-.-...-- 13,

carinata- ....______--------_.__.____.________ 4,

columbrina.. -____--______________________

diluviana-- ---------_-----_--___________________

pectinata__-----------_______-________________

ricordeana--. ...-_----_-----------.---_-_-__------_------_-______-_________

serrata.---...__________________________...

stratigraphic distribution.-- -______..___________

zeilleri----- ...___________-------_..______.___._

argentaria, Anomia---------------_---------------- -----.-..___-.-.-._.-._

atkinsi, Arctostrea-.-...-____--.__________________-._ 13,

Austin Chalk___-__________.-_.._________________

Baculites carinatus. 

columna-- __-

Bibliography._______..___......._____.________....

Black Creek Formation.__--._....___._-....________

Snow Hill Marl Member.-...-.___...._.....__....___.... 

Blufftown Formation___..._.__..____...___________.. 7, H 

Bournonia cancellata...__.____......._____.._..._____.. 17

Page 

HIS

18 

2,3,4

13 

12,17

13

17

18

18

18

17

18

17

17

,16,17

, 2,3,4

15,16

13,16

4,16

4

4,16

4

16

4

16

18

15,16

17

18

18

18

18

12

12

cancellata, Bournonia.. ..... .............................................. 17

Canoas, Mexico._.....____..._____.....___________ 16

Canon Canada, Mexico___.___..___________.______.. 16 

capax, Idonearca.--...... ...___.....________._________... 17

Cardenas Formation._.---.-.--.___....__...__________.___.. 16

carinata, Arctostrea-- _______._.._____________._ 4,13,16

Ostrea.--.-...._..__...._....__.__.._______..-.-..

carinatus, Baculites, 

centrale, Anisomyon. 

Coahuilites...... . _

sp_

 - . . ......-.................-...... 12,15

 - _-_-___._.__._-_____________._.__. 18

 -----_---_--._._._._.._--.---.----__._......----_.. 18

 18

 . . . -................................. 18

columbrina, Arctostrea-- __-..________.___._._.__......______ 4,16

columna, Baculites..-----------_-_....._..-.-........_....._.._......_.__...__ ig

conradi petichiolus, Discoscaphites-----... __.___......____.___._ 18

gulosus, Discoscaphites-.-- __...___._________...___... is

Veniella------ ..._..._________....___....__..___ 16,18

Corsicana Marl____..________________________ 17

costata, Exogyra --.--__------__--__._.________.____.. 16,17

Crassatella vadosa....__......___.__..____._____.___... ig

Crassostrea- _ ____..__.__.___.__......_________._ 1,4,6,9,10

cusseta- --- - __---__. __ _ ._ _ _ 1,4,6,10,11,12; pis. 4, 5

georgiana. ____._-______.___._____________________ 1

gigantissima. ._.__.._.______.______________._ i, 6,10,11

glabra..... ..._._____...__________._________..... 10

pantagruelis,- _______________.__________.______ n 

soleniscus______....____________________________ it 6,10,11,12

lineage.... -_ . . _ ...._...._.________._________ 1,6,10

subtrtgonalis---.-------------..___-_._____________________________________ 10

virgin-tea--. __________.________________________ ii 10

Cuesta de Nahual, Mexico..__________...._______._________ 16

Page 

cusseta, Crassostrea.. HI, 4, 6, 10, 11, 12; pis. 4,5

CussetaSand.... 6,11,12

deatsvillensis, Idonearca-- ... ,.. --- - 16

densatits, Pugnellus.- ... -- 18

diluviana, Arctostrea- ---- ---- -- ------ -- 4

Discoscaphites conradi petichiolus .. ... .. .. 18

conradi gulosus ..... -- ---- 18

ellipticum, Legumen, ------------------- ----------------------------------- 18

Escondido Formation. _. -- - 17 

Euspira rectilabrum... 18

Eutrephoceras perlatus-- - - -- -- 18 

Evolutionary trends, Crassostrea soleniscus lineage . 1,6,10 

Exogyra costata-- ... - -- -- -- 16,17

ponderosa --------------------------- --------------------------------- 12,17

floridana, Terebratulina---. ----- -- --- 18

Fox Hills Sandstone __ - -- 18

georgiana, Crassostrea--.-- .. . . - - 1

giganteus, Titanosarcolites. .... . - - 17

gigantissima, Crassostrea--- -------------- 1,6,10,11

glabra, Crassostrea- ...... ... .. . - 1°

Oryphaea.-.-. .... - -- 6

mutabilis---- ... ----- - 17

vesicularis . _ - -- -- ---- 16

guitarti, Parastroma. --- - -- - 17

Oyrodes abyssinus . ------ - --- -- 18

petrosus ------ ...... - 18

Habana Formation. 17

Idonearca-- ..... _ . --- - - - 17

capax- -------

deatsvillensis17

Jamaica.- ___ 17

jamaicaensis, Plagioptychus,-- . . ------- - ...- 17

Legumen ellipticum,-- ...... - -- - ----- 18

leprosa, Xenophora - .... ... _.- . ---- 18

Lima reticulata. ..... . ---------- - -- 18

Liopistha protexta.- ... -- -- ---- ---------- 18

lobatus, Sphenodiscus ....- -------- -.- __. ._. .- .. - 17

Longoconcha sp_..-- - ---- -- ------ 18

Lopha.----- ..- ------ - - 12

Morphologic terminology and measurements. .. - - -- 4

mutabilis, Gryphaea .. ------- .- ---- ---- -- 17

Nacatoch Sand.--- --... .. - - -- - 15

Napulus octoliratus---- .... ------ --- -- --- - 18

Neithea-- - - - -- -- 17

octoliratus, Napulus .. ... - - ---- -- 18

Orbitoides zone- - ------- ----- -- - 16

Ostrea--- _________ ._ - - --- 6,7,12

carinata. ... --------------------------------------------------------------- 12,15

- -- _ - . 13

tecticosta- ------___------------ .- -...- ..-. -- 17

travisana . - .... -- ---- ----- 13

virginica-. ___..-___. .. -- ---- --- -- 6

(Alectryonia) Aguilerae__._- -- .. .. ..-. 13

ovatus, Baculites---..... .-- - -------- - ----- 18

H21
H22 INDEX

Page 

pantagruelis, Crassostrea.................... .-. Hll

Paranomia scabra............................................................ 18

Parastroma guitarti..-......--...................... ..-- .. 17

sanchezi_______ ..--._.-.. .. ----- 17

pectinata, Arctostrea........................................................... 4,16

perlatus, Eutrep\oceras. ...-..-.....- ................. -.- - 18

petichiolus, Discoscaphites conradi.......................................------- 18

petrosus, Gyrodes...................... . -. 18

Plagioptychusjamaicaensis-........................ ._.-- .-.-. 17

Plicatulaurticosa............................................................. 18

ponderosa, Exogyra........ .-- ----- 12,17

Praebarrettia fparcilirata...................................................... 17

Prairie Bluff Chalk----------------------------------------------- 17,18

protexta, Liopistha...........................................----------- . 18

Pugnellusdensatus............................................................ 18

Pyrifusus sp _____..._-. -..-- -... ..-- 18 

Pyropsissp............... ................................................. 18

quadranguiaris, Antillocaprina.. 

gulosus, Discoscaphites conradi.

Rastellum..................................................................... 12,13

rectilabrum, Euspira.......................................................... 18

reticulata, Lima... ------ . . 18

retifera, Volviomorpha......................................................... 18

ricordeana, Arctostrea.-....................................................... 4

Ripley Formation,.------------------------------------------------------- 16,17

Chiwapa Sandstone Member________________________ 17

roanenis, Discoscaphites..-.................................................... 18

sanchezi, Parastroma....

Santa Rosalia property. 

Sargana stantoni........

scabra, Paranomia......

Page 

serrata, Arctostrea..-.-.--. ------------------------------------- _.. H16

soleniscus, Crassostrea. --.......-.........--.......................... 1,6,10,11,12

sparcilirata, Praebarrettia......... ................ 17

Sphenodiscus.. _------ --.._ _-------------- --------__ 17,18

lobatus. ...-- .............. .................. 17

stantoni, Sargana................... . . -- --------- 18

Stephenson, L. W., quoted... .___._._______.-..___..___ 12 

subovata, Ostrea. -... .. 13

subtrigonalis, Crassostrea-.....-.----------___.._..................._.. 10

Systematic paleontology.. . . . ....... ....................... 4

tecticosta, Ostrea........

Terebratulina floridana. 

thoracica, Trigonia....-

TUanosarcolites...-.-..

giganteus.-........

travisana, Ostrea.......

Trigonia th oracica......

Turritella vertebroides..

urticosa, Plicatula.

17

18

17

17

17

13

17

18

18

vadosa, Crassatdla............................................................ 18

Veniella conradi...................... . 16,18

vertebroides, Turritella.~ ....... ......................................... 18

vesicularis, Gryphaea...................................................... 16

virginica, Crassostrea.......................................................... 1,10

Ostrea-....... - 6

Volutomorpha retifera.-....-...-....................... - 18

Xenophora leprosa. 

zeilleri, Arctostrea 

18

16

U. S. GOVERNMENT PRINTING OFFICE : 1964 O - 729-8
PLATES 1-5
PLATE 1

FIGURES 1, 2. Arctostrea aguilerae (Bose) (p. H14).

1. Lateral view (X 1) of a typical left valve, from the Prairie Bluff Chalk, Wilcox County, Ala. (USGS Mesozoic 

loc. 25498), illustrating nature of the ornamentation, valve outline, position of the attachment scar, and development of the posterior auricle. A hypotype, USNM 132082.

2. Interior view (X 1) of the specimen illustrated in figure 1, showing position and development of the deeply 

incised posterior adductor muscle scar, the crenulate commissure, structures of the cardinal area, and interior 

of the posterior auricle and the overlapping lamellae at its margin. Hypotype (USGS Mesozoic loc. 25498), 

USNM 132082.
GEOLOGICAL, SURVEY PROFESSIONAL PAPER 483-H PLATE 1
PLATE 2

FIGURES 1-4. Arctostrea aguilerae (Bose) (p. H14).

1. Interior view (X J4) of a right valve, from the Prairie Bluff Chalk, Wilcox County, Ala. (USGS Mesozoic loc. 

25498), illustrating the development and position of the deep posterior adductor muscle scar and the crenulate 

commissure. Note the abnormally massive cardinal area with offset resilifer and broad lateral cardinal plates. 

A hypotype, USNM 132073.

2. Lateral view (X }4) of a small right valve, from the Chiwapa Member, Ripley Formation, Union County, Miss. 

(USGS Mesozoic loc. 25509). This specimen is closely comparable to Bose's syntype of the species (1906, 

pi. 2, fig. 2). A hypotype, USNM 132070.

3. Interior view (X 1) of a large right valve, illustrating characteristic development of the valve outline, crenulate 

commissure, and posterior auricle, which bears well developed denticles. Structures of the cardinal area are 

typically developed, but the area itself is smaller than average. The well-developed posterior adductor muscle 

scar, generally incised in thick-shelled specimens, is raised on a platform and surrounded by a raised rim in this 

thin-shelled form. A hypotype from the Prairie Bluff Chalk, Wilcox County, Ala. (USGS Mesozoic loc. 25498): 

USNM 132081.

4. Anterior view (X 1) of paired valves, illustrating the convexity of the shell, zig-zag nature of the commissure, 

flattering of the plicae on the steep anterior flank of both valves, and the chevron-shaped trace of the lamellae 

at their intersection with the anterior flank. A hypotype from the Chiwapa Member, Ripley Formation, 

Union County, Miss. (USGS Mesozoic loc. 25509); USNM 132069.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-H PLATE 2

'-- »'&& />'Ji!-V"~ '. - j'jlff^'^. ''', 4- ~^^> te'&*-'**k>^ ^ ,' l ^T_i.~- « " -W- -*» ^^M^iM^^f' * -p.

ARCTOSTREA AGUILERAE (BOSE)
PLATE 3

FIGURES 1-7. Arctostrea aguilerae (Bose) (p. H14).

1. Lateral view of a left valve (X K), showing characteristic outline and ornamentation of species. A hypotype 

from the Chiwapa Member, Ripley Formation, Union County, Miss. (USGS Mesozoic loc. 25509), the specimen 

illustrated on plate 2, figure 4; USNM 132069. Compare with Bose's syntype (1906, pi. 6, fig. 1).

2. Lateral view of a right value (X YI) from Cardenas Formation, San Luis Potosi, Mexico (USGS Mesozoic 

loc. 28181); USNM 132072.

3. Lateral view of a left valve (X %) from Santa Clara Province, Cuba (USGS Mesozoic loc. 27198), showing 

narrow umbonal ridge and steep dorsoposterior slope; slope flattened at the margin and bears straight subparallel 

plicae. A hypotype, USNM 130280.

4. A partial anterior view of a right valve (X /4), showing zig-zag nature of the commissure, flattening of the 

plicae on the steep anterior slope, and chevron-shaped trace of lamellae intersecting anterior slope. A hypotype 

from Santa Clara Province, Cuba (USGS Mesozoic loc. 27198); USNM 132078.

5. Interior view (X K) of the right valve from Cuba, illustrated in figure 4 (USGS Mesozoic loc. 27198). A 

hypotype showing the crenulate commissure and the outline and deeply incised nature of the posterior adductor 

muscle scar on thick-shelled forms; resilifer unusually shallow; USNM 132078.

6. Interior view (X %) of a right valve with abruptly recurved ventral part of shell, characteristic structures 

of the cardinal area (resilifer, lateral cardinal plates), posterior auricle, commissure, and posterior adductor 

muscle scar. A hypotype from the Chiwapa Member, Ripley Formation, Union County, Miss. (USGS Mesozoic 

loc. 25509); USNM 132071.

7. Lateral view of a right valve (X Vz) from Santa Clara Province, Cuba (USGS Mesozoic loc. 27127), showing 

characteristic valve outline and ornamentation. Note subparallel, gently curved plicae of flattened part of 

dorsoposterior flank. A hypotype, USNM 132075, comparable to one of Bose's syntypes (1906, pi. 6, fig. 2).
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-H PLATE 3 

r"*-^.

Xi/2

ARCTOSTREA AGUILERAE (BOSE)
PLATE 4

FIGURES 1-4, 6-8. Arctostrea aguilerae (Bose) (p. H14).

1. Lateral view of a left valve (X )0, illustrating exceptionally well-developed subparallel plicae on the 

dorsoposterior slope and well-defined posterior auricle. A hypotype from Santa Clara Province, Cuba 

(USGS Mesozoic loc. 27198); USNM 132079.

2. Enlarged photograph (X 4) of a weathered fragment from a left valve, showing structure of subnacreous 

shell layer. Note major flat lamellae composed of prominent vertical calcite plates transected by finer 

horizontal calcite laminae. A hypotype from the Ripley Formation of Union County, Miss. (USGS 

Mesozoic loc. 25509); USNM 132077.

3. 4. Lateral and internal views (X Yz) of a crushed palmate right valve, showing that despite subsequent 

flattening, shape and position of interior valve margins identifies specimen as having been narrow and 

strongly curved. A hypotype from Santa Clara Province, Cuba (USGS Mesozoic loc. 27127); USNM 

132076.

6. Natural section' (XI) through a left valve fragment, the specimen illustrated in figure 2, showing typical 

valve cross section and structure.of the subnacreous shell layer major horizontal plates composed of 

prominent vertical calcite crystals. A hypotype from the Ripley Formation in Union County, Miss. 

(USGS Mesozoic loc. 25509); USNM 132077.

7. Posterior adductor muscle scar (XI) from a massive left valve, showing incised nature and characteristic 

ornamentation of scar. A hypotype from the Chiwapa Member, Ripley Formation, Union County, Miss. 

(USGS Mesozoic loc. 25509); USNM 132074.

8. Interior view (X tf) of a typical left valve showing well-developed cardinal features: resilifer, lateral 

cardinal plates, marginal cardinal troughs. The specimen illustrated in figure 1; a hypotype from Santa 

Clara Province, Cuba (USGS Mesozoic loc. 27198); USNM 132079. 

5, 9, 10. Crassostrea cusseta Sohl and Kauffman n. sp. (p. H7) .

5. Dorsoposterior margin (X 1) of a right valve, illustrating the elongate trace of the denticles. A para type 

from the Cusseta Sand just below Woolridge landing, Chattahoochee River, Ala. (USGS Mesozoic loc. 

5396); USNM 132061.

9, 10. Interior and lateral views of a typical right valve (X Yz), showing valve outline, strong posterior curvature of the valve, well-defined cardinal structures (midcardinal fold, lateral cardinal troughs), caved shell 

layers over site of covered posterior adductor muscle scar, and characteristic exterior ornamentation of 

overlapping lamellae. A paratype from the Cusseta Sand below Woolridge landing, Chattahoochee River, 

Ala. (USGS Mesozoic loc. 26027) ; USNM 132060.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-H PLATE 4

.y-nr^e, -». w-r .», jf. m. \.

;> -'«,' ' \. ; ^ts \k"

Xl/2

ARCTOSTREA AGUILERAE (BOSE) AND CRASSOSTREA CUSSETA SOHL AND KAUFFMAN N. SP.
PLATE 5

[All pictures X H]

FIGURES 1-4. Crassostrea cusseta Sohl and Kauffman n. sp. (p. H7).

1. Interior view (X ^), dorsal part of a large right valve showing well-developed posterior auricle and cardinal 

structures (midcardinal fold, lateral cardinal troughs). A paratype from the Cusseta Sand at Woolridge landing, 

Chattahoochee River, Barbour County, Ala. (USGS Mesozoic loc. 28451); USNM 132058.

2. Interior view (X YZ), dorsal part of a large left valve showing well-developed resilifer, lateral cardinal folds, subcardinal cavities, posterior auricle, and the surface of the posterior adductor-muscle scar, here exposed by removal of numerous calcite lamellae on the floor of the valve. A paratype from the Cusseta Sand, Barbour 

County, Ala. (USGS Mesozoic loc. 26029); USNM 132059.

3. 4. Internal and lateral views (X }9 of the holotype, a large left valve, characteristic of the species, illustrating 

the marginal outline, lack of exposed muscle scar on large adult valves, well-defined resilifer, lateral cardinal 

folds, denticulate commissure, attachment scar, and lamellate exterior ornamentation. Specimen from the 

Cusseta Sand, below Woolridge landing, Chattahoochee River, Barbour County, Ala. (USGS Mesozoic loc. 

26027) ; USNM 132057.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 483-H PLATE 5

CRASSOSTREA CUSSETA SOHL AND KAUFFMAN N. SP.