Characteristic Marine Molluscan Fossils 

From the Dakota Sandstone and 

Intertongued Mancos Shale, 

West-Central New Mexico

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009
Characteristic Marine Molluscan Fossils 

From the Dakota Sandstone and 

Intertongued Mancos Shale, 

West-Central New Mexico

By WILLIAM A. COBBAN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009

Brief descriptions, illustrations, and 

stratigraphic sequence of the more common fossils 

at the base of the Cretaceous System

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Cobban, William Aubrey, 1916-

Characteristic marine molluscan fossils from the Dakota sandstone and intertongued Mancos shale, Westcentral New Mexico.

(Geological Survey professional paper ; 1009)

Bibliography: p.

Includes index.

1. Lamellibranchiata, Fossil. 2. Gastropoda, Fossil. 3. Ammonoidea. 4. Paleontology Cretaceous. 5. Paleontology New Mexico. I. Title: Characteristic marine molluscan fossils from the Dakota sandstone ***!!. 

Series: United States. Geological Survey. Professional paper ; 1009.

QE811.G6 564'.09789'8 76-26956

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

Washington, D.C. 20402 

Stock Number 024-001-03003-9
CONTENTS

Abstract ________________________________________--__-

Introduction ________________________________________

Acknowledgments _____________________________

Stratigraphic summary _________________________

Age of the intertongued Dakota Sandstone and Mancos Shale 

Earlier records of fossils _______________________

Resume of fossil occurrences _________________________

Geographic distribution of fossils __________________________

Characteristic fossils __________________________________

References cited ___________________________________.

Index __________________________________________

Page 

1

1

3

3

10

10

10

26

29

ILLUSTRATIONS

	[Plates follow index]

PLATES 1-3. Oak Canyon fossils.

4-5. Oak Canyon and Cubero fossils.

6. Clay Mesa fossils.

7-14. Paquate fossils.

15. Paguate and Whitewater Arroyo fossils.

16-18. Whitewater Arroyo fossils.

19-21. Twowells fossils.

FIGURE 1. Index map of part of northwestern New Mexico __

2. East-west stratigraphic changes _________.

3. North-south stratigraphic changes ________

4. External suture of Tarrantoceras rotatile _______

5. External suture of Acanthoceras amphibolum ___

6. Complete suture of Acanthoceras alvaradoense __

7. External suture of Metoicoceras aff. M. latoventer

Page

2

3

4

23

24

24

25

TABLES

TABLE 1. Fossils of Clay Mesa Shale Tongue and Paguate Sandstone Tongue _____ .

2. Fossils of Oak Canyon Member and Cubero Sandstone Tongue ____________

3. Fossils of Whitewater Arroyo Shale Tongue and Twowells Sandstone Tongue

4. Localities where fossils were collected ___________________________________

Page

6

8

9

10

in

CHARACTERISTIC MARINE MOLLUSCAN FOSSILS FROM THE

DAKOTA SANDSTONE AND INTERTONGUED MANCOS SHALE,

WEST-CENTRAL NEW MEXICO

By WILLIAM A. COBBAN

ABSTRACT

Molluscan fossils are abundant in marine rocks of early 

Late Cretaceous age (Cenomanian) on the south and southeast flanks of the San Juan Basin in northwestern New 

Mexico. Here the Cenomanian rocks are characterized by 

generally eastward-pointing tongues of Dakota Sandstone 

separated in part by westward-pointing tongues of Mancos 

Shale. From bottom to top, the sequence consists of the Oak 

Canyon Member of the Dakota Sandstone, Cubero Sandstone Tongue of the Dakota Sandstone, Clay Mesa Shale 

Tongue of the Mancos Shale, Paguate Sandstone Tongue of 

the Dakota Sandstone, Whitewater Arroyo Shale Tongue of 

the Mancos Shale, and Twowells Sandstone Tongue of the 

Dakota Sandstone. The lower part of the Oak Canyon 

Member consists of rocks of fluviatile and brackish-water 

origin; the strata of the rest of the member and of all the 

overlying intertongued Dakota Sandstone and Mancos Shale 

are dominantly of shallow-water open-marine origin.

Molluscan fossils occur in all the members. Most specimens are found in silty limestone concretions, in calcareous 

siltstone or sandstone concretions, and in very fine grained 

sandstone and siltstone beds. The upper part of the Oak 

Canyon Member and the Paguate Sandstone Tongue contain 

the greatest variety of fossils. Fifty-two kinds of bivalves, 

38 gastropods, and 15 ammonoids from these two units are 

present in the collections of the U.S. Geological Survey.

INTRODUCTION

The basal part of the Cretaceous System in westcentral New Mexico consists of a generally transgressive sequence of intertongued sandstone, siltstone, and shale. The stratigraphic framework and 

terminology of this sequence was summarized in two 

recent papers by Landis, Dane, and Cobban (1973a, 

b). Many of the characteristic molluscan fossils 

were recorded, but no attempt was made to show 

either stratigraphic ranges or geographic distributions. This paper has been prepared as a paleontologic supplement to the stratigraphic work of 

Landis, Dane, and Cobban. However, this paper is 

not intended as a detailed systematic study of the 

fauna, but rather as a generalized guide to the common fossils and their distribution. No new species

are formally described and named herein. Synonomies include only the original paper in which a species was named and, generally, one or two later 

papers that have important nomenclature changes 

or good illustrations.

ACKNOWLEDGMENTS

The photographs in this report were made by 

Robert E. Burkholder, of the U.S. Geological Survey. All illustrated specimens are stored in the National Museum of Natural History in Washington, 

D.C. The rest of the fossils, as well as some plaster 

casts of illustrated specimens, are kept in the U.S. 

Geological Survey's Mesozoic invertebrate collections at the Federal Center, Denver, Colo.

Dr. Annie Dhondt, Institut royal des Sciences 

naturelles de Belgique, kindly examined photographs 

of Neithea from the Paguate Sandstone Tongue of 

the Dakota Sandstone and Camptonectes from the 

Twowells Sandstone Tongue of the Dakota, and she 

offered suggestions regarding their specific names.

STRATIGRAPHIC SUMMARY

Landis, Dane, and Cobban (1973a, b) observed 

that the intertonguing of the Dakota Sandstone and 

Mancos Shale was formed best in the Grants-Laguna 

area in the southern part of the San Juan Basin 

(fig. 1). Here the sequence, from oldest to youngest, 

consists of Oak Canyon Member of the Dakota 

Sandstone, Cubero Sandstone Tongue of the Dakota 

Sandstone, Clay Mesa Shale Tongue of the Mancos 

Shale, Paguate Sandstone Tongue of the Dakota 

Sandstone, Whitewater Arroyo Shale Tongue of the 

Mancos Shale, and Twowells Sandstone Tongue of 

the Dakota Sandstone. Northwestward from Grants, 

the lower part of the sequence (Oak Canyon Member and Cubero, Clay Mesa, and Paguate Tongues) 

grades into a dominantly sandstone unit identified 

as the main body of the Dakota Sandstone (fig. 2).
MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

109° 108° 107°

37C

36C

35°

I COLORADO

Shiprock

Q Farmington

SAN JUAN RIO ARRIBA

O 

NJ I

MC KINLEY

H ! 

O 3,4

X

X 10

12

' x °Manuelito

x72

X13 x Fort Wingate •) 5.21

O X 14

22-24

x 25-26

11 .———-

Grants

l

8

x

O Atarque

CATRON

v ,, Mt. Taylor \ 39,40

* Seboyeta£————^\- _

O Vf^l T>_ __ _ J. ^\

x' 

X 50 56-59

X R1 X 60 c_x\ <,\o 

VALENCIA x 51-53 x ^Acoma pueblo 67 ^

X 54,55 X62-65

-68

x 69,70

71 x 0Riley

SOCORRO

20 30 MILES

10 20 30 KILOMETERS

FIGURE 1.—Part of northwestern New Mexico showing localities of mollusk collections referred to in the text and in

table 4.
EARLIER RECORDS OF FOSSILS

Southeastward from Grants, the Cubero and Paguate Sandstone Tongues grade into shale referred 

to as the lower part of the Mancos Shale. The 

nomenclature of the Grants-Laguna area is applicable northeastward from Laguna for about 50 

miles (80 km) to north-central Sandoval County 

where the Cubero and Paguate Sandstone Tongues 

disappear into the lower part of the Mancos Shale, 

which overlies a thick main body of the Dakota 

Sandstone and underlies a very thin Twowells Sandstone Tongue of the Dakota Sandstone (fig. 3).

AGE OF THE INTERTONGUED DAKOTA 

SANDSTONE AND MANCOS SHALE

The oldest molluscan fossils occur in dark-brownweathering ferruginous silty to sandy concretionary beds above the middle of the Oak Canyon Member. An ammonite, described from the Woodbine 

Formation of Texas as Acanthoceras wintoni by 

Adkins (1928, p. 234, pi. 25, figs. 2, 3), occurs 

sparsely in the ferruginous concretions in the Oak 

Canyon Member. This ammonite is middle Cenomanian in age.

The youngest fossils are found in the upper part 

of the Twowells Sandstone Tongue. Among the ammonites are Calycoceras obrieni Young and fragments of Metoicoceras resembling M. defordi Young 

and M. muelleri Cobban, which are of late Cenomanian age. In Wyoming, these ammonites occur with 

Dunveganoceras conditum Haas, a guide to the 

first ammonite zone older than that of Sciponoceras 

gracile (Shumard), which is of latest Cenomanian 

age.

EARLIER RECORDS OF FOSSILS

Fossil mollusks of Cretaceous age have been recorded from west-central New Mexico in many 

papers during the past century. Most authors, however, have made only passing remarks such as noting the local abundance of "Exogyra columbella" or 

"Gryphaea newberryi."

C. A. White was probably the first person to describe Cretaceous mollusks from west-central New 

Mexico. He reported on the collections made in connection with the geographical and geological explorations and surveys west of the 100th meridian. The 

new bivalve species Pinna petrina was described, 

but not illustrated, by White in 1874. His specimens 

came from 1 mile (1.6 km) south of Pajuate 

(Paguate). In 1877, White illustrated this species 

and also described a new gastropod, Lispodesthes 

lingulifera, from the same locality. Both species are 

probably from the Paguate Sandstone Tongue of

WEST

GALLUP AREA

(Cliff Dwellers

Canyon section)

MOUNT

POWELL GRANTS 

AREA AREA

EAST

LAGUNA 

AREA

Morrison 

Formation

EXPLANATION

Calcareous

Formational 

contact

Intraformational 

contact

Clayey

Limestone 

concretion

FIGURE 2.—East-west stratigraphic changes in Dakota Sandstone and intertongued Mancos Shale. From Landis, Dane, 

and Cobban, 1973a, fig. 3.
MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

ALAMO DAY 

SCHOOL AREA

THE NARROWS 

AREA

ACOMA 

AREA

NORTH

LA VENTANA AREA 

(Tafoya Dam section)

Morrison 

Formation

LA VENTANA AREA

(San Miguel Canyon

section)

Paguate 

Sandstone

Tongue 

of Dakota 

Sandstone

aguate Sandstone

Tongue of Dakota

Sandstone B

EXPLANATION

Bentonite

Partly covered

Carbonaceous

Calcareous

Formational 

contact

Intraformational 

contact

FIGURE 3.—North-south stratigraphic changes in Dakota Sandstone and intertongued Mancos Shale. From

Landis, Dane, and Cobban, 1973a, fig. 4.

the Dakota Sandstone, inasmuch as that unit crops 

out 1 mile south of Paguate (sandstone bed 2 of the 

Mancos Shale of Moench, 1963). White (1877, p. 

174,183, pis. 17,18) also described and illustrated the

new bivalves Exogyra costata Say var. fluminis and 

Idonearca depressa from the east bank of the Rio 

Puerco 6 miles (9.6 km) south of Casa Salazan 

(Casa Salazar). The Exogyra was later assigned to
EARLIER RECORDS OF FOSSILS

E. columbella Meek by Stanton (1893, p. 63). The 

geologic map of the Casa Salazar area by Hunt 

(1936, pi. 19) does not show any outcrops along 

the Rio Puerco 6 miles south of Casa Salazar, but 

the Dakota Sandstone and lower part of the Mancos 

Shale are shown a mile or two to the south and west 

of the fossil locality.

In a short paper, White (1881) described Pinna 

stevensoni as a new species from "about IVs miles 

southwestward from Fort Wingate, Northern New 

Mexico." Stanton (1893, p. 89) interpreted White's 

specimen to be an unusually large example of P. 

petrina.

Meek (1876) reported on the collections of fossils 

obtained by the exploring expedition of Capt. J. N. 

Macomb from Santa Fe to the junction of the 

Grand [Colorado] and Green Rivers. The new bivalve species, Exogyra columbella and Plicatula 

arenaria were described and illustrated; they were 

said to have come from Covero, which is the present 

day Cubero. Cubero is located on Water Canyon less 

than a mile north of an east tributary that exposes 

a highly fossiliferous ferruginous bed in the Oak 

Canyon Member of the Dakota Sandstone, which is 

probably the source of Meek's fossils (C. H. Maxwell, oral commun., 1975).

Lists of fossils from well-defined stratigraphic 

levels were not published until 1900 when Herrick 

and Johnson (1900, p. 187-188) listed 14 mollusks 

mostly from the strata presently included in the intertongued Dakota Sandstone and Mancos Shale. A 

highly fossiliferous "gasteropod zone" was described 

about 40 feet (12 m) above the Dakota Sandstone. 

In terms of the present nomenclature, the "gasteropod zone" lies in the upper part of the Oak Canyon 

Member of the Dakota Sandstone, where the fossils 

usually occur in dark-brown-weathering ferruginous 

concretions of calcareous siltstone or very fine 

grained sandstone. In southeastern Colorado, a 

dark-brown-weathering ferruginous concretionary 

limestone bed, the Thatcher Limestone Member of 

the Graneros Shale, contains Plicatula arenaria, 

Exogyra columbella, and other fossils known from 

the Oak Canyon Member and the basal part of the 

overlying Cubero Sandstone Tongue. This fauna will 

be referred to as the Thatcher fauna.

Darton (1910, p. 60) briefly described a stratigraphic section 2 miles northeast [northwest] of 

Laguna. "Beds were numbered 1 to 13 from the top 

to the base. Darton's bed 8, 5 feet (1.5 m) of "Sandstone, hard, red, irony," and the overlying bed 7, 

60 feet (18 m) of "Shale, dark gray to gray-green, 

sandy layers, fossiliferous," can both be assigned to

the Oak Canyon Member. Darton listed 16 mollusks 

from his bed 7 (Thatcher fauna). Bed 6, 40 feet 

(12 m) of "Sandstone, massive, hard, light buff," 

is the Cubero Sandstone Tongue, and the overlying 

bed 5, 60 feet (18 m) of "Shales with sandstone 

layers, very fossiliferous," represents the Clay 

Mesa Tongue and lower part of the Paguate Sandstone Tongue. Darton listed eight mollusks from 

his bed 5, all of which probably came from the 

lower part of the Paguate Sandstone Tongue. He 

mentioned the abundance of Exogyra columbella in 

this bed. However, this study will show that E. 

columbella is restricted to the Oak Canyon Member 

and basal part of the Cubero Sandstone Tongue and 

that the higher records of this species are based on 

a somewhat similar species, E. levis Stephenson, 

originally described as E. columbella levis Stephenson (1952, p. 77, pi. 18, figs. 1-3) from the Templeton 

Member of the Woodbine Formation of northeastern 

Texas. Darton (1910, p. 57) also mentioned that 

"Exogyra columbella Meek [E. levis Stephenson] is 

a very abundant species" in a section that he briefly 

described 3 miles (4.8 km) east of Gallup.

Lee (1912, p. 622-623) presented a section near 

San Francisco (now ruins) in the Rio Puerco valley and listed 16 mollusks from the "Gastropod 

zone" (Thatcher fauna) and 13 mollusks from a 

50-foot (15 m) shaly sandstone (Paguate) 105 feet 

(32 m) higher. Two ammonites recorded from this 

sandstone as Prionotropis sp. and Acanthocerasl sp. 

are probably Acanthoceras amphibolum Morrow. 

Later, Lee (in Lee and Knowlton, 1917, p. 194-195) 

presented a section near Casa Salazar in which he 

listed Exogyra columbella and six other bivalves 

and gastropods (Thatcher fauna) from a 55-foot 

(17 m) sandy to nonsandy shale unit, the base of 

which is 26 feet (8m) above the Upper Jurassic 

Morrison Formation. Above this shale unit (upper 

part of Oak Canyon Member), Lee measured a 37- 

foot (11 m) sandstone unit (Cubero Sandstone 

Tongue) in which he listed E. columbella and seven 

other kinds of mollusks (Thatcher fauna). A 48- 

foot (15 m) dark shale unit (Clay Mesa Shale 

Tongue) overlies the sandstone. Above the shale, 

Lee measured a 66-foot (20 m) yellow sandstone 

unit (Paguate Sandstone Tongue) containing seven 

species of mollusks.

Pike (1947) briefly described some sections in 

the intertongued Dakota Sandstone and Mancos 

Shale, but very few fossils were recorded other than 

"Gryphaea newberryi" and "Exogyra columbella." 

Most of these records probably should read Pycnodonte aff. P. kellumi (Jones) and Exogyra levis
MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

TABLE 1.—Distribution of molluscan fossils in the Clay

[Approximate stratigraphic position of single occurrences in the members is indicated by an

Species Clay Mesa Shale Tongue Paguate Sandstone Tongue

Class Bivalvia:

Idonearca blanpiedi Stephenson

Pinna petrina White

Phelapteria cf. P. linguaeformis (Evans and Shumard)

Phelopterial cf. P. aquilerae (Bose)

Pseudoptera sp.

Inoceramus arvanus Stephenson

ruthetfordi Warren 

Camptanectes sp.

Neithea cf. N. sexcostata (Woodward) 

Plicatula sp.

Pycnodante cf. P. kellumi (Jones) 

Exogyra trigeri Coquand

cf. E. oxyntas (Coquand)

levis Stephenson 

Ostrea beloiti Logan 

Granocardium enstromi (Bergquist)

trite (White)

Cymbophora emmonsi (Meek) 

Tellinimera sp. 

Veniella sp. 

Pharodina sp. 

Aphrodina cf. A. munda (Stephenson)

sp.

Legumen ellipticum Conrad 

Caryocorbulat aff. C.I ovisana Stephenson 

Pholadomya n. sp.

Psilomya aff. P. concentrica (Stanton) 

Psilomya ? sp. 

Class Gastropoda:

Turritella shuleri Stephenson ?

n. sp.

Perissoptera aff. P. prolabiata White 

Cassiope turriformis (Stephenson)

Stephenson. The uppermost sandstone tongue 

(Twowells) of the Dakota Sandstone was named by 

Pike (1947, p. 36) who reported Inoceramus labiatust in it. "Gryphaea newberryi," "Exogyra columbella," and a few other bivalves and gastropods 

were listed by Pike from the underlying shale 

(Whitewater Arroyo Shale Tongue). 

Landis, Dane, and Cobban (1973a, b) recorded
EARLIER RECORDS OF FOSSILS

Mesa Shale Tongue and Paguate Sandstone Tongue

X, and the stratigrapric range of each species, based on several occurrences, is shown by a line |

Species Clay Mesa Shale Tongue Paguate Sandstone Tongue

Helicaulaxl sp.

VasceHum mundum Stephenson

Anchura aff. A. turricula Stephenson

n. sp. 

Lispodesthes panda Stephenson

aff. L. patula Stephenson

aff. L. lirata Stephenson 

Lispodesthesl sp. 

Paleopsephaea cf. P. patens Stephenson

sp.

Carota dalli (Stanton)

aff. C. dalli (Stanton)

cf. C.? nodosa Stephenson

sp.

Avellana n. sp.. 

Hillitesl sp. 

Eilspiral sp. 

Gyrodes tramitensis Stephenson

cf. G. tramitensis Stephenson

sp.

Ringicula sp. 

Fictoacteon cf.F. humilispira Stephenson

sp. 

Class Cephalopoda:

Turrilites acutus ameticanus Cobban and Scott 

Desmoceras aff. D. japonicum Yabe 

Paracompsoceras landisi Cobban 

Tarrantocems rotatile Stephenson 

Acanthoceras alvaradoense Moreman

amphibolum Morrow

Plesiacanthoceras aff. P. wyomingense (Reagan) 

Euomphalocems aff. E. cunningtmri (Sharpe) 

Pseudocalycoceras n. sp. 

Borissiakoceras reesidei Morrow 

Eutrephocerasl sp.

many mollusks from the intertongued Dakota Sandstone and Mancos Shale. Ammonites were found in 

all the members of these two formations. (Previous 

papers seldom recorded the presence of ammonites.)

Two unusual specimens, however, have been noted. 

Northrop (1962, p. 63) mentioned the discovery of 

a very large "Mantelliceras canitaurinum Haas" 

from the Rio Puerco valley, and Owen (1969, p. 91)
MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

TABLE 2. Distribution of molluscan fossils in the Oak Canyon Member and Cubero Sandstone Tongue of the Dakota

Sandstone

[Approximate stratigraphic position of single occurrences in the member is indicated by an X, and the stratigraphic range of each species,

based on several occurrences, is shown by a linel

Species Oak Canyon Member Cubero Sandstone Tongue

Class Bivalvia:

Nuculana sp.

Barbatia?' tramitensis Stephenson

Modiolus cf. M. santaanaensis Jones

Pinna petrina White

Plesiopinna n. sp.

Gen'illia sp.

Phelopteria cf. P. linguaeformis (Evans and Shumard)

Inoceramus eulessanus Stephenson

cf. I. macconnelli Warren 

Camptonectes symmetricus Herrick and Johnson 

Plicatula arenaria Meek 

Anemia subquadrata Stanton 

Limatula sp.

Pycnodonte cf. P. kellumi (Jones) 

Exogyra columbetta Meek

aff. E. columbella Meek

aquillana Stephenson

sp. A

Ostrea beloiti Logan 

Astarte sp. 

Opisl sp. 

Mediraon sp. 

Granocardium n. sp.

cf. G. productum (Sowerby)

sp.

"Cardium" n. sp. 

Cymbophora emmonsi (Meek) 

Leptosolen angustus Stephenson 

Tellinimem sp.

Protodonax cf. P. elongatus Yokes 

Aphrodina sp. 

Cyprimeria sp. 

Parmicorbula sp.

Pholadomya aff. P. goldenensis Stephenson 

Laternula sp. 

Psilomya levis Stephenson?

aff. P. concentrica (Stanton) 

Class Gastropoda:

Turritella cf. T. shuleri Stephenson

.sp.

Cerithium n. sp.

Graciliala aff. G. umbmna (Stephenson) 

Arrhoges modesta (Cragin)? 

Euspira humilis (Cragin)? 

Gyrodes sp.

Sigaretus textilis Stanton? 

Actaeon n. sp.

Ringicula arlingtonensis Stephenson 

Nonactaeonina? sp. 

Class Cephalopoda:

Turrilites aeutus Passy 

Desmoceras sp.

Calycoceras tarrantense (Adkins) 

Bor"issiakoceras compressum Cobban 

Johnsonites sulcatus Cobban
EARLIER RECORDS OF FOSSILS

TABLE 3.—Distribution of molluscan fossils in the Whitewater Arroyo Shale Tongue and Twowells Sandstone

Tongue

[Approximate stratigraphic position of single occurrences in the member is indicated by an X, and the stratigraphic range of each

species, based on several occurrences, is shown by a linel

Species Whitewater Arroyo 

Shale Tongue Twowells Sandstone Tongue

Class Bivalvia:

Nuculana sp.

Idonearca depressa White

Pinna petrina White

Pinna sp.

Phelopteria sp.

Psendoptem sp.

Inoceramus cf. I. mesabiensis Bergquist

prefragilis Stephenson

ginterensis Pergament 

Camptonectes ex gr. C. virgatus (Nilsson)

sp.

Plicatula cf.P.ferryi Coquand 

Pycnodonte cf. P. kellumi (Jones)

aff. P. kellumi (Jones) 

Exogyra trigeri Coquand

cf. E. oxyntas Coquand

levis Stephenson

aff. E. levis Stephenson 

Ostrea beloiti Logan 

Lopha staufferi (Bergquist) 

Lucina sp. 

Astarte sp. 

Granocardium enstmmi (Bergquist)

trite (White) 

"Cardium" sp.

Cymbophora emmonsi (Meek) 

Leptosolen sp. 

Aphrodina sp. 

Parmicorbula ? sp. 

Pholadotnya sp. 

Laternulal sp. 

Class Gastropoda:

Cerithiopsis sp. 

An chum sp.

Crommium utahensis (White)? 

Class Cephalopoda:

Turrilites n. sp. 

Stomohamites sp. 

Tarrantoceras? sp. 

Calycoceras? canitaurinum (Haas)

cf. C.? canitaurinum (Haas) 

Calycoceras obrieni Young 

Metoicocems aff. M. pmecox Haas

aff. M. latoventer Stephenson

spp.
10 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

recorded "Turrilites cf. T. costatus Lamarck" from 

the upper part of the Dakota near the southwest 

corner of Sandoval County.

RESUME OF FOSSIL OCCURRENCES

Molluscan fossils are present in all members of 

the intertongued Dakota Sandstone and Mancos 

Shale. The fossils usually occur in silty limestone 

concretions, siltstone or sandstone concretions, concretionary siltstone or sandstone beds, or along bedding surfaces of very fine grained sandstone or siltstone beds. Exogyras, however, are often found as 

free specimens in silty shale, and pycnodonts may 

form coquinal beds. Large ammonites in septarian 

limestone concretions are usually fragmented and 

distorted.

The Paguate Sandstone Tongue contains the 

largest variety of mollusks. Most of the species are 

listed on table 1, which shows 25 bivalves, 27 gastropods, and 10 ammonoids in the Paguate. The upper 

part of the Oak Canyon Member also has a large 

and varied molluscan fauna; 34 bivalves, 11 gastropods, and 5 ammonoids from this member are listed 

on table 2. The Clay Mesa Shale Tongue of the 

Mancos Shale contains the fewest species; only 12 

are listed on table 1. The Whitewater Arroyo Shale 

Tongue, which is a more widespread unit than the 

Clay Mesa Tongue, contains a much larger fauna; 

19 bivalves, 2 gastropods, and 8 ammonites listed on 

table 3 are found in this unit.

GEOGRAPHIC DISTRIBUTION

The fossils illustrated in plates 1-21 are from 76 

localities in west-central New Mexico and one locality in the northwest corner of the State. The general localities of 72 of the collections are shown in 

figure 1; table 4 further describes these localities, 

gives the stratigraphic position of the fossils, and 

names the collectors in each case.

CHARACTERISTIC FOSSILS

Idonearca blanpiedi Stephenson

Plate 8, figures 1-3

1953. Idonearca blanpiedi Stephenson, U.S. Geol. Survey 

Prof. Paper 242, p. 63, pi. 11, figs. 1-4 [1952 imprint].

Idonearca blanpiedi is a very stout bivalve that 

has a subtrapezoidal outline and a very convex 

cross section. The shell is fairly smooth except for 

growth lines of irregular height and spacing and a 

few obscure radial ribs. The elongate triangular

TABLE 4.—Localities where fossils were collected

Locality 

(fig. 1)

U.S. Geol.

Survey 

Mesozoic

locality

D6200

2__ D6191

3__ D6187

4__ D9240

5__ D6182

D6183 

D6184

D6137

14__

D5764

D2077

D6164

D5762

D5754

D7338

Collector, year of collection, description 

of locality, and stratigraphic assignment

E. R. Landis and W. A. Cobban, 1967. 

Near Red Wash, 2 miles southeast of 

Bitlabito, San Juan County. Top of 

Twowells Sandstone Tongue.

Cobban, 1967. South side of Tse Bonita 

Wash, in the SW% sec. 2, T. 16 N., 

R. 21 W., McKinley County. Lower 

part of Twowells Sandstone Tongue.

Landis, 1967. Surrender Canyon, in the 

SW^ sec. 23, T. 14 N., R. 21 W., 

McKinley County. Main body of the 

Dakota Sandstone.

Cobban, 1967. Near Manuelito, in the 

SB 1/* sec. 19, T. 14 N., R. 20 W., 

McKinley County. Twowells Sandstone Tongue, from brown-weathering sandstone concretions.

Cobban, 1967. NW 1/* sec. 15, T. 4 N., R. 

20 W., Catron County. Middle of 

Paguate Sandstone Tongue.

Cobban, 1967. Same locality as D6182. 

Top of Paguate Sandstone Tongue.

Cobban, 1967. Same locality as D6182. 

Whitewater Arroyo Shale Tongue, 

from concretionary limestone bed 

about 3 ft above base.

Landis and Cobban, 1967. East of State 

Highway 32 and 4% miles (7 km) 

north of Atarque Creek, in the western part of T. 7 N., R. 17 W., Valencia County. Whitewater Arroyo Shale 

Tongue.

Landis and Cobban, 1967. Northeast of 

Gallup, in the NE% sec. 30, T. 16 

N., R. 17 W., McKinley County. 

Paguate Sandstone Tongue.

Cobban, 1959. Four miles (6.4 km) 

east-southeast of Gallup, McKinley 

County. Twowells Sandstone Tongue, 

from brown-weathering sandstone 

concretions.

C. H. Dane and Landis, 1967. SE 1^ 

SW 1/* sec. 7, T. 12 N., R 16 W., 

McKinley County. Twowells Sandstone Tongue.

Cobban, 1967. Near common corner of 

sees. 27, 28, 33 and 34, T. 16 N., R. 

15 W., McKinley County. Whitewater 

Arroyo Shale Tongue, about middle.

Cobban, 1967. NWV^NW^ sec. 20, T. 

15 N., R. 13 W., McKinley County. 

Float from basal part of Twowells 

Sandstone Tongue.

Landis, Cobban, J. F. Robertson, and 

M. W. Green, 1969. Mount Powell, 

in the E%NW% sec. 8, T. 14 N., R. 

13 W., McKinley County. Whitewater 

Arroyo Shale Tongue, about 15 ft 

(4.6 m) above base.
CHARACTERISTIC FOSSILS 11

TABLE 4.—Localities where fossils were collected—Continued

Locality 

<fi*. 1)

15__

16__

U.S. Geol.

Survey 

Mesozoic

locality

D5759

D5760

Collector, year of collection, description 

of locality, and stratigraphic assignment

D5756

D7332

19__

20__

21__

22__

23__

24__

25__

D7333

D7334

D7335

D5750

D5753

D7328

D5742

26__ D5743

Landis and Cobban, 1967.

sec. 24, T. 15 N., R. 13 W., McKinley 

County. Whitewater Arroyo Shale 

Tongue, about 10 ft. (3m) below top.

Cobban, 1967. SE^NE^ sec. 31, T. 15 

N., R. 12 W., McKinley County. 

Cubero Sandstone Tongue, from 6-ft 

bed of olive-gray sandstone and overlying brown-weathering sandstone 

concretions.

Cobban, 1967. SW%NE% sec. 28, T. 

15 N., R. 12 W., McKinley County. 

Cubero Sandstone Tongue, from 

brown-weathering sandstone concretions.

Landis, Cobban, J. F. Robertson, and 

M. W. Green, 1969. Drainage ditch 

east of State Highway 56, near 

center of sec. 5, T. 14 N., R. 12 W., 

McKinley County. Paguate Sandstone 

Tongue.

Landis, Cobban, Robertson, and Green, 

1969. Same locality as D7332. Paguate Sandstone Tongue, from darkbrown-weathering sandstone concretions.

Landis, Cobban, and Robertson, 1969. 

SW^SE^ sec. 32, T. 15 N., R. 12 

W., McKinley County. Paguate Sandstone Tongue.

Landis, Cobban, Robertson, and Green, 

1969. SE14SEV4 sec. 31, T. 15 N., R. 

12 W., McKinley County. Twowells 

Sandstone Tongue.

Landis and Cobban, 1967. SW^SW1^ 

sec. 25, T. 15 N., R. 12 W., McKinley 

County. Paguate Sandstone Tongue, 

from brown-weathering sandy limestone concretions.

Landis and Cobban, 1967. Casamero 

Lake, in the NWViNE^ sec. 30, T. 

15 N., R. 11 W., McKinley County. 

Twowells Sandstone Tongue.

Landis, Cobban, J. F. Robertson, M. W. 

Green, and T. L. Britt, 1969. NE% 

NEH sec. 25, T. 15 N., R. 12 W., 

McKinley County. Upper part of 

Paguate Sandstone Tongue.

Dane, Landis, and Cobban, 1967. Head 

of Rincon Canyon, in the NW^NE1^ 

sec. 35, T. 14 N., R. 11 W., McKinley 

County. Oak Canyon Member, from 

brown-weathering calcareous sandstone concretions in upper part.

Dane, Landis, and Cobban, 1967, NE x/4 

NE% sec. 25, T. 14 N., R. 11 W., 

McKinley County. Near top of Twowells Sandstone Tongue.

TABLE 4.—Localities where fossils were collected—Continued

Locality 

(fig. 1)

28.

29.

U.S. Geol.

Survey 

Mesozoic

locality

D5392

D5819 

D5377

Collector, year of collection, description 

of locality, and stratigraphic assignment

30__ D5380

32__

36___

38___

D5372

D5812

D5815

D5806

D5325

D5321

D5324

D5383

D5366

Landis and Cobban, 1967.

sec. 36, T. 19 N., R. 1 W., Sandoval 

County. Twowells Sandstone Tongue.

Cobban, 1967. Same locality as D5392. 

Twowells Sandstone Tongue.

Cobban, 1966. About 9/10 mile (1.4 km) 

southeast of Soda Spring on Arroyo 

Cachulie, in T. 17 N., R. 1 W., Sandoval County. Oak Canyon Member, 

from gray silty limestone concretions 

62 ft (18.9 m) above base.

Dane, Landis, and Cobban, 1966. About 

V2 mile south of Chamisa Vega 

Spring, in T. 17 N., R. 1 W., Sandoval County. Clay Mesa Shale Tongue, 

from unit of dark-brown-weathering 

siltstone concretions.

Dane, Landis, and Cobban, 1966. About 

500 ft (152 m) west of Ojito Spring, 

in the NW^NW1^ sec. 29, T. 16 N., 

R. 1 W., Sandoval County. Lower 

part of Paguate Sandstone Tongue.

Cobban, 1967. Ojito Spring, in the 

NW^NW^ sec. 29, T. 16 N., R. 1 

W., Sandoval County. Paguate Sandstone Tongue.

Cobban, 1967. About 1V2 miles (2.4 km) 

N. 30° E. of Ojito Tank, in T. 16 N., 

R. 1 W., Sandoval County. Oak Canyon Member.

Cobban, 1967. Bernalillito Arroyo, in 

the SW% sec. 21, T. 15 N., R. 1 W., 

Sandoval County. Oak Canyon Member, from dark-brown-weathering 

calcareous sandstone bed.

Landis and Cobban, 1966. NW^NE 1/* 

sec. 33, T. 15 N., R. 1 W., Sandoval 

County. Paguate Sandstone Tongue, 

from brown sandstone concretions at 

top.

Cobban, 1966. SE^SE^ sec. 12, T. 13 

N., R. 2 W., Sandoval County. Oak 

Canyon Member, from dark-brownweathering calcareous sandstone concretions.

Landis and Cobban, 1966. NWUNW 1^ 

sec. 7, T. 13 N., R. 1 W., Sandoval 

County. Paguate Sandstone Tongue.

Dane and Landis, 1966. About *4 mile 

(0.4 km) south and \Vz miles (2.4 

km) east of the northwest corner 

of Puerco Dam quadrangle, Sandoval 

County. Paguate Sandstone Tongue.

Dane and Landis, 1966. NE% sec. 29, 

T. 12 N., R. 3 W., Sandoval County. 

Oak Canyon Member, from brownweathering sandy limestone concretions 66 ft (20 m) above base.
12 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

TABLE 4.—Localities where fossils were collected—Continued

Locality 

(fig. 1)

40___

41___

U.S. Geol.

Survey 

Mesozoic

locality

D4018

D5344

42__

43__

44__

D5345

D5347

D5336

D7080

47___

D7081

D7084

49__

D7086

D5741

50__ D5737

D6130

Collector, year of collection, description 

of locality, and stratigraphic assignment

Dane, 1963. Center of sec. 29, T. 12 

N., R. 3 W., Sandoval County. Paguate Sandstone Tongue.

Cobban, 1966. Bottom of arroyo just 

east of State Highway 279, in the 

NW%NE% sec. 29, T. 11 N., R. 5 

W., Valencia County. Whitewater 

Arroyo Shale Tongue, from glauconitic calcareous sandstone concretions 46-51 ft (14-15.5 m) below top.

Dane, Landis, and Cobban, 1966. Same 

locality as D5344, but on east side of 

arroyo. Near base of Twowells Sandstone Tongue.

Dane, Landis, and Cobban, 1966. SW x/i 

NWH sec. 4, T. 10 N., R. 5 W., 

Valencia County. Lower part of Paguate Sandstone Tongue.

Dane, Landis, and Cobban, 1966. West 

end of South Oak Canyon Mesa, in 

the NWV^NWH sec. 15, T. 10 N., 

R. 5 W., Valencia County. Oak Canyon Member, from silty limestone 

concretions 25 ft (7.6 m) below top.

Cobban, 1969. NEUSE% sec. 20 and 

SWViNWV* sec. 21, T. 10 N., R. 5 

W., Valencia County. Oak Canyon 

Member, from dark-brown-weathering silty limestone concretions 56-58 

ft (17-17.7 m) above base.

Cobban, 1969. Same locality as D7080. 

Oak Canyon Member, from ledge of 

hard gray silty limestone 72 ft (22 

m) above base.

Landis, Cobban, and C. H. Maxwell, 

1969. Three miles north of Laguna, 

in the SEHNEH sec. 20, T. 10 N., 

R. 5 W., Valencia County. Paguate 

Sandstone Tongue, from brownweathering sandstone concretions.

Cobban and Maxwell, 1970. NE^/iSE 1! 

sec. 20 and SW&NWU sec. 21, T. 

10 N., R. 5 W., Valencia County. 

Twowells Sandstone Tongue.

Cobban, 1967. Sharp road bend southwest of McCartys in the SE'^iSW 1/! 

sec. 27, T. 10 N., R. 8 W., Valencia 

County. Whitewater Arroyo Shale 

Tongue, from a limestone concretion 

in upper part.

Dane, Landis, and Cobban, 1967. Las 

Ventanas Ridge, in the NW^NE 1^ 

sec. 17, T. 9 N., R. 9 W., Valencia 

County. Whitewater Arroyo Shale 

Tongue, from basal part.

Landis, Dane, and Cobban, 1967-69. 

North of Little Narrows, about 15 

miles (24 km) south of Grants, in 

the SW 1A sec. 6 and NW*4 sec. 7,

TABLE 4.—Localities where fossils were collected—Continued

Locality 

( fig. 1 )

52__

53__

56__

57__

60__

61__

U.S. Geol.

Survey 

Mesozoic

locality

D6781

D7326

D6131

D6133

D2048

D2049

D2051

D5365

D6800

D2053

62 __

63 __

D5329

D5330

Collector, year of collection, description 

of locality, and stratigraphic assignment

T. 8 N., R. 9 W., Valencia County. 

Paguate Sandstone Tongue, from 

brown-weathering sandstone concretions in lower part.

Landis and Cobban, 1968. Same locality 

as D6130. Clay Mesa Shale Tongue, 

from dark-brown-weathering limestone concretions.

Landis, Cobban, and C. H. Maxwell, 

1969. NE%NW% sec. 5, T. 8 N., R. 

9 W., Valencia County. Clay Mesa 

Shale Tongue, from septarian limestone concretions.

Dane and Landis, 1967. NE% sec. 4, 

T. 7 N., R. 10 W., Valencia County. 

Base of Twowells Sandstone Tongue.

Dane and Landis, 1967. Same locality 

as D6131. Top of Twowells Sandstone 

Tongue.

Dane, Cobban, and G. H. Bachman, 

1959. Near McCartys-Acoma Pueblo 

road, in the NE 1^ sec. 23, T. 9 N., R. 

8 W., Valencia County. Cubero Sandstone Tongue.

Dane and Cobban, 1959. West side of 

Canipa Mesa, in the NWHSE 1^ sec. 

14, T. 9 N., R. 8 W., Valencia County. 

Paguate Sandstone Member.

Cobban, 1959. West side of Canipa 

Mesa, in the SE^SE 1^ sec. 14, T. 9 

N., R. 8 W., Valencia County. Twowells Sandstone Tongue, from lower 

part.

Dane and Landis, 1966. West side of 

Canipa Mesa, in the NE^NE 1^ sec. 

23, T. 9 N., R. 8 W., Valencia County. 

Float from Twowells Sandstone 

Tongue.

C. H. Maxwell, 1970. Seama Mesa, in 

the SW%NW% sec. 19, T. 9 N., R. 6 

W., Valencia County. Lower part of 

Cubero Sandstone Tongue.

Dane, Landis, and Cobban, 1966. Deadmans Rock, about 3% miles (5.6 km) 

north-northwest of Acoma Pueblo, in 

the NEViNEH sec. 7, T. 8 N., R. 7 

W., Valencia County. Oak Canyon 

Member, from dark-brown-weathering ferruginous sandstone concretions.

Landis and Cobban, 1966. SE 1! sec. 36, 

T. 8 N., R. 8 W., Valencia County. 

Oak Canyon Member, from brownweathering calcareous siltstone concretions 62% ft (19 m) above base.

Landis and Cobban, 1966. Same locality 

as D5329. Lower part of Cubero 

Sandstone Tongue.
CHARACTERISTIC FOSSILS 13

TABLE 4.—Localities where fossils were collected—Continued

Locality 

(fig. 1)

64___

65___

U.S. Geol.

Survey 

Mesozoic

locality

D5332

D7364

66__ D6794

D6218

68__

69___

70__

71__

72__

D5771

D5785

D5787

D5795

D7345

Collector, year of collection, description 

of locality, and stratigraphic assignment

Landis and Cobban, 1966. Same locality 

as D5329. Clay Mesa Shale Tongue, 

from limestone concretions 25 ft (7.6 

m) above base.

C. H. Maxwell, 1970. Two miles west 

of Acoma Pueblo, in the SE^SW1^ 

sec. 30, T. 8 N., R. 7 W., Valencia 

County. Clay Mesa Shale Tongue, 

from a gray septarian limestone concretion 10 ft (3 m) above base.

Cobban, 1968. North side of Paradise 

Canyon, in the SW^NW 1^ sec. 24, 

T. 7 N., R. 8 W., Valencia County. 

Oak Canyon Member, from brownweathering silty limestone concretions 80 ft (24 m) above base.

Dane and Landis, 1967. About 1 mile 

southeast of Miranda windmill and 

east of Arroyo de Miranda on the 

South Garcia 15-minute quadrangle, 

Valencia County. Oak Canyon Member.

Cobban, 1967. SEi4SEi4 sec. 11, T. 3 

N., R. 7 W., Socorro County. Mancos 

Shale, from sandstone concretions 72 

ft (22 m) above base of Dakota 

Sandstone.

Cobban, 1967. SEi/4 sec. 33, T. 3 N., R. 

5 W., Socorro County. Mancos Shale, 

from white-weathering baked shale 

105 ft (32 m) above base.

Cobban, 1967. Same locality as D5785. 

Mancos Shale, float from gray septarian limestone concretions within 

25 ft (7.6 m) of base of Twowells 

Sandstone Tongue.

Cobban, 1967. About 2V2 miles (4 km) 

west of Riley, in the SW-/4 sec. 16 

and NWVi sec. 21, T. 2 N., R. 4 W., 

Socorro County. Top of Twowells 

Sandstone Tongue.

Landis, Cobban, Robertson, and Green, 

1969. NE^SEVi sec. 8, T. 15 N., R. 

13 W., McKinley County. Top of 

sandstone underlying Whitewater 

Arroyo Shale Tongue.

cardinal area covered by fine chevron-shaped ligamental grooves and the narrow hinge and conspicuous dentition are characteristic of the genus.

Stephenson's types are from the Templeton Member of the Woodbine Formation of Texas. The species is common in very fine grained calcareous sandstone concretions in the Paguate Sandstone Tongue.

Types.—Hypotypes, USNM 239606, 239607.

Idonearca depressa White

Plate 16, figures 20-24; plate 19, figures 10-12

1877. Idonearca depressa White, U.S. Geog. and Geol. Expl. 

Surveys W. of 100th Meridian (Wheeler), v. 4, pt. 

1, p. 183, pi. 18, figs. 13a, b.

1894. Trigonarca depressa (White). Stanton, U.S. Geol. Survey Bull. 106, p. 93, pi. 19, fig. 2 [1893 imprint].

This species differs from Idonearca blanpiedi 

Stephenson by having conspicuous radial ribbing 

over all the shell. The holotype came from "Strata 

of the Cretaceous period; east bank of Rio Puerco, 

6 miles below Casa Salazan [Casa Salazar], New 

Mexico" (White, 1877, p. 183). Most specimens 

from west-central New Mexico are larger than the 

holotype, and some attain lengths of 56 to 62 mm. 

The species is fairly common in the Twowells Sandstone Tongue and in sandstone beds in the Whitewater Arroyo Shale Tongue.

Types.—Hypotypes, USNM 239608-239611.

Pinna petrina White

Plate 1, figures 2, 4; plate 3, figure 8; 

plate 15, figure 21

1874. Pinna petrina White, U.S. Geog. and Geol. Expl. Surveys W. of 100th Meridian (Wheeler), v. 4, p. 182, 

pi. 13, figs. 7a, b.

1881. Pinna stevensoni White, U.S. Natl. Mus. Proc., v. 3, 

p. 47.

1894. Pinna petrina White. Stanton, U.S. Geol. Survey Bull. 

106, p. 88, pi. 19, fig. 4; pi. 20, fig. 1 [1893 imprint].

Pinna petrina is easily recognized by its long and 

narrow shell whose side view has a triangular appearance. The hingeline is very long and moderately 

straight, and the beaks are terminal. A ridge extends along the middle of each valve but disappears 

in the late growth stage. About 8 to 10 weak to 

strong narrow radial ribs are present on the ventral 

half of the shell, and that many or a few more 

weaker radial ribs are present on the dorsal half. 

All radial ribs tend to disappear in the late growth 

stages; the valves then are characterized by conspicuous, closely spaced, irregular growth lines 

(Stanton, 1893, pi. 19, fig. 4). The species attains 

lengths of 150-160 mm.

Pinna petrina is present in very fine grained 

sandy beds in the upper part of the Oak Canyon 

Member and in the Cubero, Paguate, and Twowells 

Sandstone Tongues. All specimens in the collections 

from west-central New Mexico are incomplete even 

though they usually include both valves. Most specimens are internal molds that have patches of 

brown shell material.

The holotype came from "east of Mount Taylor, 1 

mile south of Pajuate, New Mexico." The specimen
14 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

probably came from the Paguate Sandstone Tongue, 

which crops out 1 mile (1.6 km) south of Paguate, 

where it is fossiliferous and contains Pinna. 

Types.—Hypotypes, USNM 239612-239615.

Plesiopinna sp.

Plate 1, figures 1, 3

The bivalve genus Plesiopinna is characterized by 

its subtrigonal shell, terminal umbo, inflated posteroventral part, and long straight edentulous hingeline. Ornamentation on the type species, P. antriniformis Amano (1956, p. 71, pi. 1, figs. 1-5), consists of weak concentric folds and weak radial ribs.

Two specimens from the upper part of the Oak 

Canyon Member seem assignable to this genus. 

These specimens differ from the type species in 

having more conspicuous radial ribbing and in having the ribbing over all but the posterior part of the 

shell.

Figured specimens.—USNM 239616, 239617.

Phelopteria? cf. P.? aguilerae (Bbse)

Plate 7, figures 8, 9

Large pteroid bivalves in the Paguate Sandstone 

Tongue resemble, in their shape and smoothness of 

their shell, the genera Phelopteria and Panis described by Stephenson, (1952, p. 67-70) from the 

Woodbine Formation of Texas. The cardinal area 

of the Paguate specimens differs considerably, however, from that of the Woodbine genera. In the 

Paguate specimens, the cardinal area is massive and 

thick shelled like that of Panis, but the three ligamental pits of that genus are missing. If the cardinal 

area of the Paguate specimens had less breadth, it 

would be more like that of Phelopteria. The Paguate 

specimens, which are much larger than specimens 

of Phelopteria and Panis from Texas, attain a height 

of as much as 10 cm. Most specimens are about as 

long as high. The species described by Bose (1918, 

p. 227, pi. 20, figs. 1, 2, 11, 12) as Avicula aguilerae, 

from the lower Turonian of Coahuila, Mexico, closely resembles the Paguate species in its shape, but 

nothing has been published regarding the cardinal 

area of the Mexican form.

Figured specimen.—USNM 239618.

Inoceramus eulessanus Stephenson 

Plate 3, figures 3, 4

1953. Inoceramus eulessanus Stephenson, U.S. Geol. Survey 

Prof. Paper 242, p. 65, pi. 44, fig. 2 [1952 imprint].

The narrow sharp beak projecting above the 

hingeline is the most characteristic feature of this 

slightly convex species. Most specimens are suberect, and the angle between the axis of the shell 

and the hingeline is large. The height is greater 

than the length, and the outline is elongate-ovate. 

The hingeline is moderately long and straight. The 

anterior margin is broadly rounded, the ventral margin is more sharply rounded, and the posterior margin is very gently rounded to almost straight. Ornamentation consists of concentric undulations of irregular strength and spacing. The species is rather 

small; none of the specimens in the collections from 

west-central New Mexico exceed 10 cm in height.

Inoceramus eulessanus occurs sparsely in the upper part of the Oak Canyon Member. In the Thoreau 

area, a thin very fine grained calcareous sandstone 

bed that seems to be an equivalent of some part of 

the Cubero Sandstone Tongue, contains numerous 

specimens of 7. eulessanus.

The holotype of I. eulessanus is from the Woodbine Formation of Texas. Specimens referable to 

this species occur in the Thatcher Limestone Member of the Graneros Shale in southeastern Colorado 

(Cobban and Scott, 1972, p. 8, 27).

Types.—Hypotypes, USNM 239619, 239620.

Inoceramus cf. I. macconnelli Warren

Plate 2, figure 3; plate 3, figures 5-7

Small inoceramids from very fine grained sandstone slightly above the middle of the main body 

of the Dakota Sandstone show affinities with Inoceramus macconnelli Warren (1930, p. 60, pi. 4, figs. 

1-3) in having narrow sharp beaks that are curved 

anteriorly. The hingeline, which is posterior to the 

beak, is straight and moderately long. Ornamentation on most specimens consists of concentric undulations of unequal strength and spacing. The cotypes of 7. macconnelli consist of a left valve and a 

right valve which are more weakly ornamented than 

those of the New Mexico specimens.

Inoceramus cf. 7. macconnelli was found only in 

the Thoreau area in association with 7. eulessanus. 

Locally specimens are numerous (pi. 2, fig. 3).

Figured specimens.—USNM 239621-239624.

Inoceramus rutherfordi Warren

Plate 7, figures 4, 10-14

1930. Inoceramus rutherfordi Warren, Alberta Research 

Council Geol. Survey Rept. 21, p. 59, pi. 7, figs. 1-3.

1965. Inoceramus rutherfordi Warren. Hattin, Kansas Geol. 

Survey Bull. 178, pi. 4, figs. C, E, F, H.

The squarish outline, well-defined posterior auricle, and conspicuous posterior fold easily identify 

this inoceramid. The posterior fold is sharply delineated by a deep posterior auricular sulcus and,
CHARACTERISTIC FOSSILS 15

on its anterior side, by a shallow sulcus. The shallow 

sulcus is bounded on its anterior side by a weak 

fold. The shell is ornamented by moderately conspicuous rugae of irregular strength.

Inoceramus rutherfordi is widely distributed in 

the western interior of the United States. The types 

are from the Dunvegan Formation in central western Alberta. In west-central New Mexico, 7. rutherfordi is common in very fine grained sandstone concretions in the Paguate Sandstone Tongue. Most individuals are from 50 to 70 mm in height. Ostrea 

beloiti Logan encrusts many specimens.

Types.—Kypotypes, USNM 239625-239629.

Inoceramns arvanus Stephenson

Plate 6, figure 27

1953. Inoceramus arvanus Stephenson, U.S. Geol. Survey 

Prof. Paper 242, p. 65, pi. 12, figs. 6-9 [1952 imprint].

1955. Inoceramus arvanus Stephenson. Stephenson, U.S. 

Geol. Survey Prof. Paper 274-C, p. 55, pi. 4, figs. 

1-3.

This species gave rise to and closely resembles 

Inoceramus rutherfordi Warren. Both species have 

a quadrate form, folds and sulci, well defined posterior auricle, and similar ornamentation. The only 

difference is in the weaker folds and sulci of 7. 

arvanus. In large collections of 7. rutherfordi, some 

specimens have weaker folds and sulci than others 

and could easily pass for 7. arvanus.

A few inoceramids from silty limestone concretions in the upper part of the Clay Mesa Shale 

Tongue have only weak folds and sulci; these specimens are assigned to 7. arvanus.

The holotype of 7. arvanus came from the Lewisville Member of the Woodbine Formation in northern Texas. Stephenson (1955, pi. 4, figs. 1-3) illustrated several specimens from the basal part of the 

Eagle Ford Shale of Texas. In the western interior 

region, 7. arvanus has been found at a few places 

in association with Acanthoceras alvaradoense 

Moreman.

Type.—Hypotype, USNM 239630.

InoceramnS prefragilis Stephenson

Plate 19, figures 1, 2, 4

1953. Inoceramus prefragilis Stephenson, U.S. Geol. Survey 

Prof. Paper 242, p. 64, pi. 12, figs. 10-12; pi. 13, figs. 

1, 2 [1952 imprint].

This is a medium-sized, moderately inflated inoceramid whose height is much greater than its 

length. Beaks are prominent, slightly curved, and 

located at the dorsoanterior corner of the shell. The 

hingeline is long and straight, and an inconspicuous

posterior auricle is present. The anterior side of 

the shell slopes steeply. Ornamentation consists of 

low closely spaced concentric folds that tend to be 

of uniform height. A few irregularly spaced rugae 

are present.

Inoceramus prefragilis is present in silty limestone concretions in the Whitewater Arroyo Shale 

Tongue and in fine-grained sandstone concretions in 

the lower and middle parts of the Twowells Sandstone Tongue.

The types of 7. prefragilis are from the Lewisville Member of the Woodbine Formation of Texas. 

The species is widely distributed in the western interior region in the lower part of the Greenhorn 

Limestone and equivalent rocks.

.—Hypotypes, USNM 239631-239633.

Inoceramus ginterensis Pergament 

Plate 19, figure 3

1966. Inoceramus ginterensis Pergament, Akad. Nauk SSSR 

Geol. Inst. Trans., v. 146, p. 50, pi. 25, fig. 5; pi. 26, 

figs. 1, 2; pi. 27, figs. 1, 2; pi. 28, figs. 1, 2; pi. 29, 

fig. IThis species resembles Inoceramus prefragilis in 

size, shape, and convexity. Ornamentation differs, 

however, inasmuch as 7. ginterensis has numerous 

irregularly spaced rugae and lacks the evenly spaced 

concentric folds of the other species.

Inoceramus ginterensis was originally described 

from specimens collected from Cenomanian rocks in 

northwestern Kamchatka and southern Sakhalin, 

U.S.S.R. The species is abundant in the western interior region in the Hartland Shale Member of the 

Greenhorn Limestone and in the equivalent part of 

the Frontier Formation. In west-central New Mexico, 7. ginterensis occurs in fine-grained sandstone 

concretions in the upper part of the Twowells Sandstone Tongue.

Type.—Kypotype, USNM 239634.

Camptonectes symmetricus Herrick and Johnson

Plate 3, figure 1; plate 5, figures 4-7

1900. Camptonectes symmetricus Herrick and Johnson, Denison Univ. Sci. Lab. Bull., v. 11, art. 9, p. 209.

This pectinid is abundant in silty limestone concretions and calcareous siltstone beds in the upper 

part of the Oak Canyon Member. Herrick and Johnson, unfortunately, did not illustrate any specimens; 

their description is as follows:

Shell small, not over three fourths of an inch in length; 

broadly oval in outline; hingeline imperfectly seen, apparently longer than half of the width of the shell; valves 

convex; cardinal slopes from the beak forming with each 

j other nearly a right angle, straight; surface of valves marked
16 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

by very fine, numerous, irregular, hair-like radiating striae 

which curve strongly upward toward the margin, and also 

by fine concentric striae.

In the gasteropod zone below the Tres Hermanos sandstone in the Rio Puerco valley.

Camptonectes symmetricus may be a synonym for 

some one of the camptonectids described earlier 

from the European Cretaceous. Until the American 

forms are revised, Herrick and Johnson's name is 

accepted.

Types.—Hypotypes, USNM 239731-239735.

Camptonectes ex gr. C. virgatus (Nilsson)

Plate 19, figure 7

Medium-sized specimens of Camptonectes that 

have dense radial striae occur in the Twowells 

Sandstone Tongue. None is well enough preserved 

for positive specific determination, but they belong 

to the group of C. virgatus (Nilsson) according to 

Dr. Annie V. Dhondt (written commun., 1975), who 

examined a latex cast of the specimen illustrated 

here (pi. 19, fig. 7).

Figured specimen.—USNM 239742.

Neithea cf. N. sexcostata (Woodward) 

Plate 10, figures 1, 2

This pectinid has been found only in very fine 

grained sandstone in the Paguate Sandstone Tongue. 

The species has 6 main radial ribs separated by 

deep intercostal areas that bear 4 or 5 weaker ribs 

of variable width. The Paguate form closely resembles the specimen of Neithea sexcostata (Woodward) figured by Dhondt (1973, p. 44, pi. 5, figs. 

2a, b) from the Campanian rocks of Belgium.

Figured specimen.—USNM 239741.

Plicatula arenaria Meek 

Plate 1, figures 5, 6

1876. Plicatula arenaria Meek, in Macomb, J. N., Report of 

the exploring expedition from Santa Fe * * * in 

1859, U.S. Army Eng. Dept., p. 126, pi. 1, figs. 5a-c.

1894. Plicatula arenaria Meek. Stanton, U.S. Geol. Survey 

"Bull. 106, p. 70, pi. 9, figs. 3, 4 [1893 imprint].

The small size, conspicuous radial ribs, and 

sparseness of concentric folds characterize this bivalve. The broadly ovate to subtrigonal outline is 

like that of most members of the genus. Meek (1876, 

p. 127) illustrated two specimens of similar size 

and gave their dimensions as 0.5 inch in height and 

0.43 inch in length. He noted that each valve was 

ornamented by 18 to 20 "rather sharply-elevated 

plications, only about half of which extend to the 

beaks, while the intermediate ones usually extend 

from one-third to one-half way from the free margins."

Plicatula arenaria is a common species (pi. 1, fig. 

5) in calcareous and ferruginous siltstone or very 

fine grained sandstone in the upper part of the Oak 

Canyon Member. None of the specimens in the collections exceeds 11 mm in height. Meek's types came 

from "Covero," which is now the village of Cubero, 

23 miles (37 km) east of Grants, N. Mex. According to C. H. Maxwell (oral commun., 1975), of the 

U.S. Geological Survey, the upper part of the Oak 

Canyon Member of the Dakota Sandstone is well 

exposed and very fossiliferous in a small canyon 

1 mile (1.6 km) south of Cubero, in the SE^SEi/i 

sec. 24, T. 10 N., R. 7 W., Valencia County (Cubero 

7V->-minute quad.).

Outside west-central New Mexico, occurrences of 

P. arenaria are sparse. A few specimens have been 

found in the Thatcher Limestone Member of the 

Graneros Shale in southeastern Colorado (Cobban 

and Scott, 1972, p. 8).

Types.—Hypotypes, USNM 239635, 239636.

Plicatula cf. P. ferryi Coquand

Plate 9, figure 9; plate 16, figures 6-12; plate 19, figures 5, 6

Plicatula ferryi Coquand (1862, p. 221, pi. 16, 

figs. 7-9) is distinguished in attaining a moderately large size and in having numerous and conspicuous radial ribs and concentric rugae. Coquand's 

types are from the Santonian of Algeria. The species has been recorded from the Turonian to the 

Maestrichtian, mostly from Africa.

Specimens that could be P. ferryi occur in sandstone beds in the Paguate Sandstone Tongue, in 

silty limestone concretions in the Whitewater 

Arroyo Shale Tongue, and in the Twowells Sandstone Tongue. All are fragments; none is complete 

enough for a total rib count. The largest fragments 

suggest that the shells attained heights of about 40 

mm. Two specimens, preserved on a thin layer of 

pale-brown fibrous calcite from the Twowells 

Tongue, have color bands; the radial ribs are dark 

brown and the interspaces light brown (pi. 19, fig. 

5).

Figured specimens.—USNM 239637-239646.

Plicatula sp.

Plate 9, figures 4-8

Small specimens of Plicatula characterized by conspicuous growth interruptions occur in the lower 

part of the Mancos Shale in northwestern Socorro 

County. The fossils lie on bedding surfaces of hard 

noncalcareous silty shale. A Paguate age is indicated 

by the presence of Inoceramus rutherfordi Warren, 

Ostrea beloiti Logan, and Turrilites acutus americanus Cobban and Scott.
CHARACTERISTIC FOSSILS 17

Figured specimens.—USNM 239647-239651.

Limatula sp.

Plate 5, figure 8

Silty limestone concretions and calcareous siltstone beds in the upper part of the Oak Canyon 

Member contain a small species of Limatula that 

seems to be more weakly ribbed than other American Cretaceous species. None of the specimens exceeds 13 mm in its longest dimension.

Figured specimen.—USNM 239736.

Pycnodonte cf. P. kellumi (Jones)

Plate 6, figures 21-26; plate 12, figures 1-9; plate 15, figures 

17-20; plate 16, figures 1-5

Jones (1938, p. 107, pi. 3, figs. 3-5) described 

Gryphaea washitaensis var. kellumi as a new form 

from the Indidura Formation of Coahuila, Mexico. 

Two specimens, both left valves, were illustrated. 

These specimens differ from Pycnodonte washitaensis (Hill, 1889, p. 4; Hill and Vaughan, 1898, p. 59, 

pis. 19-23) by having less convexity, a longer hingeline, and a broader umbo. Jones' form is herein regarded as a separate species, and the larger of his 

figured specimens is designated the lectotype (Jones, 

1938, pi. 3, figs. 3, 4, Univ. Michigan 16127). In a 

table (Jones, 1938, table 3) that gives the geographic distribution and stratigraphic range of the 

invertebrate fossils from the areas in Coahuila investigated by Jones, P. kellumi is listed (as 

Gryphaea washitaensis var. kellumi) with fossils of 

Albian, Cenomanian, and Turonian age.

Dr. L. B. Kellum, University of Michigan, Ann 

Arbor, kindly loaned me several of the collections 

of P. kellumi, collected by T. S. Jones from Coahuila. 

Some of the collections were identified as Gryphaea 

washitaensis Hill by Jones, but all specimens seem 

referable to his variety kellumi. Many individuals 

have lengths from 30-34 mm, which is more than 

that of the types. Most specimens have a poorly defined posterior auricle that, on some individuals, is 

bounded by a low sulcus.

Pycnodonts that closely resemble P. kellumi are 

present in sandy limestone concretions in the upper 

part of the Oak Canyon Member, Clay Mesa Shale 

Tongue, and lower half of the Whitewater Arroyo 

Shale Tongue, as well as in sandstone concretions 

and very fine grained sandstone beds in the Paguate 

Sandstone Tongue. Most specimens are larger than 

P. kellumi, and many have lengths of 30-40 mm. 

Faint growth lines and growth squamae give the 

shells a smooth appearance. Chomata are present 

but not conspicuous. The posterior auricle and sulcus, which is inconspicuous in the specimens from

the Clay Mesa Tongue, tend to become a little more 

pronounced on the Paguate specimens. The right 

valves of some specimens from the Paguate Sandstone Tongue have conspicuous radial color bands 

that are dark brown and wider than the interspaces 

(pi. 15, figs. 17, 20). 

'Figured specimens.—USNM 239652-239661.

Pycnodonte aff. P. kellumi (Jones)

Plate 20, figures 1-15

1927. Ostrea (Gryphaeat) patina Meek and Hayden. Reagan, Indiana Acad. Sci. Proc., v. 36, p. 119, text 

figs. 15-26.

This species differs from Pycnodonte cf. P. 

kellumi (Jones) in attaining a slightly larger size 

and in having a more distinct posterior auricle 

bounded by a more clearly defined sulcus. The left 

valve of P. aff. P. kellumi ordinarily attains a height 

of 40-45 mm and a length of 43-49 mm. Growth 

squamae are usually conspicuous, and many specimens have irregular concentric wrinkles on the 

umbo. Most adults have a large broad umbo set 

apart from the rest of the shell by either a change 

in slope or by a depression. Chomata (small ridgelets and pits along the anterior and posterior margins of the valves) are vermiculate and as much as 

5 mm long.

Color bands that radiate from the beaks on both 

valves are present on a few individuals. The bands 

are dark brown and variable in width but wider 

than the light-brown interspaces. Similar color 

bands were observed on a specimen of P. newberryi 

(Stanton) (Stokes and Stifel, 1964).

The valves of P. aff. P. kellumi are thick, and 

some have cirripede and sponge borings like those 

described and illustrated for a Jurassic Gryphaea 

by Hallam (1963, p. 563, text fig. 5). A fine vesicular structure is visible on a few weathered specimens.

Pycnodonte aff. P. kellumi could just as well be 

referred to as P. aff. P. newberryi (Stanton) because of its intermediate character between P. cf. 

P. kellumi and P. newberryi. The species described 

by Stanton (1893, p. 60, pi. 5, figs. 1-5) as Gryphaea 

newberryi is a younger pycnodont that has a narrower shell, a more convex left valve, and a smaller 

umbo. Many records in the literature of "Gryphaea 

newberryi Stanton" are probably Pycnodonte aff. P. 

kellumi. The " 'Gryphaea' newberryi (broad form)" 

of Landis, Dane, and Cobban (1973a, p. J4, J9, J25, 

J28, J31, J32, J36) is P. aff. P. kellumi. The specimens of P. aff. P kellumi described and illustrated 

as examples of Ostrea (Gryphaeal) patina Meek
18 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

and Hayden by Reagan (1927, p. 119, text figs. 15- 

26), are from the Dakota Sandstone at Steamboat, 

on the southeastern side of Black Mesa, Apache 

County, Ariz.

Outside the Black Mesa-San Juan Basin area, occurrences of P. aff. P. kellumi are uncommon. A few 

specimens have been found in the upper part of the 

Frontier Formation in the Bighorn and Powder 

River Basins of Wyoming in association with Inoceramus ginterensis Pergament, Metoicoceras muelleri Cobban, and M. defordi Young. Farther north, 

in central Montana, P. aff. P. kellumi occurs in the 

Mosby Sandstone Member of the Greenhorn Formation.

Figured specimens.—USNM 239662-239666.

Exogyra columbella Meek

Plate 5, figures 14-22

1876. Exogyra columbella Meek, in Macomb, J. N., Report 

of the exploring expedition from Santa Fe * * * in 

1859, U.S. Army Eng. Dept., p. 124, pi. 1, figs. 3a-d.

1877. Exogyra costata Say var. fluminis White, TJ.S. Geog. 

and Geol. Surveys W. of 100th Meridian (Wheeler), 

v. 4, pt. 1, p. 174, pi. 17, figs. 3a-*d.

1953. Exogyra columbella Meek. Stephenson, U.S. Geol. Survey Prof. Paper 242, p. 77, pi. 17, figs. 4-6 [1952 

imprint!.

This is a moderate-sized species characterized 

by conspicuous radial ribs that extend over all or 

much of the left valve and by the presence of a 

prominent umbonal ridge in the early growth stages. 

The types came from "Covero," which is now the 

village of Cubero, 23 miles (37 km) east of Grants, 

N. Mex. The specimens are probably from the same 

beds in the upper part of the Oak Canyon Member 

that yielded the types of Plicatula arenaria Meek.

Meek (1876, p. 125) gave the height of the holotype as 1 inch (25 mm). Strong ribs that radiate 

from the beak completely cover this specimen. Three 

specimens were illustrated by White (1877, pi. 17, 

figs. 3a, b) as Exogyra costata Say var. fluminis, 

and later as E. columbella Meek (White, 1884, pi. 

55, figs. 5, 6). The largest of these is an adult. This 

individual reveals that the adults attain heights of 

nearly 40 mm and that costation disappears on the 

outer surface of the shell in the later growth stages. 

However, an internal mold of a large unfigured 

adult in White's type lot shows that ribbing reappears along the ventral margin of the anterior side 

of the left valve at a late growth stage.

Well-preserved examples of E. columbella occur 

in silty limestone concretions, very fine grained calcareous sandstone concretions, and concretionary 

ferruginous very fine grained sandstone beds in the

upper part of the Oak Canyon Member and lower 

part of the Cubero Sandstone Tongue. Outside the 

west-central New Mexico area, E. columbella has 

been found at many localities as far north as the 

Black Hills in northeastern Wyoming and westernmost South Dakota. In Texas, E. columbella occurs 

in the Lewisville Member of the Woodbine Formation (Stephenson, 1952, p. 77, pi. 17, figs. 5, 6). 

.— Hypotypes, USNM 239667-239671.

Exogyra aff. E. columbella Meek 

Plate 5, figures 9-13

Exogyras that resemble Exogyra columbella in 

having costation over much of the left valve occur in 

silty limestone concretions and very fine grained 

sandstone beds in the upper part of the Oak Canyon 

Member and in the overlying Cubero Sandstone 

Tongue. The shells, however, tend to be smaller and 

more convex, and the ribs are thinner and more 

numerous. Most lack an umbonal ridge on the left 

valve. Some individuals have costation only on the 

beak and umbo.

Figured specimens.— USNM 239672-239674.

Exogyra aquillana Stephenson

Plate 2, figures 1, 2

1953. Exogyra aquillana Stephenson, U.S. Geol. Survey Prof. 

Paper 243-E, p. 60, pi. 13, figs. 5-8.

The small size and smooth shell are distinctive 

features of this species. Stephenson observed that 

most specimens are less than 17 mm in height. The 

types are from the Woodbine Formation of Texas.

Exogyra aquillana is present in very fine grained 

calcareous sandstone and in silty limestone concretions in the upper part of the Oak Canyon Member 

and lower part of the Cubero Sandstone Tongue of 

the Dakota Sandstone. Many specimens attain 

heights of 18-20 mm.

Types.— Hypotypes, USNM 239675, 239676.

Exogyra levis Stephenson 

Plate 15, figures 1-16; plate 20, figures 16-18

1953. Exogyra columbella levis Stephenson, U.S. Geol. Survey Prof. Paper 242, p. 77, pi. 18, figs. 1-3 [1952 

imprint].

This species differs from Exogyra columbella 

Meek in attaining a slightly larger size, in lacking 

an umbonal ridge, and in only occasionally possessing costae on the umbo. The holotype and figured 

paratype are from the Templeton Member of the 

Woodbine Formation of Texas.

Exogyra levis is a common species in the Paguate 

| Sandstone Tongue, Whitewater Arroyo Shale
CHARACTERISTIC FOSSILS 19

Tongue, Twowells Sandstone Tongue, and in the 

basal part of the overlying part of the Mancos 

Shale. One collection from the top of the Cubero 

Sandstone Tongue may represent the oldest occurrence of the species. Specimens of unusually large 

size were collected from a very fine grained olivegray sandstone bed just beneath the Whitewater 

Arroyo Shale Tongue near Manuelito, N. Mex. 

(USGS D6187; pi. 15, figs. 11-16).

The exogyras from the upper part of the Dakota 

Sandstone of the Black Mesa area of northeastern 

Arizona, figured by Reagan (1927, p. 125-127, figs. 

3-9) as E. columbella Meek and E. laeviuscula 

Roemer, are probably costate and noncostate specimens of E, levis. Some of the records of E. columbella in west-central New Mexico are probably 

based on costate specimens of E. levis (for example, 

Barton, 1910, p. 57).

In the western interior region, E. levis is common 

only in northwestern New Mexico, northeastern 

Arizona, and southern Utah. Although the species 

has not been found in Wyoming, it does occur 

farther north in central Montana in association 

with Metoicoceras muelleri Cobban in the Mosby 

Sandstone Member of the Greenhorn Formation.

Types.—Hypotypes, USNM 239677-239684.

Exogyra sp. A

Plate 5, figure 23-28

This species, which has been found only in the 

Cubero Sandstone Tongue, attains a large size and 

has a smooth, very convex left valve. Adults attain 

heights of 60-75 mm. The species resembles 

Exogyra levis Stephenson in its form and in its 

smoothness of shell, but species A is twice as large 

and umbonal costae are lacking. Small specimens 

cannot be distinguished from similar-sized noncostate individuals of E. levis.

Exogyra sp. A resembles Rhynchostreon Bayle as 

defined and illustrated by Stenzel (1971, p. N1122, 

fig. J97). Both forms have a strongly coiled beak 

and a nearly smooth shell that lacks costae, but the 

Cubero species has a broader umbo and lacks a 

radial sulcus.

Figured specimens.—USNM 239685-239687.

Exogyra aff. E. levis Stephenson 

Plate 17, figures 1, 2, 4; plate 18, figures 1, 2

Some exogyras from the Whitewater Arroyo 

Shale Tongue and from the basal part of the Mancos 

Shale overlying the Twowells Sandstone Tongue 

resemble Exogyra levis Stephenson in their shape 

and general sculpture, but they differ mainly in having exceptionally thick shells. The umbonal area on 

the left valve has radial ribs, and on some specimens, the ribbing is very fine. Specimens that have 

both valves have not been found, but certain right 

valves in the collections probably belong to this 

species (pi. 17, figs. 1, 2, 4). These valves have 

weak growth squamae crossed by delicate radial 

ribs. Complete left valves are lacking in the collections, but the fragments suggest an adult size a 

little larger than most adults of E. levis. Color bands 

radiating from the umbo are present on the left 

valves of some individuals. The bands are dark 

brownish gray and about as wide as the lighter gray 

interspaces.

Figured specimens.— USNM 239688-239691.

Exogyra cf. E. oxyntas (Coquand) 

Plate 10, figures 7-9, 11

Fragments of large very thick-shelled costate 

exogyras from the Paguate Sandstone Tongue and 

the Whitewater Arroyo Shale Tongue may represent Exogyra oxyntas Coquand (1869, p. 140, pi. 44, 

figs. 1-9; pi. 46, figs. 14, 15). Coquand's species is a 

large form that has numerous closely spaced ribs 

covering all of the left valve. Reeside (1929, p. 268- 

270), after reviewing the published record of the 

E. oxyntas-E. olisiponensis group of species, concluded that it represented one variable species — E. 

olisiponensis Sharpe (1850, p. 185, pi. 19, figs. 1, 

2). Most illustrations of E. olisiponensis show a 

form that has widely spaced costae which are much 

narrower than the interspaces. Specimens like these 

occur at the top of the Dakota Sandstone in southern Utah associated with pycnodonts and other fossils that suggest an age slightly younger than the 

Twowells Sandstone Tongue of west-central New 

Mexico. The fragments of Exogyra from the older 

Paguate and Whitewater Arroyo Tongues have the 

closely spaced costae like that of E. oxyntas and, 

until better material is available, these fragments 

seem best compared to Coquand's species.

Figured specimens.— USNM 239692-239695.

Exogyra trigeri (Coquand)

Plate 9, figures 10-20; plate 16, figures 16-19; plate 17, 

figures 3, 5-10; plate 18, figures 3-9; plate 20, figures 19, 20

1869. Ostrea trigeri Coquand, Monographic du genre Ostrea; Terrain cretace: p. 199, pi. 51, figs. 1, 2.

1971. Exogyra trigeri (Coquand). Stenzel, in Moore, R. C., 

ed., Treatise on invertebrate paleontology, Part N, 

v. 3, Mollusca 6, Bivalvia, p. N1116, figs. 2a, b.

A left valve of low convexity ornamented by numerous rough growth squamae crossed by weak 

radial ribs characterizes this moderately large spe-
20 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

cies. Coquand's type came from the upper Cenomanian of France.

Exogyra trigeri is a common species in very fine 

grained thin sandstone layers in the Whitewater 

Arroyo Shale Tongue, where some individuals attain 

heights of as much as 10 cm. The species has a considerable stratigraphic range; it is found as low as 

the Clay Mesa Shale Tongue and as high as the basal 

part of the Mancos Shale above the Twowells Sandstone Tongue of the Dakota.

Attachment areas on the left valves of E. trigeri 

vary greatly in size. The specimens were attached 

to Inoceramus, Exogyra, Pycnodonte, Plicatula, 

Camptonectes, Granocardium, and Turritella. Many 

shells have sponge borings, and a few have cirripede 

borings.

Specimens from the Paguate Sandstone Tongue 

and some from the Whitewater Arroyo Shale 

Tongue have more erect left valves, greater convexity, and weaker and sparser radial ribs than the 

typical form. Some very massive thick shells that 

are much distorted by large attachment areas may 

be unusual representatives of this species in the 

Whitewater Arroyo Shale Tongue.

Types.—Hypotypes, USNM 239696-239712.

Ostrea beioiti Logan

Plate 1, figures 4-7

1899. Ostrea beioiti Logan, Field Columbian Mus. Geol. Ser.,

v. 1, no. 6, p. 214, pi. 25, figs. 7, 8. 

1965. Ostrea beioiti Logan. Hattin, Kansas Geol. Survey Bull.

178, pi. 4, figs. A, B, D, G, I.

This is a small, mostly smooth oyster that tends 

to be elongated and gently curved. The shape, however, is considerably varied. The left valve is convex, and the right is almost flat. Chromata are 

numerous and conspicuous. A few inconspicuous 

radial ribs are present on the ventroanterior part of 

the left valve of some individuals.

Ostrea beioiti is widely distributed in the western 

interior^-region of the United States and Canada 

(McNeil and Caldwell, 1974). In west-central New 

Mexico, the species is common in very fine grained 

sandstone concretions in the Paguate Sandstone 

Tongue. Some specimens are attached to valves of 

Inoceramus rutherfordi Warren (pi. 7, fig. 4). A few 

specimens of O. beioiti occur in silty limestone concretions in the Whitewater Arroyo Shale Tongue 

and in the upper part of the Clay Mesa Shale 

Tongue. The species ranges up into the basal part 

of the Twowells Sandstone Tongue and possibly 

down as low as the upper part of the Oak Canyon 

Member.

-Hypotypes, USNM 239713-239716.

Lopha staufferi (Bergquist)

Plate 19, figures 8, 9

1944. Ostrea (Alectryonia) staufferi Bergquist, Jour. Paleontology, v. 18, no. 1, p. 15, pi. 9, figs. 1-10.

Bergquist described Lopha staufferi as a smallto medium-sized oyster that curves toward the rear 

and is ornamented by conspicuous plications that 

generally number 10 to 12 along the anterior side of 

the right valve. The adductor muscle scar is "large, 

broad below, narrowest and indented above, situated 

close to posteroventral area." The holotype is 55 mm 

high.

A few plicate oysters from the lower part of the 

Twowells Sandstone Tongue are assigned to Lopha 

staufferi. Most are internal molds 50-85 mm in 

height.

Plicate oysters are common in the Cretaceous 

rocks of Europe and Africa, and many species have 

been described. Lopha staufferi resembles several of 

these species and may be one of them, such as L. 

diluviana (Linne), which was illustrated by 

Coquand (1869, pi. 40, figs. 1-4) and Roman and 

Mazeran (1920, pi. 9, fig. 6; pi. 10, figs. 1, 2) from 

the Cenomanian and Turonian of France.

Types.—Hypotypes, USNM 239717, 239718.

Granocardium trite (White)

Plate 21, figures 1-4, 7

1879. Cardium trite White, U.S. Geol. and Geog. Survey 

Terr. (Hayden), llth Ann. Kept. p. 291, pi. 5, figs. 

4a, b.

1894. Cardium trite White. Stanton, U.S. Geol. Survey Bull 

106, p. 100, pi. 22, figs. 7, 8 [1893 imprint].

White (1879, p. 292) gave the dimensions of the 

holotype as 35 mm high and 36 mm long. His drawing shows about 73 almost equally spaced fine radial 

ribs. White observed that every third rib had many 

small nodes or short spines. The type specimen, an 

internal mold of light-gray very fine grained sandstone, came from "Cretaceous strata, probably 

equivalent with the lower portion of the Colorado 

Group; head of Waterpocket Canon, Southern 

Utah." Latex casts of the impressions of two incomplete specimens in the lot from which White selected his type are shown on plate 21, figures 4, 7.

Marine rocks older than the Twowells Sandstone 

Tongue are unknown in southern Utah. The Dakota 

Sandstone and the overlying Mancos Shale crop out 

along the east flanks of the Waterpocket fold 

(Hackman and Wyant, 1973), where Gregory and 

Moore, (1931, p. 100) recorded Cardium [Granocardium'] trite from sandstone just above the Dakota 

Sandstone. Fred Peterson, of the U.S. Geological
CHARACTERISTIC FOSSILS 21

Survey, has recently collected G. trite associated 

with Metoicoceras defordi Young from the uppermost 3 or 4 feet of the Dakota Sandstone about 30 

miles (48 km) south of the Waterpocket fold exposures (U.S. Geol. Survey Mesozoic Iocs. D5239 

and D5240, in the NWi/4 sec. 24, T. 41 S., R. 8 E., 

Kane County. Utah). Peterson's specimens, although few in number, are very finely ribbed, but 

none has as great a rib count as indicated on 

White's drawing of the holotype.

Specimens that seem assignable to G. trite occur 

in the Twowells Sandstone Tongue and possibly in 

the Paguate Sandstone Tongue in west-central New 

Mexico. The rib densities are comparable to those 

of the specimens collected by Peterson from southern Utah.

Types.— Hypotypes, USNM 239719-239722.

Granocardium enstromi (Bergquist)

Plate 8, figures 4-7, 10, 11

1944. Cardium enstromi Bergquist, Jour. Paleontology, v. 18, 

no. 1, p. 22, pi. 1, figs. 6, 7, 12.

Granocardium enstromi is a common species in 

the Paguate Sandstone Tongue. The species closely 

resembles G. trite (White), but it has fewer ribs 

and, in most parts of the shell, every other rib is 

tuberculate. On some individuals (pi. 8, figs. 4, 5), 

the tubercles attain a large size. Ribs number about 

53.

The holotype is from northern Minnesota. Elsewhere in the western interior region, G. enstromi 

is known only from west-central New Mexico. 

.— Hypotypes, USNM 239723-239726.

Granocardium (Criocardium) cf. G. productum (Sowerby) 

Plate 3, figure 2

A few internal molds of an inflated quadrate species from the Oak Canyon Member and Cubero 

Sandstone Tongue could be the species named by 

J. de C. Sowerby (cited in Sedgwick and Murchison, 

1835, p. 417, pi. 39, fig. 15) as Cardium productum. 

An impression of part of a valve in the very finegrained sandstone matrix from one of the localities 

clearly reveals the ornamentation. Ribs are numerous, narrow, and smooth, and the intercostal space 

is occupied by closely spaced tubercles. On part of 

the surface, every other row of tubercles is larger 

than the intervening one.

Figured specimen. — USNM 239727.

Aphrodina cf. A. munda (Stephenson)

Plate 7, figures 1-3

Very fine grained sandstone concretions in the 

upper half of the Paguate Sandstone Tongue contain a few bivalves that might be Aphrodma munda 

(Stephenson, 1952, p. 106, pi. 26, figs. 14-19). The 

Paguate specimens tend to have a slightly more 

elongate shape than Stephenson's types, which are 

from the Templeton Member of the Woodbine Formation of Texas.

Figured specimens.—USNM 239737, 239738.

Legumen ellipticum Conrad

Plate 9, figures 1-3

1858. Legumen ellipticus Conrad, Acad. Nat. Sci. Philadelphia Jour., 2d ser., v. 3, p. 325, pi. 34, fig. 19.

Specimens that seem assignable to Conrad's species are present in very fine grained sandstone in the 

Paguate Sandstone Tongue. Conrad's sketch of the 

holotype shows narrower anterior and posterior 

margins than those of the Paguate specimens, but 

the topotype and hypotypes illustrated by Stephenson (1941, pi. 42, figs. 13-19) are more like the 

Paguate forms. This elongate, narrow bivalve seems 

to have a great stratigraphic range inasmuch as the 

holotype came from the Ripley Formation of Mississippi, the age of which is probably very late 

Campanian and very early Maestrichtian.

Types.—Hypotypes, USNM 239739, 239740.

Pholadomya aff. P. goldenensis Stephenson 

Plate 5, figure 3

A few pholadomyids from the upper part of the 

Oak Canyon Member resemble Pholadomya goldenensis Stephenson (1952, p. 87, pi. 21, figs. 19-22) 

in their elongate form and in their concentric folds 

crossed by conspicuous radial ribs. The Oak Canyon 

specimens, however, are smaller and have about 12 

radial ribs, whereas the types have about 14. Stephenson's types are from the Templeton Member of 

the Woodbine Formation of Texas.

Figured specimen.—USNM 239728.

Psilomya aff. P. concentrica (Stanton) 

Plate 5, figures 1, 2

Several collections of fossils from the upper part 

of the Oak Canyon Member and lower part of the 

Cubero Sandstone Tongue contain a species of 

Psilomya resembling P. concentrica (Stanton, 1893, 

p. 119, pi. 26, figs. 8-10). The New Mexico specimens differ in having finer and more closely spaced 

concentric folds on the umbonal part of the shell. 

Stanton's types are from the middle Turonian Codell 

Sandstone Member of the Carlile Shale of southcentral Colorado. The species occurs in older rocks, 

however, inasmuch as Stephenson (1952, p. 92, pi. 

22, figs. 13-20) found it in the Woodbine Formation (Cenomanian) of Texas. Homomya casei Jones
22 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

(1938, p. Ill, pi. 4, figs. 14, 18, 19), from the Indidura Formation of Coahuila, Mexico, resembles 

the New Mexico specimens in its general shape and 

convexity, but it attains a larger size and may have 

coarser sculpture.

Figured specimens.—USNM 239729, 239730.

Turritella shuleri Stephenson? 

Plate 8, figure 10

1953. Turritella shuleri Stephenson, U.S. Geol. Survey Prof. 

Paper 242, p. 153, pi. 36, figs. 14-19 [1952 imprint].

High-spired gastropods that are probably Turritella shuleri Stephenson (N. F. Sohl, written commun., 1970) occur in very fine grained sandstone 

in the Paguate Sandstone Tongue. The piece of fossiliferous sandstone illustrated in plate 8, figure 10, 

has several small ends of a Turritella that has four 

primary rows of beaded spiral ribs similar to those 

on the small end of one of the paratypes figured by 

Stephenson (1952, pi. 36, fig. 18).

Type.—Hypotype, USNM 239725.

Arrhoges modesta (Cragin)?

Plate 2, figure 4

1893. Anchura modesta Cragin, Texas Geol. Survey 4th Ann.

Rept. for 1892, p. 18. 

1953. "Anchura'' modesta Cragin. Stephenson, U.S. Geol.

Survey Prof. Paper 242, p. 179, pi. 39, figs. 7-11

[1952 imprint!.

This nearly smooth gastropod occurs in great 

numbers in very fine grained calcareous sandstone 

and siltstone and silty limestone in the upper part of 

the Oak Canyon Member. The abundance of this 

species is the source of the "Gasteropod zone" terminology of Herrick and Johnson (1900, p. 187). 

Cragin's specimens are from the Woodbine Formation of Grayson County, Texas.

Type.—Hypotype, USNM 239743.

Turrilites (Turrilites) acutus Passy

Plate 4, figures 4, 5

1832. Turrilites acutus Passy, Description geologique du Departement de la Seine-Inferieure, atlas, p. 9, pi. 16,

figs. 3, 4. 

1972. Turrilites (Turrilites) acutus Passy. Cobban and Scott,

U.S. Geol. Survey Prof. Paper 645, p. 52, pi. 14,

fig. 6, text fig. 20.

This helical ammonoid has three equal rows of 

tubercles connected by ribs that obliquely cross the 

flank of the whorls. Two rows of nearly equal sized 

tubercles lie on the flank of the whorls, and a row 

of smaller ones is present at the base of the whorls.

Turrilites acutus is present sparsely in the upper 

part of the Oak Canyon Member and lower part of 

the Cubero Sandstone Tongue. In southeastern Colorado, the species occurs in the Thatcher Limestone 

Member of the Graneros Shale.

Types.—Hypotypes, USNM 239744, 239745.

Turrilites (Turrilites) acutus americanus Cobban and Scott

Plate 10, figures 3-6, 10, 12

1972. Turrilites (Turrilites) acutus Passy americanus Cobban and Scott, U.S. Geol. Survey Prof. Paper 645, 

p. 53, pi. 11, figs. 1-11; text fig. 21.

This chronologic subspecies differs from Turrilites acutus Passy chiefly in having smaller and 

weaker tubercles at the base of the whorls. In westcentral New Mexico, Turrilites acutus americanus 

has been found only in the Paguate Sandstone 

Tongue or in age-equivalent shale, in association 

with Inoceramus rutherfordi Warren and Acanthoceras amphibolum Morrow. In southeastern Colorado, the subspecies occurs in concretionary limestone at the top of the Graneros Shale (Cobban and 

Scott, 1972, p. 7).

Types.—Hypotypes, USNM 239746-239750.

Desmoceras (Pseudouhligella) sp. 

Plate 4, figure 7

The subgenus Pseudouhligella differs from Desmoceras in having a wider umbilicus and more 

compressed whorls. The age range is late AlbianTuronian.

A large laterally crushed specimen from the upper 

part of the Oak Canyon Member is shown on plate

4. This specimen is unusual because it is septate at 

a diameter of 100 mm. Most illustrated specimens 

of Pseudouhligella have smaller phragmocones. 

Figured specimen.—USNM 239751.

Desmoceras (Pseudouhligella) aff. D. japonicum Yabe

Plate 11, figures 1-6, 9, 10

This species seems to differ from Desmoceras 

(Pseudouhligella) japonicum Yabe (1904, p. 35, pi.

5. figs. 3, 4) only in the form of the constrictions. On 

the New Mexico species, the constrictions crossing 

the venter are narrow and nearly V-shaped, whereas 

on D. (P.) japonicum they are broader and Ushaped. The occurrences in west-central New Mexico 

are in the middle and upper part of the Paguate 

Sandstone Tongue.

Figured specimens.—USNM 239752, 239753.

Calycoceras (Conlinoceras) tarrantense (Adkins)

Plate 3, figure 9; plate 4, figures 1-3, 6

1928. Metacalycocerasl tarrantense Adkins, Texas Univ.

Bull. 2838, p. 241, pi. 28, fig. 3; pi. 29, fig. 1. 

1928. Acanthoceras wintoni Adkins, Texas Univ. Bull. 2838,

p. 243, pi. 25, figs. 2, 3.
CHARACTERISTIC FOSSILS 23

This robust ammonite is characterized by sparse 

ribs that alternate in length and either lack umbilical tubercles or just show a slight thickening where 

the tubercules would be. All ribs on specimens less 

than 80-100 mm in diameter have lower and upper 

ventrolateral tubercles and a clavate midventral 

tubercle.

Adkins' specimens are from the Lewisville Member of the Woodbine Formation of Texas. The species is an uncommon fossil in the upper part of the 

Oak Canyon Member and in the lower part of the 

Cubero Sandstone Tongue.

Types.—Hypotypes, USNM 239762-239764.

Calycoceras? canitaurinum (Haas)

Plate 21, figure 17

1949. Mantelliceras canitaurinum Haas, Am. Mus. Nat. History Bull., v. 93, art. 1, p. 9, pis. 1-3; p. 4, figs. 1, 

2, 4; text figs. 1-4.

This is a large stout ammonite that is slightly 

evolute and has a squarish whorl section. Ribs alternate in length, and the longer ones rise from tubercles at the umbilical shoulder. On the adult 

whorls, all ribs rise into blunt tubercles at the ventrolateral margin and cross the venter as low, broad, 

flat ribs. Ribs on the innermost whorls are narrow 

and closely spaced, and have pointed umbilical, lateral, ventrolateral, and siphonal tubercles.

Some fragments of large ammonites in the Whitewater Arroyo Shale Tongue and Twowells Sandstone Tongue seem assignable to Calycoceras ? canitaurinum. Other fragments have more widely spaced 

ribs and are referred to as Calycoceras ? cf. C. ? canitaurinum on table 3. One of the latter forms has a 

diameter of 490 mm.

The types of C. ? cf. C. ? canitaurinum are from 

the basal part of the Cody Shale near Greybull, Wyo. 

The species has been found in the upper part of the 

Frontier Formation at many localities in Wyoming 

(for example, Rawlins area, described in Cobban 

and Reeside, 1952, p. 1944). Fragments of a large 

ammonite that might be this species were found 

much farther north in northwestern Montana (Cobban, 1951, p. 2184).

Type.—Hypotype, USNM 239754.

Tarrantoceras rotatile Stephenson

Plate 6, figures 8-10, 28, 29; plate 11, figures 7, 8, 11-16; 

plate 12, figures 13, 14; text figure 4

1955. Tarruntoceras rotatile Stephenson, U.S. Geol. Survey 

Prof. Paper 274-C, p. 59, pi. 5, figs. 1-10; also T. 

stantoni Stephenson, p. 60, pi. 5, figs. 11-21, T. 

Kllianense Stephenson, p. 60, pi. 5, figs. 22-27, and 

IT. multicostatum Stephenson, p. 61, pi. 6, figs. 21- 

23.

Tarrantoceras Stephenson (1955, p. 59) has a 

fairly wide umbilicus and flattened flanks. Numerous ribs cross the flanks and venter, and support 

nodate umbilical and lower ventrolateral tubercles 

and clavate upper ventrolateral and siphonal tubercles. The genus seems to differ from Eucalycoceras 

Spath (1923, p. 144) only in having a much simpler 

suture (fig. 4).

FIGURE 4.—External suture (X 2) of Tarrantoceras 

rotatile Stephenson (pi. 6, figs. 8-10) at a whorl 

height of 21 mm. Heavy line marks the middle of 

the external lobe; dashed line marks the umbilical 

margin. Hypotype, USNM 239755.

The types of Tarrantoceras rotatile came from 

the basal part of the Eagle Ford Shale of Texas. 

The species is variable, ranging from finely ribbed 

and weakly tuberculate to coarsely ribbed and 

strongly tuberculate. Ammonites assignable to T. 

rotatile occur in the Clay Mesa Shale Tongue and 

Paguate Sandstone Tongue.

Types.—Hypotypes, USNM 239755-239761, 239- 

783.

Acanthoceras amphibolum Morrow

Plate 8, figures 8, 9; plate 12, figures 10-12, 15-23; text 

figure 5

1935. Acanthocerast amphibolum Morrow, Jour. Paleontology, v. 9, no. 6, p. 470, pi. 49, figs. 1-4, 6; pi. 51, 

figs. 3, 4; text fig. 4.

The inner whorls of Acanthoceras amphibolum 

have nodate umbilical and lower ventrolateral 

tubercles, and clavate upper ventrolateral and siphonal tubercles. Upper ventrolateral and siphonal 

tubercles, which are located on broad ridges that 

cross the venter, are usually asymmetrically clavate, 

the steep side being forward. Adult whorls have 

ventrolateral horns and a broadly arched venter 

that supports a low midventral ridge. The suture 

(fig. 5) is about as incised as those of most illustrated specimens that have been assigned to Acanthoceras.

The holotype of A. amphibolum is from the uppermost part of the Graneros Shale of Kansas. In westcentral New Mexico, the species has been found only 

in the Paguate Sandstone Tongue of the Dakota 

Sandstone. Acanthoceras amphibolum has been collected at many localities in Colorado, Kansas, Wyo-
24 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

FIGURE 5.—External suture (X 3) of Acanthoceras amphibolum Morrow (pi. 12, figs. 22, 23) at a diameter of 77 mm. 

Heavy line marks the middle of the external lobe; curved dashed line marks the umbilical margin; and closed dashed 

lines mark the position of tubercles on the shell. Hypotype, USNM 239770.

ming, South Dakota, and Montana in association 

with Ostrea beloiti Logan and Inoceramus rutherfordi Warren.

Types.—Hypotypes, USNM 239765-239770.

Acanthoceras alvaradoense Moreman 

Plate 6, figures 1-7, 11-20; text figure 6

1942. Acanthoceras alvaradoense Moreman, Jour. Paleontology, v. 16, no. 2, p. 205, pi. 32, fig. 6; text figs. 

2O, 2T.

1955. Euomphaloceras alvaradoense (Moreman). Stephenson, U.S. Geol. Survey Prof. Paper 274-C, p. 63, 

pi. 7, figs. 1-9.

The adults of this species resemble the adults of 

Acanthoceras amphibolum Morrow. The chief difference between these species is in the inner whorls. 

The earliest whorls of A. alvaradoense usually have 

periodic constrictions, and the upper ventrolateral

and siphonal tubercles are not as elongate as those 

of A. amphibolum. In addition, some specimens of 

A. alvaradoense have a few extra siphonal tubercles 

in various places, and therefore the species shows 

some resemblance to Euomphaloceras Spath (1923, 

p. 144).

A complete suture is shown in figure 6. The first 

lateral saddle is very broad and asymmetrically bifid 

much like that of A. amphibolum Morrow (fig. 3).

Acanthoceras alvaradoense was collected from 

septarian limestone concretions in the Clay Mesa 

Shale Tongue in the Acoma area southeast of 

Grants. Moreman's type came from the basal part 

of the Eagle Ford Shale of Texas. The species has 

been foun'd at very few places in the western interior region.

.—Hypotypes, USNM 239771-239773.

V

FIGURE 6.—Suture (X 3) of Acanthoceras alvaradoense Moreman (pi. 6, figs. 19, 20) at a whorl height of 30 mm. Heavy 

line marks the middle of the external lobe; light straight line marks the middle of the internal lobe; dashed line 

marks the umbilical shoulder. Hypotype, USNM 239773.
CHARACTERISTIC FOSSILS 25

Plesiacantkoceras aff. P. wyomingense (Reagan) 

Plate 13, figures 1, 2

A few large ammonites from the Pagnate Sandstone Tongue resemble Plesiacanthoceras wyomingense (Reagan, 1924, p. 181, pi. 19, figs. 1, 2) because they are about the same size, because they retain double ventrolateral tubercles out to a large 

diameter, and because their adult whorls have conspicuous ventrolateral horns. The Paguate specimens differ, however, in tending to have a raised 

midventral ridge similar to that on some specimens 

of Acanthoceras amphibolum Morrow (1935, p. 

472).

Figured specimen.—USNM 239774.

Euompkaloceras aff. E. cunningtoni (Skarpe)

Plate 11, figures 17, 18

Euomphaloceras resembles Acanthoceras in having umbilical, lower and upper ventrolateral, and 

siphonal tubercles, but Euomphaloceras differs 

mainly in having more siphonal tubercles than ventrolateral ones. A few incomplete ammonites from 

the Paguate Sandstone Tongue have affinities with 

E. cunningtoni (Sharpe, 1854, p. 35, pi. 15, figs. 2ac) in their sparse tuberculation, but the siphonal 

tubercles are not as small and numerous as on 

Sharpe's type.

Figured specimen.—USNM 239775.

Paracompsoceras landisi Cobban

Plate 14

1972. Paracompsoceras landisi Cobban, U.S. Geol. Survey 

Prof. Paper 699, p. 10, pi. 2, figs. 24-26; pis. 6-8; 

pi. 9, figs. 5-8; text figs. 9-11 [1971 imprint].

Paracompsoceras landisi is a large stout ammonite that attains a diameter of as much as 310 mm. 

The species is moderately involute and has umbilical ratios of 25-30 percent. The early whorls are 

quadrangular in cross section and ornamented by 

ribs and tubercles. Each rib has a lower and an 

upper ventrolateral tubercle, and every other rib 

extends to the umbilicus, where it rises into a 

bullate tubercle. Each rib is matched on the venter 

by a low clavate siphonal tubercle. As the shell enlarges, all tubercles and the short ribs disappear, 

and the flanks and venter flatten. The longer ribs 

persist to the base of the body chamber; they are 

strong-est on the lower half of the whorl. The adult 

body chamber is smooth, and its cross section is 

rounded.

The types of P. landisi are from the Paguate 

Sandstone Tongue of the Grants-Laguna area (Cobban, 1971, p. 12). In west-central New Mexico, P. 

landisi has been found only in the Paguate Tongue. 

Type.—Holotype, USNM 166360.

Metoicoceras cf. M. praecox Haas

Plate 16, figure 25; plate 21, figures 8, 9

Fragments of ammonites from the Whitewater 

Arroyo Shale Tongue and the basal part of the 

Twowells Sandstone Tongue resemble Metoicoceras 

praecox Haas (1949, p. 15, pis. 5-7; text figs. 5-9). 

Haas' form is a compressed species that has umbilical tubercles on the inner whorls and none on the 

adult body chamber. Ribs are conspicuous on the 

inner whorls, cross the flanks and venter, and support ventrolateral tubercles. The innermost whorls 

of some specimens have weak clavate siphonal 

tubercles. Ribbing weakens on the body chamber but 

becomes strong again near the aperture. Haas' types 

were associated with Dimveganoceras pondi Haas 

in the basal part of the Cody Shale near Greybull, 

Wyo. The fragments from New Mexico that might 

be M. praecox consist of parts of body chambers preserved as internal molds of very fine grained sandstone.

Figured specimens.—USNM 239776, 239777.

Metoicoceras aff. M. latoventer Stepkenson

Plate 16, figures 13-15; text figure 7 

A few robust inner whorls of Metoicoceras from 

the Whitewater Arroyo Shale Tongue resemble the 

inner whorls of M. latoventer Stephenson (1952, p. 

209, pi. 53, figs. 1-9; pi. 54, figs. 9-11) in their general appearance, but the lower row of ventrolateral 

tubercles is barely discernible. The suture (fig. 7) 

is about as incised as those visible on Stephenson's 

figured specimens. Metoicoceras latoventer has been 

recorded only from the Woodbine Formation of 

northern Texas.

Figured specimen.—USNM 239778.

Metoicoceras spp. 

Plate 21, figures 5, 6, 10-16

Poorly preserved ammonites from the Twowells 

Sandstone Tongue show some resemblance to MetoiFIGURE 7.—External suture (x 3) of Metoicoceras 

aff. M. latoventer Stephenson (pi. 16, figs. 13- 

15) at a diameter of 28 mm. Heavy line marks 

the middle of the external lobe; dashed line 

marks the umbilical margin. Figured specimen, 

USNM 239778.
26 MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO

coceras muelleri Cobban (1953, p. 49, pi. 6, figs. 15, 

16; pi. 8, figs. 1-7; pi. 9) and M. defordi Young 

(1957, p. 1169, pi. 149, figs. 1-8; text fig. la, e, g, 

i). A small specimen (pi. 21, figs. 5, 6) resembles 

M. muelleri in its slender cross section and.fine ribbing, but its umbilicus is too wide. A larger specimen (pi. 21, figs. 15, 16), 93 mm in diameter, resembles M. defordi in the width of its umbilicus, in 

the number of ribs per whorl, and in the presence 

of well defined bullate umbilical tubercles, but the 

venter appears to round at too small a diameter. 

Other specimens, such as those shown on plate 21, 

figures 10-14, seem different from any described 

species.

Figured specimens.—USNM 239779-239782.

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the western interior of Canada and the United States: 

Geol. Soc. America Abs. with Programs, v. 6, no. 7, p. 867.

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of the exploring expedition from Santa Fe * * * in 1859: 

U.S. Army Eng. Dept., p. 119-133, 2 pis.
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Morrow, A. L., 1935, Cephalopods from the Upper Cretaceous 

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pis. 49-53.

Northrop, S. A., 1962, New Mexico's fossil record—The University of New Mexico, 8th annual research lecture, April 

7, 1961: Albuquerque, Univ. New Mexico Press, 74 p.

Owen, D. E., 1969, The Dakota Sandstone of the eastern San 

Juan and Chama basins and its possible correlation across 

the Southern Rocky Mountains, in Raton basin field 

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103 p., 12 pis.

Reagan, A. B., 1924, Cretacic Mollusca of Pacific slope: PanAm. Geologist, v. 41, p. 179-190.

Reeside, J. B., Jr., 1929, Exogyra olisiponensis Sharpe and 

Exogyra costata Say in the Cretaceous of the Western 

Interior: U.S. Geol. Survey Prof. Paper 154-1, p. 267- 

278, 5 pis. [1930].

———— 1927, Fossils from the Mancos-Dakota-Tununk formation in the vicinity of Steamboat, Arizona: Indiana 

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paleontologique de la faune du Turonien du Bassin d' 

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Quart. Jour., v. 6, p. 135-201, pis. 14-26.

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[1857]).

Spath, L. F., 1923, On the ammonite horizons of the Gault 

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p., 95 pis.

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144.

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27 p.

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1873, and 1874: U.S. Geog. and Geol. Expl. Surveys W. 

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6, p. 1167-1174, pis. 149-150.

INDEX

[Italic page numbers indicate descriptions and major references] 

Page Page 

Cubero Sandstone Tongue of the Dakota

Acanthoceras alvaradoense ______ 15, 24; pi. 6

amphibolum ____-5, 22, 23, 24, 25; pis. 8, 12

wintoni __________________________ 3,22

sp --___---_____-_--_--_____-__--_ 5

Acknowledgments __________________ i

acutus, Turrilites _________-.--_______ 22

Turrilitcs (Turrilites) __________ -22; pi. 4

amcricanus, Turrilitcs ____________ 16

Turrilites (Turrilitcs) ____ 3~>; pi. 10

aguilerae, Avicula _____.___.._._....__ 14

Phelopteria ____________________ .Z.4; pi. 7

alvaradoense, Acanthoceras ______ 15, 2.4; pi. 6

Euomphaloceras __________________ 24

americanus, Turrilites acutus _________ 16

Turillitcs (Turrilites) acutus __ 22; pi. 10 

amphibolum, Acanthoceras __ 5, 22, 2J, 24, 25;

pis. 8, 12 

Artcfcwra modest a ____________________ 22

antriniformis, Plcsiopinna ____________ 14

Aphrodina munda __________________ 2.Z, pi. 7

agitillana, Exogyra .-_--____-.______ iS; pi. 2

arcnaria, Plicatula ___________ 5, .Z6, 18; pi. 1

Arrhoges modesta __________________ 22; pi. 2

arvanus, Inoeeramus _______________ 15; pi. 6

Avicula aguilerac ____________________ 14

B

bcloiti, Ostrea ____________ 15, 16, 20, 24; pi. 7

blanpiedi, Idonearca ____________ iO, 13; pi. 8

Burkholder, R. E., photographs ______ 1

Calycoccras canitaurinum __________ 23; pi. 21

obrieni _---_-__--_--______________ 3

(Conlinoceras) tarrantensc __ 22; pis. 3, 4 

Camptonectes -_----__----------_.___ 20

symmctricus __._-__--__-_-__ J5; pis. 3, 5 

virgatus --------_-----------._ i6; pi. 19

canitaurinum, Calycoccras _________ 23; pi. 21

Mantelliceras --_--_---____._______ 7, 23

Cardium enstromi __-__-_----_-_--____ 21

productum -__--___-_-____________ 21

frj-e ___.______________ 20

casei, Homomya _____________________ 21

Clay Mesa Shale Tongue of the Mancos

Shale -.-1,5,10,15,17,20,23,24 

Coahuila, Mexico _----_-----------_-- 14,22

Codell Sandstone Member of the Carlile

Shale (Colorado) ______ 21

Cody Shale (Wyoming) __.--_-___-___ 25 

columbella, Exogyra ______ 3, 5, 6, 18, 19; pi. 5

levis, Exogyra ____________________ 5, 18

concentrica, Psilomya _______________ 21; pi. 5

conditum, Dunveganoccras ____________ 3

(Conlinoceras) tarrantensc,

Calycoccras --------- 22; pis. 3, 4

costata fluminis, Exogyra ............. 4, 18

costatus, Turrilites ------------------- 10

Page

H

Sandstone __ 1, 3, 5, 13, 14, 16, 18,

19, 21, 22, 23

cunningtoni, Euomphaloceras _..-_. 25; pi. 11

D

Dakota Sandstone, age .._..-_-_-.____ 3

dcfordi, Metoicoccras ------------ 3,18,21,26

dcpressa, Idonearca _________ 4, 13; pis. 16, 19

Trigonarca ----------------------- 13

Desmoceras japonicum __-___-___--_ "22; pi. 11

(Pseudouhligclla) sp ___________ 22; pi. 4

diluviana, Lopha --------------------- 20

Dunvegan Formation (Alberta) ______ 15

Dtinveganoceras conditum _______--__-_ 3

pondi ---------------------------- 25

E

Eagle Ford Shale (Texas) ..._____ 15,23,24 

Earlier records of fossils _-__-_-_--__-_ 3

cllipticum, Lcgumen ---------------- 21; pi. 9

cllipticus, Lcgumen ------------------- 21

enstromi, Cardium -------------------- 21

Granocardium ------------------ 21; pi. 8

Eucalycoceras ------------------------ 23

eulessanus, Inoeeramus _____________ 14; pi. 3

Euomphaloceras alvaradoense _________ 24

cunningtoni ------------------- 25; pi. 11

Exogyra ___________________-_-----_ 20

aguillana ----------------------- 18; pi. 2

columbella _._-.-____ 3, 5, 6, 18, 19; pi. 5 

levis --------------------- ____ 5, 18

costata fluminis ------------------ 4, 18

laeviuscula _______________________ 19

few's -.-______ 5, iS, 19; pis. 15, 17, 18. 20

olisiponens'is ---------------------- 19

oxyntas --------------- _______ 19; pi. 10

.risreri ------------ J9; pis. 9, 16, 17, 18, 20

sp. A --------..--_-.-_______ 19, pi. 5

ferryi, Plicatula _________._ ^6; pis. 9, 16, 19

fluminis, Exogyra costata _____________ 4, 18

Frontier Formation _______.-_--_-._ 15,18,23

ginterensis, Inoeeramus --------- 15, 18; pi. 19

goldenensis, Pholadomya ------------ 21; pi. 5

gracile, Sciponoceras ------------------ 3

Graneros Shale (Colorado) --__-----. 22,23

Granocardium ________________________ 20

enstromi _______-______----_____ 21; pi. 8

productum --------------------- 21; pi. 3

-rrte .---.-__.__.-_______ 20; pi. 21 

Greenhorn Limestone (western interior) 15 

Gryphaea ncu'berryi --------------- 3, 5, 6, 17

washitaensis kellumi _-_______-_-_ 17

(Gryphaea) patina, Ostrea ----------- 17

Hartland Shale Member of the Greenhorn

Limestone _.._-_-__---__-_ 15 

Homomya casci ____-__----.___-----___ 21

I

Idonearca blanpiedi ------------- 10, 13; pi. 8

deprcssa ---------------- 4, 13; pis. 16, 19

Indidura Formation of Coahuila,

Mexico -___----_---------- 17

Inoeeramus ------------------------— 20

arvanus ----------------- — ---- 15; pi. 6

eulessanus --------------------- 14; pi. 3

ginterensis ----------------- 15, 18; pi. 19

labiatus -------------------------- 6

macconnelli ----------------- 14; pis. 2, 3

prcfragilis -------------------- 15; pi. 19

ruthcrfordi _____ 14, 15, 16, 20, 22, 24; pi. 7

Introduction ___---__--_-------------- 1

japonicum, Desmoceras ------------ 22; pi. 11

K

Kamchatka, U.S.S.R. -.._---- — --.--— 15

kellumi, Gryphaea washitaensis ------- 17

Pycnodonte _____ 5, 17; pis. 6, 12, 15, 16, 20

labiatus, Inoeeramus ------------------ 6

laeviuscula, Exogyra ------------------ 19

landisi, Paracompsoccras ----------- 25; pi. 14

latoventcr, Mctoicoceras ----------- 25; pi. 16

Legumen ellipticum ---------------- 21; pi. 9

cllipticus ------------------ — ----- 21

levis, Exogyra _____ 5, 18, 19; pis. 15, 17, 18, 20

Exogyra columbella -------------- 5,18

Lewisville Member of the Woodbine

Formation (Texas) _.- 15,18,23 

lillianense, Tarrantoceras -------------- 23

Limatula sp _______---.__-__-------- 17; pi. 5

lingulifera, Lispodesthes -------------- 3

Lispodesthes lingulifera --------------- 3

Lopha diluviana ---------------------- 20

staufferi ------ ___.----.------ 20; pi. 19

M

macconnelli, Inoeeramus --------- 14; pis. 2, 3

Mancos Shale, age .___-___.___--_-_--. 3 

Mantelliceras canitaurinum ----------- 7, 23

Metacalycoceras tarrantensc __________ 22

Mctoicoceras defordi ..__-_______ 3, 18, 21, 26

latoventcr --------------------- 25; pi. 16

muelleri ------------------- 3,18,19,26

praccox ------------------ 25; pis. 16, 21

spp ------__--__--__ —— ---- 25; pi. 21

modesta, Anchura -------------------- 22

Arrhoges --------- — -------— 22; pi. 2

29
30 INDEX

Page

Mosby Sandstone Member of the Greenhorn Formation __________ 18, 19

muelleri, Metoicoccras ___________ 3, 18, 19, 26

multicostatum, Tarrantoceras ________ 23

munda, Aphrodina _________________ 21; p\. 7

N

Neithea scxcostata ________________ 16; pi. 10

newbcrryi, Gryphaea -------------- 3,5,6,17

Pycnodonte _______________________ 17

O

Oak Canyon Member of the Dakota

Sandstone ______ 1, 3, 5, 10, 13,

14, 15, 16, 17, 18,20,21,22,23 

obricni, Calycoceras ___________________ 3

olisiponcnsis, Exogyra ________________ 19

Ostrea beloiti _____________ 15, 16, 20, 24; pi. 7

trigeri ___________________________ 19

(Gryphaeal) patina ______________ 17

oxyntas, Exogyra _.----_------_.__ 19; pi. 10

Paguate Sandstone Tongue of the

Dakota Sandstone ____ 1, 3, 5, 10,

13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 25

Panis ________________________________ 14

Paracompsoceras landisi ___--____-_ 25; pi. 14

patina, Ostrea (Gryphaea) ____________ 17

pctrina, Pinna _____-__.-__ 3, 13; pis. 1, 3, 15

Phelopteria ___________________________ 14

aauilerae ______________________ 14; pi. 7

Pholadomya goldenensis _____________ 21; pi. 5

Pinna petrina _______-_-_-_ 3, 13; pis. 1, 3, 15

stevensoni ________________________ 5, 13

Plcsiacanthoceras wyomingensc ____ 25; pi. 13

Plesiopinna antriniformis _____________ 14

sp --.________.___________ 14; pi. 1

Page 

Plicatula __________-------___--- 20

arcnaria ___--__--____---__ 5, 1<>, 18; pi. 1

ferryi ......---------__ 16; pis. 9, 16, 19

sp --._____---___-_-------—— IS; pi. 9

pondi, Dunveganoceras ......--..---.-. 25

praecox, Metoicoccras _________ 25; pis. 16, 21

prcfragilis, Inoceramus ____________ 15; pi. 19

Prionotropis sp ____________--_---_-_-- 5

productwm, Cardium __________________ 21

Granocardium _-_.-___---------_ 21; pi. 3

(Pseudouhligella) sp., Desmoceras .. 22; pi. 4 

Psilomya concentrica __________--_-_ 21; pi. 5

Pycnodonte _______-_--__------__------ 20

kellumi ...------ 5, 17; pis. 6, 12, 15, 16, 20

newberryi ______--__-_--------_--- 17

u'ashitaensis _____________---_---_- 17

R

Rhynchostrcon ______--_______--------_ 19

Ripley Formation (Mississippi) ______ 21

rotatile, Tarrantoceras _--_--_ 23; pi. 6, 11, 12

ruthcrfordi, Inoceramus ... 14, 15, 16, 20, 22,

24; pi. 7

Sakhalin, U.S.S.R. __--------__.-__-- 15

Sciponoceras gracile _._.-_--_______--_ 3

shuleri, Turritella ........--.__-__ 22; pi. 8

stantoni, Tarrantoceras _______________ 23

staufferi, Lopha __________-_---_--- 20; pi. 19

stevensoni, Pinna __-__--____--__----- 5, 13

Stratigraphic summary ____-_-_-___--- 1

symmetricus Camptonectcs ______ 15; pis. 3, 5

Page

Tarrantoceras lillianense .............. 23

multicostatum _.........--.-...... 23

rotatile ___._--_-----_-_-- 23; pi. 6, 11, 12

stantoni _____________-_---__-__--- 23

Templeton Member of the Woodbine

Formation (Texas) ... 10,18,21 

Thatcher Limestone Member of the 

Graneros Shale (southeastern Colorado) .__ 5,14,16,22 

trigeri, Exogyra ...... 19; pis. 9, 16, 17, 18, 20

Ostrea ____-__-. —— ——— ————— 19

Trigonarca depressa _____--_-_______-_ 13

trite, Cardium ____--_-__----- ——._ —.. 20

Granocardium .....-....-...--. 20; pi. 21

Turrilites acutus --------------------- 22

acutus americanus __-__--__-_---_ 16 

costatus _______________ — -__ — __— 10

(Turrilites) acutus ------------ 22; pi. 4

acutus americanus --------- 22; pi. 10

(Turrilites) acutus, Turrilites ....... 22; pi. 4

acutus americanus, Turrilites __ 22; pi. 10 

Turritella ______________—— __———— 20

shuleri .........-------- —— _..-- 22; pi. 8

Twowells Sandstone Tongue of the

Dakota Sandstone ... 1,3,5,13, 

15, 16, 18, 19, 20, 21, 23, 24

tarrantense, Calycoceras

(Conlinoceras) 

Metacalycoceras -.___.

32; pis. 3, 4 

___. 22

virgatus, Camptoncctes . 

W

16; pi. 19

washitaensis, Pycnodonte ______________ 17

kellumi, Gryphaea ___--__-_-__--__ 17 

Waterpocket fold __________ ————.—— 20

Whitewater Arroyo Shale Tongue of the

Mancos Shale_---- 1, 6, 10, 13, 15,

16, 17, 18, 19, 20, 23, 25 

wintoni, Acanthoceras ---------------- 3, 22

Woodbine Formation (Texas) . 3, 14, 21, 22, 25 

u<yomingensc, Plcsiacanthoceras .... 25; pi. 13
PLATES 1-21

Contact photographs of the plates in this report are available, at

cost, from U.S. Geological Survey Library, Federal Center,

Denver, Colorado 80225
PLATE 1

[All figures natural size]

FIGURES 1,3. Plesiopinna sp. (p. 14).

Right and left valves of two specimens from USGS localities D6794 and D2053 (text fig. 1, Iocs. 66, 61).

USNM 239616, 239617. 

2,4. Pinna petrina White (p. 13).

Two incomplete specimens from USGS localities D7080 and D7081 (text fig. 1, Iocs. 45, 46). USNM 239612,

239613. 

5,6. Plicatula arenaria Meek (p. 16).

5. Slab of very fine grained sandstone that contains numerous specimens of Plicatula arenaria and a few 

bits of Pinna shells from USGS locality D6794 (text fig. 1, loc. 66). USNM 239635.

6. Latex cast of a slab of very fine grained sandstone that contains several specimens of P. arenaria as 

well as representatives of Camptonectes (a), Mediraon (b), Granocardium (c), and other bivalves, from 

USGS locality D2053 (text fig. 1, loc. 61). USNM 239636.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 1

MOLLUSKS FROM THE OAK CANYON MEMBER
PLATE 2

[All figures natural size]

FIGURES 1,2. Exogyra aquillana Stephenson (p. 18).

1. Two left valves from USGS locality D5377 (text fig. 1, loc. 29). USNM 239675.

2. Latex cast of a piece of very fine grained sandstone that has impressions of several left valves from 

USGS locality D5815 (text fig. 1, loc. 33). USNM 239676.

3. Inoceramus cf. /. macconnelli Warren (p. 14).

Numerous specimens in a slab of very fine grained sandstone from USGS locality D5756 (text fig. 1, loc. 17). 

USNM 239621.

4. Arrhoges modesla (Cragin) ? (p. 22).

Latex cast of many specimens in a slab of very fine grained sandstone from locality D5806 (text fig. 1, 

loc. 34). USNM 239743.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 2

MOLLUSKS FROM THE OAK CANYON MEMBER
PLATE 3

[All figures natural size]

FIGURE 1. Camptonectes symmetricus Herrick and Johnson (p. 15).

Latex cast of a piece of very fine grained sandstone that has examples of this pectinid (a) as well as 

Plicatula (b), Astarte (c), Parmicorbula (d), and other bivalves, from USGS locality D5336 (text fig. 

1, loc. 44). USNM 239735. 

2. Granocardium (Criocardium) cf. G. productum (Sowerby) (p. 21).

Latex cast of an impression of part of a shell in very fine grained sandstone from USGS locality D5742

(text fig. 1, loc. 25). USNM 239727. 

3,4. Inoceramus eulessanus Stephenson (p. 14).

Latex casts of two specimens from USGS locality D5760 (text fig. 1, loc. 16). USNM 239619, 239620. 

5-7. Inoceramus cf. I. macconnelli Warren (p. 14).

Right valve and two left valves from USGS locality D5756 (text fig. 1, loc. 17). USNM 239622-239624.

8. Pinna petrina White (p. 13).

Several fragments (a) associated with Exogyra columbella Meek (b), Plicatula arenaria Meek (c), and 

Calycoceras (Conlinoceras) sp. (d) from USGS locality D6794 (text fig. 1, loc. 66). USNM 239614.

9. Calycoceras (Conlinoceras) tarrantense (Adkins) (p. 22).

Side view of a phragmocone from USGS locality D2053 (text fig. 1, loc. 61). USNM 239762.
GEOLOGICAL SURVEY

b

PROFESSIONAL PAPER 1009 PLATE 3

7 »* jj r — ^,

*}£&*>& -* *

^KJL, ,^t ^-~*tjr • j_ ..=••

8

MOLLUSKS FROM THE OAK CANYON MEMBER
PLATE 4

[AH figures natural size]

FIGURES 1-3,6. Calycoceras (Conlinoceras) tarrantense (Adkins) (p. 22).

1-3. Three views of a septate fragment from USGS locality D2053 (text fig. 1, loc. 61). USNM 239763. 

6. Side view of a large phragmocone from USGS locality D6800 (text fig. 1, loc. 60). USNM 239764. 

4,5. Titrrilites (Titrrilites) acutus Passy (p. 22).

4. Two complete whorls collected by W. T. Lee in 1905 from USGS locality 3518 "about 10 miles north 

of San Ignacio." USNM 239744.

5. Part of a large whorl from USGS locality D5377 (text fig. 1, loc. 29). USNM 239745. 

7. Desmoceras (Pseudouhligella) sp. (p. 22).

Side view of a large crushed phragmocone from USGS locality D5321 (text fig. 1, loc. 36). USNM 

239751.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 4

6 7 

MOLLUSKS FROM THE OAK CANYON MEMBER AND CUBERO SANDSTONE TONGUE
PLATE 5

[All figures natural size except as indicated]

FIGURES 1,2. Psilomya aff. P. concentrica (Stanton) (p. 21).

Left and right valves from USGS locality D5366 (text fig. 1, loc. 39). USNM 239729, 239730. 

3. Pholadomya aff. P. goldenensis (Stephenson) (p. 21).

Right valve of a small specimen from USGS locality D2053 (text fig. 1, loc. 61). USNM 239728. 

4-7. Camptonectes symmetricus Herrick and Johnson (p. 15). 

From the same locality as figures 1, 2. 

4, 5. Left valves, USNM 239731, 239732. 

6, 7. Right and left valves (x 2). USNM 239733, 239734. 

8. Limatula sp. (p. 17).

Left valve (x 2) collected by W. T. Lee in 1905 from USGS locality 3518 "about 10 miles north of San

Ignacio." USNM 239736.

9-13. Exogyra aff. E. columbella Meek (p. 18). 

From the same locality as figure 3. 

9-12. Two left valves. USNM 239672, 239673. 

13. Right valve. USNM 239674. 

14-22. Exogyra columbella Meek (p. 18).

14,15. Views of a left valve from the same locality as figure 3. USNM 239667. 

16,17. Left valve from USGS loc. D5329 (text fig. 1, loc. 62). USNM 239668. 

18,21. Left valve collected by W. T. Lee and T. W. Stanton in 1912 from USGS locality 7088 "about 4

miles south of Casa Salazar." USNM 239669. 

19,20. Left valve from USGS locality D6218 (text fig. 1, loc. 67). USNM 239670.

22. Left valve from the same locality as figures 18, 21. USNM 239671. 

23-28. Exogyra sp. A (p. 19).

23. Right valve from USGS locality D5330 (text fig. 1, loc. 63). USNM 239685.

24. 25. Left valve from USGS locality D2048 (text fig. 1, loc. 56). USNM 239686. 

26-28. Left valve from the same locality. USNM 239687.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 5

26 28 

MOLLUSKS FROM THE OAK CANYON MEMBER AND CUBERO SANDSTONE TONGUE
PLATE 6

[All figures natural size]

FIGURES 1-7,11-20. Acanthoceras alvaradoense Moreman (p. 24).

I-7, 16-18. Inner whorls at diameters of 13 mm (figs. 1-4) and 21.5 mm (figs. 5-7) of a phragmocone (figs. 16-18) 57 mm in diameter from USGS locality D5332 (text fig. 1, loc. 64). 

USNM 239771.

II-13. Front, side, and rear views of a phragmocone from USGS locality D7326 (text fig. 1, loc.

53). USNM 239772. 

14, 15, 19, 20. Inner and outer whorls of part of a large phragmocone from USGS locality D7364

(text fig. 1, loc. 65). See text figure 6 for the suture. USNM 239773. 

8-10,28,29. Tarrantoceras rotatile Stephenson (p. 23).

From USGS locality D5380 (text fig. 1, loc. 30).

8-10. Three views of a septate fragment. See text figure 4 for the suture. USNM 239755. 

28, 29. Side and rear view of part of a body chamber. USNM 239756. 

21-26. Pycnodonte cf. P. kellumi (Jones) (p. 17).

From USGS locality D6781 (text fig. 1, loc. 52).

21-23. Views of both valves of a specimen of average size. USNM 239652. 

24-26. Views of both valves of a larger individual. USNM 239653. 

27. Iwoceramus arvanus Stephenson (p. 15).

Left valve from the same locality as figures 8-10, 28, 29. USNM 239630.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 6

26

10

27 28

MOLLUSKS FROM THE CLAY MESA SHALE TONGUE

29
PLATE 7

[All figures natural size]

FIGURES 1-3. Aphrodina cf. A. munda (Stephenson) (p. 21).

1, 2. Exterior and interior of a right valve from USGS locality D4018 (text fig. 1, loc. 40). USNM 

239737.

3. Exterior of a left valve from USGS locality D5325 (text fig. 1, loc. 35). USNM 239738. 

4-7. Ostrea beloiti Logan (p. 20).

4. Several specimens attached to Inoceramus rutherfordi Warren from USGS locality D5771 (text fig. 

1, loc. 68). USNM 239713.

5. Interior of a left valve from USGS locality D5324 (text fig. 1, loc. 37). USNM 239714.

6. Internal mold of a left valve from USGS locality D7328 (text fig. 1, loc. 24). USNM 239715.

7. Internal mold of a right valve that retains some of the shell material from the same locality as

figure 5. USNM 239716. 

8,9. Phelopteriat cf. P.? aguilerae (Bose) (p. 14).

Internal mold of a left valve from the same locality as figures 1, 2. USNM 239618. 

10-14. Inoceramus rutherfordi Warren (p. 14).

10, 11. Internal molds of left and right valves from USGS locality D7328 (text fig. 1, loc. 24). USNM

239625, 239626.

12-14. Internal molds of two left valves and a right valve from USGS locality D5750 (text fig. 1, loc. 

22). USNM 239627-239629.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 7

13 14 

MOLLUSKS FROM THE PAGUATE SANDSTONE TONGUE
PLATE 8

[All figures natural size]

FIGURES 1-3. Idonearca blanpiedi Stephenson (p. 10).

Left and right valves from USGS locality D7084 (text fig. 1, loc. 47). USNM 239606, 239607. 

4-7,10,11. Granocardium enstromi (Bergquist) (p. 21).

4, 5. Two views of two specimens from the same locality. USNM 239723. 

6, 7. Two views of another specimen from the same locality. USNM 239724.

10, 11. Latex casts of impressions in fine-grained sandstone from USGS locality D7345 (text fig. 

1, loc. 72). Gastropods include (a) Turritella shuleri (Stephenson)?, (b) Helicaulaxl sp., and 

(c) Paleopsephaea sp. USNM 239725, 239726. 

8,9. Acanthoceras amphibolum Morrow (p. 23).

Rear and side views of an internal mold of a small specimen from USGS locality D7333 (text fig. 1, 

loc. 19). USNM 239765.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 8

MOLLUSKS FROM THE PAGUATE SANDSTONE TONGUE
PLATE 9

[AU figures natural size]

FIGURES 1-3. Legumen ellipticum Conrad (p. 21).

1, 2. Two views of a specimen collected by W. T. Lee in 1911 from USGS locality 7192 one-half mile west 

of San Francisco, Sandoval County. USNM 239739.

3. Right valve from USGS locality D5383 (text fig. 1, loc. 38). USNM 239740. 

4-8. Plicatula sp. (p. 16).

4. 6, 7. Latex casts of specimens from USGS locality D5785 (text fig. 1, loc. 69). USNM 239647, 239649,

239650.

5. 8. Latex casts of two specimens from USGS locality D5795 (text fig. 1, loc. 71). USNM 239648,

239651. 

9. Plicatula cf. P. ferryi Coquand (p. 16).

Latex cast of an impression in very fine grained sandstone from USGS locality D7334 (text fig. 1, loc.

20). USNM 239646. 

10-20. E'xogyra trigeri (Coquand) (p. 19).

10, 11. Side view of left valve and view of right valve of same specimen from USGS locality D6130 (text

fig. 1, loc. 51). USNM 239696.

12, 13. Views of a left valve that was attached to a turritellid from USGS locality D6183 (text fig. 1, loc. 

6). USNM 239697.

14. Right valve from the same locality. USNM 239698.

15. 16. Views of a left valve that was attached to a turritellid from the same licality. USNM 239699. 

17-19. Left valve of another specimen that was attached to a turritellid from the same locality. USNM

239700. 

20. Left valve from the same locality. USNM 239701.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 9

MOLLUSKS FROM THE PAGUATE SANDSTONE TONGUE
PLATE 10

[All figures natural size]

FIGURES 1,2. Neithea cf. N. sexcostata (Woodward) (p. 16).

Two views of a right valve from USGS locality D7332 (text fig. 1, loc. 18). USNM 239741. 

3-6,10,12. Turrilites (Turrilites) acutus americanus Cobban and Scott (p. 22).

3, 4. Small spires consisting of several whorls from USGS locality D7328 (text fig. 1, loc. 24). USNM

239746, 239747.

5, 6. Side and bottom views of parts of two whorls that have a wide apical angle from the same locality. USNM 239748. 

10. Latex cast of an impression in baked shale from USGS locality D5795 (text fig. 1, loc. 71).

USNM 239749.

12. Large specimen from USGS locality D7084 (text fig. 1, loc. 47). USNM 239750. 

7-9,11. Exogyra cf. E. oxyntas (Coquand) (p. 19).

7. Fragment of a left valve from USGS locality D5347 (text fig. 1, loc. 43). USNM 239692.

8. 9. Fragments of left valves from USGS locality D2049 (fig. 1, loc. 57). USNM 239693, 239694. 

11. Large left valve from USGS locality D7084 (text fig. 1, loc. 47). USNM 239695.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 10

11 12 

MOLLUSKS FROM THE PAGUATE SANDSTONE TONGUE
PLATE 11

[All figures natural size except as indicated]

FIGURES 1-6,9,10. Desmoceras (Pseudouhligella) aff.. D. japonicum Yabe (p. 22). 

From USGS locality D7328 (text fig. 1, loc. 24). 

1-3, 6. Front, side, and rear views and side view (x 2) of a small septate specimen. USNM

239752. 

4, 5, 9, 10. Side and front views (figs. 4, 5) of the inner whorls of a large mostly septate specimen

(figs. 9, 10). USNM 239753. 

7,8,11-16. Tarrantoceras rotatile Stephenson (p. 23).

7, 8. Front and side views of a coarsely ribbed specimen like T. stantoni Stephenson (1955, pi. J>, figs.

11-21), from USGS locality D7084 (text fig. 1, loc. 47). USNM 239757. 

11, 12. Rear and side views of another coarsely ribbed specimen from USGS locality D5380 (text fig.

1, loc. 30). USNM 239758.

13. Fragment of a fine-ribbed body chamber resembling T. multicostatum Stephenson (1955, pi. 6, figs. 

21-23), from USGS locality D5372 (text fig. 1, loc. 31). USNM 239759.

14. Two fine-ribbed specimens from theh same locality as figures 11 and 12. USNM 239760.

15. 16. Rear and side views of a large specimen collected southwest of San Ysidro, Sandoval County,

by Mr. Gregg Perry, formerly at the University of New Mexico, Albuquerque. USNM 239783. 

17,18. Euomphaloceras aff. E. cunningtoni (Sharpe) (p. 25).

Rear and side views of an internal mold from USGS locality D5812 (text fig. 1, loc. 32). USNM 

239775.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 11

15

AMMONITES FROM THE PAGUATE SANDSTONE TONGUE
PLATE 12

[All figures natural size|

FIGURES 1-9. Pycnodonte cf. P. kellumi (Jones) (p. 17).

1-3. Left valve from USGS locality D7084 (text fig. 1, loc. 47). USNM 239654. 

4-6. Left valve from USGS locality D5383 (text fig. 1, loc. 38). USNM 239655. 

7, 8. Left valve from USGS locality D6182 (text fig. 1, loc. 5). USNM 239656. 

9. Exterior views of three right valves from USGS locality D5372 (text fig. 1, loc. 31). USNM

239657. 

10-12,15-23. Acanthoceras amphibolum (Morrow) (p. 23).

10-12. Rear, side, and front views of unusually stout inner whorls from USGS locality D7333

(text fig. 1, loc. 19). USNM 239766. 

15, 16. Side and rear views of normal inner whorls from USGS locality D7328 (text fig. 1, loc. 24).

USNM 239767. 

17-19. Front, side, and rear views of inner whorls from the same locality as figures 10-12. USNM

239768. 

20, 21. Front and side views of a larger septate coil from the same locality as figures 1-3. USNM

239769. 

22, 23. Rear and side views of the phragmocone of an adult from the same locality. See text figure

5 for the suture. USNM 239770. 

13,14. Tarrantoceras rotatile Stephenson (p. 23).

Rear and side views of the inner whorls of a specimen from USGS locality D5372 (text fig. 1, loc. 

31). USNM 239761.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 12

10

17

11

18

12

19

I 

13

C 

14

» 

15

I

16

21 22 

MOLLUSKS FROM THE PAGUATE SANDSTONE TONGUE

23
PLATE 13

[All figures natural size]

FIGURES 1,2. Plesiacanthoceras aff. P. wyomingense (Reagan) (p. 25).

Front and side views of the phragmocone of an adult from USGS locality D6130 (text fig. 1, loc. 51). USNM 

239774.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 13

PLESIACANTHOCERAS CF. P. WYOMINGENSE (REAGAN) FROM PAGUATE SANDSTONE TONGUE
PLATE 14

Paracompsoceras landisi Cobban (p. 25).

Side view of most of an adult (X 8/io) from USGS locality D7084 (text fig. 1, loc. 47). USNM 166360.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 14

'• : i"- "*-r .?!*,: ' Tv

f.^^: ...

\ •**?*j^ i*-!. -^ . H .-'*, -#.^'i J*' ,- "t*" '*<' ^•"/''/A'*''- v*

PARACOMPSOCERAS LANDISI COBBAN FROM PAGUATE SANDSTONE MEMBER
PLATE 15

[AH figures natural size]

FIGURES 1-16. Exogyra levis Stephenson (p. 18).

1, 2. Left valve from USGS locality D5764 (text fig. 1, loc. 9). USNM 239677.

3, 4, 7. Left valve from the same locality. USNM 239679.

5, 6, 8. Left valve from the same locality. USNM 239678.

9, 10. Left and right valves from USGS locality D7332 (text fig. 1, loc. 18). USNM 239680.

11-13. Left valve of an unusually large specimen that seems to be this species from USGS locality D6187

(text fig. 1, loc. 3). USNM 239681.

14-16. Another unusually large left valve from the same locality. USNM 239682. 

17-20. Pycnodonte cf. P. kellumi (Jones) (p. 17).

17. Right valve (uncoated) that has radial color bands from USGS locality D6182 (text fig. 1, loc. 5).

USNM 239658. 

18-20. Interior and exterior views of a right valve from the same locality. Figure 20 is uncoated to

show color bands. USNM 239659. 

21. Pinna petrina White (p. 13).

Large specimen retaining much of the shell material from USGS locality D5344 (text fig. 1, loc. 41).

USNM 239615.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 15

18 20 21 

MOLLUSKS FROM THE PAGUATE SANDSTONE TONGUE AND WHITEWATER ARROYO SHALE TONGUE
PLATE 16

[All figures natural size]

FIGURES 1-5. Pycnodonte cf. P. kellumi (Jones) (p. 17).

From USGS locality D6184 (text fig. 1, loc. 7).

1, 2. Exterior and interior views of a small right valve. USNM 239660. 

3-5. Small left valve. USNM 239661. 

6-12. Plicatula cf. P. ferryi Coquand (p. 16).

6-8, 10-12. Exterior views of specimens from the same locality as figures 1-5. USNM 239637-239642. 

9. Latex cast of an impression in silty limestone from USGS locality D6137 (text fig. 1, loc. 8). USNM

239643. 

13-15. Metoicoceras aff. M. latoventer Stephenson (p. 25).

Rear, side, and front views of the internal mold of a phragmocone from USGS locality D5787 (text fig.

1, loc. 70). See text figure 7 for the suture. USNM 239778. 

16-19. Exogyra trigeri (Coquand) (p. 19).

From USGS locality D7338 (text fig. 1, loc. 14).

16, 17. Interior and exterior views of a right valve. USNM 239702. 

18, 19. Left valve that was attached to a turritellid. USNM 239703. 

20-24. Idonearca deprcssa White (p. 13).

From USGS locality D5344 (text fig. 1, loc. 41).

20, 21. Exterior views of a small right valve. USNM 239608.

22. A larger right valve. USNM 239609.

23. 24. Views of a specimen that is missing much of the posterior part. USNM 239610. 

25. Metoicoceras cf. M. praecox Haas (p. 25).

Internal mold from USGS locality D5819 (text fig. 1, loc. 28). USNM 239776.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 16

MOLLUSKS FROM THE WHITEWATER ARROYO SHALE TONGUE
PLATE 17

[All figures natural size]

FIGURES 1, 2, 4. Exogyra aff. E. levis Stephenson (p. 19).

From USGS locality D5762 (text fig. 1, loc. 12).

1, 2. Interior and exterior views of an unusually large right valve. USNM 239690. 

4. Exterior view of a smaller right valve. USNM 239691. 

3,5-10. Exogyra trigeri (Coquand) (p. 19).

3. Exterior view of a right valve from USGS locality D5759 (text fig. 1, loc. 15), USNM 239704.

5. Fragment of a left valve that was attached to a turritellid from USGS locality D7338 (text fig. 1, loc.

14). USNM 239705. 

' 6. Another left valve that was attached to a turritellid from USGS locality D5737 (text fig. 1, loc. 50).

USNM 239706.

7, 8, 10. Three views of a large left valve from the same locality as figure 3. USNM 239707. 

9. Fragment of a left valve that was attached to a Plicatula from the same locality as figure 6. USNM 

239708.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 17

10

MOLLUSKS FROM THE WHITEWATER ARROYO SHALE TONGUE
PLATE 18

[All figures natural size]

FIGURES 1,2. Exogyra aff. E. levis Stephenson (p. 19).

Parts of left valves from USGS locality D5762 (text fig. 1, loc. 12). USNM 239688, 239689. 

3-9. Exogyra trigeri (Coquand) (p. 19).

From USGS locality D5759 (text fig. 1, loc. 15).

3-5. Views of a left valve. USNM 239709.

6, 7. Exterior and interior views of a large right valve. USNM 239710.

8, 9. Exterior and interior views of a left valve. USNM 239711.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 18

8 9 

MOLLUSKS FROM THE WHITEWATER ARROYO SHALE TONGUE
PLATE 19

[All figures natural size]

FIGURES 1,2,4. Inoceramus prefragilis Stephenson (p. 15).

All internal molds of very fine grained sandstone.

1, 2. Right valves from USGS locality D9240 (fig. 1, loc. 4). USNM 239631, 239632.

4. Fragment from USGS locality D2077 (text fig 1, loc. 10). USNM 239633. 

3. Inoceramus ginterensis Pergament (p. 15).

Latex cast of an impression of a right valve in very fine grained sandstone from USGS locality D5392

(text fig. 1, loc. 27). USNM 239634. 

5, 6. Plicatula cf. P. ferryi Coquand (p. 16).

5. Two specimens (uncoated) showing radial color bands from USGS locality D7086 (text fig. 1, loc. 

48). USNM 239644.

6. Specimen from USGS locality D6200 (text fig. 1, loc. 1). USNM 239645. 

7. Camptonectes ex gr. C. virgatus (Nilsson) (p. 16).

Latex cast of an impression in very fine grained sandstone from USGS locality D5345 fig. 1, loc. 42).

USNM 239742. 

8,9. Lopha staufferi (Bergquist) (p. 20).

8. Internal mold of a right valve from USGS locality D2051 (fig. 1, loc. 58). USNM 239717.

9. Interior view of a right valve from USGS locality D5365 (fig. 1, loc. 59). USNM 239718. 

10-12. Idonearca depressa White (p. 13).

Three views of a large specimen from the same locality as figure 8. USNM 239611.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 19

MOLLUSKS FROM THE TWOWELLS SANDSTONE TONGUE
PLATE 20

[All figures natural size]

FIGURES 1-15. Pycnodonte aff. P. kellumi (Jones) (p. 17).

1-4. Left valve from USGS locality D6133 (fig. 1, loc. 55). USNM 239662.

5-7. Two views of the left valve and one of the right valve from USGS locality D6191 (text fig. 1, loc.

2). USNM 239663. 

8, 9. Interior and exterior views of a right valve from USGS locality D7335 (text fig. 1, loc. 21). USNM

239664.

10-13. Left valve from the same locality. USNM 239665.

14, 15. Exterior and interior views of a right valve from the same locality. USNM 239666. 

16-18. E.vogyra levis Stephenson (p. 18).

From the same locality as figures 1-4.

16. Left valve. USNM 239683.

17. 18. Left valve. USNM 239684. 

19,20. E.vogyra trigeri (Coquand) (p. 19).

Left and right valves of an incomplete specimen from USGS locality D5753 (fig. 1, loc. 23). USNM 

239712.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 20

20

MOLLUSKS FROM THE TWOWELLS SANDSTONE TONGUE
PLATE 21

[All figures natural size except as indicated]

FIGURES 1-4,7. Granocardium trite (White) (p. 20).

From USGS locality D6131 (text fig. 1, loc. 54).

1, 2. Views of an internal mold of a left valve. USNM 239719.

3. Internal mold of a left valve. USNM 239720.

4. 7. Latex casts of impressions in very fine grained sandstone of right and left valves in White's 

type lot from "head of Waterpocket canyon, southern Utah" (White, 1879, p. 291). USNM 239721, 

239722. 

5,6,10-16. Metoicoceras spp. (p. 25).

5. 6. Rear and side views of an internal mold from USGS locality D5392 (fig. 1, loc. 27). USNM

239779. 

10, 11. Rear and side views of a strongly ornamented fragment from USGS locality D5743 (fig.

1, loc. 26). USNM 239780. 

12-14. Front, side, and rear views of an internal mold from USGS locality D6164 (fig. 1, loc. 11).

USNM 239781. 

15, 16. Rear and side views of an internal mold from USGS locality D5754 (text fig. 1, loc. 13).

USNM 239782. 

8, 9. Metoicoceras cf. M. praecox Haas (p. 25).

Rear and side views of part of a whorl from USGS locality D5819 (text fig. 1, loc. 28). USNM

239777. 

17. Calycocerasl canitaurinum (Haas) (p. 23).

Side view (x ¥2) of a phragmocone from USGS locality D5741 (text fig. 1, loc. 49). USNM 239754.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 PLATE 21

16 17 

MOLLUSKS FROM THE TWOWELLS SANDSTONE TONGUE