Molluscan Fauna

of the

Morrison Formation

GEOLOGICAL SURVEY PROFESSIONAL PAPER 233-B
Molluscan Fauna

of the

Morrison Formation

By TENG-CHIEN YEN

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950, PAGES 21-51 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 233-B

Illustrations and descriptions of pelecypods and gastropods 

Summary of the stratigraphy', by yohn B. Reeside^ Jr.

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1952
UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar L. Chapman, Secretary

GEOLOGICAL SURVEY

W. E. Wrather, Director

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

Washington 25, D. C.—Price 65 cents (paper cover)
CONTENTS

Page

Abstract _______________________________^_1_____________.________________.__..__ 21

Introduction ______________________________________________.____________________ 21

Acknowledgements _____________________________________..____________________ 21

Summary of the stratigraphy of the Morrison formation, by John B. Reeside, Jr.____._________________——_ 22

Review of literature________________________________________.____________________ 26

Distribution of the fossils______________________________________._____________________ 28

Age of the Morrison formation__________________________________._____________________ 31

Characteristic species of mollusks_____________________________._____________________ 32

Comparison with molluscan faunas of overlying beds___________________._____________________ 32

Comparison with molluscan faunas of European deposits________'._____-_____________________ 33

Purbeck fauna____________________________________.____________________ 33

Wealden fauna___________________________________.____________________ 34

Conclusion __—________________________________________.___________——___—_ 34

Systematic descriptions_______________________________________.__________________—_ 35

Pelecypoda ___________________________________________.____________________ 35

Gastropoda ___________________________________________-_________________—_ 38

Bibliography __———__——_________—___—____—________——______————_———_————__ 45

Index __________________________________________________-_____________________ 49

ILLUSTRATIONS

Page

PLATE 3. Unio and Vetulonaia_______________________________________________Following index

4, 5. Unio and Hadrodon________________________________________________ Following index

6. Gastropoda __—________________________________________________Following index

FIGURE 1. Map showing localities of Morrison invertebrate collections___,_____-____________________ 29

111

MOLLUSCAN FAUNA OF THE MORRISON FORMATION

By TENG-CHIEN YEN

ABSTRACT

The Morrison fauna of Colorada, Utah, Wyoming, and 

Montana has yielded 17 species of pelecypods in 3 genera 

and 32 species of gastropods in 19 genera. All of these 

are fresh-water forms. One genus (Hadrodon) and 5 species of pelecypods, and 3 genera (Amplovalvata, Mesauriculstra and Limnopsis), and 11 species of gastropods 

are described as new. Many of the genera are still living, 

though no species extends into even the immediately overlying beds. It is concluded that the Morrison fauna indicates a Jurassic age and that it may be pre-Purbeckian.

INTRODUCTION

The present paper embodies a systematic study 

of the molluscan fauna of the Morrison formation and the distribution of the fauna in Colorado, Utah, Wyoming, and Montana. It is based 

mainly on material collected by members of the 

U. S. Geological Survey supplemented by additional 

collections by me during a field trip to Colorado 

and Wyoming in the summer of 1945. All these 

collections are in the U. S. National Museum.

Among the invertebrates of the Morrison formation, mollusks are comparatively rich in species 

as well as in individuals. In general, they are well 

preserved in the limestone beds; however, the calcified specimens are brittle and difficult to prepare 

satisfactorily for study. At a few localities, the 

fossiliferous rocks are partly silicified, and the 

rich fossil content, after being etched with acid, 

furnishes more perfectly preserved specimens.

In summary, the molluscan fauna yields 17 

species of pelecypods in 3 genera and 1 family, 

and 32 species of gastropods in 19 genera representing 9 families. Among them, 1 genus and 

5 species of bivalves, 3 genera and 11 species and 

subspecies of univalves are herein described as 

new. The majority of the genera are still represented in the living fauna as well as in the intermediate geologic formations; but the species are 

entirely extinct even in the beds immediately 

above the Morrison formation.

ACKNOWLEDGMENTS

In completing the present study, which has been 

carried on at various times from 1945 to 1947, I 

have to express my thanks first of all to the Geological Society of America, for its financial support of my research project through grants from 

the Penrose Fund in 1945 and 1946. Grateful 

thanks are due to the authorities of the U. S. 

Geological Survey and the U. S. National Museum 

for their courtesies and kindnesses in putting their 

collections of material freely at my disposal; and 

in these institutions the main part of my research 

project has been carried out. I am especially indebted to Dr. John B. Reeside, Jr., who has given 

me much time in consultations and in critical 

reading of the manuscript. I am indebted also 

to Dr. T. W. Stanton for the privilege of including 

in this work a number of collections of specimens 

that he had partly identified, in manuscript.

During my field work in Colorado and Wyoming 

in the summer of 1945 I enjoyed the hospitality 

of and pleasant association with many friends in 

those States. Special thanks go to Professor Gordon Alexander, then Acting Director of the State 

University Museum of Natural History in Boulder, Colorado, for his kindness of providing me a 

working office in the Museum and transportation for a number of local trips; to Dr. J. David 

Love and Mr. H. A. Tourtelot of the U. S. Geological Survey for their assistance in visiting a 

number of localities in Wyoming; and to Mr. Vincent Evans, a resident geologist of the Carter Oil 

Company in Grand Junction, Colorado, who accompanied me on visits to localities near Grand 

Junction to collect additional fossils.

During a visit to Great Britain to examine collections of Purbeckian and the Wealden mollusks 

I was greatly aided by Dr. L. R. Cox, of the Department of Geology in the British Museum (Natural History), and Mr. R. V. Melville and Mr. C. 

P. Chatwin, of the Geological Survey of Great 

Britain, and I deeply appreciate their kindness 

and courtesy.

21
SUMMARY OF THE STRATIGRAPHY OF THE MORRISON FORMATION

By JOHN B. REESIDE, JR.]

The Morrison formation is widely distributed 

in the western interior of the United States. It 

has been recognized on the south in northern 

New Mexico and northeastern Arizona; on the 

west as far as central Utah, west-central Wyooming, and western Montana; on the north as 

far as the Canadian border in Montana; and on 

the east under the high plains of western South 

Dakota, western Nebraska, western Kansas, eastern 

Colorado, and the Oklahoma Panhandle. How much 

farther east it may confidently be recognized in wells 

is not certain, and whether it is represented in 

Canada in the Kootenay of that country is debated.

The deposits now designated the Morrison formation have, under various local names, been of 

interest to geologists since almost the beginning of 

geologic exploration of the West. As the "Atlantosaurus beds," the "Beulah clays," the "Como 

beds," and the "McElmo formation;" as part of the 

"Dakota jgroup," the "Cascade formation," the 

"Beckwith formation," the "Flaming Gorge group," 

and the "Gunnison formation;" and under several 

descriptive terms reference to them has appeared 

many times in the literature. The remains of 

giant reptiles contained in them were noted early, 

and some of their molluscan fossils were among 

the earliest invertebrates to be recorded from the 

interior region.

The continuing interest in the Morrison formation has resulted in the accumulation of a large 

body of pertinent literature. Mook (1916) listed 

and evaluated the publications to that date. Baker, 

Dane, and Reeside (1936) reviewed particularly the 

literature for the southern Rocky Mountains and 

adjacent Colorado Plateau. Stokes (1944) brought 

up to date the record for this southern area and 

considered some of the more remote areas also. No 

recent general summary of the literature has been 

made.

The Morrison formation has always been a 

subject of controversy. A difference of opinion 

appeared early as to whether the Morrison deposits should be referred to a Late Jurassic or an 

Early Cretaceous age, and this difference has persisted into rather recent years. At the present 

time opinion seems to be heavily in favor of assigning the formation to the Jurassic. The current 

differences of opinion center mainly on the placement of the boundaries in many local sections.

The name Morrison was first published by 

Whitman Cross in 1894. G. H. Eldridge was apparently the original proposer, though his discussion was not actually published until 1896 

(Emmons). The name was based on incomplete 

exposures at the town of Morrison, Colo. A paper 

by Waldschmidt and Leroy (1944) proposed the 

adoption of a complete section newly exposed in 

a road-cut 2 miles north of Morrison as the more 

practical type section.

Eldridge's original description of the formation 

included, in the upper part, sandstones and associated shaly beds that are now assigned to the 

Lower Cretaceous. Excluding these, the beds 

near Morrison form an acceptable standard section, particularly the complete exposure described 

by Waldschmidt and Leroy. In this exposure 

the "basal unit is a sandstone 30 feet thick. This 

is overlain, in succession, by 55 feet of gray and 

red shale with charophyte oogonia, 50 feet of gray 

clay and limestone, 51 feet of gray shale and 

sandstone with dinosaurian remains, 37 feet of red 

shale, and 76 feet of variegated shale and sandstone. 

The total thickness is about 300 feet.

At other places along the eastern foothills of the 

Front Range in Colorado, the lowest Jurassic unit 

is a massive cross-bedded light-colored sandstone 

that is generally correlated with the Entrada sandstone, a part of the San Rafael group of Utah. Upon 

it rest beds of sandstone and shale, and locally gypsum, to a thickness of some tens of feet, that may 

be a correlative of the marine Curtis formation, also 

a part of the San Rafael group, though distinctive 

paleontologic evidence is not known along the Front 

Range. Next above comes about 30 feet of interbedded gray shale and limestone that yields only 

fresh-water fossils, chiefly calcareous algae. This 

unit was included by Lee (1927) in his marine Sundance formation, but seems better placed, because

1 The writer is indebted for very helpful suggestions in compiling this 

discussion to W. A. Cobban, L. C. Craig, C. N. Holmes, R. W. Imlay, 

J. D. Love, and W. L. Stokes.

22
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 23

of its character and its fauna, in the Morrison formation (Reeside, 1931). The remainder of the Morrison is a unit of variegated mudstones and lenticular 

sandstones about 200 feet thick, upon which lie 

sandstones and shale of Early Cretaceous age. The 

area north of Canon City has yielded a notable 

dinosaurian fauna and, associated with it, the most 

extensive single assemblage of mollusks known from 

the Morrison formation.

In northern Mexico and northeastern Arizona the 

beds generally accepted as the Morrison formation 

show a marked change of lithologic facies from east 

to west. In northeastern New Mexico the Morrison 

formation consists of variegated mudstones and lenticular sandstones much like those of the foothills 

of the Front Range and about 200 feet thick. These 

rest on a gypsum and limestone sequence as much as 

80 feet thick that is generally called the Todilto 

limestone and accepted as representing the Curtis 

interval of Utah, though older opinions placed it at 

both higher and lower levels (Baker et al., 1947). 

It has been proposed recently (Baker et al., 1947) to 

include the Todilto and locally associated thin-bedded 

sandstones in the Wanakah formation, extending 

the use of that name from southwestern Colorado, 

and to consider the Wanakah equal to the upper part 

of the San Rafael group. The massive sandstone 

beneath the Wanakah is accepted as representing 

the Entrada, though it has been called locally Exeter 

sandstone in the east and Wingate sandstone in the 

west. The Morrison in the east is overlain sharply 

by the Purgatoire formation, a marine unit of Lower 

Cretaceous age. Westward the Morrison formation 

acquires sandstones in the lower part, apparently 

replacing the shatter beds, and this replacement continues until, adjacent to the New Mexico-Arizona 

boundary, the interval is all sandstone. It has been 

called the Zuni sandstone by Dutton (1885) and in 

part erroneously referred to the much older Navajo 

sandstone by Gregory (1917) and others. The Zuni 

sandstone of Dutton reaches a maximum thickness 

of about 600 feet but is much less than that at many 

points. It is underlain by the Wanakah formation 

and is overlain by sandstone that has generally 

been considered Cretaceous and called the Dakota 

sandstone, though the age assignment is not well 

supported by paleontologic evidence.

In western Colorado and adjacent parts of Utah 

the Morrison formation was formerly included in 

the "McElmo formation" and in the "Gunnison formation," and more recently its boundaries have been 

the subject of discussion (Stokes, 1944). The section near Grand Junction (C. N. Holmes, unpublished data) may be taken as typical. Here greenish 

thin-bedded sandstones and shales about 45 feet 

thick rest on the Entrada sandstone and have been 

correlated with the Summerville formation, the highest unit of the San Rafae\ group of Utah. On these 

lies about 25 feet of gray shales and limestones that 

contains fresh-water fossils, and in turn interbedded 

lenticular sandstone and shale about 160 feet thick. 

The sandstone unit is generally called the Salt Wash 

sandstone member of the Morrison formation, but 

the character and fauna of the limestone unit seeni 

to warrant inclusion of it also in the Salt Wash. The 

remaining uppermost part of the Morrison formation is a zone 350 feet thick made up chiefly of variegated mudstone and now called the Brushy Basin 

shale member (Gregory, 1938). Upon the Brushy 

Basin member lie sandstones and shales now designated the Burro Canyon formation (Stokes, 1948) 

and assigned to the Lower Cretaceous. A section 

measured 20 miles farther west, near the UtahColorado boundary (C. N. Holmes, unpublished 

data), shows little or no limestone resting on the 

Summerville formation, the Salt Wash member 250 

feet thick, and the Brushy Basin member 280 feet 

thick.

The correlation of the units between the sandy, 

deposits of the Salt Wash member of the Morrison 

and the JSntrada sandstone is in some dispute, because they vary in composition from place to place, 

at some places including thick-bedded gypsum and 

at others thick, massive sandstone. In this varied 

part of the section a number of formation and member names have been applied locally. In Colorado 

such names as Pony Express limestone and Wanakah 

marl (Burbank, 1930) and Bilk Creek sandstone 

and Junction Creek sandstone (Goldman, 1941) have 

been proposed. The first three may represent equivalents of the upper units of the marine San Rafael 

group of central Utah and the Junction Creek sandstone may belong to the Morrison formation. Similar 

heterogeneous units underlying the JBrushy Basin 

member in southeastern Utah have been named by 

Gregory (1938) the Bluff sandstone member, Recapture shale member, and Westwater Canyon sandstone member. The Bluff sandstone member has been 

correlated with the Entrada sandstone by some geologists, with a later part of the San Rafael group by 

others, and with post-San Rafael deposits by others. 

The Recapture and Westwater Canyon members are 

generally accepted as parts of the Morrison and as 

the lateral equivalent of the Salt Wash meni^er ancj
24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

part of the Brushy Basin member.

In central Utah (Gilluly, 1928; Baker, 1946) a 

marine Jurassic sequence (the San Rafael group) 

has been recognized, the highest unit being the Summerville formation and below it in descending order 

the Curtis formation, the Entrada sandstone, and 

the Carmel formation. Above the Summerville formation lies the rather heterogeneous Morrison 

formation, with a unit of sandstone and shale, the 

Salt Wash sandstone member, about 200 feet thick, 

in the lower part, and a dominantly variegated mudstone unit, the Brushy Basin shale member, about 

300 feet thick, above it The overlying beds below the 

Dakota sandstone are several hundred feet thick, 

are very similar to the Brushy Basin member, though 

locally containing notable conglomerates, and have 

been included by earlier writers in the Morrison 

formation. Stokes (1944) has proposed considering 

them Early Cretaceous in age and has divided them 

into the Buckhorn conglomerate below (a discontinuous unit) and the Cedar Mountain shale above. 

The boundary of the Cedar Mountain shale of Stokes 

and from his Brushy Basin shale at places where 

there is no conglomerate is difficult to establish 

though Stokes (letter of June 19, 1950) reports that 

microfossils identified by R. E. Peck assure the 

assignment of the Cedar Mountain to the Lower 

Cretaceous.

Along the south flank of the Uinta Mountains in 

northern Utah the beds assigned to the Morrison 

formation include in the east about 700 feet of variegated mudstones with lenticular sandstones and 

conglomerates that rest upon the marine Curtis formation. Westward the Morrison is said to be 1,500 

or more feet thick. These beds have yielded a varied 

dinosaur fauna that assures correlation of the unit 

with the typical Morrison formation. Upon the Morrison lie conglomerates and shales that are commonly 

assigned to the Lower Cretaceous and included under the designation "Dakota (?) sandstone" (Huddle, 

1947). Though paleontologic evidence is lacking, this 

assignment seems reasonable.

In southwestern Wyoming and the adjacent parts 

of Utah and Idaho the name Morrison has not been 

used, but an equivalent of the Morrison formation 

was most probably included locally in the Beckwith 

formation (Veatch, 1907). Where the Beckwith has 

been divided (Mansfield, 1927), as in central western Wyoming and adjacent parts of Idaho, the Ephraim conglomerate, basal formation of the Gannett 

group, must contain any equivalent of the Morrison 

formation present, for it is underlain by the marine

Jurassic Stump formation (equivalent to the Curtis 

formation faunally) and is overlain by the Peterson 

limestone, which contains a Lower Cretaceous nonmarine fauna. No paleontologic evidence has been 

presented that the Ephraim actually contains Jurassic beds, and it is usually assigned to the Lower 

Cretaceous, thus following the original assignment, 

though Stokes (1944) has tentatively identified a 

lithologic equivalent of the Morrison formation in it.

In west-central Wyoming the beds assigned to 

the Morrison formation are dominantly a variegated 

mudstone, though locally the whole zone is massive 

sandstone. The thickness in the Wind River Basin 

ranges from 125 to 175 feet (Love, 1945, 1947). 

Both boundaries are somewhat arbitrary. At localities where the lower part of the Morrison is sandstone, the separation of the marine Sundance formation from the Morrison is based largely on the 

presence of glauconite in the widespread uppermost 

sandstones of the Sundance and the absence of it 

from the Morrison. The Cloverly formation, above 

the Morrison, is generally composed of a basal chert 

conglomerate, a middle part of variegated mudstones 

containing some lenticular sandstones and conglomerates, and an upper sandy unit, commonly containing ferruginous material and weathering "rusty." 

Where the basal conglomerate is lacking, distinguishing the variegated beds of the Morrison from the 

similar beds of the Cloverly must be on minor lithologic characteristics and is a difficult task.

A series of beds totalling 370 feet in thickness, 

near the northwest end of the Wind River Range, 

was ascribed by Richmond (1945) to the Morrison 

formation and said to rest directly upon the Sundance. These beds include a basal conglomeratic 

sandstone, red and gray mudstones, sandstones, and 

shales totaling 135 feet in thickness, upon which 

rest a limestone 10 feet thick, a shale 20 feet thick, 

and another limestone 5 feet thick, and then variegated shales 200 feet thick. The next overlying deposits are "rusty beds" 240 feet thick, ascribed to 

the Cloverly formation. The 10-foot limestone has 

yielded a varied fauna of nonmarine mollusks identified by Yen and Reeside (1946) as a Jurassic fauna 

of Morrison age. The molluscan fauna has no species 

in common with any of the known Lower Cretaceous 

faunas, but it does contain four species that elsewhere are known only from Morrison horizons. R. E. 

Peck (J. D. Love, letter of January 5, 1951) has 

identified, from presumably the same limestone, 

charophyte oogonia and ostracodes belonging to a 

widespread assemblage of Early Cretaceous age. If
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 25

the identification of the horizon is valid, the interpretation of the age of the beds is left in doubt. Pending 

further investigation, the Morrison is here construed 

as including at least the beds up to the base of the 

200-foot variegated shale unit.

In the Bighorn Basin, north-central Wyoming, 

the Morison formation is stated to be about 200 feet 

thick in the southern part of the Basin and 500 feet 

or more thick in the northern part, though certainly 

some part of this greater thickness represents beds 

that are elsewhere assigned to the Lower Cretaceous 

Cloverly formation (Lee, 1927; Pierce, 1941). The 

formation is composed of sandstones and variegated 

shales.

In eastern Wyoming and adjacent South Dakota, 

particularly around the Black Hills, the Morrison 

formation is said to be about 200 feet thick at its 

maximum and to consist of variegated mudstones, 

fresh-water limestones, and minor sandstones (Darton, 1925). Beneath it at some localities lies a crossbedded sandstone, the Unkpapa sandstone, also about 

200 feet thick at its maximum. As each formation at 

its locality of maximum thickness appears to displace the other completely, it is likely that they are 

contemporaneous facies. Both locally rest on the 

marine Jurassic Sundance formation and both locally are overlain by the Lower Cretaceous Lakota 

sandstone. The Morrison in the Black Hills region 

has yielded characteristic dinosaurs and invertebrates.

In southern Montana the Morrison includes variegated mudstones, minor zones of sandstone, and at 

the top a widespread zone of carbonaceous shale and 

thin coal beds. The formation is said to range up to 

400 feet in thickness but is apparently about 250 

feet thick on the average (Thorn, 1935; Hadley, 

1945; Gardner, 1945). It rests upon the marine 

Jurassic deposits with apparent conformity and is 

overlain by the Lower Cretaceous Cleverly (or Kootenai) formation. In central and northwestern Montana the lower part of a sequence of greenish-gray 

clay shale and limestone up to several hundred feet 

thick, with sandstone and locally a commercial coal 

bed at the top, was tentatively referred by earlier 

writers (Calvert, 1909; Fisher, 1909) to the Morrison formation. By some later writers it was included in the Lower Cretaceous Kootenai formation, 

but in recent years it has again been placed in the 

Morrison formation because of its composition and 

structural relations (Cobban, 1945) and of its flora 

and fauna (Brown, 1946). The Kootenai formation 

unconformably overlies the Morrison and differs

from it in fossil content and lithologic character. The 

Morrison rests upon the marine Jurassic deposits 

with no indication of any sort of hiatus.

In general the beds that include the change from 

the marine Jurassic deposits to the nonmarine Morrison formation provide little physical evidence of 

interruption of sedimentation. There is no basal 

conglomerate and no sharp change in lithologic 

character. On the contrary, over large areas there 

is so little change in composition of the rocks that 

the basal boundary of the Morrison must be more or 

less arbitrarily selected. Nor does the paleontologic 

evidence appear to indicate a considerable gap, 

though, because of the shift from marine deposition 

represented by the underlying beds to nonmarine 

deposition represented by the Morrison formation, 

it is not easy to evaluate the data involved. The latest 

marine deposits preceding the Morrison are everywhere of essentially the same age, Oxfordian of the 

European standard sequence (Imlay, 1947), and 

some evidence is available that the Morrison vertebrates are of Kimmeridgian and possibly early Portlandian age (Baker, 1936). Yen indicates (pp. 34-35) 

that the mollusks of the Morrison suggest a greater 

age than Purbeckian, i. e., Portlandian or older. It 

would seem that such interpretations as the fossils 

permit do not favor the inference of a substantial 

break in the sequence and that the total evidence, 

physical and organic, implies little or no interruption 

in sedimentation during the change from marine to 

nonmarine deposition.

The beds that include the transition from the 

Morrison formation to the overlying Lower Cretaceous deposits, though at some places difficult to 

divide, indicate nevertheless at other places a physical boundary that is well defined. Where such units 

as the brown basal conglomeratic sandstone of the 

Cloverly formation, the Lakota sandstone, and the 

basal part of the Kootenai formation are present, the 

boundary is sharply marked. If the Morrison, on the 

basis of its dinosaurian fauna and invertebrates, be 

accepted as Portlandian or older, there is still unrepresented the highest Jurassic, the Purbeckian. 

The Gannett group of western Wyoming, the Cloverly formation of central Wyoming, and the Kootenai 

formation of Montana all contain the same Lower 

Cretaceous nonmarine mollusks, and the faunal assemblage is specifically distinct from that of the 

Morrison.

It is not possible to correlate these invertebrates 

directly with faunas outside North America, but 

such correlations have been made on the basis of
26 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

the fossil plants associated with the mollusks. Berry 

(1929), regarded the lower part of the Blairmore 

formation of Canada as Aptian or Albian of the 

European standard sequence, i e., later Early Cretaceous, and also as equivalent to part of the Lakota 

sandstone and the Fuson shale of Wyoming. The 

lower part of the Blairmore contains the same molluscan fauna as the Cloverly, Gannett, and Kootenai. He regarded the Kootenay1 of Canada, which 

unconformably underlies the Blairmore, as of Barremian age, i. e., somewhat earlier Early Cretaceous. 

Bell (1946) regarded the lower part of the Blairmore as Aptian and the Kootenay as extending perhaps from earlier Early Cretaceous to Barremian 

and certainly of Early Cretaceous age. Brown 

(1946), on the other hand, regarded the Canadian 

Kootenay as Jurassic, older than the Kootenai of 

Montana, and as equivalent to the Morrison. Whatever may be the ultimate assignment of the Canadian 

Kootenay, in the United States there is reason to infer a time interval between the Morrison formation 

and the succeeding beds that represents possibly 

part of the Portlandian, probably the Purbeckian, 

the Berriasian, the Valanginian, the Hauterivian, 

and possibly the Barremian of the standard European sequence.

REVIEW OF LITERATURE

The literature on the molluscan fauna of the Morrison formation has been reviewed briefly (Yen and 

Reeside, 1946) but, because lack of space precluded 

an adequate treatment in that paper, a fuller account 

is offered here.

Early in 1858, Meek and Hayden described Unio 

nucalis from the "southwest base of Black Hills, in 

lower part of no. 1," which was considered to be the 

lowest unit of their Cretaceous system, described in 

the stratigraphic part of their paper. They also mentioned that in the same matrix occur several specimens of small Planorbis and other univalves like 

Paludina.

In 1860, the same authors recorded Valvata scabrida, and Planorbis veternus as nomina nuda, and 

without giving a locality, but provisionally assigning them to the Jurassic. In 1861, they described 

fully Neritella nebrascensis and Melania (Potodoma) 

veterna from "head of Wind River, from a bed apparently holding a position at the base of the Cretaceous."

In 1865, Meek and Hayden fully described and 

illustrated the above five species, and in addition 

Viviparus gilli, apparently also from the "head of 

Wind River." This group of fresh-water molluscan 

species constitutes the earliest record attributed to 

the Upper Jurassic beds of North America, the Morrison formation of later years.

Further investigation in the field and additional 

collections of specimens, made during the last three 

quarters of a century, permit the following clarification of these early records:

First, the six species that Meek and Hayden described were obtained at two localities from rocks 

of different ages. Unio nucalis, Valvata scabrida, 

and Planorbis veternus, from the "southwest base 

of the Black Hills," are considered to be of Morrison

age. Neritella nebrascensis, Viviparus gilli and Lioplacodes veternus, from "head of Wind River," have 

not been found in the Morrison formation exposed 

elsewhere in the Rocky Mountain States, though they 

have been repeatedly recorded in the Cloverly formation or its quivalents, and are considered to be of 

Early Cretaceous age.

Second, "other univalves like Paludina" were 

mentioned by Meek and Hayden in 1858, but they 

were never described, and they are not to be confused with Viviparus gilli, which the authors in 

1865 described from "head of Wind River." What 

these Paludina-like snails actually were is unknown; 

possibly they were Amnicola gilloides Yen and Reeside, which has been recently recorded from the 

Morrison formation near Lower Green River Lakes, 

Mayoworth, and Freeze-out Hills, Wyoming.

Third, Valvata scabrida, whose position is discussed fully on page 29, has been incorrectly cited in 

records by later authors under different specific 

names. The distribution of this species seems to be 

restricted to the beds exposed in the Black Hills, at 

Mayoworth and Como Bluff, and in the Freeze-out 

Hills, Wyoming, and in the Grand Junction area. 

Colorado.

Fourth, Planorbis veternus seems to be a widely 

distributed species in the Morrison formation, much 

as some species of the Planorbidae are in the Recent 

fauna. Possibly, this species may be employed as an 

indicator of the Morrison formation, as it has not 

so far been recorded from beds either above or below that formation.

In 1878, C. A. White described Unio stewardi 

from Jurassic strata exposed near the bank of Green 

River in Wyoming.

The classic work on fresh-water mollusks of the

1 The preferred Canadian form of the name.
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 27

North American Jurassic did not appear until 1886, 

when C. A. White published his paper on a collection 

from the "Atlantosaurus beds" exposed 8 miles 

north of Canon City, Colorado, to which he added 

notes on the previously described species. The fossils 

from Canon City are well silicified, and this work is 

the first paper on Morrison mollusks based on a collection of well-preserved specimens from an authentic locality. The following species were described or 

recorded by White (they are listed in their original 

nomenclature) :

Unio felchi White

Unio toxonotus White

Unio iridoides White

Unio lapilloides White

Unio stewardi White

Unio macropisthus White

Valvata scabrida Meek and Hay den?

Limnaea ativuncula White

Limnaea consortis White

Limnaea? accelerata White

Planorbis veternus Meek and Hayden?

In the same paper White recorded Unio nucalis 

Meek and Hayden and Vorticifex stearnsii White 

from the "Atlantosaurus beds" exposed at Como, 

Wyoming, and noted the earlier reference to the 

Jurassic of Viviparus gilli Meek and Hayden, Lioplacodes veternus Meek and Hayden, and Neritina 

nebrascensis Meek and Hayden.

In 1900, W. N. Logan described from the FreezeOut Hills in Wyoming:

Unio willistoni Logan

Unio knighti Logan

Unio baileyi Logan

Planorbis veternus Meek and Hayden

Valvata leei Logan

The inadequate descriptions and illustrations of the 

new species make these records of little help to later 

investigators, though unquestionably the names are 

fully valid. Further information and additional 

specimens from the nearby area now permit revision 

of these species in the systematic part of this work. 

In 1915, W. I. Robinson described from the 

"Painted Desert beds" of east-central Arizona:

Valvata gregorii Robinson 

Limnaea hopii Robinson

The type material is not available for the present 

study. The "Painted Desert beds" are not Morrison 

(Jurassic) but Chinle (Triassic), so that the above 

species will not be included in the present study.

In 1935, C. C. Branson described an interesting 

collection of mollusks from beds of the Morrison 

exposed south of Mayoworth, Wyoming. The following forms (given in their original nomenclature)

were recorded or described:

Vetulonaia whitei Branson 

Vetulonaia mayoworthensis Branson 

Vetulonaia nucalis (Meek and Hayden) 

Valvata scabrida Meek and Hayden 

Valvata? jurassica Branson 

Lioplacodes veternus Meek and Hayden? 

Viviparus gilli Meek and Hayden 

Planorbis veternus Meek and Hayden 

Pentagoniostoma jurassicum Branson 

Pentagoniostoma altispiratum Branson

Most of Branson's names are useful, but to distinguish his Pentagoniostoma from Tropidina H. and A. 

Adams on morphological grounds, is almost impossible and the two species included in his new genus, 

judged by his descriptions and illustrations, are 

most probably not congeneric. Lioplacodes veternus 

of Branson may represent an imperfect specimen of 

Lymnaea ativuncula White; his Viviparus gilli may 

be related to Amnicola gilloides and its small size 

and few whorls differentiate it sufficiently from V. 

gilli; and his record of Valvata scabrida was based 

on specimens which "agree with specimens of 

White," and which then should be identical with 

Amplovalvata morrisonensis. Branson gave neither 

figure, nor measurements for this form, so that his 

record must remain uncertain.

In 1942, E. L. Holt described Vetulonaia faberi 

from an exposure in Ladder Canyon, about six miles 

south of Grand Junction, Colorado. The species is 

said to occur in association with Vorticifex stearnsii 

White. In the same paper Holt mentions the presence 

of Valvata scabrida Meek and Hayden in a limestone 

bed exposed about one mile west of the golf course 

in Fruita, Colorado.

The present author obtained additional specimens 

from Holt's locality in 1945 enabling him to conclude that Vorticifex stearnsii of Holt is the adult 

form of Amplovalvata scabrida Meek and Hayden, 

and his Valvata scabrida is Viviparus reesidei.

In 1946, Yen and Reeside described a collection of 

silicified mollusks from a locality west of Mill Creek 

below Lower Green River Lake, on the west slope of 

the Wind River Mountains in the western part of 

Wyoming. The faunule consists of the following 

species:

Valvata minuscula Yen and Reeside 

Amnicola gilloides Yen and Reeside 

Mesocochliopa assiminoides Yen and Reeside 

Mesopyrgium pendilabium Yen and Reeside 

Tortacella aff. T. haldemani (White) 

Galba ativuncula (White) 

Gyraulus veternus (Meek and Hayden) 

Graptophysa spiralis Yen and Reeside 

Physa micra Yen and Reeside 

Physa conispira Yen and Reeside
28 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Aplexa, militaria Yen and Reeside 

Aplexa morrisonana Yen and Reeside 

Unio iridoides White

This fauna is notable as the sole known occurrence 

of eight species and as the only one ascribed to 

the Jurassic that includes the genus Tortacella 

'(=Zaptychius), previously recorded only in the 

Cretaceous. It has four species in common with other 

Morrison faunas and none with the Cretaceous. 

L. D. Love reports (Letter of Jan. 5, 1951) that 

R. E. Peck has found at this locality charophyte 

oogonia and an ostracode of Early cretaceous age, 

though the writer believes the molluscan fauna assignable only to the Morrison.

DISTRIBUTION OF THE FOSSILS

The localities from which fossils have been examined in the couse of study are shown in figure 1. 

These localities are as follows:

1. Lt. 38° 31'; Long. 104° 52', Garden Park, Colorado 

Springs quadrangle, Colorado; collected by G. K. Gilbert, 

1893; U.S.G.S. Mes. loc. 1325. The fossils are imbedded in 

fine-grained silty greenish-gray limestone, and the molluscan 

shells are replaced partly by silica and partly by calcite.

2. West side of Penitentiary Ridge, 2 miles north of Canon 

City, Fremont County, Colorado; collected by C. E. Siebenthal, 1904; U.S.G.S. Mes. loc. 3211. The matrix is darkgrayish limestone and the shells are calcified.

3. Near Canon City, Fremont County, Colorado; collected 

by M. P. Felch, 1885; U.S.G.S. Mes. loc. 481. The matrix is 

in part coarse-grained limestone of grayish color and in part 

pale-reddish sandstone. The fossils are replaced by calcite.

4. Locality 8 miles north of Canon City, Fremont County, 

Colorado, known as "Bone Yard"; collected by C. A. White 

and R. T. Hills, 1885; U.S.G.S. Mes. loc. 397. The matrix is 

a hard, cherty dark-grayish limestone and the fossils are 

well silicified.

5. Felch's Ranch, Garden Park, 9 miles north of Canon 

City, Fremont County, Colorado; collected by I. C. Russell, 

1888; U.S.G.S. Mes. loc. 17997. The matrix is cherty grayish 

limestone and the abundant fossils are fully replaced by 

silica.

6. Quarry Spur section, Colorado City (west end of Colorado Springs), El Paso County, Colorado, collected by G. I. 

Finlay, 1908; U.S.G.S. Mes. loc. 5420. The matrix is a mediumgrained dark-grayish limestone. The shells are calcified.

7. About 100 yards southeast of Vernal Summit on Uncompahgre Tunnel road of Uncompahgre project, Montrose 

County, Colorado; collected by C. E. Siebenthal, 1904; U.S.G.S. 

Mes. loc. 3209. The matrix is a medium-grained yellowish 

limestone. The fossils are in part silicified and in part calcified. Three new species of Hadrodon occur in abundance.

8. West side of Gunnison Canyon north of Red Rock Canyon, Montrose County, Colorado; collected by C. E. Siebenthal, 1904; U.S.G.S. Mes. loc. 3212. The matrix is a hard, 

flint-like dark-grayish limestone. The abundant shells are 

silicified.

9. SE*4 Sec. 26, T. 14 S., R. 98 W., near the Broughton 

fruit ranch, Gunnison River, Mesa County, Colorado; about

1 mile northeast of Dominguez station and about 23 miles 

southeast of Grand Junction; collected by T. C. Yen and 

V. Evans, 1945; U.S.G.S. Mes. loc. 20322. The matrix is a 

fine-grained dark limestone and the few shells are calcified.

10. Sec. 25, T. 12 S., R. 101 W.; about 8 miles southwest of 

Grand Junction and 7/10 mile SE. of Blue Hills, on the north 

rim of Ladder Canyon, Mesa County, Colorado; collected by 

T. C. Yen and V. Evans, 1945; U.S.G.S. Mes. loc. 20323. The 

matrix is greenish-gray shale, and the fossils are abundant.

11. Sec. 24, T. 1 N., R. 3 W. Ute Mer., Mesa County, Colorado; about 2 miles due SW. of Fruita and about 1% miles 

to west of Fruita Golf Course; collected by T. C. Yen and 

V. Evans, 1945; U.S.G.S. Mes. loc. 20324. The matrix is 

cherty dark-gray limestone. Most of the fossils are silicified 

but a few are argillaceous. Only Viviparus reesidei Yen, n. 

sp., has been found. Individuals are abundant, including 

numerous young shells, apparently of the same species. The 

collection may represent a deeper-water facies of the Morrison formation.

12. Sec. 30, T. 1 N., R. 2 W. Ute Mer., Mesa County, Colorado; about 2 miles slightly south of west from the Fruita 

Golf Course; collected by T. C. Yen and V. Evans, 1945; 

U.S.G.S. Mes. loc. 20325. The matrix is of dark-grayish limestone.

13. NW%SE% sec. 34, T. 4 S., R. 92 W., Garfield County, 

Colorado; 16 feet above the Entrada sandstone; collected by 

W. L. Stokes, 1944; U.S.G.S. Mes. loc. 19407. The matrix is 

fine-grained greenish-gray sandstone and the fossils are represented by internal casts of Unio.

14. Fairplay-Como road, just east of Red Hill Gap, about 

4% miles NE of Fairplay, Park County, Colorado; collected 

by David White, 1909; U.S.G.S. Mes. loc. 6220. The matrix 

is dark-grayish limestone of fine texture. The few shells are 

calcified.

15. Two miles north of Morrison, Jefferson County, Colorado; collected by C. E. Siebenthal and N. H. Barton, 1905; 

U.S.G.S. Mes. loc. 3507. The matrix is grayish limestone of 

fine texture; fossils are few and imperfectly preserved.

16. By road side about % mile west of Hot Sulphur 

Springs, Middle Park, Grand County, Colorado; collected by 

Whitman Cross, 1891; U.S.G.S. Mes. loc. 6951. The matrix is 

light-gray limestone of fine texture.

17. Sec. 13, T. 8 N., R. 70 W., Larimer County, Colorado; 

west side of U. S. Highway 287; collected by T. C. Yen and 

G. Alexander, 1945; U.S.G.S. Mes. loc. 22408. The matrix is 

dark-grayish limestone of fine texture.

18. SE% sec. 23, T. 9 S., R. 68 W., Castle Rock, Quadrangle, 

Douglas County, Colorado; collected by B. G. Richardson, 

1911; U.S.G.S. Mes. loc. 7363. The matrix is sj.ndy light-gray 

limestone above a gypsum bed. The fossils are undeterminable forms of pelecypods and gastropods.

19. SE*4NWi4 sec. 28, T. 9 N., R. 80 W., about 7 miles west 

of Walden, near Platte River bridge, Jackson County, Colorado; collected by A. L. Beekly, 1911; U.S.G.S. Mes. loc. 7119. 

The matrix consists of rather soft silty shale, and fossils are 

imperfectly preserved and few in number.

20. SW^iNE^i sec. 33, T. 10 N., R. 81 W., Jackson County, 

Colorado; collected by A. L. Beekly, 1911; U.S.G.S. Mes. loc. 

7116. Light-gray clayey limestone of fine texture.

21. Blue limestone above upper red beds, Humbug, Wash., 

Emery County, Utah; collected by E. M. Spieker and J. B. 

Reeside, Jr., 1924; U.S.G.S. Mes. loc. 12572. Unio sp. and 

fragments of gastropods have been found.
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 29

Sundonce 0 | D A XK-~0 T A

FIGURE 1. Localities of Morrison invertebrate collections.
03

o

Distribution of species of Morrison mollusks

Unio stetoardi, "Pentagoniostoma" altispiratum Branson, and unidentifiable species of Valvata, Vivipartts, Amnicola, Hydrobia, Gyraulus, Ph

Uniofelehi. ...............................

faberi. ................................

Vicinity of 

Canyon City and 

Colorado City, Colo.

1

-

-

-

X 

X

X

X

-

-

2

-

-

-

X

-

X 

X

X

3

X

-

-

-

-

-

-

4

X

X

-

X

X

X

X

5

X

-

X

X

X

X

6

-

X

X

Vicinity of Grand Junction 

Red Rock Canyon, and 

Fairplay, Colo.

7

X

-

-

8

-

X

9

X

-

X

10

X

X

-

11

-

-

12

-

X

13

-

-

14

X

X

Vicinity of 

Morrison and 

Boulder, Colo.

15

X

-

16

X

17

-

X

18

-

-

Northwestern 

Colorado and 

Utah

19

-

-

20

-

X

21

-

-

22

X

X

23

X

-

Vicinity of 

Laramie, Wyo.

24

X

X

25

-

-

26

X

X

27

-

X

X

28

X

X

-

29

X

X

Vi

Gre

30

-

31

-
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 31

22. Near Dinosaur Quarry, Dinosaur National Monument, 

Uintah County, Utah, collected by Earl Douglas, 1913; 

U.S.G.S. Mes. loc. 8747. The matrix is a coarse-grained sandstone.

23. Forty feet above base of Morrison formation; 1,000 

feet due south of the bridge over San Rafael River on Hanksville Green River Road, about 15 miles SW. of Green River, 

Emery County, Utah; collected by H. E. Yokes, 1943; U.S.G.S. 

Mes. loc. 19472. The matrix is rather fine-grained dark-gray 

sandstone. The fossils are represented by more bivalves than 

gastropods, though the latter have the wider specific range.

24. SW% sec. 32, T. 14 N., R. 74 W., about 12 miles SW. 

of Laramie, Albany County, Wyoming; collected by N. H. 

Darton and C. E. Siebenthal, 1905; U.S.G.S. Mes. loc. 3503. 

The matrix is light-gray limestone of fine texture, and the 

fossils are calcified.

25. NW& sec. 11, T. 14 N., R. 74 W., about 8 miles SW. 

of Laramie, Albany County, Wyoming; collected by C. E. 

Siebenthal and N. H. Darton, 1905; U.S.G.S. Mes. loc. 3504. 

The matrix is fine-grained limestone of light gray color.

26. In NE 1^ sec. 10, T. 13 N., R. 76 W., Riverside Ranch, 

25 miles SW. of Laramie, Albany County Wyoming; collected by C. E. Siebenthal and N. H. Darton, 1905; U.S.G.S. 

Mes. loc. 3505. The matrix is fine-grained light-gray limestone.

27. NW% sec. 15, T. 13 N., R. 75 W., west of Dowling's 

Soda Lake, Albany County, Wyoming; collected by N. H. 

Darton, 1905; U.S.G.S. Mes. loc. 3506. The fossils are few 

and occur in grayish limestone.

28. Sec. 12, T. 22 N., R. 77 W., about 3 miles east of Como 

Lake, Albany County, Wyoming; collected by N. H. Darton, 

1905; U.S.G.S. Mes. loc. 3508; grayish limestone.

29. Sec. 9, T. 22 N., R. 77 W., Albany County, Wyoming, 

about \Vz miles north of "Dinosauria" Museum; collected by 

T. C. Yen and H. A. Tourtelot, 1945; U.S.G.S. Mes. loc. 20326. 

Grayish-brown shale below the "Dakota" sandstone.

30. North Gulch of Salt Canyon, about sec. 33, T. 41 N., 

R. 81 W., Powder River Oil Field, Natrona County, Wyoming; collected by C. M. Wegemann, 1910; U.S.G.S. Mes. loc. 

6767. Light-gray oil-saturated sandstone at base of the 

Morrison formation.

31. Hill behind the University of Wyoming cabin, Freezeout Mountains, Carbon County, Wyoming; collected by C. 

Schuchert, 1899; U.S.G.S. Mes. loc. 2389. The matrix is finegrained dark-gray sandstone, and the fossil bed is about 6 

inches thick and in the middle of a zone 100 feet thick.

32. Near center of sec. 14, T. 44 N., R. 83 W., Johnson 

County, Wyoming; collected by Vaughn Russom, 1944; 

U.S.G.S. Mes. loc. 19092. The fossils occur in a reddish-brown 

sandstone ledge, 1 to 2 feet thick, 50 to 75 feet below top of 

the Morrison formation.

33. Sec. 14, T. 44 N., R. 83 W., Mayoworth, Johnson 

County, Wyoming; collected by T. C. Yen and H. A. Tourtelot, 

1945; U.S.G.S. Mes. loc. 20327. The fossils occur in grayishgreen sandy shale.

34. NE. of Bonanza Post Office, about sec. 12, T. 49 N., 

R. 91 W., Wyoming; collected by W. C. Knight, 1903; U.S.G.S. 

Mes. loc. 3184. The fossils are weathered from a light-colored, 

rather fine-grained sandstone.

35. Basal beds of the Morrison formation in Old Woman 

anticline, Niobrara County, eastern Wyoming; collected by 

Harold J. Cook, 1945; U.S.G.S. Mes. loc. 20533.

36. North side of Big Goose Creek, Absaroka Park, l x/4

miles below mouth of Big Goose Canyon, about sec. 35, T. 55 

N., R. 86 W., Sheridan County, Wyoming; collected by T. E. 

Williard, 1907; U.S.G.S. Mes. loc. 4884.

37. West of Mill Creek below Lower Green River Lake, 

on the west slope of Wind River Mountains, Sublette County, 

Wyoming; collected by G. Richmond, W. G. Pierce, and J. D. 

Love, 1944; U.S.G.S. Mes. loc. 20328. Hard, cherty light-gray 

limestone; the shells are fully silicified.2

38. About 2 miles north of Pools Ranch on Surprise Creek, 

Great Falls coal field, near Fergus-Cascade County line, Montana; collected by C. A. Fisher, 1906; U.S.G.S. Mes. loc. 3963. 

The martix is rather fine-grained dark sandstone.

39. North of springs on Big Spring Creek, about 7 miles 

SE. of Lewiston, Fergus County, Montana; collected by W. R. 

Calvert, C. A. Fisher and T. W. Stanton, 1907; U.S.G.S. Mes. 

loc. 4763. Light-colored silty limestone 40 feet above the base 

of the Morrison.

40. On east side of the creek at Big Springs NW. corner 

of Big Snow Mountains, Fergus County, Montana; collected 

by R. W. Brown, O. O. Mueller, and R. W. Imlay, 1944; 

U.S.G.S. Mes. loc. 19418. Greenish shale near the base of the 

Morrison formation.

41. About 3 miles south of Cheadle, Fergus County, Montana; collected by J. B. Reeside, Jr., and R. W. Imlay, 1944; 

U.S.G.S. Mes. loc. 19419.

42. NE^SE 1^ sec. 5, T. 14 N., R. 19 E., Judith Basin, 

Fergus County, Montana; collected by W. R. Calvert, 1907; 

U.S.G.S. Mes. loc. 4768.

Insofar as the available collections show, the invertebrate fauna of the Morrison, in addition to the 

molluscan species, consists of ostracodes of freshwater habitat and in places spicule-like remains 

which are assumed to represent fresh-water sponges. 

No other invertebrates have been found.

The fossil flora of the formation consists chiefly 

of Charophyta, represented by oogonia and by stems. 

These occur commonly and in places very abundantly. According to Peck (1937, 1941), the charophyte 

faunas of the Morrison (Upper Jurassic) and of 

Lower Cretaceous beds are distinct and can easily 

be distinguished. If the strata below the coal bed in 

the lower part of the Kootenai formation in Montana, which are about 75 feet thick, and the underlying unit of shales, about 125 feet thick, be included in the Morrison (Brown 1946), the flora of 

this formation may be enriched by some 19 species 

of ferns, cycads and conifers.

AGE OF THE MORRISON FORMATION

The age of the Morrison formation has been a 

matter of controversy for more than half a century.

2 J. D. Love reports (Letter of January 5, 1951) that R. E. Peck has 

found at this locality charophyte oogonia and an ostracode of Early 

Cretaceous age. Because the molluscan fauna includes four species in 

common with accepted Morrison localities and none with any known Lower 

Cretaceous locality, the writer has retained the locality as Morrison. It 

is the only known locality for Zaptychius not definitely of Cretaceous age.
32 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Baker, Dane, and Reeside (1936, pp. 58-63) reviewed 

the discussions to 1936 and little has been added 

since that time. It seems to be more generally accepted in recent years that these deposits were laid 

down in Upper Jurassic time (pp. 33-34).

CHARACTERISTIC SPECIES OF MOLLUSKS

Study of the molluscan species from 42 localities 

in Colorado, Utah, Wyoming, and Montana, has convinced me that an assemblage of a few of the following species, or their association with the less abundant species, is a good indication of the presence 

of the Morrison formation.

Unio lapilloides White 

Unio stewardi utahensis Yen 

Unio mammillaris Yen 

Vetulonaia mayoworthensis Branson 

Vetulonaia whitei Branson 

Hadrodon jurassicus Yen 

Amplovalvata cyclostoma Yen 

Amplovalvata scabrida (Meek and Hayden) 

Viviparus reesidei Yen 

Viviparus morrisonensis Yen 

Lymnaea ativuncula White 

^ Gyraulus veternus (Meek and Hayden)

The table of distribution shows that all the species 

listed above occur at 2 or more localities, and in general fairly abundant. None of these species has been 

recorded from beds above or below the Morrison 

formation.

Generic identifications of fresh-water mollusks 

generally give little help in determining the age of 

the containing rocks, for most of them have long 

ranges. However, the following genera have been 

as yet reported from beds of the Morrison formation 

only:

Vetulonaia Branson 

Hadrodon Yen 

Amplovalvata Yen 

Mesopyrgium Yen and Reeside 

Mesauriculstra Yen 

Limnopsis Yen

COMPARISON WITH MOLLUSCAN FAUNAS OF 

OVERLYING BEDS

Only a few species of mollusks have been reported 

from such older fresh-water units as the Chinle formation, of Upper Triassic age, which is separated 

from the Morrison by a considerable sequence of 

deposits, part of which are marine and recognized 

to be of Jurassic age. Therefore, for the purpose of 

the present work, a comparison with the beds overlying the Morrison may be more advantageous.

Stanton (1915) compared the molluscan fauna of 

the Morrison with the scant fauna of the Potomac

group of Maryland and with that of the Kootenai 

formation of Montana. The fossils from Maryland 

came from the Arundel and Patapsco formations and 

these units have recently been placed in the Upper 

Cretaceous (Anderson, 1948), which assignment 

removes the fossils from consideration here. The 

Kootenai formation is accepted as of Lower Cretaceous age. Stanton concluded that the Lower Cretaceous mollusks are decidely distinct, specifically 

as well as in assemblage, from those of the Morrison. 

The writer reached a similar conclusion (1946) 

after studying a collection of fresh-water mollusks 

from the Cloverly formation on Sage Creek, Wyoming. The difference is easily recognizable even by 

comparing the molluscan species of the deposit at 

Sage Creek with those of the Morrison exposed near 

Lower Green River Lake only 100 miles away. The 

Lower Cretaceous beds are commonly indicated by 

the presence of such species as—

Protelliptio douglassi (Stanton) 

Protelliptio douglassi hamili (McLearn) 

Eupera onestae (McLearn) 

Stantonogyra silberlingi (Stanton) 

Lioplacodes veternus (Meek and Hayden) 

Lioplacodes cretaceus (Stanton) 

Lioplacodes convexiculus Yen

None of these species has been found in any of the 

Morrison collections available for the present study. 

Congeneric species are known from both the 

Jurassic and Lower Cretaceous formations, and the 

relationships of the congeneric forms are close. This 

element in the two faunas is not large, but the number may increase as the molluscan fauna of the 

Lower Cretaceous beds becomes better known. The 

following may be noted:

Jurassic

Viviparus reesidei Yen 

Lioplacodes jurassicus 

Yen

Mesoneritina morrisonensis Yen

Zaptychius aff. Z. haldemani (White)

Lower Cretaceous

Viviparus gilli (Meek and Hayden) 

Lioplacodes cretaceus (Stanton) 

Lioplacodes veternus (Meek and

Hayden) 

Mesoneritina nebrascensis (Meek

and Hayden) 

Zaptychius cf. Z. haldemani

(White)

On the basis of the above discussion, the Morrison 

formation is not the faunal equivalent of the Kootenai and Cloverly formations. As the stratigraphic 

position of these formations in most places is above 

the Morrison, it is logical to conclude that the Morrison formation is older than the Kootenai and 

Cloverly.
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 33

COMPARISON WITH MOLLUSCAN FAUNAS OF 

EUROPEAN DEPOSITS

The fauna of the Morrison formation has been 

compared during the last three-quarters of a century with those of Purbeckian and Wealden beds 

of Europe. Jones (1885) compared several species 

of ostracodes collected from the "Atlantosaurus 

beds" north of Canyon City, Colorado (Locality 4), 

with those described from the Purbeck beds of England. Osborn (1888) related the mammals of the 

Morrison to those of the British Purbeck. Although 

the molluscan fauna of the Morrison has been studied 

at intervals during the last 70 to 80 years, no serious comparative study of its species with contemporary forms from other parts of the world has been 

undertaken. Logan (1900) mentioned the similarity 

of four Morrison genera, Unio, Valvata, Planorbis, 

and Viviparus, to those of the Wealden, but he seems 

to have overlooked the fact, pointed out by Stanton 

(1915), that the genera considered by Logan are all 

known from formations both older and younger than 

the Wealden. Besides, Logan was evidently not 

aware that most of the genera of fresh-water mollusks have long geological ranges and so are of little 

use, for purposes of correlation.

On the basis of collections in the British Museum 

and the Museum of Practical Geology of the Geological Survey of Great Britain, the Morrison molluscan species are compared with the Purbeckian 

and the Wealden faunas. Because less is known concerning the morphological features of the species of 

pelecypods, the present comparison lays emphasis 

mainly on the gastropod species.

PURBECK FAUNA

On the basis of the available collections, none of 

the Morrison forms is specifically identical with any 

found in the Purbeck beds. However, of the 26 

species described and accepted by Arkell (1941), 8 

show a morphological resemblance to Morrison 

species. For the European species, I retain Arkell's 

nomenclature; however, I am inclined to believe 

that the respective similar forms are probably congeneric, and that the differences in nomenclature 

may be adjusted later.

Morrison species

Valvata minuscula Yen

Reeside 

Lioplacodes morrisonensis

Yen

Hydrobia sp. undet. 

Mesopyrgium pendilabium

Yen and Reeside

Purbeck species

and V, helicoides de Loriol 

V. subaudiensis Maillard 

Viviparus cariniferus (J.

Sowerby)

H. chopardiana (de Loriol) 

Promathilda microbinaria

Arkell

Morrison species ' Purbeck species

Mesoneritina morrisonensis Theodoxus fisheri Arkell

Yen 

Mesauriculstra morrisonensis Ellobium durlstonense Arkell

Yen 

Gyraulus veternus (Meek Planorbis fisheri Arkell

and Hayden)

First of all, the two Purbeckian species of Valvata 

are decidedly different from the Morrison species in 

the lower elevation of the spire, coarser sculpture, 

and wider umbilicus. Viviparus cariniferus and V. 

inftatus of the Purbeck beds are elongately highspired, have strongly and roundly convex whorls, 

and the former is probably keeled in the young shells 

along the periphery. These features remind one of 

those of Lioplacodes morrisonensis, which is described from the Freezout Mountains of Wyoming. 

The peripheral keel of the Morrison species is obscure but traceable on the body whorl of the adult. 

Hydrobia chopardiana resembles closely, except in 

its smaller size, a species recorded from Locality 26 

of the Morrison formation. This species is represented by a single example, so that its specific identification remains uncertain. One of the most interesting species of the Morrison is perhaps Mesopyrgium pendilabium, which morphologically resembles Promathilda microbinaria of the Purbeckian. 

However, according to Arkell, the Purbeckian species 

occurs in the middle Purbeck above the Cinder Bed 

in association with spscies of brackish habitat, 

whereas the Morrison species is found with truly 

fresh-water species of Amnicola, Planorbis, Physa, 

and Aplexa. Whether Theodoxus fisheri is comparable with Mesoneritina morrisonensis will have to 

depend largely on the discovery of better-preserved 

specimens of the Purbeck species, which may show 

its columellar plate and apertural features. The Morrison species is of truly fresh-water habitat, found 

in association with species of Unio, Amplovalvata, 

and Amnicola. Among the pulmonates, Mesauriculstra morrisonensis seems to be comparable with Ellobium durlstonense of the Purbeck beds. The Morrison species bears only a single oblique fold or 

plait on the columella. It is probably related to species of Ellobium and Auriculstra, moreover, Gyraulus 

veternus, a widely distributed species in the Morrison formation, is different from Planorbis fisheri, 

not only by its less strongly carinated periphery, but 

also by its much less rapidly increasing size of whorl, 

which produces a considerably different outline of 

the shell. However, they may belong to the same 

group.

The morphological features seem to deny any spe-
34 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

cific identity of these possibly related species. But 

they may be examined in assemblages, for which 

the fossils of a middle Purbeck bed exposed in Portisham, Dorest, may be taken as a group to compare 

with the molluscan faunules found north of Canyon 

City, Colorado (Locality 5), and west of Mill Creek, 

Wyoming (Locality 37). The British Museum's collection from the Purbeck in Portisham contains the 

following species:

Valvata helicoides de Loriol 

Viviparus subangulatus (Roemer) 

Hydrobia forbesi Arkell 

Ellobium jaccardi (de Loriol) 

Planorbis fisheri Arkell 

Physa cf. P. bristovii Phillips 

Physa sp. undet.

In addition to the above gastropod species, I found 

several ostracodes and some well preserved oogonia 

of charophytes with a few fragments of stem-like 

structures. The abundance of individuals of Valvata 

helicoides and Hydrobia forbesii, including numerous young shells leads to the inference that the deposit represents a deeper-water facies (in contrast 

to a shore deposit). The pulmonate species constitute a bare majority, but they are represented by 

only a few specimens. The dominance of mollusks 

in the assemblage, together with charophytes and 

ostracodes, suggest a similarity in ecological conditions with those of the Morrison formation.

WEALDEN FAUNA

It is difficult to compare the molluscan species of 

the Wealden with those of the Morrison because the 

Wealden species have not been studied in detail during recent years, as the Purbeckian species have by 

Arkell. The Wealden species were described and 

recorded from the English beds mostly by J. Sowerby from 1813 to 1836, from the German beds by 

Roemer (1835), Koch and Dunker (1837), Dunker 

(1846), Sandberger (1870), and Struckmann 

(1880). On the basis of these records, a list of the 

Wealden Mollusca was given by von Bubnoff (1935, 

p. 917). However, both Dunker and Struckmann 

included several Purbeck species in their Wealden 

division. Struekmann actually treated part of the 

Purbeck beds as his Lower Wealden.

In the collections of Wealden Mollusca in the 

British Museum (Natural History) and the Museum 

of the Geological Survey of Great Britain, I have 

found some characteristic species from the Wealden 

beds exposed in Sussex, Kent, and Ise of Wight. The 

occurrence of a few of these species in combination

may be taken as a good index of this formation, and 

these forms are listed as follows:

Anodonta becklesi Newton 

Unio valdensis Mantell 

Neomiodon medium (J. Sowerby) 

Viviparus sussexiensis (J. Sowerby) 

Campeloma carbonaria (Roemer) 

Lioplacodes elongatus (J. Sowerby) 

Amnicola roemeri (Dunker) 

"Paludina" scalariformis (Dunker) 

Paraglauconia strombaeformis (Schlotheim)

The assemblage of molluscan species from the 

Wealden shows considerable difference from that 

of the Purbeck. So far the true Wealden species of 

mollusks have not been reported from the Purbeck 

beds. Such a common Wealden species as Lioplacodes elongatus (J. Sowerby) is readly differentiated from the common Purbeck species "Viviparus" cariniferus (J. Sowerby) by its scracely convex whorls, smaller number of whorls at similar 

size of shell, and absence of an infraperipheral keel 

in the early whorls.

The molluscan fauna of the Morrison shows even 

greater difference from that of the Wealden than 

from that of the Purbeck. Of three genera of pelecypods, only Unio, and three of nine genera of gastropods (Viviparus, Lioplacodes, and Amnicola) are 

common to the Morrison and Wealden formations. 

The congeneric species are distinctly different from 

each other, and the common occurrence of such 

genera as Unio, Viviparus, and Amnicola has practically no significance in stratigraphical interpretation.

CONCLUSION

The foregoing comparisons of the molluscan 

faunas suggest that probably the Morrison formation is older than the Purbeck formation, and that 

there is little basis for correlating it with the 

Wealden beds.

It is true that in places the assemblages of the 

Morrison and Purbeck show close similarity in ecological conditions, and the congeric species of the 

two formations also indicate close relationship. I 

also readily agree with Arkell that a number of 

the Purbeck species, some of which I have had 

the opportunity of examining, resemble species of 

the Bear River formation, of Late Cretaceous age. 

However, there is no species found both in the Morrison and Purbeck formations, even of such widely 

distributed genera as Planorbis, Lymnaea, and 

Physa. Moreover, Pachychilus-like or Goniobasislike species are not known in formations earlier than 

the Purbeck and do not occur in the Morrison, but
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 35

they have been repeatedly reported from Cretaceous 

and Early Tertiary horizons in North America as 

well as in Europe. The absence of these faunas in 

the Morrison, therefore, suggests that the Morrison 

is older than the Purbeck. Conceivably, it could be 

contemporaneous with the basal part of the lower 

Purbeck, or with some unit between the Portlandian 

and the Purbeckian, but in my judgment it is older 

than the Purbeckian at least.

SYSTEMATIC DESCRIPTIONS 

PELECYPODA -

The bivalves of the Morrison formation, so far 

as the collections available for the present study are 

concerned, are represented by Unionids only. On account of lack of knowledge of the hinge features in 

several species, the generic revision of these forms 

is exceedingly difficult, if not impossible. Though 

such a generic name as Vetulonaia is useful, caution 

should be exercised when insufficiently described 

species of the early records are included under such 

genera. The change may add nothing but confusion.

Hadrodon Yen, new genus, is distinguished both 

by external features and by hinge structure. Nothing 

closely similar has been found in younger rocks, so 

far as I know. Some of the features show a gerontic 

character, and the genus may have become extinct 

shortly after Morrison time.

The possible origin of the North American Jurassic Unios is still a problem, and divergent opinions 

have been advanced. One school believes that these 

fresh-water bivalves migrated from another continent during the Jurassic time, whereas others consider that they existed in America in Triassic or 

even earlier times. Unio thomasi Henderson and 

Unio arizonensis Henderson, both from the Triassic 

beds of Arizona, seem to lend weight to the latter 

viewpoint. However, any generalization on the basis 

of incidental collections of material seems to be 

inadvisable. It seems reasonable to suppose that 

other genera of fresh-water bivalves of wide geographic distribution could exist together with the 

true unios in America, subsequently becoming extinct here but surviving elsewhere.

Family UNIONIDAE

Unio felchi White

PL 3, fig. la-c.

Unio felchi White, U. S. Geol. Survey Bull. 29, p. 16, pi. 1 

fig. 1-5, 1886. (Type locality: "Atlantosaurus beds," 

8 miles north of Canyon City, Colorado). 

The type lot (U.S.N.M. 20048) consists of 3 specimens. They are closed valves and the hinge structure is unknown. The original description of the 

external features is adequate and accompanied by 

illustration of the 3 specimens.

Figured specimen: U.S.N.M. 106992.

Unio toxonotus White 

PL 5, fig. 3a-b.

Unio toxonotus White, U. S. Geol. Survey Bull. 29, p. 17, pi. 2, 

fig. 1-2, 1886. (Type locality: "Atlantosaurus beds," 

8 miles north of Canyon City, Colorado).

The type lot (U.S.N.M. 20049) consists of a single 

specimen with closed valves, slightly injured at its 

ventral margin.

Unio macropisthus White 

PL 5, fig. 4.

Unio macropisthus White, U. S. Geol. Survey Bull. 29, p. 17, 

pi. 2, fig. 7,1886. (Type locality: "Atlantosaurus beds," 

8 miles north of Canyon City, Colorado).

The type lot (U.S.N.M. 20050) is a single internal 

mold. Further interpretation of this species will depend upon the discovery of more completely preserved specimens at the type locality.

Unio iridoides White 

PL 5, fig. 5a-b.

Unio iridoides White, U. S. Geol. Survey Bull. 29, p. 17, pi. 2, 

fig. 3-4, 1886. (Type locality: "Atlantosaurus beds," 

8 miles north of Canyon City, Colorado).

The type lot (U.S.N.M. 20051) consists of 2 specimens, a complete one with closed valves and an internal mold. The original figures are reproduced.

Unio baileyi Logan 

PL 3, fig. 2.

Unio baileyi Logan, Kansas Univ. Quart., vol. 9, p. 134, pi. 31, 

fig. 4, 6, 8, 11 1900. (Type locality: the Freeze-Out 

Hills Wyoming).

,The type-specimen is not available. Judged by the 

original description and inadequate outline figures, 

it seems to be close to, if not identical with, the preceding species.

Figured specimen: U.S.N.M. 106991.

Unio lapilloides White 

PL 5, fig. 6a-b.

Unio lapilloides White, U. S. Geol. Survey Bull. 29, p. 18, 

pi. 2, fig. 5-6, 1886. (Type locality: "Atlantosaurus 

.beds," 8 miles north of Canyon City, Colorado).

The type lot (U.S.N.M. 20052) consists of an internal mould, characterized by an elongate outline 

which differentiates it from congeneric species found 

in this area.
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Unio knighti Logan

Unio knighti Logan, Kansas Univ. Quart., vol. 9, p. 134, pi. 31, 

fig. 7-9, 1900. (Type locality: the Freeze-Out Hills, 

Wyoming).

It differs from the other two species of Unio described by Logan from the same locality mainly in 

its more elongate outline. The type specimen is not 

available. It may be closely related to, if not identical 

with, the preceding species.

Unio steward! White

Unio stewardi White, in Powell, Report on the geology of 

the eastern portion of the Uinta Mountains, p. 110, 

1876. (Type locality: Jurassic strata near the banks of 

the Green River in southern Wyoming).

The type lot (U.S.N.M. 8849) consists of 6 fragments, which are recognizable as a large species of 

Unio of thick shell substances.

Unio stewardi utahensis Yen, n. sp. 

PL 3, fig. 3a-e.

This subspecies is characterized by its subtriangular outline, broadly undulated external surface, and 

moderately thick shell substance. The pseudocardinal is well developed and moderately elevated. The 

hinge line is gently curved, having a single prominent lateral ridge on the right valve, that corresponds with a fairly deep groove on the left. The 

type measures 28.0 mm in length, 58.0 mm in height, 

and 34.0 mm in convexity.

In the type collection, there is a large series of 

well-preserved specimens with both open and closed 

valves, which were obtained by H. E. Yokes from a 

locality in Utah (no. 23), less than 200 miles southwest of the type-locality of Unio stewardi White.

Holotype: U.S.N.M. 106989, Locality 23; figured 

paratypes: U.S.N.M. 106990, unfigured paratypes: 

U.S.N.M. 107031a-n, Locality 23.

Unio willistoni Logan

PL 3, fig. 4. •

Unio willistoni Logan, Kansas Univ. Quart., vol. 9, p. 133, 

pi. 31, fig. 10, 1900. (Type locality: The Freezeout 

Mountains, Wyoming).

The type lot is not available for the present study. 

A number of specimens that Charles Schuchert collected from the Freezeout Mountains externally 

seem to be identical with this species.

Figured specimen: U.S.N.M. 106994.

Unio nucalis Meek and Hayden 

PL 3, fig. 5a-c.

Unio nucalis Meek and Hayden, Acad. Nat. Sci. Philadelphia 

Proc., vol. 10, p. 52, 1858. (Type locality: southwest 

base of Black Hills, South 'Dakota).

The type lot (U.S.N.M. 196) consists of 5 specimens, 2 with closed valves, 1 with its hinge line 

partly preserved, and 2 buried in a grayish limestone matrix.

In the present collection there are several specimens that were obtained from the basal bed of the 

Morrison formation in the "Old Woman Anticline 

in eastern Wyoming." These new well-preserved 

specimens are rather small, have moderately thick 

shells, highly convex valves, and a high but small 

pseudocardinal and a single prominent lateral in 

the right valve. *

Figured specimen: U.S.N.M. 103749.

Unio mammillaris Yen, n. sp. 

PL 4, fig. la-e.

Shell large and of very thick substances, oval to 

subtriangular in outline. External surface bears 

strong and close concentric lines of growth and one 

broad, radiating fold at some distance below the 

dorsal margin. Beaks high and prominent, at anterior end of the shell, well incurved and pointed 

somewhat forward. Beak sculpture not well preserved on the holotype. Hinge structure massive and 

strong, consisting of wide plate. Pseudocardinal 

large and heavy, of subtriangular form, with its top 

surface rugged, as shown on better-preserved specimens; single on the right, distinctly but unequally 

bisected on the left. Lateral single, prominent, and 

somewhat sharp edged on the right, bound by a 

well-incised line on both outer and inner margins; 

laterals 2 on the left valve, forming a rather deep 

and wide groove corresponding to the single lateral 

on the right, and a deep canaliculate line running 

externally next to the outer lateral. The anterior 

adductor scar is large, deep, and rough on its surface; the posterior scar as shown on an incomplete 

specimen, appears to be large but shallow. The 

measurements of the holotype, in millimeters, are 

as follows:

Altitude of shell________________________53.0 

Length of shell__________________________82.0 + 

Convexity of shell________________________47.0

This species is characterized by the heavy structure of the hinge with a rather wide plate, and thick 

shell substance. The development of the outer and 

inner incised lines along the laterals is rather variable. In some specimens they are deeply impressed, 

and often produce an appearance of having 2 laterals 

on the right valve and 3 on the left. No specimens 

in the present collections show much secondary laterals distinctly.
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 37

Holotype: U.S.N.M. 107064, Locality 39; paratypes: U.S.N.M. 107030, 106993, 107027, 107029 and 

107028, Localities 34, 39-42.

Vetulonaia white! Branson 

PI. 3, fig. 6a-b.

Vetulonaia whitei Branson, Jour. Palaeontology, vol. 9, p. 

517, pi. 56, fig. 1-5, 8-10, 13, 15, 19, 1935. (Type locality: 3 miles south of Mayoworth, Wyoming).

The paratype lot (U.S.N.M. 75499) consists of 3 

single valves and 3 closed specimens. One of the 

closed specimens has perfectly preserved traces of 

the radiating lines on the umbonal area that are 

much less coarse than the concentric lines.

Vetulonaia mayoworthensis Branson 

PL 3, fig. 7.

Vetulonaia mayoworthensis Branson, Jour. Palaeontology, 

vol. 9, p. 517, pi. 56, fig. 7, 11, 14, 16-18, 1935. (Type 

locality: 3 miles south of Mayoworth, Wyoming).

This species differs from the preceding mainly in 

its elongate outline and more massive hinge structure and thicker shell substance.

The genus resembles Pleurobema, as noted by 

Branson. The above described forms certainly remind one of such species as P. decisa and P. cor datum of the living North American fauna but, because of the long time interval, it appears desirable 

to retain the name Vetulonaia for the Jurassic species, as we know nothing at present of the genetic 

relationships.

Vetulonaia faberi Holt

Vetulonaia faberi Holt, Jour. Palaeontology, vol. 16, p. 459, 

pi. 69, fig. 1-5, 1942. (Type locality: On Ladder Canyon road, about 6 miles south of Grand Junction, 

Colorado).

This species, on the basis of the holotype, may be 

differentiated from V. whitei by its more oval outline, greater convexity, and wider and somewhat 

impressed ligamental area. Holt seems to have included heterogenous forms in his species. One of his 

paratype specimens (U.S.N.M. 103262), which is 

illustrated by his figures 3a and b of plate 69, may 

represent a different form.

Hadrodon Yen, n. gen.

Shell of thick substance, triangular to rhomboid 

in outline, with a prominent umbonal region. Beak 

subterminal, well incurved, and bearing a few coarse 

concentric ridges. External surface conspicuously 

undulated by 2 or 3 broad, radiate folds and marked 

by strong concentric lines. Hinge very strong, having a broad plate, which in some species constitutes

nearly one-fourth of the entire shell width. The margin of the hinge plate is well defined by a strong 

convex radiating ridge on the external surface of 

the shell, which forms a principal undulation on its 

surface. Pseudocardinal well developed, of triangular shape with rugged surface, bearing irregular 

and broken molar-like lines; one or two on the right 

valve, two or four on the left. The laterals are much 

more strongly developed; the primary one on the 

right valve is strongly elevated, gradually increasing 

in width towards the posterior end; it corresponds 

to a deep and wide canaliculate groove formed on 

the left valve. In some species, a secondary lateral 

is present on the right valve, just above the primary, 

and the groove formed between the 2 laterals on the 

right valve just fits a smaller lateral one on the left 

valve.

Genotype: Hadrodon jurassicus Yen, n. sp. The 

genus is characterized by its broad hinge plate 

and strong lateral teeth in combination with its conspicuous undulating external surface. In one species, 

the hinge plate has a tendency toward outward expansion, and in another species, it has an excessive 

development; such gerontic features seem to suggest 

that this group of fresh-water bivalves may have 

been extinct since Jurassic time.

Hadrodon jurassicus Yen, n. sp. 

PL 4, fig. 2a-f.

Shell features essentially those described for the 

genus. Shell subrhomboid in outline, convex and 

bearing costulate concentric lines, and broad radiating folds. One fold forms a strong convex ridge extending from the umbonal area to the posteroventral margin. The hinge plate is well defined; pseudocardinal moderately heavy and elevated, of triangular shape and rugged surface; lateral plate bears 

single high lateral tooth on the right valve, which 

corresponds with a deep groove of moderate width, 

flanked by 2 lower lateral teeth on the left valve. 

The main anterior adductor scar is broad and deep, 

with a much smaller secondary one; the posterior 

scar is larger than the anterior but is shallower; it 

also has a secondary scar just above it. Measurements of the holotype, in millimeters, are:

Altitude of shell___________________________36.0 

Length of shell___________________________44.0 

Convexity of left valve_____________________15.5

This species is characterized by its subrhomboid 

outline of shell, highly elevated pseudocardinal, and 

comparatively narrow hinge plate.
38 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Holotype: U.S.N.M. 107005, Locality 7; paratypes : U.S.N.M. 106995, 107003, 107007, 107008 and 

107009, Localities 7 and 10.

Hadrodon trigonus Yen, n. sp. 

PL 4, fig. 3a-f; pi. 5, fig. la-d.

Shell of subtriangular outline, much more strongly convex than H. jurassicus. The radiating ridge is 

more sharply angulated and submedian in position. 

The hinge line is arched, having a broader plate; 

the pseudocardinal is large; the lateral groove on 

the left valve is wider and more deeply impressed, 

possibly indicating a much stronger lateral on the 

right valve. The primary and secondary adductor 

scars are very similar ts those of the preceding species. Measurements of the holotype, in millimeters, 

are:

Altitude of shell.__________________________48.0 

Length of shell ______________________.____ 66.5 

Convexity of shell __ ._____________________ 40.C

Holotype: U.S.N.M. 107001, Locality 7; paratypes: U.S.N.M. 107002, 107003 and 107004, Locality 7.

Hadrodon lateralis Yen, n. sp. 

PL 5, fig. 2a-f.

Shell ovately rhomboid in outline, more compact 

than in H. jurassicus or H. trigonus. The main ridge 

on the external surface is convex but low. The hinge 

plate is very broad, and its superior margin somewhat expanding. The pseudocardinal is low but 

large. The primary lateral groove on the left valve 

is wide but less deeply impressed, and has one or 

two secondary grooves present above it. These 

grooves correspond to one primary and one or two 

secondary teeth on the right valve. The arrangement 

of muscular scars is similar to that of the preceding 

species. Dimensions of the holotype, in millimeters, 

are:

Altitude of shell_________________________54.5 

Length of shell _________________________67.0 + 

Convexity of right valve-__________________16.5

Holotype: U.S.N.M. 106997, Locality 7; paratypes: U.S.N.M. 106998, 106999, 107000 and 106- 

996, Localities 7 and 10.

GASTROPODA

The gastropods of the Morrison formation are 

aquatic species more heterogeneous than its pelecypods. They are essentially of holarctic type with a 

small percentage of neotropical elements. A few 

pectinibranch species somewhat resemble forms living in Lake Baikal in Siberia. It is possible that this

morphological resemblance will prove to be a result 

of genetic relationship of the forms rather than of 

ecological similarities of the habitat areas, but the 

long separation in time of the two faunas will demand more extensive collection of material from 

intermediate horizons and an intensive genetic study 

of the groups before definite conclusions can be 

reached.

Because so little information is available concerning Triassic and earlier nonmarine gastropods 

throughout the world, it is difficult to suggest a possible origin of the molluscan fauna of the Morrison 

formation. Triassic deposits of fresh-water origin 

are extensively exposed in various parts of North 

America and in Europe. From these deposits many 

species of terrestrial pulmonates and fresh-water 

bivalves have been described, but only Ammicolalike and Hydrobia-\ike aquatic gastropods. The 

scarcity of fresh-water univalves in collections from 

these earlier beds may be due to insufficient collection of material, to actual scarcity of individuals 

in the early stage in evolution of these forms, or 

to the lack of preservation.

The present collections contain about half of pectinibranch species, which bear opercula and (generally existing in a deeper water zone) respire 

through a primitive type of gills or ctenidia, and 

half of pulmonates, which possess a pulmonary 

chamber for the purpose of respiration. The pulmonary chamber is not morphologically a true lung, 

although physiologically it performs a similar function. About a third of the pulmonates such as species 

of Ellobiidae and Otinidae, are generally considered 

to be primitive, and two thirds more advanced 

species.

The divergent types included in the gastropod 

fauna of the Morrison formation make it reasonably 

certain that these fresh-water forms had a long preMorrison history. It is unlikely that lack of preservation has much to do with the scarcity in the 

earlier beds, as terrestrial pulmonates and freshwater bivalves are locally abundant. Consequently, 

the first of the above three possibilities, insufficient 

collection of material may be the answer. Until our 

knowledge of these earlier beds is increased we cannot venture an opinion on the origin of the Morrison 

gastropods.

Family VALVATIDAE 

Valvata minuscula Yen and Reeside

Valvata minuscula Yen and Reeside, Jour. Paleontology, vol. 

20, p. 53, fig. la, b, 1946. (Type locality: west of Mill 

Creek below Lower Green River Lake, on west slope 

of the Wind River Mountains, Wyoming).
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 39

Typical species of Valvata are generally small, 

of thin shell substance, with more or less flatened 

or slightly raised apical whorl, roundly convex 

whorls, descending aperture of circular outline, and 

open umbilicus. The present form seems to have all 

these features, though other species from the Morrison formation attributed to this genus are not true 

Valvata, but belong to related genera.

Amplevalvata Yen, n. gen.

Shell globose, more than 10 mm in diameter, moderately thick in substance, umbilicus open, elevated 

spire and inflated body whorl. Whorls increasing 

rapidly in size, early ones exserted and angulated, 

later ones roundly convex, bearing distinct lines of 

growth with frequent strong riblines. Suture well 

impressed. Aperture somewhat descending, continuous, almost circular in outline, slightly angular 

above, having its parietal wall more or less attached 

to the preceding whorl.

Genotype: Amplovalvata cyclostoma Yen, n. sp.

The features of Amplovalvata are characteristic 

of the Valvatidae. The general outline of the shell, 

the aperture, and umbilicus remind one of Atropidina Lindholm and Cincinna Ferussac, but its large 

size and exserted and angular early whorls readily 

distinguish it from either group of the family. It is 

also different from Megalovalvata Lindholm, a monotypic group described from the living fauna of Lake 

Baikal, Siberia, in its globose outline, elevated spire, 

and exserted early whorls.

Amplovalvata cyclostoma Yen, n. sp. 

PL 6, fig. la-f.

Shell cyclophoroid in outline, large, having an 

exserted spire and rapidly increasing body whorl. 

Apex small, but early 2 to 3 pointed whorls exserted 

and obscurely angulated and last 2 whorls rapidly 

increasing, roundly convex and somewhat descending 

near the aperture. Suture well impressed. The sculpture consists of coarse and fine growth lines. Aperture circular in outline, peristome continuous and 

moderately thick, having its parietal wall closely 

attached to the penult whorl. Umbilicus open.

Measurements of four specimens, in millimeters, 

are as follows:

Altitude of shell________13.2 11.2 10.8 9.0

Width of shell__________14.1 12.6 12.0 10.0

Diameter of aperture_____ 7.2 6.5 6.0 5.2

Diameter of umbilicus____ 3.2 3.0 3.0 2.7

Number of whorls_______ 5V2 5 5 4%

This species differs from Amplovalvata scabrida 

(Meek and Hayden) in its higher and exserted spire,

more rounded aperture, and narrower umbilicus. 

The whorls increase more rapidly in size, are more 

roundly convex and bear strong sculpture.

Holotype. U.S.N.M. 107015, Locality 5; paratypes: U.S.N.M. 107016 and 107042, Localities 1, 

2, 4, 5, and 8.

Amplovalvata scabrida (Meek and Hayden) 

PL 6, fig. 2a-o.

Valvata? scabrida Meek and Hayden, Smithsonian Contribution to Knowledge, No. 172, p. 113, pi. 4, fig. 2a, 1865. 

(Type locality: Southwest base of Black Hills, South 

Dakota.)

Vorticifex stearnsii White, U. S. Geol. Survey Bull. 29, p. 21, 

pi. 4, fig. 4-7, 1886. (Type locality: "Atlantosaurus 

beds," Como, Wyoming).

The holotoype (U.S.N.M. 316) is an immature 

specimen attached to a piece of shell, possibly of 

the same individual, imbedded in limestone. The 

specimen agrees well with the original description 

of the species, although the figure does not clearly 

show the shoulder and peripheral angulations.

The holotype consists of 3 rapidly increasing, angulated whorls measuring about 2.8 mm in width of 

shell. It is identical with young specimens of Vorticifex stearnsii White, the type of which was available for comparison, and several other specimens 

from the Morrison formation near Mayoworth, Wyoming, and Grand Junction, Colorado. The fully 

mature shell consists of about 5 whorls, rapidly increasing in size, early whorls angulated and later 

whorls more strongly convex and slightly shouldered 

above. These whorls are separated by a deeply impressed suture and bear coarse growth lines.

The measurements of a mature specimen in millimeters are:

Altitude of shell________________________11.0 

Width of shell__________________'-__________14.4

Height of aperture____—_——————————————— 8.0 

Width of aperture__________—————-—————— 7.6 

Diameter of umbilicus__——_—————————————— 3.6 

Number of whorls________——————————————— 4^

The size and features of the early whorls exclude 

this species from Valvata, while its depressed but 

not planorboid spire and deeply impressed suture, 

together with its almost circular aperture in the 

adult form, prevent its being referred to Vorticifex 

and Carinifex, tw.o genera of Planorbidae so far 

known only from late Tertiary to Recent deposits.

Figured specimens: U.S.N.M. 107010, 107011, 

107012 and 107013.
40 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Amplovalvata scabrida leei (Logan) 

PL 6, fig. 3a-c.

Valvata leei Logan, Kansas Univ. Quart., vol. 9, p. 133, pi. 

31, fig. 1-3, 1900. (Type locality: the Freeze-Out Hills, 

Wyoming).

The type is not available for this study. The specimens from the type locality contained in the present collection are somewhat distorted, though they 

seem to agree well with Logan's description. Judged 

by the examples available and by Logan's description and figure, the form is close to Amplovalvata 

scabrida (Meek and Hay den), but differs in having 

only three whorls at a maximum diameter of the 

shell of 13.0 mm, whereas the adult individual of A. 

scabrida has a width of shell 14.4 mm with 4 l/2 

whorls.

Figured specimen: U.S.N.M. 107014.

Tropidina jurassica (Branson) 

PI. 6, fig. 4a-c.

Pcntagoniostoma jurassicum Branson, Jour. Paleontology, 

vol. 9, p. 520, pi. 57, fig. 4-6, 1935. (Type locality: 

3 miles south of Mayoworth, Wyoming).

The species was described as the genotype of a 

new genus, which was considered by Branson to be 

close to Adeorbis supranitidus. Woodward (Wood, 

1842, p. 530). Adeorbis Wood (=Tornus Turton and 

Kingston in Carrington, 1830) is a true marine 

genus and was described as having "an incipent 

sinus in the upper part of the aperture," which is 

characteristically different from an angulation 

formed by a strong carina.

Among fresh-water mollusks, this species shows 

close resemblance to Tropidina tricarinata (Say.) 

and T. bicarinata Lea, to which group it is here assigned. Tropidina H. and A. Adams, 1854, generally 

considered a subgenus of Valvata Mueller, 1774, also 

includes a few species from late Tertiary deposits. 

Its long geological range, in addition to its characteristic shell features, justify its assignment as a 

distinct genus of the Valvatidae.

Figured specimen: U.S.N.M. 107063.

Liratina jurassica (Branson) 

PI. 6, fig. 5a-c.

Valvata? jurassica Branson, Jour. Paleontology, vol. 9, p. 

519, pi. 57, fig. 7^8, 1935. (Type locality: 3 miles south 

of Mayoworth, Wyoming).

One almost perfectly preserved specimen, which 

was collected from Mayoworth, Wyoming, in 1945, 

and a few less perfectly preserved examples from 

other localities, agree well with this species.

It is characterized by its linear spiral sculpture,

together with its slowly rising apex and depressed 

spire, and by an oblique aperture with continuous 

peristome and open umbilicus, more or less defined 

outwardly by an obscure angulation. Its spiral sculpture is evenly developed and more distinctly shown 

on the body whorl. The type is described as having 

4 whorls, though the illustration of the apical view 

shows only about 3 whorls.

The measurements of the figured specimen in 

millimeters are:

Altitude of shell_______________________ 2.8 

Width of shell.________________________ 4.5 

Height of aperture _______—_____________ 1.8 

Width of aperture ________________________ 2.1 

Diameter of umbilicus ._____________________ 1.6 

Number of whorls -________________________ 3%

The general outline of the shell, its sculpture, and 

the features of the aperture and umbilicus remind 

one Liratina baicalensis (Gerstfeldt), a Recent species described from Lake Baikal. As all the preserved features of this form indicate much difference from any of the species of Valvata, it seems 

more reasonable to assign this Jurassic species to 

Liratina.

Figured specimen: U.S.N.M. 107055.

Family VIVIPAEIDAE

Viviparus reesidei Yen, n. sp.

PI. 6, fig. 6a-e.

Shell subglobose, moderately thick in substance, 

smaller than the average size of the genotype of the 

genus, and narrowly umbilicated. Spire highly elevated and body whorl rapidly dilated; the spire 

nearly equal in height to the body whorl. Whorls increasing very rapidly in size, roundly convex and 

bearing distinct wavy growth lines. In some examples coarser rib lines intersecting spiral lines 

produce a malleated appearance on surface of the 

body whorl. Suture well impressed. Aperture ovate 

in outline, peristome continuous, outer lip thin and 

simple, parietal wall well defined and columellar 

margin slightly oblique. Operculum unknown. Measurements of holotype and one paratype, in millimeters, are as follows:

Altitude of shell___________________15.0 13.0

Width of shell-____________________13.2 11.0

Height of aperture__________________ 9.0 7.0

Width of aperture______________—— 8.5 6.2

Number of whorls_____————————————— 5% 5%

All the shell features seem to show the species a 

true Viviparus, although it is somewhat smaller than 

most typical species of the genus in the Recent fauna. 

Numerous adults occur in the highly silicified lime-
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 41

stone of the type locality, together with a profusion 

of young shells apparently of the same species. The 

young are small and have 3 to 4 whorls.

It may be compared with two Viviparus-like species from Lower Cretaceous beds, V. gttli (Meek and 

Hay den) and Reesidella montanensis (Stanton). V. 

reesidei differs from V. gilli in its broader outline, 

more convex whorls, and larger aperture; and it 

differs from R. montanensis (which is represented 

by several good specimens in the type lot) by its 

larger size with almost the same number of whorls, 

lower spire, absence of a prominent shoulder on the 

larger whorls, and ovately shaped aperture. This 

species differs from V. marrisonensis in its much 

smaller size.

Holotype: U.S.N.M. 107035, Locality 11; paratypes: U.S.N.M. 107,018, 107036, 107017 and 107- 

022, Localities 11, 20 and 22.

Viviparus morrisonensis Ten, n. sp. 

PI. 6, fig. 7a-d.

Shell large, subglobose, appearing to be of thin 

substance, having an elevated spire and much dilated body whorl, the former about the same height 

as the latter. Whorls increasing very rapidly in size 

(about 1:3 in proportion), gently convex and slightly shouldered below the suture. Fine lines of growth 

on some specimens. Aperture somewhat descending; 

outline of whorl surface indicates it is probably 

of subovate outline with continuous peristome.

Measurements of the holotype and two paratypes, 

in millimeters, are as follows:

Altitude of shell_____________40.5 26.0 24.0

Width of shell-_____________-35.0 24.5 21.5

Height of aperture____________26.0 18.6 15.5

Width of aperture-___________21.0 14.0 12.5

Number of whorls____________ 4+ 4 + 4+

This species is much larger than V. reesidei, increase much more rapidly in its whorls, and its surface less strongly convex. Its morphological features 

indicate it to be a species of Viviparus. None of the 

specimens from the type-locality is perfectly preserved and the umbilical features are not known.

One of the specimens from locality 29 shows a 

moderately opened umbilicus and subovate aperture.

Holotype: U.S.N.M. 107019, Locality 1; paratypes: U.S.N.M. 107020, 107021 and 107065, Localities 1, 25 and 29.

Lioplacodes jurassicus Ten, n. sp. 

PI. 6, fig. 8a-b.

Shell small, ovately oblong in outline, moderately 

umbilicated, having a highly elevated spire and descending body whorl. Whorls increasing rapidly in

size, gently convex, separated by an impressed suture and bearing distinct wavy lines of growth and 

a carinated angulation on its basal margin. This 

angulation in some examples disappears on the last 

third of the body whorl. Aperture subovate in outline with continuous and thin peristome.

Measurements of the holotype and one paratype, 

in millimeters, are as follows:

Altitude of shell _________________ 9.8+ 9.2+

Width of shell___________________ 7.0 6.0

Height of aperture________________ 5.5 5.0

Width of aperture________________ 4.0 _.__

Number of whorls_______________ 3+ 3 +

Both measured specimens have the apical whorls 

(possibly two in number) injured. The species differs from Lioplacodes vetemus Meek and Hayden, 

Lioplacodes cretaceous (Stanton), and Lioplacodes 

convexiculis Yen, from the Lower Cretaceous beds 

by its much smaller size, more convex whorls, more 

rapidly dilated body whorl, and wider umbilicus.

This species has been so far recorded from locality 31 only. All the specimens are somewhat distorted, though the general outline and features are 

sufficiently well preserved to permit the above description.

Holotype: U.S.N.M. 107054, Locality 31; paratypes: U.S.N.M. 107034 and 107051, Locality 31.

Family AMNICOLIDAE

Amnicola gilloides Yen and Keeside

PI. 6, fig. 9a.

Amnicola giUoides Yen and Eeeside, Jour. Paleontology, vol. 

20, p. 54, fig. 2a, b, 1946. (Type locality: west of 

Mill Creek, below Lower Green River Lake, on west 

slope of the Wind River Mountains, Wyoming).

The shell features of the many specimens, and 

the associated calcareous opercula, indicate that it 

is a true species of Amnicola—a genus surviving to 

Recent time.

Figured specimen: U.S.N.M. 107061.

Amnicola jurassica Yen, n. sp. 

PI. 6, fig. lOa-b.

Shell ovately oblong in outline, of thin substance, 

narrowly umbilicated, having conically elevated spire 

and descendingly inflated body whorl, the spire 

about the same height as the body whorl. Whorls 

increasing very rapidly in size, strongly convex, and 

bearing strong lines of growth and a few sparse 

spiral lines. In some specimens these spiral lines are 

indistinct. Suture well impressed. Aperture subovate 

in outline, having its perlistome thin and continuous; parietal margin well defined.
42 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Measurements of the holotype and of one paratype, in millimeters, are as follows:

Altitude of shell __________________ 9.6 10.0+

Width of shell ___________________ 7.5 8.3

Height of aperture _______________ 5.0 6.0

Width of aperture ________________ 4.0 5.0

Number of whorls _________________ 5 3+

Amnicola jurassica closely resembles A. gilloides 

Yen and Reeside, but is larger and has more strongly convex whorls, and a larger aperture. The holotype has its apical part injured, but it appears to 

consist of two to three whorls. One of the three imperfectly preserved specimens shows the parietal 

and columellar margins quite well.

Holotype: U.S.N.M. 107059, Locality 23; paratypes: U.S.N.M. 107032 and 107060, Locality 23.

Mesocochliopa assiminoides Yen and Reeside

Mesocochliopa assiminoides Yen and Reeside, Jour. Paleontology, vol. 20, p. 54, fig. 3a, b, 1946. (Type locality: 

west of Mill Creek, below Lower Green River Lake, 

on west slope of the Wind River Mountains, 

Wyoming).

The characteristic features of this monotype of 

the genus are its small size, broadly conical outline, 

and almost circular, widely opened umbilicus.

Mesopyrgium pendilabium Yen and Reeside

Mesopyrgium pendilabium Yen and Reeside, Jour. Paleontology, vol. 20, p. 56, fig. 4, 1946. (Type locality: west 

of Mill Creek, below Lower Green River Lake, on 

west slope of Wind River Mountains, Wyoming).

This species occurs abundantly in the Morrison 

formation at its type locality, but it is not known 

elsewhere. Its presence may indicate a shallowerwater facies of the Morrison formation in association with a rich growth of vegetation. This suggestion is further supported by the fact that 8 out of 

12 species of the gastropods found in the same bed 

are pulmonates.

Family NERITIDAE

Mesoneritina morrisonensis Yen, n. sp.

PL 6, fig. lla-f.

Shell small, of moderately thick substance, imperforate, having a low but elevated spire and rapidly inflated oblique body whorl. The spire constitutes three-sevenths the height of the body whorl. 

Whorls increasing rapidly in size, scarcely convex, 

and bearing fine wavy lines of growth and occasional 

former outer lip margins. Aperture broadly ovate, 

with peristome continuous; outer lip thin and simple; inner lip well defined, formed by a nearly flattened, smooth, thick plate. The basal columellar area 

is somewhat truncated.

Dimensions of the holotype, in millimeters, are 

as follows:

Altitude of shell _______________________ 7.8 

Width of shell ________________________ 7.0 

Height of aperture ___________—————————_ 6.0 

Width of aperture _————__————————————— 5.4 

Number of whorls _________———————————— 3 1/3

Mesoneritina morrisonensis differs from M. nebrascensis (Meek and Hayden), described from Lower 

Cretaceous beds, by its narrower outline, higher 

spire, and borader columellar plate.

Among the specimens available from two localities no colour pattern has been traceable. In some 

examples, faint spiral lines are visible.

Holotype: U.S.N.M. 107056, Locality 10; paratypes: U.S.N.M. 107033, 107058 and 107057, Localities 10 and 23.

Family ELLOBIIDAE 

Mesauriculstra Yen, n. gen.

Shell broadly oblong, ovately elongate, or subf usif orm in outline, with an elevated spire and narrowly 

dilated and descending body whorl. Apical whorl 

small and pointed. Early whorls increasing gradually and later ones more rapidly, in size. Whorl surface gently convex and bearing fine lines of growth; 

suture superficially incised. Aperture narrowly oblong in outline, acute at upper part and moderately 

produced below. Peristome continuous, outer lip 

margin almost straight and simple, inner lip well 

defined, bearing a more or less distinct fold at the 

columella. Umbilicus perforate or narrowly open.

Genotype: Limnaea? accelerata White.

The genus differs from Rhytophorus Meek, which 

was described from the Bear River formation, of 

the Upper Cretaceous by its truly umbilicated shell 

with pointed apical whorls and much higher spire. 

It resembles Auriculstra Martens, species of which 

are still living but differs in lacking a transverse 

parietal plait and a basal sinus. In general, the new 

genus resembles Stolidoma Deshayes, described from 

Early Tertiary beds of the Paris Basin, in outline 

but differs in having obtuse apical whorls and an 

oblique columellar fold instead of a median plait.

Mesauriculstra accelerata (White) 

PI. 6, fig. 12a-b.

Limnaea? accelerata White, U. S. Geol. Survey Bull. 29, 

p. 20, pi. 4, fig. 12-15, 1886. (Type locality: "Atlantosaurus beds," 8 miles north of Canyon City, Colorado).

White gave a detail description of the species and 

clearly recognized its characteristic features except 

the columellar fold, which is well shown on some 

of the specimens from the type locality. The species
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 43

is characterized by its subfusiform outline, more 

highly elevated spire whose height exceeds that of 

the body whorl, and a distinct oblique fold at the 

columella.

Measurements of two specimens, in millimeters, 

are as follows:

Altitude of shell _____________——21.0+ 18.0

Width of shell _________________- 8.0 7.0

Height of aperture 666____________-10.0 8.2

Width of aperture __—————————————— 5.0 ___

Number of whorls _—————————————— 5+ IVz

The larger one of the measured specimens has its 

3 or 4 apical whorls injured. The smaller specimen 

is about the size of the type.

Figured specimens: U.S.N.M. 107049.

Mesauriculstra morrisonensis Yen, n. sp. 

PL 6, fig. 13a-b.

Shell ovately oblong in outline, narrowly umbilicated, having a highly elevated and gradually tapering spire, narrowly dilated and descending body 

whorl, the spire slightly greater in height than the 

body whorl. Early whorls increasing gradually and 

the last two more rapidly, having the surface gently 

convex and marked by fine growth lines. Suture well 

'impressed. Aperture narrowly oblong, somewhat 

acutely angular above and slightly produced at the 

basal part. Paristome continuous, outer lip thin and 

smooth, inner lip well defined and somewhat thickened. Columellar fold faint but traceable.

Measurements of the holotype and a paratype, in 

millimeters, are as follows:

Altitude of shell ________———___—15.0 15.5

Width of shell _______________—— 7.0 7.3

Height of aperture_______________— 7.0 7.3

Width of aperture _________———————— 3.5 4.0

Number of whorls _______________— 8 8 1/3

The species differs from M. accelerata in its much 

smaller size with over one whorl more, broader outline, lower spire, and obscure columellar fold.

Holotype: U.S.N.M. 107043, Locality 5; paratypes : U.S.N.M. 107044 and 107048, Locality 5.

Mesauriculstra morrisonensis ovalis Yen, n. subsp. 

PL 6, fig. 14a-d.

Shell subovate in outline, perforately umbilicated, 

having an acutely conical spire and narrowly inflated and descending body whorl, the spire smaller 

than- the body whorl. Early whorls increasing 

gradually, the last two rapidly; the exposed surface 

scarcely convex and bearing distinct lines of growth. 

Aperture very similar to that of M. morrisonensis

but the parietal wall is thinner and the columellar 

fold is distinct.

Measurements of the holotype and a paratype, in 

millimeters, are as follows:

Altitude of shell_________________13.1+ 12.1

Width of shell__________________ 6.9 6.0

Height of aperture_______________ 7.0 6.0

Width of aperture_______________. 3.5 3.0

Number of whorls_________________ 6+ 7

The species differs from the preceding in its more 

ovate outline, smaller size, lower spire, and distinct 

columellar fold. The holotype is somewhat decollated, lacking probably one to two whorls.

Holotype: U.S.N.M. 107045, Locality 5; paratypes: U.S.N.M. 107046 and 107047, Localities 4 

and 5.

Mesochilina spiralis Yen, n. sp. 

PL 6, fig. 15a-b.

Shell narrowly ovate in outline, small, imperforate; the spire is about one-third the height of the 

body whorl. Whorls gently convex, increasing very 

rapidly in size, bearing strong lines of growth and 

incised spiral lines over the surface. Aperture elongately ovate in outline, peristome continuous, outer 

lip simple and slightly produced at the base, inner 

lip thickened and bearing a single, weak plica just 

below the parietal margin. Columella short and 

nearly straight.

Measurements of the holotype and of a paratype, 

in millimeters, are as follows:

Altitude of shell_________________ 6.2+ 7.8+

Width of shell________________'_ _ 4.3 4.5

Height of aperture________________ 4.0 5.2

Width of aperture________________ 2.2 2.8

Number of whorls_________________ 2.5+ 3.0+

Both of the measured specimens have their apical 

whorls injured.

Holotype: U.S.N.M. 107037, Locality 20; paratypes : U.S.N.M. 107038, Locality 20.

Zaptychius aff. Z. haldemani (White)

Tortacella aff. T. haldemani (White) Yen and Reeside, Jour. 

Paleontology, volt. 20, p. 56, fig. 5, 1946.

There seems to be little doubt that this Jurassic 

species is congeneric with the form described from 

Upper Cretaceous beds, though the single imperfect 

specimen available does not permit a satisfactory 

specific identification. It seems to have a broader 

outline, lower altitude of the shell and more convex 

whorls than Z. haldemani. If these differences are 

substantiated by additional specimens the form 

might justifiably be considered a distinct species.
44 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Family OTINIDAE 

Limnopsis Yen, n. gen.

Shell of moderate size, thin substance, globosely 

ovate outline, having a distinct but small and elevated spire and more or less laterally dilated body 

whorl, the latter constituting four-fifths of the entire shell. Whorls increasing very rapidly, and bearing distinct growth and spiral lines. Aperture large, 

ovate in outline, outer lip thin and simple, parietal 

wall imperceptable and columellar margin short.

Genotype: Limnopsis jurassica Yen, n. sp.

In general form Limnopsis resembles Otina Gray, 

a genus of amphibious habitat in the Recent fauna, 

but I am a little hesitant in referring it to the Otinidae, whose survivors are very few and much restricted. It differs from Otina Gray in its greater 

spire and larger penult whorl, and in its cancellated 

sculpture.

Limnopsis jurassica Yen, n. sp. 

PL 6, fig. 16a-c.

Shell essentially the same as described for the 

genus. The spire is small but elevated and the body 

whorl is somewhat obliquely and laterally dilated. 

The sculpture consists of both growth and spiral 

lines, the latter stronger than the former, and distinctly traceable.

Measurements of the holotype and of a paratype, 

in millimeters, are as follows:

Altitude of shell___________________ 7.5 

Width of shell____________________ 7.0 

Height of aperture_________________ 6.5 

Width of aperture_.._______________ 5.0 

Number of whorls__________________ 3

Holotype: U.S.N.M. 107052, Locality 31 

types: U.S.N.M. 107053, Locality 31.

7.0 

6.0 

5.5

4.8 

3±

paraFamily LYMNAEIDAE

Lymnaea ativuncula White

PL 6, fig. 17a-d.

Limnaea ativuncula White, U. S. Geol. Survey Bull. 29, p. 

20, pi. 4, fig. 10, 11, 1886. (Type locality: "Atlantosaurus beds," 8 miles north of Canyon City, Colorado) .

The type lot (U.S.N.M. 20054) consists of two 

specimens, both of them figured by White. This 

seems to be a widespread species in the Morrison 

formation, having been recorded from 10 localities. 

It is small, narrowly subfusiform in outline, and 

has distinct rib lines.

Figured specimen: U.S.N.M. 107039.

Lymnaea consortis White 

PI. 6, fig. 18.

Limnaea consortis White, U. S. Geol. Survey Bull. 29, p. 20, 

pi. 4, fig. 8-9, 1886. (Type locality: "Atlantosaurus 

beds," 8 miles north of Canyon City, Colorado). 

The type lot (U.S.N.M. 20055) consists of 6 specimens in various stages of development. The species 

is Radix-like in having a small spire and more ventricose body whorl.

Figured specimen: U.S.N.M. 107024.

Lymnaea morrisonensis Yen, n. sp. 

PL 6, fig. 19a-b.

Shell of moderate size, thin substance, ovately oblong outline, having a subconical and highly elevated spire and descending dilated body whorl, the 

spire smaller than the body whorl. Whorls increasing rapidly in size, gently convex, slightly shouldered below the suture and bearing distinct lines 

of growth. Aperture subovate in outline, outer lip 

thin and simple, parietal margin attenuated but 

well defined, and columella slightly twisted at its 

upper part, with its margin reflected and attached 

firmly over the umbilical area.

Measurements of the holotype and a paratype, 

in millimeters, are as follows:

Altitude of shell__________________15.0 11.0

Width of shell____________________ 8.0 5.8

Height of aperture_________________ 9.0 6.8

Width of aperture_________________ 5.0 3.8

Number of whorls_____________———_ 5 5

This species differs from Lymnaea consortis 

White in its larger size, more exserted and higher 

spire, less convex whorls and more distinctly twisted 

columella.

Holotype: U.S.N.M. 107025, Locality 5; paratypes: U.S.N.M. 107026 and 107041, Localities 2 

and 5.

Family PLANORBIDAE

Gyraulus veternus (Meek and Hay den)

PL 6, fig. 20a-l.

Planorbis veternus Meek and Hayden, Smithsonian Cont. 

Knowl., vol. 14, no. 172, p. 107, pi. 4, fig. la-c, 1864 

(1865). (Type locality: southwest base of Black Hills, 

South Dakota).

The type lot (U.S.N.M. 317) consists of a number of specimens imbedded in dark-colored limestone. They are small, none of them more than 4 

millimeters in diameter. A series of specimens ranging from 2 mm (in 2y% whorls) to 7 mm (in 5 

whorls), of various developmental stages are illustrated in the present work. These specimens were
MOLLUSCAN FAUNA OF THE MORRISON FORMATION 45

obtained from locality 5, north of Canyon City, 

Colorado.

Figured specimens: U.S.N.M. 107050.

Graptophysa spiralis Yen and Reeside

Graptophysa spiralis Yen and Reeside, Jour. Paleontology, 

vol. 20, p. 57, fig. 7, 1946. (Type locality: west of Mill 

Creek, below Lower Green River Lake, on west slope 

of the Wind River Mountains, Wyoming).

This Phy$a-\ike species is characterized by its 

spiral sculpture in combination with a fusiform outline, imperforate shell, high spire, and incised suture. It resembles Pseudophysa grabaui Yen in its 

general outline and sculpture, but it differs in its 

smaller size, much less convex whorls, and less 

pointed spire.

Family FHYSIDAE 

Fhysa micra Yen and Reeside

Physa micra Yen and Reeside, Jour. Paleontology, vol. 20, 

p. 57, fig. 8, 1946. (Type locality: west of Mill Creek, 

below Lower Green River Lake, on west slope of the 

Wind River Mountains, Wyoming).

Physa conispira Yen and Reeside

Physa conispira Yen and Reeside, Jour. Paleontology, vol. 

20, p. 57, fig. 9, 1946. (Type locality: west of Mill 

Creek, below Lower Green River Lake, on west slope 

of the Wind River Mountains, Wyoming).

This and P. micra have the features of true Physa, 

but they are much smaller than the species that have

been described from Upper Cretaceous and early 

Tertiary beds. The only other record of Physa from 

the Morrison beds is from locality 17, where an undeterminable species of the genus was found. Its 

abundance at locality 37 may indicate that the exposure there represents a shallower water facies 

of the formation.

Aplexa morrisonana Yen and Reeside

Aplexa morrisonana Yen and Reeside, Jour. Paleontology, 

vol. 20, p. 58, fig. 11, 1946. (Type locality: west of 

Mill Creek, below Lower Green River Lake, on west 

slope of the Wind River Mountains, Wyoming).

Aplexa militaria Yen and Reeside

Aplexa militaria Yen and Reeside, Jour. Paleontology, vol. 

20, p. 57, fig. 10, 1946. (Type locality: west of Mill 

Creek, below Lower Green River Lake, on west slope 

of the Wind River Mountains, Wyoming).

Although smaller, Aplexa militaria and A. morrisonana have the features of true Aplexa. A. morrisonana has more convex whorls and higher spire 

than A. militaria, though having almost the same 

number of whorls.

SYSTEMATIC POSITION UNCERTAIN 

"Pentagoniostoma" altispiratum Branson

Pentagoniostoma altispiratum Branson, Jour. Paleontology, 

vol. 9, p. 520, pi. 57, fig. 1-3, 1935. (Type locality: 

3 miles south of Mayoworth, Wyoming).

BIBLIOGRAPHY

ANDERSON, J. L., 1948, Cretaceous and Tertiary subsurface 

geology: Maryland Board Nat. Resources Bull. 2.

ARKELL, W. J., 1941, The gastropods of the Purbeck beds: 

Geol. Sec. London Quart. Jour., vol. 97, pp. 97-128, figs.

BAKER, A. A., 1946 [1947], Geology of the Green River 

Desert-Cataract Canyon region, Emery, Wayne, and 

Garfield Counties, Utah: U. S. Geol. Survey Bull. 951.

BAKER, A. A., DANE, C. H., and REESIDE, J. B., Jr., 1936, 

Correlation of the Jurassic formations of parts of Utah, 

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———— 1947, Revised correlation of Jurassic formations of 

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Am. Assoc. Petroleum Geologists Bull., vol. 31, pp. 1664- 

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BELL, W. A., 1946, Age of the Canadian Kootenay formation: 

Am. Jour. Sci., vol. 244, pp. 513-526.

BERRY, E. WILBUR, 1929, The Kootenay and Lower Blairmore 

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BRANSON, C. C., 1935, Fresh-water invertebrates from the 

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BROWN, R. W., 1946, Fossil plants and Jurassic-Cretaceous 

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———— 1950, Cretaceous plants from southwestern Colorado: 

U. S. Geol. Survey Prof. Paper 221-D.

BUBNOFF, SERGE VON, 1935, Geologic von Europa, Band 2, 

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BURBANK, W. S., 1930, Revision of geologic structure and 

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———— 1904, Comparison of the stratigraphy of the Black 

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DUTTON, C. E., 1885, Mount Taylor and the Zuni Plateau: 

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Geology of the Denver Basin in Colorado: U. S. Geol. 

Survey Mon. 27.
46 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

FISCHER, C. A., 1909, Geology of the Great Falls coal field,

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GARDNER, L. S., HENDRICKS, T. A., HADLEY, H. D., and

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GREGORY, H. E., 1917, Geology of the Navajo country—a

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———— 1938, The San Juan country, a geographic and geologic reconnaissance of southeastern Utah: U. S. Geol. 

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Graphic sections of Mesozoic and Paleozoic rocks that 

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———— 1947, Stratigraphic sections of Mesozoic rocks in 

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———— 1941, Lower Cretaceous Rocky Mountain nonmarine 

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MOLLUSCAN FAUNA OF THE MORRISON FORMATION 47

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52-58, text figs.

————1946, Triassic freshwater gastropods from southern 

Utah: Am. Jour. Sci., vol. 244, pp. 49-51, 1 pi.

INDEX

Italic numbers indicate descriptions.

Abstract . . .................................................... 21

acctiifr<i'a Lvmnaeu, ......... .................................... 27, 42

M-ieauriculstra ... . ...................... .30 (tab.) , 42, pi. 6

Acknowledgements tor aid ......................................... 21

Adeorbis supranitidus ............................................. 40

Albian 26

altispiratum, Pentagoniostoma .................................... 27, 45

Amplovalvata .................................................... 32, 39

Amnicola ......................................................... 38

gilloides ............... ....................... .26, 27, 30 (tab.) , 41

jurassica ....................................... .30 (tab.) , 41, pi. 6

roemeri ...................................................... 34

Amplovalvata cyclostoma ....................... .30 (tab.) , 32, 39, pi. 6

morrisonensis .... ........................................... 27

seabrida ................................ .27, 30 (tab.) , 32, 39. pi. 6

ieei .......................................... 30 (tab.) 40, pi. 6

Anodonta becklesi ................................................ 34

ApZezo mt'Htorto ...................................... .28, 30 (tab.) , 45

morrtsonono ....................................... 28, 30 (tab.) , 45

Aptian .......................................................... 26

arizonensis, Unio ......................................-.••••••••• 35

assiminoides, Mesocochliopa ........................... .27, 30 (tab.) , 43

ativuncula, Galba ................................................. 27

Zamnaea ..........................................-•••••••••• 27, 44

Lymnaea .................................. .27, 30 (tab.) , 32, 44, pi. 6

Atlantosaurus beds ............................................ 22, 27, 33

Atropidina ................................. ..................... 39

B

Curtis formation ........................... ..................... 24

cyclostoma, Amplovalvata __._______.____30 (tab.), 32, 39, pi. 6

D

Dakota group .................................................... 22, 24

douglassi, Protelliptio ............................................ 32

douglassi hamili, Protelliptio....................................... 32

durlstonense, Ettobium ............................................ 33

E

Eldridge, G. H., cited.

Ettobium durlstonense

jaccardi ........

elongatus, Lioplacodes

22

33

34

54

Entrada sandstone ............................................... 23, 24

Ephraim conglomerate ............................................ 24

Eupera onestae ................................................... 32

European faunas, comparisons with................................ 33-35

Exeter sandstone ................................................. 23

faberi, Vetulonaia .................................... .27, 30 (tab.), 37

felehi, Unio ......................................27, 30 (tab.), 35, pi. 3

fisheri, Planorbis ................................................ 33, 34

Theodoxus ......

Flaming Gorge group. 

forbesi, Hydrobia ....

Fuson shale .........

33

22

34

26

baicalensis, Liratina .............................................. 40

baileyi, Unio .................................... 27, 30 (tab.), 35, pi. 3

Barremian ....................................................... 26

beeklesi, Anodonta .......................... ..................... 34

Beckwith formation .............................................. 22, 24

Berriasian ....................................................... 26

Beulah clays ...................................................... 22

bicarinata, Tropidina ............................................. 40

Bilk Creek sandstone.'............................................. 23

Blairmore formation .............................................. 26

Bluff sandstone member ........................................... 23

bristovii, Physa .................................................. 34

Brushy Basin member............................................. 23, 24

Buckhorn conglomerate ........................................... 24

Burro Canyon formation........................................... 23

Campeloma carbonaria ........................................... 34

carbonaria, Campeloma ........................................... 34

cariniferus, Viviparus ............................................ 33

Carinifex ........................................................ 39

Carmel formation ................................................ 24

Cascade formation ................................................ 22

Cedar Mountain shale............................................. 24

Charophyta ...................................................... 31

Chinle formation ........................... ........ ........... 27

chopardiana, Hydrobia ............................................ 33

Cincinna ............... ......................................... 39

Cloverly formation ...................................... .... 24, 25, 26

Como beds ....................................................... 22

conispira, Physa ........................................ 27, 30 (tab.), 45

consortis, Limnaea ............................................... 27, 44

Lymnaea, ........................................30 (tab.), 44, pi. 6

convexiculus, Lioplacodes ........................................ 32, 41

cretaceus, Lioplacodes ............................................ 32, 41

Galba ativuncula ................................................. 27

Gannett group .................................................. 24, 26

Gastropoda ...................................................... 38-45

gilli, Viviparus ............................................... 26, 27, 32

gilloides, Amnicola ...................................26, 27, 30 (tab.), 41

Goniobasis ..........

grabaui, Pseudophysa

34

45

Graptophysa spiralis ....................................27, 30 (tab.), 45

gregorii, Valvata 27

Gunnison formation ............................................. 22, 23

Gyraulus vetemus ........................27, 30 (tab.), 32, 33, 44, pi. 6

H

Hadrodon .................................................... 32, 35, 37

jurassicus ............................... .30 (tab.), 32, 37, 38, pi. 4

lateralis ......................................... 30 (tab.), 38, pi. 5

trigonus ......................................30 (tab.), 38, pis. 4, 5

haldemanni, TortaceUa ........................................... 27, 43

Zaptychius ........................................ 30 (tab.), 32, 43

hamili, Protettiptio douglassi. ...................................... 32

Hauterivian ...................................................... 26

helicoides, Valvata ................................................ 33, 34

hopii, Limnaea .

Hydrobia ......

chopardiana 

forbesi ....

sp. ........

27

38

33

34

33

inflatus, Viviparus ............................................... 33

Introduction ..................................................... 21

iridoides, Unio ....................................27, 30 (tab.) 35, pi. 5

49
jaccardi, Ellobium ................................................ 34

Junction Creek standstone........................................ 23

jurassiea, Amnicola ..................................30 (tab.), 41, pi. 6

Limnopsis ......................................30 (tab.), 44, pi. 6

Liratina ........................................ 30 (tab.), 40, pi. 6

Tropidina ................ ...................... 30 (tab.), 40, pi. 6

Valvata ...................................................... 27, 40

jurassicum, Pentagoniostoma .................................. 27, 40

jurassicus, Hadrodon ..........................30 (tab.), 32, 37, 38, pi. 4

Lioplacodes .................... .............30 (tab.), 32, 41, pi. 6

Kimmeridgian . . 

knighti. Unto 

Kootenai formation 

Kootenay .......

........... 25

.27, 30 (tab.), S6 

........25, 26, 31

........... 26

Lakota sandstone ................................................ 25, 26

lapilloides, Unio ............................... .27, 30 (tab.), 32, 35, pi. 5

lateralis, Hadrodon .................................. 30 (tab.), 38, pi. 5

leei, Amplovalvata scabrida ...........................30 (tab.), 40, pi. 6

Valvata ...................................................... 27

Limnaea accelerate .........................:..................... 27, 42

ativuncula ................................................... 27, 44

contortis ..................................................... 27, 44

hopii ........................................................ 27

Limnopsis ....................................................... 32, 44

jurassiea ........................................30 (tab.), 44, pi. 6

Lioplacodes convexiculut .......................................... 32, 41

cretaceus .................................................... 32, 41

elongatus .................................................... 34

jurassicus .................................... 30 (tab.), 32, 4i, pi. 6

morrisonensis ................................................. 33

•yeternws .............................................. 26, 27, 32, 41

Liratina baicalensis ............................................... 40

jurassiea ........................................30 (tab.), 40, pi. 6

Localities, description, map....................................... 28-31

Lymnaea ......................................................... 34

ativuncula ..................................27, 30 (tab.), 32, 44, pi. 6

consortis ........................................30 (tab.), 44, pi. 6

morrisonensis ....................................30 (tab.), 44, pi. 6

M

McElmo formation ................................................ 23

macropisthus, Unio ...............................27, 30 (tab.), 35, pi. 5

mammilaris, Unio .............................. 30 (tab.), 32, 36, pi. 4

mayoworthensis, Vetulonaia ........ f .......... .27, 30 (tab.), 32, 37, pi. 3

•medium, Neomiodon .............................................. 34

Megalovalvata .................................................... 39

Melania (Potodoma) veterna ....................................... 26

Mesauriculatra ................................................... 32, 42

accelerata .......................................30 (tab.), 42, pi. 6

morrisonensia ................................30 (tab.), 33, 43, pi. 6

ovalis .......................................... 30 (tab.), 43, pi. 6

Mesochilina spiralis ..................................30 (tab.), 43, pi. 6

Mesocochliopa assiminoides ............................. .27, 30 (tab.), 42

Meson.eriti-na morrisonensis .................... 30 (tab.), 32, 33, 42, pi. 6

nebrascensis .................................................. 32, 42

Mesopyrgium ..................................................... 32

pendilabium ....... ............................27, 30 (tab.), 33, 42

TW'cra, Physa ......................................... .27, 30 (tab.), 45

microbinaria, Promathilda ........................................ 33

militaria, Aplexa ...................................... 28, 30 (tab.), 45

minuscula, Valvata ................. r ...............27, 30 (tab.), 33, 35

morrisonana, Aplexa, .................................. .28, 30 (tab.), 45

morrisonensis, Amplovalvata ...................................... 27

Lioplacodes .................................................. 33

Lymnaea ........................................ 30 (tab.), 44, pi. 6

Mesauriculstra ................................. 30 (tab.) , 33 43, pi. 6

Mesoneritina ............................ .30 (tab.) , 32. 33, 42, pi. 6

Vituparws ................................... .30 (tab.) , 32, 41, pi. 6

ovalis, Meaauriculstra ............................ 30 (tab.) , 43, pi. 6

N

nebrascensis, Mesoneritina ...................................

Neritella ................................................

Neritina ...............................................

Neomiodon medium ..........................................

Neritella nebrascenti* .......................................

Neritina nebrascensis .......................................

nweaKs, t/nio ................................. .26, 27, 30 (tab.) , 35

32, 42

26

27

34

26

27

, pi. 3 

27

onestae, Eupera ..................................................

ovalis, Mesauriculstra morrisonensis. .................. 30 (tab.) , 43,

Oxfordian ........................................................

Pachychilus .................

Painted Desert beds .........

Paludina ....................

scalariformis ............

Paraglauconia strombaeformis

32

pi. 6 

25

34

27

26

34

34

Pelecypoda ...................................................... 35-38

pendilabium, Mesopyrgium, ......................... .27, 30 (tab.), 33, 42

Pentagoniostoma altispiratum ..................................... 27, 45

jurassicum ................................................... 27, 40

Physa ........................................................... 34, 45

bristovii ..................................................... 34

conispira ......................................... .27, 30 (tab.) , 45

micro. ............................................. .27, 30 (tab.) , 45

sp. ....... ................................................ 34

Planorbis ........................................................ 33, 34

fisheri ....................................................... 33, 34

-yeternws .................................................. 26, 27, 44

Pony Express limestone ........................................... 23

Portlandian ...................................................... 25

Potodoma veterna ................................................ 26

Previous work .................................................. 26-28

Promathilda microbinaria ......................................... 33

Protelliptio douglassi ............................................. 32

douglassi hamili .............................................. 32

Pseudophysa grabaui ............................................. 45

Purbeck ...................................................... -25, 33-34

Purgatoire formation .................................-••••••••••• 23

R

Radix ............................................................ 44

Recapture member ............................................... 23

Reeside, John B., Jr., section by. ............................... 22-26

reesidei, Viviparus ........................... .27, 30 (tab.) , 32, 40, pi. 6

Rhytophorus ..................................................... 42

roemeri, 'Amnicola . ... ^. .......................................... 34

Salt Wash sandstone ............................................. 23, 24

San Rafael group................................................. 22, 23

scabrida, Amplovalvata ....................... .27, 30 (tab.), 32, 39, pi. 6

Valvata .................................................. 26, 27, 39

leei, Amplovalvata ................................30 (tab.), 40, pi. 6

scalariformis, Paludina ........................................... 34

silberlingi, Stantonogyra ........................................... 32

spiralis, Graptophysa ................................. .27, 30 (tab.), 45

Mesochilina ......................................30 (tab.), 43, pi. 6

Sponges, freshwater, in Morrison formation. ....................... 31

Stantonogyra silgerlingi ........................................... 32

50
steornait, Vorticifex .............................................. 27, 39

atewardi, Unio ............................................... 26, 27, 36

utahensis, Unio .............................30 (tab.), 32, S6, pi. 3

Unkpapa sandstone ............................................... 25

utahenais, Unio atewardi .......................................30 (tab.)

Stolidoma ....................

strombaeformis, Paraglauconia 

Stump formation .............

subangulatus, Viviparus ......

subaudiensis, Valvata ........

Summerville formation ........

Sundance formation ..........

supranitidits, Adeorbis ........

sussexiensis, Viviparua .......

42

34

24

34

33

24

22

40

34

Theodoxus fisheri ................................................. 33

thomasi, Unio .................................................... 35

Todilto limestone ................................................. 23

Tornus .......................................................... 40

Tortacella ........................................................ 28

ha.ldema.nni .................................................. 27, 43

toxanotus, Unio ..................................27, 30 (tab.), S5, pi. 5

tricarinata, Tropidina ............................................ 40

trigonus, Hadrodon ................................ 30 (tab.), S8, pis. 4, 5

Tropidina ....................................................... 27

bicarinata .................................................... 40

jurassica ........................................30 (tab.), 40, pi. 6

tricarinata ................................................... 40

Type section, Morrison formation................................. 22

U

Unio ............................................................. 33

arizonenais .................................................. 35

fcoiZejtf ......................................27, 30 (tab.), S3, pL 3

felchi ........................................27, 30 (tab.), 35, pi. 3

iridoides .................................... .27, 30 (tab.), 55, pi. 5

knighti ............................................27, 30 (tab.), 36

lapittoides ................................ .27, 30 (tab.), 32 35, pi. 5

wtocroptst/iMS ................................ .27, 30 (tab.), 35, pi. 5

mammilaris ..................................30 (tab.), 32, S6, pi. 4

nwcaKs .................................. .26, 27, 30 (tab.), 36, pi. 3

atewardi .................................................. 26, 27, S6

utahensis ................................30 (tab.), 32, S6, pi. 3

thomasi ...................................................... 35

toxonotus ...................................27, 30 (tab.), 35, pi. 5

valdensis ..................................................... 34

willistoni ....................................27, 30 (tab.), 36, pi. 3

Valanginian .. 

valdensis, Unio

gregorii .............................. ,

helicoides .................................................... 33,

jurassica ..................................................... 27,

ieet ..................................................'........

minuscula ..................................... .27, 30 (tab.) , 33,

scabrida .................................................. 26, 27,

subaudiensis .................................................

weterwo, Melania (Potodoma) .......................................

weterwws, Gyraulus ......................... .27, 30 (tab.) , 32, 33, 44, pi

Lioplacodes ............................................ 26, 27, 32,

Planorbis .................................................. 26, 27,

VetuZoTtaio ....................................................... 32,

faberi ............................................. .27, 30 (tab.) ,

mayoworthensis ........................... .27, 30 (tab.) , 32, 37, pi.

nucalis .......................................................

whitei .................................... .27, 30 (tab.) , 32, 37, pi.

VtOT'ponts ........................................................

cariniferus ...................................................

0tZK ..................................................... .26, 27,

inflatus ......................................................

morrisonensis ................................ 30 (tab.) , 32, 41, pi.

reeside. .................................. .27, 30 (tab.) , 32, 40, pi

subangulatus .................................................

sussexiensis ..................................................

Vorticifex stearnsii .............................................. 27,

W

Wanakah formation .............................................. 23

Wealden ......................................................... 33, 35

Westwater Canyon member ....................................... 23

whitei, Vetulonia ............................. .27, 30 (tag.) , 32, 37, pi. 3

willistoni, Unio .................................. .27, 30 (tab.), 36, pi. 3

Wingate sandstone ............................................... 23

Zaptychius ....................................................... 28

haldemani ..........................................30 (tab.), 32, 43

Zuni sandstone ................................................... 23

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51

PLATES 3-6
PLATE 3 

Figures la-c. Unio felchi White XI, locality 3. (p. 35)

2. Unio baileyi Logan XI, locality 31. (p. 35) 

3a-e. Unio stewardi utahensis Yen XI, locality 23. (p. 36)

4. Unio unllistoni Logan XI, locality 31. (p. 36) 

5a-c. Unio nucalis Meek and Hayden X2, locality 35. (p. 36) 

6a-b. Vetulonaia whitei Branson X 1, re-illustrations of the holotype from the Museum of the University of Missouri through

courtesy of Prof. E. B. Branson. (p. 37)

7. Vetulonaia mayoworthensis Branson X 1, re-illustration of the holotype from the Museum of the University of Missouri 

through courtesy of Prof. E. B. Branson. (p. 37)
GEOLOGICAL SURVEY PROFESSIONAL PAPER 233 PLATE 3

UNIO AND VETULONATA
PLATE 4

Figures la-e. Unio mammilaris Yen XI, a-d, paratypes, locality 40; e, holotype, locality 39. (p. 36)

2a-f. Hadrodon jurassicus Yen XI, a-b, holotype; c-d, paratypes, locality 7; e-f, paratypes; locality 10. (p. 37)

3a-f. Hadrodon trigonus Yen XI, a-b, holotype; c-f, paratypes, locality 7. (p-38)
GEOLOGICAL SURVEY PROFESSIONAL PAPER 233 PLATE 4

UNIO AND HADRODON
PLATE 5

Figures la-d. Hadrodon trigonus Yen, XI, paratypes, locality 7. (p. 38)

2a-f. Hadrodon lateralis Yen, XI, a-b, holotype; c-f, paratypes, locality 7. (p. 38) 

3a-b. Unio taxonotus White, XI, (after White), locality 4. (p.35)

4. Unio macropisthus White, XI, (after White) t locality 4. (p. 35) 

5a-b. Unio iridoides White, XI, (after White), locality 4. (p. 35) 

6a-b. Unio lapilloides White, XI, (after White), locality 4. (p.35)
GEOLOGICAL SURVEY PROFESSIONAL PAPER 233 PLATE 5

UNIO AND HADRODON
PLATE 6

Figures la-f. Amplovalvata cyclostoma Yen, X2, a-c holotype; d-f, paratype, locality 5. (p. 39)

2a-o. Amplovalvata scabrida (Meek and Hayden), X2, a-c, locality 22; d-f, m-o, locality 10; g-i, locality 23; i-1, locality 29.

(P- 39)

3a-c. Amplovalvata scabrida leei (Logan), X 2, locality 31. (p. 40) 

4a-c. Tropidina jurassica (Branson), X2, locality 33. (p. 40) 

5a-c. Liratina jurassica (Branson), X4, locality 33. (p. 40) 

6a-e. Viviparus reesidei Yen, X2. a, holotype; b-c, paratypes; c, young forms of the species imbedded in rock. Locality

11. (p. 40)

7a-d. Viviparus morrisonensis Yen, XI, a-b, holotype, locality 1; c-d, paratype, locality 29. (p. 41) 

8a-b. Lioplacodes jurassicus Yen, X2, holotype, locality 31. (p. 41)

9. Amnicola gilloides Yen and Reeside, X 2, locality 33. (p. 41) 

lOa-b. Amnicola jurassica Yen, X2, a, holotype; b, paratype, locality 23.

lOc. Amnicola sp. undet., X2, Icoality 8. (p. 41)

lla-f. Mesoneritina morrisonensis Yen, X2, a-c, holotype, locality 10; d-f, paratype, locality 23. (p. 42) 

12a-b. Mesauriculstra accelerata (White), X2, locality 5. (p. 42)

13a-b. Mesauriculstra morrisonensis Yen, X2, a. holotype; b, paratype, locality 5. (p. 43) 

14a-d. Mesauriculstra morrisonensis ovalis Yen, X2, a, holotype; b-d, paratypes, locality 5. (p. 43)

15a-b. Mesochilina spiralis Yen, .X2, a, holotype; b, paratype, locality 20. (p. 43) . "*• ~ 

16a-c. Limnopsis jurassica Yen, X 2, holotype, locality 31. (p. 44) • \ 

17a-d. Lymnaea ativuncula White, X 4, locality 5. (p. 44) .':.".

18. Lymnaea consortis White, X 2, locality 5. (p. 44)

19a-b Lymnaea morrisonensis Yen, X2, a, paratype; b, holotype, locality 5. (p. 44) 

20a-l. Gyraulus veternus Meek and Hayden, X2, locality 5. Showing developmental stages, (p. 44)
GEOLOGICAL, SURVEY

PROFESSIONAL PAPER 233 PLATE 6

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