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UNITED STATES DEPARTMENT OF THE INTERIOR

CHARACTERISTIC

MARINE JURASSIC FOSSILS FROM

THE WESTERN INTERIOR OF

THE UNITED STATES

GEOLOGICAL SURVEY PROFESSIONAL PAPER 214-B

UNITED STATES DEPARTMENT OF THE INTERIOR 

J. A. Krug, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

Professional Paper 214-B

CHARACTERISTIC MARINE JURASSIC

FOSSILS FROM THE WESTERN 

INTERIOR OF THE UNITED STATES

BY

RALPH W. IMLAY

Shorter contributions to general geology, 1947 

(Pages 13—53)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1948

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.

Price 35 cents

CONTENTS

Page

Abstract_ _ __________________________________________________________________________________________________ 13

Introduction._________________________________________________________________________________________________ 13

Faunal zones and correlations__________.________________________________________________________________________ 13

Defonticeras-Stemmatoceras Zone.-- -_______-________________________________--_-____---___-__--_-----____-_-- 13

Arctocephalites Zone______________________________________________________________________________________ 14

Arcticoceras Zone__________________________________________________________________________________________ 14

Gowericeras subitum Zone________ ___________________________________________________________________________ 15

Kepplerites cf. K. tychonis Zone___-_________-__________.-____________________-_-___--_______---__--__--_-_-_. 16

Kepplerites mclearni Zone._______________________________________________-___-_______________-__^-__________ 16

Quenstedtoceras collieri Zone.________________________________________________________________________________ 16

Cardioceras cordiforme Zone.________________________________________________________________________________ '17

Systematic descriptions_______________________________________________________________________________________ 17

Gryphaea planoconvexa WhitfiekL____________________________________________________________________________ 17

Gryphaea impressimarginata McLearn________________________________________________________________________ 18

Gryphaea nebrascensis Meek and Hayden.__-_________________________________-________________-______________ 18

Defonticeras oblatum (Whiteaves).___________________________________________________________________________ 19

Arctocephalites sawtoothensis Imlay, n. sp____________________________________________________________________ 19

Arctocephalites metastatus (Buckman) var. sweetgrassensis Imlay, n. var___________________________________________ 20

Arcticoceras codyense Imlay, n. sp______________________________________----^__--______-______________________ 20

Cadoceras shoshonense Imlay, n. sp________________________________________________________________._i________ 22

Gowericeras subitum Imlay, n. sp___________________________________________________________________________ 22

Kepplerites (Seymourites) mclearni Imlay, n. sp_____________________________-__----__--______-____-_----_-____- 24

Kepplerites (Seymourites) cf. K. tychonis (Ravn)_______________________________________________________________ 25

Quenstedtoceras (Bourkelamberticeras) collieri Reeside__________________________________________________________ 25

Index. ______________________________________________________________________________________ 33

ILLUSTRATIONS

Page 

PLATE 4. Correlation of Jurassic fonnations__---__---____________________________________________-_-_____-___-___ 16

5-9. Characteristic Jurassic fossils______________________________________________________________________ 28-32

rn

CHARACTERISTIC MARINE JURASSIC FOSSILS FROM THE WESTERN

INTERIOR OF THE UNITED STATES

BY R. W. IMLAY

ABSTRACT

The marine Middle and Upper Jurassic rocks in the western 

interior of the United States contain at least eight fauual zones 

that may be defined on the basis of their characteristic ammonites. From oldest to youngest they include the zones of Defonticeras-Stemmatoeeras, Aretoeephalites, Aretieoceras, Gowericeras subitum, Kepplerites cf. K. tychonis, Kepplerites 

mclearni, Quenstedtoceras collieri, and Cardioceras cordiforme. 

The first zone and the zone of Kepplerites cf. K. tyclionis are 

provisional and may be divisible faunally; another zone may 

exist at the top of the marine Jurassic. Descriptions are given 

of some of the most diagnostic fossils of these zones.

INTRODUCTION

Since publication in 1945 of a brief statement on the 

occurrence of Middle Jurassic rocks in the western 

interior of the United States,1 the writer has had the 

opportunity of seeing many typical sections of the 

Jurassic in all the Rocky Mountain States and of making many fossil collections, which will be the basis for 

several stratigraphic and paleontologic papers. In 

order to make some of this information promptly available to field workers, the writer has prepared summary 

discussions of the various faunas, has noted their stratigraphic positions, and has written descriptions of a few 

of the most characteristic fossils. Establishment of the 

f aimal succession within the Middle and Upper Jurassic 

sequence of rocks should be useful in making regional 

correlations and in deciding what stratigraphic nomenclature will be most appropriate and serviceable locally.

Throughout this paper the phrases United States 

National Museum and United States Geological Survey 

Mesozoic locality, are abbreviated to U.S.N.M., and 

U.S.G.S. Mes. loc., respectively.

FAUNAL ZONES AND CORRELATIONS

Eight ammonite zones have been recognized in the 

marine Jurassic of the western interior of the United 

States. From youngest to oldest they may be listed as 

follows:

Cardioceras cord if or me 

Quenstedtoceras collieri 

Kepplerites mdearni 

Kepplerites cf. K. tyclionis

Gowericeras sitbitutu

Aretieoeeras

ArctocepJialites

Defon ticeras-IStem m atoceras

These do not represent a continuous f aimal succession. 

The Defo-nticeras-Stemirina.toGeras beds at the base are 

not well known and may be divisible faunally. T^°sy 

are separated from the beds containing Arctoeephalites 

by shale and limestone that may contain other faunas, 

perhaps corresponding in part to the Granocephalites 

beds of east Greenland.2 The zones of Arctoeephalites^ 

Aretieoceras^ Gowericeras, and Kepplerites form a continuous succession. In Montana a discoiiformity between the zones of Kepplerites mclearni and Quenstedtoceras (Bourkelamberticeras} collieri represents mos4". of 

the middle and upper Callovian. Farther south the 

discoiiformity may be partly filled by the nonfossiliferous Preuss sandstone and Entrada sandstone. The 

Quenstedtoceras collieri zone is succeeded immediately 

by the Cardioceras cordifonne zone. Still higher marine beds contain a few cardioceratids that probably 

represent a distinct assemblage.

Plate 4 shows the fauna! zones and summarizes in. 

compact form many of the relations discussed in the 

following pages.

Defonticeras-Stemmatoceras Zone

This provisional zone is represented in the lower part 

of the Sawtooth formation of western Montana, the 

middle part of the Gypsum Spring formation of central 

Wyoming and southern Montana, and the basal par4-, of 

the Twin Creek limestone of western Wyoming and 

eastern Idaho. It is characterized by the ammonites 

Defonticeras, Stetmnatoceras, and Zemistephanusl and 

by numerous pelecypods, of which some have been described by Stanton 3 and by Warren.4 Oryphaea pianoconvexa Whitfield and G. impressitnarginata McLearn 

are found associated with the ammonites, although the 

latter is uncommon. The forms assigned to G. impressimarginata, differ from typical forms in the Arcto1 Imlay, R. W., Occurrence of Middle Jurassic rocks in western interior 

of United States : Am. Assoc. Petroleum Geologists Bull., vol 29, pp. 

1019-1027, 1945.

2 Spath, L. F., The invertebrate faunas of the Bathonian-Callovian 

deposits of Jameson Land (East Greenland) : Meddelelser om Gr0nland, 

Bind 87, no. 7, pp. 138, 145, 1932.

3 Stanton, T. W., Mesozoic fossils, in Geology of the Yellowstone National Park : U. S. Geol. Survey Mon. 32, pt. 2, pp. 600-632, pis. 72-75 

(in part), 1899.

4 Warren, P. S., A new pelecypod fauna from the Fernie formrtion, 

Alberta : Royal Soc. Canada Trans., 3d ser., vol. 26, sec. 4, pp. 1-36, 

pis. 1-5, 1932.

13
14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1947

cephalites and Arcticoceras beds only by a somewhat 

smaller average si2e and by lesser ventral extension of 

the ribs.

Defonticeras is the most common ammonite. It was 

found associated with Stemmatoceras at several localities in the border area of Idaho and Wyoming. It occurs with a stephanoceratid, tentatively assigned to 

Zemistephanus, in the middle limestone member of the 

Gypsum Spring formation of the west bank of the Yellowstone River, 2% miles south of Livingston, 3V£ont. 

A specimen identified as Defonticeras oblatum (Whiteaves) 5 was found 20 feet above the base of the Sawtooth formation at Swift Reservoir, Poiidera County, 

Mont. Fragments questionably assigned to Defonticeras have been found at several localities in the Gypsum 

Spring formation. Stephanoceratids are less common. 

In addition to the specimens found near Livingston, 

mentioned above, a few fragments were obtained on Cinnabar Mountain, near Gardner, Mont., about 43 feet 

below the main sill and near the middle of the Gypsum 

Spring formation. About 30 specimens resembling 

Zemistephanus vancouveri McLearn 6 were found in 

the lower part of the Gypsum Spring formation south 

of Cody, Wyo., in sec. 6, T. 51 N., R. 101 W.

The beds containing Defonticeras and Stetwnatoceras 

have been considered middle or upper Bajocian.7 Determination of their exact age must await detailed 

faunal studies, although their position not far below 

the Arctocephalites beds suggests that their age is upper 

Bajocian.

Defonticeras oblatwn (Whiteaves), G-ryphaea planoconvexa Whitfield, and G. impressimarginata McLearn 

are described and illustrated in this paper.

Arctocephalites Zone

The ammonite Arctocephalites has been found in the 

upper silty-to-sandy member of the Sawtooth formation in western Montana,8 in similar sandy beds in the 

Grassy Mountain section near Blairmore, Alberta,9 and

5 Whiteaves, J. F., On the fossils of the coal-bearing deposits of the 

Queen Charlotte Islands: Canada Geol. Survey, Mesozoic fossils, vol. 1, 

pt. 3, p. 209, 1876. McLearn, F. H., Contributions to the stratigraphy 

and palaeontology of Skidegate Inlet, Queen Charlotte Islands, B. C.: 

Canada Nat. Mus. Bull. 54, p. 16, pi. 15, fig 1,1929.

8 McLearn, op. cit., p. 20, pi. 11, figs. 1, 2.

T McLearn, F. H., Some Canadian Jurassic faunas: Royal Soc. Canada 

Trans., 3d ser., vol. 21, pp. 63, 68, 1927. Crickmay, C. H., Jurassic 

history of North America : Its bearing on the development of continental 

structure: Am. Philos. Soc. Proc., vol. 70, no. 1, p. 35, 1931. Spath, 

L. F., op. cit., p. 11.

8 Imlay, R. W., Occurrence of Middle Jurassic rocks in western interior 

of United States: Am. Assoc. Petroleum Geologists Bull., vol. 29, pp. 

1024, 1025, 1945.

* McLearn, F. H., New pelecypods from the Fernie formation of the 

Alberta Jurassic: Royal Soc. Canada Trans., vol. 18, sec. 4, pp. 39-61, 

pis. 1-9, 1924. Buckman, S. S., Jurassic Ammonoidea, in Mesozoic 

paleontology of Blairmore region, Alberta: Canada Nat. Mus. Bull. 58, 

pp. 1-27, pis. 1-3, 1929.

in the Harrison Lake area of British Columbia.10 In 

Montana most of the specimens of Arctocephalites were 

obtained from the upper 10 feet of the upper s;lty-tosandy member of the Sawtooth formation, but fragments were obtained also from the lower part of the 

member. Associated with Arctocephalites in Montana 

are large forms of Procerites, as much as 1 foot in diameter, and many pelecypods. Most of the pelecypods n 

have been described by Stanton 12 and McLearV3 but 

these are not confined to the member. Some of the most 

characteristic species are G-ryphaea impressimarginata 

McLearn, Corbula munda McLearn, and Eumicrotis 

ferniensis McLearn. The writer feels that designation 

of a zonal index fossil should await additional field 

studies.

The age of the Arctocephalites zone was considered 

lower Callovian by Buckman 14 and probably upper 

Bathonian by Spath.15 The writer considers that the 

Arctocephalites beds are of Bathonian age correlative 

with the lower part of the Cornbrash beds of England,, 

This correlation is based partly on the association of 

Procerites with Arctocephalites and partly on stratigraphic position beneath beds containing varied ammonite faunas that permit accurate correlation vdth the 

lower Callovian ammonite zones of northwest Europe. 

The beds with Kepplerites correlate with the Sigaloceras 

calloviense zone and the underlying beds with (rowericeras correlate with the Proplanulites koenigi zone, as 

will be discussed later. The Arcticoceras beds, therefore, occupy the position of the Macrocephalites macrocephalus zone, and the Arctocephalites beds, immediately below, appear to correspond to the Clydoniceras 

discus zone. A zone characterized by Cmnocephalites, 

as in east Greenland,16 has not been recognized in the 

western interior region, contrary to recent statements 

by the writer,17 who misidentified a specimen of Defonticeras, but the zone may yet be found in the middle 

part of the Sawtooth formation.

Arctocephalites sawtoothensis Imlay and A. inetastatus (Buckman) var. sweetgrassensis Imlay are described and illustrated in this paper.

Arcticoceras Zone

An ammonite zone characterized by Arcticoceras, 

previously recorded only from East Greenland 1S and

10 Crickmay, C. H., Fossils from Harrison Lake area, British Columbia : 

Canada Nat. Mus. Bull. 63, pp. 39, 60, 63, pis. 18-20, 1930.

11 Imlay, R. M., op. cit., p. 1024.

12 Stanton, T. W., op. cit., pp. 600-632, pis. 72-75 (in part).

13 McLearn, F. H., op. cit., 1924.

14 Buckman, S. S., op. cit.

« Spath, L. F., op. Cit., pp. 14, 33, 36, 144, 145.

16 Spath, L. F., op. Cit., pp. 138, 144, 145.

« Imlay, R. W., op. cit., p. 1024.

18 Spath, L. F., op. cit., pp. 138, 142, 145.
MARINE JURASSIC FOSSILS FROM THE WESTERN INTERIOR OF UNITED STATES 15

the Petchora Basin of northern Russia,19 has now been 

identified at a number of widely separated localities in 

the western interior region of the United States, including the following:

1. Basal sandstone and shale of the Sudance formation in ths Black Hills area, South Dakota and Wyoming.

2. Basal sandstone of the Sundance formation in 

the Hartville uplift, eastern Wyoming.

3. Basal shaly limestone of the Sundance formation 

near Cody, north-central Wyoming.

4. Basal shale of the Eierdon formation in the Little 

Rocky Mountains, north-central Montana.

5. Basal shale of the Eierdon formation in the Sawtooth Range, northwestern Montana.

6. Basal shale of the Rierdon formation in the Yellowstone National Park area.

Arcticoceras is associated with Cadoceras and Procerites in the Little Rocky Mountains and the Sawtooth 

Range of Montana and with small forms of Arctocephalites in the Hartville uplift of Wyoming. Pelecypods 

are common at some localities, but most of the species 

appear to range beyond the Arcticoceras zone. G-rypkaea impressimarginata McLearn attains its greatest 

development in the Arcticoceras zone in the Sawtooth 

Range and does not range above that zone. The writer 

considers that not enough is known about the fauna of 

the Arcticoceras zone to designate a zonal index.

The age of the Arcticoceras beds of Greenland and 

Russia was determined by Spath 20 as lower Callovian. 

In Greenland the Arcticoceras beds contain Cadoceras 

and probably Pleurocephalites associated with the more 

abundant Arcticoceras. Some immature Arcticoceras 

likewise occur in the upper part of the Arctocephalites 

beds.21 Other specimens of Arcticoceras are associated 

with Kepplerites in one collection, but Spath 22 thinks 

they are possibly from a different horizon. In the Petchora Basin of northern Russia, Arcticoceras is associated with Pleurocephalites krylowi (Milachewitch).23 

In central Russia near Sergatsch, southwest of Gorki 

(Nijni Novgorod), P. krylowi is associated with Cadoceras elatmae Nikitin and certain perisphinctids 24 that 

Spath 25 refers questionably to the Callovian genus

19 Keyserling, A. Graf, Wissenschaftliche Beobachtungen aiif einer 

reise in das Petschora-Land in Jahre 1843, p. 331, 1846. Sokolov, D. N., 

Ziir Ammoniten-Faiina des Petschoraschen Jura: M<5m. Com. Geol., nouvelle s6r., livr. 76, pp. 15, 49, St. P6tersbourg, 1912.

20 Spath, L. P., The invertebrate faunas of the Bathonian-Callovian 

deposits of Jameson Land (East Greenland) : Meddelelser om Gr0nland, 

Bind 87, no. 7, pp. 141, 142, 1932.

21 Spath, L. P., op. cit, p. 132.

22 Idem, p. 127.

23 Milachewitch, C., Etudes sur les couches a Ammonites macrocephalus en Russie: Soc. Imperial Moscou Bull., p. 14, pi. 1, figs, la-c, 

1879. Sokolov, D. N., op. cit., pp. 14, 19.

24 Milachewitch, C., op. cit., p. 8.

25 Spath, L. F., Revision of the Jurassic cephalopod fauna of Kachh 

(Cutch) : Palaeontologia Indica, new ser., vol. 9, Mem. 2, pt. 4, p. 312, 

1931.

Kinkeliniceras. At several places in central Russia, 

Cadoceras elatmae is associated with species of Gowvriceras, C hamoussetia, and Macrocephalites^ which is 

clearly a lower Callovian assemblage. Arkell 27 shows 

that the zone of Cadoceras elatmae in Russia is equivalent to the zones of Macrocephalites macrocephalus f.nd 

Proplanulites koenigi in northwest Europe.

The Arcticoceras zone in the western interior of the 

United States corresponds to the Macrocephalites ?^,acrocephalus zone of northwest Europe, for the immediately overlying beds in America contain abundant 

Gowericeras and appear to correspond to the Gowericeras goweri beds (Proplanulites koenigi zone) of 

Europe. The absence of Gowericeras in the collections 

from East Greenland undoubtedly influenced Spath 28 

in correlating the Arcticoc&ras beds with the Gowericeras goweri beds of England. The presence of F**ocerites in the Arcticoceras zone is interesting, as Procerites, while, normally characteristic of the Bathonian, 

has been found in the lower Callovian of the Mediterranean region.29

There remains the possibility that both the Arcticoceras and Arctocephalites zones are equivalent to the 

Mawocephalites macrocephalus zone of Europe. TMs 

seems unlikely, in view of the thickness of the Arcticoceras beds, which locally attains 60 feet, and because the 

Arctocephalites beds in places lie only about 100 feet 

above the Defonticeras beds of Bajocian age.

Arcticoceras codyense Imlay and Cadoceras shoshonense Imlay are described and figured in this paper.

Gowericeras subitum Zone

This zone is characterized by many species and individuals of Gowericeras and Cadoceras, the latter attaining sizes of more than 1 foot in diameter. Other 

ammonites include rare specimens of Procerites, Grossouvria, and Arcticoceras. Pelecypods are abundant, 

large naticoid gastropods are fairly common, and wellpreserved brachiopods occur locally. Gryphaea nebrascensi$ Meek and Hayden appears in abundance at the 

base of the zone and ranges upward to the top of the 

marine Jurassic. The characteristic fossils of the zone 

have been found at many localities in Montana and 

northern Wyoming.

The Gowericeras beds are correlated with the Proplanulites koenigi zone of northwest Europe on the b^.sis

26 Nikitin, S. N., Die Cephalopodenfauna der Jurabildungen des Gouvernements Kostroma: Russ. K. Min. Gesell. Verb., Band 20, ser. 2, p. 

84, 1884 (1885).

27 Arkell, W. J., Standard of the European Jurassic : Geol. Soc. America 

Bull., vol. 57, p. 25, 1946.

28 Spath, L. P., The invertebrate faunas of the Bathonian-Callcvian 

deposits of Jameson Land (East Greenland) : Meddelelser om Gr0n1 and, 

Bind 87, no. 7, pp. 131, 145, 1932.

29 Spath, L. P., Revision of the Jurassic cephalopod fauna of Kachh 

(Cutch) : Palaeontologia Indica, new ser., vol. 9, mem. 2, pt 4, p. 281, 

1931. Neumayr, M., Die Cephalopoden-Fauna der Oolithe von BaliT bei 

Krakau : Geo. Reichsanstalt Wien, Abh., Band 5, Heft 6, pp. 39-41, 1871.
16 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1947

of the abundance of Gowericeras, the resemblance of 

several species to Gowericerax in the Kellaways beds of 

Great Britain, the highest occurrence of Procerites, and 

stratigraphic position about 90 feet below beds containing Kepplerites^ Sigaloceras^ and Kamptokephalites.

Gowericeras 8'i(bit'um< Imlay and Grypliaea nebrascensis Meek and Hayden are described and illustrated in 

this paper.

Kepplerites cf. K. tychonis Zone

This is a provisional zone at least partly representing 

the 80 to 90 feet of beds between the Gowericeras subituni z6ne and the Kepplerites mcTearni zone. It is 

characterized by a densely ribbed species of Kepplerites 

similar to K. tychonis (Ravn) 30 from East Greenland 

and unlike any of the six known species in the Kepplerites melearni zone in Montana. Associated fossils are 

Cadocera$, Gryphaea nebrascensis Meek and Hayden, 

and various pelecypods.

The presence of a finely ribbed Kepplerites comparable with Kepplerites tychonis (Ravn) and unlike any 

species in the Kepplerites mclearni zone suggests correlation with the K. tychonis beds of East Greenland. 

Likewise the association with Cadoceras is comparable 

with that in the K. tychonis beds, where Cadocera* and 

Kepplerites occur together in abundance and contrasts 

with the nonassoeiation of these genera in the Go'wericeras s-ubitum and Kepplerites mclearni zones. Of 

course, this may reflect some local condition and not have 

any special significance regionally, considering that both 

genera in Europe occur as low as the Cornbrash beds and 

range into the middle Callovian.

The age of the Kepplerites tychonis beds of East 

Greenland has not been determined exactly. Spath 31 

indicates a correlation with the zone of Sigaloceras calloviense but discusses the possibility of the beds being 

as high as middle Callovian. He was considerably influenced by the presence of Gitlielmiceras?- a subgenus 

of Cosmoceras, which first appears in the Sigaloceras 

calloviense zone but is most common in the Cosnwceras 

jason and Erymnoceras coronatnm zones.

The age of the beds containing Kepplerites cf. K. tychonis in the western interior region is determined by 

stratigraphic position to be lower Callovian, probably 

corresponding to the lower part of the Sigaloceras calloviense zone.

Kepplerites (Seymourites] cf.K. tychonis (Ravn) is 

described and illustrated in this paper.

30 Ravn, J. P. J., On Jurassic and Cretaceous fossils from northeast 

Greenland: Meddelelser om Gr0nland, Bind 45, p. 490, pi. 37, fig. 1, 1911. 

Spath, L. F., The invertebrate faunas of the Bathonian-Calloviau deposits 

of Jameson Land (East Greenland) : Meddelelser om Gr0nland. Bind 87, 

no. 7, pp. 83-87, pi. 23, figs. 1-3 : pi. 24, figs. 2, 4, 6 ; pi. 25, figs. 1-3 : 

pi. 26, figs. 3, 6, 1932.

31 Spath, L. F., op. cit., pp. 145, 146.

32 Spath, L. F., op. cit., p. 96, pi. 24, figs. 3a, b ; pi. 26, fig. 5.

Kepplerites mclearni Zone

This zone has been identified in Montana at the top 

of the Rierdon formation in the Little Rocky Mountains, the Bearpaw Mountains, the East Butte of the 

Sweetgrass Hills, the south edge of Glacier Fational 

Park along the Great Northern Railway, and in the 

Big Snowy Mountains. It is absent in the Little Belt 

Mountains, most of the Sawtooth Range, and much of 

southwestern Montana, owing to erosion or iiondeposition in middle or upper Callovian time. It is probably 

represented in the upper part of the Yakoim formation 

of British Columbia by various species of Kepplerites^ 

and it is probably present in the Twin Creek limestone 

of Idaho and western Wyoming.

The zone is characterized by an abundance of species 

and individuals of Kepplerites belonging to the subgenus Seymourites. Other ammonites are uncommon 

but include at least two species of Kamptokephalites, one 

species of Macrocephalites, two species of Sigaloceras, 

and one species of Grossouvria. In addition one specimen of Cosmoceras (Gulielmites} from the highest unit 

of the Rierdon formation in the Sage Creek section of 

the Sweetgrass Hills probably belongs in the zone, although Kepplerites was not obtained with Gulielmites 

at that locality. The zone also contains many pelecypods, including Gryphaea nebrascensis Meek and Hayden, and locally some brachiopods.

The lower Callovian age of the Kepplerites mclearni 

zone seems evident on the basis of the ammonites. Macrocephalites and Kamiptokeplialites are probably not 

younger than the lower Callovian, Grossonvria is certainly not older, and Sigaloceras is typical. In Europe 

Cosmoceras (Gulielmites} characterizes the zone of 

Cosmoceras jason but has been recorded from the upper 

part of the Sigaloceras calloviense zone.34 This faunal 

evidence, plus the stratigraphic position of the Kepplerites mclearni zone above the Gowericeras subitum 

zone of lower Callovian age, furnishes strong argument 

for correlating the Kepplerites mclearni zone with the 

Sigaloceras calloviense zone of northwest Europe. The 

evidence would be even stronger if the isolated specimen 

of Gulielmites from the Sweetgrass Hills should prove 

to come from a higher level than the other ammonites 

in the K. mclearni zone.

Kepplerites (Seymourites} mclearni Imlay is described and illustrated in this paper.

Quenstedtoceras collieri Zone

This zone has been identified fauiially only in the 

Little Rocky Mountains and the Bearpaw Mountains of

33 McLearn, F. H., Contributions to the stratigraphy and paleontology 

of Skidegate Inlet, Queen Charlotte Islands, B. C- : Canadr Nat. Mus. 

Bull. 54, pp. 4-12, 1929.

34 Spath, L. F., Revision of the Jurassic cephalopod faun<» of Kachh 

(Cutch) ; Palaeontologia Indica, new ser., vol. 9, mem. 2, p*. 6, p. 857, 

1933.
UNITED STATES DEPARTMENT OP THE INTERIOR 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 2U PLATE 4

1

3

8

s

!

European stages 

(Arkell, 1946)

Portlandian

Kimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Toarcian

Pliensbachiarr

Sinemurian

Hettangian

English formations 

(after Arkell, 1933)

Purbeck beds

Portland beds

Kimmeridge 

clay

Corallian beds

Oxford clay

Kellaways beds

Cornbrash beds

Great oolite

Inferior oolite

Upper Lias

Middle Lias

Lower Lias

Northwest Europe 

standard zones 

(Arkell, 1946)

Titanites cigantem 

Kerberites okusensis 

Glaueolithites gorei 

Zaraiakites alixrni

Pavlovia pa/laaioides 

Pavlovia rotunda 

Pectinatites pectinatus 

Subplanitti wheatteyensw 

Subplanites sp. 

Grawsia gigas 

Gravesia gravesiana 

Aulacostephamis psnidomutabilis 

Rasenia mutabilis 

Rasenia cymodoee 

Pictonia baylei

Ringsteadia petudocordata 

Decipia decipieng 

Perigphittcteg eautisnigrae 

Perispkincteg plicatilis 

Cardioceras eordatum 

Quen&tedtocerag mariae

Qiienstedtoceras lamberti 

Peltocfras athleta 

Brymnoceras coronatum ' 

Kosnutceras jason 

Sigaloceras calloviense

Proplanulites koenigi

Maw^^Mtrocepkalus

Clydonieerag discus

(not yet determined)

Purkineonia parldnsoni 

Stephanocerag hwmphriexitmum 

Otoitee sauzei 

Smninia sowerbyi 

Lvdwigia, murchisonae 

Lioceras opalinum 

bytocerag junnae 

Hildoceras btfrons 

Barpoceros lerpentinitm 

Daftyliocrras tenuicoetatiim 

Paltoplenroceras spinatum 

Amaltheus margaritatue 

Prodactyliocerag davoei 

Tragophylloceras ibex 

Uptonia jattiesoni 

Eehioceras raricostatum 

Oxynatieerag ofynotum 

Asteroeeras obtusum 

Ariftitfs turneri 

Arnioeeras semicostatum 

Coronwerag bueklandi 

Scamnocerae angulatum 

Psiloeerag planvrtris

Characteristic fossils in 

East Greenland modified after 

Spath (1932, 1935, 1936)

Titanites' and Crasspedites

7

Crendoniteg beds

EpipaUasieeras beds

Pallasiceras beds

Pectinatites beds

' 7

, Hoplocardioceras detipisn* 

j-j^ Euprionoceras koehi 

. . Bagenia borealw 

Rasenia orbiffnyi

Amoeboceras (Prionodoceras) and 

Ringsteadia

Cardioceras aff. C. zenaidae

Cardioceras beds

7

Areticoceras beds

Arctocephalitfs beds

Cranoctphalites beds

7

Present

7

Characteristic fossils in ^^SStSS^ &SoU*e^I 

the western interior region Montana Montar

7

anrT $PP Morrison Morrison 

, formation formation Gyrcmlue veternus

Swift Swi 

formation . forma

Cardioceras spp. 

________ Cardioeerag eordiforme _____________

Qumsttdtoceras cottien

Kepplerites mclearni 3" g

Gowerieeras subitum .«• ,Rierdon .2 R ere

Areticocerag

Arctocephalites sHtetone "^ 1

,„ .,„,.,...,„. ,., .y | M

J Dark gray sha e g . 

and limestone E an 

jc w th basal ° s

•g grade eastward .B 

Stemmatoeeras and Dqfanticertu w anared BVD 

(not zoned) beds re

«• ySXS£ Wind R^er Basin Freedom

a north-central central Wyoming southees Wyoming

Morrison Morrison Eph 

formation formation conglc

t,lauconmc ._-_ Glaucontic 

t sandstone and a g sandstone 

ion sha e ocal Y |^ and „ conglomeratic ? c si,,|e ot 

g ft base - £ sane

..... £ ..................... . .

•5 Red beds at Preuss

gray sandstone

5n 8rTvashaeS ' '» Gray sha e and 

somelimestone | ^1 ^'^ 

§ eastward — "''Ml III "' "~~*~^\ 1 1 1 I 1 ha e and Red shale arid~^ ^ ^^-U 

tstone siltstone | Red beds^^-U v

a rin« c Gray.sha e and r1 Dolomite, 

hail 'S c limestbne grading mestone, Twn 

li TM 'fr-H eastwarclnto and shale lim 

nno EP dolomteand ocally pebbly 

rone =J red shale at base

assive p Massive gypsum sl-fl Massive gypsum 

-TIHl andredlieds £,|e and recTbeds, 3 beds cs f>j some dolomite

Nugget Nu 

sandstone sane

quadrangle San Rafael Swell E 

of of 

tern Idaho middle eastern Utah

ra m Morrison 

merate formation

' - •• • -•"- Summerville 

formation

iimp 

stone g

Curtis / |

8

.andstone g- sandstone <" •>. ————— | ——— ; ———

<0 

QL

1

Carme 

_ . formation Creek 

sstone

||

Jurassic C?) Glen Canyon group

b

|o"

Kayenta formation

W ngate sandstone

ilack Mil's, western 

South Dakota 

and northeastern 

Wyoming

Morison 

forrration

Redwater 

shale 

member

La1' member

Hulett sandstone member

Stocl'ade Beaver

Cannon Spr ngs 

sands*one member

Gypsurr Spring 

form'tjon

CORRELATION OF JURASSIC FORMATIONS IN PARTS OF THE WESTERN INTERIOR REGION 790080 O - 48 (Face p. 16)

MARINE JURASSIC FOSSILS FROM THE WESTERN INTERIOR OF UNITED STATES 17

north-central Montana in concretion beds from 20 to 30 

feet above the base of the Swift formation, directly beneath shales containing Cardioceras cordiforme (Meek 

and Hayden) and associated species of Cardioceras. 

Failure to find the zone elsewhere may be explained in 

part by the sandy character of beds at that stratigraphie 

position in many parts of the western interior. Also, in 

places the zone may not be represented by sediments, as 

at Red Dome on the west side of the Pryor Mountains in 

south-central Montana, where sandstone containing Cardioceras rests directly on the Rierdon formation.

The common ammonites in the Quenstedtoceras collieri zone are Quenstedtoceras (Bourkelamberticeras) 

collieri Reeside and Q. (Pavloviceras) n. spp. Rare 

ammonites include Prososphinctes n. sp., Cardioceras 

(Maltoniceras) sundancense Reeside, C. (M.) n. sp., and 

C. (Scarburgiceras) n. sp. Pelecypods are common but 

mostly undescribed. Gryphaea nebrascensis Meek and 

Hayden is abundant. Belemnites are common in silty 

shales, as is true locally for other units of the marine 

Jurassic.

The Quenstedtoceras collieri zone probably corresponds to the upper part of the Q. lamberti zone and the 

lower part of the Q. mariae zone of Europe, because of 

the abundance of Bourkelamberticeras, which subgenus 

is typical of the Q. lamberti zone but ranges into the Q. 

mariae zone, and because Pavloviceras and Scarburgiceras are characteristic of the Q. mariae zone and are 

not known below the upper part of the Q. lamberti zone.

This age determination means that in the Little Rocky 

Mountains and in the Bearpaw Mountains the Swift 

formation is separated from the underlying Rierdon 

formation by an unconformity representing most of the 

middle and upper Callovian and corresponding to the 

European zones of Cosmoceras jason, Erymnoceras coronatum, and Peltoceras athleta.

Quenstedtoceras (Bourkelamberticeras) collieri Reeside is described and illustrated in this paper.

Cardioceras cordiforme Zone

This zone has been identified at many places in the 

western interior region, in the Stump sandstone of 

Idaho and western Wyoming, the Curtis formation of 

Utah, the Swift formation of Montana, the Redwater 

shale member of the Sundance formation in the Black 

Hills area of South Dakota and eastern Wyoming, and 

ir» equivalent beds in central Wyoming. It generally 

occurs near the top of the lower third or half of these 

units but in places occurs near the base. In the Little 

Rocky Mountains and in the Bearpaw Mountains it 

occurs directly above the zone of Quenstedtoceras collieri. It is characterized by the abundance of Scarburgiceras, a subgenus of Cardioceras, and associated 

species of Goliathiceras and Pachyca^dioceras. Cardio790080—48———2

ceras (Scarburgiceras) cordiforme (Meek and Hayder) 

and C. (S.) wyomingense Reeside are the most common 

species. Associated subgenera of Cardioceras include 

Scoticardioceras, Suibverte'briceras, Cardioceras, Mcl~ 

toniceras, Vertel>riceras and Sagitticeras. In Europe 

the first three subgenera occur as low as the Q. mariae 

zone, but the last three have not been found below the 

C. cordatvm zone, according to any records examined 

by the writer. Scarburgiceras ranges from the upp^.r 

part of the Q. lamberti zone into the base of the C. 

ccrdatum zone. Goliathiceras is reported most frequently from the C. cordatum zone, although the subgenus Pachycardioceras occurs as low as the Q. mariie 

zone. Judging from these European ranges the zone of 

Cardioceras cordiforme would represent the upper part 

of the Q. mariae zone and the basal part of the C. ccrdatum zone. A suggestion that Cardioceras cordiforme 

does not range above the Q. mariae zone is furnished 

by a grossouvrid resembling Grossouvria (Poculisphinctes) trina (Buekman),35 occurring in the sane 

bed with C. cordiforme, 1 mile north of Redwater 

Creek, about 9 miles northwest of Spearfish, Butt.e 

County, S. Dak. In Europe, Poculisphinctes has been 

recorded most commonly from the P. athleta and Q. 

lamberti zones and rarely from the Q. mariae zor°!. 

Evidently more field work is necessary to determine the 

upper limit of the Cardioceras cordiforme zone and 

whether a still higher zone can be recognized in America 

in the marine Jurassic.

Cardioceras (Scarburgiceras) cordiforme (Meek and 

Hayden) and other species of this zone have been described and illustrated by Reeside 36 and are not refigured in this paper.

SYSTEMATIC DESCRIPTIONS • 

Gryphaea planoconvexa Whitfield

Plate 5, figure 6

GfrypJiaea planoconvexa Whitfield, in Ludlow, Wm., Kept. Reconnaissance Carroll, Montana, to the Yellowstone National 

Park, p. 142, pi. 2, figs. 9, 10. Washington, 1876.—Stanton, 

U. S. Geol. Survey Mon. 32, pt. 2, p. 611, pi. 72, figs. 9, 10,

This species is characterized by its subcircular outline,, 

prominent narrow beak, and moderate inflation of the 

left valve. These features distinguish it easily front 

any other Gryphaea in the Jurassic of North America. 

Among European species it resembles the flat variety of 

G. dilatata Sowerby figured by Arkell 37 but appears to> 

have a more regular form and a narrower, less incurved 

beak.

85 Buekman, S. S., Yorkshire type ammonites, TO!. 4. pi, 332, 1922.

38 Reeside, John B., Jr., Some American Jurassic ammonites of the 

genera Quenstedticeras, Cardiocera&, and Amoeboceras, Family Card'ioceratidae: U. S. Geol. Survey Prof. Paper 118, 1919 [192O3.

37 Arkell, W. J., A monograph of British Corallian Lamellibranchia: 

Paleont. Soc. Pub., pp. 160-170, pi. 20, figs. 1, 2, 5, 6, 1932.
18

Plesidtype: U.S.'N.M. 104138.

Sawtooth and Piper formations and Twin Creek limestone. G. planoconvexa Whitfield has been recorded at 

many places in the Yellowstone National Park area and 

in the nearby mountains in Montana, Wyoming and 

Idaho. All occurrences that the writer has checked are 

in the middle part of the Sawtooth formation or the 

Piper formation or the basal limestone beds of the Twin 

Creek limestone. It is rarely associated with G. impressimarginata McLearn,38 although this may be explained 

by differences in facies. It has been found associated 

with Defonticeras on the Lower Canyon of the Yellowstone River near Livingston, Mont., and with stephanoceratids on Cinnabar Mountain near Gardner, Mont. 

Easily accessible occurrences in the middle part of the 

Piper formation are (1) on the Benbow Mill road about 

30 miles southwest of Columbus, Mont., sec. 16, T. 5 S., 

R. 16 E.; (2) on the west side of Boulder River about 

20 miles southwest of Big Timber, Mont., in sec. 23, T. 

3 S., R. 12 E.; (3) on the north side of Rocky Creek 

Canyon about 1 miles southeast of Bozeman Court 

House, in sec. 19, T. 2 S., R. 7 E., Mont.; and (4) on the 

west side of the Yellowstone River about 2,y2 miles south 

of Livingston, Mont. The best-preserved specimens 

have been obtained on the north wall of Indian Creek 

in sec. 20, T. 8 S., R. 2 E., in the Madison Range, Mont.

Gryphaea impressimarginata McLearn

Plate 5, figures 9-11

Gryphaea impressimarginata McLearn, Royal Soc. Canada 

Trans., vol. 18, sec. 4, p. 44, pi. 4, figs. 1-5, 1924.

Gryphaea cadominensis Warren, Eoyal Soc. Canada, Trans., 

vol. 26, sec. 4, p. 17, pi. 3, figs. 1-4, 1932.

Gryphaea impressimarginata McLearn was described 

on the basis of small to medium-sized specimens from 

the Arctocephalites beds in the Blairmore area, Alberta, 

Canada. It was distinguished from G. nebrascensis 

Meek and Hayden by its more robust form and by the 

rather coarse ribbing on its umbo. G. cadominensis 

Warren was described on the basis of small specimens 

from the Defonticeras beds in the Cadomin area, Alberta. It was distinguished from G. impressimarginata 

by being less trigonal in outline. In the Sawtooth 

Range of western Montana, G. impressimarginata occurs in abundance in the Arctocephalites zone at the top 

of the Sawtooth formation and in the Arcticoceras zone 

at the base of the Rierdon formation. It is absent in the 

overlying Gowericeras zone, where G. nebrascensis first 

appears in abundance. It is uncommon in the dark 

shale in the lower part of the Sawtooth formation, probably owing to an unfavorable sedimentary facies. In 

eastern Idaho, westernmost Wyoming, and north-central

38 McLearn, F. H., New pelecypods from the Fernie formation of the 

Alberta Jurassic: Royal Soc. Canada Trans., vol. 18, sec. 4, pp. 44, 1924.

Utah, G. impressimarginata is common in the lower part 

of the Twin Creek limestone in association vdth Defonticeras and Stemmatoceras. Some of the immature 

forms appear to be identical with G. cadominensis, but 

the adult forms are indistinguishable from G. impressimarginata. The large number of specimens available 

shows that G. impressimarginata varies considerably in 

shape and ornamentation. Its outline ranges from 

elongate to ovate to subtrigonal and its convex'ty from 

moderate to strong. The coarse radial ribs may be 

confined to the umbo or may extend to the ventral 

margin. The beak, when well-preserved, is pointed 

and generally deflected posteriorly. In some specimens 

this posterior deflection is very pronounced and in others 

scarcely noticeable. An inflected area along the postero-clorsal margin is present on most specimens, but a 

sulcus on the post-umbonal slope is rather uncommon. 

The right valve is concave and does not have radial ribs.

Plesiotypes: U.S.N.M. 104139.

Sawtooth formation and Arcticoceras beds in the 

basal part of the Rierdon formation in the Sawtooth 

Range of western Montana. Twin Creek limestone, 

basal part, in westernmost Wyoming, easterr Idaho, 

and north-central Utah.

Gryphaea nebrascensis Meek and Hayden

Plate 5, figures 7, 8

Gryphaea, calceola var. nebrascensis, Meek and Hayden, Acad. 

Nat. Sci. Philadelphia Proc. for 1861, pp. 437-43!}, 1861.— 

Smithsonian Cont. Knowledge, vol. 14, art. 5, pp. 74-76, pi. 

3, figs, la-e and annexed cuts, 1865.

Gryphaea calceola (Quenstedt?) Meek in Simpson, Kept. Expl. 

Great Basin Terr., Utah, p. 356, pi. 3, fig. 2, 1876.

Gryphaea calceola var. nebrascen>sis Meek and Hayden. Hall 

and Whitfield, U. S. Geol. Expl. 40th Par. Kept., vol. 4, pt. 2, 

pp. 286, 287, pi. 7, fig. 11, 1877.—Whiteaves, Canad'an Naturalist, vol. 8, new ser., no. 7, p. 401, 1878.—Whiteaves, Canada Geol. Survey Kept. Progress for 1876-1877, p. 151, 1878-— 

Whitfield, Paleontology of the Black Hills, in Nekton and 

Jenny, Geology and resources of the Black Hills of Dakota: 

U. S. Geog. and Geol. Survey Eocky Mtn. Region Kept, pp. 

349, 350, pi. 3, figs. 13-16, 1880.

Gryphaea, nfbrascensis Meek and Hayden. Whiteaves, Canada 

Geol. Survey, Mesozoic fossils, vol. 1, pt. 3, pp. 244, 245, pi. 

32, figs. 2, 2a, 2b, 1884.

Gryphaea calceola var. nebrascensis Meek and Hayder. White, 

U. S. Geol. Survey 4th Ann. Kept, for 1882-1883, p. 290, pi. 

35, figs. 1-5, 1884.—Stanton, U. S. Geol. Survey Mon. 32, 

pt. 2, p. 612, pi. 72, figs. 5-7, 1899.—Butler, U. S. Geol. Survey Prof. Paper 111, pi. 10, figs. 6, 7, 1920.

Gryphaea nebrascensis Meek and Hayden. Arkell, Cotteswold 

Naturalists' Field Club Proc., vol. 25, pt. 1, p. 61, text figs. 

1-5. Gloucester, 1933.

This species is characterized in the adult by its elongate shell, prominent, narrow umbo, strongly incurved 

beak, generally well-defined sulcus on the posterior side, 

and especially by the presence of distinct, radiating 

striae on the umbonal region. Its considerable resem-
MARINE JURASSIC FOSSILS FROM THE WESTERN INTERIOR OF UNITED STATES 19

blance to Gryphaea calceohi Quenstedt from the lower 

Bajocian of Wiirttemberg was noted by Meek and Hayden in their original description. A similar species 

occurs in the Callovian of Oaxaca, Mexico. The only 

similar species in the western interior region is G. impressimarginata McLearn, which is distinguished by its 

stouter form, presence of ribs instead of striae on its 

umbo, and its less incurved beak, which is commonly 

deflected posteriorly. Some of the stouter forms of G. 

nebrascen&is may resemble the more slender forms of 

G. impressimarginata but are generally distinguished 

easily by their finer umbonal markings. In these two 

species, immature forms of less than half an inch in 

height are very similar.

The specimen herein illustrated is one of the largest 

and best-preserved in the collections of the Geological 

Survey and is typical of the species.

Plesiotype: U.S.N.M. 104136.

Gryphaea, nebrascensis Meek and Hay den appears in 

abundance in the Gowericeras subitwn zone and ranges 

to the top of the marine Jurassic. Locally it may be 

abundant, or it may be absent from beds that are within 

its vertical range. Some specimens from the Sawtooth 

formation of western Montana previously identified as 

G. nebrascensis are now considered immature forms of 

G. impressimarginata McLearn. The presence of {?. 

nebrascensis generally denotes beds younger than the 

Arcticoceras zone at the base of the Rierdon formation 

and the Sundance formation. However, a few specimens of G. nebrascensis have been found in the upper 

part of the Arcticoceras zone at several localities.

Defonticeras oblatum (Whiteaves)

Plate 5, figures 1-5

Ammonites loganianiis (?) Form A, Whiteaves, Canada Geol. 

Survey, Mesozoic fossils, vol. 1, pt. 1, p. 29, pi. 4, figs. 2, 2a, 

1876.

Stephanoceras oblatum (Wlliteaves), Canada Geol. Survey, Mesozoic fossils, vol. 1, pt. 3, p. 209,1884.

Defonticeras oblatum (Whiteaves), McLearn, Canada Nat. Mus. 

Bull. 54, p. 16, pi. 15, fig. 1, 1929.

The specimen figured herein was first placed in Cranocephalites 39 because its scaphitoid body chamber and 

ornamentation resembled that of certain species from 

Greenland, such as Cranocephalites inversus Spath,40 

and because it occurred only about 120 feet below silty 

beds containing Arctocephalites. However, after the 

details of the suture had been plotted, the relationships 

with Defonticeras were clearly seen, as shown by the 

wide, irregularly bifid second lateral lobe, which is in

39 Imlay, R. W., Occurrence of Middle Jurassic rocks in western interior of United States: Am. Assoc. Petroleum Geologists Bull., vol. 29, 

p. 1024, 1945.

40 Spath, L. P., The invertebrate faunas of the Bathonian-Callovian 

deposits of Jameson Land (East Greenland) : Meddelelser om Gr0nland, 

Bind 87, no. 7, p. 25, pi. 5, figs. 2a, b ; pi. 6, figs. 7a, b, 1932.

marked contrast to the narrow, trifid second lateral lobe 

of Oranocephalites. The specimen in hand lacks parjt 

of the body chamber and has been somewhat crusHed. 

Specific identity with D. oblctiwn (Whiteares) is shown 

by the very simple suture line and the abrupt change in 

character of the ribbing. On the sutured part of the 

outer whorl the primary ribs are fairly strong, rather 

closely spaced, and subdivide into two similarly strong 

secondary ribs. Most of the rib pairs are separated by 

intercalary ribs. Beginning with the body chamber the 

primary ribs become rather widely spaced and give rise 

to pairs of weaker secondary ribs, between which lie 

single intercalary ribs. None of the other descrbed 

species of Defonticeras is closely similar.

Plesiotype: U.S.N.M. 104134.

Ellis group, Sawtooth formation. From U.S.G.S. 

Mes. loc. 19192, about 20 feet above base of Sawtooth 

formation on north side of Swift Eeservoir, sec. 27, T. 

28 N., R. 10 W., Pondera County, Mont.

Arctocephalites sawtoothensis Imlay, n. sp.

Plate 6, figure 7

Only the holotype can at present be definitely assigned 

to tlys species. It has been compressed laterally in f ossilization, but its normal whorl section was probably 

as wide as high. The flanks and venter are moderately 

convex. The umbilicus is fairly narrow. The umbilical wall is vertical but rounds rather abruptly into 

the flanks. The body chamber occupies about tlreefourths of the last whorl and is terminated by a fairly 

deep, forwardly projecting constriction.

The posterior end of the outer whorl of the holotype 

bears fairly strong ribs. The primary ribs curve forward on the lower third of the flank, where some bifurcate, but many remain single. The ribs continue the 

forward curvature to about the upper third of the f *»nk 

and then recurve slightly and cross the venter transversely. A number of intercalary ribs arise between the 

furcation points an,d the upper third of the flanks. 

There are about 2% times as many secondary ribs as 

primary ribs. Costation disappears rapidly on the 

body chamber, most of which is quite smooth except for 

fine growth lines. The suture cannot be traced.

One small specimen (pi. 6, figs. 2, 5) has very high, 

sharp ribbing greatly resembling that of the much 

smaller ^Miccocephalites^ lanunatus Buckman 41 and 

may represent an immature form of Arctocephalites 

sawtoothensis. Its strong primary ribs curve backward 

on the umbilical wall, curve forward on the lower fourth 

of the flanks, and then bifurcate or continue singly in a 

nearly radial manner. Anteriorly, the anterior branch

41 Buckman, S. S., Jurassic Ammonoidea, in Mesozoic paleontology of 

Blairmore region, Alberta: Canada Nat. Mus. Bull. 58, p. 14, pi. 1, figs. 

4, 4a, 5, 1929.
20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1947

of each rib pair becomes more or less faintly connected 

with the primary rib. The ribbing is particularly 

prominent on the venter.

A. sawtoothensis does not greatly resemble any of the 

other five species of Arctocephalites known from the 

Sawtooth formation in Montana. Probably the most 

similar species is A. arcticus (Newton),42 which has a 

smaller umbilicus and loses its ribbing earlier. A. ornatus Spath 43 has a similar body chamber.

Holotype: U.S.N.M. 104148.

Ellis group, Sawtooth formation, upper silty to sandy 

member. U.S.G.S. Mes. loc. 19184, at head of Rierdon 

Gulch, sec. 23, T. 24 N., R. 9 W., Sawtooth Range, Teton 

County, Mont. The small specimen shown on plate 6, 

figures 2,5, was obtained near the base of the upper siltyto-sandy member of the Sawtooth formation about 15 

feet above Paleozoic rocks at the head of Lime Gulch, 

SWi/4 sec. 1, T. 20 N., R. 9 W., Lewis and Clark County, 

Mont.

Arctocephalites metastatus (Buckman) var. sweetgrassensis 

Imlay, n. var.

Plate 6, figures 1, 3

The variety is represented in the collections by % only 

one specimen, but was selected for illustration in this 

preliminary paper because of its close resemblance to 

"Metacephalites" metastatus Buckman ** from the CorJ)ula munda beds in the Fernie formation near Blairmore, Alberta.

The outer whorl of the type is subovate, as wide as 

high, thickest on lowest part of the flanks, embracing 

about three-fourths; flanks gently convex, converging 

gradually into moderately narrow, rounded "venter. 

Umbilicus fairly narrow, wall rounding rather abruptly 

into flanks. Body chamber not preserved.

The ribbing is fairly strong and somewhat flexuous 

The primary ribs are thick, elevated, incline nearly 

radially on the upper part of the umbilical wall, curve 

forward rather strongly on the lower third of the 

flanks, and then bifurcate. The secondary ribs continue the forward curvature to about the middle of the 

flanks, then become nearly radial and cross the venter 

transversely. On the middle of the flanks the secondary ribs are slightly weaker than the primary ribs but 

gradually become higher and thicker toward the venter. 

Nearly all rib pairs are separated by single intercalary 

ribs which begin slightly above the furcation points,

are more or lessi faintly connected with the preceding 

rib pairs, and are as strong as the forked rib^ on the 

upper part of the flanks and on the venter.

The suture line cannot be followed, although, in the 

type, traces are visible at the anterior end.

The specimen may be slightly compressed, but at a 

diameter of 73 millimeters the whorl height is 34 millimeters, the whorl thickness 35 millimeters, and the umbilical width 17 millimeters. The last three dimensions 

expressed as ratios of the diameter are 0.46, 0.48, and 

0.23.

The specimen figured herein agrees closely with 

"Metacephalitesv> metastatus Buckman in ornamentation 

and whorl proportions. It appears to have a more narrowly rounded venter and less sharp ribbing, but these 

minor differences may be related to conditions c f preservation. In order to avoid nomenclatorial confusion, it 

seems preferable to designate the Montana form as a 

variety until specimens of a similar size can be 

compared. '

Associated with Arctocephalites metastatvs Buckman var. sweetgrassensis Imlay are two rathe*1 similar 

species. One is distinguished by coarser, sparser ribbing and a broader whorl section. The other has finer 

ribbing, which is beginning to disappear on the lower 

parts of the flanks at a diameter comparable with the 

maximum diameter of the variety A. m. sweetgrassensis. 

Several species from the Arctic region are rather comparable. A. ellipticus Spath 45 appears to have fewer 

secondary ribs and a stouter whorl section. A . elegcms 

Spath 46 has similar ribbing and whorl shape, but has 

a smaller umbilicus and becomes smooth at an early 

growth stage. A. arcticm (Newton) 47 has fewer secondary ribs and loses its ribbing earlier. Dolikephalites 

typicus (Blake) 48 and KamptoJcephalites bedfordensis 

Spath 49 show rib curvature similar to that of the variety 

A. in. sweetgrassensis.

Holotype of variety: "U.S.N.M. 104150.

Ellis group, Sawtooth formation, upper silty-tosandy member. U.S.G.S. Mes. loc. 19601, from upper 2 

feet of Sawtooth formation on Lonesome Ridge due 

north of Green Gulch on line of sees. 33 and 34, T. 25 

N., R. 9 W., Sawtooth Range, Teton County, Mont.

Arcticoceras codyense Imlay, n. sp.

Plate 6,, figures 4, 6, 8

The holotype has been partly crushed at its anterior 

end, but the remainder of the shell appears to be nor-

** Newton, E. T., and Teall, J. J. H., Notes on a collection of rocks 

and fossils from Franz Josef Land, made by the Jackson-Harmsworth 

Expedition during 1894-96: Geol. Soc. London Quart. Jour., vol. 53, p. 

500, pi. 40, figs. 1, la, 1897. Whitfleld, R. P. Notes on some Jurassic 

fossils from Franz Josef Land, brought by a member of thr Ziegler Exploring Expedition: Am. Mas. Nat. History Bull., vol. 22, p. 131, pi. 18, 

fig. 2, 1906. Spath, L. F., op. clt., p. 32, pi. 12, fig. 2, 1932.

43 Spath, L. F., op. cit., p. 39, pi. 8, figs. 3a, b.

«* Buckman, S. S., op. cit., p. 11, pi. 3, figs. 1-4, 1929.

*» Spath, L. F., op. clt., p. 33, pi. 13, figs. 6a, b, 1932.

« Spath, L. F., op. cit., p. 37, pi. 10, figs. 4a, b, 1932.

« Newton, E. T., and Teall, J. J. H., op. cit., p. 500, pi. 40, figs. 1, la. 

Whltfield, R. P., op. clt., p. 131, pi. 18, fig 2. Spath, L. F., op. cit., p. 32, 

pi. 3, fig. 7 ; pi. 12, fig. 2,1932.

48 Blake, J. P., Fauna of the Cornbrash : Paleont. Soc., p. 42, pi. 3, 

figs, la, b, 1905.

49 Blake, J. F., op. cit., p. 43, pi. 4, fig. 1. Spath, L. F., Palaeontologia 

Indica, new ser., vol. 9, mem. 2, pt. 3, p. 172, 1928.
MARINE JURASSIC FOSSILS FROM THE WESTERN INTERIOR OF UNITED STATES 21

mal. Its form is lenticular, flattened. The whorls are 

elongate trigonal, much higher than wide, thickest near 

the umbilicus. The flanks are flattened, the venter narrowly rounded, and the umbilicus nearly closed. The 

aperture is not preserved, but the body chamber is at 

least half a whorl in length. The anterior end of the 

holotype and of two other specimens of comparable size 

show faint, forwardly inclined ribbing when viewed 

under oblique lighting. The inner whorls are not 

known. The adult whorls, represented by several specimens from the Little Rocky Mountains, in Montana, 

are entirely smooth and have a somewhat stouter whorl 

shape than the holotype.

The suture is well exposed on the holotype and on 

two larger specimens. The ventral lobe is wider than 

lon^; first lateral lobe longer than wide and irregularly 

trind; second lateral lobe as long as wide and bifid. 

Saddles much wider than lobes; ventral saddle bifid and 

its steeply inclined outer slope deeply incised by a 

secondary lobule; first lateral saddle irregularly bifid, 

with the outer branch the larger; second lateral saddle 

broad and of irregular shape.

One specimen from Chalk Butte dome in the Little 

Rocky Mountains measures about 11 inches (280 millimeters) in diameter.

The dimensions of the types in millimeters and in 

ratios of the diameter are as follows:

Specimen

Holotype, U.S.N.M. 104132. ......„._„_

Paratype, U.S.N.M. 104133a............

Paratype, U.S.N.M. 104133b_.....:i...

Diameter

85

88 181*

Whorl 

height

81 (0.60)

52 (. 59)

110 (. 60)

Whorl 

thickness

36 (0.42)

36 (.40)

91 (.SO)

Ammonites referable to Arcticoceras are represented 

in available collections by about 80 specimens representing at least 6 species. However, a number of fragments 

cannot be placed in the proper species because of defective preservation, or because the complete development 

of some species is not known. The various species are 

distinguishable according to whorl shape, degree of 

coarseness of ribbing, and loss of ribbing relative to size. 

All are characterized by a narrowly rounded venter, a 

very small umbilicus, and by forwardly inclined ribbing 

in the immature forms. These are the main features 

that distinguish Arcticoceras from ArctocephaMtes,50 to 

which the species in question were formerly referred by 

the writer.51 However, a number of species definitely 

referable to Arctocephalites in the upper silty member 

of the Sawtooth formation of western Montana are distinguishable from the species herein referred to Arcticoceras by the wider umbilicus, lower and more rounded 

whorl sections, and nearly radial ribbing. The transitional character of Arcticoceras between Arctoceplalites and Chcmwussetia^ as pointed out by Spath,32 is 

confirmed by the presence of a slightly pinched venter 

on one species of Arcticoceras from the basal part of the 

Rierdon formation in the Sawtooth Range, Mont.

One interesting feature of some of the species of Arcticoceras from the western interior region is the character of the second lateral lobe. On the holotype of 

Arcticoceras henryi (Meek and Hayden) 53 this lobe is 

broad and bifid on one side of the shell, but at the same 

position on the other side it is narrower and trif rL 

Other specimens collected by the writer in the Bla"-k 

Hills area show that the young forms of A. henryi have 

a trifid second lateral lobe, but that during growth the 

innermost lobule diminishes in size, and on some adults 

is completely absent, thereby resulting in a bifid lot10,. 

A. codyensis likewise has an irregularly bifid second 

lateral lobe. Specimens of Arcticoceras from the Yellowstone National Park area, placed by Stanton 64 in 

Oppelia? sp., include one large form that has a bifid 

second lateral lobe. An undescribed species from the 

Sawtooth Range that resembles the Greenland form 

figured by Madsen M as Macrocephalites ishmae has- a 

trifid second lateral lobe even on the adult whores, 

although the inner lobule is smaller than the other tvo. 

A similar irregularly trifid second lateral lobe having a 

short inner lobule occurs in A. kochi Spath,68 from East 

Greenland. The suture line of A. ishmae Keyserling,57 

from Petchora Land in northern Russia, as originally 

figured is not definitely trifid, but Pompeckj 58 notes 

that it was not drawn accurately. The suture of a large 

specimen of A. ishmae as figured by Sokolov 59 has a* 

trifid second lateral lobe.

Arcticoceras codyensis loses its ribbing at a smal^r 

growth stage than any of the described species of the 

Arctic region. It has a more narrowly rounded venter 

than A. henryi (Meek and Hayden), whose whorl section is comparable with A. ishmae (Keyserling).

60 Spath, L. F., op. cit., Meddelelser om Gr0nland, Bind 87, no. 7, 

pp. 32-34, 5<M»3, 1932.

M Imlay, R. W., Occurrence of Middle Jurassic rocks in western interior 

of United States: Am. Assoc. Petroleum Geologists Bull., 29, pp. 

1019-1027. 1945.

790080—48———3

62 Spath, L. P., op. cit., pp. 50-52,1932.

63 Meek, F. B., and Hayden, F. V., Paleontology of the tipper Missori-i : 

Smithsonian Contr. Knowledge, vol. 14, art. 5, pp. 123, 124, pi. 5, f <?s. 

9a-c, 1865.

M Stanton, T. W.. Mesozoic fossils, in Geology of the Yellowstone National Park: U. S. Geol. Survey Mon. 32, pt. 2, pp. 630, 631, 1899.

50 Madsen, Victor, On Jurassic fossils from Bast Greenland: Mec'delelser om Gr0nland, Bind 29, no. 6, p. 191, pi. 8, fig. 7, 1904.

«« Spath, L. F., op. cit., p. 54,1932.

w Keyserling, A. Graf, Wissenschaftliche Beobachtung auf einer Reise 

in das Petschora-Land in Jahre 1843, p. 331, pi. 20, figs. 8-10, 1P46. 

Roman, Fre'de'ric, Les ammonites jnrassiqnes et cre*tace"es, p. 216, pi. 20, 

fig. 204, 1938,

68 Pompeckj, J. F., The Jurassic fauna of Cape Flora, Franz Josef 

Land, in Nansen F., The "Norwegian North Polar Expedition, 1893-96, 

Sci. Results, vol. 1, no. 2, p. 72, Christiania, 1900.

89 Sokolov, D. N., Zur Ammoniten-Fauna des Petschoraschen Jura: 

Com. Ge"ol. M4m., nouvelle s4r., livr. 76, pi. 3, fig. 12, St. PStersbourg, 

1912.
22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1947

Holotype, U.S,N.M. 104132; pamtypes, U.S.N.M. 

104133a-c. .!•

The holotype is from a 4"foot bed of nodular to shaly 

limestone, 7 feet above the base of the Sundance formation (U.S.G.S. Mes. loc.-17106) exposed in the south 

bank of the gorge of the Shoshone River, 2 miles west 

of Cody, Wyo. Six specimens are from 1 foot of sandy 

limestone, about 4 feet above the base of the Rierdon 

formation at the northeast end of Little Warm Dome, 

Little Rocky Mountains, sec. 32, T. 26 N., R. 26 E., 

Phillips County, Mont., U.S.G.S. Mes. loc. 19589. The 

largest specimen was obtained from nodular limestone 

about 12 feet above the base of the Rierdon formation on 

Chalk Butte.Dome, Little Rocky Mountains, sec. 7, T. 

25 N., R. 26 E., Phillips County, Mont., U.S.G.S. Mes. 

loc. 19538.

Cadoceras shoshonense Imlay, n. sp.

Plate 7, figures 13, 16, 17

The species is represented in the collections by at 

least 26 specimens. It probably includes two large 

globose specimens measuring about 8 inches in diameter, 

but the ornamentation of their inner whorls could not be 

determined.

Form globose, tending to become broader and more 

nearly spherical during growth. Whorl semicircular 

in section, wider than high, becoming wider during 

growth, and embracing most of the preceding whorl. 

Flanks rounding evenly into the broadly rounded venter. Umbilicus rather narrow; wall vertical at base, 

steep above, and rounding rather abruptly into flanks. 

Body chamber apparently nearly complete on the holotype, where it comprises three-fourths of a whorl.

The ribs are coarse and high. On the inner whorls 

they are as wide as the interspaces, but during growth 

become narrower than those spaces. The primary ribs 

are faint on the upper part of the umbilical wall and are 

weak on the edge of the umbilicus, but become strong 

ventrally. They curve forward considerably on the 

lower fourth of the flank and give rise to pairs of secondary ribs that incline forward slightly on the flanks and 

arch forward gently on the venter. Occasional intercalary ribs begin just above the zone of furcation.

The last suture line of the holotype (pi. 7, fig. 13) is 

characterized by the shortness of its lobes and saddles. 

This may reflect the proximity of the body chamber, although a smaller specimen (paratype U.S.N.M. 104144) 

has several suture lines that are similarly short, and 

which contrast with those of the other species of Cadoceras in the G-owericeras beds. Comparable short 

sutural elements occur in C. tschernysch&wi Sokolov.60

The holotype at a diameter of 74 millimeters has a 

whorl height of 30 millimeters, a whorl thickness of

«° Sokolov, D. N., op. cit., pp. 19, 51, pi. 1, figs. 2a, b: pi. 2, fig. 1, 1912.

47 millimeters, and an umbilical width of 15 millimeters. A large specimen (U.S.N.M. 104140) that 

probably represents the same species has the corresponding measurements of 205 millimeters, 100 millimeters, 165 millimeters, and 30 millimeters.

Cadoceras shoshonense is distinguished by its globose 

form, coarse ribbing, and small umbilicus. Among the 

associated species of Cadoceras that have a similar form 

the ribbing is considerably finer. The species that approach it in coarseness of ribbing have a more compressed form. None of the described species from 

Alaska or Canada is closely comparable. Among foreign species, C. sublaeve J. Sowerby var. ruposa Ppath,61 

from the Kellaways Rock of England, is probably most 

similar, but has a broader umbilicus, and the ribbing is 

stronger on the umbilical edge and weaker on the venter. 

C. freboldi Spath,62 from East Greenland, has a different whorl shape and finer ribbing. Cadoceras? sp. indet. 

Spath 63 resembles C. shoshonense in whorl shape and 

umbilical width, but its ribbing is different. The rather 

blunt ribbing of C. shoshonense, especially in the young 

forms, clearly separates it from Pleurocephalites.

Holotype, U.S.N.M. 104143; paratypes, U.S.N.M. 

104141, 104144.

U.S.G.S. Mes. Iocs. 17179 and 19632, from 4 feet of 

nodular to shaly limestone, 15 feet above base of Sundance formation on south bank of Shoshone Piver 2 

miles west of Cody, Wyo. At many localities from 

nodular sandy limestone in gray shale 10 to 30 feet 

above base of Rierdon formation in Big Snowy Mountains area, Fergus and Golden Valley Counties Mont. 

U.S.G.S. Mes. loc. 19212, from nodular limestone 13 feet 

above base of Rierdon formation on Chalk Butte Dome, 

Little Rocky Mountains, Phillips County, Mont. 

U.S.G.S. Mes. Loc. 19202, from 10 feet of nodukr limestone about 25 feet above base of Rierdon formation at 

the southeast end of the Bearpaw Mountains, Mont. 

U.S.G.S. Mes. loc. 18718, from Rierdon formation on 

Lonesome Ridge opposite Green Gulch, near line of 

sees. 33 and 34, T. 25 N., R. 9,W., Sawtooth Range, 

Teton County, Mont. U.S.G.S. Mes. loc. 19607, from 

25 to 30 feet below top of Rierdon formation in sec. 21, 

T. 25 N., R. 9 W., Sawtooth Range, Teton County, Mont. 

The species has been found only in the zone of (rowericeras subitum.

Gowericeras subitum Imlay, n. sp.

Plate 7, figures 1-11

This species is represented in collections in hand by 

about 55 specimens and is much more common than any 

of the other 6 associated species of Gowericeras.

61 Spath, L. F., op. cit., p. 60, 1932. Buckman, S. S., Yorkshire type 

ammonites, vol. 4, pi. 275, 1922.

62 Spath, L. F., op. cit., p. 65, pi. 18, figs. 2a, b.

63 Spath, L. F., op. cit., p. 70, pi. 20, fig. 5.
MARINE JURASSIC FOSSILS FROM THE WESTERN INTERIOR OF UNITED STATES 23

The inner whorls are subquadrate, higher than wide, 

embrace about four-fifths, have flattened flanks that 

round rather abruptly into a flattened venter, and have 

a low, steep umbilical wall. During growth the whorls 

become subovate, wider than high, thickest near the 

umbilicus, and considerably more evolute; the flanks become gently convex and round evenly into a moderately 

broad venter; the umbilicus changes from fairly narrow to moderately wide; the umbilical wall becomes 

moderately high, nearly vertical, and rounds rapidly 

into the flanks. The body chamber is not completely 

preserved but is represented by at least half a whorl.

The character of the ribbing changes rather suddenly 

several times during growth, following a constriction 

and then an abrupt thickening of the whorl section, but 

the greatest change occurs at the beginning of the adult 

body chamber. The smallest whorls (pi. 7, figs. 1, 2, 4) 

up to a diameter of about 30 millimeters have moderately strong primary ribs that are widely spaced, incline backward slightly on the umbilical wall, incline 

forward on the lower third of the flank, and terminate 

abruptly in weak, radially elongate tubercles. From 

the tubercles arise pairs of secondary ribs that are considerably weaker than the primary ribs. Between successive rib pairs are two or three intercalary ribs that 

begin between the tubercles and the middle of the flank 

and are as strong as the paired ribs. The paired and 

intercalary ribs incline forward on the flanks and cross 

the venter transversely or with a slight forward bend.

At a diameter of about 30 millimeters the shell has a 

rather pronounced constriction, which is followed by 

an abrupt thickening of the whorl section (pi. 7, figs. 

5, 6). Several other constrictions are generally present 

in the next three-fourths whorl, up to a diameter of 

about 45 millimeters. The thickening is accompanied 

by coarsening of the primary ribs, which become relatively much stronger than the secondaries. The primaries terminate in weak radially elongate tubercles 

from which pass two or three secondaries. Intercalary 

ribs become less common anteriorly, and generally only 

one is present between successive groups of branched 

ribs. The forward inclination of the ribs is very 

marked, and the secondaries bend forward gently on 

the venter.

On the body chamber the primary ribs abruptly become much stronger and more widely spaced. The 

weak radially elongate tubercles persist, but branching 

occurs well above the tubercles at, or above, the middle 

of the flanks. For each primary there are three secondaries, of which two are connected with the primary 

and the other begins high on the flank. All secondary 

ribs bend forward considerably on the venter and are 

slightly weaker there than on the flanks.

The suture line (pi. 7, fig. 3) is rather simple. Ventral lobe longer than wide; first lateral lobe trifid, 

slightly longer than wide, a little shorter than ventral 

lobe; second lateral lobe trifid, much smaller than first 

lateral lobe. Saddles wider than lobes; ventral saddle 

bifid, with largest branch on outer side, as long as wide; 

first lateral saddle broad and bifid, much smaller tl^n 

ventral saddle. The tubercle is in the outer brand of 

the first lateral saddle. Dimensions in millimeter? of 

some of the type specimens are given below. Numbers 

in parentheses are ratios of the diameter to the other 

dimensions:

Holotype,

Specimen

(pi. 3, figs.

(pi. 3, figs.

(pi. 3, figs, 

(pi. 3, fig. 1

(pi. 3, figs.

•

1,2).......

5,6).......

9,10)--..-- 

1)-— — .. 7 ft\

Diameter

25

42

56 

61

71

Whorl 

height

———— /__

11.5 (0.46)

19. (.45)

24 (.43) 

23 (. 38)

26 (.37)

Whorl 

thickness

8.5 (0.34)

20. (.48)

25. (.45)

1

26. (.37)

TJml ilieal 

wMth

6 (0. 24)

11 (.26)

16 (. 29) 

19 (.31)

24 (.34)

The ribbing of Gowericeras subitum, resembles that on 

Eucydoceras eucyckim (Waageii),64 from the Calkvian 

of India, and on Paracadoceras harv&yi Crickmay,65 

from the Callovian of the Harrison Lake area, British 

Columbia. However, the characteristics of the suture 

line and the presence of lateral tubercles a little Hlow. 

the middle of the flanks definitely place G. subitum in 

the Cosmoceratidae. Interestingly, the three most common species of Gowericeras in the Bierdon formation 

are the least similar to figured species of Gowericeras in 

the Kellaways beds in Great Britain, although G, subitum, shows some likeness to G. curtilobum (Buckman).66 

Among the rarer species of Gowericeras in the RiQ,rdon 

formation comparisons may be made with G. approwimatum (Buckman) ,67 G. planum Buckman,68 and G. trichophorum (Buckman).69 Associated with G. subitum 

are two similar species. One differs from G. subitum 

by having much coarser ribbing, particularly en the 

body chamber. The other differs by having fewor secondary ribs and by the gradually changing character of 

the ribbing. In fact, on five of the seven species the 

ribbing coarsens gradually rather than abruptly as on 

G. subitum. Of the seven species, only G. subitwn, is 

represented by immature forms which might have a 

runcinate venter. These immature forms have a flattened venter which does not make an abrupt ang1o> with 

the flanks, such as is characteristic of the early development stages of some of the species of Gowericeras in

6* Spath, L. F., Revision of the Jurassic cephalopod fauna of Kachh 

(Cutch) : Palaeontologia Indiea, new. ser., vol. 9, mem. 2, pt. 3, p. 209, 

pL 23, figs. 4a, b; pi. 25, fig. 4; pi. 27, figs. 7a, b, 1928.

OT Crickmay, C. H., Fossils from Harrison Lake area, British Columbia : 

Canada Nat. M«s. Bull. 63, p. 55, pi. 16, figs. 1, 2, 1930.

68 Buckman, S. S., Yorkshire type ammonites, vol. 4, pi. 294, 1922.

•' Buckman, S. S., op. cit., pi. 336.

68 Buckman, S. S., op. clt., pi. 287.

69 Buckman, S. S., op. cit., pi. 291.
24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1947

Europe. The absence or early loss of runcination 

sharply distinguishes the American species of G-owericeras from Kepplerites or Sigcdoceras, and with .the 

rounded whorl section, evolute coiling, and persistence 

of lateral tubercles show their close relationships with 

the European species of Gowericeras.

Holotype, U.S.N.M. 104155; paratypes, U.S.N.M. 

104153, 104154,104156a-c.

Ellis group, Kierdon formation, from 10 to 30 feet 

above base in Big Snowy Mountains, Fergus County, 

Mont. U.S.G.S. Mes. loc. 20365, from upper 15 feet of 

Rierdon formation on Lonesome Ridge, Sawtooth 

Range near line of sees. 33 and 34, T. 25 N., R. 9 W., 

Teton County, Mont.

Kepplerites (Seymourites) mclearni Imlay, n. sp.

Plate 8, figures 1, 2, 5, 7-10; plate 9, figure 1

This is the most common species in the Little Rocky 

Mountains; it is represented by 45 specimens, most of 

which are fragmentary and compressed, although the 

various growth stages are well shown. The immature 

forms have a subquadrate whorl section about twothirds as wide as high. During growth the whorls 

become relatively stouter, and in the adult are about 

five-sixths as wide as high. The flanks are somewhat 

flattened, becoming less so during growth. The venter 

is runcinate and slightly concave up to a diameter of iy2 

inches (38 millimeters), and some flattening is visible 

up to a diameter of 214 inches (60 millimeters). Thereafter, it changes to narrowly rounded, and on the outer 

whorl is moderately rounded. The umbilical wall is 

low, rounds evenly into the flanks, is steeply inclined on 

the inner whorls, and is very gently inclined on the outer 

whorls. The umbilicus is narrow on the smallest whorls 

but widens rapidly at diameters between 4% and 6y2 

inches and thereafter is wide. The body chamber, including the lateral lappet, is completely preserved on 

the largest specimen (not figured) and is represented by 

1^4 volutions.

During growth the ornamentation remains persistent 

in character up to the body chamber. On the smaller 

whorls (pi. 8, figs. 1,2. 8) the ribs are sharp and moderately spaced. The primary ribs are strong, elevated, 

are nearly radial, or curve backward slightly on the 

umbilical wall, then curve forward on the lower fourth 

of the flanks and terminate in prominent, conical tubercles. The secondary ribs incline gently forward, are 

slightly flexuous at diameters of less than iy2 inches and 

cross the venter transversely. Bifurcation is the common mode of branching at all growth stages, but some 

trifurcation occurs at diameters greater than 2 inches. 

Most rib branches are separated by single intercalary 

ribs, which begin at or slightly above the line of tubercles. During growth the ribbing gradually becomes

coarse, and the tubercles remain fairly conspicuous as 

far as the body whorl. On the body whorl the ornamentation gradually changes. The tubercles disappear, 

single ribs become more common, and effacement of the 

ribbing occurs, especially on the lower part of the flanks. 

The specimen shown on pi. 8, fig, 9, has at a diameter of 

about V/2 inches (60 millimeters) 25 primary rib«? and 

about 85 secondary ribs. The holotype (pi. 9, fig. 1) at 

a diameter of about 8 inches (200 millimeters) has 36 

primary ribs and about 106 secondary ribs. At a diameter of 12 inches (300 millimeters) it has 68 primary 

ribs and 142 secondary ribs.

The suture line is deeply dissected. Ventral lobe 

longer than wide; first lateral lobe a little longer tha a 

ventral lobe but narrower; second lateral lobe shorter 

than first lateral lobe. Saddles slightly wider than 

lobes; ventral saddle longer than wide and divided by 

a lobule, which is shorter than the saddle, into a small 

inner branch and a large outer branch; first lateral 

saddle bifid, a little smaller than ventral saddle, knger 

than wide; second lateral saddle smaller than first lateral saddle, nearly as wide as long, and has its inner 

branch on the umbilical margin. The tubercle is in the 

outer branch of the second lateral saddle.

The holotype is slightly compressed. Another specimen that appears to be undistorted has at a diamete^ of 

about 9 inches (230 millimeters) a whorl height of 60 

millimeters, a whorl thickness of 49 millimeters, and 

an umbilical width of about 175 millimeters. The small 

specimen shown on pi. 8, figs. 7, 9, has corresponding 

dimensions, of 60 millimeters, 26 millimeters, 20 millimeters and 17 millimeters.

The species is somewhat similar to K. ffiMnsi (McLearn) ,70 but has much coarser ribbing, fewer secondaries, more prominent tubercles, more complicated 

sutures, and a longer first lateral lobe. K. plexus 

(McLearn) n and K. logariumus (Whiteaves) 72 have less 

similar ornamentation and have thicker whorl sections. 

The ornamentation is similar to that in Gowericeras, but 

the primaries are shorter, the inner whorls are much 

more tightly coiled, the suture is somewhat different, 

and the adults attain a much larger size.

Holotype, U.S.N.M. 104125; paratypes, U.S.N.M. 

104122-104124,104126-104130.

Ellis group, Rierdon formation. Mostly upper 10 

to 15 feet, at many localities in the Little Rocky Morntains, Phillips County, Mont. U.S.G.S. Mes. loc. 7124, 

from Rierdon formation one-half to three-quarters of 

a mile west of Skyland, adjacent to the Great Northern

70 McLearn, F. H., Contributions to the stratigraphy and paleontolcfity 

of Skidegate Inlet, Queen Charlotte Islands, B. C.: Canada Nat. Mus. 

Bull. 54, pi. 3, fig. 1; pi. 4, fig. 1; pi. 8, fig. 5,1929.

71 McLearn, F. H., op. cit, p. 5, pis. 1, 2.

72 Whiteaves, J. F. Canada Geol. Survey, Mesozoic fossils, vol. 1, pt. 1, 

p. 27, pi. 8, fig. 2, 1876.
MARINE JURASSIC FOSSILS FROM THE WESTERN INTERIOR OF UNITED STATES 25

Railway at the south end of Glacier National Park, 

Mont.

Kepplerites (Seymourites) cf. K. tychonis (Ravn)

Plate 8, figures 3, 4, 6

A rather densely ribbed species of Kepplerites, represented by a number of fragments, is herein illustrated 

because of its stratigraphic occurrence in beds between 

the zones of Gowvriceras subitwti and Kepplerites 

mcleami and because it greatly resembles K. tychonis 

(Ravn),73 which in East Greenland characterizes a zone 

just above the Arcticoceras beds. The species from 

Montana will be provisionally referred to K. tychonis 

until more complete specimens are found, although the 

specimens in hand show no obvious differences. The 

fragments indicate a whorl section slightly higher than 

wide and somewhat flattened on the venter. The primary ribs are short, terminate in faint to very weak 

tubercles, and give rise to 2 or 3 sharp, elevated secondary ribs that incline forward gently on the flanks. On 

some of the larger whorls the secondary ribs incline 

forward rather strongly on the upper part of the flanks 

but cross the venter nearly transversely. The ribs are 

only slightly narrower than the interspaces and are 

much more closely spaced than in any other known 

species of Kepplerites from Canada or the United 

States.

Figured specimens: U. S. N. M. 104172, 104173.

Ellis group, Rierdon formation. (1) U.S.G.S. Mes. 

loc. 19629, from 23 feet above the base of the Rierdon 

formation on Five Mile Creek, sec. 36, T. 5 S., R. 24 

E., Pryor Mountains, Mont. (2) U.S.G.S. Mes. loc. 

20390,19 feet below top of Rierdon formation on north 

side of Sawmill Creek, about half a mile above its 

mouth, near Badger Creek, sec. 3, T. 29 K, R. 11 W., 

Sawtooth Range, Pondera County, Mont. The formation in this area is about 141 feet thick. (3) U.S.G.S. 

Mes. loc. 19194, from slumped block of the Rierdon

formation, 1 mile east of Autumn. Creek on north side 

of highway, south side of Glacier Park, Mont. (4) 

U.S.G.S. Mes. loc. 20391, from upper part of Rierdon 

formation in the Northern Ordnance, Inc.-Holtz No. 1 

well, sec. 23, T. 37 N., R. 2 W., north flank of KevinSunburst Dome, Toole County, Mont. The formation 

is from 72 to 91 feet thick in this area 74 and may 1 <we 

been partly eroded before deposition of the Swift formation.75

Quenstedtoceras (Bourkelamberticeras) collier! Reesid^

Plate 7, figures 12, 14, 15, 18

This species is represented in the Geological Survey 

collections by about 200 specimens that are preserved 

mostly as pyritized fragments and show all the growth 

stages except that of the adult. The immature forms 

up to a diameter of about 18 millimeters have beer described by Reeside.76 During further growth the whorl 

section becomes higher and subtriangular; the venter 

becomes slightly more narrow; the ribs become high 

and narrow near the umbilicus, faint near the middle of 

the flanks, prominent on the venter, and indistir^tly 

united at the furcation points; the suture acquires a 

longer ventral lobe and a broader ventral saddle. The 

resulting form is similar to that of Q. henrici R. Douville,77 from France, but has a higher, thinner whorl 

section and weaker ribbing near the middle of the 

flanks.

Holotype, U.S.N.M. 32298; paratypes, U.S.] T.M. 

32299-32301; plesiotype, U.S.N.M. 104137.

Ellis group, Swift formation. From 25 to 30 feet 

above base of formation at many localities in the Little 

Rocky Mountains, Mont. From about 25 feet above 

base of Swift formation at southeast end of Bearpaw 

Mountains, Mont.

78 Ravn, J. P. J., On Jurassic and Cretaceous fossils from northeast 

Greenland: Meddelelser om Gr0nland, Bind 45, p. 490, pi. 37, fig. 1, 1911. 

Spath, L. P., The invertebrate faunas of the Bathonian-Callovian deposits of Jameson Land (East Greenland) : Meddelelser om Gr0nland, 

Bind 87, no. 7, pp. 83-87, pi. 23, figs. 1-3; pi. 24, figs. 2, 4, 6; pi. 25, 

figs. 1-3 ; pi. 26, figs. 3, 6, 1932.

74 Cobban, W. A., Marine Jurassic formations of Sweetgrass arch, 

Mont.: Am. Assoc. Petroleum Geologists Bull., vol. 29, p. 1279, 1941.

»Idem, p. 1289, 1290.

w Reesiije, John B., Jr., Some American Jurassic ammonites cf the 

Genera Quenstedticeras, Oardiooeras, and Amoeboceras Family Cirdioceratidae: U. S. Geol. Survey Prof. Paper 118, pp. 14, 15, pi. 1, flgr. 1-8, 

1919 [1920].

" DouvillS, Robert, fitudes sur les Cardiocfiratides de Dives, V'Uerssur-Mer, et quelques autres gisements: Soc. geol. Prance M6m. 4">, pp. 

55, 56, pi. 4, figs. 24-32, 1912.

PLATES 5-9

27
PLATE 5

[All figures natural size]

FIGURES 1-5. Defonticeras oblatum (Whiteaves) (p. 19). Ventral, lateral, and side views and last suture line of plesiotype, 

U.S.N.M. 104134. From 21 feet above base of Sawtooth formation at U.S.G.S. Mes. loc. 19192, north side of 

Swift Reservoir, see. 27, T. 28 N., E. 10 W., Mont.

6. Gryphaea planoconvewa Whitfield (p. 17). Left valve of plesiotype, U.S.N.M. 104138. From middle part of Sawtooth formation at U.S.G.S. Mes. loc. 19619, on north wall of Indian Creek, sec. 20, T. 8 S., E. 2 E., Mont. 

7, 8. Gryphaea nebrascensis Meek and Hayden (p. 18). Right and left valves of plesiotype, U.S.N.M. 104136. From 

upper 10 feet of Rierdon formation at U.S.G.S. Mes. loc. 19211, about 1 mile southwest of Landusky, sec. 32, 

T. 25 N., E. 24 E., Mont.

9-11. Gryphaea impressimarginata McLearn (p. 18). Left valves of plesiotypes, U.S.N.M. 104139. From basal 40 feet 

of Eierdon formation at U.S.G.S. Mes. loc. 18718, on Lonesome Ridge near line of sees. 33 and 34, T. 25 N., 

R. 9 W., Mont.

28
GEOLOGICAL SURVEY PROFESSIONAL PAPER 214 PLATE 5

VX 

^

10

JURASSIC AMMONITE AND PELECYPODS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 214 PLATE 6

JURASSIC AMMONITES
PLATE 6

[All figures natural size]

FIGUBES 1, 3. Arctocephalites inetastatus (Buckman) var. sweetgrassensis Imlay, n. var. (p. 20). Lateral and ventral views 

of holotype, U.S.N.M. 104150. From upper 2 feet of Sawtooth formation at U.S.G.S. Mes. loc. 19601, on Lonesome Ridge near line of sees. 33 and 34, T. 25 N., R. 9 W., Mont.

2, 5. Arctocephalites sp. juv., cf. A. saictoothensis Imlay (p. 19). Lateral and ventral views of specimen, U.S.N.M. 

104149. From U.S.G.S. Mes. loc. 18324, about 15 feet above Paleozoic rocks in lower 10 feet of silty-to-sandy 

member in upper part of Sawtooth formation at head of Lime Gulch, SW% sec. 1, T. 20 N., R. 9 W., Mont. 

7. Arctocephalites sawtoothensis Imlay, n. sp. (p. 19). Holotype, U.S.N.M. 104148. From U.S.G.S. Mes. loc. _19184.

In upper 20 feet of Sawtooth formation at head of Rierdon Gulch, sec. 23, T. 24 N., R. 9 W., Mont.

4, 6, 8. Arctieoceras codyense Imlay, n. sp. (p. 20). Holotype, U.S.N.M. 104132. From U.S.G.S. Mes. loc. 17106, in 4 

feet of shaly-to-nodular limestone, 7 feet above base of Smadance formation on south bank of Shoshone River, 

2 miles west of Cody, Wyo.

29
PLATE 7

[All figures natural size]

'FIGURES 1-11. G-owericeras suMtum Imlay, n. sp. (p. 22).

1, 2. Paratype, U.S.N.M. 104156a; 4, paratype, U.S.N.M. 104156b; 5, 6, paratype, U.S.N.M. 104156C. All from 

U.S.G.S. Mes. loc. 19182, from upper part of an 8-foot ledge of sandy limestone 14 feet above base of Rierdon 

formation, 2 miles southwest of Forest Grove, sec. 21, T. 14 N., R. 21 E., Mont.

3, 11. Suture line and side view of paratype, U.S.N.M. 104153. From U.S.G.S. Mes. loc. 19169, 10 to 30 feet 

above base of Rierdon formation about 1% miles southeast of Piper, sec. 15, T. 14 N., R. 20 E., FergusCounty, Mont. 

7, 8. Paratype, U.S.N.M. 104154. From U.S.G.S. Mes. loc. 19180,10 to 30 feet above base of Rierdon formation,.

about 1 mile southeast of Piper, SE% sec. 9, and NE% sec. 16, T. 14 N., R. 20 E., Mont. 

9, 10. Holotype, U.S.N.M. 104155. From same locality as figures 1-6.

12, 14, 15, 18. Quenstedtoceras (Bourkelamberticeras) collieri Reeside (p. 25). Plesiotype, U.S.N.M. 104137. From U.S.G.S. 

Mes. loc. 19577, 25 to 30 feet above base of Swift formation at southwest end of Coburn dome, Little Rocky Mountains, sec. 33, T. 25 N., R. 26 E., Mont.

13, 16, 17. Cadoceras shoshonense Imlay, n. sp. (p. 22). Last suture line and later-al and ventral views of holotype, U.S.N.M. 

104143. From U.S.G.S. Mes. loc. 17179, 4 feet of nodular sandy limestone, 15 feet above base of Sundanceformation on south bank of Shoshone River, 2 miles west of Cody, Wyo.

30
PROFESSIONAL, PAPER 2H PLATE 7

GEOLOGICAL SURVEY

JURASSIC AMMONITES
StJKVEY I; ..,,

FKOFESSIONAL PAPER 214 PLATE 8

JURASSIC AMMONJT;E£
PLATE 8

[All figures natural size]

FIGURES 1, 2, 5, 7-10. Kepplerites (Seymourites) mclearni Imlay, n. sp. (p. 24).

1, 2. Paratype, U.S.N.M. 104126. From U.S.G.S. Mes. loc. 19583, in upper 10 feet of Rierdon formation,

south side of Camp Creek dome, Little Rocky Mountains, sec. 6, T. 24 N., R. 26 E., Mont. 

5. Suture line of paratype, U.S.N.M. 104122. From U.S.G.S. Mes. loc. 10732, east slope of mountain 

south of Zortman, Little Rocky Mountains, Mont.

7. 9. Paratype, U.S.N.M. 104128. From U.S.G.S. Mes. loc. 10732, east slope of mountain south of Zortman, Little Rocky Mountains, Mont.

8. Paratype, U.S.N.M. 104127. From U.S.G.S. Mes. loc. 19584, in upper 10 feet of Rierdon formation

on east side of Matador dome, sec. 3, T. 25 N., R. 26 E., Phillips County, Mont. 

10. Paratype, U.S.N.M. 104123. From U.S.G.S. Mes. loc. 18737, in upper part of Rierdon formation,

NW% sec. 3, T. 25 N., R. 26 E., Mont. 

3, 4, 6. Kepplerites (Seymourites) cf. K. tychonis (Ravn) (p. 25).

3. Lateral view of a fragment, U.S.N.M. 104172. From U.S.G.S. Mes. loc. 20390, about 19 feet below 

top of Rierdon formation on north side of Sawmill Creek about half a mile above its mouth, sec. 

3, T. 29 N., R. 11 W., Pondera County, Mont.

4. 6. Ventral and lateral views showing mouth border of specimen, U.S.N.M. 104173. From U.S.G.S. Mes. 

loc. 19629, about 23 feet above base of Rierdon formation on Five Mile Creek, sec. 36, T. 5 S., R. 24 E., 

Mont.

31
PLATE 9

[All figures two-thirds natural size]

FIGURE 1. Kepplerites (Seymourites) mclearni Imlay n. sp. (p. 24). Holotype, U.S.N.M. 104125. From U.S.G.S. Mes. loc. 19211, in 

upper 10 feet of Rierdon formation, about 1 mile southwest of Landusky, sec. 32, T. 25 N., R. 24 E., Phillips County, 

Mont.

32
PKOFESSIONAL PAPEK 214 PLATE 9

GEOLOGICAL STJKVEY

JURASSIC AMMONITE

INDEX

Page

Abstract——__———_———_——__—___- — __——__——_— 13

Ammonites loganianus (?) Form A————._ ——— ————————— __ 19

Arcticoceras codyense_———_——_—____—___——_— 20—22: pi. 6

henryi— — ——————————————_————————— —— ———— _ 21

ishmae ____—__——_——_——___-————_________ 21

kochi_____________________________________ 21 

Arcticoceras zone___—___—————__-_,__—_ —— ————__ 14—15 

Arctocephalites arcticus—______________________ 20

elegans ________________________________ 20

ellipticus _—__———_- —— ___________________ 20

metastatus sweetgrassensis__________________ 20; pi. 6

sawtoothensis—_———————_—___———___—_—_ 19-20 : pi. 6 

Arctocephalites zone— —————__——______________ 14

Cadoceras freboldi—————__——————_— —————— ———____ 22 

shoshonense——_————————__———_______,____ 22 : pi. 7 

sublaeve rugosa————_——____________________ 22

tschernyschewi ____________________________ 22

cadominensis, Gryphaea_________________________ IS

Cardioceras cordiforme zone_—_——__—____________ 17 

codyense, Arcticoceras_—___—_______________ 20-22 ; pi. 6 

collieri, Quenstefltoceras (Bourkelamberticeras)_________ 25; pi. 7

Defonticeras oblatum_____-________________ 14, 19: pi. 5

Defonticeras-Stemmatoceras zqne____________________ 13-14

Dolikephalites typicus—_________________________ 20

Eucycloceras eucyclum__________________________ 23

Paunal zones and correlations—______________ 13—17 ; pi. 4

Gowericeras approximatum______________________ 23

• curtilobum—_____________________________ 23

planum ___—___—________________________ 23

subitum___________________________ 15-16, 22-24: pi. 7 

trichophorum_______________________________ 23

Gryphaea cadominensis—— ———————————————————— ______

calceola nebrascensis__— —— ——————— ——————— __ ————

• dilatata _____————— —————————————————— _______

impressimarginata-—— —— —————————————— - 13, 14, 18 

iiebrascensis ____—— ———— —— — —— —— 15, 16. 18—19 ;

plaiioconvexa—— —————————————— —— ———— 13, '17—18;

Page 

18 

18 

17

; pi. 5 

pi. 5 

pi. 5

impressimarginata, Gryphaea_______ ——— —— _———— 13, 14. 18 ; pi. 5

Kamptokephalites herlfordeiisis—_—— —— _.——— ———— _-_ — — 20 

Kepplerites gitinsi—— — ———— —— —————— —————————— __- 24

loganianus————————————— —— —— - ————— ——— _ ————— - 24 

plenus—————————————————————————————————————— 24 

(Seymourites) inclearni___________—_ 16, 24-25; pis. 8, 9

tychonis _______________——_————— 16, 25: pi. 8

mclearni, Kepplerites (Seymourites)___——————16, 24-25; pis. 8, 9

Macrocephalites ishmae—— —————— —————————— —— ——— 21

"Metacephalites" metastatus_———————_—--———— —— _-__ 20

"Miccocephalites" laminatus————— —— __——— —— —— —— _ —— _ 19

nebrascensis, Gryphaea__________-____—_ 15, 16. 18—19 ; pi. 5 

oblatum, Defonticeras______________-_-___-_- 14. 19 : pi, 5

Paracadoceras harveyi— ——— ———— ——— - — ——————— ——— - 23 

planoconvexa, Gryphaea—_ —— —————— ———————— 13, 17—18 ; pi. 5

Quenstedtoceras henrici__,__________——___-__——____ 25

(BourkPlamberticeras) collieri—————————————_ 16—17,, 25; pi. 7

sawtoothensis, Arctocephalites_______——__————— 19-20 ; pi. 6 

shoshonense, Cadoceras_—___________-_——___—_ 22 ; pi. 7

Ste'phanoceras oblatum—___——_———————__,——__r—__ 19 

subitum, Gowericeras———— ——————— ———————— 15—16. 22—24 ; pi. 7 

swpetgrassensis, Arctocephalites metastatus—————_——— 20: pi. 6

tychonis, Kepplerites (Seymourites)———_——_—_—__ 16. 25; pi. g 

Zemistephanus Vancouver!_______________________ 14

o 33