Cenomanian Ammonite 

Fauna from the 

Mosby Sandstone of 

Central Montana

GEOLOGICAL SURVEY PROFESSIONAL PAPER 243-D
Cenomanian Ammonite 

Fauna from the 

Mosby Sandstone of 

Central Montana

By W. A. COBBAN

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

GEOLOGICAL SURVEY PROFESSIONAL PAPER 243-D

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1953
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 55 cents (paper cover)
CONTENTS

Page

Abstract—_. ——————— ___ —— ___________________________________________ ——— _____ 45

Introduction.________________________________________________________________________________________________ 45

Stratigraphy of Mosby sandstone member of Colorado shale--__-_-_____-_-_-_______-_-_-_____---_-_-_-----------_-_ 45

Age of Mosby sandstone member________________________________________________________________________________ 46

Localities from which fossils have been collected_______________________________________________________-_______-___ 47

Description of species._________________________________________________________________________________________ 47

References.___________________________________________________________________________________________________ 54

Index._______________________________________________________________________________________________________ 55

ILLUSTRATIONS

PLATES 6- 9. Afeioicoceras_____________________________________________________________________________ Follows index

10-12. Dunveganoceras. __________________________________________________________________________ Follows index

FIGURE 3. Whorl sections of Dunveganoceras. _____________________________________________________________________ 53

in

2207S9—52

CENOMANIAN AMMONITE FAUNA FROM THE MOSBY SANDSTONE OF CENTRAL MONTANA

By W. A. COBBAN

ABSTRACT

The Mosby sandstone member of the Colorado shale contains 

an ammonite fauna consisting of two new species of Metoicoceras 

and one new species and one new subspecies of Dunveganoceras. 

Associated fossils include gastropods in great abundance but of 

little variety, and a few pelecypods. A very late Cenomanian 

age is assigned. The fauna is unknown elsewhere in the United 

States except for one possible occurrence in north-central Wyoming. Species of Dunveganoceras closely related to those of the 

Mosby sandstone member have been described from the Dunvegan and Smoky River formations of northwestern Alberta and 

northeastern British Columbia.

The Mosby sandstone member is fine to very fine-grained calcareous sandstone of shallow water origin. A section measured 

at Mosby, where the Colorado shale is 1,930 ft thick, and the 

Mosby member lies 743 ft below the top, is recommended as 

the type section.

INTRODUCTION

The Mosby sandstone member of the Colorado shale 

contains the ammonite genus Metoicoceras, represented 

by the new species M. mosbyense and M. muelleri, and 

the genus Dunveganoceras, with the new species D. 

parvum and the new subspecies D. aTbertense montanense. This is a curious mingling of a southern genus 

(Metoicoceras) and a northern genus (Dunveganoceras). These are the only ammonite genera that have 

been found in the member. The fauna is of further 

interest in that it represents the youngest of the Cenomanian zones recognized in the western interior of the 

United States.

Ammonites from nine localities were studied. Metoicoceras is represented by parts of 75 individuals and 

Dunveganoceras by about 50. Most of the material 

was collected by Mr. Oscar O. Mueller, attorney at law, 

of Lewistown, Montana, who kindly donated his collections to the United States Geological Survey. The 

photographs were made by Mr. Nelson W. Shupe of the 

Geological Survey. The types are deposited at the 

United States National Museum.

STRATIGRAPHY OF MOSBY SANDSTONE MEMBER OF 

COLORADO SHALE

The Mosby sandstone member of the Colorado shale 

was named by Lupton and Lee (1921, p. 263) for exposures near Mosby P. 0. on the Musselshell River in eastcentral Montana. There the Colorado shale is 1,930 

ft thick, and the Mosby sandstone member lies 743 ft 

below the top.

The member is exposed extensively on the Cat Creek 

and Devils Basin anticlines and in the intervening area. 

It also crops out on the flanks of the Little Rocky Mountains and the Judith Mountains.

The member is chiefly light-gray fine to very finegrained calcareous sandstone that commonly has a concretionary habit. It ranges from massive to shaly in 

short distances and shows cross bedding and ripple 

marks. The sandstone is hard and forms an easily recognized low ridge or hogback rising above the softer 

Colorado shale. At the type locality the member consists largely of two 5.5-ft sandstone beds separated by 

11 ft of sandy shale.

Fossils, chiefly gastropods, are locally very abundant, 

apparently concentrated by current action (pi. 7, fig. 1). 

A smooth gastropod, Pseudomelania hendricksoni 

Henderson, forms the bulk of the fossils, with many 

concretions composed almost entirely of this species. 

Several other gastropod genera, including ornate forms, 

are present. Pelecypods are limited to Eaeogyra columbeUa Meek, TrigonocaUista orbiculata, (Hall and 

Meek), and undescribed species of Gervillia, Inoceramus, and Gryphaea. Of these, only Trigonocallistaorbiculata is abundant. Ammonites, which are relatively scarce, are represented by Metoicoceras and Dunveganoceras. The fauna shows a blending of northern 

and southern types. Metoicoceras and Exogyra, colum* 

bella are widely distributed from central Montana 

south into Texas, but are unknown in Canada, whereas 

Dunveganoceras is a northern genus that is unkhbwn 

south of central Wyoming.

The following stratigraphic section, measured east 

of the Musselshell River from %-mile east to %-mile 

north of Mosby Post Office, in S1/^ sec. 2 and N^.sec. 

11, T. 14 N., R. 30 E., Garfield County, is recommended 

as the type section for the Mosby sandstone member. 

Descriptions of part of the Colorado shale above and 

below the Mosby member are included to show the 

lithologies of adjoining strata. 

Beds equivalent to the lower part of the Carlile shale.

Unit Fee* 

23. Shale, dark bluish-gray; forms dark outcrops

bare of grass but with abundant trees——— 36.0 

22. Bentonite, creamy-yellow———————————— 0.5

45
46 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

Beds equivalent to the lower part of the Carlile 

shale—Continued

Unit Feet 

21. Shale, dark-gray; weathers orange-brown; 

contains lenses as much as 1.5 in. thick of 

tan-weathering fossiliferous limestone. Contains fossils of Fairport age. (U.S.G.S. .. - 

Mes. loc. 21398) ; Inoceramus cf. /. laMatus 

(Schlotheim), Ostrea n. sp., Collignoniceras 

woollgari var. praecoa Haas, C. woollgari 

var. intermedium Haas, Scaphites patulus 

Cobban, Isurus cf. /. appendiculatus (Agassiz), Isurus cf. /. semiplicatus (Agassiz), 

Squalicorax falcatus (Agassiz), Ptychodus 

whipptei Marcou______——_—_———— 5. 6 

20. Bentonite, greenish-gray_______———— 0.2

19. Shale, dark-gray; weathers orange brown; 

contains a few layers of limestone less than 

% -in. thick_____________-___— 3.0 

18. Bentonite, gray and greenish-gray, finely

micaceous; weathers whitish_———_———— 1.0 

17. Limestone and shale, gray-—————————— 0.1 

16. Shale, black-gray_________________ 0.2 

15. Bentonite, creamy and gray______________ 0.2

14. Limestone and shale, gray; weathers orange 

brown; limestone layers not more than 2 in. 

thick; contains a small species of smooth 

oyster and fish scales, bones, and teeth___ 1.3 

Beds equivalent to the upper part of the Greenhorn 

formation.

13. Shale, gray, calcareous; weathers creamy 

white; upper part contains a few whiteweathering limestone concretions______ 15. 5 

12. Bentonite, creamy-white, stained rusty by 

limonite; contains at base a few whiteweathering limestone concretions_____ 2.8 

11. Shale, dark-gray; weathers medium gray; 

noncalcareous in lower part but slightly calcareous in upper; contains a few thin shaly 

siltstone and very fine-grained calcareous 

sandstone layers________________ 3. 5 

10. Shale, gray; contains closely spaced gray calcareous concretions that weather pale lavender gray and contain veins of white, yellow, 

and brown calcite_______________ 1.0 

Beds equivalent to the middle part of the Greenhorn 

formation.

9. Shale, dark bluish-gray, noncalcareous_____ 7.5

Mosby sandstone member.

8. Sandstone, light-gray, fine to very fine-grained, 

thin-bedded to shaly, soft, more or less argillaceous ; contains dark shale partings and a 

few buff-weathering calcareous concretions 

that are septarian with brown, yellow, and 

white calcite. Top of bed contains a sprinkling of black chert pebbles as much as %-in. 

in diameter. Unit weathers buff gray to tan, 

and forms an inconspicuous outcrop. Sparingly fossiliferous (U.S.G.S. Mes. loc. 

21397) ; Triffonocallista orbiculata (Hall 

and Meek)______________________ 5.6

7. Shale, dark bluish-gray, noncalcareous; contains numerous very fine-grained sandy partings in lower part______—_______ 11. 0 

6. Sandstone, light-gray, very fine-grained, thinbedded, ripple-marked, cross-bedded; contains dark shale partings particularly in

Beds equivalent to the middle part of the Greenhorn

formation—Continued 

Mosby sandstone member—Continued

Unit Feet 

upper 2 ft.; commonly passes laterally into 

buff-weathering silty, calcareous concretions. 

Unit weathers tan and forms a conspicuous 

ledge. Marine gastropods and pelecypods 

abundant in distantly spaced calcareous 

concretionary masses. (U.S.G.S. Mes. loc. 

21396) ; Gervillia sp., Inoceramus aff. /. fraffilis Hall and Meek, Gryphaea n. sp., Exogyra columlella Meek, Triffonocallista or~biculatd (Hall and Meek), Pseudomelania 

hendricksoni Henderson, Lunatia cf. L. dakotensis Henderson, Gyrodes conradi Meek, 

Anchuraf sp., Trachytriton n. sp., Metoico- ' 

ceras mosbyense Cobban, Dunveffanoceras 

albertense subsp. montanense Cobban___ 5. 6

5. Shale, dark-gray; contains sandy layers up to

1 in. thick_____________________ 3. 5

4. Sandstone, gray, very fine-grained, thinbedded ; contains dark shale partings_—— 1.5 

Beds probably equivalent to part of the Belle Fourche 

shale.

3. Shale, dark bluish-gray; contains a few soft 

very fine-grained gray sandstone layers as 

much as 2 in. thick. Few gypsum-encrusted 

pelecypods (U.S.G.S. Mes. loc. 21395); Gryphaea sp., Exogyra columbella, Meek———__ 23. 5 

. , 2. Shale, dark bluish-gray; contains large widely 

spaced calcareous concretions that weather 

bluish gray and buff and contain veins of 

brown and yellow calcite__________ 1.5

1. Shale, dark bluish-gray____________ 10.0+

AGE OF MOSBY SANDSTONE MEMBER OF COLORADO

SHALE

The ammonites of the Mosby sandstone are not known 

with certainty outside central Montana. The nearest 

similar fauna occurs in a calcareous sandy unit in the 

Frontier formation about 100 ft below the Wall Creek 

("First") sandstone member on the east flank of the 

Kaycee anticline, 1.5 miles south of Kaycee, Wyo. The 

collection from that locality (U.S.G.S. Mes. loc. 23456) 

consists of fragments of 10 or 11 specimens of a species 

of Metoicoceras. Many of these fragments match specimens of M. mosbyense, n. sp., of comparable size in the 

stoutness of the whorls and coarseness and density of 

ribbing. A few fragments suggest more slender individuals than are known from the Mosby member. The 

lack of any specimens referable to the common Mosby 

species, M. muelleri, n. sp., or to the Mosby Dunveganoceras is difficult to explain.

Just below the main group of sandstone beds in the 

Frontier formation (about 200 ft below the top) on 

the south side of the Bighorn Mountains, four miles 

east of Arminto, Wyo. (U.S.G.S. Mes. loc. 23492), is 

a unit of sandy shale containing Dunveganoceras cf. 

D. conditum Haas and a species of Metoicoceras closely 

related to M. mosbyense, n. sp. Up to a diameter of 

60 to 70 mm this species seems to be identical to M.
CENOMANIAN AMMONITES FROM THE MOSBY SANDSTONE 47

mosbyense, but at greater diameters the whorls are much 

more densely ribbed. This densely ribbed Metoicoceras and fragments of a Dunveganoceras that may be 

D. conditum Haas also have been found together in 

the Frontier formation on the east side of the Bighorn 

Mountains near Buffalo, Wyo.

The other species of Metoicoceras and Dunveganoceras from the western interior differ so much from 

the Mosby forms that there is no question that they 

mark separate f aunal zones. A continuous sequence of 

rocks bearing these genera has not been found at any 

one locality, but a consideration of two fairly fossiliferous sections makes possible the recognition of definite zoning of the Metoicoceras-Dunveganoceras faunas. 

On the north flank of the Black Hills the Greenhorn 

formation contains at its base Metoicoceras cf. M. praecox Haas and Dunveganoceras cf. D. pondi Haas, and 

near the top, Metoicoceras whitei Hyatt. Associated 

with M. whitei are Sciponoceras gracile (Shumard) 

and Scaphites delicatulus Warren. Near Buffalo, on 

the east flank of the Bighorn Mountains, Sciponoceras 

gracile and Scaphites delicatulus occur together in the 

shale less than 100 ft above the Frontier formation, 

whereas Metoicoceras cf. M. praecox is present in sandstone about 120 ft below the top of the Frontier formation. Concretions in the upper 50 ft of the Frontier 

formation contain the densely ribbed Metoicoceras 

and fragments of Dunveganoceras cf. D. conditum. 

From these two sections it is apparent that three Metoicoceras levels can be recognized which in ascending 

order are (1) M. praecox, (2) a densely ribbed new 

species, and (3) M. whitei. Of these species the Mosby 

forms are closely related to the densely ribbed species. 

This close age assignment is also supported by the 

Mosby species of Dunveganoceras, which are much 

nearer D. conditum than D. pondi. Inasmuch as the 

costal cross section of the ultimate whorl is quadrate 

for D. pondi, round for D. conditum, and ogival for 

D. albertense montanense, it is probable that the Mosby 

species is a little younger than D. conditum, assuming 

the evolutionary trend was from a truncate to a sharply 

arched venter. It thus appears that the following four 

Metoicoceras levels can be recognized in the MontanaWyoming area:

M. whitei (youngest zone)

M. mosbyense, n. sp

M. n. sp., (densely ribbed species)

M. praecox (oldest zone)

Dunveganoceras albertense montanense, n. stibsp., the 

common representative of this genus in the Mosby sandstone member, so closely resembles D. albertense (Warren) that an approximate time equivalence seems certain. The Mosby form, which differs in small details 

from Warren's species, seems best to be regarded as a 

geographic subspecies. D. albertense is considered by

Warren and Stelck (1940, p. 149) to be Upper Cenomanian. This assignment seems reasonable and is further supported by the position of the Mosby fauna in 

regard to the Metoicoceras whitei zone. The zone is 

considered to mark the base of the Turonian (Spath, 

1926, p. 80; Muller and Schenck, 1943, fig. 6). A late 

Genomanian age for the Mosby fauna is suggested also 

by the presence of at least four older Cenomanian 

faunas in the western interior (Cobban, 1951, p. 2197, 

fig. 2).

LOCALITIES FROM WHICH FOSSILS HAVE BEEN 

COLLECTED

Ammonites have been collected from the Mosby sandstone member of the Colorado shale at the following 

localities in central Montana, for which the U. S. Geological Survey Mesozoic locality number, name of collector, and year of collection are given:

10976. A. J. Collier, 1921. About 7.5 miles northeast of

Zortman, in sec. 13, T. 26 N., R. 25 E., Blaine

County. 

18741. J. B. Reeside, Jr., 1938. Bull Creek, west side of

Cyprian dome, on southwest flank of Little Rocky

Mountains, in sec. 35, T. 25 N., R. 23 E., Phillips

County. 

21396. W. A. Cobban, 1948. About %-mile northeast of

Mosby, in the NE% sec. 11, T. 14 N., R. 30 E.,

Garfield County.

21484. O. O. Mueller, 1948. Near south side of spillway of 

Yellow Water Reservoir, in the SW% sec. 7, T. 

13 N., R. 26 E., Petroleum County.

21485. O. O. Mueller, 1948. About %-mile north of Yellow 

Water Reservoir, in the SW% sec. 1, T. 13 N., R. 

25 E., Petroleum County.

21486. O. O. Mueller, 1948. About 1 mile southwest of 

Yellow Water Reservoir, in the NE% sec. 14, T. 

13 N., R 25 E., Petroleum County.

21487. O. O. Mueller, 1948. About 1.5 miles south-southwest 

of Yellow Water Reservoir, in the NW% sec. 23, 

T. 13 N., R. 25 E., Petroleum County.

21488. O. O. Mueller, 1944. One mile south-southeast of 

Yellow Water Reservoir, in the SE%SE% sec. 14, 

T. 13 N., R. 25 E., Petroleum County.

21490. O. O. Mueller, 1944. South side of Yellow Water 

Reservoir, in the SW% sec. 7, T. 13 N., R. 26 E., 

Petroleum County.

21662. W. A. Cobban, M. M. Knechtel, S. H. Patterson, W. T. 

Pecora, 1948. East Side of Morrison dome, on 

south flank of Little Rocky Mountains, in the 

SEi4XW% sec. 7, T. 24 N, R. 25 E., Phillips 

County.

21955. W. A. Cobban, C. T. Moore, O. O. Mueller, 1949. Six 

miles west of Winnett, in sec. 1, T. 14 N., R. 25 E., 

Petroleum County.

DESCRIPTION OF SPECIES

Family Acanthoceratidae de Grossouvre, 1894

Subfamily Metoicoceratinae Hyatt, 1903

Genus Metoicoceras Hyatt, 1903

1903. Metoicoceras Hyatt, U. S. Geol. Survey Mon. 44, p. 116. 

1920. Metoicoceras Hyatt. Bose, Texas Univ. Bull. 1856, p. 200 

(dated 1918, issued 1920).
48 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

1928. Metoicoceras Hyatt. Adkins, Texas Univ. Bull. 2838, p.

248. 

1931. Metoicoceras Hyatt. Reeside and Weymouth, U. S. Nat.

Museum Proc., vol. 78, art. 17, no. 2860, p. 19. 

1938. Metoicoceras Hyatt. Roman, Les Ammonites jurassiques

et cretacees, p. 437. 

1942. Metoicoceras Hyatt. Moreman, Jour. Paleontology, vol.

16, no. 2, p. 210. 

1944. Metoicoceras Hyatt. Shimer and Shrock, Index fossils

of North America, p. 561.

Metoicoceras mosbyense Cobban, n. sp. 

Plate 6, figures 1-14; plate 7, figures 1-3

Shell large for the genus, laterally compressed, moderately involute; umbilicus about Ta7 the diameter in 

young stages, gradually widening to y5 the diameter in 

older stages. Flanks flattened; venter rounded to diameter of 10 mm, flattened or excavated between diameters of 10 to 120 mm, and rounded beyond 120 mm. 

Sculpture consists of straight to slightly sinuous ribs, 

less than 36 per whorl, that bear spirally elongated 

ventral nodes to a diameter of 120 mm, and conical 

ventrolateral nodes and bullate umbilical nodes to a 

diameter of 45 mm. Suture complex for the genus.

At the earliest stage observed, about a diameter of

4 mm, the whorls have a broadly rounded venter, sharply 

rounded ventrolateral shoulder, and flattened flanks. 

At this early stage the sculpture consists of a row of

5 or 6 large ventrolateral nodes per half whorl that are 

conical, sharp, and directed straight out. Opposite 

nodes are connected by a low forward-arched rib bearing on each side of the midline of the venter an inconspicuous low conical ventral node that is barely discernible.

By a diameter of 6 mm the ventral nodes are distinct. 

Each node of a pair is separated from the other by a 

distance a little less than the distance between a ventral 

node and the nearest ventrolateral node. Each ventrolateral node passes into a low inconspicuous rib that 

trends straight across the flank to the umbilical shoulder. The cross section is rather quadrate with about 

equal distance from the middle of a ventrolateral node 

to the umbilicus and to the ventral node on the opposite 

side of the venter (pi. 6, fig. 14).

At a diameter of 10 mm the middle of the venter is 

flattened and bordered by the small ventral nodes, which 

become slightly elongated spirally. The venter narrows and the flanks lengthen radially. The ventrolateral nodes are much reduced in size, becoming; more j o

nearly the size of the ventral nodes. Between the ventrolateral nodes on the flank are smaller intercalated 

ventrolateral nodes. Each ventrolateral node is connected to a ventral node by a low forward inclined rib. 

The larger ventrolateral nodes terminate low straight 

flank ribs that extend to the umbilical shoulder. These 

ribs almost disappear midway on the flank, but become 

stronger again near the umbilicus.

Between diameters of 10 and 15 mm the ventral and 

ventrolateral nodes become of equal size. The flank 

continues to widen and the venter narrows so that at a 

diameter of 15 mm the flank is as wide as the distance 

between opposite ventrolateral nodes. Each pair of 

ventral nodes is connected by a broad straight rib. At 

a diameter of 15 mm a half whorl has about 11 ventral 

ribs.

By a diameter of 20 mm the flank is wider than the 

distance between opposite ventrolateral nodes. These 

nodes are not placed as far behind the ventral nodes as 

in younger stages. The umbilical ribs become stronger 

and even elevated into radially elongated nodes. The 

density of ribbing increases to 12 ventrolateral ribs per 

half whorl. Two ventrolateral ribs are present to each 

umbilical rib.

Between diameters of 20 and 45 mm the whorls continue to become more compressed laterally with the 

venter progressively narrowed. The ventral nodes become more spirally elongated, whereas the ventrolateral 

nodes gradually decrease in size and finally disappear at 

a diameter of about 45 mm. The ribs become straight 

and strong, attaining their maximum strength at a 

diameter of about 35 mm. The density of ventrolateral 

ribs increases from 13 to 15 per half whorl.

Between diameters of 45 and 90 mm. the venter between the spirally elongated nodes becomes smooth or 

only weakly undulated. The sculpture becomes weak 

and the umbilical nodes gradually disappear. The 

number of ventrolateral ribs increases from 14 to 18 per 

half whorl.

Between 90 and 110 mm diameter there is a marked 

decrease in rib density from 18 to 12 per half whorl. 

The ventral nodes weaken and the venter becomes less 

excavated. These nodes disappear between diameters 

of 110 and 130 mm, and the venter rounds and becomes 

broadly undulated by the ribs widening ventrally and 

crossing the venter as broad swellings. Beyond 130 

mm diameter the ribs, which have been straight since 

the loss of the ventrolateral nodes, may arch forward 

on crossing the venter. The number remains low— 

about 11 or 12 per half whorl.

Complete senile specimens were not observed. Fragments of the largest specimens suggest that some individuals attained diameters of more than 200 mm and 

possibly as much as 250 mm.

The holotype, an incomplete specimen 180 mm in 

diameter, has an umbilical width of about 36 mm (y5 

of diameter), a whorl thickness of about 55 mm (30 per 

cent of diameter), and a rib density of 12 per half 

whorl. It is septate to the last quarter whorl.

Dimensions in millimeters, ratios (in parentheses) of 

the dimensions to the diameters, and the number of ribs 

per half whorl of the types are as follows:
CENOMANIAN AMMONITES FROM THE MOSBY SANDSTONE 49

Kind of specimen and U.S.N.M. number

Paratype 10831 6a___ _ __ _ ___ __ _ _ _____

Paratype 108316b__ ____ _ _ _ __ __ _ __

Paratype 108317a_ ____ ______ ________ ___ _

Paratype 108319a_ ____ _ __ __ __ __ _ _____

Paratype 108318a____. ____ ____ __ _________

Do_____ _ ________ _ ___________________

Do________ _______ _ __ _ __ _____

Paratype 108318b__ _ __ ____ _____ _____ _ _

Paratype 1083 17b__ ___ _ __ _ _ _ __ _

Do___ _ _ _ _______ _

Paratype 108319b._. __________________

Holotype 108315. _ __________________

Diameter 

(mm)

13. 5 

20.0 

37.0 

39.0 

42. 3 

58.0 

87.0 

60.0 

57.0 

79.5 

110.0 

180.0

Umbilical width

1. 5 (0. 11) 

2. 0 ( . 10) 

2. 5 ( . 07) 

4. 7 ( . 12) 

4. 2 ( . 10) 

6. 6 ( . 11) 

10. 5 ( . 12) 

5.0 ( .09) 

4.8 ( .09) 

6. 4 ( . 08) 

12. 7 ( . 12) 

36.0 ( .20)

Whorl height

7. 4 (0. 55) 

12.0 ( .60) 

21. 0 ( . 57) 

21. 0 ( . 54) 

23. 2 ( . 55) 

31.6 ( .54) 

48. 2 ( . 55) 

34. 7 ( . 58) 

32. 3 ( . 57) 

45. 5 ( . 57) 

58. 4 ( . 53) 

82.0 ( .45)

Whorl thickness

6.2 

7.8 

16.0 

15. 2 

14.8 

19.9 

26.2 

17.7 

18. 7 

23.0 

36.0 

55.0

0.46) 

.39) 

.34) 

.39) 

.35) 

, .34)

: .so) 

; .29) 

: .33) 

: .29) 

: .33) 

; .30)

Ribs per half 

whorl

11 

13 

10 

12 

13 

15 

18 

14 

16 

17 

12 

12

The nearest described American species is probably 

Metoicoceras acceleratum Hyatt (1903, p. 127, pi. 14, 

figs. 11-14) from the Eagle Ford shale of Texas. That 

species is known only from immature specimens that 

closely resemble the comparable young stages of M. 

mosbyense but lack umbilical nodes and lose the ventrolateral nodes at a smaller diameter. Metoicoceras 

whitei Hyatt (1903, p. 122, pi. 13, figs. 3-5; pi. 14, 

figs. 1-10, 15) from the basal Turonian of the Western 

Interior and Texas is readily distinguished from M. 

mosbyense by maintaining ventrolateral nodes out to 

a much greater diameter. Likewise, M. swallovii 

(Shumard) (1859, p. 591), M. swallovii var. macrum 

Stephenson (1952, p. 209, pi. 51, figs. 4-7), M. crassicostae Stephenson (1952, p. 210, pi. 58, figs. 6-8), M. 

latoventer Stephenson (1952, p. 209, pi. 53, figs. 1-9; 

pi. 54, figs. 9-11), M. giblosum Hyatt (1903, p. 121, pi. 

15, figs. 5-8), and M. ornatum Moreman (1942, p. 211, 

pi. 32, fig. 4, text fig. 2c), all from the Woodbine and 

Eagle Ford formations of Texas, carry the ventrolateral nodes to much greater diameters than does M. 

mosbyense. The species from the Woodbine formation 

(M, swallovii, M. latoventer, and M. crassicostae] are 

also more evolute. The specimen from the Coleraine 

formation in Minnesota figured by Bergquist (1944, 

p. 30, pi. 10, figs. 10-12) as Metoicoceras aff. M. swallovii 

(Shumard) is considerably stouter than M. mosbyense 

and the ventrolateral nodes persist to greater diameters. 

The specimens described by Haas (1949, pp. 15-20, pis. 

5-7, text figs. 5-9) as Metoicoceras whitei subsp. praecox from the lower part of the Cody shale near Greybull, Wyoming, are much more evolute and the loss 

of nodes and the rounding of the venter occurs much 

earlier. Haas's form is very different from M. whitei, 

occurs in older strata, and should be regarded as a 

separate species.

From the Upper Cenomanian or Lower Turonian of 

Coahuila, Mexico, Bose (1918, p. 205, pi. 12, figs. 1-3) 

figured as "Metoecoceras sp. nov." a specimen about as 

stout as M. mosbyense of comparable diameter with 

similar rib spacing and with every second or third rib 

extending to the umbilicus. It differs, however, by its 

flexuous ribbing and wider umbilicus. Bose's specimen

was later assigned by Jones to the new species M. bosei 

Jones (1938, p. 127, pi. 10, figs. 1-3), the holotype of 

which has ventrolateral nodes persisting to a much 

greater diameter than on M. mosbyense.

Of the European species M. mosbyense has the same 

number and arrangement of ribs and nodes as M. pervinquierei (Grossouvre) (1912, p. 19, pi. 2, fig. 3), but 

differs by its much narrower umbilicus. Metoicoceras 

dumasi (Grossouvre) (1912, p. 23, pi. 2, fig. 1) seems 

close to M. mosbyense although it is stouter and the 

ventrolateral nodes persist to a greater diameter. 

Metoicoceras petraschecki (Grossouvre) (1912, p. 22, 

pi. 2, fig. 2), M. gourdoni (Grossouvre) (1912, p. 20, 

pi. 1, fig. 1), and M. antiqimm Karrenberg (1935, p. 

139, pi. 31, fig. 13) are more evolute. The specimens 

figured by Petrascheck (1902, p. 140, pi. 7, figs. 3-5, 

text fig. 5) as Pulchellia gesliniana (d'Orbigny) from 

the Upper Cenomanian of Saxony closely resemble M. 

mosbyense in its younger stages, but the Saxon species 

loses its ventral nodes at a much smaller diameter and 

the ribs are more flexuous.

Types: Holotype, U.S.N.M. 108315; figured paratypes, U.S.N.M. 108316a-b, 108317a, 108318a, 108320; 

unfigured paratypes, U.S.N.M. 108317b, 108318b, 

108319a-b.

Occurrence: U.S.G.S. Mes. loc. 21396, 21484-21487, 

21490, 21662, 21955.

Metoicoceras muelleri Cobban, n. sp. 

Plate 6, figures 15, 16; plate 8, figures 1-7; plate 9

Shell large for the genus; larger, thinner, more involute, and smoother than M. mosbyense. Flanks flattened ; venter rounded to diameter of 10 mm, flattened 

or excavated between diameters of 10 and 140 mm, and 

gradually rounded between 140 and 190 mm. Ribs 

weak, straight to sinuous, and as numerous as 46 per 

whorl. Ventrolateral nodes disappear by diameter of 

11 mm and ventral nodes are lost between diameters of 

100 and 150 mm. Suture complex for the genus.

The growth stages are shown by paratype U.S.N.M. 

108322a", an adult specimen of 215 mm diameter. This 

specimen was broken up and the inner whorls freed to 

a diameter of about 9 mm.
50 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

At a diameter of 9 mm the whorl cross section is 

nearly quadrate, with broadly rounded venter, sharply 

rounded ventrolateral shoulder, and flat, nearly smooth 

flanks. On each side of the venter is a row of small 

rounded nodes. The nodes of a row occur in pairs as 

shown by Hyatt (1903, p. 119, pi. 11, fig. 14) for the 

early stages of Metoicoceras swallovii (Shumard). 

Five ventrolateral nodes are present on the half whorl 

of 9 mm diameter. At that diameter they are rounded 

and as large as the ventral nodes, but below that diameter they are larger than the ventral nodes and quite 

pointed. Each ventrolateral node is situated back from 

the apicad node of a ventral pair by an angle of about 

30 degrees, and is separated from it by a distance comparable to that between the two rows of ventral nodes. 

A low inconspicuous straight rib trends from each ventrolateral node about half way to the umbilicus.

Between 9 and 11 mm diameter a small node appears 

in the space between the pairs of nodes of a ventral row, 

and by 13 mm all ventral nodes are of equal size. The 

ventrolateral nodes rapidly become smaller than the 

ventral nodes and disappear by a diameter of 11 mm. 

From each ventral node a small rib extends back to the 

ventrolateral node, or after that node disappears, to the 

position where it would occur, then bends and trends 

straight toward the umbilicus, although rapidly weakening and disappearing high on the flank.

Between 9 and IT mm diameter the venter gradually 

narrows and the flank widens. At a diameter of IT mm 

the ventral nodes elongate spirally, and the ribs number 

14 per half whorl. Between IT and 24 mm the venter 

continues to narrow, the flanks continue to widen, the 

whorls become more laterally compressed, and the ventrolateral margin shifts to the position of the ventral 

nodes. The ribbing becomes more pronounced and the 

density increases to 15 ribs per half whorl. The ribs, 

which are somewhat sigmoidal, extend gradually farther 

down the flank.

Between 24 and 40 mm the rib density increases to 

16 per half whorl, and the ribbing attains its maximum 

strength. The ribs are sigmoidal, strongest near the 

venter, and about every third one extends to the umbilicus. The venter, which is flat, has an excavated 

appearance owing to the rim of closely spaced spirally 

elongated ventral nodes. On this specimen the venter

has a slight constriction just ahead of the nodes terminating those ribs that extend to the umbilicus. There 

are six constrictions on the half whorl of 40 mm 

diameter.

At diameters greater than 40 mm the sculpture gradually weakens and the ribs become straight and broad. 

By a diameter of 100 mm they are so broad and flat that 

the spaces separating them are only half as wide. The 

ventral nodes are low and rather poorly denned.

Between diameters of 135 and 150 mm the rib density 

is reduced to 10 per half whorl, the nodes disappear, 

and the venter is flat but no longer excavated. However, the ribs become stronger and cross the venter as 

broad folds. Between 150 and 200 mm the venter gradually rounds, the ribbing remains strong, and the intercoastal areas become as broad as the ribs. There are 

about 10 ribs per half whorl. At diameters greater 

than 200 mm the ribs become weaker, narrower, and 

more numerous. At a diameter of 210 mm the rib count 

increases to 14 per half whorl.

Metoicoceras mueUeri becomes progressively more 

evolute throughout its growth after the first few whorls. 

Measurements of 21 specimens show a gradual increase 

in the ratio of the umbilical diameter to the diameter 

of the shell from 6 percent at a shell diameter of 62 to 

68 mm to 21 to 24 percent in shells more than 230 mm in 

diameter. The whorls are at first stout with quadrate 

cross sections, but rapidly become laterally compressed 

as growth continues. The ribbing shows a progressive 

increase in number per half whorl from 13 at shell 

diameter of 15 mm to 23 at a diameter of 94 mm. It 

abruptly decreases to 11 to 15 between 116 and 118 mm 

diameter, and then gradually declines to about 10 at 

150 mm. The number remains low to a diameter of 

about 210 mm, but at greater diameters the rib count 

increases to 15 at a diameter of 300 mm.

About seven volutions make up an adult shell. The 

species is large for the genus. One of the largest specimens at hand, unfigured paratype U.S.N.M. 108325, 

attains a diameter of 301 mm. The body chamber is 

incomplete, but a full half whorl is preserved.

The dimensions in millimeters ratios of the dimensions to the diameters, and the number of ribs per half 

whorl of the types are as follows:
CENOMANIAN AMMONITES FROM THE MOSBT SANDSTONE 51

Kind of specimen and U.S.N.M. number

Paratype 108322a_ _______ ___ _ ___ __ ___ _

Do____ __ ______ _ _____________________

Do______ _ ____________________________

Do. _____________________________________

Do. _____________________________________

Do______ _ ______ _ _

Do. ____________________________________

Do. _____________________________________

Do. ____________________________________

Paratype 108323a __ __ ______ ______ ___ ___

Paratype 1O8324. __ ____________ _ _______ _

Paratype 108323b___ __ __-_-_____-___--______

Do. _____________________________________

Paratype 108322b ___.__-_.___ _______ _ _____

Do___ ___ _______ _ _ ___ __ ___ __ _

Paratype 108322c _ _____ _______ _.__ __..___

Do. _ _______ ___ _ __ _ _ ___ ______

Paratype I08322d__ _____ _________ _________

Do. _____________________________________

Holotype 108321 __ _ ____ .... ______ ...

Do. ___________ _ _______________________

Paratype 108322e __ __ ___________ _ _____ _

Paratype 108325___ __ _________ _____ _ _

Diameter

14.5

17.0

20.0

39. 3

50.0

135. U

150.0

170.0

210.0

43.5

60. 5

81.5

113.0

92. 4

147. 3

62. 5

151.0

151. 3

190.0

118.0

222.0

254. 0

301.0

Umbilical width

4. 0 (0. 10)

4.0 ( .09)

4. 3 ( . 07)

11. 5 ( . 10)

Q 4 ( W)

21. 3 ( . 14)

4.0 ( .06)

22. 5 ( . 15)

21. 0 ( . 14)

7. 2 ( . 06)

36. 0 ( . 16)

56. 3 ( . 22)

65.0 ( .21)

Whorl height

8.2 (0.57)

22. 5 ( . 57)

24. 3 ( . 56)

34. 5 ( . 57)

62. 0 ( . 55)

52. 1 ( . 56)

73. 1 ( . 49)

36. 7 ( . 59)

75. 0 ( . 49)

74. 5 ( . 48)

68. 0 ( . 58)

107. 0 ( . 48)

111.0 ( . 44)

132. 0 ( . 44)

Whorl thickness

12. 8 (0. 33)

12. 6 ( . 29)

17. 6 ( . 29)

29. 0 ( . 26)

23. 2 ( . 25)

37. 0 ( . 25)

17.0 ( .27)

35. 5 ( . 23)

35. 0 ( . 23)

28. 6 ( . 24)

51. 3 ( . 23)

55. 7 ( . 22)

68. 5 ( . 23)

Ribs per half 

whorl

13

14

15

16

16

10

10

10

14

18

19

22

18

12

19

9

10

13

15

10

13

15

Metoicoceras muelleri can be ordinarily readily distinguished from its associate, M. mosbyense, by its thinner whorls', weaker sculpture, and persistency of a 

flattened venter to a much greater diameter. It is also 

more involute, lacks umbilical nodes, and loses the 

ventrolateral nodes at a much younger stage. There are 

a few specimens with characters of each species. These 

may have a combination of the whorl and umbilical proportions of M. muelleri and the coarse sculpture of M. 

mosbyense, or the ventrolateral nodes may persist out to 

diameters of 20 or 30 mm, which is greater than on typical M. muelleri and smaller than on M. mosbyense.

Metoicoceras muelleri differs in many respects from 

other American species with thin whorls and weak 

sculpture. Metoicoceras acceleratum Hyatt (1903, p. 

127, pi. 14, figs. 11-14), M. kanabense Hyatt (1903, pi. 

15, figs. 9-11), and M. irwini Moreman (1927, p. 92, 

pi. 13, figs. 3, 4) are all weakly ribbed compressed forms 

that lack umbilical nodes, but these species retain their 

ventrolateral nodes to greater diameters than does M. 

muelleri. The compressed specimen with flexuous ribs 

from Utah figured by Stanton (1893, p. 168, pi. 38, figs. 

1, 2) as "Buchiceras swallovi" differs from M. muelleri 

by maintaining ventrolateral nodes out to a greater 

diameter. The specimen described from New Mexico 

by Herrick and Johnson (1900, p. 213, pi. 27, figs. 3, 4) 

as "Buchiceras swallovi var. puercoensis" shows some 

resemblance to M. muelleri by its fairly smooth shell, 

but the New Mexico form is stouter and has smaller 

umbilicus, fewer ribs, and simpler suture.

The nearest described European species is Metoicoceras ~bureaui (Grossouvre) (1912, p. 22, pi. 1, fig. 2) 

from the Upper Cenomanian, which seems to differ 

from M. muelleri only by lacking distinct ventral nodes 

and by having the ribs curved back on the outer part of 

the flank. Metoicoceras pontieri Leriche (1905) from

the base of the Turonian of northern France is a thin 

densely ribbed species like M. muelleri that differs 

chiefly by the rounding of the venter at a much earlier 

stage.

The species is named for Mr. Oscar O. Mueller of 

Lewistown, Montana, whose large collections of Mosby 

ammonites made possible this study.

Types: Holotype, U.S.N.M. 108321; figured paratypes, U.S.N.M. 108322c, 108323a-b, 108324; unfigured 

paratypes, U.S.N.M. 108322a-b, 108322d-e, 108325.

Occurrence: U.S.G.S. Mes. loc. 10976, 21484, 21486, 

21487, 21955.

Subfamily Acanthoceratinae Wright, 1951 

Genus Dunveganoceras Warren and Stelck, 1940

1940. Dunveganoceras Warren and Stelck, Royal Soc. Canada,

Trans., 3d ser., vol. 34, sec. 4, p. 149. 

1949. Dunveganoceras Warren and Stelck. Haas, Am. Mus. Nat.

History Bull., vol. 93, art 1, p. 20. 

1951. Dunveganoc&ras Warren and Stelck. Haas, Am. Mus.

Novitates, no. 1490, p. 14.

Dunveganoceras albertense (Warren) subsp. montanense Cobban, 

n. subsp.

Plate 10, figures 1-7; plate 11; text figures 3b-e 

The holotype of Dunveganoceras albertense (Warren) (1930, p. 21, pi. 1, figs. 1, 2) is a large shell of 

350 mm diameter with an umbilical width of 1£0 mm 

(40 percent of diameter). The nodes disappear on the' 

ultimate whorl and the whorl cross section becomes 

ogival. The ribs are strong, straight, and moderately 

spaced, with 18 on the last whorl.

Nearly all the specimens of Dunveganoceras from 

the Mosby sandstone member seem to fall within the 

scope of D. albertense (Warren). The umbilical widths 

are similar, the strength of ribs and nodes seems identical, and the last whorls have about the same number
52 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

of ribs, lose their nodes, and assume an ogival cross 

section. However, there are some differences that seem 

to warrant treating the Mosby form as a subspecies. 

The inner whorls are more densely ribbed, with 16 to 

18 ribs per whorl between diameters of TO and 100 mm 

in comparison with 13 to 14 at similar diameters on 

the holotype of D. albertense; the nodes are lost at a 

smaller diameter; the venter rounds earlier where the 

ribs cross it; and the ultimate whorl is stouter.

The holotype of Dimveganoceras albertense montanens'e is a shell of 320 mm diameter, with umbilical 

width of 140 mm (44 percent of diameter). The last

whorl attains a coastal height of 95 mm and a thickness 

of about 100 mm. About half the body chamber is 

preserved. The nodes are lost by a diameter of 200 

mm, and by a diameter of 240 mm the coastal whorl 

section is distinctly ogival. The ribs, which number 

20 per whorl, are straight and inclined slightly forward. The suture is unusual in that the ventral lobe 

has shifted away from the median plane on the younger 

part of the last septate whorl (pi. 10, fig. 7).

The dimensions in mm, ratios of the dimensions to 

the diameters, and the number of ribs per whorl of 

the types are as follows:

Kind of specimen and U.S.N.M. number

Paratype 108327a_ ______ ____________________

Do

Paratvpe 108328 ____ ___ _ _ _ _ _

Do____ ________

Do_ ____________________________________

Paratvpe 108327b_ _________ _________ _ _ ___

Do

Holotvpe 108326 __ ___

Do_ ________________________________ ___

Paratype 108327c __ _

Diameter 

(mm)

67. 2

91.0

133. 5

185.0

265.0

255.0

310. 0

250.0

320.0

Umbilical width

18. 8 (0. 28)

28.5 ( .31)

45. 0 ( . 33)

61. 0 ( . 33)

95. 0 ( . 36)

96. 0 ( . 38)

122. 0 ( . 39)

100. 8 ( .40)

140. 0 ( . 44)

Whorl height

29. 5 (0. 44)

36. 5 ( . 40)

54. 5 ( .41)

73.3 ( .40)

102. 0 ( . 38)

92. 5 ( . 36)

98. 0 ( . 32)

87. 7 ( . 35)

95. 0 ( . 30)

130.0

Whorl thickness

28. 8 (0. 43)

36. 7 ( . 40)

54. 2 ( . 46)

72. 0 ( . 39)

91. 0 ( . 34)

72. 2 ( . 28)

80. 0±( . 26±)

70.0±( . 28±)

100. 0±( . 31±)

112.0

Eibs per 

whorl

16

17

18

19

18

18

18

20

20

Measurements of 16 specimens show a gradual widening of the umbilicus from 28 percent at a diameter of 

67 mm to 44 percent at a diameter of 320 mm. The 

number of ribs per whorl increases from 16 at diameter 

of 67 mm to an average of 18 at diameter of 150 mm, 

and at all later stages the rib count remains between 18 

and 20. The largest specimen examined (unfigured 

paratype U.S.N.M. 108327c), a fragment of a body 

whorl with a height of 130 mm and thickness of 112 mm, 

indicates that the subspecies attained diameters of more 

than 400 mm.

Types: Holotype, U.S.N.M. 108326; figured paratypes, U.S.N.M. 108327a-b, 108329; unfigured paratypes, U.S.N.M. 108327c, 108328.

Occurrence: U.S.G.S. Mes. loc. 18741, 21396, 21484, 

21486-21488, 21662, 21955.

Dunveganoceras parvum Cobban, n. sp. 

Plate 12, figures 1, 2; text figure 3a

Shell small for the genus, moderately evolute with 

umbilical width about 35 percent of the diameter. 

Whorls stout, about as wide as high; umbilical wall 

-steep ; Hanks broadly rounded; venter of ultimate whorl 

rounded. Sculpture consists of f orwardly inclined ribs, 

which on the septate whorls bear ventral and ventrolateral nodes.

The holotype, an adult shell with a little more than 

half the body chamber preserved, has the following 

dimensions in millimeters:

Diameter: 178

Umbilical width: 62.6 (35 percent of diameter)

Whorl height: 63.4 

Whorl thickness: 65 ±

Whorls below a diameter of 60 mm are not preserved. 

The ribs on the holotype are narrow, inclined forward, 

extended to the umbilical shoulder, and number 19 on 

the last whorl. On the last septate whorl each rib is 

strongly bent forward on leaving the umbilical shoulder, but abruptly curves back a little on the lower part 

of the flank, straightens, and crosses the rest of the flank 

with a forward inclination of about 20 degrees. On 

the body chamber the ribs become straighter and less 

inclined. Up to a diameter of about 70 mm each rib 

terminates in strong ventral and ventrolateral nodes. 

Between diameters of 70 to 90 mm these nodes merge 

into large rounded nodes, and the ribs cross the venter. 

By a diameter of 120 mm the ribs absorb the nodes and 

become high, but flat-crested, on crossing the venter. 

By a diameter of 150 mm both the costal and intercostal 

cross sections of the whorl are rounded on the venter.

This is the smallest known species of Dunveganoceras. It is readily distinguished from D. albertense 

(Warren) by its small size and early loss of nodes. 

The smallest species described from Canada, D. poucecoupense Warren and Stelck (1940, p. 150, pi. 2; pi. 

3, figs. 2, 5), is larger and has a truncate venter. D. 

conditwn Haas (1951, p. 5, text figs. 2-9) from the 

Frontier formation of Wyoming attains a much larger 

size and is more densely ribbed.

Types: Holotype, U.S.N.M. 108330; unfigured paratype, U.S.N.M. 108331.

Occurrence: U.S.G.S. Mes. loc. 21484, 21486, 21487, 

21662,
CENOMANIAN AMMONITES FROM THE, MOSBY SANDSTONE 53

FIGURE 3.—Whorl sections, natural size, of Dunveffanoceras from Mosby sandstone member, a, Dunveganoceras parvum Cobban 

(holotype, U.S.N.M. 108330) at diameter of 168 mm; b-d, Dunveganoceras albertense (Warren) subsp. montanense Cobban 

(paratype, U.S.N.M. 108327b) at diameters of 170, 200, and 265 mm illustrating changes in costal cross section; e, D. a. 

montanense Cobban (holotype, U.S.N.M. 108326) at diameter of 283 mm.
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

REFERENCES

Bergquist, H. R., 1944., Cretaceous of the Mesabi iron range,

Minnesota: Jour. Paleontology, vol. 18, no. 1, pp. 1-30,

pis. 1-11. 

Bbse, Emil, 1918, On a new ammonite fauna of the Lower Turonian of Mexico: Texas Univ. Bull. 1856, pp. 173-257, pis.

12-20, text figs. 1-7. 

Cobban, W. A., 1951, Colorado shale of central and northwestern

Montana and equivalent rocks of the Black Hills: Am.

Assoc. Petroleum Geologists Bull., vol. 35, no. 10, pp. 2170-

2198. 

De Grossouvre, Albert, 1912, Le Cre"tace" de la Loire-Infe'rieure

et de la Vendee: Soc. sci. nat. Quest France Bull., ser. 3,

vol. 2, pp. 1-38, pis. 1-3, text figs. 1-8.

Haas, Otto, 1949, Acanthoceratid Ammoaoidea from near Greybull, Wyoming: Am. Mus. Nat. History Bull., vol. 93, art.

1, pp. 1-39, pis. 1-15, text figs. 1-17. 

•——— 1951, Supplementary notes on the ammonoid genus Dunveganoceras: Am. Mus. Novitates, no. 1490, pp. 1-21, text

figs. 1-9. 

Herrick, C. L., and Johnson, D. W., 1900, The geology of the

Albuquerque sheet: Denison Univ., Sci. Lab., Bull., vol. 11,

art. 9, pp. 175-239, pis. 27-58, map in pocket. 

Hyatt, Alpheus, 1903, Pseudoceratites of the Cretaceous: U. S.

Geol. Survey Mon. 44. 

Jones, T. S., 1938, Geology of Sierra de la Pefia and paleontology

of the Indidura formation, Coahuila, Mexico: Geol. Soc.

America Bull., vol. 49, pp. 69-150, pis. 1-13, text figs. 1-4. 

Karrenberg, Herbert, 1935, Ammonitenfauna aus der nordspanischen Oberkreide: Palaeontographica, Band 82, Abt, A, pp.

125-161, pis. 30-33, text figs. 1-5. 

Leriche, Maurice, 1905, Sur la presence du genre Metoicoceras

Hyatt dans la Craie du Nord de la France et sur une espece

nouvelle de ce genre (Metoicoceras pontieri) : Soc. g6ol.

Nord Annales, tome 34, pp. 120-124, pi. 2, text figs. 1-3.

Lupton, C. T., and Lee, Wallace, 1921, Geology of the Cat Creek

oil fields, Fergus and Garfield Counties, Montana: Am.

Assoc. Petroleum Geologists Bull., vol. 5, no. 2, pp. 252-275,

pis. 1, 2, text fig. 1. 

Moreman, W. L., 1927, Fossil zones of the Eagle Ford of north

Texas: Jour. Paleontology, vol. 1, no. 1, pp. 89-101, pis. 13-16,

text fig. 1. 

——— 1942, Paleontology of the Eagle Ford group of north and

central Texas: Jour. Paleontology, vol. 16, no. 2, pp. 192-220,

pis. 31-34, text figs. 1, 2. 

Muller, S. W., and Schenck, H. G., 1943, Standard of Cretaceous

system: Am. Assoc. Petroleum Geologists Bull., voL 27, no.

3. pp. 262-278, text figs. 1-7. 

Petrascheck, Wilhelm, 1902, Die Ammoniten der sachsischen

Kreideformation: Beitr. Palaontologie Oesterr.-Ungarns u.

des orients, Band 14, pp. 131-162, pis. 7-12, text figs. 1-8. 

Reeside, J. B., Jr., and Weymouth, A. A., 1931, Mollusks from the

Aspen shale (Cretaceous) of southwestern Wyoming: U. S.

Nat. Mus. Proc., vol. 78, art. 17, pp. 1-24, pis. 1-4. 

Shumard, F. B., 1859, Descriptions of new Cretaceous fossils

from Texas: Acad. Sci. St. Louis Trans., vol. 1, pp. 570-610. 

Spath, L. F., 1926, On new ammonites from the English chalk:

Geol. Mag., vol. 63, pp. 77-83. 

Stanton, T. W., 1893 (issued 1894), The Colorado formation and

its invertebrate fauna: U. S. Geol. Survey Bull. 106. 

Stephenson, L. W., 1952, The larger invertebrate fossils of the

Woodbine formation (Cenomanian) of Texas: U. S. Geol.

Survey Prof. Paper 242. 

Warren, P. S., 1930, Three new ammonites from the Cretaceous

of Alberta: Royal Soc. Canada Trans., 3d ser., vol. 24, sec.

4. pp. 1-26, pis. 1-4.

Warren, P. S., and Stelck, C. R., 1940, Cenomanian and Turonian faunas in the Pouce Coupe district, Alberta and British Columbia: Royal Soc. Canada Trans., 3d ser., voL 34, 

sec. 4, pp. 143-152, pis. 1-4.
INDEX

[Italic numbers indicate descriptions]

Page 

acceleratum, Metoicoceras...... .___-___.__-__.._......._...._..._.. 49,60

Ageof Mosby sandstone member.._....____._.......__.______ 46-47

albertense, Dunveganoceras......... ...._.........._............._._. 47,51,52

montanense, Dunveganoceras.......... ________...... 45,46,47, 61, pis. 10,11

Anchura sp._..__._.......___..____._..........._........_. 46

antiguum, Metoicoceras................... _____..__....____..... 49

appendiculatus, Isurus..... ...___._....._.._______________ 46

bSsei, Metoicoceras.......

Buchiceras swallovi......

swallovi puercoensis. 

bureaui, Metoicoceras....

Carlileshale,___..._......_....._......._..._.__....._...... 45-46

Collignoniceras.............................. ..___.__._____....._.. 46

woollgari intermedium...._____....._......_...........___.... 46

woollgari praecox...... ...______________.__..........._..__ 46

Colorado shale.._..--.-.......__..__....__--.___._..___._..... 45

columbetta, Exogyra...--..........................................._...__ 45,46

conditum, Dunveganoceras........................................... ...._ 46,47,52

conradi, Gyrodes......................_____.____.__...._______ 46

crassicostae, Metoicoceras...................................................... 49

dakotensis, Lunatia..... .______..____..........._..........__. 46

delicatulus, Scaphttes...........................................__._..._ 47

dumasi, Metoicoceras...................................__......__...__ 49

Dunveganoceras.......... __________.__________..__ 45,46,47,51,52

albertense................................................._............ 47,51,52

montanense.—........———___________._... 45,46,47, 51, pis. 10,11

conditum............................................................... 46,47,52

parvum.—......................................................... 45, 5%, pi. 12

pondi..................................................................... 47

poucecoupense............................................................ 52

Exogyra columbetla............................................................ 45,46

falcatus, SqualicoraX—............................... ........________ 46

fragilis, Inoceramus........................................................... 46

Frontier formation._——______________________________ 45-46

Oervittia...............

gesliniana, Pulchellia... 

gibbosum, Metoicoceras. 

gourdoni, Metoicoceras..

................................................. 45

................................................. 49

——...—-—_—-._—.-...._..._.___...__ 49

	49 

gractie, Sciponocerat........................................................... 47

Oryphaea..................................................................... 45

sp...............................................—...........—........ 46

Gyrodes conrad i............................................................... 46

hendricksoni, Pseudomelania................................................... 46,46

Inoceramus........................_______________________ 45

fragilis................................................_____.___... 46

labiatus................................................................... 46

intermedium, Collignoniceras woollgari......................................... 46

Introduction.___________________________________ 46

irwim, Metoicoceras__________________________________ 51

Isurus appendiculatus......................................................... 46

semiplicatus............................................................... 46

kanabense, Metoicoceras.................................................... ................................................ 61

labiatus, Inoceramus........................................................... 46

latoeenter, Metoicoceras........................................................ 49

Localities, collection._______________________________ 47

Lunatia dakotensis... ..______________________________ 46

macrum, Metoicoceras swallovii................................................ 49

Metoicoceras............................................................... 45,46,47

acceleratum............................................................... 49,50

Metoicoceras—Continued 

antiguum.............

Page 

....... — ............- — .—.—.. —...... 49

.....—......-..- — ——- — - — — — — — 49

-. — . — ... — — — . — — ——— — — .-. 51

.. — ...-....-.-....... — .. — ..-. — ...-. — . 49

......_..........-.-.._.-...--.... — .-. — — — — - ——.-. 49

._._.__._______--_.--.-.-.-——.- — . — — „——— — — . 49

...-....--.... — -.---. — - — . — .- — - — - — ---.... — -.. 49

.....-..-...-.. — .. — . — ... — — ... — ——— — .. — ..— 51

kanabense................................................................. 51

latoventer......................____....._._---.-_---_-.-----...... 49

mosbyense............................................... 45,46,47, 48, 50, pis. 0,7

muellcri----......................... ......._____.___ 45,46, 49, pis. 6,8,9

ornatum....................................................---.-.._-... 49

bureaui.....

crassicostae. 

dumasi......

gibbosum....

gourdoni....

irwini.......

pervinguierei. 

petrascheld...

....................................................... 49

_.___._-———..-—.—-.-.——— — — ——.- 49

-..--...--„ — ..---—-—.-.—--—-- — -—----.. 51

praecox............................-_-_-..--_-.._. —— -.-.--.. —. —.---. 47

swallovii..........._______.___._..___....__.... ..____... 49,50

macrum............ _.----_.---..-.-„.-.-_... ——...... ——— ——— 49

tdhttei..................................................................... 47,49

whitei praecox.................................................. ————... 49

n.sp...................................................................... 47,49

montanense, Dunveganoceras albertense........................ 45,46,47, 51, pis. 10,11

mosbyense, Metoicoceras......................._____..__ 45,46,47, 48, 50,pis. 6,7

Mueller, O. O., collection.._.._..--.___...__..— — -------- — —— -.. 45

muelleri, Metoicoceras.............................__ ———.— 45,46, 49, pis. 6,8,9

orbiculata, Trigonocallista............. ___-----------——— ——. —— -------- 45,46

ornatum, Metoicoceras........................ —————. —— - —— -. — — —.. 49

Ostrea, n. sp_.——.._—--------- ————————————— ——————————— 46

parvum, Dunveganoceras................................................ 45,52,pi. 12

pervinquierei, Metoicoceras........................ ————————————————— 49

petrascheki, Metoicoceras.................. —————.... ————— —— — — —— 49

pondi, Dunveganoceras- ____..__————————...————————————— 47

pontieri, Metoicoceras.......................................................... 51

poucecoupense, Dunveganoceras..........................—. ——————————— 62

praecox, Collignoniceras wpollgari.............................................. 46

Metoicoceras.............................................................. 47

Metoicoceras whitei........................................................ 49

Pseudomelania hendricksoni. ..............................—— -- ——— ——— 45,46

Ptychodus whipplei......... ——————————————————————————— 46

puercoensis, Buchiceras swallovi——————————————————————————— 51

Pulchellia gesliniana...............................—..—.———.-..—....... 49

References. 64

O

Scaphttes delicatulus........................................................... 47

Sciponoceras gracile..................................—....-.—..—-..—.. 47

Section, stratigraphic________—-———-————————————————— 46-46 

semiplicatus, Isurus............................................~~......~—..~ 46

Sgualicoraxfalcatus......... ...............................................— 46

Stratigraphy......—.-......——————.———-——————- 46-47

swallovi, Buchiceras. —————————————————————————————————— 61 

Metoicoceras.............................................................. 49, 50

swallovii macrum, Metoicoceras--....------------------------------------------ 49

swallovi puercoensis, Buchiceras................................................ 61

Trachytriton n. sp.______———————————————————————————— 46 

Trigonocallista orbiculata.................................—.—.......—.-.— 45,46

whitei, Metoicoceras........................................................... 47,49

whitei praecox, Metoicoceras................................................... 49

whipplei, Ptychodus........................................................... 46

woollgari intermedium, Collignoniceras........................................ 46

woollgari praecox, CoUignoniceras.............................................. 46

55

PLATES 6-12
PLATE 6

[All figures natural size except as indicated on plate]

FIGURES 1—14. Metoicoceras mosbyense Cobban, n. sp. (p. 48).

1-7, Side, front, and rear views, and suture of a small internal mold, paratype U.S.N.M. 108316a, from locality

21955. 

8, 9, Front and side views of a larger specimen, paratype U.S.N.M. 108316b, from the same locality, showing the

first appearance of umbilical nodes. 

10, 11, Side and rear views of a stout paratype retaining the shell, U.S.N.M. 108317a, from locality 21484. Shows

the disappearance of the ventrolateral nodes and the elevation of the umbilical ribs into radially elongated nodes. 

12, 13, Side and rear views of an internal mold, paratype U.S.N.M. 108318a, from locality 21487, showing the

disappearance of umbilical and ventrolateral nodes.

14, Cross section of the internal whorls of paratype U.S.N.M. 108320, from locality 21662. 

15, 16. Metoicoceras muelleri Cobban, n. sp. (p. 49).

Front and side views of paratype U.S.N.M. 108324, an internal mold from locality 21487.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 243 PLATE 6

10

X2

X3

X 2

12 13

15 16

METOICOCERAS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 243 PLATE 7

METOICOCEKAS
PLATE 7

[All figures natural sizej

FIGURES 1—3. Metoicoceras mosbyense Cobban, n. sp. (p. 48).

Side and rear views and part of sixth from last suture of the holotype, U.S.N.M. 108315, an internal mold from 

locality 21484. The arrow indicates the beginning of the body chamber.
PLATE 8

[All figures natural size except as indicated on plate]

FIGURES 1-7. Metoicoceras muelleri Cobban, n. sp. (p. 49).

1, 2, Side and rear views of a small internal mold, pao-atype U.S.N.M. 108323a, from locality 21484. Shows weakness of sculpture and early disappearance of ventrolateral nodes.

3, 4, Side view and suture of a slightly larger internal mold, paratype U.S.N.M. 108322c, from locality 21486.

5, 6, Side and front views of a larger almost smooth internal mold, paratype U.S.N.M. 108323b, from locality 21484.

7, Front view of the holotype, U.S.N.M. 108321, from locality 21487. Shows change in venter from a flattened to 

a rounded form.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 243 PLATE 8

X2

r

'r<^ **$'j$Mi

'•'•> ; V"-"'/^ > y^V'

^V ^%-ii^

^"^•'.^

METOICOCERAS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 243 PLATE 9

•'«".?., '^.-vS "'^ 

'; - '.S^**:;. *. ^

,--*Vl^?iA ^>''•-•. / ' l •" •?*- ^feat£-/> /j

•J&SSF^SSF *-:V '^$^ .;'&.-; & •^•t^f. 'JP+, .- f,Jr, ^ P^ -/ " - ^i* -C: vr «f-J^y^->r-•',

!TV ><t, V\:.C^O.-T"^ ^Xf^5^i <"-i'

i?..:%i^t^§?,W sf^'i?t^5l€if& "• ^:.J?A-W; ;^rAr^

4>^^'?fel^tJ *

* "T^^S I/ ^4fcl., rjc

' ••'1^'> " ,Ci;«('-J /V-;*OT- 

'w- «-®»«!l V"* ./, •? ) >

»L.- Wv . 'M^ ^a</MMs> /^ '• IN* J ^,£ .*>.' ^•.-^*S>.5K 5^ ' T*

•^*S?1:'WH ^-*gf •^«L.

l-'ffyff- W;jt \***fi ^Tf*. '•

--.<-m- yj3.::"'" 

' -v- - >J»iSMtfM

^.'iti.

METOICOCERAS
PLATE 9

Metoicoceras muelleri Cobban, n. sp. (p. 49).

Side view, natural size, of the holotype, U.S.N.M. 108321, from locality 21487. The arrow indicates the beginning of the body 

chamber.
PLATE 10

[All figures natural size except as indicated on plate]

FIGUEES 1-7. Dunveganoceras albertense (Warren) subsp. montanense Cobban, n. subsp. (p. 51).

1-4, Front, rear, and side views, and suture at diameter of 45 mm of an internal mold, paratype U.S.N.M. 108327a,

from locality 21955.

• 5, 6, Front and side views of a smaller paratype, U.S.N.M. 108329, from locality 21662.

7, Rear view of the holotype, U.S.N.M. 108326, from locality 21488. Shows ogival shape of the ultimate whorl 

and the asymmetrical suture.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 243 PLATE 10

DUNVEGANOCERAS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 243 PLATE 11

'" ' " :^^ff

DUNVEGANOCERAS
PLATE 11

[Figure three-fourths natural size]

Dunveganoceras albertense tWarren) subsp. montanense Cobban, n. subsp. (p. 51).

Side view of the holotype, U.S.N.M. 108326, a large internal mold from locality 21488. The arrow indicates the beginning of the 

body chamber.
PLATE 12

[Both figures natural size]

FIGUEES 1, 2. Dunveganoceras parvum Cobban, n. sp. (p. 52).

Side and rear views of the holotype, U.S.N.M. 108330, an internal mold from locality 21484. The arrow indicates 

the beginning of the body chamber.
GEOLOGICAL SURVEY

PROFESSIONAL PAPER 243 PLATE 12

DUNVEGANOCERAS