U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477
The Upper Cretaceous Ammonite

Rhaeboceras Meek in the

Western Interior of the United States

By WILLIAM A. GOBBAN

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477

Descriptions and illustrations of 

an important guide fossil to 

rocks of early Maastrichtian age

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1987
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Cobban, William A., 1916-

The Upper Cretaceous ammonite Rhaeboceras Meek in the Western Interior of the United 

States.

(U.S. Geological Survey professional paper ; 1477)

Bibliography: p. 13

1. Rkaeboceras. 2. Paleontology Cretaceous. 3. Paleontology West (U.S.) I. Title. II.

Series: Geological Survey professional paper ; 1477.

QE807.A5C637 1988 564'.53 87-600272

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425 

Denver, CO 80225
CONTENTS

Abstract .........................................

Introduction .....................................

Acknowledgments .................................

Stratigraphic position of Rhaeboceras ................

Geographic distribution ............................

Classification .....................................

Systematic descriptions ............................

Rhaeboceras halli (Meek and Hayden) .............

Rhaeboceras halli (Meek and Hayden), noded variant 

Rhaeboceras mullananum (Meek and Hayden) ......

Page

Systematic descriptions Continued

Rhaeboceras subglobosum (Whiteaves) .............. 10

Rhaeboceras subglobosum (Whiteaves), noded variant . 11 

Rhaeboceras coloradoense Cobban, n. sp. ............ 11

Rhaeboceras coloradoense Cobban, n. sp., noded 

variant ....................................... 12

Rhaeboceras burkholderi Cobban, n. sp. ............. 12

Rhaeboceras cf. R. burkholderi Cobban, n. sp. ........ 13

References cited .................................... 13

Index ............................................. 15

ILLUSTRATIONS

[Plates follow index]

PLATES 1-14. Rhaeboceras

Page

FIGURE 1. Map showing localities of Rhaeboceras ............................ 3

2. Scatter diagram of ventral ribs of Rhaeboceras halli (Meek and Hayden). 7

3. Histogram of diameters at base of body chambers of Rhaeboceras halli (Meek

	and Hayden) ................................................ 8

4. Suture of Rhaeboceras halli (Meek and Hayden) .................... 8

5. Suture of Rhaeboceras coloradoense Cobban, n. sp. .................. 12

6. Suture of Rhaeboceras burkholderi Cobban, n. sp. ................... 13

TABLE

TABLE 1. Localities where Rhaeboceras was collected

in

THE UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK IN THE 

WESTERN INTERIOR OF THE UNITED STATES

By WILLIAM A. COBBAN

ABSTRACT

The genus Rhaeboceras Meek, 1876, of early Maastrichtian age, is 

characterized by its body chamber which is deflected a little from the 

regular curve of the phragmocone and by its conspicuous umbilical 

bullae. Some species, such as the type, R. halli (Meek and Hayden), 

have dense ribbing on the outer whorl of the phragmocone. The suture, 

which is typical of the scaphites, has five lobes in the external part 

that decrease progressively in height away from the venter, and the 

first lateral saddle is asymmetrically bifid with the widest part nearest 

the venter. The genus is best assigned to the family Scaphitidae Meek.

Rhaeboceras is known in North America only from western Kansas and northern Colorado northward into Alberta and Saskatchewan. 

Six species have been described, and two new ones, R. coloradoense 

and R. burkholderi, are herein described. One species, R. mullananum 

(Meek and Hayden), which is known only from the holotype, may be 

older (Santonian?) than the other species (early Maastrichtian). 

Ancestral forms of Rhaeboceras are unknown. The genus gave rise 

to Ponteixites Warren, 1934, later in the Maastrichtian.

INTRODUCTION

Meek (1876, p. 458-462, pi. 24, figs. 3a-c, text fig. 64) 

proposed the genus Rhaeboceras for an ammonite that 

seemed to combine features of both Phylloceras Suess 

(1866, p. 76) and Scaphites Parkinson (1811, p. 145, pi. 

10, fig. 10). Phylloceras is an involute form that has 

numerous fine radial ribs or lirae and a complex suture 

characterized by rounded leaf-shaped folioles in the saddles. Scaphites is a more or less involute form that 

becomes partly uncoiled in the adult stage. The type 

species of Rhaeboceras is Ammonites halli Meek and 

Hayden (1856, p. 70). Meek (1876, p. 458-462) gave a 

revised description of the two only known specimens, 

both crushed, and noted that "Should complete undistorted specimens show, as I think very probably will 

be the case, that it differs generically or subgenerically 

from Phylloceras proper, I would propose for the group 

into which it would in that case naturally fall, the name 

Rhaeboceras."

Rhaeboceras is common in parts of the Bearpaw Shale 

(Upper Cretaceous) of central Montana and southern 

Alberta and Saskatchewan and in the Larimer and 

Richard Sandstone Members of the Pierre Shale (Upper Cretaceous) of north-central Colorado. Aside from

these occurrences, specimens referable to Rhaeboceras 

are exceedingly rare; a few specimens have been collected from the base of the Lewis Shale (Upper 

Cretaceous) in central Wyoming, a single specimen was 

found in the Pierre Shale near Red Bird in eastern 

Wyoming, and one specimen each was found in the 

Pierre Shale in North Park, Colorado, southeastern 

Wyoming, northwestern Nebraska, and western Kansas. Outside North America, Rhaeboceras may be 

represented by the ammonite described as Acanthoscaphites innodosus Naidin (1974, p. 178, pi. 62) from 

the Donetz Basin, U.S.S.R. An ammonite listed as Ammonites halli Meek and Hayden? has been recorded 

from Brazil (Magalhaes and Mezzalira, 1953, p. 276).

Six species of Rhaeboceras have been described from 

the United States and Canada. These species, with their 

original generic assignments, are Ammonites opalus 

Owen (1852, p. 579), A. halli Meek and Hayden (1856, 

p. 70), A. mullananus Meek and Hayden (1862, p. 23), 

Scaphites subglobosus Whiteaves (1885, p. 52), Acanthoscaphites albertensis Warren (1930, p. 23), and 

Rhaeboceras whiteavesi Landes (1940, p. 174).

Records of Rhaeboceras from the United States are 

few and scattered in the literature. Rhaeboceras halli 

was first described by Meek and Hayden in 1856 (p. 70), 

listed by them in 1860 (p. 420) and by Meek in 1864 

(p. 24), and redescribed by Meek in 1876 (p. 458). 

Nothing new was recorded concerning this species in 

the United States until Scott and Cobban (1959, p. 128) 

noted its occurrence in the Larimer Sandstone Member 

of the Pierre Shale in northern Colorado, and Cobban 

(1962, p. 127) recorded it with Baculites jenseni Cobban in the Bearpaw Shale in central Montana.

Rhaeboceras mullananum was described by Meek and 

Hayden in 1862 (p. 23), listed by Meek in 1864 (p. 24), and 

redescribed by Meek in 1876 (p. 607). Stanton (1893, p. 187) 

repeated Meek's description and illustrations, but Stanton assigned the species to Scaphites. This assignment 

was accepted by Diener (1925, p. 201) in his classification of Upper Cretaceous ammonites as well as by Reeside (1927, p. 31) in his general account of the scaphites.

Rhaeboceras albertense, which was noted by Jensen 

and Varnes (1964, p. F10) in the upper part of the

1
UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK, WESTERN INTERIOR, U.S.

Bearpaw Shale in northeastern Montana, seems to be the 

only published record of this species in the United States.

ACKNOWLEDGMENTS

Mr. Larry C. Eichhorn, Lewistown, Mont., kindly 

made available his large and impressive collections of 

Rhaeboceras from the Bearpaw Shale. Several of his 

specimens are illustrated in this report. Other specimens 

of Rhaeboceras were donated by Richard L. Sutton, Jr., 

M.D., Prairie Village, Kans., Dr. Gale A. Bishop, Georgia 

Southern College, Statesboro, Ga., Mr. Karl F. Hirsch, 

Denver, Colo., Dr. E.A. Hamilton, Marietta, Ohio, Mr. 

Robert H. Feldman, Billings, Mont., and Mr. Howard 

Ehrle, Miles City, Mont.

The specimens illustrated in this report are stored in 

the National Museum of Natural History in Washington, DC. Plaster casts of many of the specimens are in 

the U.S. Geological Survey Mesozoic invertebrate fossil 

collections at the Federal Center, Denver, Colo. All 

photographs were made by Robert E. Burkholder of the 

U.S. Geological Survey.

STRATIGRAPHIC POSITION OF 

RHAEBOCERAS

The general stratigraphic position of Rhaeboceras was 

shown by Gill and Cobban (1966, p. A35) to include the 

zones ofBaculites reesidei Elias and B. jenseni Cobban. 

Jeletzky (1968, p. 48) later defined a "Scaphites nodosus 

and Rhaeboceras spp. zone" in the Bearpaw Shale in the 

Western Interior of Canada. In the United States Hoploscaphites nodosus (Owen) is most common and best developed in the zones ofBaculites reesidei and B. jenseni.

The large collections of Rhaeboceras now at hand seem 

to indicate only two zones. The lower zone, which coincides with the zone ofBaculites reesidei, is characterized 

by very stout forms of Rhaeboceras, and it is probably 

the level from which came the types of R. subglobosum 

and R. whiteavesi. The more slender forms of Rhaeboceras, R. halli and R. albertense, characterize the upper 

zone which coincides with the zone of Baculites jenseni. 

There is the possibility that R. mullananum marks an 

older zone, but this cannot be verified at present.

GEOGRAPHIC DISTRIBUTION

The collections of Rhaeboceras studied came from 

many localities in Montana, Wyoming, and Colorado, 

but most are from the Bearpaw Shale of central and 

north-central Montana. The localities of Rhaeboceras are

indicated in figure 1, and the individual localities are 

described hi table 1.

CLASSIFICATION

The classification of Rhaeboceras has been a problem. 

Meek (1876, p. 460) assigned it to Phylloceras because 

"In general form (at least in medium-sized specimens), 

as well as in the roundness of its periphery and the 

general characters of its septa, it agrees pretty well with 

that genus." He queried this assignment, however, 

because the suture differed somewhat from Phylloceras, 

and the body chamber deflected from the regular curve 

of the phragmocona Diener (1925, p. 121) thought Meek 

and Hayden's Ammonites halli more closely resembled 

Pusozia (Bayle, 1878, pis. 45, 46), and he assigned it with 

a query to that genus.

The ammonite described by Meek and Hayden (1862, 

p. 23) as Ammonites mullananus was considered a 

scaphite and assigned to Scaphites by Stanton (1893, 

p. 187) as well as by Diener (1925, p. 201) and Reeside 

(1927, p. 31).

Rhaeboceras albertense was originally assigned to 

Acanthoscaphites Nowak (1912, p. 565) by Warren (1930, 

p. 23) owing to its general scaphitoid appearance. Warren also suggested that Meek and Hayden's Ammonites 

halli might also be referred to Acanthoscaphites. 

Rhaeboceras subglobosum was also considered a scaphite by Whiteaves (1885, p. 52), who assigned his new 

species to Scaphites and compared it to S. nodosus 

Owen (1852, p. 581). On the other hand, Landes (1940, 

p. 174) considered Rhaeboceras distinct from the 

scaphites and assigned it to the family Cosmoceratidae 

and subfamily Acanthoceratinae. In the most recent 

treatment of the genus, Wright (1957, p. L229) placed 

it in the family Scaphitidae and subfamily Scaphitinae.

Some ammonites from the southern hemisphere, such 

as Grossouvrites Kilian and Reboul (1909, p. 26, 38) 

resemble fine-ribbed Rhaeboceras in their dense ribbing 

and conspicuous umbilical tubercles. The large specimen 

of G. gemmatus (Huppe), figured by Spath (1953, p. 29, 

pi. 5, figs, la, b) from Graham Land, closely resembles 

some specimens of Rhaeboceras (such as pi. 10), but its 

suture is quite different. Likewise, the specimen of G. 

gemmatus illustrated by Steinmann (1895, p. 68, pi. 6, 

figs, la, b) resembles R. halli in its fine ribbing and umbilical tuberculation, but the umbilicus is a little wider, 

and the tubercles are present well within the inner 

whorls.

The scaphitoid body chamber and the suture pattern 

certainly relate Rhaeboceras to the scaphites. As in the 

scaphites (Cobban, 1951, p. 4), the external suture has 

five lobes progressively decreasing in height away from
CLASSIFICATION

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FIGURE 1. Index map of part of the Western Interior of the United States showing localities of Rhaeboceras referred to in the text

and in table 1.
UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK, WESTERN INTERIOR, U.S.

TABLE 1. Localities where Rhaeboceras was collected

Locality USGS 

(fig.l) Mesozoic 

locality

Collector, year of collection, description 

of locality, and stratigraphic assignment

1 5517 V.H. Barnett, 1908. About 19 km north of Savoy, in 

the NWV4NEV4 sec. 7, T. 33 N., R. 25 E., Blaine 

County, Mont. Bearpaw Shale.

2 D1338 R.G. Schmidt, 1957. About 15 m northeast of large 

reservoir dam, in sec. 13, T. 31 N., R. 18 E., Blaine 

County, Mont. Bearpaw Shale, possibly 45-60 m 

below top.

3 2836 J.B. Hatcher and TW. Stanton, 1903. Cow Creek near 

middle of T. 27 N., R. 19 E., Blaine County, Mont. 

Bearpaw Shale.

4 D2283 B.C. Hearn, Jr., 1959. Southeast side of Bearpaw 

Mountains, in the N1/2NW1/4SE1/4 sec. 7, T. 26 N., 

R. 21 E., Blaine County, Mont. Bearpaw Shale, 

possibly 105-120 m above base.

5 D2296 B.C. Hearn, Jr., 1959. Near D2283 in the 

SE1/4NW1/4NW1/4 sec. 7, T. 26 N., R. 21 E., Blaine 

County, Mont. Bearpaw Shale.

6 22095 E.A. Hamilton, 1949. Sec. 9 or 16, T. 24 N., R. 27 

E., Phillips County, Mont. Bearpaw Shale.

7 D9514 C.A. Wolfbauer, 1975. North of Fort Peck Reservoir, 

in the NWV4SEV4NWV4 sec. 6, T. 21 N., R. 31 E., 

Phillips County, Mont. Bearpaw Shale, from a gray 

limestone concretion about 95 m below top.

8 D10233 L.C. Eichhorn, 1973. North of Fort Peck Reservoir, 

in sees. 1-4, T. 22 N., R. 31 E., and sees. 33-35, 

T. 23 N., R. 31 E., Phillips County, Mont. Bearpaw Shale.

9 D12735 Howard Ehrle, 1986. Telegraph Creek area of 

southeastern Phillips County, Mont. Bearpaw 

Shale.

10 D10223 R.L. Sutton, Jr., 1970. South side of Fort Peck Reservoir, in the center of sec. 11, T. 21 N., R. 31 E., Garfield County, Mont. Bearpaw Shale, from 

dusky-red-weathering concretions.

11 D10222 R.L. Sutton, Jr., 1970. South side of Fort Peck 

Reservoir at mouth of Devils Creek, in the SVi sec 

32, T. 22 N., R. 32 E., Garfield County, Mont. 

Bearpaw Shale, from dusky-red-weathering concretions.

12 D10221 R.L. Sutton, Jr., 1970. South side of Fort Peck Reservoir, in the NW1/* sec. 14, T. 22 N., R. 34 E., Garfield County, Mont. Bearpaw Shale.

13 D10224 R.L. Sutton, Jr., 1970. North side of Fort Peck Reservoir at mouth of Timber Creek, in the NEVi sec. 

4, T. 22 N., R. 34 E., Valley County, Mont. Bearpaw Shale, from dusky-red-weathering concretions.

14 D10225 R.L. Sutton, Jr., 1970. South side of Fort Peck Reservoir near mouth of Gilbert Creek, in the NVi T. 23 

N., R. 40 E., Garfield County, Mont. Bearpaw 

Shale.

TABLE I. Localities where Rhaeboceras was collected Continued

Locality USGS 

(fig.l) Mesozoic 

locality

Collector, year of collection, description 

of locality, and stratigraphic assignment

15 D10226 G.A. Bishop, 1973. North side of Fort Peck Reservoir, in the SWVi sec. 7, T. 24 N., R. 40 E., Valley 

County, Mont. Bearpaw Shale, 45-60 m below top.

16 23390 F.S. Jensen, 1950. Three kilometers northwest of 

Nashua, in the NEW sec. 26, T. 28 N., R. 41 E., 

Valley County, Mont. Bearpaw Shale, from a 

dusky-red-weathering concretion 80 or 90 m below 

top.

17 D10234 L.C. Eichhorn, 1970. Along drainage of Crooked 

Creek in northeastern Fergus County, Mont. Bearpaw Shale.

18 23338 O.O. Mueller, 1954. Crooked Creek in sec. 33, T. 20 

N., R. 26 E., Fergus County, Mont. Bearpaw Shale.

19 D5675 J.R. GUI, 1966. About 6.4 km north of Mosby, in the 

NWVi sec. 23, T. 15 N., R. 30 E., Garfield County, 

Mont. Bearpaw Shale, from a gray limestone concretion in a bentonitic unit about 213 m above 

base of formation.

20 D5663 R.E. Burkholder, 1966. About 11 km east of Mosby, 

in the center of the NWVi sec. 10, T. 14 N., R. 31 

E., Garfield County, Mont. Bearpaw Shale, from 

brown-weathering, ferruginous limestone concretions just below a bentonitic unit and about 204 m 

above base of formation.

21 D5664 J.R. GUI, R.E. Burkholder, and WA. Cobban, 1966. 

Same locality as D5663. Bearpaw Shale, from bentonitic unit about 205-212 m above base of 

formation.

22 D5668 J.R. GUI and R.E. Burkholder, 1966. About 7 km 

northeast of Mosby, in the SWWSWW sec. 33, T. 

15 N., R. 31 E., Garfield County, Mont. Bearpaw 

Shale, from limestone concretions in bentonitic 

unit about 213 m above base of formation.

23 21580 WA. Cobban and C.T. Moore, 1949. Eight kilometers 

east-northeast of Mosby, in the WJ/2 sec. 3, T. 14 

N., R. 31 E., Garfield County, Mont. Bearpaw 

Shale, from bentonitic unit about 205-212 m above 

base.

24 D783 H.R. Smith, P.W Richards, and WA. Cobban, 1955. 

About 23 km north-northeast of Melstone, in the 

NWVi sec. 24, T. 12 N., R. 31 E., Rosebud County, 

Mont. Bearpaw Shale, about 270-275 m above 

base.

25 D781 H.R. Smith, 1955. Nineteen kilometers northeast of 

Melstone, in the SE1/4SE1/4 SE1/4 sec. 6, T. 11 N., 

R. 32 E., Rosebud County, Mont. Bearpaw Shale, 

from gray-weathering limestone concretions about 

280 m above base.

26 21660 C.T. Moore and WA. Cobban, 1949. Sixteen 

kilometers northeast of Melstone, in the NEVi sec 

24, T. 11 N., R. 31 E., Rosebud County, Mont Bearpaw Shale, from brown-weathering limestone concretions.
SYSTEMATIC DESCRIPTIONS 5 

TABLE 1. Localities where Rhaeboceras was collected Continued TABLE 1. Localities where Rhaeboceras was collected Continued

Locality USGS 

(fig.l) Mesozoic 

locality

Collector, year of collection, description 

of locality, and stratigraphic assignment

27 D12734 R.H. Feldman, 1986. North-northeast of Melstone 

in the SE^SW'/iSWH sec. 11, T. 11 N., R. 31 E., 

Rosebud County, Mont. Bearpaw Shala

28 22094 E.A. Hamilton, 1949. T. 12 N., R. 33 E., Rosebud 

County, Mont. Bearpaw Shala

29 12853 R.S. Knappen, 1924. About 5 km northeast of Columbus, in the SWJ/4 sec. 13, T. 2 S., R. 20 E., 

Stillwater County, Mont. Bearpaw Shala

30 5006 T.W. Stanton, 1907. About 6.4 km west of Bridger, 

Carbon County, Mont. Bearpaw Shale.

31 D440 C.S. Robinson, W.J. Mapel, and W.A. Cobban, 1955. 

NEWNEV4 sec. 24, T. 56 N., R. 69 W., Campbell 

County, Wyo. Pierre Shale, about 15m above top 

of Monument Hill Bentonitic Member.

32 D3228 J.R. Gill and W.A. Cobban, 1960. Northeast flank 

of Teapot dome, in the SW'/aSW1/* sec. 24, T. 39 

N., R. 78 W., Natrona County, Wyo. Lewis Shale, 

from brown-weathering limestone concretions 

about 17 m above basa

33 D10236 K.F. Hirsch, 1972. About 3.2 km northeast of Red 

Bird, in the SEVi sec. 14, T. 38 N., R. 62 W, 

Niobrara County, Wyo. Pierre Shale, from a ferruginous concretion probably just beneath Kara 

Bentonitic Member.

34 D4943 W.A. Cobban, 1965. About 18 km north-northeast 

of Chadron in the SE'/a sec. 25, T. 35 N., R. 48 W, 

Dawes County, Nebr. Pierre Shala

35 D1382 G.R. Scott and W.A. Cobban, 1957. About 0.8 km 

east of Horse Creek, in the NE1/4SE1/4 sec. 25, T. 

17 N., R. 70 W, Laramie County, Wyo. Pierre Shale, 

from gray- and brown-weathering sandy limestone 

concretions 15 m above Larimer Sandstone 

Member.

36 D9637 D.J. Hill Madden and M.A. Moorman, 1975. Thirteen kilometers west of Walden, in the SEHSW1^ 

sec. 26, T. 9 N., R. 78 W, Jackson County, Colo. 

Pierre Shale, from a sandy limestone concretion.

37 D371 G.R. Scott, 1955. About 1.3 km southwest of Round 

Butte, in the NWy4SWy4 sec. 19, Til N., R. 68 

W, Larimer County, Colo. Pierre Shale, from a 

brown-weathering sandstone concretion in the 

Larimer Sandstone Member.

38 D374 G.R. Scott and W.A. Cobban, 1955. About 0.8 km 

south of Round Butte, in the SE'/aNW1/* sec. 19, 

Til N., R. 68 W, Larimer County, Colo. Pierre 

Shale, from brown-weathering sandstone concretions in upper 6 m of Richard Sandstone Member.

39 16093 R.G. Coffin, 1931. South bank of Reservoir No. 3, in 

the N'/fcSEVa sec. 19, T. 9 N., R. 68 W, Larimer 

County, Cola Pierre Shale, from gray silty 

limestone concretions in Richard Sandstone 

Member.

Locality USGS 

(fig.l) Mesozoic 

locality

Collector, year of collection, description 

of locality, and stratigraphic assignment

40 22921 J.B. Reeside, Jr., H.R. Christner, and W.A. Cobban, 

1950; Cobban and G.R. Scott, 1955-1972. Same 

locality and stratigraphic position as 16093.

41 D2715 G.R. Scott, 1960. Along irrigation ditch 0.2 km 

northwest of Reservoir No. 8, in the SWViSE1/^ sec 

25, T. 9 N., R. 69 W, Larimer County, Cola Pierre 

Shale, Richard Sandstone Member.

42 D1465 G.R. Scott and W.A. Cobban, 1957. About 0.8 km 

northeast of Waverly, in the SW1/4SE1/4SW1/4 sec. 

13, T. 9 N., R. 69 W, Larimer County, Cola Pierre 

Shale, from gray limestone concretions in Larimer 

Sandstone Member.

43 D300 G.R. Scott and WA. Cobban, 1955. West side of ridge 

just east of U.S. Highway 287, in the 

W1/2SW1/4SW1/4 sec. 1, T. 6 N., R. 69 W, Larimer 

County, Cola Pierre Shale, from brown-weathering 

sandstone concretions in middle of Larimer Sandstone Member.

44 D301 G.R. Scott and W.A. Cobban, 1955. Same locality 

as D300. Pierre Shale, from uppermost ledge of 

Larimer Sandstone Member.

45 D618 W.A. Cobban, 1955. About 18.5 km north-northeast 

of Sharon Springs in the NE1A sec. 31, T. 11 S., 

R. 39 W, Wallace County, Kans. Pierre Shale, from 

upper part of Lake Creek Member.

the venter, and the first lateral saddle is asymmetrically bifid with the widest part on the ventral side.

The large nodeless and densely ribbed phragmocone 

is a feature not seen on other forms of large scaphites. 

Ventrolateral tubercles, which are present on most 

scaphites of Campanian and Maastrichtian age, are absent on most specimens of Rhaeboceras.

SYSTEMATIC DESCRIPTIONS

The specimens that are described or mentioned in this 

report have the following repository abbreviations: 

USNM (National Museum of Natural History, Washington, B.C.; formerly U.S. National Museum); GSC 

(Geological Survey of Canada, Ottawa, Ontario); UA 

(Department of Geology, University of Alberta, Edmonton); and FM (Field Museum of Natural History, 

Chicago, IU.).

In the drawings of sutures, the heavy, solid straight 

line marks the middle of the venter as well as the middle of the external lobe (E); the lighter, solid straight line 

marks the middle of the dorsum as well as the middle 

of the internal lobe (I); and the dashed line marks the
UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK, WESTERN INTERIOR, U.S.

umbilical seam. Only the major lateral lobe and saddle 

are identified; L stands for the lateral lobe, and E/L 

stands for the saddle that separates this lobe from the 

external one (E).

Family SCAPHTTIDAE Meek, 1876, p. 413

Subfamily SCAPHITINAE Meek, 1876, p. 413

Genus RHAEBOCERAS Meek, 1876, p. 462

Rhaeboceras halli (Meek and Hayden)

Plates 1-5; plate 6, figures 1-15; plate 7, figure 2; plate 8, figures 1, 

2; plate 11, figures 5, 6; plate 12, figures 1-3; plate 13

1852. Ammonites opalus Owen, p. 579, pi. 8, fig. 6 (nomen oblitum). 

1856. Ammonites halli Meek and Hayden, p. 700.

1859. Ammonites halli Meek and Hayden. Hayden, p. 684.

1860. Ammonites halli Meek and Hayden. Meek and Hayden, p. 420. 

1876. Phyllocerasl halli (Meek and Hayden). Meek, p. 458, pi. 24, figs.

3a-c; Rhaeboceras halli on p. 462.

1925. Puzosiat halli (Meek and Hayden). Diener, p. 121. 

1957. Rhaeboceras halli (Meek and Hayden). Wright, p. L229, fig. 255

(5a, b). 

1983. Rhaeboceras halli (Meek and Hayden). Riccardi, p. 33, pi. 12,

figs. 1-6; pi. 13, figs. 1-4, 8; text figs. 32-35.

Types Holotype USNM 384 by original designation 

is the original of Meek and Hayden (1856, p. 70) first 

illustrated by Meek (1876, pi. 24, figs. 3a-c) from rocks 

now assigned to the Bearpaw Shale in northeastern 

Montana. Unfigured paratype USNM 389 from the 

same locality. Hypotypes USNM 413012-413038, 

413100-413102.

Diagnosis. A slender to moderately slender species 

that has extremely dense to moderately dense ribbing.

Description Meek had only two specimens of which 

the smaller and better preserved one was figured. This 

specimen, the holotype, is a small adult that consists 

of a slender uncrushed phragmocone and most of the 

body chamber which, however, is laterally crushed and 

lacks the oral end (pi. 1, figs. 11, 12). Meek gave its 

dimensions as "4.70 inches in its greatest diameter, and 

about 1.50 inches in convexity." He noted that the "surface ornamented with numerous small, bifurcating, 

slightly flexuous costae, that are larger near the umbilical side, and on the last turn of medium and large 

sized specimens become proportionally somewhat more 

prominent, more curved, and suddenly bifurcate near the 

umbilicus, and again divide and subdivide into 

numerous smaller ones, so that their number, including 

others intercalated between, amounts to from five to 

seven times as many where they pass straightly over the 

periphery, as near the umbilical side." Meek also noted 

that the umbilicus was very narrow in the phragmocone 

but proportionally wider in the body chamber. He was 

impressed by the manner in which the body chamber 

deflected from the regular curve of the inner whorls. The 

unfigured paratype, USNM 389, a large badly crushed

adult, seemed to have two deflections from the regular 

curve of the inner whorls. This angularity was undoubtedly the source of the name Rhaeboceras (Greek, 

rhaibos, bent).

The holotype has 12 primary ribs and 75 secondary 

ribs per half whorl at a diameter of 80 mm. The 

primaries curve forward and, on the body chamber and 

adjoining part of the phragmocone, rise into conspicuous bullae along the umbilical shoulder. On the 

outer part of the flank, the primaries divide into secondaries which are of equal size on crossing the venter. All 

ribs are slightly flexuous and rectiradiate.

The uncrushed phragmocone of the holotype has flattened flanks, a narrowly rounded venter, and a whorl section that is considerably higher than wide. The 

well-preserved suture was illustrated by Meek (1876, pi. 

27, fig. 3c; text fig. 64).

Meek's unpublished paratype (USNM 389) came from 

a dusky-red-weathering sideritic concretion. The 

specimen is so badly crushed as to be of little value other 

than to indicate a large adult size (248 mm in diameter) 

and to show the deflection of the body chamber from 

the regular curve of the phragmocone.

Two large collections of Rhaeboceras that seem 

referable to R. halli were available for study. Both are 

from the zone of Baculites jenseni Cobban in the upper 

part of the Bearpaw Shale of east-central Montana. The 

larger collection, made available by Mr. Larry C. 

Eichhorn of Lewistown, Mont., consists of 124 

specimens suitable for one or more measurements, such 

as umbilical ratio, diameter at base of body chamber, 

and rib count. Mr. Eichhorn kindly donated most of 

these specimens which came from map locality 17 

(D10234) on figure 1. The other collection, from USGS 

Mesozoic locality D783 (fig. 1, loc. 24), consists of 116 

specimens suitable for one or more measurements.

Most specimens in the two large collections are not 

as slender or as finely ribbed as the holotype of R. halli. 

The ratio of breadth to diameter of the shell and the 

number of ribs crossing the venter can best be shown 

by means of scatter diagrams (fig. 2). Measurements of 

the holotype of R. halli are also included; it is readily 

apparent that the type lies at the extreme slender end 

of the variation in breadth and near the fine end of the 

variation in rib density. The holotype, accordingly, is not 

typical of fairly large populations that I believe represent this species.

The extreme variation in rib density is unusual (pi. 

2). At small diameters, the spread in rib density is low, 

but as the shells enlarge the rib density increases at 

varying rates. On some individuals, the increase in rib 

density is almost abrupt (pi. 3, fig. 2).

The primary ribs, which are numerous and well defined even on the small inner whorls (pi. 1, figs. 4-6),
SYSTEMATIC DESCRIPTIONS

100

90

80

70

60

50

40

30

20

10

0 10 20 30 40 50 60 70 80 90 100 110

DIAMETER, IN MILLIMETERS

FIGURE 2. Scatter diagram showing number of ventral ribs per half whorl of Rhaeboceras halli (Meek and Hayden) from the Bearpaw Shale 

at USGS Mesozoic locality D783 (fig. 1, loc. 24). Dots connected by lines represent measurements on single specimens; open circles 

indicate two specimens that have the same measurements. The cross indicates measurements on the holotype.

120

become bullate on the umbilical shoulder of the body 

chamber and adjoining part of the phragmocone. These 

bullae have a conspicuous forward curvature. On some 

individuals, the bullae rise into bullate tubercles on the 

body chambers (pi. 4, figs. 2, 5). The bullae or tubercles 

persist to the aperture but weaken there (pi. 3, fig. 8). 

Most of the specimens in the two large collections are 

uncrushed phragmocones. A few specimens have complete or nearly complete body chambers, but these are 

usually somewhat crushed or distorted probably due to 

the work of predators. The aperture is fairly rounded and 

has a slight ventral bulge paralleling the course of the 

ribs. All ribbing weakens near the aperture (pi. 3, fig. 8).

Diameter of the shell at the base of the body chamber 

could be determined on 44 specimens in the two large 

collections. These measurements, summarized in a 

histogram (fig. 3), do not show a clear-cut separation 

into two growth sizes as would be anticipated for sexual dimorphism. The adults in these collections range 

in diameter from 115 to 205 mm. A smaller adult (pi. 

4, figs. 1-3), 91 mm in diameter, is present in a collection from another locality (fig. 1, loc. 10).

A large collection from north-central Colorado (fig. 1, 

Iocs. 39, 40), consisting of 51 specimens suitable for one 

or more measurements, includes many juveniles that 

have body chambers (pi. 6, figs. 4-6, 10-12). The first
UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK, WESTERN INTERIOR, U.S.

O f. 

LLJ D

0.

LL. 5 

O

cc 4

LLJ 

CQ

50 60 70 80 90 100 110 

DIAMETER, IN MILLIMETERS

120 130

FIGURE 3. Histogram showing range in diameter at base of body 

chamber of 44 specimens of Rhaeboceras halli (Meek and Hayden) 

from the Bearpaw Shale at USGS Mesozoic localities D783 and 

D10234 (fig. 1, Iocs. 24, 17, respectively).

E/L

FIGURE 4. Suture, nearly twice natural size, of a specimen of Rhaeboceras halli (Meek and Hayden) at a diameter of 80 mm from the Bearpaw Shale at USGS Mesozoic locality D5675 (fig. 1, loc. 19). The venter, dorsum, and umbilical seam are indicated by the heavy, light, 

and dashed lines, respectively. Hypotype USNM 413038.

two or three whorls are smooth, and ribbing does not 

become discernible until the shells attain a diameter between 5.5 and 8 mm. Both primaries and secondaries 

appear at about the same diameter and cross the venter 

with moderate forward arching. On some individuals, 

flattening of the ribs on the venter is conspicuous on 

the inner whorls of the phragmocone. Ribbing near the 

aperture on adult specimens may be weakened and 

crowded. One specimen (unfigured hypotype USNM 

413100) has a nearly smooth band 18 mm long at the 

aperture.

The suture of R. halli is quite digitate (fig. 4). Meek 

and Hayden (1856, p. 70) described the external suture 

in considerable detail, and Riccardi (1983, text figs. 

32-34) illustrated the sutures of the types of R. halli 

and R. opalus as well as another example of R. halli.

Discussion. Hiccardi (1983, p. 34) has pointed out 

that Ammonites opalus Owen (1852, p. 579, pi. 8, figs. 

6, 6a, 6b) is a phragmocone of Rhaeboceras halli, but 

that "As Owen's name has not been used since its inception, whereas Meek's has been repeatedly quoted 

and is considered to represent the type species of
SYSTEMATIC DESCRIPTIONS

Rhaeboceras Meek * * * it is appropriate to follow Art. 

23b of the ICZN and to regard 'Ammonites opalus' as 

nomen oblitum." This conclusion is accepted herein. 

Owen's illustrations are reproduced here (pi. 1, figs. 1, 2). 

The type specimen, which is at the Field Museum of 

Natural History, Chicago, has been well illustrated by 

Riccardi (1983, pi. 13, figs. 1-4).

Rhaeboceras albertense (Warren, 1930, p. 23, pi. 2, 

figs. 1, 2; pi. 4, fig. 2) may be a stout variant of R. halli 

that has fewer ribs. Riccardi (1983, p. 40, 41) noted the 

possibility that R. albertense and R. halli may represent extreme morphologic variants of a single species. 

However, in the large collections of R. halli at hand 

(D783 and D10234), there are no specimens that quite 

match the holotype of-R. albertense in its stoutness (pi. 

9, figs. 1-3). Until a large population of R. albertense 

from the type area is available for study, it seems advisable to recognize the two species.

Occurrence. Rhaeboceras halli has been collected at 

many localities between north-central Colorado and the 

United States-Canada boundary. All occurrences in 

Montana are in the Bearpaw Shale (fig. 1, Iocs. 5, 7, 8, 

10-19, 21-25, 27-30) in the zone of Baculites jenseni 

Cobban. In Wyoming, R. halli has been found at the 

base of the Lewis Shale north of Casper (fig. 1, loc. 32) 

and in the upper part of the Pierre Shale in the Black 

Hills area (fig. 1, Iocs. 31, 33). Farther south, R. halli 

occurs in the Pierre Shale near Walden, Colo. (fig. 1, loc. 

36) and in the Richard Sandstone Member of the Pierre 

Shale in the Fort Collins area in northern Colorado (fig. 

1, Iocs. 38, 41, 42).

Rhaeboceras halli (Meek and Hayden), noded variant

Plate 5, figures 1, 2; plate 13, figures 2-5

Types. Figured hypotype USNM 413037*, from the 

Bearpaw Shale about 16 km north-northeast of 

Melstone in the SW^SWVi sec. 11, T. 11 N., R. 31 E., 

Rosebud County, Mont. Figured hypotype USNM 

413025, from the Bearpaw Shale in the NWVi sec. 24, 

T. 12 N., R. 31 E., Rosebud County, Mont. Unfigured 

hypotypes USNM 413101, 413102.

Description. A most unusual specimen of Rhaeboceras (pi. 13, figs. 2-5) was collected from the Bearpaw 

Shale (fig. 1, loc. 27) by Mr. Robert H. Feldman, Billings, Mont., and kindly donated by him to the U.S. 

Geological Survey. The specimen consists of a moderately stout phragmocone 110.5 mm in diameter with an 

umbilical ratio of 0.13. A bit of the body chamber is attached. What makes the specimen so unusual is the 

presence of ventrolateral tubercles. These arise a little 

below the last quarter whorl of the phragmocone and 

disappear at the base of the body chamber. There are 

five bullate to nodate tubercles matched on each side

of the venter. Fourteen long, arcuate umbilical bullae 

are present on the outer whorl of the phragmocone. Ribbing is unusually weak and effaced in places. Ribs crossing the venter are of irregular height and spacing and 

difficult to count; there are about 100 on the outer 

whorl. Irregular ribbing like this is present on some 

specimens of R. halli from other localities (pi. 5, figs. 

3, 5), and occasional specimens have effaced ribbing (pi. 

3, fig. 4).

Another specimen (pi. 5, figs. 1, 2) from a nearby 

locality (fig. 1, loc. 24) consists of part of a phragmocone 

71 mm in diameter that has 4 nodate ventrolateral 

tubercles on the older part of the outer whorl. Two to 

five nontuberculate ribs separate the tuberculate ones.

A third noded variant (unfigured hypotype USNM

413101) was collected with R. burkholderi Cobban, n. 

sp., at its type locality (fig. 1, loc. 20). The specimen consists of the basal part of a body chamber that has 

several blunt bullate ventrolateral tubercles. 

A fourth specimen (unfigured hypotype USNM

413102), from much farther south (fig. 1, loc. 39), is the 

younger part of the outer whorl of a phragmocone that 

has 3 low, bullate ventrolateral tubercles separated by 

1 to 5 nontuberculate ribs.

Occurrence. AH noded specimens were associated 

with normal^, halli. The rarity of the noded form is emphasized by the presence of only one specimen among 

the 116 normal R. halli collected from the Bearpaw 

Shale at USGS Mesozoic locality D783 (fig. 1, loc. 24). 

There are no noded specimens in the larger collection 

of 124 specimens of-R. halli from the Bearpaw Shale at 

USGS Mesozoic locality D10234 (fig. 1, loc. 17). The 

remarkable noded specimen collected by Mr. Feldman 

(pi. 13, figs. 2-5) is from the same stratigraphic position as that of D783 but from a locality about 8 km farther south (fig. 1, loc. 27). The fragment of a noded 

specimen from the type locality of-R. burkholderi, n. sp., 

is from 204 m above the base of the Bearpaw Shale at 

USGS Mesozoic locality D5663 (fig. 1, loc. 20). Among 

the 20 larger specimens of R. halli from the Richard 

Sandstone Member of the Pierre Shale of northern Colorado, only one has ventrolateral tubercles.

Rhaeboceras mullananum (Meek and Hayden)

Plate 7, figures 7, 8

1862. Ammonites mullananus Meek and Hayden, p. 23.

1876. Ammonites'? mullananus (Meek and Hayden). Meek, p. 607,

pi. 8, figs. la-c. 

1894. Scaphites mullananus (Meek and Hayden). Stanton, p. 187,

pi. 45, figs. 2-4 [1893 imprint]. 

1898. Scaphites mullananus Meek and Hayden. Logan, p. 477, pi.

105, figs. 2-4. 

1900. Scaphites mullananus Meek and Hayden. Herrick and

Johnson, pi. 46, figs. 2-4.
10 UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK, WESTERN INTERIOR, U.S.

1925. Scaphites mulleanus (sic) (Meek and Hayden). Diener, p. 201. 

1927. Scaphites mullananus (Meek and Hayden). Reeside, p. 31. 

Not 1905. Scaphites mullananus (Meek and Hayden). Smith, text figs. 

1 (8), 3 (11).

Type. Holotype USNM 1924 from Chippewa Point 

on the Missouri River in north-central Montana.

Diagnosis. A coarse-ribbed, stout species that is 

known only by the holotype.

Description. Rhaeboceras mullananum was founded 

on two fragments of a large phragmocone whose dimensions were given by Meek and Hayden as "its greatest 

diameter 4 inches, and 2.57 inches in breadth at the 

widest part of the outer whorl." The two fragments are 

preserved at the National Museum of Natural History 

in Washington, B.C. (USNM 1924). A large piece is 

missing between the two fragments. Meek (1876, pi. 8, 

figs, la-c) illustrated only the smaller fragment, which 

represents the inner whorls. Views of a plaster cast of 

the two fragments, which have the missing piece filled 

by plaster, are shown on plate 7 (figs. 7, 8).

The species is very stout and has a whorl section that 

is wider than high. Ribbing is rectiradiate to slightly 

prorsiradiate on the flanks and arched forward a little 

on the venter. All ribs are coarse, rounded, and sparse. 

Ten primary ribs and 26 secondary ribs are present on 

the last half of the inner whorls at a diameter of about 

68 mm. Primaries are bullate on the umbilical shoulder.

The external suture, shown by Meek (1876, pi. 8, fig. 

Ic), was poorly drawn. The lobes appear to be trifid 

although Meek stated that they were asymmetrically 

bifid. The first lateral lobe, visible on the plaster cast, 

is rather symmetrically bifid and much like that of R. 

halli in its complexity.

Discussion. Specimens comparable to the holotype 

of R. mullananum are absent in the collections of 

Rhaeboceras examined by me. The type was said to 

have come from "Chippewa Point, near Fort Benton, 

on the Upper Missouri; Fort Benton Group of the 

Nebraska Cretaceous series" (Meek and Hayden, 1862, 

p. 22). These authors gave this locality as "some twenty 

odd miles below Fort Benton." Meek and Hayden's 

types of Scaphites vermiformis and S. ventricosus were 

also said to have come from this locality. Assuming the 

20-odd miles were measured as river miles, Chippewa 

Point should lie in the Coniacian to Santonian age upper part of the Marias River Shale (Colorado Shale of 

Pierce and Hunt, 1937, pi. 43). The S. vermiformis and 

S. ventricosus would certainly fit this locality and 

stratigraphic position, but the Rhaeboceras mullananum presents a problem inasmuch as all other occurrences of this genus are from the much younger 

Bearpaw and Pierre Shales. The fossils described by 

Meek and Hayden in their 1862 paper were collected by 

John Pearsall, naturalist for Lieut. John Mullan's

expedition that was seeking a wagon road route from 

the upper reaches of the Missouri River to the Pacific 

Ocean. Meek and Hayden (1862, p. 21) noted that "The 

collections containing the fossils described in this paper, 

were obtained along the Missouri River at various 

localities between Fort Benton and points 140 to 150 

miles below the Fort. The new forms here for the first 

time made known, are all labelled 'Chippewa Point.'" 

The possibility thus exists that the type of R. mullananum, although labelled Chippewa Point, could have 

come from the Bearpaw Shale which crops out less 

than 150 miles below Fort Benton. On the other hand, 

inasmuch as Meek and Hayden's species cannot be 

matched with anything in the collections of Rhaeboceras examined, R. mullananum could be from Chippewa Point as stated and possibly of Santonian age. 

The Scaphites mullananus, illustrated by Smith 

(1905, p. 641, fig. 8; p. 645, fig. 11), represents specimens 

of Ponteixites robustus Warren (1934, p. 95, pi. 3, figs. 

1-4). Smith's specimens came from the upper part of 

the Pierre Shale (zone of Baculites baculus Meek and 

Hayden) on the Cedar Creek anticline in eastern 

Montana.

Rhaeboceras subglobosum (Whiteaves)

Plate 7, figures 1, 3; plate 8, figures 3-5; plate 9, figures 4-6; plate 10

1885. Scaphites subglobosus Whiteaves, p. 52, pi. 7, fig. 3; pi. 8, figs.

1, la (not 2, 2a). 

1917. Scaphites subglobosus Whiteaves. Bowling, p. 32, pi. 31, figs.

1, la (not 2, 2a).

1925. Scaphites subglobosus Whiteaves. Diener, p. 203. 

1927. Acanthoscaphitest subglobosus (Whiteaves). Reeside, p. 34. 

1933. Scaphites subglobosus Whiteaves. Elias, p. 315. 

1940. Rhaeboceras subglobosus (Whiteaves). Landes, p. 176. 

1940. Rhaeboceras whiteavesi Landes, p. 174, pi. 6, fig. 9; pi. 7, fig.

4; pi. 8. 

1983. Rhaeboceras subglobosus (Whiteaves). Riccardi, p. 40, pis.

19-21; pi. 22, fig. 1; pi. 23, figs. 1-3; text figs. 50-56.

Types. Lectotype GSC 5339 from the Bearpaw 

Shale of southern Saskatchewan figured by Whiteaves 

(1885, pi. 7, fig. 3; pi. 8, figs. 1, la), by subsequent designation of Elias (1933, p. 315). Hypotypes USNM 

413039-413043 from the Bearpaw Shale of east-central 

Montana.

Diagnosis. A large, stout species that has depressed 

whorl sections and fairly dense ribbing.

Description. Whiteaves described and illustrated 

two phragmocones, a small one that has umbilical and 

ventrolateral tubercles and a large one without tubercles. Elias (1933, p. 315) assigned the small noded 

specimen to Scaphites plenus Meek and Hayden. Inasmuch as Whiteaves didn't designate a holotype, the 

large nontuberculate phragmocone became the lectotype by Elias' emendation.
SYSTEMATIC DESCRIPTIONS 11

Rhaeboceras subglobosum is characterized by its 

large size and great stoutness; the whorls are wider than 

high. The lectotype is a little more densely ribbed than 

indicated by Whiteaves' drawing, and on the inner half 

of the flanks, the ribs are separated into primaries and 

secondaries instead of ribs of equal size and length as 

shown by Whiteaves. As on other species of Rhaeboceras, only the primaries extend into the umbilicus, and 

they are slightly bullate on the umbilical shoulder. A 

plaster cast of the holotype reveals a ventral rib count 

of 25 per half whorl at a diameter of 68 mm and 30 per 

half whorl at a diameter of 97 mm.

Whiteaves (1885, pi. 8, fig. la) illustrated part of the 

suture of the lectotype. This suture and that of the 

holotype of R. halli, figured by Meek (1876, pi. 24, fig. 

3c; text fig. 64), are very similar.

Discussion. Rhaeboceras whiteavesi Landes (1940, 

p. 174, pi. 6, fig. 9; pi. 7, fig. 4; pi. 8) has been shown 

by Riccardi (1983, p. 41) to be the same species as R. 

subglobosum. The holotype of R. whiteavesi (pi. 9, figs. 

4-6) came from the Bearpaw Shale in Alberta, Canada.

Occurrence. Whiteaves' type came from the Bearpaw Shale on Old Wives Creek (now Notukeu Creek) in 

T. 10, R. 11, W. 3d mer., southwestern Saskatchewan. 

The species is uncommon in the Western Interior of the 

United States. A few specimens have been found in the 

Bearpaw Shale in central and north-central Montana 

(fig. 1, Iocs. 1, 3, 6, 26). Fragments of two large distorted 

specimens were collected from the Larimer Sandstone 

Member of the Pierre Shale in north-central Colorado, 

where they were associated with Baculites reesidei Elias 

(fig. 1, Iocs. 37, 43).

Rhaeboceras subglobosum (Whiteaves), noded variant

Plate 12, figures 4-7; plate 14

Types. Hypotype USNM 413043, from the Bearpaw 

Shale at USGS Mesozoic locality D12735 in Phillips 

County, Mont. (fig. 1, loc. 9); hypotype USNM 413042, 

from the Pierre Shale in Laramie County, Wyo. (fig. 1, 

loc. 35).

Description. Two stout specimens of Rhaeboceras 

subglobosum are unusual in that both have ventrolateral tubercles on the body chamber. The larger 

specimen (pi. 14) is a magnificent macroconch that was 

donated to the U.S. Geological Survey by Mr. Howard 

Ehrle, Miles City, Mont. This specimen, 153 mm long, 

is missing a part of the outer whorl of the phragmocone 

and a small piece of the body chamber. These missing 

parts were restored in plaster by Mr. Ehrle. The 

phragmocone has a fairly wide umbilicus (ratio of about 

0.20), and the outer whorl is broader than it is high. Ornament on the last half of the outer whorl consists of 

9 narrow, curved, prorsiradiate umbilical bullae and

about 30 ribs. The body chamber, which occupies threefourths of a whorl, is broken a little but not distorted 

much. It has 13 narrow umbilical bullae and 70 narrowly 

rounded, prorsiradiate ribs that cross the venter. Most 

ribs arise from the umbilical bullae or from low on the 

flank. Conspicuous bullate to nodate ventrolateral 

tubercles are present on the middle one-half of the 

phragmocone. These arise either from single flank ribs 

or from a pair of flank ribs, and they are usually connected across the venter by 2 or 3 ribs. The aperture 

is normal; it is not preceded by closely spaced ribs.

The smaller specimen (pi. 12, figs. 4-7) which may be 

a microconch, is an incomplete body chamber that 

encloses part of the phragmocone. The specimen is 

unusual in that two widely spaced pairs of ventrolateral 

tubercles are present on the body chamber. The 

specimen, 111 mm in length, includes the last one-half 

of a rather small adult body chamber that has a normal aperture preceded by a belt of closely spaced ribs 

(pi. 12, figs. 6, 7). Ribs on the rest of the body chamber 

are narrow, high, and fairly sharp. Some arise from 

sharp, narrow umbilical bullae, and others arise farther 

out on the flank. The two pairs of sharp, bullate ventrolateral tubercles lie on ribs that are separated by 10 

nontuberculate ribs. The enclosed part of the phragmocone (pi. 12, figs. 4-6) includes almost one-half of the 

older part of the outer whorl and has a diameter of 63 

mm. Its whorl section is higher than wide with a wellrounded venter and flat flanks. Umbilical bullae are narrow and closely spaced. A primary rib arises from each 

bulla, and every two primaries are separated by a secondary rib farther out on the flank. On crossing the venter, 

all ribs are coarse and well-rounded and about the size 

of the interspaces. There are no ventrolateral tubercles.

Occurrence. The smaller noded variant was collected 

at USGS Mesozoic locality D1382 in southeastern 

Wyoming (fig. 1, loc. 35). Here the specimen was found 

in a sandy limestone concretion in the Pierre Shale 15 

m above a unit of sandstone that may be the equivalent 

of the Larimer Sandstone Member of the Pierre Shale 

of areas farther south in northern Colorado. The specimen is probably from the zone of Baculites reesidei 

Elias. The large macroconch (pi. 14), which was not collected by Mr. Ehrle, does not have good locality data; 

it is from the Bearpaw Shale somewhere in the Telegraph Creek area in southeastern Phillips County, 

Mont.

Rhaeboceras coloradoense Cobban, n. sp.

Plate 6, figures 16-21; text figure 5

Types. Holotype USNM 413044 from the Richard 

Sandstone Member of the Pierre Shale at USGS 

Mesozoic locality 16093 on the south bank of Reservoir
12 UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK, WESTERN INTERIOR, U.S.

No. 3 in the NVSSEtt sec. 19, T. 9 N., R. 68 W., Larimer 

County, Colo. Paratype USNM 413045 from the 

Richard Sandstone Member at the same locality.

Diagnosis. A wide umbilicus, robust whorls, and 

coarse ribbing characterize this moderate-sized species.

Description. The holotype (pi. 6, figs. 19-21), a complete adult, has a maximum diameter of 110.5 mm and 

a breadth of 45.5 mm. The body chamber occupies threefourths of the last whorl. The deflection of the body 

chamber away from the regular curvature of the 

phragmocone produces a wide umbilicus whose ratio is 

0.25 at a diameter of 77.4 mm and 0.29 at 102.8 mm. 

In cross section, the body chamber is slightly wider 

than high and attains its greatest breadth at the umbilical shoulder; the flanks are broadly rounded, and the 

venter is more narrowly rounded. The phragmocone of 

the holotype, however, has its outer whorl slightly 

higher than wide and flattened flanks.

Ribbing on the holotype is prorsiradiate, slightly flexuous on the phragmocone, and straight on the body 

chamber. Secondary ribs are conspicuous on the phragmocone where they curve forward and are a little bullate 

on the umbilical shoulder; they number 17 on the last 

whorl. On the body chamber, the bullae rise into nine 

bullate tubercles. Secondary ribs are present on the 

outer half of the flanks of the phragmocone, but on the 

body chamber, the secondaries tend to lengthen and rise 

nearer the umbilical shoulder. Fifty-five ribs cross the 

venter on the last complete whorl of the holotype.

The suture is typical of the genus but not as digitate 

as that of R. halli. The external suture of the holotype 

is shown in figure 5.

Discussion. Rhaeboceras coloradoense differs from 

the associated R. halli in having a wider umbilicus and 

fewer ribs. The species is known only from northern Colorado where it occurs sparingly in the Richard Sandstone Member of the Pierre Shale (zone of Baculites 

jenseni Cobban) at USGS Mesozoic locality 16093 (fig. 

1, loc. 39).

Rhaeboceras coloradoense Cobban, n. sp., noded variant

Plate 7, figures 4-6

Type Paratype USNM 413046, from the Richard Sandstone Member of the Pierre Shale at USGS Mesozoic 

locality 22921 on the south bank of Reservoir No. 3 in the 

NV2SEV4 sec 19, T. 9 N, R. 68 W., Larimer County, Cola

Description. The specimen is an adult that has a 

length (height) of only 60.7 mm. Its wide umbilicus has 

a width of 8.7 mm at a diameter of 44 mm (ratio of 0.20). 

Only part of the outer whorl of the phragmocone is 

preserved; it has a whorl section that is higher than it 

is wide with rounded venter and flattened flanks. Ornament on the phragmocone consists of prorsiradiate

E/L

10 mm

FIGURE 5. Third from last external suture of the holotype of 

Rhaeboceras coloradoense Cobban n. sp. (pi. 6, figs. 19-21), from 

the Richard Sandstone Member of the Pierre Shale at USGS 

Mesozoic locality 16093 (fig. 1, loc. 39). USNM 413044.

flexuous primary ribs that arise from narrow umbilical 

bullae and 3 or 4 secondary ribs between the primaries. 

All ribs are high, rounded, and equal sized on crossing 

the venter and separated by interspaces that are the 

same size as the ribs. The body chamber, which occupies 

three-fourths of a whorl, has a whorl section that is 

higher than wide on the older part and wider than high 

on the younger part. Eleven narrow umbilical bullae are 

present on the body chamber. Each gives rise to a sharp, 

flexuous, prorsiradiate primary rib, and these ribs are 

separated by 3 to 4 secondary ribs on the older part of 

the body chamber and 1 to 3 secondaries on the younger 

part. Two ribs on the older part of the body chamber 

have sharp, bullate ventrolateral tubercles on one side 

of the shell. The aperture, which follows the trend of 

the ribs, is not preceded by close spacing of ribs.

Occurrence. The specimen was collected at the same 

locality as that of the holotype of Rhaeboceras coloradoense, n. sp., which is in the zone of Baculites jenseni 

Cobban. The specimen is interpreted as a noded 

microconch of R. coloradoense, with the holotype 

representing the macroconch.

Rhaeboceras burkholderi Cobban, n. sp.

Plate 11, figures 1-4; text figure 6

Type. Holotype USNM 413047, from the Bearpaw 

Shale at USGS Mesozoic locality D5663 about 11 km 

east of Mosby in the NWJ/4 sec. 10, T. 14 N., R. 31 E., 

Garfield County, Mont.

Name. This distinctive species is named in honor of 

Robert E. Burkholder of the U.S. Geological Survey, 

who greatly aided the author in the field and in the 

laboratory for many years. Mr. Burkholder also collected the holotype of the species.
REFERENCES CITED 13

Diagnosis. A compressed species that has a body 

chamber with flattened flanks and a slightly flattened 

venter bordered by bullate tubercles or by ribs accentuated along the ventrolateral border.

Description. The holotype (pi. 11, figs. 1-4) is a nearly complete adult that has a length of 75.5 mm and a 

breadth of 26.5 mm. Its umbilical ratio is 0.16 at a 

diameter of 53.3 mm. The body chamber includes 85 percent of the last complete whorl. As in other species of 

Rhaeboceras, the body chamber is deflected a little from 

the regular curvature of the phragmocone. Both the 

body chamber and outer whorl of the phragmocone have 

flattened flanks and whorl sections that are considerably higher than wide.

Ribbing on the holotype is sparse, prorsiradiate, and 

somewhat flexuous. Primary ribs on the last half whorl 

of the phragmocone extend from the umbilicus across 

the flanks and venter. On the outer part of the flank, 

a secondary rib appears and crosses the venter between 

two primaries. All ribs are of equal strength on the 

venter. About 20 or 21 ventral ribs are present on the 

last half whorl of the phragmocone. Ribbing on the body 

chamber is a little more closely spaced than that on the 

phragmocone, the secondary ribs are longer, and the 

primaries rise from bullate tubercles on the umbilical 

shoulder. All primaries and most secondaries rise into 

bullate tubercles on the ventrolateral shoulder on the 

older two-thirds of the body chamber. The tubercles 

gradually weaken and disappear on the younger part. 

At the point where the tubercles weaken, the ribs begin 

to arch forward on crossing the venter as they do on 

the outer whorl of the phragmocone. Where the ventrolateral tubercles are well developed, the ribs trend 

straight across the venter except for a small area on the 

holotype that has ventral ribs arranged in a zigzag 

pattern. The suture of the holotype is rather simple 

(fig. 6).

Discussion. Rhaeboceras burkholderi is an uncommon species. A slightly smaller and more densely ribbed 

adult from southern Saskatchewan, identified as 

Scaphites abyssinus Morton by Whiteaves (1885, p. 51), 

is probably R. burkholderi. A plaster cast of the Canadian specimen (GSC 5338) is in the reference collections 

of the U.S. Geological Survey, Federal Center, Denver, 

Colo.

Occurrence. The type is from a brown-weathering 

ferruginous, limestone concretion 204 m above the base 

of the Bearpaw Shale at USGS Mesozoic locality D5663 

(fig. 1, loc. 20). Part of a specimen of Rhaeboceras halli 

was found in these concretions as well as a fragment 

of the noded variant. At this locality, Baculites reesidei 

Elias was found at 200 m above the base of the Bearpaw and Baculites cf. B. jenseni Cobban was found at 

206-212 m above the base.

E/L

10 mm

FIGURE 6. Second from last external suture of the holotype of 

Rhaeboceras burkholderi Cobban n. sp., from the Bearpaw Shale 

at USGS Mesozoic locality D5663 (fig. 1, loc. 20). USNM 413047.

Rhaeboceras cf. R. burkholderi Cobban, n. sp.

Plate 11, figures 7, 8

Type. Figured specimen USNM 413048 from the 

Bearpaw Shale at USGS Mesozoic locality D5663 about 

11 km east of Mosby in the NWx/4 sec. 10, T. 14 N., R. 

31 E., Garfield County, Mont, (same locality as that of 

the holotype of Rhaeboceras burkholderi, n. sp.)

Description. This specimen is a nearly complete 

adult 128 mm in length. The slender phragmocone, 

which is uncrushed, has a piece missing at its larger end, 

where the diameter of the shell is estimated at 66 mm 

with an umbilical ratio of about 0.12. The phragmocone 

has flattened flanks and a narrowly rounded venter. 

Ornament on the outer whorl of the phragmocone consists of 9 prorsiradiate umbilical bullae and 38 ribs that 

cross the venter. The crushed body chamber occupies 

three-fourths of a whorl. Ornament on it consists of 9 

prorsiradiate umbilical bullae and about 48 ribs that 

cross the venter. Some of the ribs are accentuated a little along the ventrolateral shoulder.

Discussion. The phragmocone of this specimen is 

like that of R. halli, whereas the body chamber 

resembles that of R. burkholderi in its coarse and sparse 

ribbing. If additional collections prove that this individual is R. burkholderi, then the specimen could be 

interpreted as a macroconch because it is about twice 

as large as the holotype of R. burkholderi (the 

microconch).

REFERENCES CITED

Bayle, E., 1878, Fossiles principaux des terrains [atlas], Part 1 of 

Volume 4, Explication de la carte geologique de la France: Paris, 

Imprimerie Nationale, pis. 1-158 [text never published].

Cobban, W.A., 1951 [1952], Scaphitoid cephalopods of the Colorado 

group: U.S. Geological Survey Professional Paper 239, 42 p., 

21 pis.
14 UPPER CRETACEOUS AMMONITE RHAEBOCERAS MEEK, WESTERN INTERIOR, U.S.

___1962, New baculites from the Bearpaw Shale and equivalent 

rocks of the Western Interior: Journal of Paleontology, v. 36, no. 

1, p. 126-135, pis. 25-28.

Diener, Carl, 1925, Ammonoidea neocretacea, Part 29 of Animalia, 

[Part] 1 of Diener, Carl, ed., Fossilium catalogus: Berlin, W. Junk, 

244 p.

Bowling, D.B., 1917, The southern plains of Alberta: Geological 

Survey of Canada Memoir 93, 200 p., 35 pis.

Elias, M.K., 1933, Cephalopods of the Pierre formation of Wallace 

County, Kansas, and adjacent area: Lawrence, Kans., Kansas 

University Science Bulletin, v. 21, no. 9, p. 289-363, pis. 28-42.

GUI, J.R., and Cobban, W.A., 1966, The Red Bird section of the Upper Cretaceous Pierre Shale in Wyoming, with a section on A new 

echinoid from the Cretaceous Pierre Shale of eastern Wyoming, 

by P.M. Kier: U.S. Geological Survey Professional Paper 393-A, 

73 p.

Hayden, F.V., 1859, Catalogue of the collections in geology and natural 

history obtained by the expedition under command of Lieut. G.K. 

Warren, in Warren, G.K., Preliminary account of explorations in 

Nebraska and Dakota in the years 1855-56-57: U.S. War Department Annual Report 1858 (U.S. 35th Congress, Second Session, 

House Executive Document 2), p. 673-705.

Herrick, C.L., and Johnson, D.W., 1900, The geology of the Albuquerque sheet: Granville, Ohio, Denison University Scientific 

Laboratories Bulletin, v. 11, art. 9, p. 175-239, pis. 27-49; Albuquerque, N. Mex., New Mexico University Bulletin, v. 2, 67 p., 

22 pis.

Jeletzky, J.A., 1968, Macrofossil zones of the marine Cretaceous of 

the western interior of Canada and their correlation with the zones 

and stages of Europe and the western interior of the United States: 

Geological Survey of Canada Paper 67-72, 66 p.

Jensen, F.S., and Varnes, H.D., 1964, Geology of the Fort Peck area, 

Garfield, McCone, and Valley Counties, Montana: U.S. Geological 

Survey Professional Paper 414-F, 49 p.

Kilian, W., and Reboul, P., 1909, Les cephalopodes n6ocr6tac6s des 

lies Seymour et Snow Hill: Wiss. Ergebnisse Schwedischen 

Siidpolar-Expedition 1901-1903, v. 3, pt. 6, 75 p., 20 pis.

Landes, R.W., 1940, Paleontology of the marine formations of the Montana group, Pt. 2 of Geology of the southern Alberta plains: 

Geological Survey of Canada Memoir 221, Pub. 2453, p. 129-217, 

8 pis.

Logan, W.N., 1898, The invertebrates of the Benton, Niobrara, and 

Fort Pierre groups: Lawrence, Kans., Kansas University Geological Survey, v. 4, p. 431-518, pis. 86-120.

Magalhaes, Julio, and Mezzalira, Sergio, 1953, Moluscos f6sseis do 

Brasil: Brazil Institute Nacional Livro, ser. A, no. 4, 283 p., 94 pis.

Meek, F.B., 1864, Check list of the invertebrate fossils of North 

America; Cretaceous and Jurassic: Smithsonian Miscellaneous Collections 177, 40 p.

Meek, F.B. 1876, A report on the invertebrate Cretaceous and Tertiary fossils of the upper Missouri country: U.S. Geological Survey 

of the Territories (Hayden) Report 9, 629 p., 45 pis.

Meek, F.B., and Hayden, F.V., 1856, Descriptions of new species of 

Gasteropoda and Cephalopoda from the Cretaceous formations 

of Nebraska Territory: Academy of Natural Sciences of Philadelphia Proceedings, v. 8, p. 70-72.

____1860, Systematic catalogue, with synonyma, etc., of Jurassic, 

Cretaceous, and Tertiary fossils collected in Nebraska, by the exploring expeditions under the command of Lieut. G.K. Warren, 

of U.S. Topographical Engineers: Academy of Natural Sciences 

of Philadelphia Proceedings 1860, p. 417-432.

____1862, Descriptions of new Cretaceous fossils from Nebraska Territory, collected by the expedition sent out by the Government 

under the command of Lieut. John Mullan, U.S. Topographical 

Engineers, for the location and construction of a wagon road from 

the sources of the Missouri to the Pacific Ocean: Academy of 

Natural Sciences of Philadelphia Proceedings 1862, p. 21-28.

Naidin, D.Y., 1974, Class Cephalopoda, in Blank, M. Ya, Krymgolz, 

G. Ya, Naidin, D.Y., and Savchinskaya, O.V., Atlas 

Verkhnemelovoy Fauny Donbassa: Nedra (Moscow), p. 158-240, 

pis. 53-81.

Nowak, Jan, 1912, Die Scaphiten, Pt. 2 of Untersuchungen iiber die 

Cephalopoden der oberen Kreide in Polen: Academic des Sciences 

de Cracovie Bulletin International, ann6e 1911, ser. B, p. 547-589, 

pis. 32, 33.

Owen, D.D., 1852, Report of a geological survey of Wisconsin, Iowa, 

and Minnesota and incidentally of a portion of Nebraska Territory: 

Philadelphia, Pa., Lippincott, Grambo & Co., 638 p., illus.

Parkinson, James, 1811, Organic remains of a former world, v. 3: 

London, J. Robson, 479 p., 22 pis.

Pierce, W.G., and Hunt, C.B., 1937, Geology and mineral resources 

of north-central Chouteau, western Hill, and eastern Liberty Counties, Montana: U.S. Geological Survey Bulletin 847-F, p. 225-270.

Reeside, J.B., Jr., 1927, The scaphites, an Upper Cretaceous ammonite 

group: U.S. Geological Survey Professional Paper 150-B, p. 21-40, 

pis. 9-11.

Riccardi, A.C., 1983, Scaphitids from the upper Campanian-lower 

Maastrichtian Bearpaw Formation of the western interior of 

Canada: Geological Survey of Canada Bulletin 354,103 p., 26 pis.

Scott, G.R., and Cobban, W.A., 1959, So-called Hygiene Group of 

northeastern Colorado, in Rocky Mountain Association of 

Geologists Guidebook llth Annual Field Conference, Washakie, 

Sand Wash, and Piceance Basins, 1959: p. 124-131.

Smith, W.D., 1905, The development of Scaphites: Journal of Geology, 

v. 13, no. 7, p. 634-654.

Spath, L.F., 1953, The Upper Cretaceous cephalopod fauna of Graham 

Land: Falkland Islands Dependencies Survey, Science Report no.

3. 60 p., 13 pis.

Stanton, T.W., 1893 [1894], The Colorado formation and its invertebrate fauna: U.S. Geological Survey Bulletin 106, 288 p., 45 pis.

Steinmann, G., 1895, Die Cephalopoden der Quiriquina-Schichten: 

Neues Jahrbuch fur Mineralogie, Geologic, und Palontologie 

Abhandlungen, v. 10, p. 64-94, pis. 4-6.

Suess, E., 1866-70, Uber Ammoniten, pt. 1: Sitzungsberichte der 

Mathematisch-Naturwissenschaftlichen Classe der Kaiserlichen 

Akademie der Wissenschaften, v. 52, pt. 1, p. 71-89.

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

Alberta: Royal Society of Canada Transactions, 3d ser., v. 24, sec.

4. p. 21-26, 4 pis.

____1934, Palaeontology of the Bearpaw Formation: Royal 

Society of Canada Transactions, 3d ser., v. 28, sec. 4, p. 81-100, 

3 pis.

Whiteaves, J.F., 1885, Report on the Invertebrata of the Laramie and 

Cretaceous rocks of the vicinity of the Bow and Belly Rivers and 

adjacent localities in the North-West Territory: Geological Survey 

of Canada Contributions to Canadian Palaeontology, v. 1, pt. 1, 

89 p., 11 pis.

Wright, C.W., 1957, Superfamily Scaphitaceae Meek [p. L228-L232], 

in Arkell, W. J., Kummel, Bernhard, and Wright, C.W., Mesozoic 

Ammonoidea, in Moore, R.C., ed., Treatise on invertebrate paleontology, Part L, Mollusca 4: New York, N.Y., and Lawrence, Kans., 

Geological Society of America and University of Kansas Press, 

p. L80-L465, text figs. 124-558.
INDEX

[Italic page numbers indicate major references]

abyssinus, Scaphites ..... 

Acanthoscaphites ........

albertensis ..........

Donetz Basin, U.S.S.R

innodosus ...........

subglobosus .........

Alberta, Rhaeboceras ....

Page 

..... 13

..... 2

..... 1

..... 1

...... 1

...... 10

...... 11

albertense, Rhaeboceras .......... l,2,9;pl.9

albertensis, Acanthoscaphites ....... 1

Ammonites, Brazil ................. 1

halli .......................... 1,2,6

mullananus .................... 1,2,9

opalus ....................... l,6;pl.l

Baculites baculus .................. 10

jenseni .................... 1,2,6,12,13

reesidei ....................... 2,11,13

baculus, Baculites ................. 10

Bearpaw Shale ............ 1,6,9,10,11,12,13

Brazil, Ammonites ................. 1

burkholderi, Rhaeboceras ...... 9,72,13;pl.ll

Colorado Shale ............

coloradoense, Rhaeboceras . .

Donetz Basin, U.S.S.R.,

Acanthoscaphites

Fort Benton Group ........

..... 10 

.77,12;pls.6,7

gemmatus, Grossouvrites . . . 

Graham Land, Grossouvrites 

Grossouvrites .............

gemmatus .............

Graham Land .........

halli, Ammonites 

Phylloceras . .

10

2

2

2

2

2

1,2,6 

6

halli, Ammonites Continued Page 

Pusozia ....................... 6

Rhaeboceras ............ 2,6,9,11,12,13;

pls.1,2,3,4,5,

6,7,8,11,12,13

Hayden, F.V., quoted .............. 10

Hoploscaphites nodosus ............ 2

innodosus, Acanthoscaphites ........ 1

jenseni, Baculites .............. 1,2,6,12,13

Larimer Sandstone Member,

Pierre Shale . . .

Lewis Shale ..............

1,11 

1,9

Marias River Shale ................ 10

Meek, F.B., quoted ............... 1,2,6,10

mullananum, Rhaeboceras ........... 2,9;pl.7

mullananus, Ammonites ............ 1,2,9

Scaphites ..................... 9

mulleanus (sic), Scaphites ........... 10

nodosus, Hoploscaphites 

Scaphites .........

opalus, Ammonites ................ l,6;pl.l

Rhaeboceras ................... 8

Phylloceras ....................... 1,2

halli .......................... 6

Pierre Shale .................. 1,9,10,11,12

Larimer Sandstone Member ..... 1,11

Richard Sandstone Member .... 1,9,11,12

plenus, Scaphites .................. 10

Ponteixites robustus ............... 10

Pusozia .......................... 2

halli .......................... 6

Page 

reesidei, Baculites ................. 2,11,13

Rhaeboceras ...................... 1,2,6

Alberta ....................... 11

albertense ................... l,2,9;pl.9

burkholderi ............... 9,72,13;pl.ll

coloradoense .............. 77,12;pls.6,7

halli ............. 2,6,9,ll,12,13;pls.l,2,

3,4,5,6,7,8,11,12,13 

mullananum ................... 2,9;pl.7

opalus ........................ 8

Saskatchewan ................. 10,13

subglobosum ................. 2,70,11;

pls.7,8,9,10,12,14 

subglobosus ................... 10

whiteavesi .................... 1,2,10

Riccardi, A.C., quoted .............. 8

Richard Sandstone Member, Pierre Shale 1,9,

11,12 

robustus, Ponteixites ............... 10

Saskatchewan, Rhaeboceras .... 

Scaphites ....................

abyssinus ................

mullananus ................

mulleanus (sic) .............

nodosus ..................

plenus

10,13

1.2

13

9

10 

2

10 

subglobosus ................... 1,10

ventricosus .................... 10

vermiformis ................... 10

subglobosum, Rhaeboceras ......... 2,70,11;

pls.7,8,9,10,12,14 

subglobosus, Acanthoscaphites ...... 10

Rhaeboceras ................... 10

Scaphites ..................... 1,10

ventricosus, Scaphites . 

vermiformis, Scaphites

10

10

whiteavesi, Rhaeboceras ............ 1,2,10

15

U.S. GOVERNMENT PRINTING OFFICE: 1987 573-047/66,018 REGION NO. 8

PLATES

Contact photographs of the plates in this report are available, at cost, from the U.S. Geological Survey Library, Federal Center, Denver, CO 80225
PLATE 1

[All figures natural size. Arrow points to base of body chamber]

FIGURES 1-12. Rhaeboceras halli (Meek and Hayden) (p. 6).

1, 2. Holotype of Ammonites opalus Owen (from Owen, 1852). 

3, 7, 8. Rear, side, and front views of hypotype USNM 413012, from USGS Mesozoic locality D783 (text fig. 1, loc. 24).

4-6. Front, side, and rear views of hypotype USNM 413013, from the same locality.

9, 10. Side and rear views of hypotype USNM 413014, from USGS Mesozoic locality D10224 (text fig. 1, loc. 13). 

11, 12. Front and side views of a plaster cast of the holotype USNM 384, from northern Montana.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 1

r .' >rV^^SWW1 *. « i

'r'*' ?. '/, %>' A^.-^ "* 

10
PLATE 2

[All figures natural size. Arrow points to base of body chamber]

FIGURES 1-13. Rhaeboceras halli (Meek and Hayden) (p. 6).

1-3. Rear, side, and front views of hypotype USNM 413015, from USGS Mesozoic locality D783 (text fig. 1, loc. 24). 

4-6. Front, side, and rear views of hypotype USNM 413016, from the same locality. 

7-9. Rear, side, and front views of hypotype USNM 413017, from the same locality. 

10-12. Front, side, and rear views of hypotype USNM 413018, from the same locality.

13. Side view of hypotype USNM 413019, from USGS Mesozoic locality D10223 (text fig. 1, loc. 10). See plate 5, figure 

3 for rear view.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 2

i>~

11 12 

RHAEBOCERAS
PLATE 3

[All figures natural size. Arrow points to base of body chamber]

FIGURES 1-8. Rhaeboceras halli (Meek and Hayden) (p. 6).

1, 2. Front and side views of hypotype USNM 413020, from USGS Mesozoic locality D783 (text fig. 1, loc. 24). See

plate 11, figure 6 for rear view.

3, 4. Rear and side views of hypotype USNM 413021, from the same locality. 

5-7. Front, rear, and side views of hypotype USNM 413022, from the same locality.

8. Side view of a complete adult from the Bearpaw Shale of east-central Montana. Larry C. Eichhorn collection.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 

3

JL
PLATE 4

[All figures natural size. Arrows point to base of body chambers]

FIGURES 1-5. Rhaeboceras halli (Meek and Hayden) (p. 6).

1-3. Rear, side, and front views of hypotype USNM 413023, from USGS Mesozoic locality D10223 (text fig. 1, loc. 10). 

4, 5. Rear and side views of hypotype USNM 413024, from the same locality.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 4
PLATE 5

[All figures natural size. Arrows point to base of body chambers]

FIGURES 1-8. Rhaeboceras halli (Meek and Hayden) (p. 6).

1, 2. Rear and side views of hypotype USNM 413025, a noded variant, from USGS Mesozoic locality D783 (text fig.

1, loc. 24).

3. Rear view of hypotype USNM 413019, from USGS Mesozoic locality D10223 (text fig. 1, loc. 10). See plate 2, 

figure 13 for side view.

4. 7. Rear and side views of hypotype USNM 413026, from the same locality as figures 1 and 2.

5. 6. Rear and side views of hypotype USNM 413027, from the same locality. See plate 11, figure 5 for front view. 

8. Side view of hypotype USNM 413028, from the same locality.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 5

RHAEBOCERAS
PLATE 6

[All figures natural size. Arrows point to base of body chambers]

FIGURES 1-15. Rhaeboceras halli (Meek and Hayden) (p. 6).

From USGS Mesozoic locality 16093 (text fig. 1, loc. 39).

1-3. Rear, side, and front views of hypotype USNM 413029. 

4-6. Front, side, and rear views of hypotype USNM 413030. 

7-9. Rear, side, and front views of hypotype USNM 413031. 

10-12. Front, side, and rear views of hypotype USNM 413032. 

13-15. Side, front, and rear views of hypotype USNM 413033. 

16-21. Rhaeboceras coloradoense Cobban, n. sp. (p. 11). 

From the same locality as figures 1-15.

16-18. Rear, side, and front views of paratype USNM 413045. 

19-21. Front, side, and rear views of the holotype USNM 413044.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 6

14 15

20

RHAEBOCERAS
PLATE 7

[All figures natural size. Arrow points to base of body chamber]

FIGURES 1, 3. Rhaeboceras subglobosum (Whiteaves) (p. 10).

Rear and side views of hypotype USNM 413039, from USGS Mesozoic locality 21660 (text fig. 1, loc. 26). 

2. Rhaeboceras halli (Meek and Hayden) (p. 6).

Side view of hypotype USNM 413034, from USGS Mesozoic locality D783 (text fig. 1, loc. 24). See plate 8, figures

1 and 2 for front and rear views. 

4-6. Rhaeboceras coloradoense Cobban, n. sp., noded variant (p. 12).

Side, rear, and top views of paratype USNM 413046, from USGS Mesozoic locality 22921 (text fig. 1, loc. 40). 

7, 8. Rhaeboceras mullananum (Meek and Hayden) (p. 9).

Front and sicje views of a plaster cast of the holotype USNM 1924.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 7

RHAEBOCERAS
PLATE 8

[All figures natural size]

FIGURES 1, 2. Rhaeboceras halli (Meek and Hayden) (p. 6).

Front and rear views of hypotype USNM 413034, from USGS Mesozoic locality D783 (text fig. 1, loc. 24). See plate

7, figure 2 for side view. 

3-5. Rhaeboceras subglobosum (Whiteaves) (p. 10).

Side, front, and rear views of hypotype USNM 413040, from USGS Mesozoic locality 5517 (text fig. 1, loc. 1).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 8

i;:1J ,'/' f - i

RHAEBOCERAS
PLATE 9

[All figures natural size]

FIGURES 1-3. Rhaeboceras albertense (Warren) (p. 9).

Rear, side, and front views of a plaster cast of the lectotype UA 349. 

4-6. Rhaeboceras subglobosum (Whiteaves) (p. 10).

Front, rear, and side views of a plaster cast of the holotype of R. whiteavesi Landes, GSC 9367.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 9

RHAEBOCERAS
PLATE 10

[Figure about nine-tenths natural size. Arrow points to base of body chamber]

Rhaeboceras subglobosum (Whiteaves) (p. 10).

Side view of hypotype USNM 413041, from USGS Mesozoic locality D1338 (text fig. 1, loc. 2).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 10

RHAEBOCERAS
PLATE 11

[All figures natural size. Arrows point to base of body chambers]

FIGURES 1-4. Rhaeboceras burkholderi Cobban, n. sp. (p. 12).

Front, side, top, and rear views of the holotype USNM 413047, from USGS Mesozoic locality D5663 (text fig. 1, loc. 20). 

5, 6. Rhaeboceras halli (Meek and Hayden) (p. 6).

From USGS Mesozoic locality D783 (text fig. 1, loc. 24).

5. Front view of hypotype USNM 413027. See plate 5, figures 5, 6 for rear and side views.

6. Rear view of hypotype USNM 413020. See plate 3, figures 1, 2 for front and side views. 

7, 8. Rhaeboceras cf. R. burkholderi Cobban, n. sp. (p. 13).

Side and rear views of figured specimen USNM 413048, from the same locality as figures 1-4.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 11

vma.
PLATE 12

[All figures natural size. Arrow points to base of body chamber]

FIGURES 1-3. Rhaeboceras halli (Meek and Hayden) (p. 6).

Front, side, and rear views of hypotype USNM 413035, from USGS Mesozoic locality 16093 (text fig. 1, loc. 39). 

4-7. Rhaeboceras subglobosum (Whiteaves), noded variant (p. 11).

Hypotype USNM 413042, from USGS Mesozoic locality D1382 (text fig. 1, loc. 35). 

4, 5. Side and rear views of the inner whorls. 

6, 7. Side and rear views of the body chamber and the enclosed inner whorls.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 12

RHAEBOCERAS
PLATE 13

[All figures natural size. Arrows point to the base of body chamber]

FIGURES 1-5. Rhaeboceras halli (Meek and Hayden) (p. 6).

1. Side view of hypotype USNM 413036, from USGS Mesozoic locality D10223 (text fig. 1, loc. 10). 

2-5. Rear, front, and side views of a noded variant hypotype USNM 413037, from USGS Mesozoic locality D12734 

(text fig. 1, loc. 27).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 13

RHAEBOCERAS
PLATE 14

[All figures natural size. Arrow points to base of body chamber]

FIGURES 1, 2. Rhaeboceras subglobosum (Whiteaves), noded variant (p. 11).

Side and rear views of hypotype USNM 413043, from USGS Mesozoic locality D12735 (text fig. 1, loc. 9).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1477 PLATE 14

RHAEBOCERAS