Ordovician Fossils 

From Wells in the 

. Williston Basin 

Eastern Montana

GEOLOGICAL SURVEY BULLETIN 1021-M

A CONTRIBUTION TO GENERAL GEOLOGY

ORDOVIGIAN FOSSILS FROM WELLS IN THE 

WILLISTON BASIN, EASTERN MONTANA

REUBEN JAMES Boss, Jr.

ABSTRACT

This paper deals primarily with the stratigraphic significance of Late Ordovician brachiopods and corals and Early Ordovician trilobites from cores of five 

wells in eastern Montana.

As much as 350 feet of the uppermost limestones and shales of the Deadwood 

formation of Cambrian and Ordovician age contain trilobites ranging in age 

from very Early Ordovician (Beliefontia zone) to approximately middle Early 

Ordovician. In one well (from which samples were not available for the present 

study), 390 feet of Cambrian strata is authentically reported to occur beneath 

similar rocks of Ordovician age without apparent break.

Varied and abundant conodonts, not yet studied, are in the overlying quartzose 

sands and shales of the Winnipeg formation. Ostracoderms of types previously 

recorded from the Harding sandstone of Colorado are also abundant. Similar 

fish are now known to range into the Late Ordovician. Analysis of the fauna! 

evidence for the Middle Ordovician age of the Winnipeg and its presumed correlatives indicates the age is tenuous.

Most of the species found in the upper 300 feet of the Red River formation 

occur also in the overlying Stony Mountain formation, indicating no major 

faunal break; a similar fauna was found in the base of the questionable Leigh 

dolomite member of the Bighorn dolomite. Probable equivalence of the lower 

Red River with the lower massive member of the Bighorn is suggested by only 

scanty faunal evidence.

The fauna and lithologic character of the calcareous lower shale member of 

the Stony Mountain formation are strikingly similar to those of shaly beds in the 

uppermost Bighorn, and both are of Late Ordovician age. The few species 

Identified from the upper dolomitic member of the Stony Mountain show affinities 

with the Late Ordovician of Maritime Canada. The Red River and Stony Mountain formations in the subsurface are designated the Bighorn group. The term 

Bighorn dolomite is retained for undivided surface occurrences.

INTRODUCTION

This paper summarizes the probable stratigraphic distribution of 

Ordovician fossils in the Williston basin. It is based on a study of 

cores from five deep wells located on the Cedar Creek anticline and

439
440

northwestward of it in eastern Montana, along the western margin of 

the basin (fig. 67). The limitations of a study based on so few wells 

are obvious, but the probable value to current exploration activity 

of a list of the fossils identified to date (1954) determined the release

108° 106° 104° 102° 100°

44°

-44°

108°' '106° 104° 102° 100° 98° 

FIGURE 67. Index map showing location of wells and other localities discussed. Localities 1-5 are listed on page 441; 6, Bighorn dolomite locality, South Fork of Rock Creek; 

7, Bighorn dolomite locality, North Fork of Crazy Woman Creek; 8, Deodwood, S. Dak. 

(type area for Deadwood and Wfiitewood formations); 9>, Little Rocky Mountains; 10,

Winnipeg, Manitoba.

of this report. Illustrations and descriptions of some characteristic 

fossils are also presented as an aid in subsurface zonation.

SCOPE AND EXTENT OP INVESTIGATION

In the summer of 1952, cores from several deep wells in the Williston 

basin were made available at Billings, Mont., for paleontologic sampling and study. About 1 year later R. P. Kunkel and C. L. Nieschmidt prepared a geological age log for each of the wells, utilizing 

the results of the preliminary faunal reports. These were made 

available in open files of the Geological Survey. A reconnaissance of 

the surface exposures of supposedly correlative formations was then
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASEST, MONT. 441

undertaken during the summer of 1953 in the northern Black Hills of 

South Dakota, along the east flank of the Bighorn Mountains in 

Wyoming, and in the Little Rocky Mountains. The hope of obtaining adequate collections with which to determine exact correlation 

between formations in the subsurface and those cropping out to the 

south and west was only partly fulfilled, however.

The 1 cores studied were taken from wells located roughly along a 

line running north-northwesterly from the intersection of the 

boundaries of North and South Dakota and Montana (fig. 67). These 

wells are:

1. C. H. Musphy Corp., East Poplar Unit No. 1, Center, SW%NE%, sec. 2, 

T. 28 N., R. 51 E., Roosevelt County, Mont.

2. Shell Oil Co., Richey area, Northern Pacific R. R. No. 1, SE%NW%NW%, 

sec. 19, T. 23 N., R. 50 E., Dawson County, Mont.

3. Empire State Oil Co., Hathaway No. 1, Center, SE%NE%, sec. 6, T. 14 N., 

R. 55 E., Dawson County, Mont

4. Shell Oil Co., Pine Unit No. 1, SW%SW%NE%, sec. 30, T. 12 N., R. 57 E., 

Wibaux County, Mont.

5. Shell Oil Co., Little Beaver No. 1, NE%SW%, sec. 13, T. 4 N., R. 61 E., 

Fallen County, Mont.

Although samples of other cores have been made available or 

furnished by other companies they are not reported here either because 

they include only post-Ordovician fossils, or because there has not 

been enough time to study them.

It must be emphasized that within a given formation or zone the 

entire fossil assemblage may not be listed. In some places, particularly in the dolomitic portions of the cores, preservation is too poor 

to warrant even the best intelligent guess as to identity. In others 

new species are present but not well-enough represented to permit 

proper description. Although bryozoans and conodonts are abundant 

in some strata, for the most part they have been left out of consideration until they can be studied in detail.

The work of Miss Helen Duncan (1956) on Ordovician and Silurian corals has obviated the necessity for discussing them in detail 

in this report.

ACKNOWLEDGMENTS

Much of the sampling and collecting from the cores was undertaken by R. P. Kunkel, who with P. W. Richards aided in obtaining 

information as need arose. During the 1953 field season T. H. Rogers 

assisted the author in reconnoitering lower Paleozoic surface exposures and subsequent technical assistance was rendered by F. B. 

Rowell. Without the cooperation and interest of numerous members 

of the geologic and paleontologic staffs of oil companies the project 

would not have been possible.
442 CONTRIBUTIONS TO GENERAL GEOLOGY

Most of the fossils collected were identified by Helen Duncan and 

Jean M. Berdan, particularly the corals and ostracodes. Much of 

the preparation and preliminary identification of the brachiopods 

was done by Josiah Bridge. Specimens of fish hav,e been identified 

by D. H. Dunkle, and G. A. Cooper has given much valuable time in 

consultation. . ..

Dr. Hans Frebold, chief, Division of Stratigraphic Paleontology, 

Canadian Geological Survey, furnished casts of type specimens of 

Okulitch's (1943) Stony Mountain species. Professor J. P. Gries 

made available for examination the core of the Carter Oil Co., 

Northern Pacific No. 1 well, stored at the South Dakota School of 

Mines.

METHOD OF PRESENTATION

Although Stratigraphic information is usually presented in 

sequence from oldest to youngest, during drilling operations strata 

are encountered in the reverse order. As it is intended that this 

report be of interest to petroleum geologists in the Williston basin 

in particular, the younger formations are discussed first.

The paper is divided into three main parts: (1) a discussion of 

the formations involved, (2) listings of the faunal evidence obtained 

from each well, including the basis for placement of the Silurian and 

Ordovician boundary, and (3) brief illustrated descriptions of or 

notes on genera and species involved.

ORDOVICIAN STRATIGRAPHIC UNITS OF THE 

WESTERN WILLISTON BASIN

DERIVATION OF STRATIGRAPHIC TERMINOLOGY

The pre-Silurian strata encountered in the five cores are all of 

Ordovician age. The formations recognized since 1951 in the subsurface of the Williston basin have been traced southward from Manitoba by petroleum geologists using lithologic similarity, evidence 

from faunal studies, and data obtained by various geophysical 

methods with varying success. As a result, the terminology in use 

has been essentially that of the surface exposures of southern Manitoba, where the formations in descending order are the Stonewall, 

the Stony Mountain, the Bed River, and the Winnipeg. Because of 

distinctive lithologic features within these formations or marked 

changes between them, they can be recognized without much difficulty in most of the cores examined. The most troublesome exception is the recognition of the boundary between the Stonewall and 

(or) Stony Mountain formations and the overlying Silurian deposits, which are so similar in lithologic character that in at least one
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 443

core differentiation has been based almost entirely on fossil evidence. 

Despite proximity of many of the wells to the Black Hills of South 

Dakota the use of Whitewood dolomite has not generally been 

adopted and is not recommended here for two reasons.

First, the Whitewood limestone as defined by Darton and Paige

(1925, p. 5-7, 24r-25) is certainly equivalent to no more than the Red

River formation of the subsurface and probably not to all of that;

; no demonstrable Stony Mountain equivalent has yet been found in

-the Black Hills.

Second, the Whitewood formation as redefined by Furnish, Barragy, 

and Miller (1936, p. 1330-1332) includes underlying siltstones and 

shales of probable Middle Ordovician age as well as the "limestone" 

of Darton. Much of this lower clastic material is lithologically similar to and holds the same stratigraphic position as the Winnipeg formation. Until 1952 (McCoy) no formal designation had been offered 

for these clastic beds, and it was only natural that the Manitoban terms 

be used in the subsurface.

The Whitewood limestone of Darton is here designated the Whitewood dolomite. Its lithologic character is closely similar to that of the 

lower part of the Bighorn dolomite. The Whitewood dolomite is restricted to the dolomite and sandy dolomite of Ordovician age in the 

Black Hills, and the term is used in the same sense as that of Darton 

and Paige (1925). The underlying shales, siltstones, and sandstones 

are purposely excluded.

In 1952 McCoy (p. 44-47) proposed names for the siltstones, shales,

 and sandstones which lie beneath the true dolomites of the Whitewood 

and above the Deadwood formation in the northern Black Hills. These 

in descending order are the Roughlock siltstone, the Ice Box shale, and 

the Aladdin sandstone the last being the Scolithus sandstone of authors. Unfortunately McCoy's account was written for a guidebook 

and is necessarily abbreviated. Until a more complete treatment of 

these units is published, it will not be possible to determine their utility. 

McCoy has noted that his units change facies within short distances; 

some of these lithic changes have been verified and others found during 

the present reconnaissance. It is evident that more work needs to be 

done before his nomenclature can be evaluated or consistently applied 

even in the Black Hills.

Obviously a large portion, if not all, of the interval between the 

Whitewood and Deadwood strata is equivalent to the Winnipeg formation in position, in lithologic character, and probably in f aunal content, but published and otherwise available information is far too 

sketchy to permit interchangeability of terminology at this juncture. 

As an example, several geologists feel that the so-called Scolithus (or
444 CONTRIBUTIONS TO GENERAL GEOLOGY v. .'",J>

Aladdin of McCoy, 1952) sandstone is the same as the basal sandstone 

of the Winnipeg formation; actually we know only that earliest Early 

Ordovician fossils have been obtained just below this sandstone in;the 

uppermost Deadwood strata (Lochman and Duncan, 1950, p. 351; 

McCoy, 1952, p. 47) and that Middle Ordovician (?) shale overlies it 

in the northern Black Hills/ In the Carter Oil Co. Northern Pacific 

: No. 1 well to the north, shales and siltstones apparently equivalent to 

the Winnipeg formation occur at a depth of 8,845-8,930 feet (core is 

missing from 8,858-8,900 feet). These are underlain by limestone 

containing abundant brachiopod shells, none accurately identifiable, 

but suggesting Lower Ordovician genera. Below this limestone lies 

clean quartoze sandstone at a depth of 9,040-9,130 feet. The question 

then arises as to whether this sandstone is the extension of the so-called 

Scolithus (Aladdin of McCoy, 1952) or represents another similar 

body within the Deadwood formation; if it is the former, it cannot be 

considered the basal part of the Winnipeg beds or their equivalents. 

If it is not the so-called Scolithus sandstone, it is equally apparent from 

the core examined that the sandstone is not present at the base of the 

apparent Winnipeg at about 8,930 feet. It may later prove possible to 

trace the Roughlock, Ice Box, 'and Aladdin formations as proposed by 

McCoy beneath the surface in wells located close to the flanks of the 

Black Hills, but it would be inadvisable to use his terminology in the 

area of this report.

To the west and southwest of the Williston basin, Ordovician strata 

crop out in the Bighorn and Little Rocky Mountains. From these 

areas the Bighorn dolomite might have been followed in the subsurface and used as a basis for terminology in eastern Montana. As 

in formations in the Black Hills, however, several facts discourage any 

such usage. In the first place exploration within the Williston basin 

has spread westward from North Dakota, not eastward from the 

Eocky Mountains. Second, although the Bighorn dolomite can be 

divided into three members (in descending order the Leigh member 

of Blackwelder (1918), an unnamed member, and the Lander sandstone member of Miller (1930), it is not certain to which, if any, of 

these members the Stony Mountain, Red River, and Winnipeg formations exactly correspond.

According to paleontologic evidence presently ayailable the Bighorn dolomite, including the Lander sandstone member (Miller, 1930, 

p. 196) but excluding the "Harding" sandstone equivalent (Kirk, 

1930, p. 460-461), corresponds to all of the Red River and much of 

the Stony Mountain formations as they are developed in the Subsurface of the Williston basin; it is therefore proposed that the term
ORDOVICIAN FOSSILS PROM WELLS IN WILLISTON BASIN, MONT. 445

Bighorn group be applied to include these two formations in eastern 

Montana. It may eventually prove feasible to include the Winnipeg 

formation in this group, depending on future studies of its conodonts 

and fish. The term Bighorn dolomite of f ormational rank is retained 

for undivided surface occurrences in Montana and Wyoming.

Beneath the Winnipeg formation as indicated in two of the cores 

studied lie limestones which are glauconitic, pyritif erous and in part 

composed of intraformational conglomerates. Thin partings of 

black or very dark green shaly material are interspersed throughout 

these limestone beds, which are so similar to the upper strata of the 

Deadwood formation of the Black Hills and of the Bighorn Mountains 

(in the latter case the Gallatin limestone of recent authors) that they 

were originally logged as Upper Cambrian. Despite the fact that 

only Early Ordovician fossils have been found in these limestones in 

the two cores studies, the name Deadwood formation is here applied to 

them. Since 1950 (Lochman and Duncan, p. 351) it has been known 

that the topmost Deadwood beds in the Black Hills contain Lower 

Ordovician fossils. In addition, James L. Wilson, of the Shell Oil 

Co. (personal communication, oral and written), states that in the 

core of Shell's Southwest Richey No. 32-33B well there are 740 feet 

of Deadwood strata in the upper 350 feet of which Lower Ordovician 

trilobites are present.

The stratigraphic terminology used in this report is summarized 

in text figure 68.

THE FORMATIONS

The Ordovician formations of southern Manitoba have been discussed by Baillie (1952). His report includes descriptions of the 

Stony Mountain, Red River, and Winnipeg formations. More recently 

Steam (1953, p. 1477-1478) has concluded that the overlying Stonewall formation should be included in the Ordovician rather than in the 

Silurian system, where it has traditionally been placed. Steam's conclusions are based on faunal evidence, and they confirm the earlier 

suggestion of Baillie (1952, p. 42) that the Stonewall formation, as 

restricted by him (1951, p. 6-9), might be more closely allied to the 

underlying than to the overlying rocks. In the present report, dealing primarily with paleontology, no effort has been made to differentiate between the dolomitic strata designated by others as the Stonewall formation and the upper Stony Mountain formation. In any 

event, as long as the so-called Stonewall strata seem to be assignable 

to the Upper Ordovician it would seem best to regard them as a member of the Stony Mountain formation if they were to be separately 

designated.
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ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 447

BIGHORN GROUP

STONY MOUNTAIN FORMATION

The Stony Mountain formation was named and defined by Dowling 

(1900, p. 46-53F, 88-83F) from exposures in the vicinity of Winnipeg; 

the orginal description included extensive f aunal lists, including those 

published previously by Whiteaves (1895, p. 111-128). In 1943 

Okulitch (p. 59-74) presented the results of a more detailed study in 

which he subdivided the upper, dolomitic portion of the formation into 

three members in descending order named Birse, Gunton, and Penitentiary. The lower, shaly portion he named the Stony Mountain 

shale member.

Baillie (1952, p. 8) disregarded the Birse member, because in the 

field he was unable to differentiate it from the Gunton. Similarly 

because of the limitations placed on the present study by the wide 

spacing of wells and the discontinuous nature of the samples obtained 

from most of them, no attempt is made here to distinguish between 

the dolomitic units. These, and the Stonewall formation of Steam's 

(1953), are all grouped in an upper dolomitic member for purposes 

of this report.

In sharp contrast to the yellowish dolomitic rocks of the upper 

member, the Stony Mountain shale, of Okulitch, here designated simply the lower shale member, is composed of argillaceous limestone and 

fossiliferous shale of a predominantly reddish-gray color (Baillie, 

1952, p. 19) in its type area. Because of this contrast with units above 

and below, this member is an extremely useful marker in the subsurface. In the core of the Shell Pine Unit No. 1 well the same rock 

is present, but the color is dark green. In the Empire State Hathaway 

No. 1 core there are two intervals of green and greenish-black calcareous shale and siltstone below the upper dolomitic member; these 

are at depths of 8,718-8,728 and 8,830-8,853 feet. Between them, two 

small samples indicate the presence of lithology apparently identical 

to that of the underlying Bed River formation. Faunally the deeper 

of these two is most like the lower shale member; the upper is more 

silty than shaly and may represent the Penitentiary member of the 

Manitoban section.

The lower shale member is represented southward by red calcareous 

shales in the Carter Oil Co.'s Northern Pacific No. 1 well at depths of 

8,230-8,300 feet. An important occurrence of similar beds bearing an almost identical fauna has been overlooked by many recent 

workers; this lies in the uppermost few feet of the Bighorn dolomite 

on the South Fork of Rock Creek, Johnson County, Wyo. (Center, 

Ny2NEiASWy4SWy4, sec. 25, T. 52 N., R. 84 W.). From the red 

shaly beds at this locality (Dl (CO)) came the extensive fauna of 

Richmond age listed by Darton in 1906 (p. 4).
448 CONTRIBUTIONS TO GENERAL GEOLOGY

The prolific fauna of the lower shale member is correlative with 

deposits of Richmond age elsewhere, particularly with the Maquoketa 

shale of Iowa. The few species obtained from the upper dolomitic 

member seem to indicate close correspondence with the Upper. Ordovician deposits of Anticosti Island and Quebec.

RED RIVER FORMATION

In his report of 1900 Dowling (p. 40-46F, 63-88F) recognized beneath the Stony Mountain formation three stratigraphic units which 

he named the Upper Mottled, Cat Head, and Lower Mottled limestones. 

Foerste (1929a, p. 35) proposed the term Red River formation to include all three of these; Dowling's formations were reduced to the rank 

of members. Foerste further changed the name of the Upper Mottled 

to the Selkirk limestone and the Lower Mottled to the Dog Head limestone. No attempt has been made here to differentiate the three members of the formation.

In the core samples studied the Red River is principally limestone 

and dolomitic limestone; almost all samples have a brown or tan color. 

The limestone and dolomitic limestone are more coarsely crystalline 

than are the dolomites of the upper Stony Mountain formation and 

their brown color usually contrasts with the yellowish to creamy 

tinge of the younger dolomites. On this basis the upper limit of the 

Red River formation is thought to lie between 8,407 and 8,602 feet 

in the Murphy Corp. East Poplar Unit No. 1 well; almost no reliable 

fossil evidence is present.

Fortunately dolomitization in many samples has affected the matrix 

more than the enclosed fossils, and removal of the shells with formic 

acid has disclosed the internal structures as dolomitic casts.

Although two members of the Red River formation have a mottled 

appearance in their type areas, this characteristic must be used with 

care in the subsurface. Samples from two of the cores studied show 

pronounced cream and light-gray mottling in the fine-grained dolomite of the Stony Mountain formation.

Foerste's paper (1929b) is especially important in assembling <fcUe 

faunal evidence for the Late Ordovician dating of the Red River

formation, which had been considered Trentonian by Dowling.

"WINNIPEG FORMATION

Although the Winnipeg sandstone was first described by Dowling in 

1896, his more detailed account of the Winnipeg formation in 1900 

(p. 39-40F, 54-63F) has served as the standard reference to its typical 

exposure. The description of Baillie (1952, p. 10-14,25-27) is a more 

concise, yet thorough work; it furnishes the most complete modern 

synthesis of what is known concerning the Winnipeg lithologically and 

faunally. In its type area the formation consists of poorly bedded
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASEST, MONT. 449

basal quartzose sandstones overlain by interbedded bluish-green shales, 

sandstones, and arenaceous shales (Baillie, 1952, p. 11).

The most northerly well studied bottomed in the Winnipeg formation at a depth of 9,163 feet after passing through 118 feet of white 

quartzite; interspersed with the quartzites are beds of carbonaceous 

black shale. Most of these are thin and concentrated near the top 

of the unit. The thickest shale zone was from depths of 9,064-9,102 

feet. The deepest 10 feet of the core contains black and -white quartzites separated by black shale partings. In the Shell Pine Unit No. 1 

core Winnipeg-type rock lies between depths of 9,518 and 9,652 feet. 

Although two short sections of core 9,619-9,647 feet and 9,519-9,525 

feet were not available for examination, the formation in this well is 

composed predominantly of green and greenish-black shales, interbedded with numerous thin layers of quartzitic sandstone. The, deepest 6 feet consists of red and green mottled siltstone and shale. :

The stratigraphic distribution of sandstone and shale within the 

Winnipeg formation is probably highly variable; a persistent basal 

sandstone cannot be expected.

In the cores of two wells the formation rests upon glauconitic. limestone of the Deadwood formation. :. - :

ORDOVICIAN AND CAMBRIAN: DEADWOOD 

FORMATION

Although the Deadwood formation of the Black Hills was named 

by Darton in 1901 (p. 505-508) this early discussion is of little use 

in establishing clear-cut boundaries. In 1904 (p. 382) he denned the 

formation as though it included all beds between the pre-Cambrian 

crystalline rocks and the Whitewood limestone, including as much as 

45 feet of shale and siltstone at the top. Later (1909, p. 14, 19) he 

seems to have assigned 24 feet of "white siliceous limestone" (the upper 

calcareous siltstones of Middle Ordovician (?) age according to more 

recent interpretation) to the Whitewood beds and to have left the 

green shales (now recognized as Ordovician) in the Deadwood.

Darton and Paige (1925, p. 6) later established the lower boundary 

of the Whitewood at its present position below the true dolomite 

beds, thereby allocating all older units to the Deadwood formation. 

The discovery of Middle Ordovician (?) fossils in the siltstones and 

green shales beneath the Whitewood limestone by Furnish, Barragy, 

and Miller (1936) resulted in reassignment of the siltstones and shales 

to the Whitewood and lowering of the upper boundary of the Deadwood formation to the top of the so-called Scolithus sandstone. In 

1952 McCoy (p. 47) proposed the name Aladdin sandstone to supplant 

Scolithus beds and removed it from the Deadwood formation.

The formation as represented in the cores studied is composed predominantly of glauconitic, pyritiferous limestones containing much
450 CONTRIBUTIONS TO GENERAL GEOLOGY

intrafbrmational conglomerate with minor partings and thin layers 

of black silty.shale. Neither glauconite nor pyrite is uniformly 

abundant.

In lithologic features these rocks so closely resemble the upper 

Deadwood strata in the northern Black Hills and in the Bighorn 

Mountains (there used in the sense of Darton, 1904, p. 434) that they 

are assigned to this formation without hesitation.

Only Lower Ordovician fossils have been obtained from this unit 

in the cores of the Shell Pine Unit No. 1 and Shell, Kichey area, Northern Pacific No. 1 wells. Information furnished by James L. Wilson, 

of the Shell Oil Co., for the Shell Southwest Eichey No. 32-33B 

well indicates the presence of about 350 feet of Lower Ordovician 

and 390 feet of Cambrian strata between the base of the Winnipeg 

formation and the basement rocks. The lower 207 feet of Early 

Ordovician and upper 158 feet of Cambrian strata are composed of 

green shale, becoming slightly calcareous and micaceous upward; 

the intersystemic boundary has been located on faunal evidence only.

These facts are not wholly unexpected. In 1950 Lochman and 

Duncan (p. 351) reported that the topmost few feet were of Early 

Ordovician age in the Black Hills. In 1953 Palmer and I collected 

a fauna from the upper 10-15 feet of the Deadwood along South 

Piney Creek on the east flank of the Bighorn Mountains, which may 

be of the same age.

LATE ORDOVICIAN FAUNA

Following a brief summary of the evidence for placement of the 

Silurian-Ordovician boundary in each of the five cores studied, the 

fossils so far identified are listed by well and depth within each well. 

For purposes of comparison, collections made from two localities in 

the Bighorn dolomite along the east flank of the Bighorn Mountains 

are also listed. The faunal distribution in all of these is summarized 

on plate 44 and in the insert facing page 458.

Where formations have been designated in the faunal lists the 

designations have been made with considerable confidence. On plate 

44, however, the placement of many of the formation boundaries are 

compromises between my own observations of lithologic characteristics in complete cores or random samples, correlation charts published in the Billings Geological Society's Guidebook for 1952, and 

information obtained from other geologists.

SILUBIAN AND ORDOVICIAN BOUNDARY

The upper dolomites of the Stony Mountain formation are overlain 

by Silurian dolomites so similar in lithologic character that they can 

be distinguished only with difficulty and seldom with certainty. 

Fortunately a few fossils mostly corals of Silurian age have been
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 451

obtained; in no core has it been possible to pinpoint the Silurian and 

Ordovician boundary, but its position can be bracketed between the 

lowest Silurian and highest Ordovician specimens.

Such faunal evidence as is available for bracketing the boundary is 

given below by well and depth; obviously f aunal evidence is better in 

some wells than in others. Because the fossils are in dolomites, they 

are not very well preserved.

1. 0. H. Murphy Corp., East Poplar Unit No. 1 well

Very scant poor faunal evidence is available from this core. A Silurian 

Halysites is present at 8,345 feet. Lower in the core there are numerous relicts 

of fossils, but none certainly identifiable until a depth of 8,975-8,989 feet is 

reached. There a large specimen of ReccptacuUtes similar to those in the lower 

beds of the Bighorn dolomite is present.

2. Shell Oil Co., Riohey area, Northern Pacific R. R. No. 1 well

Depth 

(feet)

9,516 Greenfieldiat sp. (brachiopod)

Whitfieldella? sp. (brachiopod) 

9,571 Favosites sp. 

9,656 Pyonactisf sp. (horn coral) 

9,680 Favosites sp. 

9,710 Pentamerid brachiopod, similar to Virginia.

Except for Favosites the forms listed above are exclusively Silurian, 

and Favosites is a common Silurian coral.

At a depth of about 9,784 feet,rthere is a change in rock type.from, 

the creamy dolomites above to brownish dolomites below. From the 

samples studied it seems certain that at least the interval 9,974-10,169 

feet is a single lithologic unit.

In this unit very poorly preserved brachiopods at 9,974 feet suggest 

the genus Fardenia to G. A. Cooper; in my opinion these may belong 

rather to Holtedahlina. Fardenia is a common form in Silurian rocks, 

but it has been reported from Upper Ordovician strata in the Gaspe 

(Cooper and Kindle, 1936, p. 357, pi. 51, fig. 39). Holtedahlina is an 

Ordovician genus, and the specimens here are similar in general 

appearance to those in the Shell Pine Unit No. 1 core at 9,103 feet.

The fact that these specimens are from a single stratigraphic unit in 

which other Ordovician brachiopods are present at a depth of 9,980- 

9,989 feet also favors an Ordovician dating.

The Silurian and Ordovician boundary should therefore lie between 

9,710 feet and 9,974 feet, in a 260-foot thickness. For lack of better 

evidence I suggest it be placed tentatively at 9,784 feet to coincide 

with the lithologic change mentioned above.

3. Empire State Oil Co., Hathaway No. 1 well

At depths of 8,492-8,493 feet two species of Favosites and a poorly 

preserved specimen of Heliolites? sp. have been identified by Jean

389021 57 2
452 CONTRIBUTIONS TO' GENERAL GEOLOGY

Berdan, who states that the specimens are more likely to be Silurian 

than Ordovician.

At a depth of 8,556 feet are found Strophomena cf. S. hecuba, Billings,' Protozeuga cf. P. anticostiana Twenhofel, and RhyncKotrema? 

cf. R. plicata Cooper and Kindle. These are Late Ordovician species.

The Silurian and Ordovician boundary probably lies between these 

two collections.

4. Shell Oil Co., Pine Unit No. 1 well

No core is available for study from ,a depth of 8,544-8,941 feet. The 

dolomites between 8,941-8,968 feet have yielded no identifiable fossils. 

The Silurian and Ordovician boundary should lie within one of these 

two intervals.

5. Shell Oil Co., Little Beaver No. 1 well

Faunal evidence for placement of the Silurian and Ordovician 

boundary is very poor. At a depth of 8,112 feet a horn coral with dissepiments is present, though otherwise not identifiable. Jean Berdan 

(written communication, 1952) notes that dissepiments are not known 

in such corals in strata older than Silurian.

The highest identifiable Ordovician fossils are Cata&ygaf. cf. C. 

anticostiensis (Billings) and Zygospiraf cf. Z. aequivafois (Twenhofel) from a depth of 8,335 feet.

There are two lithologic changes between these two depths; based 

on lithologic comparison with other cores I suggest that the Silurian 

and Ordovician boundary may lie between depths of 8,112 and 8,153 

feet in this well.

FAUNAL LISTS

Fossils identified to date (1954) from the five well cores studied are 

listed below by well and depth. In addition, the fauna of the red 

shaly beds in the uppermost Bighorn dolomite exposed on the South 

Fork of Rock Creek in Johnson County, Wyo., and fossils obtained 

from the base of the upper (Leigh?) member of the Bighorn on the 

North Fork of Crazy Woman Creek in the same county are listed. 

Descriptions and notes on most of the species are given on pages 

473-503. (See fig. 67 for locations.)

1. C. H. Murphy Corp., East Poplar Unit No. 1 Well (Locality D88 (CO)) 

Bighorn group:

Fossils from this core are SO poorly preserved that even generic determinations have not been attempted. Shadowy aoiomitized relicts of brachiopods ai'fi

abundant in some zones. The little evidence obtained from these and a comparison of rock types suggest correlation between the 8,602-8,670-foot interval in 

this well and the 9,974-9,984-foot interval in the Shell Richey area, Northern 

Pacific No. 1 well.

The only identified fossils in the strata presumed to belong in the Bighorn 

group is a large specimen of Receptaculites from 8,975-8,989 feet and very 

poor molds which probably belong to Holtedahlinat at 8,602 feet.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 453

2! Shell Oil Co., Richey area,, Northern Pacific R'. R.,- No. 1 Well, (Locality

D89 (CO))

Bighorn group: . . 

Stony Mountain formation:

Although no diagnostic fossils have so far been obtained, it is probable that the approximate interval 9,784-9,970 feet represents the Stony Mountain formation. This opinion is based entirely on the lithologic character of the 

strata. , 

Red River formation:

9,974 feet (loc. DS9c (CO)).

Holtedahlina'! sp. (ornamentation similar to specimens illustrated

by Wang, 1949, pi. 7F), 

9,980-9,989 feet. (loc. D89b (CO)).

Megamyonia cf. M. ceres '(Billings.). 

10,123-10,135 feet. (loc. D89a (CO)). 

Cyclocrinitesf sp. (very small)

Numerous brachiopod and coral relicts were found in the dolomite 

between 9,974 and 10,170 feet, but none, other than those listed above, 

can be identified with confidence.

3. Empire State Oil Co., Hathaway No. 1 Well (Locality D90 (CO))

Bighorn group:

Stony Mountain formation: 

Dolomitic member:

8,556-8,664 feet. (loc. D90e (CO)). Same fossils throughout. 

Strophomena cf. S. hecuba Billings 

Rhynchotremal cf. JR. plicata Cooper and Kindle 

Protozeuga cf. P. anticostiana Twenhofel 

Numerous unidentifiable, fragmentary relicts of Rafinesqmna- 

', like shells.

Leperditiid Ostracoda, not generically identifiable. 

8,814 feet. (loc. D90d (CO)).

"Holophragma" sp. a horn coral distinctive of the Bighorn

dolomite.

Lower shale member: 

8,830-8,853 feet.

Fauna more fragmentary but clearly corresponds to that of

Shell Pine Unit No. 1 well at depth of 8,986-9,010 feet. 

Red River formation:

8,857 feet. (loc. D90c (CO)).

Dinorthisl sp. (relict of shell; appears same as large species

from Rock Creek locality of Bighorn dolomite). 

9,097 feet (loc. D90b (CO)).

Strophomena cf. S. rugulifera Wang 

Thaerodontal sp. or Sowerbyella"! sp. 

9,274 feet (loc. D90a (CO)).

Streptelasma (Orewingkia) robustum (Whiteaves)

This core is especially valuable in giving some idea of the faunas to 

be found in the upper dolomite of the Stony Mountain formation. 

The three' brachiopod species identified are known from Upper Ordovician strata of Anticosti Island, Quebec, and the Nicolet River 

.area.
454 CONTRIBUTIONS TO GENERAL GEOLOGY

The same problem of identification regarding Sowerbyella and 

Thaerodonta is met here at 9,097 feet as in the Shell Pine Unit No. 1 

well at 9,023-9,043 feet and 9,286-9,294 feet and in the Shell Little 

Beaver No. 1 well at 8,526 feet and 8,550 feet.

There is no evidence to suggest that any of the samples from the 

Bed River formation are older than Late Ordovician in age. 

4. Shell Oil Co., Pine Unit 1 Well (Locality D91 (CO) )

The faunas of the shalie member of the Stony Mountain formation and Red 

River» formation are better preserved in this core than, in the other submitted 

for study; however, a few genera have been found only in other cores. The 

fauna of the shale member of the Stony Mountain formation is abundant and 

many of its elements are very similar to, if not identical with, those found on 

the surface at the Rock Creek locality of the Bighorn dolomite in Wyoming. 

In general this assemblage is also similar to those of the Maquoketa shale, of 

the so-called Stonington beds of northern Michigan (Hussey, 1926), and of the 

Upper Ordovician of Anticosti Island.

Although their preservation in dolomitic rocks is generally poor, the fossils 

found in the upper 100-150 feet of the Red River formation are essentially the 

same as those from the overlying shale. A thin interval between 9,103 and 

9,116 feet has yielded poorly silicified brachiopods. At 9,286-9,292 feet two 

species of brachiopods are recognized, Megtfntyonia\<£. M. unictfstafa (Meek'and Worthen) and a species which may belong either to Sowerbyella or Thaerodonta; 

this same faunal zone may be present in the Shell Little Beaver well at 8,531- 

8,540 feet.

Fossils identified in the Shell Pine Unit No. 1 well are listed by depth: 

Bighorn group :

Stony'Mountain-^ formation: , 

Lower shale member:

8,986-9,010 feet (loc. D91f (CO)). 

Batostoma n. sp. 

Trematis? sp. 

Dinorthis (Plaesiomys) cf. P. proavita Winchell and Schuchert

sp. (large)

Platystrophia cf. P. eguiconvexa Wang 

Lepidocyclus perlamellosus (Whitfield)

gigas Wang

HypsiptychahybridaWang 

Strophoinena cf. S. vetusta James

hecuba (Billings) 

Megamyonia cf. M. ceres (Billings)

cf. M. unicostata (Meek and Worthen) 

cf. M. nitens (Billings) 

Meffamyonia sp. (equals Wang, 1949, pi. 9C)

Opikina.7 aff. O. limbrata Wang

Diceromyonia cf. D. ignota, (Sardeson) 

storeya Okulitch

Modiolopsis,?- aff. M. concentrica Hall and Whitfield 

Ptervneaf sp. 

Conularia? sp. 

laotelusf sp.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 455

Bighorn group Continued 

Red River formation:

9,023-9,043 feet (loc. D91e (CO)).

Strophomena cf. fif. rugulifera Wang

Megamyonia cf. M. nitens (Billings) 

cf. M. ceres (Billings)

Sowerbyella or Thaerodonta sp. (not identifiable as to genus)

Zygospira cf. Z. resupinata Wang

Dalmanellid species, not identified

High-spired gastropod, not identifiable generically 

9,103-9,116 feet (loc. D91d (CO)). Poorly silicified fossils.

Hesperorthis cf. H. laurentina (Billings)

Megamyonia cf. M. nitens (Billings)

Strophomena sp.

Holtedahlina aff. H. moniguensis Foerste

Catazyga sp. 

9,122-9,128 feet (loc. D91c (CO)).

Lepidocyclus cf. L. perlamellosus (Whitfield)

Hypsiptycha sp.

Zygospira cf. Z. aequivalvis Twenhofel 

9,280-9,294 feet (loc. D91b (CO)).

Megamyonia cf. M. unicostata (Meek and Worthen)

Jthaerodonta? sp. or \SQweKb.y£lla<? sp.

Oalapoecia sp. 

9,474 feet (loc. D91a (CO)).

Holysites (Catenipora) gracilis (Hall)

The collections listed above for the Ked Biver formation through 

a depth of 9,128 feet are so similar to the fauna of the overlying shale 

of the Stony Mountain formation that they should be included in 

the Upper Ordovician.

There is some doubt about the small collection from 9,286-9,294 

feet; the specimen designated Megamyonia cf. M. unicostata (Meek 

and Worthen) in its dolomitized state-.lacks the characteristically 

prominent median costella on the pedicle valve. Most of the specimens from the Maquoketa shale of the Patterson Springs locality 

(Ulrich and Bassler loc. 207g) from which Wang's figured pedicle 

valve was obtained (1949, p. 33, pi. 9A, fig. 5) have also lost the prominent costella, undoubtedly from abrasion of the shells. On the basis 

of outline, convexity, and spacing of pseudopunctae the single specimen from the core cannot be differentiated from this species. Associated are numerous small specimens which belong either to Sowerbyella or Thaerodonta and fragmentary specimens of Lepidocyclus?. 

This thin zone very probably is lithologically and faunally the same 

as that in the Shell Little Beaver well at a depth of 8,531-8,540 feet.

The presence of Holy sites (Catenipora) gracilis (Hall) at 9,474 

feet is here interpreted as indicating a Late Ordovician age, although 

some stratigraphers maintain that its range includes the Middle 

Ordovician.
456- - CONTRIBUTIONS .TO GENERAL. GEOLOGY. ....

5. Shell Oil Co., Little Beaver No. 1 Well (Locality D9% (CO))

Bighorn group: ; 

Stony Mountain formation:

No identifiable fossils obtained from this part of core. 

Bed River formation:

8,330-8,335 feet (loc. D92g (CO)).

Catazyga anticostiensis (Billings)

Zygospira cf. Z. aequivalvis Twenhofel 

8,362 feet (loc. D92g (CO)).

Paleofavosites"! sp.> 

8,378 feet (loc. T>92f (CO)).

Fossils very poorly silicified.

Abundant pelmatozoan columnal plates, circular, pentagonal, and asteriform. Small gastropods. A few fragments of brachiopods, none 

identifiable. 

8,387 feet (loc. D92f (CO)).

Very poor preservation; identifications doubtfully referred.

Holtedahlina"! cf. H. sulcata Foerste

M,eg.amyonia sp. 

8,470 feet (loc. D92e (CO)).

Calyptalaucol sp. (a single pygidium) 

8,515 feet (loc. D92e (CO)).

Megamyonia sp. 

8,524 feet (loc. D92d (CO)).

Rafinesquinat sp. (Suggestive of R. alternate, as figured by Foerste,

1924, pi. XIII, figs. 6a,c). 

8,526 feet (loc. D92c (CO)).

Rafinesquina sp. (similar in outline to R. Winchester en sis Foerste, 1910, 

p. 42, pi. V, figs. 13c, 14).

Megamyonia n. sp.(?)

T,ho>6Kpaonta sp. oxMower'byella sp. 

8,531-8,540 feet (loc. D92b (CO)).

Megamyonia cf. M. unicostata (Meek and Worthen)

Thaerodonta cf. T. recedens (Sardeson)

Zygospira cf. Z. aequivalvis Twenhofel

Bumastus"! sp. 

8,550 feet (loc. D92a (CO)).

Holtedahlina'i sp.

Thaerodontal sp. or Sowerbyella 1! sp.

6. Locality Dl (CO) Bighorn dolomite; red fossiliferous shaly beds at top. South 

Fork of Rock Creek, Center, y% W401F%flfF%f sec. 25, T. 52 N., R. 84 W., 

Johnson County Wyo.

This locality, first described by Darton (1906, p. 4) is an extremely important 

one in correlation of the lower shaly member of the Stony Mountain formation 

with surface exposures. The fauna obtained from the red shaly and silty beds in 

the top few feet of the Bighorn dolomite is very similar to that of shale of the 

Stony Mountain formation and bears a striking similarity to that of the Maquoketa shale of Iowa. Fossils identified are: 

Btreptelasma trilobatum Whiteaves

cf. 8. latusculum Billings 

"Holophragma" sp. 

Favosites (Paleofavosites) cf. F.prolificus Billings
ORDOVICIAN FOSSIL& EROM WELLS IN WILLISTON BASIN, MONT. 457

Batostoma sp.

Sceptropora cf S. facula Ulrich 

Dinorthis"! sp. (two new species) 

Plaesiomys? sp. (one new speciesi) 

Pionorthis aff. P. occidentalis Okulitch 

Lepidocyclus capax (Conrad)

perlamellosa (Whitfield) 

Hypsiptycha cf. IT. hybrida Wang

anticostiensis (Billings) 

Rhynchotrema iowense Wang 

Zygospira sp. (n. sp.?) 

Thaerodonta sp. 

Strophomena hecuba Billings 

Megamyonia n. sp. (aff. M.nitens (Billings) ) 

Opikina aff. 6. limbrata Wang 

Diceromyonia n. sp. aff. D. tersa (Sardeson)

ct.D.ignota (Sardeson)

storeya Okulitch 

Onmella sp.

Astraspis desiderata Walcott 

Eriptychius americanus Walcott

7. Locality D35 (CO) Bighorn dolomite, 15 feet above the base of the upper 

(Leighl) member, North Fork of Craay Woman Creek, Center NBy^SWy^, 

sec. 28, T. 49 N., R. 83 W., Johnson Co., Wyo. 

Hypsiptycha cf . H. hybrida Wang 

Zygospira cf. Z. resupinata Wang 

Thaerodonta cf . T. dignata Wang 

Megamyonia cf. M. unicostata (Meek and Worthen)

cf. M. ceres (Billings) 

Opikina 1! aff. 6. Umbrata Wang 

Isotelusl sp. 

Cyclocrinites cf. C. intermedius (Billings)

Compared with most collections from the Bighorn dolomite the 

specimens obtained from this locality by A. R. Palmer and me are 

fairly good casts and molds. Features such as the denticulation of 

hinge lines in Thaerodonta are unusually well preserved. The one 

specimen referred to Zygospira resupinata Wang is better preserved 

than that taken from a depth of 9,023-9,043 feet in the Shell Pine 

Unit No. 1 core.

LATE ORDOVICIAN CORRELATION

At the outset of the present study, I hoped that it might be possible 

to discover some zonal distribution of the fauna by which each of the 

Upper Ordovician formations encountered could be subdivided. Although much more work could be done on the cores, the results to 

date (1954) have been to the contrary; in the two cores with the best 

lithologic control (Shell Pine Unit No. 1 and Empire State Hathaway 

No. 1) there seems to be no significant difference between the faunas
458 CONTRIBUTIONS TO GENERAL GEOLOGY

of the lower shale member of the Stony Mountain formation and most, 

if not all, of the Red River formation. This fact is immediately evident from examination of plate 44 and the insert facing this page.

Although I have been unable to pick out any distinct zonal arrangement there are a few assemblages which suggest possible close correlation from core to core. These are given alphabetic designations in the 

insert and their positions are indicated by capital letters (A, B, C) on 

the right side of columnar sections on plate 44. In suggesting these 

possibly equivalent zones, I have relied on the general aspect of both 

the fossils and rocks, for many of the specimens are too poorly preserved for exact identification. As an example, G2 is indicated for the 

Murphy East Poplar, Shell Richey, and Shell Pine Unit wells; its 

placement in the first two is tentative, being based primarily on the 

occurrence of poor dolomitized specimens of Holteddhlina( ?), which 

seem to be the same as those in the Pine Unit well.

On the other hand, the G3 zone is indicated in the Pine Unit core 

and in the surface exposure of the Bighorn dolomite with confidence.

The occurrence of most elements of the lower Stony Mountain and 

Red River faunas in two different rock types is noteworthy. Had it 

not been for the presence of the abundant G3 fauna in the red'shaly and 

silty beds of the Bighorn dolomite at locality Dl (CO), I would have 

proposed a tentative correlation between the lower shale member of 

the Stony Mountain formation in the Shell Pine Unit well and the 

lowest beds of the Leigh (?) member of the Bighorn dolomite at locality 

D35 (CO). It is my present impression that the apparent difference 

between the faunas of the lower Stony Mountain strata and the upper 

Red River formation is one of numbers, and that this is only an illusion 

owing to difficulty in working specimens out of the dolomitized Red 

River formation. The distribution of the significant fossils is given 

in the insert.

INTERREGIONAL. CORRELATION

For many years there has been uncertainty as to the correct correlation of the Red River, Bighorn, and Whitewood formations. Should 

their age be considered Late Ordovician, Middle Ordovician, or partly 

both? Historically Bowling (1900) considered the Stony Mountain 

strata to be of Richmond age and the Red River formation to be of 

Trenton age. Similarly Darton (1906, p. 4) thought the upper 

(Leigh?) member of the Bighorn dolomite to be of Richmond age and 

the lower massive member to be Trenton in age. Mainly through the 

work of Foerste (1929) and Miller (1930) all of these formations came 

to be correlated with Upper Ordovician strata elsewhere. Diversity 

of opinion still exists and has been thoroughly summarized by Baillie 

(1952, p. 37-38) and Dunbar (in Twenhofel and others, 1954, p. 257- 

258). There is no need to review in detail both sides of the controversy here.
Distribution of Late Ordovician fossils in Wittiston basin and Bighorn Mountains 

[Arranged by zones, In large part arbitrary; for use In conjunction with plate 44]

^^\^ Well and zone 

Genus and spocies ^^\^^

Receptaculites sp. (cf. R. owcni).- _____________________

"Streptelasma" trilobatum. ___________________________

"Holophragma" sp_ ________ ___________________

Favosites (Paleofavosites) cf. F. (P.) prolificus- -________-

Halt/sites (Catenipora) gracilia---, --------------------

Trematis sp___ ____________________--_--__-_-

Dinorthisl n. sp. A___ ----------------------------

? n. sp. B ____ - ___ ____ _ ______ 

(Plaesiomys) cf. D. (P.) proavita. __________ _______

(Pionorthis) cf. D. (P.) occidentalis-.. _______ ___

Lepidocyclus capax- _ _____________ ___

gigas---- _____________ ---------------------

sp 

cf. R. plicata--- _________ -----------------------

Catazygact. C. anticostiensis ___ ________________ ____

n. sp___._ _________________________________

Rqfinesquina sp. A_ __ -----------------------

sp. "}? B '-' --- _ 

 

_ _ 

~- 

__ 

---------------- 

_ _ ___ _____ 

-----------

___________

sp. C _______ . ________ ._ _ -_-

Strophomena cf. S. vetusta,-- _________ _____________

Megamyonia cf. M. cer««_______________-__-___-_____-

sp - -----

i a^j- ------------------------------------------

CT*

Diceromyonia n. sp. off. D. tersa,. ....-.--._...--------

storcya _..----._.-------..----.----.

Pterineat sp ___ __ __ _______________________

sp. B ___ _____________________________________

Bumastus sp __ ______________ _____________

Well

Depth in 

each well 

(feet)

Formation

Arbitrary 

zone

Empire 

State 

Hathaway 

No. 1

8556-8664

Stony 

Mountain 

(dolomite 

member)

ZoneH

X

X

X

X

Empire 

State 

Hathaway 

No. l

8314

Stony 

Mountain 

(dolomite 

member)

Empire 

State 

Hathaway 

No. 1

8857

Red River

Shell Pine 

Unit No. 1

8986-9010

Stony 

Mountain 

(shale 

member)

Bighorn 

Mts. east 

flank

Top of 

Leigh(?) 

(dolomite 

member)

Bighorn 

dolomite

Zone Q»

X

X

X

X

X

X

X

X

X 

X 

X 

X

X

X 

X

X

X 

X

X 

X 

X

X 

X

X

X

X 

X 

X

X 

X

X 

X

X 

X 

X 

X

X

X

X

X

X

X

X

X 

X 

X 

X

X 

X

Empire 

State 

Hathaway 

No. 1

9097

Red River

Shell Pine 

Unit No. 1

9023-9043

Red River

Bighorn 

Mts. east 

flank

Bottom of 

Leigb(?) 

(dolomite 

member)

Bighorn

Intermediate tone Gt-Gj

X

X

X

X

X

X

X

X

X

X

X

Murphy 

E. Poplar 

Unit No. 1

8602

Red River

Shell 

Rlchey 

Northern 

Pacific No. 1

9974-9089

Red River

Shell Pine 

Unit No. 1

9103-9123

Red River

Shell 

Little 

Beaver 

No. 1

8330-8335

Red River

ZoneGt

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Shell 

Little 

Beaver 

No. 1

8362, 8387, 

8470

Red River

Gi-i?

X

X 

X

X

Empire 

State 

Hathaway 

No. 1

9274

Red River

Gi?

X

Shell Pine 

Unit No. 1

9286-9294

Red River

Shell 

Little 

Beaver 

No. 1

8515-3550

Red River

ZoneGi

X

X

X

X

X 

X

X

X

X

X

X

Murphy 

E. Poplar 

Unit No. 1

8975-8989

Red River

Shell Pine 

Unit No. 1

9474

Red River

Bighorn 

Mts. east 

flank

Bottom of 

lower 

member

Bighorn

ZoneF

X

X

X

Summary of fauna reported here by zones (G, apparently good Index 

species; U, of uncertain Index value; index to 2 or more zones; P, of 

dubious Index value in delimiting zones here.)

H

G

P

U

G

Qi

P 

G 

G

G

P

P 

G

P

G 

G 

G 

G 

G 

G 

G 

G 

U 

U 

G

G

G

G

U

U 

P 

G

G

P

G 

G 

G 

P

G 

P 

P

P

Gi-Gj

U

u

u

u 

p

u

p

p

Gj

p

u

p

p 

p

u

p 

u

G

Gi?, Gi

G

P

U

P 

P

P

P

P

P

F

G

G

Remarks

Species presumably ranges no lower but genus does. 

No zonal value here; genus ranges much lower.

Originally described from Dog Head member of Red River formation in Manitoba.

No zonal value here. 

Dubious zonal value here; has fairly extensive range within Upper Ordorician.

Genus ranges much lower; has no zonal value here.

No zonal value here. 

Zonal value very doubtful; based on Anticosti sections it should be in zone H or higher.

Reported here and in Maquoketa so far. 

May range lower.

May range lower but appears to be limited to zone Gj and Gj. 

Apparently good index to zones Gs and Ga-2.

Specimens not accurately identifiable.

Probably good index to zone H but may range lower. 

May be expected higher based on Anticosti range.

Should range higher based on Maquoketa occurrence. 

Though expected in zone Gj may prove good index to zones Gt and Gi.

Zonal value probably not limited to zone GS-J; expected in zone Ga. 

Probably good index to zones H and GS.

'Genus reported higher in Maquoketa; not necessarily limited to zones below Gs.

May prove a good index from zones Gj and GS_»; described from Maquoketa. 

Not a valid guide to zone GI; known from the Maquoketa.

No zonal value here; originally considered index to Harding sandstone and correlatives. 

Do. 

This type found in Silurian of Anticosti.

389021 56 (Face p. 458)
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 459

Throughout the fifty-odd years since their description, there has 

never,been any serious doubt as to the Richmond age of the Stony 

Mountain beds. Through the works of Ulrich (in Darton, 1906, p. 4-5) 

and Okulitch (1943) and particularly the present study, it is obvious 

that the lower shale member contains a fauna virtually identical with 

that of the uppermost Bighorn dolomite (loc. Dl (CO)); this fauna 

is comparable to that of the Maquoketa shale of Iowa, described by 

Wang (1949). The presence of large coarsely ribbed dinorthid 

brachiopods, Strophomena hecuba, and three species of Megamyonia 

(previously referred to Leptaenal) suggests equivalence with the Upper Ordovician formations of Anticosti Island, particularly with the 

English Head and Vaureal.

The small fauna from the upper dolomitic member of the Stony 

Mountain formation (Empire State Hathaway No. 1 well) also seems 

to correlate with the Upper Ordovician of Anticosti and Quebec.

A particularly interesting fossil from the red shaly beds of the 

uppermost Bighorn is the articulated bryozoan Sceptropora cf. S. 

facula Ulrich, originally described from the lower shale member of 

the typical Stony Mountain formation. The individual segments of 

this species are only a few millimeters in length and are very distinctive (pi. 37, figs. 10,11). They may prove valuable in the examination of well cuttings.

CORRELATION OF THE RED RIVER FORMATION

As noted, no fossils obtained from the upper 300 feet of the Red 

River formation in the cores can be considered significantly different from those from the overlying Stony Mountain formation. Unless 

contradictory evidence based on other or better preserved specimens 

of the same elements of the fauna is forthcoming, it seems apparent 

that approximately the upper 300 feet of this formation must be considered of Late Ordovician age.

Few fossils have been found in the lowermost part of the Red River 

formation in the cores. The only significant species is Halysites 

(Catenipora) gracilis, a Late Ordovician form, found only in the Shell 

Pine Unit No. 1 well. Although the large specimen of Receptaculites 

taken from the Murphy East Poplar No. 1 core suggests possible 

equivalence with the lowest dolomites of the Bighorn dolomite .and 

with the Whitewood dolomite, it has not been identified with certainty 

as to species.

Considering the evidence at hand the entire Red River formation, 

and therefore the Bighorn group as a whole, is believed to be of Cincinnatian age. This conclusion is based almost entirely on brachiopods and a few corals. Neither bryozoans nor conodonts, of which
460 CONTRIBUTIONS TO GENERAL GEOLOGY

many specimens are still to be removed from the cores, have been 

studied.

However, there are some objections to this conclusion. One of the 

most recent is presented by Flower (1952, p. 25-26), who clearly implies, but does not definitely state, that the Bighorn and Red River 

formations- are equivalent to the Trenton of eastern North America. 

Flower claims that a diminishing number of cephalopod genera are 

known in "indisputable Richmondian faunas" and not in Trenton assemblages. In 1929 Foerste, in reviewing the fauna of the Red River 

formation, made it clear that many genera, not only of cephalopods 

but of other invertebrates, range from Trenton into Richmond strata.

No one has yet obtained and synthesized all possible f aunal evidence 

from the lowermost Red River formation of the cores, from the lower 

dolomite member of the Bighorn formation, and from the Whitewood dolomite. When this is done it may be found that each of these 

formations is partly of Middle Ordovician age. But by the same 

token, as is pointed out in the discussion of the Winnipeg and correlative^) faunas below, the presumed Middle Ordovician dating of the 

beds which underlie each of these units the Lander(?) sandstone 

membe'r'of the Bighorn formation, the siltstones and shales just beneath the Whitewood dolomite, and the Winnipeg formation is far 

from an established fact. These all in turn may prove to be of postTrenton age.

Of the formations encountered in the five cores studied, only the 

Winnipeg contains Middle Ordovician faunal elements. Barnes 

(1953, p. 343) states that Middle Ordovician conodonts have been 

identified from the Winnipeg formation in cores of both the Shell 

Pine Unit No. 1 and Shell, Richey area, Northern Pacific No. 1 wells. 

However, neither faunal lists nor systematic descriptions of this fauna 

have been published.

Scales and plates of primitive fish are abundant in the Winnipeg 

strata of the Shell Pine Unit No. 1 and Shell, Richey area, Northern 

Pacific No. 1 cores. Several large samples of core from the Shell 

Pine Unit No. 1 well were submitted to D. H. Dunkle, of the U. S. National Museum, for identification of the fish plates. He commented as 

follows:

Occurring at restricted horizontal levels but distributed throughout submitted sections of both cores Nos. 34 and 35 (9,525-9,596 feet), I have detected 

extremely well-preserved examples of the osseous plates known as Astraspia 

desiderata Walcott and Eriptychius americanus Walcott (see pi. 6, figs. 1-4). 

Published1' reports on the occurrence of both of these presumed ostracoderm 

fishes are two: the Harding sandstone of Colorado and a supposed stratigraphic 

equivalent in Wyoming. (Walcott, 1892 ; Kirk, 1930).
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 461

Both Astraspis desiderata Walcott and EriptycMus ameticanus 

Walcott, which until May of 1954 had been considered Middle Ordovician indices, have now been identified by Dunkle in collections from 

the red shaly beds of the uppermost Bighorn dolomite (loc. Dl (CO)), 

associated with an invertebrate fauna unquestionably of Maquoketa 

age. If the evidence'of the conoddnts-reported by Barnes is correct,' 

these two fossils can no longer serve as guides to Middle Ordovician 

strata.

The apparent extension of range of these two fish is in itself no 

reason to question the Middle Ordivician dating of the Winnipeg 

formation, for the large faunal list compiled by Baillie (1952, p. 

25-27) shows Middle Ordovician affinities. Of interest is the conclusion of Macauley and Leith (1951, p. 1461-1462) that the fauna 

of the Winnipeg is post-Trenton in age.

CORRELATION WITH THE BLACK HILLS AND BIGHORN 

MOUNTAINS SECTIONS

Any discussion of the dating of the Winnipeg strata, especially 

in the subsurface, must inevitably include reference to the Black 

Hills and Bighorn Mountains sections, despite scarcity of concrete 

faunal evidence on which to base the discussionMany geologists are convinced that the Winnipeg formation beneath the surface of the Williston basin is correlative and continuous 

with the siltstones and shales (Roughlock and Ice Box of McCoy, 

1952) beneath the Whitewood dolomite of the Black Hills. On the 

evidence of conodonts and scolecodonts these have been dated as 

equivalent to the Decorah, Plattin, and Platteville formations by 

Furnish, Barragy, and Miller (1936), who noted an especially close 

tie with the Spechts Ferry shale (1936, p. 1333,1336). On this basis 

the Winnipeg formation should be of early Trenton age.

In 1942, Amsden and Miller suggested similar correlation when they 

published the results of a study of conodonts from the lower sandstones of the Bighorn formation, here designated the Harding sandstone and the Lander (?) sandy member of the Bighorn dolomite. The 

separation of these two units was earlier emphasized by Kirk (1930, 

p. 460-463). During the 1953 field season, A. R. Palmer and I observed the distinctness of the two along the east flank of the Bighorn 

Range at Billy Creek (Wi/2, T. 48 K, R. 83 W.), on the North Fork 

of Crazy Woman Creek (Center NE^SW^4, sec. 28, T. 49 N., R. 

83 W.), on the South Fork of Rock Creek (SW^SW^, sec. 25, T. 

52 N., R. 84 W.), and on the south side of South Piney Creek 

(SEi4SEi,4, sec. 14, T. 53 N., R.84 W.). At each place the Harding 

equivalent is a white poorly cemented sandstone, composed of wellrounded frosted quartz grains; the amount of interbedded greenish 

siltstone varies from one locality to the next. Excellent detailed de-
462 CONTRIBUTIONS TO GENERAL GEOLOGY

scriptions of two of these -localities are given- by Amsden and Miller 

(1942).

Fish, plates are especially abundant at the Bock Creek locality,, 

where the relations with the overlying Lander( ?) sandstone member 

of the Bighorn dolomite are well shown. Fish plates are concentrated 

at the contact between the two formations, as if by winnowing out 

of the sand before deposition of the yellowish-buff dolomitic 

Lander(?) sandstone. Some of the plates have been reworked into 

the bottom few inches of the younger formation.

At these localities the upper of the arenaceous units grades laterally 

from a sandy dolomite to a dolomitic sandstone. In the top of this 

dolomitic material and in the base of the true Bighorn dolomite large 

cephalopods and large specimens of Receptaculites are found.

In its type area it is almost impossible to separate the Lander sandstone member from the base of the Bighorn dolomite, except OH wellweathered surfaces (Peck, oral communication 1953), for the two 

meet at a gradational contact virtually imperceptible on a fresh surface. The same is essentially true on the east flank of the Bighorn 

Mountains, where the yellowish color of the Lander member stands 

out.

In their report on the conodonts of what are here considered the 

probable Harding and Lander equivalents on the east flank of the 

Bighorn Mountains, Amsden and Miller (1942) did not use the term 

Lander but clearly differentiated between the two arenaceous units. 

Their "hard medium-grained, red sandstone-3ft." (fig. 67) is the 

Lander equivalent of the present interpretation; they listed its fauna 

above the horizontal line in table 1 (p. 303). This fauna they compared with that of the siltstones and shales beneath the Whitewood 

dolomite proper but not with the Harding sandstone. According to 

their Study, it is the fauna of the lower fish-bearing sandstones which

corresponds to that formation. From this we should conclude that 

the shales, siltstones, and sandstone which lie above the so-called

Scolithus sandstone and below the Whitewood dolomite proper in the 

northern Black Hills are younger than Harding.

The following facts should be considered before reaching any conclusions regarding the age and correlation of the Harding and Lander ( ?) 

units along the east flank of the Bighorn Mountains:

1. Amsden and Miller (1942, p. 306) emphasize that ranges of

Middle and Late Ordovician conodonts are not yet well known. They

point out the "perplexing analogy" with the siltstones and shales of 

the Black Hills shared by both the Harding and Lander (?) although 

neither of these two has any conodonts in common.

2. Their fauna from the Harding equivalent contains many more 

genera and species in common with the Harding sandstone at its type 

locality and the Platteville formation than with any other formations (Amsden and Miller, 1942, table 1).
ORDOVICIAN FOSSILS PROM WELLS IN WILLISTON BASIN, MONT. 463

3. Their correlation of the Lander(?) sandstone member of the 

Bighorn dolomite with Middle Ordovician formations is based on five 

$*e.ne,ra and but a single species (1942, table 1). Branson,.Mfihl, and 

Branson (1951, p. 4) have subsequently noted that three of these genera 

(Belodiis, Oistodus, and Paltodus) plus the same single species (O. 

curvatus) are known in the Maquoketa or higher strata of the Richmond group and that Oistodus and Paltodus are actually characteristic of Richmond strata.

4. There is as yet only fair paleontologic but good stratigraphic and 

lithologic evidence for considering the Lander (?) sandstone member 

in the Bighorn Mountains equivalent to the typical Lander member

 of the Bighorn dolomite in the Wind River Mountains; the paleontologic evidence for the Late Ordovician age of the latter (Miller, 

1930) is still impressive.

In summarizing the conclusions which can be drawn from these 

facts plus earlier remarks concerning the presumed Middle Ordovician 

siltstones and shales of the Black Hills and the Winnipeg formation 

it seems evident that

1. Much more research needs to be done on the ranges of conodont 

,,gqnera and species before they can be used with certainty to differentiate Middle from Late Ordovician strata.

2. The Harding sandstone of the Bighorn Mountains is very probably correlative with the Harding sandstone at its type locality in

 Colorado and probably with the Platteville formation.

3. Statements that most or all of the Bighorn and Whitewood 

dolomites are of Trenton age (Flower, 1952, p. 25-26; McCoy, 1952, 

p. 46; Kay, in Twenhofel and others, 1954, p. 282), largely on the 

basis of generic occurrences and (or) paleogeographic interpretation, 

may be premature.

4. If the Lander (?) sandstone member is correlative with any of 

the fine-grained clastic sediments below the Whitewood dolomite, 

further detailed study of the conodonts in the Black Hills sections 

rnay> show that they are arranged zonally and that both Middle and 

Estte Ordovician strata are includfid in the siltstones and-shales. This 

would also apply to the Winnipeg formation beneath the surface of 

the Williston basin.

EARLY ORDOVICIAN FAUNA

Although not adequate for detailed correlation the collections from 

the Shell Pine Unit No. 1 and Shell, Richey area, Northern Pacific 

No. 1 wells include Early Ordovician trilobites, in addition to poorly 

jn^served graptolites and brachiopods. The<identification of the trilo- 

, bites is seriously hampered by the fortuitous sampling inherent in 

coring; as there is no possibility of working along any stratum, disarticulated cranidia are common without their original pygidia and vice
464 CONTRIBUTIONS TO GENERAL GEOLOGY

versa. Because definite identification of many trilobites, especially of 

the type collected, depends on finding heads and tails in association, 

it is difficult to assign many of the forms obtained to a particular genus 

or species.

LOWER ORDOVICIAN CORRELATION

Although cores of only two wells in which Lower Ordovician rocks

have been found (Shell Pine Unit No. 1 and Richey area, Northern

.Pacific No. 1) areariirnediately available for study, Dr. J. L. ^ilson

(Shell Oil Co.) has furnished some information on core from 'the

Shell Southwest Richey No. 32-33B well.

This indicates the presence at depths of 10,250-10,450 feet of a 

Beliefontia-Xenostegium fauna beneath the occurrence of Kainella at 

10,212 feet. This fauna has been reported by Lochman and Duncan 

(1950, p. 351) from the top of the Deadwood formation in the Black 

Hills and in the uppermost beds of the Pilgrim limestone in Montana.

SHELL, OIL, CO., PINE UNIT NO. 1 WELJL.

Figure 69 shows the vertical distribution of the fauna in the Lowevr 

Ordovician of the Shell Pine Unit No. 1 well. Although the apparent 

faunal breaks at 9,670 and 9,698 feet may not be real but due to disconDepth, in feet

S _: o«

Hexactlnellid sponge spicules ________________

Nanorthis? ep________________________

Syntrophiid brachlopods, unidentified (pi. 43. fig. 14) 

Hormotoma? sp_______________________

Apatokephalus cf. A. canadensis Kobayashi _ _ _ 

Kirkella aff. K. fillmorensis ___ ^________ __ -

Kirkella? sp. (pi. 42, fig. 17)______________.

Ogyginus? sp __________________________

Megalaspidella orthometopa Harrington ____

Asaphellus sp-------------- _________

Megalaspis planllimbata var. cyclopyge Harrington - 

Kayseraspis aff. K. asaphelloides Harrington ____

Uoydia? ep ___________________________

Undet. pygid (pi. 42, fig. 23) ---------------

Undet. pygid (pi. 43, fig. 15)---------------

Protopliomer ops sp _________________ -.- - -

Dictyonema sp. (pi. 42, fig. 24) _______-___-.

Bryograptus ? sp-----------------------

Didymograptus? sp. or Tetragraptus? sp.. 

(pi. 43, .fig. 16)

FIGURE 69. Distribution of the Early Ordovician fauna of the Shell Oil Co., Pine Unit

No. 1 well.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 465

tinuous sampling, it is possible to make a preliminary analysis of 

them.

The species present in the 9,660-9,666-foot interval (pi. 42, figs. 

5-16,19,20) are Apatokephalus cf. A. canadensis Kobayashi, Kirkella 

aff. K. fllmorensis Hintze, Megalaspidella cf. M. orthometopa Harrington, and a single pygidium bearing a resemblance to those of some 

species of Ogyginus. Also present are Hormotoma-type gastropods 

and; hexactinellid sponge spicules.

Kirkella aff. K. fillmorensis indicates correlation -with the "G" zone 

of the Garden City formation in Utah (Hintze, 1952, p. 13-14), or 

about the middle of the Lower Ordovician sequence as it is developed 

in the Basin and Range province. The pygidium tentatively referred 

to Ogyginus is similar to one described by Kobayashi (1934b, p. 553, 

plate IV, fig. 17) from his "Asaphellus zone" of Korea. Whittington 

(written communication, 1953) believes that this pygidium may belong to quite a different genus amongst the Bathyurid trilobites. As 

a genus Apatokeplialus probably has less definitive zonal value than 

has previously ,b^eii^ ascribed to it. In Argentina (Harrington, 1938, 

p. 279) it occurs in the "Asaphellus" and "Triarthrus faunas," associated with Shumardia, Asaphellus, Megalaspis, Megalaspidella, and 

Protopliomerops and well above the Kainella-Leiostegium zone. 

Hintze (1952, p. 189) on the other hand reports Apatokephalus associated with these last two genera in Utah. In'his report on theipreDevonian formations of the Canadian Cordillera Walcott (1928, 

edited by Resser) lists several sections in which Apatokephalus is 

present (p. 284, 390 feet above Kainella; p. 359, associated with Kainella and Leiostegiwn in what may be a mixed assemblage).

Kobayashi (1953, p. 52) described Apatokephalus canadensis from 

Evan's collections in the Brisco-Dogfoot map area; in his report 

Evans (1933, p. 129) lists the genus Apatokephalus in the Kamella 

zone of the MacKay group.

Megalaspidella cf. M. orthometopa Harrington (1938, p. 239-241, 

plate Xll, figs. 1-8, p. 280) belongs to the "Triarthrus fauna" of 

Argentina; its exact position in the Basin and Range sections is not 

known, but somewhat similar asaphid forms are known in the "G" 

zone. It occurs also in the next deeper unit of the present core.

Other trilobites are present in the 9,660-9,666-foot interval in the 

shale beds and partings. These are too badly deformed to identify 

accurately. Small high-spired snails like, if not actually assignable 

to, the genus Hormotoma are found in the shales (pi. 42, fig. 14); 

Cloud and Barnes (1946, p. 69) note that this genus is not known 

below the German formation in central Texas.

Between 9,672 and 9,690 feet (pi. 42, figs. 15-20, 23, 24) occur the 

species Protopliomerous sp., Megalaspidella cf. M. orthometopa
Harrington, a pygidium questioningly referred to Kirkella, an indeterminate species represented by a single pygidium which is very 

close to that illustrated by Hintze (1952, pi. IX, fig. 9), and the 

graptolite Dictyonema sp. To this list may be added a proparian 

trilobite so poorly preserved as to be very doubtfully referred to the 

genus Pilekia.

The poor specimen of Protopliomerops is probably assignable to 

P. superciliosa Ross, an "F" zone index. The indeterminate pygidium 

similar to Hintze's suggests a correlation with the lower part of the 

"G" zone. The significance of Megalaspidella orthometopa has been 

discussed above.

The trilobites in this interval are probably of the same general age 

as those between 9,660 and 9,666 feet; the differences between the two 

lists may be the result of sampling.

The interval between 9,698 and 9,715 feet is not a satisfactory one 

for the student interested in trilobites, for in it we found five different kinds of pygidia but only two types of cranidia. It is difficult to determine to which of the pygidia the two cranidia belong 

and, until this problem is solved, final identifications cannot be made. 

However, one of the pygidia can be eliminated from this problem 

(pi. 43, fig. 15); it is poorly preserved as an impression in a shaly 

matrix and is clearly not related to the other four.

The tentative identifications are:

AsapUellusl sp.

Megalaspis planilimbata var. cyclopyge Harrington 

Kayseraspis aff. K. asaphelloides Harrington 

Lloydia"! sp.

Indeterminate pygidium close to that figured by Ross (1951, pi. 19, figs 

30,31).

This association is puzzling. Kayseraspis occurs in Argentine sections above Megalaspis and Megalaspidella and well above Asaphellua (Harrington, 1938, p. 280). In this core it is identified with or

below all three. Lloydia (Bradley, 1925, p. 7) is a Beekmajitown 

form, presumably a contemporary of Leiostegium, and its presence 

is not expected in this young an association within the Lower Ordovician. The undetermined pygidium (pi. 43, fig. 15) is similar to 

one in the "F" zone of Utah.

Summarizing the trilobite fauna of the Lower Ordovician of the 

Pine Unit No. 1 core, it is my opinion that it is younger than the 

trilobite-bearing strata encountered in the Richey area, Northern 

Pacific No. 1 well at 10,500-509 feet. Several elements of the fauna 

have closer affinities to South American (Argentine) and Korean

assemblages than to any previously described in North America; a
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 467

marked resemblance is noted to some "of the collections designated 

"Megalaspis fauna" in Walcott's (1928) Canadian Cordilleran sections; these collections have never been adequately studied and in 

some cases are incorrectly designated. For instance, collection 65W 

(Walcott, 1928, p. 330) actually includes Middle Cambrian as well 

as "J" zone Lower Ordovician genera. :

SHELL. OIL. CO., RICHEST ABBA, NORTHERN PACIFIC NO. 1 WELL.

The Early Ordovician trilobite fauna obtained from the Bichey 

area, Northern Pacific No. 1 well is limited to a thin interval between 

depths of 10,500-10,510 feet. It includes the genera Leiostegiwn and 

Kainella as well as two minute hystricurid species. The assemblage 

is clearly equivalent to the "D" zone of the Lower Ordovician of Utah 

and Nevada, the lower part of the Manitou formation of Colorado, part 

of the Lower Ordovician of the Northeastern States, the lowest division of the Ordovician in Argentina (Harrington, 1938, p. 279-281; 

Kobayashi, 1935), part of the Lower Ordovician of Korea (Kobayashi, 

1953), part of the Mons formation of the Canadian Cordillera (Walcott, 1928, p. 273, 284, 331, 332, 359), and part of the MacKay group 

of British Columbia (Evans, 1933, p. 126-129). This zone is apparently equivalent to the strata at a depth of 10,212 feet in Shell's 

Southwest Bichey No. 32-33B well.

At a depth of 10,466 feet in the Bichey Area, Northern Pacific No. 1 

well poorly preserved graptolites are present. These are tentatively 

assigned to the genus Bryograptus. The same graptolite genus, 

whether it be Bryograptus or not, is present at a depth of 9,718 feet 

at the bottom of the Pine Unit No. 1 well, accompanied by a single 

minute specimen which may be an immature Didymograptus or Tetragraptus (pi. 43, fig. 16). The shale partings containing these graptolites in the two wells may not be exactly contemporaneous, but these 

two occurrences tend to support the belief that the Kainella-Leiostegium fauna is older than the lowest fauna reported in this paper from 

the Pine Unit No. 1 well.

Of more than passing interest is the occurrence of the brachiopod 

Imbricatia at a depth of 10,500-10,509 feet in the Bichey Area, Northern Pacific No. 1 well. Although no specimens good enough for illustration were obtained the ornamentation is so distinctive that there can 

be little doubt as to its identity. This genus has been described by 

G. A. Cooper (1952 p. 21-23, pi. 3E, figs. 14-19; pi. 4D, figs. 17-22) 

from the Cool Creek and Manitou formations. Its presence here suggests the possibility qf correlating the Kainella-Leiostegium trilobite 

zone with the middle of the Cool Creek formation of Oklahoma.

389021 57-
468 CONTRIBUTIONS TO GENERAL GEOLOGY

SUMMARY 

FAUNAL CORRELATION

The study of fossils found in the cores of five wells located along the 

Cedar Creek anticline and in the Bichey and Poplar areas, as well as 

collections obtained during a reconnaissance of lower Paleozoic rock 

exposures in the Black Hills and Bighorn Mountains has been limited 

almost entirely to brachiopods and corals of Late Ordovician and 

trilobites of Early Ordovician age. Conodonts and bryozoans are probably the two most important groups awaiting investigation by specialists. No cephalopods were recognized in the cores.

The Ked River and Stony Mountain formations together seem to 

include equivalents of the entire Bighorn dolomite and the term Bighorn group is applied to them in the subsurface.

The few species identified from the upper dolomitic member of 

the Stony Mountain formation show affinities with the Late Ordovician 

assemblages from Anticosti Island and Quebec. The fauna and lithologic character of the calcareous lower shale member of the Stony 

Mountain formation, particularly in the core of the Shell Pine Unit 

No. 1 well, is strikingly similar to the red shaly beds in the uppermost 

Bighorn dolomite, northwest of Buffalo, Wyo. Both are of Late 

Ordovician age and correlative with the Maquoketa shale of Iowa.

In the fauna from the cored samples of the Red River formation, 

which is characterized by brownish limestones and dolomitic limestones, no Middle Ordovician elements have been recognized. Most 

of the genera and species from the upper 300 feet of the formation 

are also present in the overlying Stony Mountain strata, indicating 

no major faunal break. This fauna also resembles a small collection 

found in the base of the Leigh member of the Bighorn dolomite. 

Unfortunately the brachiopods of the lower massive member of the 

Bighorn are virtually unknown and its probable equivalence to the 

lower Red River strata is only, suggested by scanty evidence afforded

by large Receptaculites and Holy sites (C atenipora) gracilis.

The Red River formation is underlain by quartzose sandstones and 

shales of the Winnipeg formation. In the subsurface, the Winnipeg 

is presumed to be of Middle Ordovician age and supposedly is correlative with the siltstones and shales beneath the Whitewood dolomite 

of the Black Hills; published evidence based on a study of conodonts 

has suggested correlation of these siltstones and shales not only with the 

Middle Ordovician formations of the Upper Mississippi Valley, but 

also with the Lander (?) sandstone member of the Bighorn formation 

along the east flank of the Bighorn Mountains. Analysis of the faunal 

evidence for this correlation indicates that it its tenuous and requires further study and refinement. All these beds, including the
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 469

Winnipeg formation, may eventually prove to be of Late Ordovician 

age. Astraspis desiderata and Eriptychius americanus, the presumed 

ostracoderm fish which are abundantly represented in the Harding 

sandstone of Colorado, its equivalent in the Bighorn Mountains, and 

the shales of the Winnipeg formation, are no longer valid Middle 

Ordovician indices; they have been identified in the fauna of 

Maquoketa age of the uppermost Bighorn.

As indicated in the cores the Deadwood formation in the western 

Williston basin is composed of glauconitic limestones, intraformational limestone conglomerates, and shales. As much as 350 feet of 

the upper part of this formation contain Early Ordovician trilobites, 

poorly preserved brachiopods, and graptolites. The Lower Ordovician strata are apparently conformable on those of the Upper Cambrian, no evidence of a stratigraphic break between them having been 

recognized. Trilobites range in age from very Early Ordovician 

(Beliefontia zone) to approximately middle Early Ordovician. The 

younger forms show affinities with those from the so-called "Megalaspis" fauna of British Columbia and from parts of the Lower Ordovician section in Argentina.

Selected fossils of Ordovician faunal zones in the Williston basin and 

Bighorn Mountains

Upper Ordovician (for complete lists of fossils for zones F-H see 

insert facing p. 458) 

ZoneH

Rhynchotreme cf. R. Plicata 

Protoseuga cf. P. anticostiensis 

Strophomena cf. S. li.ecuba 

Zone G (for subdivisions see insert) 

"Streptelasma" trilobatum 

Dinorthis (Plaesiomys) cf.D. (P.)proavita,

(Pionorthis) cf. D. (P.) occidental^ 

Lepidocyclus capax 

gigas

perlamellosus 

Hypsiptycha hyorida

anticostiensis 

Megamyonia cf. M. ceres

cf. M nitens 

Diceromyonia storeya 

Zone F

Receptaculites cf. R. oweni 

Halysites (Gatenipora) gracilis 

Middle Ordovician

Zone E (see pi. 44 for position of Winnipeg formation) 

Astraspis desiderata 

Eriptychius americanus 

Conodonts as yet unstudied
470 : CONTRIBUTIONS TO GENERAL GEOLOGY '"

Lower Ordovician ' . 

Zone D (SheU Pine Unit No. 1 well, 9,660-9,690 feet)

Apatokephalus cf. A. canadensis

Megalaspidella cf. M. orthometppa

KirTcella aff. K. fillmorensis

Ogyginus sp.

Protopliomerops sp. 

Zone C (Shell Pine Unit No. 1 well, 9,698-9,715 feet)

Asaphellus sp.

Megalaspidella cf. M. orthometopa

Kayseraspis aff. K. asaphelloides

Lloydia? sp.

Zone B (Shell Pine Unit No. 1 well, 9,718 feet; Shell (Eichey) 

Northern Pacific No. 1 well, 10,466 feet)

Bryograptusf sp.

Zone A (SheU (Bichey) Northern Pacific No. 1 well, 10,500- 

10,510 feet)

Imbricatia, sp.

Leiostegium manitouensis

Kainella sp.

TENTATIVE PALEOGEOGRAPHIC INTERPRETATIONS

The results of this study as summarized above, and conversations 

with E. D. McKee, have resulted in an effort to visualize the paleogeography of the Williston basin during Ordovician time. It was 

not, however, until I had read for a second time Rader's (1952, 

p. 48-53) paper on the Ordovician carbonates of the basin that I 

realized that these ideas were foreshadowed by his conclusions. Few 

conclusions can be drawn from the five cores examined; however, 

hypotheses can be presented for testing in future research, and these 

are given in the following paragraphs.

Lochman and Duncan (1950, p. 3£>1) concluded that Early Ordovician sedimentation proceeded in the same manner as that of the Late 

Cambrian in the Rocky Mountain region because of the occurrence 

of a Beliefontia fauna in the uppermost few feet of the Deadwood 

formation in the Black Hills and of the Pilgrim limestone in Montana. 

Brachiopods collected during the 1953 field season in Brown's Canyon 

in the Northern Little Rocky Mountains substantiate that a very thin 

interval of Lower Ordovician rock underlies the Bighorn dolomite 

there. As noted previously, a fauna collected by A. R. Palmer and 

me from the top 10 or 15 feet of the Deadwood formation west of 

Storey, Wyo., may prove to be of early Ordovician age.

Although the thickening from a, few tens of feet to 350 feet may

not be significant when spread over 200-300 miles, the discovery of

a VOUnger trilbbite fauna in the cored sections than is present in the

peripheral surface exposures suggests that down warping had taken 

place before the deposition of the Middle (?) and Upper Ordovician 

units. Too little information is available to be certain of the plan
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 471

of the down warped area, nor is it possible to tell whether -the 

warping took place throughout Early Ordovician timew abruptly. fj

Isopach maps by Rader (1952, p. 50, 52) and Barnes (1953, figs. 

3, 4, 5) show that in the case of .Ordovician, Silurian and Devonian, 

and Mississippian units each thickens toward the center of the Williston basin. It is conceivable that Lower Ordovician sediments were 

deposited uniformly over the entire area, downwarped, and then 

bevelled before Middle and Upper Ordovician strata were laid down 

and that this process was repeated before Silurian and Devonian, 

and Mississippian deposition. Broad basinal downwarping of a fairly 

continuous nature seems a more reasonable explanation, however. 

This may have been interrupted by stoppages in subsidence which 

resulted in nondeposition of some units or by local warping and erosion of these units particularly at the periphery. In any case it seems 

probable that the fundamental and rudimentary structure of the 

Williston basin had come into existence by the close of Early Ordovi-; 

ciantime.

The clastic nature of the Winnipeg formation and its position above 

an unconformity suggest that its sediments may have resulted from 

erosion of newly uplifted areas near the periphery of the incipient 

Williston basin. If basin subsidence had already begun at this time 

the site of deposition of the clastic sediments should have migrated 

toward the periphery of the growing basin. If this occurred, the 

Winnipeg strata in the center of the basin should be older than similar 

rocks at the borders of the basin. Possibly, therefore, the lowermost 

carbonate rocks of the Red River formation were being deposited in 

the center of the basin at the same time that sand, silt, and mud 

were being deposited at its borders. This interpretation is based 

wholly on physical evidence and needs f aunal verification.

Several blocks of rock from the Whitewood dolomite and from the 

lower massive member of the Bighorn dolomite have been partly dissolved in formic acid ; the dolomite from both contains an unusually 

large amount of clastic material in the form of very fine sand, silt, 

and clay.

McKee (1938, p. 47-49, 68-76, text fig. 22) discussed the origin of 

dolomitic rocks with a high content of detrital clastic material in his 

study of the Kaibab limestone. He concluded that this f acies, exemplified by f acies 4 of the Beta member of the Kaibab, is characteristic of 

both nearshore deposits and residual deposits of retreating seas. In 

either case, there should be shallow water with poor circulation and 

consequent concentration of salts.

On examining the samples from the Whitewood and Bighorn, dolomites which were being dissolved, McKee expressed the opinion that 

they probably should be classed with similar nearshore deposits of
472 CONTRIBUTIONS TO GENERAL GEOLOGY

the Kaibab and that these might be expected around the borders of a 

basin in the thinner stratigraphic sections.

Perusal of Barnes* (1953, fig. 3) isopach map shows clearly that 

the sections in which these detrital-rich dolomites occur (the Black 

Hills and the Bighorn Mountains) are indeed the thinner ones 

and close to the borders of the basin, although some allowance 

must be made for post-Ordovician and pre-Mississippian erosion or 

nondeposition.

In the deeper parts of the Williston basin the Red River formation, apparently holding the same stratigraphic position as the 

detrital-bearing dolomites in the Black Hills and Bighorn Mountains, 

is composed of limestone and dolomitic limestone. Samples at hand, 

perhaps because they were not taken from the deepest part of the 

basin and probably because they were picked for their fossil content 

alone, do not check entirely with Rader's (1952) observations and 

seem to indicate a higher dolomite (and fossil) content near the top 

of the Red River formation than near the bottom. None of the lower 

dolomitic rocks sampled are dolomites such as are present in the Whitewood or lower Bighorn.

It is, therefore, suggested that the lower member of the Bighorn 

dolomite, including the Lander? sandstone member, and the Whitewood limestone, possibly also including much of the underlying calcareous and dolomitic siltstone, may represent a shallow water facies 

of the Red River formation, particularly of its lower portion. If this 

is true and if the Whitewood and Bighorn are in any part transgressive, their lower beds should be younger than the lowest beds of the 

Red River in the subsurface. Currently available paleontologic information neither supports nor disproves this interpretation.

Because the lower member of the Bighorn dolomite is overlain by 

additional dolomites of the Leigh(?) member and because the Red 

River is overlain by dolomites of the Stony Mountain formation it is 

possible that these represent a regressive facies; Rader (1952, p. 51, 

53) concluded that the dolomites of the upper Red River and Stony

Mountain formations were deposited in restricted waters. The absence of Silurian and Devonian sediments in the Black Hills and of 

Silurian units in the Bighorn Mountains suggests that the region to 

the south and west was rising and causing this regression.

This results in a fairly simple hypothetical explanation for the areal 

and stratigraphic distribution of the Middle (?) and Upper Ordovician 

rock types of the Williston basin and its borders, calling for Middle (?) 

or Late Ordovician transgression followed by later Ordovician regression of the sea. However, this hypothesis raises several questions, 

not the least of which is the necessity for explaining the presence of 

the lower shale member of the Stony Mountain formation.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 473

Eader (1952, p. 52-53) indicated that the shales of this member thin 

and disappear in eastern Montana and northeastern Wyoming; however, the presence of the same facies along the South Fork of Rock 

Creek, near Buffalo, Wyo., suggests either that its distribution is 

patchy areally and (or) stratigraphically or that the tip of a tongue 

is exposed, which may extend beneath the surface to the northeastward to join the main deposit. The abundance of fossils and the evidence for abrasion to which many of them have been subjected suggest, as Rader (1952, p. 53) concluded, that the unit was deposited 

under conditions of well-circulated water where waves were active. 

Wave action might be expected in a shallowing regressive sea, but 

further speculation as to the reasons for the brief change from a restricted environment is pointless without additional data on the distribution of the shaly facies.

It may be well to note that there is no intention to imply that any 

of the subject Ordovician sediments are basinal in a strict sense 

(formed in a very deep basin of deposition). Rather I visualize an 

extremely broad area of "shelf-type" sedimentation which stretched 

southward into the present Southwestern States and perhaps westward into Nevada. Within this area of shoal water and generally 

restricted circulation the forerunner of Ordovician age of the Williston basin may have been a minor subsiding feature mainly very shallow at any given time, but undergoing greater subsidence toward its 

center than at its margins, which resulted in a broad and thinly lenticular body of chiefly dolomitic carbonate rocks.

DESCRIPTIONS OF LATE ORDOVICIAN FOSSILS

The descriptions which follow are presented in abbreviated form in 

order to point out a few of the diagnostic characteristics of each genus 

or species. If the specimens are well-enough preserved they are figured on the accompanying plates; if species are represented by poorly 

preserved specimens reference is made to publications in which adequate illustrations may be found. For the sake of brevity complete 

synonomies are not necessarily provided for each species.

Two species of Dinorthis ( ?), one of Megamyonia and one of Diceromyonia, are considered new. They are not described here because 

there has not been time to study them thoroughly. All four are from 

the uppermost Bighorn formation; at least two of the four are also 

present in the Manitoban sections of the lower shale member of the 

Stony Mountain formation.

Phylum COELENTERATA 

CLASS ANTHOZOA

The corals of the Bighorn group and correlative formations and 

their stratigraphic significance are discussed by Helen Duncan (1956),
474 ' '-. . CONTRIBUTIONS TO GENERAL -GEOLOGY

but several of them have not'been portrayed photoigraphically. Four 

species identified by her are therefore illustrated here without descrip' 

tive comment. These are .

Streptelasma trilobatum Whiteaves (pi. 37; figs. 1, 2) 

Streptelastna cf. S. latusculum (Billings) (pi. 37, figs. 4, 8) , 

"Holophragma" sp. (pi. 37, figs. 3, 5, 6, 7) 

Paleofavosites prolificus (Billings) (pi. 37, fig. 9)

The first of these occurs in strata of the Stony Mountain formation 

and uppermost Bighorn dolomite. The second was originally described from the Jupiter formation of Silurian age of Anticosti Island. 

P. prolificus is known from the same units as S. trilobatum in addition 

to the Upper Ordovician rocks of Anticosti.

Phylum BEYOZOA 

; Order TREPOSTOMATA 

Family TREMATOPOBIDAE 

Genus BATOSTOHA TTlrich, 1882

Batostoma Ulrich; Bassler, 1953, Treatise on invertebrate paleontology, part G, 

p. G113, fig. 76-la, b, c, d; 76-2.

Numerous specimens belonging to this genus have been obtained 

from the lower shale member of the Stony Mountain formation (Shell 

Pine Unit No. 1 well) and from the red shaly beds of the Bighorn 

dolomite, locality Dl (CO). E. S. Boardman (written communication, 1953) believes that these represent new species which await detailed study. Therefore no descriptions are submitted here.

Order CRYPTOSTOMATA

Family AKTHBOSTYLIDAE

Genus SCEPTROPOBA Ulrich, 1888

Sceptropora Ulrich ; Bassler, 1953, Treatise on invertebrate paleontology, part G, 

p. G130, fig. 90-3a, b.

Sceptropora cf. S. facula Tllrich 

, Plate 37, figures 1O, 11

These small club-shaped segments of articulated colonies are extremely distinctive and may prove of considerable use where well 

cuttings are obtained from drilling operations. A smooth hemispherical condyle caps the smaller end of each segment, the other end of 

which holds a bowl-shaped socket.

The collections from Eock Creek (loc. Dl (CO)) apparently contain at least two species, one being considerably more slender than
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 475

S. facula. Whether either is correctly assignable to this species will 

not be known until more detailed study is possible.

Figured, specimen. USNM 124805.

Locality. Dl (CO), red shale beds in top few feet of Bighorn dolomite, South 

Fork of Rock Creek, Johnson County, Wyo.

Discussion. At present this species is known only from Upper 

Ordovician strata, though the genus ranges into the Silurian. S. 

facula was originally described by Ulrich from the Stony Mountain 

formation of Manitoba, presumably from the lower shale member.

Phylum BRACHIOPODA 

Superfamily ORTHACEA

Genus HESPERORTHIS Schuchert and Cooper 1931 

Hesperorthis cf. H. laurentina (Billings)

Plate 37, figures 12-15

Orthis laurentina Billings, 1865, Canada Geol. Survey, Paleozoic Fossils, v.

1, p. 138-139, fig. 115.

Orthis laurentina Billings. Twenhofel, 1928, Canada Geol. Survey Mem. 154, 

p. 176, pi. XV, figs. 17,18.

All specimens collected are small. The dorsal valve is gently convex with a distinct but shallow median sulcus.

Figured specimen.*. USNM 124806,124807.

Locality. D19d (CO), Red River formation, Shell Pine Unit No. 1 well, 

9,103-9,116 ft.

Discussions. The silicified specimens obtained from the coro compare so closely in size, outline, and convexity with 3. laurentina that 

they are either conspecific or very closely related. The species may 

be distinguished from Middle Ordovician H. tricenaria (Conrad) by 

the greater convexity of the dorsal valve, fewer number of costae, 

and lower cardinal area.

Hesperorthis laurentina is described from the Ellis Bay formation 

of Late Ordovician age on Anticosti Island.

Genus DINORTHIS Hall and Clarke, 1892

Plate 37, figures 16-23 

Plate 38, figures 1-8, 11, 15, 17-19

From the red shaly beds of the uppermost Bighorn dolomite along 

Rock Creek, Wyo. (loc. Dl (CO)), over 50 specimens of large coarseribbed dinorthid brachiopods have been assembled from older collections and from those made by me. There has not been time to study 

these specimens properly, but it seems clear that a minimum of two 

new species are present.
476 CONTRIBUTIONS TO GENERAL GEOLOGY

Numerous specimens closely resemble Dinorthis ("Pionorthis"} occidentalis Okulitch, a species of Stony Mountain age, and cannot be 

distinguished from it on external features; differences in ventral 

musculature make exact synonomy dubious.

Other specimens are more finely ribbed and probably belong to 

the subgenus Plaesiomys rather than to Dinorthis (sensu stricto). 

The largest specimens of more coarsely ribbed varieties possess gibbous dorsal valves, more strongly convex than in any previously described species of Dinorthis or its subgenus Plaesiomys. Outlines of 

some shells are almost rectangular, others almost elliptical, and one 

other nearly circular.

The abundant wealth of well-preserved material warrants more detailed study than was possible during the preparation of this report.

Similar brachiopods in the cored material cannot be exactly identified but have been listed under the appropriate well. Illustrations 

of the species of Plaesiomys or Dinorthis which they most closely 

resemble are given by Wang (1949, pis. 2 C, D, E and 3C).

Genus PLATYSTROPHIA King, 1850 

Platystrophia cf. P. equiconvexa Wang

Platystrophia, equiconvexa Wang, 1949, Geol. Soc. America Mem. 42, p. 10-11, 

pi. 4B.

This species is known in one core from a poorly preserved specimen.

Locality. D91f (CO), lower shale member, Stony Mountain formation, Shell 

Pine Unit No. 1,8,986-9,010 ft.

Superfamily RHYNCHONELLACEA 

Genus RHYNCHOTREMA Hall, 1860

Rhynchotrema Hall. Wang, 1949, Geol. Soc. America Mem. 42, p. 11-12.

Many of the species originally assigned to this genus have now 

been placed in Lepidocyclus Wang or in Hypsiptycha Wang.

Rhynchotrema iowense Wang

Plate 38, figures 9, 10, 12-14 

Rhynchotrema iowense Wang, 1949, Geol. Soc. America Mem. 42, p. 12, pi. 4C

From collections obtained, it is evident that considerable variation exists in this species .in the height of fold and eulous and in their

width; though the present collection includes specimens virtually indistinguishable from those illustrated by Wang, comparison with the 

shell figured here exemplifies this variance.

Figured, specimen. USNM 124813.

Locality. Dl (CO), red shaly beds in uppermost Bighorn dolomite, South 

Fork of Rock Creek, Johnson County, Wyo.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 477 

Rhynchotrema cf. R. plicata Cooper and Kindle

Rhynchotrema plicata Cooper and Kindle, 1936, Jour. Paleontology, v. 10, no. 

5, p. 359, pi. 52, figs. 2, 3, 5, 6. - Although specimens are not well preserved in a dolomitic matrix, 

the number of costae on fold (5) and in sulcus (4) which distinguish 

this species is evident as well as a similar outline and convexity of the 

shells.

Locality. D90e (CO), dolomitic member, Stony Mountain formation, Empire 

State Hathaway No. 1 well, 8,556-8,664 ft.

Genus IEPIDOCYCLTJS Wang 

Lepidocyclus Wang, 1949, Geol. Soc. America Mem. 42, p. 12-13.

Externally shells of this genus are characterized by its strongly 

globose form and well-developed lamellae forming zigzag lines across 

the ribbing.

Rhynchonella, perlamellosa Whitfield, 1882, Paleontology [Wise. Geol. Survey]* 

Geology of Wisconsin, v. 4, p. 265, pi. 12, figs. 23-25.

Figured specimen. USNM 124816.

Locality. D91c (CO), Red River formation, Shell Pine Unit No. 1 well, 9,122- 

9,128 ft. D91f (CO), lower shale member, Stony Mountain formation, Shell 

Pine Unit No. 1 well, 8,986-9,010 ft. Dl (CO), red shaly beds in uppermost 

Bighorn dolomite, South Fork of Hock Creek, Johnson County, Wyo.

lepidocyclus capax (Conrad) 

Plate 39, figures 21,24-27

This species is distinguished from L. gigas Wang by its more acutely 

triangular outline. The two occur together in the uppermost Bighorn 

dolomite; some of the imperfectly preserved specimens referred to 

L. gigas in the cored material may also belong to this species.

Figured specimen. USNM 124820.

Locality. Dl (CO), red shaly beds in uppermost Bighorn dolomite, South 

Fork of Rock Creek, Johnson County, Wyo.

Lepidocyclus gigas Wang 

Plate 38, figures 16,20-25

Its subelliptical, rather subtriangular, outline characterizes this 

species. Like specimens of L. capax from the same locality, representatives of L. gigas from the Kock Creek locality seem to be larger than 

those reported from other regions.
478 CONTRIBUTIONS TO GENERAL GEOLOGY

Figured specimens. USNM 124814,124815. .

Locality. D91£ (CO), lower shale member, Stony Mountain formation, Shell 

Pine Unit No. 1 well, 8,986-9,010 ft. Dl (CO), red shaly beds of the uppermost 

Bighorn dolomite, South Fork of Rock Creek, Johnson County, Wyo.

Genus Hypsiptycha Wang 

Hypsiptycha Wang, 1949, Geol. Soc. America Mem. 42, p. 17.

At present this genus includes three species, H. hybrida Wang from 

the Maquoketa shale, H. neenah (Whitfield) from the Maquoketa 

shale but apparently present in the upper strata of the Montoya formation, and H. anticostiensis (Billings), described from the Upper Ordovician of Anticosti Island as well as from Manitoba.

Hypsiptycha cf. H. hydrida Wang 

Plate 39, figures 9-11 14,15,18-20, 22, 23

Specimens obtained closely resemble Wang's except that the four 

costae on the fold are of equal strength and height; in his specimens 

from the Maquoketa the outer two of these four are a little weaker 

than the middle two.

Although not previously noted, this species is apparently present 

in the shale of the Stony Mountain.

Figured specimens. USNM 124818,124819.

Locality. D91f (CO), lower shale member, Stony Mountain formation, Shell 

Pine Unit No. 1 well, 8,986-9,010 ft. Dl (CO), red shaly beds of the uppermost 

Bighorn dolomite, South Fork of Rock Creek, Johnson County, Wyo. D35 (CO), 

Bighorn dolomite, 15 ft above base of upper (Leigh?) member, North Fork of 

Crazy Woman Creek.

Hypsiptycha cf. H. anticostiensis (Billings) 

Plate 39, figures 6-8, 12, 13

Rhynchotrema anticostiensis (Billings). Twenhofel, 1928, Canada Geol. Survey 

Mem. 154, p. 207, pi. XXI, figs. 4, 5, 6.

The present specimens are considerably smaller than those from 

Anticosti Island and from beds of the Upper Ordovician in Manitoba 

(Okulitch, 1943, pi. I, figs. 5, 6). They are readily distinguished from 

H. Jiybridd Wang by their lower fold and less convex profile.

Floured specimen. USNM 124817.

Locality. Dl (CO), red shaly beds of the uppermost Bighorn dolomite, South 

Fork of Rock Creek, Johnson County, Wyo.

Superfamily SPIBJFEHACEA

Genus CATAZYGA Hall and Clark, 1893

Catazyga anticostiensis (Billings)

Catazyga anticostiensis (Billings). Twenhofel, 1928, Canada Geol. Survey Mem. 

154, p. 215-216, pi. XX figs. 10-12.

This species is similar to G. headi (Billings) but lacks, as far as 

can be seen from the poor specimens obtained, a vestige of dorsal sinus.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 479

There is, however, a shallow sinus at the front of the ventral valve. 

Its ribbing is more closely spaced than that of G. cartieri Cooper and 

Kindle; in this respect an obvious misprint should be noted in Twenhotel's description: there are 11 or 12 costellae in 5 mm at the front 

of the shell, not 8 in 1 mm.

Locality D92g (CO), Red River formation, Shell Little Beaver N6. 1 well, 

8,330-8,335 ft.

Catazygasp.

Plate 40, figures 1-3

This species differs from C. headi, C. cartieri, and C. anticostiensis 

in that the dorsal valve is more convex than the ventral. Although 

the front of the valves is broken in the most complete specimen there 

seem to have been 12-14 costellae in 5 mm, a number comparable to 

C. anticostiensis. There is no clear evidence for a ventral sulcus, and 

there certainly is none on the dorsal valve.

Specimens are too poor to warrant full description, but this may 

be a new species.

Figured specimen. USNM 124823.

Locality. D91d (CO), Red River formation, Shell Pine Unit No. 1, well, 

9,103-9,116 ft.

Genus ZYGOSPIRA Hall 1862

Zygospira cf. Z. resupinata Wang

Plate 40, figure 5 

Zygospira, resupinata, Wang, 1949 Geol. Soc. America Mem. 42, p. 18, pi. 10A.

This species is known in the cores from a single partly decorticated 

ventral valve. It is of the size and outline of a typical specimen from 

the Maquoketa. Possibly because of decortication the ventral fold 

in which there is a shallow sulcus is not so sharply developed as in the 

Iowa examples.

Figured specimen. USNM 124825.

Locality. D91e (CO), Red River formation, Shell Pine Unit No. l : well, 

9,023-9,043 ft. D35 (CO), Bighorn dolomite, 15 ft above base of upper,-(Leigh?)' 

member, North Fork of Crazy Woman Creek, Johnson County, Wyo.

Zygospira cf. Z. aequivalvis Twerihofel 

Plate 40, figures 6-9,12

Zygospira recurvirostris aequvoalvis Twenhofel, 1928, Canada Geol. Survey 

Mem. 154, p. 214, pi. XIX, figs. 10-12.

The very small specimens obtained are not well preserved and are 

difficult to study. The dorsal sulcus is so poorly defined that it is almost impossible to decide how many costae should be included in it. 

On the entire surface there are 22 in the one complete specimen worked 

free of the matrix.
480 CONTRIBUTIONS TO GENERAL GEOLOGY

. Twehhofel states that in general this species has more than 24 costae 

and notes that 24 is the common number in Z. recurvirostris according 

to Hall's original description. In checking Twenhofel's figures of Z. 

acequivalvis it appears that 18, possibly 20 costae are present, but certainly not more than 24. Furthermore, specimens figured by Hall and 

Clarke (1894, pi. LIV, figs. 1-6) for Z. recurvirostris show a more circular and less convex form than Hall's original illustrations and great 

variation in the number of costae.

The present specimens are similar to that illustrated by Twenhofel 

from the English Head formation (of Twenhofel, 1928) and are tentatively considered conspecific.

Figured, specimen USNM 124826.

Locality. D91c (CO), Red River formation, Shell Pine Unit No. 1 well, 

9,122-9,128 ft D92b (CO), Red River formation, Shell Little Beaver No. 1 

well, 8,531-8,540 ft. D92g (CO), same formation, same well, 8,330-8,335 ft.

Discussion. It is probable that Z. recurvirostris as commonly interpreted is of little use in distinguishing between Middle and Upper 

Ordovician strata, and that the species needs redefining. Besides there 

are several specimens from the red shaly beds of the uppermost Bighorn dolomite (loc. Dl (CO)) which could pass for Z. recurvirostris 

(senso latu) but which are very probably representative of an imdescribed species.

Genus PROTOZEUGA Twenhofel

Protozeuga Twenhofel. Cloud, 1942, Geol. Soc. America Special Paper 38, p. 

145-146.

Protozeuga anticostiana Twenhofel

Protozeuga anticostiana Twenhofel, 1928, Canada Geol. Survey Mem. 154, p. 

213-214, pi. XXI, figs. 15-17.

Numerous specimens referrable to this species have been obtained 

frOffl the Stony Mountain formation in the cores. Despite dolomitization a few of these retain coarsely recrystallized spiralia, directed

laterally.

Locality. D90e (CO), dolomitic member, Stony Mountain formation, Empire

State Hathaway No. 1 well, 8,556-8,664 ft.

Superfamily STB.OPHOMENACEA

Genus THAERODONTA Wang, 1949

Thaerodonta Wang, 1949, Geol. Soc. America Mem. 42, p. 19-20. 

In his description and discussion of this genus, Wang emphasized

four characteristics which differentiate it from Sowerbyella Jones. 

These, are a denticulate hinge line and accessory ridges splitting the 

right and left adductor fields in the dorsal valve, accessory hinge teeth
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 481

in the ventral valve, and paired conical cavities in the delthyrium. He 

also implied that this is a genus of Eichmond age and that Sowerbyella possesses none of these four characteristics.

The present study indicates that one or the other of these two implications is incorrect. Some Trenton species possess denticulate hinge 

lines and others have paired delthyrial cavities, though in neither case 

does there seem to be any other of the four characteristics present.

Clearly Wang had no intention of placing ironclad restrictions on 

Thaerodonta^ for he included in his generic concept T. recedens (Sardeson) in which the accessory hinge teeth are very weak or actually 

absent, as indicated by his illustrations (Wang, 1949, pi. 11 A, fig. 2). 

Furthermore, in the Maquoketa shale of Iowa a high percentage of 

the specimens of T. saxea (Sardeson) which characteristically has 

strong accessory hinge teeth may have virtually none.

In the Red River formation in three of the cores studied there is 

at least one zone in which shells of Soioerbyellci and (or) Thaerodonta 

are numerous. This same zone appears also to be located at a depth 

of 8,520-8,570 feet in the Carter Northern Pacific No. 1 well. In the 

dolomitized matrix, it has been almost impossible to obtain adequate 

interiors of these shells to tell which of the tAvo genera is present; 

this distinction may be of importance in substantiating the apparent 

Late Ordovician age of most, if not all, of the Red River formation.

If Thaerodonta is restricted to those species which, possess all four 

critical characteristics given by Wang, it can be considered certainly 

a Cincinnati index, probably being limited in range to Richmond 

strata.

If by the same token Sowerbyetta is restricted to species which possess none of these four features, then there are left numerous intermediate forms, some of Middle and some of Late Ordovician age. 

To date (1954) too little critical information has been assembled on 

the number of species which fall in this intermediate category, their 

character, and their stratigraphic occurrences to permit final classification or their use in dating strata.

Many species previously referred to Sowerbyella and Plectambonites 

belong to Thaerodonta.

Thaerodonta cf. T. recedens (Sardeson) 

Plate 40, figures 26-28

The specimens described are believed to be representative of most, 

if not all, of the Sowerbyella- and Thaerodonta-lik& forms obtained 

from the Red River formation; at present this cannot be proved, however. Fortunately, the rock matrix in the core from a depth of 

8,531-8,540 feet from the Shell Little Beaver No. 1 well is partly 

dolomitized whereas the specimens are still calcitic. The shells have 

been removed with formic acid (which acts more selectively than hy-
482 CONTRIBUTIONS TO GENERAL GEOLOGY

drochloric acid) applied very slowly with a medicine-dropper, leaving 

dolomitic casts of the interiors of a dorsal and ventral valve. From 

these, rubber molds have been made. Unfortunately some of the dolomitic matrix dissolves in this treatment, and the finest detail is lost.

The ventral valve possesses two conical cavities in the delthyrium 

separated by a thin septum; the presence of the septum is indicated 

better on the original cast (pi. 40, fig. 26) than in the rubber mold.

The dorsal hinge line (pi. 40, fig. 27) carries minute denticles for 

most of its length. The paired median septa are strong and on one 

side the rudiment of a second pair is present.

The absence of accessory teeth on the ventral hinge is supposedly 

atypical of the genus. However, T, recedens (Sardeson) possesses very 

weak accessory teeth; in the specimen figured by Wang (1949, pi. 11 A, 

(fig. 2) they are no better developed than those under discussion.

Figured, specimens. USNM 124838, 124839.

Locality. D92b (CO), Bed River formation, Shell Little Beaver No. 1 well, 

8,531-8,540 ft. Probably also D90b (CO), same formation, Empire State Hathaway No. 1 well 9,097 ft; D91b (CO) and D91c (CO), same formation, Shell 

Pine Unit No. 1 well, 9,286-9,294, 9,043 ft; D92a (CO) and D92c (COD), 

same formation, Shell Little Beaver No. 1 well, 8,550,-8,526 ft.

Genus STKOPHOMENA Blainville, 1825 

Strophomena cf. S. vetusta James

Plate 40, figure 4

Strophomena vetusta James. Foerste, 1912, Denison Univ. Sci. Lab. Bull., v. 17, 

p. 98-101, pi. VI, fig. 2E.

Although the imperfect specimen illustrated the interior of a brachial valve compares favorably with $. vetwta, it may belong properly to S. neglGGta James. Stratigraphically they are both Late

Ordovician species.

Figured specimen. USNM 124824.

Locality. D91f (CO), lower shale member, Stony Mountain formation, Shell 

Pine Unit No. 1 well, 8,986-9,010 ft.

Strophomena hecuba Billings 

Plate 40, figures 10,11,13,16

Strophomena hecuba Billings. Foerste, 1924, Canada Geol. Survey Mem. 138, 

p. 121, pi. V, fig. 4.

Unless good specimens are obtained S. heciiba can be mistaken for 

S. fluctuosa, which Billings stated occurred rarely in Trenton rocks ; 

Foerste (1924, p. 120), however, maintained that both are Late 

Ordovician species.

Figured specimens. USNM 124827,124828.

Localities. D90e (CO), dolomitic member, Stony Mountain formation, Empire State Hathaway No. 1 well, 8,556-8,664 ft. D91f (CO), lower shale mem-
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 483

ber, Stony Mountain formation, Shell Pine Unit No. 1 well, 8,986-9,010 ft. Dl 

.(CO), red shaly beds of uppermost Bighorn dolomite, South Fork of Rock 

Creek, Johnson County, Wyo.

Strophomena cf. S. rugulifera Wang

Plate 40, figure 14 

Strophomena rugulifera Wang, 1949, Geol. Soc. America Mem. 42, p. 28, pi. 8B.

It is evident that the specimens studied are much larger than 

Wang's holotype. They compare closely, however, in outline, degree, 

and spacing of geniculatioh and in wrinkled ornamentation.

Figured specimen. USNM 124829.

Locality. D90b (CO), Red River formation, Empire State Hathaway No. 1 

well, 9,097 ft. D91e (CO), Red River formation, Shell Pine Unit No. 1 well, 

9,023-9,043 ft.

Genus MEGAMYONIA Wang, 1949

Hegamyonia Wang, 1949, Geol. Soc. America Mem. 42, p. 32.

To the species placed in this genus by Wang should be added M. 

ceres (Billings) andJ/. nitens (Billings).

Megamyonia cf. M. nnicostata (Meek and Worthen) 

Plate 40, figures 23-25

Megamyonia unicostata (Meek and Worthen). Wang, 1949, Geol. Soc. America 

Mem. 42, p. 33, pi. 9A.

In this species, topotypic material indicates that near the margins 

there are about 5 radial rows of pseudopunctae in a transversely 

measured millimeter and within each row 4 or 5 pseudopunctae per 

millimeter. No radial row of pseudopunctae can be followed from 

margin to beak if costellate ornamentation has been removed either 

artificially or by natural abrasion; 5 to 7 pseudopunctae seem to be 

the most that can be followed along any radial line. The overall pattern, however, is definitely one of radial lines.

In almost all .specimens obtained from the cores, the external costellate ornamentation has been partly removed by natural abrasion 

from the visceral area of the ventral valve. As a result, there is little 

or no sign of the strong median costella from which the species takes 

its name; identifications are, therefore, tentative in most cases and 

depend on the alate outline which characterizes this species.

Unusually well-preserved casts and molds of this species have been 

obtained from the Bighorn dolomite.

Figured specimens. USNM 124835,124836,124837.

Locality. D92b (CO), Red River formation, Shell Little Beaver No. 1 well, 

8,531-8,540 ft. D91b (CO), Red River formation, Shell Pine Unit No. 1 well, 

9,286-9,294 ft. D91f (CO), lower shale member, Stony Mountain formation,

389021 57 4
484 CONTRIBUTIONS TO GENERAL GEOLOGY

Shell. Pine Unit No. 1 well, 9,007-9,008 ft. D35 (CO), Bighorn dolomite, 15 ft 

above base of upper (Leigh?) member, North Fork of Crazy Woman Creek, 

Johnson County, Wyo.

Megamyonia cf. M. ceres (Billings) 

Plate 40, figure 15, 17, 19-21

Leptaena? ceres (Billings). Twenhofel, 1928, Canada Geol. Survey Memo. 154, 

p. 185, pi. XVIII, figs. 16, 17, 18.

The specimens assigned to this species possess the very strong convexity which differentiates them from all those described and figured 

by Wang (1949, pi. 9, A, B, C, F). The semicircular outline is closer 

to M. knighti Wang than to any other species. M. ceres is more convex and less geniculate than any other species of the genus.

Figured specimens. USNM 124830, 124831, 124832.

Locality. D89b (CO), Red River formation, Shell, Richey area, Northern 

Pacific No. 1 well, 9,980-9,989 ft. D91e (CO), Red River formation, Shell Pine 

Unit No. 1 well, 9,023-9,043 ft. D91f (CO), lower shale member, Stony Mountain formation, same well, 8,986-9,010 ft. D35 (CO), Bighorn dolomite, 15 ft 

above base of upper (Leigh?) member, North Fork of Crazy Woman Creek, 

Johnson County, Wyo.

Megamyonia cf. M. nitens (Billings)

Strophomena nitens Billings, 1865, Canada Geol. Survey, Paleozoic fossils, v. 1,

p. 118, fig. 97. 

Leptaena? nitens (Billings). Twenhofel, 1928, Canada Geol. Survey Memo.

1954, p. 186, pi. XVII, fig. 19; pi. XVIII, figs. 13, 14.

This species is less convex but more geniculate than M. ceres (Billings) and is more convex but less geniculate than M. unicostata 

(Meek and Worthen). Its outline is more alate than M. ceres and 

M. knighti but less alate than M. unicostata.

Several specimens from the cores and from the red shaly beds of 

the uppermost part of the Bighorn certainly belong to a new species 

but are closer in form to M. nitens than any other. These like almost 

all others of the genus found have been so badly abraded that all 

costellae are removed from the visceral disc of the ventral valve.

Locality. D91d (CO), Red River formation, Shell Pine Unit No. 1 well, 9,103- 

9,116 ft. D91e (CO), Red River formation, same well, 9,023-9,043 ft.

Megamyonia aff. M. nitens (Billings)

Plate 41, figures 3, 4, 7

Numerous small specimens that are strongly convex, geniculate, 

and apparently smooth were found in the red shaly beds of the uppermost part of the Bighorn dolomite on Rock Creek. A few show the 

faintest suggestions of costellation around the margins, indicating 

that they may have been similarly ornamented over the entire shell 

before natural abrasion. These shells unlike typical Megamyonia are
ORDOVICIAN FOSSILS FROM WELLS IN WTLLISTON BASIN, MONT. 485

not all widest at the hinge line. In lateral profile, they are similar to 

M. nitens, but in outline they resemble M. ceres.'

Figured, specimens. USNM 124842.

Locality. Dl (CO), red shaly beds in uppermost Bighorn dolomite, South 

Fork of Rock Creek, Johnson County, Wyo. Probably also amongst specimens 

from D91f (CO), lower shale member, Stony Mountain formation, Shell Pine 

Unit No. 1 well, 8,986-9,010 ft.

Discitssion. In his description of "Leptaena?" nitens, Twenhofel 

(1928, p. 186) notes that there are associated in the English Head and 

Vaureal formations numerous "smaller, nearly smooth, greatly geniculated forms with the pa'rt below the geniculation as long as that over 

the visceral disk." These are probably conspecific or very closely 

related to the present specimens.

Megamyonia sp. 

Plate 40, figure 18

Several shells obtained from the Pine Unit core possess the outline 

and low convexity of specimens illustrated by Wang (1949, pi. 9, fig. 

C) from the Maquoketa shale of Iowa. These lack the strong geniculation of M. aft': M. nitens but are similar in the apparent lack of radial 

ornamentation, which may be the result of abrasion.

Figured specimen. USNM 124833.

Locality. D91f (CO), lower shale member, Stony Mountain formation, Shell 

Pine Unit No. 1 well, 8,986-9,010 ft.

Genus OPIKINA Salmon, 1942 

Opiklna Salmon, 1942, Jour. Paleontology, v. 16, p. 589-591.

Contrary to Salmon's implication (1942, p. 591) this genus (sensu 

lato] is not limited to formations of pre-Cincinnatian age, though it 

may be necessary eventually to split the post-Trenton forms into more 

than one genus.

(ipikina? aff. 6. limbrata Wang

Plate 41, figures 1,2

Opikina, limbrata Wang, 1949, Geol. Soc. America Mem. 42, p. 22-23, pi. 6B

figs. 1-7.

The specimens found are all dorsal valves and lack all but vestiges 

of the two pairs of lateral septa which characterize the genus.. The 

septa may have been removed during burial as there is evidence of 

abrasion of corals and other associated strophomenid shells.

Curiously no associated ventral valve has yet been found with proper 

type of pseudopunctation to be placed in the genus, though several have 

the correct general form.
486 - . . CONTRIBUTIONS TO GENERAL GEOLOGY

Figured specimens. USNM124840,124841.

Locality. D91f (CO), lower shale member,. Stony Montain formation, Shell 

Pine Unit No. 1 well, 8,986-9,010 ft. Dl (CO), red shaly beds, uppermost part, 

of the Bighorn dolomite, South Fork of Rock Creek, Johnson County, Wyo. 

D35 (CO), Bighorn dolomite, 15 ft above base of upper (Leigh?) member, 

North Fork of Crazy Woman Creek, Johnson County, Wyo.

Discussion. Not only do these specimens resemble the species from 

the Maquoketa but also 0. pergibbosa Foerste from the Stonington 

beds of Michigan (Hussey, 1926, pi, IV, figs. 7-9).

Genus HOLTEDAHLINA Foerste, 1924

Holtedahlina Foerste. Cooper, 1944, in .Shimer and Shrock, North American 

Index Fossils, p. 343, pi. 132, figs. 30-33.

Holtedahlina cf. H. sulcata Foerste

Holtedahlina sulcata Foerste, 1924, Canada Geol. Survey Mem. 138, p. 123-124, 

pi. XII, figs. 5a, b.

The specimens obtained are poorly preserved in dolomitic limestone 

but compare closely with Foerste's description and figured specimen. 

The fold and sulcus are not quite as well defined.

Locality. D92f (CO), Red River formation, Shell Little Beaver No. 1 well,. 

8,387 ft. Probably also in D92a (CO), same formation and well, 8,550 ft.

Holtedahlina cf. H. moniquensis Foerste

Plate 41, figures 8,10,11

HoltedaMina sulcata moniquensis Foerste, 1924, Canada Geol. Survey Mem. 138, 

p. 124, pi. XI, fig. 7.

This species differs from H. sulcata because it lacks a fold and sulcus 

at the front and because the hinge line is not the widest part of the shell.

The present specimens are poorly silicifie.d and fragmentary, but they 

show the cardinalia to good advantage (compare pi. 41, fig. 10 with 

Cooper, 1944, pi. 132, fig. 33).

Figured, specimens. USNM 124844,124845,124846.

Locality. D9ld (CO), Red River formation, Shell Pine Unit No. 1 well, 9,103- 

9,116 ft. Probably D89c (CO), Red River formation, Shell, Richey area, Northern 

Pacific No. 1 well, 9,974 ft.

PUNCTATE BRACHIOPODA 

Genus DICEROMYOMTA Wang 

Diceromyonia Wang, 1949, Geol. Soc. America Mem. 42, p. 35-36.

Although the three genera Diceromyonia, Resserella, and Onnielh 

are all thought to be represented in the collections from the red shaly 

beds of the uppermost Bighorn dolomite and although the first two are
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 487

apparently present in the core samples studied, most attention is given 

here to Diceromyonia. To distinguish positively between the three 

genera it is necessary to have well-preserved specimens showing the 

muscle scars of the ventral valves; it is very unlikely that positive 

generic, let alone specific identifications, can be made in the field where 

these three are found.

In Diceromyonia the diductor scars completely isolate the small oval 

adductor scars from the front of the entire muscle pattern, being 

separated from each other by a narrow ridge in most cases (pi. 41, 

figs. 13, 17; Wang, 1949, pi. 12B, fig. 7; Schuchert and Cooper, 1932, 

pi. 17, fig. 19). In Resserella the diductors are lobate in front but 

'do not meet so that the elongate but shorter adductor tracks have 

access to the front of the pattern (Schuchert and Cooper, 1932, pi. 17, 

figs. 4, 22). In Onniella both the diductor and adductor scars are of 

 equal length; hence the pattern lacks the bilobed outline found in 

the other two genera (Schuchert and Cooper, 1932, pi. 17, fig. 33).

Other differences are noted by Wang (1949, p. 35-38). Most of these 

deal with external form and should be used with care.

Three species of Diceromyonia are illustrated here; one is an undescribed species awaiting more thorough study.

Diceromyonia storeya Okulitch 

Plate 41, figures 5, 6, 9,12,16

Dalmanella storeya Okulitch, 1943, Royal Soc. Canada Trans., 3d ser., sec. 4, v. 37, 

p. 70-71, pi. I, figs. 1-4.

This species is similar in outline to D. subrotunda Wang but is much 

more convex. Musculature of the ventral valve, not previously known, 

Shows a strong ridge between the diductor scars.

Present specimens have been compared with casts of Okulitch's types 

as well as with topotypic material.

Figured specimen. USNM 124843.

Locality. D91g (CO), lower shale member, Stony Mountain formation, Shell 

Pine Unit No. 1 well, 8,986-9,010 ft. Dl (CO), red shaly beds of uppermost Bighorn dolomite, South Fork of Rock Creek, Johnson County, Wyo

Diceromyonia cf. D. ignota (Sardeson) 

Plate 41, figures 13-15,17-21

Dalmanella, ignota (Sardeson). Schuchert and Cooper, 1932, Yale Peabody Mus. 

Nat. History Mem. v. 4, pt. 1, pi. 17, fig. 19.

In outline this species is less elliptical than D. tersa and less circular 

than either D. subrotunda or D. storeya. Its convexity is comparable 

to that of D. subrotunda.

Figured, specimens. USNM 124847,124848,124849,124850. 

Locality. Dl (CO), red shaly beds, uppermost Bighorn dolomite, South Fork 

of Rock Creek, Johnson County, Wyo.
488 , CONTRIBUTIONS TO GENERAL GEOLOGY

ALGAE 

Genus CYCLOCRINITES Eichwald, 1840

Many species belonging to this genus have previously been referred 

to Pasceolus Billings. Of how much use the genus may prove stratigraphically is not yet certain. It is mentioned here because it was 

found in one of the cores.

The form of a typical specimen is globular and very much resembles 

a golf ball because of the polygonal depressions on its surface. The 

specimens from the core (Shell, Kichey area, Northern Pacific well 1, 

10, 123-10, 135 ft) are about the size of a child's marble, whereas numerous specimens obtained from the base of the Leigh (?) dolomite 

member of the Bighorn dolomite (North Fork of Crazy Woman Creek, 

Johnson County, Wyo.) are about 30 mm in diameter.

The genus is known in Middle and Upper Ordovician deposits from 

Scandinavia across the North American Arctic to the northern United 

States from Anticosti to the Eocky Mountains.

DESCRIPTIONS OF EARLY ORDOVICIAN TRILOBITES

Special attention is given to two trilobite groups; one of these possesses triangular pygidia with terminal spines. The other is characterized by the "hammer-head" outline of the front of the cranidium. 

Genera in both groups can be useful guide fossils, but misidentifications within each group can lead to stratigraphic misinterpretation. 

The importance of securing both cephalic and pygidial-parts cannot 

be overemphasized.

Many trilobites changed shape and ornamentation as they grew. 

Kecent studies on beautifully preserved silicified material by Whittington, Evitt, and Koss have emphasized this. As a result paleontologists are increasingly aware of the necessity for obtaining several 

specimens of different sizes in order to understand each species. 

Furthermore, completely articulated exoskeletons are rare. In most 

places the various parts are found scattered through the enclosing rock, 

and. correct association of heads and tails can be extremely difficult, even for the specialist.

Genus HYSTRICTJRUS Raymond, 1913

Hystricurus sp. 

Plate 43, figures 21, 22, 25, 26

The four small cranidia illustrated may actually belong to two 

genera but are tentatively considered as representing four different 

growth stages of the same species. The two smallest specimens have 

a distinct preglabellar median furrow, the third .largest has a very
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 489

faint suggestion of such a furrow, and the largest has none at all. 

This change is known in several species of Hystricurus.

Except for the lack of pustules, the smallest stage compares favorably with H. Tobustus Ross. The largest is not well enough preserved 

to be identified specifically.

Figured specimens. USNM 124891,124892,124893,124894. 

Locality. D70 (CO), Shell, Blchey area, Northern Pacific No. 1 well, 

10,500-10,509 ft.

Discussion. The stratigraphic value of these specimens is merely 

to indicate that the enclosing strata are probably of early Early 

Ordovician age.

Genus LEIOSTEGIUM Eaymond, 1913

Leiostegium manitouensis Walcott

Plate 43, figures 18-20

Leiostegium manitouensis Walcott, 1925, Smithsonian Misc. Coll., 75, no. 3, p. 

104, pi. 23, figs. 12-14.

Only cranidia and one hypostome have been obtained. The former 

compare so closely with Walcott's figured specimen from Colorado 

that the lack of pygidia does not deter assignment to his species.

The hypostome, although the single specimen is incomplete, is very 

similar to that of L. douglasi Harrington (1938, pi. 6, fig. 4). The 

subrectangular middle body is deeply creased at the sides by the middle furrow which is carried only faintly across the midline. No true 

maculae are present.

Figured specimens. USNM 124888, 124889, 124890.

Locality. D70 (CO), Shell, Richey area, Northern Pacific No. 1 well, 

10,500-10,509 ft.

Discussion. This species differs from L. quadmtus (Billings) in 

the greater relative length of the glabella and in the slight forward 

taper of the glabella. On the other hand, L. douglasi Harrington has 

a more pronounced forward taper than this species. The hypostome 

of the Argentinean species seems to be more narrowly elliptical in 

outline.

Genus LLOYDIA Vodges

Lloydia? cf. saffordi (Billings)

Plate 43, figures 11, 17

Batliyurus saffordi Billings, 1860, Canadian Field Naturalist, v. 5, p. 321, fig. 24. 

Batliyurus saffordi Billings, 186o, Geol. Survey Canada, Paleozoic fossils, v. 1, 

p. 259, 411, figures 241 a, b.
490 CONTRIBUTIONS TO GENERAL GEOLOGY

Llloydia saffordi (Billings). Raymond, 1913, Canada Geol. Survey, Victoria

Memorial Mus. Bull. 1, VIII, p. 67, pi. VII, fig. 16. 

Lloydia saffordi (Billings). Bradley, 1925, Canadian Field Naturalist, v. 39,

no. 1, p. 7.

The pygidia illustrated are very similar to L. saffordi (Billings), 

though they may not be properly assignable to that species or even 

to the genus Lloydia. Despite a concerted search no Lloydia-typQ 

cephalic parts have been found in the cores. Without these parts 

there can be no certainty that the pygidia do not belong to one of 

the other asaphid-type genera in the same stratum.

Figured specimens. USNM124883,124884.

Locality. D66b (CO), Shell Pine Unit No. 1 well, 9,690-9,709 ft.

Discussion. Lloydia saffordi (Billings) has been reported from 

Division P of the Ordovician strata at Cow Head, Newfoundland, from 

Point Levis, Phillipsburgh, and Stanbridge, Quebec. In all of these 

places it is in boulders in conglomerates. Although this species is 

considered a Beekmantown form, its exact stratigraphic position 

within the Lower Ordovician is not certain.

Genus MEGALASPIS Angelin, 1851

Megalaspis planilimbata var. cyclopyge Harrington

Plate 43, figures 5,12,13

Meyalaspis planilimbata var. cyclopyge Harrington 1938, La Plata, Univ. Nac., 

Inst. Mus. Rev., nueva ser,, tonio 1, Sec. Paleontologia no. 4, p. 238-239, pi. 

X, figs. 11, 12,16,17.

The present specimens, particularly the pygidia, compare favorably 

with those described and figured by Harrington. Unfortunately only 

a part of the front of the cranidium is known from the Argentinean 

material, and it lacks the palpebral lobes (Harrington, 1938, pi. X, 

fig. 11). The single cranidium obtained from the cores differs from 

the South American specimen in the possession of a low, narrow, but 

distinct preglabellar median ridge. Much of the preglabellar field 

has been broken off. Comparisons between the two cranidia are almost 

impossible.

The present specimen has prominent subcircular palpebral lobes 

located forward of the glabellar midpoint. A median glabellar node 

is present well to the rear. The posterolateral limbs are stout. The 

pygidia are of the general construction typical of megalaspid trilobites. Ten distinct rings make up the axis; on each of the pleural 

platforms are five pleural (or interpleural ?) ridges, between each 

pair of which is a much fainter raised line. The rim is wide, smooth, 

and gently concave; it is separated from the pleural platforms by a 

distinct but shallow marginal furrow.

Figured specimens. USNM 124877,124878,124879. 

Locality. D66b (CO), Shell Pine Unit No. 1 well, 9,701-9,705 ft.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 491

Discussion The cranidium illustrated is of particular interest for 

the distinct'pattern of muscle scars on its right side. In addition 

it is clear from the peculiar scar on the left side of the glabella that 

this individual was either injured or pathologic.

The significance of the preglabellar ridge may be greater than 

previous studies would indicate. Such ridges of course can result 

from deformation of the carapace after moulting (compare Ross, 

1951, pi. 28, fig. 5 with 1953, pi. 64, fig. 1). However, if the ridge 

is a natural morphologic feature we find similar features in Basiliella 

carinata Harrington and Basilicus marginalis (Hall), both Middle 

Ordovician species.

Although the purpose of this ridge is not known, it certainly is as 

prominent as many of the other criteria used in trilobite taxonomy. 

It seems peculiar that it should have received no consideration in 

Kobayashi's revision (1934a, p. 463-465) of the genus Basilicus, B. 

tyrannus, the genotype of Basilicus, possesses no such ridge, but with 

it Kobayshi groups B. marginalis Hall which does. For the genotype 

of Basiliella Kobayaski chose B. barrandei (Hall); this species and 

B. Tomingera are reported to be synonymous by Harrington (1938 p. 

248-249). Some specimens referred to the latter have the preglabellar 

ridge (Raymond and Narraway, 1910, pi. XVI, fig. 4). On this 

basis Harrington assigned his species carinata to Basiliella (1938, 

p. 247-249, pi. 13, figs. 12,14,15,18).

If additional specimens were available, it might be found that those 

studied belong to Basiliella rather than Megalaspis.

Regardless of taxonomic assignment these specimens indicate high 

rather than low Lower Ordovician stratigraphic position.

A species assigned tentatively to Basilicus by Ross (1951, p. 106, pi. 

27, figs. 2-5) possesses a similar ridge; it is found in the "G" zone of 

the Garden City formation. It will be noted that the Utah Basilicus ? 

sp., Basiliella carinata, and Basilicus marginalis have a subtubular 

rim around the front of the cephalon into which the median ridge runs; 

unfortunately the specimen illustrateol here lacks the frontal portion 

of the preglabellar field so that the presence or absence of this rim 

cannot be determined.

Genus MEGALASPIDELLA Kofcayasi, 1937

Megalaspidella KobayasM, 1937a, Imp. Acad. Japan Proc., v. 13, no. 1, p. 15,

Tokyo. 

Megalaspidella Kobayaski, 1937b Fac. Sci. Jour., Tokyo, Imp. Univ. Jour., Sec. II,

v. 4, pt. 4, p. 499. 

Megalaspidella Kobayashi; Harrington, 1938, La Plata, Univ. Nac., Inst. Mus. Rev.

nueva ser., tomo 1, Sec. Paleontologia no. 4, p. 239-241.

Unfortunately Kobayashi's original generic description was based 

on inadequate genotypic material, if we are to judge from his figured
492 CONTRIBUTIONS TO GENERAL GEOLOGY

specimens. Supposedly the glabella is conical, that is, the dorsal furrows converge anteriorly. The figured genoholotype (Kobayashi, 

1937b, pi. V, fig. 7) lacks the front end of the glabella, and, although 

the dorsal furrows do converge between the back of the cranidium and 

the palpebral lobes, their behaviour in front of the lobes is not certain. 

Harrington (1938, pi. XII, p. 241, figs. 4, 8) illustrates two immature 

cranidia of M. orthometopa in which the furrows do not converge but 

are nearly parallel, which difference he mentions in his text. In the 

present collections specimens tentatively assigned to Harrington's 

species show parallel dorsal furrows in immature stages, but the glabella expands slightly in front of the palpebral lobes in the larger 

specimens. The restriction to a "conical" glabella is, therefore, 

questioned.

Similarly Kobayashi's description calls for a concave border around 

the pygidium. Both of his figured specimens from the type lot have 

been deformed. Harrington's specimens (1938, pi. XII, fig. 3) show 

that the concave border is evident only in those which have been 

decorticated.

Megalaspidella cf. M. orthometopa Harrington 

Plate 42, figures 15,16,19,20

Megulaspidella orthometopa Harrington, 1938, La Plata, Univ. Nac. Inst. Mus. 

Rev., nueva ser., tomo 1, Sec. Paleontologia no. 4, p. 239-241.

The cranidia in the present collection may differ from the type 

material as noted above. In those with a length of 7.0 mm the glabella 

expands very slightly in front of the palpebral lobes; this expansion is 

distinct in cranidia 8.0 mm long. The pygidia are almost identical to 

those from the Argentine, although the strong ribbing of decorticated 

specimens has not been verified.

Figured specimens USNM124862,124863,124864.

Locality D66d (CO), Shell, Pine Unit No. 1 well, 9,672-9,690 ft.

Discussion. In Argentina (Harrington, 1938, p, 280) this species 

occurs fairly high in the Lower Ordovician strata in the upper part of 

the range of Megdlaspis planilimbata var. cyclopyge, a form which is 

present in the Pine Unit No. 1 core at a depth of 9,701-9,705 feet.

Genus KIRKELLA Kobayashi, 1942

Kirkella Kobayashi, 1942, Geol. Soc. Japan Jour., v. 49, p. 118-121.

Ptyocephalus Whittington, 1948, Jour. Paleontology, v. 22, p. 567,572.

Kirkella Kobayashi. Ross, 1951, Yale Peabody Mus. Nat. History, bull. 6,

p. 91-94. 

Kirkella Kobayashi. Hintze, 1952, Utah Geol. and Minerolog. Survey Bull. 48,

p. 181-182.

Because of their distinctive form the species of Kirkella are unusually useful index fossils. In the past, listed under such names as
493

"Asaphus curiosus" and " Billing swa^ the genus has served to mark 

high Lower Ordovician strata.

The species have special interest because they fall into one of the 

few trilobite evolutionary sequences which appear to corroborate the 

theory that "ontogeny recapitulates phylogeny." As shown by Ross 

(1951, p. 92) the pygidia change with growth from an evenly curved 

to an angular pentagonal outline in K. declevita. Hintze (1952,.p. 

181-182) has shown that this same change takes place stratigraphically; in other words, the adults of K. fiLlmorensis Hintze, from the 

"G" zone of Utah and Nevada, of K. accliva Hintze from the "H" 

zone, of K. yersini Hintze from the "I" zone, and of K. vigilans 

Whittington from the lower "J" zone represent stages in the same 

change of shape that we find taking place within the ontogeny of 

K. declevita Koss of the high " J" zone.

At a depth of 9,660-9,666 feet in the Pine Unit No. 1 core, Kirkella 

is represented by a species very similar to K. fillmorensis Hintze. It 

is characteristic of the genus even in immature stages that the marginal furrows of the pygidium be straight or almost straight from the 

anterior corners to the tip of the axis. In adults of more advanced 

species with pentagonal pygidia this results in a rim (or border) on 

each side of the triangular outline; in primitive forms and immature 

stages the rim on each side has the outline of the segment of a circle. 

In the species here noted, the marginal furrow is not straight in immature specimens, though it is in the single large adult pygidium 

found in the core. Two other immature pygidia from a depth of 

9,672-9,678 feet are virtually identical.

Kirkella aff. K. fillmorensis Hintze

Plate 42, figures 5, 6,8-12

Kirkella fillmorensis Hintze, 1952, Utah Geol. and Mineralog. Survey Bull. 48, 

p. 186, pi. XIV, figs. 1-5.

Except for the course of the marginal furrows on the pygidium 

of the immature stages, this species is identical in all features to 

Hintze's from the "G" zone of Utah. The marginal furrows are evenly 

curved as in unspecialized asaphids; these furrows in K. fillmorensis 

are almost straight or very slightly curved.

Figured specimens. USNM124852-124858.

Locality. D66d-e (CO), Shell Pine Unit No. 1 well, 9,660-9,666, 9,672-9,678 ft.

Discussion. The two pygidia from the 9,672-9,678-foot depth are 

clearly immature and are probably from the same species as the higher 

specimens. One of these is illustrated in figure 17, plate 42. Special 

attention is called to the upper left corner of figure 6, plate 42, in which 

the ventral side of the posterior portion of a small fragmentary free
494 , . . : .. ,.; CONTRIBUTIONS | TO (GENERAL; GEOLOGY

cheek is shown; this possesses the distinctive ridge and panderian 

opening always found in the genus Kirkella.

Genus OGYGINUS Raymond, 1912 

Ogyginus? sp.

Plate 42, figure 7.

The pygidium illustrated in this report is very tentatively assigned 

to Ogyginus. No cephalic parts were found in association with it, 

and Whittington (written communication, 1953) believes that some 

similar pygidia in collections from northeastern North America may 

belong to quite different bathyurid-type genera. In 1934 Kobayashi (1934b, p. 553, pi. IV, fig. 17) described a pygidium almost identical to the present specimen, assigning it to Ogyginus^ but it also 

lacked the corroborating cephalic parts. To this genus he (1937b, p. 

495, pi. V, fig. 9) assigned a quite different Bolivian specimen which 

almost certainly is a bathyurid.

Figured, Specimen. USNM 124859.

Locality. D66e (CO), Shell Pine Unit No. 1 weU, 9,666 ft.

Discussion. Ogyginus typically is from the Llandeilan of the British section. In Korea, Kobayashi (1934b) considers it a contemporary 

of Asaphellus, antedating Protopliomerops. As these last two were 

apparently coexistent in North America, there is some doubt about the 

Korean relationship. However, neither the present specimen nor 

Kobayashi's can definitely be assigned to Ogyginus.

Genus ASAPHELLUS Callaway, 1877 

Asaphellus? sp.

Plate 42, figures 21, 22.

The cranidia and pygidia illustrated furnish one of the few natural 

associations in the cores in which I have reasonable confidence. Unfortunately the free cheeks are even more fragmentary than the other 

parts; so far it has not been possible to establish whether or not genal 

spines are present.

This species possesses a much longer (sagittally) preglabellar field 

than A. catamarcensis Kobayashi (Harrington, 1938, pi. XIII, fig. 8) 

but is similar in other details of the cranidium and pygidium. From 

A. gyracanthus Raymond it is readily differentiated by the stronger 

definition of the pygidial axis. Comparisons with A. tomkolensis Kobayashi are hampered by the poorness of the material with which 

Kobayashi (1934b, pi: IV, figs. 1-7): had to work. Actually this 

species is fairly close to A. homfrayi Salter, the genotype; its pygidial
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASEST, MONT. 495

axis tapers a little more than the British species and the front of the 

glabella is a little more distinctly defined.

Figured specimens. USNM 124867,. 124868.

Local ity D66b (CO), Shell Pine Unit No. 1 well, 9,698 ft.

Discussion. Assignment of this species to one of the asaphid-type 

genera like Ptychopyge might have been considered if the remotest 

suggestion of a forked hypostome had been found in association with 

the cranidia and pygidia. The outline of the glabella is a little more 

pyrif orm than is common in AsapheUus.

Asaphid trilobites with triangular pygidia

Identification of trilobites with triangular pygidia, possessing a 

median spine, poses a particularly knotty problem. The following 

discussion should serve as a warning against attempts to use these 

pygidia without associated cephalic parts for purposes of correlation.

There are at least seven genera of asaphid type trilobites in which 

one or more species possesses a triangular pygidium. These are 

Megdlaspis Angelin, Xenostegium Walcott, Thysanopyge Kayser, Kol)ayashia Harrington, Kayseraspis Harrington, Trigonocerca Ross, 

Trigonocercella Hintze.

The genotype of Megdlaspis is M. limbata Boeck (see Schmidt, 1905, 

p. 17-20; Taf. I, figs. 9-11), a species with an almost semicircular 

pygidium; however, M. acuticauda Angelin and M. heros Dalman have 

pronouncedly triangular, pointed pygidia. Megdlaspis possesses an 

unf orked hypostome.

The hypodigm of Xenostegium Walcott (1925, p. 124) has been considerably modified from the original. In the past the distinction of 

this genus has been based in large part upon the triangular form 

of the pygidium. As a result,' several species incompatible because 

of cranidial form, were included in the genus by Walcott; Ross (1951, 

p. 100-102) discussed their separation but unfortunately overlooked 

the earlier treatment of this problem by Harrington (1938, p. 222- 

228). The latter's discussion had resulted in the erection of the genera Kobayashia and Kayseraspis. Previously Kobayashi (1934b, p. 

557-558) also had noted that Walcott's generic concept included more 

'than one type of pygidium. Harrington's discussion was based largely on this notation.

-"Xenostegium, as restricted by Ross (1951, p. 100-102), includes 

species with triangular, spined pygidia and Bellefontia-likQ cranidia 

and hypostomes. Jaanusson (written communications, 1954-55) has 

questioned this restriction because, of confusion concerning the type 

species of Xenostegium. Ross :(in Ms) is attempting to rectify this 

confusion elsewhere. - ; ;

#05&y<Z£Ma.Harrington >{1938,. p; 224) 'was based on the specie^ 

K. taurus (Walcott), the genotype, and K. eudocia (Walcott) (Wal-
496 CONTRIBUTIONS TO GENERAL GEOLOGY

eott; 1925, p. 126-127, 128-129, pi. 24, figs. 1, 2, 12), but it is probable 

that these two do not rightly belong to the same genus (Ross, 1951, 

p. 100-104, 107; Hintze, 1952, p. 135). There is no known evidence 

for a triangular-spined pygidium for K. eudocia (Walcott) which 

differs in cranidial features from K. taunts (Walcott). Following Hintze (1952, p. 135), Kobayashia must be considered a monotypic genus for the present.

Thysanopyge Kayser (Harrington, 1938, p. 225-227,231,234, pi. XI, 

figs. 6, 8-10, 13) possesses a triangular pygidium very similar to some 

species of Megalaspis but differs in that its margin is ornamented with 

many small sharp spines and in the narrowness of its axis. Three 

pairs of distinct but shallow furrows are present on the glabella, the 

posterior pair probably being analogous to the occipital furrow. The 

form of the hypostome is not known.

Trigonocerca Ross (1951, p. 104-105, pi. 26, figs. 5-13) is distinguished from other genera with triangular pygidia by the outline of 

the cranidium which is somewhat similar to that of Isotelus. The 

segmentation of the pygidium can only be distinguished in decorticated specimens if at all. The hypostome, although "winged," is 

intermediate in form between the strongly forked and unforked 

asaphid types.

Trigonocercella Hintze (1952, p. 239-240, pi. XI, figs. 1-5), at present monotypic, differs from Trigonocerca in its strongly forked 

hypostome and in the acuminate outline of its cephalon.

Finally, Kayseraspis Harrington (1938, p. 228-231, pi. X, figs. 1, 2, 

6,7,10,14,15,18; pi. XI, figs. 1,3) possesses a less triangular pygidium 

than the other genera; its terminal spine originates in the margin as 

does that of Trigonocerca and in a manner not unlike that of Bellefontial acuminiferentis Ross (1951, p. 99-100, pi. 25, figs. 7-9; Hintze, 

1952, p. 241). The axial and pleural segmentation of the pygidium 

is very faint. There are no glabellar furrows; the glabella is better 

defined than in Trigonocerca but not so well defined as in Xenostegium 

(as restricted by Ross, 1951). The hypostome has an evenly rounded 

posterior end. As noted by Harrington (1938, p. 229) the glabella 

is similar to that of certain species of Asaphellus except that it expands slightly anterior to the palpebral lobes.

Although all seven of these genera have not been found within the

same stratigraphic section, several have; it is known that Xenostegium 

(as restricted by Ross, 1951) and Trigoncerca hold to different zones 

in the Lower Ordovician strata of Utah and Nevada and are, therefore, very useful indices. Hintze (1952, p. 135) is of the opinion that 

Kobayashia is virtually a contemporary of Xenostegium (as restricted 

by Ross, 1951) but this needs verification; Walcott's faunal lists on 

one of which the opinion is based are not completely reliable (see
ORDVICIAN FOSSILS FROM WELLS UN WILLISTON BASIN, MONT. 497

pp. 465, 46Y). Exactly where the other genera, two of them Argentinean, fit into the scheme of North American zonation is not certain. 

The above problem has been stated here because at least two of the 

above genera have been recognized in the Williston basin cores. Several specimens, none well preserved, have been located in the Shell 

Pine Unit No. 1 core at 9,701-9,708 feet; these are questionably referred 

to Kayseraspis. In Shell's Southwest Kichey No. 32-33B well 

Xenostegium is found at depths below 10,250 feet.

Genus KAYSERASPIS Harrington, 1938

Kayseraspis aff. K. asaphelloides Harrington

Plate 43, figures 1-4, 6, 7

Kayseraspis asaphelloides Harrington, 1938, La Plata, Univ. Nac., Inst., Mus. 

Rev. nueva ser., tomo, Sec. Paleontologia, No. 4, pp. 228-230, pi. 10, figs. 

1, 2, 6, 7,10,14,15,18.

The specimens included here are probably not conspecific with the 

species K. asaphelloides Harrington and, because the cranidial association is uncertain, may not even belong to the same genus. The 

pygidia clearly do not belong to Thysanopyge because they lack spines 

around the border and their interpleural grooves are faint. The 

termination of the axis and its relation to the marginal furrow distinguish these pygidia from those of Xenostegium (as restricted by 

Ross, 1951). The distinctness of segmentation and definition of the 

axis especially in immature stages (compare pi. 43, figs. 6, 7, with 

Eoss, 1951, pi. 26, figs 5-9, and with Hintze, 1952, pi. XI, figs. 6, 9, 

10, 14) differentiate them from Trigonocerca and Trigonocercella. 

Except for Kayseraspis, the form of the two incomplete associated 

cranidia preclude assignment to any of the seven genera discussed 

above. As far as can be told from the fragmentary material, the 

present cranidia dift'er only slightly from those of K. asaphelloides 

(Harrington, 1938, pi. X, fig. 6). The pygidia may be a little more 

triangular in outline than those of the Argentinean species.

Figured specimens. USNM 124871-124876.

Locality. D66b (CO), Shell, Pine Unit No. 1 well, 9,701-9,708 ft.

Trilobites with "hammer-head" cranidia

There are several useful index fossils amongst the trilobites with 

"hammer-head" cranidia. This hammer-head appearance results from 

the strongly divergent course of each facial suture in front of the eyes. 

Such forms are found in both Cambrian and Lower Ordovician strata; 

distinguishing them can be important in subdividing these strata.

The present state of classification of these particular trilobites is 

unsatisfactory. For stratigraphic purposes a clarification of the classi-
498 CONTRIBUTIONS TO GENERAL GEOLOGY >

fication is riot necessary and'a few-rules of thumb will-aid in distinguishing between the various genera. , ' :

In common these trilobites have the hammer-headed frontal area of 

the cranidium, many small pits in the marginal furrow, and prominent 

raised crescentic palpebral rims above the eyes; the pygidia of all 

but two genera are digitate the pleura are tipped by sharp spines. 

In almost all species, at least one pair of glabellar furrows is present; 

these are usually sigmoid in shape.

At risk of oversimplification these trilobites can be placed in three 

groups. In the first (pi. 7, figs. 23, 24, 27-30) the glabella is almost 

rectangular, the sides being straight. A small, almost semicircular, 

fixed cheek lies inside the crescentic thickened palpebral rims. This 

group includes the Cambrian genera Richardsonella, Levisella, and 

Loganellus* and the Lower Ordovician genera Kainella and Pseudokainella. Most of the species of these genera have a wide (sagittally) 

preglabellar field on which are radiating ridges. The genal spines 

are based at the rear "corners" of the cephalon in a manner "normal" 

for trilobites.

The second group is differentiated from the first on one important 

feature in particular. There are no fixed cheeks. The glabella is 

laterally swollen between the eyes in such a way as to fill all the space 

between the crescentic palpebral lobes (pi. 42, fig. 13). The preglabellar field in this group is usually narrow (sagitally). Another 

important distinction is the point of origin of the genal spine on the 

free cheeks; it invariably stems from a point well forward in the rim, 

not from the posterolateral "corner" of the cephalon as in the first 

group. This group includes Apatokephalus and Scinocephalus.

Only one genus, Menoparia, is known in the third group which is 

almost identical with the second. The chief difference is in the fixed 

cheeks. Here the glabella is swollen between the eyes; but it does not 

extend all the way to the palpebral rims, nor is it straight sided like

the first group.

To date (1954) Kainella of the first group and Apatokephalus of

the second have been found in the cores under study.

In the first group Kainella is a very valuable index genus; it is

known from both North and South America and Korea very close to 

the bottom of the Ordovician system. It clearly is not at the very base 

of the Lower Ordovician, for it occurs in the "D" zone of the Garden 

City formation in Utah and of the Pogonip group in Nevada (Hintza, 

1952, p. 189). Pseudokainella is reported from slightly higher strata 

in Argentina (Harrington, 1938) but not in North America; Hintze's 

Pseudokainella?-armatus (1952) from Nevada and Utah clearly belongs to a more primitive genus, as yet unnamed, and probably related 

to the second group. Richardsonella .is strikingly similar to
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 499

With the possible, exception of R. granulata (Raymond) the angle at 

which projections of the diverging anterior facial sutures meet is 

under 120° in Richardsonella. In the known species of Kainella this 

angle exceeds 150°. In addition, the pygidia of Richardsonella are 

relatively wider than those of Kainella and have spinose tips on all 

the pleura; the pleura themselves are not of the elongate graceful 

form found in Kainella.

Distinction between these two genera is important, for Richardsonella has so far been reported only from Upper Cambrian rocks. 

Levisella and Loganellus are very similar to Richardso'nella but do not 

have spinose pygidia; they are both of Late Cambrian age.

For our present purposes we need only list Apatokephalus and 

Scinocephalus in the second group. The first of these apparently 

ranges through almost the entire Lower Ordovician sequence, whereas 

the latter has only been reported from about the middle third of it. 

The two are readily distinguished on the basis of their pygidia and 

on the inflation of the glabella of Scinocephalus.

The third group includes only Menoparia which has been reported 

from the Lower Ordovician strata of Utah and Nevada. Because 

its known range is more definitive than that of Apatokephalus it is to 

be hoped that Menoparia will eventually be found in some of the 

Williston basin cores.

As noted in the discussion of trilobites with triangular pygidia, it 

is extremely important that identifications of the hammer-head genera 

(and resulting stratigraphic correlations) should not be based on 

either cranidia or pygidia alone. This is made increasingly clear in 

the discussion under Kainella (pp. 501-502).

Genus APATOKEPHALUS Brogger 1897

Apatokephalus aff. A. canadensis Kobayashi

Plate 42, figure 13

Apatokephahis Canadensis Kobayashi, 1953, Japanese Jour. Geology and Geography, v. 23, p. 52, pi. Ill, fig. 1.

In general form the cranidium at hand is very similar to that of 

Apatokephalus canadensis Kobayashi but does not possess a pustulose 

surface. The anterior pair of glabellar furrows is more nearly obsolete. Across the front of the glabella close to the marginal furrow is a 

transverse crease which apparently represents the preglabellar portion of the dorsal furrow. The infinitesimal space between the crease 

and the pitted marginal furrow proper would represent the preglabellar field. A similar crease is incipient in the holotype of 

Scinocephalus solitecti Ross (1951, pi. 20, fig. 32).

Figured specimen. USNM 124860.

Locality. D66e (CO), Shell Pine Unit No. 1 well, 9,660-9,666 ft. 

389021 57 5
500 CONTRIBUTIONS TO GENERAL GEOLOGY

Discussion. Although Brogger's sketches of Apatokephdlus serratus, the genotype, indicate an extensive preglabellar field, photographs of topotype material furnished by Whittington (written 

communication, 1950) show that this is exaggerated, as do Harrington's illustrations (1938, pi. V, figs. 1, 2) of material from the Argentine. Nonetheless the space between the front of the glabella and the 

marginal rim is wider (sagittally) than in the present specimen of 

A. canadensis.

The stratigraphic significance of this specimen is very indefinite 

and is covered above (p. 465).

Genus KAINEILA Walcott, 1924

Kainella sp. 

Plate 43, figures 23, 24, 27-30

This species is represented by three fragmentary preglabellar 

fields, two cranidia from which preglabellar fields have been broken, 

three complete cranidia (all very small and immature), one free 

cheek, one fair-sized but damaged pygidium, and two very poor 

small pygidia.

The glabella is subrectangular and low. Two distinct pairs of 

glabellar furrows are present. The palpebral lobes bear strong rims 

and the outline of each is gently curved. Sagittally the preglabellar 

field is one-fifth as long as the glabella. On the field are two sets of 

bifurcating ridges. Many pits are closely spaced in the marginal 

furrow behind the wide (sagittally) rim.

The free cheek possesses a gently convex ocular platform, like the 

glabella granulose but not pustulose on its surface, and limited distally by a distinct but shallow marginal furrow. This furrow fades 

out a very short way distad on the long, slender genal spine after 

being joined in an acute angle by the lateral extension of the occipital f UITOW.

The largest and best preserved pygidium unfortunately lacks the

critical posterior portion of the axis; it shows that at least five rings 

were present. The obverse of this specimen strongly suggests, but 

does not prove, that there were only five rings ahead of a bluntly 

rounded terminus, which reached almost to the rear of tK© pygidium. 

Three pairs of pleura are present, the first two bearing slender 

spinose tips. The third pair ends bluntly as part of the confluent

posterior apron around the terminus of the axis in the manner of

K. Mlling.si Walcott. and K. orientalis Rasetti.

Figured, specimens. USNM 124895-124900.

Locality. D70 (CO), Shell Oil Co., Richey area, Northern Pacific No. 1 well, 

10,500-10,509 ft.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 501

Discussion. It is of particular importance to note that the number of paired pleura on the pygidium changes with growth. A 

pygidium only 5.25 mm in length possess but two pairs, both 

spinose. There is the merest suggestion that the third pair is about 

to be developed at this stage. Another specimen 5.8 mm in length 

has the third pair well developed and forming the circumterminal 

apron.

Intermediate problems in identification result from this discovery, 

particularly because so much weight is placed on the number of axial 

and pleural segments in determining species of this genus.

If this species with continued growth adds one more axial ring, if 

the axis shortens relative to the overall midlength of the pygidium, 

and if the pygidium eventually attains a length over 25 mm, it isalmost certainly assignable to K. billingsi Walcott. The apparent 

difference in the palpebral lobes may not be a real one. First, it can 

be demonstrated that in many trilobites during growth, the length 

(exsagittal) of the palpebral lobes does not increase proportionately 

with the increase in overall length of the cranidium, as a result young 

individuals seem to have larger eyes than adults. Second, the 

palpebral rims of the holotype of K. billwgsi Walcott (1925, pi. 22, 

fig. 1) have been broken off, and there is no certainty that their size is 

correctly portrayed in the retouched photograph.

If, on the other hand, the present specimens represent essentially 

the adult condition, confident assignment to any one of the other described species is virtually impossible.

Kainella orientalis Kasetti clearly possesses a more rotund glabella 

with very faint glabellar furrows and a relatively wider pygidium, 

though agreeing well in other details. This and K, l>illingsi are the 

only two species which can be considered certainly adult in proportions 

as described and figured.

Kainella meridionalis Kobayashi is the only other species for which 

both cranidium and pygidium are known. Descriptions and illustrations of this species present much conflicting evidence.

Kobayashi's figure of Kainella meridionalis (1935, pi. XI, fig. 10) 

has been retouched to show seven rings in front of the axial terminus 

and four pairs of spinose pleura, none without spines. In 1937 Kobayashi (1937b, pi. VI, fig. 8) published a photograph of a pygidium 

belonging to the same species. This specimen is not well preserved 

and appears asymmetric in the photograph. The front pleuron is missing on the right side, but the second and third are clearly spinose. 

Whether or not the fourth bears a spine, it is impossible to tell. Four 

axial rings are present, but it appears extremely unlikely that there 

were originally more than five in front of the axial terminus. The
502 CONTRIBUTIONS TO GENERAL GEOLOGY

previously described specimen is 15 mm long, whereas the later one 

is 9.3 mm in length. Harrington (1938, pi. IV, figs. 10,23) illustrated 

two pygidia which he assigned to K. meridionalis; one of these is too 

poor to be of critical value (fig. 10). The other (fig. 23) is about 8 

mm long. Its axis is composed of five, possibly six, rings plus the terminus ; there appears to be three pairs of spinose pleura and one pair 

without spines. This last agrees better with Kobayashi's second than 

with his first specimen.

The fact remains that none of the specimens so far described is well 

enough preserved to be certain of the specific characteristics. Comparisons with other material are extremely unsatisfactory, if not 

impossible.

Compared to the species under study, Kainella colombiana Harrington and Kay possesses relatively larger, semicircular palpebral lobes 

and a longer (sagittally) preglabellar field. No pygidium is known. 

The glabellar outline in K. conica Kobayashi contracts anteriorly and 

its preglabellar field is only one-tenth as long (sagittally) as the glabella. No pygidium is known.

According to Kobayashi (1953, p. 45, pi. Ill, fig. 9), Kainella euryracMs has six axial rings plus terminus on the pygidium, although his 

photograph shows clearly that there are only five; he has counted the 

articulating half ring. Apparently all three pleural pairs are spinose. 

Despite his remarks this specimen could not possibly be mistaken for 

K. billingsi Walcott because its axis takes up almost all of the pygidial 

midlength and consists of one less ring. If the third pair of pleura 

are actually not spinose, K. euryrachis may be synonymous with K. 

rugosa Harrington; the axial terminus is too short for the species under 

study here.

Kainella flagricauda (White), known only from a very small pygidium, possesses only four axial rings. K. inexpectans (Walcott) is 

based on an immature cranidium and is of little value for purposes of 

comparison.

In Kainella primigena Kobayashi the anterior courses of the facial 

SUtlireS diverge at a much smaller angle than is common in Kainella 

and the glabella is creased by three rather than tWO pallS Of f UrrOWS J 

this SpecieS iS almost certainly assignable to RicJiardsonella. K.

stenoracUs Kobayashi differs from all other species in the possession 

of seven axial rings in the pygidium.

Except for Kainella. 'bilUnffal and K. omentA thfiS6 SpGCJeS fllC

based on small specimens, How many, if any, will eventually be 

placed into synonymy, if and when larger more mature specimens 

are found, cannot be foretold. Other synonyms may result when 

cranidia and pygidia are discovered for all the species so far described.
ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT. 503 

Genus PROTOPLIOMEROPS Kobayashl 

Protopliomerops cf. P. superciliosa Boas 

Plate 42, figure 18

The single small poorly preserved specimen obtained indicates that 

the shapes of the glabella and of the remaining palpebro-ocular ridge 

closely resemble those of P. superciliosa Koss.

Figured specimen. USNM 124866.

Locality. D66d (CO), Shell, Pine Unit No. 1 well, 9,672-9,678 ft.

Discussion. In Utah this species is an index to the "F" zone of 

the Garden City formation (Ross, 1951, p. 28-29). It is clearly 

younger than the Kainella-Leiostegium zone and indicates approximate correlation with the bottom of the middle third of the Lower 

Ordovician strata as developed in the Basin and Kange province.

Undetermined species

Undetermined pygidium 1

Plate 42, figure 23

Although not identical, the small pygidium illustrated here is very 

similar to that figured by Hintze (1952, pi. IX, fig. 9) from the lower 

part of the "G" zone of Utah and Nevada. Hintze's specimen is 

more nearly pentagonal. The two are enough alike to suggest possible correlation.

Figured specimen. USNM. 124869.

Locality. D66d (CO), Shell, Pine Unit No. 1 well, 9,679-9,684 ft.

Undetermined pygidium 2 

Plate 43, figure 15

The illustrated specimen is poorly preserved as a flattened imprint 

in black shaly sediment. It bears a striking resemblance to a pygidium 

figured by Ross (1951, pi. 19, figs. 30, 31) from the "F" zone of the 

Garden City formation, likewise unidentified.

Figured specimen. USNM. 124886.

Locality. D66a (CO), Shell, Pine Unit No. 1 well, 9,715 ft.

Discussion. This specimen suggests a correlation with the "F" zone 

of the Lower Ordovician strata of Utah and Nevada, well above the 

Leiostegium-Kainella zone ("D" zone of Utah and Nevada) of the 

Shell Richey area, Northern Pacific No. 1 well.
504 CONTRIBUTIONS TO GENERAL GEOLOGY

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ORDOVICIAN FOSSILS FROM WELLS IN WILLISTON BASIN, MONT.

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regions: Denison Univ. Sci. Lab. Jour., v. 24, p. 27-79,3 pis.

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Harrington, H. J., 1938, Sobre las faunas del ordoviciano inferior del norte

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Hintze, L. F., 1952, Lower Ordovician trilobites from western Utah and eastern

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Kirk, Edwin, 1930, The Harding sandstone of Colorado; Am. Jour. Sci., 5th ser.,

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Kobayashi, Teiichi, 1934a, The Cambro-Ordovician formations and faunas of

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 1934b, The Cambro-Ordovician formations and faunas of South Chosen, 

part II, Lower Ordovician faunas: Jour. Fac. Sci., Tokyo, Imp. Univ., v. 3, 

pt. 9, p. 521-585, pis. I-VIII.

 1935, On the Kamclla fauna of the basal Ordovician age found in Argentina : Japanese Jour. Geology and Geography, v. 12, p. 59-67, pi. XI.

 1937a, A brief summary of the Cambro-Ordovician shelly faunas of South 

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 1937b, The Cambro-Ordovician shelly faunas of South America: Fac. 

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Lochman, Christina, and Duncan, D. C., 1950, The Lower Ordovician Belief ontia 

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Geol. Soc. America Bull., v. 62, p. 1461-1462.

McCoy, M. R., 1952, Ordovician sediments in the northern Black Hills: Billings 

Geol. Soc., Guidebook, 3d Ann. Field Conf., p. 44-48.

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506 CONTRIBUTIONS TO GENERAL GEOLOGY

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Rader, M. T., Jr., 1952, Ordovician and Silurian carbonates of the central Williston basin: Billings Geol. Soc. Guidebook, 3d Ann. Field Conf., p. 48-55. 

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p. 1-62, pis. I-VIII. 

Schuchert, Charles, and Cooper, G. A., 1932, Brachiopod genera of the suborders

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Twenhofel, W. H., and others, 1954, Correlation of the Ordovician formations

of North America, v. 65, p. 247-298, 2 charts. 

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172.

 1925, Cambrian Geology and paleontology, V., No. 3, Cambrian and Ozarkian trilobites: Smithsonian Misc. Coll., v. 75, no. 3, p. 61-173, pis. 15-24. 

1928, edited by C. E. Resser, Cambrian geology and paleontology, V; No.

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Whiteaves, J. F., 1895, Systematic list, with references, of the fossils of the

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Survey Canada, Paleozoic fossils, v. 3, pt. 2, p. 111-128.
INDEX

[italic numbers Indicate descriptions]

Page 

acclioa, Kirkella... ............... .......... 493

Acknowledgments......-----... --------- 441-442

acuminiferentis, Bellefontia......... ___ 496

acuticauda, Megalaspis.... ...___-----..... 495

aeguivalvis, Zygospira.............. .. .-.-.. 452,

455,456, 479-480; pi. 40, figs. 6-9, 12 

Aladdin sandstone.... __......__ 444,449

Algae.......------...--------...-------......- 488

alternata, Pafinesquina....................-... 456

americanus, Eriptychius............. 457,460,461,469

Anthozoa... ..---.-....... 473-474

anticostiana, Protozeuga. ........._..-- 452,469,480

anticostiensis, Catazyga ____.__ 452,456,478-479

Hypsipti/cha... 457,469,478; pi. 39, figs. 6-8,12,13

Apatokephalus.......................... 465,^98,499

canadmsis..... 464,465,470, 499-500; pi. 42, flg. 13

serratus.......... ............-. .. 500

armatus, Pseudokainella...... ..........___ 498

asaphettoides, Kayseraspis......-.............. 464,

466,470,497; pi. 43, flgs. 1-4, 6,7 

Asaphellus...........-..-......----..... 465,494,496

catamarcensis............................. 494

gyracanthus............................... 494

homfrayi.................................. 494

tomkolensis-------....................... 494

sp......... 464,466,470, 494~495; pi. 42, figs.21,22

Asaphus curiosus......_._.__-___... 493

Astraspis desiderata................. 457,460,461,469

barrandei, Basilicus........................... 491

Basilicus..................................... 491

barrandei................................ 491

marginalis....--......----................ 491

typrannus............................... 491

sp.............-.------....--------...---- 491

Basiliella..................................... 491

carinata................................... 491

romingera................................. 491

Batostoma..........----.....-----....__. 474

Sf>...................................... 454,457

Bellefmtia ........................... 464,469,470

acuminiferentis.--.....--...... .......... 496

Belodus....................................... 463

Bighorn dolomite_______________ 443, 

444,445,447,459,462,463,468,470,471,472

fossils, locality Dl (CO).-- ....... 456-457,

4,58,459,474,475,476,477,478,483,485,486,487

fossils, locality D35 (CO)... 457,458,479,484,486 

Bighorn group...... 445,446,447-448,453,454,459,468

fossils._.___...__._.__.___ 452 

Bighorn Mountains....-...-..- 461,462,463,468,472 

biUingsi, Kainella......... .............. 500,501,502

Black Hills.. -......--. 461,462,463,468,470,472

Brachiopoda............................... 475-488

punctate......... ................... 486-487

Brachiopods.. ..... ......... . .-.. 468,470

pentamerid... . ....... 451

syntrophiid, unidentified.. 464; pi. 43, fig. 14 

Bryograptus.................................. 467

sp. . .. -... .......-..... 464,470

Bryozoa................................... . 474-475

Bumastus sp_________.____..__ 450

Calapoecia sp .... .-.. __.-.. 455

Calyptalaux sp.... . __.--.. 466

canadensis, Apatokephalus.................... 464,

465,470, 499-600; pi. 42, flg. 13 

capax, Lepidocyclus.--------- .......-.....-... 457,

469,477; pi. 39, figs. 21, 24-27 

carinata, Basiliella............................ 491

Carter Oil Co., Northern Pacific No. 1 well... 442,

444,447,481 

cartieri, Catazyga.............................. 479

catamarcensis, Asaphellus..................... 494

Cata zyga anticostiensis.............. 452,456, 478-479

cartieri.................................... 479

headi................................... 478,479

sp....--..-- ... 455, 479; pi. 40, figs. 1-3

(Catenipora) gracilis, Halysites...... 455,459,468,469

ceres, Megamyonia..................... 453,454,455,

457,469,483, 484, 485; pi. 40, flgs. 15,17,19-21 

colombiana, Kainella.......................... 60S

concentrica, Modiolopsis....................... 454

cornea, Kainella............................... 602

Conodonts.-......... -...- 461,462,463,468,469

Conularia sp___.. ... ...... 454

Correlation, interrigonal Late Ordovician

fauna..__...____.____..- 468 

Late Ordovician fauna__....__... 457-458

Lower Ordovician fauna.______..... 464

Red River formation................... 459-460

curiosus, Asaphus............................. 493

curvatus, Oistodus............... ........... 463

Cyclocrintes................................... JfiB

intermedius............................... 457

sp..- ........... ...... .......... 453

cyclopyge, Megalaspis planitimbata............ 464,

465, 490-491, 492; pi. 43, flgs. 5,12,13

Dalmanellid species..___________-- 455 

Deadwoodformation...__.......__ 443,445,449

description.________._______ 449-450 

fossils -. . . . 469,470

deckvita, Kirkella............................. 493

desiderata, Astraspis................ 457,460,461,469

507
508 INDEX

Page 

Diceromyonia............................... 486-487

ignota.......... 454, 457; pi. 41, figs. 13-15,17-21

storeya..........--........................ 454,

457,469, 487; pi. 41, figs. 5,6, 9,12,16 

subrotunda................................ 487

tersa.................................... 457,487

sp - 457

Dktyonema sp 464,465 

Didymograptus................................ 467

sp- ....................^............ 464

dignata, Thaerodonta......... _________ 457

Dinorthis.......... 475-476; pl. 37, figs. 16-23;pi.38,

figs. l-8,'ll, 15,17-19 

(Pinorthis) occidentalis ................ 469,476

Plaesiomys................................ 476

(Plaesiomys) proavita................... 454,469

sp - - 453,457

douglasi, Leiostegium.......................... 489

Empire State Oil Co., HathawayNo. 1 well. 441,457

fossils in core.. . 451-452,453,477,480,482,483 

equiconvexa, Platystrophia................... 454, 476

Eriptychius americanus............. 457,460,461,469

eudocia, Kobayashia......................... 495,496

euryrachis, Kainella........................... 502

facula, Sceptropora. 457,459, 474-475; pi. 37, figs. 10,11 

Fardenia..................................... 451

Fauna, Early Ordovician...---............. 463-464

Late Ordovician, distribution... ____ 450, 

Insert facing 458; pi. 44

Middle Ordovician.--....--.------.--.. 460-461

Faunal correlation, summary ..- 468-470 

Faunal lists 452-457

Favosites (Paleofaeosites) prolificus............ 456

sp 451

fittmorensis, Kirkella.......................... 464,

465, 470, 498-494; pi. 42, figs. 5, 6, 8-12 

flagricauda, Kainella.......................... 502

fluctuosa, Strophomena........................ 482

Gastropods, Hormotoma-type.................. 465

gigas, Lepldocyclus............................ 454,

457, 469, 477-478; pi. 38, figs. 16, 20-25 

gracilis, Halysites (Catenipora)...... 455,459,468,469

Qraptolites.-----.--.----..--.........__.... 469

granulata, Richardsonella.....___. __. 499

Greenfieldia s^................................ 451

(Grewingkia) robustum, Streptelasma.......... 453

gyracanthus, Asaphellus....................... 494

Haly sites..................................... 451

(Calenipora) gracilis............ 455,459,468,469

Harding sandstone... .. 461,462,463,469 

headi, Catazyga.............................. 478,479

hecuba, Strophomena..... 452, 453, 457, 469, 482-483;

pi. 40, figs. 10,11,13,16 

Heliolitessp.................................. 451

heros, Megalaspis..................... - 495

HesperorfMs laurentina.. 455, 475; pi. 37, figs. 12-15

tricenaria................................. 475

Holophragmasp........................ 453,456,474

Holtedahlina ......................... 451,452,458

moniquensis........ 455,486; pi. 41, figs. 8,10,11

sulcata.... ........................... 456,486

sp. - 453,456

homfrayi, Asaphellus.......................... 494

Hormotoma................................... 465

sp - 464

Pagehydrida, Hypsiptycha....-.-....--- ...... 454, 457,.

469, 478; pi. 39, figs. 9-11, 14, 15, 18-20, 22, 23 

Hypsiptycha................................ 476, 478

anticostiensis... 457,469,478; pi. 39, figs. 6-8,12,13' 

hydrida................................ 454, 457,

469, 478; pi. 39, figs. 9-11, 14, 15, 18-20, 22, 23

sp. 455

Hystricurus robustus.......................... 489

Sp... 488-489; pi. 43, figs. 21, 22, 25, 26

ignota, Diceromyonia.......................... 454,

457; pi. 41, figs. 13-15,17-21 

Imbricatia.................................... 467'

sp 470

inexpectans, Kainella.......................... 502

intermedius, Cyclorcinites...................... 457

iowense, Phynchotrema........!................ 457,.

476; pi. 38, figs. 9, 10,12-14 

Isotelus....................................... 496

sp 454, 457

Kaibab limestone ..-..__ --...__ 471-472

Kainella....................... 464, 465, 467, 498-499-

billingsi.------------------------- 500, 501, 502

colombiana................................ 502

conica.................................... 508

euryrachis................................. 502'

flagricauda................................ 502

inexpectans........... ..... 502'

meridionalis............................. 601-502

orientalis-.......... _________ 500, 501, 502

primigena................................. 502

rugosa.................................... 502

stenorachis................................ 502'

sp......-- 470, 600-502; pi. 43, figs. 23. 24, 27-30

Kayseraspis........................ 466, 495, 498-497'

asaphelloides----.-----.................... 464,

466, 470, 497; pi. 43, figs. 1-4, 6, 7

Kirkella............................ 466, 498-493, 494

accliva.................................... 493

declevita ................................ 493

fittmorensis.. ----------------------------- 464,

465, 470, 493-494; pl. 42, figs. 5, 6, 8-12

sp____..___.____________ 464 

Kobayashia................................. 495-49fr

eudocia.............................. 495,495

tdUTUS...... 495, 496

knighti, Megamyonia.......................... 484

Loader sandstone member, Bighorn dolomite. 460, 

461, 462, 463, 468, 472

latusculum, Streptelasma.. ..................... 474

laurentina, Hesperorthis... 455, 476; pl. 37, figs. 12-10 

Leigh member, Bighorn dolomite.. . 458, 468, 472 

Leiostegium ........... ................. 465, 466, 467

douglasi ... ..-.-....- ... ...... .......... ... 489

manitouensis.... ------ 470, 489; pl. 43; figs. 18-20'

quadratus..--. ....................... ..... 489

Lepidocyclus -------.....--_..--...__._ 455,.476, 477

Capax. .-- - ----- 457, 469, 477; pl. 39, flgs. 21, 24-27

gigas- 454, 457, 469, 477-478; pl. 38, figs. 16, 20-25

perlamellosa. 454, 455, 457, 469, 477; pl. 39, figs. 1-5'

Leptaena... ........... ....... ... ... .. .... .... 459

nitens ..... . ......... ..... ................. 485

limbata, Megalaspis. ... .. ............. .. ..... . 495'

(jpikina. - ... 454, 457, 485-4S6; pl. 41, figs. 1,£
INDEX 509

Page

Lloydia saffordi............ 489-490; pi. 43, flgs. 11,17

sp.~ ~ -- --- 464,466,470 

LoganeiUua:...................... ----- 498,499

manitouensis, Leiostegium. 470, 489; pi. 43, flgs. 18-20 

marginalis, Basilicus.................. ......-. 491

Megalaspidella.......................... 465,491-498

orthometopa.. 464, 465, 466, 470, 492; pi. 42, flgs.

15,16,19,20 

Megalaspis..................... 465,467,469,491,495

acuticauda............. . -.--. 495

heros.......--------------- ..-.- 495

limbata................................... 495

planilimbata cyclopyge.. 464, 465, 490-491, 492;

pi. 43, flgs. 5, 12,13

Megamyonia............................ 459,483,484

ceres..453, 454, 455, 457, 469, 483, 484, 485; pi. 40,

flgs. 15, 17, 19-21

knighti.................................... 484

nitens.. 454, 455, 457, 469, 483, 484-486; pi. 41,

figs. 3, 4, 7

unicostata- 454, 455, 456, 457, 483-484; pi. 40,

flgs. 23-25

sp.-..- -- ...454,456,457,485; pi. 40, fig. 18 

Menoparia.................................. 498,499

meridionaUs, Kainella....................... 601-502

Method of presentation....... _._-._.--- 442

Modiolopsis concmtrica....................... 454

moniquensis, Holtedahlina.. 455, 486; pi. 41, figs. 8,

10,11 

Murphy Corp., C.H., East Poplar Unit No. 1

well-.----------- . 441,448,458

fossils in core.------------------ 451,452,459

Nanorthis sp - ._-_- . ___- ... 464

nitens, Leptuena.............................. 485

Megamymia.. .454, 455, 457, 469, 483, 484-488; 

pi. 41, flgs. 3, 4, 7

ocddentalis, Dinorthis (Pinorthis)............ 469,476

PinortMs................................. 457

Ogyginus..................................... 494

sp---------..-.-...464,465,470, 494; pi. 42, fig. 7

Oistodus..... ............................_ 463

curvatus.................................. 463

Onniella...................................... 486

sp.. __.__ 457

Gpikina...................................... 485

limbrata........ 454,457, 486-486; pi. 41, flgs. 1, 2

pergibbosa................................. 486

Ordovician stratigraphic units, western Williston basin....-----------.-... 442-449

orientalis, Kainella...................... 500,601,502

orthometopa, Megalaspidella.................... 464,

465, 466, 470, 492; pi. 42, figs. 15, 16, 19,20

Ostracoda, leperditiid.......................... 453

oweni, Receptaculites.......................... 469

Paleofavosites prolificus........................ 474

sp . . _________.___.... 456

(Paleofavosites) prolificus, Favosites............ 456

Paleogeographic interpretations, tenative_ 470-473

Paltodus...................................... 463

Pasceolus..................................... 488

pergibbosa, Gpikina........................... 486

Page 

perlamellosa, Lepidocyclus...................... 464

455, 457, 469, 477; pi. 39, flgs. 1-5 

Pionorthis ocddentalis......................... 457

(PinortMs) ocddentalis, Dinorthis............ 469,476

Plaesiomys sp__ -------- 457

(Plaesiomys) proavita, Dinorthis........ ... 454,469-

planilimbata cyclopyge, Megalaspis............ 464f

465, 490-491, 492; pi. 43, flgs. 5,12,1» 

Platystrophia eguiconvexa.................... 454,476'

Plectambonites................................ 481

plicata, Phynchotrema............... 452,453,469,477"

primigena, Kainella....^...................... &0%

proavita, Dinorthis (Plaesiomys)............. 454,469'

prolificus, Favosites (Paleofavosites)............ 456'

Paleofavosites............................. 474i

Protopliomerops.............................. 465,

494, 503; pi. 42, fig. 23; pi. 43, fig. 15 

superciliosa............... 466, 503; pi. 42, fig. 18

undetermined species..-..--------- .-.. 4641

sp.------------ - 464,465,47(1

Protozeugaanticostiana.................. 452,469,480'

Pseudokainella................................ 498

armatus.................................. 498

Pterinea sp... ----- 454

nychopyge................................... 495

Pycnactissp.................................. 451

guadratus, Leiostegium........................ 489

RafinesQuina alternata........................ 456

winchesterensis............................ 456

sp....-- -------- 456

recedens, Thaerodonta..... 481-488; pi. 40, flgs. 26-28

Receptaculites................... 451,452,459,462,468

oweni...___________.____----- 469

recurvirostris, Zygospira....................... 480

Red River formation........ 442,443,444,468,471..472

correlation_...._.___._._.. _ 459-460

description.......______.... .... 448

fossils. . - - 453-

454, 455, 456, 458, 475, 477,479, 480, 481-482, 483, 

484, 486. 

Resserella..................................... 486

resupinata, Zygospira...... 455, 457, 479; pi. 40, fig. 6

Rhynchotrema................................. 476

iowense......... 457, 470; pi. 38, flgs. 9, 10, 12-14

plicata.......................... 452,453,469,477

Richardsonella.......................... 498-499, 502

granulata................................. 499

robustum, Streptelasma (Grewingkia).......... 453

robustus, Hystricurus......................... 4S9

romingera, Basiliella.......................... 491

rugosa, Kainella.............................. 5Q2

rugulifera, Strophomena.. 453, 455, 483; pi. 40, flg. 141

saffordi, Lloydia............ 489-490; pi. 43, flgs. 11,17

saxea, Thaerodonta............................ 481

Sceptroporafacula...... 457, 474-476;$]. 37, figs. 10,11

Scinocephalus................................. 498

solictecti.................................. 499

Scolecodonts__------------_. 461

Scolithus sandstone 443-444, 449, 462 

Scope of investigation...._... . 440-441

Screptroporafacula............................ 459

serratus, Apatokephalus....................... 500
510 INDEX

P.ise

Shell Oil Co., Little Beaver No. 1 well.--.-.- 441

fossils in core... .. 452, 456, 480, 482, 483, 486

Shell Oil Co., Pine Unit, No. 1 well-.------.. 441

449,457, 458, 468 

fossils in core,.------------_------------ 450,

451, 454-455, 460, 463-467, 474, 475, 476, 477, 

478, 479, 480, 482, 483, 484, 485, 486, 487, 490, 

492, 493. 494, 495, 497, 499. 

Shell Oil Co., Richey area, Northern Pacific

R. R., No. 1 well---.-------.-- 441, 458

fossils in core... ..- --------- ... 450,

451, 453, 460, 463-464, 467, 484, 486, 489, 500, 503 

Shell Oil Co., Southwest Richey No. 32-33B

well....................... 445, 450, 464

Shumardia............. ------------- 465

Silurian and Ordovician boundary..__.... 450-452

soliclecti, Scinocephalus.......----------------- 499

Sowerbyella............................ 454, 480-481

sp - . -- 453, 455, 456

Sponge spicules, hexactinellid___... - __ 464,465 

stenorachis, Kainella.... ... -------- .. 502

Stonewall formation-. _____. _ 442,445,446,447 

Stony Mountain correlatives_..-..-------.-.- 459

Stony Mountain formation.__.. 442, 443, 444, 468 

description.-----------______.----.-._ 447-448

fossils in dolomitic member.. 453, 477, 480, 483 

lower shale member......_--...--.-.- 472-473

fossils 454, 458,

474, 476, 477, 478, 482-483, 484, 485, 486, 487 

storeya, Diceromyonia......................... 454,

457, 469, 487; pi. 41, figs. 5, 6, 9,12,16 

Stratigraphic terminology, derivation.... 442-445

Streptflasma (Grewingkia) robustum........... 453

latusculum..................... .. _ -. 474

trilobatum ....................... 456, 469, 474

Strophomena fluctuosa......................... 482

hecuba................................. 452, 453,

457, 469, 482-483; pi. 40, figs. 10, 11, 13, 16 

rugulifera.--.......... 453, 455, 483; pi. 40; fig. 14

vetusta.. ............... 454, 482; pi. 40, fig. 4

sp ----- .--.-...-. .. . 455

subrotunda, Diceromyonia -.-- 487 

sulcata. HoUedalina........................ 456, 486

SUperciliosa, Protopliomerops.. 466,503; pi. 42, fig. 18

taurus, Kobayashia.......................... 495,496

Page 

tersa, Diceromyonia......................... 457,487

Tetragraptus sp. . . . .. 464 

Thaerodonta............................ 454, 480-481

dignata.-.-.-----------.-.--------------.. 457

recedena............... 481-482: pi. 40, figs. 26-28

soxea..................................... 481

sp. 453,455,456,457

Thysanopyge................................ 495, 496

tomkolensis, Asaphellus....................... 494:

Trematissp................................... 454

Triarthrus.................................... 465

tricenaria, Hesperorthis........................ 475

Trigonocerca................................ 495, 496

Trigonocercetta.............................. 495,496

trilobatum, Streptelasma................. 456,469,474

Trllobites.... ~ 463-464,469

Bathyurid . - . -- 465 

descriptions of Early Ordovician..... 488-503

with "hammer-head" cranidia.. ... 497-503

with triangular pygidia.-.. .-..-- 495-497

tyrannus, Pasilicus........................... 491

unicostata, Megamyonia....................... 454,

455,456, 457, 483-484; pi. 40, figs. 23-25

vetusta, Strophomena.---....... 454,482; pi. 40, fig. 4

Virginia...........--------- ------.. 451

Wells, location......-....-.-..-..-.-....- 440,441

Whitewood dolomite.__ _-__._-... 443,

459,461,462,463, 468,471,472

Whitewood limestone.--------------.- 443,449,472

Whitfieldellasp............................... 451

Winchesterensis, Rafinesquina..'................ 456

Wind River Mountains..___________ 463 

Winnipeg formation_--------___-------- 442,

443,444,445,446,463,468,469,471 

description..________._____ 448-449 

Middle Ordovician faunal elements_ 460-461

Xenostegium............................ 464, 495, 496

Ira aequivalvis..------------------------ 452,

455,456, 479-480; pi. 40, figs. 6-9, 12 

----------------------------- 480

resupinata............. 455,457,479; pi. 40, fig. 5

sp....- . . 457
PLATE 37 

l Figures na tural size tmless otherwise Indicated] 

FiGURES I, 2. Strtpltla&ma trilobatum Whltcavcs (p. 474). 

I. Calyx; 2, left al~ r side, USNM 124800. Upper Ordovician, red shaly beds In uppermost 

part or Bighorn dolotHite, Joe. DI (CO), South Fork or Rock Creek, Johnson County, 

Wyo. 

3, 5-7. "Holophragma" sp. (p. 474). 

3. VIew of the cardinAl side, X2; 7, calyx, X2, USNM 124801. 

5. Alar side; 6, same vlew, X2, USNM 124!:101. From Upper Ordo\·lclau, red shaly beds 

In uppermost part of Bighorn dolom ite, Joe. Dl (CO), South Fork or Rock Creek, 

Johnson County, Wyo. 

4, 8. Strtpltla&ma c!. S. /atuuu!um (Billings) (p. 474). 

4. VIew of counter side; 8, calyx, USNM 124803. Upper Ordovician, red shnly beds In 

uppermost part of Bighorn doloiT' Itc, toe. Dl (COl, South F ork of Rock Creek, Johnson 

County, Wyo. 

9. FavO&fle& (Paltofa vO&ilts) cf. F. prolificus (Blllinb'S) (p. 474). 

Fragment of cornllum, USNM 124804. Upper Ordov tctan, red shaly beds tu uppermost 

part of Bighorn dolomite, Joe. Dl (CO), South Fork of Hock Creek, J ohnson County, 

Wyo. 

10, II. Sceptropora ct. S. fa cu./a Ulrich (p. 474). 

10, II. Oblique and lnteml views of one of th e articulating segments, X20, USNM 124805. 

Upper Ordovician, red shaly beds lu up permost part or Bighorn dolomite, Joe. DI (CO), 

South Fork of Hock Creek, Johnson County, Wyo. 

12- 15. Huperorthb cr. H. laurent ina (BU!ings) (p. 475). 

12, 13. Dorsal valve, external and Internal views, X3, USNM 124806. (Hight side of vah•e 

broken after photographing interior.) 

14. Interior or ventral valve, X4, USN:\! 124807. 

15. lntcrlor of dorsal valve, showing bladelikc brachlophore, X3 . All from Upper Ordo· 

vlcian, Red River formation, Joe. D9Id (CO) , Shell Oll Co., Pine Unit No. I well. 

9,103-9,116 ft. 

16, 19, 20, 23. Dinorthi• (Plaesiomv• (?)) ct. D. (P.) occidentali• Ladd (p. 475). 

16. Laternl vlew; 19, posterior view; 20, 23, dorsal and ventrul views, USN!\! 124808. 

Upper Ordovician, red slu ly beds In uppermost part of Bighorn dolomite, Joe. DI (CO), 

Sonth Fork of Rock Creek, J ohnson Cowlty , Wyo. 

17, 18, 21, 22. Dinorthis (Pionorthi& (7)) cr. D . (P.) occidentalis Okulltch (p. 475). 

li, 18. Lateral and posterior views; 21, 22, dorsal and ventral views, USNM 124809. 

Upper Ordovician, red shaly beds in uppermost part or Bighorn dolomite, Joe. Dl 

(CO), South Fork of Rock Creek . Jobnsvn Cow1ty, Wyo. 
PLATE 38 

[Figures natural size unless otherwise Indicated] 

FtnuREs I, 2, 5, 6. Dinortllis (Pionorthis(?)) n. sp. (p. 475). 

I, 2. Ventral and dorsal views; 5, 6, lateral and posterior views, USNM 124810. Upper 

Ordovician, red shaly beds in uppermost part of Bighorn dolomite, Joe. Dl (CO), 

South Fork of Rock Creek, Johnson County, Wyo. 

3, 4, 7, 8, II. Dinorthis(?) sp. (p. 475). 

3, 7, II. Lateral, posteri or, and an terior ,-iews; 4, 8, Dorsal and ventral views, USNM 

124811. Upper Ordo,·ician, red ; hnly beds in uppermost part of Bighorn dolomite, 

Joe. Dl (CO), South Fork of Rock Creek, Johnson County, Wyo. (The ventral 

valve of Okulitcb's two cotypes for Pionorthi& occidentalis may belong to this species.) 

9, 10, 12- 14. Rhyncholrema iowmse Wang (p. 476). 

9, 13. Dorsal and ventral views, X 2; 10, 12, 14, Anterior, posterior, and lateral ylews, 

X 2. US~.\1 121813. Upper Ordovician, red shaly beds in uppermost part of 

Bighorn dolomite, Joe. D1 (CO), South Fork of Rock Creek, Johnson County, 

Wyo. 

15, 17- 19. Dinorthis(?) (Pionorlhis(?)) n. sp. (p. 475). 

15, 19. Dorsal and Ycn tr al Yiews; 17, 18, posterior and lateral views, USNM 124812. 

Upper OrdoYician, red shaly beds in the uppermost part of Bighorn dolomite, Joe. 

D1 (CO), South Fork of Rock Creek, Joh nson County, Wyo. 

16, 20-25. L epidocvclus oioas Wang (p. 4n). 

16, 20, 23, Lntcrnl, anterior, and posterior views; 21, 24, dorsal and ventral views 

(specimen slightl y distorted), US :\~1 124814. 22, 25, dorsal and ventral views of 

undistorted specimen, S~M 124815, All from Upper Ordovician, red shaly beds 

In uppermost part of Bighorn dolomite, Joe. D1 (CO), South Fork of Rock Creek, 

Johnson County, 'Yyo. 

• 
PLATE 39 

FIGURES 1-5. Lepldoet;clu& perlamellosa (Whitfield) (p. 4n). 

I, 2. Dorsnl and v~ntral views, X I; 3, 4, 5, posterior, lateral, and anterior views, X 1. 

USNM 124816. Upper Ordov ician, red shaly beds of uppermost port of Ulghorn dolu· 

mite, Joe. Dl (CO), South Fork of Rock Creek, Johnson County, Wyo. 

6-8, 12, 13. Hvp&iptvcha ct. H. anticosli<1l&i• (ll!ll!ngs) (p. 478). 

6, 7, 12. Posterior, anterior, and la tera l views, X 2; 8, 13, ventral and dorsal views, X 2, 

USNM 124817. Upper Ordovician, red shaly beds In uppermost part of Bighorn dolo· 

mite, loc. Dl (CO) , South Fork of Rock Creek, Johnson County, Wyo. 

9-11, 14, 15. Hvp&iptycha cr. H . hvbrida Wang (p. 478). 

9, 14. Dorsal and ventral views, X 2; 10, II, 15, posterior, lateral, and anterior views, X 2, 

US:>!M 124818. Upper Ordovician, lower shale member, Stony Mountain formation, 

loc. D91f (CO), Shell 0 11 Co., Pine Unit No. I well, 8,986-9,010 ft. 

16,17. l&oi.<IU&f sp. 

16, Cranidium, damaged, X 2, US:>Il\I 124821. 

17. Pygidlum X 2, USN M 124822. Upper Ordovician, lower shale member, Stony l\ l ouo· 

tnin formation Joe. D91f (CO), Shell Oil Co., Pine Unit :\'o. I well, 8,986-9,010 ft. 

18-20, 22,23. !Iyp&iptvcha cC. H. hvbrlda Wang (p. 478). 

18, 22, 23. Posterior, anterior, and lateral views, X 2; 19, 20, ventral and dorsal views, X 2, 

US:>! M 124819. Upper Ordovician, rod shaly beds in uppermost part or Bighorn dolomite, 

Joe. Dl (CO), South Fork of Rock Crock, Johnson County, Wyo. 

21, 24, 25-27. LepldocvclU& capax (Conrad) (p. 4i7). 

21, 24, 27. Lateral, posterior, and anterior views, X I; 25, 26, dorsal and ventral views, X 1, 

USN!\[ 124820. Upper Ordovician, red shaly beds in uppermost part or Dighorn dolo· 

mite, Joe. Dl (CO), South Fork of Rock Creek, Johnson County, Wyo. 
PLATE 40 

[Figures natural size unless otherwise indicated] 

Fir.URES 1-3. Catazvga sp. (p. 479). 

I, 2, 3. Dorsal, ventral and lateral views of a fragmentary silicified specimen, X 3, USNM 

124823. Upper Ordovician, Red Ri\·or formation, Joe. D91d (CO), Sholl Oil Co., Pine 

Unit No . I well, 9,103-9,116 ft. 

4. Strophomma cf. S. oell,sta J ames (p. 482). 

Interior of dorsal valve, cut by coring bit, USNM 124824. Upper Ordovician, lower shale 

membN, Stony Mountain formation, Joe. D91f (CO), Shell Oil Co., Pine Unit No . 1 

woll, 8,986--9,010 ft . 

5. i'voospira cf. z. resupinata Wang (p. 479). 

Ventral view of ventral valve, X 3, USNM 124825. Upper Ordovician, Rod River !onnat!on, loc. D91e (CO), Sholl Oil Co., Pine U nit No. I well , 9,023-9,043 ft. 

6-9,12. Z vgospira ef. Z. aequi•alois Twonhofol (p. 479). 

6, 8. Ventral and dorsal views, X 3. 

7, 9, 12. Anterior, lateral, and posterior views, X 3, USNM 124826. Upper Ordovician, 

Rod River formation, Joe. D91c (CO), Sboll Oil Co., Pine Unit No. I well, 9,122-9,128!t. 

10, 11, 13, 16. Strophomena hecuba Billings (p . 482) . 

10, II, 13. Dorsal valve, dorsal, lateral, and posterior views, USNM 124827. Upper Ordovician, upper dolomitic mombor, Stony Mowltain formation, Joe . D90o (CO), Empire 

Steto Oil Co., Hathaway No. I well, 8,556-8,664 ft. 

16. Dorsal viow of a loss nasute specimen , USNM 124828. Upper Ordovician, rod shaly 

bods in uppermost part of Bighorn dolomi te , loe. Dl (CO), South Fork of Rock Creek, 

Johnson County, Wyo. 

14. Strophomena cf. S . ru.gulifera Wang (p . 483). 

Ven tral view, USNM 124829. Upper Ordovician, Rod Ri ver formation, Joe. D91o (CO) , 

Shell Oil Co. , Pine Unit No. I well , 9,023-9,043 ft. 

15, 17,19-21. Megamvonia cf. 111. cera (B U!ings) (p. 484). 

15. Interior of a ventral valve, USNM 124830. 

19. Interior of a dorsal valve, USN M 124831. 

17, 20, 21. Lateral, ventral, and posterior views of a ventral valve , USNM 124832. All 

from Upper Ordovician, lower shale member, Stouy Mountoln formation, loe. DOlt 

(CO) , Sh oll Oil Co., Pine U nit No. I well , 8,986-9,010 ft . 

18. Megamvonia sp. (cf. l\1. sp., Wang, 1949, p. 34, pl. 9C) (p. 485). 

Ventral view of \'entra l ,·ah e, USNM 124833. Upper Ordo,·ictau, lower shale mem ber, 

Stony Mountain formation, loc. D91f (CO), Shell Oil Co., Pine Unit No. I well, 8,98&-

9,010 ft. 

22. Thaerodonta sp. (p. 480). 

Dorsal view, X 2, USNM 124834. Upper Ordo\'lcian, red shaly beds of the uppermost part 

of Bighorn dolomite, Joe. Dl (CO), South Fork of Rock Creek , J ohnson Connty, Wyo. 

'l;l--25. J\1egamvonia ct. 1\1. un.ico&tata (Meek and Worthen). (p. 483). 

23. Ventral view of ventral valve, immature, tentatively referred Ulis species, X 2, USNM 

124835. 

24. In terior of ,-entral m lvc, a rubber mold madr from cast, USNM 124!S36. Upper Ordovician, Red River formation, loc. D92b (CO), Shell Oil Co., Litl.le Beaver No. I well, 

8,531--1!,540 lt, 

25. Ventral ,·lew of ventral ,·ah·e, associated with Diceromvo>~ia sp. USNM 124837. Upper 

Ordo,•ician, lower shale mrmber, Stony Mountain formation, Joe. D91f (CO), Shrll Oil 

Co., Pine Unit No. 1 well, 8,98&-9,010 ft.. 

26-28. Tliaerodonta ct. T . receden& (Sardeson) (p. 481). 

26. Internal cast of ventral valve, associated with J\{egamvonia cf. M. unico&lata, USNM 

124838. 

27. Interior of dorsal valve, a rubber mold , X 5, US1\M 124839. 

28. Interior of ventral val\·o, a rubb er mold of cast shown in fig. 26, slightly distorted to 

show delthyrial ca,·ittcs, X 2, USNM 124838. All from Upper Ordovician, Red River 

!ormallon, Joe. D92b (CO), Sholl Oil Co., Littlr Braver No. 1 well, 8,531-8,540 ft. 
PLATE 41 

(Figures natural slzo un less otherwise indicat ed] 

FIC: L'R ~ I. 2. Opikina'! a fT. 0 . limbrata Wa ng (p . 485) . 

1. In terior of large dorsal va lve, USNM 124840. 

2. I nterior of small dorsa l valve, USN M 124841. 

Upper Ordovician , lower shale mem ber, Stony 1\'Ioun t.a ln formation , loe. D91f (CO), 

Shell Oil Co., Pine Unit No. I well, 8,986-U,OIO ft. 

3, 4, 7. ,vregam yonia a fT. N . nilens (Billings) (p. 484) . 

P t•>:<·rior, w ntral, and lateral \'lews, US:-< M 124842 . E q unls in part" Lep/aena niltn$" 

Billings as described by 'l'wenhofel, 1928. Upper Ordovician, red shaly beds In uppermost part of Bighorn dolom ite, loc. D1 (CO), South Fork of Rock Creek, J ohnson 

Count y, " · yo. 

6, 6, 9, 12, 1r,. DiceromrJonia storeya Okulitch . (p. 4S7). 

5. 12. Dorsal and \'('ntra l d ews. X 2; 

6, 9, 16. Ant erior, pow·rior, and la teral views, X 2, USN M 124843. U p per Ordovlchm , red 

shaly beds in uppermost part of Bighorn dolomite, loe. Dl (CO), South Fork of Rock 

Creek, Johnson County, W yo. 

8, 10, ~ 1-loltedahlina cf. H. moniquensis Foerste (p. 486). 

8. Exterior of a dorsal \'ah ·e, X 2, USNM 124844. 

10. Interior of dorsal ,-alve , X 2, USN:vi 124845. 

II. Interior of dorsal valve, X 2, US:\' :\1 124846. 

All s pecimens poorly silicified and fragmenta ry. AJI from U pper Ordovician, llod River 

formation , loe. D 91d (C O), Shell Oil Co., Pine U ni t No. I well, O,loa-9, 11 6 ft. 

13--1fi, 17-21. Diceromvon ia cf. D. iqnota (Sardeson) (p. 487). 

13. Interior of vent ral valve, X 2, USN:\ I 124847. 

14, 15, 21. Anterior, posterior, and lateral views, X 2. 

18, 20. Ventral and dorsal \'iews, X 2, USNM 124848. U pper Ordo,·iclan , red shnly beds 

in uppermost part of Uighorn dolomite, loc. Dl (CO), So uth Fork of Rock Creek, John· 

son County, \\' yo. 

I 7. Interior of ,·entrnl valve showing narrow ridge between dlductor scars, USNM 1248·19. 

19. Interior of dorsal va lve, X 2, USNM 124850. U pper Ordo, eh~n , lower s hale rn ombrr, 

Stony M ounta in forma tion , Joe. D 9ll (CO), Shell Oil Co., Pine Unit No. I well, 8,986-

0,010 ft. 

!2-2G. Diceromv011ia n. sp. (afJ. D. teraa) (p. 487). 

22, 24, 25. Posterior, lateral, and antflrior views, X 2. 

23, 26. Ventral and dorsal views, X 2, USNM 1248..>1. Upper Ordovician , red shaly beds 

ln uppermost part of Bighorn dolomite, Joe. D1 (CO), South Fork of Rock Creek, John· 

son Coun ty , Wyo. 
PLATE 42 

F IO n~:s 1-4. Fragmentary fish plates. 

1, 2, 4. Eript ychius americanus Walcott, X 3, X 3, X 4, USNl\I 208()8, 20869, 20870. 

3. Astraspis desiduata \\"alcott, X 3, liS:\ ~! 2087 1. Winnipeg formation , Joe . D 60 (CO) , 

Shell Oil Co ., Pine Unit No . 1 well , 9,52'i- 9,53 1 ft. 

5, 6, 8-12. K irkella nff. K. fillmorensis Hintze (p. 193) . 

5. l'ygidium, X 2, US;-!l\1 12·1852. 

6. Ventral Y!cw or fragment ary postorlor portlOil or free chock and dorsal view of Immature 

cranldlum, X 3, USN M 124853. 

8. Tmmat ure pygidium, X 3, US;-! M 12·!854. 

9. Left free check, Immature, X 2, USN M 124855. 

10. llypostomo, broken, but showing charactcrist.lc "w!J1gs," X 2, USNM 12•1857. 

l l. Cranldium, immature, damaged, X 3, USNM 124856. 

12. Cranidium, damaged , rubber cnst of original, X 2, USNM 124858. All from Lower 

Ordovician, Deadwood formation, Joe . DG6c (CO), Shell Oll Co., Pine U n it No. I well, 

9,6G0-9,666 ft. 

7. Ooyoiuus'! sp. {p. 4\H). 

Pygidium, X I , U S:-.i M 12-1 859. Lower Ordo\"lclnn, D eadwood formation . Joe, D66c (CO) , 

Shell Oil Co. , P ine U nit :\"o. 1 wl'll, 9,6GQ-9,666 ft. 

13. A patokephalu s cr. A . canadensis Kobayash i (p. 499). 

Cranldlum, X 4, US;-!l\1 12·1860. Lo\\·cr Ordo,·iclan, Deadwood formation , Joe. 066e 

(CO) , Sholl Oil Co. , l'lne U nit :-.lo . 1 wull, U,GGQ-9,666 ft. 

14. H ormolomo' sp. 

Two small spoclmens, X I, US~ :\I 124861. Lower OrdoYiclan, Deadwood forma tion. 

Joe. D66c (CO) , Shell Oil Co. , P ine Unit No. I well , 9,6G0-9,666 ft. 

15, 16, 19, 20 . • \feoalaspidella cr. ''f. orthometopa U arrlng1on (p. 492). 

15. Cran1dlurn, lackl.ng palpebral lobes, X 2, US~ l\1 12·1862. 

16, 20 . J'yglditun , dorsal a nd posrerlor ,-lows, X 3, US:\:\112·1 63 . 

19. Fragmcn tnr)· hypostome , ru hher cnst, X 4, US~ M 124861. Lowur Ordovician , Dead -

wood formation, Joe. DliGd-o (CO) , Shell Oil Co., Pine Unit l\o. 1 well , 9,6G0-9,600 ft. 

17. J(irktlla? sp. (p. 41'2) . 

J>ygldl nm , X 2, US:\'.\[ 124853. P robably snmc as those fi gured above . Lower Ordovician , D oudwood format.lon, Joe. DG6d (CO) , Slloll Oil Co., Pine Unit No . I well, 9,6i2-

9,67S rt. 

18. Proto p/iomero p• cr. P . w perciliosa Ross (p. 50.1) . 

Crnnldlum, X 3, USN J\o[ 124 fl(). Lower Ordovician , D ondwood fonuatton, Joe. D G6d 

(CO) , Sholl Oil Co. , Pine Unit 1o. I well, 9,672-9,()78 ft . 

21, 22. Asapll ell ns? sp. (p. 49·1). 

21. Crnn ldium and ventral su rface or pyg id lum, X 2, USN M 124 GS . 

22 . l'yglcllnm, X 2, US:\' ~[ 1248fi7 . Lower Ordoddan, D eadwood formar ion , Joe. D66b 

(CO) , Shell Oil Co., l' lno Unit 1-'o. 1 well, 9,698 ft. 

23. Unlc!Pntlfied pygldlnm (p. 503) . 

X 3, US1>1.\f 12·1869. T his should he compared with llintzo , 1052, p l. IX, fi g. 19. Lower 

Ordodclan, D eadwood formation, Joe . D 66d (CO) . Sholl Oil Co .. Pi ne Un it No. I well , 

9,678-9,6 I ft. 

24. D ictvo11ema sp. 

X I, U SN M 121870. Lower Ordovician, D eadwood formation, Joe. DiO (CO), Shell Oil 

Co. , Ricbey area , Northrrn P acific R . R. No. 1 well , 10,484 ft. 
PLATE 43 

FJO H~s 1- 4, 6, 7. [(ayura8pi&aff. K . asaphtlloide~ llarrington (p. 407) . 

I. Fragmentary cranldlum and Immature py~tdltllll with term inal splnl', X 2, 

USNM 124871. 

2. Cranldlum lacking palpebral lobes, USNM 124872. 

3. Pygid lurn lmmatmo but with mature proportions, X 2, USNM 124873. 

4. Mature pygldlum cut by coring bit; terminal spine lncornplcto, X 2, USNM 124874. 

6, 7. Immature pygtdia, showing slight chango In shape and in dcfi n lt.lon of segment-•· 

tlon. X 4, USNl'v[ 124875, 124876. All from Lower Ordovician, Denuwoo<l formation, 

toe. D6Gb (CO), Shell Oll Co., I'lnc Unit No. I well, 0,701 - 0,708 ft . 

5,12,13. !lfegalaspis planilimbata var. cvclopyge IT arrington (p. 400). 

5. Pygtdium X 2, USNM 124877. 

12. Cranldlum with pa thologic(?) development of one muscle scar and obverse of 

pygtdtum shown In fig. 13, X 2, USNi\o[ 124878. 

13. Sma ll pygtdtum, X 2, USNM 124879, Lower Ordovician, Deadwood formation, 

toe. D6Gb (CO), Shell Oil Co., Pine Unit No. I well, 0,701-9,705 ft. 

8. Nan orthis? sp. 

X 2, USNM 124880. Dorsal vnh·c, dorsal view. Lower Ordovician, Deadwood for· 

mu tton, toe. D6Gb (CO), Shell Oil Co., Pine Unit No. I well, 9,703- 0,71 0 ft. 

9, 10. Unidentified hypostomes (p. 400, 49•1, 497). 

9. Associated with Asa plu /l us·? s p. and }.fegalaspis 7> /ani/imbata vnr. cvclopyge X 2, 

USNM 124881. 

10. Associated with Kayseraspis nff. J(. asaphelloidt8, X 2, USNM 124882. Lower 

Ordo\'lcbn. Deadwood formation , toe. D66h (CO) , Shell Oil Co .. Pine Un it No. I 

well, 9,701- 9,709 ft. 

II. 17. Lloydia cf. L. saf!ordi IJIIlln ~s) (p. 489). 

11. Snw ll pygtdium, X 2, USNM 124883. 

17. Pygidium, X 2, us:-..r:-.r 12·1S84. Lower Ordo,·ician , Dea dwood formation, toe. 

D6Gb (CO), Shell Oil Co., Pine Unit l\o. 1 well , 0,709 ft. (Species a lso present, 

D66c (CO), 9,690-9,696 ft .. ) 

H . Syntrophild brachiopod. not identified gener1C3ll y. 

Dorsal vah·c, X 2, US:-I:'v[ 12-188.5. Lower Ordovician, Deadwood formation. lor. 

D66a (CO), Shell Oil Co., Pine Unit No. I well , 9,711 lt. 

IS. Un identtOecl pygldlum (p. 50.1). 

X 2, US:-1:\1 124886. Compare with Ross, 1951, pl. 19, ll ~s . 30, 31. Lower Ordovician. 

D eadwood formation , toe. D66a (CO), Shell Oil Co., Pine Unit No. I well, 0,7i5 ft. 

16. Didymouraptus? sp. or Tetragraptus? sp. 

Im mature, X 4, USNM 124887. Lower Ordovici:ln, Deadwood formation (nssoclatcd 

with llryograptus? sp.), toe. D6Ga (CO), Slwll Oil Co .. Pine Unit :-..ro. I well, 0,715 ft. 

18-20. T.eiostegium maniloumsis Walcott (p. 489). 

18. Cran ld lum, decorticated, X 2, USN:If 124888. 

19. ll ypostome, X 4, USNM 124889. 

20. Cranidium, X 2, USN :I[ 12·1800. :\ll lrom [,ower Ordovician , Dead wood forma· 

tton , Joe. D70n (CO), Shell Oil Co., Richey area, Northern Pacific R. R . No.1 well, 

10,.50<H0,509 ft. 

21 , 22, 2.5, 26. Hy8tricurU8 sp. (p. 488) . 

Four cranldia, X 4, USNM 124891, 12-1892, 124893, 124804, showing change In med ian 

preglabellar Curro"' with growth. 25, 26, may belong to separate species (cf. H . robustu• 

Ross). All from Lower Ordovician, Deadwood formation , toe. D70n (00), Shell 

OU Co., Rich ey area , Northern Pacific R. R . No. 1 well, 10,.50Q-10,509 ft. 

23, 24, 27-30. Kainella sp. (p. 500). 

23. Front of glabella , prcgbbellar field, and rim, X 3, USNl\.f 124895. 

24. Cranldlum Immature, X 4, USNM 124896. 

27. Cranldlwn, Jacking preglnbcllar fi eld, X 3, USNM 124897. 

28. Free check, showing granulose ornamentation of oculnr pla tform, X 3, USNM 124898. 

2~. Obverse of pygtdtum shown In Og. 30, fragmen tary, X 2, USNM 124899. 

30. Pygldlum, lacking rear of axis, X 2, USN :I! 124900. All from Lower Ordo,·tclan, 

Deadwood formation, Joe. D70n (C), Sh~ll Oil Co .. RlchAy nrcn, Northern Pacific 

R. R. No. I '"~ !!. !0.500-10,.509 ft ..