Ordovician and Silurian

»

Coral Faunas of 

.Western United States

GEOLOGICAL SURVEY BULLETIN 1021-F

A CONTRIBUTION TO GENERAL GEOLOGY

ORDOVICIAN AND SILURIAN CORAL FAUNAS OF 

WESTERN UNITED STATES

By HELEN DUNCAN

ABSTRACT

A review of existing information, published and unpublished, shows that considerably more data are available on the Ordovician and Silurian coral faunas of 

western United States than is generally supposed.

Records of corals in the Lower and Middle Ordovician rocks of the West are 

few. The oldest fauna, which occurs in rocks tentatively assigned a late Early 

Ordovician age, consists of primitive favistellids. These early corals have been 

found at a good many places in western Utah and eastern Nevada. At two localities, quartzitic rocks that generally have been classed as Middle Ordovician 

contain horn corals. The Kinnikinic quartzite fauna of Idaho is now known to be 

of Late Ordovician age. The streptelasmid forms that occur in the upper beds of 

the Eureka quartzite at Cortez, Nev., are also suggestive of Late rather than of 

Middle Ordovician corals. A few Middle Ordovician corals have been found in 

the less quartzitic extensions of the lower part of the Eureka quartzite farther 

south and west in Nevada.

Corals are much more diversified and widely distributed in the Upper Ordovician rocks of the West. The Bighorn dolomite and equivalent formations in 

the region extending from South Dakota and Colorado west to California and 

from Montana and Idaho south to Texas contain an astonishingly uniform coral 

fauna that is related to the one characteristic of the Upper Ordovician rocks in 

western Canada and Arctic America. In the writer's opinion, the evolutionary 

stage of development exhibited by the horn corals in the basal strata of the Bighorn strongly favors a Late Ordovician though probably a pre-Richmond 

age for the lower part of the formation. The upper part of the Bighorn dolomite 

has long been considered of Richmond age.

The Silurian coral fauna of the West is more restricted In distribution than 

that of the Late Ordovician and commonly is not well preserved. Faunules 

from various areas, however, indicate that certain forms such as the halysitids, 

heliolitids, and certain Rugosa are ordinarily distinctive enough to differentiate 

the Silurian from the Ordovician dolomites even though other kinds of fossils 

are not found.

Current nomenclatural usage is briefly discussed. The more common, easily 

recognized, and stratigraphically useful corals in each fauna as well as certain 

forms that are likely to be misidentified or that cannot be relied on are mentioned. 

Features that help differentiate Ordovician from Silurian corals having similar 

growth forms are pointed out. A good many corals that have been neglected 

in accessible American publications or that are commonly misidentified are 

briefly characterized and illustrated.

209
210 CONTRIBUTIONS TO GENERAL GEOLOGY

INTRODUCTION

Dolomitic rocks of Late Ordovician and of Silurian age are widely 

distributed in western United States. Corals are by far the most 

abundant fossils in most of the calcareous rocks deposited in the region 

during these divisions of geologic time and at many localities are the 

only identifiable organisms. For this reason corals must be depended 

on, at times exclusively, for the differentiation of Upper Ordovician 

from Silurian strata, and in some instances for the differentiation of 

these older rocks from certain Devonian and Carboniferous dolomites 

that contain predominantly coral faunas. Devonian and Carboniferous corals are somewhat better known and in general should not 

pose much of a problem in stratigraphic work if attention is paid to 

the peculiarities of regional distribution. Considerable difficulty has 

been experienced by geologists and paleontologists, however, in distinguishing between the Ordovician and Silurian corals. Factors responsible for this situation are western coral faunules of early Paleozoic age have not been described and illustrated, several of the more 

common elements in each fauna have growth forms that are easily 

confused, and the corals themselves are commonly so crudely silicified 

or otherwise poorly preserved that the rugose forms in particular 

cannot be accurately identified.

Most of the published data have appeared in reports on areal and 

economic geology of restricted areas. Geographic coverage, though 

spotty, is relatively extensive (see fig. 42). Because the corals have 

not been described in paleontologic papers, the existence of published 

information on these faunas has been overlooked by many. In a 

recent review of the sequence of Ordovician coral faunas throughout 

the world, Hill (1951) gives no indication that corals are known in the 

Western States. Even Bassler's faunal lists of Paleozoic corals 

(Bassler, 1950) records faunules from only three localities in the Upper 

Ordovician rocks and includes none from the Silurian rocks of the 

West.

As a result, some geologists and paleontologists (for example, 

Hintze, 1951, p. 23) have concluded that the coral faunas of the rocks 

considered in the present study have little significance and are not

Utilizable in stratigraphic work. During the past feW years, the 

writer haS identified numerous early Paleozoic corals collected in 

many parta of the Rocky Mountain region and Great Basin, and also

ws extensively reviewed earlier collections m the Survey's strati" 

graphic reference sets. ^ieia instigations by the writer and associates during recent years hftVG prOYided additional «*eo«xia.tum 

on the early Paleozoic coral assemblages that occur at vanOUS lOCfll' 

ities and have verified conclusions based on studies in the laboratory.
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 211.

Vi

¥L

FIOURB 43. Principal areas from which early Paleozoic coral faunas are known in western United States. 

(See Review of geographic and stratigraphic distribution, p. 212-215.)

California

1. Inyo Mountains

2. Panamint Range and vicinity

3. Taylorsville region

Colorado

4. Bonanza mining district

5. Canyon City area

6. Pikes Peak

7. Sawatch Range

Idaho

8. Bayhorse region

9. Borah Peak quadrangle

10. Lemhi County

11. Maokay region

12. Preston quadrangle

13. Southeastern Idaho

Montana

14. Bighorn Canyon area 

16. Clark Fork area, Carbon 

County

Key to numbers on map:

Montana Continued

16. Little Rocky Mountains

17. Red Loc>ge area

18. Williston basin, subsurface

New Mexico

19. Deming quadrangle

20. Sacramento Mountains

21. Silver City quadrangle

Nevada

22. Las Vegas quadrangle

23. Nevada Proving Grounds

24. Pioche district

25. Roberts Mountains and 

Cortez quadrangles

26. Snake Range

27. Tuscarora Mountains

28. Tybo district

29. White Pine Range

South Dakota

30. Black Hills

Texas

31. El Paso quadrangle

32. Marathon region

33. Van Horn quadrangle

Utah

34. Gold Hill quadrangle

35. Ibex area

36. Logan quadrangle

37. Randolph quadrangle

38. Thomas Mountains

39. Tintlc district and vicinity

Washington

40. Metaline quadrangle

Wyoming

41. Absaroka Range

42. Afton quadrangle

43. Bighorn Mountains

44. Owl Creek Mountains

45. Wind River Mountains
212 CONTRIBUTIONS TO GENERAL GEOLOGY

This work has demonstrated that the Late Ordovician and Silurian 

faunas are extraordinarily consistent in their makeup and that certain 

forms, which are almost invariably present in any representative collection, can be used reliably in determining the age of the dolomites. 

In order to make this knowledge generally available, this bulletin 

presents a summary of basic differences, with emphasis on critical 

features that are easily recognized and that have general application 

in discrimination of the two faunas.

The writer is indebted to her colleagues Edwin Kirk and Jean M.. 

Berdan for providing information bearing on the general nature and' 

occurrence of the western early Paleozoic corals and for verifying data, 

assembled for this review. The illustrations were delineated by 

Eleanor Stromberg, whose painstaking renditions and reconstructions 

faithfully portray the writer's concepts.

REVIEW OF GEOGRAPHIC AND STRATI GRAPHIC 

DISTRIBUTION

The index map (fig. 42) indicates the extent of the territory involved. The following summary shows, by State, the areas from 

which Ordovician and Silurian coral faunas have been identified.

Insofar as possible, formation names applied to the rocks in each area 

are indicated and publications listing corals are cited, so that this 

review of distribution serves also as a summary of previous work. 

Documentation is not absolutely comprehensive. The more significant sources of published information are given, but certain articles 

that cite only one genus or species (for example. Streptelo/SW/Q/ SD, 01

Halysites gracilis) are not included, particularly if more extensive 

faunal data are given in other publications covering the same area.

Also listed are some areas from which corals have been identified in 

as jet unpublished reports of the Geological Survey, Citations to

unpublished, information refer to collections of the Survey and of tke

U. S. National Museum. Most of the paleontologic and age determinations in the literature cited were made by members of ike

Survey Walcott, Schuchert, and Ulrich in the earlier reports; Kirk

and Kindle in subsequent years; Duncan and Berdan since 1949.

Even though much of the nomenclature used in earlier reports is outmoded, it provides a general guide to the faunas if one makes allowances for the changes that inevitably occur in the course of time.

CALIFORNIA

Inyo Mountains: Mazourka formation of Phleger (1933) (supposedly an upper 

Lower Ordovician equivalent of the upper part of the Pogonip group; the

coral reported suggests that post-Lower Ordovician rocks may have been

included in the formation). (Phleger, 1933, p. 3; see also this paper p. 217.) 

Silurian (rocks assigned to the Devonian in older reports). (Merriam, 

1940, p. 47; Waite, 1953, p. 1521.)
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 213

Panamint Range including Quartz Spring area and Ubehebe Peak quadrangle: 

Ely Springs dolomite (Upper Ordovician) and Hidden Valley dolomite 

(Silurian in part). (Hopper, 1947, p. 408; McAllister, 1952, p. 15, 16-17.)

Taylorsville region: Montgomery limestone (Silurian). (Diller, 1908, p. 16-17.)

COIX>RADO

Bonanza mining district: Upper member of Tomichi limestone of Crawford (1913)

(Upper Ordovician). (Burbank, 1932, p. 11.) 

Canyon City area, Fremont County: Fremont limestone (Upper Ordovician).

(Walcott, 1892, p. 159, 161; Sweet, 1954, p. 300-301.) 

Pikes Peak: Fremont limestone (Upper Ordovician). (Cross, 1894, p. [2].) 

Sawatch Range: Fremont limestone (Upper Ordovician). (Johnson, 1944, p.

324.) ,

IDAHO

Bayhorse region, Custer County: Saturday Mountain formation (Upper Ordovician) and Laketown dolomite (Silurian). (Ross, 1937, p. 20-21, 24-25.)

Borah Peak quadrangle: Kinnikinic quartzite and Saturday Mountain formation 

(Upper Ordovician) and Laketown dolomite (Silurian). (Ross, 1947, p. 

1104-1106.)

Lemhi County: Upper Ordovician. (Umpleby, 1913, p. 33.)

Mackay region: Saturday Mountain formation (Upper Ordovician). (Umpleby, 

1917, p. 25.)

Preston quadrangle: Fish Haven dolomite (Upper Ordovician) and Laketown 

dolomite (Silurian). (Ordovician faunal data not published; Silurian, Berdan 

and Duncan, 1955.)

South-central Idaho: Kinnikinic quartzite and Saturday Mountain formation 

(Upper Ordovician) and Laketown dolomite (Silurian). (Ross, 1934, p. 950, 

953, 958.)

Southeastern Idaho: Fish Haven dolomite (Upper Ordovician) and Laketown 

dolomite (Silurian). (Mansfield, 1927, p. 58-59.)

MONTANA

Bighorn Canyon area, Bighorn and Carbon Counties: Bighorn dolomite (Upper

Ordovician). (Faunal data not published.) 

Clark Fork area, Carbon County: Bighorn dolomite (Upper Ordovician).

(Faunal data not published.) 

Little Rocky Mountains: Bighorn dolomite (Upper Ordovician). (Faunal data

not published.) 

Red Lodge area, Carbon County: Bighorn dolomite (Upper Ordovician).

(Faunal data not published.)

Williston basin, subsurface: Bighorn dolomite (Upper Ordovician) and Silurian 

 (formation not named). (Faunal data not published.)

NEW MEXICO

Deming quadrangle: Montoya limestone (Upper Ordovician). (Darton, 1917,

p. 5.) 

Sacramento Mountains, Otero County: Montoya limestone (Upper Ordovician)

and Fusselman(?) limestone (Silurian). (Pray, 1953, p. 1906, 1913-1914.) 

Silver City quadrangle: Montoya limestone (Upper Ordoviciau). (Paige, 1916,

P- 4.) 

Southern New Mexico, general: Montoya limestone (Upper Ordovician) and

Fusselman limestone (Silurian). (Darton, 1928, p. 13-14, 185-189, 200,

321.)

352503 56 2
214 CONTRIBUTIONS TO GENERAL GEOLOGY

NEVADA

Cortez quadrangle: Uppermost beds of Eureka quartzite (possibly Upper Ordovician). (Discussed in this paper p. 217.) 

Las Vegas quadrangle: Ely Springs dolomite (Upper Ordovician). (Faunal data

not published.) 

Nevada Proving Grounds, Nye County: Lone Mountain dolomite of Hague, 1883

(Upper Ordovician and Silurian). (Faunal data not published.) 

Pioche district: Tank Hill limestone (upper Lower Ordovician equivalent of the

upper part of the Pogonip) and Ely Springs dolomite (Upper Ordovician).

(Westgate and Knopf, 1932, p. 15-16; Hintze, 1952, p. 49; see also this paper

p. 216.) 

Roberts Mountains region: Middle Ordovician rocks beneath Eureka quartzite

(formation unnamed), Hanson Creek formation (Upper Ordovician), and

Roberts Mountains formation (Silurian). (Merriam, 1940, p. 11-12;

Merriam and Anderson, 1942, p. 1687; this paper, p. 217.) 

Snake Range: Upper Lower Ordovician equivalent of the upper part of the

Pogonip. (Hintze, 1952, p. 32, 74.) 

Tuscarora Mountains: Upper Ordovician and Silurian (formations not specified).

(Faunal data not published.)

Tybo district: Lone Mountain dolomite (Silurian). (Ferguson, 1933, p. 21.) 

White Pine Range: Upper Lower Ordovician equivalent of the upper part of the

Pogonip. (Hintze, 1952, p. 32, 74; see also this paper p. 216.)

SOUTH DAKOTA

Black Hills: Whitewood dolomite (Upper Ordovician). (Darton, 1909, p. 20; 

Barton and Paige, 1925, p. 7; Furnish, Barragy, and Miller, 1936, p. 1340.)

TEXAS

El Paso quadrangle: Montoya limestone (Upper Ordovician) and Fusselman

limestone (Silurian). (Richardson, 1909, p. 4.)

Marathon region: Maravillas chert (Upper Ordovician). (King, 1937, p. 41-42.) 

Trans-Pecos Texas: Montoya limestone (Upper Ordovician) and Fusselman

limestone (Silurian). (Richardson, 1908, p. 479-480.) 

Van Horn quadrangle: Montoya limestone (Upper Ordovician). (Richardson,

1914, p. 5.)

UTAH

Gold Hill quadrangle: Fish Haven dolomite (Upper Ordovician) and Laketown 

dolomite (Silurian). (Nolan, 1930, p.426; Nolan, 1935, p. 16-18.)

Ibex area, Millard County: Upper Lower Ordovician equivalent of the upper

part of the Pogonip. (Hintze, 1951, p. 21, 69; Hintze, 1952, p. 23.) 

Logan quadrangle: Fish Haven dolomite (Upper Ordovician) and Laketown

dolomite (Silurian). (Kindle, 1908a, p. 127; Kindle, 1908b, p. 17; Tomlinson,

1917, p. 129; Williams, 1948, p. 1138.)

Randolph quadrangle: Fish Haven dolomite (Upper Ordovician) and Laketown

dolomite (Silurian). (Richardson ; 1913, p. 4O9 41O; Richardson, 1941,

p. 17-18.)

Thomas Mountains: Upper Ordovician and Silurian. (Faunal data not published.)

Tintic district and Alien's Ranch quadrangle: Bluebell, dolomite unrestricted 

(Upper Ordovician, Silurian, and Devonian). (Faunal data not published.)
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 215

WASHINGTON

Metaline quadrangle: Silurian (formation not named). (Faunal data not 

published.)

WYOMING

Absaroka Range: Bighorn dolomite (Upper Ordovician.) (Love, 1939, p. 20.) 

Afton quadrangle: Bighorn dolomite (Upper Ordovician). (Faunal data not

published.) 

Bighorn Mountains: Bighorn dolomite (Upper Ordovician). (Darton, 1906a,

p. 28-29; Darton, 1906b, p. 548-550; Fisher, 1906, p. 13; Tomlinson, 1917,

p. 129-130; Savage and Van Tuyl, 1919, p. 352; Foerste, 1924, p. 23.) 

Crawford Mountains, Randolph quadrangle: Upper Ordovician. (Berdan and

Duncan, 1955.) 

Owl Creek Mountains: Bighorn dolomite (Upper Ordovician). (Faunal data

not published.) 

Western and northwestern Wyoming, miscellaneous localities: Bighorn dolomite

(Upper Ordovician). (Tomlinson, 1917, p. 129-130.) 

Wind River Mountains: Bighorn dolomite (Upper Ordovician). (Darton, 1906b,

p. 554-555; Miller, 1930, p. 198-199, 204-206.)

ORDOVICIAN FAUNAS 

EARLY AND MIDDLE ORDOVICIAN

Information on pre-Late Ordovician corals in the West is meager. 

The earliest fauna seems to have been fairly persistent through an 

area in western Utah and east-central Nevada where it occurs in the 

upper part of the Pogonip group and rocks of equivalent age. The 

age of this faunal zone has been cited as "Chazy," which in Survey 

usage was considered to be post-Beekmantown Lower Ordovician. 

As now used by most geologists (see Twenhofel and others, 1954, 

Ordovician correlation chart), the term "Chazyan" is applied to the 

lower division of the "Champlainian" and is supposed to refer to the 

early Middle Ordovician. The unfortunate result of this confused 

situation is that geologists who have studied the faunas considered 

the upper part of the Pogonip group and equivalent rocks to be upper 

Lower Ordovician, whereas others have assumed that the same rocks 

were early Middle Ordovician because the fauna at one time had 

been tagged as "Chazyan." G. A. Cooper (oral communication, 

1954) regards the fauna associated with the corals in the upper part 

of the Pogonip as Early Ordovician. Edwin Kirk (oral communication, 1954) also prefers to class these rocks as Early Ordovician and 

has suggested that it is entirely possible that the fauna in question is 

of post Beekmantown but pre-Chazy age with reference to the New 

York section. In the Ordovician correlation chart, all formations 

containing this early coral fauna were included in the Middle Ordovician ("Champlainian"). The ultimate assignment of these rocks 

depends on faunal studies not yet completed, and probably opinions 

will differ. In the present review, the upper part of the Pogonip 

and its equivalents are tentatively classed as upper Lower Ordovician.
216 CONTRIBUTIONS TO GENERAL GEOLOGY

To the extent that it is known, the earliest western coral fauna is 

less diversified than the so-called Chazy fauna of eastern America 

(see Hill, 1951, p. 13-16). The corals are simple compound forms, 

mainly Eofietcheria and Lichenaria. Eqfletcheria is reported to form 

biostromal accumulations in a dolomite intercalated between a 

quartzite called Swan Peak(?) by Hintze (1951) and the Eureka 

quartzite at several places in western Utah (Hintze, 1951, p. 21, 69, 

74). The same genus is said to occur in rocks equivalent to the upper 

part of the Pogonip at localities in eastern Nevada (Hintze, 1952, 

p. 23).

According to Kirk, (oral communication, 1954), the Tank Hill 

limestone of the Pioche district, Nevada, contains a lenticular biostrome formed by the primitive colonial corals of this early fauna. 

When the Tank Hill limestone was described and its fauna listed, 

Tetradium was recorded (Westgate and Knopf, 1932, p. 15). In 

reviewing the collections, the writer did not recognize Tetradium and 

suspects that the name was applied to the semifasciculate Lichenaria 

discussed later. The coralla of this form do, in fact, look very much 

like the coralla of some species of Tetradium. Hintze (1952, p. 49) 

identified corals from the Tank Hill limestone as "Columnaria cf. 

simplissima Okulitch." Okulitch's species was referred to Foerstephyllum by Bassler (1950, p. 270) (see pi. 24, figs. 3a, 3b); but 

without investigation of Hintze's material, it is impossible to say 

just what genus is involved. The Geological Survey collections 

from the Tank Hill limestone that have been examined by the writer 

contain two species of corals. One is a Lichenaria with large corallites (pi. 24, figs. 4a, 4b); the other comprises semifasciculate forms

that are interpreted as Lichenaria tending to become phaceloid, 

that is, approaching Eqfletcheria (see pi. 25, figs. 5a, 5b).

The writer has also identified Eofletcheria (pi. 25, figs. 4a, 4b) and

a Lichenaria, characterized by small nodular coralla and small corallites, in a collection from the upper part of the Pogonip of the White 

Pine Range, Nev. Similar corals were collected by the writer from 

dolomitic rocks underlying the Eureka quartzite at the north end of

the Wah Wah Range, Utah (Crystal Peak section of Hintze, 1951, 

p. 68-71).

Except for tb.e material from the Piocne district and. tHe White 

Pine Rang© in Nevada and from ike Wah Wah Range U1 Utah, thft

writer has not had an opportunity to examine the Early Ordovician

COralS reported from Otner localities. It is st'i" ~«* «ie~*- wj^t:uer

genera more advanced than Lichenaria and Eofletcheria OCCUr in thlS

faimal zone or whether different nomenclature has been employed 

for some of the corals that belong to the Lichenaria-Eqfletcheria 

complex.
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 217

The occurrence of "(t) Streptelasma" in the Mazourka formation 

of the Inyo Mountains, Calif. (Phleger, 1933, p. 3), is anomalous. 

The Mazourka formation of Phleger (1933) is supposed to be of the 

same age as the upper part of the Pogonip. Elsewhere the streptelasmid corals first appear in later rocks (post-Chazy of common usage). 

It is possible, of course, that younger Ordovician rocks have been 

included in Phleger's Mazourka formation.

Rocks commonly assigned to the Middle Ordovician in the Great 

Basin and Rocky Mountain region are mainly arenaceous quartzite 

and sandstone. The environment in which the sands are believed 

to have accumulated would not have been favorable for corals, and 

the writer has not found any published record of their occurrence. 

This past year, however, a few horn corals were collected from fossiliferous Middle Ordovician rocks that occur beneath the vitreous part 

of the Eureka quartzite in the Roberts Mountains quadrangle, 

Nevada. The two species found in these rocks are comparable to 

Streptelasma breve Winchell and Schuchert and Streptelasma corniculum Hall.

It was of considerable interest to learn from James Gilluly that 

horn corals had been found in the Eureka quartzite at Cortez, Nev. 

Jean M. Berdan and the writer examined the section at Cortez in 1954 

and located a coral zone near the top of the formation. Indications 

of corals are preserved as molds in vitreous quartzite. The material, 

of course, is not specifically identifiable, but the molds reveal that 

the corals were small to medium sized and had well-defined and consistently oriented curvature. Some specimens show moderately 

complex and raised axial structures, and some of the molds suggest 

that angulate coralla occur in the fauna. The morphologic features 

that can be determined suggest that these horn corals are considerably 

more advanced than the earliest streptelasmids Lambeophyllum 

prqfundum and Streptelasma corniculum. It may well be that this 

coral zone belongs to the phase of the Eureka quartzite that according 

to Merriam (1940, p. 10-11) grades into the sandy lower part of the 

Upper Ordovician Hanson Creek formation. After evaluating various 

lines of evidence, Kirk (1933, p. 42-43) also concluded that correlation 

of the upper part of the Eureka with the lower part of the Bighorn 

dolomite "seems most nearly to explain all the observed facts."

On the lithic similarity and stratigraphic position, the Kinnikinic 

quartzite in south-central Idaho was originally considered to be of 

Early or Middle Ordovician age (Ross, 1934, p. 950); but a fauna, 

including corals, found subsequently proved to be of Late Ordovician 

age (Ross, 1947, p. 1104).

So far the writer has seen only one collection of corals from the 

West that can be referred indisputably to the Middle Ordovician.
218 CONTRIBUTIONS TO GENERAL GEOLOGY

It is hoped that future work on the less quartzitic western extensions 

of the lower part of the Eureka quartzite will provide more knowledge 

of Middle Ordovician corals in the region. In the course of time, 

more coral-bearing zones should be found in the quartzites that are 

ordinarily assigned to the Middle Ordovician. Such occurrences will 

have to be evaluated individually, however, for in most areas we 

have no reliable evidence on the exact age of the quartzites; and, as 

indicated in the preceding discussion, it is likely that zones of both 

Middle and Late Ordovician age are to be distinguished in at least 

some of the quartzites.

LATE ORDOVICIAN

The most common elements in the Late Ordovician coral faunas are 

Halysites (Catenipora) gracilis Hall (pi. 27, figs, la, Ic), Calapoecia 

(pi. 26, figs. 4a, 4b), the phaceloid favistellid Palaeophyllum (pi. 25, 

figs, la, Ib), and solitary angulate streptelasmid corals (pi. 22). 

Less common but just as widely distributed are a smaller species of 

Catenipora, Favosites (including both Favosites in the strict sense and 

Palaeofavosites) (pi. 26, figs, la, Ib, 2a, 2b), the massive favistellids 

(Saffordophyllum (pi. 24, figs. 2a, 2b), Foerstephyllum (pi. 24, figs. 

3a, 3b), Favistella (pi. 24, figs. 5a, 5b), and Cyathophylloides (pi. 24, 

figs. 6a, 6b)), and Protaraea.

The streptelasmids are diverse. Some forms have conspicuous 

axial structures and are referable to the genus Grewingkia (pi. 21, 

figs. 4a, 4b). But, even though recorded in some of the older faunal 

lists, no examples of that very diagnostic species of the type Richmond, 

, Grewingkia rustica (Billings) [=Streptelasma rusticum], have been seen. 

Western species so identified are probably identical with OP related tO

Streptelasma, laiusculuvn (Billings) (pi. 21, figs- la, Ib). Angulate

streptelasmid corals range from types that are carinate only along the 

Cardinal septum (group of S. prolongation Wilson) (pi. 22, figs. 2a,

2b) through Bemitriangulate forms (group of S. Joerstii Troedsson)

(pi. 22, figs. 4a, 4b) to those with nearly quadrangular cross sections

(group of S. goniophyttoides Teichert) (pi, 22, figs, 3a, 3b), Streptelasma trilobatum Whiteaves (pi. 21, figs. 3a, 3b), which occurs very

widely in at least the upper part of the Upper Ordovician rocks, has

been interpreted as the end result of this trend to angularity (Kirk,

1925, p. 446). S. trikfatum differs from the forms just mentioned,

however, in that its coralla are longitudinally grooved not carinate 

along the alar septa. Subcalceoloid "Holophragmas" (angulate along 

the alar septa- and flattened on the counter side) (pi, 22, figs, la-lo)

Occur throughout the western Upper Ordovician rocks; they are rarely

abundant, but at least a few examples have been collected at many 

localities.
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 219

The western Late Ordovician coral assemblage is related to the fauna 

described from Arctic America and western Canada. Hill (1951, p. 

17-18) reviewed the general composition of this fauna and listed most 

of the references in which species mentioned here are described and 

illustrated. The corals have affinities with those of the Maquoketa 

shale and other formations of the northern Mississippi Valley region, 

but the fauna differs markedly from that of the Richmond in its type 

area in containing an abundance of Catenipora, Palaeophyllum, and 

angulate streptelasmid corals. Calapoecias and massive favistellids 

occur in both regions. Massive cerioid and halysitoid forms of 

Tetradium, which are characteristic of the Richmond in the East, 

are very scarce, if they occur at all, in the western Ordovician rocks. 

However, Jean M. Berdan recently identified Tetradium comparable 

to T. tubifer Troedsson from the Upper Ordovician rocks of the 

Tintic district, Utah. This species has a growth habit like that of 

T. syringoporoides Ulrich, a species typically developed in strata of 

Blackriver age in the East. The so-called single-tubed Tetradiums1 

are possibly more widely distributed in the western Upper Ordovician 

rocks than collections indicate. 1 Troedsson (1928, p. 138) states that 

Tetradium is not known from the Baltic area before Late Ordovician 

time and that "Foerste claims that this genus did not appear in the 

Arctic until the Richmond."

Some of the more unusual tabulates described from Canada and the 

Arctic have not yet been identified in collections from western United 

States; it is to be expected, however, that they may eventually be 

found.

The fauna is best known from the Bighorn dolomite of Wyoming, 

but it is found from central Colorado (Fremont limestone and Tomichi 

limestone of Crawford (1913)) and the Black Hills of South Dakota 

(Whitewood dolomite) west through the Williston basin (Bighorn 

dolomite) to Idaho (Fish Haven dolomite, Kinnikinic quartzite, and 

Saturday Mountain formation) then southwest through Utah (in 

rocks usually called Fish Haven dolomite) into eastern Nevada 

(Hanson Creek formation, Ely Springs dolomite, and the lower part of 

the Lone Mountain dolomite of Hague, 1883) and southeastern 

California (Ely Springs dolomite). In west Texas and New Mexico a 

coral fauna with many of the same elements occurs in the Montoya 

limestone, and some of the same corals are reported from the Maravillas chert of the Marathon region. The Late Ordovician corals of 

central Texas (Duncan, 1953, p. 1037) show closer affinities with the 

Richmond of eastern North America. The Red River and Stony 

Mountain formations of Manitoba carry a coral fauna comparable to

1 "Tetradium sp. nov. (occurring in small fascicles)" was reported from the Silver City area, New Mexico 

(Paige, 1916, p. 4). The collection containing this coral has not been located, so the identity of the coral 

remains unverified.
220 CONTRIBUTIONS TO GENERAL GEOLOGY

that found in the Bighorn dolomite and its equivalents. The horn 

corals particularly, in this widespread fauna, exhibit a stage of differentiation and complexity that it seems unlikely could have been 

attained by Middle Ordovician time. In any event, the horn corals 

are distinctly different from those characteristic of the type Trenton 

group in Eastern United States.

The lower Upper Ordovician rocks (Eden and Maysville groups) of 

the Cincinnati region are not coral bearing. This circumstance is one 

of several that has made it difficult to evaluate the age significance of 

Ordovician coral assemblages developed in other areas. Genera and 

species have been interpreted too loosely. Names applied to museum 

specimens and cited in faunal lists give very misleading ideas about 

actual morphologic features, variation within taxa that constitute good 

species, and stratigraphic ranges of generic and specific categories. 

Specimens that have been carelessly lumped in such "species" as 

Columnaria alveolata, Streptelasma corniculum, and Halysites catenularius obviously can be segregated into more precisely defined categories 

that have some stratigraphic significance. Studies of the morphologic 

complexity of the Ordovician corals in relation to their stratigraphic 

occurrence indicate that structural elaboration was progressive from 

the inception of the group in Early Ordovician time. General investigations of American Ordovician corals have led the writer to believe 

that the relatively diversified and advanced fauna in the lower part of 

the Bighorn dolomite and equivalent strata must be indicative of 

Late probably early Late Ordovician age. This conclusion, arrived 

at independently, coincides with recent interpretations of other 

students whose opinions are based on evidence from other groups of 

fossils (Miller, Youngquist, and Collinson, 1954; Sweet, 1954).

SILUBIAN FAUNAS

Silurian rocks have a more restricted distribution and their coral 

fauna is not so well known as the fauna of the Upper Ordovician 

rooks, partly because in many localities the Silurian dolomites contain only shadows of fossils or altered specimens that show only form 

and little if any original structure. At some places, fortunately, 

coral beds or reeflike accumulations have been silicified. The Silurian 

age of the strata in question was originally established by the occurrence of pentaxneroid brachipods (Kindle, 1908a, p. 127), which not

uncommonly are found with the corals or in associated beds.

Most of the collections from the Silurian rocks contain at least two

and commonly three species of halysitids that are readily differentiated by the Size of tneir corauites. species witix tt.o largost corajiitos

belong to Cystihaly sites (pi. 27, figs. 3d-3f); those with Small and 

medium-sized corallites generally are either Cystihalysites (pi. 27, 

figs. 3a-3c) or Halysites (sensu stricto) (pi. 27, figs. 2a-2c). A very
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 221

few examples of Catenipora have been identified in the Silurian assemblages of the region, but species of that subgemis do occur. It 

should be noted, however, that Halysites catenularius (Linnaeus), 

sometimes cited as H. catenulata, as recorded in the old lists is not 

reliably identified. The name has been applied to at least three 

subgenera and several different species and is, in fact, meaningless. 

Smith (1930, p. 320) has commented on the confusion regarding the 

identity of H. catenularius in the European Silurian.

Several species of Favosites including squamulate forms (pi. 26, 

figs. 3a, 3b) are very common. Heliolites (pi. 26, figs. 5a, 5b) is 

another diagnostic Silurian coral the genus, however, persists into 

the Devonian. Alveolites and cladoporoids are abundant in some 

faunules. At least two types of syringoporoids (possibly not Syringopora in the strict sense) have a rather haphazard distribution.

Among the Rugosa there are several colonial phaceloid forms that 

might be confused with the Ordovician Palaeophyllum or the Devonian disphyllids. One is Circophyllum (pi. 25, figs. 2a, 2b); another 

group has dissepiments (unlike any known Ordovician coral); and 

still others suggest colonial tryplasmids (compare with Aphyllostylus 

gracilis Whiteaves; see pi. 25, figs. 3a, 3b). Pycnostylus has not been 

recognized in any collections examined by the writer,2 but solitary 

Tryplasma (pi. 23, figs. 3a, 3b) as well as Porpites have been identified 

from some localities. Other tentatively identified genera include 

Entelophyllum (pi. 23, figs. 5a-5d), Pycnactis (pi. 23, figs, la, Ib), and 

Zelophyllum (pi. 23, figs. 2a-2d). Cystiphyllids and large dissepimented horn corals of uncertain affinities (Cyathophyllum of the older 

reports) seem to be somewhat less common than small ceratoid and 

vermiform types (pi. 23, fig. 4). Some specimens show indications 

of axial structures.

The Silurian coral fauna is varied and contains many elements 

that are more readily comparable to those of Asia and the Baltic 

region than they are to corals described from the Silurian strata of 

eastern North America. It is to be expected that genera hitherto 

unrecorded on this continent will form a significant proportion of the 

fauna. Much of the material examined so far is inadequate for 

positive identification of genera and for description of species. However, any collection that contains an assemblage of several different 

generic types is usually adequate for determination of Silurian age.

The coral fauna reviewed here has been found at a good many 

localities in Idaho and Utah (Laketown dolomite), in the subsurface 

of the Williston basin hi Montana, in Nevada (Roberts Mountains 

formation and Lone Mountain dolomite), and in southeastern California (Silurian part of the Hidden Valley dolomite). In the northern

8 Pycnostylus guelphensis Whiteaves is reported by Waite (1953, p. 1521) from the Silurian rocks of the 

Inyo Mountains, Calif. 

352503 56 3
222 CONTRIBUTIONS TO GENERAL GEOLOGY

Sierra Nevada, Silurian corals occur in the Montgomery limestone 

and in rocks that have been regarded as the Kennett formation (see 

Merriam, 1940, p. 47-48, for discussion of the stratigraphic problem). 

Comparable faunules occur in the Fusselman limestone of the El Paso 

region, west Texas and New Mexico. Recent work indicates that a 

Silurian coral faunule containing several unusual genera occurs in the 

Metaline quadrangle, Washington.

It has been suggested that some of the Silurian in the New MexicoTexas region may be older than Niagaran (Pray, 1953, p. 1913-1915) 

and that lower Upper Silurian may be present in California (Waite, 

1953, p. 1521). Further stratigraphic and paleontologic work is 

needed before such problems of correlation can be settled.

CRITERIA USED TO IDENTIFY THE CORALS AND 

DIFFERENTIATE THE FAUNAS

HALYSITID CORALS

It has long been known that the halysitid corals are separable into 

two groups on the presence or absence of mesopores (interstitial 

corallites or tubuli). In 1941 Chernyshev (1941a, p. 36) proposed 

the name Palaeohalysites for the group lacking mesopores, restricted 

Halysites (sensu stricto) (pi. 27 ; figs. 2a-2c) to species with horizontal

tabulae in corallites and mesopores, and defined a third genus (Chernyshev, 1941b, p. 70), Cystihalysites, (pi. 27, figs. 3a-3f), for those species 

having vesicles in the mesopores and corallites. These categories 

are useful in stratigraphic paleontology, and the writer has applied 

the names in a subgeneric sense. Later (Duncan, 1953, p. 1037) it 

was recognized that the name Palaeohalysites had been erected for the 

group of halysitids typified by the genotype of Catenipora Lamarck, 

1816. Catenipora (pi. 27, figs, la-le) was therefore revived and 

applied to halysitid corals lacking mesopores. This usage was

adopted without further investigation of nomenclatural problems

that might be raised in connection with the selection of a type specimen for H. catenularius (Linnaeus), the genotype of Halysites. Neotypes for Halysites catenularius (Linnaeus) and Catenipora escharoides

La-mixrclc: -v^eros olxosen. recently (Tli.oixJ.JXS and Smitll, 1O54, p. 765 TOO).

This action established the morphology of the genotypes so the two 

names can be used without hesitation for restricted taxa, which

Jjlnonl/Vt* (1O55^ OOrxsielers disiLcLot. ^onox-a.. Buolxlor n.j:>jj»a.roTi tly- <li<i not

know about Chernyshey's publication of the names OystMytitot and

"Palaeohalysiies- Fortunately, tK© -writer's application, of th.0 names

Catenipora and Halysiies accords with, nomenclatural usage stabilized 

t>y recent morphologic studies,

All known Ordovician halysitids belong to the subgenus Catenipora, 

C. gracilis Hall (pi. 27, figs, la-lc) is very easily recognized by its 

nearly rectangular corallites with straight adjoining sides. Not all
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 223

species referable to Catenipora, however, have rectangular or polygonal corallites. The form identified as Halysites (Catenipora) aff. 

H.jacovickii Fischer de "Waldheim (pi. 27, figs. Id, le) from the Upper 

Ordovician strata of central Texas (Duncan, 1953, p. 1037) is an 

example of a species having fusiform corallites. Halysitids with round 

or elliptical corallites generally have to be sectioned before it can be 

determined whether mesopores are present as well as to ascertain the 

character of the tabulation. Nevertheless, if a collection contains two 

or more species of halysitids with elliptical or round corallites, the 

chances are that it came from Silurian rather than from Ordovician 

rocks.

FAVOSITID CORALS

Superficially, certain massive favistellids characteristic of the 

Ordovician might be confused with Favosites (pi. 26, figs. 1-3). In 

particular, the nondescript Lichenaria (pi. 24, figs. 4a, 4b) and 

Nyctopora (pi 24, figs, la, Ib), with its small corallites and short stout 

septa, are likely to be mistaken for favositids. Sections nearly always 

must be prepared before the generic identities of corals belonging to 

these groups can be established.

Collections or faunules consisting exclusively of Favosites (sensu 

lato) do not provide reliable evidence for dating the rocks. In dolomitized specimens, such features as mural pores and septal structures 

(spines and squamulae) are commonly obliterated or modified so that 

the subgenera cannot be identified with assurance. As in living 

corals, the form of corallum developed probably was influenced by 

factors of the physical environment. The persistence of certain types 

of favositids through two or more systems, the poor quality of preservation, and the labile nature of coralla are the principal factors that 

make the favositids less useful than any other form of coral in the 

discrimination of the Ordovician, Silurian, and Devonian dolomites in 

the West. If an age determination is needed, it is essential that other 

kinds of fossils be collected from the same or associated beds.

Favositids are scarce in most of the Ordovician collections examined; 

the small heads and patchy incrustations are composed of mediumsized corallites in which the mural pores are not necessarily confined 

to the angles of the walls as they are supposed to be in Palaeofavosites 

(pi. 26, figs, la, Ib). Locally, however, fav/ositids are relatively 

abundant in Upper Ordovician strata, and coralla are reported to 

attain diameters of as much as 2 feet. The three species based on 

Ordovician material Favosites intermedius Okulitch, Palaeofavosites 

capax (Billings), and P. prolificus (Billings) all have corallites that 

range from 2 to 3 mm in diameter. Species with corallites of comparable size occur widely also in western Silurian strata, and favositids 

similar in growth form and corallite size are known in Devonian rocks.
224 CONTRIBUTIONS TO GENERAL GEOLOGY

In general favositid corals are more varied and abundant in collections from Silurian rocks than they are in older strata. Heads of 

considerable size as well as incrusting and branching coralla are 

common. Massive and laminar species characterized by corallites 

that are noticeably smaller (average diameter 1.5 mm) and larger (3 

to 5 mm in diameter) ordinarily occur in association with the intermediate form (corallites 2 to 3 mm in diameter) mentioned above. 

Some species possess squamulae (pi. 26, figs. 3a, 3b), structures that 

are not known to have developed before Middle Silurian time. 

Squamulate favostitids are abundant in Devonian rocks, however, and 

by themselves are indicative only of post-Ordovician age.

The Silurian alveolitids, the thamnoporoids, and the reticulate and 

branching cladoporoids are not likely to be confused with any corals 

characteristic of the western Ordovician strata. Similar forms do 

occur, however, in the Devonian rocks of some areas in the region,

OTHER TABULATE CORALS

' Poorly preserved Heliolites and Calapoecia have been and might be 

confused. For example, chert molds of the coral identified as Calapoeciat from the Fusselman(?) limestone of New Mexico (Pray, 1953, 

p. 1914) are generically indeterminate but on size of the corallites, 

this form could be a heliolitid. Usually, however, the cribrose 

structure of the intercorallite areas in Calapoecia (pi. 26, figs. 4a, 4b) 

is recognizable and provides an easy means of differentiating the 

genus from Heliolites (pi. 26, figs. 5a, 5b), with its characteristic 

tubular reticulum and imperforate walls. According to Kirk (1927, 

p. 286) poorly preserved Calapoecia has been mistaken for Syringopora.

Protaraea and JProtrochiscolithus, which occur in the western Ordovician, have been classified with the heliolitids, but they are aberrant

types with skeletal structures unlike the more typical heliolitid genera 

of the Silurian and Devonian. A variety of peculiar so-called heliolitid genera occur in the Ordovician of Scandinavia; most of these 

have not been identified as yet in North American faunas. However, Propora, wKicK clearly Kas Keliolitid affinities, is reported from

a good many places in the Late Ordovician of Canada and the Arctic

and occurs also in western Upper Ordovician rocks. Propora ranges 

through the Silurian and cannot be relied on to differentiate the

two fau.ns»,s.

Syringopom in the strict sense does not occur in Ordovician faunas,

The unusual Ordovician tabulates Arcturw and Labyrinth-ites are

generally classed with the syringoporoid corals. These genera, which

are probably synonymous, are based on specimens from Arctic 

America; they have not yet been reported from western United
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 225

States but probably will be found. A supposed syringoporoid comparable to Reuschia has been found in a few Ordovician assemblages, 

but the syringoporoids as a group are scarce in Ordovician rocks.

Some of the Silurian syringoporoids have horizontal or sagging 

tabulae and are not assignable to Syringopora (sensu stricto); one 

species suggests Syringoporella. Internal structures are not well 

enough preserved in most dolomitized specimens, however, to determine 

the nature of the tabulae.

FASCICULATE COLONIAL HUGOS A

Phaceloid rugose corals are the forms most likely to be misidentified in these faunas. Laboratory study is required to establish 

details of morphology used for family or generic assignment. In the 

past it was common practice to identify phaceloid corals whether 

they came from the Ordovician, Silurian, or Devonian as Diphyphyllum, a lithostrotionoid genus that is strictly Carboniferous. In 

'most instances, after material is sectioned, generic identities or at 

least general relationships can be established.

Palaeophyllum (pi. 25, figs, la, Ib), the diagnostic Ordovician 

favistellid, lacks dissepiments and an axial structure. Very large 

heads of this genus occur in Upper Ordovician rocks at some localities. 

P. thomi (Hall), which occurs in the Montoya limestone of the Southwest, has an incipient axial structure and is interpreted to be a phaceloid variant of Cyathophylloides (pi. 24, figs. 6a, 6b).

Phaceloid corals known from western Silurian strata belong to 

several families. Those with dissepiments may be either columnarids or 

primitive disphyllids. Circophyllum (pi. 25, figs. 2a, 2b) has no dissepiments but is distinguished by steeply inclined tabulae and septa 

that meet axially thereby forming a weak axial structure. Certain 

phaceloid forms with acanthine septa presumably belong to Aphyllostylus (pi. 25, figs. 3a, 3b), included in Tryplasma by Stumm (1952, 

p. 842).

CEEIOID COLONIAL HUGOS A

Massive cerioid rugose corals have not been found in Silurian rocks 

at most western localities, but the form Merriam (1940, p. 12, 48) 

described as Strombodes-likQ belongs to that category.

Cerioid favistellids (pi. 24) are fairly common in the Upper Ordovician rocks and generally can be recognized without much difficulty. 

Cyathophylloides (pi. 24, figs. 6a, 6b), which differs from Favistella 

(pi. 24, figs. 5a, 5b) in having a weak axial structure, might be mentioned as an exception. Cyathophylloides, however, has not been 

found at many localities.
226 CONTRIBUTIONS TO GENERAL GEOLOGY 

SOLITARY AND SEMICOLONIAL BUGOSA

When dealing with well-preserved material, the differentiation of 

solitary corals of Late Ordovician age from those of Silurian age 

presents little difficulty. Streptelasmids seem to be confined to the 

Ordovician some Silurian faunal lists carry the name Streptelasma 

sp., but these corals almost certainly belong to more advanced families. 

Ordovician corals as a group did not possess dissepiments, so any 

specimens exhibiting such structures immediately suggest post-Ordovician (Silurian to Permian) rocks. A single anomalous exception has 

been recorded as occurring in the Ordovician Kalstad limestone of 

Norway (Kiaer, 1932, p. 112-113). Verification of the occurrence and 

the relationships of this coral is needed.

The angulato coralla characteristic of so many of the western Late 

Ordovician Streptelasmids help in discrimination of poorly preserved 

material. A very few examples of cuneate coralla (carinate along the 

cardinal and counter septa) have been seen in collections from Silurian 

rocks, but this particular type of angulation is uncommon if it developed in the Streptelasmids no matter how much coralla are compressed, the counter side is not carinate. Many Ordovician "Holophragmas" (commonly called Lindstrdmia in older lists) have subcalceoloid coralla and are subtriangular in cross section at least in the 

apical region. This Ordovician genus, however, has an axial structure 

and lacks the cysts characteristic of Rhizophyllum, the calceolid that 

has been recognized in the Silurian strata of the Inyo Mountains, 

Calif. (Waite, 1953, p. 1521), and that may turn up elsewhere. A 

good many of the Ordovician Streptelasmids have conspicuous axial 

structures. At least some of these probably should be referred to 

Grewngkia, certain species of which (for example, 0. robusta (Whiteaves), pi. 21, figs. 4a, 4b), attained very large size. Streptelasma

trilobatum Whiteaves (pi. 21, figs. 3a, 3b), with its distinctive transverse section, is probably the most easily recognized and stratigraphically useful guide to the upper Upper Ordovician. At some localities 

the Ordovician rocks have yielded anomalous attached Streptelasmids

(compare with Streptelasma cylindricum Troedsson (pi. 21, fig. 2)) that 

might be taken for Silurian forms if they were not found with good

Ordovician assemblages,

Rhabdocyclid corals, such as Tryplasma (pi. 23, figs. 3a, 3b) and

PorpiteSj are excellent evidence for Silurian age in this region, for

solitary rugose corals with acanthine septa have not been found in the

Ordovician.8 The simple coral Pycnactis (pi. 23, figs, la, Ib) seems to

have a wide distribution in western Silurian rocks. It presumably

appears as Streptelasma or Zaphrentis in the older lists; and, if material

is poor, it might well be mistaken for a primitive Streptelasma.

 Hill (1953, p. 151-154), placed in Tryplasma Ordovician corals that appear to belong to Calapoecia and 

Foerstephyttum.
A group of nearly cylindrical or geniculate corals, with very short 

septa and a thick cortex, that formerly were probably identified as 

Amplexus seems to be assignable to Zelophyllum (pi. 23, figs. 2a-2d). 

Some examples of Tryplasma, also, undoubtedly have been called 

Amplexus.

Silurian cyathophyllids, some of them colonial with peripheral 

increase, have been identified tentatively as Entelophyllum (pi. 23, figs. 

5a-5d). Cystiphyllids also are indicative of post-Ordovician age; this 

group, however, persists into the Devonian and is not to be relied on 

as certain evidence of Silurian age.

In comparing the external forms of the solitary corals in the Silurian 

rocks with the forms characteristic of the Ordovician, one is impressed 

by the large number of Silurian species that have elongate cylindrical 

(pi. 23, figs. 2, 3a), geniculate, or vermiform (pi. 23, fig. 4) coralla. 

Some show evidence of attachment (pi. 23, fig. 3a), and many show 

indications of asexual increase (pi. 23, figs. 5a, 5b) and rejuvenation 

(pi. 23, fig. 3a) all features that are uncommon among Ordovician 

solitary corals. Information on characteristic growth forms has been 

obtained largely from silicified material etched from the matrix. 

Specimens so prepared commonly are not suitable for morphologic and 

ontogenetic studies needed to establish relationships or to identify 

genera. As studies progress and more extensive collections are made, 

however, it should be possible to place most of the western Silurian 

solitary Rugosa in their proper generic niches.

INTERPRETATION OF MOLDS AND CAVITY FILLINGS

The identification of corals whose former presence is indicated by 

molds or by tubes filled with crystalline dolomite is an important consideration in determining the age of some rocks. Commonly such 

traces only of organic remains are to be found in arenaceous rocks or 

in strongly altered dolomites. In general little can be done with 

molds of horn corals unless there is good stratigraphic control and 

the faunas are well known then some inferences may be 'warranted. 

The molds of corals that occur in the Eureka quartzite at Cortez, 

Nev., are an example (see p. 175). Some of the horn corals in the 

Fremont limestone near Canyon City, Colo., are known from molds, 

but the form of the coralla and the calicular features are so distinctive 

that specimens can be identified as to genus.

Colonial corals with diagnostic growth forms and restricted regional 

distribution are, however, more likely to be useful to the stratigraphic 

paleontologist. Some of the smaller tubular cavities apparently 

represent syringoporoids. Careful observations on the spacing and 

diameter of the holes and the character of the connecting tubes or 

mode of increase with reference to known syringoporoid species, 

whether Silurian, Devonian, or Carboniferous, have provided clues
228 CONTRIBUTIONS TO GENERAL GEOLOGY

that are strafagraphically applicable. Recent investigations suggest 

that such molds may be very useful where all other organic remains 

are lacking or destroyed. Indications of syringoporoids are rare or 

absent in Ordovician strata but are fairly common in the western 

Silurian and younger Paleozoic rocks. Utilization of these "fossils" 

requires, of course, considerable knowledge of the Paleozoic faunas of 

the region.

At some localities rocks that are known to be Silurian on other 

faunal evidence contain fasciculate tubular cavities somewhat larger 

than those characteristic of most Syringopora. Some of these probably represent phaceloid or dendroid colonial Rugosa. In other 

examples the walls have been preserved, but no other internal structures are identifiable. It is suspected that certain corals so preserved 

are either Fletcheria or a closely allied tabulate. Fletcheria (pi. 25, 

figs. 6a, 6b), which should not be confused with Pycnostylus (see Hill, 

1940, p. 390 for details), occurs in the Silurian rocks of Alaska as well 

as of Gotland and a few other European localities. Silicified tubes 

from the Fusselman(?) limestone of New Mexico (Pray, 1953 p. 

1914) identified as Eridophyllum? cf. E. proliferum (Foerste) exhibit 

quadripartite axial increase comparable to that of Fletcheria and 

Pycnostylus. Unfortunately, no trace of internal structure is preserved, so the affinities of this coral cannot be ascertained.

RECOMMENDATIONS

The stratigrapher or paleontologist concerned with the differentiation of the western early Paleozoic dolomites has at least one circumstance in his favor. Through most of the region, a considerable 

hiatus occurred between Upper Ordovician and Silurian rocks. The 

coral-bearing Devonian dolomites, which overlie the Silurian strata 

through much of the region, are apparently of Late Middle to early 

Late Devonian age. The fact that the depositional breaks were of 

considerable duration facilitates the work of the paleontologist, because 

the faunas had time to become significantly different and the problem 

of transitional faunas do not have to be COped wit/tl ill HlOSt; aMS,

In spite of superficial resemblances, the western Ordovician coral 

faunules ordinarily can be distinguished from those of Silurian age if 

attention is directed to a relatively few critical features. On 

occasion an age assignment can be made on a single specimen, but 

assemblages consisting of several genera are highly desirable and 

commonly necessary. A geologist experienced with the faunas may 

be able on casual examination to distinguish Ordovician from Silurian

assemblages in the field; but laboratory examination, including the 

preparation of oriented thin or polished sections, is ordinarily required 

for certain identification.
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 229

Detailed morphologic and systematic studies, not confined to 

western faunas, are required to clarify many nomenclatural problems. 

Careful stratigraphic collecting throughout the region is needed 

before faunal zones, which presumably exist in both the Upper Ordovician and the Silurian rocks, can be recognized. Efforts should also 

be made to get completely representative and extensive collections 

from localities where corals are comparatively well preserved so that 

enough material will be available for studies leading to description 

and illustration of these faunas.

ILLUSTRATIONS OF IMPORTANT CORALS IN WESTERN 

ORDOVICIAN AND SILURIAN FAUNAS

The accompanying plates illustrate a number of corals that either 

have not been described and figured in American publications or that 

are inadequately figured and not well understood. To facilitate comparisons and to clear up some current misapprehensions, illustrations of a good many other corals are also presented. Such 

corals as Halysites, Calapoecia, Favosites, and Heliolites should be 

recognized by anyone who has studied invertebrate paleontology, but 

they have been misidentified in the past and probably will give trouble 

in the future.

No attempt was made to illustrate all the diagnostic Ordovician and 

Silurian corals known in western faunas. Some forms are uncommon; 

others are hardly subject to misinterpretation. The alveolitids, cystiphyllids, disphyllids, syringoporoids, Porpites, Pycnostylus, Tetradium, 

and other corals mentioned in the discussion are treated to some extent 

in readily available texts. More attention has been paid to the Ordovician faunas because they contain more corals with which the average geologist is not familiar. The writer believes it is unlikely that 

the more advanced Silurian and Devonian corals will be mistaken for 

Ordovician forms once the critical differences are understood.

It is not the purpose of this paper to describe individual species. A 

few that are particularly useful in stratigrapihic work (for example, 

Streptelasma trilobatum and Halysites (Catenipora) gracilis] are briefly 

discussed and illustrated. But for the most part emphasis is placed 

on larger categories species groups, subgenera, or genera. As far as 

possible, however, the illustrations are based on species that occur in 

or are closely related to species found in the western faunas. The 

principal differences between Ordovician and Silurian coral faunas and 

the critical features that can be used for stratigraphic purposes are 

mentioned without going into technicalities any more than necessary. 

The use of some morphologic terminology was unavoidable. Most 

of these terms are defined in American textbooks or are self-explanatory. A few less well known terms are explained in the comments 

about the corals given on the plate explanations. These comments are
0

230 CONTRIBUTIONS TO GENERAL GEOLOGY

by no means diagnoses or complete descriptions of the corals referred 

to. In many instances, really critical features (for example, septal 

structure), which are of fundamental importance in classification, are 

not mentioned at all. Preservation oimost of the western Ordovician 

and Silurian corals is such that minute details of skeletal structure 

were destroyed. The paleontologist must depend, therefore, on those 

characters that can be observed, such as shape and curvature of 

coralla, growth forms, peculiarities of septal development and arrangement, axial structures if any, attitude of the tabulae, and type of 

asexual increase in colonial forms.

The illustrations are semidiagrammatic. They are intended to portray general concepts rather than individual specimens. Especially 

diagnositic features are emphasized. Structures not essential for the 

recognition of genera, subgenera, or species groups (for example, septal 

spines in the halysitids and tabulae in the streptelasmids) are not 

shown. Most of the illustrations are composite interpretations based 

on suites of specimens, thin and polished sections, and published 

figures.

External features df the solitary and semioolonial rugwe i* (p*3-

21-23) are illustrated at natural size. The student is warned, however, to place no great reliance on size at the generic or species-group 

level. In some instances it was expedient to illustrate small forms 

the figures of Grewingkia, robusta (pi. 21, figs. 4a, 4b), for example, are 

based on specimens that are only about half the size attained by some 

individuals in the species. On the other hand, the figures of Strepielasma tnlolatum (pi. 21, figS. 3a, 3b) are based On exceptionally large

specimens; most specimens referable to this species do not exceed an

inch or so in length. Following customary American practice, views 

Of calices and transverse sections of the horn corals are oriented with 

the cardinal septum, if distinguishable, at the bottom of the figure. 

Coralla of the strictly colonial rugose and tabulate corals are not 

figured because sections are nearly always required for identification

of the genera. Except for the halysitids for which transverse sections

showing the corallites at natural size are figured (pi. 27, figs. Ib, Id, 

2b, 3b, 3e), all the transverse and vertical sections of colonial corals are 

magnified two times or more. In using these illustrations, one must

keep in mind that the average diameter of corallites is one of tn6 SP6- 

cific characters in massive cerioid and phaceloid corals. Considerable 

range in size is to be expected within a genus.

In a review of this sort, it was thought inadvisable to go into the 

controversial matter of a classification for the early Paleozoic corals. 

The groupings used by Bassler (1950, p. 255-276) for the Ordovician 

corals seem to the writer to be more natural than those used by Hill 

(1951, p. 8-13). Lichenaria, Eofletcheria, Nyctopora, and probably 

Calapoecia are considered to be more closely related to the rugose
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 231

(tetracoral) line than they are to the Tabulata, the order in which they 

are placed by Hill. Palaeophyllum, which Hill (1951, p. 13) includes 

in the family Streptelasmidae, is interpreted by Bassler (1950, p. 274) 

and the writer to be a favistellid. The assignment of these primitive 

corals to any particular family depends on personal experience and is 

more subjective than objective. None of the classifications for the 

Paleozoic Rugosa offered in recent years is very satisfactory. For this 

reason the writer has avoided using formal family names. Adjectives 

and nominatives derived from well-known generic names are used to 

indicate relationships where necessary.

In assembling the plates, no particular attempt was made to arrange 

the illustrations according to any scheme of classification. To emphasize the more easily recognizable differences between Ordovician 

and Silurian corals, the illustrated material was segregated by growth 

form and by stratigraphic occurrence. Wherever possible, categories 

that have been or that are likely to be mistaken for each other are 

figured on the same plate.

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232 CONTRIBUTIONS TO GENERAL GEOLOGY

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U. S. Geol. Survey 3d Ann. Kept., 1881-82, p. 237-290. 

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 1951, The Ordovician corals: Royal Soc. Queensland Proc., v. 62, p. 1-27.

 1953, The Middle Ordovician of the Oslo region, Norway, 2, Some rugose 

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Hintze, L. F., 1951, Lower Ordovician detailed stratigraphic sections for western 

Utah: Utah Geol. Mineralog. Survey Bull. 39, 99 p.

 1952, Lower Ordovician trilobites from western Utah arid eastern Nevada:

Utah Geol. Mineralog. Survey Bull. 48, 249 p. 

Hopper, R. H., 1947, Geologic section from the Sierra Nevada to Death Valley,

Calif.: Geol. Soc. America BuUV v. 58, p. 393-432. 

Johnson, J. H., 1944, Paleozoic stratigraphy of the Sawatch Range, Colo.: GeoL

Soc. America Bull., V. 55, p. 303-378. 

Kiaer, Johan, 1932, The coral fauna of the Kalstad limestone in Meldalenr

Norske Vidensk.-Akad. Oslo Skr., Mat.-nat. Kl., 1932, bind 1, no. 4, p.

103-113, pis .12-17. 

Kindle, E. M., 1908a, Occurrence of the Silurian fauna in western America:

Am. Jour. Sci., ser. 4, v. 25, p. 125-129.

 1908b, The fauna and stratigraphy of the Jefferson limestone in the 

northern Rocky Mountain region: Bull. Am. Paleontology, v. 4, no. 20r 

39 p., 4 pis.

King, P. B., 1937, Geology of the Marathon region, Texas: U. S. Geol. Survey 

Prof. Paper 187.

Kirk, Edwin, 1925, Notes on an early collection of Paleozoic fossils from E1165-

mereland: Am. Jour. Sci., ser. 5, v. 10, p. 445-447.

 1927, [Review of] An Upper Ordovician fauna from the Rocky Mountains, British Columbia, by Alice E. Wilson: Jour. Geology, v. 35, p. 286-287.

 1933, The Eureka quartzite of the Great Basin region: Am. Jour. Sci.,

ser. 5, v. 20, p. 27-44.

Love, J. D., 1939, Geology along the southern margin of the Absaroka Range,

Wyo.: Geol. Soc. America Special Paper 20, 134 p. 

McAllister , J. F., 1952, Rocks and structure of the Quartz Spring area, northern

Panamint Range, Calif.: Calif. Div. Mines Spec. Rept. 25, 38 p. 

Mansfield, G. R., 1927, Geography, geology, and mineral resources of part of

southeastern Idaho: U. S. Geol. Survey Prof. Paper 152, 453 p.
ORDOVICIAN AND SILURIAN CORAL FAUNAS, WESTERN STATES 233

Merriam, C. W., 1940, Devonian stratigraphy and paleontology of the Roberts 

Mountains region, Nevada: Geol. Soc. America Special Paper 25, 114 p., 

16 pis.

Merriam, C. W., and Anderson, C. A., 1942, Reconnaissance survey of the Roberts 

Mountains, Nev.: Geol. Soc. America Bull., v. 53, p. 1675-1728.

Miller, A. K., 1930, The age and correlation of the Bighorn formation of northwestern United States: Am. Jour. Sci., ser. 5, v. 20, p. 195-213.

Miller, A. K., Youngquist, Walter, and Collinson, Charles, 1954, Ordovician 

cephalopod fauna of Baffin Island: Geol. Soc. America Mem. 62, 234 p., 

63 pis.

Nolan, T. B., 1930, Paleozoic formations in the Gold Hill quadrangle, Utah: 

Washington Acad. Sci. Jour., v. 20, p. 421-432.

 1935, The Gold Hill mining district, Utah: U. S. Geol. Survey Prof.

Paper 177. 

Paige, Sidney, 1916, Description of the Silver City quadrangle, New Mexico:

U. S. Geol. Survey Geol. Atlas, folio 199. 

Phleger, F. P., 1933, Notes on certain Ordovician faunas of the Inyo Mountains,

Calif.: Southern California Acad. Sci. Bull., v. 32, p. 1-21. 

Pray, L. C., 1953, Upper Ordovician and Silurian stratigraphy of Sacramento

Mountains, Otero County, N. Mex.: Am. Assoc. Petroleum Geologists Bull.,

v. 37, p. 1894-1918. 

Richardson, G. B., 1908, Paleozoic formations in Trans-Pecos Texas: Am. Jour.

Sci.; ser. 4, v. 25, p. 474-484.

 1909, Description of the El Paso quadrangle, Texas: U. S. Geol. Survey 

Geol. Atlas, folio 166.

 1913, The Paleozoic section in northern Utah: Am. Jour. Sci. ser. 4, v. 36, 

p. 406-416.

 1914, Description of the Van Horn quadrangle, Texas: U. S. Geol. Survey 

Geol. Atlas, folio 194.

1941, Geology and mineral resources of the Randolph quadrangle, UtahWyoming: U. S. Geol. Survey Bull. 923, 54 p. 

Ross, C. P., 1934, Correlation and interpretation of Paleozoic stratigraphy in 

south-central Idaho: Geol. Soc. America Bull., v. 45, p. 937-1000.

 1937, Geology and ore deposits of the Bayhorse region, Custer County, 

Idaho: U. S. Geol. Survey Bull. 877.

 1947, Geology of the Borah Peak quadrangle, Idaho: Geol. Soc. America

Bull., v. 58, p. 1085-1160. 

Savage, T. E., and Van Tuyl, F. M., 1919, Geology and stratigraphy of the area

of Paleozoic rocks in the vicinity of Hudson and James Bays: Geol. Soc.

America Bull., v. 30, p. 339-378. 

Smith, Stanley, 1930, Valentian corals from Shropshire and Montgomeryshire,

with a note on a new stromatoporoid: Geol. Soc. London Quart. Jour., v. 86,

p. 291-330, pis. 26-29. 

Stumm, E. C., 1952, Species of the Silurian rugose coral Tryplasma from North

America: Jour. Paleontology, v. 26, p. 841-843, pi. 125. 

Sweet, W. C., 1954, Harding and Fremont formations, Colorado: Am. Assoc.

Petroleum Geologists Bull., v. 38, no. 2, p. 284-305. 

Thomas, H. D., and Smith, Stanley, 1954, The coral genus Halysites Fischer

von Waldheim: Annals and Mag. Nat. History, ser. 12, v. 7, p. 765-774,

pis. 20-22. 

Tomlinson, C. W., 1917, The middle Paleozoic stratigraphy of the central Rocky

Mountain region: Jour. Geology, v. 25, p. 112-134. 

Troedsson, G. T., 1928, On the Middle and Upper Ordovician faunas of North

Greenland: Meddelelser om GrSnland, bind 72, afd. 1, 197 p., 56 pis.
234 CONTRIBUTIONS TO GENERAL GEOLOGY

Twenhofel, W. H., and others, 1954, Correlation of the Ordovician formations

of North America: Geol. Soc. America Bull., v. 65, p. 247-298. 

Umpleby, J. B., 1913, Geology and ore deposits of Lemhi County, Idaho: U. S.

oGeol. Survey Bull. 528. 

 1917, Geology and ore deposits of the Mackay region, Idaho: U. S. Geol.

Survey Prof. Paper 97. 

Waite, R. H., 1953, Age of the "Devonian" of the Kearsarge area, California

[abst.]: Geol. Soc. America Bull., v. 64, p. 1521. 

Walcott, C. D., 1892, Preliminary notes on the discovery of a vertebrate fauna.

in Silurian (Ordovician) strata: Geol. Soc. America Bull., v. 3, p. 153-172. 

Westgate, L. G., and Knopf, Adolf, 1932, Geology and ore deposits of the Pioche

district, Nevada: U. S. Geol. Survey Prof. Paper 171. 

Williams, J. Stewart, 1948, Geology of the Paleozoic rocks, Logan quadrangle.

Utah: Geol. Soc. America Bull., v. 59, p. 1121-1164.
INDEX

Page 

Acknowledgments... .. .......... 212

Alveolites...................................... 221

Alveolitid corals...------------------------- 224,229

/ImpZezW------------------------------------ 227

Aphylloftylus............................ 225; pi. 25

gracttis~.................................. 221

Arcturia-..................................... 224

Bighorn dolomite, corals_.-... ..--..... 213,

215,217,219,220; pis. 21,22

Bluebell dolomite, corals_... 214; pi. 27, figs, la-lc

Calapoeda............... 218,224,226,229,230; pi. 26

anticostiensis.............^............... pi. 26

Calceolid corals......----..-___-___-__... 226

California.---,....-....... 211,217,219,221,222,226

Catenipora. See Halysites (Catenipora).

Cavity fillings, interpretation..------------- 227-228

Circophyllum........................ 221,225; pi. 25

Cladoporoid corals.....------------------- 221,224

Classification, problems...__-_---.....- 230,231

Colorado,.---......-.......-.---... 211,219,227

Columnaria alveolata.......................... 220

simplissima. See Foerstephyllum simplissimum. 

Columnarid corals.-------------------------- 225

Cyathophyllid corals..-__.. - -------- 227

Cyathophyllddes.-.................... 218,225; pi. 24

Cyathophyllum................................ 221

Cystihalysites. See Holysites (Cystihalysites). 

Cystiphyllid corals.------------.---.. 221,227,229

Diphyphyllum, erroneously identified.-..-.--- 225 

Disphyllid corals.. ----------------- 221,225,229

Ely Springs dolomite, corals..--------. 213,214,219

Emmmsia..-.......................... pi. 26, fig. 3

Entdophyttum....................' 221,227; pi. 23

Eofletcheria.......................... 216,230; pi. 25

Erldophyttumt................................. 228

Eureka quartzite, corals... . 213,217,227

Favistella............................ 218,225; pi. 24

undulata................................. pi. 24

Favistellid corals...---. 218,219,223,225.231; pi. 24 

Favosites............................ 218,221,223,229

(Favosites)........................... 218; pi. 26

hisingeri........................ pi. 26, fig. 2

intermedius.----___-....-. -------- 223

(Palaeofavosites).................. 218,223; pi. 26

asper........................... pi. 26, fig. 1

capax--.............................. 223

prolificus..-... ..- .- -_ . 223

(Squameofavosites')........................ pi. 26

hemisphaericus bohemicus....... pi. 26, fig. 3

Favositid corals.. - _....---.-.- 223,224; pi. 26

Fish Haven dolomite, corals... -.-- 213,214,219

Page 

Fletcheria................................ 228; pi. 25

tubifera................................... pi. 25

Foerstephyttum................... 216,218,226; pi. 24

simplissimum........................ 216; pi. 24

Fremcnt limestone, corals........ __. 213,219,227

Fusselman limestone, corals.... 213,214,222,224,228

Geographic distribution..----.-.---..- 211,212-215

Orewingkia................................. 218,226

Tobusta........................... 226,230; pi. 21

rustica..................... 218; pi. 21, figs. 1, 4

HalysUes............................... 220,222.229

(Catenipora)... 218,219,221,222,223; pi. 27, figi 1 

eschar aides............................ 222

gradlis.... 212,218,222,229; pi. 27, figs, la-lc

jacovickii............ 223; pi. 27, figs. Id, le

(Cystihalysites)............. 220,222; pi. 27, fig. 3

brownsportensls........... pi. 27, figs. 3a-3c

(Halysites)................ 220,222; pi. 27, fig. 2

catenularlus..................... 220,221,222

catenulata............................. 221

Halysitid corals.. 218,219,220,221,222,223,230; pi. 27

Hanson Creek formation, corals.- - . 214,

217,219; pi. 24, fig. 6

Heliolites......................... .221,224,229; pi. 26

spongiosus................................ pi. 26

Heliolitid corals....-.-..-.-.-_. .. .--. 224

Hidden Valley dolomite, corals.-----. ---- 213,221

Holophragma......................... 218,226; pi. 22

Idaho.. ---..-- 211,219,221

Kennett formation, corals..._________ 222

Kinnikinic quartzite, corals__ _-....-.. 213,

217,219; pi. 22, fig. 2

Labyrinthites.................................. 224

Laketown dolomite, corals______ . 213,

214,221; pi. 23, flg. 2 

Lambeophyttumprofundum................... 217

Lichenaria.................. 216, 223, 230; pis. 24, 25

Lindstr6nia................................... 226

Lone Mountain dolomite, corals_.__ 214,219,221

Maravillas chert, corals_........__..... 214,219

Mazourka formation, corals____...-. . 212,217 

Molds, interpretation__..-........--.-.. 227-228

Montana. ...- .-.... 211,221

Montgomery limestone, corals_..__-.... 213,222

Montoya limestone, corals ___..__ .. 213, 

214, 219, 225; pi. 24, fig. 6; pi. 25, fig. 1

Nevada.....---- .. 211,215,216,217,219,221,227

New Mexico.................... 211,219,222,224,228

Nyctopora........................... 223, 230; pi. 24

billingsi.................................. pi. 24

235
236 INDEX

Ordovician faunas.

P.age

215-220

Palaeofaeosites. See Favosites (Palaeofavosites). 

Palaeohalysites..------------------------------ 222

Palaeophyllum.......... 218, 219, 221, 225, 231; pi. 25

thomi. .--.--.----'- 225; pi. 24, fig. 6; pi. 25, fig. 1

Pogonip group, upper part, corals.----------- 214,

215, 216; pi. 25, fig. 4 

Porpites................................ 221,226,229

Propora.-..----. .... - -. _ . .. 224

frotaraea. . .... ...... -------- 218,224

Protrochiscolithtu............................. 224

Pycnactis-.------------------------- 221,226; pi. 23

Pycnostylus..-......................... 221,228,229

guelphensis........... ..... 221

Recommendations....------................ 22§-229

Bed River formation (Manitoba), corals_... 219 

JReuschia....------..... ..._---------__.... 225

Review of previous work.....-..-..-..-.... 210,212

Rhabdocyclid corals ----------------------- 226

Rhizophyttum............................. .__ 226

Richmond corals of type area.. 218, 219; pi. 21, fig. 4 

Roberts Mountains formation, corals.-----... 214,

221; pi. 23, fig. 5

Saffordophyttum......... ...__....._.. 218; pi. 24

franklini..... .... .._____.......... pi. 24

Saturday Mountain formation, corals_.... 213,219

 Selkirk limestone (Manitoba), corals....... - pi. 21,

fig. 4; pi. 22, fig. 4 

:Silurianfaunas...--------__-____.--. 220-222

-South Dakota.......-.-....-.-.-.-.....---. 211,219

:Stony Mountain formation (Manitoba),

corals_.-----.--.--... 219; pi. 22, fig. 1

fitratigraphic distribution....--....---,--.- 212-215

Streptelasma. ............................ 217,226

breve............ .______--------- 217

corfticwZuwi..-------------------------- 217,220

cy«ndritum..------------------------ 226; pi. 21

foerstei...- . . - 218; pi. 22

goniophylloides....................... 218; pi. 22

latusculum........................... 218; pi. 21

prolongatum............... .......... 218; pi. 22

rusticum. See Orewinskia rustica. 

trilobatum...-.......... 218, 226, 229, 230; pi. 21

sp -- - 212,226

Streptelasmid corals.... 218, 219, 226, 230; pis. 21, 22

Strom&odea-like coral__ . _. 225

Syringopora.....---.--.-...-.--.---- 221,424,225,228

SyringopOTella...--... ----- -- -- 225

Syringoporoid corals.. ... 221,224,225,227,228,229

TankHilllimestone,corals.....-... :..... 214,

216; pi. 24, fig. 4; pi. 25, fig. 5 

Tetradium.-.........'................... 216,219,229

syringoporoides....--.-..--.....-...-...... 219

tubifer.................................... 219

Texas..-....-----------------..---- 211,219,222,223

Thamnoporoid corals.-------------.--------. 224

Tomichi limestone, upper member, corals_ 213,219 

Troedsson, G. T., quoted...-------_-------- 219

Try plasma....- --------___-_........... 221,

225, 226; pi. 23, figs. 2, 3; pi. 25, fig. 3 

Tryplasmid corals..__---------__... 221; pi. 25

Utah............................... 211,215,219,221

Washington.----.----------.-.----.....--. 211,222

Whitewood dolomite, corals..-._-_. ____ 214,219 

Wyoming....-..---.----......--.--... 211,219

Za/piinrtiis.................................... 225

Zelophyllum.---------. ____. 221, 227; pi. 23, fig. 2

intermedium.-..----.-..--- ...-... pi. 23, fig. 2d
PLATES 21-27
PLATE 21 

[All figures natural size]

Streptelasma aff. S. latusculum (Billings) 

Figures la, Ib

The corallum of this species is erectly trochoid in form. Expansion is gradual, and the corallum does 

not become cylindrical in adult stages. Tne calyx is fairly deep. Illustrations of & latusculum indicate 

that Billings' species has a moderately well developed axial structure. In this western species, which resembles S. latusculum in form and size of corallum, the axial structure is extremely weak or nonexistent. 

Corals of this sort are probably the forms identified as Streptelasma rustlcwn in older reports. Actually, S. 

rusticum has a complicated axial structure and is closely related to Qrewingkia robusta (figs. 4a, 4b). The 

Illustrations are based on specimens, which are about the largest examples known, collected from the top 

of the Bighorn dolomite. FIGURE la, view of the cardinal side of the corallum. Ib, diagrammatic view of 

the calyx, showing the long, thin cardinal septum, the short minor septa, and the long major septa that 

meet axially, some being slightly twisted.

Streptelasma aff. S. cylindricum Troedsson 

Figure 2

Streptelasmas with a broad basal area for attachment have been found in some collections from Upper 

Ordovician rocks but are less common than free coralla. The form illustrated has a very deep calyx, and 

the primary septa are not easily distinguishable. The illustration is based on specimens from the Upper 

Ordovician rocks of British Columbia. FIGURE 2, an alar view of the corallum, showing the broad irregular 

roots at the base and the nearly cylindrical form.

Streptelasma trilobatum. Whiteaves 

Figures 3a, 3b

As in most species of Streptelasma, the cardinal side of the corallum is convex and the counter side is concave. Carlnation is developed for a few millimeters along the cardinal septum at the apical end, but the 

cardinal lobe is rounded distally. The corallum is constricted along the alar septa so that the cross section

in aduit stages is biiobate. The cardinal septum is long and thin and extends to the axial region. This 

species does not have a Gretcmfffcto-like axial structure; the major septa meet in the axial region and, in some 

specimens, twist slightly. The illustrations are based on some of the largest known specimens, collected 

from the top of the Bighorn dolomite. FIGURE 3a, diagrammatic view of the calyx, showing arrangement

of the septa. 3b, view of the convex cardinal side of the corallum.

Grewingkia robusta (Whiteaves)

Figures 4a, 4b

This Is the largest horn coral known in the Upper Ordovician rocks of the West. The corallum is curved 

trochoid in shape and convex on the cardinal side. Carination is developed along the cardinal Septum 

for a few millimeters in the apical region. The corallum gradually expands in diameter; it does not become

cylindrical as does the common Richmond species Orewingkia r-uatica CBUllngs) t Slreptfla,ma rustic-urn ot

common usage]. Axiai structures are similar in both species. The disrupted axial parts of the major septa

anastomose, dilate, and combine with up-arched tabulae to form an axial boss in the calyx. The mustrations are based on small to medium-sized specimens from the Selkirk limestone of Manitoba and from the

lower part of tne Bighorn dolomite of Wyoming. The species is known to attain a length of at least 7 inches

measured along the convex side. FIGURE 4a. diagrammatic transverse section near the base of the calyx.

4b, view of tfao convex cardinal side ot a. aiuall corallum.
GEOLOGICAL SURVEY BULLETIN 1021 PLATE 21

y..-. ,,i ,

/^''\U^f£^ 

. . /C^3$i|r y£x * -. /*:ti >&-<r:;fK! 

.- .-.Ji'S-- : - ' '!!".?fe*fe:

'Kiiwfer.--, *T.'- ' :v v-v^jSK%;;^

Wi!^--^»fef te^* ^;:;v,-,^^^^

3b

NONANGULATE ORDOVICIAN STREPTELASMID CORALS
PLATE 22

All figures natural size except where otherwise indicated]

"Holophragma" 

Figures la-lc

Corals belonging to this genus have subcalceoloid coralla, at least in the earliest growth stages. The 

counter side of the corallum Is convex and commonly somewhat flattened. The cardinal side is concave 

and in many forms is subangular along the trace of the cardinal septum. The coralla are markedly 

angulate along the traces of the alar septa especially in the early stages. Transverse sections are subtriangular in some species. Others have cross sections that are essentially circular in adult stages, and still 

other species are extremely elongate in the plane of the alar septa and the transverse sections are crescentic. 

An axial structure is conspicuous in most species; the counter septum is dominant and commonly dilated at 

the axial end to form a solid columella. Unlike the other streptelasmid corals illustrated, the cardinal 

septum Is aborted and the cardinal fossula is conspicuous. The illustrations are based on material from the 

top of the Bighorn dolomite and from the Stony Mountain formation in Manitoba. FIGURE la, view of a 

corallum from the alar side showing angulation along the alar septum and the curvature of the corallum 

convex on the counter side, concave on the cardinal. Ib, view of the concave cardinal side showing calyx 

obliquely. Ic, diagrammatic transverse section showing the subtriangular outline, the short cardinal 

septum, fossula, and columella.

Streptelasma aff. S. prolongatum Wilson 

Figures 2a, 2b

Streptelasmids belonging to this species group are angulate only along the trace of the cardinal septum. 

Transverse sections through adult coralla are ovate. Coralla are convex on the cardinal side. The cardinal 

septum is long and thin, and the cardinal fossula is commonly inconspicuous. Most of the specimens that 

belong to this category have a slightly raised elongate axial structure. The illustrations are based on a suite 

of specimens from the Kinnikinio quartzite. FIGURE 2a, diagrammatic view of a calyx in which the axial 

structure is dominated by the counter and cardinal septa. 2b, view of the convex cardinal side of a corallum.

Streptelasma aff. S. goniophylloides Teichert 

Figures 3a, 3b

Species of this group are strongly angulate along the cardinal and alar septa. Angulation of the counter 

side is less well defined on the outside of the corallum, but transverse sections are more distinctly polygonal

than those in other species groups. The corallum is convex on the cardinal side of the corallum, but curvature is less symmetrical With reference to the cardinal-counter plane than the curvature of other nonattached

Streptelasmids. The cardinal septum is long and thin. Some forms have a very conspicuous axial structure 

comparable to that characteristic of Orewingkia. The illustrations are .based on specimens from the base of 

the Bighorn dolomite. This particular species has an axial structure that Is even more prominent than the 

kind developed in Grewingkia robusta (pi. 21, fig. 4a), but the septa are less disrupted and tend to rotate as 

In an axial vortex. FIQUBE 3a, diagrammatic transverse section through the base of the calyx. 3b, view of 

the convex cardinal side Of a corallum, showing at the left the strong angulation along one of the alar septa;

the other alar angle outlines the right side of the figure.

Streptelasma aff. 8. foerstei Troedsson

Figures 4a, 4t>

Many of the corals that belong to this group attain considerable size. The cardinal Side" uf thfl COfftlllini IS 

COnveX and StrOnglV angulate. The alar angles are somewhat less sharp at least in ephebio stages. Curvature of the counter side is concave. Carination is not developed along the counter septum, and the COUntfir

OIAO 1= T-Dt>Jit,oa i»» trD.Do^or.c, ,o<-tjoT. i>ia.mntora measured in the alar plane and In the cardinal-counter plane are about equal, The cardinal septum is long out more aencate man «»> «>« »« jw ~p-. -

the forms belonging to this species group have moderately to highly complicated axial structures CODlpftr6 

with Orewingkia. Illustrations are based on material from the seitirk limestone of Manitoba and from 

Upper Ordovician rocks of Arctic America. FIGURE 4a, diagrammatic transverse section through the base 

Of the calyx, showing an axial StrUCtlire Of the QrCWinghto type. 4b; view of a corallum from an alar side.

showing convex curvature of the cardinal side (at left) and concave curvature of the counter side (&t tight). 

This is a fairly large specimen.
GEOLOGICAL 8UEVET BULLETIN 1021 PLATE 22

X 2

X''^ :.; :^f>%. 

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ANGULATE ORDOVICIAN STREPTELAS/IID CORALS
PLATE 23

[All figures natural size except where otherwise indicated]

Pycnactis 

Figures la, Ib

Most of the corals that belong to this genus are small or medium sized. Typically the cardinal side is 

convex and the counter is concave. The calyx is deep, and transverse sections are circular. The cardinal 

septum is long and is the dominant septal element in the calyx. The counter septum is not noticeably 

different from other major septa in the counter quadrants. The major septa are excessively dilated and fill 

up the corallum from the apex to the floor of the calyx. Tabulae are not developed. Silurian corals that 

appear to belong to Pycnactis have been identified from several localities in the West. As the western 

material is embedded in dolomite, the Illustrations are based on material from Gotland and England. 

FIGURE la, view of the concavely curved counter side of the corallum. Ib, transverse section just above the 

floor of the calyx, showing characteristic dilation of the septa.

Zelophyllum

Figures 2a-2d

This genus was described for Silurian corals having very short strongly dilated septa, approximately 

horizontal tabulae, and no dissepiments. Zelophyllum has continuous rather than acanthine septa. The 

principal obvious difference between Zelophyllum and Try plasma is the septa] structure; tabulation in the 

two genera is similar, and species are likely to have comparable growth forms. Corals with very short 

contiguous and continuous septa found in a number of Silurian assemblages have been assigned to Zelophyllum. Although the genus has been recognized in Europe and Asia, the external features of coralla have not 

been described. The accompanying illustrations are based on material from Gotland, China, and Utah. 

FIGURE 2a, diagrammatic transverse section showing thick cortex formed by the short dilated septa. 2b, 

diagrammatic vertical section showing nature of tabulation. 2c, fragment of a corallum that presumably 

was solitary. This specimen came from China; it is somewhat weathered and shows no indications of an 

epitheca. Smaller fragments of a larger Zelophyllum collected in the Laketown dolomite of Idaho have an 

epitheca; therefore it seems likely that the deposit was removed by weathering. The specimen was considerably longer originally than the segment figured here. 2d, fragments of weathered and silicified corallites 

that appear to have been elements in a fasciculate corallum. This material was found in the Silurian rocks 

of Utah and is closely related to the genotype of Zelophyllum, Z. intermedium Wedeklnd.

Tryplasma 

Figures 3a, 3b

Trochoid, ceratoid, and cylindrical forms of Tryplasma are fairly common in the western Silurian rocks. 

The genus is distinguished by its acanthine septa. Illustrations are based on material from Nevada and 

California. FIGURE 3a, side view of a nearly cylindrical corallum that shows periodic rejuvenation and, in 

the apical region, the talons by which it was attached. 3b, small trochoid corallum.

Vermiform corallum, gen. indet.

Figure 4 

Vermiform and gonlculate coralla are common in western Silurian faunas but are not knOwH In the OmOvician. The specimen illustrated came from California; it has continuous septa, but other morphologic

structures are not well enough preserved to establish its relationships.

Intelophyllum

Figures 5a-5d

This oyathophyllia coral Is commonly colonial though solitary coralla have been assigned to the genus.

Corallites of Entelophyllum nave a peripheral aissepimentarium composed of imperfectly globose dissepiments. A tabularium, with approximately horizontal tabulae, occupies the axial part of the COfalHte. 

The illustrations are based on material from the Roberts Mountains formation of Nevada and from the 

European Silurian. FIGURE 6a, fragment from a compound corallum. The trumpet-Shaped and Cylindrical corallites proliferated asexually from the dissepimentarium of a parent corallite (peripheral increase).

5b, another fragment from a corallum of the same species shown in rig. k The ASfiXliaJly reproduced COfS]- 

lites are nearly cylindrical in shape and are joined by connecting processes. 5c, diagrammatic transverse 

section through the upper part of a corallite showing the broad dissepimentarium. 5d, median vertical section through a parent corallite and offset, showing the axial tabularium and the broad peripheral dissepimentarium.
GEOLOGICAL SURVEY BULLETIN 1021 PLATE 23

CHARACTERISTIC SILURIAN RUGOSE CORALS
PLATE 24

Nyctopora

Figures la, Ib

This genus has a massive corallum composed of relatively small prismatic (ceriold) corallites. Septa are 

very short and develop in a primary series of 8, then a secondary and alternating series of 8. In mature 

parts of the corallites, the 16 septa are all the same length. Mural pores do not occur. Tabulae are essentially horizontal and periodically are more closely spaced, aifeature probably related to seasonal growth 

rather than a diagnostic generic character. The illustrations are based on Bassler's figures of Nyctopora 

billingsl Nicholson and on specimens from the Upper Ordovician rocks of Texas. FIGURE la, vertical section. 

Ib, transverse section.

Saffordophyllum 

Figures 2a, 2b

Species assigned to this genus differ from those of Nyctopora hi having 8,12, or 20 septa, which are widely 

spaced and very short. The tabulae tend to be more closely spaced than hi Nyctopora, and some species 

have much larger corallites than are known in Nyctopora. The illustrations were adapted from Bassler's 

figures of Saffordophyllum franklini (Salter), an Arctic species. FIGURE 2a, vertical section. 2b, transverse 

section. .

Foerstephyllum 

Figures 3a, 3b

This genus is interpreted to be a forerunner of Favistella, from which it differs significantly only hi having 

shorter septa. There are normally 24 or more septa. Tabulae are horizontal and tend to be more crowded 

in zones. Mural pores are wanting. Illustrations were adapted from Bassler's figures of Foerstephyllum 

simplissimum (Okulitch). FIGURE 3a, transverse section. 3b, vertical section.

Lichenaria 

Figures 4a, 4b

This genUS iS Characterized by its very simple structure. The prismatic corallites are not pierced by 

mural pores. There are no septa. Tabulae are horizontal. The illustrations are based on an undetermined 

species with unusually large coralUtes, occurring in the Tank Hill limestone of the Pioche district, Nevada. 

FIGURE 4a, transverse section. 4b, vertical section.

Favistella

Figures 5fl, 5b

The septa of Favistella are considerably longer than those of Foerstep/n/iium; in other respects, the two 

genera are very similar. Most species have 12 or more major septa; alternating minor septa occur in many

forms. The Illustrations were adapted from Bassler's figures of Favistella undulata Bassler. FIGURE 1)8, 

transverse section 5b, vertical section.

Cyathophylloid.es

Figures 6a, 6b

This genus differs from Favhteila in having major S6ptB that meet 8t the center of the corallites and proe^ce ^ incipient axiai structure. Tabulae are not horizontal hi a true median section the peripheral margins are turned down and the axiai part is aepressea. f<a^0fkvn^.m ekoml C33:&n> tram tbo Montoya

limestone of Texas is a phaceloid version of Cyathophylkldes. The illustrations are based On material from 

the Burnam limestone of Texas and the Hanson Creek formation of Nevada. FIGURE 6a, transverse section. 

6b, median vertical section.
GEOLOGICAL SURVEY BULLETIN 1021 PLATE 24

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X 4

X 3

X 3

5b

X 3

MASSIVE CERIOID ORDOVICIAN FAVISTELLID CORALS
PLATE 25 

Palaeophyllum 

Figures la, Ib

This genus Is a phacelold derivative of Favistella. Tabulae are nearly horizontal, and In most species 

the septa do not reach the center of the corallites. In P. thomi (Hall) from the Montoya limestone of 

Texas the major septa do meet at the axis, and the tabulae are like those of Cyathophylloides. (pi. 24, fig. 6b). 

The illustrations are based on material of Late Ordovlcian age from Utah. FIGURE la, transverse section 

showing minor septa alternating with the major septa. Ib, vertical section showing nature of the tabulation, 

The longitudinal lines crossing the tabulae are traces of the septa.

Circophyllum 

Figures 2a, 2b

In this phaceloid Silurian genus the major septa meet and twist slightly at the center of the corallites. 

The tabulae are tent shaped, a feature that can be seen only in a median vertical Section. Weathered surfaces exhibit a slight but persistent axial structure. The coral has no dissepiments. Asexual Increase is 

peripheral and parricidal. The Illustrations are based on specimens from the Silurian rocks of Utah, which 

closely resemble the Gotlandian genotype. FIGURE 2a, transverse section showing the major septa Joining 

at the center. 2b, vertical section through two corallites showing, in the upper half, the tent-shaped tabulae 

as they appear in a true median section. The lower part of the illustration shows the more nearly horizontal 

attitude of the tabulae and the traces of the septa where the section does not cut the center of the corallites. 

Sections that are off center are misleading because they suggest a dlssepimented coral.

Aphyllostylus 

Figures 3a, 3b

Colonial tryplasmlds with small phacelold corallites had a worldwide distribution during the Silurian. 

They are distinguished from other phaceloid corals by their acanthlne septa and conspicuously slant'ing 

tabulae. Aphyllostylus has been considered a synonym of Tryplasma, but the phacelold form deserves 

subgenerlc status. The Illustrations are based on material from the Silurian rocks of Washington which 

closely resembles species occurring in Australia and China. FIGURE 3a, transverse section showing acanthine septa. 3b, vertical section showing slanting tabulae and acanthine septa.

Eofletcheria 

Figures 4a, 4b

This early Ordovician coral has tubular corallites with widely spaced horizontal tabulae and no septa. 

Eofletcheria was contemporaneous with Lkhenaria but was probably derived from the cerioid coral. 

Asexual proliferation was by lateral Increase. The Illustrations are based on material from the upper part 

or tne Fogonip group of Nevada. FIGURE 4a, vertical section. 4b, transverse section.

Lichenaria, semiphaceloid Variant approaching Eofletcheria 

Figures 5a, 5b

This form has the same characters as cerioid Lichenarias (pi. 24, figs. 4a, 4b) . Most of the corallites are in 

contact and have polyhedral cross sections, but some become free and tend to have circular sections like 

Tabulae are moderately abundant. Neither septa nor mural pores are developed. The

rial from the Tank Hill limestone of the PiOChe district, Nevada. FIGURE

53, Vertical section. 5b, transverse section.

Fletcheria

Figures 6a, 6b

This genus has thick walls whose structure resembles that round in the syringoporoid corals. Tabulae 

range from horizontal to cystose. Septa and septal spines seem to be absent. Asexual proliferation WflS Dy 

callcular Increase and characteristically was not quadripartite as In Pycnostylus, which some workers have 

erroneously considered to be the same as Fletcheria. The illustrations are based OH thin Sections Of the genotype, F. tubifera Milne Edwards and Haime, from the SUurian rocks of Gotland. FIGURE 6a, transverse 

section showing strongly thickened walls and calicular "buds." 6b, vertical section showing a corainte 

splitting into several individuals.
GEOLOGICAL SURVEY BULLETIN 1021 PLATE 25

X 2

X 2

O

O

©

3a

X 2

3b

X 2

4b

X 2

5b

5a

X 2

X 2

MASSIVE FASCICULATE GENERA OF ORDOVICIAN AND SILURIAN CORALS
PLATE 26

Favosites (Palaeofavosites) 

Figures la, lb

Favositld corals In which the mural pores are confined to the angles of junction between corallltes weredesignated Palaeofavosites by Twenhofel. Investigators who based their opinions on studies of large suites 

of specimens of the genotype claim that mural pores are not always restricted to the angles; however, thecategory seems useful for a subgeneric rank. Some, but not all, Ordoviclan favosltids belong to Palaeofavosites. Commonly, mural pores are not abundant. Septal spines occur in some species but are not shown, 

here. The illustrations were adapted from Ting's figures of a nonseptate form of Favosites asper Orblgny,. 

the genotype of Palaeofavosites. FIGURE la, transverse section, lb, vertical section.

Favosites (Favosites) 

Figures 2a, 2b

"Typical" Favoeites has nearly horizontal tabulae and mural pores that perforate the flat sides of thecorallite walls. Septal spines are present in many species and are Illustrated here. The Illustrations wereadapted from Ting's figures of Favosites hisingeri Milne Edwards andJHaime. FIQURE 2a, transversesection. 2b, vertical section.

Favosites (Squameofavosites) 

Figures 3a, 3b

This subgenus differs from Favosites, in the strict sense, in having squamulae (septal spines modified' 

Into irregular linguliform or wavy transverse structures) that replace the septal spines entirely or In partTabulae are present but tend to be somewhat irregular. The end result of this evolutionary trend is Emmonsia in which squamulae are so excessively developed that they take the place of the tabulae. Chernyshev 

(1941a, p. 24-25) proposed Sguameofavosites as a genus, but most students have included favositids possessingboth squamulae and tabulae in Favosites, Sguameofavosites seems applicable for a subgeneric category.. 

Squamulate favositids are not known before Middle Silurian time. The illustrations were adapted from 

Chernyshev's figures of Sguameofavosites hemisphaericus bohemicus (Pocta), the genotype. FIGURE 3a,. 

transverse section showing linguliform squamulae. 3b, vertical section showing squamulae and Irregular' 

tabulae,

Calapoecia

Figures 4a, 4b

The systematic position of Calapoecia is uncertain; some consider it an aberrant tabulate coral; othersbelieve it is a derivative of the favlstellids. The genus Includes species in which the corallites are prismaticand not separated by Interstitial deposits as well as forms with cylindrical corallites that are separated by 

"coenenchyme." Most of the western forms seem to belong to the latter category, which is illustrated here. 

Calapoecia has 20 short wedge-shaped septa that arise periodically from the septal ridges. The corallite wallsare regularly perforate (crlbrose). The illustrations are based on thin sections of C. anticostiensis Billings,.

the genotype. In this species the septa project as short spines into the corallites and extend into the intercorallile areas as somewhat irregular processes called costae. Tabulae in the corallites are irregular. Intercorallitc spaces are crossed by thickened transverse elements called diaphragms, which with costae and

vesicles form the so-called coenenchyme. FIGURE 4a, vertical section showing at the left the cribrose structure formed by intersection of costae with diaphragms near the corallite wall. A median section tuTOUgh

taterwralUte "Coenenchyme" Is shown at center right separating two corallites; the thickened transverseelements are diaphragms, the vertical elements are remants of costae or vesicles. 4b, transverse section showing the splnose septa with their costal processes, which are partly disrupted In the Intercoralllte areas.-

Heliolites 

Figures 5a, 5b

TLie skeletal morphology of I-Jcliotitea differs conspicuously from thiat o t Galayzoecia.. Tt»e tabularla (macro- corallites) are separated by a reticulum of tubuli (microcorallites), The tabuiaria have wen-defined wau>

and are crossed by complete tabuiae.J The tubuli are crossed by transverse plates called sola. There are nomural pores or perforations. Septa, when present, always number 12; they may t>e lameiiar or spmose.

The illustrations were adapted from Amsden's figures of Heliolites spongiosus Foerste, a Silurian species: ffiat Ms septa. Fioufii Ga< Tortioai Beotioa s&owg m ^man* ana ^ ^iol^s * . **, *«».

verse section showing nature of the reticulum surrounding the tabuiaria (macrocorallites).
 GEOLOGICAL SURVEY BULLETIN 1021 PLATE 26

X 5

X 5

X 5

X 8

X 5

FAVOSITES, CALAPOECIA, AND HELIOLITES
PLATE 27

[All figures natural size except where otherwise Indicated] 

Halysites (Catenipora) 

Figures la-le

The compound coralla of Halysites are formed by small tubular coralHtes united In single series that 

Intersect or anastomose with other chains. Catenipora differs from the other subgenera In lacking mesopores 

(interstitial coralHtes or tubuli). The coralHtes have horizontal tabulae. Septal spines in cycles of 12 

are present .In many of the species referable to Catenipora but are not Illustrated here. Mural pores are not 

developed. The illustrations are based on material from the Upper Ordoviclan part of the Bluebell dolomite of Utah and from the Burnam limestone of Texas. FIGURE la, vertical section of Halysites (Catenipora) 

gracilis Hall. Ib, transverse section through part of a corallum of C. gracilis, showing the nearly quadrangular shape of the coralHtes and the nature of the meshwork. Ic, transverse section of two coralHtes of C. gracilis, showing comparative thinness of the walls with reference to the size of the corallites. Id, transverse 

section through part of the corallum of Halysites (Catenipora') cf. C. jacovickii Fischer de Waldhelm, showing 

the very small coraUltes and the fine meshwork. The meshes are formed by very few corallites, only three 

or four in many instances, le, transverse section showing the fusiform corallites of Catenipora cf. C. jacovickii. The walls are comparatively thick. Rosettelike spots at the junctions of corallites suggest mesopores, but thin sections show that these spots are actually solW deposits In which the fibers are oriented at 

angles to the fibrous material of the corallite walls.

Halysites (Halysites) 

Figures 2a-2c

This section of the genus has mesopores between the corallltes, which commonly are oval In transverse 

section. Tabulae are horizontal In the mesopores but may be somewhat flexuous in the coralHtes. Septal 

spines occur In most species but are not shown hi the accompanying figures because they have no bearing

on the recognition of the subgenus. Illustrations are based mairJy on material from the Ootlandlan of 

Europe and figures published by Fischer-Benzon. FIGURE 2a, vertical section, showing nature of tabulation 

in corallites and mesopores. 2b, transverse section through part of a corallum, showing oval corallites 

separated by mesopores. 2c, transverse section through two corallites.

Halysites (Cystihalysites)

Figures 3a-3f 

Cystihalysites also has mesopores but differs from Halysites (sensu stricto) in having cystose tabulae in the

mesopores and, In some species, lining the coraUltes. Septal spines occur In some species but are not shown

here. Illustrations are based on material from the Silurian rocks of utah and California and on figures published by Amsden and Chernyshev. FIGURE 3a, vertical section showing nature of tabulation in Halysites 

(Cystihalysites) afl. C. brownsportensis Amsden. 3b, transverse section through part of corallum of 

CytllilMll/JttCS afl, (7. brQiensportenais, showing nearly circular corallites separated by small mesapores. 3c,

transverse section of a few corallites of Cystihalysitet afl. C. brownsportensis. 3d, vertical section of a

species of Cystihaly sites having very large coralHtes, showing nature of tabulation in a corallite and parts of

adjoining mesopores. 3e, transverse section through part of the corallum of a characteristic species of

Cyztihalyati.es found la the Silurian rocks of the West, showing the exceptionally large coralHtes and coarse

mesbwork. zt, transverse section of a corallite from tfao form of C^MlhatvtUt, Illustrated ! figures 3d and

3e, showing extreme development of cystose tabulae in the coramte and mesopores.
GEOLOGICAL SURVEY BULLETIN 1021 PLATE 27

one

2c

ORDOVICIAN AND SILURIAN HALYSITID CORALS

U. S. GOVERNMENT PRINTING OFFICE: 1956