Early Silurian Graptolites 

From Southeastern Alaska 

and Their Correlation With 

Graptolitic Sequences in 

North America and the Arctic

GEOLOGICAL SURVEY PROFESSIONAL PAPER 653
Early Silurian Graptolites 

From Southeastern Alaska 

and Their Correlation With 

Graptolitic Sequences in 

North America and the Arctic

By MICHAEL CHURKIN, JR., and CLAIRE CARTER

GEOLOGICAL SURVEY PROFESSIONAL PAPER 653

Descriptions and illustrations of $9 species of 

Graptoloidea and correlation of the assemblages 

with other graptolitic successions in North 

America, the Soviet Arctic, and Great Britain

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress Catalog-card No. 78-605140

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price $1 (paper cover)
CONTENTS

Page

Abstract-_ _________________________________________ 1

Introduction-______________________________________ 1

Acknowledgments. ____ __--_-_________-____-__-______ 1

Graptolites of the Descon Formation, southeastern

Alaska__ _____________________________________ 2

Description of the Descon Formation.________..___ 2

Graywacke sandstone and banded mudstone___ 2

Conglomerate and sedimentary breccia. _______ 3

Black chert and siliceous shale________________ 3

Quartzo-feldspathic arenite.__________________ 3

Volcanic rocks,_____________________________ 3

Stratigraphic relations to other units and age___--_- 3

Standard graptolite zones for the Lower Silurian___-_._- 

Lower Silurian graptolites in western North America-___ 

Systematic descriptions._____________________________

Class Graptolithina.____________________________

Order Graptoloidea_-___________---___-__-_-

Family Diplograptidae__________________

Family Dimorphograptidae______________

Family Monograptidae__________________

References cited.___________________________________

Index ____.._______-__ __-_______-__-___---__-__---

ILLUSTRATIONS

Page 

6 

6

13 

13 

13 

13

33

34

46

49

[Plates 1-4 follow index]

PLATE 1, Climacograptus, Pseudoclimacograptus, and Diplograptus.

2. Diplograptus, Glyptograptus, and Orthograptus.

3. Orthograptus, Petalograptus, Dimorphograptus, Akidograptus, and Monograptus.

4. Monograptus and Rastrites. Page 

FIGUBE 1. Geologic map of Prince of Wales Island area_________________--____-_--_-------_----_------_-------- 4

2. Index map showing Silurian graptolite localities_______________--_-_-----------_--------------------- 7

3. Correlation diagram showing graptolitic sequences-_____-__-_--___---__-_---------------------------- 9

4-5. Columnar sections showing graptolite localities:

4. Esquibel Island.________________-_________________-_------_-------_----------------------- 11

5. San Fernando Island.__________________________-_______-_-__--_---___--------------------- 12

6-19. Camera lucida drawings of:

6. Climacograptus. ________________-________________-_____-___-___-_-_-__-------------------- 13

7. Climacograptus- ________________-_______-____-__-_--__---_----_--------------------------- 17

8. Climacograptus and Pseudoclimacograptus. ______________________-_-__-__-----_----_--_------- 18

9. Diplograptus. __________________________________--___----___--_-_--__--------------------- 21

10. Glyptograptus and Diplograptus... _____________--__---_-----__-------_--_------------------- 22

11. Glyptograptus _______________________________________----_____--_--__-_-_----------------- 25

12. Glyptograptus and OrtAogrrapfus______---__--_----------------------------------------------- 26

13. ^.Orthograptus, Petalograptus, Dimorphograptus, and Akidograptus. ________-__------------------- 31

14. Dimorphograptus and Monograptus... ____________________-_______-._____------------_-------- 35

15. Monograptus... _______________________________________-______--------------------_------- 36

16. Monograptus_______________________________________-_--_______-___----------_----------- 38

17. Monograptus..- ________________________________________________-______----_--__----------- 40

18. Monograptus... _______________________________________________-____-_--_----------------- 41

19. Rastrites............ ___________ ______ _ _____________________.._-_-._--.-_--.---- 45

TABLES

Page

TABLE 1. Partial list of graptolites from northeastern Nevada showing British ranges and associations on single talus

slabs--_-________________________________________________--_-___----_----------------------- 1

2. Silurian graptolite faunas from Prince of Wales Island area, Alaska__-____-_-__------------------------ 10

3. Lower Silurian graptolites of Alaska and Nevada showing a comparison of their zonal ranges to the same or

similar species in Canada, Great Britain, and the Soviet Arctic.__________-_-----_------------------- ^

ill

EARLY SILURIAN GRAPTOLITES FROM SOUTHEASTERN ALASKA AND THEIR CORRELATION 

WITH GRAPTOLITIG SEQUENCES IN NORTH AMERICA AND THE ARCTIC

By MICHAEL CHURKIN, JR., and CLAIRE CARTER

ABSTRACT

A succession of graptolite faunas across the Ordovician-Silurian 

boundary has been discovered in North America. The earliest 

Silurian graptolite zones, characterized by the association of 

the biserial graptolites Climacograptus, Glyptograptus, and 

Orthograptus, established much earlier in the Ordovician 

together with the first Silurian monograptids, Akidograptus and 

Dimorphograptus are described for the first time in North 

America. These new collections of Lower Silurian graptolites 

are from dark shales in southeastern Alaska and Nevada. The 

occurrence of Silurian graptolites in western North America 

is reviewed, and the Alaskan graptolite faunas are correlated 

with other graptolitic successions in North America and the 

Soviet Arctic. The Alaskan graptolite species and zonal succession 

are remarkably similar to that in the Birkhill Shales of Scotland, 

the type section for the standard Lower Silurian graptolite 

zones. From Alaska, graptolite assemblages equivalent to the 

zones of Akidograptus acuminatus, Monograptus cyphus, and 

Monograptus grcgarius are recognized and illustrated. In addition, 

the following new graptolite species are established: Climacograptus indivisus esquibelensis, C. innotatus obesus, C. tnedius 

brevicaudatus, C. stenotelus, C. rectangularis abbreviatus, Diplograptus mucroterminatus, D. elongatus, Glyptograptus tamariscus 

magnus, G. lanphcrei, G. laciniosits, G. gnomus, G. kayi, Orthograptus eberleini, 0. insectiformis minutus, Dimorphograptus 

physophora alaskensis, Monograptus calamistratus, M. buddingtoni, M. noyesensis, M. kerri, M. hamatus, Rastrites orbitus.

INTRODUCTION

Graptolite faunas, especially from black shale sequences bordering North America, show a remarkable 

similarity in species and faunal succession to the British 

graptolites made famous first by Charles Lapworth, 

then by Elles and Wood (1901-18). In Australia 

(Thomas, 1960), Asia (Sun, 1933; Hsii, 1934; Obut, 

1959, 1960), and North Africa (Waterlot, 1945), where 

good graptolite sections are known, the similarity in 

species and succession of faunas above the initially 

somewhat provincial Lower Ordovician faunas is again 

remarkable. Despite the cosmopolitan character of 

graptolites, the lowest Silurian graptolite zones are 

relatively unknown outside of Great Britain. The 

lowest Silurian graptolite zones characterized by the 

association of biserial genera such as the longestablished Ordovician Climacograptus, Glyptograptus, 

and Orthograptus and the appearance of the new

Dimorphograptus (proximally uniserial and distally 

biserial) together with the first monograptids were not 

reported in Ruedemann's (1947) cataloging of Nor^h 

American graptolites.

More recently, Ross, (1962) described several lower 

Silurian species from Illinois, but they are fragmentary 

and poorly preserved. Another lower, but not lowest, 

Silurian graptolite collection that has beautifully 

preserved specimens was recently made from talus in 

a mine dump in Nevada (Kerr, 1962; Churkin and Kay, 

1967). These graptolites are illustrated for the first 

time in this paper.

The senior author in the company of G. D. Eberleni 

and M. A. Lanphere made several discoveries of considerably older Silurian graptolite faunas in southeastern Alaska during the 1964 field season. Subsequently in 1965, new lower Silurian graptolite localities 

were found by Eberleiii, A. T. Ovenshine, and Churkin. 

The most important of these localities was revisited 

by Churkin in 1968, and the highest Ordovician graptolites were found just below the previously known lowest 

Silurian faunas, thus establishing the OrdovicianSilurian boundary. The earliest Silurian graptolite 

zones are present in some of these localities the first 

record of their occurrence in North America. The 

purpose of this paper is to describe this new material, 

briefly review the occurrence of Lower Silurian graptolites in western North America and the Soviet Arctic, 

correlate the Alaskan graptolites within these areas, 

and show the differences in associations of certain 

critical graptolite species that most likely reflect 

changes in their stratigraphic range from one region 

to another.

The biostratigraphic section is by Michael Churkin, 

and the systematic descriptions are largely by Claire 

Carter, who also did all of the camera lucida drawings 

of the graptolites.

ACKNOWLEDGMENTS

The authors are indebted to the collecting zeal of 

G. D. Eberlein, A. T. Ovenshine, M. A. Lanphere, and 

Charles Carter, without whose help this report would

1
EARLY SILURIAN GRAPTOLITES FROM ALASKA

not be possible; to G. D. Eberlein for much stratigraphic data on southeastern Alaska; to Marshall Kay 

for helping to collect the Nevada graptolites; to O. M. B. 

Bulman for pointing out literature on the British 

succession; to A. M. Obut for Soviet graptolite literature 

and helpful comments regarding comparisons with 

Asian species; to Dennis Jackson for the latest references 

covering western Canadian Silurian graptolite localities; to William Kerr and Hans Trettin for the latest 

Canadian Arctic graptolite locations; to W. B. N. 

Berry for examining the New species Orthogmptus 

eberleini and for several helpful suggestions; to Kenji 

Sakamoto for tackling the difficult task of graptolite 

photography, and especially to Peter Toghill for making 

available his thesis covering the graptolites of the 

Birkhill Shales, for carefully examining the Alaskan 

and Nevadan graptolites, and for making numerous 

suggestions on their comparison with British graptolites, 

especially those from the Birkhill Shales.

GRAPTOLITES OF THE DESCON FORMATION, 

SOUTHEASTERN ALASKA

DESCRIPTION OP THE DESCON FORMATION

Silurian graptolites have long been known to occur 

in various parts of southeastern Alaska (Buddington 

and Chapin, 1929; Ruedemann, 1947; Muffler, 1967, 

p. ClO). Most of these collections were made from 

isolated exposures of graptolitic shale during rapid 

reconnaissance mapping. These earlier field investigations, supported mainly by the paleontological studies 

of Edwin Kirk, Rudolf Ruedemann, and G. H. Girty, 

showed the completeness of the Paleozoic sequence 

in the vicinity of Craig on the northwest coast of 

Prince of Wales Island.

Eberlein and Churkin (1969) selected this area 

indicated in figure 1 for detailed geologic mapping and 

biostratigraphic study. The Lower Silurian graptolites 

that are described in this paper were collected during 

this mapping of the Craig B-4, C-4, C-5, C-6, and 

parts of the D-4 and D-5 quadrangles that are now 

being prepared for publication. All the Ordovician and 

Silurian graptolites within the Craig area occur in the 

Descon Formation of Early Ordovician through Early 

Silurian age (Eberlein and Churkin, 1969). In exception, 

graptolites of earliest Devonian age associated with 

vascular plants are known to occur in the lower part 

of the Karheen Formation on northeastern Noyes 

Island (Churkin and others 1969).

The Descon Formation is a thick sequence composed 

of marine predominantly graywacke-type coarse- and 

fine-grained rocks interbedded with basaltic volcanics 

that is the oldest known rock sequence exposed in the 

northwest coastal area of Prince of Wales Island

(Eberlein and Churkin, 1969). The general distribution 

of these rocks is shown in figure 1, but they are known 

to extend much farther to the north and east on 

Kosciusko and Prince of Wales Island. Their extension 

to the south is imperfectly known, but it is likely that 

their metamorphic equivalents have been included in 

the Wales Group as mapped by Buddington and 

Chapin (1929).

Geologic mapping has demonstrated the practicality 

of informally subdividing the Descon Formation into 

five general lithofacies:

1. Graywacke sandstone and banded mudstone.

2. Conglomerate and sedimentary breccia.

3. Black chert and siliceous shale with minor lenses of 

limestone.

4. Basaltic volcanic rocks, including pillow basalt flows, 

breccia, volcanic conglomerate, and agglomerate.

5. Quartzo-feldspathic arenite.

These are interbedded and some of the clastic lithologies 

can be demonstrated to be distal or proximal equivalents of one another. Their designation as formal 

members may be called for eventually, but outcrop 

limitations have made it impossible to extend the units 

with sufficient confidence.

GRAYWACKE SANDSTONE AND BANDED MUDSTONE

These are the most widespread and quantitatively 

important lithologies of the Descon Formation. The 

graywacke is typically dark-greenish-gray massive 

medium- to coarse-grained compact poorly sorted 

sandstone composed mainly of relatively fresh mineral 

and intraformational rock fragments set in a chloride 

matrix that has generally undergone some degree of 

mimetic recrystallization. Much of the graywacke is 

essentially a volcanic sandstone with the texture of a 

microbreccia that is composed mainly of intraformational basaltic debris and subordinate chert and mudstone fragments. Although beds of graywacl'e as much 

as 20 feet thick are common, they may range from a 

few inches to 150 feet or more in thickness In many 

outcrops 110 bedding is apparent, but locally a crude 

stratification is manifest by interbeds and pebble 

strings of intraformational siltstone and banded mudstone. At some places even the coarser grained and 

thicker beds exhibit large-scale vertical grading. Cross 

laminae, when developed, are confined within parallelbedded sets that rarely exceed 3 inches in thickness.

The banded mudstone interbedded with the graywacke occurs as thin-bedded intervals of olive-gray to 

grayish-black thin-layered siltstone and very fine to 

medium-grained dusky-yellow sandstone. Individual 

beds seldom exceed a few inches in thickness- and most 

are less than 1 inch thick. Contacts between adjacent
GRAPTOLITES OF THE DESCON FORMATION

beds are normally sharp and may show evidence of 

penecontemporaneous erosion. Cross laminations, confined to single beds, are not uncommon and many of 

the sets show excellent graded bedding. These rocks 

generally are indurated and lack fissility. The textural 

features and sedimentary structures of this lithofacies 

in the Descon Formation are similar to those in turbidites, which are commonly attributed to deposition 

from turbidity currents.

CONGLOMERATE AND SEDIMENTARY BRECCIA

Although quantitatively subordinate to graywacke, 

conglomerate and sedimentary breccia are just as widely 

distributed as the finer grained equivalents with which 

they are interbedded. Their composition is quite 

variable and ranges all the way from wholly volcaniclastic material to polymictic varieties with megaclasts 

of varicolored chert, limestone, felsic volcanics, and 

granitic to gabbroic rock types.

A common variety of conglomerate and breccia 

consists predominantly of porphyritic basaltic detritus 

rich in euhedral pyroxene crystals that is petrologically 

identical to the flows in the Descon Formation. Subordinate amounts of mudstone, graywacke, graygreen chert, and rare limestone make up the remaining 

megaclasts. In most places, 40 percent or less of 

indurated matrix is present, and the megaclasts tend 

to be in contact with one another. Sizing is poor and 

there tends to be a complete gradation from the coarsest 

to finest grained detritus, especially in oligomictic 

varieties. Locally, however, the largest fragments are 

completely separated by sand-size matrix. This is 

especially common in the basaltic sedimentary breccias.

BLACK CHERT AND SILICEOUS SHALE

An important, albeit comparatively minor, lithologic 

assemblage within the Descon Formation consists of 

thin-bedded black to dark-gray chert and siliceous 

siltstone with black shale partings. The importance of 

this facies derives mainly from the fact that it occurs 

interbeided with all the other lithologies, and its shaly 

interbeds have proved to be a good source of wellpreserved graptolites excellent for dating and correlation. Individual chert beds range in thickness from a 

fraction of an inch to as much as 6 inches, but most are 

%-\ inch thick. Locally, lenses of laminated mediumdark-gray limestone as much as 3 feet thick and beds of 

graywacke and chert arenite several inches thick are 

also present.

Because these fine-grained rocks commonly preserve 

graptolites, it is fortunate they have such a large 

areal, as well as stratigraphic, distribution. On the 

southwest shore of Heceta Island, good exposures 

occur 2.3 and 3.3 miles northwest of Point Desconocida

(fig. 1). Excellent exposures also occur on the islands 

at the north and south entrances to Big Salt Lake, 

where the chert and siliceous shale are interbedded 

with fragmental basaltic volcanics and graywacke. 

Other occurrences that have yielded useful graptolite 

collections are on the east shore of Steamboat Bay 

(Noyes Island), the northeast shore of Noyes Island, 

Esquibel Island, the west coast of Anguilla Island, and 

in the Harmony Islands.

QUARTZO-FELDSPATHIC ARENITE

Gritstone and medium- to fine-grained sandstone, 

rich in feldspar and commonly containing 5-10 percert 

of detrital quartz, locally occur interbedded with 

graywacke and banded mudstone of the Descon 

Formation.

Typically, these rocks are poorly sized, massive, 

compact, quartzo-feldspathic arenites that tend to 

weather to orange brown within the tidal zone. Fresh 

surfaces are medium gray to various shades of pistachio 

green, due mainly to the development of epidote in 

the matrix. Individual beds range in thickness from 

several inches to 20 feet or more. The thicker beds in 

some places exhibit a poorly developed parallel interns I 

stratification and may show very crude grading. The 

principal constituents are angular grains of pale-green 

and gray chert, broken crystals of twinned plagioclase, 

and broken, partly rounded euhedra of clear quartz, 

which are ubiquitous but rarely exceed 15 percent of 

the rock by volume.

VOLCANIC ROCKS

Flows and associated fragmental volcanics, in the 

form of agglomerate and flow breccia, appear sporadically throughout the Descon Formation. The interbedded graptolite shales imply that repeated volcanism 

occurred from different centers during Early Ordovician 

through Early Silurian time.

The lavas are predominantly medium-olive-gray 

porphyritic, vesicular, and amygdaloidal basalts. 

Stubby phenocrysts of diopsidic augite, locally as 

much as 10 mm in diameter, are set in a groundmass of 

small granular augite, plagioclase microlites (generally 

in the range An35-An48), and chloritic alteration 

products, probably derived in part from former glass. 

Thus, these rocks have the petrographic characteristic? 

of basalts except that the plagioclase normally if 

andesine rather than labradorite or bytownite (G. D. 

Eberlein, oral commun., 1968).

STRATIGRAPHIC RELATIONS TO OTHER UNITS AND

AGE

The base of the Descon Formation is not exposed in 

the area studied. In the Heceta-Tuxekan Islands area,
EARLY SILURIAN GRAPTOLITES FROM ALASKA

' \ \ v \\ - y

\ ^\x \C\\X"

liiifcShT^ ;.;..-DSk .'

V, /1 -y^ a Ml iTiii^u, 138 M1139 iTiii^w, M1286 ITI ±£.uu, >7T »»/',... V:::^ ' M1288> M1289- M1290

St Joseph 

Island

Steamboat M1143

:;::= ISLAND:;:;;;;;;':

SAN

ALBERTO 

BAY

55°30'

FIGUEE 1. Northwest coastal area of Prince of Wales Island (modified from Eberlein and Churkin, 1969).

Descon conglomerate and graywacke are overlain conformably by the Heceta Limestone (Eberlein and 

Churkin, 1969). At the south end of Two Crack Island, 

the Heceta Limestone rests upon deformed dark-gray 

calcareous siltstone and siliceous shale with thin interbeds of fine-grained graywacke and silty limestone. 

South of the Harmony Islands, where the Heceta Limestone is missing, clastic rocks of the Karheen Formation 

rest unconformably upon the Descon Formation. There 

is 110 evidence for major discontinuities within the formation. In fact, numerous graptolite collections indicate 

virtually continuous deposition from Early Ordovician

into Early Silurian time, with episodes of volcanism in 

the late Early and late Middle Ordovician, and locally 

in the Early Silurian.

Beds as old as Early Ordovician have been recognized 

at several rather widely separated places. On the east 

shore of Steamboat Bay, Noyes Island (see fig. 1, loc. 

USGS M1031-CO), black shale partings interbedded 

with thin-bedded dark-gray chert and chert arenite contain Tetragmptus cf. T. serra, Cardiograptusf, and 

Didymograptust indicative of a late Early Ordovician 

(Arenigian) age. On the west side of Anguilla Island 

(fig. 1, loc. USGS M1032-CO), about the spine Lower
GRAPTOLITES OF THE DESCON FORMATION

EXPLANATION

is A ."« O

~ is r

s>.

Peratrovich Formation

Wadleigh Limestone

St. Joseph Island Volcanics

Karheen Formation 

UNCONFORMITY

LOCAL CONFORMITY IN 

NORTHERN PART OF AREA

Heceta Limestone

Descon Formation

Contact

Approximately located; queried 

where doubtful

Fault

Dashed where approximately 

located; qite ried where doubtful; dotted where concealed

. Ml 142 

Graptolite locality

Ordovician stratigraphic position is indicated by Didymograptus protobifidus, Didymograptus sp., and Phyllograptus anna in gray siltstoiie interbedded with volcanic 

graywacke and basaltic sedimentary breccia.

The most widespread and richest graptolite faunas 

are, however, Middle Ordovician, equivalent to the 

lower Caradocian zones 9 and 10 of Elles and Wood 

(1901-18). Very large collections from this horizon,

which is well developed from the Big Salt Lake area, 

commonly have the following species:

Glossograptus spp. 

Cryptograptus tricornis 

Dicellograptus sextans 

Climacograptus bicornis 

Didymograptus sp. 

Glyplograptus teretiusculus 

Orthograptus calcaratus vars. 

Retiograptus geinitzianus

Other Middle Ordovician collections have been obtained 

from the west shore of Warm Chuck Inlet Q.5 mile south 

of triangulation station Silla, the Harmony Islands, the 

east side of Cruz Pass, and the north shore of Shinaku 

Inlet. In practically all places the fossil control has come 

from shaly partings in thin-bedded black to dark-graygreeii chert and cherty siltstoiie with minor laminated 

limestone.

A slightly higher horizon, lower Upper Ordovician, 

about Caradocian zone 13 of Elles and Wood, is indicated by collection USGS M1033-CO from tH 

north tip of Anguilla Island, which contains Orthograptus truncatus, Dicellograptus sp., and Leptograptv,s 

flaccidus, in addition to certain of the more common 

Ordovician genera listed above. About the same horizon 

is represented by Orthograptus truncatus, Lasiograptrs 

sp., and Orthoretiolitest from northeastern Noyos 

Island, locality USGS M1034-CO. The highest Ordovician graptolites occur on Esquibel Island directly 

below the earliest Silurian graptolite collections (USGS 

M1286-SD, M1287-SD, M1288-SD, Ml289-Sr, 

M1290-SD, M1138-SD, M1139-SD) described hen?. 

The association of Dicellograptus complanatus var. 

ornatus, Climacograptus hastatus, Climacograptus supernus, and Orthograptus truncatus in beds directly below 

a good Early Silurian fauna with Akidograpt-us indicates correlation with the zone of Dicellograptus ancep1? 

(D. complanatus ornatus zone of Jackson and Lenz, 

1962) at the top of the Ashgillian. The highest Ordovician graptolites, Climacograptus cf. C. hastatus, Dicellograptus complanatus?, and Orthograptus truncatus, 

were also found at locality USGS M1035-CO on the 

south shore of Heceta Island.

The exceptionally rich earliest Silurian graptolites 

described here (see also fig. 1) were collected on the 

east shore of Esquibel Island (USGS M1286-SD, 

M1287-SD, M1288-SD, M1289-SD, M1290-SD, 

M1138-SD, M1139-SD), the west shore of San Fernando Island (USGS M1140-SD), east coast of Noye? 

Island (USGS M1142-SD), and on the east shore of 

Steamboat Bay of Noyes Island (USGS M1143-SD). 

These are among the first discoveries of Early Silurian 

graptolites in western North America and are fur the:" 

described in detail in this paper.
6 EARLY SILURIAN GRAPTOLITES FROM ALASKA

The youngest known beds of the Descon Formation 

are conformably overlain by the Middle and Upper 

Silurian Heceta Limestone (Eberlein and Churkin, 

1969) 3.6 miles northwest of Point Desconocida on 

southwestern Heceta Island and on the south end of 

Two Crack Island. Thin-bedded siliceous siitstone 

with interbedded graywacke occurs approximately 

1,500 feet stratigraphically beneath the contact (loc. 

USGS M1144-SD) and contains Petalograptus cf. P. 

palmeus var. tennis, Monograptus triangiilatus predecipiens, M. sedgwickii, M. cf. co?icinmi-s or nudits, and 

M. ex gr. lobiforus. This assemblage suggests a late 

Llandoverian age about equivalent to the zone of M. 

sedgwickii (middle Early Silurian). At the south end 

of Two Crack Island (loc. USGS M1145-SD), approximately 50 feet of deformed siitstone, shale, and silty 

limestone, with thin graywacke interbeds, occurs 

beneath the Heceta Limestone. The shales contain the 

graptolites, Monograptus ex gr. M. priodon and Monograptus cf. M. elongatus,1 indicative of about the same 

position in the Llandoverian as those on southwestern 

Heceta Island.

STANDARD GRAPTOLITE ZONES FOR THE LOWER 

SILURIAN

The most complete and undeformed section of the 

lowest Silurian graptolitic shales in the British Isles is 

the Birkhill Shales of Dobb's Linn in the Moffat area 

of Scotland.

Lapworth's careful stratigraphic studies here in the 

1870's led to the establishment of the lowest Silurian 

graptolite zonal succession that with minor modification is the world standard used today. Toghill, (1965, 

1968) provides a modern description of the stratigraphy 

and graptolite succession of the Birkhill Shales of Dobb's 

Linn with special emphasis on the basal beds that 

show variations in Akidograptus and Dimorphograptus 

and their relation to Monograptus evolution. The 

Birkhill Shales have in their bas^l 20 feet a unique 

purely biserial graptolite fauna characterized by beds 

with Glyptograptus persculptus in the first 4 feet and by 

species of Akidograptus in the remaining 16 feet. The 

first Monograptus, Dimorphograptus, and Rhaphidograptus make their appearance exactly together at the base 

of the Orthograptus vesiculosus zone, 20 feet above the 

base of the Birkhill Shales. The earliest dimorphograptids in the lower 2 feet of the 0. vesiculosus zone 

have unusually long uniserial parts. Only 4 feet above 

the first monograptids the next higher zone of Monograptus cyphus is characterized by dimorphograptids 

with shorter uniserial parts such as D. confertus swanstoni and D. physophora (Toghill, 1965).

 Thecae as in elongatus, but Alaska specimens seem to be more tightly coiled.

The possible development of Monograptus by progressive lengthening of the uniserial part of Dimorphograptus is therefore inconsistent with the stra tigraphical 

succession of its earliest species, D. elongatus, which 

possesses long uniserial parts, and with several of the 

later species, for example D. confertus swanstoni and 

D. physophora, which have short uniserial parts (Bulman, 1960; Toghill, 1965, 1968). The Birkhill Shales at 

Dobb's Linn represent extremely attenuated graptolite 

zones measuring only several to tens of feet thick. 

Despite their thinness, no unsuspected stratigraphic 

breaks can be postulated on the basis of more complete 

graptolite succession known elsewhere. In fact the same 

lowest Silurian graptolite zones that are reported here 

for the first time in North America are similarly attenuated. On Esquibel Island in southeastern Alaska, for 

example, Akidograptus acuminatus lies only about 7 

feet above highest Ordoviciaii graptolites *vnd only 6 

or less feet stratigraphically below a good Orthograptus 

vesiculosus zone fauna. The first Monograptus occurs together with vesiculosus only a few feet higher. Another 

place in North America where graptolite zones are 

relatively thin is in the vicinity of Trail Creek, Idaho, 

where more than seven graptolite zones occur in a 

300-foot section of nearly pure shale (Churkin, 1963).

Questions concerning the placement of the Ordovician-Silurian boundary in the graptolitic shale 

sequences of North America and the succession of 

Lower Silurian graptolite faunas (across the boundary) 

must be referred to the classical Birkhill Shales which 

can then be compared with the Esquibel Island section 

described here.

The basal beds of the Birkhill Shales, tie zones of 

G. persculptus and Akidograptus acuminatus that lie 

between the highest Ordoviciaii strata (Hartfell Shales) 

with purely biserial graptolites below and strata with 

the earliest uniserial Monograptus above, could be 

included in the Ordoviciaii (Elles, 1922; Davies, 1929) 

because of their biserial graptolites. The lase of the 

Llandovery, however, was taken by Lapworth at the 

base of the Birkhill Shales to coincide with a marked 

change in lithology, thereby placing the first appearance 

of Monograptus some 20 feet above the base of the 

Silurian.

LOWER SILURIAN GRAPTOLITES IN WESTERN NORTH 

AMERICA

Silurian graptolifces in western North America are 

known largely from the dark shales formed in parts of 

the Cordilleran geosyncline from California and Nevada 

in the south to British Columbia, southeastern Alaska, 

and southern Yukon Territory on the north (fig. 2). 

Another belt with graptolitic shales, the Franklinian 

geosyncline, is exposed in the Canadian Arctic Islands
LOWER SILURIAN GRAPTOLITES IN WESTERN NORTH AMERICA

(fig. 2). In east-central Alaska and parts of northern 

Yukon Territory, Silurian graptolites are known from 

the thin shales of the Yukon shelf and from thicker 

shale sections in the Richardson Basin. Despite the

rather extensive distribution of Silurian graptolitic 

shales and an even better known development of 

Ordovician graptolitic shales, especially in the Cordilleran geosyncline, no succession of graptolites across the

120°E 100°E 80°E

120°W 100°W

FIGUEE 2. Silurian graptolite localities of western North America and the Arctic region. 1. Prince of Wales Island area, 

southeastern Alaska (this paper). 2. Yukon River, east-central Alaska (Churkiii and Brabb, 1965). 3. Porcupine River, 

east-central Alaska (Churkin and Brabb, 1967). 4. Richardson 

Mountains, Yukon Territory (Jackson and Lenz, 1962). 5. 

Melville Island (Tozer and Thorsteinsson, 1964). 6. Bathurst 

Island (Thorsteinsson and Glenister, p. 589, and McLaren, 

p. 601, in Fortier and others, 1963). 7. Cornwallis Island 

(Thorsteinsson, 1958). 8. Ellesmere and Axel Heiberg Island 

(J. W. Kerr and H. P. Trettin, written communs., 1968). 

9. Pelly River area, Yukon Territory (Wheeler and others, 

1960a, b). 10. South Nahanni River area, Northwest Territory

80°W

(Lenz and Jackson, 1964). 11. Northern Rocky Mountains, 

northeastern British Columbia (Jackson and others, 1965). 

12. Rocky Mountains, southeastern British Columbia (Walcott, 1924; Walker, 1926). 13. Trail Creek, central Ida.ho 

(Churkin, 1963). 14. Nevada: northeastern (Churkin and Kay, 

1967); central (Gilluly and Masursky, 1965; Kay and Crawford, 1964). 15. Klamath Mountains, Calif. (Churkin, 1965). 

16. Kolyma Massif, northeastern U.S.S.R. (Obut and others, 

1967). 17. Taimyr Peninsula (Obut and others, 1965). 18. 

Birkhill Shales, Scotland (Toghill, 1968). 19. Chukotsk Peninsula (A. M. Obut, oral commun., 1967). 20. Sweden (Tornquist, 

1899).
EARLY SILURIAN GRAPTOLITES FROM ALASKA

Ordovician-Siluriaii boundary has been reported anywhere in North America. This apparent absence of 

lowest Silurian graptolite faunas coincides with an 

unconformity above the highest Ordoviciaii zone of 

Dicellograptus complanatus ornatus in northern British 

Columbia (Jackson and others, 1965). However, in 

east-central Alaska (Churkin and Brabb, 1965) and 

in northern Yukon Territory (Jackson and Lenz, 1962; 

Lenz and Churkin, 1966) nongraptolitic and in places 

largely covered intervals of shale separate the D. complanatus ornatus zone from middle and upper Llandoverian graptolites (fig. 3).

Probably more graptolite localities of widely varying 

age are known in the Great Basin (Iocs. 13 and 14, 

fig. 2) than in any other comparable area in North 

America. However, because of intense structural deformation, details of the stratigraphy in the graptolite 

shale and chert facies are known only in local areas. 

In the Toquima Range area of central Nevada (Kay 

and Crawford, 1964), there seems to be an unconformity separating Ordovician rocks from Silurian, 

whereas at Trail Creek, Idaho, the boundary falls in 

a small covered interval with no sign of a stratigraphic 

break (Churkin, 1963).

The oldest Silurian graptolite collection in the Great 

Basin was recently made from large slabs of slate in 

a mine dump in northeastern Nevada (Kerr, 1962). 

Most of the species are found together on the individual 

rock slabs. This distribution indicates that only a single 

fossil horizon was mined. These beautifully preserved, 

three-dimensional pyritized specimens were re-collected 

and a more extensive fossil list was published (Churkin 

and Kay, 1967, p. 663). The graptolite assemblages 

found together on individual rock slabs are characterized by coiled monograptids that indicate correlation 

with the interval of the zone of Monograptus gregarius

to M. convolutus of middle Llandoverian age. The 

revised fossil list given in table 1 is the result of reexamination of the material reported in Churkin and Kay 

and comparison with the new Alaskan graptolites 

described in this paper. Several of these pyritized 

specimens are also formally described and illustrated 

for the first time in this paper.

The new graptolite collections (USGS M1286-SD, 

M1287-SD, M1288-SD, M1289-SD, M1290-SD, 

M1138-SD, M1139-SD, and M1141-SD) from southeastern Alaska described in this paper represent the 

oldest Silurian graptolite faunas known in North 

America (Table 2). Akidograptus acuminatus in collections USGS M1286-SD, M1287-SD, M1141-SD, and 

M1139-SD indicates correlation with the zone of 

Akidograptus acuminatus, virtually the lowest graptolite zone in the standard graptolite succession of the 

British Isles. In Great Britain the zone of Glyptograptus 

persculptus has been recognized below the Akidograptus 

zone and the Ordovician-Silurian boundary has been 

drawn at the base of the G. persculptus zone (Toghill, 

1968). The G. persculptus beds, however, ar-* only 3.5 

feet thick, and the fauna is not as readily distinguished 

as is the Akidograptus zone fauna. Nevertheless, G. 

persculptus was found in the Esquibel Island section 

in several feet of beds separating the Akidograptus 

acuminatus zone from the highest Ordovicim graptolites of the Dicellograptus anceps zone (Churkin and 

others, 1969). Akidograptus in the Alaskan collections 

is associated only with biserial graptolites as it is in 

the Birkhill Shales of Scotland. The presence of Dimorphograptus, Orthograptus vesiculosus, and several 

species of Monograptus including M. cyphus together 

with Akidograptus in collection USGS M1139-SD 

suggested that this original collection, made only over 

an interval of some 10 feet, is a mixture of several

TABLE 1. Partial list of graptolites from northeastern Nevada showing British ranges and associations on single tal'.ts slabs.

[Range in Toghill (1965) ; Range in Elles and Wood (1901-18) ------J

Glyptograptus kayi n. sp 2 _ _

tamariscus _ __

Monograptus cf. M. denticulatus

hamatus n. sp 2

cf . M. jaculum _ _ _

kerri n. sp 2 _ _

lobiferous 2 __

cf.M.millepeda..-

cf. M. nobilis

Rastrites sp _

Zonei

16 17 18 19 20 21 22 1

V

______ X

__ X

______ ........................ x

......

..___. X

______ X

v

______ X

11, 12

X

v

X

X

X

X

X

X

X

Slab No.

13, 14

X

v

X

X

X

X

X

v

66

v

X

X

X

X

X

X

X

57,68

v

X

X

X

X

X

X

X

X

1 Zone 16, A. acuminatus zone; 17, O. vesiculosus zone; 18, M. cyphus zone; 19. M. gregarius zone; 20, M. cmvolutus zone; 21, M. sedgwicki zone; 22, R. maximus zone. 2 Described in this paper.
o

o

g g S ;.;': ;;. g v.'-; g v .;-:-;.- . g . g

,....,1,1,1,1,1.1,1.1,1,1 Vi'i'i i n n'l'i'n'i 

.1. i. i, 11111 -1 -1 -1.11. ii i!i!iHili!i!i!i!i!i!i!i!i!i!i!i!i!i!i!i!Ti!i!i!i!i!i i!i!i!i!ili!i!i!i!i!i,i!i i!i,i!i!u!i!

ilVJiiliSVlVlS'lVl'lllllS'lSlR^dRi^erFormU i!i! iii !!i!i i!i!i i' i' l I r i i' i I I i t i i i i i t' i' i i' i i i r i I I r I I I i I I I r I' I I I' Koad Kiver p ormai

i i i i 11 i i i i i i i i i i i i i i i i 11 i i 11 i 11 11 i i 11 i i i i i i i i i i i i IJ,°TI;I I?i,i,u i
10 EARLY SILURIAN GRAPTOLITES FROM ALASKA

graptolite ^zoiies. A careful examination of the shale 

slabs on which Akidograptus occurs did not reveal any 

monograptids or biserial graptolite species characteristic of any zone above that of A. acuminatus. Collection 

USGS M1138-SD, which contains a somewhat different fauna, was made only 10 feet above M1139-SD 

(fig. 4). Thus the cherty black shale section here represents several extremely attenuated graptolite zones 

not unlike those in the Birkhill Shales of Scotland.

The association of the biserial genera, Climacograptus, 

Pseudoclimacograptus, Diplograptm, Glyptograptus, and 

Orthograptus together with Dimorphograptus and Monograptus in collection USGS M1138-SD implies correlation with zone (18) of Monograptus cyphus of Lapworth

TABLE 2. Silurian graptolite faunas from Prince of Wales Island area, Alaska 

[Frequency: a, abundant; c, common; f, frequent; r, rare]

QQQQf-lQQQQQ oacQOQoaoaoaoaoaoaoa

aooooBooojcoco-*-*-*

. ««««?».-<,-<,-<Wrl,-<

Genus and species SSSSSSSSSS

oacQoacQoaoaoaoaoaoa 

0000000000 

oacQoawoaoaoaoQoaoa

pppppppppp

Climacograptus indivisus esquibelensis n. subsp___-____________-_____-______-------------------------- r ----------------

-Vmo.a.us Nicholson_________________________________________________-----.-----_------ f ---- c f ____________

obesus 11. subsp_______________________________________________-----_--------------------- r ----------------

cf. C. werfz'ws Tornquist-__________________________________________________ c c c ________ r c ____ c ____

medius brevicaudatus n. subsp_-___________________________________--_--_--------------------------------------- &

minutus? Carmthers________-____________________________________-_-------------------------- r ----------------

cf. C. rectangularis (M'Coy)____-___________________________________--------------------------- c r ________ r

rectangularis abbreviatus n. subsp__________________________________-_-_------------------------- r f ____________

scalaris (Hisinger) ________________________________________________--_-_--.------------ a c? a a ____________

stenotelus n. sp_________________________________________________________---------.-------------------- c ________

frz7_.Vs Manck__ _________________________________________________________ f -_____-------___---_ r _--________-

Pseudoclimacograptus (Metaclimaccgraptus) hughesi (Nicholson) _______________----------------- f __-- f r ____________

cf. P. (M.} undulatus (Kurck)___________-__________________________----------------------------------- c ________

Diplograptus elongatus n. sp__________________________________________________--------------------- f _-__-----____---

modestus var. dz'm inutus Elles and Wood_______________________________--_------ r r? -_-___--__--_-______ a ___.

mucroterminatus n. sp.____________________________________________-__-_--------_------------------------------ c

n. sp___________________________________________________________________--------------_----- r __________--_-_-

n. sp____________________________ __ ___ _ ________ _____________-_-___---------------_----- r ______---______-

Glyptograptus cf. G. enodis var. enodis Packham________________________________---------- f? -------- r _______--._____--

cf. G. enodis var. lotus Packham______________________________________-_-_-__------------------------------_---. a

gnomus n. sp____________________________________________J______________-------------------__ r ________________

incertus Elles and Wood,________________________________________--__-___-------_-------____-- f __--___-_____---

laciniosus n. sp __________________________________________________________________________________ a ____ r f

lanpherei 11. sp___________________________________________________________________________________ f ____________

tamariscus magnus n. subsp______________________________________-_---_----_______--____-__--- f r ____________

cf. G. tamariscus tamariscus (Nicholson) ___________________________-______---_--___--_----_____---__-_-- f r? r

?n. sp._____________________________________________________________________________________________________ r

Orthograptus bellulus Tornquist__-_-_______-____________________________-_-__----_----_--__---_-_--__-_______------ r

eberleini n. sp _______________________________________________________________________________ r r ____________

insectiformis minutus n. subsp_________________________________________________________________________ r ____ r

cf. O. mutabilis Elles and Wood________________________________________________________________ r _______-____-_-.

vesiculosus Nicholson____________ _____________ ___ __ _____ ______________ ______ f c c a r ____________

? n. sp.______.__________________________________________________________ a f ____--_-_-______ f ____-_----_.

Petalograptus minor Elles__________________________________________________________________________________________ f

palmeus (Barrande)__________________________________________________________________________________ f ________

Dimorphograptus confertus swanstoni (Lapworth) _____________________________________________ f ____ c r ____________

physophora alaskensis n. subsp_____________________________________________________________ r r ________________

Akidograptus acuminatus (Nicholson)___________________________________________ f r? ________________ r ____ f ___.

Monograptus acinaces T6rnquist___________________________________________________________ f c f r ____________

atavus Jones________________________________________________________________________________ f r ________ ?r

buddingtoni 11. sp____________________________________________________________________________________ f ________

calamistratus n. sp ___________________________________________________________________________________________ c

cf. M. crenularis Lapworth___ ________________________________________________________________________ a ______--

cyphus Lapworth,___________________________________________________________________ r? ____ r r ________ r

cf. M. difformis T6rnquist__ __________________________________________________________________________________ r

gregarius Lapworth__________________________________________________________________________________________ c

cf. M. incommodus Tornquist-_________________________________________________________ f ____ f r ____________

noyesensis n. sp______________________________________________________________________________________________ a

revolutus Kurck_____________________________________________________________________________________________ f

tenuis (Portlock) ____________________________________________________________________________ a

aff. M. undulatus Elles and Wood_____________________________________________________________ _________ f ________

Rastrites cf. R. longispinus (Perner) ________________________________________________________________________________ r

orbitus n. sp__________________________________________________________________ ________ ____ ____________ f

aff. R. peregrinus (Barrande) __________________________________________________________________________ f
LOWER SILURIAN GRAPTOLITES IN WESTERN NORTH AMERICA 11

g

01

VI

SILURI

^

^J

0

o

o

05

O

01 .2

0)

VI

sverian

c

a

01

Zone

- -

Monograptus 

cyphus

Orthograptus 

vesiculosus

Akidograptus

acuminatus

Dicellograptus 

anceps

FE

170 

160

140

120

100 

Mean 

high 

tide

on

60

40

20

n

'.El

~^

-

-

Heavy forest cover 

at top of bluff

A x~ /"^/

/V^Y-;^7-

.&° ' ? : %' 

. ' -C^1 ' " . °. .

' -p'"-^ ? ' ' 

^ r^-o /> '- 

 " U. - .. 

v ° ry £? -'

. "£> ' ^>". ° o ." -

SfeSiSiSi

 ~j

.==> c== CZ^ = 

=<*Ijf*;' * *

 -__ ^^ ~ ^^^ o J^ y

^M®^t:®@

 ' * 

 ~ ~r~. 

_^-_^ _ _^- _= 

zr^Z^EH-^Z-^ET-^

~ ~

 L _- 

 

. ~r^^~r~. . rr~rv. : " 

* Q ° ° . °

 ~ ~

Sedimentary breccia rich in volcanic detritus; forms 

small bluff. Potassium-argon isotope dating of 

detrital hornblende in progress

Diabase dike

-N

M1290 Orthograptus vesiculosus, Monograptus acinaees 

M1289 0. vesiculosus, Pseudoclimacograptus hughesi, 

Dimorphog raptus confertus swa nstoni,

M1288 Orthograptus vesiculosus

M1287 Akidograptus (?) 

M1286 Akidograptus acuminatus, Climacograptus trifilis >

Lithic, crystal tuff with some siliceous pebbles 

Climacograptus spp. 

Climacograptus supernus, Orthograptus truncatus n. var. 

'Climacograptus supernus, Orthograptus truncatus cf. var. pauperatus 

C. supernus, O. truncatus ef. var. pauperatus, Dicellograptus complanatus 

ornatus, Climacograptus hastatus 

O. truncatus cf. var. pauperatus 

Dicellograptus complanatus ornatus, Climacograptus supernus, 

Orthograptus truncatus cf. var. pauperatus

Graywacke, siltstone, and rare argillaceous interbeds, (nonfossiliferous) cross laminated

Siltstone and siliceous mudstone; very thin interbeds

of graywacke

Chert-rich graywaeke

Siliceous mudstone and siltstone; convolute bedding

USGS 

Mi 139

Wave- cut terrace exposing 

very thin bedded, ehert7 

shale with graptoliterich shale partings; rar° 

Vt in. to % in. thick graywacke interbeds

Covered in beach that separates 150 + ft of 

graywacke and graywacke conglomerate 

exposed in small island (at high tide) 

farther down section

FIGURE 4, Succession of graptolite localities across the Ordovician-Silurian boundary; east shore Esquibel Island, southeastern

Alaska.
12 EARLY SILURIAN GRAPTOLITES FROM ALASKA

(Elles and Wood, 1901-18) and the identically named 

zone of Toghill (1968). The presence of Dimorphograptus confertus swanstoni and a variety of D. 

physophora, both easily recognizable forms characteristic of the cyphus zone, further supports this 

correlation. Although the overall aspect of the fauna 

is definitely most like that of the Birkhill's M. cyphus 

zone, individual species listed below, most of which 

are difficult to identify, are found elsewhere only in 

the overlying zone of Monograptus gregarius and 

higher:

Climacograptus scalaris 

Glyptograptus cf. G. enodis var. enodis 

Glyptograptus incertus 

Monograptus tennis

On the other hand, Orthograptus vesiculosus, easily 

recognized by the conspicuous vane structure (Jones 

and Kickards, 1967), is the guide to the underlying 0. 

vesiculosus zone but is also known from the M. cyphus 

zone in the Birkhill Shales (Toghill, 1968). In Yukon 

Territory, Canada (Jackson and Lenz, 1962), and in 

the Kolyma Massif region of northeastern U.S.S.R. 

(Obut and others, 1967), Orthograptus vesiculosus 

occurs biostratigraphically higher and in association 

with Dimorphograptus ex gr. D. confertus as it does in 

Alaska.

The graptolite collections (USGS M1138-SD and 

M1139-SD) from Esquibel Island were found during 

a rapid reconnaissance of the area. The original collecting was done during high tide from two approximately 

10-foot-thick intervals of graptolitic shale. Although 

the early Silurian age of the graptolites was realized 

during the time of collecting, the presence of several 

extremely thin graptolite zones over the interval 

collected was not appreciated until the faunas were 

studied in the laboratory. In 1968, Churkin returned 

to Esquibel Island to check the interpretation that 

collection USGS M1139-SD is a mixture of Akidograptus acuminatus and Orthograptus vesiculosus zones 

and to search for graptolites of Ordovician age at the 

base of the section. Accordingly, the entire section 

was re-collected bed by bed. More than 15 stratigraphically separate graptolite collections were made. 

This more detailed examination proves that Akidograptus in the Esquibel Island section occurs together 

only with biserial graptolites as it does in collection 

USGS M1141-SD from Noyes Island and in the 

British Isles. Orthograptus vesiculosus, the guide to the 

next higher graptolite zone, lies 3 feet above the highest 

occurrence of Akidograptus. Beds rich in species of 

Monograptus and Dimorphograptus are still stratigraphically higher in the section. Not only was it possible 

to stratigraphically follow the same faunal succession 

as in the standard Akidograptus acuminatus, Orthograptus vesiculosus, and Monograptus cyphus zones but 

in the underlying few feet of beds, exposed only at 

low tide, graptolites of the highest Ordovician zone of 

Dicellograptus anceps were found. The position of the 

Silurian-Ordovician boundary and the exr^t stratigraphic position of key graptolite species based on 

this new data is shown in figure 4. The main Silurian 

species identified at each locality are listed in table 2. 

A detailed account of the Ordovician species and a 

discussion of the Ordoviciaii-Siluriaii boundary is being 

separately prepared (Churkin and others, 19^9).

Slightly younger Silurian graptolites from the upper 

part of the Descoii Formation are represented by collection USGS M1142-SD from Noyes Islard and by 

collection USGS M1140-SD (fig. 5) from San Fernando 

Island. In collection USGS M1142-SD (table 2) the 

common occurrence of Monograptus together with 

abundant species of the biserial genera Climacograptus, Diplograptus, Glyptograptus, and Orthograptus implies in itself a position in the Llandovery 

equivalent to the vesiculosus zone (lower Llandovery) 

or higher.

The presence of species of Petalograptus and Rastrites 

further restricts the age of collection USGS M1142-SD 

to the next higher zone of Monograptus gregarius or 

younger. Finally, numerous specimens of M. gregarius 

in association with M. revolutus, M. cf. M. ctavus and 

a new variety of Orthograptus insectiformis implies 

correlation with the zone of M. gregarius.

FEET

75 -|

50 -

25 -

0

Covered by water

Volcanic graywacke, cross laminated; some basalt boulders; 

forms small bluff

 USGS M1140SD

Thinly interbedded graptolitic 

shale and siltstone; lower 

part covered at high tide

FIGURE 5. Lower Silurian graptolite locality (USGS 

M1140-SD) about 800 feet northwest of Sword Point on 

the southwest shore of San Fernando Island, southeastern 

Alaska.

Graptolite collection USGS M1140-SD (table 2; 

and fig. 5) is an assemblage similar to USGS Ml 142- 

SD, but USGS M1140-SD has Pseudoclimacograptus 

cf. P. extremus, Monograptus cf. M. crenularis, and 

M. aft'. M. undulatus that suggest the slightly younger 

horizon of the zone of Monograptus convolutus. Collection USGS M1140-SD is provisionally assigned to 

the interval between the upper part of the M. gregarius 

zone and the lower part of the M. convolutus zone.
SYSTEMATIC DESCRIPTIONS 13

SYSTEMATIC DESCRIPTIONS 2

Class GRAPTOLITHINA

Order GRAPTOLOIDEA

Family DIPLOGRAPTIDAE

Subfamily CLIMACOGRAPTINAE

Genus CLIMACOGRAPTUS Hall, 1865

Climacograptus Hall. Bulman, 1955, Geol. Soc. America, treatise 

on invertebrate paleontology, pt. V, p. V85, fig. 63, la-dRhabdosome biserial, scandent. Thecae with angular 

sigmoidal curvature, so that ventral wall is nearly 

parallel to axis of rhabdosome and apertures are 

situated in narrow excavations. Lower Ordovician to 

Lower Silurian, worldwide.

Climacograptus indivisus esquibelensis n. subsp. 

Text figure QA; plate 1, figure 1

Description. According to Waern (in Waern and 

others, 1948, p. 456-457), the rhabdosome of C. indivisus is slender and straight, without a visible septum. 

It widens from an initial width of 0.6-0.7 mm to a 

maximum of 1.0-1.1 mm at theca 6 which is thereafter 

maintained. The virgella can attain a considerable 

length (2.8 mm) and is forked at a distance of approximately 1 mm from the aperture of the sicula. The two 

branches form an angle of 40°-60° with each other. 

Thecae number 11 per centimeter.

The Alaskan form is similar to G. indivisus in general 

appearance. It differs by (1) being wider distally, 

1.6-1.9 mm (this could be due partly to flattening), (2) 

having a distinctly tapering appearance, (3) having a 

longer virgella, and (4) having a smaller angle of divergence between the two branches of the virgella.

Discussion. The extremely long virgella is very 

distinctive. On the best specimen (fig. QA; and pi. 1, 

fig. 1), the virgella is 16 mm long, and it forks approximately 3 mm below the aperture of the sicula. The two 

branches are more or less parallel, and one of the 

branches has apparently forked about 8 mm below the 

first fork. The virgella of the second specimen is broken 

off so that it only measures 5.0 mm. It forks 1.2 mm 

below the sicular aperture, and the angle between 

branches is approximately 15°.

The Alaskan specimens resemble Rhaphidograptus 

toernguisti in having a slender proximal end but differ 

from it by having theca I 2 present and not missing as 

in Rhaphidograptus. They also resemble C. medius but 

differ by being wider and having a split virgella.

2 Buhnan's (1955) terminology and classification have been used in the following 

descriptions.

Occurrence. Ml 138-SD.

Range. C. indivisus occurs in the lower part of the 

zone of Akidograptus acuminatus at Kinnekulle, Sweden 

(Waern, in Waern and others, 1948, p. 456-457), 

and in the zone of Glyptograptus persculptus in Great 

Britain (Davies, 1929). The Alaskan variety occurs 

considerably higher in the zone of Monograptus cyphus 

(table 3).

FIGURE 6. Climacograptus. A, C. indivisus esquibelensis n. subsp., holotype (USNM 161604) 

(same as pi. 1, fig. 1), X 4. B, C. innotatus Nicholson (USNM 161606), X 5. C, C. minutusf Carruthers (USNM 161627) (same as pi. 1, fig. 6), 

X 5. D, E, C. innotatus obesus n. subsp. D, Holotype (USNM 161611) with spines broken off, 

showing sicula, X 5. E, (USNM 161610) X 5. 

F, C. cf. C. medius Tornquist (USNM 161614), 

X 5.

Dimensions (in millimeters).-

Length of 

Specimen No. rhabdosome *

USNM-161604 2 __ >15 

161605 - >13. 7

Width Thecae Length

Theca 1 1 Maximum centimeter virge^a

0. 7 1. 6 10 16 

.6 1. 9 11 3 5

i Exclusive of virgella length. 

2 Figured specimen. 

3 Broken.

369-097 O - 70 - 3
14 EARLY SILURIAN GRAPTOLITES FROM ALASKA

TABLE 3. Lower Silurian graptolites of Alaska and Nevada showing a comparison of their zonal ranges to the same or similar species in

Canada, Great Britain, and the Soviet Arctic

Data largely from: Elles and Wood (1901-18); Toghill (196 

Bondarev (1965), Obut, Sobolevskaya and Nikolaiyev(1967)

Genus and species

Climacograptus 

indivisus esquibelensis n. subsp.1 

in nota tus Nicholson

obesus n. subsp. 

cf. C. merfn/.s'Tdrnquist

medius brevicaudatus n. subsp. 

minutus ? Carruthers 

cf. C. rectangularis (M'Coy)

rectangularis abbreviatus n. subsp. 

scalaris (Hisinger)

stenotelus n. sp.

Pseudoclimacograptus (Metaclimacograptux ) 

hughesi (Nicholson)

cf. P. (M.) undulatus (Kurck)

Diplogmptus 

elongatus n. sp. 

modest us var. dir.iinutus Elles and Wood

m ucmterm inatus n. sp. 

n. sp. A 

n. sp. B

Glyptograptus 

cf. G. enodis var. enotliH Packham 

cf. G. enodis var. latux Packham 

gnomus n. sp. 

incertus Elles and Wood 

kayi n. sp. 

laciniosus n. sp.

lanpherei n. sp. 

tamariscus magnus n. subsp. 

cf. G. tamariscus tamariscus (Nicholson) 

? n. sp.

8), Jacks 

Russiai

Illustrations

Plate; 

figure

i;i 

1;2

1;3 

1;4,5

1;12 

1;6 

l;7-9

1;15 

1; 10, 11

1; 13, 14

1; 16, 17 

1;18

1;19,20 

2; 19

1;21

2;1

2; 2 

2; 3, 4 

2; 16 

2; 5, 6 

2; 15 

2; 17, 18

2; 9, 10

2; 7, 8

Text 

figure

6A 

65

&D,E 

&F

ID 

6C

TA, B

8C 

7C

SA.B

SE 

BD

9C,Z> 

10G

94, B 

9E,F

WA 

105, C 

UE,F 

IOD,E 

12E,F

no 

nc

11A,B 

10F 

12Z?

on and Lenz (1%2), Thorsteinsson (1958), Packham (1962), Obut, Sobolevskaya, and

USGS

Collection 

No.

M1138 

M1138, M1139 

M1289 

M1138 

M1138.M1139 

M1141.M1286 

M1287.M1288 

M1142 

M1138 

M1138.M1139, 

M1142 

M1138,M1139 

M1138, M1139 

M1289,M1290(?> 

M1140

M1138, M.1139, 

Nev.,M1289 

M1140

M1138 

M1141.M1287 

M1288 (?) 

M1142 

M1138 

M1138

M1138,M1288(?) 

M1142 

M1138 

M1138 

Nevada 

M1139.M1141, 

M1142 

M1139 

M1138.M1139 

M1140, M1142 

M1142

"I"-! .2 S S w j= * « Sw S 

g -tle ^« ^2 "S-§ « § US |s f i |l S^ g^ g | g| |-| -c.|

Mil I-i II |r |l l-i If 0 ^ § J$ | |*> |8 II ^§

_ _ _ _ _ . _ . _

?

__._.__.__..

 

?______?

______

JRanges of new subspecies are compared with ranges for the old species

Material. Two compressed, somewhat poorly preserved specimens. Named after Esquibel Island, 

Alexander Archipelago, Alaska.

Holotype. USNM 161604.

Climacograptus innotatus Nicholson 

Text figure 6B; plate 1, figure 2

Climacograptus innotatus Nicholson. Elles and Wood, 1901-18, 

Mon. British Graptolites, Palaeontographical Soc., 

p. 212-213, text fig. 143, pi. 27, fig. lOa-e.

Climacograptus innotatus Nicholson. Hundt, 1924, Grapt. d. 

deutsch. Silurs, p. 57, pi. 1, figs, 5-7.

Discussion. The specimens under study he.ve more 

closely set thecae (16-18 thecae per centimeter) than 

those described by Elles and Wood (1901-18).

Occurrence. M1138-SD, M1139-SD, M1289-SD.

Range. Llandoverian zones (17 and 18) of Orthograptus vesiculosus and Monograptus cyphus (Birkhill 

Shales) in Great Britain (Toghill, 1968). Lower
SYSTEMATIC DESCRIPTIONS 15

TABLE 3. Lower Silurian graptolites of Alaska and Nevada showing a comparison of their zonal ranges to the same or similar species in

Canada, Great hritain, and the Soviet Arctic Continued

Genus and species

Orthograptus 

bellulus Tflrnquist 

eberleini n. sp. 

insectiformis minutus n. subsp. 

cf . 0. mutabilis Elles and Wood 

vesiculosus Nicholson

1 n. sp.

Petalograptus 

m inar Elles 

pal me us (Barrande) 

var. ten u is Barrande

Dimorphograptus 

confertus swanstoni (Lapworth)

physophora alaskensis n. subsp. 

Akidograptus acuminatus (Nicholson)

Monograptus 

atinaces Tornquist

argutus Lapworth 

atavus Jones

buddingtoni n. sp. 

calamistratus n. sp. 

cf. M. crenularis Lapworth

cyphus Lapworth

cf. M. difformis Tornquist 

gregarius Lapworth 

hamatus n. sp. 

cf. M. incommodus Tornquist

kerri n. sp. 

lobiferus (M'Coy) 

noyesensis n. sp. 

revolutus Kurck 

tennis (Portlock) 

aff. M. undulatus Elles and Wood

Rastrites 

cf . R. longispinus (Perner) 

orbitus n. sp. 

aff. R. peregrinus (Barrande)

Illustrations

Plate; 

figure

3;1 

3; 2

2; 14 

2; 11-13

3; 4

3; 5 

3; 6 

3; 3

3; 8 10

3; 7 

3; 16, 17

3

1O 1C

4; 16 

3; 11

4; 7, 8 

4; 12 

3; 18,23- 

25 

4; 5, 6

3; 22 

4;1 

4; 15 

3; 20

4; 11 

3; 12, 21 

4; 9, 10 

3; 19 

4; 2, 3 

4; 4

4; 17 

4; 18, 19 

4; 13, 14

Text 

figure

12G 

12A,B 

12C, H, I

13Z>

1%E,F 

13G 

13,4

UC,D 

IBH,I

13B, C

14A

UB 

UE

15D,E 

15A-C

16 A, B, 

D,E

16F

ISE 

16C 

11D,E 

ISA

17F

18G 

18Z> 

18B,C, F

19C 

19 A, B

USGS

Collection 

No.

M1142 

M1138.M1139 

M1140.M1142 

Ml 138 

M1138, M1139 

M1288.M1289 

M1290 

M1139.M1286 

M1287

M1142 

M1140 

Nevada

M 1138, M 1139, 

M1289 

M1138, M1290

M1139, M1141 

M1286,M1287(?)

M1138,M1139, 

M1289.M1290 

Nevada 

M1138.M1139 

M1142 (?) 

Ml 140 

Ml 142 

Ml 140

M1138, M1139 

M1142,M1289(?) 

M1142 

M1142 

Nevada 

M1138.M1139 

M1289 

Nevada 

Nevada 

M1142 

M1142 

M1138 

Ml 140

M1142 

M1142 

M1140

.§ 2 05 05 00 05 05 05

a,.g j| g s 05 _s _s w j| 05 _s.w

^ ^l-'s ^ » » £ ! § ^-S ^"S -i ^ §> s ? 1 e ,3 e= S £ eg e.^ -tsg 0 S k.-5 * ^ ^"^ lie * *s * 5 *- .S ill! 11 1 5 !| fi !l IS

o ^8 $« | S°" j 8 I s WS

 . . . 

____

.._.._.._

 

.. _ ___ _

-- = - - 

"

Keilorian (lower) Llandovery in Australia (Thomas, 

1960). Also reported in the zone of Demirastrites 

triangulatus from Bohemia, Czechoslovakia, by Pribyl 

(1948). Varieties reported from the following formations 

in North America: Road River Formation, Yukon 

Territory, Canada, in Ashgillian zone of Dicellograptus

complanatus var. ornatus (Jackson and Lenz, 1962); 

Phi Kappa Formation, Trail Creek, Idaho, in Caradocian zones (12 and 13) of Dicranograptus clingani 

and Pleurograptus linearis (Churkin, 1963); Williamsburg, Ohio, (Fail-mount Limestone Member of the 

Fairview Formation) (Ruedemann, 1947).
16 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Dimensions (in millimeters) . 

Specimen No.

USNM-161606__-----_-

161607 »____ _-

161608__-_--_--

161609g-_ ------

161609h__. _ _-

Length of 

rhabdosome

_-__ 4.5

____ 6.0

____ 5.5

____ 6.0

-___ 6.2

Width of 

rhabdosome

1.3 

1.25 

1.25 

1.2 

1.25

Thecae per 

centimeter

16 

16 

16 

17

18

i Figured specimens.

Material. About 28 compressed, well-preserved 

specimens. 

Figured specimens. USNM 161606, 161607.

Climacograptus innotatus obesus n. subsp. 

Text figure 6D, E; plate 1, figure 3

Description. The rhadbosome widens very rapidly 

from an intial width of 0.4 mm to a maximum of 1.5-2.0 

mm, at theca 4 or 5, which is thereafter maintained, 

making the margins approximately parallel. The thecae 

are like those of C. innotatus, numbering 15-16 per 

centimenter. The sicula is 1.6 mm long with a virgella 

as much as 1.4 mm long. The apex of the sicula extends 

to the level of the aperture of theca 22 .

Discussion. The features that distinguish this subspecies from C. innotatus are its greater width and its 

more sharply tapering proximal end.

Occurrence. Ml 138-SD.

Range. Zone of M. cyphus in Alaska.

Dimensions (in millimeters). 

Length of

usNM-161610 L161611 1__

161612--.

161613 L_

some

3.

5.

5.

5.

5

0

9

5

Theca H

0.8

.8

.9

.8

Width

Theca 4i

1.

1.

1.

1.

7

6

75

5

Maximum

1.

1.

2.

1.

7

7

0

6

Thecae

meter

15

16

16

16

i Figured specimens.

Material. About six compressed, well-preserved 

specimens. Named after Latin "obesus"=fat, corpulent. 

Figured specimens. USNM 161610, 161611, 161613. 

Holotype ISNM 161611.

Glim icograptus cf. C. medius Tbrnquist 

Tr-xt figure 6F; plate 1, figures 4, 5

Climacograptus -nedius Tornquist. Elles and Wood, 1901-18,

Mon. British Graptolites, Palaeontographical Soc.,

p. 189-1J 0, text fig. 122, pi. 26, fig. 4a-f. 

Climacograptus medius Tornquist. Hundt, 1924, Grapt. d.

deutsch. Silurs, p. 56, pi. 1, figs. 22, 23, 35, 36. 

Climacograptus medius Tornquist. Sun, 1933, Palaeont. Sinica,

ser. B, v. 14, pt. 1, p. 23, pi. 4, fig. 2a, b. 

Climacograptus medius Tornquist. Obut, 1949, Polyevoi Atlas,

Rukovodyashchich graptolitov vyerkhnyevo Silura Kirgizskoi SSR, p. 13, pi. 1, fig. 3a, b.

Climacograptus medius Tornquist. Stein, 1965, Nenes Jahrb. 

Geologie u. Palaontologie Abh., p. 163-16f. text fig. 

16a-g.

Discussion. In the general shape of the rhabdosome, 

character and number of thecae, and long virgella, 

our specimens closely resemble C. medius and Rhaphidograptus toernguisti. The Alaskan species is, however, 

narrower (maximum width 1.8 mm) than either C. 

medius (maximum width 2.5 mm) or R. toernguisti 

(maximum width 2.0 mm). In addition, tHca I2 is 

characteristically missing in R. toernguisti but is present 

in our specimens.

Occurrence. Ml 138-SD, M1139-SD, M1141-SD, 

M1286-SD, M1287-SD, M1288-SD.

Range. Llandoverian zones (16-18) of Glyptograptus 

persculptus to M. cyphus (Birkhill Shales) in Great 

Britain (Toghill, 1968). Llandoverian zor°s of G. 

persculptus to M. cyphus in the Frankenwald (northeast 

Bavaria) (Stein, 1965). Llandoverian zones of Demirastrites pectinatus to D. triangulatus in Bohemia, 

Czechoslovakia (Pribyl, 1948). Also reported from 

Malaya (Kobayashi and others, 1964) and CHna (Sun, 

1933).

Dimensions (in millimeters). 

USNM--161614 2

161615 2

161616-

161617-

161619 

161618 2

161620-

Length

rhabdo- Theca

some i I1

14 07

23

15

21

11.5

28

19.5

5

9

6

5

5

6

Width

Theca Maxi51 mum

1.

1.

1.

1.

1.

1.

1.

1

2

5

1

0

0

3

1.

1.

1.

1.

1.

1.

1.

25

5

8

5

1

4

6

Tt ecae Length

crnti- virgella

m^ter

12

11

11

11

11

10-11

10-11

2.

9.

5.

6.

1.

1.

2.

6

7

0

0

8

9

2

' Exclusive of virgella length. 

2 Figured specimens.

Material. Approximately 15 compressed, moderately well preserved specimens, some of which are 

fragmentary.

Figured specimens. USNM 161614, 161615, 161618.

Climacograptus medius brevicaudatus n. sulsp. 

Text figure ID] plate 1, figure 12

Description. The rhabdosome is as much as 2.5 cm 

long, widening rapidly from a width of 0.8-0.9 mm at 

the first pair of thecae to a maximum of as much as 2.3 

mm, so that it has a parallel-sided appearance for most 

of its length. The thecae number 10-11 per centimeter, 

with the free edge of the ventral wall approximately 

straight and vertical, and the apertural mrrgin horizontal. The proximal end is wide, with a short, robust 

virgella (0.5-0.6 mm long).

The rhabdosome widens rapidly and measures 1.3-1.6 

mm wide at the fifth thecal pair. It resembles C. 

medius in this respect. The excavations are rery small
SYSTEMATIC DESCRIPTIONS 17

FIGURE 7. Climacograptus. A, B, C. cf. C. rectangularis 

(M'Coy): A, (USNM 161631), X 5; B, (USNM 

161632) (same as pi. 1, fig. 8), X 5. C, C. scalaris 

(Hisinger) (USNM 161653), X 5. D, C. medius 

brevicaudatus n. subsp., holotype (USNM 161621) 

(same as pi. 1, fig. 12), X 5.

in the proximal part, occupying less than a fifth of the 

width of the rhabdosome. They increase in depth 

distally to about a third of the width of the rhabdosome.

Discussion. This form resembles C. medius very 

closely except that the Alaskan variety has a much 

shorter virgella. It has a much broader proximal end 

and is less tapering than C. rectangularis as depicted 

by Elles and Wood (1901-18) in their plate 26, figure 

5a, b, c, and e. It does, however, resemble their figure 

5d on plate 26.

Occurrence. M1142-SD.

Range. Zone of M. gregarius in Alsaka.

Dimensions (in millimeters). 

Material. About 18 compressed specimens. About 

five are well preserved; the rest are fragmentary. 

Named after the Latin "brevis"=short and "ca-udatus"=tailed.

Holotype. USNM 161621.

Climacograptus minutus? Carruthers 

Text figure 6C; plate 1, figure 6

Climacograptus minutus Carruthers. Elles and Wood, 1901-18, 

Mon. British Graptolites, Palaeontographical Soc., p. 211- 

212, text fig. 142, pi. 27, fig. 12a-c.

Climacograptus minutus Carruthers. Hsii, 1934, Graptolites of 

the Lower Yangtze Valley, p. 61, pi. 4, fig. 10.

Discussion. Our specimens closely resemble C. 

minutus but are too poorly preserved for positive 

identification and are questionably referred to tl is 

species.

Occurrence. Ml 138-SD.

Range. Llandoverian zones (17,18) of 0. vesiculosus 

and M. cyphus (Birkhill Shales) in Great Britain (Elles 

and Wood, 1901-18). Ruedemann (1947) reports a 

minutus-ltike form from the Ordovician Phi Kapna 

Formation in Idaho. Also reported in the basal part of 

the Kaochiapien Shale (zone with A. ascensus} in ChHa 

(Hsii, 1934).

Dimensions (in millimeters}. 

Specimen No.

USNM 161627 1 _--- -

161628- ___ ._

161629. ___-_

Length of 

rhabdosome -

>6. 5

5.3

9

Width

Theca 1*

0.8

.8

. 7

Maximum

1. 25 

1. 0 

1. 25

Thecae per 

centimete- 

(approximpte)

14

12

USNM-161621 '__ 

161622a_- 

161622b__ 

161623--. 

161624e- .

161625.--

161626. __

i Figured specimens.

Length of

some Theca H

>18 0.9

15. 5 .8 

>8. 6 .8 

>10 .8

">18

11.5 .8

Width

Theca 5i

1.6 

1.3 

1.6 

1.4

1.5

Maximum

2.3 

1.8 

1.8 

1.9

2 2

2.1

Thecae

meter

10 

10-11 

11 

10 

10

1011

i Figured specimen.

Material. About four compressed, poorly preserved 

specimens.

Figured specimen. USNM 161627.

Climacograptus cf. C. rectangularis (M'Coy) 

Text figure 7A, B; plate 1, figures 7-9 

Climacograptus rectangularis (M'Coy). Elles and Wood, 1901-18,

Mon. British Graptolites, Palaeontographical Soc., p.

187-188, text fig. 121, pi. 26, fig. 5a-e. 

Climacograptus rectangularis (M'Coy). Hundt, 1924, Grapt. d.

deutsch. Silurs, p. 56, pi. 1, figs. 14, 15, 24, 25. 

Climacograptus rectangularis (M'Coy), Obut, 1949, Polyeroi

Atlas, Rukovodyashchich graptolitov vyerkhnyevo Silura

Kirgizskoi SSR, p. 12, pi. 1, fi. 2a b. 

Climacograptus rectangularis (M'Coy). Stein, 1965, Neues Jahrb.

Geologic u. Palaontologie Abh., p. 160-163, text figs.

I5a-c, 16 h. 

Hedrograptus rectangularis (McCoy). Obut, Sobolevskaya, and

Bondarev, 1965, Graptolity Silyura Taimyra, p. 29, pi.

1, figs. 7-9. 

Hedrograptus rectangularis (McCoy). Obut and Sobolevskaya,

1966, Graptolity rannyevo Silyura v Kazakhstanye, p.

10-11. text fig. 3, pi. 3, fig. 4.
18 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Discussion. The Alaskan specimens are mostly narrower than those described by Elles and Wood (1901- 

18), and the sigmoidal curvature of their thecae becomes 

more gentle distally. Also, their siculae are free on one 

side for only about 0.4 mm. The gradual widening, 

short virgella, and number of thecae per centimeter 

are like O. rectangularis.

Occurrence. M1138-SD, M1139-SD, M1142-SD.

Mange. Llandoverian zones (16-19) of A. acuminatus 

to M. gregarius (lower part of Birkhill Shales and 

equivalents) in Great Britain (Elles and Wood, 1901- 

18; Toghill, 1968). Zone of M. cyphus (middle part of 

Road River Formation) in Yukon Territory, Canada 

(Jackson and Lenz, 1962). Reported from the Edgewood Limestone, zone (17) of D. modestus, of northeast 

Illinois by Ross (1962). Llandoverian zone of 0. vesiculosus (approximate) in Pulau Langgon, Langkawi 

Island, Malaya (Kobayashi and others, 1964). Also 

reported from: Portugal (Romariz, 1962), Germany 

(Hundt, 1924), Russia (Obut, 1949; Obut and others, 

1965; Obut and Sobolevskaya, 1966), Bohemia (Pribyl, 

1948).

Dimensions (in millimeters). 

Length of 

Specimen No. rhabdosome

Width

Theca 1» Theca 51 Maximum

Thecae per 

centimeter

USNM-161631 L_ 21. 5 

161632 '__ 13. 8 

161633_ 15. 0 

161634.-- >16 

161635 L_ 12. 5 

161636-. 8.5 

161637_ >13. 5 

161638_ 9. 8 

161639 »__ >16. 5 

161640_ 9. 6 

161641__. >7. 5 

161642... 8.0

1.2

1.3 

1. 3 

1. 0 

1. 5 

1.3 

1.3 

1. 1 

1. 2 

1. 2 

1. 25 

1.3

2.0 

2.0 

1. 8 

1.5 

2.2

1.7

1.8 

1.6 

2.0 

1.7

1.5

1.6

11-12

10-11

11-12

10

11

12

10-11 

10 

10

10

11

12

1 Figured specimen.

Material. Approximately 30 compressed, fairly well 

preserved specimens (about half are fragmentary).

Figured specimens. USNM 161631, 161632, 161635, 

161639.

Climacograptus rectangularis abbreviates n. subsp. 

Text figure 8C; plate 1, figure 15

Description. -The short, robust rhabdosome is 1-2 cm 

long and increases gradually in width throughout its 

length from 0.8 to 0.9 mm at theca I1 to a maximum of 

2.0-2.5 mm. The thecae are markedly alternate and 

number 10-12 per centimeter with an overlap about 

a third of their length. The apertural margins are horizontal and are in deep excavations occupying fully a 

third of the width of the rhabdosome. The geniculum 

is very sharp, and the free ventral wall above it is

slightly inclined to the axis of the rhabdosome. The 

characters of the sicula are unknown, but a rhort, fine 

virgella is present.

Discussion. This form closely resembles G. rectangularis but has a generally shorter rhabdosome. (G. 

rectangularis measures 1-4 cm in length). It also has a 

smaller, less conspicuous virgella than rectangularis. It 

is wider than Glimacograptus cf. G. rectangularis, described in this paper. This variety also resembles G. 

latus, but lacks the basal spines and has deeioer excavations. It is characterized by relatively great width in 

proportion to its length, and by the markedly alternate 

thecae, especially in the proximal part.

er"

FIGURE 8. Climacograptus and Pseudoclimacograptus. A, 

B, C. stenotelus n. sp.: A (USNM 161673), X 5; B, 

Holotype (USNM 161666) (same as pi. 1, fig. 14), showing slight distortion, X 5; C, C. rectangularis abbreviates 

n. subsp., Holotype (USNM 161643), X 5. D, P. 

(Metaclimacograptus) cf. P. (M.) undulatus (Kurck) 

(USNM 161690) (same as pi. 1, fig. 18) showing some 

distortion, X 9. E, P. (Metaclimacograptus) hughesi 

(Nicholson) (USNM 161674) (same as pi. 1, fig. 16), X 5.

Occurrence M1138-SD, M1139-SD. 

Range. Zone of M. cyphus in Alaska. 

Dimensions (in millimeters'). 

Specimen No.

USNM-161643 1 _--_-

161645----..

1616461 __ .

161647..--.

161648. _---

161649 - --

161650. _ --

161651C--__-

161652e- -._-

l61652f__-_-

Lengtli of Width 1

Theca 1» Maximum

8.5

_ >18. 5

8.0

16. 0

15.0

11.5

>7

>5. 6

>6

4.5

0.9 

. 8 

.9 

. 8 

.9 

.9 

.9 

1.0 

.9 

. 8

2.0 

2.3 

1. 8 

2. 3 

2. 5 

2.2 

1.7 

1.7 

2. 0 

1.3 --

'hecae per 

/entimeter

12 

10-11 

12-13 

10-12 

9-11 

11 

10 

11 

11

Figured specimen.

Material. Approximately 10 compressed, well-preserved specimens.
SYSTEMATIC DESCRIPTIONS 19

Holotype. USNM 161643.

Figured specimens. USNM 161643, 161646.

Climacograptus scalaris (Hisinger) 

Text figure 1C; plate 1, figures 10, 11

Climacograptus scalaris (Hisinger) (Linne1 ?). Elles and Wood, 

1901-18, Mon. British Graptolites, Palaeontographieal 

Soe., p. 184-185, text fig. 118, pi. 26, fig. la-c.

Climacograptus scalaris (Hisinger). Hundt, 1924, Grapt. d. 

deutseh. Silurs, p. 55, pi. 1, figs. 27-31.

Climacograptus scalaris scalaris (Hisinger). Stein, 1965, Neues 

Jahrb. Geologic u. Palaontologie Abh., p. 149-150, 157, 

text fig. 13a-h, pi. 14, figs, a, b.

Discussion. The Alaskan specimens agree closely 

with the description of C. scalaris by Elles and Wood 

(1901-18). However, some specimens have a few more 

thecae per centimeter (11-14 vs. nine to 11 for Elles 

and Wood, 1901-18).

Occurrence M1138-SD, M1139-SD, M1289-SD, 

M1290-SD(?).

Range. Llandoverian zones of M. convolutus to M. 

sedgwickii (middle part of Road River Formation) in 

Yukon Territory, Canada. Varieties reported from same 

area in Ashgillian. zone of Dicellograptus complanatus 

var. ornatus and Llandoverian zone of M. millepeda 

(Jackson and Lenz, 1962), Llandoverian zones (19-22) 

of M. gregarius to M. turriculatus (upper Birkhill 

Shales, lower Gala Beds) in Great Britain (Elies and 

Wood, 1901-18; Toghill, 1968). Also found in: Germany 

(zones 10-15) (Hundt, 1924); Portugal (zone 19-22) 

(Romariz, 1962); Bohemia, Czechoslovakia (Llandoverian zones of Demirastrites convolutus to M. sedgwickii) 

(Pribyl, 1948); Australia (Bolindian to lower Keilorian) 

(Thomas, 1960). Varieties are reported from Maine 

(Clinton? age) and Arkansas (Lower Silurian Blaylock 

Sandstone) by Reudemann (1947), and from Russia 

by Obut (1949). Apparently O. scalaris in southeastern 

Alaska ranges down into the zone of M. cyphus, a zone 

lower than it occurs in the British Isles.

Dimensions (in millimeters}. 

Specimen No.

USNM-161653 1 __ _ _

161654--------

161655--------

161656--. __ __-

161657 __. ___

161658 1 ___ _

161659-------

161660------ __

161661 __ _ .

161662 _ _ _____

161663 »________

161664_____---_

161665 .- __ --

Length of Maximum Thecae per 

rhabdosome width centimeter

--__ 7.5

.-__ 10.5

---_ 6.5

---- 7.2

---. 20.8

-_-_ 9.3

9

--__ 13.3

---- 21.5

17.5

\ Q

 11.5

>8

1. 5 

1.5 

1.3 

1.5 

1.5 

1.4 

1.5 

1.3 

1. 5 

1.5 

1.5 

1.5 

1. 5

12 

12 

12 

12 

11 

14 

12 

12 

12 

12 

12 

13 

12

i Figured specimens.

Material. About 63 compressed, well-preserved 

specimens.

Figured specimens. USNM 161653, 161658,

Climacograptus stenotelus n. sp. 

Text figure 8A,B; plate 1, figures 13, 14

Description. The rhabdosome is as much as 3 cm 

long and 0.5-0.6 mm wide initially, reaching a maximum width of approximately 2.0 mm. The thecae are 

of the general climacograptid type, numbering 14-16 

per centimeter. The proximal end is gently tapering in 

appearance, with a virgella about 1 mm long.

Discussion. Because the specimens are somewhat 

deformed, it is difficult to say what their true appearance was. Generally, this is a long form with closely 

set thecae and a tapering proximal end. It is larger 

than C. scalaris, narrower and with more closely set 

thecae than C. rectangular is and C. medium and rlso 

with a shorter virgella than C. medius. It has a narrower 

and more tapering proximal end than C. minimus. Its 

most distinctive feature is the narrow proximal end 

with its closely set thecae.

Occurrence. Ml 140-SD.

Range. Zone of M. gregarius to M. convolutus in 

Alaska.

Dimensions (in millimeters] . 

Specimen No.

USNM-161666 1 .. 

161668f._ 

161668g 

161669 _ 

161670-_ 

161671... 

161672... 

161673 1 ._ 

161667 »__

Length of Width

some Theca I1 Theca 51 Maximum

>11. 3

5 

>27. 5 

5 

24

11 

>15. 5

0 6 

5 

6 

5 

5 

5 

6 

6 

6

1. 

1. 

1. 

1. 

1. 

1. 

1. 

1. 

1.

4 

25 

4 

1 

2

1 

4 

4 

2

1. 

1. 

1. 

1.

1. 

1. 

1. 

1.

9 

5 

5 

5

5 

9

8

7

Thecae 

per centimeter

16 

16 

20 

14-15 

14 

15 

14 

16 

13-16

1 Figured specimens.

Material. Approximately 50 compressed, distorted 

specimens, somewhat poorly preserved. Named after 

the Greek "stenos"=narrow and "telus"=end.

Holotype. USNM 161666.

Figured specimens. USNM 161666, 161667, 161673.

Genus PSEUDOCLIMACOGRAPTUS Pribyl, 1947

Pseudoclimacograptus Pribyl, 1947, Bull, internat. de 1'Acad.

tcheque Sei., v. 48, p. 21 

Pseudoclimacograptus Pribyl, Bulman and Rickards, IT'58,

Palaeontology, v. 11, pt. 1, p. 2

Rhabdosome diplograptid, with zigzag, angular, or 

undulating median septum. Thecae of "Glypto-climacograptus" type; apertural excavations short and deep, 

often introverted. A genicular hood present in some
20 EARLY SILURIAN GRAPTOLITES FROM ALASKA

late representatives. Lower Ordovician to Lower 

Silurian; Europe, Asia, Australia, and North America.

Subgenus P. (METACHMACOGRAPTUS) Bulman and Rickards

1968

P. (Metaclimacograptus) Bulman and Rickards, 1968, Palaeontology, v. 11, pt. 1, p. 3.

Climacograptids with gently convex or nearly 

straight supragenicular walls; apertural excavations 

short, deep, and introverted and partly covered by a 

hood growing from the geniculum of the succeeding 

theca. Angular to undulating median septum. Lower 

Silurian; Europe, Asia, Australia, and North America.

P. (Metaclimacograptus) hughesi (Nicholson) 

Text figure 8 E; plate 1, figures 16, 17

Climacograptus Hughesi (Nicholson). Elles and Wood, 1901-18,

Mon. British Graptolites, Palaeontographical Soc., p.

208-210, text fig. 140, pi. 27, fig. lla-e. 

Climacograptus Hughesi Nicholson. Hundt, 1924, Grapt. d.

deutsch. Silurs, p. 56, pi. 1, figs. 8-10. 

Climacograptus hughesi (Nicholson). Hsii, 1934, Graptolites of

the lower Yangtze Valley, p. 67-68, pi. 5, fig. 7a-c. 

Climacograptus hughesi (Nicholson). Harris and Thomas, 1937,

Victoria Dept. of Mines, Mining and Geol. Jour., July

1937, p. 69, pi. i, fig. 1. 

Pseudoclimacograptus hughesi (Nicholson). Pribyl, 1948, Knihovna

Stdt. geol. list. Csk. Republiky, sv. 22, p. 18. 

Pseudoclimacograptus hughesi (Nicholson). Obut and Sobolevskaya, 1966, Graptolity rannyevo Silyura v Kazakhstanye,

p. 12-13, text fig. 4, pi. 3, figs. 5, 6. 

Pseudoclimacograptus (Metaclimacograptus) hughesi (Nicholson).

Bulman and Rickards, 1968, Palaeontology, v. 11, pt.

1, p. 3-6, text figs. la-c.

Discussion. The pyritized specimens from Nevada 

agree very closely with the description and dimensions 

given by Bulman and Kickards (1968, p. 3-5) except 

for the shape of the median septum. The Nevada 

specimens have a more angulate septum, similar to 

that of P. (M). undulatus, as described by Bulman and 

Rickards (text fig. Id). In their discussion (p. 5), they 

state that in some of the earlier specimens of hughesi 

(from the acinaces zone) "there are traces of the 

angularity characteristic" of the median septum in 

P. (M.) undulatus. However, our (pyritized) specimens 

are from a higher horizon (gregarius zone). Traces of 

the genicular hoods are visible in some of the pyritized 

specimens.

Occurrence. M1138-SD, M1139-SD, M1289-SD. 

Nevada: Central Independence Range, locality 4 of 

Kerr (1962).

Range. Zone of M. cyphus (Cape Phillips Formation) in Canadian Arctic (Thorsteinsson, 1958). Questionably from Silurian black slate at Houlton, Maine 

(Ruedemann, 1947). Llandoverian zones of M. cyphus 

and M. gregarius (Birkhill Shales) in Great Britian 

(Toghill, 1968). Llandoverian zone of M. gregarius in 

New South Wales, Australia (Sherrard, 1954). Upper 

Bolindian through Keilorian in Victoria, Australia 

(Thomas, 1960). Also reported from Germany (Hundt, 

1924), Bohemia (Pribyl, 1948), Portugal (F.omariz, 

1962), Russia (Obut and Sobolevskaya, 1966), and 

China (Hsii, 1934). 

Dimensions (in millimeters). 

Specimen No.

Flattened 

(F) or in 

relief (R)

Length of rhabdosomeWidth

Theca H Maximum

Theca?. Length

 per cenM- of

meter sicula

USNM-161674 » ..

161675 .....

161676......

161677......

161678. .....

161679. .....

161680......

161681...... 

161682. ..... 

161683......

161684..... _ 

161685. .....

161686... ...

1616871..... 

161688...... 

161689. .....

F

F

F

F

F

F

R

R 

R 

R

R 

R

R

R 

R 

R

9.5

5.7

9.1

7.0

12.5

6.3

11.0 ...

7.8 

2.8 

7.3 ...

8.4 

6.0 ...

5.0

11.3 

7.6 

16.3

0.8

.7

.7

.7

.8

.8

.6 

.5

.5

.4

.7 

.6 

.6

1.0

.9

1.0

1.0

1.0

1.0

1.0 

.7 

.7

.8

.6

.9 

.75 

1.0

14

14

14

15

12

16

12

14 

13 

14

12 

13

12

14 

14 

KW2 ....

.5

.7 

.5

.6

.5 

.6

i Figured specimens.

Material. About 20 compressed, well-preserved 

specimens and 10 pyritized specimens preserved in 

relief.

Figured specimens. USNM 161674, 161687.

P. (Metaclimacograptus) cf. P. (M.) undulatus (Kvrck)

Text figure 8D; plate 1, figure 18

Climacograptus extremus H. Lapworth. Elles and Wood, 1901-18,

Mon. British Graptolites, Palaeontographical Soc., p.

210-211, text fig. 141, pi. 27, fig. 13a, b. 

Pseudoclimacograptus (Metaclimacograptus) undulatus (Kurck).

Bulman and Rickards, 1968, Palaeontology, v. 11, pt.

1, p. 6-8, text figs. Id-j, 3e.

Discussion. Because our specimens are distorted, 

identification is difficult. The zigzag septa, larie number of thecae per centimeter, and small rhabdosomes 

of our specimens indicate that they are probably 

P. (M.) undulatus. One specimen (text fig. 8D) has a 

sicula 0.65 mm long.

Occurrence. Ml 140-SD.

Range. Llandoverian zones of M. cyphus and 

M. millepeda (Cape Phillips Formation) in the Canadian 

Arctic (Thorsteinsson, 1958). Questionably from Ordovician shale, Mount Joli, Perc£, Quebec (Ruedemann, 

1947). Llandoverian zones of M. cyphus to M. sedgwickii and possibly M. turriculatus in Great Britain 

and Sweden (Bulman and Rickards, 1968).
SYSTEMATIC DESCRIPTIONS 21

Dimensions (in

Specimen No.

USNM-161690 1 -.-

161691--

161692... _

161693....

161694....

161695 .

161696 .

millimeters} .-

Length of

4.5

5.0

8.5

5.0

>9.0 .

9.0

9.0

Width

Theca 1>

0.65 

.8 

.5 

.5

.7 

.5

Maximum

1.1 

.8 

.9 

1.0 

1.0 

1.1 

1.0

Thecae per 

centimeter

20 

18 

18 

16 

20 

19-20 

17-18

1 Figured specimen.

Material. About 40 compressed specimens (some 

show slight relief), which have been moderately 

distorted.

Figured specimen. USNM 161690.

Subfamily DIPLOGRAPTINAE

Genus DIPLOGRAPTUS M'Coy, 1850

(= MESOGRAPTUS Elles and Wood, 1901-18)

Diplograptus M'Coy. Bulman, 1955, Geol. Soc. America, Treatise 

on invertebrate paleontology, pt. V, p. V85, fig. 63, 2a, b.

Rhabdosome biserial, scandent. Thecae strongly 

sigmoidal with apertures in broad semicircular excavations at proximal end, gradually becoming more 

gently sigmoid and almost straight distally. Periderm 

attenuated and with apertural lists proximally. Middle 

Ordovician to Lower Silurian; Europe, North America, 

Australia, and Asia.

Diplograptus elongatus n. sp. 

Text figure 9C, D; plate 1, figures 19, 20

Description. The rhabdosome is about 2.5 mm long, 

or longer, widening gradually from an initial width of 

approximately 0.8 mm to a maximum of 2.5 mm. The 

thecae number eight to 13 per centimeter and are of the 

climacograptid type (thecae with angular sigmodial 

curvature, free ventral wall subparallel to rhabdosome 

axis, apertures in semicircular excavations) up to about 

the fifth thecal pair, above which they change gradually 

to the glyptograptid type (thecae with gentle sigmoidal 

curvature). The characters of the sicula are unknown. 

A short virgella, measuring approximately 0.8 mm, is 

commonly present.

Discussion. The whole rhabdosome has a tapering 

appearance. This form is characterized by its relative 

narrowness in comparison to other species of Diplograptus, by the tapering shape of the rhabdosome, and 

by the small number of climacograptid-type thecae. In 

general appearance it resembles D. multidens var. 

compactus but lacks the basal spines and the more 

closely set thecae (12-14 per centimeter) of that form.

Occurrence. Ml 138-SD.

Range. Zone of M. cyphus in Alaska.

C DBF

FIGURE 9. Diplograptus. A, B, D. mucroterminatus n. sp.: 

A, Holotype (USNM 161707) showing proximal spines, 

X 5; B, Immature specimen (USNM 161705), X 5. C, D, 

D. elongatus n. sp.: C, Holotype (USNM 161698) (sar-e 

as pi. 1, fig. 20), X 4; D, (USNM 161697) X 5. E, F, 

Diplograptus n. sp.: E, fragmentary specimen (USNM 

161711) (same as pi. 2, fig. 1), X 5; F, (USNM 161712), 

X 5.

Dimensions (in millimeters). 

Length of

USNM-161697 1

161698 *

161699

161732

161700 *

some

10.

25.

22.

25.

18.

5

2

6

7

0

Theca 1»

0. 8

.7

.7

. 8

Width

Theca 5»

1.

1.

1.

1.

1.

3

3

3

3

3

Maximum

1,

2.

1.

2.

2.

75

0

75

0

4

Thecae

met?r

11-13

8-10

10-13

9

9-11

1 Figured specimens.

Material. Approximately 16 compressed specimens; 

about four are well preserved, the others are fragmentary. Named after the Latin "elongatus"=prolonged.

Holotype. USNM 161698.

Figured specimens. USNM 161697, 161698, 161700.

369-097 O - 70 - 4
22 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Diplograptus modestus var. diminutus Elles and Wood 

Text figure IQG; plate 2, figure 19

Diplograptus (Mesograptus) modestus var. diminutus Elles and 

Wood, 1901-18, Mon. British Graptolites, Palaeontographical Soc., p. 265, text fig. 182, pi. 31, fig. 13a-c.

Discussions. This variety resembles D. modestus 

very closely but differs by its smaller size and more 

closely set thecae. The rhabdosome is not more than 

1.5 cm long, and its width increases quickly from 0.6 

mm initially to about 1.5 mm distally. The thecae are 

the same as in D. modestus s.s. but number 14-16 per 

centimeter.

Occurrence. M1141-SD, M1287-SD, M1288-SD (?).

FIGURE 10. Glyptograptus and Diplograptus. A, G. cf. G. 

enodis enodis Packham (USNM 161715) (same as pi. 2, 

fig. 2), X 5. B, C, G. cf. G. enodis lotus Packham: B, 

(USNM 161718) (same as pi. 2, fig. 3), X 8; C, (USNM 

161717 ) (same as pi. 2, fig. 4), X 8. D, E, G. incertus Elles 

and Wood: D, (USNM 161730) (same as pi. 2, fig. 

5), X 5; E, (USNM 161731), X 5. F, G. cf. G. tamariscus 

tamariscus (Nicholson) (USNM 161986), X 5. G, 

Diplograptus modestus var. diminutus Elles and Wood 

(USNM 161701a) (same as pi. 2, fig. 19), X 5.

Range. D. modestus diminutus is found in the 

Llandoverian zones (16-18) of A. acuminatus to 

M. cyphus (Birkhill Shales) in Great Britain (Elles 

and Wood, 1901-18). D. modestus is found in: The 

Llandoverian zone of D. modestus (Road River Formation) in Yukon Territory, Canada (Jackson and 

Lenz, 1962); the zone of M. cyphus (Cape Phillips 

Formation) in the Canadian Arctic (Thorsteinsson,

1958); the Llandoverian zones of D. acuminatus and 

M. cyphus in the Frankenwald (northeastern Pavaria) 

(Stein, 1965); the lower Llandovery in Portugal 

(Romariz, 1962); the lower Llandovery (Parhsa-pye 

graptolite beds) in the Langkawi Islands, Malaya 

(Kobayashi and others, 1964); the zones of Oystograptus 

vesiculosus and Pristiograptus cyphus in Russia (Obut 

and others, 1965); the Lower Silurian of China (Sun, 

1933; Hsu, 1934); the Keilorian of Australia (Thomas, 

1960). 

Dimensions (in millimeters). 

Specimen No.

USNM-16l701a '__..__

161702

161703

Length of rhabdo- - 

some

.___ 5.3

.___ 5.4

_.__ 5.0

.__. >3. 8

Width Thecae

Theca H

1.0 

.9 

.9 

.9

Maximum centimeter

1.7 16 

1.4 16 

1.8 18 

1. 6 20(?)

> Figured specimens.

Material. Approximately 12 compressed, fairly well 

preserved specimens. 

Figured specimen. USNM 161701a.

Diplograptus mucroterminatus n. sp. 

Text figure 94, B; plate 1, figure 21

Description. The rhabdosome is wide and relatively 

short; none exceed about 1.5 cm in length. The maximum width ranges from 2.3 to 3.0 mm with the average 

specimen being approximately 2.5 mm wide. The 

proximal end is greatly tapered, widening rapidly 

from a width of 0.6-0.9 mm at the first pair cf thecae 

to 2.0-2.6 mm at the fifth thecal pair. The thecae 

number 11-12 per centimeter, strongly climac^graptid 

proximally, then changing rapidly to orthcqrraptidtype thecae distally. The sicula is free for a part of 

its length on one side and has a short virgella (0.5-0.8 

mm long). Frequently the virgula extends for a distance 

(18.5 mm maximum) above the distal end of the 

rhabdosome.

Discussion. The characteristic feature of this form 

is the strongly tapered proximal end. The first three 

pairs of thecae are climacograptid, with excavations 

occupying approximately one-fourth to one-third the 

width of the rhabdosome. The fourth thecal pair is 

more or less intermediate in type and the ortho.^raptidtype thecae appear in the fifth thecal pair. The rhabdosome tapers to about the fifth pair; above this point 

the margins of the rhabdosome are nearly parallel. The 

orthograptid-type thecae are short, wide, straight 

tubes, inclined to the rhabdosome axis, with everted 

apertural margins. In some specimens, the rhaVdosome 

narrows slightly distally. From a maximum vddth of 

2.8 mm, 3.0 mm, and 2.6 mm, three specimens narrow
SYSTEMATIC DESCRIPTIONS 23

to 2.0 mm, 2.3 mm, and 2.0 mm wide, respectively, at 

the last pair of thecae. One specimen (fig. 9A) seems 

to have a proximal spine (possibly three spines) growing 

out almost horizontally from the first theca near its 

change of growth direction. There appear to be traces 

of two other spines close by. No other specimen had 

spines preserved.

This species resembles D. modestus somewhat, but 

it widens more rapidly and is smaller than modestus. 

The distal part resembles Orthograptus bellulus, but 

the proximal end of 0. bellulus has no climacograptid 

thecae.

Occurrence. M1142-SD.

Range. Zone of M. gregarius in Alaska.

Dimensions (in millimeters). 

Length of Width

Specimen No. rhabdo- Thecae per

some Theca Theca Maxi- centimeter

USNM-161704_____-_

161705 '-._-._

161706 '._____ leiro? 1 ..---.

161708C-----.

16l708d---_.

161709. . _---

161710__----.

11.

7.

12

Q

15

5

12

3.

1 0

0

5

5

5 __.

5

9

8

7

8

8

6

9

?,

?,

9,

?,

?,

1

?,

2.

6

0

3

1

1

9

?,

4

?,

?,

3

?,

?,

?,

9,

2.

8

6

5

3

6

4

12

12

12

12

11

12

i Figured specimens.

Material. Twelve compressed, fairly well preserved 

specimens. Named after the Latin "mucro"=sharp 

point, and "terminatus"=end.

Holotype. USNM 161707.

Figured specimens. USNM 161705-161707.

Diplograptus n. sp. A 

Text figure 9E, F; plate 2, figure 1

Description. The rhabdosome is more than 2 cm 

long, widening from an initial width of 0.9 mm at the 

first thecal pair to a maximum width of about 2.5 

mm. The thecae number nine to 11 per centimeter, 

and are of the climacograptid type proximally, becoming 

orthograptid type thecae distally.

Discussion. Only two specimens are known and one 

of these is fragmental. This species has a distinctively 

long and slender rhabdosome. The proximal end tapers 

from a width of 0.9 mm at the first pair of thecae to a 

width of 1.5 mm at the fifth thecal pair. The thecae are 

climacograptid up to about the tenth pair. Then they 

change to the orthograptid type, with straight ventral 

walls and horizontal or slightly everted apertural 

margins. The characteristics of the sicula are unknown.

This form differs from other species of Diplograptus 

by being narrower and having fewer thecae per centimeter. It differs from Diplograptus elongatus in having 

distal thecae of the orthograptid type, whereas Diplograptus elongatus has distal thecae of the glyptograDtid 

type. This new species is not named because of the 

scarcity and poor preservation of specimens.

Occurrence . M1138-SD.

Range. Zone of M. cyphus in Alaska.

Dimensions (in millimeters). 

Length of Width 

Specimen No. rhab- Thecae per

dosome Theca Theca Maxi- centimeter

USNM-161711 

161712 >23 0. 9 1. 5

2. 0 

2.5

9-10

10-11

i Figured specimens.

Material. Two compressed specimens. 

Figured specimens. USNM 161711, 161712.

Diplograptus n. sp. B

Discussion. A diplograptid of great length and 

relative narrowness, distally resembling a large glyptograptid such as G. serratus. Only two specimens of this 

species are present in our collection, and on both the 

proximal end is missing.

Occurrence . M1138-SD.

Range. Zone of M. cyphus in Alaska.

Dimensions (in millimeters). 

Specimen No.

Length of 

rhabdosome

Width

Minimum Maximum

Thecae per 

centimeter

USNM-161713._- >53 

>60

1. 1 

1.3

3.0 

3.0

8-10 

8-9

Genus GLYPTOGRAPTUS Lapworth, 1873

Glyptograptus Lapworth. Bulman, 1955, Geol. Soc. America, 

Treatise on invertebrate paleontology, pt. V, p. V86 fig. 

4a, b.

Rhabdosome biserial, scandent. Thecae with gently 

sigmoidal curvature, apertural margins frequently 

undulate. Lower Ordovician to Lower Silurian, worldwide.

Glyptograptus cf. G. enodis var. enodis Packham 

Text figure 104; plate 2, figure 2

Glyptograptus enodis enodis Packham, 1962, Palaeontology, v. 5, 

p. 517, pi. 71, figs. 18, 19, 21; pi. 72, fig. 1, text fig. 4g-j.

Description. According to the original description, 

the rhabdosome is nearly 4 cm long, increasing rapidly 

in width until the fifth pair of thecae from whence it 

is parallel sided or slowly widening. The thecae number 

8^-11 per centimeter, have gentle sigmoidal curvature 

and everted apertures and overlap approximate!^ a 

third of their length. The virgella is stout.

At theca I 1 , the rhabdosome is about 0.6 mm wide, at 

tlieca 51 it is about 0.9-1.2 mm wide, and its maximum
24 EARLY SILURIAN GRAPTOLITES FROM ALASKA

width is 1.7 mm. Above the geniculum the free ventral 

walls of the thecae are inclined to the axis of the 

rhabdosome. The common canal is approximately 

uniform in width beyond the fifth pair of thecae and 

occupies about half the width of the rhabdosome in 

that region and less proximally.

Discussion. According to Packharn (1962), G. enodis 

can be distinguished from G. tamariscus by the more 

gentle curvature of the thecae, the longer and less 

definite excavations occupying a smaller proportion 

of the rhabdosome width, and by a greater overlap 

of the thecae."

Only two specimens are present in our collections, 

and one is wider than the specimens described by 

Packham (1962). Both of our specimens look like 

Packham's flattened specimen (1962, text fig. 4j) with 

nonalternating thecae, and both have a good stout 

virgella.

Occurrence. M1138-SD, M1288-SD(?).

Range. Llandoverian zone of M. gregarius in Great 

Britain (Packham, 1962). The occurrences of G. enodis 

enodis in Alaska with assemblages that otherwise indicate correlations with the zones of M. cyphus and 

0. vesiculosus suggests it ranges lower in western 

North America.

Dimensions (in millimeters'). 

Specimen No.

Length Width of 

rhabdo- Theca Theca 

some I1 5l

Maximum

Thecae Length

per of 

centl- virgella 

meter

USNM-161715 1 .. >20. 5 0.8 1.2 1.6 8-11 

161716-_ 28.0 .8 1.5 2.0 10

2. 0 

2.0

1 Figured specimens.

Material. Two compressed, moderately well preserved specimens. 

Figured specimen. USNM 161715.

Glyptograptus cf. G. enodis var. latus Packham

Text figure WB, C; plate 2, figures 3, 4

Glyptograptus enodis latus, Packham, 1962, Palaeontology, v. 5, 

p. 518, pi. 71, fig. 20, text fig. 4e.

Description. According to Packham (1962), this is 

a long form of G. enodis that increases in width throughout its length and reaches a maximum width of 1.4 mm 

distally. The common canal widens steadily throughout 

the rhabdosome and occupies about half the width at 

the distal end. The thecae have a gentle sigmoidal 

curvature, everted apertures, and an overlap of about 

a third. The excavations occupy about a third of the 

width of the rhabdosome.

Discussion. Packham's (1962) only specimen measures 0.65 mm wide at thl 1 , 1.1 mm wide at thS1 , 

and 1.4 mm wide maximum. It has nine to 11 thecae

per centimeter and is preserved in relief. The Alaskan 

specimens are wider proximally and have one more 

theca per centimeter, but this may be due in part to 

the fact that the Alaskan material is flattened.

Occurrence. M1142-SD.

Range. Llandoverian zone of M. gregarius in Great 

Britain (Packham, 1962).

Dimensions (in millimeters). 

] 

Specimen No. 

r

USNM-1617171..... 

1617181..... 

161719......

161720......

161721---. 

161722-. . 

161723 . 

161724.. . 

161624L.... 

161801m.... 

161725b..... 

161726......

Length Width

habdo- Theca Theca 

some I1 5»

>5.5 

8.0 

7.2 

5.0 

8.0 

5.0 

4.0 

>8.0 

>6.0 

4.0 

>7.0 

5.3

0.8 

.8 

.8 

.75 

.75 

.8 

.7 ..

.8 

.8 

.7 

.75 

.8

1.1 

1.3 

1.3 

1.4 

1.3 

1.4

1.4 

1.4 

1.4 

1.4 

1.4

1

Maximum

1.2 

1.4 

1.3 

1.4 

1.3 

1.5 

1.4 ..

1.6 

1.5 

1.4 

1.5 

1.4

Thecae Length Length of 

per of sicula free 

centi- Thepa on one 

meter I1 side

11-12 

11 

12 ...

10 

11 

11-12

11 

12 

12 ...

12 ...

12 ...

1.0 0.4 

.9 .35

.9 .5 

.8 .45 

.9 .35 

1-0 ...

1.0 ..........

.8 ..........

i Figured specimens.

Material. About 17 compressed, fairly v^ell preserved specimens.

Figured specimens. USNM 161717, 161718.

Glyptograptus gnomus n. sp. 

Text figure HE, F; plate 2, figure 16

Description. The rhabdosome is less than 2 cm long, 

widening from a width of about 0.6 mm at theca I 1 

to a maximum of about 1.8 mm. The thecae number 

11-14 per centimeter, overlap approximately $. third of 

their length, and have relatively long free ventral walls 

above the geniculum which are inclined to the rhabdosome axis. The apertural margins are horizontal or 

slightly everted. The excavations are moderately deep 

and approximately the same size throughout the length 

of the rhabdosome, so that the common canal increases 

in width as the rhabdosome increases in width. The 

geniculum becomes more gentle distally. The sicula is 

about 1 mm long, extending up to the level of the 

aperture of theca I2, and free on one side for about 

half of its length. The virgella is conspicuous and 

about 0.6 mm long.

Discussion. This form differs from G. tc.mariscus 

(Packham, 1962) by having inclined free ventral 

walls above the geniculum, shallower excavations, 

and a more tapering shape. It looks somewhs t similar 

to Obut and Sobolevskaya's (1966) G. tamariscus 

nikolayevi, but the positions of theca I 1 and theca I2 

are different. Obut and Sobolevskaya (1£36, text 

fig. 6) show the aperture of theca I 1 to be slightly 

above the aperture of theca I2 . In the Alaskan specimens, the situation is reversed. It might possibly be
SYSTEMATIC DESCRIPTIONS 25

\

FIGURE 11. Glyptograptus. A, B, G. tamariscus magnus n. 

subsp.: A, Holotype (USNM 161765), proximal part 

(same as pi. 2, fig. 7), X 5; B, (USNM 161771), X 4. 

C, G. lanpherei n. sp., holotype (USNM 161759), X 5. 

D, G. laciniosus n. sp., holotype (USNM 161746) (same 

as pi. 2, fig. 18), X 5. E, F, G. gnomus n. sp.: E, holotype 

(USNM 161644) (same as pi. 2, fig. 16), detail of the 

proximal part, X 5; F, (USNM 161727), X 5.

the proximal part of G. serratus, but Elles and Wood 

(1901-18) do not give a sufficiently detailed description for comparison.

Occurrence. Ml 138-SD.

Range. Zone of M. cyphus in Alaska.

Dimensions (in millimeters). 

]

USNM-161644 1 __ 

161727 L_

161728.-- 

161729 -.

> Figured specimens.

Length of

some

12. 5 

6.5

15. 5 

4. 2

Theca

0.7 

.6

.7 

. 6

Width

Theca 51

1. 5 

1.3

1.2

Maximum

1.7

1.4

Thecae

centimeter

11-14 

13

12 

13

Length

Theca

0.75

.8

.8 

1. 0

Material. Four compressed, well-preserved specimens. Named after New Latin "gnomus" = diminutive 

fabled being, dwarf.

Holotype USNM 161644.

Figured specimens. USNM 161644, USNM 161727.

Glyptograptus ineertus Elles and Wood

Text figure 10D, E; plate 2, figures 5, 6

Diplograptus (Glyptograptus) tamariscus var. incertus Elles and 

Wood, 1901-18, Mon. British Graptolites, Palaecntographical Society, p. 249, text fig. 168a, b, pi. 30, fig. 

9a-d.

Glyptograptus incertus Elles and Wood. Packham, 1962, Palaeontology, v. 5, p. 518-519, pi. 72, figs. 6, 7, text fig. 4a-d.

Description. According to Packham (1962), the 

rhabdosome is about 2 cm long and is virtually parallel 

sided, with a broad proximal end. The thecae lave 

distinct sigmoidal curvature that is more pronounced 

proximally than distally. They number 11-14 per 

centimeter and overlap approximately a third of their 

length.

The rhabdosome is 0.6-0.8 mm wide at the first pair 

of thecae, widens gradually to about 1.4 mm at 5 mm 

from the proximal end and reaches a maximum width 

of about 1.6 mm. Thecal shape varies throughout the 

rhabdosome; proximally the sigmoidal curvature is very 

strong but decreases in intensity distally. There is a 

resulting lengthening of the excavations toward the 

distal end. The excavations occupy a half or mor3 of 

the rhabdosome width proximally and slightly more 

than a third distally. The apertural margins are horizontal or slightly everted, and the free ventral walls 

above the geniculum are inclined to the rhabdosome 

axis.

Discussion. The Alaskan specimens fit the atove 

description very closely except for being somewhat 

narrower proximally. Also, the proximal thecae on our 

specimens are more nearly climacograptid in shape than 

those figured by Packham (1962).

Occurrence. Ml 138-SD.

Range. Llandoverian zones of M. convolutus to M. 

sedgwickii (Road River Formation) in Yukon Territory, Canada (Jackson and Lenz, 1962). Zones (20 and 

21) of M. convolutus to M. sedgwickii (Birkhill She-les, 

Skelgill Beds) in Great Britain (Elles and Wood, 

1901-18; Toghill, 1968; Packham, 1962). Also reported 

from Portugal by Romariz (1962), in the zone? of 

M. gregarius to M. turriculatus. This species in Alaska 

seems to range lower, into the zone of M. cyphus.
26 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Dimensions (in millimeters). 

Specimen No.

USNM-161730 1 - 

161731 !__ 

161733___ 

161734i__ 

161735. __

Length of rhabdo- - 

some

23. 5 

8. 5 

12 

14 

>13

Theca 1»

0. 5

. 5 

. 5 

. 5

Width

Theca 5 1

1. 1 

1 

1.2 

1. 2 

1.3

Maximum

1. 7 

1.4 

1.7 

1.4 

1. 8

Thecae 

per centimeter

10-12 

12 

11-13 

12 

11-13

i Figured specimens.

Material. About 10 compressed specimens, five of 

which are well preserved.

Figured specimens. USNM 161730, 161731, 161734.

Glyptograptus kayi n. sp. 

Text figure 12E, F; plate 2, figure 15

Description. The rhabdosome tapers from an initial 

width of 0.5-0.6 mm at theca I 1 to a maximum width 

of 1.5-2.0 mm, which is attained at about the seventh 

thecal pair. Thereafter the sides of the rhabdosome 

are approximately parallel. The thecae number 10-13 

per centimeter and are of the glyptograptid type, 

overlapping one-third to one-half of their length. The 

sigmoid curvature of the thecae is much more pronounced distally than proximally; the proximal thecae 

exhibit very little sigmoid curvature. The apertural 

margins are mostly everted, though in some specimens 

they are horizontal or slightly introverted. The proximal end tapers to a short virgella. The sicula is hidden 

on both sides of the rhabdosome, and there is no visible 

septum.

Discussion. This form is unique among Lower 

Silurian glyptograptids in having a hidden sicula and 

no visible median septum. It resembles G. sinuatus 

somewhat but lacks the septum and the rapid widening of the rhabdosome above a slender proximal 

region characteristic of sinuatus.

Occurrence. Nevada: Central Independence Range, 

locality 4 of Kerr (1962).

Range. Zone of M. gregarius in Nevada.

Dimensions (in millimeters'). 

Lengt 

Specimen No. ofrhat 

dosom

USNM-161736--

161737-.

161738---

161739b_.

161739C. _

161740___

161741 '__

161742-._

161743 L.

163744. __

161745- .

3.

13.

6.

9.

4.

6.

12.

8.

7.

10.

12.

h Width )- 

e Theca

0

5

3

6

0

5

5

2

3

7

0

0 5

6

6

5

6

5

6

5

6

5

4

Theca 5>

1.

l'.

1.

1.

1.

1.

1.

1

9

3

3

1

2

2

1

9

Maximum

1.

2.

1.

1.

1.

1.

1.

1.

1.

1.

1.

1

0

5

7

2

5

8

5

5

5

4

Thecae 

per cen- Thecal 

timeter overlap

13

10-12

14

12-13

13

10

10-12

14

9-10

12

10-11

>1/2}!

>Ji

$

ys

%

%

Yi A1

}i-%

i Figured specimens.

H I

FIGURE 12. Glyptograptus and Orthograptus. A, B, 0. 

eberleini n. sp.: A, Holotype (USNM 161783) (same as 

pi. 3, fig. 2), X 5; B, (USNM 161782), X 5. C, H, I, 0. 

insectiformis minutus n. subsp.: C, Small, immature 

specimen showing sicula (USNM 161624b), X 8; H, 

Holotype (USNM 161785), X 5; 7, Small, immature 

specimen (USNM 161624a), X 8. D, fGlyptoy-aptus n. 

sp. (USNM 161776), X 5. E, F, G. kayi n. sp.: E, Holotype (USNM 161741) (same as pi. 2, fig. 15), preserved in 

relief, X 5; F, Proximal fragment (USNM 161743) preserved in partial relief, X 5. G, 0. bellulus 'lornquist 

(USNM 161779) (same as pi. 3, fig. 1), X 5.

Material. Eleven pyritized specimens preserved in 

relief. Named in honor of Professor Marshall Kay of 

Columbia University.

Holotype. USNM 161741.

Figured specimens. USNM 161741, 161743.

Glyptograptus laciniosus n. sp. 

Text figure UD; plate 2, figures 17,18

Description. The rhabdosome is long and slender, 

measuring as much as 2.5 cm in length. It widens 

quickly from a width of 0.6-0.7 mm to a maximum of 

about 1.5 mm and is approximately parallel sided for 

most of its length. The thecae number 10-14 per 

centimeter, exhibit only slight sigmoidal curvature, and 

overlap about a third of their length. The r,pertural 

margins are nearly horizontal and are situated in 

excavations occupying approximately a fourth of the 

width of the rhabdosome. A short virgella is present 

on some specimens.

Discussion. The distinctive feature of thip species 

is the shape of the thecae. The free ventral wall is 

nearly straight. Some thecae show more curvature
SYSTEMATIC DESCRIPTIONS 27

than others, but it is never very pronounced as in 

G. tamariscus. The thecae resemble those of G. serratus, 

but the rhabdosome is considerably narrower and 

shorter than that of G. serratus. The occurrence of a 

number of subscalariform views (pi. 2, fig. 17) indicates 

that the rhabdosome must have been nearly circular 

in cross section.

Occurrence Ml 139-SD, M1141-SD, M1142-SD.

Range. Zones of A. acuminatus, M. cyphus, and 

M. gregarius in Alaska.

Dimensions (in millimeters}.

Specimen No.

USNM-161746 1 - 

161747... 

161748___ 

161749-.. 

161750... 

161751 !._ 

161752.. _ 

161753-.. 

161754... 

161755... 

161756__. 

161757e_. 

161757f__

Length of rhabdosome

23. 7 

25 

>20. 5

21. 6

14 

10. 5 

8 

13 

9 

>8. 5

Theca I 1

0-6

. 7

6

7 

6 

8 

6

. 6

Width

Theca 51 Maximum

1. 2 

1. 2

1. 1 

1. 1 

1. 1 

1.2 

1.2

1. 3

1. 5 

1.7 

1. 5 

1.5 

1. 5 

1.4 

1. 5 

1. 5 

1.5 

1. 5 

1. 5 

1. 5 

1. 5

Thecae 

per centimeter

12-14 

12-13 

11 

12 

12 

11-14 

10-14 

11-13 

12 

11-13 

10 

10 

12

»Figured specimens.

Material. About 35 compressed, fairly well preserved specimens. Named after the Latin "laciniosus" = 

jagged, full of indentations.

Holotype. USNM 161746.

Figured specimens. USNM 161746, 161751.

Glyptograptus lanpherei n. sp. 

Text figure 11C; plate 2, figures 9, 10

Description. The rhabdosome is approximately 1 cm 

long and as much as 2 mm wide. It is wide at its origin 

and may gain close to its maximum width by the fifth 

thecal pair, so that the margins are subparallel for 

most of its length. Most specimens continue to widen 

slightly beyond the fifth thecal pair. The thecae number 10-12 per centimeter, overlap about a third of their 

length and have horizontal or slightly everted apertural 

margins situated in excavations which occupy about 

a fourth of the width of the rhabdosome. The virgella 

is very long, measuring as much as 11.8 mm. The 

virgula is frequently distally prolonged.

Discussion. The thecae exhibit gentle sigmoidal 

curvature. The geniculum is smoothly rounded, and 

the excavations are long. The rhabdosome has a robust 

appearance. It is about 1 mm wide at theca I 1 and 

from 1.4 mm to 2.0 mm wide at the fifth thecal pair. 

The characteristic features of this species are: (1) The 

long virgella, (2) the wide proximal end, (3) the gentle 

sigmoidal curvature of the thecae. In its wide width

and general shape it resembles Diplograptus modertus, 

but all its thecae are glyptograptid. It is also similar 

in appearance to G. kaochiapienensis Hsu (1934), b^'ng 

approximately the same size, with the same number 

of thecae per centimeter and the same amount of 

thecal overlap, a third. Both have a distally prolonged 

virgula and excavations occupying a fourth of the 

width of the rhabdosome. It differs from G. kaochiapienensis by having a wider proximal end, a slightly 

narrower rhabdosome, a longer virgella, and apertural 

margins that are horizontal or slightly everted instead 

of horizontal or introverted.

Occurrence. Ml 139-SD.

Dimensions (in millimeters'). 

Length of

some > Theca

Width

Theca MaxiI1 S1 mum

USNM-161758 2 -

161759 2 -

161760 2 -

161761---

161762.--

161763 

161764.. _

10.

9.

10.

9.

7.

^>7.

17.

2

0

5

2

0

0

7

1.

1.

1.

1.

1.

0

0

9

9

0

1

0

1.

1.

1.

1.

1.

2.

1.

8

9

4

4

5

0

7

2.

2.

1.

1.

1.

2.

2.

0

0

6

7

6

0

0

Thecae Length

centi- virpella

meter

11

11

10-12

12

12

11

10

2.

3.

11.

~^>1.

11.

6.

>H.

3

4

0

0

3

0

8

1 Exclusive of virgella. 

2 Figured specimens.

Material. Seven compressed, well-preserved specimens. Named in honor of Marvin A. Lanphere of the 

U.S. Geological Survey.

Holotype. USNM 161759.

Figured specimens. USNM 161758-161760.

Glyptograptus tamariscus magnus n. subsp. 

Text figure 11A, B; plate 2, figure 7, 8

Description. The rhabdosome is as much as 5 cm 

long, smoothly tapering from 0.7 mm wide at tbeca 

I 1 through 1.0 mm wide at theca 51 to a maximum 

width of about 2.2 mm distally. The thecae vary in 

shape throughout the rhabdosome and number seven 

to 11 per centimeter. The apertural margins are even 

and horizontal. The excavations occupy approximately 

a fourth of the width of the rhabdosome. The virgula 

is stout and measures as much as 2.0 mm long.

Proximally, the thecae number 10-11 per centimeter. 

The geniculum is abrupt, and the free ventral vail 

above the geniculum is approximately vertical p,nd 

much longer than the margin below the geniculum. As 

the rhabdosome widens, so do the excavations, so that 

they always occupy about a fourth of the width of the 

rhabdosome. Distally, the geniculum becomes less 

abrupt and more rounded, the excavations become 

longer and more open, and the free ventral wall above 

the geniculum becomes relatively shorter and more
28 EARLY SILURIAN GRAPTOLITES FROM ALASKA

nearly equal in length to the margin below the geniculum.

Discussion. The characteristic features of this form 

that distinguish it from G. tamariscus are: (1) The long 

smoothly tapering rhabdosome, (2) the narrow, elongated appearance of the proximal end, (3) the varying 

shapes of the thecae, (4) the long, stout virgella and 

(5) the greater width of the rhaddosome.

Occurrence. M1138-SD, M1139-SD.

Range. Zone of M. cyphus in Alaska.

Dimensions (in millimeters'). 

i Figured specimens.

Material. Approximately 15 compressed, well-preserved specimens. Named after the Latin "magnus"= 

large, great.

Holotype. USNM 161765.

Figured specimens. USNM 161765, 161766, 161771.

Glyptograptus cf. G. tamariscus var. tamariscus (Nicholson) 

Text figure 10F

Diplograptus (Glyptograptus) tamariscus Nicholson. Elles and 

Wood, 1901-18, Mon. British Graptolites, Palaeontographical Soc., p. 247, text fig. 167a-e, pi. 30, fig. 8a.

Glyptograptus tamariscus tamariscus (Nicholson). Packham, 1962, 

Palaeontology, v. 5, p. 504-506, pi. 71, figs. 1-4, 11, 13, 

text fig. Ig-j, m-u.

Description. According to Packham (1962), the 

rhabdosome is narrow and tapering, reaching a width 

of 1.3 mm in flattened specimens. The thecae are 

alternating, numbering eight to 14 per centimeter and 

having a small amount of overlap. The excavations 

occupy approximately half the width of the rhabdosome, 

and the apertural margins are horizontal to slightly 

everted. The free ventral wall above the geniculum is 

nearly perpendicular and longer than the length of the 

excavation. The geniculum is rounded.

Discussion. G. tamariscus s.s. as described by 

Packham (1962) differs from G. tamariscus as described 

by Elles and Wood (1901-18) in the following ways: 

(1) It is wider (2 mm wide vs. 1 mm wide in Elles and 

Wood), (2) it has horizontal or everted apertural 

margins instead of horizontal or introverted apertural 

margins as in Elles and Wood, (3) it has seven to 14

Specimen No.

USNM-161765 L_ 

161766 »._ 

161767- _ 

161768- _ 

161769.-- 

161770- -_ 

161771 L161772- _ 

161773- _ 

161774. __ 

161775- -

Length of Width

some Theca 1' Theca 51 Maximum

42 0 

25. 5 

20. 0 

24. 2 

16.5 

37. 5 

>49 

34. 5 

8.5 

>12. 7 

17

7 

7 

7 

7 

6 

7

7 

7 

7 

7 

7

1. 0 

1. 0 

1. 0 

1.0 

1. 0

1. 0 

1. 0 

1. 0 

.9 

1. 0

2. 25 

1.8 

1.75 

1. 2 

1.7 

2. 0 

2. 1 

2.2 

1. 2 

1. 5 

1.6

Thecae per 

centimeter

8-10 

10 

9-11 

10 

11 

7-11 

8-11 

8^-11 

13

12

thecae per centimeter instead of the 12-14 tHcae per 

centimeter reported by Elles and Wood.

G. tamariscus var. tamariscus is a tapering form of 

G. tamariscus, reaching 1.3 mm in width and having 

deep and relatively long thecal excavations. The 

specimens from locality M1140-SD have bQ,eii distorted and are questionably referred to this sp gcies.

Occurrence. Ml 140-SD, M1142-SD.

Range. Llandoverian zones (18-21) of M. cyphus 

to M. sedgwickii (Birkhill Shales) in Great Britain 

(Packham, 1962). G. tamariscus is reported from the 

following localities: Llandoverian zones of D. modestus 

and M. cyphus (Road River Formation) in Yukon 

Territory, Canada (Jackson and Lenz, 1962); the zone 

of M. cyphus (Cape Phillips Formation) in the Canadian 

Arctic (Thorsteinsson, 1958); Llandoverian zones of 

M. cyphus to M. sedgwickii, in Portugal (Romariz, 

1962); Llandoverian zone of Demirastrites convolutus in 

Bohemia, Czechoslovakia (Pribyl, 1948); Germany 

(Hundt, 1924); Russia (Obut, 1949; Obut and others, 

1965); Llandoverian zone with M. leei (lower Kaochiapien, Shale) in China (Hsii, 1934); Middle Polindiaii 

to Middle Keilorian stages in Australia (Thomas, 1960; 

Sherrard, 1954; Harris and Thomas, 1949).

Dimensions (in millimeters). 

]

USNM-161630--

161985 

161986 L161987- .

length of

some

7.0

3. 0

>4. 0

9.0

Theca H

0. 5

. 5

Width

Theca 51 Maximuir

-------- 1.0

7

.8 __.._.__

_-__-___ 1.0

Thecae

meter

12

15

12

14

1 Figured specimen.

Material. About 23 compressed specimens; the two 

imdeformed specimens are fragmentary, and the rest 

are distorted.

Figured specimen. USNM 161986.

?Glyptograptus n. sp. 

Text figure 12D

Description. The rhabdosome is approximately 1 cm 

long, increasing gradually in width from about 0.9 mm 

at the first thecal pair to a maximum of about 2 mm. 

The thecae number 11-12 per centimeter and have a 

large amount of sigmoid curvature so that they are 

almost climacograptid in appearance. The geniculum is 

rather abrupt, and the free ventral wall above it is 

nearly vertical.The apertural margins are apprc ximately 

horizontal.

Discussion. This species is intermediate hi appearance between Glyptograptus and Climacograptus. The 

excavations are deep and narrower than usual for a 

glyptograptid. They occupy about a third of the width
SYSTEMATIC DESCRIPTIONS 29

of the stipe. The characteristic features of this form are: 

(1) The wide proximal part and (2) the shape of the 

thecae. Because of the scarcity and poor quality of 

preservation of the specimens, this form has not been 

named.

Occurrence. Ml 142-SD.

Range. Zone of M. gregarius in Alaska.

Dimensions (in millimeters).

Specimen No.

Length of

some Theea li

Width

Theca 5«

Maximum

Thecae 

per centimeter

Length 

of 

Theca li

USNM-161776 1 -. :

161777-.

161778__ _ >

>9 3

4 3

10. 0

0.9

.9

1. 0?

1.7

1.5?

1.6?

2. 0 1

1. 7

1V»-12

12 1. 0

12 _.___

i Figured specimen.

Material. About five compressed, poorly preserved 

specimens.

Figured specimen. USNM 161776.

Genus ORTHOGRAPTUS Lapworth, 1873

Orthograptus Lapworth. Bulman, 1955, Geol. Soc. America, 

Treatise on invertebrate paleontology, pt. V, p. V87, fig. 

63, 5a-c.

Rhabdosome biserial, scandent. Thecae nearly 

straight or slightly curving. Large basal spines fairly 

common. Some species have paired apertural spines. 

Middle Ordovician to Lower Silurian, worldwide.

Orthograptus bellulus Tornquist 

Text figure 12<?; plate 3, figure 1

Diplograptus (Orthograptus) bellulus Tornquist. Elles and Wood, 

1901-18, Mon. British Graptolites, Palaeontographical 

Soc., p. 231-232, text fig. 152, pi. 29, fig. 2a-e.

Diplograptus bellulus Tornquist. Hundt, 1924, Grapt. d. deutsch., 

Silurs, p. 60, pi. 2, figs. 14-16.

Diplograptus (Orthograptus) bellulus Tornquist. Stein, 1965, Neues 

Jahrb. Geologic u. Palaontologie Abh., p. 170-171, text 

fig. 19a, b.

Discussion. Elles and Wood (1901-18) state that 

0. bellulus has 10-14 thecae per centimeter. However, 

then- figured specimens (pi. 29, fig. 2a-d) have 16-18 

thecae per centimeter proximally, as do the Alaskan 

specimens. (Note: The table of dimensions below gives 

the number of thecae extrapolated to 1 cm even though 

none of the specimens are that long.) The virgellas on 

the Alaskan specimens are shorter than the 8-mm 

virgellas cited by Elles and Wood (1901-18), but this 

may be due to poor preservation.

Occurrence. Ml 142-SD.

Range. Llandoverian zones (19-21) of M. gregarius 

to M. sedgwickii (upper Birkhill Shales) in Great 

Britain (Elles and Wood, 1901-18). Toghill (1968)

limits the range of 0. bellulus in the Birkhill Shale? to 

the zone of M. convolutus. Llandoverian zones of 

Demirastrites convolutus to M. sedgwickii in Bohemia, 

Czechoslovakia (Pribyl, 1948). Also found in Germany 

(Hundt, 1924). Thorsteinsson (1958) reported an 

0. bellulus-like form from the zone of M. cyphus (Cape 

Phillips Formation in the Canadian Arctic. 

Dimensions (in millimeters). 

Length

of 

Specimen No. rhabdosome Theca ! Theca 5i Maximum

Width

Thecae Lergth 

per of

centimeter virpjlla

USNM-161779L 5.7

161780__ >5

161725c. >4

161781__ 6

0.9

.8

.8

.7

1.6

1.6

1.5

1. 5

2.0

1.8

1.7

1.6

16

16

20

16

1. 2

5.4

1. 0

1. 0

i Figured specimen.

Material. About five compressed, fairly well preserved specimens. 

Figured specimen. USNM 161779.

Orthograptus eberleini n. sp. 

Text figures 12A, B; plate 3, figure 2

Description. The rhabdosome is small and slender, 

being less than 7 mm in length and 1.5 mm in width. 

The sicula is about 1.5 mm long. The thecae are narrow, 

numbering 12 per centimeter and overlapping onethird to one-half their length. The apertural margins 

are horizontal and very slightly undulate, occupying 

about one-fourth the width of the rhabdosome.

The rhabdosome is gently curved. Theca I 1 has a 

short spine near its origin, which is near the aperture 

of the sicula. The sicula is free on one side for al out 

0.3 mm and the virgella is very short (about 0.25 n?m). 

The thecae average about 1 mm long, but some ar°. as 

much as 1.3 mm long.

Discussion. This species resembles 0. cyperoides and 

differs from it by having: (1) Greater width, (2) a 

shorter sicula, (3) a shorter theca I 1 and, (4) a shelter 

free edge on the sicula. In general appearance. 0. 

eberleini resembles Akidograptus. However, Altidograptus is characterized by loss or reduction of theca I 2 

and a slender, elongate-looking proximal part in 

which the apex of the sicula is well below the level of 

the aperture of theca I 1 . The apex of the sicula in 

0. eberleini extends to approximately the level of the 

aperture of theca I 1 , and the proximal region is relatively wide.

Occurrence. M1138-SD, M1139-SD.

Range. Zones of M. vesiculosus and M. cyphus in 

Alaska.

Dimensions (in millimeters).

369-097 O - 70 - 5
30 EARLY SILURIAN GRAPTOLITES FROM ALASKA

USNM-161782i__ 

161783 i__ 

161784...

Length

some

6.0 

6.4 

2. 3

Width

Theca I 1 Maximum

__.__._- 1.5 

1.0 1. 3 

1.0 1.2

Thecae

centimeter

12 

12

Length

Sicula

1. 3 

1.5 

1.5

i Figured specimens.

Material. Five compressed, fairly well preserved 

specimens. Named in. honor of G. Donald Eberlein of 

the U.S. Geological Survey.

Holotype. USNU 161783.

Figured specimens. USNM 161782, 161783.

Orthograptus insectiformis minutus n. subsp. 

Text figure 12C, H, I

Description. This is a small variety of 0. insectiformis. The rhabdosome readies 1.5 cm in length and 

is about 1 mm wide (exclusive of spines). There are 

16-20 thecae per centimeter (in contrast to 10-12 

thecae per centimeter reported by Elles and Wood, 

1901-18). The apertural margins are prolonged into 

apertural spines, some of which are paired. The sicula 

is about 0.8 mm long with one-half to one-third of its 

length free on one side.

The rhabdosome reaches its maximum width by 

about the fourth thecal pair. It is 0.8-0.9 mm wide at 

theca I1 and about 1.0 mm wide at theca 31 , thereafter 

being approximately parallel sided. The apertural 

spines have a maximum length of about 0.7 mm, and 

often, two spines per theca can be seen.

Discussion. Because all the specimens are flattened, 

it is not possible to determine with certainty if the 

apertural spines actually are two separate spines or if 

a single spine is forked near its base.

The features that distinguish this subspecies from 

0. insectiformis are: (1) Its smaller size, (2) its more 

closely set thecae, (3) its shorter sicula, and (4) its 

paired spines.

Occurrence. M1140-SD, M1142-SD.

Range. Toghill (1968) gives the range of 0. insecfiformis s.s. in Great Britain (Birkhill Shales) as the 

zone of M. gregarius. In southeastern Alaska, the new 

subspecies occurs in the zones of M. gregarius and M. 

convolutus.

Dimensions (in millimeters). 

Length 

Specimen No. of rhabdosome

USNM-161785 1 .. 

161624a !_ 

161624bi. 

161786a__ 

161786b__

9 

2.8 

2.0

Width (exclusive of

spines)

Theca li

0.8 

.8 

.9

Theca

1. 0 

1. 0 

1.0

Maximum

1. 1 

1.0 

1. 0

.8 

. 8

Thecae 

per centimeter

16 

20 

20 

16 

16

Length 

of 

spines

0.7

.75 

.3

1 Figured specimens.

Material. About eight compressed, fragmentary 

specimens. Named after the Latin "minutus"=lit tie, 

small.

Holotype. USNM 161785.

Figured specimens. USNM 161785,161624a, 16124b.

Orthograptus cf. 0. mutabilis Elles and Wood 

Plate 2, figure 14

Diplograptus (Orthograptus) mutabilis Elles and Wood, 1901-18, 

Mon. British Graptolites, Palaeontographical Soc., p. 

232-233, text fig. 153, pi. 29, fig. la-d.

Description. According to Elles and Wood (1901- 

18), the rhabdosome of 0. mutabilis is large, 4-5 cm 

long, widening rapidly from the origin until a maximum 

width of 3-3.5 mm is reached, after which the margins 

are nearly parallel. The thecae number nin^ to 12 

per centimeter and overlap one-half to two-thirds of 

their length. The apertural margins are slightly lobate 

and have a fairly conspicuous rim or flange. The sicula 

is large.

Discussion. Three incomplete specimens are present 

in the collections under study. All are about 2.5 cm 

long, and range in width from 2.8 to 3.1 rrm. The 

thecae have lobate apertural margins similar to those 

of 0. mutabilis and number eight to 10 per certimeter. 

These specimens agree with 0. mutabilis in every respect, but the absence of any proximal ends prohibits 

positive identification.

Occurrence. M1138-SD.

Range. Llandoverian zones of M. cyphus and M. 

gregarius in Great Britain (Elles and Wood, 1901-18).

Figured specimen. USNM 161787.

Orthograptus vesiculosus Nicholson 

Plate 2, figures 11-13

Diplograptus (Orthograptus) vesiculosus Nicholson. Elles and 

Wood, 1901-18, Mon. British Graptolites, lalaeontographical Soc., p. 229-230, text fig. 151, pi. 28, fig. 8a-d.

Diplograptus vesiculosus Nicholson. Hundt, 1924, Grapt. d. 

deutsch. Silurs, p. 60, pi. 18, figs. 1, 12.

Cystograptus vesiculosus (Nicholson). Obut, Sobolevskaya, and 

Bondarev, 1965, Graptolity Silyura Taimyra, p. 34-35, 

pi. 2, figs. 1-4.

Discussion. The Alaskan specimens have araertural 

margins that are distinctly more lobate than those 

figured by Elies and Wood (1901-18). TH most 

characteristic feature of this species is the consnicuous, 

"three-vaned" membranous body within the rhabdosome (see Jones and Kickards, 1967).

Occurrence. Ml 138-SD, M1139-SD, M1288-SD, 

M1289-SD, M1290-SD.

Range. Llandoverian zones of M. cyphus to M. 

miUepeda (Road River Formation) in Yukon Territory, 

Canada (Jackson and Lenz, 1962). Llandoverif.n zones
SYSTEMATIC DESCRIPTIONS 31

of A. acuminatus to M. cyphus (Birkhill Shales) in 

Great Britain (ToghilJ, 1968). Llandoverian zones of 

0. vesiculosus and M. cyphus in Portugal (Romariz, 

1962). Llandoverian zone of Pristiograptus cyphus in 

Bohemia, Czechoslovakia (Pribyl, 1948). Lower Llandovery in Pulau Langgon, Langkawi Island, Malaya 

(Kobayashi and others, 1964). Lower Silurian (basal 

part of Fuchih Shale) in Hupei, China (Sun, 1933). 

Also reported from Germany (Hundt, 1924, 1953) and 

Russia (Obut and others, 1965). 

Dimensions (in millimeters). 

Specimen No.

USNM-161788 !-___.

161789 _ __.

161790 i____.

161791. __ _.

161792. _____

161793. _____

161794. _____

Length of Width 1

Theca li Maximum

>15. 5

7.5

22. 0

20.0

>15. 0

13.0

. >25. 0

1.9 

1. 8 

2.2

1.7

1.8

3. 5 

3.5 

4.3 

2. 5 

3.6 

3. 2 

4.0

fhecae per 

ientimeter

12 

14 

8-10 

8ft 

10 

10 

10

1 Figured specimens.

Material. -Approximately 40 compressed, wellpreserved specimens, some of which are fragmentary. 

Figured specimens. USNM 161788, 161790, 161794.

?0rthograptus n. sp. 

Text figure 13I>: plate 3, figure 4

Description. The rhabdosome is small, measuring 

as much as 2 cm long with a width of 0.5-0.7 mm at 

theca I 1 and a maximum width of 1.5 mm (including 

apertural lobes). There are usually 10 thecae per 

centimeter although one specimen has 12-14 per 

centimeter. The proximal end bears five to six long, 

slender spines that measure not more than 1.5 mm in 

length. The rhabdosome is smoothly tapering for about 

the first 5 mm of its length, after which it becomes approximately parallel sided.

Discussion. The most characteristic features of this 

species are the proximal spines and the fact that it is 

always preserved in what appears to be a subscalarif orm 

view. In this view, the thecae appear to have straight, 

nearly parallel, vertical walls. The rhabdosome is 

crossed at regular intervals by the traces of the apertural 

margins. Short, thick lobes developed at the ends of 

the apertures project beyond the outline of the rhabdosome. The arrangement of the proximal spines is 

slightly variable. Generally, there are three to four 

slender, some what flexed spines grouped very closely 

together and growing from the extreme end of the 

rhabdosome. At the same time, one to two spines are 

a short distance from the main cluster. Because of the 

subscalariform preservation, the thecal character is unD

FIGUEE 13. Orthograptus, Petalograptus, Dimorphograptus, 

and Akidograptus. A, P. palmeus var. tennis Barrande, 

(USNM 161811), reverse view, preserved in relief, X 5. 

B, C, Akidograptus acuminatus (Nicholson): B, (USNM 

161832) (same as pi. 3, fig. 17) X 5; C, (USNM 161833), 

X 5. D, ?Orthograptus n. sp. (USNM 16l796b), proximal 

and distal parts, in subscalariform view, X 5. E, F, P. 

minor Elles: E, Immature specimen showing sicula, Y 5; 

F, (USNM 161800) (same as pi. 3, fig. 5), X 5. G, P. 

palmeus (Barrande) (USNM 161808) (same as pi. 3, 

fig. 6), X 5. H, I, D. physophora alaskensis n. subsp.: H, 

Holotype (USNM 161826), showing sicula (same as p1 . 3, 

fig. 7), X 5; /, Proximal fragment (USNM 161S27), 

showing long sicula, X 5.

certain, and therefore this species has not been named. 

However, the lobed apertural margins and the seined 

proximal end suggest Orthograptus.

Occurrence Ml 139-SD, M1286-SD, M1287-SD.

Range. Zone of A. acuminatus in Alaska.

Dimensions (in millimeters) . 

Specimen No. Length of

Width (including 

spines) T

Theca I1 Maximum

USNM-161795 1 . 

161796b'_ _. _-

161796a__--_-

161797-------

161798------

7.5 

17. 3 

14 _.

19

7

0.5

. 7

. 5 

.6

1.2 

1. 4 

1. 5 

1. 5 

1.5 _.

hecae per 

entitueter

12-14 

10 

10 

10

Figured specimens.

Material. Five compressed, fairly well preserved 

specimens, all in subscalariform view. 

Figured specimens. USNM 161795, 161796b.
32 EARLY SILURIAN GRAPTOLITES PROM ALASKA

Subfamily PETALOGRAPTINAE

Genus PETALOGRAPTUS Suess, 1851

Petalograptus Suess. Bulman, 1955, Geol. Soc. America, Treatise 

on invertebrate paleontology, pt. V, p. V87, figs. 63, 6a, b.

Rhabdosome tabular, leaf shaped. Thecae long, 

nearly straight or with gentle ventral curvature, at a 

considerable angle to the rhabdosome axis, with large 

overlap. Septum partial or absent, sicula largely 

exposed. Lower Silurian; Europe, Australia, China, 

North Africa, and North America.

Petalograptus minor Elles 

Text figure 1BE, F; plate 3, figure 5

Petalograptus minor Elles. Elles and Wood, 1901-18, Mon. 

British Graptolites, Palaeontographical Soc., p. 279-281, 

text fig. 193, pi. 32, fig. 5a-e.

Petalograptus minor Elles. Sun, 1933, Palaeont. Sinica, ser. B, 

v. 14, pt. 1, p. 33, pi. 5, fig. 5a, b.

Discussion. The Alaskan specimens agree with the 

description of P. minor by Elles and Wood (1901-18) 

except for the number of thecae per centimeter. Elles 

and Wood state that P. minor has 12 thecae per 

centimeter, and their figures (pi. 32, fig. la-c) show 

14-16 thecae per centimeter. The Alaskan specimens 

have about 20 thecae per centimeter, and in this 

respect they resemble P. posterns Ruedemann (1947), 

which was found in the same area of Alaska. However, 

Ruedemann's figures are rather indistinct and prevent 

positive identification. The long sicula, small size, 

and protracted proximal end of the Alaskan specimens 

indicate that they are P. minor.

Occurrence. Ml 142-SD.

Range. Llandoverian zones (19 and 20) of M. 

gregarius to M. convolutus (Birkhill Shales) in Great 

Britain (Elles and Wood, 1901-18). Llandoverian 

zones of Demirastrites pectinatus to D. triangulatus in 

Bohemia, Czechoslovakia (Pribyl, 1948). Lower Silurian 

(Fuchih Shale) in Changyang district, Hupei, China 

(Sun, 1933). Also, Petalograptus cf. P. minor reported 

from Llandoverian zone (20) of M. convolutus (Phi 

Kappa Formation) in Idaho (Churkin, 1963).

Dimensions (in millimeters'). 

Specimen No.

Length of Maximum Thecae Length of 

rhabdo- width of per sicula 

some rhabdo- centimeter 

some

TJSNM-161799----__-_

161800 L... _

161801c-.._ _

161802 __ ___.

4.8

4.5

3.0

6.3

3.6

3.2

2.6

3.3 ..

20 

90

20?

1 t\

1.2

1.6

Figured specimen.

Material. Approximately seven compressed, moderately well preserved specimens. 

Figured specimen. USNM 161800.

Petalograptus palmeus (Barrande) 

Text figure 13(?; plate 3, figure 6

Petalograptus palmeus s. s. (Barrande). Elles and Wood, 1901-18 

Mon. British Graptolites, Palaeontographical Soc., p. 

274-275, text fig. 188, pi. 32, fig. la-d.

Diplograptus palmeus Barrande. Hundt, 1924, Grapt. d. deutsch. 

Silurs, p. 58, pi. 2, figs. 24-26.

Petalograptus palmeus (Barrande). Sun, 1933, Palaeont. 

Sinica, ser. B, v. 14, pt. 1, p. 31-32, pi. 5, fig. 4a-b.

Diplograptus (Petalograptus) palmeus (Barrande). Obut, 1949, 

Polyevoi Atlas, Rukovodyashchich graptolitov vyerkhnyevo Silura Kirgizskoi SSR, p. 15, pi. 1, fig. 7a, b.

Discussion. The specimens under study compare 

closely with the description and illustrations of P. 

palmeus s.s. by Elles and Wood (1901-18).

Occurrence. Ml 140-SD.

Range. Llandoverian zones of M. millepida to 

M. turriculatus (Road River Formation) of Yukon 

Territory, Canada (Jackson and Lenz, 1962). Zone of 

M. turriculatus (Cape Phillips Formation) in the 

Canadian Arctic (Thorsteinsson, 1958). Liandoverian 

zones (19-22) of M. gregarius to M. turriculatus 

(Birkhill-Gala) in Great Britain (Elles and Wood, 

1901-18). Lower Silurian Fuchih Shale at Lungma, 

Ichang, Hupei, China (Sun, 1933). Also reported from 

Germany (Hundt, 1924, 1953), Portugal (Romariz, 

1962), and Russia (Obut, 1949).

Dimensions (in millimeters). 

Specimen No.

USNM-161803.. 

161804 . 

161805b..-.

161806 

161807 

1618081. . 

161809 ...

Length

rhabdosome

9 0

7.0 

6.5

8.5

13

9

1st 

thecal 

pair

1.4?

1.0?

1.1 

1.0

Width

3d

thecal 

pair

9 n?

2.0 

. 1.7

1.7 

1.6

Maximum

2.5

2.0 

2.5

2.5

2.5

2.5 

2.5

Thecae

centimeter

14

14 

15

14

15? .

13 

13

of 

sicula

1.8 

1.E

2.'0

LQUErtli

of 

thecae

0. 5-1. 5 

.5-1.7

1.6

1.5

.5-1.5 

.5-1.5

1 Figured specimen.

Material. Approximately 10 compressed distorted 

specimens, half of which are fragmentary. 

Figured specimen. USNM 161808.

Petalograptus palmeus var. tenuis Barrande 

Text figure ISA; plate 3, figure 3

Petalograptus palmeus var. tenuis Barrande. Elles anc1 Wood, 

1901-18, Mon. British Graptolites, Palaeontofaphical 

Soc., p. 276-277, text fig. 190, pL 32, fig. 3a-d.
SYSTEMATIC DESCRIPTIONS 33

Description. According to Elles and Wood (1901-18, 

p. 276), this variety differs from P. palmeus s.s. in (1) 

its extreme narrowness, (2) the smaller number of 

thecae per centimeter, and (3) the relative proportions 

of the thecae and the general absence of curvature of 

their walls.

The Nevadan specimens are somewhat wider than 

those described by Elles and Wood (1901-18). They 

exhibit a partial septum there is no trace of a median 

septum on the reverse side.

Discussion. P. palmeus tenuis differs from P. minor, 

the other small petalograptid in our collection, by 

having a much smaller angle of inclination of its thecae. 

Also P. minor has more thecae per centimeter (about 

20) than does P. palmeus tennis.

Occurrence. Nevada: Central Independence Range, 

locality 4 of Kerr (1962).

Range. Llandoverian zone of M. turriculatus ( Road 

River Formation) in Yukon Territory, Canada (Jackson and Lenz, 1962). Llandoverian zones of M. sedgwickii and R. maximus (Birkhill Shales) in Great

Discussion: There is considerable variation in the 

Alaskan species. The specimens under study range from 

as much as 2.2 mm in width, through all gradations to a 

narrow form measuring as little as 1.25 mm in width. 

The number of thecae per centimeter ranges from nine 

to 13. The sicula is approximately 2 mm long, extending 

up to the level of the aperture of theca 1, and bears a 

short virgella. Theca 1 originates slightly above the 

aperture of the sicula so that the sicula alone forms the 

proximal termination of the rhabdosome. The Alaskan 

specimens are generally narrower than those described 

by Elles and Wood (1901-18). Also, the abrupt widening 

of the rhabdosome where it becomes biserial is less 

pronounced in the Alaskan material.

Occurrence M1138-SD. M1139-SD, M1289-SE.

Range. Llandoverian zone of M. cyphus (BirMiill 

Shales) in Great Britain (Toghill, 1968). Also reported 

from Germany (Hundt, 1924, 1953) and Russia 

and others, 1967).

Dimensions (in millimeters}. 

Britain (Toghill, 1968). Zones of R. linnaei to M. 

griestoniensis in Bohemia, Czechoslovakia (Pribyl, 

1948). 

Dimensions (in millimeters). 

Length of Maximum Thecae 

Specimen No. rhabdo- width of per Length of 

some rhabdo- centimeter sicula 

some

USNM-161810___. _______ 3.5 1. 5 ________ 2.0?

161811 1 __________ 5.5 2.8 13-14 ________

161812 L _ __ _ 5.0 2.0 12 2.8

1 Figured specimen.

Material. About five pyritized specimens preserved 

in relief. 

Figured specimens. USNM 161811, 161812.

Specimen No.

USNM-161813____.

161814 i 

161815_.__.

161816 i___.

161817d.__.

161817e-__.

161817f___.

161818 __ .

161819.- _-

161820____.

161821 __ .

161822__.-.

161823 i.-..

161824 » __.

161825.-. __

Length 

of rhabdosome

11.5

15. 5

15.1

16. 5

9.7

10.5

i o e

21

13

9. 5

9.2

10. 0

.__ >12

__ >15

Width 

of biserial 

part

2.2 

2.0 

2. 0 

1.8 

1.7 

1.3 

1.5 

1.5 

1.25 

1.4 

1.7 

1.5 

1.5 

1.5 

1. 8

Uniserial part

Length Width

6.5 0 

6. 0 

5. 0 

5.8 

4.75 

5 

4.5 

5 

6. 1 

6.5 

4.6 

4.5 

5.7 

7

5

5 

5 

5 

5 

5 

3 

5 

4 

3 

4 

4 

3 

5 

25 

4

Thecae 

per 

centimeter

13 

12 

12 

12 

11

14 

11 

9 

11 

11 

12 

12 

10 

12

1 Figured specimens.

Family DIMORPHOGRAPTIDAE 

Genus DIMORPHOGRAPTUS Lapworth, 1876

Dimorphograptus Lapworth. Bulman, 1955, Geol. Soc. America, 

Treatise on invertebrate paleontology, pt. V, p. V90-91, 

fig. 67, 2a, b.

Proximal part of rhabdosome uniserial, becoming biserial distally. Thecae of orthograptid or glyptograptid 

type. Uniserial part of varying length. Lower Silurian; 

Europe, China, North America.

Dimorphograptus confertus var. swanstoni (Lapworth) 

Text figure 14C, D; plate 3, figure 8-10

Dimorphograptus conjertus var. swanstoni (Lapworth). Elles and 

Wood, 1901-18, Mon. British Graptolites, Palaeontographical Soc., p. 350-352, text fig. 228, pi. 35, fig. 4a-f.

Dimorphograptus swanstoni Lapworth, Hundt, 1924, Grapt. d. 

deutsch. Silurs, p. 78, pi. 7, figs. 13-21.

Material. Approximately 30 compressed, fairly well 

preserved specimens, some of which are fragmentary.

Figured specimens. USNM 161814, 161816, 161823, 

161824.

Dimorphograptus physophora alaskensis n. subsp. 

Text figure 13H, I; plate 3, figure 7

Description. The rhabdosome is less than 1 cm long 

and has a maximum width of about 2.3 mm. The 

uniserial part is very short and straight, and the 

biserial part is also straight. The sicula is long and 

conspicuous. The thecae number 12-14 per centimeter 

and overlap one-half to two-thirds of their length. The 

apertural margins are approximately horizontal.

The uniserial part of the rhabdosome is composed of 

only one theca. At the aperture of theca I1, the rhab-
34 EARLY SILURIAN GRAPTOLITES FROM ALASKA

dosome measures 1.0 mm in width; it increases to as 

much as 1.9-2.0 mm at the commencement of the biserial 

part. The maximum width is attained shortly thereafter, and the margins of the rhabdosome are approximately parallel for most of their length. The sicula is 

about 2.0 mm long. The free ventral margins of the 

thecae are nearly straight; the apertural margins show 

a tendency to eversion at the proximal end of the 

rhabdosome but quickly become horizontal distally.

Discussion. This subspecies differs from D. physophora in (1) having a wider proximal end with only 

one uniserial theca, (2) having more closely set thecae, 

(3) having a longer sicula, (4) showing little or no 

evidence of a proximal disc, and (5) having a shorter 

rhabdosome (maybe due to immaturity).

Occurrence. M1138-SD, M1290-SD.

Range. Zone of M. cyphus in Alaska.

Dimensions (in millimeters). 

Specimen No.

Length of

some Theca

Width

Theca

12

Maximum

Thecae 

per centimeter

Length 

of 

sicula

USNM-161826'__ 

161827!__ 

161828_ 

161829___

8. 5 1. 0

3. 6 1. 0

5. 0 1. 0

3. 0 1. 0

1.9 

2. 1

1. 9

2. 0

2.2

2.3 

2. 1 

2. 0

12

14

14

14

2. 0 

2. 0 

2. 0 

2. 0

1 Figured specimens.

Material. Four compressed, well-preserved specimens. Named after Alaska, the 49th state of the Union 

and North America's last major frontier.

Holotype. USNM 161826.

Figured specimens. USNM 161826, 161827.

Genus AKIDOGRAPTUS Davies, 1929

Akidograptus Davies. Bulman, 1955, Geol. Soc. America* 

Treatise on invertebrate paleontology, pt. V, p. V91, 

fig. 67, 1.

Rhabdosome mostly biserial; thecae climacograptid 

or orthograptid; proximal end characteristically exhibits loss or reduction of theca I2 , but there is no 

apparent uniserial part due to the shortening of theca 

22 ; initial bud downwardly directed at origin. Lower 

Silurian; Europe, northeastern USSR, China, and 

Alaska.

Akidograptus acuminatus (Nicholson) 

Text figure 13B, C; plate 3, figures 16, 17

Cephalograptus(?) acuminatus (Nicholson). Elles and Wood, 

1901-18, Mon. British Graptolites, Palaeontographical 

Soc. p. 289-295, text fig. 199, pi. 32, fig. lla-d.

Diplograptus acuminatus Nicholson. Hundt, 1924, Grapt. d. 

deutsch. Silurs, p. 59, pi. 2, figs. 9, 10, 17.

Diplograptus, (Akidograptus) acuminatus acuminatus Nicholson. 

Stein, 1965, Neues Jahrb. Geologic u. Palaontologie Abh., 

121, 2; p. 174-175, text fig. 22e, f, pi. 15, fig. c.

Akidograptus acuminatus (Nicholson). Obut, Sobolevskaya, and 

Nikolaiyev, 1967, Graptolity i stratigraphiia nizhnego 

Silura okrainnykh podniatii kolymskogo ma^siva, p. 

74-75, pi. 6, figs. 10-13.

Akidograptus acuminatus (Nicholson). Toghill, 1965 (unpub. 

thesis) p. 61-65, figs. 7-4, 7-5, 7-6.

Description. According to Elles and Wood (1901- 

18), the rhabdosome is 1-3 cni long and straight or 

slightly curved. It increases gradually in width from a 

narrow protracted proximal end to a maximum width 

of 1.5 mm, which is thereafter maintained. The sicula 

is very long (2.5 mm) and slender. The thecae are of 

the orthograptid type, numbering about 10 per centimeter, and overlapping one-half their length. The 

outer walls of the thecae may exhibit gentle sigmoid 

curvature; the apertural margins are introverted and 

develop an acute denticle when compressed.

D'iscussion. Akidograptus acuminatus is a fairly distinctive form. The narrow, protracted proximal end 

serves to distinguish it from the diplograptids. The 

orthograptid-type thecae distinguish it from other 

species of Akidograptus.

Occurrence. M1139-SD, M1141-SD, Mir^6-SD, 

M1287-SD(?).

Range. Llandoverian zone of A. acuminatus (Birkhill Shales) in Great Britain (Elles and Wood, 1901-18; 

Toghill, 1968). Llandoverian acuminatus zone in the 

Frankenwald (Northeastern Bavaria) (Stein, 1965). 

Zone of A. acuminatus A. ascensus in Russia (Kolyma 

Massif) (Obut and others, 1967).

Dimensions (in millimeters). 

Length of Width of rhabdosome Thecae per Sicula Specimen No. rhabdo- centimeter length 

some Theca I1 Maximum

USNM-ieiSSO 1 ..

161831 _

161832 i__

161833 !__

13. 0

7. 5

3. 7

5 9

0.4 __

. 5 __

.5

1.5

1. 5

12 ________

2 13

2 12 _ ______

1 Figured specimens.

2 Approximate.

Material. Four compressed, fragmentary specimens. 

Figured specimens. USNM 161830, 161832, 161833.

Family MONOGRAPTIDAE

Subfamily MONOGRAPTINAE

Genus MONOGRAPTUS Geinitz, 1852

Monograptus Geinitz. Bulman, 1955, Geol. Soc. America, Treatise 

on invertebrate paleontology, pt. V, p. V92, fig. 6£, la-g.

Rhabdosome scandent, uniserial, straight or curved. 

Thecae highly variable in form, straight, curved, or 

distally isolate. Many species with at least two thecal 

types in same rhabdosome. Silurian, worldwide.
SYSTEMATIC DESCRIPTIONS 35

Monograptus acinaces Tornquist 

Text figure UA; plate 3, figures 13-15

Monograptus acinaces Tornquist. Elles and Wood, 1901-18, 

Mon. British Graptolites, Palaeontographical Soc., 

p. 364-365, text fig. 237, pi. 36, fig. 2a-d.

Monograptus acinaces Tornquist. Hsii, 1934, Graptolites of the 

Lower Yangtze Valley, p. 91-92, pi. 7, fig. la-d.

Discussion. ~The Alaskaii specimens are mostly the 

arcuate proximal ends with long, slender thecae that 

characterize this species. Numerous distal fragments 

with less curvature of the rhabdosome and greater 

thecal overlap are also present (pi. 3, fig. 14).

Occurrence. Ml 138-SD, M1139-SD, M1289-SD, 

M1290-SD.

Dimensions (in

Specimen No.

USNM-161834,__ 

161835 i__ 

161836 i__ 

161837___ 

161838. _. 

161839. __

millimeters) , 

Jength of Width

some Initial Maximum

14 0 

21 

15. 5 

17.5 

14 

24 ____

3? 0 

2 

3? 

3? 

25

7 

75 

75 

7 

5 

5

Thecae per 

centimeter

9 .

9

9 .

8 .

9

8 .

Leng-th 

of sicula

4.5

>1. 6

FIGURE 14. Dimorphograptus and Monograptus. A. M. 

acinaces Tornquist (USNM 161835), proximal fragment 

showing sicula (same as pi. 3, fig. 13), X 5. B, M. argutus 

Lapworth (USNM 161841) (same as pi. 4, fig. 16), 

X 6. C and D, D. confertus swanstoni (Lapworth): C, 

Narrow form showing sicula (USNM 161823), X 5; 

D, (USNM 161814) (same as pi. 3, fig. 10) showing sicula, 

X 5. E, M. atavus Jones (USNM 161842) (detail of pi. 3, 

fig. 11), X 5.

Range. Llandoverian zone of M. cyphus (Road 

River Formation) in Yukon Territory, Canada (Jackson and Lenz, 1962). Llandoverian zones of 0. msiculosus and M. cyphus (Birkhill Shales) in Great Britain 

(Toghill, 1968). Llandoverian zone of Pristiograptus 

cyphus in Bohemia, Czechoslovakia (Pribyl, 1948). 

Lower part of Kaochiapien Shale (zone with M. leei) 

near Nanking and central Anhui, China (Hsii, 1934).

1 Figured specimens.

Material. About 11 compressed, fairly well preserved specimens, mostly fragmental.

Figured specimens USNM 161835, 161836, 161f40.

Monograptus argutus Lapworth 

Text figure 145; plate 4, figure 16

Monograptus argutus Lapworth. Elles and Wood, 1901-18, Mon.

British Graptolites, Palaeontographical Soc., p. 408-409,

text fig. 274, pi. 40, fig. 3a-e. 

Monograptus argutus Lapworth. Sun, 1933, Palaeont. Sinica, ser.

B, v. 14, pt. 1, p. 44, pi. 7, fig. 4a, b. 

Monograptus argutus Lapworth. Hsii, 1934, Graptolites of the

Lower Yangtze Valley, p. 97, pi. 7, fig. 8a-e.

Description. According to Elles and Wood (1901-18, 

p. 409), M. argutus is characterized by thecae that show 

conspicuous sigmoidal curvature and have introverted 

and introtorted apertural regions. The thecae thus 

resemble those of Dicettograptus. The rhabdosome has a 

maximum width of 1.5 mm, and the thecae are as much 

as 3 mm long and number eight per centimeter.

Discussion. Only one specimen (a distal fragment) 

has been found, but it is well preserved and shows the 

characteristic thecal form noted by Elles and Wood 

(1901-18, p. 409). The width of the distal fragment is 

1.3 mm and the thecae are 2.5 mm long. The thecae 

overlap two-thirds and number eight to nine per 

centimeter. The protheca shows a conspicuous expansion at the junction with the metatheca, but the 

metatheca is then immediately constricted and continues at a diameter of 0.2 mm. The metatheca shows 

conspicuous sigmoidal (convex) curvature, and the 

apertural region is introverted with a slight took 

developed. The aperture points directly inwards, and 

the apertural region is slightly introtorted.

Occurrence. Central Independence Range, Nev., 

locality 4 of Kerr (1962).

Range. Llandoverian zones (19 and 20) of M. 

gregarius and M. convolutus (Birkhill Shales) in Great 

Britain (Elles and Wood, 1901-18) (Toghill, 19 f'S). 

Zone of Demirastrites convolutus in Bohemia, Czechoslovakia (Pribyl, 1948). Lower Silurian (Sintan Shale) 

at Lunshan, Kiangsu, China (Sun, 1933). Lower part of 

the Kaochiapien Shale (zone with M. leei) at Lunsl an,
36 EARLY SILURIAN GRAPTOLITES FROM ALASKA

near Nanking, China (Hsii, 1934). Reported from the 

Blaylock Sandstone of Blaylock Mountain, Montgomery 

County, Ark. (Ruedemann, 1947).

Material. One pyritized specimen, preserved in 

relief. Identified by P. Toghill (oral commun., 1968).

Figured specimen. USNM 161841.

Monograptus atavus Jones 

Text figure 14E; plate 3, figure 11

Monograptus atavus Jones. Elles and Wood, 1901-18, Mon. 

British Graptolites, Palaeontographical Soc., p. 403- 

404, text fig. 270, pi. 39, fig la-d.

Discussion. The collection consists of fragments 

varying widely in width. The rhabdosomes are straight 

or with slight dorsal or ventral curvature. The thecae 

overlap less than one-half their length and have varying 

amounts of sigmoidal curvature.

Occurrence. M1138-SD, M1139-SD, M1142-SD(?).

Range. Llandoverian zones (17-19) of 0. vesiculosus 

to M. gregarius (Birkhill Shales) in Great Britian 

(Elles and Wood, 1901-18) (Toghill, 1968). Lower part 

of the Kaochiapien Shale (zone with M. leei) in China 

(Hsu, 1934). Monograptus cf. atavus reported from slate 

at Waterville, Maine (Ruedemann, 1947).

Dimensions (in millimeters). 

1 Figured specimen.

Material. Approximately 20 compressed, fairly well 

preserved, fragmentary specimens. 

Figured specimen. USNM 161842.

Monograptus buddingtoni n. sp. 

Text figure 15Z), E; plate 4, figures 7, 8

Description. The rhabdosome is small, approximately straight distally, and more or less abruptly 

curved proximally so that it has a J-shape. The rhabdosome widens from an initial with of about 0.3 mm 

to a maximum of 0.6 mm. The thecae number 12-18 

per centimeter and are simple tubes with only slight 

overlap and even horizontal or everted apertural 

margins.

Specimen No.

USNM-161842 !_.______

161843a_ _______

161843b__ _

161844

161845

161846

161847

161848 ________

161849___ _ ___

Length of 

rhabdosome

>48

____ >20

____ >25

^>15

____ >30

____ >23

____ >30

Width of 

rhabdosome

0. 7-0. 8

. 8

. 7-0. 8

.75

. 4-0. 5

. 6-0. 7

. 6

. 6-0. 7

1. 0-1. 1

Thecae per 

centimeter

7tf-8

8

8

8

9

8

8

9

8

E

FIGURE 15. Monograptus. A-C, M. calamistratus n. sp.: A, 

Holotype (USNM 161865), proximal end missing, X 8; 

B, Proximal fragment (USNM 161864) with sicula(?) and 

apertural spines, X 8; C, Proximal frgament (USNM 

161624c), showing apertural spines and hornlike apertural 

projections, X 8. D and E, M. buddingtoni n. sp.: D, 

Specimen showing sicula (USNM 161853a), X 5; E, 

Holotype (USNM 161850) (same as pi. 4, fig. 8), X 5.

The characteristic features of this species are the 

strong dorsal curvature, the closely set, simple thecae, 

and the small amount of overlap of the thecae. Because 

of distortion of the specimens, some exhibit a rather 

abrupt bend at about th6-7, on either side of which they 

are fairly straight (fig. 15Z7), and some exhibit a more 

gently curving rhabdosome (fig. 15E). The thecal 

apertures range from everted to inverted due to distortion, but all thecae show the characteristically 

slight overlap, which ranges from almost none to 

about a third of the total thecal length. TH sicula 

measures about 1.0 mm long and reaches to approximately the level of the aperture of thl.

Discussion. This species resembles the mono^raptids 

of the M. cyphus-M. acinaces-M. gregarius group in 

the character of its thecae (straight, simple, overlapping 

tubes) and the dorsal curvature of its rhabdosome. 

However, it has far less thecal overlap than M. cyphus 

or M. acinaces and differs from M. gregarius by having 

a much shorter sicula and a more sharply curved 

rhabdosome. In thecal shape and the small amount 

of thecal overlap, it resembles M. jaculum, but the 

rhabdosome of M. jaculum is approximately straight 

and that of the Alaskan species is always curbed.

Occurrence. Ml 140-SD.

Range. Zones of M. gregarius to M. convolutus in 

Alaska. 

Dimensions (in millimeters). 
SYSTEMATIC DESCRIPTIONS 37

Length of Width Thecae per

Minimum Maximum

USNM-ieiSSO 1 -. 11 0 

161851 !__ >10 

leiSSSa1 .. >10 

161854. ._ 15 

l61855-__ 13 

161853b__ 15 

I6l853c__ >8 

161856. __ >8 

161857___ >11 

161858_-_ 9 

l61805a-_ >13 

!61859--_ >15 

161860c__ >10 

161861--- >11 

161862a__ 12 

161863a-_ >8 

l61852-__ >20

3 0 

5 

3 

25 

5 

4 

5 

4 

5 

5 

5 

3 

5 

4 

2 

4 

3

5 16 

55 14 

55 13-15 

5 13 

65 18 

5 16 

5 14 

6 15 

6 14 

5 12 

6 14 

4 12 

5 16 

5 12 

6 18 

5 18 

6 18

i Figured specimens.

Material. Approximately 30 compressed, distorted 

specimens. Named in honor of A. F. Buddington, whose 

reconnaissance geologic mapping in. southeastern Alaska 

laid a good basic framework for subsequent geologic 

investigations. 

Holotype USNM 161850. 

Figured specimens. USNM 161850, 161851, 161853a.

Monograptus calamistratus n. sp.

uiscusswn. Aiie unaracierisnc leatures 01 ims lonn 

are: (1) the coiled rhabdosome, (2) the elongated p^othecae, and (3) the apertural spines. It resembles M. 

involutus in its spiral rhabdosome, but the new species 

has a wider proximal end and more thecae per centimeter. 

Occurrence . M 1 142-SD . 

Range. Zone of M. gregarius in Alaska. 

Dimensions (in millimeters). 

Specimen No. Width of Thecae r°r 

rhabdosome centimeter

USNM-161624C 1 . __-_---__-_____-____ 0.3-0.5 14

161864 1 __-_---__-___---__--__ .25-0.5 16-20

leises 1 .-- ___ -_ _ -_____- .4-0.5 11-14

161866-___-___-___-_-___--___ .3-0.5 14

161867 _ ______ _____ ____ .5 14

161ooo _____________ __ .5 iZyy- 14 

1618691_______-____-___-_--__ .4-0.5 11-14

161869m- ___ _ ___ _____ .3-0.5 12-16

161869n_-___________ _ ___ __ .5 14

1 Figured specimens.

Material. Approximately 10 compressed, poorly 

preserved specimens. 

Named after the Latin "calamistratus" = curled. 

Holotype. USNM 161865. 

Figured specimens.USNM 161624c, 161864, 161865, 

161988.

Text figure 15A-C; plate 4, figure 12

Description. The rhabdosome is small and coiled 

into a flat spiral. The thecae number approximately 14 

per centimeter and are long and narrow with the outer 

end of the apertural margin retroverted so as to appear 

beaklike. They have relatively long prothecae, short triangular metathecae, apertural spines, and little or no 

overlap. The sicula is at most 0.9 mm long.

The rhabdosome is tightly coiled initially, becoming 

more loosely coiled distally, so that the overall shape is 

an irregular spiral. The spiral has about 2% whorls and 

measures about 5 mm in diameter.

The protheca (proximal part of graptoloid theca 

before differentiation of the succeeding theca (Bulman, 

1955, p. V6)) measures from 0.5 mm long at the proximal end of the rhabdosome to about 0.9 mm long at the 

distal end. The metatheca (distal part of a graptoloid 

theca (Bulman, 1955, p. V6)) is approximately triangular in outline and measures 0.25-0.5 mm high. Spines 

on the tips of the metathecae are frequently preserved 

and may measure as much as about 0.3 mm long. One 

specimen (fig. 15(7) shows two metathecal projections, 

which may indicate that the apertural region is divided 

into two hornlike projections. Thl appears to originate 

near the aperture of the sicula and grows upward from 

there.

Monograptus cf. M. crenularis Lapworth. 

Text figure 164, B, D, E; plate 3, figures 18, 23-25

Monograptus crenularis Lapworth. Elles and Wood, 1901-18, 

Mon. British Graptolites, Palaeontographical Soc., p. 

414-415, text fig. 281, pi. 41, fig. 7a-e.

Monograptus crenularis Lapworth. Sun, 1933, Palaeont. Sinica, 

ser. B, v. 14, pt. 1, p. 42-43, pi. 7, fig. la-e.

Description. According to Elles and Wood (1901- 

18, p. 414), the rhabdosome is long and slightly arcuate 

throughout, widening very gradually from 0.5 mm to 

a maximum of 1 mm. The thecae number 10-12 per 

centimeter and overlap two-thirds of their length. 

The apertural margins are slightly everted and occasionally are situated in distinct excavations (fig. 16/?).

The rhabdosome is characteristically slender, and 

the maximum width is attained some distance from 

the proximal end. It is nearly straight distally and 

curved dorsally at the proximal end. The thecae show 

an apparent narrowing in the apertural region and in 

some, as a result of compression, the twisted apertural 

region shows a tendency to isolation and retroversion.

Discussion. Elles and Wood's figures (1901-18, pi. 

41, fig. 7a-e) show a form very similar to the specimens 

under study: fairly straight rhabdosome with a curved 

proximal part, and with the proximal thecae hooked 

or lobate in appearance. Some of the Alaskan specimens
38 EARLY SILURIAN GRAPTOLITES FROM ALASKA

show a greater amount of dorsal curvature in the 

proximal end (pi. 3, fig. 18) than do Elles and Wood's 

(1901-18) specimens. Because of its tighter curvature 

and broaden proximal end, the specimen illustrated 

on plate 3, figure 18, appears to have affinities with 

M. argenteus and is only provisionally grouped with 

crenularis. In this respect, the Alaskan specimens 

resemble Sun's (1933, pl.7, fig. la-e) specimens. Our 

specimens have between 11 and 13 hooked proximal 

thecae. The sicula was probably about 1.0 mm long 

(the specimens are distorted) and extends above the 

highest region of theca 1 but below the highest region 

of theca 2.

Occurrence. Ml 140-SD.

Range. Llandoverian zone (20) of M. convolutus 

(Birkhill Shales) in Great Britain (Elles and Wood, 

1901-18; Toghill, 1968). Llandoverian zone of Demirastrites convolutus in Bohemia, Czechoslovakia (Pribyl, 

1948). Lower Silurian Fuchih Shale from Hupei, China 

(Sun, 1933).

Dimensions (in millimeters}. 

Proximal 

Specimen No. (P) or 

distal (D) 

fragment

USNM-161870 i... 

161871a i.. 

161872 i 

161873 I... 

161874 i 

161875... . 

161876.-.. 

161877.... 

161878.-. 

161879.-. 

161880.-. 

161881.-- 

161860a.- 

161860b... 

161882.... 

161693d 

161883..- 

161871C... 

161871d 

161884....

D 

P 

P 

D 

P 

P 

P 

P 

P 

P 

P 

P 

D 

D 

D 

D 

D 

D 

D 

D

Width

Mini- Maximum mum

27.5 ........

17 2 o. 5 

54 .7 

29 ........

55 .5 

10 .7 

12 2.5 

15 .5 

15 .8 

14 .5 

5 2.5 _

11 2.5 

30 ........

103 ........

13 .5 

15.5 ........

12 .7 

14 ........

6 ........

9.5 .6

0.55 

.9 

1.1 

.5 

1.1 

.8 

.9 

.9 

.7 

.7

.9 

1.5 

1.5 .

.6 

.5 

.8 

.7 

1.0 

.7

Thecae Num.- Length 

per her of 

centi- hooked sicula 

meter thecae

13-14 

12-13 

11-12 ..

12-13 

10?

12? 

10 

13

13 

13-14 ...

10 ...

10 ...

10 ...

7 ...

10 ...

13 ...

11

7 ..

10 ..

11 -

12 

13 

12 

11 -

12

0.8

1.5 

1.2 

1.0

1.2

.8?

i Figured specimens. 

2 Theca 1.

Material. A large number are compressed and distorted; most are poorly preserved specimens. Two 

nearly complete specimens are present; the rest are 

fragments.

Figured specimens. USNM 161870, 161871a, 

161872-161874.

Monograptus cyphus Lapworth 

Text figure l&F; plate 4, figures 5, 6

Monograptus cyphus Lapworth. Elles and Wood, 1901-18, Mon.

British Graptolites, Palaeontographical Soc., p. 362-364,

text fig. 236, pi. 36, fig. la-e. 

Pristiograptus cyphus (Lapworth). Obut, Sobolev&kaya, and

Bondarev, 1965, Graptolity Silyura Taimyra, p. 66, pi.

11, figs. 1, 2.

Description. The rhabdosome is more than 4 cm 

long, with a maximum width of 1.8 1.9 mm. The 

thecae number seven to 10 per centimeter and are 

simple, straight, or slightly curving tubes, broad in 

relation to their length. They overlap about one-half 

their length and are inclined to the rhabdosome axis. 

The apertural margins are even and everted.

Discussion. All of the specimens under study are 

fragmentary and none have proximal ends preserved. 

Some have approximately straight rhabdosomes, and 

some have very gentle dorsal curvature. One specimen 

has broad ventral curvature.

M. cyphus is distinguished from similar forms by 

the width of its distal part, the simple character of its 

thecae, and the curvature of its rhabdosome.

Occurrence. M1138-SD, M1139-SD, M1142-SD, 

M1289-SD(?).

ABE F

FIGURE 16. Monograptus. A, B, D, and E, M. cf. M. 

crenularis Lapworth: A, D, Distal and proximrl ends 

of specimen (USNM 161874) (same as pi. 3, fi~. 23), 

X 5; B, Distal part (USNM 161870) showing apertural 

margins in distinct excavations, X 5; E, (USNM 

161871a) detail of proximal end of pi. 3, fig. 18, showing 

sicula, X 5. C, M. gregarius Lapworth (USNM 161894) 

showing long sicula (same as pi. 4, fig. 1), X 5. F, M. 

cyphus, distal fragment (USNM 161885) (detail of pi. 

4, fig. 5), X 5.
SYSTEMATIC DESCRIPTIONS 39

Range. Handover!an zone of M. cyphus (Birkhill 

Shales) in Great Britain (Toghill, 1968). Zone of 

Pristiograptus cyphus in Russia (Obut and others, 

1965). Lower Keilorian in Australia (Thomas, 1960).

Dimensions (in millimeters}. 

Specimen No.

USNM-161885 1 ---------

161886---------

161887_-------__-

161888____--__-_-

161889d___-_____.

161889e__-_ _ __

161890 1 _________

161891__________.

161892 __________

Length of 

rhabdosome

36

9

33

17

28

35

29

9Q

40

Width of Thecae per 

rhabdosome centimeter

1.9 

1.8 

1.8 

1. 7 

1. 5 

1.6 

1. 7-1. 8 

1. 5 

1. 9

9 

9

8 

7 

8 

10

7/2-7 

8 

8

1 Figured specimens.

Material. Approximately 10 compressed, fairly well 

preserved specimens. Identified by P. Toghill (oral 

comimm., 1968).

Figured specimens. USNM 161885, 161890.

Monograptus cf. M. difformis TSrnquist

Text figure 18E; plate 3, figure 22

Monograptus difformis Tornquist. Elles and Wood, 1901-18. 

Mon. British Graptolites, Palaeontographical Soc., p. 

386-387, text fig. 256a, pi. 38, fig. 4a-c.

Description. According to Elles and Wood (1901-18, 

p. 386), the rhabdosome of M. difformis is several 

centimeters long, is arcuate distally, and has an involute proximal part. It widens gradually to a maximum 

width of about 1 mm. There are 10 12 thecae per 

centimeter, and they are of two types: the proximal 

thecae have a tendency to sigmoidal curvature and have 

conspicuously retro verted apertural regions; the distal 

thecae are simple tubes with even and somewhat 

everted apertural margins and overlap one-half their 

length.

Discussion. Our only specimen is more than 2 cm 

long, has a maximum width of 1.0 mm, and has 10 

thecae per centimeter. It closely resembles M. di.fformis, 

which is very rare in Great Britain. M. difformis is 

somewhat similar to M. revolutus but differs by having 

a more robust proximal end and greater retroversion 

of the proximal thecae than revolutus.

Occurrence. M1142-SD.

Range. Llandoverian zones (18 and 19) of M. 

cyphus and M. gregarius (Birkhill Shales) in Great 

Britain (Elles and Wood, 1901-18; Toghill, 1968). 

Zone of Pristiograptus cyphus in Bohemia, Czechoslovakia (Pribyl, 1948).

Material. One compressed rather poorly preserved 

fragmentary specimen.

Figured specimen. USNM 161893.

Monograptus gregarius Lap worth 

Text figure 16C; plate 4, figure 1

Monograptus gregarius Lapworth. Elles and Wood, 1901-18,

Mon. British Graptolites, Palaeontographical Soc., p.

365-366, text fig. 238, pi. 36, fig. 3a-d. 

Monograptus gregarius Lapworth. Hundt, 1924, Grapt. d.

deutsch. Silurs, p. 73, pi. 5, fig. 4. 

Monograptus gregarius Lapworth. Ruedemann, 1947, Graptclites

of North America, Geol. Soc. America Mem. 19; p. 481,

pi. 84, fig. 1.

Discussion. The main characteristics of this species 

according to Elles and Wood (1901-18, p. 366) are: 

(1) The stiffly curved rhabdosome, (2) the robust 

proximal end, and (3) the relatively gigantic sicula 

reaching up to theca 5. The Alaskan specimens ckrely 

agree with the dimensions of M. gregarius given by 

EUes and Wood (1901-18, p. 366). The length of the 

siculas in the Alaskan species, however, seems considerably less, and the sicula may extend only to tl eca 

3. Unfortunately, poor preservation and scarcit3T of 

specimens make it difficult to make comparisons in 

sicular structure.

Occurrence.~Ml 142-SD.

Range. Zone of M. cyphus (Cape Phillips Format: on) 

in Canadian Arctic (Thorsteinsson, 1958). Reported, 

with doubt, from the Silurian Blaylock Sandstone, 

Arkansas (Ruedemann, 1947). Llandoverian zoner; of 

M. cyphus and M. gregarius (Birkhill Shales) in Great 

Britain (Toghill, 1968). Llandoverian zone of M. 

gregarius in the Frankenwald (northeastern Bavaria) 

(Stein, 1964, 1965). Llandoverian zones of M. cyphus 

to M. convolutus in Portugal (Romariz, 1962). Llardoverian zones of Demirastrites pectinatus (=fimbriatus) 

to Rastrites approximatus geinitzi (=M. argenteus in 

England) in Bohemia, Czechoslovakia (Pribyl, 1948). 

Llandoverian zone of M. gregarius at Four Mile Creek, 

New South Wales, Australia (Sherrard, 1954).

Dimensions (in millimeters). 

Specimen No.

USNM-161894 L_

161895.--

161896.--

161897.--

161898 _

Length of rhabdosome

8

5

5

7. 7

>7. 5

Width of rhabdosome

0 7

6

55

5

6

Thecae

centimeter

11

12

10

11

10

Sicula

Length

3.0

3. 0?

3. 3

3.5

Maxinum

width

0.25

.25

. 2

. 3

i Figured specimen.

Material. Approximately 10 compressed, rather 

poorly preserved specimens, about half of which are 

fragmentary.

Figured specimen. USNM 161894.
40 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Monograptus hamatus n. sp. 

Text figure 17D, E; plate 4, figure 15

Description, The rhabdosome is very long and 

straight and increases gradually in width from about 

0.3 mm wide proximally to a maximum of about 1.0 

mm wide distally. The thecae number about eight 

per centimeter and are long, very slender, gently

th<

E

th

F

FIGURE 17. Monograptus. A-C, M. noyesensis n. sp.: 

A, Proximal fragment (USNM 161930), X 5; B, 

Proximal fragment (USNM 161929) (same as pi. 4, 

fig. 10), X 5; C, Holotype (USNM 161928), distal 

fragment (same as pi. 4, fig. 9), X 5. D, M. hamatus 

n. sp., (USNM 161902) distal fragment preserved in 

relief, X 5. E, Schematic cross section of M. hamatus 

n, sp., showing common canal (cc) and thecae (th). 

F, M. kerri n. sp., (USNM 161910) proximal fragment showing sicula (broken), preserved in relief 

X 7.

curving tubes. They grow nearly parallel to the 

rhabdosome axis and have hooked apertural regions. 

They overlap about two-thirds of their length. The 

characters of the sicula are unknown.

Discussion. This form has a very distinctive appearance. The free ventral wall of each theca forms a 

gentle convex curve, so that in outline, the ventral 

margin of the rhabdosome is a series of shallow convex 

curves, each curve between two hooked apertural 

regions. The thecae, in cross section, have the shape of 

a flattened oblong (fig. 17F). Only a small fraction of 

the thecal length is involved in the apertural hook.

Occurrence. Nevada: Central Independence Range, 

locality 4 of Kerr (1962).

Range. Zone of M. gregarius in Nevada. 

Dimensions (in millimeters). 

Specimen No. Length of 

rhabdosome

Width "heeae per 

centimeter

USNM-161899_________.

161900_________.

161901 1 ________.

161902 !____ _.

161903__ ___ _.

_ _ 5

45

21

17.5

.___ 13

1. 0

. 8-1. 0

. 3-0. 8

1.0

. 25-0. 6

8

8

8

1 Figured specimens.

Material. Five pyritized specimens preserved in 

relief. Named after the Latin "hamatus" = with hooks, 

hooked.

Holotype USNU 161901.

Figured specimens. USNM 161901, 161902.

Monograptus cf. M. incommodus Tornquist

Text figure ISA; plate 3, figure 20

Monograptus incommodus Tornquist. Elles and Wood, 1901-18, 

Mon. British Graptolites, Palaeontographical So?., p. 406, 

text fig. 272, pi. 40, fig. la-e.

Monograptus incommodus Tornquist. Ruedemann, 1947, Graptolites of North America, Geol. Soc. America Mem. 19, 

p. 481, pi. 85, fig. 26.

Pribylograptus incommodus (Tornquist). Obut and SobcTevskaya, 

1966, Graptolity rannyevo Silyura v Kazakstanye, p. 

34-35, pi. 6, fig. 9, text fig. 25.

Description. According to Elles and Wood (1901-18, 

p. 406), the rhabdosome is long and slender, with irregular curvature. It widens from a slender, slightly 

arcuate, or straight proximal part to a flexed distal 

part with an average width of 0.5-0.6 mm. The thecae 

number seven to eight per centimeter, are inclined at 

a very small angle, and overlap one-third to on^-half of 

their length. The apertural margins are even and 

slightly introverted.

The curvature of the rhabdosome is generally dorsal. 

The sicula is fully 3 mm long and reaches to the level 

of the aperture of theca 1, which originates at a point 

about halfway up the sicula. The thecae show slight 

sigmoidal curvature.

Discussion. Some of the Alaskan specimens have 

more strongly curved rhabdosomes than those figured 

by Elles and Wood (1901-18, pi. 40, fig. la~^). Poor 

preservation makes determination of thecal characters 

difficult. The thecae appear to overlap about a third 

of their length, and some have slightly introverted 

apertures.

Occurrence. M1138-SD, M1139-SD, M1289-SD.

Range. LJaiidoverian zones of 0. vesiculosus to 

M. gregarius (Birkhill Shales) in Great Britain (Toghill, 

1968). Reported from the Silurian Blaylock Sandstone 

of Arkansas (Ruedemann, 1947). Llandoverian zones of 

Pristiograptus cyphus to Demirastrites pectinoius (=
SYSTEMATIC DESCRIPTIONS 41

fimbriatus) in Bohemia, Czechoslovakia (Pribyl, 1948). 

Distal fragment reported from the Lower Silurian

FIGURE 18. Monograptus. A, M. cf. M. incommodus Tornquist (USNM 161904), showing long sicula, X 5. B, C, 

and F, M. aff. M. undulatus Elles and Wood: B, Distorted 

distal fragment (stretched widthwise) (USNM 161955), 

X 5; C, Distal part of pi. 4, fig. 4 (USNM 161862b), X 5; 

F, Proximal fragment (USNM 161957), slightly distorted, 

X 5. D, M. tennis (Portlock) distal fragment (USNM 

161940), X 5. E, M. cf. M. difformis, incomplete specimen 

(USNM 161893) (same as pi. 3, fig. 22), X 5. G, M. revolutus 

Kurck, incomplete specimen (USNM 161937) (same as 

pi. 3, fig. 19), X 5.

Kaochiapien Shale, Kiangsu, China (Sun, 1933). Also 

reported from Russia (Obut and Sobolevskaya, 1966). 

Dimensions (in millimeters). 

Length of Width Maximum Theeae Length of 

Specimen No. rhabdosome of sicula width of per suofa

rhabdosome centimeter

USNM-161904i__ 

161905 i__

161906b._

161906C-.

161907--. 

161908- .

161909---

30 

14 -.

20 -.

17

20 

35 _.

11 __

0.25

.2

. 2

0.4 

.3

.4

.3 .

.5 

. 5

.4

9 

q

8 -_

6

714-8

6 _-

3.7

4. 1

3.5

1 Figured specimens.

Material. About 10 compressed, poorly preserved 

specimens.

Figured specimens. USNM 161904, 161905.

Monograptus kerri n. sp. 

Text figure 17^; plate 4, figure 11

Description. The rhabdosome is very small end 

slender, with strong dorsal curvature. The proximal 

part is relatively robust and abruptly recurved. The 

thecae number 10-12 per centimeter and are hooked, 

with about a third of the thecal length involved in the 

hook. They resemble the thecae of M. irfonensis r.nd 

M. scanicus, and they overlap about a fourth of their 

length. The sicula is as much as 1.4 mm long, r.nd 

theca 1 starts one-fourth to one-third of the way up its 

length.

Discussion. This form resembles M. leei Hsii (1934, 

p. 97-98) very closely in size and shape of the rhabdosome. The thecae and details of the sicula are entirely 

different, however. The sicula of M. leei is 2 mm long, 

and its apex reaches to the level of the aperture of 

theca 3. The sicula on this form is, at most, 1.4 mm long 

and reaches no higher than midway between theca 1 

and theca 2. The thecae of M. leei have apertures that 

are wide, even, and perpendicular to the general trend 

of the rhabdosome. The thecae on this form hp.ve 

distinctly hooked apertural regions.

The characteristic features of this species are: (1) 

The hooked thecae, (2) the small size of the rhabdosone, 

(3) the strong dorsal curvature of the rhabdosome.

Occurrence. Nevada: Central Independence Ran^e, 

locality 4 of Kerr (1962).

Range. Zone of M. gregarius in Nevada.

Dimensions (in millimeters'). 

Specimen No.

USNM-161910 1 _ 

161911 L- _ 

161912_____

161913-__-

161914.. ___

161915. 

Length Width

dosome Theca 1 Maximum

3. 0 0. 5 

7 .3 

4.3 __-__-

2.5 .3 

5 ______

12 ______

0.65 

.6 

.75 

.3

.7 

1.0?

Theeae 

per Lengtl of 

centi- sieuli 

meter

13 

10 

10-12 __

11 

10-12 __

10 __

1.4 

1.2

1.0

1 Figured specimens.
42 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Material. Six pyritized specimens preserved in 

relief. Named in honor of J. William Kerr of the 

Canadian Geological Survey.

Holotype USNM 161911.

Figured specimens. USNM 161910, 161911.

Monograptus lobiferus (M'Coy) 

Plate 3, figures 12, 21

Monograptus lobiferus (M'Coy). Elles and Wood, 1901-18, Mon.

British Graptolites, Palaeontographical Soc., p. 448-450

text fig. 308, pi. 45, fig. la-f. 

Monograptus (Streptograptus) lobiferus (M'Coy). Obut, 1949,

Polyevoi Atlas, Rukovodyashchich graptolitov vyerkhny"

evo Silura Kirgizskoi SSR. Akademiia Nauk SSSR, p. 23,

pi. 4, fig. 6a-c. 

Monograptus lobiferus (M'Coy). Romariz, 1962, Revista da

Faculdade de Ciencias, Lisbon Univ., ser. 2, C, v. 10,

pt. 2, p. 251, pi, 18, fig. 8. 

Monograptus lobijerus (McCoy). Obut, Sobolevskaya, and

Nikolaiyev, 1967, Graptolity i stratigrafiia nizhnego

Silura okrainnykh podniatii kolymskogo massiva (severovostok SSSR), Akademiia Nauk SSSR, p. 93-94, pi. 10,

figs. 3, 4.

Discussion. Most of the Nevada specimens are 

proximal or near-proximal fragments. They compare 

very closely with the dimensions given by Elles and 

Wood (1901-18, p. 448). They have the lobed thecae 

and dorsally recurved proximal end characteristic of 

M. lobifems. They also resemble Globosograptus wimani 

(Obut and others, 1967, pi. 13, fig. 2) but lack its 

ventral proximal curvature.

Occurrence. Nevada: Central Independence Range, 

locality 4 of Kerr (1962).

Range. Llandoverian zone (20) of M. convolutus 

(Phi Kappa Formation) in Idaho (Churkin, 1963). 

Llandoverian zone (20) of M. convolutus (Birkhill 

Shales) in Great Britain (Elles and Wood, 1901-18; 

Toghill, 1968). Llandoverian zones of M. gregarius to 

M. turriculatus in Portugal (Romariz, 1962). Also reported from Russia (Obut, 1949; Obut and others, 1967).

Dimensions (in millimeters). 

Specimen No. Length of 

rhabdosome

Width Thecae per 

centimeter

USNM-161916.. ._--____

161917___-_-____

161918_________-

161919 L_-_ 

161920a________-

161920b_________

161920c_-_-_--_-

161920d___-__-_-

161921_____ _ ..

161922___--____-

161923 L. _______

161924__________

161925__--_---_-

161926__________

161927__. _______

8. 5

17.5

4.5

11.5

12.5

11.5

9.0

13.7

11.5

32

10

3.5

11.5

14

27

1.3

. 5-1. 1

. 5-0. 6

1.2

1. 0-1. 2

1. 4-1. 5

1. 1

2.0

1.8

1. 5-1. 7

. 8

. 4-0. 5

. 8

1. 5

1. 5-1. 7

6

8~1C

8-1C

7

7

7

8

&A

8

9

9

10

9

7

7

1 Figured specimens.

Material. About 30 pyritized specimens preserved 

in relief.

Figured specimens USNM 161919, 161923.

Monograptus noyesensis n. sp. 

Text figure 11A-C; plate 4, figures 9, 10

Description. The rhabdosome is broadly arched, 

with the proximal end moderately curved snd the 

thecae on the convex side with little or no overlap. 

The early thecae are somewhat elongated. The distal 

thecae are bluntly triangular, widening from the beginning of the protheca to the apertural region, which is 

hooked.

The rhabdosome is curved throughout, with the 

amount of curvature greatest in the proximal region 

(first four to five thecae). The sicula measures 1.0-1.2 

mm long and 0.2-0.3 mm wide. It extends up to about 

the level of the aperture of theca 1 and usually exhibits a very short virgella. Theca 1 has a slender protheca, and the hooked metatheca is about 0.4 mm 

high. Up to about theca 6, the thecae have an elongated 

appearance because of their relatively slender, slowly 

widening prothecae. Above theca 5 and 6 the thecae 

become more and more bluntly triangular. They 

widen from the beginning of the protheca and attain 

a maximum height of about 1.0 mm. There ar^ 11-12 

thecae per centimeter distally. The thecae are curved 

into a prominent hooked shape in the apertural region, 

with the apertural margin on some specimens approximately parallel to the axis of the rhabdosone. The 

dorsal outline of the thecae has a rounded hunchback 

appearance.

Discussion. Distally, this form is very similar in 

appearance to Monograptus pseudoplanus ^udbury 

(1958, p. 523-524, text fig. 22a, pi. 22, figs. 94-96). 

The thecae have almost exactly the same shape in 

the flattened condition. It differs from M. pseudoplanus 

by being somewhat smaller and by having a much 

different proximal end. The proximal thecae of M. 

pseudoplanus are greatly elongated, with very small 

hooked metathecal parts, and the proximal region 

itself is broadly arched. The proximal region of the 

Alaskan species exhibits a greater amount of curvature, 

and its proximal thecae are much larger and much 

less elongated than those of M. pseudoplanus.

Monograptus noyesensis resembles M. communis in 

the proximal region, but the distal thecae of M. communis have less of an apertural hook than those of the 

Alaskan species.

It also resembles M. millipeda and M. lobiferus but 

is more slender than M. millipeda and has a more 

strongly recurved proximal end than M. lobiferus. It 

also differs in the characters of the distal thecae, the
SYSTEMATIC DESCRIPTIONS 43

hook, or lobe, being less conspicuous and involving a 

smaller part of the thecal length.

Occurrence. M1142-SD.

Range. Zone of M. gregarius in Alaska.

Dimensions (in millimeters). 

Specimen No.

Length 

of rhabdosome

Width Thecae Length

 per of 

Maxi- Theca Theca Theca Theca centi- sicula 

mum 1245 meter

USNM-161928L..

161929 i..

161930 1.- 

161931 -

161932....

161933.-.. 

161934-... 

161935...- 

161936C..- 

161936d....

18

8

5

5

14

9

9

2.5

9

1.0

.7 0.4 

.4

0.5 

.5

0.7 0.7

.7

1.0 

1.2

.7 .7

1.2 

1.2 

1.2

»Figured specimens.

Material. Approximately 20 compressed fragmentary fairly well preserved specimens. Named after 

Noyes Island in southeastern Alaska.

Holotype. USNM 161928.

Figured specimens. USNM 161928-161930.

Monograptus revolutus Kurck 

Text figure 18G; plate 3, figure 19

Monograptus revolutus Kurck. Elles and Wood, 1901-18, Mon.

British Graptolites, Palaeontographical Soc., p. 384-385,

text fig. 254, pi. 38, fig. la-e. 

Monograptus revolutus Kurck. Sudbury, 1958, Royal Soc.

London, Philos. Trans. ser., B, no. 685, v. 241, p. 533-536,

text figs. 26, 27a, 28, table 4. 

Pernerograptus revolutus (Kurck). Obut and Sobolevskaya, 1966,

Graptolity rannyevo Silyura v Kazakhstanye, p. 32-33,

text fig. 23, pi. VI, figs. 5-7.

Description. According to Elles and Wood (1901- 

18, p. 384-385), the rhabdosome is several centimeters 

long, with an involute or broadly recurved proximal 

part. It widens from a threadlike initial part to a 

maximum width of about 1 mm. The thecae number 

eight to 10 per centimeter and are long narrow tubes 

of two types. The early thecae have the outer end of the 

apertural margin retroverted so as to appear beaklike 

or rostellate; the mature thecae are simple tubes with 

even apertural margins, and overlap two-thirds of their 

length.

Discussion. Our largest specimen (fig. 1869 nas a 

maximum width of 1.4 mm and compares closely with 

the "B"-form of Sudbury (1958, p. 534, fig. 26b). 

The others are about 1 mm wide and resemble form 

"A" of Sudbury (1958, p. 534, fig. 26a). Distally the 

thecae number 10-11 per centimeter and proximally, 

six to nine per centimeter. The narrow part of the

proximal end is approximately straight, and the rtabdosonie starts to curve at the point where it starts to 

widen.

Occurrence. Ml 142-SD.

Range. Llandoverian zones (18 and 19) of M. cyphus 

and M. gregarius (Birkhill Shales) in Great Britain 

(Elles and Wood, 1901-18jToghill, 1968). Llandoverian 

zone of Pristiograptus cyphus in Bohemia, Czecho^ovakia (Pribyl, 1948). A proximal fragment reported 

from the Lower Kaochiapien Shale near Nanking, China 

(Hsii, 1934). Also reported from Germany (Hundt, 

1924) and Russia (Obut and Sobolevskaya, 1966).

Dimensions (in millimeters'). 

Le

Specimeu No. rhal

USNM 161937 '__ 

161938 _ 

161939.--

ngth of

22 

17 

20

Width Th

Initial Maximum (

0. 2? 

. 2 

.2

1.4

. 7 

1. 0

iecae per Theca/3 per 

itimeter centimeter 

distal) (proxhnal)

10 

1011

7-8 

6 

7-8

' Figured specimens.

Material. Approximately seven compressed rather 

poorly preserved fragmentary specimens. 

Figured specimen. USNM 161937.

Monograptus tenuis (Portlock) 

Text figure 18D; plate 4, figures 2, 3

Monograptus tenuis (Portlock). Elles and Wood, 1901-18, Mon.

British Graptolites, Palaeontographical Soc., p. 407-408,

text fig. 273, pi. 40, fig. 2a-e. 

Pristiograptus tenuis (Portlock). Romariz, 1962, Revista da

Faculdade de Ciencias, ser. 2, v. 10, pt. 2, p. 286, pi. 2,

fig. 4; pi. 3, fig. 4; pi. 4, fig. 3.

Discussion. The Alaskan specimens possess the general characters of M. tenuis. The thecae have distinctly 

sigmoidal curvature and overlap one-third to one-half 

of then1 length. The rhabdosomes reach a maximum 

width of 1 mm and are straight or very slightly curved. 

The apertural margins are even and slightly introverted. 

The thecae exhibit an abrupt expansion in the apertural 

region that tends to produce an acute denticle on the 

apertural margin. The Alaskan specimens have more 

thecae per centimeter than those described as five to 

seven per centimeter by Elles and Wood (1901-18, p. 407).

Occurrence. M113 8-SD.

Range. Llandoverian zones of M. sedgwickii and 

Rastrites maximus (Birkhill Shales) in Great Britain 

(Toghill, 1968). The same zones in Portugal (Romariz, 

1962). Reported from the lower Llandoverian PanHapye beds at Pulau Langgon, Langkawi Islands, northwestern Malaya (Kobayashi and others, 1964).
44 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Dimensions (in millimeters) . 

Specimen No. Length of Width of Thecae per 

rhabdosome rhabdosome centimeter

USNM-161940» 

161941._ 

161942__ 

161943a

161944._

161945.-

161943e

161946__

161947--

161948__

161949__

161950__

161951..

161952_

161953.-

20

20

9.5

20

21

15

15

34

15

20

36. 5

13

17

12. 6

62

0.8 

. 8 

.5

7-0. 8

1.0

1. 0

.7

7-0. 75 

. 6

5-0.6

6-0.75 

4-0. 5 

.5

3-0.4

4-0.7

10

7

7

1 Figured specimens.

Material. A large number of compressed, fairly well 

preserved, fragmentary specimens.

Figured specimens. USNM 161940, 161943a, 

161943e; M. cf. M. tennis, USNM 161954.

Monograptus aff. M. undulatus Elles and Wood 

Text figure 18B, C, F; plate 4, figure 4

Monograptus undulatus Elles and Wood, 1901-18, Mon. British 

Graptolites, Palaeontographical Soc., p. 432, text fig. 295, 

pi. 45, fig. 5.

Description. The rhabdosome is long and slender, 

with gentle dorsal curvature and a recurved proximal 

end. It increases very gradually in width, so that it 

appears to be about the same width throughout its 

length. The thecae have their apertural regions coiled 

into lobes involving about a third of the thecal length. 

The lobes occupy approximately a half of the total 

width of the rhabdosome. The sicula extends almost to 

the level of the highest region of theca 3 (fig. 18.F).

Discussion. The Alaskan specimens resemble M. 

undulatus in general appearance. Because all our 

specimens are distorted, it is difficult to state what their 

true dimensions were. In comparison to M. undulatus, 

they seem to have generally more thecae per centimeter. 

M. undulatus is ventrally flexed in its distal part, where 

as all our specimens are nearly straight or are dorsally 

curved. The apex of the sicula of M. undulatus is on a 

level with the highest region of theca 1, and the sicula 

on our specimens reaches to theca 3.

The Alaskan specimens also resemble M. runcinatus 

var. pertinax, but it lias a nearly straight rhabdosome, 

and the lobed part of the thecae occupies only about a 

third of the width of the rhabdosome.

Ruedemann (1947, p. 488-89) describes a specimen 

from Dall Island, in southeastern Alaska, which he 

calls "Monograptus sp. nov. aff. undulatus." It is 

slender and strongly flexed, with the thecae on the

convex side. The thecae number 10 per centimeter 

and are very elongate, with slight ogee curvature. The 

apertural region is isolate and retroverted, and nearly 

a third of the thecal length is involved. The lobes thus 

formed occupy about half the width of the rhabdosome. 

This description corresponds very closely to curs, but 

Ruedemann (1947) did not illustrate his specinen.

Occurrence. M1140-SD.

Range. M. undulatus is found in the Llandoverian 

zones (20-23) of M. convolutus to M. crispus in Great 

Britain (Elles and Wood, 1901-18). It also occurs in 

the upper Keilorian of Australia (Thomas, 1960).

Dimensions (in millimeters). 

Specimen No. Length of 

rhabdosome

Width Thecae per 

centimeter

USNM-161955 '

161862b 1 -_---___

161956

161957 l

161958

161959

161960

161961

161962a__ _______

161962b ____-__.

161962c _ _ ___.

161963a

161964

161965d

161963b

161966 ___ _____

161965e

161967.___..___.

31

29

22

12

10

21.5

21

14

22

101

55

45

30

22

42

17

18

97

1.0

. 5-0. 7

. 5-1. 0

. 5

. 5-0. 75

. 5-0. 8

. 6-0. 7

. 6-0. 75

. 7-0. 8

. 7-1. 2

. 6-0.7

. 65-0. 9

. 5-0. 7

. 5-0. 6

1. 0

1. 0-1. 2

1. 0-1. 3

. 7-1. 0

14

9-10

13

10-13

12 9-10

10-11

10-11

9-12

7-13

9-10

10

11-12

10-11

13

13

12

11

i Figured specimens.

Material. About 30 compressed distorted sp ecimens. 

Figured specimens. USNM 161955, 161862b, 

161957.

Genus RASTRITES Barrande, 1850

Rastrites Barrande. Bulman, 1955, Geol. Soc. America, Treatise 

on invertebrate paleontology, pt. V, p. V93, fig. 68, 2a, b.

Rhabdosome uniserial, curved or hook shaped, with 

threadlike common canal. Thecae widely spaced, 

straight, isolated, with tiny hooked apertures, extending from common canal at high angles. Lower Silurian 

(middle and upper parts); Europe, North Africa, Asia, 

Australia, Greenland, and North America.

Rastrites cf. R. longispinus (Perner) 

Text figure 19C; plate 4, figure 17

Rastrites longis-pinus (Perner). Elles and Wood, 1901-18, Mon.

British Graptolites, Palaeontographical Soc., p. 489-490,

text fig. 344, pi. 50, fig. 2a-g. 

Rastrites longispinus (Perner). Obut, Sobolevskaya, and Bondarev, 1965, Graptolity Silura Taimyra, p. 90-91, pi. 17,

figs. 8, 9.

Description. According to Elles and Wood (1901 

18, p. 489-90), the rhabdosome is arcuate, with a 

proximal part nearly semicircular in shape. Tl °> thecae
SYSTEMATIC DESCRIPTIONS 45

number seven to eight per centimeter and are very 

long in proportion to the width of the interspaces 

between thecae. The thecae are 3-5 mm long, have 

distinctly reflexed apertural terminations, and are set 

nearly perpendicularly to the rhabdosome axis. The 

interspaces are about 1 mm long.

FIGURE 19. Rastrites. A and B, R. orbitus n. sp.: A, 

Holotype (USNM 161969) (same as pi. 4, fig. 18), X 8; 

B, Proximal fragment (USNM 161970) showing sicula, 

X 8. C, R. cf. R. longispinus (Perner), broken and bent 

fragment (USNM 161968) (same as pi. 4, fig. 17), X 5.

Discussion. The specimens at hand are fragmentary. 

The largest has thecae as much as about 3.0 mm long, 

numbering eight to 10 per centimeter. The overall 

shape and curvature of the Alaskan species is unknown. The long thecae and their general spacing 

suggests R. longispinus.

Occurrence. Ml 142-SD.

Range. Llandoverian zones (19 and 20) of M. 

gregarius and M. convolutus (Birkhill Shales) in Great 

Britain (Elles and Wood, 1901-18) (Toghill, 1968). 

Llandoverian zones of M. gregarius to M. sedgwickii 

in Portugal (Romariz, 1962). Llandoverian zones of 

Demirastrites pectinatus to D. trianguLatus in Bohemia, 

Czechoslovakia (Pribyl, 1948). Tentatively identified 

from the subzone of M. trianguLatus near Cadia, New 

South Wales, Australia (Sherrard, 1954). Also reported 

from Russia (Obut and others, 1965).

Dimensions (in millimeters). 

Specimen No. Length of 

thecae

Width of Thecae per 

interspaces centimeter

usNM-ieiges 1 ---...

161869h__--_.

2.9 

1.0-1.7

1. 0-1. 2

. 8-1. 3

8-10

l}i-\2}i

1 Figured specimen.

Material. Two compressed fragmentary specimens. 

Figured specimen. USNM 161968.

Rastrites orbitus n. sp. 

Text figure 19^4, B; plate 4, figures 18, 19

Description. The rhabdosome is small and arcuate 

to nearly circular in shape. The thecae are on the 

convex margin; they number seven to 12 per centimeter, and are 0.6-1.8 mm long. They are inclined to 

the rhabdosome axis and have apertural regions 

curved into a hook or barb. The interspaces are 0.8-1.4 

mm wide.

The rhabdosome is always greatly curved and, in 

the more nearly complete specimens, forms a circle 

or spiral. The thecae are relatively short, mostly 

measuring about 1.0-1.4 mm in length, with the 

maximum measured at 1.8 mm. The interspace width 

ranges from 0.7 to 1.4 mm, producing seven to 14 

thecae per centimeter. The theca forms an angle with 

the common canal of anywhere from 90° to 45°, with 

the average being about 70°-80°. The apertural end 

of each theca is sharply curved into a barb very similar 

to that on R. hybridus. One fragmentary specimen 

(fig. 19.B) bears what appears to be the sicula. TMs 

sicula measures about 0.6 mm in length and extends up 

to the level of the first theca. Theca 1 is 0.2 mm long, 

theca 2 is 0.5 mm long, and theca 3 is 0.6 mm long. 

The proximal thecae are thus smaller than the distal 

thecae, but otherwise very similar to them in 

appearance.

Discussion. The characteristic features of this 

species are the circular or spiral shape of the rhabdosome and the relatively short, inclined thecae. It is 

similar in general appearance to M. trianguLatus 

extremus Sudbury (1958), but R. orbitus has shorter 

thecae and no apparent overlap.

Occurrence. M1142-SD.

Range. Zone of M. gregarius in Alaska.

Dimensions (in millimeters}. 

Specimen No. Length of 

theca*

Width of 

interspaces

Thecae por 

centimeter

USNM-161969 1 ___.___

161970 1 __.__-_

161971 i___ _

161972-_.-._-_

161973d.__-._-

1619736------.

161974----.---

161975-_--___.

_-_-- 0. 7-1. 1

_-_._ .2-0.6

_-.-- .8-1.4

-__._ .8-1.3

._-_- 1.3-1.8

-_._. 1.0-1.5

__--- .7-1.8

____- .6-1.4

0. 9-1. 0

. 9-1. 0

1. 0-1. 4

. 8-0. 9

1. 0-1. 4

.8-1.1

. 8-1. 0

. 7-0. 9

10-11

10-11

7-10

7-10

9-123^

10-123^

11-14

' Figured specimens.

Material. Eight compressed somewhat poorly preserved specimens. 

Named after the Latin "orbitus"=circular.

Holotype. USNM 161969.

Figured specimens. USNM 161969-161971.
46 EARLY SILURIAN GRAPTOLITES FROM ALASKA

Rastrites aff. R. peregrinus (Barrande) 

Plate 4, figures 13, 14

Rastrites peregrinus (Barrande). Elles and Wood, 1901-18, Mon.

British Graptolites, Palaeontographical Soc., p. 488-489,

text fig. 343, pi. 50, fig. la-e. 

Rastrites peregrinus Barrande. Hundt, 1924 Grapt. d. deutsch

Silurs, p. 11, fig. 6-8.

Description. According to Elles and Wood (1901-18 

p. 488-489), the rhabdosome is small and arcuate, appears never to exceed 3 cm in length, and has a short 

sharply recurved proximal part. The thecae number 

eight to 10 per centimeter, and are 1.0-2.5 mm long, 

with narrow interspaces about 1 mm long. They are 

somewhat club shaped, with apparently rounded extremities due to the very slight apertural reflexion. The 

proximal part is recurved so as to present the appearance 

of a small fishhook.

Discussion. The specimens under study are fragmentary and somewhat distorted. The Alaskan species 

has more thecae per centimeter than those described 

by Elles and Wood (1901-18, p. 488-489) but otherwise 

resembles R. peregrinus. The change in thecal direction 

on specimen USNM 161976 (pi. 4, fig. 14) is definitely 

due to twisting of the rhabdosome and is not an original 

character as that described in Corymbites sigmoidalis 

(Obut and others 1967, p. 133).

Occurrence. M1140-SD.

Range. Llandoverian zone of M. millepeda (Road 

River Formation) in northern Yukon Territory, Canada 

(Jackson and Lenz, 1962). Llandoverian zones (19 and 

20) of M. gregarius and M. convolutus (Birkhill Shales) 

in Great Britain (Elles and Wood, 1901-18; Toghill, 

1968). Llandoverian zones of M. gregarius to M. crispus 

in Portugal (Romariz, 1962). Llandoverian zones of 

Demirastrites convolutus to M. sedgwickii in Bohemia, 

Czechoslovakia (Pribyl, 1948). Also reported from 

Germany (Hundt, 1924), Rastrites cf. R. peregrinus reported from a Silurian shale at Houlton, Maine (Ruedemann, 1947).

Dimensions (in millimeters'). 

Specimen No.

Length of Length of 

rhabdo- thecae 

some

Width of Thecae 

interspaces per

centimeter

USNM-161976 1 . 

161978!. 

161980- 

161979-

161981-

161982-

161983- 

161977- 

161984-

17

10

13

10

7

25

8

10

7.5

1. 0-1. 5

1. 0-1. 3

1. 0-1. 5

1. 1-1. 3

1. 2-1. 8

. 7-1. 1

. 9-1. 0

1.1

1.5

. 7-0. 9 

.7

. 7-0. 8 

. 7-0. 9 

. 7-0. 8 

. 7-0. 8 

. 8-1. 0 

. 7-0. 9 

. 7-0. 8

12

13

10

11

14

13

12

12

12

1 Figured specimens.

Material. About 17 compressed distorted somewhat 

poorly preserved specimens. 

Figured specimens. USNM 161976, 161978.

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48 EARLY SILURIAN GRAPTOLITES FROM ALASKA

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INDEX

[Italic page numbers indicate descriptions and major references]

Page

abbreviates, Climacograptus rectaiigulariS- 10, 18; pi. 1 

acinaces, Monograptus-------------- 10, SB, 36; pi. 3

acuminatus, Akidograptus- _____________ ______ 6,8,

10, 34; pi. 3 

Cephalograptus ___________________________ 34

Diplograptus _____________________________ 22, 34

(Akidograptus) acuminatus-- __________ 34

acuminatus, Diplograptus (Akidograptus)-- 34 

Akidograptus-__.-___-__-____.____ 5, 6, 8,10,12,29,34

acuminatus-----...--.---.... _____________ 6, 8,

10, 34; pi. 3 

Zone_____-____ ______ 6,8,10,12,13,18,22,27,31,34

zone.__-_-_-_----___--_.__________________ 8

(Akidograputs) acuminatus acuminatus, Diplograptus. ----------_-_-____________ 34

alaskensis, Dimorphograptus physophora_.lQ, 33; pi. 3 

anceps,Dicellographs, zone... ______________ 5,8,12

anna, Phyllograptus... __------________________ 5

approximatus geinitzi, Bastrites, zone,_________ 39

argenteus, Monograptus __.----________________ 38

argutus, Mo7iograptus--------.-__._________ SB; pi. 4

atavus, Monograptus- _---_--_________ 10,12, 36; pi. 3

B

bellulus, Diplograptus- _-------______._________ 29

Diplograptus (Orthograptus) _ _____________ 29

Orthograptiis__. ___________________ 10, 23,.._.; pi. 3

bicornis, Climacograptus. _____________________ 5

Birkhill Shales of Dobb's Limi_ _____________ _2, 6,10

brepicaudatus, Climacograptus medius____ 10, J6; pi. 1

buddingtoni, A ronograptus___--...-.---.. 10, 36,- pi. 4

calamistratus, Monograptus .___._._... 10,37; pi. 4 

calcaratus, Orthograptus.- _____________________ 5

Cardiograptits--..- ------------------------ 4

Cephalograptus acuminatus-- ---------------. 34

Chert and shale of the Descon Formation, ____ 3

Climacograptinae. _ ___----_--__-_-_-_-________ 13

Climacograptus---------------- 1,10,12, 13, 28

bicomis.------------------------ 5

extrcmus---------- -___---___-____________ 20

hastatus---.- ----------------------- 5

hughesi ------------------------------ 20

indivisus----------------------------- 13

esquibelensis------------- --__-_._ 10,IS; pl.l

innotatus.. _________________ _____ 10, /4,16; pi. 1

obesus...-..-.-----....-.-..... 10, J6; pi. 1

latus.--------------------- ---------- 18

..?«..«*_-_.___-___-_-. --__ 10, 13, 16, 17, 19; pi. 1 

brevicaudatus-................... 10, 16; pi. 1

minimus...................._--_..-._..... 19

mjn...M8.--__----__--___________._. 10,17; pl.l

rectangularis----------------- 10, J7, 18, 19; pi. 1

abbnviatus.-.--.....-.-. ...-.. 10, i8; pi. 1

scalaris...---...-...-......... 8, 10, 12, 19; pi. 1

stenotelus- ________ _________________ 10,19; pi. 1

supcrnus. --------------------- 5

-r./z-.s ---------------_-_-_______ _- 10

clingani,Dicranograptus,zone---..--..- ______ 15

communis, Monograptus... ___________ 42

compactus, Diplograptus multidc ..«___________ _ 21

complanatus, Dicellograptus.

ornatus, Dicellograptus. _-

concinnus, Monograptus-.--- _

confertus, Dimorphograptus ._

Page 

____________ *>

____--___--_ 5

____________ 6

____________ 12

swanstoni, Dimorphograptus .... 6, 10, 12, 33; pi. 3

Conglomerate and sedimentary breccia of

Descon Formation __ ____________ 3

convolutus, Demirastrites, zone_____ _ 19, 28, 29, 35, 38, 46

Monograptus, zone __--__--___________-____ 8, 12,

19, 25, 29, 30, 32, 35, 38, 39, 42, 45, 46 

Cordilleran geosyncline.--------.---. --------- 7

Corymbites sigmoidalis_.__ __---.____________--_ 46

crenularis, Monograptus-- -____.____- 10, 12, 37; pi. 3

crispus, Monograptus, zone. ---------- _________ 44,46

Cryptograptus tricorn is..---.. ------------------ 5

cyperoides, Orthograptus ... ___________-----_-_- 29

cyphus, Monograptus..--- _-_--__--_ 8, 10, 36, 38; pi. 4 

Pristiograptus .... . ______---___---_--__--___ 38

Cystograptus vesiculosus. ______________________ 30

zone. ___-_---__--_-_-_----__-------------_- 22

D

Demirastrites convolutus, zoiie._____ 19,28,29,35,38,46

pectinatus, zone..-- _____________ 16,32,39,40,45

triangulatus, zone..----------- ______ 15,16,32,45

denticulatus, Monograptus. ____________________ 8

Descon Formation, black chert and siliceous

shale----------------------------- 3

conglomerate and sedimentary breccia. _. 3 

description._---_. ________________________ %

graywacke sandstone and banded mudstone. _____-___-_-___-_-___-__---_ %

quartzo-feldspathic arenite____._-___----. 3

volcanic rocks.-_---_-_--._--_--_-_-___-_- 3 

youngest known beds____________________ 6

Dicellograptus................................ 35

anceps, zone.. ____________________________ 5,8,12

complanatus.............................. 5

or;ia.M*-_------------------------------ 5

zone of Jackson and Lenz__ _ _ _ _ 5,8,15,19

sextans--..---------------.-----.--------- 5

sp.--_------------------------------------ 5

Dicranograptus clingani, zone -___.____.__.__--- 15

Didymograptus.------------------- ---------- 4

protobifidus-------------------- _-__-__-_- 5

sp. --------------------------------------- 5

difformis, Monograptus _________________ 10, 39; pi. 3

diminutus, Diplograptus modestus- _.___- W,£2; pi. 2 

Dimorphograptidae_---------__--_ __-__-_--- 33

Dimorphograptus-------- ___________ 1,6,8,10,12,33

confertus ------------------------ 12

swanstoni ..________._._____ 6,10,12,33;pl.3

elongatus. ..___________________-------_--- 6

physophora ____________________-_----__- 6,12,34

alaskensis.---------------------- 10,33; pi. 3

swanstoni... ___.____________.____-_-__---- 33

Diplograptidae. ___._____-_________-___-__---- 13

Diplograptinae. _ __-__------_____-----------_- 21

Diplograptus-.------------------- _______ 10,12,21

acuminatus..--.-._......-,......-.....-.. 34

zone. _________.____---______-_--_----_

bellulus.-.- ------.-------------.------ 29

elojigatiis----------------------- 10,2/,23; pi. 1

Page 

Diplograptus Continued

modestus-.. _____________--__-__..._____ 22,23,27

zone.__-._ ___---__-_-___.-.._-._. 18,22,28

diminutus..-.-------..-.... _____ 10,«; pi. 2

mucroterminatus-----------........ 10,M; pl.l

multidens compactus _.__--___-_-___-_-_-_. 21 

palmeus,....-...---...-.-.--....--....... 32

vesiculosus-------------------------------- 30

(Akidograptus) acuminatus acuminatus...- 34 

(Glyptograptus) -amamc_t«________________ 28

tajjiariscus incertus------ _____________ 25

(Orthograptus) bellulus.--.--.-.---.-.----- 29

mutabilis ............................ 30

vesiculosus-......--.-...-----.-.-----. 30

(Petalograptus) palmeus __________________ 32

n. sp. A-_.___------------------------- 2S; pi. 2

n.sp.B-__-.--------------------------_ 23

Sp.--------------------------------------- 10

E

eberleini, Orthograptus.--....----.-.- 2,10, 2£; pi. 3

elongatus, Diplograptus-..-----.-.... 10, «, 23; pi. 1

Monogra ptus......-.------.....----------. 6

enodis, Olyptograptus.... ......-.-.--....-.- 24

Glyptograptusenodis. ______ 10,12, 23, 24; pi. 2

enodis, Olyptograptus.... _____ 10,12, 23, 24; pi. 2

tows, Olyptograptus....---.---..--.- 10, 24; pi. 2

esquibelensis, Climacograptus indivisus.-- 10, JS; pi. 1 

extremus, Climacograptus...................... 20

Monograptus triangulatus..-............... 45

Pseudodimacograptus.............. ..... 12

F

flaccidus, Leptograptus... 

Franklinian geosyncline.

Q

geinitzi, Rastrites approximatus... _____________ 39

geinitzianus, Retiograptus..................... 5

Globosograptus wimani............-.-....----- 42

Glossograptus sp.----------------------------- 5

Glyptograptus--.------------------ 1,10,12, 23, 28

enodis.....-------------------------------- 24

enodis..---------------- 10,12, 23, 24: pi. 2

latus ------------------------- 10, 24; pi. 2

gnomus- --.----------------------- 10, 2^; pi. 2

incer-tta.. .----------. ----- 10,12, 25; pi. 2

kaochiapienensis ---------------------- 27

fcai.._...-... --- --- ---- 8,26; pi. 2

.ocinioaua..------------------------ 10,26; pi. 2

.or-pAmi------------------------- 10,27, pi. 2

persculptus.-------------------------- 6,8,13,16

zone... ------------------------- 6.8,13,16

serratus. ---- ----- 23,25,27

sinuatus. --------------------------------- 8. 26

tamariscus. -------------------------- 8,24, 27,28

magnus. ----------------------- 10,27; pi. 2

nikolayevi----------------------------- 24

tamariscus-------------- 10,28; text fig. 10 F

.ere.iMsc-.JMS------------------------------ ^

sp... . 10. »

49
50 INDEX

Page 

(Olyptograptus) tamariscus, Diplograptus------ 28

tamariscus incertus, Diplograptus-, .-_._-.. 25 

gnomus, Olyptograptus.----------------- 10,34; pi. 2

Oraptolite zones for the lower Silurian ______ 6'

Graptolites, Lower Silurian hi western North

America- _ - --- --__ 6 

Graptolites of the Descoii Formation, southeastern Alaska ___________________ 2

Graptolithina------_---------_--__-_------.-- 13

Graptoloidea.- _.______ __ ___ _ _ __ is

Graywacke sandstone and banded mudstone. 2 

Great Basin graptolite localities__ ____ 8

gregarius, Monograptus----------- 10,12,36, 39; pi. 4

griestoniensis, Monograptus -..._.........___. 33

H

hamatus, Monograptus------------------- 8, 40; pi. 4

HartfellShale...---.. ._________.--______. 6

hastatus, Climacograptus. .____-_---__________. 5

Heceta Limestone-___-_-_---______-._--____-. 4,6

Hedrograptus rectangularis, ................... 17

hughesi, Climacograptiis------.--.------------- 20

Pseudodhnacograptus (Metaclimacograptus)

8,10, iO\ pi. 1 

hybridus, Rastrites.................._-. _._.. 45

incertus, Diplograptus (Olyptograptus)

Glyptograptus.-.. ------------ 10, 12, 25; pi. 2

incommodus, Monograptus _ ____________ 10,40; pi. 3

Pribylograptus- ...-----.. ......._.. ... 40

indimsus, Climacograptus. ............_....... 13

esguibelensis, Climacograptus- ._____. 10, JS; pi. 1 

innotatus, Climacograptus - _-......... 10, J4, 16; pi. 1

obesus, Climacograptus-------------- 10, J6; pi. 1

insectiformis, Orthograptus- --------- -------- 12,30

minutus, Orthograptus---. ..._............ 10,30

inpolutus, Monograptus--- ..................... 37

irfonensis, Monograptus-- --------------------- 41

iaculum, Monograptus.

kaochiapienensis, Olyptograptus---.----------- 27

Karheen Formation........ ________________ 2, 4

fcaz/i, Glyptograptus---.------------------ 8, 26; pi. 2

fcern, Monograptus----------------------- 8, 4f; pi- 4

laciniosus, Olyptograptus................ 10, #6; pi. 2

lanpherei, Olyptograptus--.------------- 10, 27; pi. 2

Lapworth's stratigraphic studies .-__-.____ 6

Lasiograptus sp.------------------------------ 5

tots, Climacograptus...---------------------- 18

Olyptograptus enodis.--------------- 10, #4,- pi. 2

-«./, Monograptus--.--------.--------.-- 28,35,36,41

Leptograptus flaccidus......................... 5

linearis, Plturograptus.----------------------- 15

linnaei, Rastrites.........._......-......-..... 33

lobiferus, Monograptus. ................ 6, 8, 43; pi. 3

Monograptus (Streptograptus)............. 42

longispinus, Rastrites................... 10, 44,' pi- 4

M

magnus, Olyptograptus tamariscus------- 10, #7; pi. 2

maximus, Rastrites, zone - ____ - 33,43

medius, Climacograptus...---- 10,13, ^6,17,19; pi. 1

brevicaudatus, Climacograptus..----- 10, J6; pi. 1

(Metaclimacograptus), Pseudoclimacograptus-.. 20

hughesi, Pseudoclimacograptus__._ 8,10, #0; pi. 1

undulatus, Pseudoclimacograptus--.- 10, #0; pi. 1

?)! illepeda, Monograptus..........----........-- 8,42

minimus, Climacograptus.... .............___-_ 19

Page 

minor, Petalograptus................ 10, S#, 33; pi. 3

minutus, Climacograptus...--.-----.-.-. 10, J7; pi. 1

Orthograptus insectiformus................. 10,30

modestus, Diplograptus__.----------------- 22,23,27

diminutus, Diplograptus-........... 10,&_; pi. 2

Monograptidae -.......---.............-.-...- 34

Monograp tinae -_--____--___-_-___--___--.____ 34

Monograptus.......................... 6,8,10,12,34

acinaces......................... 10, 35,36; pi. 3

argenteus................................. 38

argutus-............................. 35, pi. 4

afaz'MS____.-..-.----.....---.--_ 10, 12, 36; pi. 3

buddingtoni--.-------------------- 10, 36; pi. 4

calamistratus...................... 10, 37; pi. 4

co??j munis....._.......-....... ......... 42

concinnus................................ 6

convolutus, zone__----------- ---------- 8,

12,19, 25,29, 30,32, 35, 36, 38, 39,42,44,45,46 

crenularis---------------------- 10,12,37; pi.3

crispus ...................................44,46

cyphus.--.-.--------------- 6, 8,10,36,38; pi. 4

zone..-------------------------------- 10,

12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 25, 

27, 28, 29, 30, 31, 33, 34, 35, 39, 43 

denticulatus.............................. 8

difformis.------------------------- 10, 39; pi. 3

elongatus.................--...-- ......- 6

gregarius ----------------- 10,12, 36, 39; pi. 4

zone... _ _ __ _ _ _ 12, 

17, 18, 19, 20, 23, 24, 25, 26, 27, 29, 30, 32, 

35,36,37,39,40,41, 42,43,45,46 

griestoniensis, zone.-___-_-_-__----------_- 33

hamatus---............. ........... 8, 40; pi. 4

incommodus. .......-........--.. 10,40;pi. 3

involutus .- - --.--.---------.--..-------.- 37

irfonensis.... ...-....................... 41

jaculum.....------------------------------ 8,36

kerri-. .............................. 8,4?;pl.4

leei......... -------------------- 28,35,36,41

lobiferus ------------------------ 6,8,40,-pl. 3

millepeda------ .-.__....__-- ------------- 8,42

zone. _...___..._-....__...._..._- 19, 20, 30,32,46

nobilis.-----._..-......................... 8

noyesensis........................... 10, 42; pi. 4

nudug.................................... 6

priodon................................... 6

pse u dopla nus............................. 42

revolutus...................... 10,12,39,43; pi. 3

runcinatus pertinax....................... 44

scanicus.................................. 41

sedgw ickli..------------------------------- 6

zone. _________ 6,19,20,25,28,29,33,43,45,46

tenuig............................ 10,12,4S;pl 4

triangulates, subzone._--.-._---_-----_--- 45

extremus ............................ 45

predecipiens................-.-....---. 6

turriculatus, zone- _ _____._-__ 19,20,25,32, 33,42

undulatus. .__._____..__-_-__-- 10,12,20,44; pi. 4

(Streptograptus) lobiferus..---------------- 42

mucrotenninatus, Diplograptus-.------.. 10, gg; pi. 1

multidens compactus, Diplograptus............ 21

mutabilis, Diplograptus (Orthograptus) _...-- 30 

.----------.----------- 10, SO; pi. 2

N

nikolayevi, Glyptograptus tamariscus.. --------- 24

nobilis, Monograptus-.--.----...---.---------- 8

noyesensis, Monograptus.... ....___-_-__- 10, 42; pi. 4

nudus, Monograptus .-.-. ................... 6

O

obesus, Climacograptus Innotatus........ 10, 16; pi. 1

orbitus, Rastrites.-------------- __-__--_ 10, 45; pi. 4

Ordovician-Silurian boundary in graptolitic

shale--____. _-__.-____...-______- 8,9

ornatus, Dicellograptus complanatus..--------- 5, 8

Orthograptus.............-...... -..- . 1,10,12,29

Page

Orthograptus Continued

bellulus.......--...------.....- 10, S3, 19; pi. 3

calcaratus. ___ _ ___________________________ 5

cyperoides................................. 29

eberleini----.-------.------- 2,10, #0; pi. 3

? nsectiformis.............................. 12,30

minutus................................ 10,30

mutabilis....--.____-__-_._-._-__-___ 10, 30; pi. 2

.rancafris-..-._-_---_------.__-------_-_.- 5

vesiculosiis-............--...-..-.-. ..... 6,8,

10,12, SO; pi. 2 

zone. __.._____. 6,12,14,17,18,29,31,35, 36, 40

(Orthograptus) bellulus, Diplograptus..-....... 29

mutabilis, Diplograptus.... _-______-_.._-__ 30

vesiculosus, Diplograptus ------------------ 30

Orthograptus .- -.-.-------.---------- 10,S^;pl. 3

Orthoretiolites. ---...-.......-...-.--.-.--...-. 5

palmeus, Diplograptus. ....................... 32

Diplograptus (Petalograptus)..-.-.-.-.--.- 32 

Petalograptus ... .................. 10, S#, 33; pi. 3

tenuis, Petalograptus ... ___________ __6. 8, 32; pi. 3

pectinatus, Demirastrites ..... ___-__.___12, 32, 39, 40,45

peregrinus, Rastrites..-. ............. --_-10, 46; pi. 4

Pernerograptus revolutus. ..................... 43

persculptus, Olyptograptus. ..................... .6, 8

pertinax, Monograptus runcinatus. ............ 44

Petalograptinae. --__.._.-_._._-_._..__--._._- 32 

Petalograptus ....... ............. ............. 12, 32

w?reor--------_---_-.--__.__-__---10, S#, 33; pi. 3

palmeus-------- ---------- .-.--.-.10, 32, 33; pi. 3

tenuis.. ............ -.___-_-. ___6 8, S3; pi. 3

postfrus- -...--.-.-.---.-.--.---..-.--..-- 32 

(Petalograptus) palmeus, Diplograptus ..... ..-- 32

Phyllograptus anna.. ..-.._................... 5

physophora, Dimorphograptus. .............. _6, 12, 34

alaskensis, Dimorphograptus .... _--.__10, S3; pi. 3

Pleurograptus linearis, zone. ------------------ 15

posterus, Petalograptus-.- ..................... 32

predecipiens, Monograptus triangulatus. ...---. (i

Pribylograptus incommodus ................... 40

priodon , Monograptus. ........................ 6

Pristiograptus cyphus.-. ...................... 38

zone ------------------ 22,31,35,39,40,43

tenuis .............. ........... ........... 43

protobifidus , Didymograptus- ------------------ 5

Pseudoclimacograptus. .........-....-....... 10,19

extremus..--------.----------------------- 12

(Metaclimacograptus) --------------------- 20

hughesi.------ ...........S 10,20;pl.l

undulatus..------.------------- 10,20;pl. 1

pseudoplanus , Monograptus. ........-.-....--. 42

Q

Quartz-feldspathic arenite of Descon Formation. __ ------------------------- 3

s«r«es---- --------------------------------- 12,44

approximatus geinitzi, zone, __ - - . -- 39 

-------------------------- 45

linnaei, zone.------.----. -------------- 33

Zonffispmus- ------------------------ 10, 44,' P^ 4

maximus, zone.--------------------------- 33, 43

orbitus. ---------------------------- 10,45;pl-4

------------------------ 10, 4*>; pi- 4

sp.

rectangularis, Climacograptus.--.- 10, 17, 18,19;

Hedrograptus.............................

abbreviatus, Climacograptus..-- ------- 18,

Retiograptus geinitzianus ......................

revolutus, Monograptus......... 10, 12, 39, 43;

Pernerograptus...........................

Rhaphidograptus.........................

toernquisti...........................

runcinatus pertinax, Monograptus .....

pi. 1 

17

pl.l

5

pi. 3

43

6,13

13,16

44
INDEX

Page

S

scalaris, Climacograptus^.---------- 8,10,12, W; pi. 1

scanicus, Monograptus......-..--------------- 41

sedgwickii, Monograptns.-------------- ------ 6

serra, Tetragraptus..-------------------------- 4

serratus, Glyptograptus............. --- - 23,25,27

sextans, Dicellograptus------------------------ 5

sigmoidalis, Corymbites...---.-----.---------.- 46

Silurian graptolite zones, lowest ______________ 1

standard--------------------------------- f>

Silurian graptolites in western North America. 6 

smuztus, Olyptograptus--.-------------------- 8,26

stenotelus, CZ-mfzeogTaptaS-____-__-___.__ 10, 19; pi. 1

Stratigraphic relations of Descon Formation to

other units arid age-__.___________ 3

(Streptograptus) lobiferws, Mojiograptus........ 42

supernus, Climacograptus___________________ 5

swanstoni, Dimorphograptus___ .--______-___ 33

Dimorphograptus confertus. - _ _ _ 6,10,12, 33; pi. 3

Page

tamariscus, Diplograptus (Olyptograptus). .. 28 

Glyptograptus..-.-..---....--.------. 8,24,27,28

tamariscus ............................ 10,28

incertus, Diplograptus (Glyptograptus)---- 25

magnus, Glyptograptus.............. 10, #7; pi. 2

nikolayevi, Glyptograptus.................. 24

tamariscus, Glyptograptus.-------.-------- 10,28

tennis, AJonograptus.................. 10,12,43; pi.4

Petalograptus palmeus............ 6, 8, 38; pi. 3

Pristiograptus__ __---___-_____-----_---- 43

teretiusculus, Glyptograptus................... 5

Tetragraptus serra......-.------.-...-.-...-.. 4

toernquisti, Rhaphidograptus_______-___._--__ 13,16

triangulates, Demirastrites, zone.-------- 15,16,32,45

Monograptus, subzone.-_________--_--_---_ 45

extremus, Monograptus.................... 45

predecipiens, Monograptus ---------------- 6

tricornis, Cryptograptus.--.------------------- 5

trifills, Climacograptus........................ 10

truncatus, Orthograptus----------------------- 5

Turbidites. -.------_-----..----------._---- 3

turriculatus, Monograptus, zone _ _ _ 19, 20,25,32,33,42

U

undulatns, Monograptas...._.......10,12,44;p\- 4

Pseudoclimacograptus (Metadimacograptus)......................... 10,»;pl.l

oesiculosus, Cystograptus...................... 30

zone...-----------------__---_.._-__._____ 22

Diplograptus............................. 30

(Orthograptus)........................ 30

Monograptus. ._-_-__--____-______._-._____ 29

Orthograptus................. 6,8,10,12,30; pi. 2

zone..-------__---___-- 14,17,18,31,35,36,40

Volcanic rocks of Descon Formation.._._._._- 3

W

Wales Group....---.-._ 

wimani, Olobosograptus.

PLATES 1-4
PLATE 1

FIGURE 1. Climacograptus indivisus esquibdensis n. subsp. (p. 13). 

USNM 161604, X 3.5. Holotype.

2. Climacoyi aptus innotatus Nicholson (p. 14). 

USNM 161607, X 5.3.

3. Climacograptus innotatus obesus n. subsp. (p. 16).

USNM 161613, X 5.4. 

4, 5. Climacograptus cf. C. medius Tornquist (p. 16).

4. USNM 161615, X 5.4.

5. USNM 161618, X 3.5. 

6. Climacograptus minutust Carruthers (p. 17).

USNM 161627, X 5.4. 

7-9. Climacograptus cf. C. rectangularis (M'Coy) (p. 17).

7. USNM 161639, X 5.5.

8. USNM 161632, X 5.4.

9. USNM 161635, X 5.3. 

10, 11. Climacograptus scalaris (Hisinger) (p. 19).

10. USNM 161658, X 5.4.

11. USNM 161663, X 5.2. 

12. Climacograptus medius brevicaudatus n. subsp. (p. 16).

USNM 161621, X 5.1. Holotype. 

13, 14. Climacograptus stenotelus n. sp. (p. 19).

13. USNM 161667, X 4.4.

14. USNM 161666, X 4.5. Holotype, slightly distorted. 

15. Climacograptus rectangularis abbreviatus n. subsp. (p. 18).

USNM 161646, X 5.5. 

16, 17. Pseudodimacograptus (Metadimacograptus) hughesi (Nicholson) (p. 20).

16. USNM 161674, X 5.5.

17. USNM 161687, X 5.2. Pyritized specimen. 

18. Pseudodimacograptus (Metadimacograptus) cf. P. (M.) undulatus (Kurck) (p. 20)

USNM 161690, X 4.7. Slightly distorted. 

19, 20. Diplograptus elongatus n. sp. (p. 21).

19. USNM 161700, X 5.4.

20. USNM 161698, X 3.6. Holotype. 

21. Diplograptus mucroterminatus n. sp. (p. 22). 

USNM 161706, X 5.0.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 653 PLATE 1

16 ^^ 18 ^H^l^ 19 ^^^" 20 

CLIMACOGRAPTUS, PSEUDOCLIMACOGRAPTUS, and DIPLOGRAPTUS

21
PLATE 2

FIGURE 1. Diplograptus n. sp. A (p. 23).

USNM 161711, X 5.3. Proximal end broken off. 

2. Glyptograptus cf. G. enodis var. enodis Packham (p. 23).

USNM 161715, X 5.3. 

3, 4. Glyptograptus cf. G. enodis var. latus Packham (p. 24).

3. USNM 161718, X 5.1.

4. USNM 161717, X 5.2. 

5, 6. Glyptograptus incertus Elles and Wood (p. 25).

5. USNM 161730, X 3.5.

6. USNM 161734, X 4.7. 

7, 8. Glyptograptus tamariscus magnus n. subsp. (p. 27).

7. USNM 161765, X 2.2. Holotype.

8. USNM 161766, X 5.3. 

9, 10. Glyptograptus lanpherei n. sp. (p. 27).

9. USNM 161758, X 5.8. Subscalariform view.

10. USNM 161760, X 5.4. 

11-13. Orthograptus vesiculosus Nicholson (p. 30).

11. USNM 161794, X 3.6. Proximal end fragmentary.

12. USNM 161790, X 3.5. Subscalariform view.

13. USNM 161788, X 5.4. Subscalariform view.

14. Orthograptus cf. O. mutabilis Elles and Wood (p. 30).

USNM 161787, X 5.2. Distal fragment, retouched photograph.

15. Glyptograptus kayi n. sp. (p. 26).

USNM 161741, X 5.2. Holotype, pyritized specimen.

16. Glyptograptus gnomus n. sp. (p. 24). 

USNM 161644, X 5.5. Holotype. 

17, 18. Glyptograptus laciniosus n. sp. (p. 26).

17. USNM 161751, X 3.5. Subscalariform view.

18. USNM 161746, X 3.5. Holotype.

19. Diplograptus modestus var. diminutus Elles and Wood (p. 22). 

USNM 161701a, X 4.8.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 653 PLATE 2

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DIPLOGRAPTUS, GLYPTOGRAPTUS,a.nd ORTHOGRAPTUS
PLATE 3

FIGUKE 1. Orthograptus bellulus Tornquist (p. 29). 

USNM 161779, X 5.3.

2. Orthograptus eberleini n. sp. (p. 29). 

USNM 161783, X 5.2. Holotype.

3. Petalograptus palmeuf var. tennis Barrande (p. 32). 

USNM 161812, X 5.2. Pyritized specimen.

4. Wrthograptus n. sp. (p. 31).

USNM 161795, X 5.4. Subscalariform view.

5. Petalograptus minoi Elles (p. 32). 

USNM 161800, X 5.2.

6. Petalograptus palmeus (Barrande) (p. 32). 

USNM 161808, X 4.9.

7. Dimorphograptus physophora alaskensis n. subsp. (p. 33).

USNM 161826, X 5.2. Holotype. 

8-10. Dimorphograptus confertus var. swanstoni (Lapworth) (p. 33).

8. USNM 161824, X 5.3. Narrow form.

9. USNM 161816, X 5.4. 

10. USNM 161814, X 5.3. 

11. Monograptus atavus Jones (p. 36).

USNM 161842, X 3.4. 

12, 21. Monograptus lobiferus (M'Coy) (p. 42).

12. USNM 161923, X 5.2. Pyritized distal fragment. 

21. USNM 161919, X 5.2. Pyritized distal fragment. 

13-15. Monograptus acinaces Tornquist (p. 35).

13. USNM 161835, X 5.5. Proximal fragment with sicula.

14. USNM 161840, X 3.4. Proximal fragment without sicula.

15. USNM 161836, X 5.3. Proximal fragment without sicula. 

16, 17. Akidoyraptus acuminatus (Nicholson) (p. 34).

16. USNM 161832, X 4.9.

17. USNM 161830, X 4.9. Proximal fragment. 

18, 23-25. Monograptus cf. M. crenularis Lapworth (p. 37).

18. USNM 16187la, X 4.4. Proximal fragment (see first paragraph p. 38).

23. USNM 161874, X 2.1. Nearly complete specimen.

24. USNM 161872, X 2.0. Nearly complete specimen.

25. USNM 161873, X 3.0. Distal fragment.

19. Monograptus revolutus Kurck (p. 43). 

USNM 161937, X 5.5.

20. Monograptus cf. M. incommodus Tornquist (p. 40).

USNM 161905, X 5.5. 

22. Monograptus cf. M. difformis Tornquist (p. 39).

USNM 161893, X 5.3.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 655 PLATE 3

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ORTHOGRAPTUS, PETALOGRAPTUS, DIMORPHOGRAPTUS, AKIDOGRAPTUS,a.nd MONOGRAPTUS
PLATE 4

FIGUEE 1. Monograptus gregarius Lap worth (p. 39). 

USNM 161894, X 5.4.

2. Monograptus cf. M. tenuis (Portlock) (p. 43). 

USNM 161954, X 5.4. Distal fragment.

3. Monograptus tenuis (Portlock) (p. ).

USNM 161943a (vertical) and USNM 161943e (horizontal), X 5.3. Distal 

fragments.

4. Monograptus aff. M. undulatus Elles and Wood (p. 44).

USNM 161862b, X 2.2. Proximal fragment. 

5, 6. Monograptus cyphus Lapworth (p. 38).

5. USNM 161885, X 3.5. Distal fragment.

6. USNM 161890, X 3.5. Distal fragment. 

7, 8. Monograptus buddingtoni n. sp. (p. 36).

7. USNM 161851, X 4.6.

8. USNM 161850, X 5. Holotype9, 10. Monograptus noyesensis n. sp. (p. 42).

9. USNM 161928, X 5.5. Holotype; distal fragment. 

10. USNM 161929, X 5.5. Proximal fragment.

11. Monograptus kerri n. sp. (p. 41).

USNM 161911, X 5.1. Holotype, pyritized. Photograph retouched and somewhat restored distally.

12. Monograptus calamistratus n. sp. (p. 37).

USNM 161988, X 5.3. 

13, 14. Rastrites aff. R. peregrinus (Barrande) (p. 46).

13. USNM 161978, X 4.8.

14. USNM 161976, X 4.8.

15. Monograptus hamatus n. sp. (p. 40).

USNM 161901, X 5.3. Holotype, pyritized proximal fragment, photograph 

retouched.

16. Monograptus argutus Lapworth (p. 35).

USNM 161841, X 5.0. Pyritized distal fragment.

17. Rastrites cf. R. longispinus (Perner) (p. 44).

USNM 161968, X 5.3. 

18, 19. Rastrites orbitus n. sp. (p. 45).

.18. USNM 161969, X 5.2. Holotype. 

19. USNM 161971, X 4.8.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 653 PLATE 4

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MONOGRAPTUS and RASTRITES

V. S. GOVERNMENT PRINTING OFFICE : 1970 O - 369-097