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Silurian Trilobites from
the Northern Yukon Territory

Rolf Ludvigsen and Ronald R Tripp

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LIFE SCIENCES CONTRIBUTIONS 153

Silurian Trilobites from
the Northern Yukon Territory

Rolf Ludvigsen

and
Ronald R Tripp

ROM

ROYAL ONTARIO MUSEUM
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Rolf Ludvigsen is research associate, Department of Invertebrate Palaeontology,
Royal Ontario Museum, Toronto, and head of the Denman Institute for Research
on Trilobites, 4062 Wren Road, Denman Island, British Columbia VOR ITO.

Ronald P. Tripp is also research associate. Department of Invertebrate Palaeon-
tology, Royal Ontario Museum, Toronto. He currently resides at 41 Kirk Drive,
Thornhill, Ontario L3T 3K8.

Canadian Cataloguing in Publication Data

Ludvigsen, Rolf, 1944-

Silurian trilobites from the northern Yukon Territory

(Life sciences contributions, ISSN 0384-8159 ; 153)
Includes bibliographical references.
ISBN 0-88854-349-2

1. Trilobites. 2. Paleontology — Silurian.
3. Paleontology — Yukon Territory. I. Tripp, Ronald
P. (Ronald Pearson), 1914- . II. Royal Ontario
Museum. III. Title. IV. Series.

OE821.L83 1989 565'.393'097191 €89-09501 1-3

Publication date: 1 February 1990

ISBN 0-88854-349-2

ISSN 0384-8159

100 Oueen's Park, Toronto, Canada M5S 2C6

PRINTED AND BOUND IN CANADA BY GAGNE PRESS

Contents

Abstract 1
Introduction 1
Stratigraphy 2

Road River Formation 2
Unnamed Carbonates 4
Age and Correlation 4

AA 2-4.5 (Road River Formation) 4
BB 131 (Unnamed Carbonates) 4
AA 95 (Road River Formation) 5
Trilobite Associations 5
' Otarion Association 5
Stenopareia Association 5
Hedstroemia Association 6
Materials and Methods 7
Systematic Palaeontology 8

Family Styginidae Vogdes, 1890 8
Subfamily Bumastinae Raymond, 1916 8
Genus Paracybantyx gen. nov. 8

Paracybantyx asulcatus sp. nov. 8
Indeterminate bumastine 9
Subfamily Scutelluinae Richter and Richter
Genus Kosovopeltis Snadjr, 1958 9
Kosovopeltis borealis (Poulsen, 1934)
Kosovopeltisl spp. 14
Indeterminate scutelluine 14
Family Illaenidae Hawle and Corda, 1847 14
Subfamily Illaeninae Hawle and Corda, 1847
Genus Stenopareia Holm, 1886 14

Stenopareia illtyd sp. nov. 14
Indeterminate illaenid 15
Family Proetidae Salter, 1864 15

?Subfamily Crassiproetinae Osmolska, 1970
Genus Hedstroemia Pfibyl and Vanek 15

Hedstroemia kutchini sp. nov. 15
Hedstroemia sourdoughi sp. nov. 17
Subfamily Warburgellinae Owens, 1973 17
Genus Prantlia Pfibyl, 1946 17
Prantlia vagrans sp. nov. 17
Subfamily uncertain 19

Indeterminate proetid A 19
Indeterminate proetid B 19
Family Aulacopleuridae Angelin, 1854 20
Genus Otarion Zenker, 1833 20

Subgenus Songkania Chang, 1974 20
Otarion (Songkania) socialis (Poulsen, 1934)
Family Harpidae Hawle and Corda, 1847 21
Genus Scotoharpes Lamont, 1948 21

Scotoharpes raaschi Norford, 1973 21

111

Family Cheiruridae Hawle and Corda, 1847 22
Subfamily Cheirurinae Hawle and Corda, 1847 22
Genus Cheirums Beyrich, 1845 22
Cheimrus sp. 22
Family Encrinuridae Angelin, 1854 22
Subfamily Encrinurinae Angelin, 1854 22
Genus Cromus Barrande, 1852 22

Cromus princeps (Poulsen, 1934) 22
Genus Encrinuraspis Webby, Moors, and McLean, 1970 24

Encrinuraspis sp. 24
Genus Balizoma Holloway, 1980 24

Balizoma aff. B. obtusus (Angelin, 1851) 24
Indeterminate encrurine 25
Family Calymenidae Milne-Edwards, 1840 26
Subfamily uncertain 26

Indeterminate calymenid 26
Family Lichidae Hawle and Corda, 1847 26
Subfamily Lichinae Hawle and Corda, 1847 26
Genus Dicranopeltis Beyrich, 1845 26
Dicranopeltis sp. 26
Subfamily uncertain 26
Indeterminate lichid 26
Family Odontopleuridae Burmeister, 1843 27
Subfamily Odontopleurinae Burmeister, 1843 27
Genus Leonaspis Richter and Richter, 1917 27

Leonaspis semiglabra (Poulsen, 1934) 27
Indeterminate odontopleurine 28
Acknowledgements 29
Literature Cited 30
Plates 34

Silurian Trilobites from
the Northern Yukon Territory

Abstract

Silurian trilobites are described from two contrasting facies in the northern Yukon
Territory: basinal sediments of the Road River Formation at Prongs Creek and
shallow-water limestones of the Illtyd Range. An Otarion Association from dark
grey, argillaceous lime mudstones (Lower Silurian) consists of Kosovopeltis, Otarion
(Songkania), Cromus, and Leonaspis. These trilobites are identical to those described
by Poulsen (1934) from his Cape Schuchert Formation of North Greenland. A
Stenopareia Association from off-white biosparites (Lower Silurian) includes Steno-
pareia, a bumastine, Kosovopeltis, and Scotoharpes. AHedstroemia Association occurs
in an Upper Silurian debris flow. It includes Hedstroemia, Prantlia, Balizoma, and
Paracybantyx.

An incomplete ontogeny of Kosovopeltis borealis (Poulsen) comprises a protaspis
and four different transitory pygidia.

The bumastine genus Paracybantyx is new. New species are Paracybantyx asulcatus,
Stenopareia illtyd, Hedstroemia kutchini, H. sourdoughi, and Prantlia vagrans.

Introduction

Silurian rocks crop out as two contrasting facies in
the northern Yukon Territory: as basinal shales of the
Road River Formation within the Richardson and
Blackstone troughs in the Peel River-Wind River area
(Lenz, 1972), and as thick-bedded to massive carbon-
ates, yet unnamed, on the Mackenzie Platform in the
Bonnet Plume River area and on the Yukon Block in
the Porcupine River area (Text-fig. 1). In the basinal
shales exceptionally complete stratigraphic successions
of graptolites are present (Lenz and Pedder, 1972;
Lenz, 1982), but in the platform carbonates well-pre-
served fossils of Silurian age are uncommon, with the
exception of locally abundant tabulate corals and pen-
tamerid brachiopods. The best-preserved and most-
diverse assemblages of Silurian shelly fossils in the
Yukon Territory are found in dark grey, argillaceous
limestones deposited on the margins of the troughs,
close to facies transitions with shallow-water carbon-
ates in areas along the Wind River such as Prongs
Creek (Raasch, Norford, and Wilson, 1961; Lenz, 1970)
and Royal Creek (Lenz, 1977; Jackson, Lenz, and Ped-
der, 1978). These assemblages are strongly dominated
by brachiopods, but a few include substantial numbers

of trilobites of types that are either unknown from
northern Canada or incompletely documented.

Rich Silurian trilobite assemblages have been
described from the Whittaker and Delorme formations
farther to the south in the Mackenzie Mountains of the
District of Mackenzie (Perry and Chatterton, 1977;
Chatterton and Perry, 1983), and smaller assemblages
have been described from different localities to the
north in the Canadian Arctic Islands (Bolton, 1965;
Perry and Chatterton, 1977; Thomas and Narbonne,
1979) and North Greenland (Poulsen, 1934; Lane,
1979, 1984; Lane and Owens, 1982). In the Yukon
Territory, however, Silurian trilobites have been docu-
mented from only two Lower Silurian localities — one
from dark grey limestones of the Road River Formation
at Prongs Creek (Raasch, Norford, and Wilson, 1961)
and one from off-white limestone in the nearby Illtyd
Range (Norford, 1973). In this paper, we reevaluate
and describe fully both these trilobite assemblages on
the basis of larger and more complete collections than
were available to previous investigators. We also deal
with a new trilobite fauna from the Upper Silurian part
of the Road River Formation on Prongs Creek.

LOCALITY MAP

AND

SILURIAN LITHOFACIES

shale and interbedded
dar1( limestone^

light coloured carbonates

Text-FIG. 1. Lx)cality map of the northern Yukon Territory showing Section AA on Prongs Creek
and Section BB in the Illtyd Range. The generahzed Silurian hthofacies map is adapted from Lenz
(1972, fig. 9).

Stratigraphy

ROAD RIVER FORMATION
The Road River Formation was raised to group status
by Fritz (1985), who considered four undesignated map
units in the Richardson Mountains to constitute forma-
tions. Until such time as these map units are defined
and formally named, we retain the formational status
of the Road River. Within the Richardson Trough
north of the Peel River, the Road River Formation
consists of more than one thousand metres of shales,
cherts, and limestones of Cambrian, Ordovician, Silu-
rian, and Devonian age. The axis of this intracratonic
trough swings east along the Bonnet Plume River to
join the Selwyn Trough to the south (Lenz, 1979, fig. 1;
Norris, 1985:40). During the Silurian, a narrow north-
south embayment off the Richardson Trough devel-
oped near the headwaters and along the tributaries
of the Wind River. Here, the Road River Formation
comprises a recessive sequence of calcareous shales
and argillaceous limestones which rests abruptly on
resistant Ordovician carbonates (see Lenz, 1972, fig. 8;
Norris, 1985, fig. 10). On Prongs Creek, the lower con-

tact of the Road River is concordant, but apparently
disconformable because Upper Ordovician (Rich-
mondian; Norford, 1964) strata are followed directly by
mid-Lower Silurian strata. Unconformities of similar
magnitude occur at the same interval in shelf succes-
sions of most other areas of western North America
(Lenz, 1976).

Starting about 50 m above its base on Prongs Creek
(Text-fig. 2), the Road River Formation begins to dis-
play evidence of relief associated with nearby carbonate
banks. Contorted bedding, slumps, and thick debris
flows consisting of jumbled fossils and small lithoclasts
become common. The debris flows were probably
derived from the flanks of shallow carbonate banks
such as those now exposed in the Illtyd Range to the
east or near the headwaters of the Hart River to the
southwest.

Sample AA 2-4.5 was obtained from medium-bed-
ded, highly argillaceous lime mudstones of deep-water
aspect, at the base of the Road River Formation. Sam-
ple AA 95 was collected from a prominent 2-m-thick

SECTION AA

SECTION BB

PRONGS CREEK
65"17'N. 135"42'W

ILLTYD RANGE
65"14'N.135"12'W

UNNAMED 0

ORDOVICIAN

CARBONATES

AAgs

C/D

180m-

1 )

160-

lAfl-

IfU

120-

)

100-

■•

80-

60-

)

^ 40-

=i 9n-

1 1

So ^U

)

AA 2-4.5

BB131

LIMESTONE

SHALE

COVERED INTERVAL

»io§?,oo^o) DEBRIS FLOW
SLUMP

Text-fig. 2. Graphic lithological log of Section AA, through the lower part of the Road River
Formation on Prongs Creek, and of Section BB, through unnamed Ordovician and Silurian carbonates
in the Illtyd Range. Sample BB 131 was collected 131 m above the base of massive and resistant Silurian
limestones, that is, at unit 3 of Norford's (1964) Section 5.

debris flow located 95 m above the base of the for-
mation.

UNNAMED CARBONATES
The Illtyd Range exposes a thick sequence of poorly
fossiliferous, thick-bedded to massive, shallow-v^ater
limestones of probable Ordovician, Silurian, and De-
vonian age (Norford, 1964; Lenz, 1972; Norris, 1985).

This carbonate bank maintained itself while sediments
of the Road River Formation accumulated in the Rich-
ardson Trough farther to the north.

Norford (1964:36) measured a distinctive unit 3 of
the unnamed carbonates consisting of 200 m of massive,
crystalline off-white limestone, which weathers into
steep pinnacles; Norford's unit 3 is probably entirely of
Early Silurian age. Sample BB 131 was collected 131 m
above the base of this unit.

Age and Correlation

AA 2-4.5 (ROAD RIVER FORMATION)
Raasch, Norford, and Wilson ( 1961) described brachio-
pods, trilobites, and graptolites from samples collected
at unspecified levels across a 50-m interval, starting at
the top of the resistant Ordovician carbonates at the
gorge of Prongs Creek. These samples included a trilo-
bite fauna with Aulacopleura socialis, herein referred
to as Otarion (Songkania) socialis and identical to the
fauna from our sample AA 2-4.5, as well as a graptolite
fauna representing the Lower Silurian Monograptus
turriculatus Zone. A measured section in Norford
(1964:49,127) located the O. (5.) socialis fauna in the
lower 6 m of the Road River Formation on Prongs
Creek, the M. turriculatus Zone a few metres higher,
followed by the M. spiralis Zone some 10 to 21 m
upsection.

Both Raasch, Norford, and Wilson (1961) and Nor-
ford (1964) indicated a late Llandovery age for the
Otarion fauna on Prongs Creek based on its position
relative to the position of the M turriculatus Zone. This
age assessment receives support from an abundant, but
low-diversity, conodont fauna from sample AA 2-4.5.
According to Godfrey Nowlan of the Geological Survey
of Canada (pers. comm., 1987), the sample is domi-
nated by "Oulodus" fluegeli (Walliser) and includes
Dapsilodus obliquicostatus, Ozarkodina excavata exca-
vata, Panderodus gracilis, and Walliserodus sancticlair.
Nowlan noted that, in other parts of the Yukon Terri-
tory, "O. "fluegeli is common in strata bearing grapto-
lites of the M. turriculatus Zone and further suggested
that this association of conodont elements probably
represents a deep-water biofacies.

Raasch {in Raasch, Norford, and Wilson, 1961) rec-
ognized that the four species of trilobites comprising
the O. (S.) socialis fauna on Prongs Creek are identical
to those described by Poulsen (1934), which had been
collected by Lauge Koch from different localities of the
Cape Schuchert Formation in Washington Land, North
Greenland. These trilobites must have been conspicu-
ous elements of the Cape Schuchert Formation because

Koch had previously referred these strata to the "Are-
thusina ( = Aulacopleura) beds" (see Dawes and Haller,
1979; Hurst, 1980:74).

There is considerable uncertainty about the prove-
nance of the Otarion fauna in North Greenland. The
Silurian stratigraphic framework of Washington Land
was revised by Hurst (1980), who restricted Koch's
Cape Schuchert Formation to black bituminous lime
mudstones of Llandovery age; the overlying shales and
mudstones were assigned to the Lafayette Bugt Forma-
tion of middle Llandovery to Ludlow age. Koch's local-
ity data were definitely generalized and possibly
unreliable (Norford, 1972:9). Apparently Otarion
occurs in both formations, but neither Norford (1972)
nor Hurst (1980) located this trilobite in Lower Silurian
stratigraphic sections of Washington Land. It is known
with certainty from only a single stratigraphically
located collection in North Greenland. According to
John S. Peel of the Greenland Geological Survey, O.
(S.) socialis and Cromus princeps occur in GGU sample
216841, collected from Norford's (1972:13) unit 4,
which is overlain (in unit 6) by graptolites of the M.
turriculatus Zone. These rock units were assigned to
the Cape Phillips Formation by Norford (1972) and to
the Lafayette Bugt Formation by Hurst (1980).

In summary, trilobite collection AA 2-4.5, with Ota-
rion {Songkania), Kosovopeltis, Cromus, and Leonaspis
from the lowest Road River Formation on Prongs
Creek, is Early Silurian in age and equivalent to, or
slightly older than, the M. turriculatus Zone. A faunule
with Otarion {Songkania) and Cromus from the Lafa-
yette Bugt Formation near Kap Schuchert in North
Greenland is approximately the same age.

BB 131 (UNNAMED CARBONATES)

Norford (1964, 1973) recorded a sparse trilobite fauna
of Scotoharpes raaschi Norford, Encrinurus cf. E.
princeps Poulsen, Scutellum sp., and an illaenid at GSC
locality 53109 from a 1-m interval 425 m above the base

of an unnamed carbonate unit in the liltyd Range; he
dated this fauna as late Llandovery. This interval of
massive, off-white, coarsely crystalline biosparite,
located 131m above the base of Norford's unit 3, was
re-collected as locality BB 131. A meagre conodont
fauna of 14 fragmentary specimens, including l^Oulo-
dus" fluegeli, Panderodus gracilis, and Walliserodus sp.,
was identified by G. Nowlan (pers. comm., 1987), who
suggested that it was probably of late Llandovery age.

AA 95 (ROAD RIVER FORMATION)
Lenz (1970) described a moderately rich fauna of Late
Silurian brachiopods from a thick limestone bed
located 106 m above the base of the Road River Forma-
tion on Prongs Creek. Re-collection of this bed yielded
a large number of well-preserved trilobites. According
to Ludvigsen's measured section, this bed is located

95 m above the base of the formation; therefore, our
sample is designated AA 95. On the basis of graptolite
faunas below and above, Lenz (1970) correlated the
fossiliferous bed with either the latest Ludlow or
the earliest Pridoli, an age assignment consistent with
biostratigraphic information from a meagre conodont
fauna. Later Jackson, Lenz, and Pedder (1978:20)
assigned the overlying graptolite collection to the
Monograptus formosus Zone, which in central Europe
comprises the basal zone of the Pridoli.

The trilobite fauna from AA 95 consists largely of
new species and, therefore, contributes little informa-
tion toward an age assignment and correlation of this
unit. We tentatively correlate AA 95 with the upper
Ludlow on the basis of the overlying graptolites. The
trilobites, in particular Prantlia vagrans sp. nov. and
Balizoma aff. B. obtusus (Angelin), have greater affini-
ties to Ludlow than to Pridoli species.

Trilobite Associations

Each of the three samples of Silurian trilobites from the
northern Yukon Territory dealt with here is dominated
numerically by a different family (Text-fig. 3, Table 1),
and each association clearly owes its composition to
environmental factors (see also Ludvigsen et al., 1986).

OTARION ASSOCIATION

Because of its size, Kosovopeltis is the most conspicuous
trilobite in sample AA 2-4.5, but the association is
named for Otarion which, though small, is numerically
dominant. The Otarion Association occurs in dark grey,
highly argillaceous lime mudstones of the lower few
metres of the Road River Formation at Prongs Creek,
in association with a low-diversity brachiopod fauna
(Norford, in Raasch, Norford, and Wilson, 1961). The
strata appear to be of deep-water aspect, a setting that
receives support from the low diversity of the trilobite
fauna and from the association of conodont elements
(G. Nowlan, pers. comm., 1987).

Aulacopleurids typically constitute minor elements
of trilobite associations in off-platform graptolite shale
basins (for example, Thomas, 1979, fig. 2), but we are
not aware of any published account of another trilobite
assemblage such as the Otarion Association that is dom-
inated by an aulacopleurid.

STENOPAREIA ASSOCIATION

A small collection from locality BB 131 is dominated by
Stenopareia and an indeterminate bumastine. It came

from an interval of off-white crystalline biosparite in
the Lower Silurian part of an unnamed unit in the Illtyd
Range; this unit records shallow-water carbonate bank
deposition during most of the Silurian and Early Dev-
onian (Text-fig. 1). The Stenopareia Association shows
no evidence of transportation and is, presumably,
autochthonous. This association in the Illtyd Range is
very similar to that described by Lane (1979) from
white, coarsely crystalline limestones of the upper part
of the Alequatsiad Fiord Formation (mid-Lland-
overy) near Kap Schuchert, North Greenland,
which also is dominated by Stenopareia and bumastines.

The Early Silurian Stenopareia Association of the
Yukon Territory and Greenland is clearly part of the
illaenid-cheirurid associations that also occur widely in
Ordovician carbonate build-ups and in subtidal shelf
settings in other areas of Laurentia (Westrop, 1983).
The Stenopareia Association itself seems to be a shelf
assemblage; it differs from contemporaneous build-up
assemblages in, for example, the Pentamerus Bjerg For-
mation of North Greenland, which is dominated by a
proetine and a scutelluine (Lane and Owens, 1982), or
the Hopkinson Dolomite of Iowa, which is character-
ized by a lichid and a cheirurid (Mikulic, 1981).

Within the limits of correlation possible using con-
odont biostratigraphy of the Road River Formation on
Prongs Creek and of unnamed carbonates of the Illtyd
Range, the Otarion Association from dark grey, argilla-
ceous lime mudstones is of the same age as the higher-
diversity Stenopareia Association from off-white
biosparites.

PARACYBANTYX

BAUZOMA

HEDSTROEMIA

PRANTUA

AA95 n=172

HEDSTROEMIA ASSOCIATION

UPPER SILURIAN

CROMUS

LEONASPIS

KOSOVOPELTIS.

SCOTOHARPES

OTARION

KOSOVOPELTIS

STENOPAREIA

AA2-4.5

OTARION ASSOCIATION

n=420

BUMASTINE

BB131 n=29

STENOPAREIA ASSOCIATION

LOWER SILURIAN

Text-fig. 3. Pie diagrams showing generic relative abundance of specimens in the three trilobite
associations deah with in this study.

HEDSTROEMIA ASSOCIATION

A 2-m-thick debris flow in the Upper Silurian part of
the Road River Formation on Prongs Creek yielded
a diverse brachiopod fauna of 17 species, dominated
numerically by the smooth atrypoid Cryptatrypa (Lenz,
1970), and a trilobite assemblage of 7 species that we
name the Hedstroemia Association. About two-thirds
of the specimens in this association belong to 3 proetine
and warburgelline species; the remaining specimens
are bumastines, encrinurids, and lichids.

The debris flows display scoured bases and lack inter-
nal grading. They appear to be the products of slumps
that swept shells and small (less than 1 cm) limestone
clasts off the sides of the adjoining carbonate banks
and into the centre of the shale embayment (see also

Lenz, 1977).

The Hedstroemia Association is different from the
few Upper Silurian trilobite faunas described from
northern Canada to date. Faunas from shallow subtidal
settings in the Road River Formation on Cornwallis
Island in the Canadian Arctic appear to be dominated
by the warburgelline Helokybe, the encrinurid Encri-
nurus, and the lichid Hemiarges (Thomas and Nar-
bonne, 1979).

The dominance of proetines and warburgellines in
the Hedstroemia Association is matched by the ProetusI
Warburgella Association from shelf limestones of the
British Wenlock (Thomas, 1979), but that association
shows considerably higher generic diversity.

Table 1. Summary of frequencies.

comp., complete; craAj., cephala/cranidia;/jy/>o., hypostomes;/?>'g., pygidia; to/a/, number of specimens
of the most frequent part; %, percentage of the total number of specimens.

Species

comp.

cran.

hypo.

pyg-

total

Lower Silurian

AA 2^.5, Prongs Creek
Kosovopeltis borealis
Otarion (Songkania) socialis
Cromus princeps
Leonaspis semiglabra

BB 131, Illtyd Range
Kosovopeltis'? spp.
Indeterminate bumastine
Stenopareia illtyd sp. nov.
Indeterminate illaenid
Indeterminate proetid B
Scotoharpes raaschi
Cheirurus sp.
Encrinuraspis sp.
Indeterminate calymenid
Dicranopeltis sp.
Indeterminate odontopleurine

Otarion Association

116

270

Stenopa

reia

Association

—

Upper Silurian

AA 95, Prongs Creek
Paracybantyx asulcatus gen. et sp. nov.
Indeterminate scutelluine
Hedstroemia kutchini sp. nov.
Hedstroemia sourdoughi sp. nov.
Prantlia vagrans sp. nov.
Indeterminate proetid A
Balizoma aff. B. obtusus
Indeterminate encrinurine
Indeterminate lichid

Hedstroemia Association

—

Materials and Methods

All the figured specimens that were collected have been
deposited at the Royal Ontario Museum; their regis-
tered numbers bear the prefix ROM. Other specimens
illustrated are in the collection of the Geological Survey
of Canada, Ottawa, and are prefixed GSC.

As far as possible, plates are arranged in the order
of the systematic section. Upper Silurian trilobites from
AA 95 constitute Plates 1, 6, 7, 11. Lower Silurian
trilobites from AA 2-4.5 constitute Plates 2-4, 8, 10,
12; Plate 4 comprises scanning electron micrographs
prepared at the University of Toronto. Lower Silurian

trilobites from BB 131 constitute Plates 5 and 9. Plate
13 comprises photographs of plaster casts of Poulsen's
(1934) original specimens from North Greenland. Orig-
inals are housed in the Mineralogical and Geological
Museum, University of Copenhagen (MMH).

The terminology used is essentially that defined by
Harrington, Moore, and Stubblefield {in Moore,
1959:117-126). Glabellar lobes, furrows, and muscle
impressions are numbered from back to front and sym-
bolized by L, S, and G, respectively. The occipital ring
is regarded as part of the glabella.

Systematic Palaeontology

Family Styginidae Vogdes, 1890

DISCUSSION

Lane and Thomas (1983:141) have argued that numer-
ous genera previously referred to separate famihes and
subfamihes of effaced trilobites should be included in

an undivided family Styginidae. In this paper we prefer
to continue the use of the subfamilies Stygininae, Scu-
telluinae, and Bumastinae as an aid to grouping the
large number of genera in the family.

Subfamily Bumastinae Raymond, 1916

Genus Paracybantyx gen. nov.

DERIVATION OF NAME

Name derived from Latin para (beside) and Cybantyx.
Gender masculine.

DIAGNOSIS

Cranidium broad, lacking anterior border and furrow.
Axial furrow bowed inward, faint posteriorly. Pygidium
convex, 85 to 100 per cent as wide as long, effaced.
Surface finely pitted.

TYPE SPECIES

Paracybantyx asulcatus sp. nov., locality AA 95 (Upper
Silurian), Road River Formation, Prongs Creek, Yukon
Territory, Canada.

OTHER SPECIES

None.

DISCUSSION

The absence of the anterior border and furrow pre-
cludes inclusion of this species in the genus Cybantyx,
Lane and Thomas {in Thomas, 1978), which it other-
wise resembles.

Paracybantyx asulcatus sp. nov.

PI. 1, figs. 1-15; PI. 11, figs. 1-5

DERIVATION OF NAME

Specific name derived from Latin a (without) and sul-
catus (furrowed), referring to the absence of the ante-
rior border furrow.

HOLOTYPE

ROM 45344 (cranidium, PI. 1, figs. 4,5), locality AA
95 (Upper Silurian), Road River Formation, Prongs
Creek, Yukon Territory, Canada.

DIAGNOSIS

As for genus.

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 19 crani-
dia, 4 librigenae, 2 hypostomes, 24 pygidia.

DESCRIPTION

Cranidium 85 to 95 per cent as long as wide, longitu-
dinal curvature strongest toward front, evenly convex
transversely, broadly rounded in outline anteriorly.
Glabella wide, narrowest opposite palpebral lobe
where it occupies two-thirds width between margins,
widening forward and backward. Small tubercle near
posteromedian margin. Occipital ring and furrow
effaced. Axial furrow broad and shallow at back, deep-
ening forward, bowed more or less strongly inward,
terminating in large, rounded anterior pit opposite one-
tenth cranidial length from front. On larger specimens,
axial furrow effaced anteriorly and posteriorly. Genal
muscle impression alongside axial furrow on fixigena
almost one-fifth length of cranidium, situated at own
length anterior to posterior margin; outline of impres-
sion running parallel to that of palpebral lobe. Palpe-
bral lobe slightly swollen and gently rounded in outline,
one-quarter length of cranidium, with posterior
extremity opposite that of lateral muscle impression.
Anterior border and furrow absent. Anterior branch of
facial suture running outward, parallel to axial furrow
at first, and then curving forward and inward; posterior
branch directed backward and slightly outward. Crani-
dium faintly pitted, with faint terrace ridges running
parallel to anterior margin at front.

Incomplete librigenae show a comparatively small
eye without socle. Genal angle aspinous. Doublure
broad, weakly convex. Anterior extension curves
inward and upward; on inner margin, just in front of
eye, a single pit projects inward and dorsally upward
(PI. 11, fig. 2). This pit would lie immediately below
anterior pit at front of axial furrow — compare Failleana
calva Chatterton and Ludvigsen (1976, pi. 6, figs. 5,12-
16). The pit in the doublure, which opposes the anterior
pit in Remopleurides (Whittington, 1959, fig. 3c), is anal-
ogous.

Hypostome incomplete but comparable to that of

Bumastus and Cyhantyx in the swollen middle body,
lateral lobe consisting of large macula, and depressed
border. Prosopon of middle body rugose and pitted.

Pygidium strongly convex, rounded triangular to
nearly subovate in outline, 85 to 100 per cent as long
as wide, almost completely effaced; height 45 to 55 per
cent sagittal length. Immature pygidia wider than long.
Triangular axis faintly marked by slight change of con-
vexity in some specimens. Articulating facet marked off
by a faint oblique ridge; coarse terrace lines running
parallel to and overstepping posterior ridge, with steep
surface facing backward; raised lines bending perpen-
dicularly backward at margin. Doublure broad, 30 per
cent length of pygidium; about 15 shallow discontinu-
ous terrace ridges, equally spaced, running parallel to
margin. Surface finely pitted; fine, short raised lines
running inward/backward for a short distance abaxially
(PI. 1, fig. 15).

DISCUSSION

The pygidium of this species is remarkably similar to
that of specimens from the Lower Silurian of northeast
Greenland, described as "Goldillaenid Genus and spe-
cies indet. 2" by Lane (1972:347, pi. 62, figs. 10-14).
The cranidium differs from that of Lane's material in
being much wider, with wider glabella, and in having
axial furrows bowed inward and shallowing posteriorly.
Lane's material has a terraced anterior border and
border furrow similar to that of Cyhantyx anaglyptos
Lane and Thomas {in Thomas, 1978:18, pi. 5, figs. 1-8).
The absence of the border and border furrow in the
Road River material is the main feature of the new
genus Paracybantyx. Both the Yukon and the Green-
land species resemble the type species of Cyhantyx in
the comparatively narrow, featureless pygidium. Vari-
able features in the cranidium of P. asulcatus sp. nov.
are the degree of inward curvature of the axial furrows,
the anterior and posterior effacement of the axial fur-

rows in larger specimens, and the proportions and con-
vexity of the pygidium.

Ptilillaenus Lu (1962), a monotypic genus from the
Middle Silurian of China, has an extended axial furrow
terminating in an anterior pit and lacks the anterior
border, but in that taxon the glabella is narrow.

Indeterminate bumastine

PI. 5, figs. 13,14

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 8 crani-
dia, 1 pygidium.

DESCRIPTION

Cranidium 60 per cent as long as wide, strongly convex.
Glabella effaced, except for lunule at 60 per cent length
from front. Posteromedian tubercle at 10 per cent
length from back. Anterior pits small, shallow, and
rounded, 70 per cent maximum width of cranidium
apart, and 20 per cent length of cranidium from front.
Palpebral lobe 40 per cent length of cranidium, placed
far back, weakly rounded.

Pygidium (not illustrated) 65 per cent as long as wide,
strongly convex. Axis 60 per cent anterior width, dying
out in a short distance. Anterolateral angle oblique.
Surface smooth except for faint terrace ridges on front
of cranidium.

DISCUSSION

The presence of the anterior pits suggests a relationship
to species such as Bumastus? phrix Lane and Thomas
{in Thomas, 1978:14, pi. 3, figs. 1-22) and B.l xestos
Lane and Thomas {in Thomas, 1978:16, pi. 4, figs. 2-5,
7,18), both from the British Wenlock. The present
species is distinguished by a number of features, partic-
ularly the effacement of the axial furrows.

Subfamily Scuteliuinae Richter and Ricliter, 1955

Genus Kosovopeltis §najdr, 1958

TYPE SPECIES

Kosovopeltis svobodai Snajdr, 1958, Kopanina Forma-
tion (Upper Silurian), Kosov, Prague district, Czecho-
slovakia.

Scutellum horealis — Raasch in Raasch, Norford, and
Wilson, 1961:477, figs. 5.6-8,10 (non fig. 5.9 = Leo-
naspis semiglahra).

Scutellum horealis — Norford, 1962, pi. 8, fig. 7.

Scutellum horealis — Norford et al., 1970, pi. 8, fig. 9.

Kosovopeltis horealis (Poulsen, 1934)

PI. 2, figs. 1-12; PI. 3, figs. 1-10; PI. 4, figs. 1-13; PI.
13, figs. 1,2; Text-figs. 4, 5 A

Goldius horealis Pouisen, 1934:27, pl. 3, figs. 14,15.

HOLOTYPE

MMH 3267 (cranidium, figured by Poulsen, 1934, pl. 3,
fig. 14; in this paper, Pl. 13, fig. 1), Cape Schuchert
Formation (Lower Silurian), Kap Schuchert, North
Greenland.

I 0.5 mm ^

1mm

Text-FIG. 4. Incomplete ontogeny oi Kosovopeltis borealis (Poulsen). v4, Protaspis, ROM 42160. B,
Smallest transitory pygidium, ROM 42166. C, Meraspid cranidium, ROM 42161. D, Transitory pygid-
ium, ROM 42165. E, Transitory pygidium with two protothoracic segments attached, ROM 42163. F,
Transitory pygidium with one protothoracic segment attached, ROM 42162.

MATERIAL

From AA 2-4.5 (Lower Silurian), Prongs Creek: 2 dor-
sal shields, 78 cranidia, librigenae, rostral plates, 19
hypostomes, 116 pygidia.

DESCRIPTION

Cephalon about 25 per cent as long as wide. Glabella
moderately convex for most of its length, strongly con-
vex and downturned at front, narrowing strongly back-
ward to 30 to 40 per cent anterior width; anterolateral
angles strongly rounded. Width of occipital ring greater
than width across posterior glabellar ring. Occipital
ring bowed backward, summit at posterior margin;
minute occipital tubercle centrally situated. Occipital

furrow deep and broad mesially, expanding laterally
into large, smooth muscle impressions. LI not swollen,
defined only by short, oblique SI; a faint transverse
depression marks off preoccipital ring on internal sur-
face only. Muscle scar Gl slightly depressed, 15 per
cent length of glabella, placed at about own length
anterior to occipital furrow, 30 per cent width of gla-
bella; G2 and G3 indicated by faint, short, smooth
lateral depressions at 50 per cent and 25 per cent length
of glabella from front, respectively. Anterior border of
cranidium extending only a short distance laterally in
front of glabella and fixigena. Axial furrow deepening
steadily backward, bowed inward. Fixigena broad, con-
vex. Genal muscle area extending alongside LI and

Text-fig. 5. Reconstructions of the four trilobite species from AA 2^.5, Prongs Creek. ^4, Kosovo-
peltis borealis (Poulsen). B, Otarion (Songkania) socialis (Poulsen). C, Cromus princeps (Poulsen). D,
Leonaspis semiglabra (Poulsen).

Gl, smooth, slightly depressed. Posterior border much
wider (exsag.) than occipital ring adaxially, narrowing
strongly to midwidth of fixigena. Posterior border fur-
row shallow and strongly oblique adaxially. Palpebral
lobe at summit of fixigena, opposite LI, 25 per cent
length of glabella, horizontal, standing higher than gla-
bella. Eye ridge running obliquely backward and out-
ward from opposite G3, dying out toward back of
palpebral lobe. Anterior branch of facial suture run-
ning forward and outward, curving forward strongly
at anterior margin. Posterior branch curving obliquely
outward, cutting posterior margin slightly beyond
extent of palpebral lobe.

Librigena falcate, sloping steeply outward; genal
spine narrowing slowly backward, extending to third
thoracic segment. Eye strongly convex; fully developed
lenses hexagonal in outline, 0.02 mm in diameter (PI.
4, figs. 8,9). Socle absent. Subocular furrow broad. Field
divided by a depression widening and curving inward
toward back; outer area narrower and more strongly
swollen, widening backward. Lateral border sloping
inward to a broad border furrow, furrow also widening
backward. Doublure strongly convex, widening and
projecting at front, extending to inner area of librigena,
and becoming less convex posteriorly.

Rostral plate 25 per cent as long as wide, as wide as
glabella anteriorly, extending 30 per cent sagittal length
of cranidium, subtrapezoidal in outline, with anterior
and posterior margins evenly convex forward and paral-
lel. Convexity moderate; posterolateral angle upturned.
Rostral suture submarginal, with connective sutures
bowed gently inward.

Hypostome shield-shaped, 80 per cent as long as
wide. Anterior wing narrowly pointed, wide (tr.), with-
out articulating process. Middle body strongly swollen.
Middle furrow short but strong, marking off small lat-
eral lobe and macula. Lateral furrow broad. Postero-
lateral border of uniform width, with inward slope
decreasing posteriorly. Posterior margin broadly
rounded.

Number of thoracic segments uncertain (dorsal
shield [PI. 2, fig. 2] appears to be complete with eight
segments, but has some telescoping at the back). Axis
25 per cent width of thorax, narrowing slightly back-
ward, gently convex transversely. Articulating half-
rings half sagittal length of rings, bearing faint, trans-
verse raised lines. Pleural lobe horizontally extended
as far as fulcrum at 70 per cent width, sloping gently
outward abaxially. Pleura narrows abaxially; articulat-
ing facet bluntly terminated. Doublure extends to
fulcrum.

Pygidium 70 to 85 per cent as long as wide, gently
convex. Axis 20 per cent length and width of pygidium,
swollen. Articulating half-ring strongly marked off by

continuous furrow. Three rings distinguishable on
internal surface. Posterior area tripartite, with median
lobe swollen, and marked off by longitudinal depres-
sions; three apodemal pits in longitudinal depression
marking positions of fourth to sixth ring furrows. Axial
furrow uniformly deep throughout. Pleural lobe with
seven subequal pairs of ribs, and a median rib flaring
posteriorly to three times anterior width. Rib furrows
almost straight, progressively wider and shallower
toward back, not quite reaching margin. Longitudinal
ridge extending for much of postaxial length. Doublure
35 per cent sagittal length of pygidium, weakly convex
in ventral view; anterior margin simple, marked on
dorsal surface by a low ridge separating convex inner
area of pleural lobe from concave outer area (holcos
of Helbert et al., 1982:132). Seven broad depressions
corresponding to pleural ribs. Longitudinal ridge ante-
riorly. Fifteen or more semicontinuous terrace ridges
running parallel to anterior margin, fainter, wavy, and
more closely spaced in outer area.

Wavy, raised lines on surface, except in furrows and
muscle areas, distantly spaced, but more closely spaced
near margins. Lines run as follows: gently convex for-
ward on glabella; convex inward on fixigena, outward
on field of librigena; V backward on lateral border,
with outer limbs longer and more closely spaced; longi-
tudinal on inner side of genal spine; forming a reticu-
late pattern at base of genal spine; parallel to margin on
rostral plate; convex backward on hypostome, including
macula; longitudinal on thoracic segments; oblique on
first two pygidial ribs and essentially transverse on sub-
sequent ribs.

Protaspides. Protaspis 0.8-0.9 mm in sagittal length
(PI. 4, figs. 1,2; Text-fig. 4A), subquadrate, slightly
wider than long. Cranidium 55 per cent total length;
glabella parallel sided, 25 per cent width of cranidium,
strongly convex transversely, weakly convex longitudi-
nally. Occipital ring as wide as glabella, convex. Occipi-
tal furrow broad, more shallow than axial furrow. Axial
furrow deep and broad. Cheek broad and subquadrate,
strongly convex and downturned laterally, apparently
without border or librigena; a pair of tubercles, 70 per
cent maximum width of protaspis apart, toward front.
Posterior border 15 per cent sagittal length of crani-
dium, sharply convex. Posterior border furrow deep
and broad. Genal spine not preserved. Pygidium tripar-
tite, very strongly inflated, comprising three segments
ending in free points, and a broadly rounded unseg-
mented area with a fourth pair of small free points
laterally. Axis 15 per cent width of pygidium anteriorly;
narrowing backward to a point at posterior margin;
separating, but lower than, the even more strongly con-

vex pleural lobes; with three rings strongly marked off
by broad ring furrows. Axial furrow strong. First and
second pleural ribs almost as strongly developed as
occipital segment, becoming less swollen laterally and
produced into slender, backwardly directed spines 15
per cent sagittal length of protaspis. Third pleural rib
weak. Third spine at least as long as first and second,
projecting beyond margin for half its length.

Meraspides. Meraspid cranidium 1.5 mm in sagittal
length (PI. 4, figs. 3,4; Text-fig. 4C), Raymondaspis -like
in its subparallel-sided glabella. Glabella 80 per cent
as wide as long, with basal width 60 per cent anterior
width, strongly convex anteriorly. Axial furrow deep.
Anterior border indistinct mesially, developing abaxi-
ally; anterior margin flexed upward mesially. Fixigena
strongly convex, twice width of glabella at back; eye
ridge near front almost transverse. Posterior border
depressed, transverse. Posterior border furrow widens
abaxially, shallow. Transverse raised lines on glabella;
fixigena faintly granular.

Smallest transitory pygidium 0.4 mm in sagittal
length (PI. 4, figs. 12,13; Text-fig. 4B), incorporating
four segments with free points. Articulating half-ring
as long as first ring, strongly convex. First free point
directed outwardly, second obliquely, third and fourth
posteriorly, hindmost longest and projecting well
beyond posterior margin. Convexity of pleural lobe of
future pygidium increasing rapidly backward, rising
above axial area. Surface finely granular.

Transitory pygidium 0.8 mm in sagittal length (PI. 4,
figs. 10,11; Text-fig. 4D), incorporating six segments
with free points. Triangular in outline, 50 per cent as
long as wide. Segments decreasing in definition back-
ward, and free points becoming less oblique. Future
pygidium strongly convex; axis shorter, more elevated
above convex pleural lobe. Surface granular.

Transitory pygidium 2.5 mm in sagittal length (PI. 4,
figs. 6,7; Text-fig. 4E), incorporating two protothoracic
segments with free points and pygidium with seven
pleural ribs. Triangular in outline, 55 per cent as long
as wide. Axis 20 per cent anterior width, 50 per cent
length. Free points becoming successively shorter.
Pygidium convex toward back, axis not depressed. Sur-
face smooth.

Transitory pygidium 2.8 mm in sagittal length (PI. 4,
fig. 5; Text-fig. 4F), incorporating one protothoracic
segment with free points. Future pygidium with four
axial rings, large and swollen terminus, and seven pleu-
ral ribs; broadly rounded and more adult in outline, 60
per cent as long as wide. Pygidium strongly convex,
particularly at back. Axis 20 per cent width and 35 per
cent length. First two pygidial ribs much wider (exsag.)

than subsequent pleurae. Surface smooth.

DISCUSSION

K. borealis (Poulsen, 1934:27, pi. 3, figs. 14,15) from
the Cape Schuchert Formation, North Greenland, was
based on four cranidia. Cranidia from the Road River
Formation are identical in gross morphology. Minor
features supporting specific identity are the minute
occipital tubercle and heavy occipital prosopon. The
Road River specimens are distinguished from the Kap
Schuchert material by the following differences: (1) the
prosopon of raised lines is more dense; (2) granulation
of the exoskeleton is absent; (3) the eye ridge is broader
(exsag.).

The species complies with Snajdr's diagnosis oiKoso-
vopeltis (1958:177; 1960:65). It differs from the type
species, K. svobodai Snajdr, and from K. partschi, both
from the Kopanina Formation of Czechoslovakia, in
that the glabella expands evenly and not abruptly near
the front, and that the pygidium is more broadly
rounded.

Two scutelluine ontogenies have been described
from well-preserved material of the Taemas Formation
(Lower Devonian) of New South Wales: Dentaloscutel-
lum hudsoni Chatterton (1971:12, pi. 1, figs. 1-22; pi. 2,
figs. 1-14; pi. 3, figs. 1-12; pi. 24, fig. 15) and Scutellum
calvum Chatterton (1971:22, pi. 3, figs. 21,22; pi. 4, figs.
1-24; pi. 5, figs. 1-24). The Road River Formation
protaspides described above bear a general resem-
blance to the late protaspides of both species from the
Taemas Formation, differing in having a narrow and
parallel-sided glabella, broad fixigena, and longer
spines. The meraspid cranidium from the Road River
Formation differs in having broader fixigena and large
eyes that are forwardly placed, and in lacking an occipi-
tal spine. There is a close resemblance between the
smallest transitory pygidia of K. borealis and S. calvum
(Chatterton, 1971, text-fig. 6D); larger transitory pygi-
dia of K borealis differ from those of 5. calvum in having
protothoracic spines of equal length (cf. alternating
lengths). The adult oiK. borealis does not resemble the
adult of either Taemas Formation species.

Snajdr (1960, pi. 3, fig. 6) has illustrated a meraspid
cranidium of the type species bearing an occipital spine;
this spine was lost in the hoiaspis. It is unlikely that
such a spine was present in K. borealis.

Feist (1970) has described protaspides and meras-
pides of Breviscutellum (Meridioscutellum) sp. from the
Emsian and Eifelian of the Montagne Noire, France.
The smallest protaspis, 1.96 mm in sagittal length, has
8 protothoracic segments developed; the largest has 10,
the number in the adult. These protaspides contrast
sharply with those from the Road River Formation

described above in most features; our largest protas-
pides are 0.9 mm in length and have only 4 segments,
indicated by free points. There is some similarity in the
meraspides in the development of the adult pygidial
characters.

in K. borealis, with terrace ridges more widely spaced
and more strongly scalloped. The three pygidia differ
from each other in the construction of the axis and the
median rib, amongst other features, but all are probably
attributable to Kosovopeltis.

Kosovopeltisl spp.

PI. 9, figs. 8-11

Indeterminate scutelluine

PI. 11, figs. 6,7

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1 crani-
dium, 3 pygidia.

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 1 cra-
nidium.

DISCUSSION

The fragmentary cranidium differs from K. borealis in
having a straighter axial furrow, longer occipital ring,
weaker occipital furrow, narrower fixigena, and small
palpebral lobe posteriorly placed. The three pygidia
belong to more than one species. All differ from K.
borealis in having a wider axis, more strongly curved
posterior rib furrows, and an evenly convex surface;
one specimen shows the doublure, which is longer than

DISCUSSION

This cranidium differs from Paracybantyx asulcatus sp.
nov. in being less convex and in having an anterior
border, a faint occipital furrow, a smaller genal muscle
area and palpebral lobe, broader fixigena, a conspicu-
ous eye line, and coarsely pitted prosopon. The crani-
dium is somewhat similar to that of Planiscutellum
kitharos Lane and Thomas {in Thomas, 1978:27, pi. 6,
figs. 1-8) from the British Wenlock, but it has a much
wider axis and a faint occipital furrow.

Family Illaenidae Hawie and Corda, 1847
Subfamily Illaeninae HawIe and Corda, 1847

Genus Stenopareia Holm, 1886

TYPE SPECIES

Illaenus linnarssoni Holm, 1882, Boda Limestone (Ash-
gill), Dalarna, Sweden.

cent length of cranidium, at own length from posterior
margin. Axial furrows convergent. Dendritic muscle
impressions strongly developed on glabella and fixi-
gena. Axis of pygidium subtriangular, long, and wide.

Stenopareia illtyd sp. nov.

PI. 5, figs. 1-11

DERIVATION OF NAME

Specific name derived from the Illtyd Range, Yukon
Territory.

HOLOTYPE

ROM 42168 (cranidium, PI. 5, figs. 3,4), locality BB 131
(Lower Silurian), unnamed carbonates, Illtyd Range,
Yukon Territory, Canada.

MATEIUAL

From BB 131 (Lower Silurian), Illtyd Range: 9 crani-
dia, 6 pygidia.

DIAGNOSIS

Cranidium with strong convexity; palpebral lobes 1 0 per

DESCRIPTION

Length (in normal view) 65 to 80 per cent width, con-
vexity strong. Glabella 55 per cent basal width, narrow-
ing forward, but widening slightly at forefont;
independent convexity slight. On internal moulds of
glabella, shallow radiating ridges and furrows arranged
in dendritic pattern alongside smooth median area;
foremost ridge large, extending beyond glabella, and
continuous with ridges radiating in a quarter segment
from posterior inner extremity of fixigena. Axial furrow
broad, directed inward for most of length, widening
into shallow depressed lunule, and curving outward
at front. Fixigena sloping steeply outward with weak
convexity. Palpebral lobe 10 per cent length of crani-
dium, situated at own length from posterior margin,
level, and continuous with fixigena. Anterior branch of
facial suture running almost straight forward from eye;
posterior branch running outward and backward. Inter-
nal surface smooth except for muscle impressions.

External surface sparsely pitted. Faint, transverse
raised lines on front of cranidium.

Pygidium 50 to 60 per cent as long as wide, convexity
strong posteriorly. Axis subtriangular, 35 per cent ante-
rior width, undefined at back except by slight convexity.
Axial furrow broad and shallow anteriorly, becoming
steadily shallower and dying out anterior to midlength.
Pleural lobe sloping steeply outward, anterolateral
angle narrowly rounded, facet steep. Surface covered
with transverse anastomosing wavy lines on well-pre-
served specimens.

DISCUSSION

S. illtyd sp. nov. closely resembles 5.? julli Norford
(1981:7, pi. 6; pi. 10, figs. 8-10) from the Attawapiskat
Formation of northern Ontario, but differs in having
much stronger cranidial axial furrows and a less trian-
gular pygidium. In both species, the muscle scars, or
caecal markings, on glabellae and fixigenae are compa-
rable. Both species also resemble Stenopareia sp. of
Lane (1972:348, pi. 61, figs. 13-15) from the Drommebj-
erg Limestone (Lower Silurian), northeastern Green-
land, a species with comparable muscle scars that are
preserved on the external surface of the glabella only.

Indeterminate illaenid

PI. 5, fig. 12

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1
cephalon.

DESCRIPTION

Cephalon 50 per cent as long as wide, strongly convex.
Glabella as long as wide, parallel sided. Palpebral lobe
35 per cent length of cephalon, 50 per cent own length
from posterior margin. Librigena narrow, gently con-
vex. Eye separated from cheek by broad depression.
Genal angle broadly rounded. Surface of cranidium
with extremely faint raised lines convergent backward
on glabella; minute occipital tubercle posteriorly
placed.

DISCUSSION

The cephalon differs from S. illtyd in having a parallel-
sided glabella, shallower axial furrows, and compara-
tively large eyes sited far back. It is unlikely that this
cephalon can be included in Stenopareia, and its generic
affinities are not clear.

Family Proetidae Salter, 1864
?Subfamily Crassiproetinae Osmolska, 1970

Genus Hedstroemia Pfibyl and Vanek, 1978

TYPE SPECIES

Proetus delicatus Hedstrom (1923:4, pi. 1, figs. 1-15),
Halla Beds, unit b (upper, probably uppermost, Wen-
lock), Horsne Canal, Gotland, Sweden.

nine rings and eight pairs of pleurae. Prosopon finely
granular.

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 9 crani-
dia, 14 librigenae, 2 hypostomes, 40 pygidia.

Hedstroemia kutchini sp. nov.

Pi. 6, figs. 1-14

DERIVATION OF NAME

Species named after the Kutchin tribe who formerly
inhabited extensive areas of the northern Yukon Ter-
ritory.

HOLOTYPE

ROM 45347 (cranidium, PI. 6, figs. 3,4), locality AA
95 (Upper Silurian), Road River Formation, Prongs
Creek, Yukon Territory, Canada.

DIAGNOSIS

Cephalon with intramarginal ridge between field and
border. Genal spine absent. Pygidium elongate with

DESCRIPTION

Glabella 90 per cent sagittal length of cranidium, 80 to
90 per cent as wide as long, moderately convex, strongly
defined, olive shaped or tongue shaped in outline.
Occipital ring narrowing rapidly abaxially, with small
occipital tubercle placed slightly posterior to mid-
length. Occipital furrow and axial furrow moderately
deep and narrow. Occipital lobe large, convex, strongly
demarcated, extending sideways well beyond main part
of ring. LI faintly defined, with slight independent con-
vexity, almost 30 per cent maximum glabellar width.
SI convex forward, directed inward and backward, wid-
ening near midlength, fading at back; SI bifurcates
adaxially, with anterior branch short, shallow, and
transverse. S2 shallow, 25 per cent width of glabella,
directed slightly backward, situated at 35 per cent
length of glabella from front. S3 faint, parallel to S2,
situated at 25 per cent length of glabella from front.

Anterior border of uniform width (sag., exsag.),
upturned, convex, wider (tr.) than glabella. Anterior
border furrow deep and broad. Between front of fixi-
gena and anterior border furrow, a uniformly narrow
and slightly oblique intramarginal ridge, continuous or
discontinuous mesially, marked off from preocular area
of fixigena by a clear-cut furrow and by independent
convexity; prosopon agreeing with the anterior border
and differing from the preocular fixigena in lacking
granulation; this ridge continuing onto the librigena.
Preocular area of fixigena moderately swollen. Palpe-
bral lobe 25 per cent length of cranidium, horizontal,
with midlength just posterior to front of SI and anterior
extremity just posterior to S2; palpebral furrow faint,
shallow, running parallel to margin. Postocular fixigena
unknown. Anterior branch of facial suture commencing
close to axial furrow, curving forward and outward at
first, and then running longitudinally. Glabella, preocu-
lar fixigena, and palpebral lobe, except in furrows,
closely, uniformly, and finely granular; anterior border
smooth except for raised lines running parallel to
margin.

Eye strongly convex, sloping outward, with subocular
furrow deep and broad. Socle swollen, narrowing back-
ward, marked off by a strong furrow. Field gently con-
vex; intramarginal ridge at front of fixigena continuing
abaxially on field of librigena as a lateral ridge, widen-
ing somewhat backward and dying out before reaching
posterior border furrow. Lateral border furrow slightly
stronger than furrow marking off the lateral ridge and
also dying out before posterior border furrow. Lateral
and posterior borders strongly convex, confluent. Genal
angle broadly rounded. Field coarsely and shallowly
pitted, matching prosopon of fixigena. Surface of field
roughened, with raised lines parallel to margin on lat-
eral border.

Hypostome as wide as long. Middle body large, well
defined, convex, extending to anterior margin. Middle
furrow oblique, short and shallow, commencing at 65
per cent length of middle body from front. Lateral lobe
with oval macula abaxially, merging with middle body
adaxially. Lateral furrow deepens and widens steadily
backward, continuous with posterior furrow, which is
broad and strongly convex backward. Lateral borders
raised, subparallel, widening steadily backward, and
slightly outturned just posterior to level of middle fur-
rows. Posterior border depressed, strongly convex back-
ward in outline. Anterolateral wing subquadrate,
downturned; articulating process absent. Middle body
faintly and coarsely pitted, bearing raised lines mesi-
ally, divergent backward for most of length, transverse
anteriorly. Raised lines on lateral border running paral-
lel to margin.

Pygidium 60 to 75 per cent as long as wide, strongly

convex in both directions, high in profile, with height
60 to 70 per cent sagittal length. Axis convex, 45 to 50
per cent maximum width and 80 to 90 per cent length
of pygidium, narrowing strongly backward to rounded
tip, composed of nine rings and a short terminus. Ring
furrows shallow, gently sinuous, bowed backward mesi-
ally; furrows toward front strong, becoming successively
fainter toward back, particularly abaxially. Paired mus-
cle insertion scars distinguishable on some specimens.
Axial furrow clear cut. Pleural lobe convex. Seven well-
defined pleurae; eighth faint. First pleural furrow
broad, narrowing abaxially, but reaching lateral margin;
first interpleural furrow well developed, dying out at
lateral depression. Subsequent pleural and interpleural
furrows successively fainter, dying out at lateral depres-
sion. Lateral border uniformly narrow, sloping outward
with moderate convexity. Border depression strong but
ending at first pleura. Articulating facet smooth. Sur-
face densely but somewhat variably granular.

DISCUSSION

H. kutchini sp. nov. closely resembles the type species,
H. delicata (Hedstrom, 1923:4, pi. 1, figs. 1-15), Halla
Beds, Horsne Canal, Gotland, Sweden; an allied form
has been described under open nomenclature by Hel-
bert et al. (1982:138) from the Lower Silurian of the
Oslo Region, Norway. Bob Owens (pers. comm., 1987)
confirms that H. delicata has a flat intramarginal area
between the border furrow and the change of slope of
the field of the fixigena and librigena, comparable with
the intramarginal ridge of H. kutchini; Owens also con-
firms that H. kutchini differs from H. delicata in having
stronger lateral glabellar furrows and a less-angular
frontal glabellar lobe, in lacking a genal spine, in having
a hypostome with more pronounced posterior wings
and a broader posterior border furrow, and in having a
pygidium composed of fewer segments with a narrower
border. Shared features are the greatly swollen occipi-
tal lobes; similar hypostomes, particularly as regards
the prosopon; and the faint pygidial ring furrows with
paired muscle scars abaxially. H. kutchini bears a resem-
blance to Coniproetus {Coniproetus) affinis affinis
(Boucek, 1933; see Snajdr, 1980:73, pi. 9, figs. 3-11),
from the basal Lochov Formation (Lochovian), Repor-
yje, Prague, Czechoslovakia, particularly as regards gla-
bellar features, the librigena, the hypostome, and the
distinctably faint ring furrows of the pygidium. H. kut-
chini differs in having stronger lateral glabellar furrows,
a narrower (sag., exsag.) anterior border, more posteri-
orly placed palpebral lobes, an intramarginal ridge, and
a more elongate pygidium with eight pleural ribs. The
pygidium of//, kutchini also differs in proportions, and
in having stronger pleural segmentation, and a much

narrower and more strongly defined border; these
pygidial features readily distinguish Hedstroemia from
Coniproetus.

The hypostome bears a resemblance to that of Co-
niproetus (C) whittakerensis (Chatterton and Perry,
1977, pi. 1, figs. 7-10) from the Early Devonian of
northwestern Canada, but differs in having a more-
rounded posterior border and raised lines on the front
of the middle body that run transversely, not longitudi-
nally. There is little resemblance between the cranidia
of the two species — H. kutchini has a much broader (tr.)
glabella, and narrower (sag., exsag.) anterior border.

Hedstroemia sourdoughi sp. nov.

PI. 6, figs. 16-24

DERIVATION OF NAME

Species named after those prospectors (Sourdoughs)
who chose the all-Canadian route to the goldfields —
down the Mackenzie River, up the Peel River, up the
Wind River, past Prongs Creek, and then overland to
the Klondike.

HOLOTYPE

ROM 45332 (cranidium, PI. 6, figs. 22,23), locality AA
95 (Upper Silurian), Road River Formation, Prongs
Creek, Yukon Territory, Canada.

DIAGNOSIS

Glabella strongly convex, frontal lobe rounded. Pygi-
dium short, composed of eight rings and six pairs of
pleurae; axis comparatively narrow; ring furrows well
defined; border broad. Prosopon coarsely granular.

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 8 crani-
dia, 2 librigenae, 25 pygidia.

DESCRIPTION

Cranidium closely similar to//, kutchini sp. nov. in many
respects, differing in the following features. Glabella
more convex. Occipital tubercle small or absent. Occi-
pital furrow deeper, SI stronger, S2 and S3 fainter.
Intramarginal ridge present but discontinuous mesially.
Pygidium shorter, 50 to 60 per cent as long as wide.
Axis of eight rings and a short terminus; ring furrows
much deeper and less sinuous. Paired muscle insertion
scars distinct on surface of most specimens. Pleural
lobe more convex, with six pleurae and deeper and
broader border depression; border broader, of uniform
width. Prosopon of cranidium and pygidium coarsely
and densely (cf. finely) granular.

DISCUSSION

H. sourdoughi sp. nov. closely resembles //. kutchini sp.
nov. in cranidial features, particularly in the presence
of the intramarginal ridge. It also stands close to Co-
niproetus bohemicus Hawle and Corda (see Snajdr,
1980:58, pi. 6, figs. 1-14; pi. 61, fig. 4; pi. 63, fig. 6) from
the Koneprusy Limestone, Czechoslovakia, particularly
as regards glabellar outline, the definition of the lateral
glabellar furrows, strong pygidial ring furrows, broad
pygidial border, and coarse prosopon. H. sourdoughi sp.
nov. differs from H. kutchini in having an intramarginal
ridge and stronger pygidial furrows. The cranidium
of //. sourdoughi differs from that of C. bohemicus in
having a narrower (sag.) anterior border, smaller palpe-
bral lobes, and an intramarginal ridge (discontinuous
mesially).

Subfamily Warburgellinae Owens, 1973

Genus Prantlia Pfibyl, 1946

TYPE SPECIES

Proetus longulus Hawle and Corda, 1847, Kopanina
Formation, Upper Silurian, Prague district, Czecho-
slovakia.

Prantlia vagrans sp. nov.

PI. 7, figs. 1-15

HOLOTYPE

ROM 45363 (pygidium, PI. 7, figs. 6,7), locality AA
95 (Upper Silurian), Road River Formation, Prongs
Creek, Yukon Territory, Canada.

DIAGNOSIS

A warburgelline with short frontal area, glabella 80 per
cent sagittal length of cranidium, supplementary lobe
adaxial to LI, strong SI, and posterior bands of second
and third pygidial pleurae crossing border.

DERIVATION OF NAME

Specific name derived from Latin vagrans (wandering),
in allusion to the wide distribution of this genus.

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 16 crani-
dia, 22 librigenae, 48 pygidia.

DESCRIPTION

Glabella 80 per cent sagittal length of cranidium, 75
per cent as wide as long, moderately convex, strongly
defined, anterior outline narrowly rounded. Occipital
ring narrowing rapidly abaxially; occipital tubercle
small, centrally placed. Occipital lobe large, convex,
strongly demarcated, extending sideways well beyond
main part of ring. Occipital furrow deep and moder-
ately broad. LI strongly defined, subtriangular, with
strong independent convexity, 30 per cent maximum
glabellar width. SI deepening rapidly, running
obliquely inward and backward, shallowing and widen-
ing at back. In several specimens, SI forming a short,
transverse branch of varying strength toward front of
LI, defining a small supplementary lobe marked by
a short furrow posteriorly and by slight independent
convexity. S2 faintly impressed, 25 per cent width of
glabella, almost transverse, situated at 30 per cent
length of glabella from front. S3 as S2 but slightly con-
vergent forward, situated at 25 per cent length of gla-
bella from front. Axial furrow straight, extremely deep
and broad. Preglabellar area marked off from preocu-
lar fixigenae by a shallow, almost transverse depression.
Anterior border one-third length of preglabellar area,
hardly narrowing abaxially, convex. Anterior border
furrow shallow but distinct. Frontal area weakly convex
and marked off from the more strongly convex preocu-
lar fixigena by a faint but broad depression convex
forward. Palpebral lobe small, 25 per cent length of
cranidium, horizontal, with anterior extremity opposite
S2; palpebral furrow faint, shallow. Postocular fixigena
unknown. Anterior branch of facial suture commencing
close to axial furrow, curving forward and outward, and
bending inward at anterior border furrow. Glabella
closely granular, except in furrows, with granulation
becoming finer toward front; anterior border finely
granular, with delicate raised lines running parallel to
that border; preglabellar area and preocular fixigena
coarsely and shallowly pitted, with raised lines and a
few scattered granules; palpebral lobe finely granular.
Eye strongly convex and sloping outward, separated
by shallow furrow from low, narrow socle set on a ridge
narrowing backward. Field convex. Lateral border fur-
row deep and broad, continuing into genal spine; lateral
border ill defined, half minimum width of field, extend-
ing alongside genal spine. Posterior border strongly
developed and extended alongside broad-based genal
spine reaching backward for about 35 per cent esti-
mated sagittal length of cephalon. Field coarsely and
shallowly pitted, matching prosopon of fixigena. Closely
spaced raised lines run forward and inward on outer
area of lateral border; posterior to midlength, raised
lines become chevron shaped, with shorter, posteriorly

directed limb on inner area of border; posterior border
with similar prosopon alongside spine.

Pygidium 60 to 70 per cent as long as wide, moder-
ately convex in both directions. Axis 30 to 35 per cent
maximum width of pygidium, 85 to 90 per cent length
of pygidium, narrowing slowly backward to rounded
tip, composed of twelve rings and a short terminus.
Ring furrows gently sinuous, strong anteriorly, becom-
ing successively fainter, particularly abaxially. Axial
furrow narrow. Pleural lobe convex; border depression
strong but dying out at first pleura. Seven well-defined
pleurae; eighth faint. First pleural furrow broad, nar-
rowing abaxially, but reaching lateral margin; first inter-
pleural furrow uniformly narrow and shallow, just
reaching lateral margin. Subsequent pleural and inter-
pleural furrows deep and broad adaxially, successively
fainter, and dying out at lateral border furrow, except
second and third posterior bands and interpleural fur-
rows extending halfway across lateral border. Lateral
border narrowing slightly forward, sloping outward
with moderate convexity. Articulating facet smooth.
Doublure as wide as lateral border. Ten almost-contin-
uous terrace lines running subparallel to margin. Sur-
face granular; raised lines directed inward and forward
on anterior part of border. One pygidium (PI. 7, fig. 13)
showing a deformity in having a slight embayment in
the posterior outline.

A meraspid cranidium, 2.2 mm in sagittal length (PI.
7, fig. 10), differing little from adult cranidium except
in its narrower glabella and smaller occipital lobe.

DISCUSSION

P. vagrans sp. nov. bears a close resemblance to the
type species, Prantlia longula Snajdr (1980:180, pi. 34,
figs. 1-8), in many respects, such as the following: gla-
bellar outline, development of the lateral glabellar fur-
rows, large occipital lobes, segmentation and narrow
axis of pygidium, and the manner in which the lateral
border furrow dies out at the first pleura. P. vagrans
differs from the type species in the following features:
(1) the glabella is 80 per cent the length of the crani-
dium (cf. 65 to 70 per cent), the preglabellar field being
much shorter; (2) S2 is transverse (cf. slightly conver-
gent backward); (3) the frontal lobe is narrower; (4)
the pygidium is relatively longer, being comprised of 12
(cf. 10) rings, and has a narrower and more convex
border; (5) the postaxial ridge on the pygidium is
absent.

The librigena of P. vagrans resembles that of the
warburgelline Tetinia in morphology and also particu-
larly in the oblique raised lines on the outer area of the
lateral border. Prantlia differs from Warburgella in the

absence of the tropidium.

Other species of Prantlia — P. longifrons (Lindstrom,
1885), from the Hemse Beds (Upper Silurian), Got-
land, Sweden; P. grindrodi Owens (1973; Thomas,
1978), Wenlock Shale, Malvern, United Kingdom; and
P. canberrensis Chatterton and Campbell (1980), Lower
Silurian, Canberra, Australia — differ considerably
from the type species and from P. vagrans, as the com-
parison in Table 2 demonstrates; the subgenus Ma/vem-
ocare has been proposed for P. grindrodi by Pfibyl and
Vanek (1978). Chatterton and Campbell (1980:85) con-
sidered Latiproetus Lu (1962:162) to be synonymous

with Prantlia, drawing attention to the similarity
between the type species L. latilimbatus (Grabau) and
P. grindrodi. Kobayashi (1985:419) considered Latiproe-
tus to be valid, and he referred Prantlia biloba Koba-
yashi and Hamada (1974:118, pi. 12, figs. 8,9a,b),
Okanari, Shikoku Island, Japan, to Latiproetus; he
regarded Chuanqianoproetus Wu, 1977; Xiushuiproetus
Q. Zhang in Qiu et al., 1983; and possibly Malvernocare
as subgenera of the genus. In our opinion, more
detailed knowledge about the morphology of the taxa
concerned is required before a satisfactory revision can
be proposed.

Table 2. Summary of diagnostic characters of the species oi Prantlia.
glab., glabellar; %, as percentage of; cranid., cranidial; no., number.

Species

longula

vagrans

canberrensis

longifrons

grindrodi

CEPHALON

glab. shape

triangular

bell

glab. length % cranid. length

genal spines

yes

THORAX

no. of segments

PYGIDIUM

no. of rings

9-10

no. of pleurae

faint

Subfamily uncertain

Indeterminate proetid A

PI. 6, fig. 15

Indeterminate proetid B

PI. 9, figs. 4,5

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 1
hypostome.

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1 crani-
dium, 1 hypostome, 1 pygidium.

DISCUSSION

One small hypostome (PI. 6, fig. 15) lacks the posterior
embayment of warburgellines, and differs greatly from
the hypostome of H. kutchini in the following features:
it is much more elongate, with different prosopon; the
middle body is pinched in and produced anteriorly;
paired posterolateral denticles are present. We do not
know of a comparable hypostome and leave its system-
atic position undecided.

DESCRIPTION

Fragmentary cranidium with subquadrate glabella as
long as wide. Lateral lobes apparently absent. Pregla-
bellar and axial furrows shallow. Occipital ring 10 per
cent length of cranidium. Occipital tubercle and lobe
absent. Preglabellar area 20 per cent length of crani-
dium, not downturned; preglabellar field gently convex.
Anterior border short. Anterior furrow shallow.

On hypostome, width across posterior wings 85 per
cent length. Middle body swollen, strongly defined.

Middle furrow commencing at 60 per cent length of
hypostome from front, inclined backward and inward
for 20 per cent width. Lateral lobe composed almost
entirely of strongly swollen, smooth macula. Lateral
furrow shallow anteriorly, becoming deeper and
broader toward back, bending outward opposite mac-
ula. Posterior furrow convex backward, broad, and shal-
low. Lateral border narrow, raised, continuous with
posterior border; posterior border broader mesially;
lateral denticle absent. Raised lines running backward

and outward on middle body, parallel to margin on
borders.

DISCUSSION

The hypostome resembles that of Hedstroemia kutchini
sp. nov., particularly in the rounded posterior outline
and large maculae, but differs in having an undepressed
posterior border and in prosopon. The cranidium and
unillustrated pygidium are unlike Hedstroemia and are
unidentifiable.

Family Aulacopleuridae Angelin, 1854

Genus Otarion Zenker, 1833

TYPE SPECIES

Otarion diffractum Zenker, 1833, from Upper Silurian
rocks near Beroun, Prague district, Czechoslovakia.

DISCUSSION

In their review of the family Aulacopleuridae, Thomas
and Owens (1978) suggested that Otarion {Otarion) be
restricted to Late Silurian aulacopleurid species with,
among other features, faint eye ridges visible on inter-
nal moulds, a subparallel-sided glabella, weakly diver-
gent preocular facial sutures, and 13 to 17 thoracic
segments, the sixth segment bearing an axial spine.
They proposed that O. {Aulacopleura) be restricted to
species from the Ordovician to Middle Devonian with
strong eye ridges evident on the external surface and
with 18 to 22 thoracic segments, none bearing an axial
spine. Aulacopleura socialis (Poulsen), from the Early
Silurian, bears conspicuous eye ridges, a glabella of
parabolic outline, widely divergent facial sutures, and
12 thoracic segments, with an axial spine on the sixth
segment in some specimens. These features preclude
assignment to either subgenus, but are shared with
Songkania Chang from the Early Silurian of southwest
China, which we regard as a third subgenus of Otarion.

Subgenus Songkania Chang, 1974

TYPE SPECIES

Songkania hanjiadianensis Chang, 1974, Early Silurian,
southwest China.

Otarion {Songkania) socialis (Poulsen, 1934)

PI. 4, fig. 14; PI. 8, figs. 1-12; PI. 12, figs. 14-16; PI.
13, figs. 3-6; Text-fig. 5B

Aulacopleura socialis Poulsen, 1934:21, pi. 2, figs. 24-

27.

Aulacopleura socialis — Raasch in Raasch, Norford, and
Wilson, 1961:471, fig. 4.1-9.

HOLOTYPE

MMH 3251 (cranidium, figured by Poulsen, 1934, pi. 2,
fig. 25; in this paper, PI. 13, figs. 3,4), Cape Schuchert
Formation (Lower Silurian), Kap Schuchert, North
Greenland.

MATERIAL

From AA 2-4.5 (Lower Silurian), Prongs Creek: 7 dor-
sal shields, 270 cranidia, librigenae, 3 hypostomes, 78
pygidia.

DESCRIPTION

Length of cephalon 40 per cent width opposite occipital
ring. Glabella 80 to 90 per cent as wide as long, 55
to 60 per cent length of cranidium (in normal view),
subquadrate, gently convex; anterolateral angles
broadly rounded. Occipital ring moderately convex,
with posterior margin bowed backward. Occipital
tubercle centrally placed. Occipital furrow shallower
than axial furrow. LI with slight independent convexity,
30 per cent length of glabella and 20 per cent width of
glabella. SI broad and strong anteriorly, becoming
weak posteriorly, running obliquely backward to occipi-
tal furrow. S2 short, distinct only on internal surface.
Preglabellar and axial furrows continuous, deepening
posteriorly. Preglabellar field as long as glabella when
measured along surface, curving downward with mod-
erate convexity, confluent with fixigena. Fixigena wide,
sloping inward from palpebral lobe. Palpebral lobe hor-
izontally extended, with extremities almost twice width
of glabella apart; midlength of palpebral lobe opposite
midlength of glabella. Eye ridge strong, slightly oblique,
divided by a median furrow. Anterior border moder-
ately wide and convex, with sagittal length greater than
exsagittal length. Anterior border furrow uniformly
well defined. Anterior branch of facial suture running
sinuously forward and outward, cutting anterior margin

at 65 per cent width across genal angles. Posterior
branch running backward and outward, cutting margin
at 80 per cent width across genal angles. Doublure
extending to border furrow.

Eye 20 per cent sagittal length of cephalon; strong
convexity differentiating from narrow socle; socle
marked off from librigena by a broad, shallow furrow.
Field of librigena considerably wider than preglabellar
area, moderately convex, sloping outward; caecae pres-
ent on some specimens. Lateral border convex, 30 per
cent minimum width of field, continuous with anterior
and posterior borders; anterior and posterior borders
widening rapidly adaxially. Genal spine long and slen-
der, extending to sixth' thoracic segment, arising
abruptly at genal angle, directed slightly outward and
backward, almost straight.

Rostral plate unknown. Hypostome elongate. Mid-
dle body large, extending to anterior margin, strongly
convex. Lateral lobes large, uniting to form a posterior
lobe with independent convexity. Middle furrow
oblique, shallow. Anterior wing small. Lateral border
narrow, convex, directed longitudinally for much of
length, diverging posteriorly, and curving round to
unite with rounded posterior border. Lateral denticle
absent.

Thorax composed of 12 segments. Axis 30 per cent
width of thorax anteriorly, narrowing to 65 per cent
anterior width of axis posteriorly, gently convex trans-
versely. Axial furrow well defined. First five rings with
swollen lateral nodes. Articulating half-ring more than
half length of ring. Pleural lobe horizontally extended
adaxially, gently downturned at fulcrum at 60 per cent
width. Pleura composed of anterior and more strongly
swollen posterior bands, separated by median pleural
furrow; extremity of pleura rectangular. Axial spine on
sixth ring on at least two individuals (PI. 8, figs. 6-8),
tapering slowly and curving low over axis to twelfth
ring; spine certainly absent on other specimens (PI. 8,
fig. 5).

Pygidium 35 to 40 per cent as long as wide. Axis 30
per cent anterior width of pygidium, 85 per cent length
of pygidium, moderately convex. Terminus broadly
rounded. Five rings clearly marked by continuous ring
furrows, successively shorter. Pleural area increases
strongly in convexity toward back. Border uniformly
narrow, continuous. Four well-defined pleurae and a
posterior area; anterior bands confluent with border,
widening abaxially. Posterior bands more swollen, nar-
rowing out at border furrow, delimited by pleural and
interpleural furrows; pleural and interpleural furrows
fuse to form border depression. Doublure narrow.

Surface smooth except as follows: coarse granules on
glabella; two pairs of small granules on adaxial area
of fixigena, anterior pair closer to axial furrow than
posterior pair; a row of granules on occipital and tho-
racic rings; faint granules on axis of pygidium. External
surface of field of librigena closely and shallowly pitted;
lateral border of librigena with very faint, closely
spaced raised lines running parallel to margin. Internal
surface of librigena smooth.

DISCUSSION

The only differences between the specimens from the
Road River Formation and the type material from
North Greenland are the stronger granulation and the
weaker development of S2 in the Road River Forma-
tion material. It is not known whether or not an axial
thoracic spine was present in the Greenland material;
the material under description is dimorphic in this
respect.

The cranidium of O. (5. ) socialis resembles O. {S. )
pijiazhaiensis Chang (1974:174, pi. 81, fig. 10) more
closely than it does the type species, O. (S. ) hanjiadia-
nensis Chang (1974:174, pi. 80, figs. 3,4; pi. 81, fig. 9);
differences in the Road River Formation material from
that of both other species are the broader LI, the longer
preglabellar field, and the presence of granulation.

Family Harpidae Hawie and Corda, 1847

Genus Scotoharpes Lamont, 1948

TYPE SPECIES

Scotoharpes domina Lamont, 1948, Whether Law Linn
Formation (upper Llandovery), Whether Law Linn,
North Esk Inlier, Scotland.

Scotoharpes raaschi Norford, 1973

PI. 9, figs. 1-3

Scotoharpes raaschi Norford, 1973:20, pi. 2, figs. 1,3-5.

HOLOTYPE

GSC 27794 (cephalon, figured by Norford, 1973, pi. 2,
figs. 1,3-5), Lower Silurian, GSC locality 53109 (proba-
bly the same as BB 131), Illtyd Range, Yukon Territory,
Canada.

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 2 cephala.

DESCRIPTION

Cephalon 65 per cent as long (sag.) as wide. Glabella

40 to 45 per cent length of cephalon and 20 per cent
width of cephalon, moderately swollen, as wide as long.
Width of occipital ring equal to width across LI; occipi-
tal tubercle strong, anteriorly placed. Occipital furrow
shallow, transverse. LI small, 30 per cent length of
glabella, projecting only slightly sideways. SI shallow,
curving inward and dying out anterior to midlength of
LL Preglabellar and axial furrows continuous, shallow.
Ala moderately large, 30 per cent width of glabella,
sloping outward and depressed abaxially, narrowing
and dying out anterior to midlength of glabella. Fixed
cheek convex; a low ridge outlining ala anteriorly. Eye
tubercle only slightly elevated, 30 per cent width of
cephalon from midline, situated opposite forefront of
glabella. Eye ridge clearly defined, essentially trans-
verse; ridge of comparable strength running obliquely
outward from eye tubercle to cheek roll. Cheek roll
extending almost to glabella anteriorly, sloping steeply
outward, narrowing and dying out at 60 per cent length

from front. Posterior border short, convex, curving
strongly backward abaxially. Girder weak. Brim flat-
tened, slightly wider anteriorly than laterally; prolonga-
tion 40 per cent sagittal length of cephalon, narrowing
slowly backward, slightly inturned posteriorly. Mar-
ginal band narrow, smooth. Doublure of occipital ring
almost reaches occipital furrow. Glabella, occipital
ring, and ala smooth; cheek coarsely pitted, with pits
on cheek roll finer than on cheek and arranged in
ramifying, radiating rows separated by fine caecae. Cae-
cae continuing 20 per cent distance across brim. Brim
finely pitted. Pits on either side of girder larger.

DISCUSSION

A point of particular resemblance of our material to S.
raaschi Norford is the ridge running obliquely outward
from the eye tubercle. The occipital tubercle described
above is present on the external surface only and is not
preserved on the holotype cephalon.

Family Cheiruridae Hawle and Corda, 1847
Subfamily Cheirurinae Hawle and Corda, 1847

Genus Cheirurus Beyrich, 1845

TYPE SPECIES

Cheirurus insignis Beyrich, 1845, Liten Formation
(Upper Silurian), Prague district, Czechoslovakia.

DESCRIPTION

Anterior part of glabella (all that is known) expanding
slightly forward, moderately convex. S2 and S3 curving
gently backward, 30 per cent width of glabella. Anterior
border short; anterior border furrow shallow mesially,
deeper abaxially. Prosopon faintly granular. The unil-
lustrated librigena is of generalized cheirurine type.

Cheirurus sp.

PI. 5, figs. 15,16

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1 crani-
dium, 1 fragmentary librigena.

DISCUSSION

This species differs from C. certus Poulsen (1934:28, pi.
3, fig. 16) and C. hyperboreus Poulsen (1934:29, pi. 3,
figs. 17,18), both from the Cape Schuchert Formation,
North Greenland, in its shorter, less-expanded frontal
lobe.

Family Encrinuridae Angelin, 1854
Subfamily Encrinurinae Angelin, 1854

Genus Cromus Barrande, 1852

TYPE SPECIES

Trilobites intercostatus Barrande, 1846, Kopanina For-
mation (Upper Silurian), Prague district, Czechoslo-
vakia.

Cromus princeps (Poulsen, 1934)

PI. 10, figs. 1-8; PI. 13, figs. 7-12; Text-fig. 5C

Encrinurus moderatus Poulsen, 1934:31, pi. 3, fig. 20

(non figs. 21,22).
Encrinurus princeps Poulsen, 1934:33, pi. 3, figs. 23-27.
Encrinurus princeps — Raasch in Raasch, Norford, and

Wilson, 1961, fig. 5.1-5.
Encrinurus cf. E. princeps — Norford, 1962, pi. 8, fig. 14.
Encrinurus cf. E. princeps — Norford et al., 1970, pi. 8,

fig. 14.
Cromus princeps — Strusz, 1980:10.
Cromus princeps — Snajdr, 1985:16.
Encrinurus moderatus — Lane, 1988:99, pi. 5, figs. 7,?8.

HOLOTYPE

MMH 3276 (cranidium, figured by Poulsen, 1934, pi. 3,
fig. 23; in this paper, PI. 13, figs. 10,11), Cape Schuchert
Formation (Lower Silurian), Kap Schuchert, North
Greenland.

MATERIAL

From AA 2-4.5 (Lower Silurian), Prongs Creek: 1 dor-
sal shield, 10 cranidia, librigenae, 4 hypostomes, 23
pygidia.

DESCRIPTION

Cranidium 45 per cent as long as wide. Glabella 70 to
80 per cent as wide as long, moderately convex in both
directions; width across L2 60 to 65 per cent maximum
width. Occipital ring wider than width across LI, with
transverse posterior margin narrowing slightly abaxi-
ally. Occipital furrow broad and shallow mesially, shal-
lower than axial furrow abaxially; rounded apodeme at
extremity. LI consisting of a ridge 35 per cent width
of glabella, directed somewhat forward adaxially; L2
shorter than L3, nodular; L3 subquadrate. SI almost
continuous; S2 and S3 broad abaxially, dying out adaxi-
ally, 35 per cent width of glabella. Frontal lobe 40
to 45 per cent length of glabella, evenly and strongly
rounded in outline. Axial furrow deeper and broader
than preglabellar furrow, widening backward; apo-
demes adaxially at extremities of SI and S2. Preglabel-
lar furrow deep and wide abaxially, becoming shallower
and narrower mesially. Anterior border of cranidium
moderately wide abaxially, narrowing and almost dying
out mesially. A longitudinal median depression cross-
ing anterior border and preglabellar furrow, and run-
ning onto forefront of glabella; this depression stronger
in small specimens. Fixigena wide, sloping inward from
eye with strong convexity and outward to genal angle
with weaker convexity. Palpebral lobe almost 20 per
cent length of cranidium and marked off from fixigena
by a broad, shallow depression; anterior extremity of
palpebral lobe placed opposite, and at twice width
across, L3. Posterior border narrower (exsag.) than
occipital ring, widening slowly abaxially and rapidly
adjacent to genal angle, depressed well below level of
fixigena abaxially. Lateral border ill defined. Posterior
border furrow deep adaxially, where continuous with
lateral furrow. Genal spine thornlike, very short,
directed backward and slightly outward. Anterior
branch of facial suture curving forward and inward,
delimiting anterior border of cranidium. Posterior
branch curving outward and backward, cutting lateral
margin opposite occipital furrow.

Eye pedunculate; lens surface occupying half height
of stalk; stalk marked off by a broad depression from

field. Field of librigena gently convex. Preglabellar lobe
25 per cent length of cranidium, weakly convex. Lateral
border strongly convex, less than half minimum width
of field, continuous with anterior border, curving
inward and widening at back. Lateral border furrow
uniformly deep and broad. Anterior border furrow
deep and broad at axial furrow, narrowing and dying
out by midwidth of preglabellar lobe.

Rostral plate unknown, but conformation between
librigenae indicating a narrow plate widening forward,
as shown in reconstruction.

Hypostome 75 per cent as wide as long. Middle body
strongly swollen, longitudinally ovate, with a less-
inflated terminal area. Rhynchos broad, with indepen-
dent convexity anteriorly but projecting slightly, length
equalling half that of middle body. Lateral lobe com-
prising a small, smooth macula. Lateral furrow demar-
cating middle body strongly. Lateral border narrow,
flattened, merging with posterior tongue; tongue 25 per
cent length of hypostome and with rounded tip. Middle
body closely and shallowly pitted, more coarsely so
anteriorly.

Pygidium triangular in outline, 55 to 60 per cent as
long as wide. Axis 25 per cent anterior width and 90
per cent length of pygidium, composed of 20 rings;
first six rings continuous, subsequent rings becoming
discontinuous mesially. Ring furrows successively shal-
lower toward back. Axial furrow deep and broad anteri-
orly, becoming narrower and shallower posteriorly.
Pleural lobe weakly convex to midwidth, downcurved
abaxially. Ten pleural ribs; tenth rib postaxial, with tip
generally bluntly fused with ninth; ribs flat topped,
widening steadily; tips of ribs pointed and outturned,
more bluntly so posteriorly. Ribs successively directed
increasingly backward and outward, tenth parallel. Rib
furrows deep and broad, widening slightly abaxially.
Anterior band of first pleura with clear articulating
facet. Four congruent axial and pleural segments. Ven-
tral border uniformly narrow; inner margin straight;
junction evenly rounded, unembayed.

Surface of cephalon, except on occipital segment and
in furrows, closely tuberculate; tubercles of mixed sizes,
diameter of largest being 8 per cent maximum width of
frontal lobe; about one hundred tubercles on adult
glabella, many perforate. A quincunx of small tubercles
composed of Ll-1; Sl-0; L2-1. Remainder of tubercles
randomly distributed. Occipital segment finely and
sparsely granular. A single row of tubercles on anterior
border of cranidium. Tubercles on genae larger adaxi-
ally. Pygidium granular; three or four small median
tubercles on axis of pygidium randomly spaced. Attri-
bute coding (Temple and Tripp, 1979): 1-0; 2-20; 3-0;
4-1; 5-1; 6-10; 7-0; 8-1; 9-4; 10-1; ll-'/2; 12-1; 13-1; 14-
1; 15-0; 16-1; 17-0; 18-0; 19-0; 20-0; 21-1; 22-1; 23-0; 24-

0; 25-1; 26-0; 27-100; 28-12; 29-0; 30-2.5; 31-0; 32-1; 33-
8; 34-0.

Small pygidia have fewer segments and more strongly
developed ring furrows. On one pygidium, 3 mm in
sagittal length (PI. 10, fig. 5), ninth and tenth rings
bifurcate laterally, third and fourth right ribs fused
abaxially.

DISCUSSION

The holotype of Encrinurus moderatus Poulsen
(1934:31, pi. 3, fig. 20), from the Cape Schuchert For-
mation, St. George Fiord, North Greenland, is a small
cranidium, 5.0 mm in length, attributable to Cromus
princeps; thus moderatus is a junior subjective synonym
of princeps. The two pygidia from the same horizon and
locality referred to E. moderatus by Poulsen (1934, pi.
3, figs. 21,22) are not attributable to Cromus; they are
distinct from the pygidium from Cape Constitution
named Encrinurus inflatus by Poulsen (1934, pi. 3, fig.
19).

C princeps most closely resembles C. novaki (Freeh,
1888:735, pi. 29, figs. 5-9), from beds of Middle Silurian
age in the Carnic Alps; C. novaki also possesses an
anteromedian furrow and short genal spines. C.
princeps differs in that the eyes are placed farther back
and the tuberculation is coarser.

congruent axial and pleural segments. Apart from the
four axial tubercles, prosopon greatly subdued.

DISCUSSION

This pygidium has much in common with Balizoma —
the low number of rings and pleurae, large axial tuber-
cles, and longitudinal axial furrow — but must be
excluded from Balizoma under Ramskold's (1986)
definition on account of the high ring-to-pleura ratio.
Furthermore, the pleural area is not strongly down-
turned, and the pleural ribs are narrow and without
large tubercles.

Snajdr (1985) reestablished Encrinuraspis Webby,
Moors, and McLean (1970), considered by Strusz
(1980) as a junior synonym of Cromus. The case for
retention is disputable, but Encrinuraspis may prove to
be a useful taxon for species not readily attributable
elsewhere, and the Illtyd Range pygidium is a case in
question.

Genus Balizoma Holloway, 1980

TYPE SPECIES

Calymene variolaris Brongniart, 1822, Much Wenlock
Limestone Formation, Dudley, West Midlands, United
Kingdom.

Genus Encrinuraspis Webby, Moors, and McLean,

1970

TYPE SPECIES

Encrinuraspis optimus Webby, Moors, and McLean,
1970, Malongulli Formation (?Caradoc Series), New
South Wales, Australia.

Balizoma aff. B. obtusus (Angelin, 1851)

PI. 11, figs. 8-10,12-18

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 5 crani-
dia, 1 librigena, 1 hypostome, 27 pygidia.

Encrinuraspis sp.

PI. 9, fig. 6

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1
pygidium.

DESCRIPTION

Pygidium 70 per cent as long as wide, moderately and
evenly convex. Axis 30 per cent anterior width and 80
per cent length, tapering to a point. Twelve rings, of
which first six continuous; a longitudinal median
depression as deep as ring furrows interrupting poste-
rior rings. Large median tubercles on fourth, sixth, and
eighth rings. Pleural lobe downcurved with seven ribs
widening slightly and a broad postaxial ridge compris-
ing fused eighth ribs. Ring-to-pleura ratio 1.7. Two

DESCRIPTION

Glabella 90 per cent as wide as long, with width across
L2 60 per cent width across frontal lobe, moderately
rounded in outline, uniformly convex longitudinally
and transversely. Occipital ring short (sag.), wider than
base of preoccipital glabella, strongly arched trans-
versely; occipital furrow deep and broad. Frontal lobe
45 percent sagittal length of glabella. LI and SI almost
obsolete. L2 and L3 represented by comparatively small
nodular tubercles. S2 and S3 short, broad, shallow fur-
rows, discontinuous mesially. Axial furrow deep and
broad, with fossula near front. Preglabellar furrow shal-
low. Eleven moderately sized tubercles on anterior
border of cranidium; lateral tubercle not enlarged.
Fixigena convex. Posterior border short (sag.), incom-
plete; posterior border furrow deep and broad. Genal
angle unknown. Cranidium finely and densely tubercu-
late; larger tubercles perforate. Basal diameter of wid-

est glabellar tubercles 10 per cent maximum width of
glabella across L4; a pair of larger tubercles opposite
L2; remaining tubercles not clearly symmetrically
arranged; total number about 60. A single row of small
tubercles on occipital ring and posterior border.

Librigena incompletely known, with comparatively
small field and broad lateral border. Rostral plate
unknown.

Hypostome rhombic, with width (excluding anterior
wings) 75 per cent length and anterior margin narrowly
rounded. Middle body inflated, well defined by strong
lateral furrow. Rhynchos large, projecting somewhat
anterior to middle body, widening slightly backward,
and dying out near midl6ngth of middle body. Macula
small but distinct. Anterior border short. Anterior wing
large, sloping obliquely upward. Lateral border narrow,
depressed. Posterior tongue almost 20 per cent length
of hypostome, horizontally extended. Surface of middle
body granular, with a few pits and folds.

Pygidium triangular in outline, strongly convex in
both directions, high in profile, with width 85 to 95 per
cent length (average width-to-length ratio 1.1:1). Axis
35 per cent maximum width of pygidium, strongly con-
vex transversely, with 13 rings and a terminus; postaxial
ridge short, reaching posterior margin in a few speci-
mens. Rings continuous. Sagittal groove lacking on
external moulds, shallower than ring furrows alongside
tubercles on internal moulds. Ring furrows broad and
deep. Sagittal tubercles only slightly larger than abaxial
ring tubercles, absent on first and second rings, fre-
quently on successive rings toward back. Axial furrow
deep anteriorly, becoming weaker posteriorly. Nine
strong pleural ribs; tenth pair short and joined at tips,
or fused in a postaxial ridge; ribs parallel sided, directed
increasingly strongly backward, curving downward at
fulcrum. Four or five small tubercles on each pleural
rib. Tips of ribs projecting in short free points. Four
rings and pleurae congruent. Rib furrows deep and
broad throughout. Ring-to-pleura ratio (R/P) as
defined by Ramskold (1986:529) 1.2-1.3.

DISCUSSION

It is Ramskold's opinion (pers. comm., 1987) that this
material falls within the range of the abundant Swedish
species B. obtusus (Angelin, 1851:3, pi. 4, fig. 9; see
Ramskold, 1986:561, pi. 40, fig. 2; pi. 48, figs. 1-14; pi.
49, figs. 1-10), from the Mulde Beds (Middle Silurian),
Klinteberg Marl, Hemse Beds, and Eke Beds (Upper
Silurian), Gotland, Sweden. Ramskold recognized
three morphological forms: Form A, the "type form,"
restricted to the northeastern limestone areas in the
Hemse Beds and the Eke Beds at Lau Backar; Form

B, restricted to the "marl" west and south of the south-
western outcrops of the Hemse Beds limestone area;
and Form C, known only from pygidia from the upper
Eke Beds. The hypostome from AA 95 is similar in
main characters to that of 5. obtusus (Ramskold, 1986,
pi. 48, fig. 1) but differs in having a less strongly defined,
unwaisted rhynchos; in size, it is appropriate to B. aff.
B. obtusus, but it should possibly be attributed to the
indeterminate encrinurine described below. The pygi-
dia under description most closely resemble B. obtusus
Form B, but differ in the width-to-length proportions —
85 to 95 per cent for Road River Formation specimens,
compared to 65 to 85 per cent for B. obtusus Form B.
Ramskold (1986:66) has discussed the possibility that
B. rosensteinae (Tripp, Temple, and Gass, 1977:860,
pi. 115, figs. 1-13), from the Ludlow Series, United
Kingdom, and B. dimitrovi Perry and Chatterton
(1979:589, pi. 72, figs. 1-3; pi. 73, figs. 1-17,29-31; pi.
74, figs. 1-14,18-23,30-35), from the upper Whittaker
and lower Delorme formations (Wenlock to lower Lud-
low), Delorme Range, Mackenzie Mountains, Canada,
are synonymous with B. obtusus. Ramskold (1986:561)
has restricted the genus Balizoma to species with a
ring-to-pleura ratio (R/P) of 1.1-1.4, thus excluding the
two Bohemian species of Pridoli age Encrinur-
aspisl subvariolaris concomitans Pfibyl and Vanek,
1962, and Encrinuraspis? testosteron Snajdr, 1981, which
have higher ring-to-pleura ratios (R/P) of 1.6 and 1.8,
respectively.

Indeterminate encrinurine

PI. 11, fig. 11

MATERIAL

From AA 95 (Upper Silurian), Prongs Creek: 1
cranidium.

DISCUSSION

This single cranidium differs considerably from that of
Balizoma aff. B. obtusus and of most other species of
Balizoma in the following features: (1) twice as large;
(2) glabella narrowing more strongly backward; (3)
smaller, multituberculate lateral lobes; (4) tubercles on
glabella and anterior border of cranidium double in
number and much smaller in size; (5) smaller tubercles
adaxially on fixigena. Balizoma is the genus that this
cranidium most closely resembles, but the small tuber-
cles and lateral glabellar lobes exclude this cranidium
from that genus as currently understood. The lateral
lobes are completely unlike Cromus, and the shape of
the cranidium and features of the prosopon are unlike
Encrinuraspis.

Family Calymenidae Milne-Edwards, 1840
Subfamily uncertain

Indeterminate calymenid

PI. 9, fig. 7

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1
pygidium.

DESCRIPTION

Length 65 per cent width; convexity strong. Axis 35 per
cent anterior width, 95 per cent length of pygidium,
narrowing steadily backward to broadly rounded tip,
composed of eight rings and a terminus. Ring furrows
deep and broad anteriorly, becoming successively

weaker toward back. Articulating half-ring and furrow
well developed. Axial furrow deep, increasing in width
toward back. Pleural lobe evenly convex; four strongly
developed, flat-topped ribs curving outward and back-
ward; fifth rib flanking axial furrow and directed back-
ward. Interpleural furrows weak, dying out adaxially;
pleural furrows strong. Articulating half pleura strong
adaxially. Surface smooth.

DISCUSSION

It is impossible to assign this single pygidium to a genus
or subfamily.

Family Lichidae Hawle and Corda, 1847
Subfamily Lichinae Hawle and Corda, 1847

Genus Dicranopeltis Beyrich, 1845

TYPE SPECIES

Lichas Scabra Beyrich, 1845, Liten Formation (Upper
Silurian), Prague district, Czechoslovakia.

Dicranopeltis sp.

PI. 10, figs. 10-12

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1 crani-
dium, 1 pygidium.

DESCRIPTION

Cranidium strongly convex in both directions. Occipital
ring incomplete. Occipital furrow as deep as axial fur-
row. Median lobe narrowing slowly and steadily back-
ward to about 50 per cent anterior width when opposite
SI, and then expanding posteriorly; preoccipital de-
pression connecting inner extremities of S 1 . Bullar lobe
half length of cranidium, with strong independent con-
vexity. LI and fixigena fused. Basal glabellar lobe

absent. Longitudinal furrow deep and narrow. Axial
furrow continuous with SI, curving gently inward to
longitudinal furrow.

Pygidium 65 per cent as long as wide. Axis strongly
convex, 30 per cent anterior width, narrowing steadily
backward, not pointed; three rings and furrows contin-
uous across axis; a swollen terminus sloping downward
and backward to depressed tip of axis. Axial furrows
deep and narrow anteriorly, becoming shallow posteri-
orly, convergent. Pleural lobe flattened; three pairs of
furrowed pleurae ending in short, free points. Dou-
blure gently convex; terrace ridges strong.

Prosopon tuberculate, coarser on pygidium than on
cranidium.

DISCUSSION

The cranidium resembles that of the type species D.
scabra (Beyrich; see Barrande, 1852, pi. 28, figs. 22-26)
in conformation and in the presence of the preoccipital
furrow, but differs in the absence of basal glabellar
lobes. The pygidium is distinctive in its long, swollen,
and strongly segmented axis.

Subfamily uncertain

Indeterminate lichid

PI. 7, figs. 16-20

MATERLVL

From AA 95 (Upper Silurian), Prongs Creek: 3 crani-
dia, 2 hypostomes, 5 pygidia.

DISCUSSION

This lichid material is too sparse to justify formal
description. The two incomplete cranidia illustrated
are similar in gross morphology, but have different
prosopon features and slight differences in convexity
of lobes and in courses of furrows; in both cranidia, the

longitudinal furrow is continuous anteriorly, and it is
unknown whether a basal glabellar lobe was present or
not. The specimens appear to belong to the subfamily
Trochurinae (= Ceratarginae, see Thomas and Hol-
loway, 1988). The two hypostomes would unhesitatingly
be referred to the subfamily Trochurinae on account
of the broad, unembayed posterior border and circum-
scribed middle body. All the pygidia are remarkable in
that they resemble Amphilichas (subfamily Tetralichi-
nae, recorded only from the Ordovician System) in the
pointed axis and absence of pleural furrows on the third
pleurae; there is a small median embayment in the
posterior margin, but no extended free point to the
third pleura. These pygidia differ conspicuously from
those of the Trochurinae in outline, in having an
unswollen posterior band, and in the absence of a lat-
eral border. At first sight, therefore, the pygidia belong
to a different subfamily from that of the cranidia and
hypostomes.

A comparable conflict arises regarding the lichid
described as Dicranogmus skinneri by Perry and Chat-
terton (1977:308, pi. 6, figs. 16-21), from Cape Phillips
Formation (Middle Silurian), Baillie-Hamilton Island,
Canadian Arctic Archipelago. The cranidium of this

species closely resembles that of the trochurine Dicra-
nogmus pustulatus Hawie and Corda (1847:146, pi. 7,
fig. 77a,b), the type species, from the Upper Silurian,
Czechoslovakia, the hypostome and pygidium of which
are unknown. The hypostome of D. skinneri is trochur-
ine also. The pygidium isAmphilichas-like in its pointed
axis and unfurrowed, flattened third pleurae. The origi-
nal grounds for associating the parts, based on occur-
rence and particularly on the prosopon, are convincing.

Although the Prongs Creek and the Baillie-Hamilton
Island specimens are dissimilar in many respects, these
two enigmatic associations in northern Canada are
unlikely to be coincidental. The Tetralichinae and Tro-
churinae are sister subfamilies, and it may be that a
rootstock persisted in this area into the Silurian Period.

Subfamilies of the Lichidae are consistent in the
morphology and comparative anatomy of the parts with
the exception of the above examples and another sur-
prising anomaly in the Cape Phillips Formation. This
is the form described as Lichid n. gen., n. sp. (subfamily
Ceratarginae) by Perry and Chatterton (1977:303, pi.
7, figs. 1-9), in which pygidia of Radiolichas type are
associated with inappropriate cranidia.

Family Odontopleuridae Burmeister, 1843
Subfamily Odontopleurinae Burmeister, 1843

Genus Leonaspis Richter and Richter, 1917

TYPE SPECIES

Odontopleura leonhardi Barrande, 1846, Kopanina For-
mation (Upper Silurian), Prague district, Czechoslo-
vakia.

Leonaspis semiglabra (Poulsen, 1934)

PI. 12, figs. 1-13; PI. 13, figs. 13,14; Text-fig. 5D

Ceratocephala (sens, lat.) groenlandica Poulsen,

1934:24, pi. 3, fig. 5 (non figs. 6,7).
Ceratocephala (Leonaspisl) semiglabra Poulsen,

1934:25, pi. 3, fig. 8 (non fig. 9 = groenlandica).
Leonaspis semiglabra — Raasch/n Raasch, Norford, and

Wilson, 1961:474, fig. 4.10-18.
Scutellum borealis — Raasch in Raasch, Norford, and

Wilson, 1961:474, fig. 5.9 (non figs. 6-8).

HOLOTYPE

MMH 3261 (cranidium, figured by Poulsen, 1934, pi. 3,
fig. 8; in this paper, PI. 13, fig. 13), Cape Schuchert
Formation (Lower Silurian), Kap Schuchert, North
Greenland.

MATERIAL

From AA 2-4.5 (Lower Silurian), Prongs Creek: 1 dor-
sal shield, 8 cranidia, librigenae, 4 hypostomes, 11
pygidia.

DESCRIPTION

Cranidium 25 per cent length of dorsal shield, 60 per
cent as long as wide, moderately convex. Glabella 80
to 85 per cent as wide as long. Occipital ring 20 per cent
length of cranidium, without lobes or spines; occipital
tubercle somewhat enlarged. Central lobe well defined
by strong independent convexity, subparallel sided but
constricted opposite LI and L2, expanding anteriorly;
frontal lobe, where broadly rounded, 60 per cent width
across LI. LI rounded, swollen, 30 per cent basal width
of glabella. SI deep, oblique, widening at apodeme
at extremity, shallow at back. L2 elongatedly ovate,
swollen, 25 per cent glabellar width, circumscribed. S2
oblique, apodeme at extremity, thence running back-
ward, shallowing at SI. L3 and S3 absent. Axial furrows
strongly divergent backward, comparatively shallow.
Anterior border uniformly short, transverse. Fixigena
15 per cent width of cranidium, narrowing steadily for-
ward, gently convex. Eye ridge narrow (tr.), extending
almost to posterior border furrow.

Librigena sloping outward. Eye sessile, posteriorly
placed. Field broad, gently convex. Lateral border 20
per cent minimum width of field, widening backward.
Lateral border furrow shallow. Genal spine curving
backward and outward, extending as far as seventh
thoracic segment. Seventeen or more outwardly
directed lateral spines, hindmost on genal spine; ante-
rior few spines shorter than width of border, squat, and
blunt; subsequent spines longer than width of border
and successively longer, slender, and pointed. Dou-
blure smooth, extending to lateral border furrow.

Hypostome subquadrate, squat, slightly wider than
long. Middle body subquadrate, gently swollen, extend-
ing to anterior margin. Middle furrow short, oblique.
Lateral lobe half length of middle body abaxially, nar-
row. Lateral border narrow, convex, widening and less
swollen posterior to midlength; posterior wings project
strongly, situated 60 per cent length from front. Lateral
furrow very shallow alongside lateral lobe, broad and
well defined posteriorly. Posterior border essentially
transverse but bowed backward mesially, weakly
convex.

Thorax 55 per cent length of dorsal shield; nine tho-
racic segments on disarticulated dorsal shield. Axis 30
per cent anterior width of thorax, arched transversely;
lateral nodes well developed. Axial furrow shallow and
broad. Pleura horizontal, comprising a short (exsag.),
slightly swollen anterior band separated by a broad,
shallow furrow from longer (exsag.) and much more
swollen posterior band; posterior band terminating in
a long, slender spine. Spines successively longer and
more backwardly directed. A row of granules on poste-
rior margin of rings; posterior bands of pleurae weakly
granular.

Pygidium, excluding spines, 30 to 35 per cent as long
as wide. First ring and furrow strong. Second ring
almost equally swollen; ring furrow dying out abaxially.
Third ring stunted; posterior margin bowed backward.
Axial furrow shallow alongside first ring, deep and
broad posteriorly. Pleural lobe largely occupied by
swollen rib running obliquely from opposite first ring to
great spine. Lateral border widening backward, faintly
developed at great spine. Five pairs of spines: foremost

pair small; second and third pairs gradational in length
to fourth pair (great spines); fourth pair twice sagittal
length of pygidium; fifth pair as long as third pair.

Prosopon consisting of tubercles of various sizes; a
single row of tubercles on anterior border and eye
ridge.

DISCUSSION

The holotype cranidium of L. semiglabra (Poulsen) is
incomplete posteriorly, and it is not possible to be cer-
tain whether occipital spines were present or not. The
Road River Formation cranidia agree in other features,
and we follow Raasch in Raasch, Norford, and Wilson
(1961) in considering these cranidia conspecific with
the L. semiglabra holotype. The holotype cranidium of
L. groenlandica (Poulsen, 1934:24, pi. 3, fig. 6), also
from Kap Schuchert, differs markedly from L. semigla-
bra in its rounded anterior margin and broader fixigena.
Only one form of the various odontopleurid skeletal
elements is present in the Road River Formation mate-
rial, indicating a single species. The librigena attributed
to L. groenlandica by Poulsen (1934, pi. 3, fig. 5; this
paper, PI. 13, fig. 14) corresponds to our material; it
differs from the one referred to semiglabra by Poulsen
(1934, pi. 3, fig. 9) in its narrower border and denser
tuberculation.

Indeterminate odontopleurine

PI. 10, fig. 9

MATERIAL

From BB 131 (Lower Silurian), Illtyd Range: 1
cranidium.

DISCUSSION

This cranidium differs from the cranidia attributed to
L. semiglabra in having a more parallel-sided median
glabellar lobe, a more convex frontal lobe, coarser
tuberculation, and a nontuberculate adaxial portion
of the fixigena. Although this specimen is probably
attributable to Leonaspis, the generic reference is best
left undecided.

Acknowledgements

We thank Bob Owens, Alan Thomas, and Lars Ram-
skold for information and opinions on some of these
trilobites. Valdemar Poulsen of the University of
Copenhagen kindly provided plaster casts of C.
Poulsen's trilobite types from North Greenland. We
thank Godfrey Nowlan of the Geological Survey of
Canada for identification of the conodont faunas. Brian

O'Donovan printed the trilobite photographs from our
negatives. The figures were prepared by David Sargent
and Ilgvars Steins. David Rudkin, Janet Waddington,
and Joan Burke of the Royal Ontario Museum were
very helpful with a variety of palaeontological, curato-
rial, and editorial matters. This project was supported
by NSERC Operating Grant A3825 to Rolf Ludvigsen.

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Plate 1, figs. 1-15.

Paracybantyx asulcatus gen. et sp. nov., locality AA 95, Road River Formation, Prongs Creek, Yukon
Territory, Canada.

1-3. Cranidium, dorsal, frontal, and oblique views, ROM 45343, x 2.

4,5. Holotype cranidium, lateral and dorsal views, ROM 45344, x 4.

6. Cranidium, dorsal view, ROM 45376, x 3.

7-9. Cranidium, dorsal, frontal, and oblique views, ROM 45330, x 4.

10,11. Pygidium, lateral and dorsal views, ROM 45342, x 2.

12. Hypostome, latex impression, ventral view, ROM 45375, x 6.

13,14. Pygidium, lateral and dorsal views, ROM 45360, x 2.

15. Pygidium, lateral view enlarged to show prosopon, ROM 45360, x 4.

Plate 2, figs. 1-12.

Kosovopeltis borealis (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek, Yukon
Territory, Canada.

1,2. Complete specimen, dorsal views, ROM 42143, x 4.

3. Librigena, ventral view, ROM 42144, x 3.

4. Rostral plate, ventral view, ROM 42145, x 4.

5,6. Cranidium, dorsal and oblique views, ROM 42146, x 4.

7. Hypostome, ventral view, ROM 42147, x 9.

8. Hypostome, ventral view, ROM 42148, x 9.

9. Cranidium, dorsal view, ROM 42149, x 9.

10. Pygidium, latex impression, dorsal view, ROM 42150, x 9.

11. Pygidium, dorsal view, ROM 42151, x 1.4.

12. Pygidium, dorsal view, ROM 42152, x 1.4.

Plate 3, figs. 1-10.

Kosovopeltis borealis (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek, Yukon
Territory, Canada.

1. Cranidium, latex impression, dorsal view, ROM 42153, x 4.

2. Pygidium, latex impression, dorsal view, ROM 42154, x 1.7.

3-5. Cranidium with rostral plate, dorsal, anterior, and ventral views, ROM 42155, x 2.

6. Librigena, dorsal view, ROM 42156, x 3.

7. Pygidium, latex impression, ventral view, ROM 42157a, x 1.7.

8. Slab crowded with pygidia, ROM 42157, x 1.

9. Librigena, dorsal view, ROM 42158, x 4.

10. Cranidium, latex impression, dorsal view, ROM 42159, x 4.

Plate 4, figs. 1-14.

Figs. 1-13. Kosovopeltis borealis (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek,
Yukon Territory, Canada.

1,2. Protaspis, latex impression, dorsal and oblique views, ROM 42160, x 56.

3,4. Meraspid cranidium, oblique and dorsal views, ROM 42161, x 24.

5. Transitory pygidium with one protothoracic segment attached, dorsal view, ROM 42162, x 12.

6,7. Transitory pygidium with two protothoracic segments attached, latex impression, dorsal and
oblique views, ROM 42163, x 12.

8,9. Internal mould of lens surface of holaspid eye, ROM 42164, x 100 and x 500.

10,11. Transitory pygidium, latex impression, oblique and dorsal views, ROM 42165, x 50.

12,13. Smallest transitory pygidium, ROM 42166, x 56 and x 92.

Fig. 14. Otarion {Songkania) socialis (Poulsen), locality AA 2-4.5, Road River Formation, Prongs
Creek, Yukon Territory, Canada, hypostome, ventral view, ROM 42204, x 24.

Plate 5, figs. 1-16.

All specimens are from locality BB 131, unnamed carbonates, Illtyd Range, Yukon Territory, Canada.

Figs. 1-11. Stenopareia illtyd sp. nov.

1,2. Cranidium, dorsal and oblique views, ROM 42167, x 3.

3,4. Holotype cranidium, dorsal and anterior views, ROM 42168, x 3.

5,6. Cranidium, dorsal and anterior views, ROM 42169, x 3.

7. Pygidium, dorsal view, ROM 42170, x 9.

8,9. Pygidium, dorsal and lateral views, ROM 42171, x 4.

10,11. Pygidium, dorsal and oblique views, ROM 42172, x 5.

Fig. 12. Indeterminate illaenid, cephalon, dorsal view, ROM 42173, x 3.

Figs. 13,14. Indeterminate bumastine, cranidium, dorsal and anterior views, ROM 42174, x 9.

Figs. 15,16. Cheirurus sp., cranidium, lateral and dorsal views, ROM 42175, x 5.

Plate 6, figs. 1-24.

Figs. 1-14. Hedstroemia kutchini sp. nov., locality AA 95, Road River Formation, Prongs Creek,
Yukon Territory, Canada.

1,2. Cranidium, dorsal and oblique views, ROM 45371, x 5.

3,4. Holotype cranidium, dorsal and oblique views, ROM 45347, x 6.

5. Cranidium, dorsal view, ROM 45348, x 6.

6,7. Pygidium, dorsal and lateral views, ROM 45334, x 4.

8. Pygidium, dorsal view, ROM 45335, x 4.

9,10. Pygidium, dorsal and lateral views, ROM 45328a, x 4.

11. Librigena, dorsal view, ROM 45372, x 6.

12. Librigena, latex impression, dorsal view, ROM 45358, x 5.

13. Hypostome, ventral view, ROM 45329, x 8.

14. Hypostome, ventral view, ROM 45370, x 8.

Fig. 15. Indeterminate proetid A, locality AA 95, Road River Formation, Prongs Creek, Yukon
Territory, Canada, hypostome, ventral view, ROM 45338b, x 8.

Figs. 16-24. Hedstroemia sourdoughi sp. nov., locality AA 95, Road River Formation, Prongs Creek,
Yukon Territory, Canada.

16. Pygidium, dorsal view, ROM 45333, x 4.

17-19. Pygidium, posterior, lateral, and dorsal views, ROM 45331, x 6.

20. Pygidium, dorsal view, ROM 45323, x 5.

21. Cranidium, latex impression, dorsal view, ROM 45357, x 4.
22,23. Holotype cranidium, dorsal and oblique views, ROM 45332, x 4.
24. Cranidium, dorsal view, ROM 45326, x 6.

Plate 7, figs. 1-20.

Figs. 1-15. Prantlia vagrans sp. nov., locality AA 95, Road River Formation, Prongs Creek, Yukon
Territory, Canada.

1. Cranidium, dorsal view, ROM 45339, x 4.

2. Cranidium, dorsal view, ROM 45340, x 4.

3. Cranidium, latex impression, dorsal view, ROM 45353, x 6.

4. Cranidium, dorsal view, ROM 45365, x 6.

5. Librigena, showing narrow doublure, ventral view, ROM 45327, x 5.
6,7. Holotype pygidium, dorsal and oblique views, ROM 45363, x 6.

8. Pygidium, dorsal view, ROM 45337, x 4.

9. Pygidium, dorsal view, ROM 45336a, x 4.

10. Meraspid cranidium, latex impression, ROM 45351, x 8.

11. Pygidium, showing narrow doublure, ventral view, ROM 45364, x 4.

12. Pygidium, dorsal view, ROM 45328b, x 4.

13. Pygidium, dorsal view, ROM 45341, x 5.

14. Librigena, oblique view, ROM 45338a, x 5.

15. Librigena, latex impression, oblique view, ROM 45355, x 4.

Figs. 16-20. Indeterminate lichid, locality AA 95, Road River Formation, Prongs Creek, Yukon
Territory, Canada.

16. Pygidium, dorsal view, ROM 45361, x 2.

17. Pygidium, dorsal view, ROM 45366b, x 2.

18. Cranidium, dorsal view, ROM 45349, x 5.

19. Cranidium, dorsal view, ROM 47356, x 5.

20. Hypostome, latex impression, ventral view, ROM 45354, x 5.

Plate 8, figs. 1-12.

Otarion (Songkania) socialis (Poulsen), locality AA 2-4.5, Road River Formation, Prongs Creek,
Yukon Territory, Canada.

1,2. Complete specimen, dorsal and oblique views, ROM 42176, x 7.5.

3,4. Cranidium, dorsal and anterior views, ROM 42177, x 9.

5. Complete specimen lacking axial spine on sixth segment, dorsal view, ROM 42178, x 7.5.

6,7. Complete specimen with axial spine on sixth segment, dorsal and oblique views, ROM 42179,
X 6.

8. Cephalon and thorax with axial spine on sixth segment, oblique view, ROM 42180, x 5.

9. Librigena, oblique view, ROM 42181, x 9.

10,11. Complete specimen, dorsal and oblique views, ROM 42182, x 7.5.
12. Librigena, oblique view, ROM 42183, x 9.

Plate 9, figs. 1-11.

All specimens are from locality BB 131, unnamed carbonates, Illtyd Range, Yukon Territory, Canada.

Figs. 1-3. Scotoharpes raaschi Norford, 1973.

1,3. Cephalon, dorsal and oblique views, ROM 42184, x 5.

2. Cephalon, latex impression, dorsal view, ROM 42185, x 5.

Figs. 4,5. Indeterminate proetid B.

4. Hypostome, ventral view, ROM 42186, x 5.

5. Cranidium, dorsal view, ROM 42187, x 5.

Fig. 6. Encrinuraspis sp., pygidium, dorsal view, ROM 42188, x 9.

Fig. 7. Indeterminate calymenid, pygidium, dorsal view, ROM 42189, x 4.

Figs. 8-11. Kosovopeltisl spp.

8. Pygidium, dorsal view, ROM 42190, x 5.

9. Cranidium, dorsal view, ROM 42191, x 9.

10. Pygidium, dorsal view, ROM 42192, x 4.

11. Pygidium, dorsal view, ROM 42193, x 4.

Plate 10, figs. 1-12.

Figs. 1-8. Cromus princeps (Poulsen), locality AA 2-4.5, Road River Formation, Prongs Creek,
Yukon Territory, Canada.

1,2. Cranidium, oblique and dorsal views, ROM 42194, x 4.

3. Hypostome, ventral view, ROM 42195, x 9.

4. Librigena, oblique view, ROM 42196, x 5.

5. Pygidium (deformed), dorsal view, ROM 42197, x 9.

6. Cranidium, dorsal view, ROM 42198, x 9.

7. Pygidium, dorsal view, ROM 42199, x 4.

8. Pygidium, dorsal view, ROM 42200, x 4.

Fig. 9. Indeterminate odontopleurine, locality BB 131, unnamed carbonates, Illtyd Range, Yukon
Territory, Canada, cranidium, dorsal view, ROM 42201, x 9.

Figs. 10-12. Dicranopeltis sp., locality BB 131, unnamed carbonates, Illtyd Range, Yukon Territory,
Canada.

10,11. Cranidium, dorsal and oblique views, latex impression, ROM 42202, x 9.
12. Pygidium, dorsal view, ROM 42203, x 9.

Plate 11, figs. 1-18.

Figs. 1-5. Paracybantyx asulcatus gen. et sp. nov., locality AA 95, Road River Formation, Prongs
Creek, Yukon Territory, Canada.

1. Pygidium, dorsal view, ROM 45345, x 2.

2. Librigena, ventral view showing pit in doublure, ROM 45366a, x 4.

3. Librigena, latex impression, oblique view showing doublure, ROM 45352, x 4.

4. Pygidial doublure, latex impression, ventral view, ROM 45374, x 4.

5. Pygidium, dorsal view, ROM 45369, x 6.

Figs. 6,7. Indeterminate scutelluine, locality AA 95, Road River Formation, Prongs Creek, Yukon
Territory, Canada, cranidium, dorsal view, ROM 45359, x 4 and x 8.

Figs. 8-10, 12-18. Balizoma aff. B. obtusus (Angelin), locality AA 95, Road River Formation, Prongs
Creek, Yukon Territory, Canada.

8. Pygidium, dorsal view, ROM 45325, x 6.

9,10. Pygidium, latex impression, oblique and dorsal views, ROM 45350, x 4.

12. Cranidium, dorsal view, ROM 45336b, x 4.

13,14. Pygidium, dorsal and lateral views, ROM 45324, x 4.

15,16. Pygidium, posterior and dorsal views, ROM 45367, x 4.

17,18. Hypostome, oblique and ventral views, ROM 45362, x 6.

Fig. 11. Indeterminate encrinurine, locality AA 95, Road River Formation, Prongs Creek, Yukon
Territory, Canada, cranidium, dorsal view, ROM 45373, x 3.

Plate 12, figs. 1-16.

Figs. 1-13. Leonaspis semiglabra (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek,
Yukon Territory, Canada.

1. Cranidium, latex impression, dorsal view, ROM 42205, x 9.

2. Hypostome, ventral view, ROM 42206, x 9.

3. Pygidium, dorsal view, ROM 42207, x 9.

4. Cranidium, latex impression, dorsal view, ROM 42208, x 9.

5. Cranidium, latex impression, dorsal view, GSC 15399, x 9.

6. Cranidium, latex impression, dorsal view, GSC 15398, x 9.

7. Cranidium, latex impression, dorsal view, ROM 42209, x 9.

8. Pygidium, dorsal view, GSC 15700, x 9.

9. Pygidium, dorsal view, GSC 15701, x 9.

10. Pygidium, dorsal view, ROM 42210, x 9.

11. Librigena, oblique view, ROM 42211, x 9.

12. Pygidium, dorsal view, ROM 42212, x 9.

13. Incomplete specimen, dorsal view, ROM 42213, x 6.

Figs. 14—16. Otarion (Songkania) socialis (Poulsen), locality AA 2-4.5, Road River Formation, Prongs
Creek, Yukon Territory, Canada.

14. Cranidium, dorsal view, GSC 15392, x 9.

15. Pygidium, dorsal view, ROM 42214, x 9.

16. Pygidium, dorsal view, GSC 15393, x 9.

Plate 13, figs. 1-14.

Figs. 1,2. Kosovopeltis borealis (Poulsen), Cape Schuchert Formation of Poulsen (1934), Kap Schu-
chert. North Greenland.

1. Holotype cranidium, dorsal view, MMH 3267, x 3.

2. Cranidium, dorsal view, MMH 3268, x 3.

Figs. 3-6. Otarion (Songkania) socialis (Poulsen), Cape Schuchert Formation, Kap Schuchert, North
Greenland.

3,4. Holotypecranidium, dorsal and anterior views, MMH 3251, x 9. Note caecae crossing preglabel-
lar field abaxially.

5. Librigena, oblique view, MMH 3252, x 6.

6. Pygidium, dorsal view, MMH 3253, x 9.

Figs. 7-12. Cromus princeps (Poulsen), Cape Schuchert Formation, Kap Schuchert, North Greenland.

7. Pygidium, dorsal view, MMH 3278, x 3.

8. I^gidium, dorsal view, MMH 3279, x 3.

9. Pygidium, dorsal view, MMH 3280, x 3.

10,11. Holotype cranidium, dorsal and oblique views, MMH 3276, x 4.

12. Librigena, oblique view, MMH 3277, x 3.

Figs. 13,14. Leonaspis semiglabra (Poulsen), Cape Schuchert Formation, Kap Schuchert, North
Greenland.

13. Holotype cranidium, dorsal view, MMH 3261, x 9.

14. Librigena, oblique view, attributed to L. groenlandica by Poulsen, MMH 3258, x 9.

Life Sciences Contributions are a numbered series of scientific publications of varied
subject matter published by the Royal Ontario Museum. Most recent contributions
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145 An Annotated Checklist of the Fishes of the Chagos
Archipelago, Central Indian Ocean

Richard Winterbottom, Alan R. Emery, and Erling Holm
1989, 226 pp., ill., $48.50, ISBN 0-88854-329-8

146 Stipatocrinus, a New and Unusual Camerate Crinoid
from the Lower Silurian of Western New York
James D. Eckert and Carlton E. Brett

1987, 17 pp., ill., $6.00, ISBN 0-88854-336-0

147 Biostratigraphy and Palaeontology of the Scollard
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Loris S. Russell

1987, 23 pp., ill., $7.00, ISBN 0-88854-338-7

148 Shallow-Water Hydroids of Bermuda: The
Athecatae

Dale R. Calder

1988, 107 pp., ill., $24.50, ISBN 0-88854-339-5

149 Occurrence of the Cladid Inadunate Crinoid
Thalamocrinus in the Silurian (Wenlockian) of
New York and Ontario

George C. Mcintosh and Carlton E. Brett
1988, 17 pp., ill., $7.75, ISBN 0-88854-342-5

150 Late Cretaceous-Early Tertiary Dinoflagellates
and Acritarchs from the Kashi Area, Tarim Basin,
Xinjiang Province, China

Mao Shaozhi and Geoffrey Norris

1988, 93 pp., ill., $23.00, ISBN 0-88854-334-4

151 The Structure of the Call Note System of the
Warbling Vireo

Daryl Howes-Jones and Jon C. Barlow

1988, 36 pp., ill., $10.25, ISBN 0-88854-343-3

152 The Type Species of the Ordovician Trilobite Genus
Isotelus: I. gigas Dekay, 1824

David M. Rudkin and Ronald P. Tripp

1989, 19 pp., ill., $10.25, ISBN 0-88854-345-X

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