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Life Sciences Contributions
Royal Ontario Museum 1 34

Upper Cambrian and
Lower Ordovician Trilobite

Biostratigraphy of the
Rabbitkettle Formation,
Western District of Mackenzie

Rolf Ludvigsen

ROM

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LIFE SCIENCES CONTRIBUTIONS
ROYAL ONTARIO MUSEUM
NUMBER 134

a Upper Cambrian and
Lower Ordovician Trilobite
Biostratigraphy of the
Rabbitkettle Formation,
Western District of Mackenzie

This paper is dedicated to the memory of David G.
Perry of Vancouver, Robert K. Jull of Windsor, and
Zoltan Hadnagy of Calgary—three close friends and
colleagues who died in a helicopter accident in
western Alberta on August 2, 1979.

r
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ROLF LUDVIGSEN is Associate Professor in the Department of Geology, University of Toronto, Toronto,
Ontario, and Research Associate, Department of Invertebrate Palaeontology, Royal Ontario Museum.

Canadian Cataloguing in Publication Data

Ludvigsen, Rolf, 1944—

Upper Cambrian and Lower Ordovician trilobite
biostratigraphy of the Rabbitkettle Formation,
Western District of Mackenzie
(Life sciences contributions, ISSN 0384-8159 ; no.
134)

Bibliography: p.
ISBN 0-88854-287-9

1. Trilobites. 2. Paleontology — Cambrian.

3. Paleontology — Ordovician. 4. Paleontology —
Northwest Territories — Mackenzie. I. Royal Ontario
Museum. II. Title. Ill. Series.

QE821.L835 565’ .393 C82-094215-4

Publication date: 16 April 1982
ISBN 0-88854-287-9
ISSN 0384-8159

© The Royal Ontario Museum, 1982
100 Queen’s Park, Toronto, Canada M5S 2C6
PRINTED AND BOUND IN CANADA AT THE ALGER PRESS

Contents

Abstract 1
Introduction 2
Regional Setting and Stratigraphy 4
Biostratigraphy 7
Cambrian 7
Yukonaspis Zone 8
Yukonaspis kindlei Fauna 10
Bowmania americana Fauna_ 11
Elkanaspis corrugata Fauna 13
Ordovician 13
Parabolinella Zone 14
Missisquoia mackenziensis Fauna 15
Missisquoia depressa Subzone 15
Apoplanias rejectus Fauna 16
Symphysurina Zone 16
Symphysurina brevispicata Subzone 17
Note on Construction of Composite Section KK 17
Cambrian-Ordovician Boundary 17
Lithofacies and Environment 22
Grand Cycle Boundary 30
The Biomere Concept 32
Ptychaspid-‘*Hystricurid’’ Biomere Boundary 34
Systematic Palaeontology 43
Family Agnostidae 43
Subfamily Agnostinae 43
Geragnostus Howell, 1935 44
Geragnostus (Micragnostus) Howell, 1935 44
Family Diplagnostidae 47
Subfamily Pseudagnostinae 47
Pseudagnostus (Pseudagnostina) Palmer, 1962 47
Rhaptagnostus Whitehouse, 1936 48
Family Ptychopariidae 49
Subfamily Eulominae 49
Euloma (Plecteuloma) Shergold, 1975 49
Family Shumardiidae 50
Idiomesus Raymond, 1924 50
Family Tricepicephalidae 53
Meteoraspis Resser, 1935 53
Family Olenidae 54
Subfamily Oleninae 55
Parabolinites Henningsmoen, 1957 55
Parabolinella Brogger, 1882 58
Apoplanias Lochman, 1964a_ 65
Bienvillia Clark, 1924 67

Family Entomaspidae 67
Bowmania Walcott, 1925 69
Heterocaryon Raymond, 1937 72
Family Catillicephalidae 74
Triarthropsis Ulrich, in Bridge, 1931 74
?Family Kingstoniidae 75
Larifugula gen. nov. 75
Family Plethopeltidae 80
Plethometopus Ulrich, in Bridge, 1931 80
Leiocoryphe Clark, 1924 81
Family Norwoodiidae 82
Levisaspis Rasetti, 1943 82
Family Saukiidae 84
Calvinella Walcott, 1914 84
saukiid indet. 86
Family Ptychaspididae 87
Subfamily Euptychaspidinae 87
Euptychaspis Ulrich, in Bridge, 1931 88
Kathleenella gen. nov. 90
Liostracinoides Raymond, 1937 94
Subfamily Eurekiinae 96
Eurekia Walcott, 1916 98
Yukonaspis Kobayashi, 1936a 102
Family Kainellidae 105
Naustia gen. nov. 106
Elkanaspis gen. nov. 109
Family Leiostegiidae 116
Subfamily Pagodiinae 116
Ptychopleurites Kobayashi, 1936b 116
Family Missisquoiidae 119
Missisquoia Shaw, 1951 119
Family Asaphidae 125
Subfamily Symphysurininae 125
Symphysurina Ulrich, in Walcott, 1924 125
Family Nileidae 126
Tatonaspis Kobayashi, 1935 126
Family Ceratopygidae 128
ceratopygid indet. 129

Acknowledgements 129
Literature Cited 178

Upper Cambrian and

Lower Ordovician Trilobite
Biostratigraphy of the
Rabbitkettle Formation,
Western District of Mackenzie

Abstract

Two measured sections of the upper Rabbitkettle Formation in the
western District of Mackenzie are separated by a thrust fault. These
sections provide a record of silicified trilobite faunas across the
Cambrian-Ordovician boundary in open marine carbonate rocks along
the deeper portion of the shelf—a North American palaeogeographic
setting not previously extensively sampled for macrofossils.

A new biostratigraphy is proposed for the Trempealeauan to Lower
Tremadocian interval in this setting. A Yukonaspis Zone with three
divisions (in ascending order, Yukonaspis kindlei Fauna, Bowmania
americana Fauna, and Elkanaspis corrugata Fauna) is based on
eurekiine, entomaspid, and olenid trilobites. The Yukonaspis Zone is
of Trempealeauan age and is considered equivalent to the Saukia
Zone. A Parabolinella Zone with three divisions (in ascending order,
Missisquoia mackenziensis Fauna, Missisquoia depressa Subzone,
and Apoplanias rejectus Fauna) is based on olenid, missisquoiid, and
leiostegiid trilobites. The Parabolinella Zone is of Early Tremadocian
age and is considered to be largely equivalent to the Missisquoia Zone.
The Symphysurina brevispicata Subzone of the Symphysurina Zone
(Early Tremadocian) is represented by a single collection.

The base of the Ordovician System is drawn at the first appearance
of Parabolinella at the base of the Parabolinella Zone. This horizon
probably correlates closely with the base of the Tremadocian and it
may be slightly older than the base of the Ordovician as recognized
elsewhere in the North American Province (that is, the base of the
Missisquoia Zone).

The coincident base of the ‘‘Hystricurid’’ Biomere and a Grand
Cycle occurs at the base of the Elkanaspis corrugata Fauna of the
Yukonaspis Zone (correlative with the base of the Corbinia apopsis
Subzone of the Saukia Zone) at the abrupt appearance of black
laminated lime mudstones above light grey, burrowed lime wacke-
stones. The mudstones contain a new fauna dominated by kingstoniid
(?), olenid, and kainellid trilobites. This horizon, located 70 m below

the top of the Rabbitkettle Formation, is a biogeographic boundary
which separates the shelf-biogeographic region below from the slope-
biogeographic region above. The extinction, immigration, speciation,
and diversity patterns that define the Ptychaspid-**Hystricurid’”’
Biomere boundary are explained with reference to the diversity-area
relationships inherent in the equilibrium model of biogeography.

Forty-six species of trilobites are described and illustrated. Four
new genera are proposed (Larifugula, Kathleenella, Naustia, and
Elkanaspis). Eleven species are new (Parabolinella panosa,
Larifugula triangulata, *‘Calvinella’’ palpebra, Kathleenella subula,
Kathleenella hamulata, Eurekia bacata, Naustia papilio , Elkanaspis
futile, Elkanaspis corrugata, Missisquoia mackenziensis, and
Tatonaspis diorbita.

‘‘Acidaspis’’ ulrichi Bassler is a junior synonym of Bowmania
americana (Walcott), which is reassigned to the Entomaspidae.
‘‘Leiobienvillia’’ leonensis Winston and Nicholls is assigned to a new
kingstoniid (?) genus, Larifugula. Liostracinoides Raymond and
Kathleenella gen. nov. are assigned to the Euptychaspidinae.
Yukonaspis Kobayashi is assigned to the Eurekiinae and Ptychopleur-
ites Kobayashi to the Pagodiinae.

Introduction

In 1972, as a part of a thesis project on silicified Middle Ordovician trilobites of the
southern District of Mackenzie, I measured and collected a 750 m-thick section
(Section K, Fig. 1) near the headwaters of the Broken Skull River. I had hoped to
sample the fossiliferous deeper-water equivalents of the Sunblood, Esbataottine, and
lower Whittaker formations that are exposed farther to the east in the Mackenzie
Mountains ((Ludvigsen, 1975; 1979b). This hope was not realized. Black
argillaceous limestones and cherts of the upper part of this section, which were
assigned to the Road River Formation, proved to be equivalent to the lower part of the
Sunblood Formation, but these strata yielded only inarticulate brachiopods and
conodonts (Tipnis et al., 1979). The lower part of Section K, below a conspicuous
lower black dolostone member of the Road River Formation, was assigned to the
Rabbitkettle Formation and these strata proved more interesting because they
contained a number of collections with abundant silicified trilobites of types not seen
in Ordovician strata to the east. Etching of these samples in the laboratory yielded 12
collections of Late Cambrian trilobites. Two collections from higher in the section
contained abundant and well-preserved specimens of Parabolinella, Missisquoia, and
Geragnostus of apparently earliest Ordovician age. Section K, therefore, was
potentially of considerable importance in providing a detailed trilobite biostratigraphy
across the Cambrian-Ordovician boundary in this area of northern Canada. The
samples acquired in 1972, however, were too widely spaced to allow definite
conclusions about the distribution of trilobites across this boundary.

An opportunity to revisit Section K came in 1977 and, at that time, the 240 m
Stratigraphic interval of the upper Rabbitkettle Formation was systematically
sampled. The new section was designated Section KK. Thirty-five bulk limestone

samples, varying in weight from 2 kg to more than 20 kg, were collected. All but
four of these yielded silicified trilobites.

The sequence of collections forms the basis for a new trilobite biostratigraphy of
the boundary interval between the Cambrian and the Ordovician in an outer platform,
Open marine setting in western North America. A companion paper on conodont
biostratigraphy of the same sequence of samples has already been published (Landing
et al., 1980).

Although the present paper is based on a single measured section, the critical
boundary interval was sampled twice. This was made possible by a fortuitously
placed and previously unrecognized thrust fault. The collections also provide a
trilobite and conodont record across the Ptychaspid-‘‘Hystricurid’’ Biomere boundary
and a new model is proposed to account for the extinction, immigration, speciation,
and diversity patterns which define this level in North America.

127°00'

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? MACKENZIE
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Fig. 1 Map of western District of Mackenzie showing location of Section K near the headwaters of the

Broken Skull River. Base of measured section is to the west. Section KK covers the middle part
of line of Section K.

Regional Setting and Stratigraphy

Section K is located near the western margin of the Mackenzie Platform—a stable
tectonic feature that received dominantly shallow-water sediments from the Helikian
to the Late Devonian (Gabrielse, 1967). Flanking the Mackenzie Platform to the west
is the epicontinental Selwyn Basin which is characterized by thick sequences of fine
clastic rocks. The southwestern margin of the Selwyn Basin is bordered by the
Pelly-Cassiar Platform which was initiated in the Late Cambrian as a site of andesitic
volcanism and, in the Silurian and Devonian, was the locus of shallow-water
carbonate sedimentation (Tempelman-Kluit, 1977). Tempelman-Kluit and Blusson
(1977) and Tempelman-Kluit (1977) have provided evidence that, prior to
mid-Cretaceous right-lateral movement on the Tintina Fault, the Pelly-Cassiar
Platform was a narrow belt at the shelf-slope break at least 1000 km long. The Yukon
Crystalline Terrane and its southern extension, the Omineca Crystalline Belt,
comprise severely metamorphosed and tectionized sedimentary rocks that are
probably in part equivalent to the unmetamorphosed Lower Palaeozoic sedimentary
rocks on the shelf (Tempelman-Kluit, 1977: fig. 45.2). The relationship of these
Lower Palaeozoic tectonic elements is shown in Fig. 2.

Three carbonate formations of Late Cambrian and Early Ordovician age are
exposed across the Mackenzie Platform between latitudes 62°N and 64°N. From east
to west, these are the Franklin Mountain Formation in the Mackenzie River Valley,
the Broken Skull Formation in the eastern and central Mackenzie Mountains, and the
Rabbitkettle Formation in the western Mackenzie Mountains and the Selwyn
Mountains (Aitken et al., 1973; Gabrielse et al., 1973; Norford and Macqueen,
1975). These formations are not well dated. The Franklin Mountain Formation
contains brachiopods, molluscs, and trilobites of Dresbachian to middle Canadian age
(Norford and Macqueen, 1975: 12; Aitken et al., 1973: 31). The Broken Skull
Formation contains trilobite, brachiopod, and conodont faunas which range in age
from late Franconian to late Canadian (Gabrielse et al., 1973: 49, Ludvigsen, 1975;
Tipnis et al., 1979). Only a single fossil collection has been recovered from typical
exposures of the Rabbitkettle Formation in the Selwyn Mountains. This is a trilobite
collection of Franconian age (Gabrielse et al., 1973: 51). In the Howards Pass area,
near Summit Lake, some 50 km southwest of Section K, the Rabbitkettle is
conformably overlain by the Road River Formation which here contains early
Arenigian graptolites near its base (Ludvigsen, 1975: 675). In other areas, the lower
Road River Formation appears to be a facies equivalent of the Rabbitkettle
Formation.

The thick package of predominantly carbonate rocks of the Mackenzie Platform
rests unconformably on Middle Cambrian and older formations. This is the
‘*sub-Franconian unconformity’’ of Gabrielse et al. (1973) and the ‘‘sub-Dresbachian
unconformity’’ of Aitken et al. (1973).

The outcrop belts defined by the Franklin Mountain, Broken Skull, Rabbitkettle,
and lowermost Road River formations are approximately parallel to one another and
parallel to the western margin of the Mackenzie Platform. A _ generalized
palaeoenvironment may be interpreted for each formation.

Norford and Macqueen (1975) have presented a detailed discussion of the
lithologic character and palaeoenvironment of the Franklin Mountain Formation at its
type area in the Mackenzie River Valley. Here, the formation consists of laminated to

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KILOMETRES

Fig. 2 Early Palaeozoic tectonic elements of the northern Cordillera. Reconstruction was made by
restoring 450 km of right lateral displacement on the Tintina Fault (Tempelman-Kluit, 1977).
Section K is located near the western margin of the Mackenzie Platform. Line of cross-section in
Fig. 3 is indicated.

thickly bedded dolostones which range from coarsely to very finely crystalline. The
middle part of the formation is characterized by rhythmic alternations of oolitic or
bioclastic grainstones/packstones and banded, very finely crystalline and silty
dolostones. The middle and upper parts of the formation are characterized by
well-developed hemispheric stromatolites and stromatolitic dolostones. The Franklin
Mountain Formation clearly represents deposition in shallow subtidal and intertidal
environments along the interior portions of the Mackenzie Platform.

The basal portion of the Broken Skull Formation in the Mackenzie Mountains
(Gabrielse et al., 1973: 45-48) consists of sandy dolomitic mudstones, siltstones, and
dolostones with mudcracks, cross-beds, and trace fossils. The bulk of the formation
comprises thick bedded to flaggy limestones and dolostones that are variably silty and
sandy and weather in shades of buff, grey, and brown. Planar and cross-laminations
are occasionally present and some beds contain abundant pisolites. The Broken Skull
Formation probably represents deposition in a wide range of palaeoenvironments,
from intertidal to moderately deep subtidal. On balance, it appears to be somewhat
deeper than the Franklin Mountain Formation.

The Rabbitkettle Formation is a thick sequence of monotonous thin-bedded to
massive silty limestones and calcareous siltstones exposed in the Selwyn Mountains
(Blusson, 1968: 13, 14; Gabrielse et al., 1973: 48). The limestones are finely grained
and characterized by planar and wavy banding of silty layers, some of which are
graded (Gabrielse et al., 1973: pls. 19, 20). An upper member of the Rabbitkettle
consisting of finely laminated, dark grey to black muddy limestones and shales is
herein reassigned to the Road River Formation. The palaeoenvironment of the
Rabbitkettle Formation is poorly understood. Presumably, it represents relatively
deep-water deposition in open marine settings along the western portion of the
Mackenzie Platform and, perhaps, in part on the decline into the Selwyn Basin.

The Upper Cambrian and Lower Ordovician parts of the Road River Formation
have been studied by Cecile (1978) in the Misty Creek Embayment of the Selwyn
Basin, some 200 km north-northeast of Section K. In this area, the Road River
consists of thin bedded, yellowish weathering muddy limestones according to Cecile.
He noted (1978: 374) that these strata ‘‘have all the characteristics of a slope facies:
including slumps, in situ slump breccias, carbonate clast conglomerates and breccias,
trains of ripple-drift cross laminae, lensed and scoured bedding’’.

A diagrammatic cross-section of Upper Cambrian and Lower Ordovician rocks
from the interior portion of the Mackenzie Platform to the Yukon Crystalline Terrane
is Shown in Fig. 3.

According to recent mapping of the Nahanni Sheet by Gordey (1980), the
Stratigraphic succession in the vicinity of the Section K consists of a conformable
sequence of Upper Hadrynian to Lower Ordovician rocks (that is, the Backbone
Ranges, Sekwi, Rockslide, Rabbitkettle, and Broken Skull formations) which is
disconformably overlain by Upper Ordovician to Devonian rocks (that is, the
Whittaker and Road River formations). The Rabbitkettle Formation as recognized in
this paper apparently corresponds to the Rabbitkettle Formation as mapped by
Gordey. I believe, however, that the name Broken Skull Formation is inappropriately
applied to the dark grey to black dolostones and black argillaceous limestones which
overlie the Rabbitkettle in this area. These strata are, herein, assigned to the Road
River Formation (Figs. 4, 5).

Yukon al Peny Selwyn Mackenzie Platform
Crystalline] Cassiar | Basin
Terrane [Platform

slates andesitic volcanics muddy limestones banded & silty sandy & silty laminated & stromatolitic
quartzites phyllites shales limestones carbonates dolostones
slump breccias siltstones oolites

Fig. 3 Diagrammatic cross-section of Trempealeauan formations from the Mackenzie Platform in the
east to the Yukon Crystalline Terrane in the west (Fig. 2). Not to scale.

Biostratigraphy

Cambrian

Winston and Nicholls (1967) proposed a four-fold subzonal division of the Saukia
Zone for shallow-water carbonate rocks in central Texas which was based largely on
saukiid and eurekiine trilobites. They named the upper three subzones and Longacre
(1970) later named the lowest subzone. This biostratigraphic scheme has been
applied, in part or in its entirety, to successions in Oklahoma (Stitt, 1971b, 1977),
Alberta (Derby et al., 1972), and New York (Taylor and Halley, 1974). Biofacies
differentiation among latest Cambrian trilobites hampers the utility of the four-fold
subzonal division of the Saukia Zone outside the interior portions of the Middle
Carbonate Belt of Palmer (1960a). These subzones cannot be recognized within the
Inner Detrital Belt developed in the upper Mississippi Valley where the Saukia Zone
and its divisions (Bell et al., 1956) are based largely on dikelocepvhalid and sauktid
trilobites that have not been found in Texas and Oklahoma (Stitt, 1977: 15). Nor can
the subzones be applied to coeval shelf-edge carbonate rocks carrying Hungaia
associations in Newfoundland, Quebec, Vermont, and Alaska. In addition, the
striking biofacies change at the Upper Cambrian shelf-slope break outlined by Taylor
for western United States prevents the recognition of the Saukia Zone in
autochthonous Trempealeauan Outer Detrital Belt sediments and Taylor (1976)
assigned the slope trilobites in central Nevada to the Hedinaspis Local Range Zone
(Franconian and Trempealeauan).

Upper Cambrian strata of the Rabbitkettle Formation exposed at Section KK carry
trilobites that show affinities to both those of the Saukia Zone and those of the
Hungaia associations. Significant differences, notably the virtual absence of saukiid
trilobites, preclude the application of the Texas/Oklahoma _biostratigraphic

SERIES SELWYN BASIN MACKENZIE PLATFORM
STAGES

Mackenzie
River Valley

Bonnet Plume | Selwyn : Mackenzie Mountains
map -area Mountains
SUNBLOOD
FORMATION

ROAD ROAD fe
RIVER RIVER
FORMATION| FORMATION

ROAD
RIVER )
FORMATION

BROKEN
SKULL
FORMATION FRANKLIN
MOUNTAIN
FORMATION

Section KK

RABBIT -
KETTLE Z
FORMATION

RABBITKETTLE

TREMPEALEAUAN FORMATION

FRANCONIAN

CECILE (1978 ) BLUSSON ( 1968 ) THIS PAPER LUDVIGSEN (1975) NORFORD &
MACQUEEN (1975)

Fig. 4 Correlation chart of Upper Cambrian and Lower Ordovician formations across the Mackenzie
Platform to the Selwyn Basin.

nomenclature to the District of Mackenzie succession. Instead, a Yukonaspis Zone
comprising three informal biostratigraphic units is proposed for these deep platform
carbonate rocks. The Yukonaspis Zone and its three faunas are based largely on
eurekiine, entomaspidid, and olenid trilobites. This biostratigraphic terminology 1s
probably more widely applicable to Trempealeauan platform margin rocks in western
and, possibly, eastern North America than is the Saukia Zone and its subzones.

It is evident from the preceding discussion and from Rowell et al. (1973, fig. 11)
that it is no longer possible to accept only a single standard biostratigraphic system for
latest Cambrian trilobites of North America. Robison (1976, text-fig. 5) reached
similar conclusions for Middle Cambrian trilobites of western North America. It will
be necessary to take cognizance of as many as four parallel zonal schemes of
Trempealeauan trilobites to effectively account for the environmental heterogeneity
of these faunas:

1. A Saukia Zone and its array of subzones for the Inner Detrital Belt and the inner
parts of the Middle Carbonate Belt.

2. A Yukonaspis Zone and its eventual subzones for the outer parts of the Middle
Carbonate Belt.

3. A zone or zones based on elements of the Hungaia associations for shelf-edge
carbonate sites.

4. A zone or zones based on elements of the Hedinaspis Local Range Zone for the
Outer Detrital Belt.

The Yukonaspis Zone and its three faunas from the upper Rabbitkettle Formation at
Section KK are defined below.

Yukonaspis Zone (177 m-60 m of composite Section KK)

The lower 117 m of composite Section KK are dominated by species of Yukonaspis,
Eurekia, Kathleenella gen. nov., Larifugula gen. nov., Idiomesus, Bowmania,
Elkanaspis. gen. nov., and Geragnostus. Other genera are less common—
Euptychaspis, Rhaptagnostus, Heterocaryon, Leiocoryphe, Tatonaspis, Euloma,
Naustia gen. nov., Pseudagnostus , Triarthropsis, Liostracinoides , Plethometopus ,
Bienvillia, Parabolinites. This generic assemblage constitutes the Yukonaspis Zone.
Specifically, the zone is defined by the body of strata from the first appearance of
Yukonaspis to the first appearance of Parabolinella. Only three genera of the
Yukonaspis Zone (that is, Geragnostus , Plethometopus, and Parabolinites) continue
into the superjacent zone.

The Yukonaspis Zone of the District of Mackenzie is undoubtedly equivalent to, at
least, the middle and upper parts of the Saukia Zone of Texas and Oklahoma. Many
of the Yukonaspis Zone genera are confined to the Saukia Zone. The upper
boundaries of the Yukonaspis and Saukia Zones must be closely correlative because
Larifugula leonensis (Winston and Nicholls) is confined to the highest fauna of the
Yukonaspis Zone and the highest subzone of the Saukia Zone. In addition, the base of
the Cordylodus oklahomensis Zone (= C. proavus Zone) occurs a short distance
below the top of both the Yukonaspis and Saukia zones (Landing et al., 1980; Miller,
1978). Thus, the Yukonaspis Zone appears to be an outer carbonate platform
equivalent of the Saukia Zone which is typically developed in carbonate and clastic
rocks higher on the platform.

SECTION: =K SECTION KK

measured August ,1972 measured August,1977
ed 3 123%9
Sees)" © x
6 See 50 °K 2845 om
Y === on 2400 Be
t Pg ®
<I Sat Ov 2 285 Pa
= See) 4° K 2200 20 eae iO KK 20
a ae | Ok 21415 Pee Ones
O sone | Pin ees Sago
me See Seana Or ikK. 233
—— O K2050 Bie
— Oo «2020 4 Bese
past] © K1985 FP Lg Kk 43
a aioe
pede eq 0 EKT930 <pness Q KK 48
eae 1200 ot KK 50
ay aay as Pizl = 9 KK 56
mcg asa 60S
Way aa Seni eae lo (Caan
Ta ee p=ciiie a
25 SA o Berk 22
aa e RoI Ta. peg
Pasema/ a O ieee
e/a = (ie Pe ed ae) KK 77
PRITAM Cay 8 CE AEAIEsB
eEa/enall Oo ses
ST as O KK 86.5
ae cree oO ial el as
wee ED a @ Wl a Ise KK 90
Fal lcefisanlia =a
Wee ny al SEI ane 2 oO
—/ aaa ‘= 10 SSaaiSoe
wassaay a (Re Gace eS Thrust Fault
iene aaa ae =aee
(ey Ey 5 U ss Oo KK 106
enya o ee on Oo KK 109
aaa a == PIS o KK hia
aD co ek OE OS pws)
= Sean KK 116
120F== 2 KK 1135
oO KK :
Oo K1155 Ean a KK es
iiaae cee canKKe TT ore
Ze © K1075 Eee Kies
O saeeeans
_ Orr az 14 ieaiesieasl(o KK 141
ze eee] S Kk 143
= C t=) KK 146
= © K 880 H
O Oo K 845 O! IKKNTSS
ue 16
©: KK Met
OPK 7a195
HS er KK 77
Oo K 595 18041 | [-.[}°o kk 180
K 550 Cae
BK 525 OE IEG Ss ae Tne
uu aisapey (o> KOO a-ss5eq.
zd paleaijet OC: 1K 470 (a a a a)
s See K 425 eae ed
a =| 0 K 390 20 | I-11 fo KK 201
a TT--. [--)o K 340 t=O KK 208
= (cman ae [een OK S245 ees eral a
== ele aa) a Ss ay KK 211
co Papen ik 270 imei eee
mo) Perate k 233 Fa:
< ae a 2204 ae]. “O_KK 220
~ ae ian a
Sele a a
aa an
a Se,
© K 20
ZA0
metres metres

Fig. 5 Graphic lithology log of upper Rabbitkettle Formation and lower Road River Formation at
Section K showing location of samples obtained in 1972 (K prefix). The thrust fault was not
recognized when Section K was measured. The upper 240 m of the Rabbitkettle was remeasured
in 1977 and designated Section KK. Location of 1977 samples are indicated (KK prefix).

The Yukonaspis Zone may also be recognized in the Road River Formation, Bonnet
Plume map-area (GSC loc. C-7562; Aitken et al., 1973: 73). It occurs on Jones Ridge
and Squaw Mountain, east-central Alaska (the Trempealeauan-2 Fauna of Palmer,
1968) and within the Cow Head Group, western Newfoundland (C.H. Kindle
Collection, Geological Survey of Canada, Ottawa).

A tripartite division of the Yukonaspis Zone is proposed below and is shown in
Figs. 6 and 7.

Yukonaspis kindlei Fauna (177 m-96 m of composite Section KK). The lower
81 m of composite Section KK (Fig. 7) comprise the Yukonaspis kindlei Fauna. Its
base is defined at the first appearance of the nominate species and it extends upward
to the first appearance of Bowmania americana. The following species occur in the Y.
kindlei Fauna (Note: in this and in following faunal lists, those species that continue
from the subjacent fauna are indicated by — and those that continue into the
Superjacent fauna are indicated by +):

JHANGING WALL FOOT WALL

SYMPHYSURINA

Zone

°kKK25 SYMPHYSURINA

BREVISPICATA. See THRUST
APOPLANIAS APOPLANIAS
40 exxk43 REJECTUS Fauna REJECTUS Fauna KK1Q6—8
Sikso MISSISQUOIA rae AIO RTHA MISSISQUOIA KEI Texte
DEPRESSA Subzone DEPRESSA Subzone Ree 120
60 aye M.MACKENZIENSIS Founa KK | 22.573
ELKANASPIS ELKANASP/S KKN 247
CORRUGATA Fauna CORRUGATA Fauna kki33-e
0 Sig Bos baa
8 BOWMANIA BOWMANIA
"5 AMERICANA AMERICANA
2 Fauna Fauno xx156 e
100 160
KK166 e
THRUST K710
KK177 e
te Ha Kki80 *-- ] BO
KK189 e
YUKONA SP/S
KINDLED ot 5) = Ole)
aquna

220

240

Metres

Fig. 6 Correlation of the foot wall and the hanging wall of the unnamed thrust fault in the upper
Rabbitkettle Formation. The thrust fault repeats at 58m interval. The boundaries of
biostratigraphic units are shown. The collections from the two fault blocks were combined to
form composite Section KK.

‘“‘Calvinella’’ palpebra sp. nov.
+ ceratopygid indet.
Elkanaspis futile gen. et sp. nov.
Euloma (Plecteuloma) sp.
Euptychaspis typicalis Ulrich
Eurekia bacata sp. nov.
Eurekia ulrichi (Rasetti)
+ Eurekia spp.
Geragnostus sp.
+ Heterocaryon tuberculatum Rasetti
+ Idiomesus intermedius Rasetti
Idiomesus tantillus Raymond
Kathleenella hamulata gen. et sp. nov.
+ Kathleenella subula gen. et sp. nov.
+ Larifugula triangulata gen. et sp. nov.
+ Leiocoryphe spp.
Meteoraspis? sp.
Naustia papilio gen. et sp. nov.
Pseudagnostus (Pseudagnostina) sp.
Rhaptagnostus clarki (Kobayashi)
saukiid indet.
Tatonaspis diorbita sp. nov.
Triarthropsis limbata Rasetti
Yukonaspis kindlei Kobayashi

The Yukonaspis kindlei Fauna is probably correlative to most of the Saukiella junia
Subzone of Texas and Oklahoma (Longacre, 1970; Stitt, 1977), but the correlation is
not entirely satisfactory because none of the species of the Y. kindlei Fauna is
confined to the S. junia Subzone. Euptychaspis typicalis, however, is most
commonly found in the S. junia Subzone of the southern United States. A firmer
correlation can be made with the Trempealeauan-2 Fauna of east-central Alaska
(Palmer, 1968) based on the co-occurrence of Eurekia ulrichi, Rhaptagnostus clarki,
and Yukonaspis kindlei. Four species of the Y. kindlei Fauna (that is, Eurekia ulrichi,
Heterocaryon tuberculatum, Idiomesus intermedius, and I. tantillus) also occur in
Vermont (Raymond, 1924, 1937) and Quebec (Rasetti, 1944, 1945) and the Y.
kindlei Fauna is undoubtedly equivalent to parts of the Hungaia assemblages of these
areas.

Bowmania americana Fauna (96 m-—70 m of composite Section KK). The next
26 m of composite Section KK (Fig. 7) comprise the Bowmania americana Fauna.
Its base is defined by the first appearance of the nominate species and its top is
defined by the first appearance of Elkanaspis corrugata. The following species occur
in the B. americana Fauna:

Bowmania americana (Walcott)
— ceratopygid indet.
Elkanaspis? sp.
— + Furekia spp.
— Heterocaryon tuberculatum Rasetti

— + Larifugula triangulata gen. et sp. nov.
— Leiocoryphe spp.
Liostracinoides vermontanus Raymond
+ Plethometopus obtusus Rasetti
+ Yukonaspis sp.

The Bowmania americana Fauna appears to be correlative to most of the Saukiella
serotina Subzone of the Saukia Zone. In the well-sampled Upper Cambrian sections
of Texas and Oklahoma (Longacre, 1970; Stitt, 1971b), B. americana is confined to
the S. serotina Subzone. Only four of the twelve species that comprise the B.
americana Fauna in the Rabbitkettle Formation are restricted to this biostratigraphic
unit; seven continue from the subjacent fauna and four continue into the superjacent

fauna.
-
es
XK
S 8 s
HY
S Q 2 So NP NS
= ‘ar NS SS xvO S
x oe eS > Xe &
x SILOAM ete ec SERS S
RD ~ ~ ~
ORE 2 SX Sw S8y ZF SS RoBsMGRaT Yo &
~ GB wy SO HF VON TZ SP xxASSEOKReQ SS &
CS2QN gal GS & GRAS GC BH WMZISNSe2aoHdk& &
BLSd GS Sees SSS ~ =s ENSN SX > KIGL 9
SECTION KK aSRIQERS 7s BONRSSS SZI85 Sa QURLO Seg Sha eee
. ” _ ” ”
UPPER RABBITKETTLE HeoUBVR¥YG VGURCSGY Key XN #0. Ok gEONME y SIV CIN
FORMATION Se TNO SORE RG AT, KOQG Og SN BquyQSS “GC gS LGTRSL “YTS
j SI GUESSES TERN GT GEG ONG BLESSES eS BLS OS BG SG SSE §
SECERSS SS OSES SER SOR OC LESS SS BORE SURO BSNS ONG SRG S
: SSEESESOSESSECSSSE TSE SEES OS GES BOSSE RS URE NSS
< Ny GUS ySoaNAaauys PSSS ETL TI TSRLTE YTS
= SHTLSTTOGESRITIS CSTE WH QOT STS FTI LT SI IGTS TITS
= = qu
Subzone

ORDOVICIAN

“ HYSTRICURID ”

BIOMERE

METRES
Fig.
Formation.

SYMPHYSURINA BREVISPICATA

MISSISQUOIA —_DEPRESSA Subzone

ELKANASPIS CORRUGATA

e Abundant > 20 specimens
© Common

< 5 specimens

BIOMERE

PARABOLINELLA ZONE

“ HYSTRICURID “

FL ree OKK 86.5 r=
Ef KK 90 < Zz
a OKK156 <q
fea) re) =
S| LEE KK 96 ORO 5, ae ae ye ee a a eg a
iS ls 130 shies “lQ\5
XE = eh 5 ol4|<
na lee KK177 ae)
< <q 140— KK180 a. >
9 LE n
« 5 LEELA ©KKI89 < Q
> Ss © KK201
SE AIS 07 NE YUKONASPIS KINDLE/ — Fauna aS
zo KK211 ss

— Idiomesus intermedius Rasetti
— Kathleenella subula gen. et sp. nov.

ORDOVICIAN

7 Occurrences of 46 species of trilobites in composite Section KK of the upper Rabbitkettle

Elkanaspis corrugata Fauna (70 m-60 m of composite Section KK). The abrupt
appearance of dark lime mudstones and olenid trilobites at the 70 m level of the
composite section signals a new lithologic and faunal sequence in the Rabbitkettle
Formation. The lower 10 m are assigned to the El/kanaspis corrugata Fauna. Its base
is defined by the first appearance of the nominate species and its top by the first
appearance of Missisquoia mackenziensis. The following species occur in the
Elkanaspis corrugata Fauna:

Bienvillia cf. corax (Billings)
Elkanaspis corrugata gen. et sp. nov.
ih RE ULekia: Spp:
Idiomesus levisensis (Rasetti)
Larifugula leonensis (Winston and Nicholls)
— Larifugula triangulata gen. et sp. nov.
Missisquoia sp.
+ Parabolinites cf. williamsoni (Belt)
+ Plethometopus obtusus Rasetti
— Yukonaspis sp.

Larifugula leonensis is restricted to the Elkanaspis corrugata Fauna in the District
of Mackenzie and to the Corbinia apopsis Subzone of the Saukia Zone in Texas,
Oklahoma, and Utah (Winston and Nicholls, 1967; Stitt, 1971b, 1977; Hintze et al.,
1980) and these biostratigraphic units are undoubtedly wholly or partially correlative.
The only other species that occur in both the E. corrugata Fauna and the C. apopsis
Subzone are /diomesus levisensis and Plethometopus obtusus, but these species have
wider teilzones in both Oklahoma and the District of Mackenzie.

The base of the E. corrugata Fauna marks the arrival of olenids (Parabolinites and
Bienvillia) and missisquoiids (Missisquoia) in the Rabbitkettle Formation (Fig. 8).
Trilobites of these families assume increasing importance and abundance in the next
four biostratigraphic units recognized in Section KK.

Ordovician

Winston and Nicholls (1967) proposed the Missisquoia Zone as a basal Ordovician
biostratigraphic unit in the Middle Carbonate Belt of central Texas and recognized a
succeeding Symphysurina Zone (first defined by Hintze, 1953 in Nevada and Utah).
These zones were also recognized in similar rocks of Oklahoma by Stitt (1971b) who
later (Stitt, 1977) redefined the base of the Symphysurina Zone and divided the zones
into two subzones each; from base to top, Missisquoia depressa, M. typicalis,
Symphysurina brevispicata, and S. bulbosa subzones. Both Missisquoia and
Symphysurina occur in the upper Rabbitkettle Formation, but in these dark grey to
black, argillaceous lime mudstones the trilobite assemblages are strongly dominated
by the olenid trilobites Parabolinella and Apoplanias (Figs. 7 and 16). The rocks are
best assigned to the Outer Detrital Belt of Palmer (1960a) and the faunas are
Suggestive of Cambrian and Ordovician assemblages known from shallow settings at
high palaeolatitude sites or from deep settings at low palaeolatitude sites (Taylor,
1977). A Parabolinella Zone with three divisions is proposed for the lowermost

Ordovician rocks of the Rabbitkettle Formation at Section KK. This zone appears to
be the Outer Detrital Belt equivalent of the Missisquoia Zone. The Parabolinella
Zone holds promise as a biostratigraphic index for basal Ordovician rocks in
shelf-edge or off-shelf localities where Missisquoia is rare or absent. A single poorly
preserved free cheek of Symphysurina cf. brevispicata Hintze above the
Parabolinella Zone indicates the presence of the Symphysurina Zone in the higher
beds of the Rabbitkettle Formation.

Parabolinella Zone (60 m—25 m of composite Section KK)

Parabolinella is a common to very abundant trilobite through a 17 m interval of the
upper Rabbitkettle Formation at Section KK. The abundance 1s locally quite

INDET.

COMPOSITE
OSECTION KK
METEORASP/S ?
"CALVINELLA”
EUPTYCHASPIS
RHAPTAGNOSTUS
HETEROCARYON
LE/OCORYPHE
GERAGNOSTUS
TATONASPIS
PSEUDAGNOSTUS
TRIARTHROPSIS
LIOSTRACINOIDES
PLETHOMETOPUS
BIENVILLIA
PARABOLINITES
M/SSISQUOIA
PARABOLINELLA
PT YCHOPLEURITES
LEVISASPIS

EULOMA
SYMPHYSUR/INA

KATHLEENELLA
ELKANASP/S
EUREKIA
YUKONA SP/S
NAUSTIA
SAUKIID
CERATOPYGID
IDIOME SUS
LARIFUGULA
BOWMANI/A
APOPLANIAS

ORDOVICIAN i: is

YUKONASPIS

cawarian] ||| Hl

Fig. 8 Stratigraphic ranges of 31 trilobite genera in composite Section KK.

remarkable. Nearly 500 cranidia of Parabolinella cf. prolata were recovered from
four collections of the Missisquoia depressa Subzone (see Fig. 16). The
Parabolinella Zone is established for the interval from the base of the Missisquoia
mackenziensis Fauna to the base of the Symphysurina Zone; that is, from the first
occurrence of Parabolinella to the first occurrence of Symphysurina cf. brevispicata.

The Parabolinella Zone is dominated by species of Parabolinella, Geragnostus,
Missisquoia, Ptychopleurites , and Apoplanias. Other genera are rare. Plethometopus ,
Parabolinites , and Levisaspis have been recovered from one or two collections each.
The Parabolinella Zone is undoubtedly largely correlative with the Missisquoia
Zone. The two zones share a Missisquoia depressa Subzone in their lower parts, both
contain Apoplanias rejectus in their upper parts, and both are overlain by the
Symphysurina brevispicata Subzone of the Symphysurina Zone. The lower boundary
of the Parabolinella Zone may be slightly older than the base of the Missisquoia
Zone. The Missisquoia mackenziensis Fauna, the lowest fauna of the Parabolinella
Zone, is not known from Oklahoma where the Missisquoia Zone starts with the
Missisquoia depressa Subzone, but it could well be represented in the | or 2m
unfossiliferous interval between the Saukia and Missisquoia Zones in the Arbuckle
and Wichita mountains.

A tripartite division of the Parabolinella Zone is proposed below and is shown
diagrammatically in Fig. 9.

Missisquoia mackenziensis Fauna (60 m-57 m of composite Section KK). Two
collections from the lowest few metres of the Parabolinella Zone in the Rabbitkettle
Formation are dominated by species of Parabolinella, Geragnostus, and Missis-
quoia. This is the Missisquoia mackenziensis Fauna which contains the following
Species.

+ Geragnostus (Micragnostus ) subobesus (Kobayashi)
Missisquoia mackenziensis sp. nov.
— Parabolinites cf. williamsoni (Belt)
Parabolinella panosa sp. nov.
+ Parabolinella cf. prolata Robison and Pantoja-Alor
— + Plethometopus obtusus Rasetti

This association of mainly new species cannot be correlated to other faunal
successions in the Cambrian-Ordovician boundary interval in North America. It has
greater affinity for younger faunas than for older faunas and its occurrence above the
Yukonaspis Zone and below the Missisquoia depressa Subzone (previously
considered the basal biostratigraphic unit of the North American Ordovician; Stitt,
1977) suggests that the Missisquoia mackenziensis Fauna is the oldest Ordovician
trilobite fauna discovered so far on this continent.

Missisquoia depressa Subzone (57 m-44 m of composite Section KK). The next
13 m of the composite section comprise the Missisquoia depressa Subzone of the
Parabolinella Zone. This subzone is defined in the same manner as is the Missisquoia
depressa Subzone of the Missisquoia Zone in Oklahoma (Stitt, 1977); that is, from
the first occurrence of M. depressa to the first occurrence of Apoplanias rejectus . The
following species characterize this subzone:

— Geragnostus (Micragnostus ) subobesus (Kobayashi)
Levisaspis glabrus (Shaw)
Missisquoia depressa Stitt
Parabolinella hecuba (Walcott)
— Parabolinella cf. prolata Robison and Pantoja-Alor
— Plethometopus obtusus Rasetti
Ptychopleurites brevifrons (Kobayashi)

This subzone shares Missisquoia depressa and Ptychopleurites brevifrons with the
M. depressa Subzone of Oklahoma (Stitt, 1977) and P. brevifrons and Geragnostus
(Micragnostus) subobesus with the Ptychopleurites Fauna of east-central Alaska
(Kobayashi, 1936a) and it is certainly correlative with these two biostratigraphic units
(Fig. 9). The presence of Missisquoia depressa (see Systematic Palaeontology) and a
species of Geragnostus (Micragnostus ) that is very similar to G. (M.) subobesus in
the Fengshan Formation of Hopeh Province, China suggests that the Mictosaukia
orientalis Assemblage of Zhou and Zhang (1978) is of Early Ordovician age and
correlative with the M. depressa Subzone of North America. The Parabolina
assemblage in the lower Tinu Formation of southern Mexico (Robison and
Pantoja-Alor, 1968) contains Parabolinella prolata, P. hecuba, and a species of
Mictosaukia. This assemblage may also be correlative to the M. depressa Subzone.

Apoplanias rejectus Fauna (44 m-25 m of composite Section KK). Two
collections above the Missisquoia depressa Subzone in the Rabbitkettle Formation
have yielded low diversity olenid assemblages. The Apoplanias rejectus Fauna is
defined. from the first occurrence of pA. rejectus. to the first) occuttence:*ot
Symphysurina cf. brevispicata. Only two species occur in this fauna.

+ Apoplanias rejectus Lochman
Parabolinella sp.

Apoplanias rejectus is a scarce trilobite in the Missisquoia typicalis and
Symphysurina brevispicata subzones of Oklahoma (Stitt, 1971b, 1977). In the
Rabbitkettle Formation, A. rejectus occurs in both the A. rejectus Fauna and the
Symphysurina brevispicata Subzone. A correlation of the A. rejectus Fauna with the
M. typicalis Subzone is proposed. A. rejectus also occurs a few metres above Saukia
Zone trilobites in the subsurface Deadwood Formation of Montana (Lochman, 1964a)
and in the Basal Silty Member of the Survey Peak Formation of Alberta (Dean,
1978). Lochman (1964a) defined an A. rejectus faunule for the occurrences in
Montana. This faunule is, at least in part, correlative with the A. rejectus Fauna.

Symphysurina Zone (25 m—O m of composite Section KK)

I follow Stitt’s (1977: 32) definition of the base of the Symphysurina Zone in placing
this boundary at the first occurrence of Symphysurina cf. brevispicata Hintze. Only a
single collection from high in the Rabbitkettle Formation is assigned to this zone.
This collection differs markedly from other Symphysurina Zone assemblages in being
dominated by olenid trilobites of the genus Apoplanias and by lacking hystricurine
trilobites.

Symphysurina brevispicata Subzone (25 m of composite Section KK). A single
collection 25 m below the top of the Rabbitkettle Formation is assigned to the
Symphysurina brevispicata Subzone. Only two species occur in this fauna, in
addition to very poorly preserved specimens of Geragnostus.

— Apoplanias rejectus Lochman
Symphysurina cf. brevispicata Hintze

These trilobites are generally poorly preserved, but the assemblage is very similar
to those of the more diverse Symphysurina brevispicata Subzone of Oklahoma (Stitt,
1977) and the Rabbitkettle collection is confidently assigned to that subzone.

Note on Construction of Composite Section KK

An unnamed thrust located 102 m below the top of the Rabbitkettle Formation at
Section KK repeats a 58 m interval of the upper part of the formation such that the
interval KK 102 to KK 160 of the foot wall is duplicated by the interval KK 44 to
KK 102 of the hanging wall. The repetition of strata was initially suspected in the
field in 1977 by the repeat of the 15 m thick wavy banded unit above a thin recessive
interval at KK 120 and KK 60 (Fig. 4). The field observations were later
corroborated when it was determined that the Bowmania americana Fauna, the
Elkanaspis corrugata Fauna, the Missisquoia depressa Subzone, and the Apoplanias
rejectus Fauna occur in both the hanging and foot walls of the thrust (Fig. 6). The
Yukonaspis kindlei Fauna occurs only in the foot wall and the Symphysurina
brevispicata Subzone only in the hanging wall. The thin Missisquoia mackenziensis
Fauna was recovered only from the foot wall; the correlative beds in the hanging wall
(between KK 56 and KK 64) were not sampled.

A correlation of the foot and hanging walls of the thrust permits the compilation of
a composite Section KK (Fig. 7). The trilobite biostratigraphy and the trilobite
occurrences in the section on Systematic Palaeontology are keyed to this composite
section. Thus, the 240-m-thick Section KK as originally measured (Fig. 5) is reduced
to a true stratigraphic thickness of about 180 m (Fig. 7).

Cambrian-Ordovician Boundary

In North America, the base of the Ordovician System has traditionally been placed at
the base of the Canadian Series (Twenhofel, 1954). More recently, the base of the
Canadian Series has been specified to occur at the base of the Missisquoia depressa
Subzone, the lower subzone of the Missisquoia Zone in Oklahoma (Stitt, 1977). The
Canadian Series, however, can be interpreted to be based either on the Levis
Formation, near Quebec City, or on the ‘‘Calciferous Sandrock’’ (Beekmantown
Group) of New York State and eastern Quebec (see Fahraeus, 1977: 982, 983).
Neither of these stratigraphic units includes a Missisquoia Zone at its base. The Levis

Formation (Tremadocian? and Arenigian) is part of the Taconic Allochthon and
nowhere is it seen in conformable contact with Upper Cambrian rocks and the
Beekmantown Group has recently been revised downward to include lower Upper
Cambrian rocks of the Potsdam Formation (Fisher, 1977: 37, 38). In eastern New
York State, the Missisquoia Zone in the Whitehall Formation (Taylor and Halley,
1974) occurs well up in the Beekmantown. Therefore, the base of the Canadian Series
(if based on the Beekmantown) falls well below the base of the Ordovician as defined
in Oklahoma and Texas by Stitt (1977) and Winston and Nicholls (1967). The
Canadian cannot be used as a lower series of the Ordovician System in North
America.

In Europe and elsewhere, the base of the Ordovician has been drawn variously at
the base of the Arenigian Series, at the base of the ‘‘Upper Tremadocian’’ Series, or
at the base of the Tremadocian Series (Henningsmoen, 1973). The base of the
Tremadocian has become the most widely used level and that is herein accepted to
constitute the extra-North American base of the Ordovician.

Over the past decade, the base of the Tremadocian has been correlated to a number
of horizons within the North American Upper Cambrian and Lower Ordovician
faunal succession. These include (1) the base of the Saukia Zone (Wolfart, 1970:
Whittington and Hughes, 1974), (2) the base of the Corbinia apopsis Subzone of the
Saukia Zone (Stitt et al., 1976; Jaanusson, 1979), (3) the base of the Missisquoia
depressa Subzone of the Missisquoia Zone (Landing et al., 1978), and (4) near the
base of the Symphysurina Zone (Fortey and Skevington, 1980). I concur with the
conclusion of Jaanusson (1979: 138) that, “‘the overlap between the Tremadocian and
the Trempealeauan, if present at all, seems to be inconsiderable’’ and suggest that the
base of the Tremadocian Series correlates to a horizon close to the base of the
Missisquoia Zone.

In the type area of the Tremadocian at Harlech Dome in north Wales, the contact of
the Tremadoc Slates with the underlying Dolgelly Beds is everywhere marked by an
unconformity, or it is a fault contact (Cowie et al., 1972; Henningsmoen, 1973).
Only two unfaulted basal contacts were known to Stubblefield (1956: 37). At the
more complete of these, at Ogof-ddu east of Ciccieth, the basal Tremadoc is marked
by a bed of phosphate nodules followed by 6 m of striped mudstones with sporadic
Dictyonema flabelliforme sociale below the main D. f. sociale ‘*‘Band’’. The
underlying Dolgelly Beds contain trilobites of the Peltura scarabaeoides and other
zones (Rushton, 1974: 67).

Because the Dictyonema flabelliforme Zone in northern Wales has few trilobites, it
is necessary to employ a reference section in order to relate the graptolite
biostratigraphy of the Lower Tremadocian in the type area to the olenid trilobite
biostratigraphy of the Lower Tremadocian of Europe and parts of North America.
The thick Tremadocian section at Rio Santa Victoria, Province of Salta, northern
Argentina is such a section. According to the data presented by Harrington and
Leanza (1957: 8, 9, fig. 2), the 725-m-thick Parabolina argentina Zone is dominated
by Jujuyaspis keideli Kobayashi and Parabolinella argentinensis Kobayashi. These
two Species enter 255 m above the base of the zone and are followed some 15 m
higher by Dictyonema flabelliforme sociale and D. f. flabelliforme. These data
suggest that the base of the Tremadocian in the Rio Santa Victoria section should be
drawn at the 255 m level at the appearance of J. keideli and P. argentinensis and not
at the base of the P. argentina Zone as proposed by Harrington and Leanza (1957).

The 255 m level in the Parabolina argentina Zone provides a useful reference for
the base of the Tremadocian; one that can be correlated closely to the succession in
northern Europe because Jujuyaspis keideli occurs with D. f. sociale and D. f.
parabola near the base of the D. flabelliforme Zone at Oslo (Henningsmoen, 1957:
264). It may also be correlated to the Mexican succession because Parabolinella
argentinensis, P. prolata Robison and Pantoja-Alor, and P. hecuba (Walcott) occur
with Parabolina cf. argentina (Kayser) and Mictosaukia in the Parabolina
Assemblage of the Tinu Formation of southern Mexico (Robison and Pantoja-Alor,
1968, figs. 2-4).

Parabolinella does not occur at or near the base of the Tremadocian in northern
Europe (Henningsmoen, 1957), but three observations suggest that this widespread
olenid genus has potential as a contributor to the definition of the Cambrian-
Ordovician boundary: (1) a species of Parabolinella appears just below the first
occurrence of D. flabelliforme in Argentina, (2) four species of Parabolinella occur
in Lower Tremadocian rocks of southern Mexico, and (3) species of Parabolinella
have never been definitely identified in pre-Tremadocian rocks. The supposed
Cambrian occurrences of this genus from North America cited by Henningsmoen

OKLAHOMA EASTERN
= % DISTRICT OF MACKENZIE Arbuckle ALASKA VERMONT
ate Broken Skull River and Wichita Jones Ridge Highgate
aS Mountains Squaw Mtn. Falls

TRILOBITES CONODONTS

SYMPHYSURINA
BULBOSA

Subzone

SYMPHYSURINA
BREVISPICATA
Subzone
MI/SSISQUOIA
TYPICALIS
Subzone
MI/SSISQUOIA
DEPRESSA

Subzone

SYMPHYSURINA
BREVISPICATA
Subzone
APOPLANIAS
REJECTUS
Fauna

MISSISQUOIA CORDYLODUS
DEPRESSA OKLAHOMEN S/S

Subzone Tare

TREMADOCIAN

MISSISQUOIA | ( Undivided )
MACKENZIENSS 8

CORB/INIA
APOP S/S

Subzone

ELKANASP/S
CORRUGATA

Fauna

SAUKIELLA
SEROTINA

BOWMAN/A
AMERICANA

Fauna

Assemblage

PROCONODONTUS
Zone

( Undivided )

SAUKIELLA
JUNIA TREMPEALEAUAN-2

Subzone Fauna

YUKONA SP/S
KINOL E/
Fauna

TREMPEALEAUAN
YUKONASP/S Zone

HUNGATA

(ZONE 1)

CAMBRIAN ORDOVICIAN

THIS PAPER LANDING et al.
(1980) So sritt (1971,1977 ) KOBAYASHI(19360) payMOND (1924,1937) ,
PALMER (1968 ) SHAW(1951),

GILMAN CLARK and
SHAW (1968)

Fig. 9 Correlation of biostratigraphic successions across the Cambrian-Ordovician boundary in the
District of Mackenzie, Oklahoma, Alaska, and Vermont. Correlation of the Hungaia
assemblage is largely based on conodont biostratigraphy by Landing (1978, 1979).

(1957: 133) have either been wrongly dated or been based on species that since have
been reassigned to other genera (see also Landing et al., 1978).

Most previous investigators have defined the Cambrian-Ordovician boundary in
North America at the base of the Missisquoia Zone (Winston and Nicholls, 1967;
Stitt, 1971b; Derby et al., 1972); specifically at the base of the Missisquoia depressa
Subzone of the Missisquoia Zone (Stitt, 1977; Hintze et al., 1980). This subzone has
been recognized with certainty only in two stratigraphic sections in Oklahoma; one in
the Arbuckle Mountains and one in the Wichita Mountains (Stitt, 1971b, 1977).
Here, the base of the M. depressa Subzone lies 1.2 m and 1.8 m above the highest
occurrence of Corbinia apopsis Subzone trilobites. Hintze et al. (1980) reported the
M. depressa Subzone from a single collection in western Utah. Here, the base of the
M. depressa Subzone lies 1.5 m above the highest occurrence of C. apopsis. Thus, in
Oklahoma and Utah, the initial appearance of Missisquoia is at the base of the M.
depressa Subzone, a metre or two above the highest occurrence of such ‘*‘Cambrian”’
genera as Corbinia, Idiomesus , Larifugula, and Triarthropsis . Parabolinella does not
occur in the Oklahoma and Utah sections, but in Vermont, central Texas, and Nevada
(Shaw, 1951; Winston and Nicholls, 1967; Taylor, 1976) this genus first appears in
the Missisquoia Zone.

Section KK through the upper part of the Rabbitkettle Formation contains abundant
representatives of both Missisquoia and Parabolinella, including M. depressa, P. cf.
prolata, and P. hecuba. In this section, the base of the Missisquoia depressa Subzone
of the Parabolinella Zone corresponds neither to the first appearance of Missisquoia
nor to the first appearance of Parabolinella. In the foot-wall portion of Section KK,
Missisquoia first appears immediately above the base of the ‘‘Hystricurid’’ Biomere
at the base of the E/kanaspis corrugata Fauna of the Yukonaspis Zone (13.5 m below
the first occurrence of M. depressa) and Parabolinella first appears at the base of the
Missisquoia mackenziensis Fauna of the Parabolinella Zone (3.5 m below the first
occurrence of M. depressa). The multi-element conodont species Cordylodus
oklahomensis (senior synonym of the form species C. proavus; Landing et al., 1980)
first appears high in the Elkanaspis corrugata Fauna (4.5 m_ below the first
occurrence of M. depressa).

The important first and last faunal appearances in the Cambrian-Ordovician
boundary interval of the foot-wall portion of Section KK are shown in Table 1.

The chief drawback to a definition of a systemic boundary at the base of the
Missisquoia depressa Subzone is the difficulty posed by attempts at inter- and
intra-continental correlation. This boundary cannot be correlated directly with
trilobite successions in Europe (Landing et al., 1978) and, on this continent, it can be
specified only in four sections—two in Oklahoma and one each in Utah and the
District of Mackenzie. By changing the criterion for recognition from that of the
lowest occurrence of Missisquoia at the base of the Missisquoia Zone to that of the
lowest occurrence of Parabolinella at the base of the Parabolinella Zone, it is
possible to improve the correlation potential of this horizon with only a very minor
change in its actual placement. Stitt (1977: 26) defined the base of the M. depressa
Subzone at the first occurrence of M. depressa Stitt, Plethopeltis arbucklensis Stitt,
and Ptychopleurites brevifrons (Kobayashi). In the District of Mackenzie, such a
level defines the upper boundary of the 3-m-thick Missisquoia mackenziensis
Fauna—a biostratigraphic unit that includes both Missisquoia and Parabolinella. A
boundary located at the first appearance of Missisquoia mackenziensis sp. nov.,

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Parabolinella cf. prolata Robison and Pantoja-Alor, P. panosa sp. nov., and
Geragnostus (Micragnostus) subobesus (Kobayashi) at the base of the M.
mackenziensis Fauna, the lowest division of the Parabolinella Zone, is very close to
the commonly accepted base of the North American Ordovician and it has the
advantage of being correlatable to a level at, or close to, the base of the Tremadocian
in the Rio Santa Victoria section in Argentina. The base of the Parabolinella Zone
also corresponds to the highest occurrence of such *‘Cambrian’’ genera as Larifugula,
Idiomesus , Yukonaspis, and Eurekia.

I suggest that the base of the Dictyonema flabelliforme Zone and the base of the
Parabolinella Zone are closely correlative and, in combination, these define an
operational base to the Tremadocian Series and the Ordovician System.

Lithofacies and Environment

The upper Rabbitkettle Formation at Section KK is, at first glance, remarkably
uniform. It is a platy bedded to medium bedded unit of grey limestone with thin, buff,
yellow, brown, or brick-red weathering silty and argillaceous partings. These impart
a pronounced banded aspect to the outcrops. Despite the platy nature of many of the
beds, the unit weathers massive (Fig. 10A). The only apparent differentiation in the
180 m of strata at composite Section KK is a lower 120 m unit of planar banded
limestone and an upper 60 m unit of undulose banded limestone (Fig. 5).

The impression of uniformity of these strata was quickly dispelled when the
limestones were examined in thin sections, by acetate peels and in polished hand
samples. Such investigations demonstrated that major textural and colour changes
correspond to changes in trilobite composition and a study of the carbonate rock
textures was undertaken in order to get a fuller picture of the environmental
significance of the rocks and the faunas.

Below, the textures of the limestones in four segments of composite Section KK
are discussed. The boundary coincidence of the lithofacies segments and the trilobite
biostratigraphic divisions demonstrate that the benthic trilobite associations dealt with
in this paper are packages of taxa whose composition and relative abundance are
controlled by both environmental and temporal factors. This conclusion, of course,
provides constraints on the use of these faunas (and, indeed, most other trilobite
biostratigraphic units) in correlation.

180 to 96 m of Composite Section

The most commonly encountered lithology in the lower part of Section KK is light to
medium grey lime mudstones and wackestones that are finely interbedded with
yellow-brown laminated silty layers (Fig. 10B). The lime mudstone/ wackestone beds
are a few centimetres thick and typically discontinuous laterally. They are terminated
at near-vertical incursions or by broad waves of the laminated silt-rich layers. These
mud supported limestones generally lack internal features, but occasionally show
vague parallel laminations and rare horizontal burrows. This lithofacies apparently

records deposition on the seaward side of a carbonate shoal in water depths exceeding
that of effective wave base. In the Rabbitkettle Formation, this lithofacies yielded
only a few trilobites. Most of the silicified trilobites of the Yukonaspis kindlei Fauna
came from irregularly interbedded 5- to 10-cm-thick beds of light grey to medium
grey lime grainstone or packstone in which the major allochems are trilobites,
pelmatozoan ossicles, and ooids. Some of these grain-supported allochem limestones
show crude grading (Fig. 12A) and they were probably deposited by non-turbid
traction currents which periodically swept off the higher parts of the carbonate shelf.

Fig. 10 Outcrop photographs of the upper Rabbitkettle Formation at Section KK.

A Upper Cambrian part of Rabbitkettle. Dotted line separates the Yukonaspis kindlei Fauna
below from the Bowmania americana Fauna above. Location of photograph in Fig. 10B is
indicated by ‘‘b’’. Figure in left centre provides scale.

B Thinly bedded medium grey lime mudstones separated by yellow-brown finely laminated
silty layers. About 50 cm of strata are shown. Yukonaspis kindlei Fauna.

96 to 70 m of Composite Section

The silty lime mudstone/wackestone facies which dominates the lower part of
Section KK persists into higher rocks carrying the Bowmania americana Fauna, but
here the facies assumes a Subordinate role. The bulk of this 26 m interval comprises
medium to thick bedded, dove-grey, porcelaneous, burrowed, and pelletoid lime
wackestones with wispy silt laminations (Figs. 12B, 14). Such a facies suggests
deposition on an open, low-relief shelf in quiet, moderately shallow, and
well-oxygenated water below effective wave base. Similar burrowed lime
wackestone facies have been described from the Nevada/ Utah area, in lower
Dresbachian strata by Lohmann (1976), and in lower Franconian strata by Brady and
Rowell (1976). In the Mackenzie Mountains, the burrowed lime wackestone facies
forms the top of the Ptychaspid Biomere; in Nevada/ Utah, it occurs at the top of the
Marjumiid Biomere and at the top of the Pterocephalid Biomere.

70 to 57 m of Composite Section

At the 70 m level in composite Section KK, at the base of the E/kanaspis corrugata
Fauna, the grey burrowed lime wackestone facies is replaced sharply by a sequence of
thinly bedded, dark grey to black, non-burrowed lime mudstones and finely
laminated clay and silt-rich layers. Many of these beds display sedimentary
boudinage (Figs. 11B, 13D) and most of the lime mudstones have vague parallel
laminations (Fig. 12C). The striking colour change between the Bowmania americana
interval and the EF. corrugata interval is best appreciated in polished hand samples
(Fig. 14). The black laminated mudstone facies was deposited in waters that were
deeper, colder, or less oxygenated than were the underlying lithofacies and it 1s best
assigned to the Outer Detrital Belt of Palmer (1960a). A similar dark grey to black
laminated lime mudstone facies was described from lower Dresbachian strata of
Nevada/ Utah by Lohmann (1976). The black laminated mudstone facies of the upper
Rabbitkettle Formation is also very similar to the autochthonous slope lithofacies of
black, shaly lime mudstone and wackestone described by Taylor and Cook (1976)
and Cook and Taylor (1977) from the Franconian and Trempealeauan Hales
Limestone of Nevada.

Fig. 11 Outcrop photographs of the upper Rabbitkettle Formation at Section KK.

A Uppermost Cambrian and lower Ordovician parts of Rabbitkettle. View is across unnamed
thrust fault (white dotted line) that repeats Cambrian-Ordovician boundary at base of
Parabolinella Zone (dashed double line). Location of photographs in Figs. 11B and I 1c is
indicated by *‘b’’ and ‘‘c’’.

B Thinly bedded dark grey to black lime mudstones and laminated silty layers (note
sedimentary boudinage). Hammer in Fig. 11c provides scale. Elkanespis corrugata Fauna.

c Rubbly bedded dark grey lime mudstones. Missisquoia depressa Subzone.

base of

Lt
7
Wy
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aq
a

a)
=
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—N

57 to 0 m of Composite Section

The higher parts of the upper Rabbitkettle Formation at Section KK, assigned to the
Missisquoia depressa Subzone to Symphysurina brevispicata Subzone, consist of a
series of medium to thin beds of dark grey, broadly laminated lime mudstones
separated by thin undulose silty and argillaceous laminae (Figs. 11C, 13). In places,
adjacent silty laminae meet to produce irregular boudins. Like the underlying facies,
the undulose lime mudstone facies is best assigned to the Outer Detrital Belt. It is
similar in many respects to the silty lime mudstone/wackestone facies occurring in
the lower part of the upper Rabbitkettle, but it differs consistently by being darker in
colour, by having thicker and irregular nodular bedding, by lacking burrows, by
lacking grain-supported allochem limestones, and by containing abundant, in situ
trilobites. In this lithofacies the silicified trilobites are found in both the silty laminae
and in the dark mudstone.

Conclusion

The 180 m composite section through the upper Rabbitkettle Formation records
finely alternating carbonate mud and terrigenous silt deposition on the seaward side of
the broad Mackenzie Platform and adjacent to the Selwyn Basin (Fig. 3). With the
exception of occasional thin beds of grainstone and packstone low in the section, lime
sands are absent, suggesting a depositional setting far removed from high-energy
carbonate shoal complexes. Despite the occurrence of dark lime mudstones of slope
aspect in the upper part of the composite section, no portion of the upper Rabbitkettle
is judged to have been deposited on the slope. Typical slope features are found in the
Road River Formation, depositionally seaward of the Rabbitkettle Formation (Fig. 3;
Cecile, 1978).

A similar sequence of lithofacies has been documented by Lohmann (1976) for
platform-margin and deep platform settings in the lower Dresbachian interval of the
Great Basin of Nevada and Utah. Lohmann outlined a platform-margin, high energy
complex of grainstone and packstone, in part stromatolitic and oolitic, deposited
above wave base, and a deep platform, low energy complex composed of three,
progressively deeper, lithofacies: a burrowed wackestone lithofacies, a nodular
mudstone lithofacies, and a laminated mudstone lithofacies. By correlating the tops
of shallowing-upward cycles across the platform margin and by assuming comparable
sediment compaction in sand and mud-size sediment, Lohmann was able to estimate
palaeoslopes of 0.3 to 2.4 m/km for this portion of the shelf and water depths for
each of the lithofacies. He concluded that the high energy complex of grainstones and
packstones accumulated in waters shallower than 15 m and that the low energy
complex of mudstones and wackestones accumulated below effective wave base from
15 m to greater than 30 m. Of particular importance is Lohmann’s conclusion that a
lithofacies such as the black laminated mudstone facies, generally considered to be
‘deep water’’, could have been deposited in water depths not much greater than
30 m.

If the water depths estimated for similar, and presumably environmentally
correlative, lithofacies in Nevada/Utah are used as guides, then it is possible to
propose tentative palaeobathymetries for the two main lithofacies segments of the

esis
es

VAR) wa mete AE

Fig. 12 Negative prints of acetate peels of limestones from the upper Rabbitkettle Formation. All are cut
perpendicular to bedding with the exception of Fig. 12B which is cut parallel to bedding. Bar
represents | cm. Arrow indicates stratigraphic top.

A Trilobite-rich lime grainstone/packstone showing crude grading. Yukonaspis kindlei
Fauna, K 525.

B Burrowed lime wackestone. Bowmania americana Fauna, KK 156.
Cc Broadly laminated lime mudstone. El/kanaspis corrugata Fauna, KK 64.

D Lime mudstone with sedimentary boudinage; light-coloured and laminated bands are
clay-rich. Missisquoia mackenziensis Fauna, KK 122.5.

ra |

Fig. 13. Negative prints of acetate peels of limestones from the upper Rabbitkettle Formation. All are cut
perpendicular to bedding. Bar represents 1 cm. Arrow indicates stratigraphic top.
A,B Wavy bedded lime mudstones with clay-rich seams. Missisquoia depressa Subzone,
KK 119.5 and K 880.
Cc Wavy bedded lime mudstone with clay-rich seams. Apoplanias rejectus Fauna, KK 106.
D Lime mudstone. Symphysurina brevispicata Subzone, KK 25.

— 44m—

MISSISQUOIA
DEPRESSA

Subzone

ed 7 i,

MISSISQUOIA
MACKENZIENS/5

Fauna

ORDOVICIAN

Ser OM

“HYSTRICURID ” BIOMERE

ELKANASPIS
CORRUGATA

Fauna

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BOWMANIA 2 S
AMERICANA || ©
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96 m—— a.

Fig. 14 Lithologic, textural, and colour spectra across the Ptychaspid-‘*Hystricurid’’ Biomere boundary
and the Cambrian-Ordovician boundary displayed by selected polished and oiled hand samples
cut perpendicular to bedding. Sample from B. americana Fauna is a dove-grey, burrowed, and
thickly bedded lime wackestone deformed by steeply dipping tension fractures. Samples from E.
corrugata Fauna and higher intervals comprise dark grey to black, nonburrowed, crudely
laminated, and thinly and irregularly bedded lime mudstones.

upper Rabbitkettle Formation at Section KK. The light to medium grey and burrowed
lime mudstone and wackestone facies with minor grainstone or packstone beds in the
lower part of the composite section (180-70 m) were probably deposited in water
depths of 15 to 30 m and below wave base. This interval is assigned to the Middle
Carbonate Belt of Palmer (1960a) and it records a gradual shallowing caused by
progradation of the grey burrowed wackestone facies. The dark grey to black and
non-burrowed lime mudstone facies in the upper part of the composite section
(70-0 m) was probably deposited in water depths deeper than 30 m, but probably not
much deeper. This interval is assigned to the Outer Detrital Belt of Palmer (1960a).

Grand Cycle Boundary

Aitken (1966) defined the Grand Cycle as a large scale asymmetric depositional cycle
consisting of a lower shaly half-cycle gradually overlain by an upper carbonate
half-cycle. The lower and upper boundaries are sharp. Grand Cycles are substantial
Stratigraphic units. In the southern Canadian Rocky Mountains, each cycle extends
through 275 to 800 m of strata and Aitken (1978) showed that the Grand Cycle
pattern can be mapped along the Cambrian platform from northern British Columbia
to Utah, a distance of some 2000 km. Aitken (1966) outlined eight Grand Cycles
from Middle Cambrian to Middle Ordovician rocks in the southern Canadian Rocky
Mountains and attributed the cyclicity to regular and periodic shifts of Palmer’s
(1960a) facies belts—the lower shaly half-cycle comprises either the Outer Detrital
(OD) Belt or the Inner Detrital (ID) Belt and the upper carbonate half-cycle comprises
the Middle Carbonate (MC) Belt.

In his recent analysis of Grand Cycle patterns, Aitken (1978: 532, 533, figs. 8, 9)
provided environmental interpretations and lithofacies maps of these cyclical deposits
in the area between Jasper and Salt Lake City. According to this synthesis, the higher
levels of the MC Belt of a Grand Cycle comprise a broad, outer peritidal carbonate
complex which expands cratonwards by progradation and a narrow, inner subtidal
carbonate mud lithofacies which grades cratonwards into fine and coarse clastics of
the ID Belt. A rapid transgression drowns all or part of the MC Belt and the
terrigenous muds are distributed by currents across most or all of the previous MC
Belt. These clastics record the initial deposits of the succeeding Grand Cycle. The
supply of terrigenous mud decreases as the transgression continues and carbonate
deposition initiates again on sites near the edge of the platform. To put it simply, the
Grand Cycle records the gradual expansion and rapid contraction (or collapse) of the
MC Belt.

In the well-studied stratigraphic succession at Sunwapta Pass, Jasper National
Park, Aitken (1966) placed the base of a Grand Cycle at the appearance of recessive
Shales and calcareous siltstones (ID Belt) of the Survey Peak Formation above
thick-bedded limestones with large domal stromatolites (MC Belt) of the Mistaya
Formation. Here, the base of the Survey Peak corresponds to the base of the Corbinia
apopsis Subzone of the Saukia Zone (Dean, 1978).

The sharp vertical juxtaposition of the MC Belt and the OD Belt in the upper
Rabbitkettle Formation that was documented previously invites comparison with the
Grand Cycle pattern. At the 70 m level in composite Section KK, grey burrowed

wackestones of the MC Belt are abruptly succeeded by dark grey to black,
non-burrowed lime mudstones of the OD Belt. This level is concluded to be a Grand
Cycle boundary (Fig. 14). The base of the Grand Cycle in Section KK corresponds to
the base of the Elkanaspis corrugata Fauna of the Yukonaspis Zone and is
synchronous with the base of the Grand Cycle in the Sunwapta Pass section (Fig. 9).
It is reasonable to suppose that the grey limestones of the upper Mistaya and the upper
Rabbitkettle are parts of the same continous MC Belt and that the distinct lithologic
aspects of these carbonate units reflect merely different palaeobathymetric
positions—the upper Mistaya was part of the carbonate shoal complex and the upper
Rabbitkettle (between 180 and 70 m of the composite section) was deposited in
deeper water on the seaward side of such a complex. The rapid deepening at the
Grand Cycle base will result in different lithologic records at different positions along
this palaeobathymetric profile. In the southern Rocky Mountains the stromatolitic
limestones of the Mistaya Formation are succeeded by shales and siltstones of the
Survey Peak Formation (ID Belt); whereas in the Mackenzie Mountains the lime
wackestones of the Rabbitkettle Formation are succeeded at the 70 m level by dark
lime mudstones (OD Belt). A single Grand Cycle boundary, therefore, will be of the
ID/MC type on the shallow platform margin and of the OD/MC type on the deep
platform.

Aitken (1978) proposed that the cyclicity pattern of Grand Cycles was induced
externally—a rapid transgression causing a shift from carbonate to fine clastic
deposition. Matti and McKee (1976) and Palmer and Halley (1979: 54, fig. 34) have
proposed alternate models for large scale carbonate-clastic cycles. These two models
differ in detail, but both were presented as largely internally controlled and
self-regulating systems because the cyclicity was interpreted to be a_ natural
consequence of active carbonate production on a slowly subsiding shelf during a
period of a gradual rise in sea level. The Palmer and Halley model may be restated in
a slightly modified format as follows:

a) A shallow subtidal carbonate-producing belt becomes established on a slowly
subsiding shelf which is also receiving a steady supply of terrigenous clastics.
This carbonate factory supports the entire MC Belt and supplies, not only in situ
Sediment to the subtidal zone, but also transported sediment to the peritidal zone
and to the deep shelf as peri-platform ooze (Mcllreath and James, 1978).

—

The MC Belt progrades landward and seaward because carbonate sediments
generally accumulate at a greater rate than subsidence (James, 1977) and
eventually to sea level to form shoal and peritidal carbonate complexes and,
possibly, carbonate islands. These complexes are net consumers of carbonate
sediment.

—

The peritidal and shoal complexes continue to prograde across the shallow
subtidal carbonate factory so that the quantity of carbonate sediment is
diminished. At a critical level, the area occupied by the carbonate factory becomes
too small to maintain the now very broad carbonate platform and, because
subsidence and sea-level rise continues apace, the entire MC Belt either founders
or is displaced and reduced markedly in size.

—

Terrigenous clastics of the ID Belt now spread out across the inner portions of the
MC Belt while dark limestones and shales of the OD Belt encroach upon the outer
portions.

This internally controlled model adequately accounts for the asymmetric cyclicity
of Grand Cycles and, in particular, provides plausible explanations for the
nonuniform lithofacies successions across a single Grand Cycle boundary at different
localities in western North America.

The shut-down of the carbonate factory, coupled with the gradual eustatic sea-level
rise and continued subsidence, results in a moderate deepening across the shelf. On
the outer part of the shelf this deepening could have been sufficient to permit the
spread of cold oceanic and oxygen-poor waters onto the relatively shallow shelf.
Cook and Taylor (1975) and Taylor and Forester (1979) have presented evidence for
the existence of a two-layered thermally stratified ocean in the Lower Palaeozoic—
warm-water thermosphere and cold-water psychrosphere. A Grand Cycle boundary
on the outer part of the shelf, therefore, may Separate warm-water environments,
below, from cold-water environments, above.

The Biomere Concept

The biomere was defined as an Upper Cambrian biostratigraphic unit of stage
magnitude that is bounded by abrupt and diachronous nonevolutionary changes in the
polymerid trilobites and that is characterized by an internal pattern of increasing
Species diversities and increasing Species ranges (Palmer, 1965a,b; Stitt, 1975). This
concept has stimulated considerable interest in recent years, both among
biostratigraphers concerned with correlation of Cambrian rocks and fossils and
among palaeontologists interested in the possible evolutionary implications of such a
closed system of limited stratigraphic extent which is bounded by significant
extinction horizons.

At present, four biomeres have been named. These extend from the late Middle
Cambrian to the Early Ordovician—the Marjumiid, Pterocephaliid, Ptychaspid, and
‘‘Hystricurid’’ biomeres (Fig. 15; Stitt, 1977, figs. 3, 4). Of these, only the
Pterocephaliid and Ptychaspid biomeres have been fully documented (Palmer, 1965b;
Longacre, 1970; Stitt, 1971b, 1977). The upper boundary of the *‘Hystricurid’’
Biomere remains to be defined. Each biomere typically spans 250 m to 350 m of
Strata and each apparently lasted for 5 Ma to 7.5 Ma (Palmer, 1979: 40).

Both Palmer (1965a, 1979) and Stitt (1971b, 1975, 1977) have maintained that
biomere boundaries cannot be located by physical criteria in a rock column because
they are not associated with unconformities or with drastic lithologic changes. This
conclusion was disputed by Johnson (1974) who noted that Palmer’s own (1965b)
data for the base of the Pterocephaliid Biomere showed a lithologic change in each of
10 columnar sections in Nevada and Utah. Moreover, Miller (1978: 16-21) devoted
an entire chapter to a discussion of lithologic changes at the revised base of the
‘*Hystricurid’’ Biomere in North America.

Palmer’s (1965a) contention that the biomere differs from other biostratigraphic
units by its diachronous boundaries was disputed by Henderson (1976) who
maintained that the data for diachrony of the base of the Pterocephaliid Biomere are
not conclusive. In this regard it is important to recognize that all subsequent graphical
depictions have shown biomere boundaries at isochronous zonal boundaries (Stitt,
1977, fig. 4; Palmer, 1979, fig. 1); this suggests that any diachrony of a biomere

boundary cannot be resolved by the available biostratigraphic framework.

A biomere is a biostratigraphic unit and, as such, it comprises a sequence of Strata
which is unified by its fossil content. Its distribution is controlled by temporal,
environmental, and biogeographic factors and, therefore, any explanation of the
biomere pattern must address not only the vertical faunal changes in terms of
composition, diversity, and range, but also lateral and vertical faunal (biofacies) and
lithologic (lithofacies) relationships, as well as possible biogeographic influences.
Previous explanations of the biomere pattern have been based almost exclusively on
the vertical distribution of trilobites in separate measured sections. Biofacies and
lithofacies changes have not been considered. Thus, in the most comprehensive
statement on the biomere pattern to date, Stitt (1975) interpreted the Ptychaspid
Biomere as an adaptive radiation of a single trilobite community (emphasis added).
This radiation, apparently fuelled by increasing environmental stability, came to a
halt as environmental deterioration caused extensive extinction at the biomere top

STAGES/SERIES TRILOBITE ZONES BIOMERES

SYMPHYSURINA
TREMADOCIAN

MISSISQUOIA
TREMPEALEAUAN

“HYSTRICURID”
BIOMERE

LOWER
ORD.

C. apopsis

SAUKIA

ELLIPSOCEPHALOIDE S
FRANCONIAN

TAENICEPHALUS

I. major

PTYCHASPID
BIOMERE

ELVIN/IA

DUNDERBERGIA
PREHOUSIA
DICANTHOPYGE
DRESBACHIAN
APHELASPIS
CREPICEPHALUS
MARJUMIID
A
i eet BIOMERE

BOLASPIDELLA
BATHYURISCUS —
ELRATHINA

Fig. 15 Sequence of upper Middle Cambrian, Upper Cambrian, and lower Lower Ordovician trilobite
zones (based largely on successions in southwestern United States) and boundaries of the four
named biomeres. The lower boundaries of the Ptychaspid and ‘‘Hystricurid’’ Biomeres are
shown as revised by Palmer (1979).

PTEROCEPHALIID
BIOMERE

UPPER CAMBRIAN

MIDDLE
CAMBRIAN

(see also Bretsky and Lorenz, 1970; Ashton and Rowell, 1975; Stitt, 1977; and
Eldredge, 1977 for a concise review).

As Eldredge (1977: 313) noted, ‘‘Stitt’s [(1971a, 1975)] explanatory models of the
ecologic and evolutionary dynamics accounting for biomere patterns are imaginative
but cannot be taken as demonstrated until some more definitive, testable hypotheses
are formulated and tested with the data.’’ Nonetheless, Stitt’s (1975) interpretation of
the biomere as an adaptive radiation which issued from a few ancestral species was
accepted by Stanley (1979: 246-250) who then used Palmer’s (1965b) data for the
Pterocephaliid Biomere to calculate remarkably high rates of diversification for Late
Cambrian trilobites—rates that far exceed those of ammonites, graptoloids, and
mammals (Stanley, 1979, fig. 9-1)! In the face of such anomalously high rates of
diversification, it would seem prudent to critically examine the basic tenet of
monophyly (or pauciphyly) for the species proliferation pattern of the biomere.
Stanley’s calculation of rates of diversification for 27 species of trilobites near the
middle of the Pterocephaliid Biomere was based on the assumption of either a single
ancestral species or aS many as five ancestral species. However, the Pterocephaliid
Biomere includes eight families of trilobites and the Ptychaspid Biomere eleven
families or more and such numbers would seemingly provide a logical estimate for
the minimum numbers of ancestral species. If an adaptive radiation model is to be
applied to the biomere pattern, then the reasonable postulate of as many as ten
ancestral species would bring the rate of diversification of these trilobites more in line
with those of other faunal groups (Stanley, 1979, fig. 9-1).

The concept of the biomere as an in situ adaptive radiation of a single trilobite
community has never been demonstrated, nor has it ever been seriously questioned. A
full critique of this idea is beyond the scope of the present paper, but the faunal and
lithologic spectra across the Ptychaspid-‘‘Hystricurid’’ Biomere boundary at Section
KK, combined with an evaluation of the boundary interval at other localities in
western North America, cast serious doubt on a strict evolutionary interpretation of
the biomere pattern. Instead, these data suggest that each biomere consists of a
succession of biofacies and lithofacies and that the change in faunal diversity and
composition are responses to changes in the environment. The environmental or
facies packages seen in superpositional sequence will, of course, also be expressed
laterally or geographically and, in this context, the biomere emerges as a
manifestation of dynamic biogeography.

Ptychaspid-‘‘Hystricurid’’ Biomere Boundary

Stitt (1975) placed the lower and upper boundaries of the Ptychaspid Biomere at the
base of the Taenicephalus Zone and the base of the Missisquoia Zone, respectively,
and considered the Corbinia apopsis Subzone to be the highest (stage 4) division of
the Ptychaspid Biomere. Palmer (1979) argued convincingly that both of these
boundaries should be lowered slightly to or near the base of the /rvingella major
Subzone and to or near the base of the C. apopsis Subzone, so that the C. apopsis
Subzone becomes the lowest (stage 1) division of the ‘‘Hystricurid’’ Biomere (Fig.
15). Palmer’s relocation of these boundaries placed the biomere concept in a new

light. Stitt’s (1975: 385) final stage of ‘‘evolutionary desperation’’ now becomes an
initial stage of immigration of new taxa and proliferation of old taxa. The biomere
boundary is no longer primarily an extinction level. Furthermore, the base of the
‘*Hystricurid’’ Biomere is now coincident with major changes in the conodonts
(Miller, 1978), as well as coincident with significant lithofacies changes on the outer
parts of the platform.

Palmer (1979: 33) stated that a biomere commences with a brief crisis period
during which rare elements of the soon-to-be-dominant new fauna are associated with
opportunistic bursts of both new and old faunal elements. Applying these criteria to
the faunal record in the upper Rabbitkettle Formation at Section KK, it is clear that
the Elkanaspis corrugata Fauna, the highest division of the Yukonaspis Zone,
constitutes such a crisis interval. The base of this interval is marked by the
disappearance of Bowmania and Kathleenella; the first appearance of Parabolinites ,
Bienvillia, and Missisquoia; minor increase in Idiomesus and Elkanaspis; and
significant increase in Larifugula. Eurekia, Yukonaspis, Geragnostus, and
Plethometopus continue from the underlying Bowmania americana Fauna; the last
two continue into the overlying Parabolinella Zone (Fig. 16).

The base of the Elkanaspis corrugata Fauna is the base of the ‘‘Hystricurid’’
Biomere in Section KK and this level is correlative with the base of the Corbinia
apopsis Subzone which constitutes the base of the ‘‘Hystricurid’’ Biomere in
Oklahoma (Stitt, 1977; Palmer, 1979), Texas (Longacre, 1970), Alberta (Dean,
1978), and Utah (Hintze et al., 1980).

The level defined by the base of the E/kanaspis corrugata Fauna and the base of the
Corbinia apopsis Subzone is not only the base of a biomere, it is also the base of a
Grand Cycle. The boundary coincidence of two major stratigraphic units, one based
on fossils and one based on lithostratigraphy, encourages ecologic and biogeographic
explanations for the biomere boundary events.

The boundary between the Ptychaspid and ‘‘Hystricurid’’ biomeres in the upper
Rabbitkettle Formation can profitably be viewed as a boundary between trilobite
biofacies: a lower biofacies dominated by Bowmania, Kathleenella, and Yukonaspis
that occurs in light to medium grey and burrowed lime wackestones and an upper
biofacies dominated by Larifugula, Parabolinites, and Elkanaspis that occurs in
black and nonburrowed lime mudstones (Fig. 16). The lower biofacies has clear
affinity for associations that lived on the broad Upper Cambrian shelf and the upper
biofacies has characteristics in common with associations that lived on the Upper
Cambrian and Lower Ordovician slope.

The faunal succession across the biomere boundary in Section KK shown in Fig.
16 is very similar to the vertical biofacies transition from the nileid to the olenid
communities in the Lower Ordovician of Spitsbergen (Fortey, 1975, figs. 4, 6) and to
the lateral transition from Biofacies III to IV in the Middle Ordovician of the District
of Mackenzie (Ludvigsen, 1979a, figs. 12, 13). I suggest that the resemblance is
Significant and it implies that there is nothing uniquely Cambrian about the biomere
pattern.

Biofacies and community studies of Late Cambrian benthic faunas in North
America have only just been started. The only study that deals with such biofacies at a
scale appropriate for the present problem is that of Taylor (1977) which defined an
undifferentiated shelf trilobite biofacies for the Inner Detrital (ID) and Middle
Carbonate (MC) belts and two slope biofacies from the outer MC Belt and Outer

Detrital (OD) Belt along a 3000 km transect of Trempealeauan rocks from Wisconsin
to Nevada.

Using Taylor’s (1977, table 3) occurrence data of 41 genera, supplemented by
Stitt’s (1971b, 1977) and Longacre’s (1970) data from Oklahoma and Texas, and the
data from the present study, it is possible to outline approximately the major features
of trilobite biofacies development for the interval immediately below the
Ptychaspid-’’ Hystricurid’’ Biomere boundary. At least four trilobite associations may
be defined for these upper Trempealeauan rocks:

(1) The ID Belt in the upper Mississippi Valley contains abundant dikelocephalid,
saukiid, and eurekiine trilobites. These biofacies are here designated ‘‘di-
kelocephalid associations’’.

(2) The inner MC Belt in Oklahoma and, possibly, Texas and New York State
contain abundant plethopeltid (particularly Stenopilus), eurekiine, euptychas-
pidine, and saukiid trilobites. These diverse biofacies are here designated
‘*plethopeltid-eurekiine associations’ ’.

trilobite
* collections é
2038 Wl lds
Ss Wt
95
15488

“HYSTRICURID”
BIOMERE

ZONE

%
54
KH
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10 x BIOMERE
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15 |
mM
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SS ~
Sar 6 ce gigi ie Si heiizew Gee Gl
SoS S09. See ce. oe SSR ee ce
eek Sue Meiss e, O age f= &€ ay

Fig. 16 Percentage abundances of 19 genera of trilobites across the Ptychaspid-‘*Hystricurid’’ Biomere
boundary in the upper Rabbitkettle Formation at composite Section KK. Open limestone symbol
represents light grey, burrowed lime wackestones; stippled limestone symbol represents dark
grey to black, nonburrowed lime mudstones. Stratigraphic interval extends from the lower
Bowmania americana Fauna to the upper Missisquoia depressa Subzone. Note the expansion of
Larifugula and the appearance of the olenids Parabolinites and Bienvillia immediately above the
biomere boundary.

(3) The outer MC Belt in the District of Mackenzie and, possibly, Nevada and Utah
contains abundant entomaspid (particularly Bowmania), eurekiine, euptychas-
pidine, and kainellid trilobites. These biofacies are here designated ‘‘Bowmania
associations’’.

(4) The OD Belt in Nevada contains olenid, papyriaspid, asaphid, and kainellid
trilobites. These faunas are of Franconian to mid-Trempealeauan age (Taylor,
1976), but they could well extend into the late Trempealeauan. They are included
here under the name ‘‘Hedinaspis associations’’.

The diverse Hungaia faunas, best known from boulders in slope facies of
Trempealeauan age in Quebec and Newfoundland, are not included in this synthesis
because of the uncertain provenance of these transported blocks. They may have been
derived from shelf-edge or upper slope reef mounds, a facies that could have been
widespread in marginal settings around North America (James, 1980).

The interval immediately above the base of the ‘‘Hystricurid’’ Biomere in western
North America includes two associations that are probably attributable to biofacies
developments:

(5) The MC Belt in Oklahoma, Texas, and Utah contains trilobite faunas that are
dominated by the eurekiine Corbinia, but also includes kainellid, kingstoniid (?),
catillicephalid, and plethometopid trilobites. These biofacies are here designated
‘‘Corbinia associations’ ’.

(6) Lithofacies of OD Belt aspect on the outer shelf in the District of Mackenzie
contain trilobite faunas that are dominated by the kingstoniid (?) Larifugula and
the olenid Parabolinites. Minor elements include kainellid, eurekiine, shumar-
diid, and missisquoiid trilobites. These biofacies are here designated ‘‘Larifugula
associations’’.

Faunas from a basal ‘‘Hystricurid’’ Biomere position in the ID Belt are not
definitely known.

Higher levels in the ‘‘Hystricurid’’ Biomere include two contrasting trilobite
biofacies developments:

(7) The MC Belt in Oklahoma, Texas, and Utah contains trilobite faunas that are
strongly dominated by the plethopeltid Plethopeltis and the missisquoilid
Missisquoia. Rare elements include agnostid, leiostegiid, and olenid trilobites.
These biofacies are here called ‘‘Plethopeltis associations’ ’.

(8) Lithofacies of OD Belt aspect on the outer shelf in the District of Mackenzie and
Vermont contain trilobite faunas that are dominated by the olenid Parabolinella,
the agnostid Geragnostus, and by Missisquoia. Minor elements include
plethopeltid, leiostegiid, norwoodiid and, in Vermont, asaphid trilobites. These
biofacies are here called ‘‘Parabolinella associations’ ’.

Each of the eight trilobite associations outlined above comprises one or more
trilobite biofacies. These associations can be placed on a space-time framework along
an Inner Detrital Belt to Outer Detrital Belt transect from the Late Trempealeauan to
the Early Tremadocian (Fig. 17A) and their positions followed across the coincident
biomere and Grand Cycle boundary (Fig. 17B). This way of examining the biomere

boundary events differs from those of previous investigators in that it emphasizes that
migration and extinction are ecologic and biogeographic events that occur in
communities and environments, and not primarily at stratigraphic levels in measured
sections.

During Saukiella serotina Subzone and Bowmania americana Fauna time a
succession of trilobite-dominated assemblages lived on a variety of carbonate and
terrigenous clastic substrates on a broad, warm water shelf about 2000 to 3000 km
wide (Fig. 17A). The shelf extended farther into the marginal shale basin than the
previous time interval because this interval represents the time of maximum
progradation of carbonates near the top of the Grand Cycle (see Aitken, 1978, figs.
8.4 and 9.6 for similar conditions near the tops of older Grand Cycles). This was also
the time of maximum species diversity of trilobites. The bathymetry of this broad
shelf was controlled largely by offshore peritidal and shoal complexes consisting of a
variety of subenvironments which contained the biofacies assigned to the
‘*plethopeltid-eurekiine associations’’. The carbonate shoal complexes formed the
bulk of the MC Belt and they flanked an inshore basin of subtidal and peritidal
carbonate and clastic sediments which contained the ‘“‘dikelocephalid associations’’.
‘‘Bowmania associations’’ occur in subtidal carbonate mud environments seaward of
the carbonate shoal complexes. Carbonate mounds or reefs with Hungaia faunas may
have occupied the same general position. Seaward of the MC Belt occurred dark lime
and terrigenous muds with the ‘‘Hedinaspis associations’’. This slope assemblage
apparently inhabited deep, cold, and poorly oxygenated waters below the thermocline
(Taylor and Cook, 1976).

Cessation of carbonate deposition over large parts of the shelf at the Grand Cycle
top initiated a chain reaction of faunal events which defines the biomere boundary
(Fig. 17B).

During Corbinia apopsis Subzone and Elkanaspis corrugata Fauna time the MC
Belt became much narrower and, possibly, confined to separate and discontinuous
regions. Clastic deposition continued apace, encroached upon the MC Belt from
shoreward and seaward directions, and probably merged in a number of places.

The appearance of terrigenous clastics and lime grainstones in otherwise uniform
lime mudstone successions in the uppermost Cambrian of southwestern United States
was taken by Miller (1978) to be evidence for a short-lived sea-level drop during the
C. apopsis Subzone followed by a sea-level rise during the Missisquoia depressa
Subzone. An alternate explanation of the same data is provided above. The model of
cessation of carbonate deposition and displacement of facies belts that is proposed

Fig. 17 Inferred lithofacies and biofacies developments across the coincident Ptychaspid-‘‘Hystricurid”’
biomere and Grand Cycle boundary in western and southern North America.

A Schematic cross-section of near-shore to off-platform rocks showing position of eight
trilobite associations and three lithofacies belts in the biomere and Grand Cycle boundary
interval. Note size decrease of the Middle Carbonate (MC) Belt at the biomere and Grand
Cycle boundary and mixture of Outer Detrital (OD) Belt and Inner Detrital (ID) Belt
sediments in front of the MC Belt. See text for discussion.

BA series of schematic block diagrams showing positions of lithofacies belts and trilobite
associations for the interval below and above the biomere and Grand Cycle boundary. Note
the spread of OD Belt and ID Belt sediments and the size decrease of the MC Belt in the
basal ‘‘Hystricurid’’ Biomere interval. Positions of key locations are indicated on the upper
block diagram (note that this is not a map). See text for discussion.

SUNWAPTA PASS, UPPER
ALBERTA MISSISSIPPI VALLEY

SECTION KK.2-7 EF.
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E_zaa E2
BS PARABOLINELLA

AND
MISSISQUOIA
TIME

E. CORRUGATA
AND

C. APOPSIS
TIME

SUBTIDAL PERITIDAL & SHOAL

YUKONASP/S
AND
SAUKIA
TIME

OUTER MIDOLE CARBONATE INNER
DETRITAL BELT DETRITAL
BELT BELT

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PARABOLINELLA
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OUTER DETRITAL BELT MIDDLE CARBONATE BELT INNER DETRITAL BELT

here is preferred because it is simpler and, furthermore, strongly supported by the
lithofacies relationships seen at the edge of the platform.

Breaching of the carbonate shoal complexes at the base of the ‘‘Hystricurid’’
Biomere permitted the migration of modified slope biofacies to positions on the
platform and permitted access of deep platform biofacies to the interior portions of the
platform. The ‘‘Larifugula associations’? of the Elkanaspis corrugata Fauna are
amalgams of slope trilobites (Parabolinites, Bienvillia, and possibly Elkanaspis),
‘‘exotic’’ elements (that is, trilobites with an extra-North American origin; possibly
Missisquoia), and elements of the underlying ‘‘Bowmania associations’ (primarily
Larifugula, Yukonaspis, Eurekia, and Idiomesus). The ‘‘Corbinia associations’’ of
the Corbinia apopsis Subzone are amalgams of deep platform trilobites from both the
‘‘Bowmania associations’? and the Hungaia faunas (Larifugula, Liostracinoides ,
Apatokephaloides, and Triarthropsis) and elements of the underlying
‘*plethometopid-eurekiine associations’’ (Corbinia, Stenopilus, and Acheilops).

The ‘‘Corbinia associations’’ are typically found in the reduced MC Belt and in
adjacent parts of the ID Belt whereas the ‘‘Larifugula associations’’ occur in the OD
Belt on the outer part of the platform. Differentiation of the OD Belt from the ID Belt
is Sometimes impractical in those areas where the intervening MC Belt is missing.

The biofacies associations of the basal ‘‘Hystricurid’’ Biomere gave rise to
successor associations in slightly younger rocks assigned to the Missisquoia depressa
Subzone of the Missisquoia and Parabolinella zones. The ‘‘Larifugula associations’
are followed in the OD Belt on the outer platform by the ‘‘Parabolinella
associations’’ which comprise slope trilobites (Parabolinella and Geragnostus) and
probable exotic elements (Missisquoia and Ptychopleurites). The ‘‘Corbinia
associations’’ are followed in the MC Belt and adjacent ID Belt by the ‘*Plethopeltis
associations’’ which comprise trilobites from the underlying associations (Plethopel-
tis) and exotic trilobites (Missisquoia). Ptychopleurites and Geragnostus are rare
elements in these associations. The ‘‘Plethopeltis associations’’ are succeeded by
trilobites dominated by Symphysurina and Hystricuris of uncertain provenance.

The coincident biomere and Grand Cycle boundary separates distinct lithofacies
and biofacies across an Upper Cambrian environmental profile and, thus, it is
expressed differently in inner platform settings than in outer platform settings. On the
inner platform, the boundary is of the MC/MC type or the ID/MC type and it is
expressed by both significant generic extinction and by a decrease in species diversity
from the ‘‘plethopeltid-eurekiine associations’ below to the ‘‘Corbinia associations’
above. Here, the biomere boundary event affects highly diverse trilobite associations
and the source of the new elements above the boundary is the outer platform. On the
outer platform the boundary is of the OD/MC type and it is expressed by minor
generic extinction and by a minor increase in species diversity from the ‘“‘Bowmania
associations’’ below to the ‘‘Larifugula associations’? above. Here, the biomere
boundary event affects less diverse trilobite associations and the main source of the
new elements above the boundary is the slope.

Cook and Taylor (1975) and Taylor (1977) have demonstrated that the abrupt
change in trilobite faunas at the Upper Cambrian shelf-slope break is a
palaeobiogeographic boundary that separates the warm-water North American
Province from the cold-water Chiangnan Province. The Grand Cycle boundary is
expressed by a shift of this palaeobiogeographic boundary (Fig. 17) and the
coincident biomere boundary is characterized by extinction, immigration, species

diversity changes, and biofacies reorganization. These are items of biogeography,
which suggests that biogeographic models, rather than evolutionary models, should
be applied to the faunal dynamics at the biomere boundary.

One of the more promising of such models is the equilibrium model of
biogeography of MacArthur and Wilson (1967) which states that the size of the biota
in a region represents a dynamic equilibrium of extinction of existing species and
immigration of new species. Because extinction increases as population size
decreases and because smaller regions, in general, support smaller populations, then
if the size of a biogeographic region is decreased, the model predicts that extinction
rates will increase and the diversity of the region will be lowered. Conversely, if the
size of a biogeographic region is increased, the diversity of the region will be raised
with increasing rates of immigration and speciation. The equilibrium model was
originally applied to species changes in small areas over ecologic time, but
Simberloff (1972, 1974) has suggested that it may fruitfully be applied to geologic
time in areas as large as continents, and be expressed on generic and higher levels.

An equilibrium model of biogeography showing the faunal dynamics across a
biomere boundary is summarized in Fig. 18. Here, the two biogeographic regions are
shown to comprise belts with cold-water, geographically widespread trilobites on the
slope and warm-water, geographically restricted trilobites on the shelf. A thermocline
separates the biogeographic regions. An expansion of the slope-biogeographic region
and concomitant contraction of the shelf-biogeographic region defines the biomere
boundary.

Most of the genera that were able to cross the biomere boundary became extinct
within or at the top of the Elkanaspis corrugata Fauna and the Corbinia apopsis
Subzone. Whether these extinctions were synchronous cannot be determined within

THERMOCLINE

16: ese) 9? 96.28.

eo Te 2. ©) ‘ee
.

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BIOMERE Ieee -°.°.'° immigration & speciation -. ee ne extinction & competition’ *
BORNDARY sey tert et ans eee Peay s Wa. sesame
“<lOw Diversity. he [TC VERY HIGH DIVERSITY >» |

TEURYGEOGRAPHIC &
| CRYOPHILIC. TRILOBITES

OUTER DETRITAL MIDDLE CARBONATE INNER
BELT THERMOCLINE BELT DETRITAL
SLOPE SHELF
BIOGEOGRAPHIC BIOGEOGRAPHIC
REGION REGION

Fig. 18 Equilibrium model of biogeography applied to the faunal dynamics on a space-time diagram
across a biomere and Grand Cycle boundary. The expansion of the slope-biogeographic region
and contraction of the shelf-biogeographic region define the biomere boundary and these area
changes cause the extinction, immigration, and specification events above the boundary.

the present biostratigraphic framework. The biomere boundary was originally defined
as an extinction level (Palmer, 1965a) and it is perhaps understandable why later
investigators have assumed that by identifying the cause of the extinction they have
discovered the cause for the biomere boundary. Thus, Stitt (1975, 1977) suggested
that the trilobites became extinct because the temperature of the shelf seas declined
and Johnson (1974) and Miller (1978) attributed the extinction to a sudden regression.
The application of the equilibrium model of biogeography to the biomere problem
suggests another explanation for the extinction of ‘‘Cambrian’’ genera in the vicinity
of the revised Ptychaspid-*‘Hystricurid’’ Biomere boundary. On the inner shelf, the
extinction of Saukia Zone trilobites in the Corbinia apopsis Subzone may be
explained as a simple consequence of the decrease in the area of the shelf-
biogeographic region caused by the partial cessation of carbonate production and
deposition at the base of a Grand Cycle. There is no need to identify specific causes.
A different situation existed on the outer shelf. Most of the Yukonaspis Zone trilobites
that crossed the biomere boundary became extinct at the top of the Elkanaspis
corrugata Fauna. Here, the biomere boundary also represents a boundary between
biogeographic regions. Again, it is doubtful that a special explanation is required for
the extinction of these trilobites. Their failure to speciate in a new biogeographic
region is sufficient reason.

In the preceding pages I have attempted to demonstrate that the boundary between
the Ptychaspid and ‘‘Hystricurid’’ biomeres is at the same level as a Grand Cycle
boundary on the outer part of the platform in western North America. I do not suggest
that the lower boundary of each of the older biomeres is necessarily coincident with a
Grand Cycle boundary or that each biomere has a corresponding Grand Cycle, but
this possibility cannot be discounted.* The boundary coincidence of a fossil-based
unit and a rock-based unit has important implications, not only for the biomere
boundary itself, but also for the nature of the internal differentiation of this
biostratigraphic unit. The Grand Cycle/biomere boundary is a rapid facies shift
which affects a lateral sequence of environmentally controlled trilobite biofacies,
each with its own composition and diversity. It is evident from Walther’s Principle
that these biofacies must have some superpositional relationship within the biomere.
The idea of the biomere pattern as a faunal response to a Grand Cycle is attractive in
its simplicity; that is, changing composition and an increase in trilobite diversity and
longevity through the biomere is controlled by the lateral progradation of the MC Belt
and the formation and expansion of shoal complexes. But whether the biomere is
merely an analogue (Palmer, 1979: 39) or a homologue of the Grand Cycle remains to
be demonstrated. The common occurrence of internally controlled (autogenic) faunal
and lithic successions in Phanerozoic strata, such as the ecologic successions of
Walker and Alberstadt (1975), lends support to a fundamental unity of the biomere

* Large-scale facies shifts of the OD Belt over the MC Belt, similar to the shift at the base of the
‘*Hystricurid’’ Biomere at Section KK, have been shown to occur in Nevada and Utah near the base of
the Marjumiid Biomere (Robison, 1976, text-fig. 2), the Pterocephaliid Biomere (Palmer, 1971, fig.
16 E,F), and the Ptychaspid Biomere (Taylor, 1977, text-fig. 5; Brady and Rowell, 1976, p. 160), as
well as in the southern Canadian Rocky Mountains (Aitken et al., 1972, figs. 3, 4).

and Grand Cycle. It is of more than passing interest to note that the faunal attributes
of the four ecologic stages of Ordovician to Cretaceous reefs (Walker and Alberstadt,
1975: 240-243) closely resemble those of the four evolutionary stages of the
Ptychaspid Biomere (Stitt, 1975: 383-386); even their descriptions are remarkably
similar. There are certainly important differences in scale, setting, duration, and
fossil groups between the Grand Cycle /biomere and an ecologic reef succession, but
the ecologic controls on these asymmetric cyclical units may well be identical.

The main conclusion of the present investigation is that the biomere is an ecologic
and biogeographic phenomenom, not primarily an adaptive radiation. Attempts to
apply a strict evolutionary explanation to the biomere pattern have been misdirected.
The recognition that the base of the ‘‘Hystricurid’’ Biomere is defined by area
changes in the shelf- and slope-biogeographic regions permits this biomere boundary
event to be explained in terms of the equilibrium model of biogeography. The
application of this model to biomere boundaries removes much of the supposed
uniqueness of these abrupt faunal events. Similar shifts in slope and shelf lithofacies
and biofacies with similar speciation, immigration, and extinction responses are
known throughout the Phanerozoic record.

Systematic Palaeontology

Repositories

The illustrated specimens from the Rabbitkettle Formation are housed at the
Department of Invertebrate Palaeontology, Royal Ontario Museum, Toronto (ROM
prefix). Other illustrated specimens from the Yukon-Alaska border, Texas, and
Vermont are housed at the Geological Survey of Canada, Ottawa (GSC prefix),
National Museum of Natural History, Washington (USNM prefix), and Peabody
Museum of Natural History, Yale University, New Haven (YPM prefix).

Measurements

Most of the silicified specimens from the Rabbitkettle Formation are small and fragile
and measurements cannot be made in a conventional manner. All cited dimensions
were measured on photographs of known magnification. Abbreviations used when
giving measurements are: exsag.—exsagittal, sag.—sagittal, and tr.—transverse.

Order Miomera Jaekel

Suborder Agnostina Salter

Family Agnostidae M’Coy, 1849
Subfamily Agnostinae M’Coy, 1849

Genus Geragnostus Howell, 1935

Type Species

Agnostus sidenbladhi Linnarsson, 1869 from the Tremadocian of Sweden (by original
designation).

Geragnostus sp.
Fig. 69A-C

Occurrences

Rabbitkettle Formation, Broken Skull River (five collections between 114 m and
177 m below top of formation), Yukonaspis kindlei Fauna.

Remarks

Geragnostus sp. is characterized by a transverse pygidium with very wide borders
which carry a pair of minute posterolateral spines. The first and second transverse
furrows on the pygidial axis are very shallow and the axial pygidial node is small. The
anterior furrow on the glabella is faint and expressed only medially. Both the
cephalon and pygidium are finely granulose.

Subgenus Micragnostus Howell, 1935

Type Species

Agnostus calvus Lake, 1906 from the Tremadocian of Wales (by original
designation).

Geragnostus (Micragnostus) subobesus (Kobayashi, 1936a)
Figs. 19, 47A—P, 70M

Agnostus subobesus Kobayashi, 1936a: 161, pl. 21, figs. 1, 2.

Occurrences

Jones Ridge Limestone, Jones Ridge, east-central Alaska, Ptychopleurites Fauna
(Kobayashi, 1936a; Palmer, 1968). Rabbitkettle Formation, Broken Skull River (10

collections between 46 m and 60 m below top of formation), Missisquoia depressa
Subzone and Missisquoia mackenziensis Fauna.

Lectotype (here designated)

A cephalon from the Jones Ridge Limestone, east-central Alaska illustrated by
Kobayashi (1936a, pl. 21, fig. 1) and herein (Fig. 70M).

Description

Cephalon is subcircular in outline, slightly wider than long and strongly convex.
Maximum height is about 60 per cent width (tr.). Borders are wide and flat; marginal
furrows are well incised. Acrolobe is evenly convex, unconstricted, and inflated; it is
of the same width (tr. and sag.) around glabella. A median preglabellar furrow does
not occur. Glabella occupies 80 per cent cephalic length and about 40 per cent
cephalic width; it is parallel sided and evenly rounded anteriorly. Glabella comprises
a transversely suboval and inflated anterior lobe separated from a rectangular and
strongly inflated posterior lobe by a forwardly concave anterior furrow. An axial
glabellar node which is faint and drop shaped is located slightly in front of mid-length
of the posterior lobe. Basal lobes are rather small, triangular, and only moderately
inflated. Genal angles are small blunt spines, between which the posterior margin is
straight in dorsal view. In posterior view, posterior margin rises in U-shaped notch
between basal lobes.

Anterior thoracic segment is rectangular, three and a half times as wide (tr.) as
long. Convex axis occupies 70 per cent of width of segment; it comprises three

Fig. 19 Geragnostus (Micragnostus) subobesus (Kobayashi, 1936a). Reconstruction of cephalon and
pygidium. Bar represents | mm.

lobes—a trapezoidal and inflated central lobe which is separated by a pair of
posteriorly diverging furrows from two drop-shaped lateral lobes.

Pygidium is subquadrate in outline, slightly wider than long and strongly convex.
Maximum height is about 60 per cent of width (tr.). Borders are flat and widest
posterolaterally, marginal furrows are well incised. Acrolobe is evenly convex and
unconstricted; it narrows towards rear. Axis is inflated and nearly parallel sided; it
occupies 85 to 90 per cent pygidial length and about 40 per cent pygidial width.
Anterior lateral furrows isolate lateral lobes of first segment. Second axial segment
does not extend as far laterally; it is defined posteriorly by faint and nearly transverse
furrow. An elongate axial pygidial node separates second axial lobes; it may extend
forwardly to articulating furrow as a low ridge. Posterior axial lobe is semicircular
and inflated: its length (sag.) equals that of the anterior two segments combined. A
pair of inwardly curving posterolateral spines are located just in front of a transverse
line posing through posterior margin of axis.

Remarks

The type collection of Agnostus subobesus Kobayashi from the Jones Ridge
Limestone, east-central Alaska consists of a well-preserved cephalon (here
designated the lectotype, Fig. 70M) and a poorly preserved and exfoliated pygidium.
Kobayashi (1936a) suggested that the Alaska species belonged in the group of
agnostids typified by Homagnostus obesus (see Henningsmoen, 1958, pl. 5, figs.
13-16). As Robison and Pantoja-Alor (1968: 775) have noted, differentiation with
the Geragnostus-Homagnostus plexus of species in the Late Cambrian and Early
Ordovician is difficult because diagnostic characters tend to intergrade. Kobayashi’s
Species 1S assigned to Micragnostus Howell, 1935 based on its similarity to
Micragnostus calvus (Lake) and I follow Shergold (1971: 23) in considering
Micragnostus a subgenus of Geragnostus.

Few species of Geragnostus attain the degree of convexity shown by both the
cephalon and pygidium of G. (M.) subobesus. This species is perhaps closest to G.
(M.) intermedius Palmer which occurs in the Franconian of Alaska and Oklahoma
(Palmer, 1968; Stitt, 1977) and the early Tremadocian of Mexico (Robison and
Pantoja-Alor, 1968). G. (M.) subobesus differs in having a higher degree of
convexity, a parallel-sided glabella, a forwardly concave anterior glabellar furrow,
and a narrower pygidial axis.

Geragnostus (Micragnostus) chiushensis (Kobayashi) which occurs with Missis-
quoia depressa Stitt (senior synonym of Tangshanaspis zhaogezhuangensis Zhou and
Zhang) in the Mictosaukia orientalis Assemblage in Hopeh Province, China (Zhou
and Zhang, 1978) is very similar to G. (M.) subobesus . The Chinese form appears to
have a more prominent axial glabellar node. It is not known whether it has the
convexity characteristic of the North American form.

The species illustrated as G. (M.) bisectus (Matthew) from the Missisquoia Zone of
Vermont by Shaw (1951, pl. 23, figs. 11-18) is inflated to nearly the same degree as
G. (M.) subobesus. The Vermont form differs in possessing narrower cephalic and
pygidial borders and in lacking an axial glabellar node.

Geragnostus reductus (Winston and Nicholls, 1967) from the Missisquoia and
Symphysurina zones of Texas and Oklahoma (Fig. 70D-G) differs from the present

species in being much less inflated, in having a shorter and tapered glabella and
pygidial axis, and in having constricted cephalia and pygidial acrolobes. The latter
feature led Shergold (1975: 55) to tentatively assign G. reductus to Geragnostus
(Strictagnostus) Shergold.

Family Diplagnostidae Whitehouse, 1936
Subfamily Pseudagnostinae Whitehouse, 1936

Genus Pseudagnostus Jaekel, 1909

Type Species

Agnostus cyclopyge Tullberg, 1880 from the Upper Cambrian of Sweden (by original
designation).

Subgenus Pseudagnostina Palmer, 1962

Type Species

Pseudagnostina contracta Palmer, 1962 from the Dresbachian of Nevada and
Alabama (by original designation).

Pseudagnostus (Pseudagnostina) sp.
Figs. 20, 47Q, R

Occurrence

Rabbitkettle Formation, Broken Skull River (single collection 165 m below top of
formation), Yukonaspis kindlei Fauna.

Nae

Fig. 20 Pseudagnostus (Pseudagnostina) sp. Reconstruction of pygidium. Bar represents | mm.

Remarks

Pseudagnostus (Pseudagnostina) sp. is characterized by a subquadrate pygidium with
deep marginal furrows and an unconstricted and evenly inflated acrolobe. Lateral rim
is broad and somewhat rounded (tr.). Accessory furrows and deuterolobe are not
differentiated. Axial furrows are nearly parallel and extend to the rear of a prominent
axial pygidial node. A faint transverse furrow extends inwards from axial furrow at
half length of node. Short posterolateral spines are directed backwards. On the
cephalon, rim 1s broad, axis is parallel sided, transverse anterior furrow is concave
forwardly, and median glabellar furrow is absent.

In lacking both a median preglabellar furrow and a distinctly outlined deuterolobe
on the pygidium, these specimens belong in the Contracta group of Pseudagnostus as
defined by Shergold (1977). They are most similar to P. (P.) contracta Palmer, but
differ slightly in having a forwardly concave transverse anterior furrow on the
glabella and a deeper transverse furrow on the pygidial axis.

P. (Pseudagnostina) has previously been known only from the early Late
Cambrian (Dresbachian, Mindyallan, and Kushanian) of North America, Australia,
and eastern Asia (Shergold, 1977: 84). The occurrence in the Rabbitkettle Formation
is the first from the Late Cambrian (Trempealeauan).

Genus Rhaptagnostus Whitehouse, 1936

Type Species

Agnostus cyclopygeformis Sun, 1924 from the Upper Cambrian Kaoli Limestone,
Shantung, China (by original designation).

Rhaptagnostus clarki (Kobayashi, 1935)
Fig. 520-S

Pseudagnostus (Plethagnostus) clarki Kobayashi, 1935: 47, pl. 9, figs. 1, 2.
Pseudagnostus laevis Palmer, 1955: 97, pl. 19, figs. 8, 9, 11, 12.
Pseudagnostus clarki—Palmer, 1968: 29, pl. 15, figs. 10, 13, 14.
Pseudagnostus clarki—Shergold, 1975: 61, pl. 1, 2, figs. 1, 2, pl. 3, 4, 5.
Rhaptagnostus clarki—Shergold, 1977: 86, pl. 15, figs. 14, 15.

Occurrences

Jones Ridge Limestone, east-central Alaska, Trempealeauan-1 and Trempealeauan-2
Faunas (Palmer, 1968). Windfall Formation, Eureka District, Nevada, Trem-

pealeauan (Palmer, 1955). ‘“‘Chatsworth Limestone’’, Queensland, Australia,
Pre-Payntonian A and Pre-Payntonian B (Shergold, 1975). Rabbitkettle Formation,
Broken Skull River (two collections between 152 m and 177m below top of
formation), Yukonaspis kindlei Fauna.

Lectotype

A pygidium from the Jones Ridge Limestone, east-central Alaska illustrated by
Palmer (1968, pl. 15, fig. 13) and Shergold (1977, pl. 15, fig. 15).

Remarks

The recent discussions in Palmer (1968: 29) and Shergold (1975: 61; 1977: 86)
adequately characterize this effaced pseudagnostine species. Of the five subspecies
established by Shergold (1977), the Rabbitkettle specimens are closest to
Rhaptagnostus clarki clarki (Kobayashi) from the Trempealeauan of east-central
Alaska, but differ from this subspecies in having a slightly wider pygidium with the
posterolateral spines located slightly farther toward the rear.

Order Ptychopariida

Suborder Ptychopariina

Superfamily Ptychopariacea

Family Ptychopariidae Matthew, 1887
Subfamily Eulominae Kobayashi, 1955

Genus Euloma Angelin, 1854

Type Species

Euloma laeve Angelin, 1854 from the Lower Ordovician of Ostergotland, Sweden
(subsequent designation by Vogdes, 1925).

Subgenus Plecteuloma Shergold, 1975

Type Species

Euloma (Plecteuloma) strix Shergold, 1975 from the ‘‘Chatsworth Limestone’’,
Queensland (by original designation).

Euloma (Plecteuloma) sp.
Fig. 57V

Occurrence

Rabbitkettle Formation, Broken Skull River (single collection 165 m below top of
formation), Yukonaspis kindlei Fauna.

Description

This small eulomine cranidium is probably an immature specimen. It measures about
2 mm between anterior and posterior margins and has a rectangular glabella with two
oblique, lateral furrows. Preglabellar field is long. Straight anterior border furrow is
interrupted medially by a minute plectrum. Small palpebral lobes are located about
half-way out on cheeks; faint palpebral ridges run into axial furrows. Facial sutures
diverge slightly in front of eyes and markedly behind.

Remarks

Euloma (Plecteuloma) has hitherto been known only from the Late Cambrian of
Australia. The small eulomine cranidium with a minute plectrum from the
Rabbitkettle Formation establishes the presence of this subgenus in the Late
Cambrian of North America.

Superfamily Conocoryphacea
Family Shumardiidae Lake, 1907

Genus Idiomesus Raymond, 1924

Type Species

Idiomesus tantillus Raymond, 1924 from the Gorge Formation, Highgate Falls,
Vermont (by original designation).

Remarks

Since its definition, Jdiomesus has been classified with Shumardia Billings in the
family Shumardiidae. The discovery of the pygidium of /. intermedius lends support
to this assignment which previously was based on cranidial features only. The

pygidium is similar in outline and general aspect to those of ‘‘Shumardia’’ pusilla
(Sars) and ‘‘Shumardia’’ exopthalma Ross, 1967. Both of these species possess
pygidia that are quite distinct from that of Shumardia and they are probably not
congeneric with S. granulosa, the type species of Shumardia (Dean, 1973: 8),
although both are undoubtedly assignable to the family Shumardiidae.

Contrary to the statement of Poulsen (in Moore, 1959: 245), Shumardia and
‘‘Shumardia’’ both possess facial sutures (Whittington, 1965: 328, pl. 16, fig. 17;
Young, 1973, pl. 1, figs. 1, 5, 6). These are marginal in position and, in ‘‘S.’’
exopthalma, they isolate yoked free cheeks. Very similar facial sutures occur in
Idiomesus tantillus Raymond (Fig. 54Q, R).

Idiomesus tantillus Raymond, 1924
Fig. 54P—U

Idiomesus tantillus Raymond, 1924: 397, pl. 12, fig. 10.
Idiomesus tantillus—Rasetti, 1946: 538, pl. 1, figs. 1-3.

Occurrences

Gorge Formation, Highgate Falls, Vermont, Zones 2 and 3—Hungaia Assemblage
(Raymond, 1924; Rasetti, 1946). Rabbitkettle Formation, Broken Skull River (single
collection at 165 m below top of formation), Yukonaspis kindlei Fauna.

Holotype

A cranidium from the Gorge Formation, Highgate Falls, Vermont illustrated by a
drawing in Raymond (1924, pl. 12, fig. 10).

Remarks

Even though the Rabbitkettle material is coarsely silicified, it shows certain features
not displayed by the Vermont material studied by Raymond and Rasetti.

One specimen (Fig. 54P-R) is a cephalon missing only the right free cheek. This
cephalon shows a narrow (tr.) lateral border furrow running along the inner side of the
facial suture. This furrow is a forward continuation of the deeper posterior border
furrow and it extends as far forward as the front part of the glabella. The lateral border
is wide (lateral view) and slightly inflated; it descends vertically and is, in part,
curved under the cephalon. The lateral border becomes wider towards the bluntly
rounded genal corner which bears one (or perhaps two) minute spines. The anterior
border is curved under frontal part of cephalon. The free cheeks are yoked and the
border carries poorly defined terrace lines. In anterior view the facial sutures are seen
to descend gently in both anterior and posterior directions from high points located on
front part of cheek.

Idiomesus tantillus Raymond differs from the remaining four species of Jdiomesus
from North America (Taylor, 1976: 685) in possessing a relatively narrow glabella
which is poorly defined and widest anteriorly, and which is crossed, or partly
crossed, by 1s furrow. Other glabellar furrows are not developed.

Idiomesus levisensis (Rasetti, 1944)
Fig. 57N, O

Idiomesus levisensis—Taylor, 1976: 686, pl. 3, figs. 12, 13 (see for synonymy).

Occurrences

Levis Formation, North Ridge, Levis, Quebec, Hungaia Assemblage (Rasetti, 1944).
Wilberns Formation, central Texas, Saukiella pyrene to Saukiella serotina subzones
(Longacre, 1970). Snowy Range Formation, Bridger Mountains, Montana,
Illaenurus Zone (Grant, 1965). Hales Limestone, Hot Creek Range, Nevada,
Hedinaspis Zone (Taylor, 1976). Rabbitkettle Formation, Broken Skull River (three
collections between 61 m and 70 m below top of formation), Elkanaspis corrugata
Fauna.

Syntypes

Two cranidia from an Upper Cambrian boulder, North Ridge, Levis, Quebec
illustrated by Rasetti (1944, pl. 37, figs. 8, 9).

Remarks

Taylor (1976) has demonstrated that minor differences separate the two similar and
contemporaneous species, /diomesus levisensis (Rasetti) and J. intermedius Rasetti.
These differences are best seen in small cranidia. A few small specimens from the
Elkanaspis corrugata Fauna display the complete 1s furrow and pitlike 2s and 3s
furrows that apparently are characteristic of J. levisensis.

Idiomesus intermedius Rasetti, 1959
Fig. 57 G-M

Idiomesus intermedius Rasetti, 1959: 393, pl. 51, figs. 25, 26.
Idiomesus intermedius —Winston and Nicholls, 1967: 73, pl. 10, fig. 21.
Idiomesus intermedius—Longacre, 1970: 55, pl. 4, figs. 13, 14.
Idiomesus levisensis (Rasetti), Stitt, 1971b: 45, pl. 5, figs. 1-S.

Occurrences

Conococheague Limestone, Maryland, Saukia Zone (Rasetti, 1959). Wilberns
Formation, central Texas, Saukiella junia to Corbinia apopsis subzones (Winston and
Nicholls, 1967; Longacre, 1970). Signal Mountain Limestone, Wichita and Arbuckle
Mountains, Oklahoma, Rasettia magna to Corbinia apopsis subzones (Stitt, 1971b,
1977). Notch Peak Formation, Utah, Saukiella serotina Subzone (Hintze et al.,
1980). Rabbitkettle Formation, Broken Skull River (11 collections between 80 m and
165 m below top of formation), Bowmania americana Fauna and Yukonaspis kindlei
Fauna.

Holotype

A cranidium from the Conococheague Limestone, Washington County, Maryland
illustrated by Rasetti (1959, pl. 51, fig. 25).

Description

The discussion by Taylor (1976: 686, text-fig. 7) effectively describes the cranidium
of Idiomesus intermedius. The pygidium is described here for the first time.

Pygidium is semicircular in outline with a transverse or slightly re-entrant posterior
margin; length is about two-thirds width (tr.). Axis is convex, less than one-third
pygidial width, and it extends to posterior border furrow. Three axial rings and a
terminal piece are separated by sharply incised and narrow (sag.) furrows. In
longitudinal profile each ring comprises a low, asymmetric cuesta with its steep flank
facing forward. Pleural field is flat, it is crossed by four narrow (exsag.) pleural
furrows. Border furrows are complete and firmly impressed. Lateral and posterior
borders are narrow and rimlike; they stand well above the pleural field and their outer
portions descend steeply to margin.

Superfamily Crepicephalacea
Family Tricepicephalidae Palmer, 1954

Genus Meteoraspis Resser, 1935

Type Species

Ptychoparia? metra Walcott, 1890 from the Upper Cambrian of Texas (by original
designation).

Meteoraspis? sp.
Fig. 68R-T

Occurrence

Rabbitkettle Formation, Broken Skull River (single collection 177 m below top of
formation), Yukonaspis kindlei Fauna.

Description

Cranidium possesses a rather long glabella outlined by deep and parallel axial furrows
that die out before reaching a very deep and forwardly bowed border furrow. The
occipital furrow is straight and sharply incised. Lateral glabellar furrows are not
present. The eyes are located far out on the cheeks, at or just behind mid-length of
cranidium. The posterior limbs are bent backward. The anterior border furrow houses
a pair of large and very deep pits whose presence cannot be detected on the dorsal
side. On the ventral side, they protrude as large rectangular knobs whose long axes
are aligned along the anterior border furrow.

Remarks

The identification of these peculiar cranidia is extremely tentative and is based merely
on the presence of the pair of deep pits in the anterior border furrow.
Tricrepicephalids have not been recorded in rocks younger than Dresbachian. In
general proportions, Meteoraspis? sp. is vaguely similar to species such as
Meteoraspis mutica Rasetti, 1961, but differs markedly in lacking a preglabellar
furrow. The similarity could well be spurious.

The only other post-Dresbachian trilobite with a pair of deep pits in the anterior
border furrow is Bifodina Robison and Pantoja-Alor, 1968 from the early
Tremadocian of Mexico. This genus, however, has a forwardly tapering glabella, a
preglabellar furrow, a broad frontal area, and a shallow and broad anterior border
furrow.

Superfamily Olenacea Burmeister, 1843
Family Olenidae Burmeister, 1843

Remarks

Fortey (1974: 13) provided a brief diagnosis of this family in which he placed prime
emphasis on the yoked cheeks united by a narrow doublure, the simple diagonal
pleural furrows on the thoracic segments, and the very thin exoskeleton.

The yoked cheeks of Apoplanias and the general cephalic similarity of this genus to
Parabolinella suggest that Lochman (1964a) was correct in assigning this taxon to the
Olenidae.

Subfamily Oleninae Burmeister, 1843
(= Triarthrinae Ulrich, in Bridge, 1931)

Remarks

Poulsen (in Moore, 1959) assigned Parabolina and Parabolinites to the Oleninae and
Parabolinella and Angelina to the Triarthrinae. These genera are similar
(Henningsmoen, 1957: 156; Robison and Pantoja-Alor, 1968: 785) and should be
classified in the same subfamily. Indeed, I can discern no characters in the diagnoses
of the Oleninae and Triarthrinae (Poulsen, in Moore, 1959: 262, 267) that would
justify separation of these taxa and I agree with Henningsmoen (1957: 96) that the
Triarthrinae is a junior synonym of the Oleninae.

Genus Parabolinites Henningsmoen, 1957

Type Species

Parabolinella laticauda Westergaard, 1922 from the Upper Cambrian of Sweden (by
original designation).

Remarks

Henningsmoen (1957: 129) separated Parabolinites from Parabolina Salter on the
basis of the greater sagittal length of the preglabellar field and on the non-spinose
pygidium of Parabolinites laticaudus . In his diagnosis of Parabolina (1957: 113), he
stated that this genus comprises species with and without pygidial spines. Of the 13
species of Parabolina with known pygidia which were treated by Henningsmoen
(1957: 114-129), 12 have three (rarely two) to five pairs of spines, one has a single
pair of spines, and one lacks pygidial spines. Parabolina argentina (Kayser), the
species which supposedly lacks spines, does, in fact, possess three pairs of short,
sharp spines on the pygidium (Harrington and Leanza, 1957, fig. 25-3), so that this
species conforms in pygidial characters to the larger group of Parabolina species.
Henningsmoen was apparently following Matthew (1903) when he described the
pygidium of Parabolina dawsoni Matthew as having a single pair of short spines. The
type collection of P. dawsoni from the Peltura Zone at Escasonie, Cape Breton Island
(ROM 327CM, 1199CM, 1201CM, and 1208CM) includes two pygidia, neither of
which possesses a spine pair such as that illustrated by Matthew (1903, pl. 17, fig.

6f). One of the pygidia shows a very slight protuberance at the anterior part of the
pygidial border similar to that of another pygidium of P. dawsoni illustrated by
Hutchinson (1952, pl. 3, fig. 12). In both cranidial and, now, pygidial features,
Parabolina dawsoni is very similar to its contemporary, Parabolinites laticaudus
from Sweden, and Matthew’s species should be reassigned to Parabolinites. This
leaves Parabolina with a well-defined set of diagnostic characters, including three
(rarely two) to five pairs of marginal spines on the pygidium.

In addition to the type species and P. dawsoni, Parabolinites includes
Parabolinella williamsoni (Belt, 1868) (= Parabolinella caesa Lake, 1913) from the
upper Dolgelly Beds of northern Wales and possibly also Olenus longispinus (Belt,
1868) from the same stratigraphic and geographic location. These four species are
approximately the same age; that is, Peltura minor or P. scarabaeoides zones. The
youngest member of the genus, Parabolinites cf. williamsoni from the Rabbitkettle
Formation, is of latest Trempealeauan and earliest Tremadocian age.

Parabolinites cf. williamsoni (Belt, 1868)
Figs. 21, 50P, Ss, SIA-K

Conocoryphe? Williamsonii Belt, 1868: 9, pl. 2, figs. 7-11.
Parabolinella williamsoni—Lake, 1908: 64, pl. 6, fig. 12.
Parabolinella williamsoni—Lake, 1913: 65, pl. 7, fig. 1.
Parabolinella caesa Lake, 1913: 66, pl. 7, fig. 2.
Parabolinites? williamsonii—Henningsmoen, 1957: 131.
Parabolinella? caesa—Henningsmoen, 1957: 140.

Occurrences

Rabbitkettle Formation, Broken Skull River (five collections between 60 m and 70 m
below top of formation), Missisquoia mackenziensis Fauna and Elkanaspis corrugata

(fon feornetnt iy

qT)

Fig. 21 Parabolinites cf. williamsoni (Belt, 1868). Reconstruction of cephalon and pygidium (prosopon
omitted). Bar represents 1 mm.

Fauna. Parabolinites williamsoni (Belt) occurs in the upper Dolgelly Beds of
northern Wales (late Merionethian, Rushton, 1974: 67).

Description

Cephalon is semicircular in outline and strongly arched (tr. and sag.); it is surrounded
by firmly impressed border furrows and narrow, convex borders whose lateral
portions continue posteriorly as slender genal spines of unknown length. Convex
glabella narrows only very slightly towards the front, it occupies somewhat less than
one-third width of cephalon. It is outlined by deep and narrow (tr.) axial furrows
which, in front of palpebral ridges, merge with forwardly arched preglabellar furrow.
Occipital furrow is shallow, but distinct; laterally it bifurcates. Occipital ring carries
median tubercle. Three pairs of firmly impressed lateral glabellar furrows do not
connect with axial furrows; Is is sigmoid, located at about glabellar mid-length; 2s
and 3s are forwardly convex, located close together on anterior quarter of glabella.
Preglabellar field is one-fifth the length (sag.) of glabella and, in large cranidia, is
steeply sloping to anterior border furrow; in small cranidia, it declines gently.
Palpebral lobe is large, well raised over genal field; it is located half-way out on the
cheek, opposite 2s and 3s. It is confluent with short (exsag.) and raised transverse
palpebral ridge which is bounded on both sides by furrows. Posterior branch of facial
suture proceeds obliquely backwards and outwards along somewhat sigmoid path.
Anterior branch proceeds nearly straight forward in small cranidia and is divergent in
large cranidia. Genal and preglabellar fields are covered by irregular, but generally
radial, scrobiculate and ropy caecal network. Cephalic borders bear prosopon of fine
parallel terrace lines.

Hypostome is quadrate, longer than wide, and convex (sag.). Inflated central body
is slightly waisted anteriorly and is circumscribed by deep border furrows. Anterior
wings are not fully preserved, but apparently are triangular. Anterior margin is gently
arched forwardly and is steeply raised over anterior border furrow. Lateral border is
arched above a deep antennal notch. Posterior border is very narrow (sag.).

Pygidium is transversely semielliptical in outline and moderately arched (tr.).
Narrow, convex axis tapers slightly; it consists of six rings and a short blunt terminal
piece; and it extends to posterior border furrow. Pleural field is crossed by five,
sharply incised interpleural furrows that are hooked backwardly adjacent to border
furrow. Five pleural furrows are confined to distal part of pleural field. Both
interpleural and pleural furrows terminate against shallow border furrow which
defines narrow and rather flat pygidial border.

Remarks

Lake (1908, 1913) described and illustrated a large and incomplete external mould of
an olenid trilobite which he identified as Parabolinella williamsoni (Belt, 1868).
According to Lake, this species is characterized by a large, anteriorly rounded
glabella with two oblique pairs of lateral furrows and a relatively large pygidium with
four interpleural furrows. Lake (1913: 66) also described a similar species,

Parabolinella caesa Lake, which he separated from P. williamsoni ‘‘with some
hesitation’ on the basis of the presence of three pairs of lateral glabellar furrows.
Both of these species occur in the upper Dolgelly Beds (Peltura scarabaeoides Zone,
late Merionethian; Rushton, 1974) of northern Wales. Henningsmoen (1957: 131,
140) assigned P. williamsoni to Parabolinites? and P. caesa to Parabolinella?. Lake
(1913), however, noted that these species are closely allied and both differ
significantly from other species of Parabolinella in having much larger pygidia. I
suggest that the two Welsh species are conspecific and referable to Parabolinites . The
minor differences apparent in Lake’s descriptions and illustrations are probably
attributable to preservational differences (similar differences are seen in the cranidia
of P. cf. williamsoni from the Rabbitkettle Formation; compare pl. 6, fig. 12 and pl.
7, fig. 2 of Lake with Fig. 50S and Fig. 51C of this paper).

The similarity between Parabolinites williamsoni from the late Merionethian of
Wales and P. cf. williamsoni from the latest Trempealeauan/ earliest Tremadocian of
the District of Mackenzie is best seen in the pygidia (compare Lake, 1913, pl. 7, fig.
1 and this paper, Fig. 511). P. williamsoni has one or two fewer axial ring furrows and
interpleural furrows than P. cf. williamsoni, but the pygidial outline, the shape of the
tapering axes, and the aspect of the shallow border furrows and flat borders appear to
be identical.

The large pygidium and narrow glabella of Parabolinites cf. williamsoni
distinguish this species from P. laticaudus and P. dawsoni. The glabella of P. cf.
williamsoni is also narrower (tr.) than that of P. williamsoni.

Genus Parabolinella Brogger, 1882
Type Species

Parabolinella limitis Brogger, 1882 from the Ceratopyge Shale (Tremadocian) of
Oslo, Norway (subsequent designation by Bassler, 1915).

Diagnosis

A genus of olenine trilobites possessing a parallel-sided to slightly forwardly tapered
glabella with two or three pairs of oblique lateral glabellar furrows; 1s furrow
bifurcates laterally. Preglabellar field is relatively long; its posterior flank is variably
inflated. Palpebral lobes are located close to glabella, opposite 3p lobe. Facial sutures
are subparallel to slightly divergent in front of eyes. Genal spines are long and
slender. Pygidium is small, transverse; axis consists of two axial rings and a blunt
terminal piece.

Remarks

One feature that has been overlooked by previous framers of diagnoses of
Parabolinella (Henningsmoen, 1957: 132; Poulsen, in Moore, 1959: 267; Robison

and Pantoja-Alor, 1968: 789) is the variable inflation of the preglabellar field. In
uncompressed specimens this inflation may be no more than a rounded rim in front of
the preglabellar furrow (for example, in P. cf. prolata, Figs. 48A—C, 49A-C) or it may
involve the entire preglabellar field (for example, in P. hecuba [Walcott], Fig. 52E;
Robison and Pantoja-Alor, 1968, pl. 102, fig. 12; Harrington and Leanza, 1957, fig.
39-2c; P. panosa sp. nov., Fig. 50Q). This feature may also be seen in flattened
specimens (for example, in P. argentinensis Kobayashi, Robison and Pantoja-Alor,
1968, pl. 102, fig. 2; P. limitis Brogger, Henningsmoen, 1957, pl. 12, fig. 3; P.
triarthra [Callaway], Henningsmoen, 1957, pl. 12, fig. 6; Lake, 1913, pl. 7, fig. 8).

Inflation of the preglabellar field is not seen in the species of Parabolinites that
may otherwise be confused with Parabolinella (for example, in Parabolinites
williamsoni [Belt] Lake, 1908, pl. 6, fig. 12; P. dawsoni Matthew, 1903, pl. 17, fig.
6a; and P. cf. williamsoni [Belt], Fig. 51G).

According to the diagnosis above, Parabolinella is confined to the Tremadocian of
northern Europe (Henningsmoen, 1957), South America (Harrington and Leanza,
1957), Mexico (Robison and Pantoja-Alor, 1968), Maritime Canada (Hutchinson,
1952), and western North America. Tjernvik (1956) reported questionable
occurrences of Parabolinella from the early Arenigian of Sweden. The supposed
Cambrian occurrences of Parabolinella from North America cited by Henningsmoen
(1957: 133) have either been wrongly dated or been based on species that since have
been reassigned to other genera.

The occurrences of Parabolinella in Vermont, Alaska, Nevada, Texas, Mexico,
Newfoundland, and District of Mackenzie appear to be in Lower Tremadocian rocks
correlative with the Parabolinella, Missisquoia, or Symphysurina zones. The
presence of Parabolinella in higher Lower Ordovician rocks or in Upper Cambrian
rocks in North America has not been demonstrated.

Parabolinella cf. prolata Robison and Pantoja-Alor, 1968
Figs. 22, 48, 49, 50M, N

Parabolinella prolata Robison and Pantoja-Alor, 1968: 789, pl. 102, figs. 3, 6, 9.

Fig. 22 Parabolinella cf. prolata Robison and Pantoja-Alor, 1968. Reconstruction of cephalon and
pygidium (prosopon omitted). Bar represents | mm.

Occurrences

Rabbitkettle Formation, Broken Skull River (10 collections between 46 and 60 m
below top of formation), Missisquoia depressa Subzone and Missisquoia macken-
ziensis Fauna. Parabolinella prolata occurs in the Parabolina assemblage (Lower
Tremadocian) of the Tinu Formation, Mexico.

Description

Cephalon is semicircular in outline and about half as high as wide (tr.). Glabella rises
steeply out of axial furrows; it is one-third the width (sag.) and three-quarters the
length (sag.) of cephalon; and it narrows slightly towards front from widest point at
occipital ring. Preglabellar furrow is sharply incised and has moderate forward
curvature. A triangular depressed area is formed at juncture of preglabellar and axial
furrows. Occipital furrow is well-incised medially; it bifurcates and shallows
laterally. Occipital lobe thus comprises three poorly outlined lobes: a lenticular
central lobe bearing prominent median tubercle and two triangular lateral lobes. Two
pairs of lateral glabellar furrows are oblique and firmly impressed, neither reaches
axial furrow; 1s bifurcates laterally and 2s is located in line with palpebral lobes.
Preglabellar field is relatively long (sag.) and steeply sloping towards anterior border
furrow; its anterior edge comprises a narrow (sag.) inflated rim which extends from in
front of axial furrows. In lateral view, crest of glabella slopes evenly downward from
horizontal posterior portion; preglabellar field continues this curvature, but at a
slightly higher level. Anterior border furrow is sharply incised and marked by closely
spaced pits; it is continuous in even curve with lateral border furrows. Narrow convex
anterior and lateral borders are continued posteriorly as long straight and gradually
tapering genal spines. Posterior border is somewhat wider (exsag.) and less convex
than lateral border. Palpebral lobes are large and located half-way out on cheek
opposite anterior glabellar lobe. A faint curved palpebral furrow defines interior
edge. Posterior branch of facial suture proceeds obliquely backward and outward
before swinging exsagitally to cross posterior border. Anterior branch of facial suture
proceeds straight forward (or very slightly inward) in large cephala and then inward
along anterior border to define yoked cheeks. In smaller cephala, anterior sutures may
diverge. In anterior view, the ventral margin of cephalon rises in a broad low arch
towards midline. On interior convex doublure extends to border furrows. Inner edge
of anterior doublure is very finely toothed so that each tooth connects with a pit in the
anterior border furrow (see Fortey, 1974, fig. 4 C for an identical structure in another
olenid). Cephalon is covered by extremely fine granules. Borders carry prosopon of
fine terrace lines arranged parallel to margin. Similar, but transverse and irregular
prosopon occurs on preglabellar field.

Hypostome has large, oval, and greatly inflated central body. Middle furrow
parallels lateral margin; it terminates medially in transversely directed macula.
Anterior wing is wide (tr.) and triangular. Anterior margin is moderately curved.
Lateral border is narrow and convex. Posterior border and margin are poorly
preserved.

Number of thoracic segments is unknown. Axis is highly convex; it is crossed by
well-incised articulating furrow and surmounted by prominent median tubercle.
Interior third of pleura is horizontal; outer two-thirds declines at 40 degrees along
straight path. Pleura is crossed at very low angle by pleural furrow which nearly
reaches pointed terminus. Spine tip is encased by flat doublure which carries fine
terrace lines. With the exception of articulating half ring, articulating devices are not
seen on thoracic segments.

Pygidium is elliptical in outline, three times as wide as long (sag.). Moderately
convex axis consists of two rings and a blunt terminal piece; it extends to border
furrow. Pleural region is crossed by two deep pleural furrows and two shallow
interpleural furrows, both furrow types terminate against narrow and flat border. In
posterior view, ventral margin of pygidium is arched beneath axis. Narrow doublure
carries fine terrace lines.

Remarks

Parabolinella cf. prolata Robison and Pantoja-Alor is, by far, the most abundant
trilobite in the Parabolinella Zone of the upper Rabbitkettle Formation at Section KK
and accounts for the bulk of the Parabolinella frequency histogram in Fig. 16.

Among species represented by noncompressed material, Parabolinella cf. prolata
is most similar to P. prolata and the poorly known P. punctolineata Kobayashi,
1936a from the Lower Tremadocian of Mexico and the Alaska-Yukon border,
respectively. From both of these species, P. cf. prolata is distinguished by the
presence of a narrow inflated rim which defines the front edge of both the preglabellar
furrow and the axial furrow and by the slightly more anteriorly located eyes.

A surprising feature of Parabolinella cf. prolata is the high degree of convexity of
both the cephalon and the thoracic segments. The ratio of height at the axis to
transverse width is about 5:10 for the cephalon and 4:10 for a segment near
mid-length of thorax. If a thin-shelled trilobite such as this species is flattened in
shale, extensive deformation of morphological features and significant alterations of
proportions will result. Nonetheless, tentative comparisons may be made with some
species of Parabolinella preserved in flattened states. The compressed cranidia of P.
limitis Brogger, P. rugosa Brogger, P. triarthra (Callaway), and P. argentinensis
Kobayashi illustrated by Hutchinson (1952), Henningsmoen (1957), Harrington and
Leanza (1957), and Robison and Pantoja-Alor (1968) all possess rectangular
glabellae that are only slightly longer (sag.) than wide (tr.), three pairs of lateral
glabellar furrows, and relatively small eyes. The course of the anterior facial suture
varies in these species from slightly divergent in P. triarthra to markedly divergent in
P. argentinensis. P. cf. prolata differs from these species in having a slightly
tapering glabella that is generally longer than wide, but the proportions vary
considerably (compare Fig. 48A and 48F, Fig. 49A and 49M), and in having only two
pairs of lateral glabellar furrows.

Parabolinella hecuba (Walcott, 1924)
Figs. 23, 52A-

Moxomia hecuba Walcott, 1924: 59, pl. 12, fig. 3.

Moxomia angulata (Hall and Whitfield), Walcott, 1925: 107, pl. 22, figs. 8, 9.
Moxomia angulata—Henningsmoen, 1957: 160, fig. 19.

Parabolinella hecuba—Harrington and Leanza, 1957: 107, fig. 39 2a-e.
Parabolinella tumifrons Robison and Pantoja-Alor, 1968: 790, pl. 102, figs. 10-16.
[non] Parabolinella hecuba—Ross, 1970: 71, pl. 10, figs. 10-13.

Occurrences

Chushina Formation, Mount Robson area, British Columbia (Walcott, 1924, 1925).
Tinu Formation, southern Mexico, Lower Tremadocian Parabolina assemblage
(Robison and Pantoja-Alor, 1968). Rabbitkettle Formation, Broken Skull River (two
collections 48 m and 50 m below top of formation), Missisquoia depressa Subzone.

Holotype

An incomplete cranidium from the Chushina Formation, British Columbia, illustrated
by Walcott (1925, pl. 22, figs. 8, 9) and by Harrington and Leanza (1957, fig. 39
2c-).

Remarks

Walcott (1924: 59) established a new genus Moxomia with the terse diagnosis,
‘‘Moxomia is characterized by the quadrate glabella and cranidium and the small eyes
situated far forward.’’ The designated type species, M. hecuba Walcott from the

Fig. 23 Parabolinella hecuba (Walcott, 1924). Reconstruction of cranidium (prosopon omitted). Bar
represents 1 mm.

Ozarkian of British Columbia, was not described and was merely illustrated by a line
drawing. The following year, Walcott (1925: 107), without explanation, changed the
type species of Moxomia to Crepicephalus (Bathyurus?) angulatus Hall and
Whitfield, 1877, and provided a more complete diagnosis of the genus. His
illustration of Moxomia angulata, however, was a retouched photograph of the same
specimen from British Columbia that he had illustrated the previous year by a line
drawing as Moxomia hecuba and not the holotype of Moxomia angulata from the
Pogonip Group, White Pine District, Nevada.

Harrington and Leanza (1957: 107) examined the types of both Moxomia hecuba
Walcott, 1924, and Moxomia angulata (Hall and Whitfield, 1877). They concluded
that Hall and Whitfield’s species probably belongs in Dunderbergia and that
Walcott’s species is congeneric with Parabolinella limitis Brogger, the type species
of Parabolinella.

A complete description of the cranidium of Parabolinella hecuba (as P. tumifrons
Robison and Pantoja-Alor) was presented by Robison and Pantoja-Alor (1968: 790).
These authors suggested that P. tumifrons differs from P. hecuba in having a more
tapered and more elongate glabella, more anteriorly situated eyes, and convergent
rather than divergent facial sutures. The present material from the Rabbitkettle
Formation includes cranidia with both broad glabellae with little forward taper similar
to P. hecuba (Fig. 52A) and with elongate glabellae with moderate forward taper
similar to P. tumifrons (Fig. 52F). Because the material from British Columbia,
Mexico, and the District of Mackenzie shares the tumid and steeply sloping
preglabellar field and a sigmoid 1s furrow, it is united under the name P. hecuba. The
eye position appears to be similar in these cranidia and the direction of the anterior
facial sutures varies only a few degrees on either side of exsagittal.

The cranidium from the Goodwin Limestone in Nevada that was identified as
Parabolinella hecuba by Ross (1970: 71, pl. 10, figs. 10-13) lacks the tumid and
steeply downsloping preglabellar field of the holotype and it is probably not
conspecific with P. hecuba.

Parabolinella panosa sp. nov.
Fig. 5OA-L, O, Q, R

Diagnosis

A small species of Parabolinella with deep axial furrows; a long, narrow, and
inflated glabella bearing three pairs of very shallow and short (tr.) lateral furrows;
large palpebral lobes located opposite 2s and 3s furrows; faint occipital furrow; and a
tumid preglabellar field.

Occurrences

Rabbitkettle Formation, Broken Skull River (two collections 59.5 m and 60 m below
top of formation), Missisquoia mackenziensis Fauna.

Holotype

A cranidium (ROM 37731) from KK 122.5 (59.5 m below top of Rabbitkettle
Formation) illustrated in Fig. 50Q, R.

Name

From panosus—like bread (Latin) in reference to the loaf shape of the glabella.

Remarks

Parabolinella panosa sp. nov. is represented by well-preserved material of small size
in two collections from the Missisquoia mackenziensis Fauna. If cranidia of the same
size are compared (2.5-3.5 mm, sagittal length), P. panosa (Fig. 500, Q) differs
from P. cf. prolata (Figs. 49D, M, 50N) in having a longer (sag.) and more inflated
glabella which has only faint traces of lateral furrows and a tumid preglabellar field.
The pygidia of the two species appear to be identical. The tumid and steeply sloping
preglabellar field of P. panosa is reminiscent of that of P. hecuba (Walcott). That
latter species has a broader (tr.) glabella and deeper lateral glabellar furrows.

An incomplete ontogenetic sequence of P. panosa is preserved in rather coarsely
crystalline silica. A few of the better specimens are shown in Fig. 50A-J. An early
meraspid specimen (Fig. 50C) demonstrates that immature olenids, at least, were
capable of sphaeroidal enrollment (see Bergstrom, 1973: 21). A conspicuous row of
long and slightly curved spines runs along the axes of meraspid specimens from the
occipital ring to the first segment in front of the transitory pygidium (Fig. 50E).

Parabolinella sp.
Fig. 52J—N

Occurrences

Rabbitkettle Formation, Broken Skull River (single collection 43 m below top of
formation), Apoplanias rejectus Fauna.

Remarks

A single collection from the Apoplanias rejectus Fauna has yielded cranidia of a
Parabolinella in which the lateral glabellar furrows are nearly effaced. Two kinds of
cranidia are present. One type (Fig. 52J) has a relatively broad glabella and a
preglabellar furrow that is shallower than the axial furrows. The other type (Fig. 52L,
M), has a relatively narrow glabella and a preglabellar furrow of the same depth as the

axial furrows. It is possible that these types represent distinct species, but it is equally
possible that they comprise a single variable effaced species related to, and possibly
derived from, Parabolinella hecuba (Walcott) which occurs a few metres below
Parabolinella sp. Both cranidial types have close counterparts in P. hecuba (compare
Fig. 52) with Fig. 52A and Fig. 52L, M with Fig. 52F, H).

Genus Apoplanias Lochman, 1964a

Type Species

Apoplanias rejectus Lochman, 1964a from the Lower Ordovician part of the
Deadwood Formation, Montana (by original designation).

Diagnosis

A genus of olenine trilobite possessing a forwardly tapering glabella with a truncate
front margin and two pairs of deep and oblique lateral glabellar furrows; preglabellar
field is long (sag.) and gently declining; palpebral lobes are large and located close to
glabella near its mid-length. Pygidium is short (sag.) and inverted V-shaped in
posterior view; high axis is crossed by single axial ring furrow; posterior margin
carries three pairs of flattened spines which decrease in size towards rear.

Remarks

Lochman’s (1964a) assignment of pygidia to Apoplanias rejectus appears to be
incorrect. The two nonspinose pygidia attributed to this species (pl. 15, figs. 15, 17)
came from a different drill hole than the one that yielded the holotype cranidium.
These pygidia are associated with two cranidia that Lochman assigned to A. rejectus ,
but these differ from the holotype in possessing palpebral lobes that are located far
from the glabella and, apparently, in lacking lateral glabellar furrows. These cranidia
and pygidia are excluded from A. rejectus. It is explicit from the synonymy of A.
rejectus , below, and from the association of cranidia and pygidia in collections from
the Rabbitkettle Formation, that A. rejectus possessed a spinose pygidium.

Apoplanias rejectus seems to be restricted to the upper Missisquoia Zone and lower
Symphysurina Zone and this olenine is clearly similar and presumably closely related
to the contemporaneous and younger species, Highgatella cordilleri (Lochman,
1964b). The cranidium of H. cordilleri differs from that of A. rejectus in having
wider (tr.) fixed cheeks, deeper lateral glabellar furrows, a distinct third pair of
glabellar furrows, an inflated preglabellar field, and pronounced pitting in the anterior
border furrow. Although Lochman (1964b: 464) stated that the pygidium of H.
cordilleri was not known, she tentatively assigned a meraspid pygidium to this
species (pl. 63, fig. 35). I agree with Hu (1971: 104) that this pygidium probably
belongs to a species of Symphysurina.

Apoplanias rejectus Lochman, 1964a
Figs. 5IM-T, 69K-Q

Apoplanias rejectus Lochman, 1964a: 57, pl. 14, figs. 26-31 (only).
Apoplanias rejectus—Stitt, 1971b: 46, pl. 8, fig. 16.

Highgatella facila Hu, 1971: 103, pl. 21, figs. 1-26.

Highgatella facila—Hu, 1973: 90, pl. 1, figs. 25-28, 30-32.
Apoplanias rejectus—Stitt, 1977: 45, pl. 4, figs. 8, 9.

Occurrences

Deadwood Formation, Montana, Wyoming, South Dakota, Lower Ordovician
(Lochman, 1964a; Hu, 1971, 1973). Signal Mountain Limestone, Wichita and
Arbuckle Mountains, Oklahoma, Missisquoia typicalis and Symphysurina brevis-
picata subzones (Stitt, 1971b, 1977). Survey Peak Formation, western Alberta,
Missisquoia Zone (Derby et al., 1972; Dean, 1978). Rabbitkettle Formation, Broken
Skull River (three collections between 25 m and 44 m below top of formation),.
Symphysurina brevispicata Subzone and Apoplanias rejectus Fauna.

Holotype

An incomplete cranidium from the Deadwood Formation, Montana illustrated by
Lochman (1964a, pl. 14, figs. 26, 28).

Remarks

The available material of this olenine from the upper part of the Rabbitkettle
Formation is badly deformed for the main part. Some of the better preserved cranidia
(Figs. 510, 69K, L) conform well to those of Apoplanias rejectus from the Williston
Basin and Oklahoma.

The pygidium associated with the A. rejectus cranidium (Fig. 69M-O) is transverse
in dorsal view and inverted V-shaped in posterior view; it carries a highly convex and
bluntly rounded axis with a single axial ring and a semicircular terminal piece. The
pleural field descends steeply and it is crossed by two firmly impressed pleural
furrows. The posterior margin of the pygidium bears three pairs of short flattened
spines which decrease in size towards the rear. I suggest that this pygidium belongs to
A. rejectus despite Lochman’s (1964a) assignment of two nonspinose pygidia to this
species. Very similar spinose pygidia from the Deadwood Formation of Wyoming
were assigned to a new species, Highgatella facila, by Hu (1971). Because the
cranidia of H. facila are indistinguishable from those of A. rejectus from Montana,
Oklahoma, and the District of Mackenzie, Hu’s species is considered to be a junior
subjective synonym of A. rejectus.

Cr * Se

Genus Bienvillia Clark, 1924

Type Species

Dikelocephalus? corax Billings, 1865 from the Levis Formation, Point Levis,
Quebec (by original designation).

Bienvillia cf. corax (Billings, 1865)
Fig. 57S

Bienvillia corax—Henningsmoen, 1957: 143, pl. 1, fig. 6 (see for synonymy).

Occurrences

Rabbitkettle Formation, Broken Skull River (two collections 64 m and 70 m below
top of formation), Elkanaspis corrugata Fauna.

Remarks

The silicified cranidia from the Rabbitkettle Formation are much smaller than the
holotype of Bienvillia corax illustrated by Rasetti (1944, pl. 36, fig. 51) and because
they are incomplete and somewhat wrinkled, the comparison with B. corax is
tentative. Three pairs of lateral glabellar furrows are evident in B. cf. corax; the
posterior pairs extend from the axial furrows and connect across the glabella in a
chevron shape. The anterior pair extends from near the mid-line towards, but does not
reach, the anterolateral corner of glabella. The illustrated cranidium of B. cf. corax
differs from B. corax in having a transverse preglabellar field.

Superfamily Solenopleuracea

Family Entomaspidae Ulrich, in Bridge, 1931
(= Family Heterocaryonidae Hupé, 1953;
emend. Gilman Clark and Shaw, 1968)

Assigned Genera

Entomaspis Ulrich, in Bridge, 1931; Bowmania Walcott, 1925; Heterocaryon
Raymond, 1937; Hypothetica Ross, 1951; and, possibly Conococheaguea Rasetti,
1959.

Remarks

In his diagnosis of the Entomaspidae, Rasetti (in Moore, 1959) emphasized the
closely aligned, oblique, and backwardly directed anterior and posterior branches of
the facial suture and the narrow strip of free cheek which connects the eye to the
cephalic border of Entomaspis radiatus Ulrich. The backwardly directed anterior
branch of the facial suture certainly lends a singular aspect to the Entomaspis
cephalon and that, coupled with the wide flat border, apparently encouraged
comparisons with both harpids and trinucleids (Rasetti, 1952; Hupé, 1953). Rasetti
(1952: 801) hypothesized that Entomaspis formed part of the lineage leading to the
Trinucleidae and both Rasetti (¢n Moore, 1959) and Hupé (1953) included the
Entomaspidae in the Harpina.

The general similarity of Entomaspis and the Harpina does not necessarily mean
that these taxa are closely related. I suggest that Entomaspis has much more in
common with Bowmania and Heterocaryon and should be classified with these
genera.

The possibility that Entomaspis is related to genera that were previously assigned
to the Heterocaryonidae Hupé was first suggested by Winston and Nicholls (1967: 89)
who stated that Bowmania sagitta Winston and Nicholls is probably intermediate
between B. americana (Walcott) and Entomaspis radiatus (see also Stitt, 1977: 41).

My recognition that the yoked and spiny cheeks previously assigned to Acidaspis
ulrichi Bassler actually belong to Bowmania americana lends further credence to a
close relationship of Bowmania and Entomaspis. It is possible to transform a
Bowmania cephalon to an Entomaspis cephalon by fusing the lateral array of cephalic
spines and by shifting the anterior facial sutures forward to the edge of the cephalon
and by shifting the preocular sutures outward and backward. This hypothetical
transformation does not imply that Bowmania necessarily gave rise to Entomaspis.

This study also demonstrates that the pygidia of both Bowmania and Heterocaryon
are very similar to those assigned to Entomaspis radiatus. In addition, the pygidium
which formed the basis for Entomaspis bridgei Rasetti, 1952 is more similar to
Bowmania than it is to Entomaspis and Rasetti’s species should be assigned to the
former genus.

I conclude that the Heterocaryonidae Hupé should be synonymized with the
Entomaspidae Ulrich.

Rasetti (1952) discussed the possible relationship of the entomaspids to the
trinucleids. Two entomaspid genera, Entomaspis and Bowmania, also exhibit marked
similarity to Doremataspis Opik, 1967 from the Mindyallan (early Late Cambrian) of
Queensland which Opik assigned to the family Liostracinidae Raymond (compare
Opik, 1967, fig. 138 and Rasetti, 1952, figs. 1, 3 and this paper, Fig. 24). These
genera possess similarly shaped cephala and glabellae with similar markings. The
difference in the degree of divergence of the anterior branches of the facial suture in
the three genera is striking, but in this feature Doremataspis is intermediate between
Bowmania and Entomaspis. Whether the cephalic similarity between this liostracinid
and the entomaspids is indicative of close phyletic connection is uncertain. The
pygidium attributed to Doremataspis has little in common with those of the
entomaspids and its cephalon is distinguished by a pair of bacculae and by the
presence of a very large rostral plate that extends for nearly the full width of the
cephalon.

Genus Bowmania Walcott, 1925

Type Species

Arethusina americana Walcott, 1884 from Upper Cambrian rocks of the Eureka
District, Nevada (by original designation).

Revised Diagnosis

A genus of Entomaspidae with a glabella of parabolic outline, deep axial furrows, and
two or three lateral glabellar furrows. Preglabellar field is long and forwardly
declined. Widely set eyes are located opposite mid-length of glabella. Palpebral
ridges are prominent. Anterior and posterior branches of facial suture curve outward
from the eye; anteriorly, suture runs along and bisects slightly convex anterior border.
Free cheeks are yoked. Genal spines are long and backwardly directed. Lateral and
anterior flanks of cephalon carry prominent fringe of marginal spines whose lengths
decrease posteriorly. Pygidium is small, broadly triangular, and three times as wide
as long. Prominent axis with five or six rings is slightly tapering. Horizontal pleural
portion has four or five interpleural furrows and faint pleural furrows. A narrow
raised rim forms anterior and posterior border of pygidium.

Bowmania americana (Walcott, 1884)
Figs. 24, 53K-S, 54A-0

Arethusina americana Walcott, 1884: 62, pl. 9, fig. 27.

Acidaspis ulrichi Bassler, 1919: 355, pl. 37, figs. 6-8.

Bowmania americana—Walcott, 1925: 73, pl. 15, figs. 15, 16.
Bowmannia americana [sic |—Hupé, 1953: 150, fig. 132-2.
‘‘Acidaspis’’ cf. ulrichi—Kindle and Whittington, 1958: 332.
‘‘Acidaspis’’ ulrichi—Rasetti, 1959: 393, pl. 51, fig. 27.

‘‘Acidaspis’’ ulrichi—Kindle and Whittington, 1959: 17.

Bowmania americana—Winston and Nicholls, 1967: 89, pl. 10, fig. 18.
Bowmania americana—Longacre, 1970: 56.

Bowmania americana—Stitt, 1971b: 22, pl. 7, figs. 7-9.

Occurrences

Upper Cambrian, Eureka District, Nevada (Walcott, 1884). Wilberns Formation,
central Texas, Saukiella serotina Subzone (Winston and Nicholls, 1967; Longacre,
1970). Signal Mountain Limestone, Arbuckle Mountains, Oklahoma, Saukiella
serotina Subzone (Stitt, 1971b). Notch Peak Formation, Utah, Saukiella serotina
Subzone (Hintze et al., 1980). Lime Kiln Member of Frederick Limestone,

Maryland, Saukiella serotina Subzone (Rasetti, 1959; M.E. Taylor, in Reinhardt,
1974). Cow Head Group, Broom Point, western Newfoundland, Hungaia
Assemblage (Kindle and Whittington, 1959; C.H. Kindle Collection at Geological
Survey of Canada, Ottawa). Rabbitkettle Formation, Broken Skull River (seven
collections between 75 m and 96 m below top of formation), Bowmania americana
Fauna.

Holotype

An incomplete cranidium from the Hamburg Limestone (?), Dunderberg Mine,
Eureka District, Nevada illustrated by Walcott (1884, pl. 9, fig. 27), Walcott (1925,
plels: figs. 15; 16)

Description

Cephalon (exclusive of genal and marginal spines) is semicircular in outline and
moderately convex. Glabella is inflated and parabolic in outline. Its length is one-half
that of cephalon and its width is less than one-third that of cephalon at level of eyes.
Broad preglabellar field curves steeply to anterior border furrow. Deep axial furrows
are connected in even curve with narrow and sharply incised preglabellar furrow.
Three short and approximately equally spaced lateral glabellar furrows extend inward
and backward. Occipital ring is relatively long (sag.) and is surmounted by large
curved median spine. Occipital furrow is complete and slightly backwardly curving.
Eyes are located at about half length of glabella; a little more than one-half the
distance out on the cheeks. Crescentic palpebral lobe is continuous adaxially with
prominent palpebral ridge which extends across fixed cheek with slight forward
curvature to join axial furrow at level of 3s furrow. Cephalic borders are relatively
long (sag.) and very gently convex anteriorly; become narrower and convex laterally
and posteriorly; they are demarcated by deep border furrows which connect in
semicircular continuum. Posterior branch of facial suture curves outward and
backward to cut posterior margin inside base of genal spine. Anterior branch of facial
suture curves laterally a short distance before turning in to cross anterior border
furrow. It continues along anterior border in a path parallel with anterior margin.
Genal spine is long, gradually tapering, backwardly directed with faint adaxial
curvature distally, and circular in cross-section. Its interior flank contains a single
row of small, closely spaced spines. Outside margin of entire cephalon is fringed by a
single row of long, slim, horizontally disposed spines that number about 50 in total.
Anterior spines are about as long as glabella, forwardly pointed with slight lateral
curvature distally. Posteriorly, these spines decrease in length and are progressively
swept backward. Each of the marginal spines is circular in cross-section and each
projects abruptly from the tubelike anterior and lateral borders and the genal spines.

Cephalon inside border furrows is covered by sparsely distributed tubercles, some
of which are perforated.

Pygidium is semielliptical in outline and three times as wide as long. Convex axis
extends to posterior border and is outlined by deep, straight, and slightly converging
axial furrows. It comprises five well-defined axial rings and a terminal piece. Flat

pleural field is crossed by four or five deep interpleural furrows and an equal number
of faint pleural furrows. These furrows extend to, and terminate against, narrow and
raised posterior border which rims edge of pygidium. Posterior margin of pygidium is
vertical to slightly overhanging.

Remarks

The holotype of Bowmania americana (Walcott) is an incomplete cranidium of
moderate convexity. It measures about 6.5 mm in sagittal length and it possesses
backwardly swept palpebral ridges. This cranidium differs somewhat from most of
the silicified cranidia from the Rabbitkettle Formation assigned to B. americana.
These are, for the most part, smaller and tend to have steeply curving preglabellar
fields and prominent median occipital spines. Whether the holotype has a median
occipital spine cannot be determined because the central part of the occipital ring is
exfoliated. In addition, the palpebral ridges of the silicified specimens tend to be
directed only slightly posterior of transverse—but this feature is difficult to evaluate

Fig. 24 Bowmania americana (Walcott, 1884). Reconstruction of cephalon and pygidium. Bar
represents 1 mm.

because each of the cranidia is somewhat sheared and wrinkled. Significantly, the
largest silicified cranidium recovered (sagittal length 5.0 mm, Fig. 53L) is very
similar to the holotype from Nevada. The differences between the Rabbitkettle
specimens and the holotype may well be attributable to size and preservation. The
cranidia of B. americana from Oklahoma (Stitt, 1971b, pl. 7, figs. 7-9) are smaller
than the holotype and rather similar to the Rabbitkettle specimens.

Longacre (1970: 56) suggested that the separation of Bowmania americana from B.
pennsylvanica Rasetti, 1959 may be artificial and Stitt (1971b: 22) implied that B.
americana is gradational with B. sagitta Winston and Nicholls, 1967. These species
of Bowmania are confined to the Saukiella serotina Subzone in both Oklahoma and
Texas and, because each has considerable morphologic variation, it may eventually
be necessary to unite them under the name B. americana. In this regard, it should be
noted that the type material of B. pennsylvanica occurs in the same collection as
‘‘Acidaspis’’ ulrichi in Maryland (Rasetti, 1959). Cook and Taylor (1977, fig. 2)
indicated a nearly complete overlap of the stratigraphic ranges of Bowmania and
‘‘Acidaspis’’ in the upper Whipple Cave Formation of the Egan Range, Nevada.

Genus Heterocaryon Raymond, 1937

Type Species

Heterocaryon platystigma Raymond, 1937 from Zone 1 (Hungaia Assemblage),
Highgate Falls, Vermont (by original designation).

Heterocaryon tuberculatum Rasetti, 1944
Figs. 25, SSA-N

Heterocaryon tuberculatum Rasetti, 1944: 241, pl. 36, fig. 55.

Heterocaryon cf. tuberculatum—Winston and Nicholls, 1967: 76, pl. 11, figs. 15,
18.

Heterocaryon cf. tuberculatum—Longacre, 1970: 57.

Heterocaryon tuberculatum—Stitt, 1971b: 22, pl. 7, fig. 11.

Occurrences

Levis Formation, North Ridge, Levis, Quebec, Hungaia Assemblage (Rasetti, 1944).
Wilberns Formation, central Texas, Saukiella serotina Subzone (Winston and
Nicholls, 1967; Longacre, 1970). Signal Mountain Limestone, Wichita and Arbuckle
mountains Oklahoma, Rasettia magna to Saukiella serotina subzones (Stitt, 1971b,
1977). Notch Peak Formation, Utah, Saukiella serotina Subzone (Hintze et al.,
1980). Rabbitkettle Formation, Broken Skull River (eight collections between 90 m
and 177 m below top of formation), Bowmania americana Fauna and Yukonaspis
kindlei Fauna.

Holotype

An incomplete cranidium from the Levis Formation, Levis, Quebec illustrated by
Rasetti (1944, pl. 36, fig. 55).

Description

Cephalon is crescentic in outline and strongly convex (sag. and tr.). Glabella is large,
inflated, and oval in outline. It expands somewhat towards the front and is about
one-third the width and four-fifths the sagittal length of cephalon. Preglabellar field is
short and nearly vertically disposed. Axial furrows are deep and are continuous with
evenly rounded and shallow preglabellar furrow. Three short (tr.) lateral glabellar
furrows are approximately equally spaced and are barely perceptible. Occipital ring is
short (sag.); occipital furrow is nearly straight. Eyes are located far out on cheek,
opposite 3s furrow. Palpebral lobe is distinct and nearly exsagittally directed.
Palpebral ridge is faint and narrow (exsag.). It curves across wide and inflated fixed
cheek to join axial furrow at midlength of 4p lobe. Cephalic borders are tubelike;
border furrows are deep. Posterolateral corner is extended into short, backwardly and
slightly upwardly curving genal spine. Anterior branch of facial suture runs forward
and inward in even curve on to anterior border. Posterior branch of suture runs
backward and outward. Entire cephalon is densely covered by tubercles, some of
which are perforated.

Pygidium is broadly triangular and two and a half times as wide as long. Axis
consists of four or five highly arched rings and a blunt terminal piece. Deep axial
furrows converge posteriorly. Flat pleural field is crossed by four distinct interpleural
furrows. Faint pleural furrows may be seen on some specimens. Five pairs of
flattened spines and a larger median unpaired spine project back and over vertical
posterior margin of pygidium. Each spine has an oval base, above which it expands
and is flattened in line with pygidial margin. Each spine has a saddle-shaped tip in
plan view. Pygidium bears sparsely distributed perforate tubercles, including one or

two pairs of each axial ring.

gee,

Fig. 25 Heterocaryon tuberculatum Rasetti, 1944. Reconstruction of cephalon and pygidium (prosopon
omitted). Bar represents 1 mm.

Remarks

The type species, Heterocaryon platystigma Raymond (1937, pl. 3, fig. 13; see also
Gilman Clark and Shaw, 1968, pl. 125, figs. 4-6), differs from H. tuberculatum in
having a shorter and highly inflated glabella with deep and oblique 1s furrows and a
longer and concave preglabellar field.

The similarity of the pygidia of Bowmania americana, Heterocaryon tuber-
culatum, and Entomaspis radiatus provides strong support for their inclusion in the
same family.

Family Catillicephalidae Raymond, 1938

Genus Triarthropsis Ulrich, in Bridge, 1931

Type Species

Triarthropsis nitida Ulrich, in Bridge, 1931 from the Eminence Dolomite
(Trempealeauan), Eminence, Missouri (by monotypy).

Triarthropsis limbata Rasetti, 1959
Fig. 57U

Triarthropsis limbata Rasetti, 1959: 382, pl. 52, figs. 1-8.
Triarthropsis limbata—Stitt, 1971b: 16, pl. 7, fig. 3.

Occurrences

Conococheague Limestone, Maryland, Saukia Zone (Rasetti, 1959). Signal
Mountain Limestone, Wichita and Arbuckle mountains, Oklahoma, Saukiella junia
to Corbinia apopsis subzones (Stitt, 1971b, 1977). Rabbitkettle Formation, Broken
Skull River (single collection 165 m below top of formation), Yukonaspis kindlei
Fauna.

Holotype

A cranidium from the upper Conococheague Limestone, Washington County,
Maryland illustrated by Rasetti (1959, pl. 52, figs. 1, 2).

Remarks

The specimens from the Rabbitkettle Formation possess wide fixed cheeks, large
palpebral lobes, shallow axial and preglabellar furrows, and long (sag.) preglabellar
fields. They appear to conform to Rasetti’s (1959) description and illustrations of T.
limbata.

? Family Kingstoniidae Kobayashi, 1933

Genus Larifugula gen. nov.

Type Species

Larifugula triangulata sp. nov. from the Upper Cambrian part of the Rabbitkettle
Formation.

Diagnosis

A small genus of kingstoniid (?) trilobite possessing an anteriorly expanding or
subrectangular glabella with two pairs of faint lateral furrows. Occipital ring bears a
long slender median spine. Preglabellar field is long and evenly downcurved to weak
anterior border furrow. Palpebral lobes are small and slightly raised; they are located
opposite frontal glabellar lobe. Genal spines are long, slender, and gently curved.
Facial sutures follow outwardly arcuate path from posterior margin to eye and then
forward to join median connective suture on sagittal line—thus outlining a
subtriangular to semicircular cranidium. Pygidia are subtriangular to subcircular in
outline with variably developed axes, pleural fields, and borders.

Name

From /arifuga—vagabond (Latin) in reference to the widespread occurrences of this
small trilobite. Feminine.

Assigned Species

The type species occurs in the Yukonaspis kindlei Fauna to Elkanaspis corrugata
Fauna interval in the Rabbitkettle Formation. The only other species assigned to the
new genus 1s Larifugula leonensis (Winston and Nicholls, 1967) which occurs in the
Corbinia apopsis Subzone in Texas, Oklahoma, and Nevada and in the Elkanaspis
corrugata Fauna in the District of Mackenzie.

Remarks

Taylor (1977: 408) remarked in a footnote that the supposed olenid Leiobienvillia
leonensis Winston and Nicholls, 1967 probably represents an undescribed genus.
Examination of the type material of L. leonensis from Texas (Fig. 70H-L) confirms
that this trilobite is neither congeneric with Leiobienvillia laevigata Rasetti, 1954 nor
an olenid. L. leonensis and a new species from the Rabbitkettle Formation are here
assigned to a new genus, Larifugula, whose affiliation may lie with the kingstoniids.

Larifugula differs from Leiobienvillia Rasetti in having an ovate glabella, deeper
cephalic furrows, an anterior border furrow, an occipital spine, and a subtriangular
cranidium (compare Fig. 26A and Rasetti, 1954, fig. 3).

The cranidium of the new genus shares some features with three genera that
Raymond defined for one or two small and poorly preserved cranidia from the Upper
Cambrian of Vermont. These are Zacompsus Raymond, 1924 (type species, Z.
clarki), Pseudosalteria Raymond, 1924 (type species, P. laevis), and Strotocephala
(type species, S. howelli). Of these, Zacompsus is most similar to Larifugula in
having an anteriorly expanding and bulb-shaped glabella. Raymond’s genus differs
from the new genus by possessing prominent palpebral ridges and, apparently, by
lacking an anterior border furrow and an occipital spine. Pseudosalteria and
Strotocephala have semicircular cranidia with faintly outlined and subcircular
glabellae, anteriorly placed eyes, and very faint occipital and posterior border
furrows. In addition, Strotocephala bears a long slim occipital spine. The cranidia of
Pseudosalteria and Strotocephala do not appear to differ from Leiobienvillia and
these taxa should probably be united under the senior name, Pseudosalteria.

Larifugula shares a number of cranidial and pygidial features with the
Dresbachian/ Franconian genus Bynumia Walcott, 1924 and with the Trempealeauan
genus Bynumiella Resser, 1942 and this similarity is the basis for the tentative
assignment of Larifugula to the Kingstoniidae. The three genera share a triangular
cranidial outline and similarly placed palpebral lobes of the same size. The pygidium
of Bynumia bears a faintly ribbed axis and lacks both border furrows and furrows on
the pleural region. On the interior, the pygidium of Bynumia eumus Walcott (= B.
venusta Resser, B. robsonensis Resser, and B. sawbackensis Resser; see Greggs,
1962: 116, 117) from the Sullivan Formation, Banff National Park (Resser, 1942, pl.
9, figs. 24-26, 34, 44) displays five or six pleurae that terminate against a
‘‘quasi-border’’. B. eumus, therefore, appears to possess an exterior pygidial
morphology similar to the exterior of the Larifugula triangulata pygidium and an
interior morphology similar to the exterior of the L. Jeonensis pygidium. Exfoliated
pygidia of Kingstonia alabamensis Resser (see Palmer, 1962, pl. 6, fig. 12) also
display a morphology similar to that of L. leonensis.

Larifugula can be distinguished from Bynumia by possessing deeper cephalic
furrows, an unfurrowed glabella that expands anteriorly, an occipital spine, and long
slender genal spines. The anteriorly expanding and unfurrowed glabella and the
occipital spine also distinguish it from Bynumiella, but it is significant that Greggs
(1962: 120) noted that B. typicalis Resser, 1942 from the Saukia Zone of the Bison
Creek Formation, Banff National Park, bears two pairs of shallow lateral glabellar
furrows and a short, sharp medial tubercle on the occipital ring. These features bring
Bynumiella close to Larifugula.

The Lower Ordovician genus Yumenaspis Chang and Fan (type species Y.
yumenensis Chang and Fan; see Lu et al., 1965, pl. 132, figs. 1-6) has a cranidium
that is rather similar to that of Larifugula. It differs from Larifugula in having a
glabella that expands markedly towards the front, a broad (tr.) anterior border on the
cranidium, prominent palpebral ridges, eyes located closer to the glabella, and in
lacking an occipital spine. In addition, the ribbed pygidium attributed to Yumenaspis
is broadly triangular and bears a marginal rim.

Larifugula triangulata gen. et sp. nov.
Figs. 26A; 56A-O0, Q-S

Diagnosis

A species of Larifugula with an anteriorly expanding and drop-shaped glabella and a
subtriangular pygidium bearing a convex axis with two rings and a long terminal
piece and an unfurrowed pleural region which slopes evenly to margin.

Occurrences

Rabbitkettle Formation, Broken Skull River (eight collections between 61 m and
165 m below top of formation), Elkanaspis corrugata Fauna, Bowmania americana
Fauna, Yukonaspis kindlei Fauna.

Holotype

A cranidium (ROM 37643) from K 550 illustrated on Fig. 56A-C.

Name

From triangulus—having three angles (Latin) in reference to the shape of the
pygidium.

Preservation

These silicified specimens are extremely small; the largest cranidium measures
2.0 mm (exclusive of occipital spine) and the largest pygidium only 0.7 mm in
sagittal length. In addition, the specimens from the E/kanaspis corrugata Fauna have
exceedingly thin and wrinkled shells. Some of these specimens show small-scale
deformation that could be mistaken for true morphologic features; for example, the

prominent “‘palpebral ridge’’ on the left side of the cranidium in Fig. 56G. The
specimens are difficult to handle and a number were destroyed in attempts to remove
them from their mounting pins after photography.

Description

Cephalon is crescentic in outline and moderately vaulted. Glabella is oval to
bulb-shaped and it expands somewhat towards front; it is outlined by deep axial
furrows and variably developed and shallow preglabellar furrow. Two pairs of short
(tr.) lateral glabellar furrows extend inward a short distance. Occipital furrow is faint
to effaced. Occipital ring is triangular; it protrudes well beyond the posterolateral
edge of cephalon. A long slim occipital spine extends nearly straight back; it is almost
as long (sag.) as glabella. Preglabellar field slopes evenly to the faint anterior border
furrow which is generally defined by no more than a change in slope. In many
cranidia a poorly differentiated median longitudinal ridge traverses preglabellar field
to narrow (tr.) anterior border. Small palpebral lobe is raised slightly above cheek at
weakly incised palpebral furrow; it is located opposite widest part of glabella, at
two-thirds glabellar length. Deep and transverse posterior border furrow defines
narrow and convex posterior border. It continues on to free cheek and swings forward
and shallows markedly as it becomes lateral border furrow. Genal spine is oval in
cross-section and is about as long as glabella; it is slender and curves slightly inward.
Anterior branch of facial suture swings forward along outwardly curved path to meet
median connective suture on sagittal line. Posterior path of suture proceeds backward
and outward to cross posterior margin at right angle. Surface of cephalon is smooth;
occipital and genal spines carry fine terrace lines which run parallel to their margins.
Minute pygidium is triangular in outline and moderately vaulted (tr.). Narrow axis
consists of two short (sag.) rings and long, tapering terminal piece; it extends to just
in front of posterior margin. Pleural region is unribbed, but most specimens carry a

Fig. 26 A_ Larifugula triangulata gen. et sp. nov. Reconstruction of cranidium and pygidium. Bar
represents 1 mm.
B_ Larifugula leonensis (Winston and Nicholls, 1967). Reconstruction of cranidium and
pygidium. Same scale as 26a.

few irregular transverse undulations; its interior portion is nearly flat, distally it
declines steeply to lateral margin. Pleural region carries irregular fine terrace lines
that are oriented parallel to lateral margin.

Remarks

The cranidium of Larifugula triangulata gen. et sp. nov. differs from that of L.
leonensis (Winston and Nicholls) in having an anteriorly expanding, drop-shaped
glabella and fainter occipital, preglabellar, and anterior border furrows. The pygidia
of the two species differ considerably. That of L. triangulata is subtriangular in
outline and lacks a border; that of L. leonensis is semicircular in outline and bears a
narrow and outwardly concave border which has an inner raised rim (Fig. 26).

Larifugula leonensis (Winston and Nicholls, 1967)
Figs. 26B, 56P, 670-R, 7OH—-L

Leiobienvillia leonensis Winston and Nicholls, 1967: 75, pl. 11, figs. 16, 20, 21.
Leiobienvillia leonensis—Longacre, 1970: 18.
Leiobienvillia leonensis—Stitt, 1971b: 26, pl. 7, fig. 12.

Occurrences

Wilberns Formation, central Texas, Corbinia apopsis Subzone (Winston and
Nicholls, 1967; Longacre, 1970). Signal Mountain Limestone, Wichita and Arbuckle
mountains, Oklahoma, Corbinia apopsis Subzone (Stitt, 1971b, 1977). Notch Peak
Formation, Utah, Corbinia apopsis Subzone (Hintze et al., 1980). Survey Peak
Formation, western Alberta, Corbinia apopsis Subzone (Derby et al., 1972).
Rabbitkettle Formation, Broken Skull River (two collections 61 m and 70 m below
top of formation), E/kanaspis corrugata Fauna.

Holotype

A cranidium from the Wilberns Formation, central Texas illustrated by Winston and
Nicholls (1967, pl. 11, fig. 20) and herein (Fig. 70H—J).

Remarks

The holotype cranidium of Larifugula leonensis (Winston and Nicholls) from Texas
(Fig. 70H-J) is slightly larger and somewhat more inflated than the cranidia from the
Rabbitkettle Formation which are assigned to this species (Figs. 56P, 67P, Q). The
single deformed pygidium of L. leonensis from the Rabbitkettle (Fig. 67R) is more

transverse than the paratype pygidium from Texas (Fig. 70K).

A fragmentary thorax of L. leonensis (Fig. 670) consists of six articulated
segments. Each segment comprises an arched axis, a horizontal inner portion of the
pleura, and a gently declined outer portion. A transverse pleural furrow continues
nearly to the tip of the segment. A long median spine projects posteriorly from the
axis of one of the segments. This spine carries a longitudinal prosopon of very fine
ridges; identical to that on the occipital spine.

Family Plethopeltidae Raymond, 1925

Genus Plethometopus Ulrich, in Bridge, 1931

Type Species

Bathyurus armatus Billings, 1860 from the Levis Formation, Point Levis, Quebec
(by original designation).

Remarks

Plethometopus differs from the related genus Plethopeltis Raymond, 1913 in the
absence of axial furrows in front of the eyes and the absence of an anterior border
furrow (Longacre, 1970: 19; Taylor and Halley, 1974: 25).

The Rabbitkettle material of P. obtusus Rasetti extends the range of Plethometopus
into the lower part of the Missisquoia depressa Subzone. Previously, the youngest
record of the genus was in the Corbinia apopsis Subzone in Texas and Oklahoma.
Stitt (1977: 28, 29) demonstrated that Plethopeltis , previously thought to be restricted
to the Trempealeauan (Lochman-Balk, 1970, fig. 7), also extends as high as the M.
depressa Subzone in Oklahoma.

Plethometopus obtusus Rasetti, 1945
Figs. 27, 56T-Vv

Plethometopus obtusus—Taylor and Halley, 1974: 24, pl. 1, figs. 11-14 (see for
synonymy).

Occurrences

Levis Formation, Levis, Quebec, Hungaia Assemblage (Rasetti, 1945). Con-
ococheague Formation, Maryland, Saukia Zone (Rasetti, 1959). Wilberns Forma-

tion, central Texas, Saukiella serotina and Corbinia apopsis subzones (Winston and
Nicholls, 1967; Longacre, 1970). Signal Mountain Limestone, Wichita and Arbuckle
mountains, Oklahoma, Saukiella serotina and Corbinia apopsis subzones (Stitt,
1971b, 1977). Whitehall Formation, New York, Saukiella serotina Subzone (Taylor
and Halley, 1974). Rabbitkettle Formation, Broken Skull River (five collections
between 55 m and 77 m below top of formation), Missisquoia depressa Subzone,
Missisquoia mackenziensis Fauna, Elkanaspis corrugata Fauna, and Bowmania
americana Fauna.

Holotype

A cranidium from an Upper Cambrian boulder, North Ridge, Levis, Quebec
illustrated by Rasetti (1945, pl. 62, fig. 1).

Remarks

The characteristic features of Plethometopus obtusus Rasetti and the differences with
other species of Plethometopus have recently been discussed by Longacre (1970: 19),
Stitt (1971: 35) and Taylor and Halley (1974: 24). The Rabbitkettle cranidia agree, in
all respects, with the type and other attributed cranidia of P. obtusus.

Genus Leiocoryphe Clark, 1924

Type Species

Leiocoryphe gemma Clark, 1924 from an Upper Cambrian boulder, Levis, Quebec
(by original designation).

Fig. 27 Plethometopus obtusus Rasetti, 1945. Reconstruction of cranidium. Bar represents | mm.

Leiocoryphe spp.
Fig. 57A—F

Occurrences

Rabbitkettle Formation, Broken Skull River (seven collections between 86.5 m and
177 m below top of formation), Bowmania americana Fauna and Yukonaspis kindlei
Fauna.

Remarks

In the Rabbitkettle Formation, Leiocoryphe is represented by a few small cranidia and
pygidia. On the basis of the associated pygidia, the generic identification is firm. I
have not attempted to identify these specimens to the species level. Some cranidia
(Fig. 57A, B) are subtriangular in outline and inflated above and over the anterior
margin. These cranidia are associated with typical pod-shaped Leiocoryphe pygidia-
(Fig. 57F) whose anterior margin is located on the anteroventral edge (note position of
articulating furrow in the anterior view in Fig. 57E). Other cranidia (Fig. 57C) are
transverse and only slightly inflated. Associated pygidia (Fig. 57D) are nearly flat and
equally transverse. These are similar to the specimens assigned to L. platycephala
Kobayashi, 1935 (for example, by Stitt, 1971b, pl. 4, figs. 9, 10, 12).

Superfamily Norwoodiacea
Family Norwoodiidae Walcott, 1916

Genus Levisaspis Rasetti, 1943

Type Species

Levisaspis typicalis Rasetti, 1943 from Lower Ordovician limestone conglomerate at
North Ridge, Levis, Quebec (by original designation).

Remarks

Shaw (1951: 105) considered Levisaspis to be a subgenus of Holcacephalus Resser.
Later, he (Shaw, 1953: 145) proposed that Levisaspis be considered a junior synonym
of Hardyoides Kobayashi, an arrangement also favoured by Lochman (in Moore,
1959: 302). Palmer (1965b) reviewed the classification of Holcacephalus,
Levisaspis , and Hardyoides and concluded (p. 54) that Levisaspis is not congeneric
with Hardyoides and that Holcacephalus belongs to a separate family from Levisaspis

and Hardyoides. Herein, Levisaspis is considered to have full generic status within
the Norwoodiidae.

Levisaspis glabrus (Shaw, 1951)
Figs. 28, 680-Q

Holcacephalus (Hardyoides) glabrus Shaw, 1951: 106, pl. 24, figs. 1-3 (only).
Hardyoides glabrus—Shaw, 1953: 145, pl. 18, figs. 20, 21.
Levisaspis glabrus—Palmer, 1965: 54.

Occurrences

Gorge Formation, Highgate Falls, Vermont. Missisquoia Zone (Shaw, 1951).
Rabbitkettle Formation, Broken Skull River (two collections 45 m and 45.5 m below
top of formation). Missisquoia depressa Subzone.

Holotype

A cranidium from the Gorge Formation, Highgate Falls, Vermont illustrated by Shaw
(95K; pl. 24, fis. 1).

Description

Cranidium crescentic in outline, twice as wide as long, and convex. Genal corners
bear fixigenal spines of unknown length. Axial furrows deep; continuous with
shallow preglabellar furrow. Evenly inflated glabella is subrectangular in outline with
rounded anterolateral corners. Occipital ring is short (sag.), defined by faintly incised
occipital furrow. A single pair of short (exsag.) lateral glabellar furrows extends
inwardly a short distance. Preglabellar field is nearly vertically disposed towards deep
and narrow (sag.) anterior border furrow which defines narrow, rimlike and slightly
curving (tr.) anterior border. Distinct and tubelike palpebral ridge curves outward
from anterolateral corner of glabella; terminates as small, convex palpebral lobe.

Fig. 28 Levisaspis glabrus (Shaw, 1951). Reconstruction of cranidium. Bar represents | mm.

Facial suture is proparian; its posterior course is laterally curving; anteriorly, it curves
slightly adaxially. Dorsal surface of cranidium is finely granulose.

Remarks

Levisaspis glabrus differs from the only other known species, L. typicalis Rasetti, in
having a shorter preglabellar field, more convex palpebral ridges, eyes located closer
to the glabella, and, possibly, longer fixigenal spines.

The holotype of L. glabrus was illustrated only in lateral view by Shaw (1951) so
some uncertainty exists about the morphology of this species. Even though the
illustrated Rabbitkettle specimen has a glabella that is less rounded anteriorly, it is
considered to be conspecific with the two paratype heads of L. glabrus from
Vermont.

Superfamily Dikelocephalacea
Family Saukiidae Ulrich and Resser, 1933

Genus Calvinella Walcott, 1914

Type Species

Dikelocephalus spiniger Hall, 1863 from the Trempealeau Formation, Trempealeau,
Wisconsin (by original designation).

Remarks

Longacre (1970: 45) and Taylor and Halley (1974: 27) have summarized the features
that have been used to distinguish Calvinella from other saukiid genera (unequally
divided pygidial pleurae, occipital spine, granular prosopon on the cranidium).
Taylor and Halley emphasized that these features are of doubtful taxonomic
significance because some are shared with Tellerina Ulrich and Resser, 1933 and
Prosaukia Ulrich and Resser, 1933 and these authors further noted that these saukiid
generic names should be used advisedly until such time as their respective type
species have been fully re-evaluated.

‘*Calvinella’’ palpebra sp. nov.
Figs. 29, 58A—J, 69D, E

Diagnosis

A species of ‘‘Calvinella’’ with wide (tr.), long (exsag.) and crescentic palpebral
lobes located close to the glabella and two pairs of lateral glabellar furrows. Small
cranidia possess slender occipital spines; these are reduced to tubercles in large
cranidia.

Occurrence

Rabbitkettle Formation, Broken Skull River (two collections 165 m and 177 m below
top of formation), Yukonaspis kindlei Fauna.

Holotype

A cranidium (ROM 37466) from K 510 (177 m below top of Rabbitkettle Formation)
illustrated on Fig. 58C, D.

Fig. 29 *‘Calvinella’’ palpebra sp. nov. Reconstruction of cephalon and pygidium (prosopon omitted).
Bar represents | mm.

Name

From palpebra—eyelid (Latin) in reference to the large and conspicuous palpebral
lobes.

Remarks

‘‘Calvinella’’ palpebra sp. nov. is so similar to ‘‘Calvinella’’ prethoparia Longacre,
1970 that a comparison with that well-described species (Longacre, 1970; Taylor and
Halley, 1974) is presented in lieu of a description. The Rabbitkettle material of
‘‘Calvinella’’ is much smaller than the Texas and New York material. In spite of the
size difference, ‘‘C .’’ palpebra is seen to have consistently larger palpebral lobes that
are located closer to the glabella than does *‘C.’’ prethoparia (compare the cranidia
of increasing sizes illustrated by Longacre, 1970, pl. 6, figs. 10, 9, 7 with those in
this paper, Fig. 581, D, 69E). ‘‘C.’’ palpebra has only two pairs of lateral glabellar
furrows, of which Is is complete across the glabella in only the largest available
cranidia. ‘‘C.’’ prethoparia has three pairs of furrows, of which Is extends across the
glabella in both small and large cranidia.

saukiid indet.
Fig. 57P-R

Occurrence

Rabbitkettle Formation, Broken Skull River (single collection 165 m below top of
formation), Yukonaspis kindlei Fauna.

Remarks

Several saukiid specimens occur in a single collection from the Rabbitkettle
Formation. A fragmentary cranidium (Fig. 57Q, R) is unlike that of any saukiid genus
in North America in having an inflated rectangular glabella; straight, narrow (sag.),
and bandlike 1s and 2s furrows that are complete across the glabella; a narrow
anterior border furrow that undercuts front part of the glabella; and a pair of small,
anteriorly directed spines located on the vertical anterior border. In the nature of the
front part, this cranidium has affinity to the Australasian genus Lophosaukia
Shergold, 1971, but that genus has a triangular crest, and not a pair of spines, on the
anterior border.

An associated pygidium (Fig. 57P) is similar to those of North American saukiids.
It is semicircular in outline and has a convex axis of, at least, five rings, which
terminates as a pointed post-axial ridge. The pleural field declines gradually to a
broad border and it is crossed by six backwardly curving interpleural furrows. The

pleurae are subequally divided by pleural furrows. Such a pygidium could belong to
Calvinella Walcott, 1914 or Tellerina Ulrich and Resser, 1933. It is unlikely that
these specimens are conspecific or even congeneric.

Family Ptychaspididae Raymond, 1925
Subfamily Euptychaspidinae Hupé, 1953
(pro Euptychaspidae Hupé, 1953)

Diagnosis

Ptychaspididae with deep axial furrows, faintly to firmly impressed anterior border
furrow, short preglabellar field, generally wide (tr.) fixed cheeks, and short (exsag.)
raised palpebral lobes defined by deep palpebral furrows and lacking distinct
palpebral ridges. Pygidium is elliptical to triangular in outline; axis is short (sag.),
axial rings are few in number; border is broad and declined.

Assigned Genera

Euptychaspis Ulrich, in Bridge, 1931; Liostracinoides Raymond, 1937; Kathleenella
gen. nov.

Remarks

Hupeé (1953) established the family Euptychaspidae for Euptychaspis Ulrich, Keithia
Raymond, and Keithiella Rasetti. This family was synonymized with the
Ptychaspididae by Lochman-Balk (in Moore, 1959). I propose to retain the name
Euptychaspidinae Hupé for ptychaspidids with a preglabellar field, small eyes,
inflated fixed cheeks lacking conspicuous palpebral ridges, and characteristic pygidia
with broad and declined borders.

Liostracinoides Raymond was assigned to the family Liostracinidae by Raymond
(1937), Hupé (1953) and Howell (in Moore, 1959). Opik (1967: 387) has pointed out
that the only feature of the type species, Liostracinoides vermontanus , that allies it to
Liostracina Monke and related genera is the longitudinal preglabellar furrow—a
feature that occurs in a number of unrelated trilobites. An examination of the holotype
cranidium of L. vermontanus suggests that this rare genus belongs in_ the
Euptychaspidinae.

The euptychaspidines are confined to the Trempealeauan. The earliest known
member, Kathleenella frontalis (Longacre), occurs in the Saukiella pyrene Subzone
of Texas and in the correlative Rasettia magna Subzone of Oklahoma. An early
species of Kathleenella probably gave rise to Euptychaspis (see Longacre, 1970: 41),
which first appears in the Saukiella junia Subzone of Texas and Oklahoma and the
Yukonaspis kindlei Fauna of the Mackenzie Mountains. Liostracinoides , as well, was

Q7
(

probably derived from an early Trempealeauan species of Kathleenella because L.
vermontanus is most similar to K. hamulata sp. nov. from low in the Y. kindlei
Fauna. Both Kathleenella and Euptychaspis persist to the top of the Ptychaspid
Biomere in Texas, Oklahoma, and the Northwest Territories (that is, to the base of
the Corbinia apopsis Subzone and the base of the Elkanaspis corrugata Fauna). Of
the euptychaspidines, only Liostracinoides texana (Longacre) continues across the
Ptychaspid-‘‘ Hystricurid’’ Biomere boundary into the C. apopsis Subzone.

Kathleenella and the subfamily Euptychaspidinae were probably derived from
Ptychaspis or another ptychaspidine genus during the late Franconian (see Longacre,
1970, text-fig. 1).

Both Winston and Nicholls (1967) and Longacre (1970) suggested that Macronoda
Lochman, 1964 represents an offshoot from Euptychaspis and Longacre even
suggested that the two genera are synonymous. The elongate and triangular pygidium
attributed to Macronoda prima by Lochman (1964a, pl. 53, figs. 15, 18, 19, 21, 22)
is markedly dissimilar to that of Euptychaspis typicalis. If the M. prima pygidium is
correctly assigned, then it is unlikely that Macronoda and Euptychaspis belong to the
same subfamily.

Genus Euptychaspis Ulrich, in Bridge, 1931

Type Species

Euptychaspis typicalis Ulrich, in Bridge, 1931 from the Eminence Dolomite
(Trempealeauan), Eminence, Missouri (by original designation).

Euptychaspis typicalis Ulrich, in Bridge, 1931
Figs. 30, 58K—w

Euptychaspis typicalis—Taylor and Halley, 1974: 26, pl. 2, figs. 4-11 (see for
synonymy).

Occurrences

Eminence Dolomite, Missouri, Saukia Zone (Ulrich, in Bridge, 1931). Con-
ococheague Formation, Maryland, Saukia Zone (Rasetti, 1959). Wilberns Forma-
tion, central Texas, Saukiella junia Subzone (Winston and Nicholls, 1967; Longacre,
1970). Signal Mountain Limestone, Wichita and Arbuckle mountains, Oklahoma,
Saukiella junia and Saukiella serotina subzones (Stitt, 1971b, 1977). Notch Peak
Formation, Utah, Saukiella junia Subzone (Hintze et al., 1980). Whitehall
Formation, New York, Saukiella serotina Subzone (Taylor and Halley, 1974).
Rabbitkettle Formation, Broken Skull River (three collections between 152 m and
177 m below top of formation), Yukonaspis kindlei Fauna.

Syntypes

Two cranidia from the Eminence Dolomite, Missouri illustrated by Ulrich (in Bridge,
1931, pl. 29, figs. 5-7).

Remarks

Little can be added to Taylor and Halley’s (1974) exhaustive description of cranidia,
pygidia, and free cheeks of Euptychaspis typicalis from New York. The silicified
Rabbitkettle material shows the palpebral lobes, the occipital ring, and the prosopon
of this trilobite to perfection. The palpebral lobe is semicircular in outline with its
long axis directed exsagittally. Its mid-point contains a single minute perforation.
Identical structures occur in the Ordovician trilobites Ceraurinella, Encrinuroides ,
and Cybeloides (Chatterton and Ludvigsen, 1976, pl. 8, fig. 5, pl. 15, fig. 2;
Ludvigsen, 1979b, pl. 20, fig. 28). Such perforations were probably occupied by
sensory setae.

The triangular occipital spine of EF. typicalis can now be seen to be a composite
spine composed of a median ridge that arises directly from the depressed occipital
ring and which lies in a triangular trough formed by foldlike projections of the
posterior cephalic border.

The silicified free cheek (Fig. 580) suggests that Euptychaspis has a median
connective suture crossing the narrow anterior cephalic doublure and _ the
reconstruction (Fig. 30) has been drawn on that basis.

The identical prosopon of reticulate ridges seen on the silicified cranidia and
pygidia removes any doubt about the correctness of Taylor and Halley’s (1974: 26)
assignment of the single exfoliated (?) pygidium to E. typicalis.

Fig. 30 Euptychaspis typicalis Ulrich, in Bridge, 1931. Reconstruction of cephalon and pygidium
(prosopon omitted). Bar represents 1 mm.

Longacre (1970: 42) stated that Euptychaspis typicalis from central Texas
possesses a Short (sag.) and flat anterior border and Taylor and Halley (1974: 26)
noted that same feature in some cranidia of E. typicalis from New York and on one of
Ulrich’s syntypes from Missouri. Each of the silicified cranidia from the Rabbitkettle
Formation possesses an anterior border furrow and a short anterior border which is
commonly no more than a narrow rim. In view of the difficulty in exposing this
feature in nonsilicified material (Longacre, 1970: p. 42), it seems probable that all
cranidia of the type species of Euptychaspis possess anterior border furrows and
anterior borders.

Genus Kathleenella gen. nov.

Type Species

Kathleenella subula gen. et sp. nov. from the Upper Cambrian part of the
Rabbitkettle Formation, District of Mackenzie.

Diagnosis

A genus of euptychaspine trilobite possessing a subrectangular glabella with two or
three pairs of straight lateral glabellar furrows. Preglabellar field is short and anterior
border furrow is deep. Cephalon has slim genal spines and an anterior prow in front of
glabella. Palpebral lobes are knoblike and located anterior of mid-length of glabella.
Fixed cheeks are wide. Occipital ring carries simple, curved spine. Pygidium is
triangular; it comprises a high axis flanked by depressed and triangular pleural field
and a broad and gradually sloping border.

Name

For my wife, Kathleen MacKinnon. Feminine.

Other Species

Kathleenella hamulata gen. et sp. nov. and Euptychaspis frontalis Longacre, 1970.

Remarks

The new genus is established to accommodate two new species from the late
Trempealeauan part of the Rabbitkettle Formation. Euptychaspis frontalis Longacre,
1970 from the early Trempealeauan part of the Wilberns Formation, central Texas

and the Signal Mountain Limestone, Oklahoma (Stitt, 1977) differs from the type
species of Euptychaspis , E. typicalis Ulrich, in possessing a rectangular glabella with
straight lateral glabellar furrows that do not join, a distinct preglabellar field in many
Specimens, a deep anterior border furrow, and anteriorly placed eyes. All of these
features ally E. frontalis to Kathleenella subula sp. nov. and Longacre’s species is
therefore assigned to Kathleenella.

Kathleenella is similar in some respects to the eastern Asian and Australian genus
Asioptychaspis Kobayashi, 1933. The similarity is well seen by a direct comparison
of the pygidium of A. delta Shergold (1975, pl. 29, figs. 2-4) from early Payntonian
of Queensland with that of K. subula (Fig. 59M, 60H). Both of these species possess
triangular pygidia bearing high axes with few rings and inflated and broadly sloping
pygidial borders that are crossed by transverse ribs and that bear terrace lines which
run parallel to the margins. The cranidium of A. delta, however, is of the Ptychaspis
type and differs considerably from that of K. subula in lacking an anterior border
furrow and an occipital spine. The cranidia of both Ptychaspis and Asioptychaspis are
sufficiently similar to that of Kathleenella to support a derivation of this
euptychaspidine genus from the ptychaspidines in the late Franconian.

Kathleenella subula gen. et sp. nov.
Figs. 31, 59, 60A—-K

Diagnosis

A species of Kathleenella with anteriorly expanding axial furrows on the cephalon,
three pairs of lateral glabellar furrows, a short preglabellar field lacking a longitudinal
furrow, a high occipital spine, and long slender genal spines.

Occurrences

Rabbitkettle Formation, Broken Skull River (13 collections between 77 m and 148 m
below top of formation), Bowmania americana Fauna and Yukonaspis kindlei Fauna.
Road River Formation, Bonnet Plume map area, GSC loc. C-7562 (collection at
Geological Survey of Canada, Ottawa), Yukonaspis kindlei Fauna.

Holotype

A complete cranidium (ROM 37429) from KK 177 (114 m below top of Rabbitkettle
Formation) illustrated on Fig. 59A-c.

Name

From subula—aw] (Latin) in reference to the long pointed genal spines.

Description

Cephalon (exclusive of genal spines and anterior prow) is semicircular in outline and
strongly convex. Deep axial furrows widen (tr.) towards front and define arched and
rectangular glabella. Preglabellar furrow has median posterior deflection. Three pairs
of lateral glabellar furrows extend part way, and occasionally full way, across
glabella. Occipital ring is long (sag.) and lenticular in outline. A high curved spine
occupies central position. Small, knoblike and high palpebral lobe is located far out
on cheek; opposite 3p lobe. Palpebral lobe is constricted at base by deep, curved
palpebral furrow. Anterior border furrow is deep and, in anterior view, is slightly
arched. It defines posterior edge of an inflated triangular prow which constitutes
anterior border. Preglabellar field is short (sag.) and steeply inclined; its central part
is flat to slightly concave. Cheek is inflated; anteriorly it swells into rounded ridge
which defines forward terminus of axial furrow. Lateral border furrows are narrow
(tr.) and not noticably impressed, except near the base of genal spines. Anteriorly,
they are continuous with deep anterior border furrow. Facial suture follows
subangular path from posterior border forward and slightly inward to eye and then
across cheek to anterior prow. Genal spines are long (at least twice sagittal length of
cephalon), slender, and directed backwardly and gently inwardly. Base of genal spine
carries short carina between parallel extensions of lateral and posterior border
furrows. Entire cephalon, exclusive of cephalic furrows, is covered by prosopon of
densely distributed and coarse granules.

Because the hypostome is unique among Trilobita, it is difficult to identify
homologous features and, indeed, to decide on its orientation. The ‘‘lower’’ concave

Fig. 31 Kathleenella subula gen. et sp. nov. Reconstruction of cephalon and pygidium in dorsal view
and hypostome in oblique view (prosopon omitted). Bar represents 1 mm.

a2.

surface is herein called the ventral surface and the two prominent knobs are assumed
to occupy posterior positions. Ventral face of hypostome is smooth, broadly oval in
outline, wider than long, and gently concave. A broad tonguelike projection,
extending for the entire width of hypostome, is directed obliquely downward. From
the recurved inner portion of this tongue, rises the posterior part of the hypostome
which carries a pair of large knobs on margin. The knobs are separated by a V-shaped
indentation of the inner margin.

Pygidium is broadly triangular and inflated with steeply curving flanks. Convex
axis consists of two arched rings and a small terminal piece which carries a pair of
minute spines. Axis is well defined by deep axial furrows; it extends for slightly more
than half length of pygidium. Flanking the axis is a depressed triangular area that is
bounded by faint ridges which parallel pygidial borders. Outside these ridges, the
broad pygidial border slopes gradually to margin. The border is crossed by a few
transversely directed undulations and is covered by anastomosing terrace lines which
run parallel to pygidial margin.

Remarks

Kathleenella subula gen. et sp. nov. differs from K. frontalis (Longacre) from the
Saukiella pyrene Subzone in central Texas in possessing both anteriorly expanding
axial furrows and a prominent anterior prow on the cephalon. In addition, the species
from Texas has only two pairs of lateral glabellar furrows and more posteriorly placed
palpebral lobes which are located closer to the glabella.

Kathleenella hamulata gen. et sp. nov.
Figs. 32, 550-T

Diagnosis

A species of Kathleenella with a median longitudinal furrow crossing the preglabellar
field, two pairs of lateral glabellar furrows, short and hooked genal spines, and a
Short occipital spine.

Occurrences

Rabbitkettle Formation, Broken Skull River (four collections between 152 m and
177 m below top of formation), Yukonaspis kindlei Fauna.

Holotype

A complete cranidium (ROM 374559) from K 510 (177 m below top of Rabbitkettle
Formation) illustrated on Fig. 550, P.

Name

From hamulate—hooked (Latin) in reference to the inward twist of the tip of the
genal spine.

Remarks

Kathleenella hamulata sp. nov. occurs stratigraphically below K. subula sp. nov. and
is obviously related to that species. K. hamulata is distinguished by the presence of a
distinct median longitudinal furrow crossing the preglabellar field, by possessing a
proportionately shorter (sag.) glabella with only two pairs of lateral furrows, and by
having shorter genal spines.

Genus Liostracinoides Raymond, 1937

Type Species

Liostracinoides vermontanus Raymond, 1937 from Zone | (Hungaia Assemblage) of
the Gorge Formation, Highgate Falls, Vermont (by original designation).

Remarks

Liostracinoides vermontanus is similar to Kathleenella hamulata sp. nov. (compare
Fig. 32 and Fig. 33). This similarity is seen in the general form of the glabella and
palpebral lobes and, particularly, in the form of the furrows on the frontal area of the
cranidium. L. vermontanus , however, is readily distinguished by its conical glabella,

Fig. 32 Kathleenella hamulata gen. et sp. nov. Reconstruction of cephalon (prosopon omitted). Bar
represents 1 mm.

wider (tr.) anterior border on the cranidium, strongly divergent posterior branches of
the facial suture, and by lacking an occipital spine.

Few species have been assigned to Liostracinoides. I have not been able to verify
Raymond’s (1937: 1093) assignment of Conocephalites winona Hall to Lios-
tracinoides . Liostracinoides? yukonensis Palmer, 1968 from the Trempealeauan of
the Alaska-Yukon border has a bullet-shaped glabella which lacks furrows, eyes
located close to the axial furrows, divergent anterior facial sutures, and a medially
interrupted anterior border furrow. These features are unlike those of the type species
and Palmer’s species should not be assigned to Liostracinoides .

Liostracinoides? sp. from the Mindyallan of Queensland (Opik, 1967: 386, pl. 10,
fig. 9) has a glabella of pentagonal outline, forwardly convex anterior border furrow,
and a vague longitudinal preglabellar furrow. It does not appear to be congeneric with
Liostracinoides vermontanus .

As Longacre (1970: 58) pointed out, Westonaspis? texana Longacre differs from
Westonaspis Rasetti in having an anterior border furrow, wider fixed cheeks, and a
faint longitudinal furrow crossing the preglabellar field. This species is better
accommodated in Liostracinoides .

Liostracinoides vermontanus Raymond, 1937
Figs. 33, 53A—D, 70P

Liostracinoides vermontanus Raymond, 1937: 1092, pl. 1, fig. 20.
Phylacterus saylesi Raymond—Gilman Clark and Shaw, 1968: 1022, pl. 127, figs.
24-26.

Occurrences

Gorge Formation, Highgate Falls, Vermont, Hungaia Assemblage (Raymond, 1937;
Gilman Clark and Shaw, 1968). Rabbitkettle Formation, Broken Skull River (single
collection 86.5 m below top of formation), Bowmania americana Fauna.

Holotype

An internal mould of an incomplete cranidium from the Gorge Formation, Highgate
Falls, Vermont illustrated on Fig. 7OP.

Description

Glabella is inflated, conical in outline and delimited by deep axial furrows that
converge along nearly straight paths towards short (tr.), somewhat rounded
preglabellar furrow. Three pairs of lateral glabellar furrows are short (tr.); only Is is
clearly evident. Occipital furrow is straight and firmly impressed; occipital ring lacks

spine. Fixed cheek is as wide as glabella at mid-length and is inflated. Palpebral lobe
is located in line with half-length of glabella. An extremely faint palpebral ridge joins
axial furrow at level of 3s furrow. Anterior branches of facial suture converge
forwardly on to anterior border where they are parallel with anterior border furrow.
Posterior branches diverge widely. Anterior border furrow is firmly impressed and
has slight backward curvature medially. A deep longitudinal furrow crosses the
inflated preglabellar field. Cranidium is covered by densely distributed and fine
granules.

Remarks

The Liostracinoides material from Vermont and the District of Mackenzie differs
somewhat in the courses of the sutures and degrees of inflation of the cranidia. Only a
few incomplete cranidia are available from either area and a conservative taxonomic
approach has been adopted in considering these specimens conspecific.

Liostracinoides texana (Longacre, 1970) from the Corbinia apopsis Subzone of
central Texas differs from L. vermontanus in possessing a narrower and less conical
glabella, more distinct palpebral ridges, a shallower longitudinal furrow on the
preglabellar field, and a nearly transverse anterior border furrow that has only very
slight backward curvature medially.

Subfamily Eurekiinae Hupé, 1953

Diagnosis

Ptychaspididae with an inflated glabella that is subrectangular or forwardly narrowing
and that bears two pairs of oblique lateral furrows (or faint traces of such furrows).
Semicircular or elliptical palpebral lobes are located close to glabella near cephalic
mid-length. Preglabellar field is short (sag.) or absent; anterior border is variably
upturned. Genal corner is either a sharp angle or it carries a genal spine of variable
dimensions. Oblong hypostome is longer than wide, with a central body completely

Fig. 33 Liostracinoides vermontanus Raymond, 1937. Reconstruction of cranidium (prosopon omitted).
Bar represents 1 mm.

circumscribed by border furrows. Pygidium is wider than long; axis is well defined
and inflated, it reaches or nearly reaches posterior margin; axial ring furrows and
interpleural furrows each number one to three. Four or five pairs of blunt or pointed
marginal spines project downward and backward. Dorsal surface is either smooth or it
is covered by dense granulate or tuberculate prosopon.

Assigned Genera

Eurekia Walcott, 1916; Bayfieldia Clark, 1924; Corbinia Walcott, 1924; Yukonaspis
Kobayashi, 1936a, Magnacephalus Stitt, 1971; and, questionably, Maladia Walcott,
1924.

Remarks

The diagnosis of the Eurekiinae, above, has been modified to accommodate two
partially effaced genera, Yukonaspis and Magnacephalus , whose previous classifica-
tion was unsatisfactory.

Yukonaspis has previously been known only from cranidia. Kobayashi (1936a) did
not assign this genus to a family, but noted similarities with both illaenurids and
leiostegiids. Hupé (1953) assigned Yokunaspis [sic] to the Illaenuridae. Lochman
(1953; in Moore, 1959) considered both Tatonaspis Kobayashi, 1935 and Yukonaspis
to be junior subjective synonyms of Macelloura Resser. Palmer (1968) demonstrated
that Tatonaspis and Yukonaspis have separate generic status and that neither is
congeneric with Macelloura. He assigned Tatonaspis to the Nileidae and left
Yukonaspis unclassified as to family.

Magnacephalus was established by Stitt (1971b) for a new species based on both
cranidia and pygidia from the Saukia Zone in Oklahoma. Stitt did not assign this
genus to a family and, curiously, did not comment upon the pronounced similarity of
the Magnacephalus pygidium to those of eurekiine genera.

Effaced trilobites are difficult to classify. The cranidia of both Yukonaspis and
Magnacephalus are similar to those of Eurekia and Corbinia. The pygidium of
Yukonaspis has now been identified and it is becoming clear that this pygidium, and
that of Magnacephalus, can barely be distinguished from those of Bayfieldia and
Eurekia. The large curving genal spine of Yukonaspis lends a unique aspect to the
cephalon, but this spine can be viewed as an extreme development of the small
triangular genal spine seen in Eurekia. In spite of the effacement of some cephalic
furrows, the available evidence suggests that Yukonaspis and Magnacephalus should
be classified with Eurekia, Bayfieldia, and Corbinia in the subfamily Eurekiinae.

The eurekiines are typical trilobites of the Middle Carbonate Belt during the
Trempealeauan. The earliest known eurekiine (if the poorly known Maladia Walcott
is excluded) is Yukonaspis from the late Franconian of Oklahoma. Eurekia and
Bayfieldia first appear near the base of the Trempealeauan; Corbinia and
Magnacephalus first appear somewhat higher in the Trempealeauan. Eurekia,
Corbinia, and Yukonaspis persist into the late Trempealeauan (Corbinia apopsis
Subzone and Elkanaspis corrugata Fauna).

Genus Eurekia Walcott, 1916

Type Species

Ptychoparia (Euloma?) dissimilis Walcott, 1884 from the Windfall Formation of Late
Cambrian age, Eureka District, Nevada (by original designation; see Taylor, 1978).

Remarks

Taylor (1978) has recently provided convincing evidence that Walcott’s (1924)
designation of Eurekia granulosa Walcott, 1924 as type species of Eurekia is invalid.
The type species is Ptychoparia (Euloma?) dissimilis Walcott and E. granulosa is a
junior subjective synonym of E. eos (Hall, 1863). Taylor’s redescription and
illustration of both E. dissimilis and E. eos now provide a firm foundation for
evaluating other members of this common taxon of Late Cambrian trilobites. Taylor
also demonstrated that the drawings of the Eurekia cephalon by Walcott (1924, pl.
12, fig. 1) and by Lochman-Balk (in Moore, 1959, fig. 240-3) are highly inaccurate
in showing both the course of the facial suture and the size of the genal spine.
Unfortunately, Taylor’s own reconstruction of E. eos is also inaccurate in
underrepresenting the width (tr.) of the palpebral lobes, and in not showing the deep
palpebral furrows of this species (compare Taylor’s reconstruction in text-fig. 2 with
the photograph on pl. 1, fig. 11).

Eurekia ulrichi (Rasetti, 1945)
Figs. 34, 61

Bayfieldia ulrichi Rasetti, 1945: 465, pl. 60, figs. 17-19.
Corbinia ulrichi—Winston and Nicholls, 1967: 85.
Bayfieldia sp. 2, Palmer, 1968: 64, pl. 15, figs. 8, 11.

Occurrences

Levis Formation, North Ridge, Levis, Quebec, Hungaia Assemblage (Rasetti, 1945).
Jones Ridge Limestone, Jones Ridge area, Alaska- Yukon border, Trempealeauan-2
Fauna (Palmer, 1968). Rabbitkettle Formation, Broken Skull River (three collections
between 145 m and 177 m below top of formation), Yukonaspis kindlei Fauna.

Holotype

A cranidium from an Upper Cambrian boulder, Levis Formation, Levis, Quebec
illustrated by Rasetti (1945, pl. 60, figs. 17, 18).

Description

Cephalon is subrectangular in outline; length is five-sevenths width; anterolateral
corners are rounded; it is strongly (tr.) and moderately (sag.) convex. Glabella is
subrectangular in outline and moderately inflated. Two pairs of short (exsag.) and
backwardly curving lateral glabellar furrows are present at mid-length. Occipital
furrow is sharply incised and nearly straight; it turns forward adjacent to axial furrow.
Occipital ring is rather flat; it carries a small median node on its forward flank. Deep
axial furrows diverge very slightly to mid-length of glabella, then converge slightly
along gentle curve to meet deep and transverse anterior border furrow. Lateral and
anterior border furrows are confluent; they define convex and tubelike cephalic
borders. Small spine is located at genal corner. In anterior view, anterior border rises
in gentle arch towards sagittal line. Posterior border furrows are transverse and deep.
Palpebral furrow defines wide (tr.), large (as long as one-half sagittal length of
cephalon) and crescentic palpebral lobe. Base of eye marked by convex and
longitudinally striated eye socle. Anterior branch of facial suture proceeds straight
forward to anterior border furrow, then turns inwardly along anterior border to
median connective suture. Posterior branch swings outward along path subparallel
with posterior border furrow; just in front of genal corner, it angles straight back.

Cephalon is densely covered by small tubercles which, on the borders, merge with
coarse terrace lines that run parallel to margin. On the free cheek, each tubercle is
irregularly stellate in shape.

Hypostome is oblong, longer than wide; with rounded posterolateral corners and
triangular wings located on either side of a forwardly rounded and ventrally turned
anterior margin. Central body is completely circumscribed by border furrows that are
deepest laterally. A pair of oblique middle furrows is present on back portion of
central body. Ventral surface of hypostome is smooth, with the exception of terrace
lines on the lateral borders.

Pygidium is semielliptical in outline; twice as wide as long. Convex axis stands
well above moderately inflated pleural portions. Articulating furrow is deep behind

as
TS,

Fig. 34 Eurekia ulrichi (Rasetti, 1945). Reconstruction of cephalon and pygidium (prosopon omitted).
Bar represents | mm.

prominent articulating half ring. One axial ring furrow is complete, a second is
incomplete. First interpleural furrow is deep, proceeds on to base of first marginal
Spine; two or three pleural furrows are only faintly defined. Five pairs of blunt,
digitate marginal spines extend backward and downward. First four spine pairs are
equal in size; fifth pair is slightly smaller. Cephalic micro-ornament is duplicated on
pygidium. On spine tips, tubercles merge with coarse terrace lines that run parallel to
pygidial margin and across spines.

Remarks

The only differences between Eurekia ulrichi Rasetti from the Rabbitkettle Formation
and the type material from the Levis Formation are the slightly shorter (exsag.)
palpebral areas and a slightly wider and more inflated glabella of the Quebec
cranidium. Rasetti’s figured cranidium is considerably larger than any available from
the Rabbitkettle and these differences are probably the result of the size discrepancy.

The exfoliated cranidium and pygidium from the Trempealeauan of the Jones
Ridge Limestone of east-central Alaska (Palmer, 1968, pl. 15, figs. 8, 11) are larger
than both the Levis and Rabbitkettle material. These specimens are similar to, and in
all likelihood conspecific with, E. ulrichi.

Eurekia ulrichi differs from all other species of Eurekia in possessing a relatively
long and only moderately inflated glabella with faint lateral glabellar furrows, large
and semicircular palpebral areas, and a pygidium with digitate and bluntly rounded
marginal spines. In addition, the pervasive tubercles of E. ulrichi are finer than those
in most other species of Eurekia.

Eurekia bacata sp. nov.
Figs. 35, 62A—J

Diagnosis

A species of Eurekia possessing a moderately inflated glabella with maximum width
between eyes. Occipital ring is long (sag.). Anterior cephalic border is sharply
upturned. Cephalic furrows are deep and trenchlike. A row of large tubercles
surrounds base of eye. Wide pygidial axis is undercut by axial furrows; it overhangs
posterior margin. Five pairs of marginal spines hang below posterior border. Anterior
Spine pairs are paddle-shaped with concave outer faces.

Occurrences

Rabbitkettle Formation, Broken Skull River (three collections between 152 m and
172 m below top of formation), Yukonaspis kindlei Fauna.

100

Holotype

A large pygidium (ROM 37708) from K 525 (172 m below top of Rabbitkettle
Formation) illustrated on Fig. 62F, G.

Name

From bacatus—adorned with pearls (Latin) in reference to the string of circular
tubercles which surrounds the base of the eye.

Remarks

The shape of the marginal pygidial spines, the row of tubercles below the eye, and the
narrow fixed cheek in front of the eye of Eurekia bacata sp. nov. clearly differentiate
this species from all other species of Eurekia.

Eurekia spp.
Fig. 62K-Q

Occurrences

Rabbitkettle Formation, Broken Skull River (12 collections between 61 m and 148 m
below top of formation), E/kanaspis corrugata Fauna, Bowmania americana Fauna,
and Yukonaspis kindlei Fauna.

Fig. 35 Eurekia bacata sp. nov. Reconstruction of cephalon and pygidium (prosopon omitted). Bar
represents 1 mm.

10]

Remarks

Eurekia is moderately rare in the upper part of the Cambrian succession in Section
KK. The genus is represented by small, fragmentary, and often tectonically deformed
specimens which are difficult to classify. These specimens are probably assignable to
more than one species.

A few of the better specimens are illustrated on Fig. 62K-Q. Some of the cranidia
(Fig. 62K, P, Q) are rather similar to that of Eurekia ulrichi, but the palpebral areas
tend to be larger. Likewise, some pygidia (Fig. 62M) are similar to that of E. ulrichi
whilst others (Fig. 62L, O) with pointed marginal spines approach the morphology of
pygidia assigned to Corbinia. Association of cranidia and pygidia cannot be made at
the present time.

This fragmentary material does establish the presence of Eurekia in the Elkanaspis
corrugata Fauna of the Northwest Territories. According to Winston and Nicholls
(1967), Eurekia occurs rarely in the Corbinia apopsis Subzone of central Texas—an
interval correlative to the Elkanaspis corrugata Fauna.

Genus Yukonaspis Kobayashi, 1936a

Type Species

Yukonaspis kindlei Kobayashi, 1936a from Upper Cambrian rocks (Trempealeauan,
Palmer, 1968) on Squaw Mountain, Alaska- Yukon border (by original designation).

Remarks

Yukonaspis differs from Magnacephalus Stitt, 1971b in possessing deeper axial
furrows, a more inflated glabella, a pronounced upturned anterior border, and a
narrower (tr.) and shorter (sag.) pygidial axis.

During the Trempealeauan, Yukonaspis was a characteristic shelf-edge taxon in
North America. It occupied outer shelf sites on the Alaska-Yukon border, in the
District of Mackenzie, in Utah (Taylor, 1977, table 3), in western Newfoundland
(undescribed material in C.H. Kindle Collection, Geological Survey of Canada,
Ottawa), and in Vermont (undescribed material in C.H. Kindle Collection).

Yukonaspis kindlei Kobayashi, 1936a
Figs. 36, 63A—-N, 69F-I, 70A-C

Yukonaspis kindlei Kobayashi, 1936a: 164, pl. 21, figs. 3-6.
Yukonaspis kindlei—Palmer, 1968: 100, pl. 15, figs. 15, 19.

102

Occurrences

Jones Ridge Limestone, east-central Alaska, Trempealeauan-2 Fauna (Kobayashi,
1936a; Palmer, 1968). Cow Head Group, Cow Head, western Newfoundland,
Hungaia Assemblage (C.H. Kindle Collection at the Geological Survey of Canada,
Ottawa). Rabbitkettle Formation, Broken Skull River (eight collections between
112 m and 177 m below top of formation), Yukonaspis kindlei Fauna.

Holotype

An incomplete cranidium from Squaw Mountain, north of Tatonduk River,
Alaska- Yukon border illustrated by Kobayashi (1936a, pl. 21, figs. 3, 4) and herein
(Fig. 70A-C).

Description

Little can be added to Palmer’s (1968: 100) description of Yukonaspis kindlei cranidia
from east-central Alaska. As Palmer noted, lateral glabellar furrows are absent in this

Fig. 36 Yukonaspis kindlei Kobayashi, 1936a. Reconstruction of cephalon and pygidium. Bar represents
1 mm.

103

species. Muscle insertion areas may be represented by two pairs of oblique, oval
areas of thin shell material whose presence is often indicated by ragged holes on the
glabellar flanks of the silicified specimens (Fig. 63J, K). The anterior course of the
facial suture cannot be clearly determined in Kobayashi’s and Palmer’s illustrated
material. The specimens from the Rabbitkettle Formation show this suture to proceed
forward from the palpebral lobe with faint outward curvature until it passes on to the
narrow arched anterior border. It then proceeds inward along the highest part of the
border to the mid-line where it meets the median connective suture.

Description of the free cheek and pygidium of Y. kindlei can now augment
Palmer’s description of the cranidium.

Interior portion of free cheek, below convex visual surface of eye, curves steeply to
lateral border furrow which is narrow and deep anteriorly and little more than an
abrupt change in slope posteriorly. Lateral border is very narrow and sharp anteriorly;
it becomes a broad flat field below eye. This field merges with the base of long genal
spine which curves outward and backward for a distance equal to sagittal length of
cephalon. Genal spine is tapering and is oval in cross-section. In lateral view, border
of free cheek descends steeply and curves backward and inward, beneath genal spine,
to join posterior cephalic margin. In lateral view, genal spine is seen to rise gently.
Borders contain fine, ledgelike terrace lines. Similar lines occur on genal spine where
they are largely exsagittally directed.

Pygidium is semielliptical in outline, nearly three times as wide (tr.) as long (sag.),
and gently arched (tr.). Axis is moderately convex; it comprises two axial rings
outlined by sharply incised furrows and a long (sag.) terminal piece. Axis is outlined
by moderately deep axial furrows; it extends to posterior margin. Pleural field is
triangular in outline and crossed by a single deep interpleural furrow. Two other
interpleural furrows are faintly defined. Five pairs of marginal spines project
backward and slightly downward. Each spine is triangular in outline. Fifth pair is
small and well separated. Prosopon consists of low granules.

Remarks

Palmer’s (1968) cranidium of Yukonaspis kindlei has somewhat larger palpebral areas
than are present on either the holotype cranidium or the cranidia from the Mackenzie
Mountains. This difference, however, is not considered to be sufficient basis for
Species Separation.

The association of the Y. kindlei cranidium and the peculiar free cheek suggested in
this paper has been substantiated by a spectacular cephalon in the C.H. Kindle
Collection from western Newfoundland at the Geological Survey of Canada, Ottawa.
This specimen shows an identical free cheek attached to a Y. kindlei cranidium.

The only other species assigned to Yukonaspis is Stigmacephaloides verticalis Stitt
(1977, pl. 2, figs. 7-9;)see also Stitt, 1971b, pl. 3, f1gs."16, 17) from) the late
Franconian of Oklahoma. Yukonaspis verticalis differs from Y. kindle in possessing a
more inflated glabella, wider (tr.) fixed cheeks in front of the eyes, smaller palpebral
areas, and a very narrow (sag.) preglabellar field. The similarity in the cranidia and
free cheeks of the two species is considerable and Stitt’s species is confidently
assigned to Yukonaspis.

104

Yukonaspis sp.
Fig. 67L—-N

Occurrence

Rabbitkettle Formation, Broken Skull River (eight collections between 61 m and
96m below top of formation), Elkanaspis corrugata Fauna and Bowmania
americana Fauna.

Remarks

Tectonically deformed and fragmentary material of at least one other species of
Yukonaspis occurs in the Rabbitkettle Formation above the collections with Y.
kindlei. These are best characterized by the free cheeks (Fig. 67M, N) which differ
from those of Y. kindlei in having a deep curved lateral border furrow that,
apparently, is continuous with the anterior and posterior border furrows of the
cranidium. The genal spines are shorter than those of Y. kindlei. The associated
cranidia are generally so deformed that they yield little critical information. These
Specimens are assigned to Yukonaspis sp.

Superfamily Remopleuridacea
Family Kainellidae Ulrich and Resser, 1930
(= Apatokephalopsidae Zhou and Zhang, 1978)

Assigned Genera

Kainella Walcott, 1925; Richardsonella Raymond, 1924; Apatokephaloides
Raymond, 1924; Pseudokainella Harrington, 1938; Sigmakainella Shergold, 1971;
Apatokephalops Lu, 1975; Jiia Zhou and Zhang, 1978; Aristokainella Zhou and
Zhang, 1978; Naustia gen. nov.; and Elkanaspis gen. nov.

Remarks

The name Richardsonella has served as a catch-all for a number of Franconian to
Tremadocian remopleuridacean species that are certainly not all congeneric (Palmer,
1968: 78; Shergold, 1971: 37). The type species of Richardsonella, R. megalops
(Billings), is represented by only two incomplete cranidia (Rasetti, 1944, pl. 39, figs.
48, 49). The pygidium attributed to this species by Whittington (in Moore, 1959, fig.
242-3b) actually belongs to Elkanaspis unisulcata (Rasetti) (Hupé, 1955, fig.
147-6). The uncertainty about attribution of exoskeletal elements other than cranidia
to the type species of Richardsonella suggests that the Richardsonellinae Raymond,

105

1924 is poorly suited as a suprageneric taxon of remopleuridacean trilobites. Shergold
(1975: 159) suggested that the Kainellidae Ulrich and Resser is better because
Kainella is known from complete specimens.

Zhou and Zhang (1978) established the Apatokephalopsidae for Apatokephalops
Lu, Jiia Zhou and Zhang, and Wanliangtingia Lu; all from Tremadocian strata of
China. As Lu (1975: 304) noted, Apatokephalops and Pseudokainella have similar
eyes, free cheeks, anterior facial sutures, and preglabellar fields. Apatokephalops
differs by lacking an intraocular fixed cheek and by possessing a longer (sag.)
anterior cephalic border. A pygidium is not known for Apatokephalops, but that of
Jiia (Zhou and Zhang, 1978, pl. 3, figs. 16, 17) is very similar to those herein
assigned to Elkanaspis gen. nov. The cranidial differences between Apatokephalops
and Pseudokainella are certainly valid on a generic level, but hardly justifiable on a
familial level. I conclude that the Apatokephalopsidae Zhou and Zhang should be
synonymized with the Kainellidae Ulrich and Resser.

Genus Naustia gen. nov.

Type Species

Naustia papilio sp. nov. from the Upper Cambrian part of the Rabbitkettle
Formation, District of Mackenzie.

Diagnosis

A genus of kainellid trilobite possessing a parallel-sided glabella with two or more
lateral furrows. Preglabellar field is long (sag.); anterior border furrow is distinct.
Large, semicircular palpebral lobe is located close to axial furrow; its length (exsag. )
is half that of glabella (sag.). Palpebral furrow is distinct. Facial sutures are
transverse behind eye and markedly divergent in front of eye. Pygidium is large and
semicircular. Slender, convex axis consists of seven well-defined rings and a terminal
piece with a postaxial ridge that reaches posterior margin. Six or seven pairs of
interpleural furrows cross flat pleural regions. Pleural furrows are faint or absent.
Seven or eight pairs of slender, backwardly directed spines fringe pygidium.

Name

Acronym for North America and Australia, the two continents where the genus
occurs. Feminine.

Other Species

Richardsonella? kainelliformis Shergold, 1971 (= ‘‘Tostonia’’ sp. of Shergold,

106

1971) from the Gola Beds (Franconian) of western Queensland.

Richardsonella tyboensis Taylor, 1976 (= Genus and species undet. A of Taylor,
1976) from the Franconian part of the Hales Limestone of Nevada.

Richardsonella? sp. 2 of Palmer, 1968 from the Trempealeauan-1 Fauna of
east-central Alaska.

Pygidia assigned to Tostonia iole (Walcott) by Walcott (1925, pl. 18, figs. 13, 14)
from the Upper Cambrian of the Eureka District, Nevada.

Pygidium assigned to Dikelocephalus sp. by Billings (1865, fig. 384) from the Levis
Formation near Quebec City.

Remarks

A number of authors have documented the presence of large, semicircular and ribbed
kainellid pygidia in Franconian and Trempealeauan rocks of North America and in
correlative rocks of Australia and have noted the similarity of these pygidia to those
erroneously attributed to Tostonia iole by Walcott (1925). Palmer (1968: 78) noted
the association of a ‘‘Tostonia’’ pygidium and a Richardsonella cranidium in
Nevada. Shergold (1971: 42) and Taylor (1976: 698) both described such pygidia
from collections that also included cranidia similar to that of Richardsonella
megalops, the type species of Richardsonella. Shergold and Taylor each considered
the possibility that the ‘‘Tostonia’’ pygidium should be associated with the
Richardsonella cranidium and each stated that if such an association could be
demonstrated, it would define a new genus of Richardsonellinae. They concluded,
however, that the establishment of a new genus was premature.

‘“‘Tostonia’’-type pygidia and Richardsonella-type cranidia also co-occur in
separate collections from the Rabbitkettle Formation of the District of Mackenzie—
one from Section KK described below and one from the Bonnet Plume map area,
some 200 km north-northwest of Section KK, to be described later. The size of these
sclerites and elimination of other cranidium-pygidium associations leave little doubt
that the ‘‘Tostonia’’-type pygidia belong with the Richardsonella-type cranidia.

The association of these unique kainellid pygidia and Richardsonella-type cranidia
in collections from five localities on two continents is additional evidence that these
elements were parts of the same trilobite. A new genus, Naustia, is established to
receive the Franconian and Trempealeauan species listed above.

Naustia papilio gen. et sp. nov.
Figs. 37, 64Q—-U

Diagnosis

A species of Naustia with two pairs of deep and curving lateral glabellar furrows,
seven pairs of interpleural furrows on the pygidium, and eight pairs of marginal!
spines on the pygidium.

107

Occurrence

Rabbitkettle Formation, Broken Skull River (single collection 165 m below top of
formation), Yukonaspis kindlei Fauna.

Holotype

A nearly complete pygidium (ROM 37628) from K 550 (165 m below top of
Rabbitkettle Formation) illustrated on Fig. 64Q.

Name

From papilio—butterfly (Latin) in reference to the shape of the pygidium.

Description

Gently inflated glabella is bounded by deep parallel axial furrows which diverge
slightly around occipital ring. Glabella is nearly twice as long (sag.) as wide. Two
pairs of distinct lateral furrows extend one-third the way across glabella; 1s curves
inward and backward; 2s curves backward, asymptotically to a transverse line.
Occipital furrow is well incised medially; laterally it bifurcates. Preglabellar furrow is
deep and gently bowed forwardly. Preglabellar field is one-third the length (sag.) of
glabella (including occipital ring). Its inner portion is slightly inflated; forwardly it
declines gently towards anterior border furrow. Anterior border is relatively long
(sag.) Palpebral area is semicircular; palpebral lobe is crescentic and slightly raised; it
is defined by firmly impressed palpebral furrow which just touches axial furrow.
Posterior portion of facial suture is transversely directed; anterior portion curves
widely outward, nearly to the exsagittal level of the edge of palpebral lobe, and then
inward across anterior border.

Pygidium is large, flat, and semicircular in outline; slightly wider (tr.) than long.
Convex axis is slender, one-fifth the width (tr.) of pygidium, and only slightly
tapering. It consists of seven well-defined axial rings and a triangular terminal piece
that extends axis to posterior margin. Pleural region is crossed by seven distinct
interpleural furrows that become deeper and progressively backwardly swept toward
rear. These furrows terminate in a shallow border furrow. Pleural furrows are
extremely faint. Eight pairs of backwardly directed marginal spines fringe pygidium.
Posterior pairs are slender; anterior pairs are apparently stouter.

Remarks

Naustia papilio gen. et sp. nov. differs from N. kainelliformis (Shergold, 1971) in
having less divergent anterior branches of the facial suture, two pairs of deep lateral

108

glabellar furrows, and a pygidium with eight pairs of marginal spines. N. papilio
differs from N. tyboensis (Taylor, 1976) in having a less inflated glabella, deeper
axial furrows, somewhat larger palpebral areas, and an inflated posterior portion of
the preglabellar field. The immature pygidia of N. tyboensis (Taylor, 1976, pl. 3,
figs. 9, 11) appear to be identical to immature pygidia of N. papilio (Fig. 64R, S).

Genus Elkanaspis gen. nov.

Type Species

Elkanaspis futile sp. nov. from the Upper Cambrian part of the Rabbitkettle
Formation, District of Mackenzie.

Diagnosis

A genus of kainellid trilobite possessing a glabella which has slightly outwardly
bowed sides and is constricted near front. Palpebral lobes are long (exsag.) and
crescentic; anterior and posterior ends of palpebral furrow merge with axial furrow,
thus isolating a narrow (tr.) intraocular fixed cheek. Free cheek is broad (tr.).
Preglabellar field is short; equal in sagittal length to convex anterior border. Genal
corner is a right angle or obtuse angle; genal spine is slender. Pygidium is elliptical to
quadrate in outline. Pygidial axis consists of two to four arched rings and a terminal
piece. Axis is well defined by furrows; it tapers slightly and is sharply raised over
pleural regions; it terminates before reaching posterior margin. Three or four pleural

STITT)

Fig. 37 Naustia papilio gen. et sp. nov. Reconstruction of cranidium and pygidium. Bar represents
1 mm.

109

furrows cross flat to slightly inflated pleural region. Interpleural furrows and border
furrows are faint. Three or four pairs of flattened and pointed marginal spines curve
backward and inward; they decrease in size posteriorly.

Name

Patronym for Elkanah Billings, Canada’s first palaeontologist, plus aspis—shield
(Greek). Feminine.

Other Species

Richardsonella unisulcata Rasetti, 1944 from the Levis Formation of Quebec.

Richardsonella quadrispinosa Palmer, 1968 from the Franconian-2 Fauna of
east-central Alaska.

Richardsonella variagranula Robison and Pantoja-Alor, 1968 from the Tinu
Formation of Mexico.

Elkanaspis corrugata sp. nov.

Remarks

Shergold (1971: 37) suggested that Richardsonella unisulcata Rasetti, R. quadris-
pinosa Palmer, and four other species of Richardsonella from North America could
be accommodated in Pseudokainella Harrington, 1938. Taylor (1976: 696) suggested
the same generic assignment for R. variagranula Robison and Pantoja-Alor from
Mexico. There is little doubt that these North American kainellid trilobites are related
to Pseudokainella; but its type species, P. keideli Harrington (see Harrington and
Leanza, 1957, figs. 51, 52), displays a number of differences which suggest that it is
not congeneric with the three species of Richardsonella mentioned above. These
include:

a. An extremely narrow preglabellar field. Harrington and Leanza’s (1957, fig.
52-5, 7, 10) photographs show the glabella to terminate in the anterior border
furrow and a preglabellar field cannot be distinguished.

. Widely divergent anterior branches of the facial suture.
The glabella is not constricted anteriorly.
. The posterior end of the palpebral furrow does not merge with the axial furrow.

The anterior pygidial spine pair is very long.

A new genus, Elkanaspis, is established for some of the species from Quebec,
Alaska, and Mexico that Shergold and Taylor suggested might be assigned to
Pseudokainella and for two new species from the Rabbitkettle Formation. Only those
Species with known pygidia are definitely assigned to the new genus.

Whether the other Argentinian and British species of Pseudokainella (that is, P.

110

lata [Kobayashi], P. pustulosa Harrington and Leanza, and P. impar [Salter] [see
Whitworth, 1969]) should be assigned to Elkanaspis is unresolved. Each of these
Tremadocian species has a narrow preglabellar field which is somewhat longer (sag.)
than that of P. keideli, but still shorter than that of E/kanaspis, and each lacks an
anterior glabellar constriction. The pygidia, however, are very close to that of
Elkanaspis . These species are, for the present, retained in Pseudokainella. Kobayashi
(1953) chose Pseudokainella lata as the type for a new subgenus, Parakainella,
which was subsequently synonymized with Pseudokainella by Harrington and Leanza
(1957).

Kainella, Richardsonella, Sigmakainella, and Naustia differ from Elkanaspis in
having longer preglabellar fields and parallel-sided or forwardly narrowing glabellae
lacking anterior constrictions. If Rasetti’s (1944: 255) synonymy of
Proapatokephaloides with Richardsonella is correct, then these five kainellid genera
bear distinctive pygidia: Kainella (Walcott, 1925, pl. 22, fig. 4), Richardsonella
(Fig. 700; Shergold, 1971, fig. 9b), Sigmakainella (Shergold, 1971, fig. 12b),
Naustia (Fig. 37), and Elkanaspis (Figs. 38, 39).

Elkanaspis differs from Apatokephalops Lu, 1975 in having an intraocular fixed
cheek, deeper lateral glabellar furrows, larger eyes, and a shorter preglabellar field.
Both the cranidium and pygidium of Jiia Zhou and Zhang, 1978 are reminiscent of
those of Elkanaspis (particularly E. corrugata sp. nov.). The cranidium of Jiia is
distinguished by the broad (tr.) occipital ring, the forwardly narrowing glabella which
lacks an anterior constriction, the forwardly located palpebral lobes, and the short
(sag.) and depressed preglabellar field.

Elkanaspis futile gen. et sp. nov.
Figs. 38, 64A—P

Diagnosis

A species of Elkanaspis with either extremely faint or effaced axial furrows,
advanced genal spines that are long and curving, an elliptical pygidium with a
goblet-shaped axis comprising two rings and a terminal piece, and short pygidial
spines.

Occurrences

Rabbitkettle Formation, Broken Skull River (six collections between 125 m and
177 m below top of formation), Yukonaspis kindlei Fauna.

Holotype

A pygidium (ROM 37532) from K 510 (177 m below top of Rabbitkettle Formation)
illustrated on Fig. 64G, H.

Name

From futile —a vessel broad above and pointed below (Latin) in reference to the shape
of the pygidial axis.

Description

Cephalon is elliptical in outline, one and a half times as wide (tr.) as long, and only
slightly inflated. Posterolateral corner is defined by 120 degree angle located on
transverse line which passes through one-third sagittal length of cephalon.
Barrel-shaped glabella is modified anteriorly by a rounded notch where it is
constricted by palpebral lobe. Axial furrows are deep opposite moderately arched and
simple occipital ring. In front of occipital furrow, axial furrow is reduced to a thin
groove which connects anterior and posterior ends of much deeper and more strongly
curved palpebral furrow. In some specimens, the axial furrow cannot be seen; its
position 1s indicated by a faint change in slope. Three pairs of lateral glabellar furrows
curve inward and backward; Is is firmly impressed and does not extend to axial
furrow; 2s and 3s are thin grooves extending inward from axial furrow. Front part of
glabella is moderately inflated over distinct preglabellar furrow which has slight
forward curvature. Preglabellar field is flat and depressed between subparallel
courses of preglabellar furrow and anterior border furrow; it widens and merges
laterally with equally flat and depressed genal field on free cheek. In sagittal length,
preglabellar field is equal to that of anterior border. Anterior border furrow and
anterior border maintain their character as they follow evenly curved path to become
lateral border furrow and lateral border. The border is extended posteriorly as long,
gradually tapering genal spine that has slight inward curvature and is one and a half
times sagittal length of cephalon. Crescentic palpebral lobe is wide (tr.) and long

Fig. 38 Elkanaspis futile gen. et sp. nov. Reconstruction of cephalon and pygidium. Bar represents
1 mm.

(equal to half sagittal cephalic length). It stands as high as glabella. Deep palpebral
furrow merges front and back with axial furrow to isolate a small semielliptical and
depressed fixed cheek. Posterior branch of facial suture curves outward and forward
before turning back across posterior border furrow and border to bisect posterior
margin. Anterior branch of facial suture swings outward at about 30 degrees to
sagittal line to a point half-way across anterior border and then cuts abruptly inward
along border to meet connective suture on mid-line. Front portion of cranidium is
about as wide (tr.) as distance between palpebral furrows.

Cephalon has prosopon of fine and irregularly disposed terrace lines on posterior
part of cranidium and on genal spines; remainder is apparently finely granulose.

Pygidium is transverse, twice as wide as long (sag.) and very gently arched (tr.).
Axis is high and consists of two short (sag.) rings and a terminal piece. A short
postaxial ridge extends nearly to posterior margin and provides axis with a goblet
shape. Axial furrows are deep; they undercut axial flanks. Pleural field is crossed by
three pleural furrows that are little more than transverse depressions. A faint border
furrow extends in even arc from anterolateral corner to tip of postaxial ridge. Four
pairs of compressed marginal spines that decrease gradually in size posteriorly curve
backward and inward. Each spine is broad-based and terminates in a point.

Remarks

Elkanaspis futile sp. nov. is most similar to E. unisulcata (Rasetti, 1944) from the
Levis Formation of Quebec. It differs from the Levis species in having shallower
axial furrows, three pairs of lateral glabellar furrows, less divergent anterior branches
of the facial suture, and a pygidium with only three pairs of marginal spines. The
cranidium of Elkanaspis cf. quadrispinosa (Palmer, 1968) from east-central Alaska is
similar to that of FE. futile, but that species lacks a median connective suture and,
apparently, has a straight posterior cephalic margin (Palmer, 1968, pl. 14, figs. 7, 8).

Elkanaspis corrugata gen. et sp. nov.
Figs. 39, 60L—V

Diagnosis

A species of Elkanaspis with a long glabella that is waisted anteriorly by indentation
of front part of palpebral furrows. It has straight preglabellar furrow, large palpebral
lobes, straight posterior cephalic margin, short and straight genal spines, and a
subrectangular pygidium with a long axis composed of three rings and a terminal
piece, and four pairs of deep pleural furrows that continue on to four pairs of pointed
bladelike marginal spines that curve slightly inward (with the exception of the fourth
pair which is hooked outwards).

Occurrences

Rabbitkettle Formation, Broken Skull River (three collections between 64 m and
70 m below top of formation), E/kanaspis corrugata Fauna.

Holotype

A pygidium (ROM 37555) from KK 64 (64 m below top of Rabbitkettle Formation)
illustrated on Fig. 60T.

Name

For corrugatus—wrinkled (Latin) in reference to the state of preservation of these
thin-shelled silicified trilobites.

Remarks

Elkanaspis corrugata sp. nov. is so similar to E. quadrispinosa (Palmer, 1968) from
the Franconian-2 Fauna of east-central Alaska that a comparison with this
well-described species will suffice as a description. E. corrugata differs from the
Alaska species in the following features:

Fig. 39 Elkanaspis corrugata gen. et sp. nov. Reconstruction of cephalon and pygidium (prosopon
omitted). Bar represents | mm.

114

a. The glabella is narrower across the occipital ring. It has three pairs of lateral
furrows and is bounded in front by a straight preglabellar furrow.

b. The preglabellar field is slightly narrower (tr.)
c. The genal spines are shorter.

d. The pygidial axis includes only three rings and a terminal piece. The pleural
regions are less inflated and the marginal spines are flatter, broader, and more
inwardly turned. The fourth spine pair is located much closer together and has a
distinct outward twist. In addition, the pleural furrows continue along the
marginal spines, but this feature could well have been accentuated by
compression.

Small cranidia of Richardsonella arctostriata (Raymond, 1937) from the Upper
Cambrian of Vermont are very similar to those of Elkanaspis corrugata. The
pygidium attributed to R. arctostriata (Fig. 700) has a short (sag.) axis and a
scalloped posterior margin of five pairs of spines. These features preclude an
assignment to Elkanaspis. The holotype cranidium of R. arctostriata (Fig. 70N)
possesses a relatively wide glabella that is bounded anteriorly by a gently curved
preglabellar furrow and a long (sag.) preglabellar field.

The type species of Apatokephaloides Raymond, A. clivosus Raymond, 1924, has
a long glabella that is constricted anteriorly in a manner similar to Elkanaspis
corrugata, A. clivosus, however, has a long (sag.) occipital ring, small posteriorly
placed eyes, two pairs of slotlike lateral glabellar furrows, and long (exsag.) posterior
limbs on the cranidium.

Elkanaspis? sp.
Figs. 40, 630-S

Occurrences

Rabbitkettle Formation, Broken Skull River (two collections 86.5 m and 94 m below
top of formation), Bowmania americana Fauna.

Remarks

Elkanaspis? sp. has a short (sag.) preglabellar field and a forwardly constricted
glabella. These features suggest an assignment to Elkanaspis, but the assignment is
queried because a pygidium has not been recovered. The great sagittal convexity of
the cranidium and the nearly vertical frontal lobe of the glabella are, apparently,
unique among kainellid trilobites. The cranidial fragment identified as
Richardsonella arctostriata (Raymond) by Gilman Clark and Shaw (1968, pl. 127,
fig. 33) is similar to Elkanaspis? sp. and could be conspecific. Gilman Clark and
Shaw (1968: 1020) described both a flat brim and an elevated border on this
specimen. Their photograph shows neither.

LAD

Superfamily Leiostegiacea Bradley, 1925
Family Leiostegiidae Bradley, 1925
Subfamily Pagodiinae Kobayashi, 1935

Genus Ptychopleurites Kobayashi, 1936b

Type Species

Ptychopleura brevifrons Kobayashi, 1936a from lowermost Ordovician rocks, Jones
Ridge, east-central Alaska (by original designation).

Remarks

Kobayashi (1936a) did not assign Ptychopleurites to a family, but indicated that he
thought it was related to the solenopleurid Solenopleurella. Ptychopleurites was
relegated to ‘‘unrecognizable genus’’ status by Lochman-Balk (in Moore, 1959: 525)
and Stitt (1977) chose not to assign this genus to a family. The recovery of pygidia of
P. brevifrons from the Rabbitkettle Formation indicates that this genus belongs in the
subfamily Pagodiinae and that it shows particular affinity for Pagodia (Oreadella)
Shergold, 1975 from the Late Cambrian of Australia and China.

The pygidia of Ptychopleurites brevifrons, Pagodia (Oreadella) buda Resser and
Endo, and P. (O.) cf. buda share a similar outline and trilobed shape, a highly convex
axis with few axial rings, inflated and unfurrowed pleurae, and steep flanks above a
narrow, convex border (compare Fig. 66Q, R, T, U with Endo and Resser, 1937, pl.
53 fig. 14, pl. 72, fig. 3 and with Shergold, 1975, pl. 36, fig. 2). The cranidia of P.
(Oreadella) differ only slightly from those of Ptychopleurites in having wider fixed

omer

Fig. 40 Elkanaspis? sp. Reconstruction of cephalon. Bar represents 1 mm.

116

cheeks, somewhat constricted glabellar flanks, and more posteriorly placed palpebral
lobes (compare Fig. 66K with Endo and Resser, 1937, pl. 53, fig. 10 and with
Shergold 1975, pl. 36, fig. 1). The free cheek of P. (Oreadella) differs from that of
Ptychopleurites in having a narrower border and slim and short genal spine (compare
Fig. 66S with Endo and Resser, 1937, pl. 53, fig. 13).

According to the correlation chart in Jones, Shergold and Druce (1971), the
Chinese and Australian occurrences of Pagodia (Oreadella) would correlate with the
late Franconian and Trempeauleauan of North America. Thus, this taxon 1s somewhat
older than Ptychopleurites .

Punctularia Raymond, based on P. ornata Raymond, 1937 from Zone 1 (Hungaia
Assemblage) of the Gorge Formation at Highgate Falls, Vermont, is a possible junior
subjective synonym of Ptychopleurites Kobayashi. Aside from a somewhat greater
convexity in Ptychopleurites , the cranidia assigned to these genera are indistinguish-
able (compare Gilman Clark and Shaw, 1968, pl. 127, fig. 1 with Stitt, 1977, pl. 4,
fig. 6). A pygidium is not known for Punctularia.

Ptychopleurites brevifrons (Kobayashi, 1936a)
Figs. 41, 66H—U

Ptychopleura brevifrons Kobayashi, 1936a: 165, pl. 21, figs. 7, 8.
Ptychopleurites brevifrons—Kobayashi, 1936b: 922.
Ptychopleurites brevifrons—Stitt, 1977: 46, pl. 4, figs. 6, 7, pl. 5, fig. 10.

Occurrences

Jones Ridge Limestone, Jones Ridge, Yukon River at Alaska-Yukon boundary,
Ptychopleurites Fauna (Kobayashi, 1936a; Palmer, 1968: 104). Signal Mountain
Limestone, Wichita and Arbuckle mountains, Oklahoma, Missisquoia depressa
Subzone (Stitt, 1977). Rabbitkettle Formation, Broken Skull River (six collections
between 50 m and 57 m below top of formation), Missisquoia depressa Subzone.

Holotype

An incomplete cranidium from Lower Ordovician rocks, Jones Ridge, east-central
Alaska illustrated by Kobayashi (1936a, pl. 21, fig. 7) and Stitt (1977, pl. 5, fig. 10).

Description

Cephalon is semicircular in outline and strongly convex (tr.). Posterolateral corner is
a sharp angle. Glabella is moderately inflated, barrel-shaped in outline; narrowing
slightly toward front. Axial furrows are deep. Three faint and short lateral glabellar
furrows are directed obliquely backward; these shorten towards front. Occipital ring
is broadly rectangular; it occupies highest portion of cephalon. Preglabellar furrow is

117

short (sag.) and sharply incised; it has slight forward curvature. Deep border furrows
define convex and broad cephalic borders. In front view, anterior border furrow rises
towards, but does not reach, preglabellar furrow; a short (sag.) and nearly flat
preglabellar field is thus defined. Eye is located half-way out on cheek, anteriorly of
mid-length of glabella. Semielliptical palpebral lobe is well defined by straight
palpebral furrow; it stands somewhat lower than inflated fixed cheek. Below eye,
genal field descends at about 45 degrees to lateral border furrow. Anterior branch of
facial suture curves forward and inward across anterior border. Rostral suture on free
cheek (Fig. 660) suggests presence of lenticular rostral plate. Posterior branch of
facial suture curves widely outward and backward to cut posterior margin well inside
genal corner. Dorsal surface of cephalon covered by fine granules.

Pygidium is strongly convex (tr.) and subtriangular in outline. Inflated axis
continues to posterior margin and consists of four rings that are separated by deep
axial ring furrows and a blunt terminal piece. Pleural field is inflated and, anteriorly,
it is the Same width as axis, giving a pronounced trilobed aspect to the pygidium.
Four deep interpleural furrows are present. Laterally, pygidial flank descends steeply
to lateral border furrow. Inflated and narrow (tr.) border is covered by closely spaced
and parallel terrace lines.

Remarks

Ptychopleurites brevifrons appears to be confined to Lower Tremadocian rocks of
Alaska, Oklahoma, and the District of Mackenzie. The genus has also been reported
from rocks of similar age in central Nevada (M.E. Taylor, in Stitt, 1977: 47).

>
Oar

Fig. 41 Ptychopleurites brevifrons (Kobayashi, 1936a). Reconstruction of cranidium and pygidium. Bar
represents 1 mm.

118

Family Missisquoiidae Hupé, 1955

Remarks

Only two genera are assigned to this family—Missisquoia Shaw from the Missisquoia
and Parabolinella zones in North America and from the Mictosaukia orientalis
Assemblage in China, and Parakoldinoides Endo from the Upper Cambrian of China
and from Australia (late Franconian; Jones et al., 1971).

I follow Shergold (1975) in assigning the Missisquoiidae to the Leiostegiacea. It
should be noted, however, that Missisquoia bears close resemblance to some genera
that are firmly assigned to the illaenacean family Styginidae. Such similarity is
perhaps best seen in a comparison of Missisquoia depressa (Fig. 42) and
Perischoclonus capitalis Raymond (Whittington, 1963, pl. 22, figs. 4, 13) from the
Middle Ordovician of western Newfoundland. It is possible that the Styginidae,
which appears to be the ancestor to the Illaenidae and the Scutelluidae (Ludvigsen and
Chatterton, 1980), was derived from the Missisquolidae in the latest Cambrian or
earliest Ordovician.

Genus Missisquoia Shaw, 1951

Type Species

Missisquoia typicalis Shaw, 1951 from the Lower Ordovician part of the Gorge
Formation (Missisquoia Zone), Highgate Falls, Vermont (by original designation).

Subjective Synonyms

Lunacrania Kobayashi, 1955; Macroculites Kobayashi, 1955; Rhamphopyge
Kobayashi, 1955 (see Dean, 1977); Tangshanaspis Zhou and Zhang, 1978;
Paranumia Hu, 1973.

Assigned Species

Missisquoia typicallis Shaw, 1951 (? = M. graphica Hu, 1973)

Missisquoia enigmatica (Kobayashi, 1955) (= M. nasuta Winston and Nicholls,
1967 and Paranumia triangularia Hu, 1973; also see Dean, 1977: 4)

Missisquoia inflata Winston and Nicholls, 1967

Missisquoia depressa Stitt, 1971b ( = Tangshanaspis zhaogezhuangensis Zhou and
Zhang, 1978)

Missisquoia cyclochila Hu, 1971

Missisquoia manchuriensis (Resser and Endo, in Endo and Resser, 1937)

Missisquoia mackenziensis sp. nov.

119

Remarks

From the recent assessment of Missisquoia by Dean (1977), it is clear that the genus
now includes species that display a remarkably wide range of morphologies,
particularly in pygidial and glabellar shapes and in degrees of inflation.

Missisquoia has a wide geographic range in North America. The genus occurs in
Newfoundland (Fortey and Skevington, 1980), Vermont (Shaw, 1951), New York
(Taylor and Halley, 1974), Oklahoma (Stitt, 1971b, 1977), South Dakota (Hu,
1973), Texas (Winston and Nicholls, 1967), Utah (Hintze et al., 1980), Nevada
(Cook and Taylor, 1977), Wyoming (Hu, 1971), Alberta and British Columbia
(Dean, 1977), and now the District of Mackenzie.

The generic synonymy of Missisquoia above extends the geographic range of the
genus to Hopeh and Liaoning Provinces, China. Tangshanaspis zhaogezhuangenis
Zhou and Zhang, 1978 from Hopeh Province is assigned to Missisquoia depressa Stitt
because the differences between Tangshanaspis and Missisquoia listed by Zhou and
Zhang (1978: 25) are, in essence, those that distinguish M. depressa from M.
typicalis. The single pygidium from the Wanwan Formation of Liaoning Province
that was illustrated by Endo and Resser (1937, pl. 73, fig. 11) as Encrinurus (?)
manchuriensis Resser and Endo is assigned to Missisquoia.

The genus Paranumia Hu, 1973 was based on small, but well-preserved cranidia
and pygidia of P. triangularia Hu from the Deadwood Formation of South Dakota.
Hu (1973: 86) did not attempt comparisons with Missisquoia, but he did state (p. 89)
in his discussion of ontogeny that the earliest instars of P. triangularia are closely
similar to those of Missisquoia cyclochila which he had described earlier (Hu, 1971).
He claimed that later meraspid stages of P. triangularia could be differentiated from
M. cyclochila on pygidial and glabellar shapes and absence of a preglabellar field.
Hu’s arguments are not convincing. P. triangularia does not have a preglabeilar
field, and neither does Missisquoia. Both cranidia and pygidia of P. triangularia are
highly similar to those assigned to Missisquoia enigmatica by Dean (1977). I

Fig. 42 Missisquoia depressa Stitt, 1971b. Reconstruction of cephalon and pygidium (prosopon
omitted). Bar represents 1 mm.

120

conclude that Paranumia is a junior synonym of Missisquoia and that Paranumia
triangularia is probably a junior synonym of Missisquoia enigmatica (Kobayashi).

Missisquoia depressa Stitt, 1971b
Figs. 42, 43, 65, 66A-G

Missisquoia depressa Stitt, 1971b: 25, pl. 8, figs. 5-8.
Tangshanaspis zhaogezhuangensis Zhou and Zhang, 1978: 17, pl. 1, figs. 22, 23.

Occurrences

Signal Mountain Limestone, Arbuckle and Wichita mountains, Oklahoma, Missis-
quoia depressa Subzone (Stitt, 1971b, 1977). Notch Peak Formation, Utah,
Missisquoia depressa Subzone (Hintze et al., 1980). Fengshan Formation, Hopeh
Province, China, Mictosaukia orientalis Assemblage (Zhou and Zhang, 1978).
Rabbitkettle Formation, Broken Skull River (seven collections between 46 m and
57 m below top of formation), Missisquoia depressa Zone.

Holotype

An incomplete cranidium from the Signal Mountain Limestone, Joins Ranch Section,
Arbuckle Mountains, Oklahoma illustrated by Stitt (1971b, pl. 8, fig. 5).

Fig. 43 Missisquoia depressa Stitt, 1971b. Olbique view of reconstructed cephalon.

121

Description

The cranidium and pygidium of Missisquoia depressa have been described by Stitt
(1971b: 25). The material from the Rabbitkettle Formation includes both free cheeks
and hypostomes and these are described below. Minor differences between the type
material of M. depressa and that illustrated here include the variable developments of
the anterior border furrow on the cranidium. These vary from deep furrows with a
well-developed median notch (Fig. 65B, K, R), to nearly straight furrows (Fig. 65P),
to effaced or nearly effaced furrows (Fig. 65A, N). The silicified pygidia of M.
depressa have as many as six axial ring furrows in front of the terminal piece and the
pleurae can be seen to terminate as short, blunt spines. On interior, the convex
doublure narrows forwardly from behind axis where it is one-quarter the sagittal
length of the pygidium.

Free cheek has evenly curved lateral margins. Weak lateral border furrow defines
wide and slightly inflated border. Posterolateral corner carries long and tapering genal
spine which diverges at about 30 degrees to sagittal line. On interior, genal spine
encased by doublure which, anteriorly, becomes tubelike and extends inwardly as far
as lateral border furrow.

Rostral plate has not been recovered, but judging from the shape of rostral suture
seen in Fig. 65M, it must have been transverse with posteriorly convergent sides.

Hypostome is subrectangular in outline, longer than wide, with small anterior
wings. Posterolateral corner is rounded; a small specimen (Fig. 66B) carries a short
Spine at this corner. Median body is only slightly inflated, it is delineated anteriorly
by median ovate depression and laterally by moderately deep border furrows which
tend to converge posteriorly. Median body is unequally divided by middle furrows
which nearly meet on sagittal line.

Remarks

Missisquoia depressa Stitt differs from both M. typicalis Shaw and M. enigmatica
(Kobayashi) (see Dean, 1977: 4, for synonomy) by its slightly inflated glabella and its
semicircular pygidium of low convexity. The free cheek of M. typicalis illustrated by
Taylor and Halley (1974, pl. 3, figs. 5, 6) has a deeper lateral border furrow and a
genal spine that projects posteriorly in an even curve.

Despite minor differences, the two specimens from the Fanshang Formation of
Hopeh Province assigned to Tangshanaspis zhaogezhuangensis by Zhou and Zhang
(1978) are considered conspecific with M. depressa. The Chinese cranidium appears
to have the palpebral lobe located slightly further forward than M. depressa and the
pygidium has slightly larger marginal spines.

The single pygidium of Missisquoia manchuriensis (Resser and Endo, in Endo and
Resser, 1937, pl. 73, fig. 11) from the Wanwan Formation of Liaoning Province is
closely similar to M. depressa, but may be distinguished by the size of the marginal
spines which are longer and slimmer than those of M. depressa.

122

Missisquoia mackenziensis sp. nov.
Figs. 44, 67A-K

Diagnosis

A species of Missisquoia possessing a moderately inflated glabella with an evenly
rounded anterior portion and three pairs of lateral furrows. Prominent palpebral ridge
runs immediately inside cephalic border furrow. Genal spines are short. Pygidium is
semicircular in outline and moderate in convexity. It bears an annulate axis, six
furrowed pleurae, and a narrow convex border.

Occurrence

Rabbitkettle Formation, Broken Skull River (single collection 60 m below top of
formation). Missisquoia mackenziensis Fauna.

Holotype

A complete cranidium (ROM 37563) from KK 123 (60 m below top of Rabbitkettle
Formation) illustrated on Fig. 67A-C.

eee
Ss
Be
oe]
Sel

Fig. 44 Missisquoia mackenziensis sp. nov. Reconstruction of cephalon and pygidium (prosopon
omitted). Bar represents 1 mm.

Name

From the Mackenzie Mountains.

Remarks

Missisquoia mackenziensis sp. nov. is best differentiated from other species of
Missisquoia by the course of the palpebral ridge and the anterior cephalic border
furrow. In M. mackenziensis, the lateral border furrow crosses the facial suture
immediately in front of the eye and, on the fixed cheek, defines the front edge of the
palpebral ridge (Fig. 67A, D). In other species of Missisquoia, the lateral border
furrow crosses the facial suture well in front of the eye and the palpebral ridge, if
present, is distinctly separated from the anterior border furrow. Such a pattern is well
shown on the front part of the fixed cheek of M. typicalis Shaw, M. cyclochila Hu,
M. inflata Winston and Nicholls, and M. depressa Stitt (see Taylor and Halley, 1974,
pl. 3, figs. 1, 3; Hu, 1971, pl. 20, fig. 19; Winston and Nicholls, 1967, pl. 13, fig. 7;
Fig. 65K, O).

The pygidium of M. mackenziensis differs from those of similar size of M.
typicalis, M. depressa, and M. manchuriensis in possessing a narrow convex border
and by lacking marginal spines. The pygidium of M. enigmatica (Kobayashi) also
lacks marginal spines, but this pygidium (Dean, 1977, pl. 1, fig. 3; Hu, 1973, pl. 1,
fig. 23) is arched (tr.) and carries a highly inflated axis with only a few ring furrows.

Missisquoia sp.
Fig. 69)

Occurrence

Rabbitkettle Formation, Broken Skull River (single collection 70 m below top of
formation), Elkanaspis corrugata Fauna.

Remarks

Were it not for its co-occurrence with acknowledged Cambrian trilobite genera such
as Idiomesus , Eurekia, and Yukonaspis in the lower part of the E/kanaspis corrugata
Fauna of the Yukonaspis Zone, these small, immature cranidia of Missisquoia would
not deserve mention. These specimens now demonstrate that the first occurrence of
Missisquoia in the Rabbitkettle Formation is 10m below the base of the
Parabolinella Zone. The size of the cranidium precludes identification to species
level, but it is similar to M. depressa cranidia of the same size.

124

Superfamily Asaphacea
Family Asaphidae Burmeister, 1843
Subfamily Symphysurininae Kobayashi, 1955

Genus Symphysurina Ulrich, in Walcott, 1924

Type Species

Symphysurina woosteri Ulrich, in Walcott, 1924 from the Oneota Dolomite,
Trempealeau, Wisconsin (by original designation).

Symphysurina cf. brevispicata Hintze, 1953
Figs. 45, 57T

Symphysurina brevispicata—Stitt, 1971: 15, pl. 8, figs. 19-21 (see for synonymy).
Symphysurina brevispicata—Hu, 1973: 94, pl. 2, figs. 21-28.
Symphysurina brevispicata—Stitt, 1977: 37, pl. 4, fig. 10.

Occurrences

Summarized by Stitt (1977: 32-36) in his discussion of the Symphysurina
brevispicata Subzone. Rabbitkettle Formation, Broken Skull River (single collection
25 m below top of formation), Symphysurina brevispicata Subzone.

Fig. 45 Symphysurina cf. brevispicata Hintze, 1953. Drawing of interior of fragmentary free cheek. Bar
represents | mm.

Remarks

The single, fragmentary free cheek recovered during the present study is generally
similar to those of Symphysurina brevispicata Hintze, 1953; 8. woosteri Ulrich, in
Walcott, 1924; and S. bulbosa Lochman, 1964b. The size of the genal spine suggests
an affinity with S. brevispicata, a species that occurs in Utah (Hintze, 1953),
Montana (Lochman, 1964b), Texas (Winston and Nicholls, 1967), South Dakota
(Hu, 1973), and Oklahoma (Stitt, 1971b, 1977).

Family Nileidae Angelin, 1854

Genus Tatonaspis Kobayashi, 1935

Type Species

Tatonaspis alaskensis Kobayashi, 1935 from the Trempealeauan-1 Fauna (Palmer,
1968) of east-central Alaska (by original designation).

Remarks

Lochman-Balk’s (1953, and in Moore, 1959) proposal to synonymize Tatonaspis
with Macelloura Resser, 1935 was rejected by Palmer (1968: 67) who noted that
persistent differences separate the two taxa. Palmer’s argument is accepted.

Four species are now assigned to TJatonaspis: T. alaskensis Kobayashi; T.
levisensis Rasetti, 1944; T. breviceps (Raymond, 1924); and T. diorbita sp. nov.
Rasetti (1944: 257) considered //laenurus punctatus Raymond, 1937 to be a species
of Tatonaspis. Because this species was not illustrated, it is difficult to evaluate.
Raymond (1937: 1091) stated that 7. punctatus differs from /. breviceps only in the
presence of large punctae.

The new species of Tatonaspis is somewhat closer to Macelloura than either of T.
alaskensis or T. levisensis in possessing a well-defined glabella, a deep anterior
border furrow along the front margin, and a rimlike anterior border. The assignment
of T. diorbita to Tatonaspis instead of Macelloura is based on the size and position of
the palpebral lobe, the absence of palpebral or occipital furrows, the direction of the
anterior facial sutures, and the presence of a doublure that is identical to that of 7.
alaskensis .

Tatonaspis is confined to Trempealeauan rocks in North America. It occurs at
Shelf-edge sites in Quebec (Rasetti, 1944), Vermont (Raymond, 1924), Nevada
(Taylor, 1976), Alaska (Palmer, 1968), and now the District of Mackenzie.

Palmer (1968) placed Tatonaspis in the family Nileidae without commenting on
this assignment. The general cephalic form of Tatonaspis as well as the shape,
orientation, and prosopon of the cephalic and pygidial doublures are similar to those

126

of many nileids (see Schrank, 1972; Fortey, 1975). Possible phyletic relationships
between the Trempealeauan Tatonaspis and the Tremadocian Symphysurus and
Nileus have yet to be discovered.

Tatonaspis diorbita sp. nov.
Figs. 46, 68A-N, 69R-T

Diagnosis

A species of Tatonaspis with deep axial furrows outlining narrow and parallel-sided
glabella; palpebral lobes are large and semicircular; genal corners are rounded.
Pygidium is semielliptical in outline with a convex, U-shaped axis and a faint border
furrow defining flat border.

Occurrence

Rabbitkettle Formation, Broken Skull River (two collections 165 m and 172 m below
top of formation), Yukonaspis kindlei Fauna.

Holotype

A cranidium (ROM 37619) from K 550 (165 m below top of Rabbitkettle Formation)
illustrated on Fig. 68A, B.

Fig. 46 Tatonaspis diorbita sp. nov. Reconstruction of cephalon and pygidium. Bar represents | mm.

127

Name

From diorbita—a two-wheeled track (Latin) in reference to the deep parallel axial
furrows.

Description

Cephalon is arched (tr.), semicircular in outline, and slightly wider than long (sag.).
Glabella is rectangular (length is twice width), moderately convex; it lacks any trace
of lateral or occipital furrows. Anterior border furrow is short (sag.), deep, and
transverse. Anterior border is a very short (sag.) rim which extends on to free cheeks;
in anterior view it arches up towards mid-line. Palpebral lobe is a large, semicircular
flap that droops slightly outward; its length is nearly half sagittal length of cephalon
and its mid-point is located opposite mid-length of cephalon. Posterior border furrow
is not developed. Cheek slopes steeply to margin below eye. A very narrow lateral
border is present on anterolateral flank of cephalon. Genal angle is bluntly rounded.
Anterior branch of facial suture swings forward and inward to anterior border and
then across anterior margin. Median path of suture is ventral-intramarginal. The
cheeks are yoked. Posterior branch of facial suture follows sigmoid path to posterior
border. A broad, upturned doublure with a wide median notch is evident in anterior
view. Doublure is longest medially where it plunges under cephalon at about 70
degrees; it narrows and becomes flatly convex posteriorly until, near genal angle, it is
oriented parallel with cephalic flank. Prosopon on cephalon consists of fine pits.
Doublure carries fine terrace lines.

Pygidium is twice as wide as long; it has evenly curved posterior margin between
nearly exsagittally directed lateral margins. Convex axis extends for two-thirds
pygidial length and is outlined by firmly impressed and U-shaped axial furrows. Only
an articulating furrow crosses axis. Pleural region is faintly inflated inside very
shallow border furrow which follows a path subparallel with posterior margin.
Posterior border is rather broad and flat. Doublure is wide and flat; it extends inward
beyond border furrow and its median part is tucked into posterior part of axis.

Remarks

Tatonaspis diorbita sp. nov. is readily distinguished from 7. alaskensis Kobayashi,
T. levisensis Rasetti, and T. breviceps (Raymond) by its narrow, well-defined
glabella, large eyes, rounded genal corners, and the absence of both occipital and
posterior border furrows.

Superfamily Ceratopygacea
Family Ceratopygidae Linnarsson, 1869

128

ceratopygid indet.
Fig. 53E-J

Occurrence

Rabbitkettle Formation, Broken Skull River (six collections between 78 m and 165 m
below top of formation), Bowmania americana Fauna and Yukonaspis kindlei Fauna.

Remarks

Small and coarsely silicified cranidia and free cheeks from the Rabbitkettle Formation
probably belong to this family. In having a glabella that expands towards a short
(sag.) anterior border and rather large posteriorly placed palpebral lobes, the cranidia
are similar to some species of Onychopyge Harrington, 1938. They differ markedly
from Onychopyge, however, in having greater convexity, and in lacking palpebral
and slotlike lateral glabellar furrows. Pygidia that are similar to the characteristic
ceratopygid pygidium do not occur in the single collection that contained the
illustrated cranidia and free cheeks.

Acknowledgements

I am indebted to S.L. Blusson of the Geological Survey of Canada who, in 1972,
provided the initial impetus for this study by suggesting that the area around the
headwaters of the Broken Skull River should yield an interesting sequence of Lower
Palaeozoic faunas. He was right. I am also grateful to D.B. Craig, Resident Geologist
at Whitehorse, who, in mid-winter of 1973 located and rescued about a quarter of a
ton of silicified fossil samples (including the entire lot from Section K) that had been
lost along the Canol Road.

Peter Fenton assisted in the field in 1977. Christine Dudar provided curatorial
assistance. The trilobite reconstructions were prepared by David Sargent under my
Supervision. The drafting is by Subhash Shanbhag. Brian O’Donovan printed the
trilobite photographs from my negatives. My wife, Kathleen MacKinnon, assisted in
picking and sorting many of these samples of silicified trilobites.

I thank M.P. Cecile, B.D.E. Chatterton, R.A. Fortey, S.P. Gordey, E. Landing,
B.S. Norford, A.R. Palmer, J.H. Shergold, J.H. Stitt, and M.E. Taylor for
information and suggestions. Discussions with S.R. Westrop helped to clarify my
ideas on the nature of the biomere boundary events.

The initial field work in 1972 was financed by the Department of Indian and
Northern Affairs and by the National Research Council (through a grant to A.C.
Lenz). I acknowledge the continuing support of the Natural Sciences and Engineering
Research Council Canada (Grant No. A-3825) for my investigations of Lower
Palaeozoic trilobite biostratigraphy of northern Canada.

129

Fig. 47 Geragnostus (Micragnostus) subobesus (Kobayashi, 1936a).
A Cephalon, dorsal view, X 9, ROM 37485, KK 113.
B Pygidium, dorsal view, X 9, ROM 37486, KK 113.
C Cephalon, dorsal view, X 9, ROM 37487, KK 113.
D Pygidium, dorsal view, X 8, ROM 37484, KK 113.

E,F Cephalon, dorsal and posterior views, X 9, ROM 37617, KK 113.
G,H Pygidium, dorsal and posterior views, X 8, ROM 37614, KK 113.
1) Cephalon, dorsal and anterior views, X 9, ROM 37615, KK 113.

K,L Pygidium, dorsal and lateral views, X 9, ROM 37613, KK 113.
M,N Cephalon, dorsal and lateral views, < 9, ROM 37616, KK 116.
o,P Anterior thoracic segment, dorsal and anterior views, X 13, ROM 37618, KK 113.
Pseudagnostus (Pseudagnostina) sp.
Q Pygidium, dorsal view, X 11, ROM 37632, K 550.
R Complete specimen, dorsal view, X 11, ROM 37631, K 550.

130

131]

Fig. 48 Parabolinella cf. prolata Robison and Pantoja-Alor, 1968.
A-D Cranidium, dorsal, anterior and lateral views, X 5.5, oblique anterior view, < 9, ROM
37473, KK 113.
E Cranidium, ventral view, < 5.5, ROM 37474, KK 113.
F Cranidium, dorsal view, X 6, ROM 37475, KK 113.
G-1_ Cephalon, dorsal, anterior and oblique views, X 13, ROM 37609, KK 113.
J Pygidium, dorsal view, X 9, ROM 37476, KK 113.
K,L Cranidium, dorsal and oblique views, X 7, ROM 37608, KK 113.
M-O Yoked cheeks, anterior, oblique and dorsal views, X 5.5, ROM 37610, KK 113.
Q Pygidium, dorsal and posterior views, X 9, ROM 37490, KK 116.
R Pygidium, ventral view, X 9, ROM 37491, KK 116.
Ss Cephalon, dorsal view, X 11, ROM 37478, KK 113.
T Pygidium and partial thorax, dorsal view, X 11, ROM 37477, KK 113.
U Hypostome, ventral view, X 18, ROM 37492, KK 116.

132

133

Fig. 49 Parabolinella cf. prolata Robison and Pantoja-Alor, 1968.

134

INXE:

Cranidium, dorsal, anterior and oblique views, X 6, ROM 37488, KK 116.
Cranidium, dorsal and oblique views, X 8, ROM 37489, KK 116.
Hypostome, ventral and posterior views, X 13, ROM 37525, KK 119.5.
Thoracic segment, posterior and dorsal views, X 6, ROM 37510, KK 119.5.
Yoked cheeks, dorsal view, X 9, ROM 37513, KK 119.5.

Yoked cheeks, dorsal and anterior views, X 6, ROM 37514, KK 119.5.
Cranidium, dorsal view, <X 8, ROM 37512, KK 119.5.

Pygidium, dorsal view, X 9, ROM 37516, KK 119.5.

Pygidium and partial thorax, ventral view, X 9, ROM 37515, KK 119.5.
Pygidium and partial thorax, dorsal view, X 11, ROM 37654, KK 119.5.
Partial thorax, ventral view, X 8, ROM 37653, KK 119.5.

Thoracic segment, dorsal view, X 6, ROM 37511, KK 119.5.

Partial thorax, dorsal view, <X 8, ROM 37652, KK 119.5.

Fig. 50 Parabolinella panosa sp. nov.

136

Q,R

Protaspid, dorsal view, X 27, ROM 37735, KK 122.5.

Meraspid cephalon, dorsal view, X 27, ROM 37733, KK 122.5.

Enrolled meraspid specimen, oblique view, X 27, ROM 37730, KK 122.5.

Meraspid specimen (M.2), dorsal and lateral views, X 27, ROM 37729, KK 122.5.
Meraspid specimen (M.3), dorsal view, X 27, ROM 37734, KK 122.5.

Meraspid specimen (M.3 or M.4), dorsal view, X 27, ROM 37732, KK 122.5.
Meraspid specimen (M.7), ventral view, X 18, ROM 37728, KK 122.5.

Meraspid specimen lacking free cheeks (M.9), lateral and dorsal views, X 18, ROM 37590,
KK123:

Yoked cheeks, dorsal view, X 11, ROM 37727, KK 122.5.

Pygidium, dorsal view, X 13, ROM 37592, KK 123.

Cranidium, dorsal view, X 11, ROM 37596, KK 123.

Holotype cranidium, dorsal and oblique lateral views, X 11, ROM 37731, KK 122.5.

Parabolinella cf. prolata Robison and Pantoja-Alor, 1968.

M,N

Cranidium, oblique lateral and dorsal views, X 13, ROM 37591, KK 123.

Parabolinites cf. williamsoni (Belt, 1868).

P
S

Cranidium, dorsal view, X 13, specimen lost, KK 133.
Cranidium, dorsal view, X 8, ROM 37597, KK 133.

tile

Fig. 3)

138

Parabolinites cf. williamsoni (Belt, 1868).

A,B
C

E
F,G
H
1,J
K

Cranidium, dorsal and lateral views, X 8, ROM 37691, K 845.
Cranidium, dorsal view, X 7, ROM 37560, KK 64.

Cranidium, dorsal view, X 8, ROM 37690, K 845.

Cranidium, dorsal view, X 11, ROM 37561, KK 64.

Hypostome, ventral and oblique views, X 11, ROM 37693, K 845.
Free cheek, dorsal view, X 9, ROM 37699, KK 64.

Pygidium, dorsal and lateral views, <X 11, ROM 37692, K 845.
Pygidium, dorsal view, X 8, ROM 37700, KK 64.

Trilobite indet. (not described).

Pygidium, dorsal view, X 13, ROM 37562, KK 64.

Apoplanias rejectus Lochman, 1964a.

M,N
O

R
ST

Cephalon, dorsal and oblique views, X 13, ROM 37680, KK 25.
Cranidium, dorsal view, X 9, ROM 37684, KK 43.

Cranidium, ventral view, <X 8, ROM 37688, KK 43.

Cranidium, dorsal view, X 13, ROM 37682, KK 235.

Cranidium, dorsal view, X 13, ROM 37681, KK 235.

Cranidium, oblique and dorsal views, X 11, ROM 37679, KK 25.

Fig. 52 Parabolinella hecuba (Walcott, 1924).
A,B Cranidium, dorsal and lateral views, X 5.5, ROM 37703, KK S50.
Cc Cranidium, dorsal view, X 11, ROM 37706, KK S50.
D Cranidium, dorsal view, X 7, ROM 37705, KK SO.
E-G Cranidium, oblique view, X 11, dorsal and lateral views, X 6, ROM 37702, KK 50.
H,1_ Cranidium, dorsal and oblique views, <X 7, ROM 37704, KK 50.
Parabolinella sp.
J,K Cranidium, dorsal and anterior views, X 8, ROM 37683, KK 43.
L Cranidium, dorsal view, X 9, ROM 37686, KK 43.
M_ Cranidium, dorsal view, X 8, ROM 37685, KK 43.
N Free cheek, dorsal view, X 11, ROM 37687, KK 43.
Rhaptagnostus clarki (Kobayashi, 1935).
O Cephalon, dorsal view, < 11, ROM 37604, K 510.
Pygidium, dorsal view, X 7, ROM 37601, K 510.
Pygidium, dorsal view, X 11, ROM 37602, K 510.
Cephalon, ventral view, X 9, ROM 37600, K 510.
Pygidium, ventral view, X 11, ROM 37603, K 510.

nWNO wv

140

Fig. 53 Liostracinoides vermontanus Raymond, 1937.
A,B Cranidium, dorsal and anterior views, X 13, ROM 37745, KK 86.5.
C,D Cranidium, oblique and dorsal views, X 18, ROM 37746, KK 86.5.
Ceratopygid indet.
E Free cheek, dorsal view, < 13, ROM 37751, KK 211.
F Cranidium, dorsal view, <X 13, ROM 37747, KK 211.
G Cranidium, dorsal view, X 13, ROM 37749, KK 211.
H,1 Cranidium, dorsal and anterior views, X 13, ROM 37748, KK 211.
J Cranidium, dorsal view, < 13, ROM 37750, KK 211.
Bowmania americana (Walcott, 1884).
K Pygidium, dorsal view, < 13, ROM 37744, KK 141.
Cranidium, dorsal view, X 7, ROM 37737, KK 77.
Genal spine, dorsal view, X 8, ROM 37743, KK 141.
Cranidium, dorsal view, X 11, ROM 37739, KK 141.
Cranidium, dorsal view, X 11, ROM 37741, KK 141.
Yoked cheeks, dorsal view, X 8, ROM 37742, KK 141.
Cranidium, lateral view, X 9, ROM 37738, KK 77.
Cranidium, oblique and dorsal views, X 11, ROM 37740, KK 141.

142

Fig. 54 Bowmania americana (Walcott, 1884).

A-C Cranidium, dorsal, anterior and lateral views, X 8, ROM 37663, KK 156.
D Cranidium, dorsal view, < 11, ROM 37664, KK 156.
E Cranidium, dorsal view, X 11, ROM 37665, KK 156.

F,G Yoked cheeks, ventral and anterior views, X 7, ROM 37662, KK 156.

H,! Pygidium, dorsal and posterior views, X 11, ROM 37666, KK 156.
J Pygidium, dorsal view, X 11, ROM 37668, KK 156.

K,L Pygidium, posterior and dorsal views, X 11, ROM 37667, KK 156.
M_ Yoked cheeks, dorsal view, X 13, ROM 37671, KK 156.
N Genal spine, dorsal view, X 11, ROM 37670, KK 156.
O Genal spine, dorsal view, X 11, ROM 37669, KK 156.

Idiomesus tantillus Raymond, 1924.

P-R Cephalon, dorsal, anterior, and oblique views, X 13, ROM 37645, K 550.
Ss Cranidium, dorsal view, X 18, ROM 37644, K 550.

T,U Cranidium, dorsal and anterior views, X 13, ROM 37646, K 550.

144

145

Fig. 55 Heterocaryon tuberculatum Rasetti, 1944.

146

A-C
D-F

Cranidium, dorsal anterior and oblique views, X 9, ROM 37464, K 510.
Cranidium, dorsal, lateral and anterior views, X 9, ROM 37453, KK 177.
Free cheek, exterior view, X 11, ROM 37538, K 510.

Cranidium, dorsal view, X 11, ROM 37454, KK 177.

Pygidium, posterior, dorsal and oblique views, X 11, ROM 37461, K 510.
Cranidium, dorsal view, < 11, ROM 37650, K 550.

Pygidium, dorsal view, X 13, ROM 37462, K 510.

Pygidium, ventral view, X 13, ROM 37463, K 510.

Kathleenella hamulata gen. et sp. nov.

OH?
Q
R
S,f

Holotype cranidium, dorsal and oblique views, < 11, ROM 37459, K 510.
Free cheek, exterior view, X 11, ROM 37537, K 510.

Cranidium, dorsal view, X 11, ROM 37460, K 510.

Cranidium, dorsal and oblique views, <X 18, ROM 37649, K 550.

147

Fig. 56. Larifugula triangulata gen. et sp. nov.
A-C Holotype cranidium, dorsal, anterior and oblique views, X 13, ROM 37643, K 550.

Cranidium, dorsal view, <X 13, ROM 37574, KK 180.
Cranidium, dorsal view, X 13, ROM 37651, K 550.
Cranidium, anterior and dorsal views, <X 13, ROM 37566, KK 64.
Cranidium, dorsal view, X 13, ROM 37565, KK 64.
Pygidium, dorsal view, < 18, specimen lost, KK 133.
Cranidium, dorsal view, X 11, ROM 37586, KK 133.
Cranidium, dorsal view, < 13, ROM 37587, KK 133.
Pygidium, dorsal view, X 18, ROM 37568, KK 64.
Free cheek, exterior view, X 11, ROM 37567, KK 64.
Free cheek, exterior view, X 11, ROM 37593, KK 133.
Cranidium, dorsal view, < 13, specimen lost, KK 133. |
Pygidium, dorsal view, X 18, specimen lost, KK 133.
Cranidium, dorsal view, X 13, ROM 37696, K 845.

S Free cheek, exterior view, X 11, ROM 37594, KK 133.
Larifugula leonensis (Winston and Nicholls, 1967).

P Cranidium, dorsal view, X 18, specimen lost, KK 133.
Plethometopus obtusus Rasetti, 1945.
T-U Cranidium, anterior, lateral and dorsal views, X 8, ROM 37518, KK 119.5.

148

Fig. 57 Leiocoryphe spp.

150

A,B Cranidium, dorsal and anterior views, X 13, ROM 37675, KK 156.
c Cranidium, dorsal view, X 13, ROM 37446, KK 177.
D Pygidium, dorsal view, X 13, ROM 37447, KK 177.
E,F Pygidium, anterior and dorsal views, X 13, ROM 37676, KK 156.
Idiomesus intermedius Rasetti, 1959.
G,H Cranidium, dorsal and anterior views, X 13, ROM 37442, KK 177.
1 Pygidium, dorsal view, X 13, ROM 37444, KK 177.
J Pygidium, dorsal view, X 13, ROM 37445, KK 177.
K Cranidium, dorsal view, X 18, ROM 37443, KK 177.
L Cranidium, dorsal view, X 13, ROM 37583, KK 180.
M _ Pygidium, dorsal view, X 13, ROM 37580, KK 180.
Idiomesus levisensis (Rasetti, 1944).
N Cranidium, dorsal view, < 13, ROM 37599, KK 133.
O Cranidium, dorsal view, X 18, specimen lost, KK 133.
Saukiid indet.
Pp Pygidium, dorsal view, X 6, ROM 37633, K 550.
Q,R Cranidium, anterior and dorsal views, X 11, ROM 37640, K 550.
Bienvillia cf. corax (Billings, 1865).
S Cranidium, dorsal view, < 13, ROM 37564, KK 64.
Symphysurina cf. brevispicata Hintze, 1953.
T Free cheek, interior view, X 11, ROM 37678, KK 25.
Triarthropsis limbata Rasetti, 1959.
U Cranidium, dorsal view, X 11, ROM 37636, K 550.
Euloma (Plecteuloma) sp.
Vv Cranidium, dorsal view, X 11, ROM 37634, K 550.

Fig. 58

152

‘‘Calvinella’’ palpebra sp. nov.

A,B
(C5)D)
12
F

G
H
I

Cranidium, dorsal and anterior views, X 11, ROM 37465, K 510.

Holotype cranidium, oblique and anterior views, X 9, ROM 37466, K 510.

Cranidium, ventral view, X 9, ROM 37467, K 510.

Free cheek, dorsal view, X 8, ROM 37469, K 510 (specimen is stretched in a transverse
direction).

Pygidium, dorsal view, X 13, ROM 37471, K 510.

Pygidium, dorsal view, X 13, ROM 37472, K 510.

Cranidium, dorsal view, < 13, ROM 37468, K 510.

Pygidium, ventral view, X 11, ROM 37470, K 510.

Euptychaspis typicalis Ulrich, in Bridge, 1931.

K-M
N
O,P

Cranidium, dorsal, oblique anterior and oblique views, < 9, ROM 37456, K 510.
Free cheek, dorsal view, X 11, ROM 37536, K 510.

Free cheek, dorsal and lateral views, X 9, ROM 37535, K 510.

Cranidium, dorsal view, X 11, ROM 37458, K 510.

Cranidium, ventral view, X 11, ROM 37455, K 510.

Pygidium, posterior, dorsal and lateral views, X 13, ROM 37714, K 595.
Cranidium, dorsal and oblique anterior views, X 11, ROM 37457, K 510.

Meant

WE:
ty

—_"
Nn
>

Fig. 59 Kathleenella subula gen. et sp. nov.
A-C Holotype cranidium, dorsal, anterior and oblique views, X 11, ROM 37429, KK 177.
Cranidium, oblique anterior view, X 11, ROM 37427, KK 177.
Cranidium, dorsal and oblique anterior views, X 13, ROM 37428, KK 177.
Cranidium, dorsal view, X 13, ROM 37430, KK 177.
Cranidium, dorsal view, X 11, ROM 37431, KK 177.
Cranidium, ventral view, X 11, ROM 37432, KK 177.
Pygidium, posterior and dorsal views, X 13, ROM 37434, KK 177. ;
Cranidium, dorsal view, X 9, ROM 37426, KK 177. )
Pygidium, dorsal view, X 13, ROM 37435, KK 177.
Pygidium, dorsal view, X 13, ROM 37436, KK 177.
Hypostome, dorsal, posterior and oblique views, X 18, ROM 37437, KK 177.
Hypostome, dorsal view, X 18, ROM 37438, KK 177.
Free cheek, dorsal view, < 8, ROM 37440, KK 177.
Free cheek, dorsal view, X 8, ROM 37441, KK 177.
Cranidium, dorsal view, X 13, ROM 37433, KK 177.

(eo) —_ ™
62 20 Rw om oS

crn w

154 |
|

Fig. 60 Kathleenella subula gen. et sp. nov.

156

(€
D,E
F

G
H,I
J,K

Cranidium, dorsal view, X 11, ROM 37572, KK 180.

Cranidium, ventral view, X 9, ROM 37573, KK 180.

Cranidium, dorsal view, X 11, ROM 37569, KK 180.

Hypostome, posterior and oblique views, X 18, ROM 37585, KK 180.
Free cheek, dorsal view, X 7, ROM 37576, KK 180.

Pygidium, dorsal view, X,11, ROM 37577, KK 180.

Pygidium, dorsal and posterior views, X 13, ROM 37579, KK 180.
Free cheek, dorsal and lateral views, X 8, ROM 37575, KK 180.

Elkanaspis corrugata gen. et sp. nov.

<2 GS) Ot oe a) Oo 7 =

Cranidium, dorsal view, X 9, ROM 37694, K 845.
Cranidium, dorsal view, X 7, ROM 37552, KK 64.
Cranidium, dorsal view, X 11, ROM 37558, KK 64.
Free cheek, dorsal view, X 7, ROM 37698, KK 64.
Cranidium, dorsal view, X 11, ROM 37695, K 845.
Pygidium, dorsal view, X 8, ROM 37553, KK 64.
Free cheek, dorsal view, < 8, ROM 37556, KK 64.
Cranidium, dorsal view, X 13, ROM 37557, KK 64.
Holotype pygidium, dorsal view, X 11, ROM 37555, KK 64.
Pygidium, dorsal view, X 8, ROM 37554, KK 64.
Pygidium, dorsal view, X 7, ROM 37697, KK 64.

Fig. 61

158

Eurekia ulrichi (Rasetti, 1945).
A,B Cranidium, oblique and dorsal views, X 9, ROM 37539, K 510.
Cc Cranidium, ventral view, < 8, ROM 37540, K 510.
D Cranidium, dorsal view, < 11, ROM 37541, K 510.
Cranidium, dorsal and oblique views, < 9, ROM 37542, K 510.
Free cheek, interior view, X 9, ROM 37545, K 510.
Free cheek, exterior view, X 9, ROM 37543, K 510.
Free cheek, exterior view, X 9, ROM 37544, K 510.
Pygidium, dorsal, posterior, and lateral views, X 7, ROM 37546, K 510.
Pygidium, dorsal view, X 9, ROM 37548, K 510.
Pygidium, ventral view, X 8, ROM 37547, K 510.
Hypostome, dorsal view, X 9, ROM 37551, K 510.
Hypostome, ventral view, X 11, ROM 37550, K 510.
Hypostome, ventral view, X 9, ROM 37549, K 510.

TE ‘y
ic Sp 28) (Qa)

re) Gey ©) 72S

Fig. 62 Eurekia bacata sp. nov.

160

A-C
D,E
F,G

H
I
J

Cranidium, dorsal, lateral and anterior views, X 5.5, ROM 37709, K 525.
Pygidium, dorsal and posterior views, X 9, ROM 37711, K 525.

Holotype pygidium, posterior and dorsal views, X 5.5, ROM 37708, K 525.
Cranidium, dorsal view, X 5.5, ROM 37712, K 5SO.

Free cheek, exterior view, X 5.5, ROM 37710, K 525.

Free cheek, exterior view, X 5.5, ROM 37713, K 550.

Eurekia spp.

Oo 2S &

Cranidium, dorsal view, <X 11, ROM 37450, KK 177.

Pygidium, dorsal view, X 9, ROM 37582, KK 180.

Pygidium, dorsal view, X 13, ROM 37581, KK 177.

Hypostome, ventral view, X 11, ROM 37452, KK 177.
Pygidium, dorsal view, X 11, ROM 37451, KK 177.

Cranidium, dorsal and oblique views, X 8, ROM 37449, KK 177.

—EEEEEE

16]

Fig. 63 Yukonaspis kindlei Kobayashi, 1936a.

162

A,B Cranidium, dorsal and oblique views, X 9, ROM 37715, K 595.
Cc Pygidium, dorsal view, X 11, ROM 37717, K 595.
D,E Cranidium, dorsal and anterior views, X 9, ROM 37502, K 510.
F,G_ Pygidium, posterior and dorsal views, X 11, ROM 37716, K 510.
H,| Free cheek, dorsal and lateral views, < 8, ROM 37505, K 510.
j Cranidium, dorsal view, X 9, ROM 37504, K 510.
K,L Cranidium, dorsal and oblique views, < 9, ROM 37503, K 510.
M_ Free cheek, dorsal view, X 8, ROM 37506, K 510.
N Cranidium, dorsal view, X 9, ROM 37718, K 510.
Elkanaspis? sp.
O Free cheek, exterior view, X 11, ROM 37674, KK 156.
P Free cheek, exterior view, X 18, ROM 37673, KK 156.
Q-S Cranidium, dorsal, anterior and lateral views, X 13, ROM 37672, KK 156.

Fig. 64 Elkanaspis futile gen. et sp. nov.
A,B Cranidium, dorsal and oblique views, < 8, ROM 37528, K 510.
Cc Cranidium, dorsal view, X 9, ROM 37527, K 510.

Free cheek, dorsal view, X 7, ROM 37533, K 510.
Cranidium, dorsal view, X 11, ROM 37529, K 510.
Free cheek, dorsal view, X 9, ROM 37534, K 510.
Holotype pygidium, posterior and dorsal views, X 11, ROM 37532, K 510.
Pygidium, dorsal view, X 11, ROM 37530, K 510.
Pygidium, dorsal view, X 11, ROM 37531, K 510.
Pygidium, dorsal view, X 11, ROM 37639, K 550.
Cranidium, dorsal and oblique views, X 11, ROM 37637, K 550.
Free cheek, dorsal view, X 7, ROM 37642, K 550.
Free cheek, dorsal view, X 7, ROM 37641, K 550.

P Cranidium, dorsal view, X 11, ROM 37638, K 550.
Naustia papilio gen. et sp. nov.

Q Holotype pygidium, dorsal view, X 5.5, ROM 37628, K 550.

R Pygidium, dorsal view, X 9, ROM 37629, K 550.

Ss Pygidium, dorsal view, X 9, ROM 37630, K 550.

T Cranidium, dorsal view, X 11, ROM 37635, K 550.

U Cranidium, dorsal view, X 13, ROM 37648, K 550.

Q
0

Ss
@) Ze ee a te its

164

165

Fig. 65 Muissisquoia depressa Stitt, 1971b.

166

lag

x
PaaS nga SZ oes Me ee eee Git ae G@ nics

Cranidium, dorsal view, X 13, ROM 37479, KK 113.

Cranidium, dorsal view, X 8, ROM 37493, KK 116.

Cranidium, dorsal view, X 11, ROM 37501, KK 116.

Pygidium, dorsal view, X 13, ROM 37480, KK 113.

Pygidium, ventral view, X 11, ROM 37495, KK 116.

Pygidium, dorsal and lateral views, X 11, ROM 37494, KK 116.
Cranidium, ventral view, X 11, ROM 37499, KK 116.

Pygidium and incomplete thorax, ventral view, X 11, ROM 37500, KK 116.
Free cheek, ventral view, < 11, ROM 37497, KK 116.

Cranidium, dorsal and oblique views, X 11, ROM 37498, KK 116.
Free cheek, oblique view, X 11, ROM 37496, KK 116.
Cranidium, dorsal view, X 11, ROM 37519, KK 119.5.
Cranidium, dorsal view, X 11, ROM 37521, KK 119.5.
Cranidium, dorsal view, X 11, ROM 37520, KK 119.5.

Pygidium, dorsal view, X 11, ROM 37523, KK 119.5.

Cranidium, dorsal view, X 11, ROM 37522, KK 119.5.

Pygidium, dorsal view, X 11, ROM 37524, KK 119.5.

Fig. 66 Missisquoia depressa Stitt, 1971b.

168

A Hypostome, ventral view, X 18, ROM 37655, KK 119.5.
Hypostome, ventral view, X 18, ROM 37656, KK 119.5.
Hypostome, ventral view, X 18, ROM 37661, KK 116.
Free cheek, dorsal view, X 13, ROM 37658, KK 119.5.
Free cheek, dorsal view, X 11, ROM 37526, KK 119.5.
Cranidium, dorsal view, X 13, ROM 37659, KK 116.

G Meraspid specimen, dorsal view, X 18 (specimen lost), KK 116.
Ptychopleurites brevifrons (Kobayashi, 1936a).
H-J_ Cranidium, dorsal, anterior and oblique views, X 11, ROM 37481, KK 113.
K-M Cranidium, dorsal, anterior and lateral views, X 11, ROM 37517, KK 119.5.
N-P Cranidium, dorsal, anterior and oblique views, X 9, ROM 37707, KK 50.
Q,R Pygidium, dorsal and posterior views, X 13, ROM 37611, KK 113.

Ss Free cheek, oblique view, X 13, ROM 37483, KK 113.
T,U Pygidium, dorsal and lateral views, < 13, ROM 37482, KK 113.

169

Fig. 67 Missisquoia mackenziensis sp. nov.
A-C Holotype cranidium, dorsal, anterior and oblique views, X 13, ROM 37563, KK 123.
D_ Free cheek, dorsal view, X 18, ROM 37589, KK 123.
F Pygidium, dorsal and posterior views, X 13, ROM 37588, KK 123.
G_ Pygidium, dorsal view, X 18, ROM 37677, KK 123.
H Cranidium, dorsal view, X 18, ROM 37719, KK 123.
1 Cranidium, dorsal view, X 18, ROM 37720, KK 123.
J Pygidium, dorsal view, X 18, ROM 37721, KK 123.
K Hypostome, ventral view, X 18, ROM 37660, KK 123.
Yukonaspis sp.
L Cranidium, dorsal view, X 13, ROM 37725, KK 124.
M,N Free cheek, dorsal and lateral views, < 11, ROM 37726, KK 124.
Larifugula leonensis (Winston and Nicholls, 1967).
Oo Partial thorax, dorsal view, X 13, ROM 37722, KK 124.
P,Q Cranidium, dorsal and oblique views, X 11, ROM 37723, KK 124.
R_ Pygidium, dorsal view, X 13, ROM 37724, KK 124.

170

Fig. 68 Tatonaspis diorbita sp. nov.

A,B

Holotype cranidium, dorsal and anterior views, X 6, ROM 37619, K 550.
Cranidium, dorsal view, X 6, ROM 37620, K 550.

Cranidium, dorsal view, X 7, ROM 37621, K 550.

Cranidium, dorsal view, X 13, ROM 37627, K 550.

Yoked cheeks, oblique, anterior and dorsal views, X 9, ROM 37626, K 550.
Pygidium, dorsal view, X 9, ROM 37622, K 550.

Pygidium, posterior, dorsal and lateral views, X 8, ROM 37623, K 550.
Pygidium, ventral view, X 8, ROM 37625, K 550.

Pygidium, ventral view, X 11, ROM 37624, K 550.

Levisaspis glabrus (Shaw).

O-Q

Cranidium, dorsal, oblique and anterior views, X 13, ROM 37612, KK 113.

Meteoraspis? sp.

Cranidium, dorsal view, X 18, ROM 37507, K 510.

Ss Cranidium, dorsal view, <X 18, ROM 37508, K 510.

Cranidium, ventral view, < 18, ROM 37509, K 510.

173

Fig. 69 Geragnostus sp.

174

A Pygidium, dorsal view, X 13, ROM 37605, K 510.
B Pygidium, dorsal view, X 13, ROM 37607, K 510.
Cc Cephalon, dorsal view, X 13, ROM 37606, K 510.
‘‘Calvinella’’ palpebra sp. nov.
D Cranidium, dorsal view, <X 11, ROM 37753, K 510.
E Cranidium, dorsal view, X 6, ROM 37752, K 510.
Yukonaspis kindlei Kobayashi, 1936a.
F-H Pygidium, posterior, lateral and dorsal views, < 5.5, ROM 37754, K 510.
1 Free cheek, ventral view, X 9, ROM 37755, K 510.
Missisquoia sp.
J Cranidium, dorsal view, <X 13, ROM 37756, KK 133.
Apoplanias rejectus Lochman, 1964a.
K,L Cranidium, dorsal and lateral views, < 13, ROM 37757, KK 43.
M-O Pygidium, dorsal, posterior and lateral views, X 11, ROM 37759, KK 43.
P,Q Cranidium, oblique and dorsal views, X 11, ROM 37758, KK 43.
Tatonaspis diorbita sp. nov.
R Cranidium, dorsal view, X 11, ROM 37760, K 525.
S Pygidium, dorsal view, X 13, ROM 37761, K 525.
T Cranidium, dorsal view, <X 7, ROM 37762, K 525.

i bs

Fig. 70 Yukonaspis kindlei Kobayashi, 1936a.

176

A-C_ Holotype cranidium, dorsal, oblique, and anterior views, X 9, Gsc 8718, Upper Cambrian
limestone, Squaw Mountain, north of Tatonduk River, Alaska- Yukon boundary.
Geragnostus reductus (Winston and Nicholls, 1967).
Both from Missisquoia typicalis Subzone, Wilberns Formation, central Texas.
D,E Pygidium, dorsal and posterior views, X 9, USNM 1185940.
F,G Holotype cephalon, dorsal and anterior views, X 9, USNM 1185941.
Larifugula leonensis (Winston and Nicholls, 1967).
All from Corbinia apopsis Subzone, Wilberns Formation, Leon Creek, Mason County, central
Texas.
H-J_ Holotype cranidium, dorsal, anterior and oblique views, X 13, USNM I185888.
kK Pygidium, dorsal view, X 13, USNM I185887.
L Cranidium, dorsal view, X 13, USNM 1185889.
Geragnostus (Micragnostus ) subobesus (Kobayashi, 1936a).
M Lectotype cephalon, dorsal view, X 9, GSc 8717, Lower Ordovician limestone, Jones
Ridge, north of Tatonduk River, Alaska- Yukon boundary.
Richardsonella arctostriata (Raymond, 1937).
Both from Zone 1, Gorge Formation, Highgate Falls, Vermont.
N Holotype cranidium, dorsal view, X 5.5, yPM 14701A.
O Pygidium, dorsal view, <X 5.5, YPM 14701C.
Liostracinoides vermontanus Raymond, 1937.
P Holotype cranidium, dorsal view, X 13, ypM 14710, Zone 1, Gorge Formation, Highgate
Falls, Vermont.
Richardsonella spiculata (Raymond, 1937).
Q Holotype pygidium, dorsal view, <x 9, ypM 14704, Zone 1, Gorge Formation, Highgate
Falls, Vermont.

177

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188

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ISBN 0-88854-287-9
ISSN 0384-8159

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