^ B = oo P.S. = a> Ro = a> £ = 0) 682 ^■^ UJ ■3 = o no . 153 s = -^ = o ce = T*~ < -CD 1 ^1^ o - ^~ -1 "CO •* " >- o E — ROM Royal Ontario Museum I a Hciai I Mcrii K5 CONTRIBUnONS Silurian Trilobites from the Northern Yukon Territory Rolf Ludvigsen and Ronald R Tripp ROYAL ONTARIO MUSEUM LIFE SCIENCES PUBLICATIONS INSTRUCTIONS TO AUTHORS Authors should prepare their manuscripts carefully accord- ing to the following instructions; failure to do so will result in the manuscript's being returned to the author for revision. All manuscripts are considered on the under- standing that they are not currently offered for publication elsewhere. 1. General Papers for publication are accepted from ROM staff members and research associates, and from researchers reporting on work done with ROM collec- tions. Monographs on the flora and/or fauna of Ontario may be considered for publication by authors not affiliated with the ROM. Financial contributions to- wards publication will be welcome. 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Authors are reminded that when illustrations are reduced magnification factors will change, and that they are responsible for the conver- sion. For details, see Guide to Authors. LIFE SCIENCES CONTRIBUTIONS 153 Silurian Trilobites from the Northern Yukon Territory Rolf Ludvigsen and Ronald R Tripp ROM ROYAL ONTARIO MUSEUM TORONTO ROYAL ONTARIO MUSEUM PUBLICATIONS IN LIFE SCIENCES The Royal Ontario Museum publishes three series in the Life Sciences: contributions: a numbered series of original scientific publications. OCCASIONAL papers: a numbered series of original scientific publications, primarily short and of taxonomic significance. MISCELLANEOUS PUBLICATIONS: an unnumbered series on a variety of subjects. All manuscripts considered for publication are subject to the scrutiny and editorial policies of the Life Sciences Editorial Board, and to independent refereeing by two or more persons, other than Museum staff, who are authorities in the particular field involved. LIFE SCIENCES EDITORIAL BOARD Senior editor: D. C. Darling Editor: R. W. Murphy Editor: J. H. McAndrews External editor: C. S. Churcher Manuscript editor: E. J. Crossman Production editor: J. E. Hawken Rolf Ludvigsen is research associate, Department of Invertebrate Palaeontology, Royal Ontario Museum, Toronto, and head of the Denman Institute for Research on Trilobites, 4062 Wren Road, Denman Island, British Columbia VOR ITO. Ronald P. Tripp is also research associate. Department of Invertebrate Palaeon- tology, Royal Ontario Museum, Toronto. He currently resides at 41 Kirk Drive, Thornhill, Ontario L3T 3K8. Canadian Cataloguing in Publication Data Ludvigsen, Rolf, 1944- Silurian trilobites from the northern Yukon Territory (Life sciences contributions, ISSN 0384-8159 ; 153) Includes bibliographical references. ISBN 0-88854-349-2 1. Trilobites. 2. Paleontology — Silurian. 3. Paleontology — Yukon Territory. I. Tripp, Ronald P. (Ronald Pearson), 1914- . II. Royal Ontario Museum. III. Title. IV. Series. OE821.L83 1989 565'.393'097191 €89-09501 1-3 Publication date: 1 February 1990 ISBN 0-88854-349-2 ISSN 0384-8159 © Royal Ontario Museum, 1989 100 Oueen's Park, Toronto, Canada M5S 2C6 PRINTED AND BOUND IN CANADA BY GAGNE PRESS lb Contents Abstract 1 Introduction 1 Stratigraphy 2 Road River Formation 2 Unnamed Carbonates 4 Age and Correlation 4 AA 2-4.5 (Road River Formation) 4 BB 131 (Unnamed Carbonates) 4 AA 95 (Road River Formation) 5 Trilobite Associations 5 ' Otarion Association 5 Stenopareia Association 5 Hedstroemia Association 6 Materials and Methods 7 Systematic Palaeontology 8 Family Styginidae Vogdes, 1890 8 Subfamily Bumastinae Raymond, 1916 8 Genus Paracybantyx gen. nov. 8 Paracybantyx asulcatus sp. nov. 8 Indeterminate bumastine 9 Subfamily Scutelluinae Richter and Richter Genus Kosovopeltis Snadjr, 1958 9 Kosovopeltis borealis (Poulsen, 1934) Kosovopeltisl spp. 14 Indeterminate scutelluine 14 Family Illaenidae Hawle and Corda, 1847 14 Subfamily Illaeninae Hawle and Corda, 1847 Genus Stenopareia Holm, 1886 14 Stenopareia illtyd sp. nov. 14 Indeterminate illaenid 15 Family Proetidae Salter, 1864 15 ?Subfamily Crassiproetinae Osmolska, 1970 Genus Hedstroemia Pfibyl and Vanek 15 14 15 Hedstroemia kutchini sp. nov. 15 Hedstroemia sourdoughi sp. nov. 17 Subfamily Warburgellinae Owens, 1973 17 Genus Prantlia Pfibyl, 1946 17 Prantlia vagrans sp. nov. 17 Subfamily uncertain 19 Indeterminate proetid A 19 Indeterminate proetid B 19 Family Aulacopleuridae Angelin, 1854 20 Genus Otarion Zenker, 1833 20 Subgenus Songkania Chang, 1974 20 Otarion (Songkania) socialis (Poulsen, 1934) Family Harpidae Hawle and Corda, 1847 21 Genus Scotoharpes Lamont, 1948 21 Scotoharpes raaschi Norford, 1973 21 20 111 Family Cheiruridae Hawle and Corda, 1847 22 Subfamily Cheirurinae Hawle and Corda, 1847 22 Genus Cheirums Beyrich, 1845 22 Cheimrus sp. 22 Family Encrinuridae Angelin, 1854 22 Subfamily Encrinurinae Angelin, 1854 22 Genus Cromus Barrande, 1852 22 Cromus princeps (Poulsen, 1934) 22 Genus Encrinuraspis Webby, Moors, and McLean, 1970 24 Encrinuraspis sp. 24 Genus Balizoma Holloway, 1980 24 Balizoma aff. B. obtusus (Angelin, 1851) 24 Indeterminate encrurine 25 Family Calymenidae Milne-Edwards, 1840 26 Subfamily uncertain 26 Indeterminate calymenid 26 Family Lichidae Hawle and Corda, 1847 26 Subfamily Lichinae Hawle and Corda, 1847 26 Genus Dicranopeltis Beyrich, 1845 26 Dicranopeltis sp. 26 Subfamily uncertain 26 Indeterminate lichid 26 Family Odontopleuridae Burmeister, 1843 27 Subfamily Odontopleurinae Burmeister, 1843 27 Genus Leonaspis Richter and Richter, 1917 27 Leonaspis semiglabra (Poulsen, 1934) 27 Indeterminate odontopleurine 28 Acknowledgements 29 Literature Cited 30 Plates 34 IV Silurian Trilobites from the Northern Yukon Territory Abstract Silurian trilobites are described from two contrasting facies in the northern Yukon Territory: basinal sediments of the Road River Formation at Prongs Creek and shallow-water limestones of the Illtyd Range. An Otarion Association from dark grey, argillaceous lime mudstones (Lower Silurian) consists of Kosovopeltis, Otarion (Songkania), Cromus, and Leonaspis. These trilobites are identical to those described by Poulsen (1934) from his Cape Schuchert Formation of North Greenland. A Stenopareia Association from off-white biosparites (Lower Silurian) includes Steno- pareia, a bumastine, Kosovopeltis, and Scotoharpes. AHedstroemia Association occurs in an Upper Silurian debris flow. It includes Hedstroemia, Prantlia, Balizoma, and Paracybantyx. An incomplete ontogeny of Kosovopeltis borealis (Poulsen) comprises a protaspis and four different transitory pygidia. The bumastine genus Paracybantyx is new. New species are Paracybantyx asulcatus, Stenopareia illtyd, Hedstroemia kutchini, H. sourdoughi, and Prantlia vagrans. Introduction Silurian rocks crop out as two contrasting facies in the northern Yukon Territory: as basinal shales of the Road River Formation within the Richardson and Blackstone troughs in the Peel River-Wind River area (Lenz, 1972), and as thick-bedded to massive carbon- ates, yet unnamed, on the Mackenzie Platform in the Bonnet Plume River area and on the Yukon Block in the Porcupine River area (Text-fig. 1). In the basinal shales exceptionally complete stratigraphic successions of graptolites are present (Lenz and Pedder, 1972; Lenz, 1982), but in the platform carbonates well-pre- served fossils of Silurian age are uncommon, with the exception of locally abundant tabulate corals and pen- tamerid brachiopods. The best-preserved and most- diverse assemblages of Silurian shelly fossils in the Yukon Territory are found in dark grey, argillaceous limestones deposited on the margins of the troughs, close to facies transitions with shallow-water carbon- ates in areas along the Wind River such as Prongs Creek (Raasch, Norford, and Wilson, 1961; Lenz, 1970) and Royal Creek (Lenz, 1977; Jackson, Lenz, and Ped- der, 1978). These assemblages are strongly dominated by brachiopods, but a few include substantial numbers of trilobites of types that are either unknown from northern Canada or incompletely documented. Rich Silurian trilobite assemblages have been described from the Whittaker and Delorme formations farther to the south in the Mackenzie Mountains of the District of Mackenzie (Perry and Chatterton, 1977; Chatterton and Perry, 1983), and smaller assemblages have been described from different localities to the north in the Canadian Arctic Islands (Bolton, 1965; Perry and Chatterton, 1977; Thomas and Narbonne, 1979) and North Greenland (Poulsen, 1934; Lane, 1979, 1984; Lane and Owens, 1982). In the Yukon Territory, however, Silurian trilobites have been docu- mented from only two Lower Silurian localities — one from dark grey limestones of the Road River Formation at Prongs Creek (Raasch, Norford, and Wilson, 1961) and one from off-white limestone in the nearby Illtyd Range (Norford, 1973). In this paper, we reevaluate and describe fully both these trilobite assemblages on the basis of larger and more complete collections than were available to previous investigators. We also deal with a new trilobite fauna from the Upper Silurian part of the Road River Formation on Prongs Creek. 1 LOCALITY MAP AND SILURIAN LITHOFACIES shale and interbedded dar1( limestone^ light coloured carbonates Text-FIG. 1. Lx)cality map of the northern Yukon Territory showing Section AA on Prongs Creek and Section BB in the Illtyd Range. The generahzed Silurian hthofacies map is adapted from Lenz (1972, fig. 9). Stratigraphy ROAD RIVER FORMATION The Road River Formation was raised to group status by Fritz (1985), who considered four undesignated map units in the Richardson Mountains to constitute forma- tions. Until such time as these map units are defined and formally named, we retain the formational status of the Road River. Within the Richardson Trough north of the Peel River, the Road River Formation consists of more than one thousand metres of shales, cherts, and limestones of Cambrian, Ordovician, Silu- rian, and Devonian age. The axis of this intracratonic trough swings east along the Bonnet Plume River to join the Selwyn Trough to the south (Lenz, 1979, fig. 1; Norris, 1985:40). During the Silurian, a narrow north- south embayment off the Richardson Trough devel- oped near the headwaters and along the tributaries of the Wind River. Here, the Road River Formation comprises a recessive sequence of calcareous shales and argillaceous limestones which rests abruptly on resistant Ordovician carbonates (see Lenz, 1972, fig. 8; Norris, 1985, fig. 10). On Prongs Creek, the lower con- tact of the Road River is concordant, but apparently disconformable because Upper Ordovician (Rich- mondian; Norford, 1964) strata are followed directly by mid-Lower Silurian strata. Unconformities of similar magnitude occur at the same interval in shelf succes- sions of most other areas of western North America (Lenz, 1976). Starting about 50 m above its base on Prongs Creek (Text-fig. 2), the Road River Formation begins to dis- play evidence of relief associated with nearby carbonate banks. Contorted bedding, slumps, and thick debris flows consisting of jumbled fossils and small lithoclasts become common. The debris flows were probably derived from the flanks of shallow carbonate banks such as those now exposed in the Illtyd Range to the east or near the headwaters of the Hart River to the southwest. Sample AA 2-4.5 was obtained from medium-bed- ded, highly argillaceous lime mudstones of deep-water aspect, at the base of the Road River Formation. Sam- ple AA 95 was collected from a prominent 2-m-thick SECTION AA SECTION BB PRONGS CREEK 65"17'N. 135"42'W ILLTYD RANGE 65"14'N.135"12'W UNNAMED 0 ORDOVICIAN CARBONATES AAgs C/D 180m- J 1 ) 160- ^ lAfl- V IfU 120- 1 ^ ) 100- ■• 80- 60- o., hypostomes;/?>'g., pygidia; to/a/, number of specimens of the most frequent part; %, percentage of the total number of specimens. Species comp. cran. hypo. pyg- total % Lower Silurian AA 2^.5, Prongs Creek Kosovopeltis borealis Otarion (Songkania) socialis Cromus princeps Leonaspis semiglabra BB 131, Illtyd Range Kosovopeltis'? spp. Indeterminate bumastine Stenopareia illtyd sp. nov. Indeterminate illaenid Indeterminate proetid B Scotoharpes raaschi Cheirurus sp. Encrinuraspis sp. Indeterminate calymenid Dicranopeltis sp. Indeterminate odontopleurine Otarion Association 2 78 19 116 116 27 7 270 3 78 270 65 1 10 4 23 23 5 1 8 4 11 11 3 Stenopa reia Association — 1 — 3 3 11 — 8 — 1 8 29 — 9 — 6 9 32 — 1 — — 1 3 — 1 1 1 1 3 - 2 — — 2 7 — 1 — 1 1 3 — — 1 1 3 — — 1 1 3 - 1 — 1 1 3 — 1 — — 1 3 Upper Silurian AA 95, Prongs Creek Paracybantyx asulcatus gen. et sp. nov. Indeterminate scutelluine Hedstroemia kutchini sp. nov. Hedstroemia sourdoughi sp. nov. Prantlia vagrans sp. nov. Indeterminate proetid A Balizoma aff. B. obtusus Indeterminate encrinurine Indeterminate lichid Hedstroemia Association 19 2 24 24 14 1 — — 1 1 9 2 40 40 23 8 — 25 25 14 16 — 48 48 28 1 1 1 5 1 27 27 15 1 — — 1 1 3 5 5 5 3 Materials and Methods All the figured specimens that were collected have been deposited at the Royal Ontario Museum; their regis- tered numbers bear the prefix ROM. Other specimens illustrated are in the collection of the Geological Survey of Canada, Ottawa, and are prefixed GSC. As far as possible, plates are arranged in the order of the systematic section. Upper Silurian trilobites from AA 95 constitute Plates 1, 6, 7, 11. Lower Silurian trilobites from AA 2-4.5 constitute Plates 2-4, 8, 10, 12; Plate 4 comprises scanning electron micrographs prepared at the University of Toronto. Lower Silurian trilobites from BB 131 constitute Plates 5 and 9. Plate 13 comprises photographs of plaster casts of Poulsen's (1934) original specimens from North Greenland. Orig- inals are housed in the Mineralogical and Geological Museum, University of Copenhagen (MMH). The terminology used is essentially that defined by Harrington, Moore, and Stubblefield {in Moore, 1959:117-126). Glabellar lobes, furrows, and muscle impressions are numbered from back to front and sym- bolized by L, S, and G, respectively. The occipital ring is regarded as part of the glabella. Systematic Palaeontology Family Styginidae Vogdes, 1890 DISCUSSION Lane and Thomas (1983:141) have argued that numer- ous genera previously referred to separate famihes and subfamihes of effaced trilobites should be included in an undivided family Styginidae. In this paper we prefer to continue the use of the subfamilies Stygininae, Scu- telluinae, and Bumastinae as an aid to grouping the large number of genera in the family. Subfamily Bumastinae Raymond, 1916 Genus Paracybantyx gen. nov. DERIVATION OF NAME Name derived from Latin para (beside) and Cybantyx. Gender masculine. DIAGNOSIS Cranidium broad, lacking anterior border and furrow. Axial furrow bowed inward, faint posteriorly. Pygidium convex, 85 to 100 per cent as wide as long, effaced. Surface finely pitted. TYPE SPECIES Paracybantyx asulcatus sp. nov., locality AA 95 (Upper Silurian), Road River Formation, Prongs Creek, Yukon Territory, Canada. OTHER SPECIES None. DISCUSSION The absence of the anterior border and furrow pre- cludes inclusion of this species in the genus Cybantyx, Lane and Thomas {in Thomas, 1978), which it other- wise resembles. Paracybantyx asulcatus sp. nov. PI. 1, figs. 1-15; PI. 11, figs. 1-5 DERIVATION OF NAME Specific name derived from Latin a (without) and sul- catus (furrowed), referring to the absence of the ante- rior border furrow. HOLOTYPE ROM 45344 (cranidium, PI. 1, figs. 4,5), locality AA 95 (Upper Silurian), Road River Formation, Prongs Creek, Yukon Territory, Canada. DIAGNOSIS As for genus. MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 19 crani- dia, 4 librigenae, 2 hypostomes, 24 pygidia. DESCRIPTION Cranidium 85 to 95 per cent as long as wide, longitu- dinal curvature strongest toward front, evenly convex transversely, broadly rounded in outline anteriorly. Glabella wide, narrowest opposite palpebral lobe where it occupies two-thirds width between margins, widening forward and backward. Small tubercle near posteromedian margin. Occipital ring and furrow effaced. Axial furrow broad and shallow at back, deep- ening forward, bowed more or less strongly inward, terminating in large, rounded anterior pit opposite one- tenth cranidial length from front. On larger specimens, axial furrow effaced anteriorly and posteriorly. Genal muscle impression alongside axial furrow on fixigena almost one-fifth length of cranidium, situated at own length anterior to posterior margin; outline of impres- sion running parallel to that of palpebral lobe. Palpe- bral lobe slightly swollen and gently rounded in outline, one-quarter length of cranidium, with posterior extremity opposite that of lateral muscle impression. Anterior border and furrow absent. Anterior branch of facial suture running outward, parallel to axial furrow at first, and then curving forward and inward; posterior branch directed backward and slightly outward. Crani- dium faintly pitted, with faint terrace ridges running parallel to anterior margin at front. Incomplete librigenae show a comparatively small eye without socle. Genal angle aspinous. Doublure broad, weakly convex. Anterior extension curves inward and upward; on inner margin, just in front of eye, a single pit projects inward and dorsally upward (PI. 11, fig. 2). This pit would lie immediately below anterior pit at front of axial furrow — compare Failleana calva Chatterton and Ludvigsen (1976, pi. 6, figs. 5,12- 16). The pit in the doublure, which opposes the anterior pit in Remopleurides (Whittington, 1959, fig. 3c), is anal- ogous. Hypostome incomplete but comparable to that of 8 Bumastus and Cyhantyx in the swollen middle body, lateral lobe consisting of large macula, and depressed border. Prosopon of middle body rugose and pitted. Pygidium strongly convex, rounded triangular to nearly subovate in outline, 85 to 100 per cent as long as wide, almost completely effaced; height 45 to 55 per cent sagittal length. Immature pygidia wider than long. Triangular axis faintly marked by slight change of con- vexity in some specimens. Articulating facet marked off by a faint oblique ridge; coarse terrace lines running parallel to and overstepping posterior ridge, with steep surface facing backward; raised lines bending perpen- dicularly backward at margin. Doublure broad, 30 per cent length of pygidium; about 15 shallow discontinu- ous terrace ridges, equally spaced, running parallel to margin. Surface finely pitted; fine, short raised lines running inward/backward for a short distance abaxially (PI. 1, fig. 15). DISCUSSION The pygidium of this species is remarkably similar to that of specimens from the Lower Silurian of northeast Greenland, described as "Goldillaenid Genus and spe- cies indet. 2" by Lane (1972:347, pi. 62, figs. 10-14). The cranidium differs from that of Lane's material in being much wider, with wider glabella, and in having axial furrows bowed inward and shallowing posteriorly. Lane's material has a terraced anterior border and border furrow similar to that of Cyhantyx anaglyptos Lane and Thomas {in Thomas, 1978:18, pi. 5, figs. 1-8). The absence of the border and border furrow in the Road River material is the main feature of the new genus Paracybantyx. Both the Yukon and the Green- land species resemble the type species of Cyhantyx in the comparatively narrow, featureless pygidium. Vari- able features in the cranidium of P. asulcatus sp. nov. are the degree of inward curvature of the axial furrows, the anterior and posterior effacement of the axial fur- rows in larger specimens, and the proportions and con- vexity of the pygidium. Ptilillaenus Lu (1962), a monotypic genus from the Middle Silurian of China, has an extended axial furrow terminating in an anterior pit and lacks the anterior border, but in that taxon the glabella is narrow. Indeterminate bumastine PI. 5, figs. 13,14 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 8 crani- dia, 1 pygidium. DESCRIPTION Cranidium 60 per cent as long as wide, strongly convex. Glabella effaced, except for lunule at 60 per cent length from front. Posteromedian tubercle at 10 per cent length from back. Anterior pits small, shallow, and rounded, 70 per cent maximum width of cranidium apart, and 20 per cent length of cranidium from front. Palpebral lobe 40 per cent length of cranidium, placed far back, weakly rounded. Pygidium (not illustrated) 65 per cent as long as wide, strongly convex. Axis 60 per cent anterior width, dying out in a short distance. Anterolateral angle oblique. Surface smooth except for faint terrace ridges on front of cranidium. DISCUSSION The presence of the anterior pits suggests a relationship to species such as Bumastus? phrix Lane and Thomas {in Thomas, 1978:14, pi. 3, figs. 1-22) and B.l xestos Lane and Thomas {in Thomas, 1978:16, pi. 4, figs. 2-5, 7,18), both from the British Wenlock. The present species is distinguished by a number of features, partic- ularly the effacement of the axial furrows. Subfamily Scuteliuinae Richter and Ricliter, 1955 Genus Kosovopeltis §najdr, 1958 TYPE SPECIES Kosovopeltis svobodai Snajdr, 1958, Kopanina Forma- tion (Upper Silurian), Kosov, Prague district, Czecho- slovakia. Scutellum horealis — Raasch in Raasch, Norford, and Wilson, 1961:477, figs. 5.6-8,10 (non fig. 5.9 = Leo- naspis semiglahra). Scutellum horealis — Norford, 1962, pi. 8, fig. 7. Scutellum horealis — Norford et al., 1970, pi. 8, fig. 9. Kosovopeltis horealis (Poulsen, 1934) PI. 2, figs. 1-12; PI. 3, figs. 1-10; PI. 4, figs. 1-13; PI. 13, figs. 1,2; Text-figs. 4, 5 A Goldius horealis Pouisen, 1934:27, pl. 3, figs. 14,15. HOLOTYPE MMH 3267 (cranidium, figured by Poulsen, 1934, pl. 3, fig. 14; in this paper, Pl. 13, fig. 1), Cape Schuchert Formation (Lower Silurian), Kap Schuchert, North Greenland. I 0.5 mm ^ 1mm 1mm Text-FIG. 4. Incomplete ontogeny oi Kosovopeltis borealis (Poulsen). v4, Protaspis, ROM 42160. B, Smallest transitory pygidium, ROM 42166. C, Meraspid cranidium, ROM 42161. D, Transitory pygid- ium, ROM 42165. E, Transitory pygidium with two protothoracic segments attached, ROM 42163. F, Transitory pygidium with one protothoracic segment attached, ROM 42162. MATERIAL From AA 2-4.5 (Lower Silurian), Prongs Creek: 2 dor- sal shields, 78 cranidia, librigenae, rostral plates, 19 hypostomes, 116 pygidia. DESCRIPTION Cephalon about 25 per cent as long as wide. Glabella moderately convex for most of its length, strongly con- vex and downturned at front, narrowing strongly back- ward to 30 to 40 per cent anterior width; anterolateral angles strongly rounded. Width of occipital ring greater than width across posterior glabellar ring. Occipital ring bowed backward, summit at posterior margin; minute occipital tubercle centrally situated. Occipital furrow deep and broad mesially, expanding laterally into large, smooth muscle impressions. LI not swollen, defined only by short, oblique SI; a faint transverse depression marks off preoccipital ring on internal sur- face only. Muscle scar Gl slightly depressed, 15 per cent length of glabella, placed at about own length anterior to occipital furrow, 30 per cent width of gla- bella; G2 and G3 indicated by faint, short, smooth lateral depressions at 50 per cent and 25 per cent length of glabella from front, respectively. Anterior border of cranidium extending only a short distance laterally in front of glabella and fixigena. Axial furrow deepening steadily backward, bowed inward. Fixigena broad, con- vex. Genal muscle area extending alongside LI and 10 B Text-fig. 5. Reconstructions of the four trilobite species from AA 2^.5, Prongs Creek. ^4, Kosovo- peltis borealis (Poulsen). B, Otarion (Songkania) socialis (Poulsen). C, Cromus princeps (Poulsen). D, Leonaspis semiglabra (Poulsen). Gl, smooth, slightly depressed. Posterior border much wider (exsag.) than occipital ring adaxially, narrowing strongly to midwidth of fixigena. Posterior border fur- row shallow and strongly oblique adaxially. Palpebral lobe at summit of fixigena, opposite LI, 25 per cent length of glabella, horizontal, standing higher than gla- bella. Eye ridge running obliquely backward and out- ward from opposite G3, dying out toward back of palpebral lobe. Anterior branch of facial suture run- ning forward and outward, curving forward strongly at anterior margin. Posterior branch curving obliquely outward, cutting posterior margin slightly beyond extent of palpebral lobe. Librigena falcate, sloping steeply outward; genal spine narrowing slowly backward, extending to third thoracic segment. Eye strongly convex; fully developed lenses hexagonal in outline, 0.02 mm in diameter (PI. 4, figs. 8,9). Socle absent. Subocular furrow broad. Field divided by a depression widening and curving inward toward back; outer area narrower and more strongly swollen, widening backward. Lateral border sloping inward to a broad border furrow, furrow also widening backward. Doublure strongly convex, widening and projecting at front, extending to inner area of librigena, and becoming less convex posteriorly. Rostral plate 25 per cent as long as wide, as wide as glabella anteriorly, extending 30 per cent sagittal length of cranidium, subtrapezoidal in outline, with anterior and posterior margins evenly convex forward and paral- lel. Convexity moderate; posterolateral angle upturned. Rostral suture submarginal, with connective sutures bowed gently inward. Hypostome shield-shaped, 80 per cent as long as wide. Anterior wing narrowly pointed, wide (tr.), with- out articulating process. Middle body strongly swollen. Middle furrow short but strong, marking off small lat- eral lobe and macula. Lateral furrow broad. Postero- lateral border of uniform width, with inward slope decreasing posteriorly. Posterior margin broadly rounded. Number of thoracic segments uncertain (dorsal shield [PI. 2, fig. 2] appears to be complete with eight segments, but has some telescoping at the back). Axis 25 per cent width of thorax, narrowing slightly back- ward, gently convex transversely. Articulating half- rings half sagittal length of rings, bearing faint, trans- verse raised lines. Pleural lobe horizontally extended as far as fulcrum at 70 per cent width, sloping gently outward abaxially. Pleura narrows abaxially; articulat- ing facet bluntly terminated. Doublure extends to fulcrum. Pygidium 70 to 85 per cent as long as wide, gently convex. Axis 20 per cent length and width of pygidium, swollen. Articulating half-ring strongly marked off by continuous furrow. Three rings distinguishable on internal surface. Posterior area tripartite, with median lobe swollen, and marked off by longitudinal depres- sions; three apodemal pits in longitudinal depression marking positions of fourth to sixth ring furrows. Axial furrow uniformly deep throughout. Pleural lobe with seven subequal pairs of ribs, and a median rib flaring posteriorly to three times anterior width. Rib furrows almost straight, progressively wider and shallower toward back, not quite reaching margin. Longitudinal ridge extending for much of postaxial length. Doublure 35 per cent sagittal length of pygidium, weakly convex in ventral view; anterior margin simple, marked on dorsal surface by a low ridge separating convex inner area of pleural lobe from concave outer area (holcos of Helbert et al., 1982:132). Seven broad depressions corresponding to pleural ribs. Longitudinal ridge ante- riorly. Fifteen or more semicontinuous terrace ridges running parallel to anterior margin, fainter, wavy, and more closely spaced in outer area. Wavy, raised lines on surface, except in furrows and muscle areas, distantly spaced, but more closely spaced near margins. Lines run as follows: gently convex for- ward on glabella; convex inward on fixigena, outward on field of librigena; V backward on lateral border, with outer limbs longer and more closely spaced; longi- tudinal on inner side of genal spine; forming a reticu- late pattern at base of genal spine; parallel to margin on rostral plate; convex backward on hypostome, including macula; longitudinal on thoracic segments; oblique on first two pygidial ribs and essentially transverse on sub- sequent ribs. Protaspides. Protaspis 0.8-0.9 mm in sagittal length (PI. 4, figs. 1,2; Text-fig. 4A), subquadrate, slightly wider than long. Cranidium 55 per cent total length; glabella parallel sided, 25 per cent width of cranidium, strongly convex transversely, weakly convex longitudi- nally. Occipital ring as wide as glabella, convex. Occipi- tal furrow broad, more shallow than axial furrow. Axial furrow deep and broad. Cheek broad and subquadrate, strongly convex and downturned laterally, apparently without border or librigena; a pair of tubercles, 70 per cent maximum width of protaspis apart, toward front. Posterior border 15 per cent sagittal length of crani- dium, sharply convex. Posterior border furrow deep and broad. Genal spine not preserved. Pygidium tripar- tite, very strongly inflated, comprising three segments ending in free points, and a broadly rounded unseg- mented area with a fourth pair of small free points laterally. Axis 15 per cent width of pygidium anteriorly; narrowing backward to a point at posterior margin; separating, but lower than, the even more strongly con- 12 vex pleural lobes; with three rings strongly marked off by broad ring furrows. Axial furrow strong. First and second pleural ribs almost as strongly developed as occipital segment, becoming less swollen laterally and produced into slender, backwardly directed spines 15 per cent sagittal length of protaspis. Third pleural rib weak. Third spine at least as long as first and second, projecting beyond margin for half its length. Meraspides. Meraspid cranidium 1.5 mm in sagittal length (PI. 4, figs. 3,4; Text-fig. 4C), Raymondaspis -like in its subparallel-sided glabella. Glabella 80 per cent as wide as long, with basal width 60 per cent anterior width, strongly convex anteriorly. Axial furrow deep. Anterior border indistinct mesially, developing abaxi- ally; anterior margin flexed upward mesially. Fixigena strongly convex, twice width of glabella at back; eye ridge near front almost transverse. Posterior border depressed, transverse. Posterior border furrow widens abaxially, shallow. Transverse raised lines on glabella; fixigena faintly granular. Smallest transitory pygidium 0.4 mm in sagittal length (PI. 4, figs. 12,13; Text-fig. 4B), incorporating four segments with free points. Articulating half-ring as long as first ring, strongly convex. First free point directed outwardly, second obliquely, third and fourth posteriorly, hindmost longest and projecting well beyond posterior margin. Convexity of pleural lobe of future pygidium increasing rapidly backward, rising above axial area. Surface finely granular. Transitory pygidium 0.8 mm in sagittal length (PI. 4, figs. 10,11; Text-fig. 4D), incorporating six segments with free points. Triangular in outline, 50 per cent as long as wide. Segments decreasing in definition back- ward, and free points becoming less oblique. Future pygidium strongly convex; axis shorter, more elevated above convex pleural lobe. Surface granular. Transitory pygidium 2.5 mm in sagittal length (PI. 4, figs. 6,7; Text-fig. 4E), incorporating two protothoracic segments with free points and pygidium with seven pleural ribs. Triangular in outline, 55 per cent as long as wide. Axis 20 per cent anterior width, 50 per cent length. Free points becoming successively shorter. Pygidium convex toward back, axis not depressed. Sur- face smooth. Transitory pygidium 2.8 mm in sagittal length (PI. 4, fig. 5; Text-fig. 4F), incorporating one protothoracic segment with free points. Future pygidium with four axial rings, large and swollen terminus, and seven pleu- ral ribs; broadly rounded and more adult in outline, 60 per cent as long as wide. Pygidium strongly convex, particularly at back. Axis 20 per cent width and 35 per cent length. First two pygidial ribs much wider (exsag.) than subsequent pleurae. Surface smooth. DISCUSSION K. borealis (Poulsen, 1934:27, pi. 3, figs. 14,15) from the Cape Schuchert Formation, North Greenland, was based on four cranidia. Cranidia from the Road River Formation are identical in gross morphology. Minor features supporting specific identity are the minute occipital tubercle and heavy occipital prosopon. The Road River specimens are distinguished from the Kap Schuchert material by the following differences: (1) the prosopon of raised lines is more dense; (2) granulation of the exoskeleton is absent; (3) the eye ridge is broader (exsag.). The species complies with Snajdr's diagnosis oiKoso- vopeltis (1958:177; 1960:65). It differs from the type species, K. svobodai Snajdr, and from K. partschi, both from the Kopanina Formation of Czechoslovakia, in that the glabella expands evenly and not abruptly near the front, and that the pygidium is more broadly rounded. Two scutelluine ontogenies have been described from well-preserved material of the Taemas Formation (Lower Devonian) of New South Wales: Dentaloscutel- lum hudsoni Chatterton (1971:12, pi. 1, figs. 1-22; pi. 2, figs. 1-14; pi. 3, figs. 1-12; pi. 24, fig. 15) and Scutellum calvum Chatterton (1971:22, pi. 3, figs. 21,22; pi. 4, figs. 1-24; pi. 5, figs. 1-24). The Road River Formation protaspides described above bear a general resem- blance to the late protaspides of both species from the Taemas Formation, differing in having a narrow and parallel-sided glabella, broad fixigena, and longer spines. The meraspid cranidium from the Road River Formation differs in having broader fixigena and large eyes that are forwardly placed, and in lacking an occipi- tal spine. There is a close resemblance between the smallest transitory pygidia of K. borealis and S. calvum (Chatterton, 1971, text-fig. 6D); larger transitory pygi- dia of K borealis differ from those of 5. calvum in having protothoracic spines of equal length (cf. alternating lengths). The adult oiK. borealis does not resemble the adult of either Taemas Formation species. Snajdr (1960, pi. 3, fig. 6) has illustrated a meraspid cranidium of the type species bearing an occipital spine; this spine was lost in the hoiaspis. It is unlikely that such a spine was present in K. borealis. Feist (1970) has described protaspides and meras- pides of Breviscutellum (Meridioscutellum) sp. from the Emsian and Eifelian of the Montagne Noire, France. The smallest protaspis, 1.96 mm in sagittal length, has 8 protothoracic segments developed; the largest has 10, the number in the adult. These protaspides contrast sharply with those from the Road River Formation 13 described above in most features; our largest protas- pides are 0.9 mm in length and have only 4 segments, indicated by free points. There is some similarity in the meraspides in the development of the adult pygidial characters. in K. borealis, with terrace ridges more widely spaced and more strongly scalloped. The three pygidia differ from each other in the construction of the axis and the median rib, amongst other features, but all are probably attributable to Kosovopeltis. Kosovopeltisl spp. PI. 9, figs. 8-11 Indeterminate scutelluine PI. 11, figs. 6,7 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 crani- dium, 3 pygidia. MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 1 cra- nidium. DISCUSSION The fragmentary cranidium differs from K. borealis in having a straighter axial furrow, longer occipital ring, weaker occipital furrow, narrower fixigena, and small palpebral lobe posteriorly placed. The three pygidia belong to more than one species. All differ from K. borealis in having a wider axis, more strongly curved posterior rib furrows, and an evenly convex surface; one specimen shows the doublure, which is longer than DISCUSSION This cranidium differs from Paracybantyx asulcatus sp. nov. in being less convex and in having an anterior border, a faint occipital furrow, a smaller genal muscle area and palpebral lobe, broader fixigena, a conspicu- ous eye line, and coarsely pitted prosopon. The crani- dium is somewhat similar to that of Planiscutellum kitharos Lane and Thomas {in Thomas, 1978:27, pi. 6, figs. 1-8) from the British Wenlock, but it has a much wider axis and a faint occipital furrow. Family Illaenidae Hawie and Corda, 1847 Subfamily Illaeninae HawIe and Corda, 1847 Genus Stenopareia Holm, 1886 TYPE SPECIES Illaenus linnarssoni Holm, 1882, Boda Limestone (Ash- gill), Dalarna, Sweden. cent length of cranidium, at own length from posterior margin. Axial furrows convergent. Dendritic muscle impressions strongly developed on glabella and fixi- gena. Axis of pygidium subtriangular, long, and wide. Stenopareia illtyd sp. nov. PI. 5, figs. 1-11 DERIVATION OF NAME Specific name derived from the Illtyd Range, Yukon Territory. HOLOTYPE ROM 42168 (cranidium, PI. 5, figs. 3,4), locality BB 131 (Lower Silurian), unnamed carbonates, Illtyd Range, Yukon Territory, Canada. MATEIUAL From BB 131 (Lower Silurian), Illtyd Range: 9 crani- dia, 6 pygidia. DIAGNOSIS Cranidium with strong convexity; palpebral lobes 1 0 per DESCRIPTION Length (in normal view) 65 to 80 per cent width, con- vexity strong. Glabella 55 per cent basal width, narrow- ing forward, but widening slightly at forefont; independent convexity slight. On internal moulds of glabella, shallow radiating ridges and furrows arranged in dendritic pattern alongside smooth median area; foremost ridge large, extending beyond glabella, and continuous with ridges radiating in a quarter segment from posterior inner extremity of fixigena. Axial furrow broad, directed inward for most of length, widening into shallow depressed lunule, and curving outward at front. Fixigena sloping steeply outward with weak convexity. Palpebral lobe 10 per cent length of crani- dium, situated at own length from posterior margin, level, and continuous with fixigena. Anterior branch of facial suture running almost straight forward from eye; posterior branch running outward and backward. Inter- nal surface smooth except for muscle impressions. 14 External surface sparsely pitted. Faint, transverse raised lines on front of cranidium. Pygidium 50 to 60 per cent as long as wide, convexity strong posteriorly. Axis subtriangular, 35 per cent ante- rior width, undefined at back except by slight convexity. Axial furrow broad and shallow anteriorly, becoming steadily shallower and dying out anterior to midlength. Pleural lobe sloping steeply outward, anterolateral angle narrowly rounded, facet steep. Surface covered with transverse anastomosing wavy lines on well-pre- served specimens. DISCUSSION S. illtyd sp. nov. closely resembles 5.? julli Norford (1981:7, pi. 6; pi. 10, figs. 8-10) from the Attawapiskat Formation of northern Ontario, but differs in having much stronger cranidial axial furrows and a less trian- gular pygidium. In both species, the muscle scars, or caecal markings, on glabellae and fixigenae are compa- rable. Both species also resemble Stenopareia sp. of Lane (1972:348, pi. 61, figs. 13-15) from the Drommebj- erg Limestone (Lower Silurian), northeastern Green- land, a species with comparable muscle scars that are preserved on the external surface of the glabella only. Indeterminate illaenid PI. 5, fig. 12 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 cephalon. DESCRIPTION Cephalon 50 per cent as long as wide, strongly convex. Glabella as long as wide, parallel sided. Palpebral lobe 35 per cent length of cephalon, 50 per cent own length from posterior margin. Librigena narrow, gently con- vex. Eye separated from cheek by broad depression. Genal angle broadly rounded. Surface of cranidium with extremely faint raised lines convergent backward on glabella; minute occipital tubercle posteriorly placed. DISCUSSION The cephalon differs from S. illtyd in having a parallel- sided glabella, shallower axial furrows, and compara- tively large eyes sited far back. It is unlikely that this cephalon can be included in Stenopareia, and its generic affinities are not clear. Family Proetidae Salter, 1864 ?Subfamily Crassiproetinae Osmolska, 1970 Genus Hedstroemia Pfibyl and Vanek, 1978 TYPE SPECIES Proetus delicatus Hedstrom (1923:4, pi. 1, figs. 1-15), Halla Beds, unit b (upper, probably uppermost, Wen- lock), Horsne Canal, Gotland, Sweden. nine rings and eight pairs of pleurae. Prosopon finely granular. MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 9 crani- dia, 14 librigenae, 2 hypostomes, 40 pygidia. Hedstroemia kutchini sp. nov. Pi. 6, figs. 1-14 DERIVATION OF NAME Species named after the Kutchin tribe who formerly inhabited extensive areas of the northern Yukon Ter- ritory. HOLOTYPE ROM 45347 (cranidium, PI. 6, figs. 3,4), locality AA 95 (Upper Silurian), Road River Formation, Prongs Creek, Yukon Territory, Canada. DIAGNOSIS Cephalon with intramarginal ridge between field and border. Genal spine absent. Pygidium elongate with DESCRIPTION Glabella 90 per cent sagittal length of cranidium, 80 to 90 per cent as wide as long, moderately convex, strongly defined, olive shaped or tongue shaped in outline. Occipital ring narrowing rapidly abaxially, with small occipital tubercle placed slightly posterior to mid- length. Occipital furrow and axial furrow moderately deep and narrow. Occipital lobe large, convex, strongly demarcated, extending sideways well beyond main part of ring. LI faintly defined, with slight independent con- vexity, almost 30 per cent maximum glabellar width. SI convex forward, directed inward and backward, wid- ening near midlength, fading at back; SI bifurcates adaxially, with anterior branch short, shallow, and transverse. S2 shallow, 25 per cent width of glabella, directed slightly backward, situated at 35 per cent length of glabella from front. S3 faint, parallel to S2, situated at 25 per cent length of glabella from front. 15 Anterior border of uniform width (sag., exsag.), upturned, convex, wider (tr.) than glabella. Anterior border furrow deep and broad. Between front of fixi- gena and anterior border furrow, a uniformly narrow and slightly oblique intramarginal ridge, continuous or discontinuous mesially, marked off from preocular area of fixigena by a clear-cut furrow and by independent convexity; prosopon agreeing with the anterior border and differing from the preocular fixigena in lacking granulation; this ridge continuing onto the librigena. Preocular area of fixigena moderately swollen. Palpe- bral lobe 25 per cent length of cranidium, horizontal, with midlength just posterior to front of SI and anterior extremity just posterior to S2; palpebral furrow faint, shallow, running parallel to margin. Postocular fixigena unknown. Anterior branch of facial suture commencing close to axial furrow, curving forward and outward at first, and then running longitudinally. Glabella, preocu- lar fixigena, and palpebral lobe, except in furrows, closely, uniformly, and finely granular; anterior border smooth except for raised lines running parallel to margin. Eye strongly convex, sloping outward, with subocular furrow deep and broad. Socle swollen, narrowing back- ward, marked off by a strong furrow. Field gently con- vex; intramarginal ridge at front of fixigena continuing abaxially on field of librigena as a lateral ridge, widen- ing somewhat backward and dying out before reaching posterior border furrow. Lateral border furrow slightly stronger than furrow marking off the lateral ridge and also dying out before posterior border furrow. Lateral and posterior borders strongly convex, confluent. Genal angle broadly rounded. Field coarsely and shallowly pitted, matching prosopon of fixigena. Surface of field roughened, with raised lines parallel to margin on lat- eral border. Hypostome as wide as long. Middle body large, well defined, convex, extending to anterior margin. Middle furrow oblique, short and shallow, commencing at 65 per cent length of middle body from front. Lateral lobe with oval macula abaxially, merging with middle body adaxially. Lateral furrow deepens and widens steadily backward, continuous with posterior furrow, which is broad and strongly convex backward. Lateral borders raised, subparallel, widening steadily backward, and slightly outturned just posterior to level of middle fur- rows. Posterior border depressed, strongly convex back- ward in outline. Anterolateral wing subquadrate, downturned; articulating process absent. Middle body faintly and coarsely pitted, bearing raised lines mesi- ally, divergent backward for most of length, transverse anteriorly. Raised lines on lateral border running paral- lel to margin. Pygidium 60 to 75 per cent as long as wide, strongly convex in both directions, high in profile, with height 60 to 70 per cent sagittal length. Axis convex, 45 to 50 per cent maximum width and 80 to 90 per cent length of pygidium, narrowing strongly backward to rounded tip, composed of nine rings and a short terminus. Ring furrows shallow, gently sinuous, bowed backward mesi- ally; furrows toward front strong, becoming successively fainter toward back, particularly abaxially. Paired mus- cle insertion scars distinguishable on some specimens. Axial furrow clear cut. Pleural lobe convex. Seven well- defined pleurae; eighth faint. First pleural furrow broad, narrowing abaxially, but reaching lateral margin; first interpleural furrow well developed, dying out at lateral depression. Subsequent pleural and interpleural furrows successively fainter, dying out at lateral depres- sion. Lateral border uniformly narrow, sloping outward with moderate convexity. Border depression strong but ending at first pleura. Articulating facet smooth. Sur- face densely but somewhat variably granular. DISCUSSION H. kutchini sp. nov. closely resembles the type species, H. delicata (Hedstrom, 1923:4, pi. 1, figs. 1-15), Halla Beds, Horsne Canal, Gotland, Sweden; an allied form has been described under open nomenclature by Hel- bert et al. (1982:138) from the Lower Silurian of the Oslo Region, Norway. Bob Owens (pers. comm., 1987) confirms that H. delicata has a flat intramarginal area between the border furrow and the change of slope of the field of the fixigena and librigena, comparable with the intramarginal ridge of H. kutchini; Owens also con- firms that H. kutchini differs from H. delicata in having stronger lateral glabellar furrows and a less-angular frontal glabellar lobe, in lacking a genal spine, in having a hypostome with more pronounced posterior wings and a broader posterior border furrow, and in having a pygidium composed of fewer segments with a narrower border. Shared features are the greatly swollen occipi- tal lobes; similar hypostomes, particularly as regards the prosopon; and the faint pygidial ring furrows with paired muscle scars abaxially. H. kutchini bears a resem- blance to Coniproetus {Coniproetus) affinis affinis (Boucek, 1933; see Snajdr, 1980:73, pi. 9, figs. 3-11), from the basal Lochov Formation (Lochovian), Repor- yje, Prague, Czechoslovakia, particularly as regards gla- bellar features, the librigena, the hypostome, and the distinctably faint ring furrows of the pygidium. H. kut- chini differs in having stronger lateral glabellar furrows, a narrower (sag., exsag.) anterior border, more posteri- orly placed palpebral lobes, an intramarginal ridge, and a more elongate pygidium with eight pleural ribs. The pygidium of//, kutchini also differs in proportions, and in having stronger pleural segmentation, and a much 16 narrower and more strongly defined border; these pygidial features readily distinguish Hedstroemia from Coniproetus. The hypostome bears a resemblance to that of Co- niproetus (C) whittakerensis (Chatterton and Perry, 1977, pi. 1, figs. 7-10) from the Early Devonian of northwestern Canada, but differs in having a more- rounded posterior border and raised lines on the front of the middle body that run transversely, not longitudi- nally. There is little resemblance between the cranidia of the two species — H. kutchini has a much broader (tr.) glabella, and narrower (sag., exsag.) anterior border. Hedstroemia sourdoughi sp. nov. PI. 6, figs. 16-24 DERIVATION OF NAME Species named after those prospectors (Sourdoughs) who chose the all-Canadian route to the goldfields — down the Mackenzie River, up the Peel River, up the Wind River, past Prongs Creek, and then overland to the Klondike. HOLOTYPE ROM 45332 (cranidium, PI. 6, figs. 22,23), locality AA 95 (Upper Silurian), Road River Formation, Prongs Creek, Yukon Territory, Canada. DIAGNOSIS Glabella strongly convex, frontal lobe rounded. Pygi- dium short, composed of eight rings and six pairs of pleurae; axis comparatively narrow; ring furrows well defined; border broad. Prosopon coarsely granular. MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 8 crani- dia, 2 librigenae, 25 pygidia. DESCRIPTION Cranidium closely similar to//, kutchini sp. nov. in many respects, differing in the following features. Glabella more convex. Occipital tubercle small or absent. Occi- pital furrow deeper, SI stronger, S2 and S3 fainter. Intramarginal ridge present but discontinuous mesially. Pygidium shorter, 50 to 60 per cent as long as wide. Axis of eight rings and a short terminus; ring furrows much deeper and less sinuous. Paired muscle insertion scars distinct on surface of most specimens. Pleural lobe more convex, with six pleurae and deeper and broader border depression; border broader, of uniform width. Prosopon of cranidium and pygidium coarsely and densely (cf. finely) granular. DISCUSSION H. sourdoughi sp. nov. closely resembles //. kutchini sp. nov. in cranidial features, particularly in the presence of the intramarginal ridge. It also stands close to Co- niproetus bohemicus Hawle and Corda (see Snajdr, 1980:58, pi. 6, figs. 1-14; pi. 61, fig. 4; pi. 63, fig. 6) from the Koneprusy Limestone, Czechoslovakia, particularly as regards glabellar outline, the definition of the lateral glabellar furrows, strong pygidial ring furrows, broad pygidial border, and coarse prosopon. H. sourdoughi sp. nov. differs from H. kutchini in having an intramarginal ridge and stronger pygidial furrows. The cranidium of //. sourdoughi differs from that of C. bohemicus in having a narrower (sag.) anterior border, smaller palpe- bral lobes, and an intramarginal ridge (discontinuous mesially). Subfamily Warburgellinae Owens, 1973 Genus Prantlia Pfibyl, 1946 TYPE SPECIES Proetus longulus Hawle and Corda, 1847, Kopanina Formation, Upper Silurian, Prague district, Czecho- slovakia. Prantlia vagrans sp. nov. PI. 7, figs. 1-15 HOLOTYPE ROM 45363 (pygidium, PI. 7, figs. 6,7), locality AA 95 (Upper Silurian), Road River Formation, Prongs Creek, Yukon Territory, Canada. DIAGNOSIS A warburgelline with short frontal area, glabella 80 per cent sagittal length of cranidium, supplementary lobe adaxial to LI, strong SI, and posterior bands of second and third pygidial pleurae crossing border. DERIVATION OF NAME Specific name derived from Latin vagrans (wandering), in allusion to the wide distribution of this genus. MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 16 crani- dia, 22 librigenae, 48 pygidia. 17 DESCRIPTION Glabella 80 per cent sagittal length of cranidium, 75 per cent as wide as long, moderately convex, strongly defined, anterior outline narrowly rounded. Occipital ring narrowing rapidly abaxially; occipital tubercle small, centrally placed. Occipital lobe large, convex, strongly demarcated, extending sideways well beyond main part of ring. Occipital furrow deep and moder- ately broad. LI strongly defined, subtriangular, with strong independent convexity, 30 per cent maximum glabellar width. SI deepening rapidly, running obliquely inward and backward, shallowing and widen- ing at back. In several specimens, SI forming a short, transverse branch of varying strength toward front of LI, defining a small supplementary lobe marked by a short furrow posteriorly and by slight independent convexity. S2 faintly impressed, 25 per cent width of glabella, almost transverse, situated at 30 per cent length of glabella from front. S3 as S2 but slightly con- vergent forward, situated at 25 per cent length of gla- bella from front. Axial furrow straight, extremely deep and broad. Preglabellar area marked off from preocu- lar fixigenae by a shallow, almost transverse depression. Anterior border one-third length of preglabellar area, hardly narrowing abaxially, convex. Anterior border furrow shallow but distinct. Frontal area weakly convex and marked off from the more strongly convex preocu- lar fixigena by a faint but broad depression convex forward. Palpebral lobe small, 25 per cent length of cranidium, horizontal, with anterior extremity opposite S2; palpebral furrow faint, shallow. Postocular fixigena unknown. Anterior branch of facial suture commencing close to axial furrow, curving forward and outward, and bending inward at anterior border furrow. Glabella closely granular, except in furrows, with granulation becoming finer toward front; anterior border finely granular, with delicate raised lines running parallel to that border; preglabellar area and preocular fixigena coarsely and shallowly pitted, with raised lines and a few scattered granules; palpebral lobe finely granular. Eye strongly convex and sloping outward, separated by shallow furrow from low, narrow socle set on a ridge narrowing backward. Field convex. Lateral border fur- row deep and broad, continuing into genal spine; lateral border ill defined, half minimum width of field, extend- ing alongside genal spine. Posterior border strongly developed and extended alongside broad-based genal spine reaching backward for about 35 per cent esti- mated sagittal length of cephalon. Field coarsely and shallowly pitted, matching prosopon of fixigena. Closely spaced raised lines run forward and inward on outer area of lateral border; posterior to midlength, raised lines become chevron shaped, with shorter, posteriorly directed limb on inner area of border; posterior border with similar prosopon alongside spine. Pygidium 60 to 70 per cent as long as wide, moder- ately convex in both directions. Axis 30 to 35 per cent maximum width of pygidium, 85 to 90 per cent length of pygidium, narrowing slowly backward to rounded tip, composed of twelve rings and a short terminus. Ring furrows gently sinuous, strong anteriorly, becom- ing successively fainter, particularly abaxially. Axial furrow narrow. Pleural lobe convex; border depression strong but dying out at first pleura. Seven well-defined pleurae; eighth faint. First pleural furrow broad, nar- rowing abaxially, but reaching lateral margin; first inter- pleural furrow uniformly narrow and shallow, just reaching lateral margin. Subsequent pleural and inter- pleural furrows deep and broad adaxially, successively fainter, and dying out at lateral border furrow, except second and third posterior bands and interpleural fur- rows extending halfway across lateral border. Lateral border narrowing slightly forward, sloping outward with moderate convexity. Articulating facet smooth. Doublure as wide as lateral border. Ten almost-contin- uous terrace lines running subparallel to margin. Sur- face granular; raised lines directed inward and forward on anterior part of border. One pygidium (PI. 7, fig. 13) showing a deformity in having a slight embayment in the posterior outline. A meraspid cranidium, 2.2 mm in sagittal length (PI. 7, fig. 10), differing little from adult cranidium except in its narrower glabella and smaller occipital lobe. DISCUSSION P. vagrans sp. nov. bears a close resemblance to the type species, Prantlia longula Snajdr (1980:180, pi. 34, figs. 1-8), in many respects, such as the following: gla- bellar outline, development of the lateral glabellar fur- rows, large occipital lobes, segmentation and narrow axis of pygidium, and the manner in which the lateral border furrow dies out at the first pleura. P. vagrans differs from the type species in the following features: (1) the glabella is 80 per cent the length of the crani- dium (cf. 65 to 70 per cent), the preglabellar field being much shorter; (2) S2 is transverse (cf. slightly conver- gent backward); (3) the frontal lobe is narrower; (4) the pygidium is relatively longer, being comprised of 12 (cf. 10) rings, and has a narrower and more convex border; (5) the postaxial ridge on the pygidium is absent. The librigena of P. vagrans resembles that of the warburgelline Tetinia in morphology and also particu- larly in the oblique raised lines on the outer area of the lateral border. Prantlia differs from Warburgella in the 18 absence of the tropidium. Other species of Prantlia — P. longifrons (Lindstrom, 1885), from the Hemse Beds (Upper Silurian), Got- land, Sweden; P. grindrodi Owens (1973; Thomas, 1978), Wenlock Shale, Malvern, United Kingdom; and P. canberrensis Chatterton and Campbell (1980), Lower Silurian, Canberra, Australia — differ considerably from the type species and from P. vagrans, as the com- parison in Table 2 demonstrates; the subgenus Ma/vem- ocare has been proposed for P. grindrodi by Pfibyl and Vanek (1978). Chatterton and Campbell (1980:85) con- sidered Latiproetus Lu (1962:162) to be synonymous with Prantlia, drawing attention to the similarity between the type species L. latilimbatus (Grabau) and P. grindrodi. Kobayashi (1985:419) considered Latiproe- tus to be valid, and he referred Prantlia biloba Koba- yashi and Hamada (1974:118, pi. 12, figs. 8,9a,b), Okanari, Shikoku Island, Japan, to Latiproetus; he regarded Chuanqianoproetus Wu, 1977; Xiushuiproetus Q. Zhang in Qiu et al., 1983; and possibly Malvernocare as subgenera of the genus. In our opinion, more detailed knowledge about the morphology of the taxa concerned is required before a satisfactory revision can be proposed. Table 2. Summary of diagnostic characters of the species oi Prantlia. glab., glabellar; %, as percentage of; cranid., cranidial; no., number. Species longula vagrans canberrensis longifrons grindrodi CEPHALON glab. shape triangular triangular bell bell bell glab. length % cranid. length 68 82 66 61 62 genal spines yes yes yes ? yes THORAX no. of segments 9 ? 8 9 10 PYGIDIUM no. of rings 10 12 9-10 10 7 no. of pleurae 8 8 faint 8 5 Subfamily uncertain Indeterminate proetid A PI. 6, fig. 15 Indeterminate proetid B PI. 9, figs. 4,5 MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 1 hypostome. MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 crani- dium, 1 hypostome, 1 pygidium. DISCUSSION One small hypostome (PI. 6, fig. 15) lacks the posterior embayment of warburgellines, and differs greatly from the hypostome of H. kutchini in the following features: it is much more elongate, with different prosopon; the middle body is pinched in and produced anteriorly; paired posterolateral denticles are present. We do not know of a comparable hypostome and leave its system- atic position undecided. DESCRIPTION Fragmentary cranidium with subquadrate glabella as long as wide. Lateral lobes apparently absent. Pregla- bellar and axial furrows shallow. Occipital ring 10 per cent length of cranidium. Occipital tubercle and lobe absent. Preglabellar area 20 per cent length of crani- dium, not downturned; preglabellar field gently convex. Anterior border short. Anterior furrow shallow. On hypostome, width across posterior wings 85 per cent length. Middle body swollen, strongly defined. 19 Middle furrow commencing at 60 per cent length of hypostome from front, inclined backward and inward for 20 per cent width. Lateral lobe composed almost entirely of strongly swollen, smooth macula. Lateral furrow shallow anteriorly, becoming deeper and broader toward back, bending outward opposite mac- ula. Posterior furrow convex backward, broad, and shal- low. Lateral border narrow, raised, continuous with posterior border; posterior border broader mesially; lateral denticle absent. Raised lines running backward and outward on middle body, parallel to margin on borders. DISCUSSION The hypostome resembles that of Hedstroemia kutchini sp. nov., particularly in the rounded posterior outline and large maculae, but differs in having an undepressed posterior border and in prosopon. The cranidium and unillustrated pygidium are unlike Hedstroemia and are unidentifiable. Family Aulacopleuridae Angelin, 1854 Genus Otarion Zenker, 1833 TYPE SPECIES Otarion diffractum Zenker, 1833, from Upper Silurian rocks near Beroun, Prague district, Czechoslovakia. DISCUSSION In their review of the family Aulacopleuridae, Thomas and Owens (1978) suggested that Otarion {Otarion) be restricted to Late Silurian aulacopleurid species with, among other features, faint eye ridges visible on inter- nal moulds, a subparallel-sided glabella, weakly diver- gent preocular facial sutures, and 13 to 17 thoracic segments, the sixth segment bearing an axial spine. They proposed that O. {Aulacopleura) be restricted to species from the Ordovician to Middle Devonian with strong eye ridges evident on the external surface and with 18 to 22 thoracic segments, none bearing an axial spine. Aulacopleura socialis (Poulsen), from the Early Silurian, bears conspicuous eye ridges, a glabella of parabolic outline, widely divergent facial sutures, and 12 thoracic segments, with an axial spine on the sixth segment in some specimens. These features preclude assignment to either subgenus, but are shared with Songkania Chang from the Early Silurian of southwest China, which we regard as a third subgenus of Otarion. Subgenus Songkania Chang, 1974 TYPE SPECIES Songkania hanjiadianensis Chang, 1974, Early Silurian, southwest China. Otarion {Songkania) socialis (Poulsen, 1934) PI. 4, fig. 14; PI. 8, figs. 1-12; PI. 12, figs. 14-16; PI. 13, figs. 3-6; Text-fig. 5B Aulacopleura socialis Poulsen, 1934:21, pi. 2, figs. 24- 27. Aulacopleura socialis — Raasch in Raasch, Norford, and Wilson, 1961:471, fig. 4.1-9. HOLOTYPE MMH 3251 (cranidium, figured by Poulsen, 1934, pi. 2, fig. 25; in this paper, PI. 13, figs. 3,4), Cape Schuchert Formation (Lower Silurian), Kap Schuchert, North Greenland. MATERIAL From AA 2-4.5 (Lower Silurian), Prongs Creek: 7 dor- sal shields, 270 cranidia, librigenae, 3 hypostomes, 78 pygidia. DESCRIPTION Length of cephalon 40 per cent width opposite occipital ring. Glabella 80 to 90 per cent as wide as long, 55 to 60 per cent length of cranidium (in normal view), subquadrate, gently convex; anterolateral angles broadly rounded. Occipital ring moderately convex, with posterior margin bowed backward. Occipital tubercle centrally placed. Occipital furrow shallower than axial furrow. LI with slight independent convexity, 30 per cent length of glabella and 20 per cent width of glabella. SI broad and strong anteriorly, becoming weak posteriorly, running obliquely backward to occipi- tal furrow. S2 short, distinct only on internal surface. Preglabellar and axial furrows continuous, deepening posteriorly. Preglabellar field as long as glabella when measured along surface, curving downward with mod- erate convexity, confluent with fixigena. Fixigena wide, sloping inward from palpebral lobe. Palpebral lobe hor- izontally extended, with extremities almost twice width of glabella apart; midlength of palpebral lobe opposite midlength of glabella. Eye ridge strong, slightly oblique, divided by a median furrow. Anterior border moder- ately wide and convex, with sagittal length greater than exsagittal length. Anterior border furrow uniformly well defined. Anterior branch of facial suture running sinuously forward and outward, cutting anterior margin 20 at 65 per cent width across genal angles. Posterior branch running backward and outward, cutting margin at 80 per cent width across genal angles. Doublure extending to border furrow. Eye 20 per cent sagittal length of cephalon; strong convexity differentiating from narrow socle; socle marked off from librigena by a broad, shallow furrow. Field of librigena considerably wider than preglabellar area, moderately convex, sloping outward; caecae pres- ent on some specimens. Lateral border convex, 30 per cent minimum width of field, continuous with anterior and posterior borders; anterior and posterior borders widening rapidly adaxially. Genal spine long and slen- der, extending to sixth' thoracic segment, arising abruptly at genal angle, directed slightly outward and backward, almost straight. Rostral plate unknown. Hypostome elongate. Mid- dle body large, extending to anterior margin, strongly convex. Lateral lobes large, uniting to form a posterior lobe with independent convexity. Middle furrow oblique, shallow. Anterior wing small. Lateral border narrow, convex, directed longitudinally for much of length, diverging posteriorly, and curving round to unite with rounded posterior border. Lateral denticle absent. Thorax composed of 12 segments. Axis 30 per cent width of thorax anteriorly, narrowing to 65 per cent anterior width of axis posteriorly, gently convex trans- versely. Axial furrow well defined. First five rings with swollen lateral nodes. Articulating half-ring more than half length of ring. Pleural lobe horizontally extended adaxially, gently downturned at fulcrum at 60 per cent width. Pleura composed of anterior and more strongly swollen posterior bands, separated by median pleural furrow; extremity of pleura rectangular. Axial spine on sixth ring on at least two individuals (PI. 8, figs. 6-8), tapering slowly and curving low over axis to twelfth ring; spine certainly absent on other specimens (PI. 8, fig. 5). Pygidium 35 to 40 per cent as long as wide. Axis 30 per cent anterior width of pygidium, 85 per cent length of pygidium, moderately convex. Terminus broadly rounded. Five rings clearly marked by continuous ring furrows, successively shorter. Pleural area increases strongly in convexity toward back. Border uniformly narrow, continuous. Four well-defined pleurae and a posterior area; anterior bands confluent with border, widening abaxially. Posterior bands more swollen, nar- rowing out at border furrow, delimited by pleural and interpleural furrows; pleural and interpleural furrows fuse to form border depression. Doublure narrow. Surface smooth except as follows: coarse granules on glabella; two pairs of small granules on adaxial area of fixigena, anterior pair closer to axial furrow than posterior pair; a row of granules on occipital and tho- racic rings; faint granules on axis of pygidium. External surface of field of librigena closely and shallowly pitted; lateral border of librigena with very faint, closely spaced raised lines running parallel to margin. Internal surface of librigena smooth. DISCUSSION The only differences between the specimens from the Road River Formation and the type material from North Greenland are the stronger granulation and the weaker development of S2 in the Road River Forma- tion material. It is not known whether or not an axial thoracic spine was present in the Greenland material; the material under description is dimorphic in this respect. The cranidium of O. (5. ) socialis resembles O. {S. ) pijiazhaiensis Chang (1974:174, pi. 81, fig. 10) more closely than it does the type species, O. (S. ) hanjiadia- nensis Chang (1974:174, pi. 80, figs. 3,4; pi. 81, fig. 9); differences in the Road River Formation material from that of both other species are the broader LI, the longer preglabellar field, and the presence of granulation. Family Harpidae Hawie and Corda, 1847 Genus Scotoharpes Lamont, 1948 TYPE SPECIES Scotoharpes domina Lamont, 1948, Whether Law Linn Formation (upper Llandovery), Whether Law Linn, North Esk Inlier, Scotland. Scotoharpes raaschi Norford, 1973 PI. 9, figs. 1-3 Scotoharpes raaschi Norford, 1973:20, pi. 2, figs. 1,3-5. HOLOTYPE GSC 27794 (cephalon, figured by Norford, 1973, pi. 2, figs. 1,3-5), Lower Silurian, GSC locality 53109 (proba- bly the same as BB 131), Illtyd Range, Yukon Territory, Canada. MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 2 cephala. DESCRIPTION Cephalon 65 per cent as long (sag.) as wide. Glabella 21 40 to 45 per cent length of cephalon and 20 per cent width of cephalon, moderately swollen, as wide as long. Width of occipital ring equal to width across LI; occipi- tal tubercle strong, anteriorly placed. Occipital furrow shallow, transverse. LI small, 30 per cent length of glabella, projecting only slightly sideways. SI shallow, curving inward and dying out anterior to midlength of LL Preglabellar and axial furrows continuous, shallow. Ala moderately large, 30 per cent width of glabella, sloping outward and depressed abaxially, narrowing and dying out anterior to midlength of glabella. Fixed cheek convex; a low ridge outlining ala anteriorly. Eye tubercle only slightly elevated, 30 per cent width of cephalon from midline, situated opposite forefront of glabella. Eye ridge clearly defined, essentially trans- verse; ridge of comparable strength running obliquely outward from eye tubercle to cheek roll. Cheek roll extending almost to glabella anteriorly, sloping steeply outward, narrowing and dying out at 60 per cent length from front. Posterior border short, convex, curving strongly backward abaxially. Girder weak. Brim flat- tened, slightly wider anteriorly than laterally; prolonga- tion 40 per cent sagittal length of cephalon, narrowing slowly backward, slightly inturned posteriorly. Mar- ginal band narrow, smooth. Doublure of occipital ring almost reaches occipital furrow. Glabella, occipital ring, and ala smooth; cheek coarsely pitted, with pits on cheek roll finer than on cheek and arranged in ramifying, radiating rows separated by fine caecae. Cae- cae continuing 20 per cent distance across brim. Brim finely pitted. Pits on either side of girder larger. DISCUSSION A point of particular resemblance of our material to S. raaschi Norford is the ridge running obliquely outward from the eye tubercle. The occipital tubercle described above is present on the external surface only and is not preserved on the holotype cephalon. Family Cheiruridae Hawle and Corda, 1847 Subfamily Cheirurinae Hawle and Corda, 1847 Genus Cheirurus Beyrich, 1845 TYPE SPECIES Cheirurus insignis Beyrich, 1845, Liten Formation (Upper Silurian), Prague district, Czechoslovakia. DESCRIPTION Anterior part of glabella (all that is known) expanding slightly forward, moderately convex. S2 and S3 curving gently backward, 30 per cent width of glabella. Anterior border short; anterior border furrow shallow mesially, deeper abaxially. Prosopon faintly granular. The unil- lustrated librigena is of generalized cheirurine type. Cheirurus sp. PI. 5, figs. 15,16 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 crani- dium, 1 fragmentary librigena. DISCUSSION This species differs from C. certus Poulsen (1934:28, pi. 3, fig. 16) and C. hyperboreus Poulsen (1934:29, pi. 3, figs. 17,18), both from the Cape Schuchert Formation, North Greenland, in its shorter, less-expanded frontal lobe. Family Encrinuridae Angelin, 1854 Subfamily Encrinurinae Angelin, 1854 Genus Cromus Barrande, 1852 TYPE SPECIES Trilobites intercostatus Barrande, 1846, Kopanina For- mation (Upper Silurian), Prague district, Czechoslo- vakia. Cromus princeps (Poulsen, 1934) PI. 10, figs. 1-8; PI. 13, figs. 7-12; Text-fig. 5C Encrinurus moderatus Poulsen, 1934:31, pi. 3, fig. 20 (non figs. 21,22). Encrinurus princeps Poulsen, 1934:33, pi. 3, figs. 23-27. Encrinurus princeps — Raasch in Raasch, Norford, and Wilson, 1961, fig. 5.1-5. Encrinurus cf. E. princeps — Norford, 1962, pi. 8, fig. 14. Encrinurus cf. E. princeps — Norford et al., 1970, pi. 8, fig. 14. Cromus princeps — Strusz, 1980:10. Cromus princeps — Snajdr, 1985:16. Encrinurus moderatus — Lane, 1988:99, pi. 5, figs. 7,?8. 22 HOLOTYPE MMH 3276 (cranidium, figured by Poulsen, 1934, pi. 3, fig. 23; in this paper, PI. 13, figs. 10,11), Cape Schuchert Formation (Lower Silurian), Kap Schuchert, North Greenland. MATERIAL From AA 2-4.5 (Lower Silurian), Prongs Creek: 1 dor- sal shield, 10 cranidia, librigenae, 4 hypostomes, 23 pygidia. DESCRIPTION Cranidium 45 per cent as long as wide. Glabella 70 to 80 per cent as wide as long, moderately convex in both directions; width across L2 60 to 65 per cent maximum width. Occipital ring wider than width across LI, with transverse posterior margin narrowing slightly abaxi- ally. Occipital furrow broad and shallow mesially, shal- lower than axial furrow abaxially; rounded apodeme at extremity. LI consisting of a ridge 35 per cent width of glabella, directed somewhat forward adaxially; L2 shorter than L3, nodular; L3 subquadrate. SI almost continuous; S2 and S3 broad abaxially, dying out adaxi- ally, 35 per cent width of glabella. Frontal lobe 40 to 45 per cent length of glabella, evenly and strongly rounded in outline. Axial furrow deeper and broader than preglabellar furrow, widening backward; apo- demes adaxially at extremities of SI and S2. Preglabel- lar furrow deep and wide abaxially, becoming shallower and narrower mesially. Anterior border of cranidium moderately wide abaxially, narrowing and almost dying out mesially. A longitudinal median depression cross- ing anterior border and preglabellar furrow, and run- ning onto forefront of glabella; this depression stronger in small specimens. Fixigena wide, sloping inward from eye with strong convexity and outward to genal angle with weaker convexity. Palpebral lobe almost 20 per cent length of cranidium and marked off from fixigena by a broad, shallow depression; anterior extremity of palpebral lobe placed opposite, and at twice width across, L3. Posterior border narrower (exsag.) than occipital ring, widening slowly abaxially and rapidly adjacent to genal angle, depressed well below level of fixigena abaxially. Lateral border ill defined. Posterior border furrow deep adaxially, where continuous with lateral furrow. Genal spine thornlike, very short, directed backward and slightly outward. Anterior branch of facial suture curving forward and inward, delimiting anterior border of cranidium. Posterior branch curving outward and backward, cutting lateral margin opposite occipital furrow. Eye pedunculate; lens surface occupying half height of stalk; stalk marked off by a broad depression from field. Field of librigena gently convex. Preglabellar lobe 25 per cent length of cranidium, weakly convex. Lateral border strongly convex, less than half minimum width of field, continuous with anterior border, curving inward and widening at back. Lateral border furrow uniformly deep and broad. Anterior border furrow deep and broad at axial furrow, narrowing and dying out by midwidth of preglabellar lobe. Rostral plate unknown, but conformation between librigenae indicating a narrow plate widening forward, as shown in reconstruction. Hypostome 75 per cent as wide as long. Middle body strongly swollen, longitudinally ovate, with a less- inflated terminal area. Rhynchos broad, with indepen- dent convexity anteriorly but projecting slightly, length equalling half that of middle body. Lateral lobe com- prising a small, smooth macula. Lateral furrow demar- cating middle body strongly. Lateral border narrow, flattened, merging with posterior tongue; tongue 25 per cent length of hypostome and with rounded tip. Middle body closely and shallowly pitted, more coarsely so anteriorly. Pygidium triangular in outline, 55 to 60 per cent as long as wide. Axis 25 per cent anterior width and 90 per cent length of pygidium, composed of 20 rings; first six rings continuous, subsequent rings becoming discontinuous mesially. Ring furrows successively shal- lower toward back. Axial furrow deep and broad anteri- orly, becoming narrower and shallower posteriorly. Pleural lobe weakly convex to midwidth, downcurved abaxially. Ten pleural ribs; tenth rib postaxial, with tip generally bluntly fused with ninth; ribs flat topped, widening steadily; tips of ribs pointed and outturned, more bluntly so posteriorly. Ribs successively directed increasingly backward and outward, tenth parallel. Rib furrows deep and broad, widening slightly abaxially. Anterior band of first pleura with clear articulating facet. Four congruent axial and pleural segments. Ven- tral border uniformly narrow; inner margin straight; junction evenly rounded, unembayed. Surface of cephalon, except on occipital segment and in furrows, closely tuberculate; tubercles of mixed sizes, diameter of largest being 8 per cent maximum width of frontal lobe; about one hundred tubercles on adult glabella, many perforate. A quincunx of small tubercles composed of Ll-1; Sl-0; L2-1. Remainder of tubercles randomly distributed. Occipital segment finely and sparsely granular. A single row of tubercles on anterior border of cranidium. Tubercles on genae larger adaxi- ally. Pygidium granular; three or four small median tubercles on axis of pygidium randomly spaced. Attri- bute coding (Temple and Tripp, 1979): 1-0; 2-20; 3-0; 4-1; 5-1; 6-10; 7-0; 8-1; 9-4; 10-1; ll-'/2; 12-1; 13-1; 14- 1; 15-0; 16-1; 17-0; 18-0; 19-0; 20-0; 21-1; 22-1; 23-0; 24- 23 0; 25-1; 26-0; 27-100; 28-12; 29-0; 30-2.5; 31-0; 32-1; 33- 8; 34-0. Small pygidia have fewer segments and more strongly developed ring furrows. On one pygidium, 3 mm in sagittal length (PI. 10, fig. 5), ninth and tenth rings bifurcate laterally, third and fourth right ribs fused abaxially. DISCUSSION The holotype of Encrinurus moderatus Poulsen (1934:31, pi. 3, fig. 20), from the Cape Schuchert For- mation, St. George Fiord, North Greenland, is a small cranidium, 5.0 mm in length, attributable to Cromus princeps; thus moderatus is a junior subjective synonym of princeps. The two pygidia from the same horizon and locality referred to E. moderatus by Poulsen (1934, pi. 3, figs. 21,22) are not attributable to Cromus; they are distinct from the pygidium from Cape Constitution named Encrinurus inflatus by Poulsen (1934, pi. 3, fig. 19). C princeps most closely resembles C. novaki (Freeh, 1888:735, pi. 29, figs. 5-9), from beds of Middle Silurian age in the Carnic Alps; C. novaki also possesses an anteromedian furrow and short genal spines. C. princeps differs in that the eyes are placed farther back and the tuberculation is coarser. congruent axial and pleural segments. Apart from the four axial tubercles, prosopon greatly subdued. DISCUSSION This pygidium has much in common with Balizoma — the low number of rings and pleurae, large axial tuber- cles, and longitudinal axial furrow — but must be excluded from Balizoma under Ramskold's (1986) definition on account of the high ring-to-pleura ratio. Furthermore, the pleural area is not strongly down- turned, and the pleural ribs are narrow and without large tubercles. Snajdr (1985) reestablished Encrinuraspis Webby, Moors, and McLean (1970), considered by Strusz (1980) as a junior synonym of Cromus. The case for retention is disputable, but Encrinuraspis may prove to be a useful taxon for species not readily attributable elsewhere, and the Illtyd Range pygidium is a case in question. Genus Balizoma Holloway, 1980 TYPE SPECIES Calymene variolaris Brongniart, 1822, Much Wenlock Limestone Formation, Dudley, West Midlands, United Kingdom. Genus Encrinuraspis Webby, Moors, and McLean, 1970 TYPE SPECIES Encrinuraspis optimus Webby, Moors, and McLean, 1970, Malongulli Formation (?Caradoc Series), New South Wales, Australia. Balizoma aff. B. obtusus (Angelin, 1851) PI. 11, figs. 8-10,12-18 MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 5 crani- dia, 1 librigena, 1 hypostome, 27 pygidia. Encrinuraspis sp. PI. 9, fig. 6 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 pygidium. DESCRIPTION Pygidium 70 per cent as long as wide, moderately and evenly convex. Axis 30 per cent anterior width and 80 per cent length, tapering to a point. Twelve rings, of which first six continuous; a longitudinal median depression as deep as ring furrows interrupting poste- rior rings. Large median tubercles on fourth, sixth, and eighth rings. Pleural lobe downcurved with seven ribs widening slightly and a broad postaxial ridge compris- ing fused eighth ribs. Ring-to-pleura ratio 1.7. Two DESCRIPTION Glabella 90 per cent as wide as long, with width across L2 60 per cent width across frontal lobe, moderately rounded in outline, uniformly convex longitudinally and transversely. Occipital ring short (sag.), wider than base of preoccipital glabella, strongly arched trans- versely; occipital furrow deep and broad. Frontal lobe 45 percent sagittal length of glabella. LI and SI almost obsolete. L2 and L3 represented by comparatively small nodular tubercles. S2 and S3 short, broad, shallow fur- rows, discontinuous mesially. Axial furrow deep and broad, with fossula near front. Preglabellar furrow shal- low. Eleven moderately sized tubercles on anterior border of cranidium; lateral tubercle not enlarged. Fixigena convex. Posterior border short (sag.), incom- plete; posterior border furrow deep and broad. Genal angle unknown. Cranidium finely and densely tubercu- late; larger tubercles perforate. Basal diameter of wid- 24 est glabellar tubercles 10 per cent maximum width of glabella across L4; a pair of larger tubercles opposite L2; remaining tubercles not clearly symmetrically arranged; total number about 60. A single row of small tubercles on occipital ring and posterior border. Librigena incompletely known, with comparatively small field and broad lateral border. Rostral plate unknown. Hypostome rhombic, with width (excluding anterior wings) 75 per cent length and anterior margin narrowly rounded. Middle body inflated, well defined by strong lateral furrow. Rhynchos large, projecting somewhat anterior to middle body, widening slightly backward, and dying out near midl6ngth of middle body. Macula small but distinct. Anterior border short. Anterior wing large, sloping obliquely upward. Lateral border narrow, depressed. Posterior tongue almost 20 per cent length of hypostome, horizontally extended. Surface of middle body granular, with a few pits and folds. Pygidium triangular in outline, strongly convex in both directions, high in profile, with width 85 to 95 per cent length (average width-to-length ratio 1.1:1). Axis 35 per cent maximum width of pygidium, strongly con- vex transversely, with 13 rings and a terminus; postaxial ridge short, reaching posterior margin in a few speci- mens. Rings continuous. Sagittal groove lacking on external moulds, shallower than ring furrows alongside tubercles on internal moulds. Ring furrows broad and deep. Sagittal tubercles only slightly larger than abaxial ring tubercles, absent on first and second rings, fre- quently on successive rings toward back. Axial furrow deep anteriorly, becoming weaker posteriorly. Nine strong pleural ribs; tenth pair short and joined at tips, or fused in a postaxial ridge; ribs parallel sided, directed increasingly strongly backward, curving downward at fulcrum. Four or five small tubercles on each pleural rib. Tips of ribs projecting in short free points. Four rings and pleurae congruent. Rib furrows deep and broad throughout. Ring-to-pleura ratio (R/P) as defined by Ramskold (1986:529) 1.2-1.3. DISCUSSION It is Ramskold's opinion (pers. comm., 1987) that this material falls within the range of the abundant Swedish species B. obtusus (Angelin, 1851:3, pi. 4, fig. 9; see Ramskold, 1986:561, pi. 40, fig. 2; pi. 48, figs. 1-14; pi. 49, figs. 1-10), from the Mulde Beds (Middle Silurian), Klinteberg Marl, Hemse Beds, and Eke Beds (Upper Silurian), Gotland, Sweden. Ramskold recognized three morphological forms: Form A, the "type form," restricted to the northeastern limestone areas in the Hemse Beds and the Eke Beds at Lau Backar; Form B, restricted to the "marl" west and south of the south- western outcrops of the Hemse Beds limestone area; and Form C, known only from pygidia from the upper Eke Beds. The hypostome from AA 95 is similar in main characters to that of 5. obtusus (Ramskold, 1986, pi. 48, fig. 1) but differs in having a less strongly defined, unwaisted rhynchos; in size, it is appropriate to B. aff. B. obtusus, but it should possibly be attributed to the indeterminate encrinurine described below. The pygi- dia under description most closely resemble B. obtusus Form B, but differ in the width-to-length proportions — 85 to 95 per cent for Road River Formation specimens, compared to 65 to 85 per cent for B. obtusus Form B. Ramskold (1986:66) has discussed the possibility that B. rosensteinae (Tripp, Temple, and Gass, 1977:860, pi. 115, figs. 1-13), from the Ludlow Series, United Kingdom, and B. dimitrovi Perry and Chatterton (1979:589, pi. 72, figs. 1-3; pi. 73, figs. 1-17,29-31; pi. 74, figs. 1-14,18-23,30-35), from the upper Whittaker and lower Delorme formations (Wenlock to lower Lud- low), Delorme Range, Mackenzie Mountains, Canada, are synonymous with B. obtusus. Ramskold (1986:561) has restricted the genus Balizoma to species with a ring-to-pleura ratio (R/P) of 1.1-1.4, thus excluding the two Bohemian species of Pridoli age Encrinur- aspisl subvariolaris concomitans Pfibyl and Vanek, 1962, and Encrinuraspis? testosteron Snajdr, 1981, which have higher ring-to-pleura ratios (R/P) of 1.6 and 1.8, respectively. Indeterminate encrinurine PI. 11, fig. 11 MATERIAL From AA 95 (Upper Silurian), Prongs Creek: 1 cranidium. DISCUSSION This single cranidium differs considerably from that of Balizoma aff. B. obtusus and of most other species of Balizoma in the following features: (1) twice as large; (2) glabella narrowing more strongly backward; (3) smaller, multituberculate lateral lobes; (4) tubercles on glabella and anterior border of cranidium double in number and much smaller in size; (5) smaller tubercles adaxially on fixigena. Balizoma is the genus that this cranidium most closely resembles, but the small tuber- cles and lateral glabellar lobes exclude this cranidium from that genus as currently understood. The lateral lobes are completely unlike Cromus, and the shape of the cranidium and features of the prosopon are unlike Encrinuraspis. 25 Family Calymenidae Milne-Edwards, 1840 Subfamily uncertain Indeterminate calymenid PI. 9, fig. 7 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 pygidium. DESCRIPTION Length 65 per cent width; convexity strong. Axis 35 per cent anterior width, 95 per cent length of pygidium, narrowing steadily backward to broadly rounded tip, composed of eight rings and a terminus. Ring furrows deep and broad anteriorly, becoming successively weaker toward back. Articulating half-ring and furrow well developed. Axial furrow deep, increasing in width toward back. Pleural lobe evenly convex; four strongly developed, flat-topped ribs curving outward and back- ward; fifth rib flanking axial furrow and directed back- ward. Interpleural furrows weak, dying out adaxially; pleural furrows strong. Articulating half pleura strong adaxially. Surface smooth. DISCUSSION It is impossible to assign this single pygidium to a genus or subfamily. Family Lichidae Hawle and Corda, 1847 Subfamily Lichinae Hawle and Corda, 1847 Genus Dicranopeltis Beyrich, 1845 TYPE SPECIES Lichas Scabra Beyrich, 1845, Liten Formation (Upper Silurian), Prague district, Czechoslovakia. Dicranopeltis sp. PI. 10, figs. 10-12 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 crani- dium, 1 pygidium. DESCRIPTION Cranidium strongly convex in both directions. Occipital ring incomplete. Occipital furrow as deep as axial fur- row. Median lobe narrowing slowly and steadily back- ward to about 50 per cent anterior width when opposite SI, and then expanding posteriorly; preoccipital de- pression connecting inner extremities of S 1 . Bullar lobe half length of cranidium, with strong independent con- vexity. LI and fixigena fused. Basal glabellar lobe absent. Longitudinal furrow deep and narrow. Axial furrow continuous with SI, curving gently inward to longitudinal furrow. Pygidium 65 per cent as long as wide. Axis strongly convex, 30 per cent anterior width, narrowing steadily backward, not pointed; three rings and furrows contin- uous across axis; a swollen terminus sloping downward and backward to depressed tip of axis. Axial furrows deep and narrow anteriorly, becoming shallow posteri- orly, convergent. Pleural lobe flattened; three pairs of furrowed pleurae ending in short, free points. Dou- blure gently convex; terrace ridges strong. Prosopon tuberculate, coarser on pygidium than on cranidium. DISCUSSION The cranidium resembles that of the type species D. scabra (Beyrich; see Barrande, 1852, pi. 28, figs. 22-26) in conformation and in the presence of the preoccipital furrow, but differs in the absence of basal glabellar lobes. The pygidium is distinctive in its long, swollen, and strongly segmented axis. Subfamily uncertain Indeterminate lichid PI. 7, figs. 16-20 MATERLVL From AA 95 (Upper Silurian), Prongs Creek: 3 crani- dia, 2 hypostomes, 5 pygidia. DISCUSSION This lichid material is too sparse to justify formal description. The two incomplete cranidia illustrated are similar in gross morphology, but have different prosopon features and slight differences in convexity of lobes and in courses of furrows; in both cranidia, the 26 longitudinal furrow is continuous anteriorly, and it is unknown whether a basal glabellar lobe was present or not. The specimens appear to belong to the subfamily Trochurinae (= Ceratarginae, see Thomas and Hol- loway, 1988). The two hypostomes would unhesitatingly be referred to the subfamily Trochurinae on account of the broad, unembayed posterior border and circum- scribed middle body. All the pygidia are remarkable in that they resemble Amphilichas (subfamily Tetralichi- nae, recorded only from the Ordovician System) in the pointed axis and absence of pleural furrows on the third pleurae; there is a small median embayment in the posterior margin, but no extended free point to the third pleura. These pygidia differ conspicuously from those of the Trochurinae in outline, in having an unswollen posterior band, and in the absence of a lat- eral border. At first sight, therefore, the pygidia belong to a different subfamily from that of the cranidia and hypostomes. A comparable conflict arises regarding the lichid described as Dicranogmus skinneri by Perry and Chat- terton (1977:308, pi. 6, figs. 16-21), from Cape Phillips Formation (Middle Silurian), Baillie-Hamilton Island, Canadian Arctic Archipelago. The cranidium of this species closely resembles that of the trochurine Dicra- nogmus pustulatus Hawie and Corda (1847:146, pi. 7, fig. 77a,b), the type species, from the Upper Silurian, Czechoslovakia, the hypostome and pygidium of which are unknown. The hypostome of D. skinneri is trochur- ine also. The pygidium isAmphilichas-like in its pointed axis and unfurrowed, flattened third pleurae. The origi- nal grounds for associating the parts, based on occur- rence and particularly on the prosopon, are convincing. Although the Prongs Creek and the Baillie-Hamilton Island specimens are dissimilar in many respects, these two enigmatic associations in northern Canada are unlikely to be coincidental. The Tetralichinae and Tro- churinae are sister subfamilies, and it may be that a rootstock persisted in this area into the Silurian Period. Subfamilies of the Lichidae are consistent in the morphology and comparative anatomy of the parts with the exception of the above examples and another sur- prising anomaly in the Cape Phillips Formation. This is the form described as Lichid n. gen., n. sp. (subfamily Ceratarginae) by Perry and Chatterton (1977:303, pi. 7, figs. 1-9), in which pygidia of Radiolichas type are associated with inappropriate cranidia. Family Odontopleuridae Burmeister, 1843 Subfamily Odontopleurinae Burmeister, 1843 Genus Leonaspis Richter and Richter, 1917 TYPE SPECIES Odontopleura leonhardi Barrande, 1846, Kopanina For- mation (Upper Silurian), Prague district, Czechoslo- vakia. Leonaspis semiglabra (Poulsen, 1934) PI. 12, figs. 1-13; PI. 13, figs. 13,14; Text-fig. 5D Ceratocephala (sens, lat.) groenlandica Poulsen, 1934:24, pi. 3, fig. 5 (non figs. 6,7). Ceratocephala (Leonaspisl) semiglabra Poulsen, 1934:25, pi. 3, fig. 8 (non fig. 9 = groenlandica). Leonaspis semiglabra — Raasch/n Raasch, Norford, and Wilson, 1961:474, fig. 4.10-18. Scutellum borealis — Raasch in Raasch, Norford, and Wilson, 1961:474, fig. 5.9 (non figs. 6-8). HOLOTYPE MMH 3261 (cranidium, figured by Poulsen, 1934, pi. 3, fig. 8; in this paper, PI. 13, fig. 13), Cape Schuchert Formation (Lower Silurian), Kap Schuchert, North Greenland. MATERIAL From AA 2-4.5 (Lower Silurian), Prongs Creek: 1 dor- sal shield, 8 cranidia, librigenae, 4 hypostomes, 11 pygidia. DESCRIPTION Cranidium 25 per cent length of dorsal shield, 60 per cent as long as wide, moderately convex. Glabella 80 to 85 per cent as wide as long. Occipital ring 20 per cent length of cranidium, without lobes or spines; occipital tubercle somewhat enlarged. Central lobe well defined by strong independent convexity, subparallel sided but constricted opposite LI and L2, expanding anteriorly; frontal lobe, where broadly rounded, 60 per cent width across LI. LI rounded, swollen, 30 per cent basal width of glabella. SI deep, oblique, widening at apodeme at extremity, shallow at back. L2 elongatedly ovate, swollen, 25 per cent glabellar width, circumscribed. S2 oblique, apodeme at extremity, thence running back- ward, shallowing at SI. L3 and S3 absent. Axial furrows strongly divergent backward, comparatively shallow. Anterior border uniformly short, transverse. Fixigena 15 per cent width of cranidium, narrowing steadily for- ward, gently convex. Eye ridge narrow (tr.), extending almost to posterior border furrow. 27 Librigena sloping outward. Eye sessile, posteriorly placed. Field broad, gently convex. Lateral border 20 per cent minimum width of field, widening backward. Lateral border furrow shallow. Genal spine curving backward and outward, extending as far as seventh thoracic segment. Seventeen or more outwardly directed lateral spines, hindmost on genal spine; ante- rior few spines shorter than width of border, squat, and blunt; subsequent spines longer than width of border and successively longer, slender, and pointed. Dou- blure smooth, extending to lateral border furrow. Hypostome subquadrate, squat, slightly wider than long. Middle body subquadrate, gently swollen, extend- ing to anterior margin. Middle furrow short, oblique. Lateral lobe half length of middle body abaxially, nar- row. Lateral border narrow, convex, widening and less swollen posterior to midlength; posterior wings project strongly, situated 60 per cent length from front. Lateral furrow very shallow alongside lateral lobe, broad and well defined posteriorly. Posterior border essentially transverse but bowed backward mesially, weakly convex. Thorax 55 per cent length of dorsal shield; nine tho- racic segments on disarticulated dorsal shield. Axis 30 per cent anterior width of thorax, arched transversely; lateral nodes well developed. Axial furrow shallow and broad. Pleura horizontal, comprising a short (exsag.), slightly swollen anterior band separated by a broad, shallow furrow from longer (exsag.) and much more swollen posterior band; posterior band terminating in a long, slender spine. Spines successively longer and more backwardly directed. A row of granules on poste- rior margin of rings; posterior bands of pleurae weakly granular. Pygidium, excluding spines, 30 to 35 per cent as long as wide. First ring and furrow strong. Second ring almost equally swollen; ring furrow dying out abaxially. Third ring stunted; posterior margin bowed backward. Axial furrow shallow alongside first ring, deep and broad posteriorly. Pleural lobe largely occupied by swollen rib running obliquely from opposite first ring to great spine. Lateral border widening backward, faintly developed at great spine. Five pairs of spines: foremost pair small; second and third pairs gradational in length to fourth pair (great spines); fourth pair twice sagittal length of pygidium; fifth pair as long as third pair. Prosopon consisting of tubercles of various sizes; a single row of tubercles on anterior border and eye ridge. DISCUSSION The holotype cranidium of L. semiglabra (Poulsen) is incomplete posteriorly, and it is not possible to be cer- tain whether occipital spines were present or not. The Road River Formation cranidia agree in other features, and we follow Raasch in Raasch, Norford, and Wilson (1961) in considering these cranidia conspecific with the L. semiglabra holotype. The holotype cranidium of L. groenlandica (Poulsen, 1934:24, pi. 3, fig. 6), also from Kap Schuchert, differs markedly from L. semigla- bra in its rounded anterior margin and broader fixigena. Only one form of the various odontopleurid skeletal elements is present in the Road River Formation mate- rial, indicating a single species. The librigena attributed to L. groenlandica by Poulsen (1934, pi. 3, fig. 5; this paper, PI. 13, fig. 14) corresponds to our material; it differs from the one referred to semiglabra by Poulsen (1934, pi. 3, fig. 9) in its narrower border and denser tuberculation. Indeterminate odontopleurine PI. 10, fig. 9 MATERIAL From BB 131 (Lower Silurian), Illtyd Range: 1 cranidium. DISCUSSION This cranidium differs from the cranidia attributed to L. semiglabra in having a more parallel-sided median glabellar lobe, a more convex frontal lobe, coarser tuberculation, and a nontuberculate adaxial portion of the fixigena. Although this specimen is probably attributable to Leonaspis, the generic reference is best left undecided. 28 Acknowledgements We thank Bob Owens, Alan Thomas, and Lars Ram- skold for information and opinions on some of these trilobites. Valdemar Poulsen of the University of Copenhagen kindly provided plaster casts of C. Poulsen's trilobite types from North Greenland. We thank Godfrey Nowlan of the Geological Survey of Canada for identification of the conodont faunas. Brian O'Donovan printed the trilobite photographs from our negatives. The figures were prepared by David Sargent and Ilgvars Steins. David Rudkin, Janet Waddington, and Joan Burke of the Royal Ontario Museum were very helpful with a variety of palaeontological, curato- rial, and editorial matters. This project was supported by NSERC Operating Grant A3825 to Rolf Ludvigsen. 29 Literature Cited ANGELIN, N. P. 1851 Palaeontologia Svecicae. I: Iconographia crusta- ceorum formationis transitionis. Holmiae. Fasc. 1:1-24. 1854 Palaeontologia Scandinavica. I: Crustacea forma- tionis transitionis. Academiae Regiae Scientar- ium Suecanae, Holmiae, pp. 21-92. BARRANDE, J. 1846 Notice preliminaire sur le Systeme Trilobites de Boheme. 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United States Geological Survey, Bulletin 63:1- 177. WEBBY, B. D., H. T. MOORS, and R. A. McLEAN 1970 Malongullia and Encrinuraspis, new Ordovician trilobites from New South Wales, Australia. Jour- nal of Paleontology 44:881-887. WESTROP, S. R. 1983 The life habits of the Ordovician illaenine trilo- bite ^MWfl^to/rfe*. Lethaia 16:15-24. WHITTINGTON, H. B. 1959 Silicified Middle Ordovician trilobites: Remo- pleurididae, Trinucleidae, Raphiophoridae, 32 Endymioniidae. Harvard Museum of Compar- ZENKER, J. C. ative Zoology, Bulletin 121:371-496. 1833 Beitrage zur Naturgcschichtc dor Urwclt. Organ- wu, H. ische Restc (Petrefecten) aus der Altcnburger 1977 Comments on new genera and species of Silurian- Braunkohlen-Formation dem Blankenburger Devonian trilobites in southwest China and their Ouadersandstein, jenaischen bunten Sandstein significance. Acta Palaeontologia Sinica 16:95- und bohmischen Uebergangsgcbirge. Jena. 67 pp. 117. 33 Plate 1, figs. 1-15. Paracybantyx asulcatus gen. et sp. nov., locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1-3. Cranidium, dorsal, frontal, and oblique views, ROM 45343, x 2. 4,5. Holotype cranidium, lateral and dorsal views, ROM 45344, x 4. 6. Cranidium, dorsal view, ROM 45376, x 3. 7-9. Cranidium, dorsal, frontal, and oblique views, ROM 45330, x 4. 10,11. Pygidium, lateral and dorsal views, ROM 45342, x 2. 12. Hypostome, latex impression, ventral view, ROM 45375, x 6. 13,14. Pygidium, lateral and dorsal views, ROM 45360, x 2. 15. Pygidium, lateral view enlarged to show prosopon, ROM 45360, x 4. 34 13 Plate 2, figs. 1-12. Kosovopeltis borealis (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1,2. Complete specimen, dorsal views, ROM 42143, x 4. 3. Librigena, ventral view, ROM 42144, x 3. 4. Rostral plate, ventral view, ROM 42145, x 4. 5,6. Cranidium, dorsal and oblique views, ROM 42146, x 4. 7. Hypostome, ventral view, ROM 42147, x 9. 8. Hypostome, ventral view, ROM 42148, x 9. 9. Cranidium, dorsal view, ROM 42149, x 9. 10. Pygidium, latex impression, dorsal view, ROM 42150, x 9. 11. Pygidium, dorsal view, ROM 42151, x 1.4. 12. Pygidium, dorsal view, ROM 42152, x 1.4. 36 Plate 3, figs. 1-10. Kosovopeltis borealis (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1. Cranidium, latex impression, dorsal view, ROM 42153, x 4. 2. Pygidium, latex impression, dorsal view, ROM 42154, x 1.7. 3-5. Cranidium with rostral plate, dorsal, anterior, and ventral views, ROM 42155, x 2. 6. Librigena, dorsal view, ROM 42156, x 3. 7. Pygidium, latex impression, ventral view, ROM 42157a, x 1.7. 8. Slab crowded with pygidia, ROM 42157, x 1. 9. Librigena, dorsal view, ROM 42158, x 4. 10. Cranidium, latex impression, dorsal view, ROM 42159, x 4. 38 Plate 4, figs. 1-14. Figs. 1-13. Kosovopeltis borealis (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1,2. Protaspis, latex impression, dorsal and oblique views, ROM 42160, x 56. 3,4. Meraspid cranidium, oblique and dorsal views, ROM 42161, x 24. 5. Transitory pygidium with one protothoracic segment attached, dorsal view, ROM 42162, x 12. 6,7. Transitory pygidium with two protothoracic segments attached, latex impression, dorsal and oblique views, ROM 42163, x 12. 8,9. Internal mould of lens surface of holaspid eye, ROM 42164, x 100 and x 500. 10,11. Transitory pygidium, latex impression, oblique and dorsal views, ROM 42165, x 50. 12,13. Smallest transitory pygidium, ROM 42166, x 56 and x 92. Fig. 14. Otarion {Songkania) socialis (Poulsen), locality AA 2-4.5, Road River Formation, Prongs Creek, Yukon Territory, Canada, hypostome, ventral view, ROM 42204, x 24. 40 Plate 5, figs. 1-16. All specimens are from locality BB 131, unnamed carbonates, Illtyd Range, Yukon Territory, Canada. Figs. 1-11. Stenopareia illtyd sp. nov. 1,2. Cranidium, dorsal and oblique views, ROM 42167, x 3. 3,4. Holotype cranidium, dorsal and anterior views, ROM 42168, x 3. 5,6. Cranidium, dorsal and anterior views, ROM 42169, x 3. 7. Pygidium, dorsal view, ROM 42170, x 9. 8,9. Pygidium, dorsal and lateral views, ROM 42171, x 4. 10,11. Pygidium, dorsal and oblique views, ROM 42172, x 5. Fig. 12. Indeterminate illaenid, cephalon, dorsal view, ROM 42173, x 3. Figs. 13,14. Indeterminate bumastine, cranidium, dorsal and anterior views, ROM 42174, x 9. Figs. 15,16. Cheirurus sp., cranidium, lateral and dorsal views, ROM 42175, x 5. 42 Plate 6, figs. 1-24. Figs. 1-14. Hedstroemia kutchini sp. nov., locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1,2. Cranidium, dorsal and oblique views, ROM 45371, x 5. 3,4. Holotype cranidium, dorsal and oblique views, ROM 45347, x 6. 5. Cranidium, dorsal view, ROM 45348, x 6. 6,7. Pygidium, dorsal and lateral views, ROM 45334, x 4. 8. Pygidium, dorsal view, ROM 45335, x 4. 9,10. Pygidium, dorsal and lateral views, ROM 45328a, x 4. 11. Librigena, dorsal view, ROM 45372, x 6. 12. Librigena, latex impression, dorsal view, ROM 45358, x 5. 13. Hypostome, ventral view, ROM 45329, x 8. 14. Hypostome, ventral view, ROM 45370, x 8. Fig. 15. Indeterminate proetid A, locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada, hypostome, ventral view, ROM 45338b, x 8. Figs. 16-24. Hedstroemia sourdoughi sp. nov., locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada. 16. Pygidium, dorsal view, ROM 45333, x 4. 17-19. Pygidium, posterior, lateral, and dorsal views, ROM 45331, x 6. 20. Pygidium, dorsal view, ROM 45323, x 5. 21. Cranidium, latex impression, dorsal view, ROM 45357, x 4. 22,23. Holotype cranidium, dorsal and oblique views, ROM 45332, x 4. 24. Cranidium, dorsal view, ROM 45326, x 6. 44 Plate 7, figs. 1-20. Figs. 1-15. Prantlia vagrans sp. nov., locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1. Cranidium, dorsal view, ROM 45339, x 4. 2. Cranidium, dorsal view, ROM 45340, x 4. 3. Cranidium, latex impression, dorsal view, ROM 45353, x 6. 4. Cranidium, dorsal view, ROM 45365, x 6. 5. Librigena, showing narrow doublure, ventral view, ROM 45327, x 5. 6,7. Holotype pygidium, dorsal and oblique views, ROM 45363, x 6. 8. Pygidium, dorsal view, ROM 45337, x 4. 9. Pygidium, dorsal view, ROM 45336a, x 4. 10. Meraspid cranidium, latex impression, ROM 45351, x 8. 11. Pygidium, showing narrow doublure, ventral view, ROM 45364, x 4. 12. Pygidium, dorsal view, ROM 45328b, x 4. 13. Pygidium, dorsal view, ROM 45341, x 5. 14. Librigena, oblique view, ROM 45338a, x 5. 15. Librigena, latex impression, oblique view, ROM 45355, x 4. Figs. 16-20. Indeterminate lichid, locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada. 16. Pygidium, dorsal view, ROM 45361, x 2. 17. Pygidium, dorsal view, ROM 45366b, x 2. 18. Cranidium, dorsal view, ROM 45349, x 5. 19. Cranidium, dorsal view, ROM 47356, x 5. 20. Hypostome, latex impression, ventral view, ROM 45354, x 5. 46 Plate 8, figs. 1-12. Otarion (Songkania) socialis (Poulsen), locality AA 2-4.5, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1,2. Complete specimen, dorsal and oblique views, ROM 42176, x 7.5. 3,4. Cranidium, dorsal and anterior views, ROM 42177, x 9. 5. Complete specimen lacking axial spine on sixth segment, dorsal view, ROM 42178, x 7.5. 6,7. Complete specimen with axial spine on sixth segment, dorsal and oblique views, ROM 42179, X 6. 8. Cephalon and thorax with axial spine on sixth segment, oblique view, ROM 42180, x 5. 9. Librigena, oblique view, ROM 42181, x 9. 10,11. Complete specimen, dorsal and oblique views, ROM 42182, x 7.5. 12. Librigena, oblique view, ROM 42183, x 9. 48 Plate 9, figs. 1-11. All specimens are from locality BB 131, unnamed carbonates, Illtyd Range, Yukon Territory, Canada. Figs. 1-3. Scotoharpes raaschi Norford, 1973. 1,3. Cephalon, dorsal and oblique views, ROM 42184, x 5. 2. Cephalon, latex impression, dorsal view, ROM 42185, x 5. Figs. 4,5. Indeterminate proetid B. 4. Hypostome, ventral view, ROM 42186, x 5. 5. Cranidium, dorsal view, ROM 42187, x 5. Fig. 6. Encrinuraspis sp., pygidium, dorsal view, ROM 42188, x 9. Fig. 7. Indeterminate calymenid, pygidium, dorsal view, ROM 42189, x 4. Figs. 8-11. Kosovopeltisl spp. 8. Pygidium, dorsal view, ROM 42190, x 5. 9. Cranidium, dorsal view, ROM 42191, x 9. 10. Pygidium, dorsal view, ROM 42192, x 4. 11. Pygidium, dorsal view, ROM 42193, x 4. 50 Plate 10, figs. 1-12. Figs. 1-8. Cromus princeps (Poulsen), locality AA 2-4.5, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1,2. Cranidium, oblique and dorsal views, ROM 42194, x 4. 3. Hypostome, ventral view, ROM 42195, x 9. 4. Librigena, oblique view, ROM 42196, x 5. 5. Pygidium (deformed), dorsal view, ROM 42197, x 9. 6. Cranidium, dorsal view, ROM 42198, x 9. 7. Pygidium, dorsal view, ROM 42199, x 4. 8. Pygidium, dorsal view, ROM 42200, x 4. Fig. 9. Indeterminate odontopleurine, locality BB 131, unnamed carbonates, Illtyd Range, Yukon Territory, Canada, cranidium, dorsal view, ROM 42201, x 9. Figs. 10-12. Dicranopeltis sp., locality BB 131, unnamed carbonates, Illtyd Range, Yukon Territory, Canada. 10,11. Cranidium, dorsal and oblique views, latex impression, ROM 42202, x 9. 12. Pygidium, dorsal view, ROM 42203, x 9. 52 Plate 11, figs. 1-18. Figs. 1-5. Paracybantyx asulcatus gen. et sp. nov., locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1. Pygidium, dorsal view, ROM 45345, x 2. 2. Librigena, ventral view showing pit in doublure, ROM 45366a, x 4. 3. Librigena, latex impression, oblique view showing doublure, ROM 45352, x 4. 4. Pygidial doublure, latex impression, ventral view, ROM 45374, x 4. 5. Pygidium, dorsal view, ROM 45369, x 6. Figs. 6,7. Indeterminate scutelluine, locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada, cranidium, dorsal view, ROM 45359, x 4 and x 8. Figs. 8-10, 12-18. Balizoma aff. B. obtusus (Angelin), locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada. 8. Pygidium, dorsal view, ROM 45325, x 6. 9,10. Pygidium, latex impression, oblique and dorsal views, ROM 45350, x 4. 12. Cranidium, dorsal view, ROM 45336b, x 4. 13,14. Pygidium, dorsal and lateral views, ROM 45324, x 4. 15,16. Pygidium, posterior and dorsal views, ROM 45367, x 4. 17,18. Hypostome, oblique and ventral views, ROM 45362, x 6. Fig. 11. Indeterminate encrinurine, locality AA 95, Road River Formation, Prongs Creek, Yukon Territory, Canada, cranidium, dorsal view, ROM 45373, x 3. 54 Plate 12, figs. 1-16. Figs. 1-13. Leonaspis semiglabra (Poulsen), locality AA 2^.5, Road River Formation, Prongs Creek, Yukon Territory, Canada. 1. Cranidium, latex impression, dorsal view, ROM 42205, x 9. 2. Hypostome, ventral view, ROM 42206, x 9. 3. Pygidium, dorsal view, ROM 42207, x 9. 4. Cranidium, latex impression, dorsal view, ROM 42208, x 9. 5. Cranidium, latex impression, dorsal view, GSC 15399, x 9. 6. Cranidium, latex impression, dorsal view, GSC 15398, x 9. 7. Cranidium, latex impression, dorsal view, ROM 42209, x 9. 8. Pygidium, dorsal view, GSC 15700, x 9. 9. Pygidium, dorsal view, GSC 15701, x 9. 10. Pygidium, dorsal view, ROM 42210, x 9. 11. Librigena, oblique view, ROM 42211, x 9. 12. Pygidium, dorsal view, ROM 42212, x 9. 13. Incomplete specimen, dorsal view, ROM 42213, x 6. Figs. 14—16. Otarion (Songkania) socialis (Poulsen), locality AA 2-4.5, Road River Formation, Prongs Creek, Yukon Territory, Canada. 14. Cranidium, dorsal view, GSC 15392, x 9. 15. Pygidium, dorsal view, ROM 42214, x 9. 16. Pygidium, dorsal view, GSC 15393, x 9. 56 Plate 13, figs. 1-14. Figs. 1,2. Kosovopeltis borealis (Poulsen), Cape Schuchert Formation of Poulsen (1934), Kap Schu- chert. North Greenland. 1. Holotype cranidium, dorsal view, MMH 3267, x 3. 2. Cranidium, dorsal view, MMH 3268, x 3. Figs. 3-6. Otarion (Songkania) socialis (Poulsen), Cape Schuchert Formation, Kap Schuchert, North Greenland. 3,4. Holotypecranidium, dorsal and anterior views, MMH 3251, x 9. Note caecae crossing preglabel- lar field abaxially. 5. Librigena, oblique view, MMH 3252, x 6. 6. Pygidium, dorsal view, MMH 3253, x 9. Figs. 7-12. Cromus princeps (Poulsen), Cape Schuchert Formation, Kap Schuchert, North Greenland. 7. Pygidium, dorsal view, MMH 3278, x 3. 8. I^gidium, dorsal view, MMH 3279, x 3. 9. Pygidium, dorsal view, MMH 3280, x 3. 10,11. Holotype cranidium, dorsal and oblique views, MMH 3276, x 4. 12. Librigena, oblique view, MMH 3277, x 3. Figs. 13,14. Leonaspis semiglabra (Poulsen), Cape Schuchert Formation, Kap Schuchert, North Greenland. 13. Holotype cranidium, dorsal view, MMH 3261, x 9. 14. Librigena, oblique view, attributed to L. groenlandica by Poulsen, MMH 3258, x 9. 58 Life Sciences Contributions are a numbered series of scientific publications of varied subject matter published by the Royal Ontario Museum. Most recent contributions include: 145 An Annotated Checklist of the Fishes of the Chagos Archipelago, Central Indian Ocean Richard Winterbottom, Alan R. Emery, and Erling Holm 1989, 226 pp., ill., $48.50, ISBN 0-88854-329-8 146 Stipatocrinus, a New and Unusual Camerate Crinoid from the Lower Silurian of Western New York James D. Eckert and Carlton E. 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