A Revision of the Upper Ordovician Trilobite Genus Erratencrinurus with a Description of a New Species from Hadeland

A revision of the upper Ordovician trilobite genus Erratencrinurus with a description of a new species from Hadeland

ALAN W. OWEN & RACHEL A. HEATH

Owen, A. W. & Heath, R. A.: A revision of the upper Ordovician trilobite genus Erratencrinurus with a description of a new species from Hadeland. Norsk Geologisk Tidsskrift, Vol. 69, pp. 225--233. Oslo 1989. ISSN 0029-196X.

Two subgenera are recognized in Erratencrinurus: E. (Erratencrinurus) and E. (Ce/tencrinurus) each containing two species groups. A third group of taxa here termed E. (sensu lato) comprises a mid Caradoc to late Ashgill stock which retains many of the characters of the oldest known species of Erratencrinurus, E. (s.l.) spicatus (Tripp). This species is also closest to the probably ancestral Encri nuroides torulatus-Encrinuroides uncatus line age. Erratencrinurus ( Erratencrinurus) inopinatus sp. nov. is described from a newly discovered, unusually diverse fauna in the upper Ashgill (probably Rawtheyan) Kalvsjø Fm. in the Hadeland district of the Oslo Region.

A. W. Owen, Department of Geology and App lied Geology, The University, Glasgow G/2 BQQ, Scotland; R. A. Heath, Department of Geo/ogy, The University, Dundee DDI 4HN, Scot/and.

The upper Ordovician (?Rawtheyan) Kalvsjø Fm. the recognition of species groups and subgenera in Hadeland is largely a limestone unit and has within Erratencrinurus. This pa per addresses hitherto yielded few trilobites. This is in marked these problems and is undertaken in conjuction contrast to the underlying, more argillaceous, with Owen's revision of the Encrinuridae for the Kjørrven Fm. which contains at least 26 trilobite Treatise on Invertebrate Paleontology and · species (Owen 1978; 1981 Table 1). However, Heath's study of the latest Ordovician-early Silu road widening excavations north of Sverigetjern rian stratigraphy and sedimentology in Hadeland. [NM80908620] in 1988 exposed several metres of fossiliferous shales, siltstones and impure lime stones containing species of the trilobites Bra chyaspis, Stygina, Prionocheilus, Toxochasmops, Systematic palaeontology an indeterminate lichid and Erratencrinurus. Other elements of the fauna comprise at least The encrinurine terminology used herein is essen nine brachiopod species, streptelasmatid corals, tially that of Evitt & Tripp (1977) but the glabellar crinoids and stick bryozoans. Most of the genera tubercle notation is Iargely that of Strusz (1980, in this fauna are also known from the underlying pp. 3-5) with the minor modifications suggested Kjørrven Fm. suggesting a localized, brief, return by Owen (1981, pp. 47--48). Thus rows of to similar environmental conditions. Whilst the tubercles are numbered O, l, 2, 3 etc. away from other trilobites are too incompletely known for the sagittal line. Each row of tubercles on the specific identification, it is clear that the Erra posterior part of the glabella is related to the pair tencrinurus species is new and is not E. ( E.) of lo bes or furrows which it links. Longitudinally brutoni which occurs abundantly in the underlying paired tubercles are indicated by a pair of formation. asterisks, e.g. 2L-O;. As noted by Edgecombe & Erratencrinurus is known from the mid-Cara Chatterton (1987, p. 344) this tubercle ter doc to late Ashgill of Laurentia, Baltica and the minology is descriptive, not necessarily based on Anglo-Welsh area. Specificdifferentiation is rela precise homologies, and is essentially based on tively easy as it is largely based on semi-quanti the condition in adult specimens. It is accepted, tative criteria such as cephalic tuberculation and however, that a degree of variation, including pygidial segmentation. However, analysis of the ontogenetic migration of tubercle position may Kalvsjø Fm. material has highlighted problems of be present in a species. The specimens from Hade- 226 A. W. Owen & R. A. Heath NORSK GEOLOGISK TIDSSKRIFT 69 (1989) land are housed in the Paleontologisk Museum, vector. Temple & Tripp (1979, p. 244) suggested Oslo (PMO). that this might best be expressed at subgeneric level; a view supported in principle by Strusz (1980, p. 9) who none the less maintained separate genera. Owen (1981, p. 48) formally recognized Family ENCRINURIDAE Angelin, 1854. the two groups as subgenera and described three Subfamily ENCRINURINAE Angelin, 1854 new species from the Ashgill of the Oslo Region: Genus Erratencrinurus Krueger, 1971 E. (E.) imperfectus, E. (E.) brutoni andE. (C.)

Type species. - Subsequently designated Krueger kiaeri. Lesperance & Tripp (1985) also adopted (1972), Erratencrinurus capricornu Krueger, this taxonomic position but restricted the concept 1971, pp. 1147-1149, pl. 6, figs. l, 2; pl. 7, figs. of Erratencrinurus (Celtencrinurus) to exclude 1-3; text-figs. l, 3G, 13, 14, from glacial erratics (inter alia) E. praecursor and E. kiaeri. These of the Rakvere Stage (F) (upper Caradoc, were reassigned to Erratencrinurus (s.J.). approximately Marshbrookian-Actonian) near The use of a weakly constrained sensu lato Binz (Rostock district), East Germany. grouping is clearly undesirable but there are some instances in trilobite taxonomy where it has been Historical background. - The genus Erraten a necessary, pragmatic approach. The late Ordo crinurus was established by Krueger (1971) for a vician species of Calymene (see lngham 1977, p. group of species bearing glabellar spines occurring 98) and some species of Harpidella (see Owen & in Pleistocene erratics of mid to late Caradoc Bruton 1980, p. 19) are notable examples. The age in the Baltic area. With the exception of E. problem in Erratencrinurus is emphasized by the seebachi (Schmidt) these species were also new, Jack of consensus in the placement of some species namely E. capricornu, E. kauschi, E. nebeni, E. even before Lesperance & Tripp's restricted diag ceras, E. kummerowi andE. paetzensis. Krueger nosis of E. (Celtencrinurus). Thus, for example, also described three Ashgill species from erratics 'Encrinurus' cornutus was ascribed to Celten which he ascribed to Encrinurus: E. melzenensis crinurus by Evitt & Tripp (1977) and Strusz Krueger, E. moe Mannil and E. striatus (1980), Erratencrinurus (Erratencrinurus) by (Angelin). The latter two had previously been Owen (1981) and plotted with other members described from in situ in Estonia and Sweden, of the latter group in Temple & Tripp's (1979) respectively. analysis. 'Encrinurus' kingi Dean was assigned Evitt & Tripp (1977, p. 120) considered that to Erratencrinurus by McNamara (1979) and E. Erratencrinurus was derived from the North (Erratencrinurus) by Owen (1981) but to Cel American Encrinuroides torulatus-Encrinuroides tencrinurus by Strusz (1980). uncatus Jineage as was another new genus, Cel The new species from Hadeland apparently tencrinurus. This genus was essentially the Encri Jacks glabellar spines which hitherto have been nurus punctatus group of species from the upper considered diagnostic of Erratencrinurus (Erra Caradoc and Ashgill of Scotland, Northern Ire tencrinurus) by several authors. However, it has land and E. Canada (Tripp 1957). Added to this a tubercle pattern which is much closer to mem was Encrinuruscornutus lngham, 1974, from the bers of that group than to species of Erra mid-Ashgill of Northern England. Celtencrinurus tencrinurus (Celtencrinurus). It highlights the fact was thus defined as compnsmg C. that there are no individual diagnostic criteria multisegmentatus(Portlock) (the type species), C. distinguishing groups within Erratencrinurus.The trispinosus (Reed), C. laurentinus (Twenhofel), recognition of subgenera and species groups must C. lamonti (Tripp), C. praecursor (Tripp) and C. rest on combinations of characters. An appreci cornutus (lngham). ation of possible phylogenies also helps greatly. The multivariate analysis of the Encrinurinae undertaken by Temple & Tripp (1979) showed Groupings within Erratencrinurus. - Fig. l shows the two gtoups of species previously assigned to features of the cranidium and pygidium shared by Erratencrinurus and Celtencrinurus were clearly groups of species within Erratencrinurus. Charac separated from other members of the subfamily ters common to all species (such as tuberculiform on the second eigenvector of the Principal Com glabellar lobes L2 and L3 and the presence of 3L- ponent Analysis. The two groups showed some 1 tubercles) are not included. Most of the features separation from each other on the third eigen- have been used in earlier diagnoses of Erra- NORSK GEOLOGISK TIDSSKRIFf 69 (1989) Ordovician trilobite from Hadeland 227

Taxa ...... inopinatus nov . .." " c. cornutus 9-11 •..• .. "o � seebachi 9-11 �"'...... 36 11 • • ku mmerowi .. .Q .. . � .. nebeni 9-11 t.i kause hi l 25 8-10 ? 1 o ' v/gl/ans 28 ...... " c. ceras .. "o " � .-: Cl paetzensis .. " � ".. .. capricornu 8 • o .. 10 ... ".... imperfectus .. Q, �- brutoni 11-13 lli"

...... "., trispinosus 31 12 .... " -�!! /aurentinus 40 15 o:c. " 11 ..�Ila. o perceensis e.a multi- 12-13 .....

.. A 21 8 .." � sp. "o .,_ sp. B ·� � � ... " melzens is .. "' c: • Q) .. 25 11 .. _"' kingi Lu striatus 26 11-12

Fig. l. The distribution of selected cranidial and pygidial characters in species of Erratencrinurus. Horizontal shading indicates the presence of a character, dots its absence. E. (s.l.) sp. A andE. (s.l.) sp. Bare the indeterminate species described by Tripp (1974) and Lesperance & Tripp (1985) respectively. Approximate tempora( succession within each lineage indicated by arrows.

tencrinurus and Celtencrinurus (at generic or single 3S-Otubercle is present in some specimens, subgeneric leve!) and the terms are Iargely self thus marking the anterior corner of an 'open' evident. The exception is the 'Ll-S2 pentagon', pentagon. Some morphological features such as which refers to the arrangement of tubercles on the degree of asymmetry in glabellar tuber the posteromesial part of the glabella of some culation, the shape of L l and Sl and the presence species. Tubercles lL-1 (or lS-1), 2L-1 and a of weak tubercles on the pygidial axis have been sagitally arranged 2L-O pair mark the corners used as diagnostic criteria by earlier workers but and, in the case of the posterior 2L-O tubercle, do not vary in any consistent way and have been the centre of the pentagon. In one instance, E. excluded from Fig. l. (E.) cornutus, there are no 2L-Otubercles, but a 'Encrinurus'spicatus Tripp, 1974 from the mid- 228 A. W. Owen & R. A. Heath NORSK GEOLOGISK TIDSSKRIFT 69 (1989)

Caradoc of Wisconsin, provided the link between may have occurred independently in different both E. (Erratencrinurus)andE. (Celtenbrinurus) groups and reversals to the 'primitive' condition and the other encrinurines on Temple & Tripp's are evident in the later histories of some lineages. (1979) PCA ordination of species. It was assigned In view of this, the Jack of ontogenetic infor to Celtencrinurus by Strusz (1980) andE. (Erra mation, the incomplete knowledge of some tencrinurus) by Owen (1981) thus emphasizing species and the stratigraphical uncertainties similarities to both groups as it is both a mor inherent in several species being known on! y from phological and tempora! intermediate between glacial erratics, a rigorous cladistic or strato them and the probably ancestral Encrinuroides phenetic analysis of Erratencrinurus is not under torulatus-Encrinuroides uncatus lineage. It and taken. None the less, a possible phylogenetic several other species are here considered to scheme is shown on Fig. 2. belong in Erratencrinurus but represent a stock In order to avoid a formal taxonomy which is or stocks (E. (sensu lato)) which may have given too divisive and yet conserve established names, rise to the two named subgenera in the mid Erratencrinurus (Erratencrinurus) and E. (Cel Caradoc. E. (s.l.) sp. A (= Encrinurus sp. of tencrinurus) are here de fined and each considered Tripp 1974) fromthe same gross unit (the Galena to contain two species groups. A revised diagnosis Fm.) asE. (s.l.) spicatushas a 28-0 tubercle and of the genus as a whole is not given here as it thus approaches the Ll-S2 pentagonal arrange must await the revision of the other encrinurine ments of tubercles of E. (E.) nebeni and its allies. genera. Subgeneric diagnoses are restricted to It may therefore be a link with that group of characters distinguishing the subgenera from each species. other and from the species included in E. (s.l.). The features of Erratencrinurus (s.l.) spicatus the nominate subgenus is considered last as it could be viewed as representing the primitive precedes the description of the new species from condition for the genus but some 'derived' states Hadeland.

E "• t •ncrinuru • l Err• t •nc, ;nu, usJ E Erratenctinutus (Cettencrinurus) - rratenctinurus ______r- --,- ______--... C s.l. J capticornu multise gmentatus nebeni group kl ae ti group group gro up

inopinatus kiae ti ttispinosus sp. nov. sttiatus btu toni l laurentinus l l perce ensis cotnu tus kingi multise gmentatus l lamonti mefzensis impe tfectus moe

se ebachi sp. B

capricornu l l ku mmerowi. pae tzensis l c et as nebenil

pr ae cursor rlgllans sp. � spicatus

Fig. 2. Suggested phylogeny of species of Erratencrinurus showing the groupings recognized herein. Precise mid-Caradoc age of

E. (s.l.) spicatus not known nor are the relative positions of Caradoc species of E. (Erratencrinurus). E. (s.l.) sp. A ( = Encrinurus sp. of Tripp 1974) may betong to the main lineage of that group or (as shown here) to a side branch possibly leading to E. (Erratencrinurus). E. (s.l.) sp. Bis E. (s.l.) sp. of Lesperance & Tripp 1985. NORSK GEOLOGISK TIDSSKRIFf 69 (1989) Ordovician trilobite from Hadeland 229 Subgenus Erratencrinurus (Celtencrinurus) Evitt (s.l.) kingi (Dean), E. (s.l.) melzensis (Krueger),

& Tripp, 1974. E. (s.l.) striatus Angelin, E. (s.l.) sp. A ( = En crinurussp. of Tripp 1974), andE. (s.l.) sp. B. Type species. - Original designation, Calymene ( = Erratencrinurus (s.l.) sp. of Lesperance & multisegmentatusPortlock, 1837, p. 6, pl. 2, Fig. Tripp 1985). 7, from the Killey Bridge Fm. (Cautleyan), Pomeroy, Co. Tyrone, Northern Ireland (see Occurrence and range. - Middle and upper Cara Tunnicliff 1978). doc of North America, middle Ashgill (Caut leyan) of N. England, Ashgill (precise leve! not Included species. - E. (C) multisegmentatus known) of Sweden and the Baltic area. (Portlock), E. (C) lamonti (Tripp), E. (C) per ceensis(Cooper), E. (C)laurentinus (Twenhofel), Discussion. - These species have the glabella E. (C) trispinosus (Tripp), E. (C) praecursor parallel-sided or expanding anteriorly, bearing (Tripp), E. (C) moe (Mannil), E. (C) kiaeri about 23-35 large tubercles most of which are Owen. symmetrically arranged. L1 is ridge-like. A lL-1 tubercle dose to sagittal line invariably present Occurrence and range. - Upper Caradoc to upper but median tubercles are very uncommon oppo Ashgill (Rawtheyan) of the Scoto-Appalachian site Ll-L3. The pygidium has only about 21-26 area (Scotland, N. Ireland, E. Canada) lower axial rings and 6-12 pleural ribs. Ashgill of Estonia, Rawtheyan of Norway. Although geographically dispersed, the mem bers of this group retain most of the 'primitive' Diagnosis. - Glabella narrow posteriori y, expand characters of its oldest member E. (s.l.) spicatus. ing in front of S2, bearing 20-40 large sym The only species with a median tubercle on the metrically arranged tubercles but not spines. posterior part of the glabella are E. (s.l.) sp. A Tubercles lL-0 and immediately adjacent lL-1 from the Galena Fm. in Iowa which has a 2S-O invariably present as are 2L-Oand 3L-O in all but tubercle and E. (s.l.) spicatus from the Boda the oldest part of the Scoto-Appalachian lineage. Limestone of Siljan, Sweden where lL-0 is Posterior cranidial border tuberculate in some present. The posterior border of the cranidium is species. Pygidium bearing about 26-40 axial rings tuberculate in the Caradoc species E. (s.l.) spi and 10-15 pleural ribs. catus andE. (s.l.) sp. B and (distally only) in E. (s.l.) melzensis, the precise Ashgill age of which Discussion. - Erratencrinurus (Celtencrinurus) is not known. The posterior border of the Caut comprises two species groups (Figs. l & 2). The leyan E. (s.l.) kingi is smooth. Although some more primitive of these is the upper Caradoc species are incompletely known, the upper Cara to up per Ashgill lineage leading from E. (C) doc and Ashgill species have a greater number praecursor from Scotland through the Estonian of glabellar tubercles, pygidial axial rings and E. (C) moe toE. (C) kiaeri from Norway. Like pygidial pleural ribs than does E. (s.l.) spicatus. E. (s.l.) spicatus and its allies, members of this There are a few axial tubercles on the pygidium species group Jack 2L-O and 3L-O tubercles and of E. (s.l.) spicatus. and E. (s.l.) sp. A but not have a tuberculate posterior cranidial border. on those of E. (s.l.) kingi and E. (s.l.) striatus. These features contrast with those of the probable Pygidia of the other species have not been rec derivative of this primitive group, the Ashgill orded. Scoto-Appalachian species which constituted Lesperance & Tripp's (1985) more restricted con Subgenus Erratencrinurus ( Erratencrinurus) cept of E. (Celtencrinurus). This latter gro up also Krueger, 1971. consistently has eight tubercles on the anterior Type species. - As for genus. cranidial border as does E. (C. ) praecursor but Included species. - E. (E.) capricornu Krueger, not E. (C. ) moe and E. (C.) kiaeri which have E. (E.) ceras Krueger, E. (E. ) imperfectusOwen, ten. Only E. (C.) laurentinus and E. (C.) tri E. (E.) brutoni Owen, E. (E. ) kauschi, Krueger, spinosus have axial tubercles on the pygidium. E. (E. ) nebeni Krueger, E. (E. ) kummerowi Krueger, E. (E. ) seebachi (Schmidt), E. (E.) Erratencrinurus (sensu lat o) cornutus (lngham), E. (E.) inopinatus sp. nov. Included species. - E. (s.l.) spicatus (Tripp), E. andE. (E. ?) vigilans (Hall). 230 A. W. Owen & R. A. Heath NORSK GEOLOGISK TIDSSKRIFT69 (1989)

Occurrence and range. - Mid/upper Caradoc but only extends across the glabella in E. (E.) (approximately Woolstonian to Actonian) of the paetzensis. The anterior part of the cranidium and Baltic area, Ashgill (Pusgillian to Rawtheyan) of the pygidium are unknown or very poorly known Norway, mid Ashgill (Cautleyan) of N. in E. (E. ) ceras and E. (E.) paetzensis, thus England, ?Mid Caradoc of Eastern North Amer preventing generalization being made on the mor ica. phology of these areas. E. ( E.) capricornu and E. (E. ) imperfectus have eight tubercles on the Diagnosis. - Glabella expanding forwards bearing anterior cranidial border (the 'primitive' state for 30-50 large glabellar tubercles, most symmetri the genus) but the youngest species, E. (E.) cally arranged and one or more extended as spines brutoni, has ten. The pygidia of these three (? except in the youngest species unequivocally species lack axial tubercles and show a progressive ascribed to the subgenus, E. (E.) inopinatus sp. increase in the number of pleural ribs. nov). Tubercle lL-1 present in one species group and 2L-O (rarely 2S--O) in the other group. The latter also has a pentagonal arrangement of tubercles on the posterior part of the glabella whereas the former has only a very sparse tuber The E. ( E.) nebeni gro up culation here. Posterior border of cranidium This group includes the mid-upper Caradoc Baltic smooth. Pygidium bearing about 25-36 axial rings species E. (E. ) kauschi, E. (E.) nebeni, E. and 8-13 pleural ribs. Erratencrinurus ( E.?) vigi (E. ) kummerowi and E. (E. ) seebachi and prob lans Hall - see Ludvigsen 1979, Fig. 27) from the ably gave rise to E. (E. ) cornutus from the Caut Trenton Group of New York and Ontario (mid leyan of N. England and (separately) E. (E. ) Caradoc) lacks glabella spines and may best be inopinatussp. nov. from the Rawtheyan of Hade viewed as closed to the ancestor of the subgenus. land. The last of these differs from the other members of the subgenus in probably lacking Discussion. - There are two distinct species glabellar spines - a reversal to the 'primitive' groups within E. (Erratencrinurus) centred on E. condition for the genus. (E.) capricornu and E. (E. ) nebeni. They may The E. (E. ) nebeni group is typified by the eventually be best separated at subgeneric leve! pentagonal arrangement of tubercles/spines at but important gaps in knowledge of species in the lL-1 (or lS--1) and 2L-l-Ot. E. (E. ) cornutus E. (E. ) capricornu group (Fig. l) preclude this lacks the longitudinally paired 2L-O tubercles but being done satisfactorily at the moment. The two some specimens to have a tubercle at 2S--O, con species groups recognized here are not the same stituting the apex of the pentagon. This penta as those of Krueger (1971) whose criteria were gonal arrangement of tubercles was considered either difficult to discern accurately or related to by Strusz (1980, p. 9) to be a diagnostic feature features not preserved in some species (see also of Erratencrinurus (excluding 'Celtencrinurus'), Owen 1981, p. 48). The scheme used here does, but it is confined to the E. (E.) nebeni group. It however, correspond to the grouping of Baltie is not, however, unique to this one group of species on Krueger's text-figs. 2 and 3. encrinurines and was evolved independently in other lineages such as the 'Encrinurus variolaris plexus' of Strusz (1980, see also Edgecombe & Chatterton 1987) and Balizoma Holloway (see The E. (E.) capricornu group Ramskold 1986). The number of glabellar This group comprises the Baltic upper Caradoc tubercles is consistently large (35-40) and there species E. (E. ) ceras, E. (E.) paetzensis and E. are commonly nine tubercles on the anterior bor (E.) capricornutogether with E. (E. ) imperfectus der of the cranidium although this is less certain and E. ( E.) brutoni from the Pusgillian and Raw in E. (E. ) inopinatus sp. nov. andE. (E. ) cornutus theyan respectively of the Oslo Region. It is char has eight. Sl either circumscribes L1 or is directed acterized by the very sparse tuberculation of the transversely without being continuous across the posteromesial part of the glabella - lL-1 and lL- glabella. The pygidium bears 8-11 pleural ribs 0 are invariably absent, 2L-O is only present in and has a few tubercles on the axis in E. (E.) E. (E. ) paetzensis and 3L-O in the Norwegian kauschi andE. (E.) seebachi but not in the other species. In all species, Sl is transversely directed species. NORSK GEOLOGISK TIDSSKRIFr 69 (1989) Ordovician trilobite from Hadeland 231

Fig. 3. E"atencrinurus (E"atencrinurus) inopinatus sp. nov. from the upper Kalvsjø Fm. (?high Rawtheyan) of Hadeland. All except D from Lunner-Sløvika road, SOm N of Sverigetjern. A, latex east of holotype cephalon, dorsal view. PMO 118.555, X 2!. B. Latex east of paratypefree eheek, lateral view. PMO 118.556, X 3i. C. Internal mould of pygidium, dorsal view. PMO 118.557, x 4!. D. lnternal mould of pygidium, dorsal view. PMO 118.568, x 2!, Bjertnestangen shore seetion. E. Latex east of incomplete eranidium, dorsal view. PMO 118.559, x 2. F. Latex east of free eheek, lateral view. PMO 118.560, x 3. G. Latex east of paratype pygidium, dorsalview. PMO 118. 561, x 2i. H. Internal mould of pygidium, dorsal view. PMO 118. 562, x 3.

Erratencrinurus (Erratencrinurus) inopinatus sp. diverse trilobite fauna including this species in a nov. unit which bad previously yielded few trilobites. Fig. 3A-H. Diagnosis. - Glabella moderately swollen, ex Holotype. - A cephalon (PMO 118. 555, Fig. 3A) panding even forward and bearing about 45-50 fromthe upper part of the Kalvsjø Fm. (probably large, symmetrically arranged tubercles but prob late Rawtheyan) on the Lunner-Sløvika road 50 m ably not spines. Tubercle formula: lL-2-1; N of Sverigetjem, Hadeland (NM 80908620). ZL-(3)-2-1-0;·; 3L-3-2;-1-0; 4L-3-2-1-0. Paratypes. - A free cheek (PMO 118.556, Fig. Posteromesial part of glabella bears pentagonally 3B) and two pygidia (PMO 118.561 and 118.562, arranged tubercles. Ll tuberculiform. Anterior Fig. 3G, H respectively) from the type locality border of cranidium bearing nine or ten tubercles. and horizon. Fixed cheek with smooth border and heavily tuberculate field. Free cheek field sparsely Other material. - An incomplete cranidium, a tuberculate, border strongly so. Pygidium with fixed cheek fragment, a free cheek, two pygidia eight pleural ribs and over 30 axial rings. No (all topotypes) and a pygidium from the upper tubercles on pygidial axis. most Kalvsjø Fm. on the shore section at Bjer nestangen (NM 76158720). A topotype partial Description. - Glabella expanding gently and cranidium and a freecheek were destroyed during evenly forward in front of the occipital ring to l. 7 preparation but latex casts are illustrated here times its width at Ll. Occipital ring about 1.4 (Fig. 3E, F) as they add morphological infor times the glabellar width at L1 and occupying mation not preserved in the other material. about 10% of the sagittal glabellar length. Pos terior edge of ring arched gently forwards Derivation of name. -Latin inopinatus - unex mesially; anterior edge almost transverse and pected; referring to the discovery of a relatively defined by very narrow (sag., exsag.) shallow 232 A. W. Owen & R. A. Heath NORSK GEOLOGISK TIDSSKRIFT 69 (1989)

occipital furrow. Ll-L3 tuberculiform. Glabella arated by deep furrows which are narrow on the bearing about 45-50 tubercles which are large external surface but very much broader on inter but apparently not extended as spines. Tubercle nal moulds. formula: lL-2-1; 2L-(3}-2-1--0:; 3L-3-2:-1--0; 4L-3-2-1--0. Mesial tubercles in lL and 2L posi Discussion. - The large number of glabellar tions form a filled pentagon. Some adventitious tubercles and pentagonal arrangement of mesial tubercles present on anterior part of gla tubercles on the posteromesial part of the glabella beila. Preglabellar furrow shallow but distinct, place E. (E.) inopinatus in the nebeni species arched strongly forwards. Anterior border of group. However, it differsfrom all other members cranidium bears nine or ten large tubercules but of the group in apparently lacking glabellar poor preservation in the mesial part of this area spines, possibly in having ten tubercles on the makes this difficult to assess. Axial furrow weak anterior cranidial border, in having a markedly but marks breaks in slope of both glabella and tuberculiform L1 ( = tubercle lL-2) and in having the swollen fixedcheek. Posterior border smooth, longitudinally paired 3L--O tubercles. The only transversely directed, broadening (exsag.) other member of the nebeni group with a median distally. Genal spine of unknown length directed tubercle opposite L3 isE. (E.) cornutus (Ingham) abaxially at about 20° to the sagittal line; bearing from the Cautleyan of northern England in which three large tubercles proximally. One of these a single spine is developed at this position. Both tubercles is at the angle between posterior border E. (E.) inopinatus and E. (E.) cornutus were and spine, and the other two are anteriorly placed probably late, independent, derivatives from the along the short ( exsag.) cranidal part of the lateral main, Baltic nebeni group lineage. Both show border. Field of fixed cheek densely covered in significant deviations from the more homo large tubercles, some overhanging the shallow geneous morphology of the earlier members of posterior border furrow. Base of palpebral stalk the group (Fig. l) but the scheme introduced well away from glabella opposite L3. Posterior herein enables their taxonomic position to be branch of facial suture transverse proximally, recognized. directed abaxially rearwards at 30° to the sagittal Acknowledgements. - We thank Ken Dorning for his help in line over its outer three quarters. Course of collecting in Hadeland. Heath's work was undertaken during anterior branch not known. the tenure of a NERC Research Studentiship which is gratefully Free cheek triangular. Broad, gently swollen acknowledged. This paper has benefited greatly from the com border bears about 20 large tubercles. Pre ments of an anonymous referee. cranidial lobe with an outer row of about four Manuscript received May 1989 large tubercles and an inner one of about five smaller tubercles. A few small tubercles also present on outer row adjacent to lateral border. Border furrow broad and shallow. Field gently References swollen, coarsely pitted and bearing a few scat Angelin, N.P. 1854: Paleontologica Scandinavica 1: Crustacea tered tubercles dose the steep visual surface. formationis transitionis Fase. 2, 21-92, pls. 25-41, Lund. Hypostoma and thorax not known. Edgecombe, G. D. & Chatterton, B. D. E. 1987: Heterochrony Pygidium triangular in outline; precise pro in the Silurian radiation of encrinurine trilobites. Lethaia 20, portions not known but probably broader than 337-351. Evitt, W. R. & Tripp, R. P. 1977: Silicified middle Ordo long. Gently convex (tr.) axis occupying most of vician trilobites from the families Encrinuridae and Stauro the length of the pygidium; tapering rearwards at cephalidae. Palaeontographica Abteilung A. 157, 109-174. about 15° and composed of more than 30 rings. Ingham, J. K. 1974: A monograph of the upper Ordovician No tubercles on axis. Anterior two rings con trilobites from the Cautley and Dent Districts of Westmorland tinuous with anterior two of eight pleural ribs. and Yorkshire. Palaeontographical Society (Monographs) (2), 59-87. Axial furrows little more than break in slope Ingham, J. K. 1977: A monograph of the upper Ordovician between axis and ftat-lying inner part of pleural trilobites from, the Cautley and Dent districts of Westmorland lobe. Pleural ribs arched abaxially rearwards; and Yorkshire. Palaeontographical Society (Monographs) anterior rib directed at about 60° to sagittal line, (3), 89-121. Krueger, H. -H. 1971: Encrinuriden aus ordovizischen Ge posterior rib almost parallel to and extending schieben. Geologie 20, 1132-1169. beyond axis. Outer part of pleural lobe gently Krueger, H. -H. 1972: Nachtrag zu 'Encrinuriden aus ordo declined. Ribs end in short free points. Ribs sep- vizischen Geschieben, 1971'. Geologie 21, 858. NORSK GEOLOGISK TIDSSKRIFf 69 (1989) Ordovician trilobite from Hadeland 233

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