Ctenopyge sp.

Ahlberg, Per, Szaniawski, Hubert, Clarkson, Euan N. K. & Bengtson, Stefan, 2005, Phosphatised olenid trilobites and associated fauna from the Upper Cambrian of Västergötland, Sweden, Acta Palaeontologica Polonica 50 (3), pp. 429-440 : 431

Ctenopyge sp.

Fig. 2B–H .

Material.—Two left librigenae with intact eyes but broken genal spines, and five pygidia can be assigned to a species of Ctenopyge . Two fragmentary cranidia are tentatively referred to the same species.

Description.—The extraocular cheeks are narrow, less than half the width of the eye, and the genal spine is directed outwards at angle of about 90 ° to the palpebral suture. The genal spine is ovoid in cross−section, probably curving gently backwards, and the base of the spine is slightly narrower than the width of the extraocular cheek. A scale−like ornament is present, particularly distinct on the genal spine. The posterior branch of the facial suture is strongly curved anteriorly behind the eye and then sweeps backwards to make a sharp angle with the lateral margin. The eye is large, reniform, and inflated, occupying at least half the length of the librigena, as inferred. There are at least 100 lenses, regularly arranged in a standard system of hexagonal close−packing in subconcentric rows below the almost straight palpebral suture.

The pygidia are subtriangular with a tapering axis continuing into a prominent, stoutly−based caudal spine. Anteriorly the axis is narrower than the pleural field. The axis consists of a distinct, semicircular half−ring and four or five axial rings. Subdued axial nodes are present on the axial rings, fading posteriorly. The posterior axial ring carries a prominent, broad−based spine, directed backwards and upwards. The spines are broken to reveal a circular cross−section. The pleural fields have shallow pleural furrows, directed outwards and increasingly backwards towards the rear. The postero−lateral margins are almost straight and bear five or six pairs of thorn−like spines. The anterior spines are directed sharply upwards. The angle these marginal spines make with the horizontal plane decreases posteriorly so that the rearmost pair is horizontal. In this respect the pygidia are similar to that of Ctenopyge ceciliae Clarkson and Ahlberg, 2002 from the Peltura scarabaeoides Zone of Scania, southern Sweden.

A single pygidium ( Fig. 2E ) represents a juvenile stage in development. It may well belong to the same species. This transitory pygidium is more semicircular in outline and the first segment is defined posteriorly by a transverse furrow and an incipient articulating half−ring, as almost ready for release. It has four axial rings and a terminal piece. The spine on the posterior axial ring is broken off at the base, but the horizontal caudal spine is nearly complete. Six pairs of marginal spines are present, more closely spaced and longer posteriorly than in other pygidia.

The glabella of the fragmentary cranidia ( Fig. 2B ) tapers forwards, but in both specimens it is broken off anteriorly. The occipital ring (about 0.8 mm wide) has an evenly rounded posterior margin, and a slender, tapering spine extends from its middle part. S0 is transglabellar with two lateral indentations. L1 is about the same length (sag.) as L0 and is bounded anteriorly by S1, which is broad and transglabellar. A granular ornament is present over all parts of the surface, except for the furrows.

Figures

Fig. 2. A. Parabolina sp., juvenile pygidium, SMNH Ar59711 (3.13), sample 2. B–H. Ctenopyge sp. B. Fragmentary cranidium, SMNH Ar59712 (2.8), sample 2. C. Left librigena with intact eye, SMNH Ar59713 (1.12), sample 1. D. Left librigena with intact eye, SMNH Ar59714 (1.13), sample 1. E. Small pygidium, SMNH Ar59715 (1.23), sample 1. F. Pygidium, SMNH Ar59716 (2.6), sample 2. G. Pygidium, SMNH A59717 (2.2), sample 2. H. Pygidium, SMNH Ar59718 (1.4), sample 1. I–K. Sphaerophthalmus humilis (Phillips, 1848). I. Cranidium, SMNH Ar59719 (2.20), sample 2. J. Pygidium, SMNH 59720 (1.5), sample 1. K. Pygidium, SMNH Ar59721(2.5), sample 2. L, M. Sphaerophthalmus cf. alatus (Boeck, 1838). L. Right librigena with intact eye, SMNH Ar59722 (1.20), sample 1. M. Left librigena, SMNH Ar59723 (1.14), sample 1. N, O. Sphaerophthalmus cf. majusculus Linnarsson, 1880. N. Pygidium, SMNH Ar59724 (1.15), sample 2. O. Pygidium, SMNH Ar59725 (2.1), sample 2. P. Sphaerophthalmus sp. A?, juvenile cranidium, SMNH Ar59726 (2.11), sample 2. Q–R. Sphaerophthalmus sp. A, sample 1. Q. Cranidium, SMNH Ar59727 (1.8). R. Cranidium, SMNH Ar59728 (1.10). Scale bars 0.1 mm.