Sphaerophthalmus sp. A

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 : 433

Sphaerophthalmus sp. A

Figs. 2P ?, 2Q–R, 3A.

Material.—Six cranidia, ranging in length (excluding the occipital spine) from 0.5 to 0.8 mm.

Description.—The larger cranidia ( Figs. 2Q, R , 3A ) are subquadrate in outline and slightly wider than long. The anterior and posterior margins are almost straight and transverse. The anterior branch of the facial suture is curved backwards at approximately 45 ° from the anterior margin. The palpebral lobe is narrow, curved, and long, approximately half the total length of the glabella (L0 excluded), and narrows posteriorly. The centre of the palpebral lobe is situated opposite the posterior third of the glabella excluding L0 to S1. The posterior branch of the facial suture extends from opposite S1 to the posterior margin, and curves backwards and slightly outwards from the palpebral lobe, then runs backwards and inwards. A pair of tiny intergenal spines is present where the facial suture terminates against the posterior margin. The glabella is parallel−sided, broadly rounded in front, extends to the anterior border, and occupies about a third of the total width of the cranidium. S1 is prominent, transglabellar, and curved backwards medially. There is no indication of S2 or S3. L0 is subtriangular and is provided with a long and stoutly−based occipital spine, circular in cross−section, and arising backwards and upwards from the posterior half of L0. The spine is about three−quarters the length of the glabella (L0 excluded), and is sharply pointed at its tip. Some specimens show a subdued, somewhat reticulate surface ornament.

Remarks.—The smallest cranidium ( Fig. 2P ) is provisionally referred to the same species, though it differs in being slightly longer relative to its width, having a slightly tapering glabella, and in having an occipital node rather than a spine. Two small nodes are present on the anterior border on either side of the glabella. The palpebral lobe is less sharply marked off, and is set further backwards. Moreover, the anterior branch of the facial suture curves backwards more sharply from the anterior margin. This small cranidium probably represents a juvenile form.

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.

Fig. 3. A. Sphaerophthalmus sp. A, cranidium, SMNH Ar59729 (2.21), sample 2. B. Sphaerophthalmus sp. B, right librigena with intact eye, SMNH Ar59730 (3.11), sample 2. C. Sphaerophthalmus sp. C, incomplete thoracic tergite, SMNH Ar59731 (2.19), sample 2. D–F. Peltura cf. transiens (Brögger, 1882). D. Pygidium, SMNH Ar59732 (1.3), sample 1. E. Pygidium, SMNH Ar59733 (2.7), sample 2. F. Small pygidium, SMNH Ar59734 (3.12), sample 2. G. Peltura cf. paradoxa (Moberg and Möller, 1898), pygidium, SMNH Ar59735 (1.7), sample 1. H, I. Peltura sp. A. H. Pygidium, SMNH Ar59736 (1.2), sample 1. I. Transitory pygidium, SMNH Ar59737 (1.21), sample 1. J. Peltura sp. B, transitory pygidium, SMNH Ar59738 (1.6), sample 1. K–P. Indeterminate olenid fragments. K–M. Occipital rings. K. SMNH Ar59739 (1.19), sample 1. L. SMNH Ar59740 (1.15), sample 1. M. SMNH Ar59741 (2.14), sample 2. N. Axial ring seen edge on, SMNH Ar59742 (1.18), sample 1. O. Axial ring, SMNH Ar59743 (2.22), sample 2. P. Incomplete thoracic tergite, SMNH Ar59744 (1.24), sample 1. Scale bars 0.1 mm.