Sphaerophthalmus cf. alatus ( Boeck, 1838 )

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 cf. alatus ( Boeck, 1838)

Fig. 2L, M .

Material.—Two librigenae, one left and one right.

Description.—Nearly intact left and right librigena (1.2 and 0.7 mm long respectively), the latter with an intact eye, probably belong to this species. They are very narrow, curving and tapering anteriorly, and with the eyes set in the posterior third, where the librigena is widest. Long genal spines (broken) emerge from a level opposite the eye at an angle of 70–80 ° to the sagittal line. The postero−lateral margin between the spine and the facial suture is almost straight and very short, less than the length of the eye. The antero−lateral margin in front of the spine is three to four times as long as the postero−lateral margin. It is almost straight laterally and then curves forwards and inwards to terminate very sharply against the facial suture. The anterior branch of the facial suture is almost straight anteriorly, and then slightly curved to meet the eye, where it curves sharply inwards and outwards again, encompassing the rear part of the eye. The posterior branch is short and curves slightly inwards to meet the posterior margin.

The eye is ovoid, slightly expanded posteriorly, and provided with about 50 thin lenses, which are slightly larger towards the rear. The librigenae are very small and clearly belong to juvenile specimens, and the eyes have fewer lenses and are more elongated than in adult specimens from Andrarum, Scania, southern Sweden (see Clarkson 1973: 756).

Sphaerophthalmus cf. majusculus Linnarsson, 1880 Fig. 2N, O .

Material.—Two pygidia, 0.6 and 0.8 mm long.

Description.—The pygidia are subtriangular, wider than long, and with the postero−lateral margins slightly concave and a somewhat rounded posterior end. The axis occupies slightly more than the central third of the total width anteriorly, tapers regularly backwards and almost reaches the posterior border. It consists of an articulating half−ring, three axial rings, and a terminal piece. The pleural fields become distinctly narrower backwards and have two or three shallow pleural furrows. The pygidial border is raised and continuous, lacking undulations, and provided with several distinct, subparallel terrace lines. The pygidial surface lacks distinct ornamentation other than the terrace lines and some faint granulation on the central part of the axial rings, and, on the larger specimen ( Fig. 2O ), on the anterior part of the pleural field.

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.