Sphaerophthalmus Angelin, 1854

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 : 431-433

Genus Sphaerophthalmus Angelin, 1854 Sphaerophthalmus humilis ( Phillips, 1848)

Fig. 2I–K .

Olenus humilis n. sp.; Phillips 1848: 55, 347, figs. 4–6. Sphaerophthalmus humilis ( Phillips, 1848) ; Żylińska 2001: 344, pl. 2:

1a, pl. 3: 2–3 [see for complete synonymy].

Material.—Two cranidia and three pygidia.

Description.—The two cranidia are 0.8 and 1.3 mm long, respectively. The smaller one ( Fig. 2I ) is almost complete except for the occipital ring. The specimens agree in most respects with Henningsmoen´s (1957) description of the species. The palpebral lobes are very narrow, becoming wider anteriorly, with their centres situated on a transverse line slightly in front of S1. A tiny intergenal spine is present on the rounded postero−lateral margin. The surface is very finely granulated.

The three pygidia (0.7, 0.8, and 0.9 mm long) can confidently be assigned to the species. They are triangular in shape with nearly straight and slightly undulating postero−lateral margins. The axis is very broad, anteriorly occupying six−tenths of the total width, and tapers backwards almost to the tip of the pygidium. It consists of a prominent articulating half−ring, three axial rings, and a terminal piece. The pleural fields are very narrow and there is a distinct, raised postero−lateral border with two, possibly three, elongated lobes opposite the axial rings, arranged parallel to the margin. The surface of the pygidium is covered with granules except on the articulating half−ring. These are most prominent on the central part of the axial rings and behind the axis. On the pleural fields the granules are more elongated, subparallel with the postero−lateral margin. Terrace lines are present on the postero−lateral borders, being especially well developed on the most anterior lobes.

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.