. Bulletin of the British Museum (Natural History), Geology. ARENIG IN SOUTH WALES 163 gently backwards into the pygidial axis. On the sixth segment the width of the axis is only slightly greater than the width of the pleurae. Pygidium three times as wide as long, with gently convex pleural fields, and a well-defined flat to gently convex border. Axis occupies one-third or less of pygidial width at anterior margin, and this width exceeds its length; posterior taper very gentle to broadly rounded tip at border furrow. Although the half-ring is prominent no axial rings are defined. Posterior bor
. Bulletin of the British Museum (Natural History), Geology. ARENIG IN SOUTH WALES 163 gently backwards into the pygidial axis. On the sixth segment the width of the axis is only slightly greater than the width of the pleurae. Pygidium three times as wide as long, with gently convex pleural fields, and a well-defined flat to gently convex border. Axis occupies one-third or less of pygidial width at anterior margin, and this width exceeds its length; posterior taper very gentle to broadly rounded tip at border furrow. Although the half-ring is prominent no axial rings are defined. Posterior border widest posterolateral^. Doublure coincident with border, carrying very sparse terrace ridges. Discussion. Although the Lake District specimen is not well preserved it is clearly identical to the species from the Llanfallteg Formation and from Shropshire. The latter was originally described with the specific name brevicaudatum Whittard. Whittard (1966) described the thorax of the articulated specimen from the Hope Shales as 'almost barrel-shaped'. We regard this observation as mistaken, because the barrel-like appearance of Whittard's pi. 50, fig. 10 is produced by partial breakage of the thoracic axis at its anterior end. Comparison of all this material with the type of obtusicaudatus Hicks is more difficult because of the imperfect preser- vation of the unique specimen from Llanvirn quarry. It is, however, certainly a Gastropolus, showing the six segments, transverse pygidium and short pygidial axis typical of the genus. The pygidial pleural fields are slightly less transversely extended but it is doubtful whether much importance can be attached to this in view of the degree of distortion often found in Llanvirn quarry specimens. Since almost all the species originally described by Hicks from Llanvirn quarry have also been recognized in the early Llanvirn of the Llanfallteg Formation it is likely that this applies to the Gastropolus as well. We have one fragment of a thora
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