This is the third of M Coy's original species. The specimen in the Cambridge Museum has its carapace ovate-oblong or somewhat boat-shaped in outline, 50 mm. (2 inches) long, 18 mm. high; moderately convex; straight or very slightly arched above and more strongly arched below (both edges are partly imbedded in the matrix of the original specimen, b/5, M Coy's fig. 4). The anterior end (damaged) was neatly rounded, sloping up gracefully from below. The posterior is obliquely truncate from above downwards and outwards, with the postero-dorsal angle distinct, and the posteroventral angle prominent and blunt. There is no eye-spot. Traces of longitudinal striæ are visible on the impressions of the valves in the grey, micaceous, Upper-Ludlow sandstone, from Benson Knot, near Kendal, Westmoreland; two specimens (one of them good) are in the British Museum, No. 44342, from the same locality.