Kirkbya costata (M ’Coy)

8. Kirkbya costata (M ’Coy) View in CoL .

(Pl. III. figs. 13 a,b, 14 a, b; var. fig. 15.)

Cythere costata, M'Coy, 1844 , Syn. Char. Carb. Foss. p. 165, pl. xxiii. fig. 11.

Kirkbya costata, J. & K., 1866 , Ann. & Mag. Nat. Hist. ser. 3, xviii. p. 43.

Kirkbya costata, J., K., & B., 1884 , Monogr. Brit. Foss. Biv. Entom. Pal..Soc. p. 89, pl. 7. fig. 17.

Subovate or ovate-oblong, flat-sided, rather highest behind, height more than half the length; thick-shelled, and strongly ribbed with subconcentric ridges. Dorsal border straight or nearly so, and over two thirds of the maximum length; ventral border more or less convex; extremities rounded, the anterior smaller than the other, and both somewhat angular above. Subcentral pit circular, rather above the median line, and showing internally as a raised spot. Edge view (lateral contour) long-ovate with flattened sides (fig. 13 b, 14b). The extreme anterior portion of each valve is smooth, but from near the centre of that portion spring two strong ribs, one curving abruptly up and the other down, and then passing along the valves rather obliquely and sinuously to near the postero-ventral angle, where they curve to each other and join; between them are two or three somewhat smaller but similar ribs, also free at their anterior ends, but connected at the other. Other ribs come in below, more or less parallel to the lowest of those just described; and others come in above and fill up the triangular space between the upper large rib and the dorsal border, the highest being nearly as strong as the two first-mentioned. There is considerable variation in the curvatures and connections of the riblets. Surface not re ­ ticulated so tar as known. Length inch.

The above description is taken from specimens which we identify with Prof. M'Coy ’s Cythere costata , but which do not exactly agree with the figures of the species in his ‘ Synopsis of the Characters of the Carboniferous Fossils of Ireland.’ In all probability his specimens may not have been so perfect as ours; or the latter may possibly differ somewhat from the Irish examples. However this may be we think it well to assume that the highly costated species now described is the same as M£Coy ’s.

Localities.— England. Carboniferous-Limestone series: Steeraway, Salop; Weston-super-Mare, Somerset; Railway ­ cutting near He versham, Westmoreland; Cam Beck, Cum ­ berland; Plashetts, Northumberland.

Scotland. Carboniferous Limestone (Lower): Brockley, Lanarkshire; Cults Lime-works, Fifeshire.