Kirkbya spiralis, Jones & Kirkby.

6. Kirkbya spiralis, Jones & Kirkby.

(Pl. III figs. 11, a, b.)

Kirkbya spiralis (J. & K. MS.) , Kirkby, 1880, Quart. Journ. Geol. Soc. vol. xxxvi. pp. 564, 568, 573, 588.

Kirkbya spiralis, Jones, 1884 , Proc. Berwicksh. Nat. Club, vol. x. p 323, pl. ii. figs. 12, 13.

Carapace subovate or oblong, highest behind, compressed, slightly lobate; height half the length or more. Dorsal border straight and about two thirds of the valve-length; ventral border incurved and sloping downwards to maxi ­ mum height, which is in the posterior third; extremities rounded, the posterior being the larger and more projecting. The subcentral pit, which is transverse, is placed somewhat nearest the dorsal and posterior portions of the valve. A marginal rim bounds each valve, and is continued as a ridge from the dorsal centre downwards, and concentrically with the margins to or near the subcentral pit; within the central area thus formed is a longitudinal and somewhat sinuous ridge, which is free at the ends. Edge view (fig. 11, b, lateral contour) narrow, ovate, and rather constricted near the centre. Surface smooth. Length A t inch.

This species does not vary among individuals much in character, except perhaps a little in relative length.

It appears to be confined to the lower portion of the Car ­ boniferous series, where it is very abundant at some horizons, as already noted (p. 176).

K. spiralis has been described by one of us in the 1 Proceed ­ ings of the Berwickshire Naturalists ’ Club,’ from somewhat imperfect specimens collected by the late Mr. George Tate, of Alnwick.

Localities.—England. Lower Carboniferous: Tweedmouth, Northumberland. Scar or Mountain Limestone: Meathop (near Grange-over-Sands), Westmoreland; Calces, Cumber ­ land.

Scotland. Calciferous Sandstone: on the coast near the fol ­ lowing places:—east of Pittenweem, Billow Ness, Kilminning, llandcrstone, and Kingsbarns, in Fifeshire; Oakbank Sand ­ stone Quarry, Linlithgowshire.