Kirkbya oblonga, Jones & Kirkby.

3. Kirkbya oblonga, Jones & Kirkby. View in CoL

(Pl. III. fig. 3; and varieties, figs. 4, 5, and 6, a, b.)

Kirkbya oblonya, J. & K., 1867 , Trans. Geol. Soc. Glasgow, vol. ii. p. 221; 1871, vol. iii. Suppl. p. 28.

Kirkbya oblonya, Armstrong and others, 1876, Catal. W.-Scot. Foss, p. 44.

Oblong-ovate, convex; height (which is uniform in the central third) equal to half the length or more. Dorsal border almost straight, but rather concave; ventral border usually straight in the central third; extremities boldly rounded and almost alike. In some cases the regular convexity of the valves is scarcely broken except by a slight medio-dorsal depression; in others this depression is more pronounced and the valves become rather humped towards the extremities; and in some specimens a circular boss appears in the. centre. A slight rim bounds the free margins of the valves; in certain specimens a second is added, and occasionally the reticulation of the surface shows a tendency to develop itself into other less regular concentric wrinkles. Lateral contour subovate. Subcentral pit oval, often obscure. Surface covered with rather large hexagonal reticulation. Length inch.

This species was discovered by our friend Mr. John Young, of Glasgow. It is a near ally of K. permiana ; but, although the latter sometimes takes on a curved subcentral riblet (see Trans. Tyneside, 1859, pl. x. a. fig. 5 a), yet it never loses its marginal rims or its strong dorsal angles.

Localities.—Scotland. Carboniferous Limestone (Lower): Brockley, Lanarkshire; Craigenglen, Stirlingshire; coast east of St. Monans, Fifeshire. Carboniferous Limestone (Upper): near Kinneil Mill and Orchard Quarry.

Under this name ( K. oblonga } we also place certain speci ­ mens that occurred to us first from the Carboniferous-Lime ­ stone series of Fife (figs. 4 and 6). The character of their reticulated surface, central pit, and ventral riblets sufficiently identify them with Kirkbya . We describe them thus:—

Varying from subreniform to suboblong and subquadrate in outline, often compressed; height two thirds of the length. Dorsal border straight for from about a third to a fourth less than the maximum length; ventral border curved or straight in central third; extremities rounded, the anterior being slightly the more acute. Surface reticulated (hexagonal or pentagonal meshes) and with two or more faint concentric riblets (including a slight marginal rim) below. Length inch. Edge view (lateral contour, fig. 6 b) is acute-oval.

Discovered by Mr. James Bennie in the Lower-Carbon ­ iferous Limestone, on the coast near Seafield Tower, Fifeshire.

Figs. 5 a, 5 6, represent a form that Mr. Robertson has from Williamswood, near Glasgow. It is relatively shorter than K. permiana , and the dorsal line is only about two thirds of the total length; it is thus nearly oblong, with rounded ends. The valves have each a slight marginal rim, are humpy towards the ends, or faintly lobed, and more coarsely reticulated than is usual with K. penniana ; and there is a weak submedial riblet in some individuals. We figure it so as to keep it in view, as it is a form requiring further study. A somewhat similar short form, but more convex and more definitely ridged, we have seen in Air. C. Moore ’s collection from Steeraway, Salop. Probably they are all closely allied to K. oblonga .