Page:Quarterly Journal of the Geological Society of London, vol. 34.djvu/41

Rh

, R. Eth., Jun. Pl. II. figs. 22, 23 (and 21?).

Leptodomus? clavatus, R. Eth., Jun., Ann. & Mag. Nat. Hist. 1876, xviii. p. 102, pl. 4. figs. 9, 10.

''Sp. char.'' Somewhat clavate, a little arcuated, very inequilateral, gibbous in the umbonal region; length much exceeding the height. Anterior side short, convex, its margin rounded; posterior side much more compressed, transversely elongated, its margin sharply truncated; umbones prominent, quite anterior, but the beaks not terminal. A blunt diagonal ridge traverses each valve from the umbo to the posterior ventral angle; posterior slope a little concave. Dorsal margin long, slightly arcuated; dorsal and ventral posterior angles sharp and well defined. Ornamentation consisting of concentric striæ, which are suddenly deflected on reaching the diagonal ridge, and traverse the posterior slope parallel to the posterior margin in a very regular manner.

Obs. My former description of this species was drawn up from crushed specimens; but the acquisition of nearly perfect examples enables me to give a more definite diagnosis. For individuals in the crushed state the characters given in the 'Annals' are quite appropriate; for it is a fact worthy of note that, when crushed, all specimens of this species which have come under my notice appear to be compressed into a similar form and to a like degree the outline becomes more clavate and arcuated, the posterior end recurved and truncated obliquely, the posterior slope still more concave, and divided down its centre by a groove from the beak backwards, and the surface a good deal wrinkled.

The reference to Pandora is made exclusively on the close external resemblance this species bears to that genus. I have not seen any of the internal characters; neither can I say whether the shell was inequivalve or not, as it should be if a true Pandora. P.? typicaresembles in many respects Lutraria elongata, M'Coy, and to some extent Pandora clavata, M'Coy , and will, perhaps, occupy an intermediate position between the two. I have assigned to the species the name typica, from its great prevalency in certain beds of shale in the Cement-stone group around Edinburgh. Mr. Henderson notices its occurrence, under the name of Pandora sp., in his paper on the Wardie Shales, previously referred to.

''Loc. and Horizon''. In the bed of shale at Woodhall, as before; Drumsheugh, near Dean Bridge, in a similar bed; in ditto behind the western breakwater at Granton Harbour; in ditto above the sandstone at Craigleith Quarry. Cabinets of Messrs. Henderson and Gall; and collection Geol. Survey Scotland, collected by Mr. James Bennie.

I also give figures of two undetermined bivalves (figs. 24 & 25) in the collection of Mr. Gall and Mr. Henderson, from Drumsheugh and Water of Leith respectively.