OCR Text |
Show 361 marked by exceedingly fine, obscure, closely- arranged, concentric stride, which are crossed on the posterior umbonal slopes by a few stronger radiating lines, extending from near the beaks to the posterior and pos-tero- basal margins. Hinge and interior unknown. Length and height, 0.15 inch; breadth or convexity, 0.12 inch. This delicate little shell resembles Cardium subquadratum of Evans and Shumard, but is much more gibbous, and more rounded in outline, than specimens of that species of its own size. JX also differs in having much mooe distinct radiating lines on its posterior side; those on Cardium sub-qwdratuw being almost entirely obsolete. In the roundness of its outline, as well as in the gibbous character of its valves, it approaches Cardium rmmm of Evans and Shumard } still, its posterior margin is more truncated, fund its radiating lines much more fltofciuct. It likewise differs from both of these species in being a much smaller shell than either of them; though it may be the young of < even a larger species. Mir. Gototo has described two Cretaceous species of this group in the California Geological Reports, under the jiames Protooardia Plaoerensis and P. iwnslutiila, that may, one or both, be related to tbia, though they diflfar in outline. Locality anil position.- Komooks, Vancouver's Island; Cretaceous. Genus CYPRIMERIA, Conrad. CYPRUEERU! TENUIS, Meek. Plate 2, figs. 5,5 a, ana 5 b. Dosiniat tenuis, Meek ( 1861), Proceed. Acad. Nat. Soi. Philad., xiii, 315. Shell circular or slightly oval, extremely thin, and much compressed; lateral and basal margins regularly rounded, very thin, and sharp; beaks small, compressed, central, projecting little above the dorsal margin ; lunule small and rather deep; surface marked by fine concentric striae. Length and height* each 1.26 inches; convexity about 0.22 inch. I have merely placed this species provisionally in the genus Cyprimeria, not having seen specimens showing either the hinge or other internal characters. It has much the appearance of a Lucina, but some of the internal casts appear to show that its anterior muscular impressions are not as in that genus, while they also give indications of a double oblique tooth just in front of the beaks, more nearly as we< see in Omrimeria. m It is a rather common species, and will be readily identified by its circular compressed form and extreme tbhmess. It is closely allied, so far as regards general appearance, to Artemis lentisularis of Forbes from the Cretaceous at Pondi< 5herry, Southern India ( Trans. Geol. Soc. Lond., vol. vii, pi. 18, fig. 7). Locality ana position.- At several places near Nanaimo, Vancouver's Island, and on New < 3astie Island; Cretaceous. * In tbecasi represented, by figs. 5 a and 5 &, the tooth does not show its double character BO clearly as others. |