OCR Text |
Show 586 MR. E. A. SMITH ON THE GENUS MYODORA. [Nov. 16, curved on the anterior dorsal margin, and the pallial sinus is much less deep. The microscopic radiating striee on the present species are very conspicuous. 19. MYODORA PROXIMA, sp. nov. (Plate LIII. figs. 8, Sa, 8b.) M. trianyularis, A. Ad. M S . in Mus. Cuming. Shell subequilateral, triangular, thick ; dorsal lines converging to a sharp point, anterior a little convexly curved, posterior a trifle concave near the umbones ; anterior and hinder ends rather sharply rounded, subangular, the latter sometimes more or less obliquely truncated ; ventral margin broadly arcuate. Deep valve not very convex, with only a trace of a depression down the posterior side, rather coarsely lirated from margin to margin ; upper valve flat or very slightly convex, sulcated very nearly as coarsely as the other valve. A single impressed ray in the interior, curving from near the umbones to the inner or lateral boundary of the small pallial sinus in the flat valve, and nearer the centre in the deep one. Posterior scar subrotund ; anterior one more elongate, subpyriform. Length 10 millims., width 10^, diam. 3. Hab. Japan, 22-47 fathoms (Capt. H. C. St. John, R.N.) ; China (Mus. Cuming). This species approximates very closely to M. trigona from the Philippine Islands. It may, however, be specifically separated on account of the more acute apical angle, its greater depth from the umbo to the ventral margin, the less-distinct posterior depression on the convex valve, the slighter truncation of hinder margin, and the less regularity and less elevation of the concentric ridges. 20. MYODORA REEVEANA, sp. nov. (Plate LIII. figs. 10, 10a.) M. reeveana, A. Adams, M S . in Mus. Cuming. Shell transversely ovate, posteriorly broadly truncated, anteriorly rounded, subequilateral; front dorsal slope of deep valve nearly rectilinear, only feebly arcuate, hinder rather incurved; concentric ridges very fine, continuous from margin to margin ; upper valve flat, with a slight depression down the posterior side, finely concentrically striated. Internal impressed ray a little curved, extending to the inner side of the pallial sinus. Length 5^ millims., width 7|> diam. 2. Hab. China. This species is remarkable for the fine concentric sculpture, in which respect it differs from its congeners. M. convexa is lirated nearly as finely, but differs in form. Young specimens of M. pandoriformis would probably agree very fairly in the latter character; but their concentric lira? are much too remote. The truncation at the posterior end is very abrupt in this species, and forms almost a right angle with the hinder dorsal slope. The microscopic sculpture is excessively fine in comparison with that of other species. |