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Show 584 MR. E. A. SMITH ON THE GENUS MYODORA. [Nov. 16, 15. MYODORA NOV^E-ZEALAND^, sp. nov. (Plate LIII. figs. 5, 5a, 5b.) Shell inequilateral, subequilaterally triangular ; deep valve considerably convex, with an indistinct shallow groove posteriorly near the margin, concentrically rather coarsely sulcated, the sulci extending from the front margin to near the posterior side, where they suddenly stop, leaving a smooth narrow space between their termination and the edge, or, in other words, a plain posterior dorsal area. The front dorsal margin is nearly straight and a trifle longer than the posterior, the latter being feebly incurved ; ventral margin arcuate. Interior pearly, marked with two subparallel or slightly diverging rays or striae, radiating from the umbo a little beyond the centre of the valve. Flat valve a trifle concave, with much finer concentric sculpture than the other valve ; anterior dorsal margin straight, acute. Length from apex to ventral margin 8^- millims., width 94r. Hab. Stewart Island (C. Traill); N e w Zealand. This species is more equilaterally triangular than any other in the genus, and is remarkable for the abrupt termination of the concentric grooves on the deep valve, the smooth posterior dorsal area, and particularly for the two divergent impressed rays within both of of the valves radiating from the umbones as far as the pallial impression. The sinus in the latter is rather deep ; and the hinder muscular scar is higher up or nearer the umbo than the anterior one. The shallow depression or groove proceeding down the hinder side of the deep valve is near the margin, and very conspicuous. 16. MYODORA SUBROSTRATA, sp. nov. (Plate LIII. figs. 6, 6a, 6b, 6c.) Shell subtrigonally ovate, posteriorly rather acuminated and scarcely truncated at the extremity, anteriorly sharply curved; ventral margin curved and feebly sinuated posteriorly, giving the shell a somewhat rostrated appearance. Deep valve moderately convex (in young specimens much flatter), with only a trace of a shallow depression down the posterior side; its hinder dorsal margin almost rectilinear, the anterior much arcuated; concentric sulci rather coarse, generally continued to the margins. Other valve quite flat, with finer sculpture. Hinge-cartilage furnished with a small pellucid clavicle. Interior with a single impressed ray, curving from the umbones to the sinus in the pallial impression in the flat valve, and further within the valve in the deep one. Anterior scar somewhat elongated, posterior more circular. Length 14^ millims., width 18, diameter 5. Hab. New Zealand (Colonel Bolton fy Mus. Cuming) ; Stewart Island (0. Traill). This species may have been confounded with M. ovata, which is included by Hutton among the species of this genus said to be found at New Zealand. M. ovata is not so narrowed posteriorly, is broadly truncated, and more elongated transversely. Its sculpture too is coarser; and the apical angle formed by the convergence of the dorsal slopes is |
