OCR Text |
Show 1880.] MR. E. A. SMITH ON THE GENUS MYODORA. 587 21. M Y O D O R A TENUISCULPTA, sp. nov. (Plate LIII. figs. 11, 11a.) Shell thin, inequilateral, abruptly truncated behind, and sharply rounded at the other end ; anterior dorsal slope rectilinear, longer than the posterior ; the latter is remarkably incurved. Deep valve only slightly convex, with a very feeble depression posteriorly, and with very shallow concentric sulci, scarcely apparent to the naked eye. Flat valve a trifle concave, concentrically finely striated. Impressed ray of the interior curved, meeting the inner boundary of the mantle-impression in the flat valve and falling a little further within in the deep valve. Posterior scar subrotund; anterior elongate, much narrower. Length 5 millims., width 7, diam. Ii. Hab. ? This is the most finely sculptured species in the genus, and is less equilateral than M. reeveana. 22. MYODORA COMPRESSA, sp. nov. (Plate LIII. figs. 12, 12«.) Shell compressed, rather thin, subtrigonal, posteriorly obliquely truncated, acutely rounded in front. Hinder dorsal slope rather incurved, shorter than the anterior, the latter being nearly rectilinear. Ventral curve slight. Lower or deep valve very shallow, with a feeble depression posteriorly near the margin, and marked with shallow concentric sulci and striae, the interstitial ridges being most prominent at a short distance from the hinder extremity, or, in other words, on that part of the surface which bounds the depression. Angle formed by the truncated end and the dorsal margin rather abrupt, of about 90 degrees. Upper valve flat, with a shallow depression posteriorly, finely concentrically striated. Impressed ray of the interior curved a little, extending in the flat valve to the inner boundary of the pallial sinus, and a little nearer the centre in the other valve. Length 7-?r millims., width 9, diam. 1%. Hab. ? This is a very compressed species, and very finely sculptured. It is thinner than M. proxima, with a straighter anterior dorsal margin, more finely sulcated upon both valves, broader and flatter. It is hardly so finely sculptured as M. tenuisculpta, and of a different form, being much less elongated transversely. EXPLANATION OF PLATE LIII. Figs. 1, la. Myodora oblonga, p. 582. 2, 2a. ovata, p. 582. 3, 3a. trigona, p. 582. 4, 4a. plana, p. 582. 5, 5a, 5b. novcB-zealandice, p. 584. 6, 6a, 6b, 6c. subrostrata,584. 7, 7a. antipodum, p. 585. Figs. 8, 8a, 8b. Myodora proxima, p. 586. 9, 9a, 9b, 9c. boltoni, p. 585. 10, 10a. reeveana, p. 586. 11, 11a. tenuisculpta, p. 587. 12, 12a. compressa, p. 587. 39* |