796 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



AXINODON ELLIPTICUS, new species. 

 (Plates XC, figs. 5, 6; XCII, fig. 1.) 



Shell small, nearly smooth, swollen, transversely elliptical and some- 

 what oblong, with rather prominent nmbos and with the beaks con- 

 siderably behind the middle and curved forward. The antero-dorsal 

 margin is decidedly convex and somewhat excurved, the anterior end 

 is longer and a little broader than the posterior; both are nearly evenly 

 rounded; the ventral margin is broadly rounded and nearly straight 

 for a short distance along the middle; the postero-dorsal margin is con- 

 vex and merges into the posterior end in a regular curve. The lunular 

 area is rather distinct, but without any very definite boundary. The 

 surface is nearly smooth, covered only with fine, close lines of growth, 

 which, under the microscope, appear as delicate, raised lines, separated 

 by grooves of about the same width; this sculpture is very regular 

 over most of the surface, but on the umbos some of the ridges are so 

 large as to appear like small undulations. The interior surface is 

 smooth and white ; the muscular scars are indistinct ; the hinge-margin is 

 rather thin; the posterior ligament is prominent, wedge-shaped, widest 

 distally, and occupies a distinct groove covering the whole breadth 

 and extending about one third the length of the postero-dorsal margin 

 and running forward under the beaks. In the left valve there are two 

 slightly raised, minute, obscure, rounded teeth under the beak, of which 

 the anterior is a little more distinct than the other; farther forward, 

 and separated from the latter by a slight notch, there is an elongated 

 thickening of the margin forming a sort of lateral tooth or lamina and 

 separated from the outer edge by a narrow groove. In the right valve 

 the anterior tooth-like thickening is less distinct and there is only a 

 very slight rounded swelling of the lunular margin under the beak. 



Length, 3.5 mm.; height, 3 mm. 



Two live specimens (No. 35175), station 2096, 8. lat. 39 22' 20", W. 

 long. 70 52' 20", in 1,451 fathoms, 1883. 



LEPTAXINUS, new genus. 



Type. Lepiaxinus minutus, new species. 



Shell small, short-ovate, inequilateral, with the anterior end the 

 longer, and rounded, and the posterior end tapered and angulated, 

 with a slight plication. Hinge-plate well developed, with a delicate, 

 lateral tooth on both sides of the beak in the right valve, and one pos- 

 terior lateral tooth in the left valve; in both valves with the proximal 

 end of the hinge-plate enlarged and thickened near the beak, that of 

 the left valve most developed and rising into a blunt tooth-like promi- 

 nence. Ligament commencing under the beak and running back on 

 the ventral side of the posterior hinge-plate, so that for the greater 

 part of its length it is internal. 



