NO. 1139. DKEP- WATER MOLLUSC A VERRILL AND Ill'sH. 7!>5 



AXINOPSIS CORDATA, new species. 

 (Plate XCVII, figs. 5, 6.) 



Shell small, white, smoothish, rouuded or somewhat cordate, longer 

 anteriorly, with small, little prominent beaks curving forward. Antero- 

 dorsal margin a little convex, sloping gradually and passing somewhat 

 abruptly into the anterior margin, which is broadly and obtusely 

 rounded; ventral margin strongly convex, somewhat produced in the 

 middle; posterior margin pretty evenly rounded, except in the middle, 

 where there is a slightly produced portion corresponding to the plica- 

 tion; postero-dorsal margin strongly convex in the middle. The sur- 

 face is marked by fine, microscopic, concentric strioe and irregular lines 

 of growth which, on the umbo, appear as slight undulations. The liga- 

 mental area is relatively large, prominent in the middle, and defined by 

 a distinct groove, beyond which there is a well-marked but low radiat- 

 ing ridge or plication which forms an inconspicuous projection at the 

 margin ; anterior to this there is a very slight wave-like depression of 

 the surface, much as in most species of Cnjptodon. The hinge-margin 

 is decidedly thickened; in both valves there is a rather large, obtuse 

 tooth just below the beak, from which it is separated by a rather large 

 space for the ligament which runs backward for a short distance in a 

 conspicuous submargiual groove, becoming internal distally; anteriorly 

 the groove is narrow and outside the margin. 



Length, about 2 mm.; height, the same. 



This species is referred to the genus Axinopsis with some doubt, 

 although it has the distinct cardinal tooth and ligament-groove. It 

 has, however, a single posterior plication similar to that seen in some 

 species of Cryptodon; but the character of the plications vary in that 

 genus, in some cases being very strong and in others obsolete, or nearly 

 so. In fact, the genus Axinopsis can hardly be distinguished from it 

 except by the distinctly developed cardinal tooth, which is only par- 

 tially differentiated from the proximal end of the anterior hinge-plate. 



A few separate valves and two live young were found at six stations 

 between N. lat. 40, W. long. 71 14' 30", and N. lat. 35 42', W. long. 

 74 54' 30", in 43 to 202 fathoms, 1880-1884. 



The young specimens from stations 870 and 943 are referred to this 

 species with considerable doubt, as they have a much more rounded 

 outline, although the hinge-margin is similar. 



AXINODON, new genus. 



Type. Axinodon ettipticus, new species. 



Shell thin, rounded or ovate, without plications. Hinge with one or 

 two small or subrudirnentary teeth. Ligament internymphal, poste- 

 riorly so far internal that its inner end, distally, is attached below the 

 inner edge of the hinge-plate, and therefore covers its entire breadth. 



