NO. 1139. DEEP-WATER MOLLUSCAVEERILL AXI> l',l sil. 797 



This genus differs from Cryptodon in the more internal position of 

 the ligament and in having distinct lateral teeth. From Ajchuxl<>n, in 

 the stronger hinge plate, in the presence of the lateral teeth, in having 

 a posterior plication, and in lacking distinct cardinal teeth. 



LEPTAXINUS MINUTUS, new species. 

 (Platr LXXXIX, li-js. :;-5.) 



Shell minute, broadly ovate, with a slightly produced obtuse point 

 near the middle of the posterior end, and a somewhat produced, 

 broadly rounded anterior end. Beaks behind the middle, rising a little 

 above the dorsal margin and turned forward, leaving a small, rather 

 deep lunular area. Antero-dorsal margin a little convex, sloping but 

 little; anterior margin broadly and evenly rounded, forming nearly a 

 semicircle, and passing continuously into the ventral margin, which 

 is a little more broadly rounded ; the posterior margin is somewhat 

 angular, with a distinct prominence a little below the middle, where 

 the radial ridge terminates, below this for a short space the mar- 

 gin is nearly straight or slightly incurved; above, the postero-dorsal 

 margin is straight as far as a slight angle in the ligamental area, above 

 which it is convex to the beak. The hinge-margin is a little thickened, 

 and in the left valve forms a rather prominent and somewhat angular 

 tooth just below and slightly in front of the beak ; the ligamental groove 

 is barely visible on the inner face of the posterior hinge-margin, and 

 runs forward as a narrow groove beneath the beak; in the r:ght valve 

 there is a somewhat less prominent tooth just under the beak, behind 

 which the ligamental groove forms a distinct notch in the margin. 

 Under the microscope there is seen in both valves a distinct submargi- 

 nal ridge with a conspicuous groove behind it, commencing a consider- 

 able distance behind the beak and running in and along the inner 

 hinge-margin; there is also in the right valve a short, indistinct groove 

 along the end of the hinge-margin in front of the beak. Externally a 

 rather shallow, depressed undulation runs from the beak to the pos- 

 tero-ventral margin; behind it is a narrow, but slightly prominent, 

 radial ridge running to the posterior angle; back of or above this a 

 rather short ligameutal area projects beyond the margin. The surface 

 is covered with a thin, greenish yellow epidermis and is marked by 

 tine, pretty regular, parallel, raised lines of growth, and also faint and 

 rather numerous radiating lines which are not visible except under a 

 high power. 



Length, nearly 2 mm.; height, If mm. 



One live specimen (Xo. 45080), station 949, X. lat. 40 3', W. long. 70 

 31', in 100 fathoms, 1881. 



