1895. PROCEEDINGS OF THE NATIONAL MUSEUM. 311 



a few forms grouping- with it, appear to be nearly allied and to stand on 

 the borderland between the two genera. In these species the hinge line 

 is generally incurved at or near the beaks, and (piite a distinct vestige 

 of a cardinal is often found, and occasionally rudimentary laterals. 



LEPIDODESMA, new genus. 



In China there are found a couple of species of remarkable fresh- 

 water bivalves of large size, thin structure, and greatly inflated form, 

 with slightly nacreous interiors and triangular outlines. These mollusks 

 were placed by Heude in the genus initio, and by him were named U. 

 lauf/uilati and U. aligerus, the latter of which he makes a variety of the 

 former, but which seems to me (|uite distinct. The shell has a strong-, 

 elevated, sharp ridge running from the beaks to the posterior ventral 

 l)ortion, and another more faintly developed behind this, which ends on 

 the edge of the dorsal slope, thus making it strongly biangulate behind. 

 The young shell, until it is half grown, is sculptured into exceedingly 

 strong, concentric ridges, which follow the growth lines, and which, 

 in the later growth, become more crowded and less elevated, and are 

 covered with a thick lamellar ei)idermis. 



Tlie ligament is enormous; wide, elevated, and rather short, dark 

 brown and shining, and composed of concentric scales, which lap over 

 each other in a posterior direction, the whole looking like the back of a 

 short, stout myriapod. The hinge line in a general way makes a rounded 

 sweep, conforming to the high arch of the beaks, but directly under 

 them it is incurved. 



In the left valve are two elevations which probably stand for cardinals, 

 the anterior being elongated, running inwardly in a diagonal manner 

 across the narrow hinge plate, and ending abruptly at the anterior 

 muscle scar. Behind this is a vestige of another, much shorter and 

 fainter, but running- parallel with the flrst, this being on the incurved 

 part of the hinge plate, and just forward of the beaks. 



Beneath the ligament are two strong lamellar laterals, the inner 

 much the higher, and with its upper portion strongly curved out- 

 ward. Just beneath the posterior part of the ligament this tooth is 

 suddenly truncated, but the base extends some distance farther on. 

 Kising from the dorsal slope of this large tooth, and growing partly 

 out of it, is a smaller, lamellar tooth, truncated abruptly behind, and 

 having its upper edge curved outward. 



In the right valve there is a single large lateral, truncated behind, 

 curving out at its upper edge, and fitting between the two laterals of 

 the left valve. Anteriorly its hinge plate slopes inward, and bears at 

 its inner edge a low, somewhat elongated cardinal, running nearly par- 

 allel with the outer edge of the shell. From the beaks to a considerable 

 distance in front of them is a kind of scaly, folded growth, of modified 

 epidermis perhaps, which extends from the outside of the shell half- 

 way across the hinge plate, which, in life, no doubt, keeps the dorsal 



