OSTEODESMACEA. MOLLUSCA. COCHLODESMA. 49 



COCHLODESMA LEA'NA. 



Shell thin, white, sub-oval, the shorter side of the right or 

 more convex valve truncated ; rib-like support directed backwards. 



FIGURES 29, 30. 

 State Coll., No. 230. Soc. Cab., No. 1726. 



Anatina Leana, CONRAD ; Journ. dead. Nat. Sc., vi. 263, pi. 11, f. 11. 

 Cochlodesma Leana, COUTHOUY ; Bost. Journ. Nat. Hist. } ii. 170. 



Shell sub-oval, thin and brittle, white, with a thin, yellowish 

 epidermis ; the right valve convex, and truncated at the shorter 

 end ; the left valve nearly flat, and rounded at both ends ; posterior 

 end gaping, a little the shortest, and usually a little the narrowest ; 

 beaks very small, scarcely prominent, cleft at one side ; a faint, 

 wave-like ridge passes from them to the lower posterior angle ; 

 surface slightly wrinkled by the lines of growth, somewhat pearly 

 beneath ; interior chalky-white, the muscular and palleal impres- 

 sions superficial, pearly. The spoon-shaped hinge process nearly 

 horizontal, directed across the shell, and resting on a rib-like sup- 

 port, directed to the posterior muscular impression, immediately 

 in front of which is another thread-like branch in the direction of 

 the cleft in the beak. Ossiculum none. Length If inch, 

 height 1 inch nearly, breadth ^ inch. 



Found about Cape Cod in almost every direction, inhabiting 

 sandy beaches ; also about Nantucket. I have never heard of it 

 on the north shore of Massachusetts Bay, but it is more abun- 

 dant to the south of us. 



The animal has the mantle closed in front, except an opening for a 

 broad, compressed foot, extending the whole length of the small ab- 

 dominal mass ; edges of the mantle a little thickened and wrinkled ; 

 siphons long, slender, separate in their whole extent. 



This genus, proposed by Mr. Couthouy, has, I observe, been ad- 

 mitted by J. E. Gray, in the " Annals of Science," and I have there- 

 fore adopted it without hesitation. 



This species very closely resembles My a (Cochlodesma) pratenuis 

 of Pennant (Ligula prcetenuis, Montagu), but differs in being more 

 rounded, less convex, less narrowed behind, and has no signs of a 

 granulated or shagreened epidermis, like that shell. 



7 



