74 DESCRIPTION OF NEW 



the central portion of the disk only), and in the outline being suban- 

 gular. 



Unio discus. Plate XVIII. fig. 57. 



Testa elliptica, valdh compressa, inoequilaterali ; valvulis crassis ; natibus prominentibus ; 

 dentibus cardinalibus magnis; later alibus longis, U cardinalibus separatis; margarila purpurea 

 et iridescente. 



Shell elliptical, very much compressed, inequilateral; valves thick; beaks promi- 

 nent ; cardinal teeth large ; lateral teeth long, being separated from the cardinal teeth ; 

 nacre purple and iridescent. 



Hab. India. 



My Cabinet. 

 Diam. 1-4, Length 3-3, Breadth 5-2 inches. 



Shell elliptical, very much compressed, biangular behind, inequilate- 

 ral ; substance of the shell thick ; beaks prominent ; ligament long 

 and thick; cardinal teeth large, regularly sulcate and deeply cleft in 

 the left valve ; lateral teeth long, thicker at the posterior end, and sepa- 

 rated from the cardinal tooth ; anterior cicatrices distinct ; posterior 

 cicatrices confluent; dorsal cicatrices .placed across the base of the cardi- 

 nal tooth; cavity of the shell very shallow; cavity of the beaks ra- 

 ther small and subangular ; nacre purple and iridescent. 



Remarks. — This description is made from a single decorticated valve, 

 procured of Mr B. Tanner, who purchased it in a lot of shells brought 

 from India. When I first saw this specimen it was evident to me 

 that it differed from any known American species ; and finding, subse- 

 quently, that it was most probably a native of India, I could no longer 

 hesitate as to its being new. It bears some resemblance to U. crassidens 

 (Lam.) and U. alatus (Say). It differs from the former in being flatter? 

 more spread out, and the substance of the shell being less thick. From 

 the latter it differs in being thicker in the substance of the shell, in 

 being ovate, and being without a wing. It is very much to be regret- 

 ted that the exterior should be so much deprived of its epidermis as to 



