AND OTHER FAMILIES. 181 



Shell subtriangular, inflated, singularly compressed on the posterior part, which is 

 striate ; valves remarkably thick; beaks very prominent ; cardinal teeth large ; late- 

 ral teeth thick and nearly straight ; nacre in the cavity very light purple. 



Hab. Tennessee. G. B. Sowerby. 



My Cabinet. 



Cabinet of Mr Sowerby. 



Diam. 1-5, Length 1*7, Breadth 1-8 inches. 



Shell subtriangular, inflated, singularly compressed on the posterior 

 part, which is filled with stria? passing from the beak to the posterior 

 and posterior-basal margins, the anterior part being inflated and smooth ; 

 slightly emarginate at posterior basal margin ; substance of the shell 

 very remarkably thick, less so on the posterior part ; beaks large and 

 very prominent ; ligament short and thick ; epidermis bright brown, 

 smooth and shining before, striate behind ; cardinal teeth large, sulcata, 

 elevated and cleft in the left valve, and emerging from a pit in the 

 right valve ; lateral teeth thick, short and nearly straight ; anterior and 

 posterior cicatrices both distinct ; dorsal cicatrices situated on the under 

 part of the cardinal teeth ; cavity of the beaks shallow and subangular ; 

 nacre very light purple in the cavity, and white on the anterior margin. 



Remarks. — To the kindness of G. B. Sowerby, Esq., one of the 

 most distinguished writers on conchology in England, I owe the pos- 

 session of this truly interesting shell, and to him I with great pleasure 

 dedicate it. He received it from the state of Tennessee, but from 

 what river I do not know. In general outline it resembles somewhat 

 the trigonus (nobis), but differs from it in being more rotund, in hav- 

 ing the posterior part compressed and striate, and in being coloured 

 inside. It has a stronger resemblance to the Haysianus (nobis) than to 

 any other species known to me, but diflfers from it in being more com- 

 pressed behind, in being more striate, in being much larger (to judge 

 from the few specimens I have seen of both), and in the difference of 

 the colour of the nacre, the Haysianus being dark chocolate, while the 

 Sowerbianus is of a very light purple, approaching to flesh colour. 



48 



