FRESHWATER AND LAND SHELLS. 31 



Diam. -9, Length 1*3, Breadth 2'5 inches. 



Shell elliptical, transverse, somewhat inflated, inequilateral, biangu- 

 lar behind and rounded before ; substance of the shell somewhat thick ; 

 beaks rather prominent ; ligament rather short and thin ; epidermis 

 nearly black, and apparently without rays ; cardinal teeth compressed, 

 single in the right and double in the left valve ; lateral teeth rather 

 long and somewhat curved ; anterior cicatrices distinct; posterior cica- 

 trices confluent ; dorsal cicatrices placed in the centre of the cavity of 

 the beaks; cavity of the shell deep; cavity of the beak rather small; 

 nacre purple and iridescent. 



Remarks. — ^This was among the shells procured by Professor Shep- 

 ard, from near Darien, and may be considered to be between the com- 

 planatus (Soland.) and confertus (nobis). It is disposed to be more 

 cylindrical than the former, and has a less elevated umbonial slope than 

 the latter. The curve of the basal margin is greater than either. 

 Possessing but a single specimen, I am unable to determine if the co- 

 lour of the nacre varies in this species as it does in most of those allied 

 to complanatus. 



Unio Barnesianus. Plate X. fig. 26. 



Testa subtriangulari, compressd, incequilaterali ; valvulis crassis ; natibus subprominulis ; 

 dentibus cardinalibus parvis ; lateralibus subrectis ; mar garita alba et iridescente. 



Shell subtriangular, compressed, inequilaleral ; valves thick ; beaks rather prominent ; 

 cardinal teeth small ; lateral teeth nearly straight; nacre white and iridescent. 



Hab. Cumberland River, Ten. Professor Troost. 

 Cabinet of Professor Troost. 

 Diam. '6, Length 1, Breadth 1-4 inches. 



Shell subtriangular, compressed, inequilateral ; substance of the shell 

 thick ; beaks rather prominent, short ; epidermis chestnut brown, with 

 interrupted rays and strong marks of growth ; cardinal teeth small, 

 somewhat compressed ; lateral teeth nearly straight, and enlarged at 

 the posterior end ; anterior cicatrices distinct; posterior cicatrices dis- 



