AND OTHER FAMILIES. 39 



My Cabinet. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 

 Cabinet of Mr Stewart. 

 Cabinet of Mr Hyde. 

 Diam. -9, Length 1-4, Breadth 2-7 inches. 



Shell trapezoidal, very inequilateral, transverse, compressed, angular 

 behind ; substance of the shell rather thin ; umbonial slope subcarinate ; 

 beaks slightly prominent, placed near the anterior margin and concen- 

 trically wrinkled ; carina much elevated ; ligament long, narrow and 

 nearly straight ; epidermis dark brown, wrinkled and sometimes ob- 

 scurely rayed ; cardinal teeth oblique and double in both valves ; lateral 

 teeth nearly straight and lamelliform ; anterior cicatrices distinct, pos- 

 terior cicatrices confluent ; dorsal cicatrices situated in the centre of 

 the cavity of the beaks ; cavity of the beaks shallow : nacre purple and 

 iridescent. 



Remarks. — This interesting species is one of the collection made by 

 Mr Stewart in the Bayou Teche. It is a very distinct and beautiful 

 species. Its form is more like a trapezium than that of any other spe- 

 cies with which I am acquainted. It resembles most the U. compla- 

 natus (Soland.). It differs from it, however, in its remarkable outline, 

 in its teeth, in the concentric wrinkles of the beaks, and in the beaks 

 being placed nearer to the anterior margin. The angle of the poste- 

 rior margin is also more acute. In the deep brown colour of the epi- 

 dermis and in outline of the margin it approaches the U. obesus (nobis). 

 It is, however, much less inflated. 



Unio Taitianus. Plate IV. fig. 11. 



Testa subtriangulari. obliqud crasstique ; valvuUs antice crassioribus ; dentibus 

 cardinalibus grandibus ct elevatis, lateralibus crassis et subcurvis ; margaritd 

 alba. 



Shell subtriangular, thick and oblique; valves thicker anteriorly ; cardinal teeth large 

 and elevated ; lateral teeth thick and slightly curved ; nacre pearly white. 



