OF Tin: immii.v OP N \i \ih>. 1 j? 



posterior slope, and from the ventricosUs in not being globose 

 over the umbones; and of course is much less in diameter. 

 The quite large impression of the mantle under the callus, 

 between the lateral and cardinal teeth, is v< t \ remarkable in 

 these three species. 



9. Unto Seccbis. Plate XI. fiir. 17 



.-• 



Testi'i Bubtriangulari, itueqwilateraU, per umbones valde complanat . 

 vah'ulis craaris ; natibua tl< rati*, recutvatia, eompruHeritniaqut ; dent* 

 cardinali magno, lateral* crasso; ligamento bretmuculo, craseoque; 

 margaritd alba et iridescente. 



-,' 



Shell sub-triangular, inequilateral, flattened over the umbones; valves 

 thiek : beaks elevated, recurved, much compressed ; cardinal tooth Lai [ 

 lateral tooth thiek; ligament rather short and thick; nacre pearly while 

 and iridescent. 



Hah. Ohio. T. G. Lea. 



My Cabinet 

 Cabinet of T. G. Lea. 

 Cabinet of Prof. Vanuxem. 

 Cabinet of the Academy of Natural Sciences. 

 Unio dt jut ssa of Rafinesque. 

 Diam. -9, Length 1-5, Breadth 1*9 inches. 



Shell sub-triangular, transversely wrinkled, inequilateral, 

 much Battened over the umbones; substance of the shell 

 thick, often ponderous; beaks elevated, much compressed, 

 recurved: dorsal margin angular; posterior dorsal margin ob- 

 lique; posterior margin angular; basal and posterior basal 

 margin curved; anterior and anterior basal and dorsal mar- 

 gins round ; posterior slope flattened, this view presents the 

 sheilas a long ellipsis ; epidermis olive-yellovt passing into 

 olive-brown, shining and transversely wrinkled; rays formed 

 by small spots, alternately darker and lighter than the g" q< - 

 ral colour of the epidermis, which cau-e the rays to look likl 

 a minute chain, these rays are from one to two eighths of an 

 inch apart, and extend over the whole •! i-k . the spaces be- 



