45 



tured j fossule confluent ; anterior muscular im- 

 pression punctured. 



SPECIES XXXIX. Obliquaria pusilla ( Unio 

 pusilla.) 



Shell thick, convex, perfectly rounded ; epi- 

 dermis smooth, blackish ; nacre white. Length 

 diam. % axis ^ of the breadth. 



This species is very rare ; found in the lower 

 part of the Ohio ; breadth scarcely more than 

 half an inch ; resembles in shape and appearance 

 the Cyclas ; cardinal tooth almost smooth ; 

 lamellar tooth linear. May this not be a young 

 individual ? 



Fifth Sub-Genus SCALENAKIA. 



Form obliquely triangular, scarcely transversal, 

 but very inequilateral ; axis almost lateral ; car- 

 dinal tooth scarcely anterior; lamellar tooth 

 straight ; ligament oblique. 



