53 



straight, or rather unilateral ; axis quite lateral or 

 posterior ; lamellar tooth vertical ; cardinal tooth 

 slightly wrinkled, under the apex which is supe- 

 rior, terminal ; four muscular impressions , animal 

 similar to that of the Unio, except anus and sy- 

 phons, which are inferior. 



SPECIES LI. Pleurobema mytiloides (Unio 

 mytiloides.) 



Shell thick, and ventricose superiorly, attenu- 

 ated at both ends ; apices prominent, entire ; epi- 

 dermis almost smooth, reddish brown, with some 

 oblique black longitudinal bands ; nacre bluish ; 

 lamellar tooth narrow; breadth f diam. of 

 the length axis of the breadth. 



This species rare; found in the Wabash; 

 length two inches; apices somewhat angular, 

 very prominent, entire, heart-shaped ; lamellar 

 tooth very straight; muscular impressions and 

 fossule deep. 



SPECIES LIT. Pleurobema cuneata (Unio 

 cuneata.) 



Shell thick, ventricose superiorly, oblong-oval, 

 attenuated, wedge-shape inferiorly, rounded su- 



