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Sixth Genus OBOVARIA. 



Shell oboval, almost equilateral ; axis nearly 

 medial ; ligament curved ; cardinal tooth striated; 

 lamellar tooth almost vertical, slightly curved ; 

 marginal contour thickened ; three muscular im- 

 pressions ; animal similar to that of the Unio, but 

 having the anus below. 



SPECIES XLV. Obovaria obovalis (Unio 

 obovalis.) 



Shell thick, ventricose, rounded inferiorly ; 

 apices prominent ; epidermis yellowish brown, 

 wrinkled ; nacre white. Inferior breadth | 

 diam. f of the length axis medial. 



Common in the Ohio and adjacent rivers. 

 Length from two to three inches ; cardinal tooth 

 broad, thick, rugose ; lamellar tooth carinated, 

 somewhat oblique : muscular impressions deep. 



SPECIES XLVI. Obovaria torsa (Unio torsa.} 



Shell very thick, ventricose, rounded inferior- 

 ly ; epidermis brownish ; nacre purple ; medial 

 breadth f diam. f of the length axis medial. 



5* 



