62 

 UNIO STAPES. 



Plate XXXV.— Fig. 1. 



DESCRIPTION. 



Shell subtriangular, compressed, thick; anterior side 

 with numerous approximate, angulated, slightly ele- 

 vated tubercles; disks with a distinct furrow from 

 beaks to base; umbonial slope swelling; posterior 

 slope greatly contracted, tuberculated, angulated sub- 

 medially, and forming a right angle with the umbonial 

 slope; posterior margin direct, forming a regular curve 

 with the ligament margin; emarginate inferiorly; base 

 slightly emarginate; within white; cardinal teeth thick, 

 direct; lateral teeth short, very oblique. 



SYNONYME. 



U. stapes, Lea. Trans. Amer. Phil. Soc, (new series,) vol. iv. 



p. 77, pi. vii. fig. 8. 

 Cab. A. N. S. No. 20408. 



OBSERVATIONS. 



A rare species, remarkable for the small area be- 

 hind the umbonial slope, which gives it somewhat the 

 form of U. truncahis, Raf. It approaches nearest to 

 the metanevra, but is very distinct. The shell is not 

 in the least oblique, and the beaks are central, flat- 

 tened and prominent. I found it only in the Alabama 

 river, near Claiborne, where it was first obtained by 

 Judge Tait and forwarded to Mr. Lea. 



