34 



U. latissima, Raf. An. gen. des Sc. Phys. vol. 5. p. 31. Poul- 



son's trans, p. 25. 

 U. pr^longus, Barnes. Silliman's Jour. vol. vi. p. 261. 

 Cab. A. N. S.No. 1112. 



OBSERVATIONS. 



This shell resembles in outline U. nasutus, Say, U. 

 la?iceolatus, Lea, and U. teres, Raf. With the latter 

 it has most affinity. It is a common western species, 

 found as far north as the Ouisconsin, and inhabits 

 the Alabama river near Claiborne. The figure was 

 taken from a fine male specimen in Mr. Poulson's 

 cabinet. 



UNIO CRASSUS. 



Plate XVI. 

 DESCRIPTION. 



Male. Shell ovate, thick, yellowish, with brown 

 rays, obsolete inferiorly; umbo broad, flattened; beaks 

 obtuse, nearly terminal; umbonial slope angulated; 

 posterior side cuneiform; posterior dorsal margin 

 arcuate; basal margin dilated behind the middle; pos- 

 terior extremity angular; within salmon colour or 

 white, with a horn-coloured margin; cardinal teeth 

 direct, thick, very prominent, subtrifid. 



Female. Shell oval quadrate, ventricose, posterior 

 side dilated; posterior margin widely truncated, di- 

 rect; umbo oblique and terminal. 



