53 



nently distinguished by the peculiarity of its pale 

 epidermis. The sexes are well marked by difference 

 of outline. 



Not uncommon in the Western rivers, and in Bayou 

 Teche, Louisiana, where it is ornamented with pale 

 green rays. In the Alabama river it is partial to a 

 muddy bed, and rare on the bars. 



I have figured a specimen in Mr. Poulson's cabinet, 

 brought from the west and labelled by Rafinesque. 



UNIO SAGERI. 



Plate XXIX. Fig. 1. 



DESCRIPTION. 



Shell narrow elliptical, moderately thick on the 

 anterior and thin on the posterior side; disks slightly 

 contracted from beak to base, causing the basal mar- 

 gin to be slightly sinuous; anterior side short, margin 

 regularly rounded; posterior side produced, somewhat , 

 pointed, extrem||| obtuse; ligament margin elevated; XUf- 

 umbo not prominent, flattened; umbonial slope round- 

 ed; within bluish-white and iridescent; cardinal tooth 

 in the right valve thick, direct, divided at the summit 

 by a deep groove; in the left valve widely bifid, with 

 a submedial lamelliform elevation; lateral teeth com- 

 pressed. 



OBSERVATIONS. 



This interesting species was found in Detroit river, 

 Michigan, by Dr. Abraham Sager, of Detroit, to whom 



