56 



SYNONYMES. 



U. fragilis, Raf. Ann. gen. des Sc. Phys. vol. v. p. 29. Poul- 

 son's trans, p. 22. Say, Amer. Conch. No. 6. 



U. gracilis, Barnes. Silliman's Journ. vol. vi. p. 174. 



U. fragilis, Swains. 



Symphyxota gracilis, Lea. Trans. Amer. Philos. Soc. new se- 

 ries, vol. iii. p. 66. 



Cab. A. N. S. No. 1657. 



OBSERVATIONS. 



Allied to U. alatus, but is longer in proportion, 

 thinner, and lighter coloured in the interior and epi- 

 dermis. In some localities the wing is small, but in 

 others generally elevated. 



Found by Mr. Schoolcraft in Fox river; it inhabits 

 the Detroit river, Michigan, lakes, and the western 

 rivers generally, and I found it common in the Ala- 

 bama at Claiborne. 



UNIO ALATUS. 



Plate XXXI. 



DESCRIPTION. 



Shell triangular, ovate, moderately thick; disks 

 flattened anteriorly, and inflated over the umbonial 

 slope; anterior side narrow, margin obliquely recti- 

 linear above; posterior side profoundly dilated, and 

 rising into an elevated connate wing; umbo oblique, 

 inclined, not prominent; posterior lunule with two 

 subangulated lines; umbonial slope regularly rounded; 

 wing emarginate inferiorly; posterior end biangulated; 



