11 



UNIO MORTONI. 



Plate VI.— Fig. 1. 



DESCRIPTION. 



Shell suborbicular, not thick, ventricose; disk flat- 

 tened, or slightly furrowed from beaks to base, co- 

 vered with irregular tubercles; anterior margin sub- 

 truncated; posterior margin straight, direct; ligament 

 margin subarcuate, oblique, forming an angle with 

 the posterior margin; umbo with an oblique furrow, 

 prominent; beaks rather retuse, decorticated; umbo- 

 nial slope angular, slightly arcuate; posterior slope 

 flattened; epidermis yellowish brown, with fine crowd- 

 ed wrinkles; within white; anterior margin not thick- 

 ened; cardinal teeth compressed, very prominent, 

 oblique. 



Cab. J. N. S. No. 1874. 



OBSERVATIONS. 



This pretty species is common in Bayou Teche, 

 Louisiana; but I have seen it from no other locality; 

 it approaches nearest to the (jiiadrulus, Raf., but dif- 

 fers greatly in size, convexity, and want of a distinct 

 furrow from beak to base. It is dedicated to my 

 friend Dr. S. G. Morton, whose exertions have fur- 

 nished a splendid collection of American and foreign 

 fresh water shells to the Academy of Natural Sci- 

 ences. 



