40 

 UNIO CARIOSUS. 



Plate XIX. 

 DESCRIPTION. 



Shell subovate, ventricose, thick anteriorly; epider- 

 mis yellowish or straw coloured, very smooth and 

 polished, with a few narrow dark green rays poste- 

 riorly, more numerous on the posterior slope; umbo 

 prominent, decorticated; umbonial slope angulated; 

 ligament margin elevated; ligament prominent; basal 

 margin swelling posteriorly; within white; cardinal 

 teeth double in each valve, prominent, oblique. 



SYNONYMES. 



U. cariosus, Say. Nich. Enc. (Amer. ed.) art. Conch, pi. iii. 



fig. 2. female. 

 U. luteola, Lam. An. sans vert. vol. vi. p. 79. 

 U. ovatus, Valenc. 

 Cab. A. N. S. No. 1022. 



OBSERVATIONS. 



This is one of the most abundant species in the 

 tide waters of the middle states, but I found it com- 

 paratively rare in the Potomac and James rivers. In 

 varieties of form it much resembles U. crassus, and 

 both male and female are represented, in order to 

 convey a clear idea of sexual differences, which are 

 so striking in a large proportion of the species. It 

 is very often destitute of rays, and I have seen only 

 one specimen in which the rays extended over the 

 disk to the anterior margin. 



