44 



umbonial slope angulated; basal margin arcuate; epi- 

 dermis green olive, with green capillary rays over 

 the umbo; within chocolate colour; cardinal teeth 

 very large, direct, prominent, trifid in the right valve; 

 cavity of the beak very profound. 



SYNONYMES. 



U. tuberculatus, Raf. Ann. gen. ties Sc. Phys. vol. v. p. 42. 



Say. Avner. Conch. No. G. Ferr. Mag. de Zool. 

 U. verrucosus, Barnes. Silliman's Journ. vol. vi. p. 125, pi. 5, 



fig. 6. 

 U. tuberculosa, Valeric. 

 Cab. A. N. S. No. 1430. 



OBSERVATIONS. 



Some varieties of this species closely resemble U. 

 bullatas exteriorly, but independent of other charac- 

 ters, the chocolate coloured interior, which, though 

 sometimes pale, never wholly disappears, will at once 

 distinguish the present species from all its congeners. 

 It is a very variable shell; some specimens from the 

 Harpeth river, Tennessee, being much dilated and 

 compressed, and the ligament margin so much ele- 

 vated as to give the posterior side an alated appear- 

 ance. Other specimens are far more elevated in 

 proportion to their length, and the posterior sulcus 

 and emargination profound. These great differences 

 may be sexual characters, but require an anatomical 

 investigation of the animal to settle that point. 



Common in the western rivers, and inhabits Lake 

 Erie and the Ouisconsin, according to Mr. Barnes. 

 It is not found in Alabama south of the Tennessee 

 river and its tributaries. 



