TRYONIA. 67 



Genus TRYONIA, Stimpson. 



I admit the two following species with some 

 hesitation, because no fresh specimens have 

 ever been found, and it is not at all unlikely 

 that they are both of them entirely extinct. 



1. TRYONIA CLATHRATA, Stimpsm. 

 Plate 17, fig. 20. 



Shell elongated, narrow, apex of spire acute, 

 sutures deeply impressed ; whorls eight, with 

 generally about twelve longitudinal ribs cross- 

 ing them, sometimes crossed by revolving striae 

 or ridges, and angulated in the middle. Aper- 

 ture rounded oval, very small. 



Alt. 5, diam. 1*5 mill. 



Colorado Desert, Southern California. In 

 the dried bed of an ancient lake. 

 (48) 



