TRYONIA. 67 
Genus TRY ONTIA, 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, Stimpson. 
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 strize 
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) 
