16 



PHTSA VIRGATA, Gould. Santa Ana River, Los Angelos Co. 

 PHTSA HETEROSTKOPHA, Say. Dry Creek, Butte Co. Clear Lake, Centerville, 

 Oakland. 



7. ANCYLCS FRAGILIS, Tryon, t. 1, f. 15. 



Description. Shell very small and fragile, sides nearly parallel or slightly in- 

 curved in the middle, but diverging anteriorly; ends rounded. Apex elevated, 

 acute, curved backwards, with about two-thirds of the shell anterior to it. 



Dimensions. Size of the largest specimen. Length 4 mill., breadth 1-15 

 mill., heigth 1 mill. Most of the specimens do not exceed two-thirds of these 

 dimensions. 



Hab. Laguna Honda, California. Rev. J. Rowell. My cabinet and cabi- 

 net of Mr. Rowell. 



Observations. This species is smaller, thinner, and wants the convex lateral 

 margins of our Anc. rivularis, Say. It agrees with that shell, however, in the 

 greater width of its anterior end, while in the shape of its lateral margins it 

 resembles Anc. parallelus, Hald. It is much the smallest of our species. 



PLANORBIS AMMON, Gould. Pajaro River, Monterey Co. 

 PLANOKBIS TRIVOLVIS, Say. Mountain Lake. 

 PLANORBIS GRACILENTUS, Gould. Mountain Lake. 

 PLANORBIS VEMICULARIS, Gould. Mountain Lake. 

 PLANORBIS ORERCULARIS, Gould. Mountain Lake 

 PLANORBIS NEWBEKRYI, Lea. Clear Lake. 



