200 PLANORBIS. 
Diam. 19, alt. 8 mill. 
California to Mexico. ‘ 
All the West Coast specimens, included by 
Mr. Binney in Pl. trivolvis, are referable to 
this species, which entirely replaces trivolvis 
west of the Rocky Mountains. It differs from 
trivolvis in its fragility, carina, etc. 
15. PLANORBIS OREGONENSIS, Tryon. 
Plate 6, fig. 10, 11, 12. 
Shell very like Pl. trivolvis, but whorls 
more rapidly increasing in volume; aperture 
oblique, ear-shaped, large, extending above 
and below the plane of the volutions; texture 
thin, striz not very close, coarse and irregu- 
lar. Color dark horn. : 
Diam. 9, alt. 4 mill. 
Pueblo Valley, near the boundary between 
Oregon and Nevada, 60 miles west of the east 
boundary of Oregon.— W. M. Gabb. 
This interesting species is from a thermal 
spring, the water of which has a temperature 
(47) 
