200 PLANORBIS. 



Diam. 19, alt. 8 mill. 



California to Mexico. 



All the West Coast specimens, included by 

 Mr. Binney in PI. 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, striae 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) 



