PLANORBIS. 189 
Typical Species. 
The aperture in the plane of volution and 
not expanded. 
A. West Coast SPECIES. 
1. PLANORBIS SUBCRENATUS, Carp. 
Plate 5, figs. 1, 2. 
Shell tumid, very thin, horn-colored ; 
whorls six, rounded, sutures impressed, with 
sharp radiating, somewhat crowded and occa- 
sionally minutely crenulated ridges; aperture 
rounded; parietal wall small, scarcely touch- 
ing the penultimate whorl; labrum slightly 
deflected, fuscous within ; umbilicus deep. 
Diameter 23, alt. 9 mill. 
Oregon. Washoe Mining District. 
In its flatness this species resembles the Pl. 
glabratus, Say, of the Atlantic States, but it 
is larger and not nearly so smooth. 
(36) 
