CONCHOLOGIA CESTRICA. 69 
Genus PLANORBIS, Guetrarp, 1756. 
Animal of P. bicarinatus.—({W. G. B.] 
Fig, 136, 
, 
Shell, dextral, discoidal; spire depressed; whorls 
numerous, visible on both sides; aperture crescentic, 
or transverse-oval; peristome thin, the upper margin 
produced. 
Animal, tentacles slender, filiform; foot short, ovate. 
Sub-genus PLANORBELLA, HaLpeman, 1842. 
Shell, with few whorls; aperture campanulate, or ex- 
panded, prominent. 
P. campanulatus, Say. 
Planorbis campanulatis, Say, Jour. Acad. Phila. F. S., 
is erS2n, 
Shell, with 4 whorls, longer than wide > P. campanulatus, 
[W. G. B.] 
spire plane, or nearly so; body whorl 
abruptly dilated, near the aperture, sub- 
campanulate; umbilicus profound. H. 
7, W. 17-12, mill., in its greater and less 
diameters. 
Station, in rivers and ponds. Dela- 
ware Water Gap, Pennsylvania. 


Sub-genus HELISOMA, Swainson, 1840. 
Shell, ventricose ; spire sunk below the body whorl; 
whorls few, often angulated. 
