188 PLANORBIS. 
Genus PLANORBIS, Guetiard. 
Besides the typical group, the following 
well-founded subgenera have been adopted : 
PLANORBELLA, Haldeman. Shell with the 
whorls few; aperture expanded, campanulate 
or bell-shaped, prominent. 
Hetisoma, Swainson. Shell ventricose, the 
spire sunk below the body whorl; whorls few, 
often angulated. 
ApuLa, H. Adams. Shell with the whorls 
rounded and very numerous, deeply umbili- 
cated on the upper, and convex on the under 
side; aperture campanulate. 
Menetus, H. and A. Adams. Shell de- 
pressed ; whorls rapidly increasing, periphery 
angulated. 
Navutitina, Stein. Shell small, orbicular 
above, flat beneath; whorls few, rapidly in- 
creasing. 
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