PLANORBIS. 207 
lips embracing three-fourths of that part of 
the whorl which is beneath the carina. 
Diam. 6, alt. 1:5 mill. 
California. 
Allied to Pl. exacutus, but is larger, less 
compressed and less delicate, and the peri- | 
phery, instead of being sharp-edged, has a 
blunted keel, like Pl. carinatus of Europe. 
It is a common species in the waters of Cali- 
fornia. 
20. PLANORBIS EXACUTUS, Say. 
Hald. Monog. p. 21, t. 4, figs. 1—3. 
Inhabits all the Northern, Middle and 
Western States, but is replaced in California 
by the preceding species. 
I agree with Mr. W. G. Binney in including 
Paludina hyalina, Lea, and Planorbis lenticu- 
laris, Lea, in the synonymy of this species, 
but Planorbis Buchanensis, also here included 
by Mr. Binney, is, I think, identical with Pl. 
dilatatus, Gould. 
(54) 
