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 PI. exacutus, but is larger, less 

 compressed and less delicate, and the peri- 

 phery, instead of being sharp-edged, has a 

 blunted keel, like PI. carinatus of Europe. 



It is a common species in the waters of Cali- 

 fornia. 



20. PLANORBIS EXACUTUS, Satj. 



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 liyalina, Lea, and Planorbis lenticu- 



laris, Lea, in the synonymy of this species, 



but Playiorbis Buchanensis, also here included 



by Mr. Binney, is, I think, identical with PI. 



dilatatus, Gould. 

 \ ^54) 



