PLANORBIS. 



103 



Fig. 174. 



Foot short, 



PI.A:V0RBIS, Guettakd. 



Tentacles slender, filiform, 

 ovate. 



Shell dextral, discoidal ; spire depressed, 

 whirls numerous, visible on both sides; aper- 

 ture crescentic, 



or transversely ^^* ' 



oval ; peristome thin, incomplete, 

 the upper margin produced. 

 Jaw single, superior, arched. 

 Lingual membrane — ? 



Animal of Plmiorbis 

 hicarinatua. 



Animal of Planorhis. 



The genus Planorhis is widely 

 distributed over the globe, but 

 usually prefers the more temperate regions. It is found in every 

 part of this continent, reaching info Mexico, and apparently much 

 more abundant there than the other genera of the family. 



Most of the sections or subgenera are represented in Xorth 

 America. The South American Taphius is most nearly allied to 

 the Carinifex of the Pacific coast. 



The name Planorhis is now universally applied to the genus. 



The species of this genus have a dextral shell, but the orifices 

 of the generative, excretory, and respiratory organs are on the 

 left of the animal, as in Physa. They are sluggish in their habits, 

 preferring stagnant pools. 



Say considered the shells sinistral, a fact which must be borne 

 in mind while studying his descriptions. 

 On this account I have represented the fac- Fig. 176. 



similes of his figures in a diflPerent position 

 from those of* other authors. 



Planorliis sul»crenatus, Cpr. — Shell 

 tumid, very thin, horu-colored ; whirls six, 

 rounded, sutures impressed ; with sharp radiat- 

 ing, somewhat crowded and occasionally mi- 

 nutely crenulated, ridges ; aperture rounded, 

 parietal wall small, scarcely touching the penul- 

 timate whirl ; labrum slightly deflected, fuscous 

 within ; umbilicus deep. Long. .05, lat. .08, 

 alt. .36. 8 Planorhis subcrenatus. 



