PHYSA. 21 



internal base of the tentacles: inner and poste- 

 rior edge of the mantle digitated. Organ of the 

 deferent canal immediately behind the left ten- 

 tacle, corresponding organ posterior to it, upon 

 the same side, and near the pulmonary orifice. 

 Shell sinistral, subglobular or lengthened, 

 smooth, and polished; with a pointed exserted 

 spire: aperture longitudinal, with the labrum 

 sharp, and not reflected: labium extending upon 

 the last whirl. 



OBSERVATIONS. 



The animal is distinguished from Limnea by 

 the digitated mantle, and setaceous tentacles; 

 and in having the foot slender, and generally 

 keeled, instead of oval. This organ is better 

 adapted for locomotion than in any of the allied 

 genera; as the animal moves about with great 

 ease and rapidity; with a uniform, gliding mo- 

 tion; and not by extending the foot forward, 

 and drawing up the body. 



The PhyssB are generally less inclined to rest 

 than the allied genera; they spend less time in 

 a state of repose, and move about as usual, 

 when Limnea and Planorbis are nearly torpid 

 with cold. On the other hand, they do not 



