338 



SHELLS AND SHELL-FISH. 



PART II. 



transverse testaceous partitions, into chambers, which 

 communicate with each other by triradiated apertures. 

 Representing the Cephalopoda. 



S. lacustris Flem. ' 



LiMNEA Lam. Very thin spiral ; the spire 

 variable in length, but always pointed; 

 aperture large, effuse ; outer lip, typically, 

 much dilated and rounded. 

 L. stagnalis. Sow. Man. f. 308. {fig. 99.) 

 aserta. lb. f. 309. 



Leptolimnea Sw. Nearly cylindical ; spire 

 thick, lengthened, longer than the aper- 

 ture; which latter is small. 



L. elongata. Sow. Gen. f. 6. 



Physa Drap.* Shell generally reversed, smooth, and 

 poUshed; aperture oval, not dilated, {^fig. 100.) 

 rivalis. {fig. 100. 6.) fontinalis. lb. f. 9. {fig. 100. a.) 

 Guildingii Sw. {fig. 100. c, d, e.) 



100 



^^ 



Potomophila Sw. Shell resembling a Limnea, but with 

 a distinct fold on the pillar. 

 P. bulimoides. En. Meth. 459. f. 7. (fig. 31. p. 187.) 



Ancylus Lam. Shell thin, patelUform ; resembling a 

 limpet. 



A. fluviatilis. Sow. Man. f. 246. 



Family TURBID^. 

 SheU solid, but not perlaceous, spiral ; aperture entire, 

 closed by an operculum. 



* Between the shells o^ Physa and Lymnea there is no great difference; 

 but their animals are too distinct to be united in any system of malacology. 



