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. Ib. 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 

 polished; aperture oval, not dilated, (fig. 100.) 

 rivalis. (Jig. 100. 6.) fontinalis. Ib. f. 9. (fig. 100. a.) 

 Guildingii Sw. (fig. 10O. c, 



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 3 patelliform ; resembling a 



limpet. 



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



FAMILY TURBID^E. 



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

 closed by an operculum. 



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

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



