192 



of Limnaea, observing that the circumstance of the 

 Physa? being heterostrophe shells, is not a sufficient 

 generic distinction to warrant their separation ; as they 

 differ in no other respect from the G. Lymneea. 

 Physa castanea Physa hypnorum 

 fontinalis snbopaca 



LYMN.EA. 



HELIX STAGNALIS. LilinCBUS. 



Sowerbys Genera, No. 7, pi. 6. 



The numerous species of this genus of shells, and their 

 being aquatic, renders the separation of them necessary 

 from the G. Helix and G. Bulimus, but more particular- 

 ly the characters of each being in other respects so ve- 

 ry different. It is an aquatic shell, oblong, sometimes 

 turreted and more or less ventricose; spire projecting; 

 aperture ovate, entire, and sharp, the lower part reflect 

 ed upon the columella, and forming an oblique plait 

 on re-entering the opening; substance not pearly, and 

 generally thin: no operculum. The first species men- 

 tioned by Lamarck, L. columnaris, being a terrestrial 

 shell, he has in the last volume of his work removed il fo 



