96 LIMN.^ID^. 



behind, attached to the upper part of the body by a very short 

 and broad stalk or pedicle. 



Shell conic-oval or oblong : spire produced, sinistral or 

 turning from right to left. 



This peculiar and characteristic genus has intermediate 

 relations with Planorbis and Limncea. It resembles the 

 first in its long tentacles, as well as in some of the organs 

 being placed on the left, instead of on the right side of 

 the body ; and it agrees with the latter in the form of 

 its shell : but it difi'ers from both in the spire being 

 sinistral, although that is not a very important cha- 

 racter. The shells of Physa have a remarkably polished 

 appearance, caused in some cases by their being more 

 or less enveloped by an expansion or lobe of the mantle, 

 the lubricating friction of which always keeps the surface 

 smooth and bright. These little mollusks frequent shal- 

 low, and generally clear water, and are gregarious. Their 

 eggs are deposited in strips of a gelatinous consistency, 

 which are fixed to submerged stones as well as to the 

 stalks and leaves of aquatic plants. 



A. Mantle having plain edges and not expanded over the shell, 

 which is covered with an epidermis and has a long spire. 



1. Physa hypno'rum*, Linne. 



Bulla hypnorum, Linn. Syst. Nat. ed. xii. p. 1182. P. hypnorum, F. & H. 

 iv. p.'l43, pi. cxxii. f. 6, 7. 



Body lustrous, dark grey, dusky brown, or almost black, with 

 sometimes a faint tint of blue, covered with very minute black 

 or dark-grej" specks : tentacles long, slender, and pointed, di- 

 verging considerably at their base : eyes very small and not 

 very distinct : foot lance-shaped, narrow, blunt and truncate in 

 front, compressed and rather pointed behind. 



Shell oblong, spindle-shaped, thin, highly poHshed, semi- 



* Frequenting the Hijpnuvi, a kind of moss. 



