AUEICULID^. 189 



the fresh-water Univalve Mollusca. They have the 

 sessile eyes of the Pond-snails, placed behind instead 

 of in front of the tentacles, and the subcylindrical 

 tentacles of the Land-snails ; but the tentacles are not 

 retractile under the skin of the neck. In the same 

 manner the Carychia and the Acmea are terrestrial, 

 living in damp moss ; the Conovuli live in the mud 

 at the mouths of rivers, or in the sea — they seldom 

 leave salt or at least brackish water. There are some 

 foreign species which live in ponds, and have all the 

 habits of our Pond-snails, only their pillar is more 

 distinctly plaited. 



Montagu observes : " A remarkable character of 

 this shell ( Valuta denticulata) is that the columella 

 extends no further than the upper part of the body 

 volution, the superior spires (whorls) being destitute 

 of any pillar or internal spiral division." This pe- 

 culiarity is common to most species of this family, 

 and is one of its best conchological characters : the 

 absence is generally caused by the animal absorbing 

 the septa which separate the upper whorls, and thus 

 converting the spire into a single cavity, as it en- 

 larges the shell at the edges of the mouth below. 

 In Scarabus, the septa between the whorls appear 

 to be originally formed imperfect. (See Phil. Trans. 

 1833.) 



Many of the animals of this family rest in their 

 growth, and form a more or less complete new mouth 

 after they have formed half a whorl to the shell. 

 This is most easily observed in the genus Scarabus, 

 where the varices form a ridge down each side of 

 the shell, as in the marine genus Apollon. It is to 



