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 Carycliia 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 ( Voluta denticulatd) 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 Scarahusy 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 Scarobus^ 
where the varices form a ridge down each side of 
the shell, as in the marine genus Apollon, It is to 
