104 LAND AND FRESH-WATER MOLLUSKS. 
and Succmea , smooth, with a more or less pro¬ 
minent beak in the middle 
of its lower edge (see fig* 
18, which represents the 
horny jaw or buccal plate 
of the cellar snail). 
When the animal crawls, the shell is balanced 
nearly horizontally on its back. The tentacles 
are protruded and withdrawn with surprising 
quickness. The species feed on vegetable sub¬ 
stances, and inhabit damp or shady places, as 
under stones, or among grass or moss. 
The species are very difficult to distinguish ; 
I have given therefore full descriptions of each. 
The following analytical table may be found 
useful:—- 
Fig. 18 . 
1. 
( Shell depressed, umbilicus apparent ... 
... ... 2 
( „ trochiform, umbilicus minute 
... H.fulva 
2. 
( Opacity around the umbilicus. 
... ... 3 
( No opacity .. .,. 
. 4 
f Umbilicus large ; very clouded below... 
II. cellaria 
3. 
< Upper surface more convex, dull ... ... 
( Shell smaller, surface shining... .. 
H. nitidula 
II. alliaria 
4. 
( Shell white . .. 
. 5 
( „ horn-coloured. .. 
... ... 6 
5. 
( Whorls not rapidly enlarging... 
II. crystallina 
( Last whorl capacious . 
... S. pur a 
6. 
( Umbilicus very large . .. 
II. excavata 
\ Umbilicus moderate . 
. 7 
>7 
j Surface radiately striated . 
H. radiatula 
i . 
} „ transversely wrinkled. 
H. nitida 
