LAND SNAILS. 165 
be observed, in full-grown shells, a tubercle-like 
tooth ; the length is’ usually about a quarter of 
an inch. The shell varies in size, shape, and 
colour ; greenish-white and transparent examples 
have been found. The dental formula is 292°, 
This species is generally distributed through- 
out Britain. In moist weather, these snails may 
be seen in some numbers on the trunks of trees; 
in dry weather, sheltering beneath the loose 
bark, or in the hollows and crevices of the trunks. 
Other favourite haunts are among decaying wood 
and dead leaves, or lurking in moss, or even on 
the tops of old ivied walls. . 
It occurs in a fossil state at Grays, in Essex. 
Genus Cravsiti1a (Close Snails). 
The animal, closely resembling that of Bulimus, 
has a short, broad, and obtuse foot; the upper 
tentacles are short and the lower ones very small 
(PLIX., fig. 94). The shell is fusiform, of many 
reversed whorls; the last one is smaller than the 
one before it; the aperture is elliptical or pear- 
shaped, united all round,and toothed. In addition 
to the contraction and folds of the shell for the 
protection of the snail within, there is added 
an elastic appendage termed the clausiwm, which 
is capable of closing the aperture. The clausium 
is situated at the distance of about half a whorl 
