150 LAND AND FRESH-WATER MOLLUSKS. 
when viewed under a lens, darker spots and 
markings are seen arranged in a_ beautiful 
pattern. The tentacles are cylindrical, granu- 
lated, and distinctly club-shaped. The dental 
formula is 242-27, 
B. obscurus is distributed throughout Britain, 
but not generally frequent; it is very local in 
Ireland ; its habitats are under stones in woods, 
on rocks, and more frequently, when of course 
it is not hybernating, upon the trunks of trees. 
This little snail, in all stages of growth, covers 
itself with a coating adapted to the different 
situations in which it is found, rendering its 
detection difficult. ‘If its abode,” according 
to Mr. Sheppard, ‘‘ be upon the trunk of a tree 
covered with lichens, then is the epidermis so 
constructed as to cause the shell to resemble a 
little knot on the bark, covered with such sub- 
stances. If on a smooth tree, from whose bark 
issue small ‘sessile buds, as is frequently the 
case, it will pass off very well for one of them ; 
and on a dry bank, or the lower part of the body 
of a tree splashed with mud, its appearance will 
be that of a little misshapen pointed piece of 
dirt.” 
Genus Zva. 
This genus is distinguished from Bulimus by 
the glossy transparent shell, and the thickened 
