LUNG-BREATHING MOLLUSKS. Sl 
dage is very minute, concealed within the substance 
of the mantle, or altogether wanting. Our own coun- 
try furnishes examples of each of these kinds. All 
the native species are comprised in five families, — 
Cyclostomade, Auriculade, Limneade, Helicide, 
and Limacide. 
FAMILY CYCLOSTOMADA. 
This is an extensive family, though represented 
in Britain by but a single species. The great majority 
of its members are elegantly formed and beautifully 
sculptured shells from warm countries. The shell 
is spiral, ample in its dimensions, with a circular 
aperture, generally surrounded in the adult with a 
frill-like, shelly expansion ; it is closed by a spiral, 
shelly operculum. 
The animal has a broad foot, divided longitu- 
dinally ; a central spiral body, enveloped in a single- 
edged mantle. There are two tentacles, which are 
lengthened and. contractile, with an eye placed on 
the outer side of the. base 
ofeach. The sexes. are 
distinct. All the species 
are terrestrial, and are ge- 
nerally found on trees, on 
the leaves of which they 
feed. The only British 
species (Cyclostomaelegans) 
is a little shell, about half an inch in length, and 
rather less in width, of a grey or purplish yellow 
hue, often marked with two rows of dark spots. 
The spire is composed of five rounded whorls, 
marked with numerous close-set, raised lines, run- 
ning spirally, with finer longitudinal ones between 
G 
THE ELEGANT CYCLOSTOMA. 
