125 
GALLERY.] NATURAL HISTORY. 
Plectophorus it is divided into two parts, the front part 
being shield-shaped, and the hinder elongate, bearing an 
external conical shell. In the remaining genera of this 
family the mantle is simple, thin, and covered with an ex¬ 
ternal shell. Among the genera of this group, which in¬ 
cludes a very large proportion of the species of the order, 
the Testacella are peculiar for having the mantle and shell 
on the posterior extremity of the body. This animal also 
has the power of extending the edge of the mantle, so that 
it can cover up the whole of the contracted body, and thus 
protect it from drought; its lips are cylindrical and retrac¬ 
tile, like the tentacles : they live, the greater part of their 
time, in holes under the ground, where they feed on earth¬ 
worms. In all the other genera the mantle and shell are 
on the central part of the foot, and the lips are short and 
rounded, and sometimes serrated or torn beneath. As 
the animals of the different genera are so similar, it is 
necessary to divide them into sections, according to the 
form of the shell. The first section, which have been 
generally called Snails, have the whorls twisted round a 
short axis into a subglobose shell. The animal has a dis¬ 
tinct and variously divided vesicula multijida . The true 
Helices , Helicodonta, &c., have the peristoma of the shell 
thickened, while the Helicophanta , Epistylium , and Proser¬ 
pina have it thin and sharp. The second group chiefly 
differ in the whorls being on a longer axis, so that the shell 
is oblong. These animals have no vesicula multijida , and 
the mouth of the shell is longer than it is broad. This 
group is again subdivided into those that have the mouth of 
the shell continued without interruption into the pillar lip. 
The axis of their shell is generally perforated, especially 
in the young state, for the animal, as it grows, sometimes 
covers the perforation with the reflexed portion of the inner 
lip; and the eyes are placed, as in the snails, on the tips of 
the blunt tentacles. The genera of this section, as in the 
snails, is distinguished by the modifications that the mouth 
of the shell assumes when the animal has arrived at its per¬ 
fect state; for during their growth they all have the same 
thin, simple lips. Thus the Bulimi have simple, thick¬ 
ened, reflexed lips, and gradually enlarging whorls. 
The Pupce have one or more solid teeth formed by the 
thickening of the inner edge of the lips, and the 
