NATURAL HISTORY. 
69 
GALLERY.] 
former whorls, which gives the shell a distorted or as it were crushed ap¬ 
pearance. The animal of the Lamp Snails, ( Anastoma ,) on the con¬ 
trary, when it has arrived at its full size, suddenly turns itself over, 
forming the permanent mouth of the shell on what was the upper or 
spiral side, thus reversing its natural position. The other genera 
are chiefly distinguished by the form and armature of the mouth of the 
shell. The second group chiefly differ in the whorls being on a longer 
axis, so that the shell is oblong. These animals have no vesicula mul- 
tifida , 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, are dis¬ 
tinguished by the modifications that the mouth of the shell assumes 
when the animal has arrived at its perfect state ; for during their growth 
they all have the same thin, simple lips. Thus the Bulimi have simple, 
thickened, 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 w 7 horls enlarge in diameter so 
gradually (after the very early age of the animal) that the shell generally 
assumes a cylindrical form. The Chondri chiefly differ from the 
former in the mouth being armed with long plaits, formed by the in¬ 
flection of the surface of the shell w r hen the animal is about to complete 
its mouth, which forms external grooves and internal ridges. The 
Clausilice are similar to the latter, but have a continuous groove in 
front of the last whorls, and the animal forms, a short time before it 
arrives at the adult age and is about to complete the mouth of the shell, 
an expanded plate, (w 7 hich is evidently a peculiar modification of a tooth,) 
attached to the pillar of the shell by a slender pedicel, and placed in 
such a position that it closes the throat of the shell when the animal is 
inclosed, while the animal can push it on one side behind the plait formed 
by the groove above referred to, when it desires to protrude itself from 
its shell and walk about to search for food. The Siphonostoma only 
differ from the former in not having the plate-like tooth above described. 
Other genera, as Succinea , Amphibulina, and Bulimulus , have most of 
the characters of Bulimi, but differ in the edge of the peristoma being 
thin and acute. 
The group containing the Achatince , on the contrary, have the front 
of the mouth truncated, the axis of the shell imperforated in all its 
stages of growth, and the edge of the lips thin, whilst the tips of the 
upper tentacles of the animal are acute and produced beyond the eyes. 
They generally form a shelly epiphragma with a long impressed line 
near the outer hinder edge of the mouth of the shell, over the 
respiratory hole of the mantle; and they deposit very large eggs, which 
are generally covered with a hard shell. 
The family of VERONiCELLLDiE have the head retractile into a 
sheath formed by the front edge of the mantle; the foot, the sides of 
the body, and the four tentacles are contractile, and the low T er pair of 
tentacles are bifid. The mantle is smooth, coriaceous, extending the 
whole length of the back, and edging the foot. The vent and the open- 
