58 NATURAL HISTORY. [EAST. ZOOL. 
Buccina with a very reduced shell, like the Viirince among the snails 
(Helices ). 
2. The Phytophagous Gasteropodes, (Phytophaga,) so called 
because they live chiefly on vegetable food, are destitute of any distinct 
syphon for the passage of water to the branchial cavity, and therefore 
have no canal in front of the mouth of the shell; their eggs are mem¬ 
branaceous, and often deposited on the surface of other shells; but 
many of the animals are ovoviviparous. Many of them have a spiral 
operculum or lid, which is attached to the back of the hinder part of the 
foot of the animal: this operculum turns round backwards on the apex 
of its spire, as it increases in size, by the addition of new matter to the 
edge of its last whorl, so that this edge is always in the same position 
in the mouth of the shell. They are divided into two sections ac¬ 
cording to the position of their eyes, as Podophthahni and Eriophthalmi, 
p. 58. 
The Podophthalmi have their eyes placed on short pedicels at the 
back inner angle of the tentacles; their heart generally surrounds the 
rectum. 
In most the sides of the body are furnished with a fringe sending 
out a series of filaments or tentacles. These are all marine, often 
living on rocks near the shore ; when left by the tide they shut a 
quantity of fluid into the respiratory cavity, and close the mouth of the 
shell with the operculum to prevent its evaporation until the water 
again covers them. Many of them are hermaphrodite, like the snails, 
( Helicidce ). 
The family of Turbos (Turbinxm:, Case 16) have solid spiral shells, 
with a roundish aperture, which is generally pearly within. Their 
operculum is spiral, and protected by a hard external shelly deposit; 
and the tentacles have a leaf-like appendage at their bases. They are 
mostly covered with a thick periostraca, but some, as PhasianeUa, are 
covered with a very thin transparent one, shewing the brilliant colours 
of the shell through it. The Turbo Sarmaticus is peculiar for having 
a layer of blackish animal matter between the outer opaque and the inner 
pearly coat of the shell; this coat forms a dark zone between the edges 
of the two coats, just within the aperture of the shell. The Turbos 
have a round mouth. The Imperators are top-shaped shells, and have 
an oblong or four-sided mouth like the Trochi , with which they have 
generally been confounded, and the pheasants ( PhasianeUa ) have an 
oblong ovate shell with an ovate mouth. The Thicolice chiefly differ 
from the latter in the animal being less ornamented with beards. 
The family of Top-shells (Trochim:, Case 17) chiefly differ from the 
former in having a more conical shell with a square mouth ; the oper¬ 
culum, which is generally orbicular, is formed of many slowly enlarging 
whorls, is destitute of any shelly coat, and the bases of the tentacles are 
without appendage. They live on the rocks and sea weed near the low 
water mark, and sometimes in the deeper part of the seas. The greater 
number of the genera are top-shaped with an oblong or four-sided 
mouth. In Pyramis, the front of the inner lip has a slight canal, and 
in Cardinalia it appears notched. In Trochus , Polydonta , Clangulus 
and Phorcus, the inner lip has a fold behind leading into the cavity of 
the shell, and the axis is imperforated. In Trochus the inner lip is 
smooth, in Polydonta it is grooved, in Clangulus it is toothed, and in 
