116 
NATURAL HISTORY* [.EAST* ZOOL. 
cels 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 respira¬ 
tory cavity, and close the mouth of the shell with the oper¬ 
culum to prevent its evaporation until the water again 
covers them. Many of them are hermaphrodite, like the 
snails. 
The family of Turbos ( Turbinidce , Case ) 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 
an appendage at their bases. They are mostly covered 
with a thick periostraca, but some, as Phasianella , are 
covered with a very thin transparent one, shewing the 
brilliant colours of the shell through it. The Turbo Sar - 
maticus 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 family of Top-shells Trochidce (Case ) chiefly 
differ from the former in having a more conical shell, with 
a square mouth; the operculum, which is generally formed 
of many slowly enlarging whorls, is destitute of any shelly 
coat, and the bases of the tentacles are without appendage. 
The family of Stomatellas ( Stomatellidoe , Case ) are 
very like the former, but the mouth of the shell is large 
and expanded compared with the size of the spfre and 
operculum. 
The family of Ear-shells ( Haliotidce , Case ) have even 
a more expanded mouth than the former; they have no oper¬ 
culum, and the side of the foot of the animal is covered with 
a hard warty skin; but their most peculiar character con¬ 
sists in their having usually a groove or slit in the mantle, 
over the part where their gills are situated. In Stomatia 
the place of this slit is marked in the shell by a groove, 
while in Halioiis , and the allied genera, the groove of the 
shell is pierced with a series of holes in front, which are 
gradually filled up behind as new ones are required to be 
