89 
EAST. ZOOL. GAL.] NATURAL HISTORY. 
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 17) 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 ( Stomatellidce , Case 18) are 
very like the former, but the mouth of the shell is large 
and expanded compared with the size of the spire and 
operculum. 
The family of Ear-shells ( Haliotidce , Case 18) 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 Haliolis, 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 
formed by the growth of the animal, the last being occu¬ 
pied by the vent; and in Scissurella and Pleurotomaria 
there is a long slit in the shell, over the opening in the 
mantle. 
The family of the Keyhole Limpets [Tissurellidce , Case 
18) have an animal very like the Ear-shells, but the shell is 
depressed, simply conical, not pearly, and furnished either 
with a hole, placed in the front of the apex, as in Fis - 
surella , or with a notch in the front of the edge, as in 
Fmarginula and Parmophorus, These holes or grooves 
afford a passage for the water to the respiratory organs, 
and for the expulsion of the faeces. In Pupillia the shell is 
surrounded by a sharp white edge; and in Lucapina the 
mantle covers the cancellated shell. 
Here must also be placed the family of the Tooth-shells, 
(Dentaliadce , Case 18,) which have been, till lately, re- 
