SHELL-FISH. 
245 
If we now come to the other great Class of shelled ani- 
mals, that named Gastropoda, we find we have to make 
a considerable leap to pass the hiatus. For, in fact, there 
is no very closo relation between the Bivalves and the Uni- 
valves. Possibly species may yet be discovered which will 
supply the links that are wanting ; but this is scarcely 
likely. Not that there is no transition. If we take that 
interesting shell called the Cap of Liberty, or the Torbay 
Bonnet ( Pileopsis Ilangaricus), we canuot but bo struck 
with the resemblance which it bears to a single valve of 
such a shell as the Heart ( Isocardia cor) ; and in some of 
its near allies, as the little Cup and Saucer ( Calyptrea 
Sinensis ), there is a subordinate shelly plate in the interior, 
which has been considered as the vanishing representative 
of the second valve. 
The form of the shell in this Class is that of a cone, 
with the apex on one side of the centre. In the Limpets 
{Patella), the cone is short and low, and therefore unmis- 
takeable ; in the Torbay Bonnet the summit is a little 
rolled over, the commencement of that spiral form which 
we see in the Whelk and the Snail. Nay, if we take the 
extremes of this condition, as we see in the long many- 
whorled shells of the genera Turritella, Scalaria, and the 
like, it is not difficult to trace the same form, a cone drawn 
out to great length and twisted spirally on an axis. 
The animals of these shells are much higher in organic 
development than the Conchifera. They have a distinct 
head, with organs of touch, of vision, of hearing, and of 
smell, and a mouth armed with a complex array of teeth 
for the purpose of rasping away the solid food on which 
they subsist. They have the faculty of locomotion, the 
