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 close 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 Hungaricus), we cannot but be struck 

 with the resemblance which it bears to a single valve of 

 such a shell as the Heart (Jsocardia 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. VawtwyYV ^M!k$Ulj 



LyThe 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 



