GASTROPODS. 
3§5 
The eyes are situated at the truncate ends of the long, cylindrical stalks, and, 
like those of the Cephalopods, are more highly organised than in many fishes, 
having a distinct crystalline lens, with a highly-coloured iris. The foot is unlike that 
crawling; 
being a powerful, muscular 
pelican’s foot [Aporrhais pes-pelecani). 
of ordinary gastropods, and not adapted for 
organ, so modified as to serve the purpose 
of a lever in their hopping or leaping mode 
of progression. The operculum is claw¬ 
shaped, and attached to the hinder branch 
of the foot. These molluscs are great 
scavengers, and feed upon decomposing 
animals of any description. About sixty 
species of Strombus have been described, 
almost exclusively confined to tropical seas. 
The beautiful pink 8. gigas, of the West 
Indies, is brought to Europe in immense 
numbers, and, when ground to powder, 
employed in the manufacture of the finer 
kinds of porcelain. It is also used for 
cameo-carving, and produces pink pearls. 
The spider - shells ( Pteroceras ), with the 
claw-like projections from the outer lip, have already been referred to. The beak- 
shells ( Rostellaria ) are remarkable for the long, acuminate spire, and the prolonged, 
slender, anterior rostrum. On the contrary, in Terebellum, the last genus of this 
family, there is no canal whatever, but merely a slight sinus or emargination at the 
base of the outer lip. Allied to this family are the Aporrhaiidod and Struthio- 
lariidce, the former including some 
remarkable fossil forms. Aporrhais 
pespdecani is a common British 
shell, occurring all round the coast, 
and usually known as the pelican’s 
foot. In the Cerithiidce the shell 
is typically elongate, and more or 
less pointed, with a notch or recurved 
canal at the front part of the aper¬ 
ture, which is rather short. It is 
generally solid,tubercular,or ribbed, 
and has no periostracum. The 
animals are very like the peri¬ 
winkles, and are provided with a 
horny operculum. They are vege¬ 
table - feeders, very numerous in 
species, and inhabit both salt and 
brackish water. Whereas the 
species of Cerithium are all marine, such forms as Potamides , Pyrazus, and 
Cerithidea occur in brackish marshes, and at the mouths of rivers. The fossil 
species of this family far exceed the recent, both in point of numbers and 
vol. vi.—25 
worm-shell (Vcrmetus lumbricalis). 
