GASTROPODS. 



385 



pelican's foot (Aporrhais pes-pelecani). 



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 

 of ordinary gastropods, and not adapted for crawling ; being a powerful, muscular 

 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 Strombws have been described, 

 almost exclusively confined to tropical seas. 

 The beautiful pink S. 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 Terebdlum, 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 Aporrhaiidce and Struthior 



lariidce, the former including some 

 remarkable fossil forms. Aporrhais 

 pespelecani 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 



Blillllllllil&^ii^^ 



worm-shell ( Vermetus lumhricalis). 



