FRONT-GILLED GROUP 



3355 



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 mollusks are great jgy ~ -=.-=.. _^-.,_.^-^ s ^ 



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 6". 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 (P/eroceras) , with the 

 from the outer lip, 

 The beak 



claw-like projections from the 

 have already been referred to. 



shells (Rostellaria] are remarkable for the PELICAN'S FOOT (Aporrhais pes-pelecani) . 

 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 Aporrhaiida and Struthio- 



lariidce, the former including some 

 remarkable fossil forms. Aporrhais 

 pes-pelecani 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 aperture, 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 the point of numbers and size; Cerithium 

 giganteum, an Eocene form, attaining quite a foot and a half in length. 



One of the most curious groups of gastropods is that of the worm-shells 

 ( Vermetidcz) , in which the shells might be mistaken for the tubes of marine worms, 



(Vermetus lumbricalis). 



