2s Guide to the Mollusca. 



vigorous leaps. They act as scavengers, feeding on decomposing 



animal matter. 



Strombus gigas, or 'the Fountain-shell', occurs in great 

 numbers in the West Indies, and is a very heavy solid shell. At 

 one time it was used for cameo-carving and was also employed in 

 the manufacture of porcelain, as many as 300,000 shells having 

 been imported into Liverpool in one year for that purpose. 



The Scorpion-shells (Pterocera), or ' Spider-claws ', as they are 

 sometimes called, possess singular claw-like projections, which 

 are developed on the outer lip of the shells. 



The ' Trumpet-shells ' (Cymatiidae) have strengthening ribs at 

 intervals, like the Murices ; the largest species, Cymatium varie- 

 gatum, is used by South Sea Islanders as a horn or trumpet. 

 A hole is made in the upper part of the spire to blow through, and 

 the sound produced can be modulated or varied by inserting the 

 hand in the aperture or mouth of the shell. 



Fig. 19. 



Scala scalar is. Case 44. 



The ' Helmet- shells ' (Cassididae) were used for cameo-carving ; 

 they consist of different layers, so that the ground colour of the 

 carving is of a different tint from the subject engraved. 



The ' Tun-shells ' (Doliidae or Tonnidae) are remarkable for the 

 globoseness of the shells, which are covered with very regular ribs. 



The Atlantidae, Pterotracheidae, and Carinariidae, at various 

 times recognized as forming a distinct sub-class or an order of 

 Gastropoda, under the name of Heteropoda, are now regarded as 

 specialized Taenioglossa organized for swimming in the open sea, 

 the foot being compressed to form a sort of fin. The Atlantas 

 are found in great numbers in warm and temperate latitudes, 

 and are provided with a thin, flat, spiral shell. The shell of 

 Garinaria is one of the most beautiful structures of any mollusc ; 

 the animal is large, semi-transparent, and elongate. Species of 

 this genus are found in the Mediterranean and warmer parts 

 of the Atlantic and Indian Oceans. They feed on Jellyfish of 

 various kinds, and probably on other soft-bodied animals. 



