22 SHELL GALLERY. 



ment. They act as scavengers, feeding on decomposing animal 

 matter. 

 fCase Of..' The Strombus gigas, or " Fountain-shell," occurs in great 

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

 is a favourite ornament for rockwork and fountains in gardens, 

 and, like the Helmet-shells, is used for cameo-carving. It is also 

 employed in the manufacture of porcelain, as many as 300,000 

 having been imported into Liverpool in one year for that purpose. 

 The Scorpion-shells or " Spider-claws/' as they are sometimes 

 called (Pterocera) , possess singular claw-like projections, which are 

 developed on the outer lip of the shells. 

 [Cases The Onustidce, with the genera P/wi'us and Onustus, have the 



9h-10a. singular habit of cementing to the exterior of their shell, stones, 

 pieces of coral, and fragments of other shells ; hence they have 

 been called " Carrier-shells," and, according to the kind of material 

 chosen, have been named " Conchologists " and " Mineralogists." 

 Beyond acting as a disguise, and consequently as a protection, 

 there does not appear to be any special utility in thus adding to 

 the weight of their own shells. The animals do not glide like 

 most other mollusks, but scramble along like the Strombs, the 

 form of their foot being small, divided into a front, expanded, and 

 a hind tapering portion admirably adapted to the nature of the 

 ground on which they live, which usually consists of broken and 

 dead shells. 

 fCase 10, The Nerites are mostly found in tropical countries, and, like the 

 a-c.J Winkles, are very strongly made, to resist the force of the breaking 



waves. The Neritinas are partly found in the sea, and partly in 

 fresh water, and are less solid shells. The third section of Neritidts, 

 the Xavicellas, are shaped very much like Limpets, except that the 

 apex is at one end instead of central. They are, however, very 

 different animals, and furnished with a shelly operculum imbedded 

 in the foot. 

 [Cases The Turbinidce and Trochidce are two extensive families, the 



IOd-IIb.j an ^ ma } s f which are very much alike, and mainly distinguished by 

 the operculum, which in the former is shelly, and horny in the 

 latter. The shells of these families are beautifully pearly within, 

 and the external shelly coat is generally brightly coloured and 

 highly ornamented. Several very pretty species are found on our 



