UNIVALVE MOLLUSCS 377 



home is the tropics, their fragile shells are occasionally cast ashore in countries 

 so remote from one another as the British Isles and Patagonia. 



To the same section of gastropods belong the handsome wing-shells of the 

 family Strombidce, of which there are about a hundred species. Among these may 

 be noticed, on account of its size and beauty, the West Indian Strombus gigas, a 

 pink-mouthed shell formerly imported into London in immense numbers from the 

 Bahamas for the purposes of the almost extinct art of cameo-cutting. It is this 

 species which yields the rare and beautiful pink pearls. The shells, which attain 

 a length of about ten inches, weigh from four to five pounds ; this great weight being 

 due to the fact that the spire and spines of the shell are filled up internally with solid 

 carbonate of lime as the animal increases in age. In the same family are included 

 the curious scorpion-shells (Pteroceras rugosum) of the Indo-Pacific, in which the 

 shell is like that of a Strombus when young, but with advancing age develops a 

 series of long claw-like projections on the outer margin, the hindmost of which 

 lies close to the spire and forms the posterior channel to the mouth of the shell. 



Nearly allied are the solid and handsome helmet-shells, constituting the 

 genus Cassis and the family Cassididce. Among these may be mentioned the 

 orange-red bull-mouthed helmet (G. rufa) of West Africa, the pale queen-conch 

 (G. madagascariensis) of Madagascar and Mauritius, and the black-mouthed 

 G. flammed of the West Indies and South America. These shells were likewise 

 formerly in great demand for cameo-cutting ; their special excellence for this 

 purpose being due to the fact that there are layers of different colours in the shell, 

 so that by cutting down to the proper layer the background of the cameo is 

 caused to be of different, and generally darker, tint from that of the subject selected 

 for engraving. 



The handsome trumpet or triton shells, forming the family Lotoriidce, have 

 taller spires, and a number of vertical ribs for the purpose of affording additional 

 strength. The shells of the great Lotorium, or Triton, variegatum of the South 

 Pacific are used by the Polynesians and Melanesians as trumpets or horns ; a hole, 

 through which to blow, being made in the upper part of the spire. By partially 

 blocking the mouth of the shell with the fingers, variations and modulations can be 

 effected in the notes of these natural trumpets. 



Another striking group is represented by the tun-shells of the family Boliidce, 

 which are globose in shape, with short spires and large mouths; the typical 

 Dolium galea, of which the shell may measure as much as ten inches in length, 

 being the largest Mediterranean gastropod. In the tropical and subtropical seas 

 the genus is more richly represented. Near akin are the gastropods of the family 

 Fasciolariidce ; among these being the largest members of the whole group, the 

 great Megalotractus aruanus of the Aru Islands and north and western Australia, 

 and the equally large Fasciolaria fasciata from the seas off the coast of South 

 Carolina, measuring in some instances at least a couple of feet in length. 



The murexes, Muricidw, form another large family, the shells of many of the 

 members of which are characterised by the length of the channel at the lower end 

 of the mouth and the development of spines of various shapes carried on more or 

 less prominent longitudinal ribs. One of the smaller species with the greatest 

 development of these spines and a long beak is the so-called " thorny woodcock " 



