18 SHELL GALLERY. 



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. At one time it was also 

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

 been imported into Liverpool in one year for that purpose. 

 Cases The Scorpion-shells, or " Spider-claws," as they are sometimes 



51-52. called {Pterocera), possess singular claw-like projections, which are 



developed on the outer lip of the shells. 

 Cases The " Trumpet-shells " (SepHdoi) have varices or strengthening 



53-55. j.^i^g g^i^ intervals, like the Murices ; the largest species. Septa 

 variegata, 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. 

 Cases The " Helmet-shells " {Gassididce) are used for cameo-carving ; 



55-56. j^\^Qj consist of differently coloured layers, so that the ground-colour 

 of the carving is of a different tint from the subject engraved. The 

 most artistic shell-cameos are produced in Italy, whence the art has 

 been introduced into France and England. The Cassis madagas- 

 cariensis (Fig. 12 on p. 19) is in special request by shell-carvers on ac- 

 count of the strong contrast of the white upper layer with the dark 

 ground beneath. Extinct forms of Cassis are found fossil in Tertiary 

 formations, but none of them equal in size the largest living species. 

 Cases The " Tun-shells " {Doliidce) are remarkable for the globoseness 



56-57. qJ |-}jg shells, which are covered with very regular revolving ribs. 



Cases The Fasciolariidm contains two of the largest living Gastro- 



pods : Megalatractus aruanus, from North and West Australia, and 

 Fasciolaria gigantea, which is found off the coast of South Carolina, 

 and attains at times a length of two feet. 

 Cases The Mitras {Mitridce) are great favourites with shell-collectors, 



61-64. Qj^ account of their beautiful colours and varied sculpture. There 

 are about 600 living species already known, and between one and 

 two hundred have been found in a fossil state. Shells of this group, 

 like the FasciolaricB, are distinguished by a few plaits or folds on 

 the inner side of the aperture (the columella). Mitras are almost 

 exclusively found in tropical or subtropical regions, the majority 

 being met with either at low-water mark or in comparatively shallow 

 water. 

 Cases The family of Buccinidce also contains a very large and varied 



64-66. assemblage of forms. Among them may be mentioned the Whelks 

 {Buccinum). (See Fig. 13 on p. 19.) 



