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. 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. 
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 " (Lotoriidce) have varices or strengthening 
53-54. ribs at intervals, like the Murices ; the largest species, Lotorium 
variegatum, 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 " (Cassididce) are used for cameo-carving ; 
.).)-;>«. they 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- 
lariensis (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. 
Case 57. The " Tun-shells " (Doliidce) are remarkable for the globoseness 
of the shells, which are covered with very regular revolving ribs. 
Cases The Fasciolariidm contains two of the largest living Gastro- 
58-60. p d 8 : Megalatractus araanus, 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, 
<;i-64. on 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 Fasciolaria, 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 various 
64-66. assemblage of forms. Among them may be mentioned the Whelks 
{Bucoinum). (See Fig. 13 on p. 19.) 
