WHELKS, ETC. 177 
been made to substitute various materials, such as 
porcelain and glass, for the ancient cameos (which 
were cut in onyxes and other precious stones); 
but their great inferiority has caused them to be 
neglected. The best and now most-used substi- 
tutes are shells, several kinds of which afford the 
necessary difference of colour, and at the same 
time are soft enough to be worked with ease, and 
hard enough to resist wear. The shells used are 
those of the flesh-eating univalves, which are pe- 
culiar as being formed of three layers of calcareous 
matter, the layers being;perpendicular lamine placed 
side by side. 
The cameo-cutter selects those shells which have 
the three layers composed of different colours, as 
they afford him the means of relieving his work ; 
but the kinds now employed, and which experience 
has taught him are best for his purpose, are the 
Bull’s-mouth (Cassis rufa) from the Indian seas, 
the Black Helmet (C. Madagascariensis), a West 
Indian shell, the Horned Helmet (C. cornuta), from 
Madagascar, and the Queen Conch (Strombus gigas), 
a native of the West Indies. The first two are the 
best shells. 
After detailing the peculiarities of these shells, 
Mr. Gray proceeded to give an account of the pro- 
gress of the art, which was confined to Italy until 
within the last twenty years, at which period an 
Italian commenced the making of cameos in Paris ; 
and now about three hundred persons are employed 
in this branch of trade in that city. The number 
of shells used annually, thirty years ago, was about 
three hundred, the whole of which were sent from 
England, the value of each shell in Rome being 
30s. The increase of the trade is shown by the 
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