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 substitutes 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 peculiar as being formed of three layers of calcareous matter, the layers being perpendicular laminæ 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 progress 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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