in zoology. See TESTUDO.

*Tortoise-shell*, the shell, or rather scales, of the testaceous animal called a tortoise; used in inlaying, and in various other works, as for snuff-boxes, combs, &c. Mr Catesby observes, that the hard strong covering which incloseth all sorts of tortoises, is very improperly called a shell; being of 117. a perfect bony texture; but covered on the outside with scales, or rather plates, of a horny substance; which are what the workmen call tortoise-shell.

There are two general kinds of tortoises, viz. the land and sea-tortoise, testudo terrapinis and marina. The sea-tortoise, again, is of several kinds; but it is the caret, or testudo imbricata of Linnæus, alone which furnishes that beautiful shell so much admired in Europe.

The shell of the caretta, or hawksbill tortoise, is thick; and consists of two parts, the upper, which covers the back, and the lower the belly: the two are joined together at the sides by strong ligaments, which yet allow of a little motion. In the fore-part is an aperture for the head and fore-legs, and behind for the hind-legs and tail. It is the under shell alone that is used: to separate it, they make a little fire beneath it, and as soon as ever it is warm, the under shell becomes easily separable with the point of a knife, and is taken off in laminae or leaves.

The whole spoils of the caret consist in 13 leaves or scales, eight of them flat, and five a little bent. Of the flat ones, there are four large ones, sometimes a foot long, and seven inches broad. The best tortoise-shell is thick, clear, transparent, of the colour of antimony, sprinkled with brown and white. When used in marquetry, &c., the workmen give it what colour they please by means of coloured leaves, which they put underneath it.

*Working and joining of Tortoise-shell.*—Tortoise shell and horn become soft in a moderate heat, as that of boiling water, so as to be pressed, in a mould, into any form, the shell or horn horn being previously cut into plates of a proper size. Plumer informs us, in his Art de Tourner, that two plates are likewise united into one by heating and pressing them; the edges being thoroughly cleaned, and made to fit close to one another. The tortoise-shell is conveniently heated for this purpose by applying a hot iron above and beneath the juncture, with the interpolation of a wet cloth to prevent the shell from being scorched by the irons; these irons should be pretty thick, that they may not lose their heat before the union is effected. Both tortoise-shell and horns may be stained of a variety of colours, by means of the colouring drugs commonly used in dyeing, and by certain metallic solutions.