in natural history, the name of a species of coralline, &c. The characters of which are these: they are of a flaky or coral-like hardness, and resemble a woven cloth in their texture; and the microscope informs us, that they consist of arrangements of very small cells, whose surfaces appear much in that form, Linnaeus makes it a species of millepora, in the class of lithophytes. See Plate CXLVIII. fig. 9-10.

The narrow-leaved hornwrack, fig. 9, divides as it rises, into narrow leaves made up of regular rows of oblong square-shaped cells placed alternately by each other, and opposite to an equal number on the other side of the leaf, like an honeycomb; from these leaves proceed other still smaller foliaceous ramifications, many of which seem to be connected at the lower part by tubuli, as in the corallines; by which means they can ply to and fro more freely in the water;—Gives the natural appearance of this coralline. E represents two leaves with their tubuli and cells magnified. E 1 is a cross section of one of the leaves at E, showing the partition and inner form of their cells.

The broad-leaved hornwrack, fig. 10, when fresh taken out of the sea, is of a spongy soft texture, and smells very fishy; but when it has lain for some time on the shore, it becomes stiff and horny, like some sort of withered leaves. Both surfaces, when examined by glaies, appear to be covered with cells; and, when a piece of it is cut across, one may discover the thin membrane that serves as a base to the cells of each surface. The form of the cells is very remarkable, each one being arched at the top, and contracted a little at the lower part of the sides to make way for the arches of the two next adjoining cells; so that by this particular construction no room is lost. The entrance of the cells is immediately under the arch of each cell, and the walls of the cells seem to be fortified with spines. Jussieu discovered small polypes extending themselves out of these cells, which he has described in the memoirs of the Academy of Sciences 1742.—Gives the natural appearance of a leafy branch of this coralline. F is a part of a leaf magnified to show the superficial figure of the cells, and the manner in which they are disposed. F 1 shows a cross section of a leaf, and discovers the several partitions of the cells.

At the entrance of many of the cells a small tectaceous body like a bivalve shell is discovered: F 2, the figure of the cell, with the shell in it; it is of a transparent amber colour, so clear that one may see the dead animal through it, represented by the black spot.