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Show 576 DR. J. E. GRAY ON THE CERATELLADJE. [NOV. -('' smaller branches and the cell-like projections on their surface were covered with spines, they could scarcely belong to the " Alcyoniens amies" of M . Milne-Edwards, and they at once differed from all the known forms of that group of animals by the skeleton being formed of horn. One naturalist to whom I showed them declared that they must be plants belonging to the Algae. But this cannot be the case; they have none of the characters, except the mere external form of Algae; and their external form is as like to that of some corals as to any genus of Algae that I am acquainted with. In general appearance they combine with their plant-like form some characters of the spicular alcyonoid polypes, the texture of the very porous coral called Porites, and the horny consistence of the coarser horny sponges. After very mature consideration, I am inclined to regard them, until their internal organization and growth is known, and the animal that forms them has been observed and described, as belonging to that very polymorphous group of animals which has been called Sponges. At the same time, I know no group of sponges with which they can be compared. If they are sponges, they must be arranged with the keratose sponges ; but, unlike all the known sponges of that group, they have a series of conical protuberances on the sides of the branchlets, which are developed as the branchlets grow in length, just as the cells of Alcyonoids and stony Madrepores are developed by the budding of new cells from the bases of the last formed ones. The branches and these cells are all formed by the projecting terminations of the horny fibres. The stem and older branches are formed of hard, horny, translucent fibres, of a nearly uniform cylindrical form, which are very closely united together into a horny network, with very small circular openings in all directions. This network is very like that found in the older parts of the genus Porites among the stony Madrepores; but in that genus the network is hard and stony, in this it is hard, horny, and translucent. This hard horny network is very little softened by being soaked in water even for many hours. The surface of the stem is either smooth and covered with a very large number of very minute, close, cylindrical canals, or with transverse ridges of a similar structure to the stem. The upper branches and branchlets are chiefly composed of and covered with agglutinated, closely packed, projecting terminations of the horny fibres; and on the sides of the branches are placed, in a more or less regular manner, a number of small, short, conical or subcylindrical projections, formed of similar spiculum-like fibres, some of which project beyond the tips of the projections. These projections are placed on the side of the branchlet, which also terminates with a similar tuft of spines, the branchlet increasing in length by the development of new tufts or cells from the base of the old one. The texture of the stem and branches would lead one to suppose that the entire coral or sponge is covered with sarcode or flesh in the living state, as in Porites and most sponges. True there is not the |