Clionites (_Morris_) _Lign. 130._--A recent parasitical sponge (first described by Dr. Grant under the name of _Cliona_), consisting of a fleshy substance, full of siliceous tubular pin-shaped spicula, gives rise to those perforations with which oysters and other shells are often completely riddled,[216] Certain bivalve shells in the cretaceous seas appear to have been peculiarly obnoxious to the depredations of similar zoophytes, and in consequence of the cavities left by the decay of the sponge having subsequently been filled up by flint, a curious series of fossil bodies has resulted, which we shall more particularly notice hereafter. These fossils Mr. Morris has distinguished by the name _Clionites_, to indicate their origin; they are not, however, the silicified sponge, but inorganic casts, moulded in the excavations. The common species is _C. Conybearei_: "cells irregular, somewhat polygonal, with one or more papillæ; surface finely tuberculated; connecting threads numerous."[217] [216] For an account of the characters of the recent Cliona, see a monograph by Mr. Hancock, Annals of Nat. Hist. May 1851. [217] Ann. Nat. Hist. August 1851, pl. iv, fig. 8. Spicula, or spines of Porifera. _Lign. 75._--Siliceous spicules, as we have had occasion to mention, occur in immense quantities in some of those deposits which abound in the remains of spongites. These spines are tubular, and of various shapes; some are acicular, or needle-like; others of a stellate form; many are tri-radiate or multi-radiate; and some have the shape of a trident; a few of these fossils are figured in _Lign. 75_. As the _Actinia_, _Gorgonia_, and _Alcyonia_, possess spicula, some of the fossil spines may have been derived from those zoophytes. The larger spicules may be discovered with a lens of moderate power, or even by the unassisted eye; but all will amply repay a microscopical examination, and the minutest can only thus be detected. [Sidenote: SPINIFERITES IN FLINTS.] [Illustration: Lign. 77. A group of Spiniferites in Flint. (Seen by transmitted light.) Fig. 1.--A thin-translucent chip of flint; _nat._ 2.--The same magnified, and viewed by transmitted light; showing a group of five Spiniferites. 3.--The same more highly magnified. 4.--Spin. ramosus; one of the animalculites seen in fig. 3, very highly magnified. 5.--Spin. Reginaldi; one of the same group; × 300 diameters. 6.--A variety of S. ramosus; another of the same cluster of Spiniferites. ]