Fig. 12. This is a portion of a delicate ramose sponge (_Spongites ramosus_, of Mantell), whose remains are abundant in the chalk-flints, and have given rise to the irregularly branched siliceous nodules. A specimen nine inches long, with seven branches, is figured in Fossils of the South Downs, Pl. XV. fig. 11. Siliceous spicula are thickly interspersed throughout the mass. [Illustration: Plate XL.] PLATE XL. Fossil Corals, &c. Fig. 1. The shells of Oysters, and other mollusca, are subjected to the ravages of a parasitical sponge, (_Cliona_, of Dr. Grant,) which is beset with minute siliceous spines or spicula, and inhabits hollows formed in the substance of the shell. Shells thus honeycombed, as it were, may often be found on the sea-shore with the excavated parts filled up by sponge. I have shells collected by my eldest son on the shores of New Zealand, that are hollowed out in a similar manner, and occupied by sponge. Whether these cavities are produced by mechanical means, or are the result of the decay and absorption of the shell induced by the growth of the parasite, are questions still undetermined. There are several kinds of shells found fossil, which were infested with a similar parasitical sponge; and when the cavities thus produced have been filled up by flint, and the shell has subsequently decomposed, or been worn away, the surface of the flint is studded with the casts of the cells, in the form of small irregular globular bodies, connected by filaments or strings of flint. The fossil, fig. 1, is a fossil of this kind, described by Mr. Parkinson as being "covered with minute round bodies, the nature of which is unknown;" fig. 12, is an enlarged view of five of these globular casts connected by filaments. The origin of these fossils was first pointed out by the Rev. W. Conybeare.[29] The fibrous shells of a fossil genus of bivalves named _Inoceramus_, of which several species abound in the Chalk, appear to have been particularly subjected to depredations of this kind. Hence among partially water-worn flints, specimens of the siliceous casts are common; figs. 8, and 10, are examples from the Hackney gravel-pits. [Footnote 29: See Medals of Creation, vol. i. p. 396, fig. 94.] Mr. Morris has named these fossils, _Clionites_; fig. 1, is _C. Parkinsoni_. Figs. 2, 4, 7, are portions of a recent species of jointed zoophyte (_Isis_), from a modern concretionary deposit on the shores of the Mediterranean, Sicily. Fig. 3. A branched fossil coral (_Millepora ramosa_, of Dr. Fleming), imbedded in compact oolitic limestone from Wiltshire. A portion of the surface magnified is represented in fig. 11.