238 THE MEDALS OF CREATION. Cuap. VII: 
In the Devonian slates of Polperro some curious fossils, 
supposed to be remains of fishes, have been ascertained by 
Prof. McCoy to be Amorphozoa, and are described by that 
eminent paleontologist under the name of Steganodictyum.* — 
CrionitEs (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.f 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 par- — 
ticularly notice hereafter. These fossils Mr. Morris has — 
distinguished by the name Clionztes, to indicate their origin ;— 
they are not, however, the silicified sponge, but inorgani¢ 
casts, moulded in the excavations. The common species is — 
C. Conybeart: “cells irregular, somewhat polygonal, with — 
one or more papillee ; surface finely tuberculated ; connecting 
threads numerous.” ¢ 
SPICULA, OR SPINES OF PoriFERA. ign. 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 triradiate or rultinadigee and — 
some have the ahaa of a trident; a few of these fale 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 
* “Synopsis of the Classification of the British Paleozoic Fossils,” — 
by Prof. Sedgwick and Fred. McCoy. 4to. Fas. 2, p. vil. pl. 2a. 1852. q 
+ For an account of the characters of the recent Cliona, see a 
monograph by Mr. Hancock, Annals of Nat. Hist. May 1851. 4 
+ Ann. Nat. Hist. August 1851, pl. iv. fig. 8 a 
