VENTRICULITES. 947 
white limestone is uncoloured, may be explained by the 
chemical changes to which the decomposition of animal. 
matter under such circumstances would give rise. If sulphu- 
_retted hydrogen were evolved from the putrifying zoophytes 
imbedded in calcareous mud containing iron in solution, the 
sulphur would enter into combination with the iron, the 
hydrogen escape, and a sulphate or sulphuret of iron be 
deposited, atom by atom, and thus impart colour and per- 
manence of form to the original. 
When the inclosed organisms in the flint nodules have 
perished, chalcedony, quartz crystals, or crystallized pyrites, 
sometimes of great beauty, are found occupying the cavities ; 
in short, numerous modifications of the petrifactive process 
are beautifully exhibited in these common, but highly in- 
teresting, cretaceous fossils. 
The species to which the previous remarks more imme- 
diately refer, is named Ventriculites radiatus ; from the radi- 
ated appearance of the external integument ; some of the 
expanded specimens are more than one foot in diameter.* 
VENTRICULITES ALCYONOIDES. Lign. 83.—Under the name 
of “ Ocellaria inclusa,” the late Mr. Konigt figured and de- 
scribed an elegant fossil zoophyte not uncommon in the 
chalk and flints of Sussex. This fossil is inversely conical, 
and somewhat resembles the cast of the cavity of Ventriculites 
radiatus, but a little attention will enable the collector to 
distinguish it. The flint that is moulded in VY. radiatus, is 
surrounded by the substance of the zoophyte, and if found 
detached, with the investing material removed, shows no struc- 
* The reader interested in the history of these objects should con- 
sult Foss. South Downs, p. 167, plates x. xi. xii. xiii. xiv. A memoir 
by the Author on these fossils, under the name of Alcyoniwm chonoides, 
with four beautiful plates, was published in the Linnean Transactions, 
vol. xi. 1821. The Ventriculites are the only organic remains figured 
in Conybeare and Phillips’s Geology of England and Wales, p. 76, 
+ Icones Foss. Sect. fig. 98. 
