150 
PROF. T. RUPERT JONES—ORIGIN AND 
parasitic shells, polyzoans, and annelids often bear evidence also to 
that fact. Wot unfrequently such Echinoids have been crnsbed 
before imbedment, probably by ground-feeding fishes having 
grabbed them as prey, and for some reason dropt them more 
or less injured; The Starfishes are not so numerous in the Chalk ; 
but Or easier, Goniaster, Stellaster, Arthraster, and Ophiura are 
good representatives of this great group of the Echinodermata in 
the Chalk sea. 
It is to be remarked, in the case of Echinoderms and of such shells 
as Ostrea and Inoceramus, that although retaining their substance 
in the Chalk itself, the substance has often disappeared when these 
fossils occur in flint that has been at all exposed to the action of 
air and water, whether within the Chalk or outside on the ground. 
This is to be accounted for by the fact, that these tests, plates, 
spines, and ossicles of Echinoderms and the shells of the Conchifera 
alluded to have never been changed into flint, as is the Chalk 
around them (as far as the individual nodules of flint are concerned), 
and that when submitted to the action of water they have been 
dissolved away, and corresponding cavities have been left. These 
hollows have in some cases been subsequently more or less occupied 
by chalcedonic flint while still in the Chalk. 
Eolyzoa and Corals .— Another group of organisms, small in size 
but numerous, are the Eolyzoa of Busk (Bryozoa of Ehrenberg), 
belonging to the Molluscoida , but at first sight often looking like 
corals. Many genera and species occur in the Chalk — Eiastopora , 
Clypeina , Idmonea , Eesmepora , Eetalopora, Eustulopora, Holostoma, 
Marginaria, and others, either free or parasitic, which are worthy of 
further study.* * * §4 Of Corals there are but few and small kinds in 
the Chalk of England. Earasmilia, Trochosmilia, Caryophyllia , and 
Eihlasus are the most common. 
Sponges. —“ Remains of sponges abound in the Chalk ; for 
mineralized sponge-tissue and the spicula of sponges are scattered 
throughout, and often thickly imbedded, as may be found with 
care in the Chalk itself, and readily seen in the flint which has 
replaced much of the Chalk in nodular and tabular masses.” f 
Ventriculites and Siphonia (Choanites ) are among the most common 
of the sponges in the Chalk of the South of England J; but Selis- 
cothon, Verruculina, Stichophyma , Scytalia, and Eachinion are 
characteristic Sponges in the Chalk of Yorkshire. In his Memoir 
on 1 ‘ Fossil Sponge-Spicules from a hollow flint in the Upper 
Chalk at Horstead in Norfolk,”§ Dr. G. J. Hinde described and 
illustrated 160 forms of spicules; referring them to 38 species of 
32 genera of Sponges. In his greater work, a “ Catalogue of the 
Fossil Sponges in the British Museum,” with its numerous beautiful 
plates, || he enumerates the known Sponges of the Upper White 
* Dixon’s 1 Geol. Sussex,’ 2nd ed., p. 314, etc. 
t Ibid. , p. 287: 
l Ibid., Prof. Sollas’ remarks, p. 287 and p. 448, etc. 
§ 8vo. 1880. 
|| 4to. 1883. 
