— 67. — 
bed a somewhat similar skeletal mesh in Fwérochus clausus 
from the Cambridge Coprolite-bed. Geo. Mag. 1876. p. 398, 
Pl. XIV). 
Cystispongia sp. 
(Plate V, figs. 20, 21). 
The skeletal mesh is formed of spicules with relatively 
short arms and large sub-spherical solid nodes. The arrange- 
ment of the skeleton is very irregular. Distance between the 
nodes 0,225 mm.; thickness of spicular arms 0,033 mm.; 
diameter of central node 0,11 mm. In addition to these frag- 
ments there are others with the spicular arms much closer 
arranged which appear to be dermal portions of the same 
sponge. The remains of this sponge are more abundant in 
the Horstead flint than those of any other Hexactinellid. 
The only Cretaceous sponges with which these fragments 
can be compared are those of the Genus Cystispongia, Roemer, 
Figures and description of Cystsspongia (Cephalites) bursa, 
Quenstedt, sp. are given by Prof. Quenstedt in his work on 
«Die Schwamme» p. 492, Taf. 138, fig. 17 and I have had 
the opportunity of comparing examples of this species with 
the Horstead fragments. C. dursa is usually of an oval form, 
the outer surface is composed of a very delicate lamina of 
silica, immediately beneath which is a layer of closely arranged 
spicular mesh work with large spherical nodes, much resemb- 
ling that of my fig. 21. Within the oval-shaped case of 
silica there are thin folded layers made up of spicular meshes, 
but the solid spherical nodes are not so large in proportion 
to the arms as in the Horstead examples. I have discovered 
at Horstead fragments of lamina not unlike that forming the 
exterior membrane of Cystispongia, but none of these frag- 
ments had any portions of the spicular mesh attached, so 
that it is doubtful whether they really belong to this genus 
of sponge, but the resemblance of the fragments of the ske- 
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