354 Dr. G. J. Hinde on a true Leuconid Calcisponge 
there are indications of the larger apertures of excurrent 
canals. As, however, the intermediate spaces in the spicules 
of the wall are generally filled with an extremely fine pow- 
dery matrix, the courses of the canals, even on the supposition 
that they were similar to those of existing Leucones of corre- 
sponding dimensions, would be to a great extent unrecog- 
nizable. 
The examples of this species occur detached and free in a 
decayed rusty rock, mingled with sand and oolitic grains and 
broken-up fragments of Crinoidea or other Echinoderms. 
Many retain their outer form as perfectly as any specimen of 
Grantia which might be met with on our coasts at the present 
day ; others have been fractured, and small portions of their 
wall are found separately. The sand-grains &c. now attached 
to the bases of some of the specimens are probably the original 
materials on which the sponge fixed itself during its growth. 
Not only do these sponges retain their outer form, but the 
structure of their walls with their loosely arranged interfelted 
spicules is apparently undisturbed. As already mentioned, 
the sponges are now infilled with a powdery rusty matrix, 
much in the same way as recent specimens will get charged 
with muddy sediment; and this matrix can be partially re- 
moved by gentle washing, leaving the loose spicular wall 
exposed nearly in its pristine condition (fig. 6). By breaking 
off a fragment of the sponge and still further treating it with 
water or with a drop or two of spirits of wine, aided by gently 
touching with a needle or camel’s-hair brush, the spicular 
felt-work becomes disentangled, and its individual constituents 
separated from each other as readily as those of recent Calci- 
sponges by the action of caustic potash. In reality the struc- 
ture of these fossil sponges has been preserved almost unaltered 
and uninjured, in spite of the fact that the spicules of which 
they consist are exceedingly slender, fragile, and minute, and 
that they are only loosely and irregularly intermingled 
together. 
As regards brittleness, however, the spicules of the Lias 
sponges now fracture much more readily than those of existing 
analogues, and it is exceptional to find perfect forms in micro- 
scopic mountings from them. Under the microscope the 
spicules vary but slightly in appearance from recent forms; 
their lustre is hardly so brilliant, but their surfaces are equally 
smooth and even, and show no traces of erosion. In polarized 
light they behave the same as recent Calcisponge spicules. I 
have not noticed any traces of axial canals; but even in recent 
spicules of similar dimensions it is very rarely that the canals 
can be distinguished. 
