Dr. G. J. Hinde—Spitsbergen Chert- Deposits. 247 
different from those of Dr. Dunikowski, that it will be necessary for 
me to state in some detail the structural features on which they are 
founded. 
Little requires to be said of the outer form of the Sponges. They 
are in some cases flattened or discoid bodies, with circular, oval, or 
irregular outlines, in others nearly round, and, as is so frequently 
the case with the Paleeozoic sponges, they show no stem or surface of 
attachment. Their exterior surfaces are usually uneven, with blunted 
warty eminences irregularly dispersed over them. Under favourable 
circumstances the surface also exhibits between the elevations a 
reticulation or network of siliceous translucent fibres, bounding 
circular or subpolygonal interspaces of a dark appearance. 
The sponges are now compact throughout; in sections or fractured 
surfaces they exhibit a mesh of the translucent siliceous fibres, some 
of which have a generally radial direction from the central portion 
to the surface of the sponge, whilst others run transversely, and unite 
with the radial fibres, and thus form a connected meshwork, the 
spaces between which, as at the surface, are of a dark mineral (PI. 
VIII. Figs. 1, 2). The sponges are now mostly of silica, but in all 
the specimens examined there is a slight reaction with acid. 
In microscopic sections the dark portion of the sponge is seen to 
consist chiefly of minute particles and rods of an opaque material, 
probably of carbonaceous, though some may be of ferruginous origin, 
imbedded in a lighter granular (?) matrix; in this, also, are rod- 
shaped or acerate siliceous spicules, disposed quite irregularly both 
with respect to each other and to the direction of the interspaces in 
which they occur. Further, the spicules are by no means uniform in 
shape or in size in the same specimen, or in the same portion of it. 
There is every probability that, as suggested by Dunikowski, the 
dark rods mentioned above are merely replacements of siliceous 
spicules. 
The translucent siliceous fibres of these sponges, when seen in 
microscopic sections, are either colourless or of a yellowish tint, their 
margins are uneven, they consist of fibrous radiating chalcedonic and 
crystalline silica, which gives brilliant tints between crossed Nicols. 
In this ground-mass there are frequently microscopic crystals of 
calcite, and here and there elongate rod-like spicules with stumpy 
lateral projections (Pl. VIII. Fig.2). These spicules are frequently 
isolated in the fibres, their length corresponding with the direction of 
the fibre ; occasionally several occur together closely united, evidently 
in their natural positions, by the apposition of their blunt projections to 
the surfaces of adjoining spicules (Pl. VIII. Fig. 4). They have the 
same general characters, and the same mode of union with each other 
as the spicules of lithistid sponges. Though, as a rule, only a few of 
these spicules now remain in the translucent fibres, their outlines 
are, for the most part, peculiarly distinct, and, strangely enough, 
though there can be no doubt that they are the spicules of siliceous 
sponges, and they are at present imbedded in a siliceous ground-mass, 
yet they are now chiefly composed of clear calcite. The fact is of 
importance also, that though there are plenty of acerate and smooth 
