Dr. G. J. Hinde—Spitzbergen Chert-Deposits. 249 
The dark portion of the sponge, which I regard as infilled material 
from the sea-bottom, is clearly of the same nature as many portions 
of the rock-matrix, which show in microscopic sections dark 
granules, rod-like bodies, and spicules of various forms interspersed 
in a siliceous matrix. It is quite in accordance with our experience 
of fossil sponges—and of recent forms as well—to find their canals 
and interspaces between their skeletal fibres filled with a varied 
assortment of spicules, often of a character quite different from those 
proper to the sponge itself. Further, in one of the Spitzbergen 
specimens the supposed canals are distinct cylindrical siliceous fibres, 
whilst the dark portion—the supposed skeleton—hardly shows 
traces of spicules, and passes uninterruptedly into the surrounding 
rock-matrix, and cannot be distinguished from it. 
On Dunikowski’s view that the siliceous fibres were originally 
canals, it is difficult to account for the presence in them of lithistid 
spicules exclusively, and it is equally as difficult to imagine that 
whilst foreign spicules and other materials were accidentally intro- 
duced into what are stated to be the skeletal tissues, none should 
have found their way into what are stated to have been the empty 
canals of the sponge. 
But the most convincing evidence that the translucent portions in 
these sponges are, in reality, the skeletal fibres, and not the canals, 
is afforded by sections, prepared by v. Dunikowski, of a specimen 
from the Cyathophyllum limestone of Gypshook. The translucent 
portions in these sections are in places filled with the original spicules, 
running parallel with each other, and evidently in their natural 
position in the fibre. Unfortunately the outlines of these spicules 
have been rendered very indistinct by the fossilization, so that their 
complete forms cannot be made out definitely, and they appear to 
differ from the typical forms of Pemmatites in being furcate at one 
or both ends (PI. VIII. Fig. 7). Unlike the specimens from Axel’s 
Island, the spicules in these sections are not replaced by calcite, but 
consist of chalcedonic silica. The dark portions in these sections do 
not contain many spicules, and no doubt can be felt that they are 
simply the rock-matrix. The sections are named by Dunikowski, 
P. arcticus, var. latituba, but it is probable, judging from the form of 
the spicules, that the sponge is generically distinct from Pemmatites. 
The grounds above stated appear to me to justify the view that 
these Spitzbergen sponges are really lithistid and not monactinellid 
forms. On this interpretation the diagnosis of the genus given by 
Dunikowski requires to be fundamentally altered; but as the term 
Pemmatites has reference to the outer form of the sponges merely, 
and no bearing on their inner structures, there is no reason why it 
should not be retained with the amended description as below :— 
Order: Silicispongiee. 
Suborder: Lithistide. 
Family: Rhizomorina. 
Genus: Pemmatites, v. Dunikowski, emend. Hinde. 
1884, Kong]. Svenska Vet.-Akad. Handl. Bd. 21, No. 1, p. 138. 
