250 Dr. G. J. Hinde—Spitzbergen Chert-Deposits. 
Discoid, compressed or globular, sponges, apparently without stem 
or surface of attachment. The skeleton consists of a meshwork of 
subcylindrical anastomosing fibres, which are composed of rod-shaped. 
lithistid spicules with blunted and facetted lateral processes. The 
open spaces between the fibres form an indefinite canal-system, with 
circular or polygonal apertures at the surface of the sponge. 
I do not propose here to enter upon the detailed descriptions of 
the species and varieties given by Dunikowski, which appear to me 
to be substantially correct as regards the measurements and other 
particulars relating to the form and direction of the fibres, ete., but 
I may remark that in referring to them we must bear in mind that 
the structures described as canals are the skeletal fibres, whilst the 
so-termed fibres are only the interspaces between the real fibres, 
now infilled with matrix. Hxamined from the new point of view, 
the sponges described as varieties macropora and latituba (loc. cit. 
pp. 15, 16) appear to be sufficiently distinct from P. areticus to be 
considered as separate species. 
The lithistid spicules in these sponges, as shown by the accom- 
panying figures (Pl. VIII. Figs. 5-6), vary somewhat in size and 
form; for the most part they consist of a straight or shghtly curved 
rod-like axis, truncated or obtusely pointed at the ends, with short 
lateral projections terminating in minute facets.’ They vary from 
-4 to °6 mm. in length, and about ‘06 mm. in thickness. 
I have not been able to detect a dermal layer (Deckschicht) as 
distinct from the fibres, in any of the sponges; the structure so 
named and figured by Dunikowski appears to me to be merely a 
thin layer of matrix incrusting the surface of the sponge. 
Whilst thus differing from Dr. Dunikowski as to the interpretation 
of the structure of these sponges, I wish to bear testimony to the very 
careful manner in which he has investigated and described their 
characters. ‘The specimens are in a very unfavourable state of pre- 
servation, and owing to the very complicated changes which take 
place in the fossilization, it is, without special experience, easy 
to make a mistake in determining the original characters of these 
organisms from the older rocks. 
SUMMARY. 
Specimens of chert-rock from the Productus-chert division of the 
Permo-Carboniferous series of Spitzbergen are shown to consist 
largely of detached siliceous sponge spicules, thus indicating the 
probable derivation of this rock from the skeletal remains of these 
organisins. The chert is of the same character as that of the Yoredale 
beds of the British Isles, and it occurs on the same relative geological 
horizon. The Productus-chert division has a thickness on Axel’s 
Island of 876 m., of which 265 m. are chert, and 111 m. dark siliceous 
schists, likewise containing sponge remains, but less abundantly than 
the chert. The chert had previously been regarded as connected in 
some way with the igneous rocks of the island. 
1 As already mentioned, the spicules in Pemmatites latituba differ in form, and 
they are more slender than in the other species described. 
