248 Dr..G. Si. Hinde—Spitsbergen Chert-Deposits. 
rod-shaped spicules in the dark portion of the sponge, none of these 
forms can be seen in the translucent fibres, and, similarly, the lithistid 
spicules of the fibres do not occur in the dark interspaces. There is 
further a general uniformity in the character of these lithistid spicules, 
not only in the same specimen, but in those of distinct species. 
Dr. v. Dunikowski attaches, in his paper, but little significance to 
these lithistid spicules. He does indeed mention the occurrence of 
a few nodose irregular Jithistid spicules with some of tetractinellid 
origin, but he thinks they have probably nothing to do with the 
proper skeleton of the sponges, but should be considered as merely 
accidentally introduced forms. I find, however, that they are very 
generally present in the translucent fibres of the sections” prepared 
and studied by this author. 
Dr. v. Dunikowski considers that the dark portions of these 
sponges, which form, as already mentioned, the irregular inter- 
spaces between the translucent anastomosing fibres, are the true 
skeletal fibres, and the acerate spicules imbedded in them irregularly, 
as the monactinellid spicules proper to the skeleton. The translucent 
connected portions, on the other hand, which in this paper I have 
denominated fibres, are described by this author as the original canals 
of the sponge, which, after the death of the animal, have been 
infilled with crystalline quartz free from any admixture of those 
foreign substances which have given such a dark appearance to the 
rest of the sponge. ‘These so-termed canals are described as main 
canals, and concentric or connecting canals. 
My interpretation of the characters of these sponges totally differs 
from that of Dr. Dunikowski, for, in my opinion, the translucent 
anastomosing fibres—the “canals” of Dunikowski—are in reality the 
fibres of the sponge which were originally composed of lithistid 
spicules. Most of these have been dissolved, and their spaces filled 
with chaceldony and quartz; some remain, either singly or united 
in their natural positions in the fibres. The dark portions of the 
sponge—the “skeletal fibres” of Dunikowski—I regard as merely 
the irregular interspaces between the true skeletal fibres, in which 
the water circulation was carried on during the lifetime of the 
animal, and which after its death became infilled with the materials 
of the sea-bottom, consisting of a fine siliceous mud, with numerous 
spicules, chiefly of disintegrated monactinellid sponges, dispersed 
through it. 
In support of my view, I may state that fossil lithistid sponges, 
in which the fibres have been replaced in a similar manner to these 
Spitzbergen forms, are of not unfrequent occurrence. I have before 
me microscopic sections of Aulocopium and Astylospongia from the 
Silurian strata of Gotland, in which the process has taken place ; 
and, in one instance, the lithistid spicules are now of calcite, 
imbedded in a chalcedonic matrix, under the same circumstances as 
those of Pemmatites. 
1 Loe. cit. p: ie 
2 They are present in seven out of ten slides of P. arcticus, in both of the slides of 
P. verrucosus, in two out of three slides of the var. macropora, and in two out of 
three slides of the var. /atitwba, which were sent to me by Prof. Lindstrém. 
