Vol. 52.] FROM THE CARBONIFEROUS LIMESTONE. 439 



a few much larger, simple, fusiform spicules, 0-8 mm. in length. 

 No dermal layer has been preserved. 



In outward aspect this sponge looks like a flattened waterworn 

 nodule of a greyish tint and a slightly roughened surface, and its 

 organic character was not fully apparent until sections had been 

 made through it. The interior is solid, compact, and consists mainly 

 of chalcedonic silica. The spicules have, for the most part, been 

 replaced by calcite, but they still retain their details of form very 

 perfectly. The fibres of the sponge, examined under the micro- 

 scope, both in vertical and in transverse sections, have a very irregular 

 and indefinite appearance, and in some places the spicules are 

 loosely massed together, and scarcely show any definite arrange- 

 ment. The fibres, where best preserved, are crowded with spicules, 

 some parallel with the direction of the fibre, others transverse to its 

 course and projecting into the spaces between the fibres, which are 

 very seldom free from spicules. The spicules are usually so crowded 

 and intermingled together that it is difficult to distinguish indi- 

 vidual forms ; but, though there is considerable variation, the main 

 type has a straight or curved shaft, with notched or digitate ex- 

 tremities. The spicules appear to be but very lightly connected 

 together ; sometimes their shafts are closely apposed, at others 

 they are attached by the interlocking of their short terminal pro- 

 cesses or by the knobs at the end of one spicule fitting into the 

 notched ends of a proximate one. No axial canals could be seen in 

 the ordinary spicules of the fibres, but in some of the larger fusiform 

 spicules they have been preserved. These latter spicules appear in 

 small bundles of two or three together in the interspaces of the 

 fibres. A single cylindrical spicule was also met with in the sponge, 

 but it is probably adventitious. 



The genus Pegmatites, to which this sponge belongs, was estab- 

 lished by E. von Dunikowski l for some compressed discoidal sponges 

 from the Permo-Carboniferous strata of Spitzbergen, which were 

 considered by this author to be monactinellid in character, from 

 the presence of simple fusiform spicules within the sponge. These, 

 however, proved to be in the interspaces of the fibres of the sponge, 

 while the fibres themselves were described by E. von Dunikowski as 

 the canals. An examination of the type-specimens showed that 

 the spicules of the fibres had been almost entirely obliterated, but 

 a few remained, and these proved that the fibres were originally 

 composed of lithistid spicules. 2 The discovery of the present speci- 

 men, in which the fibre-spicules are numerous and well preserved 

 and lithistid in character, and, moreover, are accompanied by some 

 fusiform spicules in the interspaces, fully confirms the lithistid 

 nature of the genus Pemmatites. 



The present species comes nearest to P. latituba, Dun., 3 in the 

 form of the spicules, but the fibres are much more closely arranged. 



1 * Ueber Permo-Cai-bon-Sckwamme von Spitzbergen,' K. svenska Vetensk.- 

 Akad. Handl. vol. xxi. (1884) no. 1, pp. 1-18 & pis. i.-ii. 



3 Geol. Mag. 1888, p. 246. 



3 Op. tit. p. 16, pi. i. figs. 2 & 12 ; also Geol. Mag. 1888, p. 249, pi. viii. fig. 7. 

 Q. J. G. S. No. 207. 2 h 



