Br. G. J. Hinde — On a Palceozoic Sponge. 339 



are no traces of any enveloping structure inclosing the bundle. The 

 rods vary from *15 to '5 ram. in thickness, they are now of chalce- 

 donic silica, and for the most part solid throughout, in only a single 

 instance did I see an indication of an axial canal. Delicate wrinkled 

 lines cross the rods transversely and apparently represent the slight 

 projecting frills met with in other specimens. 



In all important characters, Dr. Hicks's specimen so closely re- 

 sembles the typical example of Hyalostelia {Pyritonema) fasciculus, 

 M'Coy, 1 that there is no reason to regard it as specifically distinct. 

 The individual rods do not reach the maximum thickness of some of 

 those in the typical form of the species, but the differences are not so 

 great as to be of specific value. 



Having established the similarity between these forms, it is desir- 

 able to point out that the relationship, indicated by M'Coy, of Pyri- 

 tonema fasciculus to the glass-rope of Hyalonema mirabile, Gray, is of 

 a genuine character. This has been called in question, amongst others, 

 by Prof. G. Lindstrom, 2 who states that M'Coy's species "is nothing 

 but a silicified and consequently somewhat altered Heliolites. It 

 must be confessed that the purely diagrammatic figure given by 

 M'Coy (Brit. Pal. Foss. pi. i. B, fig. 18a) might readily give rise to 

 this conclusion. Prof. F. Eoemer 3 also states that the systematic 

 position of the genus, in which species allied to the present one are 

 placed, is very uncertain. I also found the specimens of this species 

 in the Jermyn Street Museum, placed with the Annelida of the 

 Llandeilo group, probably on account of their close resemblance to 

 Hyalostelia (Serpala) parallela, M'Coy, sp., from which they can 

 hardly be distinguished. 



At the time when M'Coy compared Pyritonema fasciculus with the 

 rope of Hyalonema mirabile, Gray, the true sponge nature of this 

 latter form was stoutly denied by Dr. Gray, who then regarded the 

 rope as the skeleton of a Zoophyte, and M'Coy also adopted this 

 opinion. It is now well known that ropes or tufts of long spicular 

 rods are common appendages in many of the deep-sea hexactinellid 

 sponges, and the resemblance of these to the fossil forms is very 

 striking. 



In both recent and fossil examples there is a similar form and arrange- 

 ment of the spicular rods in bundles ; the rods correspond in dimen- 

 sions, in their siliceous composition, and, when the fossil forms are well 

 preserved, in the possession of axial canals, and even the concentric 

 layers of the rods can be seen. In some species, though not in the 

 present one, some of the fossil rods terminate in four recurved hooks, 

 precisely as in the recent examples. In another structural feature 

 also, which has not hitherto been particularly noticed, there is a 

 well-marked correspondence between Hyalostelia fasciculus and the 

 recent Hyalonema mirabile. This is the occurrence, on the surface 

 of some of the rods, of minute annular or spiral projecting ridges 

 or frills, which look like so many wrinkled lines crossing the rods. 

 The frilled rods are irregularly interspersed in the same bundle with 



1 Brit. Pal. Foss. p. 10, pi. i. B. fig. 13. 



2 Bih. till K. Svenska Vet. Akad. Handl. Bd. 8, No. 9, 1883, p. 13. 



3 Letluea Palseozoica, 1880, p. 318. 



