110 BRITISH PALEOZOIC SPONGES. 



belonged to the same Sponge. In some instances, however, the spicular ropes and 

 detached spicules occur in beds in which no hexactinellid spicules have as yet been 

 met with ; but this may in part be accounted for by the fact that even during the 

 life of the Sponge the anchoring spicules would be buried in the bottom ooze, and 

 would thus escape the disturbing influences which have probably scattered and 

 destroyed the body-spicules after the death of the Sponge. 



These anchoring spicules, in the best preserved examples, exhibit all the 

 characters of similar spicules in recent hexactinellid Sponges met with in deep-sea 

 dredgings. They are composed of silica deposited in concentric layers, they are 

 traversed by an axial canal, and many of them likewise terminate in four recurved 

 hooks. Further, in one species the surface of many of these spicules is ornamented 

 with slight projecting frills of a character similar to those present in the anchoring 

 spicules of the recent Hyalonema mirabile, Gray. As the recent anchoring spicules 

 are in all cases associated with a Sponge body consisting of hexactinellid spicules, it 

 may be concluded that the fossil anchoring spicules were similarly associated, even 

 though they now occur in beds in which the hexactinellid body-spicules are rare or 

 apparently absent. 



Pyritonema, M'Coy, and Acestra, F. Roemer, have been founded exclusively on 

 the bundles of anchoring spicules. On the ground of priority, M'Coy' s term might 

 be claimed as the designation of this genus, but as objection could be taken to 

 employing it for hexactinellid body-spicules as well as for the anchoring spicules, 

 it seems preferable to adopt Zittel's name Hyalostelia, which includes both kinds of 

 spicules. 



Both M'Coy and Portlock regarded the anchoring spicules occurring in the 

 Carboniferous Limestone of Ireland as the tubes of annelids, and placed them 

 in the genus Serpula. 



Hyalostelia is first known in Cambrian strata (Tremadoc Group), and it is also 

 present in Ordovician, Silurian, and Lower-Carboniferous Rocks. Detached 

 hexactinellid spicules in the Upper Chalk have been assigned to the genus, but the 

 ropes or bands of anchoring spicules have not been met with above the Carboni- 

 ferous Rocks. 



3. Hyalostelia fasciculus, M'Coy sp. Plate I, figs. 3, 3 a, 3 b. 



1850. Pyritonema fasciculus, M'Coy. Ann. and Mag. Nat. Hist., ser. ii, 



vol. vi, p. 273. 



1854. — — Morris. Cat. Brit. Eoss., p. 63. 



1855. — — M'Ooy. Brit. Pal. Eoss., p. 10, pi. i b, fig. 13. 

 1869. Eophyton explanatum, Ricks. Geol. Mag., vol. vi, p. 534, pi. xx, 



figs. 1 a — e. 



