106 BRITISH PALEOZOIC SPONGES. 



point of conjunction." This view of the spicular character of the skeleton was 

 much nearer the truth than that of Dr. Bowerbank, who stated that the structures 

 were not spicules, but horny fibres replaced by pyrites. 1 



Different opinions are held as to whether the spicules in this genus were free, 

 and merely held in position by the soft structures of the animal, or whether they 

 were organically attached together by a deposition of silica at the junction of the 

 rays with each other. So far as I have been able to judge from the few instances 

 in which the spicular rays are seen in contact, they appear to have been cemented 

 or fused together at their junction with each other, though there is not that 

 complete coalescence of the adjacent rays which exists in regular Dictyonine 

 hexactinellids. The spicular rays do not interlace with each other sufficiently to 

 account for the preservation of connected portions of the meshwork in the fossil 

 state, and without a certain degree of organic attachment they would, almost 

 inevitably, have fallen entirely apart from each other. The fusion of the rays at 

 their points of contact does not, however, appear to have been sufficiently strong 

 to prevent that partial disruption of the spicular wall which has taken place in 

 most of the examples, or the isolation of the larger spicules in many cases. 



1. Protospongia fenestrata, Salter. PL I, figs. 1, 1 a. 



1864. Pbotospongia eenestbata, Salter. Quart. Journ. Geol. Soc, vol. xx, 



p. 238, pi. xiii, figs. 12 a, b. 



1873. — — — Cat. Cambrian and Sil. Foss. Cam- 



bridge, p. 3. 



1877. — — Zittel. Studien, Ab. 1, p. 45; Konigl. 



bayer. Akad. der Wiss., CI. ii, 

 Bd. xiii, Ab. 1 ; Neues Jahrbuch, 

 p. 354. 



1877. — " — Carter. Ann. and Mag. Nat. Hist., ser. 4, 



vol. xx, p. 177. 



1880. — — F. Roemer (in part). Lethsea palseozoica, 



Th. 1, p. 316, fig. 59 a. 



1881. — — 'Eiheridge, senr. Mem. Geol. Surv., vol. iii, 



2nd ed., Appendix, p. 472. 



1882. — — Zittel. Neues Jahrb., Bd. ii, p. 203. 



1883. — — Hinde. Catalogue Foss. Sponges, p. 129, 



pi. xxviii, fig. 2. 



The fragments of the wall of this species which have been preserved are 

 insufficient to indicate the probable form of the Sponge. The cruciform spicules 



1 ' Quart. Journ. Geol. Soc.,' vol. xx, p. 239. 



