106 BRITISH PALASOZOIC 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.* 
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. Prorosponcia renestrata, Salter. Pi. I, figs. 1, 1 a. 
1864. Provrosponata FENESTRATA, Salter. Quart. Journ. Geol. Soc., vol. xx, 
p. 238, pl. xin, figs. 12 a, b. 
1878. — _ — Cat. Cambrian and Sil. Foss. Cam- 
bridge, p. 3. 
1877, — _— Zittel. Studien, Ab. 1, p. 45; Konigl. 
bayer. Akad. der Wiss., Cl. 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). Lethxa paleozoica, 
Th. 1, p. 316, fig. 59a. 
1881. a _- Etheridge, 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, 
pl. 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. 
