Vol. 56.] FEOM THE EOCENE OE VICTORIA. 53 



-calcisponges from the Cretaceous and Jurassic rocks of this country, 1 

 and it occurs also in the recent Petrostroma ScJiulzei, 2 Doderl. 

 from the Japanese Sea. 



The minute four-rayed spicules of the inner portion of the dermal 

 layer have stout, tapering rays : the facial are often curved, while 

 the apical is straight, conical, and sometimes minutely spined (PI. Ill, 

 figs. 16-20, 22, 24). It is probable that some of these four-rayed 

 forms may represent early stages of the skeletal mesh-spicules, seeing 

 that the termination of the facial rays in some instances appears 

 &x eady in process of expansion (PI. Ill, figs. 21, 27). 



Basal Layers. 



At the base of the sponge, and also at different levels or stages 

 of its growth, there are thin layers of closely-arranged spicules 

 extending transversely across the spicular mesh and the canals, and 

 forming floors or platforms of the same contour as the summit of 

 the sponge. In places these particular layers are accompanied by an 

 outside layer of fine rods or needles similar to the dermal layer, but 

 they also occur without these accessories. The basal layers are 

 built up of small spicules, extremely variable in form, which are 

 united together to make an intricate and closely-arranged mesh- 

 work. Hardly any two of these spicules are alike, and the figures 

 given of them (PI. Ill, figs. 48-82) will convey a better idea of their 

 remarkable diversity than any verbal description. They appear to 

 be all four-rayed spicules, in which one ray, corresponding to the 

 apical ray in the normal four-rayed calcisponge-spicule, is conical, 

 pointed, and either smooth or partly covered with small prickles. 

 The three other rays, the equivalents of the facial rays in normal 

 spicules, are mostly unequal in length in the same spicule, straight 

 or curved irregularly in a direction opposite to that of the apical ray ; 

 they scarcely taper, if at all, and they are usually armed with stout 

 prickles or spines. In some instances these facial rays terminate 

 obtusely (PI. Ill, figs. 79, 81), but more frequently their ends are 

 expanded so as to form flattened or concave facets with evenly 

 rounded or lobate margins. 



The spicules of the basal layers are of small size ; the rays vary 

 from 0*025 to 0-13 mm. in length, and from 0*01 to 0*02 mm. 

 in thickness. llarely, however, a larger form occurs in a free 

 condition, which approximates in size and other features to the 

 mesh-spicules (PI. IV, fig. 9). 



These spicules are united to form the meshwork of this basal 

 layer by the close apposition of the terminal expansions of the facial 

 rays of the spicules to the rays of proximate spicules, in much the 

 same way as the mesh-spicules in the Lithistid genera Dory derma, 

 Zittel, and Lyidium, O. Schmidt (PI. Ill, fig. 83, & PL IV, figs. 2, 3). 



1 Hinde, Ann. & Mag. Nat. Hist. ser. 5, vol. x (1882) p. 199 & pi. xii ; Monogr. 

 Palseont. Soc. 'Brit. Foss. Spong.' pt. iii (1893) p. 214 & pi. xiv, fig. Id, 

 p. 220 & pi. xv, figs. 3/, 2>g. 



2 Zool. Jahrb. vol. x (1898) p. 20 & pi. iii, figs. 1-9. 



