82 THE VOYAGE OF H.M.S. CHALLENGER. 



membrane, a dermal network of spicules, and a subjacent bast-lite layer of reticulating 

 spiculo-fibres. The interior of the sponge is composed of a compact reticulate tissue, 

 containing both spiculo-fibres and free spicules, and penetrated by branches of the 

 canal system. Megasclera, oxea, sharp-pointed or blunt, passing into strong}da in 

 some species. In one genus (Oceanapia) microsclera are present in the form of sigmata. 



Genus Rhizochalina, Schmidt (Pis. VIIL, IX.). 



1867. Biemna, jMrs, Gray, Proc. Zool. Soc. Lond., 1867, p. 538. 



1870. RMzochalina, Schmidt, Spong. Atlant. Gebiet., p. 35. 



1882. Phlosodidyoji, imrs, Carter, Ann. and Mag. Nat. Hist., ser. 5. vol. x. p. 122. 



No microsclera present. 



Rhizochalina Jistulosa,^ Bowerbank, sp. (PL VIIL figs. 2, 2a ; PI. IX. fig. 4). 



1873. Desmacidon fistulosa, Eowerbank, Proc. Zool. Soc. Lond., 1873, p. 19, pi. iv. figs. 7, 8. 

 1884. Rhizochalina fistulosa, Eidley, Zool. Coll. H.M.S. "Alert," Brit. Mus., p. 420. 



Sponge (PI. VIIL fig. 2) more or less globular, solid, with fistulae arising abruptly 

 from all parts of the surface. Colour in spirit yellowish to white, when dry light 

 brownish-yellow (Bowerbank's specimen). Size of the body very variable, from 

 6 mm. in diameter upwards. Fistulie broken oflf (?) in all cases so as to exhibit open 

 ends, no branching visible. Texture firm and compact throughout in well-preserved 

 specimens. In broken specimens from a great depth the internal portion appears to 

 have undergone disintegration and run out, leaving little but the external rind formed 

 mainly of the tough bast-like layer. Surface smooth, covered with a very thin 

 transparent membrane. 



Skeleton. — (a) A dermal network of oxeote spicules, which are a trifle shorter than 

 those lying below, measuring 0-213 mm. in length, (h) A bast-like reticulation of spiculo- 

 fibres, which are, however, not so coarse and stout as in Oceanapia rohusta. (c) A 

 reticulation of spiculo-fibre filling up the centre of the sphere and supporting the canal 

 systems. Some of the canals are lined hy a very dense layer of oxeote spicules arranged 

 vertically to their walls, and not collected into fibres. 



Spicules. — Oxea (PL IX. fig. 4), usually slightly curved, moderately sharp, tapering more 

 abruptly towards the ends, but much less abruptly than in Rhizochalina p)utriclosa, and 

 measuring in the deeper parts of the sponge 0"265 by 0'0126 mm. 



' Since this account was written we have discovered in one of the specimens from Station 188, which we have 

 here referred to Ehizoclmlina fistulosa, numerous .sigmata. This fact necessarily modifies our views both as to the 

 species and genus. Probably Rhizochalina, Schmidt, and Oceanapia, Norman, should be united in one genus, but it is 

 now too late to make any such radical alteration in the present work. As regards the species Rhizochalina fiskdosa, it 

 is still very possible that we are correct in our determination, and that the sigmata have hitherto simply been 

 overlooked, as Bowerbank at first overlooked them in describing his Desmacidon Jcffreysii ( = Oceanapia rohusta), cf. 

 Mon. Brit. Spong., vol. ii. p. 347, and vol. iii. p. 162. 



