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



relations of this rare form of spicule in other sponges are so obscure as to afford no ap^^arent 

 clue to its classificatory importance, if it has any. As examples of other genera in which 

 it occurs we may cite Spongilla and Higginsia. 



Dendropsis hidentifera,^ Eidley and Dendy (PI. XXXVIII. fig. 1 ; PI. XL. figs. 7, 7a, 



7b, 7c; PI. XLVI. fig. 8). 



1886. Dewlropds hidentifera, Kidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 483. 



Sponge (PI. XXXVIII. fig. 1) erect, stipitate, dichotomously branched ; stem 

 cylindrical, branches flattened (especially towards their apices), and all approximately in 

 the same plane. The largest specimen has a total height of about 200 mm.; the stem is 

 75 mm. long and about 8 mm. in diameter ; the branches are at first of nearly the same 

 diameter as the stem, but lessen upwards. Colour in spirit greyish-yellow. Texture 

 tough and hard. Surface rough, with numerous minute prominences, and hispid. 



Skeleton. — There is a dense, compact, axial core (PI. XLVI. fig. 8, «) of closely in- 

 terlacing, for the most part sublongitudinally disposed, smooth stylote si^icules ; from 

 this central axis very much larger, stout, smooth, stylote spicules radiate to the surface, 

 beyond which the apices of many of them project. Usually these spicules occur in loose 

 bundles or bands of three or four together, the bases of those nearest to the centre being 

 embedded in the axial core ; they are surrounded by dense sheaves (PL XLVI. fig. 8, h) 

 of the characteristic stylote spicules, the apices of which also often project beyond the 

 surface. 



Spicides. — (a) Megasclera ; (l) smooth, stout, sharply pointed styli (PI. XL. fig. 7, o), 

 commonly with a rather sharp bend towards the base, towards which also the spicule 

 usually narrows ; in the dense central axis these spicules commonly measure about 

 0'35 by 0'025 mm.; these are, however, very much smaller than those radiating to 

 the surface, which measure about I'l by 0"044 mm. There occur also very long and 

 slender, smooth styli (PL XL. fig. 7, a) ; these are not nearly so abundant as either 

 of the foregoing, but still can hardly be called rare ; they are of variable size, and 

 may measure about 175 by 0'02 mm.; sometimes, through the blunting and rounding 

 off" of the apex, the long slender styli give rise to strongylote spicules (PL XL. 

 fig. 7, h). (2) The " bidentate" styli (PL XL. figs. 7, c, 7a, 7h) ; long, straight, slender, 

 slightly fusiform and hastately pointed, each with two small, sharp spikes projecting 

 from the base, which may be slightly enlarged. In the base the axial thread is also 

 slightly enlarged, and seems to give off" a branch to each spike. These spicules are very 

 constant in shape and size, measuring about 0'56 by 0'0075 mm.; their disposition 

 in the sponge has already been indicated, (b) Microsclera ; small, entirely spined oxca 

 (PL XL. fig. 7c), each one haiang usually a rather sharp bend in the centre ; size about 



1 So-called from tlie jiresence of tlie two spikes on the base of the characteristic stylus. 



