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



Thrinacophora cervicornis, Eidley aud Dendy (PI. XXXVI. fig. 1 ; PI. XL. figs. 4, 4a). 



1886. Tlirinacopliora cervicornis, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, 



vol. xviii. p. 483. 



Sponge (PI. XXXVI. fig. 1) erect, branching dichotomously, subcylindrical, flattened 

 towards tlie points of furcation ; altogether much resembling a stag's antler. Total 

 height 175 mm. ; diameter of stem about 6 mm., of branches about the same or a little less. 

 Colour in spirit greyish-yellow. Texture firm and tough, stem and branches flexible 

 and very elastic. Swface beset with minute monticular eminences, so as to resemble 

 the surface of a coarse file ; from each of these eminences there projects, where the 

 surface is uninjured, a single, very long, setiform spicule, extending for .3 or 4 mm. 

 beyond the surface. 



Skeleton. — When the sponge is microscopically examined it is readily seen that it 

 possesses a thick central axis of horny consistency and appearance, which gives to it its 

 firm and elastic character, and which is surrounded by a comparatively thin external 

 coat of choanosome which readily peels off". After mounting in balsam the horny 

 matter is no longer apparent, and in the place of the central axis we see a dense 

 reticulation of short oxeote spicules, appearing almost uniserial in arrangement, without 

 any distinct fibre. It is this dense reticulation of spicules, all united together by horny 

 cementing material, which gives rise to the central axis. In the soft layer which coats 

 the axis there are numerous long and very slender oxeote and stylote spicules, arranged 

 longitudinally, but in no definite order ; the short oxea also occur scattered in a similar 

 manner outside the axis. We have already mentioned the very large, setiform (stylote) 

 spicules, which project for a long distance beyond the surface of the sponge and give 

 rise to a coarse hispidity ; these have their bases embedded in the central axis, from 

 which they project at right angles ; each one as it leaves the sponge is surrounded by 

 a whorl or tuft of divergent spicules of very much smaller size. These are very slender 

 styli (? occasionally oxea), whose divergent ends project for a short distance beyond the 

 dermal membrane. Sometimes two of the large styli come out together. 



Spicules. — (a) Megasclera; (l) short, stout oxea (PI. XL. fig. 4, h), rather abruptly 

 and usually very sharply pointed, occasionally unequal- ended, with the large end very 

 blunt; size about 0'28 by 0"018 mm.; occurring mainly in the axis and forming the 

 greater portion of the skeleton. (2) The long, smooth styli projecting from the surface ; 

 these are almost straight and measure about 5*2 by 0'037 mm. (3) The straight, smooth, 

 slender styli (PI. XL. fig. 4, a) projecting in whorls around the last mentioned ; these are 

 usually sharply pointed, but sometimes become blunted at the apex; size about 0"52 

 by 0'0075 mm. The long, slender oxea, .styli and strongyla, longitudinally disposed 

 in the choanosome, are to be regarded merely as slight varieties of (3) and measure 

 about the same. (6) Microsclera ; trichodragmata (PI. XL. fig. 4a), fairly plentifully 



