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



embedded in the horny axis, while the outer end projects beyond the surface in the 

 form of a tuft of smaller stylote spicules ; these tufts are sometimes seen with a single 

 large stylote spicule in the centre, surrounded by the smaller ones. The primary 

 skeleton lines are crossed by both vertical and horizontal secondary fibres, which are 

 probably in part formed by the branching of the central axis. The whole system of 

 fibres is rather confused. 



Spicules. — (a) Megasclera ; smooth styli, of two chief sizes; (1) stout, almost 

 straight, unusually sharply pointed, variable in length, measuring up to about 0'7 by 

 0"023 mm. (PI. XIX. fig. 2); (2) slender, straight, sharply pointed, variable in length, 

 measuring up to about 0'7 by 0'0063 mm. (PL XIX. fig. 2a). The distribution of these 

 two kinds of spicules has already been indicated ; in addition to the tufts of slender spicules 

 which project from the surface there is a zone of very slender, longitudinally placed styli 

 at a short distance below the surface ; indeed it is here that the slender styli attain their 

 greatest length and slenderness, being both longer and more slender than those of the 

 tufts, and it is from one of these longest that the above measurements have been taken. 

 There is little doubt that we have in all these only slight modifications of one form 

 of spicule, (h) Microsclera; (1) small palmate isochelse (PI. XIX. fig. 2h), extremely 

 abundant in the dermal membrane but scanty below; length up to about 0'025 mm. 

 (2) A very few smooth toxa, about 0'07 mm. long; we have only seen a few of these, 

 so they may be foreign, but we think not. 



The most remarkable feature of this sponge is the extraordinary development of 

 horny matter. The whole sponge, its megasclera, and their arrangement, much recall 

 the genus Ra»pailia. 



Locality. — Off Port Jackson; depth, 30 to 35 fathoms. One specimen. 



Espenopsis challengeri^ Ridley, sp. (PL XVIII. ; PL XIX. figs. 8, 8a, 8i). 



1885. Amphilectus ehallengeri, Eidley, Karr. Chall. Exp., vol. i. pt. 2, p. 570, fig. 187. 



1886. Espenopsis ehallengeri^ Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 341. 



Sponge (PL XVIII. figs. 1, 2, 3) of very definite, beautiful and symmetrical external 

 form, a good idea of which will be obtained by reference to the figures.^ From a slightly 

 expanded base, which has evidently served to attach the sponge to the bottom upon 

 which it grew, arises a straight or slightly curved stem, composed of densely packed and 

 firmly united stylote spicules. This stem is very much compressed laterally, and from its 

 anterior edge (as we shall term it) arise a number of short, simple branches, placed one 

 above the other at gradually increasing intervals, thus dividing the stem into a series of 

 unequal " internodes," the longest of which is at the top. The stem itself, and each of 



^ These drawings are by Dr. J. J. Wild, artist to the Expedition. 



