110 THE VOYAGE OF H.M.S. CHALLENGEE. 



character wliieh would seem to be not confined to this subgenus, for Mr. Carter fisrures a 

 similar structure in the isochelate spicules of his Microciona affinis;^ further information 

 concerning the latter species is, however, much needed, especially with regard to the 

 megasclera. 



The new Challenger species are very closely related to that of Johnston and 

 Bowerbank, and it is exceedingly interesting to meet with such intimately related forms 

 in such distant localities as Great Britain, Kerguelen, and the Cape of Good Hope. 



Desmacidon [Homceodictya) herguelenensis, Ridley and Dendy (PI. XXIII. figs. 3, 

 3a, 36, 3c ; PL XXIV. fig. 3). 



1886. Hommodidya herguelenensis, Eidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5. 



vol. xviii. p. 346. 



Sponge (PI. XXIV. fig. 3) lobate or digitate. The larger of the two specimens 

 obtained consists of a short peduncle, narrower towards the base and then expanding 

 and dividing into two divergent, stout, finger-like lobes of very unequal size. Height 

 of the sponge 69 mm. Diameter of lobate processes 13 mm. Colour in .spirit 

 light brownish-yellow. Texture soft, spongy and resilient. Surface rough to the 

 touch, woolly-looking and minutely hispid. Dermal membrane delicate, transparent. 

 Oscida few, small and scattered. Pores irregularly scattered, abundant in parts, 

 diameter about O'l mm. 



Skeleton. — Very loose and Ul-defined, consisting of an irregular, somewhat Isodictyal 

 reticulation of oxeote spicules, occasionally forming fibres. 



Spicules. — (a) Megasclera; of one kind only, viz., simple oxea (PI. XXIII. 

 figs, 3, 3a) short and rather stout, tapering gradually to a sharp point at each end ; 

 size about 0'35 by 0"019 mm. (6) Microsclera; the peculiar palmate isochelae of the 

 genus {vide supra; and PI. XXIII. figs. 3&, 3c); length about 0'028 mm. 



We were at first inclined to regard this sponge as a variety of the British species, 

 Desmacidon [Homceodictya) palmata, which it very nearly approaches both in external 

 form and in spiculation. There can be no doubt that the two are closely related, but 

 on the whole it appears better to separate the Kerguelen form as distinct. The main 

 difi'erences between the two concern (l) the size of the oxeote spicules, which in 

 Desmacidon (Homceodictya) j)almata (according to Bowerbank's preparations in the 

 British Museum) are little more than half as long as in the Kerguelen form ; (2) the 

 skeleton fibre, which is more distinct and highly developed in Bowerbank's than in the 

 Challenger specimens. The isochelse are of about the same size in the two specie.*, 

 and present no important structural difi"erences. The ends of the anterior palms are, 

 as a rule, more turned out in the British species, and the angle which they make with 



1 Ayin. and Mag. Nat. Hist., ser. 5, vol. vi. p. 41, pi. iv. fig. 15. 



