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



firm aud compact. Surface even, very minutely hispid. Dermal membrane thin and 

 difficult to distinguish. Pores scattered (?). Oscula none observed; the sponge 

 appears to be lipostomous. 



Skeleton. — The main skeleton is a somewhat Isodictyal reticulation of stout stylote 

 spicules ; there is no very distinct fibre (although one can usually distinguish primary 

 skeleton lines running towards the surface and crossed at right angles by secondary lines), 

 but there is a fair amount of horny connecting substance at the nodes of the reticulation ; 

 the whole arrangement is rather vague and confused. In addition to the smooth stylote 

 spicules, which form the chief portion of the main skeleton, there are numerous spined 

 styli, some of which appear to echinate the main skeleton while others are scattered 

 loosely through the soft tissues (some of the latter may have been forced from their 

 proper position in cutting the sections ; there can be little doubt that these spined 

 spicules are really homologous with the echinating spicules of allied species). The 

 primary fibres end on the surface in dense tufts of slender stylote spicules whose points 

 project outwards; mingled with these are more of the echinating spined styli already 

 mentioned, while the centre of each tuft is occupied by one or more large, smooth styli 

 like those of the main skeleton. 



Spicules. — {a) Megasclera; (l) Smooth, stout, usually slightly curved styli 

 (PI. XXIX. fig. 4), tapering gradually to a sharp point at the apex aud narro-^ving 

 towards the rounded base; size of full grown examples about 0'4 by 0"025 mm.; these 

 form the main skeleton. (2) Much smaller, straight, slender styli or subtylostyli 

 (PI. XXIX. fig. 4c), rounded and usually very faintly spined at the base and tapering 

 gradually to a sharp point at the apex, size about 0"23 by 0"0065 mm.; these form 

 the tufts at the ends of the primary fibres. (3) Small, spined styli (PI. XXIX. fig. 4a), 

 almost or quite straight, very sharply pointed and with large, curved spines, shaped like 

 the thorns on a briar. These spines are very unequally distributed, they are abundant 

 at the base of the spicule, where they are arranged so as to point towards the apex, then 

 they almost cease and at about the centre of the spicule become suddenly abundant 

 again ; in this second position they are very large, stout and curved so as to point 

 towards the base; size of spicule about 0'175 by 0"013 mm; their arrangement has 

 already been indicated. (5) Microsclera ; of two kinds, (l) Very minute, palmate 

 isochelse, about O'Ol mm. long ; abundant. (2) Toxa (PI. XXIX. fig. 4&), with spined ends, 

 size about 0"14 by 0'0024 mm., also abundant. 



Vosmaer ^ briefly describes under the name Clathria lobata a new species from the 

 Cape of Good Hope ; this sponge certainly has a very remarkable resemblance to the 

 Challenger species under discussion, but the description is so short and imperfect that an 

 absolute identification would be impossible without comparison of specimens ; till such 

 is practicable we shall consider the Challenger sponge as a variety of Vosmaer's sjjecies, 



1 Notes from the Leyden Museum, vol. ii. p. 151, 1880. 



