46 THE VOYAGE OF H.M.S. CHALLENGEE, 



Spicules. — (a) Megasclera ; large, smooth, fairly stout oxea, rather gradually and 

 sharply pointed at each end, and with a slight bend in the centre; size, about 07 by 

 0"03 mm. (JS) Microsclera; (1) large, stout, very strongly curved, sharply pointed, 

 simple and contort sigmata, very abundant, measuring about 0"07 by 0"0063 mm. ; 

 (2) smooth, sharp-pointed toxa, with very obtuse central angle, unusually large, 

 measuring about O'lS l)y 0'0063 mm. ; exceedingly abundant all through the sponge, 

 more especially so lining the subdermal cavities. 



Vosmaer's GcUius arcoferus,^ an Arctic form, certainly comes very near to this species, 

 especially if, as Dr. Vosmaer suggests, the real form is that of a fan; it differs, however, 

 in the proportions of the sigmata and toxa, inter se, the former being very much smaller 

 as compared with the latter than in Gellius jlabelUformis ; this much we can deduce from 

 the figures, but as to the actual sizes of the spicules in Gellius arcoferus, we are 

 unfortunately able to say nothing, for Dr. Vosmaer gives no measurements. 



Gellius cmgulatus, Bowerbank, also approaches Gellius Jlahelliformis in spiculation, 

 being also possessed of toxa, but differs in external form and in the very much 

 smaller size of the microsclera. 



Locality. — Station 320, February 14, 1876; lat. 37° 17' S., long. 53° 52' W. ; off 

 the mouth of the Rio de la Plata; depth, 600 fathoms; bottom, green sand; bottom 

 temperature, 37°'2. One large piece and several small ones. 



Gellius sp. (PL XIII. fig. 3). 



Sponge consisting of a pear-shaped body, tapering to a point at one end, which has a 

 fibrous appearance, and where possibly a stalk has been attached. Body solid. Length 

 29 mm., greatest breadth 12 mm. Colour in spirit pale greyish -yellow. Texture very 

 soft and fragile. Surface even, slightly hirsute. Oscula small and scattered. Dermal 

 memhrane thin and delicate. 



Skeleton. — Arranged much as in the body of Gellius calyx, altogether very loose. 



Spicules. — (a) Megasclera, of one kind only, viz., oxeote (PI. XIII. fig. 3), slightly 

 curved and rounded ofi'at each end; size 0"6 by 0*022 mm. (b) Microsclera ; (l) small 

 sigmata, size 0"019 by 0"0015, mm.; (2) very long, thin, hair-like spicules, apparently 

 not arranged in bundles ; size 0'7 by 0'003 mm. 



Again we have only one specimen of the sponge present, and that possiljly imperfect. 

 As it comes from the same station and agrees in several particulars with Gellius calyx 

 it is very likely a close ally of the latter; this hypothesis will be strengthened if the 

 examination of more specimens shows that the fine hair-like spicules are also really 

 proper to Gellius calyx. In the form of the oxeote spicules and the presence of hair- 

 like ones, together with the sigmata, the species in question agrees pretty closely 



1 Sponges of the "Willem Barents" Expedition, 1880 and 1881, p. 2D, pi. iv. figs. 18, 19 ; pi. v. figs. 87-90. 



