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



Skeleton. — (1) Of the body at large ; the outermost portion of the skeleton consists 

 of a dense layer (PL XLII. fig. 4, a) of thickly set brushes of small, slender, t3'lostylote 

 spicules, whose points project beyond the surface of the sponge ; this layer, the most 

 external layer of the cortical skeleton, is about 0"28 mm. thick;' it is immediately suc- 

 ceeded below by a very much thicker layer (PI. XLII. fig. 4, h) of large stylote orsubtylo- 

 stylote spicules, closely and for the most part more or less vertically placed, and with a 

 few small tylostyli amongst them ; this layer constitutes the remainder, which is by far 

 the greater portion, of the cortical skeleton. Below the cortex the skeleton is no longer 

 definitely arranged, but consists of a confused mass of thickly scattered spicules, often 

 forming rude fibres. (2) In the mammiform projections there is no such thick cortex 

 as on the main l)ody, they are, comparatively speaking, thin-walled. The outermost 

 layer of the cortical skeleton, consisting of closely packed, small tylostylote spicules, is, 

 however, still present, and below this we find definite longitudinal bands of stout spiculo- 

 fibre, composed of the large megasclera, and a loose network of similar spicules irregularly 

 disposed. 



Spicules. — Megasclera; (1) small, straight or slightly curved, fusiform tylostyli 

 (PI. XLII. fig. 5a), sharply and gradually pointed at the apex and with well developed, 

 pointedly oval heads ; size about 0'28 by 0"008 mm. (2) Large, straight, smooth, 

 fusiform styli or subtylostyli (PL XLII. figs. 5, 5&, 5c), tapering very gradually to a sharp 

 point at the apex and narrowing considerably towards the base ; size about 0'98 by 

 0-022 mm. 



The species is distinguished from its congeners by its very pure white colour and the 

 very large size and flattened form of the larger mammiform processes. 



Zoca%.— Station 125, September 12,1873; lat. 10° 46' S., long. 36° 2'W.; between 

 Pernambuco and Bahia ; depth, 1200 fathoms ; bottom, red mud. One specimen. 



Polymastia agglutinam, Ridley and Dendy (PL XLI. fig. 6 ; PL XLII, figs. 

 1, 2, 2a, 2h, 3). 



1886. Polymastia agijlutinans, Kidley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 488. 



Sponge (PL XLI. fig. 6) sessile ; encrusting and enveloping pebbles, &c., and 

 collecting and cementing on to its own surface numerous fragments of shells, grains of 

 sand, and other foreign objects (whence the specific name), and giving ofi" long, slender, 

 cylindrical, fistular processes, each with a distinct canal up the centre but closed at the 

 top. These processes are quite clean and free from any coating of foreign objects such as 

 covers the body of the sponge. There are two specimens in the collection, the largest of 

 which has a body of irregularly globular form, about 12 to 18 mm. in diameter, and 

 with a great deal of coarse foreign matter inside and adhering to it, quite disguising it 



' Many of the spicules in this layer are drawn out into long, hair-like points, not shown in the figure. 



