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



same form were also obtained. Three sides of tliis irregularly quadrangular plate, which 

 measured about 1 foot square, exhibited much torn margins, but on the fourth the natural 

 border was preserved. On the very probable supposition that this border, which is 

 about 40 cm. in length, represents the upper margin of the sponge, and that no great 

 portion is wanting, the whole form would be that of a sack or cup, whose upper 

 aperture would be about 13 cm. in diameter. At the much destroyed margin, opposite 

 to the intact border, and, therefore, probably the lower, the sponge is as much as 1 cm. 

 in thickness, and decreases gradually from this point to the upper somewhat sharp 

 margin. In order to convey an idea of the character of the outer and inner surfaces I 

 have figured a portion from the middle in its folded position (PI. XVIII. fig. 1). While 

 the outer surface appears uniformly fiat, and merely exhibits numerous subdermal 

 cavities of varied size, the inner surface bears numerous round excurrent orifices be- 

 longing to the efi"erent passages, and varying from 3 to 12 mm. in diameter. These are 

 irregularly distributed, at intervals of 5 to 15 mm., and show at the bottom that they 

 are ramified. Between these wide excurrent orifices a comparatively flat surface is seen, 

 only perforated here and there by small apertures. 



The principalia forming the supporting framework of the entire sponge are hexacts 

 with long smooth and flexible rays,^ which are accompanied by long, thin, and very flexible 

 comitalia. The parenchyma also contains numerous hexacts, of median size, with tubercled 

 rays, further smaU hexacts with smooth rays, and finally rosettes of two kinds. Among 

 the latter the oxyhexasters, which are present in great abundance, first attract attention. 

 They bear on each of their short principal rays, which are somewhat exj)anded 

 outwardly, four long narrow terminals (PI. XVIII. fig. 10). The second form of rosette, 

 which belongs to the discohexaster type, is smaller, and bears, on the gently convex 

 transverse terminal disc of each principal ray, a bundle of about thirty delicate 

 terminals which become broader towards the outer extremities, and which are beset 

 laterally with numerous small barbs, and provided terminally with a four-pronged 

 transverse disc (PL XVIII. figs. 3, 5). 



The hypodermalia of the dermal skeleton have a slightly spindle-like thickened 

 distal ray with scaly teeth, a long smooth proximal which runs to a point, and four 

 simple, smooth pointed, transverse rays (PI. XVIII. figs. 2, 8). Whether the large and 

 strongly-developed floricomes which occur very abundantly scattered on the outer 

 surface in many regions (PI. XVIII. fig. 4), are regularly attached to the distal rays of 

 the hypodermalia, as in the Euplectellinse, I cannot definitely assert, since I have not 

 found them in this position. It is, however, quite possible that, on account of the great 

 softness of the whole plate, they have been pushed out of their original position. 



The hypogastralia are Likewise hexacts with a prolonged parenchymal ray, but the 

 freely projecting proximal is not thickened into a spindle, nor scaly and j)ronged, like 

 1 In PI. XVIIL fig. 2, the rays of these hexacts are represented much too short and too straight. 



