REPORT ON THE HEXACTINELLIDA. 87 



diacts, wliicli are either scattered at random, or aggregated in bundles. Several forms of 

 rosettes also occur, and in greatest abundance, simple oxybexasters with short principal rays, 

 and with two to four straight or hook-like, moderately diverging, terminal rays on the 

 extremity of each of the principal rays (PI. XIV. fig. 13 ; PI. XV. figs. 9, 11, 12). The 

 number of the terminal rays may vary from one to three on each of the main rays (PI. 

 XIV. fig. 8; PI. XV. fig. 11). These remarkable skeletal elements from whose globular 

 centre four, three, or two rays spring, which are greatly bent in one plane, or even 

 spirally twisted, I regard as arrested derivatives of oxyhcxasters (PI. XIV. figs. 10-12; 

 PI. XV. fig. 10). In the outer part of the parenchyma, graphiohexasters with close 

 bundles of almost parallel fine terminal rays appear (PL XV. fig. 19). 



Whether the elegant discohexasters represented in PL XIV. fig. 9, which are provided 

 with an S-like terminal ray, and with very small terminal discs, really belong to this 

 species, or are not rather intruded bodies, I have lately begun to doubt. 



These and similar discohexasters also aj^pear in that fragment of Holascus which is 

 represented in PL XV. fig. 14, and the individual spicules are figured after WyviUe 

 Thomson in figs. 15 to 23 of the same plate. 



The dermal skeleton consists of sword-shaped hypodermaUa with greatly prolonged 

 proximal rays which run out to sharp points at the extremities, with a thick scaly or 

 toothed distal ray, and with four transverse rays intersecting at right angles, obliquely 

 pointed at the extremity, and of median length. Upon these, as on the proximal ray, 

 small pointed elevations may often be observed. 



The tangential arms of these hypodermalia always lie somewhat beneath the dermal 

 membrane, which is raised up in a conical elevation by the distal ray. Close to the outer 

 portion of the proximal ray, and over the whole distal ray, — even extending beyond the 

 outer extremity of the latter, — thin diacts are disposed which run out to points at both 

 ends. These may serve as defensive weapons in place of the floricomes which are here 

 absent (PL XIV. fig. 6). 



The gastral skeleton consists of hexact sword-shaped hypogastralia, in general 

 resembling the hypodermalia, but somewhat more delicate. Thin diacts are here and 

 there apposed to the spicular rays, and are even more delicate than those of the outer 

 skin. 



2. Holascus fibulatus, n. sp. (PL XV. figs. 1-5; PL XVI.). 



A species of Holascus, markedly characterised by the possession of numerous double- 

 hooked fibulae, is included among the sponges of the Challenger expedition. Three 

 specimens were obtained, one (represented in PL XV. fig. 1) in a trawling to the south 

 Australia (Station 160, lat. 42° 42' S., long. 134° 10' E.), at a depth of 2600 fathoms, 

 from a red clay bottom ; while the other two were got in a trawling which was made in 



