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



oxyh exacts with slightly curved slender rays occur, similar to those which were found 

 so abundantly in the former species (PI. XLVIII. figs. 1, 10). In certain regions, for 

 instance somewhat abundantly below the outer skin, a skeletal element, not represented 

 in Poliopogon amadou, occurs — in the form of small spindle-shaped smooth oxydiacts, 

 (0'15 to 0*25 mm. in length) which have a maximum thickness either in the neighbour- 

 hood of their centre (PI. XLVIII. fig. 3) or more rarely nearer one end (PI. XLVIII. fig. 7). 

 Here and there, especially in the neighbourhood of the external surface, long uncinates 

 occur, with narrow appressed pointed barbs covering minute depressions. I have not 

 been able to determine whether the amphidiscs of varied form and size, which occur 

 scattered in great abundance in the parenchyma (PL XLVIII. fig. 1), are really true 

 parenchymalia, or have grown in from the bounding surfaces of the external skin, of 

 the gastral cavity, or of the canals. 



The dermal skeleton consists of rather strongly developed smooth oxypentacts. 

 The autodermal pinules are indeed for the most part pentacts, but others not unfrequently 

 occur, in which the sixth proximal radial ray is more or less distinctly developed 

 (PI. XLVIII. figs. 8, 11). The four basal rays of the ordinary pentact pinules are some- 

 what long, and bear externally short spines projecting obliquely outwards, while the 

 extreme outer end is rounded off or even truncated, though rarely pointed. As a rule 

 the basal rays are like those of the dermal pinuli in Poliopogon amadou, bent like the 

 middle portion of a figure 8 (PI. XLVIII. figs. 5, 9). The freely projecting, radial distal 

 ray is not so long and slender as in Poliopogon amadou, but rather broad and only 

 about 0"15 mm. in length. It is beset with lateral spines, which are curved somewhat 

 markedly outwards, and terminally apposed in bud-like fashion. Less frequently the distal 

 ray ends in a point (PI. XLVIII. fig. 5). The large amphidiscs lying in the dermal 

 membrane have a length of about 0'2 mm. Their axial rod is somewhat uniformly beset 

 with small tubercles. The campanulate umbels have usually eight, less frequently 

 more rays, which are of considerable length, often almost meeting, and but slightly 

 divergent (PL XLVIII. fig. 2). Besides these, there is an abundant occurrence of small 

 amphidiscs with short, hemispherical, eight-rayed terminal umbels and slender axial rod 

 (PL XLVIII. figs. 4, 6). 



Whether the gastral skeleton surrounding the cavity closely resembles the dermal I 

 was unable certainly to determine, owing to the want of sufiicient material from that 

 portion of the giant sponge. It is, however, extremely probable, from analogy with the 

 related species of Poliopogon amadou, that the structure of the canalicular skeleton 

 lining the larger ducts and lacunae essentially resembles that of the skin. Pinules are 

 not wholly absent, but occur as slender, scattered, canalicular pentacts or hexacts, with 

 long, narrow, pointed basal rays, and a slender free radial, which ends in a delicate point, 

 and bears isolated, short, straight, oliliquely projecting lateral spines. In the larger ducts 

 and lacunse, numerous large and small amphidiscs occur of the form described in the 



