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



upper terminal surface is covered by a terminal sieve membrane lying flatly over the 

 parenchyma of the body. Eound about this sieve-plate, on the somewhat sharp lateral 

 margin, an inconspicuous circular fringe of spicules projects. On the lateral surface of the 

 cone, remnants of the delicate dermal lattice-work are here and there recognisable (PI. 

 XXXIII. fig. 8), and through the latter large grooves and inhalent apertures are 

 visible. 



The parenchyma is supported by medium-sized smooth oxyhexacts and by numerous 

 thin and pliable oxydiacts of various sizes, wdth or without central swelling. More rarely 

 diacts occur with one or two club-shaped swollen ends. Straight, smooth, small 

 oxyhexacts occur in moderate abundance. 



The dermal skeleton consists of medium-sized smooth h}^odermal oxypentacts. The 

 autodermal pentact pinuli are relatively long (about 0"4 mm.), and bear four slim medium- 

 sized basal rays, and a distal beset with somewhat long spines (PL XXXIII. fig 15). 



The superior sieve-network is supported by reticulate strands of strongly developed, 

 moderately long, smooth oxydiacts, which, as a rule, exhibit at the middle only two 

 hemispherical or flatly apposed nodes. Between these, simple, strong, smooth oxy- 

 tetracts occur here and there, and also ^jentacts witli rays of a simdar character. The 

 autodermal pentact pinuli of this terminal sieve-plate are, for the most part, like the 

 dermal, though in some regions longer (PL XXXIII. fig. 14). 



Since the abundant amphidiscs of the external skin and those of the terminal sieve- 

 membrane are exactly alike, I will describe them for both localities at once. Most 

 strikiog is the largest form (about 0"2 mm. long), which exhibits a strongly developed axial 

 rod, smooth with the exception of four cruciately disposed central protuberances, and 

 with very gently arched terminal umbel rays, extending only over about one-third of a 

 sphere, and provided with eight teeth. These short umbel rays are very broad, and 

 terminate in a paddle or leaf-like point (PL XXXIII. fig. 9). Besides these, amphidiscs 

 of medium size occur with irregularly toothed axial rods, and with terminal umbels, 

 hemispherical or longer, with eight slender rays (PL XXXIII. fig. 11). Similar forms 

 sometimes occur with longer and more divergent umbel rays (PL XXXIII. fig. 12). As 

 in almost all species of Hyalonema numerous small many-rayed amphidiscs occur, as 

 figured in PL XXXIII. fig. 13. 



The marginalia exhibit a long toothed distal ray, a smooth proximal, and four 

 cruciate hemispherical rudiments of the tangentials. 



The spicules of the isolated basal tuft, which was found beside the body of the sponge, 

 and most probably belongs to it, exhibit on their inferior extremity a very remarkable 

 anchor-like structure. On the somewhat thickened terminal portion, four twisted, strongly 

 developed rays project transversely in a circle, and then bend upwards at right angles 

 along the equally long terminal portion. The latter portion is somewhat curved, and 

 runs gradually to a point (PL XXXIII. fig. 10). On the prolongation of the axis there 



