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



but usually about 0"2 mm. in diameter (PI. XL. fig. 10). The spicules represented 

 on PL XL. figs. 3, 11, 13, also occur here and there in the parenchyma, but do not really 

 belong to this species, being extrinsic importations from other forms, perhaps from a 

 Crateromorpha. 



The basis of the dermal skeleton consists of strongly developed smooth oxypentacts. 

 The apposition of the tangential rays of the latter forms the square-meshed lattice-work, 

 which can be recognised even with the unaided eye (PI. XL. fig. 2). This gives this 

 sponge a greater compactness than is possessed by any other species of Hyalonema. The 

 radially directed proximal ray is longer than the tangentials. Adjacent to the latter 

 lie strands of smooth oxydiacts with central swelling or nodes. The autodermal 

 pentact pinuli exhibit comparatively long, straight, spinose basal rays, about 0"05 mm. in 

 length, while the somewhat short (about O'l mm.) projecting distal is characterised by 

 the long lateral spines, directed upwards and outwards, which begin at some distance 

 from the base, are somewhat distantly inserted in the middle portion, become more 

 closely apposed in the upper part of the ray, and finally form a kind of bud, in the 

 middle of which lies the end of the ray, in nowise thin or gradually pointed, but rather 

 thick and ending in a conical point (PI. XL. fig. 16). 



The abundant and characteristic amphidisc in the skin is a large, strongly developed 

 form, 0"4 mm. in length, in which the thick smooth axial rod is centrally beset by eight 

 slim tubercles or bosses. The somewhat broad, but not very long terminal umbels are 

 not uniformly hemispherically arched, but are at their outer end slightly truncated. The 

 eight umbel rays with broad, blade-like, longitudinal bases, have a broad paddle-like form 

 and a rounded end (PL XL. fig. 7). 



Besides these, there is a frequent occurrence of those small amphidiscs with hemi- 

 spherical, twelve- or more rayed terminal umbels, and with slim delicate axial rod, which 

 occur in the skin of all species of Hyalonema (PL XL. fig. 15). In the gastral membrane, 

 however, the hypogastral pentacts are either whoUy absent, or of very sparse occurrence, 

 while the strongly developed smooth oxydiacts and the associated pentact autogastral 

 pinuli are very abundant. The latter exhibit rather long slightly spinose basals, and a 

 free fir-tree-like ray, which runs out into a thin terminal point and bears short curved 

 lateral spines. I did not find any large amphidiscs in the gastral membrane, but the small 

 forms occur in great abundance. 



The marginal fringe of the superior oscular aperture is formed of oxydiacts which 

 attain a length of only 1 mm. The freely projecting distal ray is beset with hook-shaped 

 externally curved spines, while the proximal bears only small pointed tubercles. At the 

 boundary between the two, on the thickest portion of the spicule, four cruciately disposed 

 hemispherical bosses project (PL XL. fig. 6). 



In the basal pad numerous strong spicules with six to two rays occur, in which the 

 blunt ends are thickly beset with spines. It may be frequently observed, especially in 



