20G THE VOYAGE OF H.M.S. CHALLENGER. 



the middle of the parenchyma, and in the most varied relations to the dermal surface. 

 In contrast to most other species of Hyalonema, small oxyhexacts with straight 

 (PI. XXIX. fig. 9) and with bent (PI. XXIX. fig. 10) rays are not abundant. The latter 

 occur indeed in very sparse isolation. Both forms are characterised by this, that the rays 

 are throughout their whole extent thickly beset with small barbs, turned obliquely 

 inwards, i.e., towards the middle. 



The dermal skeleton is supported by medium or small-sized, simple, smooth, Ivy^o- 

 dermal oxypentacts without a trace of a distal sixth ray, and also by numerous medium- 

 sized hypodermal oxydiacts, which all lie tangentially. Above these hypodermalia, auto- 

 dermal pentact pinuli occur, which exhibit short, slightly toothed, basal rays of moderate 

 strength, and a narrow distal, 0'4 to O'o mm. in length, with somewhat long narrow 

 obliquely inserted, pointed lateral spines. Large dermal amphidiscs, 0'35 mm. in leno-th 

 (PI. XXIX. fig. 6) are tolerably abundant. In their breadth and in the somewhat flatly 

 arched short terminal umbels, with eight broad, lancet-shaped, umbel rays, they at once 

 recall the approximately equal, strong dermal amphidiscs of Hyalonema sieboldii. They 

 are all disposed at right angles to the surface, with their centre in the dermal membrane 

 (PI. XXIX. fig. 5). Besides these, numerous smaller amphidiscs with short hemispherical 

 terminal umbels (PI. XXIX. fig. 8) occur in tangential disposition. Less frequently 

 medium-sized amphidiscs occur, essentially resembling the greater above described (PI. 

 XXIX. fig. 7). 



In the sieve-membrane covering the superior terminal surface of the sponge, and to a 

 large extent coalescent with the subjacent parenchymal layer, skeletal elements occur 

 similar to those in the external skin. The inner surface of the large lacunae and 

 passages penetrating the parenchyma, and also of the efferent canals is here smooth, 

 exhibiting no gastral or canahcular skeleton, containing neither hypogastral jjentacts 

 nor pinuli nor amphidiscs, in fact, solely supported by weakly developed, somewhat 

 curved diacts like those which occur so abundantly in the parenchyma. 



The marginaha, which form a continuous projecting fi'inge on the sharp upper margin 

 of the body, are straight oxydiacts, whose proximal end inserted in the parenchjmia is 

 smooth, while the much longer and very gradually pointed distal end is beset with lateral 

 spines projecting obliquely downwards (PI. XXIX. fig. 5). At the boundary between the 

 distal and proximal portions, four cruciately disposed hemispherically arched knobs project, 

 being traces of the rudimentary transverse rays. 



The basal pad of the smaller (PL XXIX. fig. 4) and of the large funnel-shaped 

 specimen (PI. XXIX. fig. 1) consists of six- to two-rayed, strongly developed spicules, 

 with cylindrical, externally truncated, or rounded straight rays. These agree thoroughly 

 with similar structures in the hitherto described species of Hyalonema. The proximal 

 portion of each ray is smooth ; the distal, on the other hand, is thickly beset with coarse 

 conical spines ; more rarely the whole surface of the spicule is uniformly spinose. 



