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



especially long aud strougly developed, aud liave an approximately perpeudicular disposi- 

 tion (PI. LVI. figs. 1, 2). 



The principal spicules of the parenchyma are large and medium-sized oxydiacts of 

 varying length, which are tubercled towards the pointed ends, and are in the middle 

 either smooth or provided with an annular swelling, or with four projecting bosses or 

 ray-rudiments. They occur either in isolated distribution or in strands which vary 

 in direction. They are, for the most part, parallel to the outer and inner bounding 

 surface, or disposed radially to the same. Some especially large and thick diacts lie 

 longitudinally near the gastral surface. I have hardly ever observed large hexacts, 

 though here and there isolated medium-sized regular oxyhexacts occur, with sUghtly 

 spinous rays. Small hexact forms also occur with smooth rays. On the other hand, all 

 through the parenchyma, in tolerably uniform though scattered distribution, oxyhexasters 

 occur with short principal rays, and with a varying number of long divergent smooth 

 terminals, two of which are usually borne at the end of each principal ray (PI. LVI. 

 fig. 7). Besides these, we have to note the less abundant occurrence of small disco- 

 hexasters with four or more long, tolerably straight terminals, each provided with a small 

 four-toothed, terminal, transverse disc (PI. LVI. fig. 9). Not unfrequently, also, some- 

 what larger discohexasters occur, in which each of the short simple principaLs bears from 

 three to six or more slightly S-shaped terminals. These are united in a usually somewhat 

 slender, perianth-like bundle, and are terminally roughened on their outer extremities, 

 which always bear a four-toothed disc (PL LVI. figs. 3, 4). In quite isolated distribution 

 small discohexasters occur, with moderatelj^ short principal rays terminally expanded 

 into a disc, which bears on its outer convex surface a large number of delicate diverging 

 terminals, forming a brush-like tuft, and bearing on their extremities minute four-toothed 

 discs (PL LVI. figs. 10, 11). 



In the dermal skeleton, medium-sized, smooth hypodermal oxypentacts occur, in 

 which the proximal ray is radially disposed, while the four long tangentials, intersecting 

 at right angles, follow the superficial curvature of the sponge in being slightly curved 

 inwards. 



In the large rectangular meshes of these pentact hypodermalia, numerous autodermal 

 pentacts and tetracts occur in the dermal membrane. They agree exactly with the small 

 rough dermalia in the genus RosseUa. It has to be noted, however, that the number of 

 tetracts exhibiting a simple right-angled intersection of rays (PI. LVI. fig. 5) is in 

 proportion to that of the otherwise very similar pentacts (PI. LVI. fig. 6) decidedly 

 greater in this Acanthascus than in RosseUa (PI. LVI. fig. 2). These rough dermal 

 pentacts when compared wdth those of the genus RosseUa exhibit a slight divergence 

 in this, that there is no boss- or knob-like rudiment of the sixth distal ray. The tetracts 

 are also without any such rudimentary ray (PI. LVI. figs. 5, 6). 



On the inner side of the body-wall, the special gastral skeleton is represented by a 



