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



rays of these pinuli exhibit a median curvature like that of the figure 8, as we formerly 

 saw in the dermal pentact pinuli of Poliopogon. The free strongly developed distal ray 

 has usually a length of about 0"15 mm., and is beset with strong, though not long, lateral 

 spines bent like hooks upwards and outwards. The very upper end forms a free point 

 (PL LI. figs. 5, 13). 



As to amphidiscs, I find a large isolated form about 0'25 mm. long, with thick knotted 

 axial rod, and short, broad, terminally somewhat transversely truncate umbels. The eight 

 broad rays are paddle-like and terminally rounded (PI. LI. fig. 10). Beside these, though 

 also but sparsely, a similar form of medium-size occurs (PI. LI. fig. 8), and somewhat 

 more abundantly the familiar small type with hemispherical terminal umbels, 0"02 to 0"03 

 mm. in length (PL LII. fig. 7). More frequent than in the stretched, freely exposed, 

 dermal lattice-work, is the occurrence of these various amphidiscs in the portions of the 

 skin which lie over the insertion of the parenchymatous canalicular wall (PL LII. fig. 3). 



The same kinds of spicules, but with somewhat different development and dimensions, 

 compose the skeleton which forms the wide-meshed sieve-network in the oscular regions 

 of the bevelled sides and of the superior extremity of the whole sponge body. The large 

 supporting pentacts exhibit indeed the same fundamental form and dimensions as those 

 of the dermal membrane, but reductions of individual rays very frequently occur, with 

 the production of rounded ends, or with the formation of slight, terminal, club-shaped 

 swellings. The downward curvature at right angles, exhibited by some of the tangential 

 rays, is also of very common occurrence. Especially remarkable, however, is the con- 

 siderable length attained by the free distal ray of the pinuli. As a rule, this thick ray, 

 beset with short hook-like lateral spines, measures 0*5 mm. in length, and ends in a 

 projecting point. The four basal rays are moderately long, less curved, and terminally 

 somewhat spinose and rounded (PI. LI. fig. 4). Besides these, shorter pinuli occur with 

 slimmer distal ray. The strong eight-rayed amphidiscs (figured in PL LI. fig. 10) occur 

 here more abundantly than in the dermal lattice-work, and always exhibit in successful 

 preparations the characteristic disposition represented in PL LII. fig. 3. Numerous 

 eight-rayed amphidiscs of similar form, but of medium size occur, and also quite minute 

 forms with hemispherical umbels. 



It is noteworthy that neither pinuli nor amphidiscs occur on either of the bounding 

 surfaces of the parenchymatous septa between the afierent and efi"erent canals, but only 

 the familiar parenchymalia, including numerous medium-sized oxypeutacts, with numerous 

 bent, or with more or less reduced rays. I have, however, frequently found — instead of 

 the familiar small oxypentacts with several laterally projecting, somewhat bent spines, 

 — pentacts of similar structure, in which the sixth ray was either wholly absent, or 

 represented only by a- small conical elevation. 



The freely projecting portion of the basal tuft exhibits spicules up to 20 cm. in length, 

 which terminate superiorly in a very gradual point, while the lower end forms a strongly 



