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



hemispherical umbels, with many (usually twelve) rays, and thin axial rods, either smooth 

 or with median nodes (PI. XXXVIII. figs. 8, 9). 



The gastral skeleton exhibits smooth hj^jogastral pentacts similar to those occurring 

 in the skin, the same form of pinuli as autogastralia, and similar or somewhat smaller 

 amphidiscs (PI. XXXVIII. figs. 1, 12). While the smooth pentacts and the amphidiscs 

 are confined to the gastral membrane and to the lining of the largest efi'erent passages, 

 the pinuli have a somewhat wider distribution, and, becoming scarcer as the four basal 

 rays are more prolonged, are continued into the eiferent system of canals even to the fine 

 terminal branches, where they finally entirely cease (PI. XXXVIII. fig. 1). 



The projecting fringe of spicules on the external sharp margin of the oscular region 

 consists of marginal oxydiacts at least 0'5 mm. in length, with long distal ray bearing 

 minute obliquely disposed spines. The proximal ray, which is about a third shorter, bears 

 very small backwardly directed teeth. At the boundary between the two rays four 

 cruciately disposed hemispherical or somewhat larger knobs protrude (PI. XXXVIII. 

 fig. 11). 



In the lower narrowed end of the body, and especially in the basal pad, compact six 

 to two-rayed spicules with blunt, toothed, or spinose ends occur, like those in the same 

 position in most species of Hyalonema. The spicules of the basal tuft vary greatly in 

 lencfth, and resemble in structure those of Hyalonema sieboldii, to which Hyalonema 

 apertum presents a close resemblance in the general structure of its spicules. Whde the 

 upper portion of these long-stalked anchors is c^uite smooth, the lower bears oblique rows 

 of barbs on projecting ridges, and, on the very end, borne on a smooth narrow neck, a 

 hemispherical or helmet-shaped terminal knob with four to eight shovel-shaped marginal 

 anchor teeth, which are directed obliquely upwards and outwards. The intersection of 

 the axial canals in these long anchor spicules always lies in the lower swollen end, in 

 the head of the anchor. 



In a rich collection of Japanese forms brought home by Dr. Hilgendorf, and deposited 

 in the Berlin Zoological Museum, are several dried and well-preserved spirit specimens of 

 Hyalonema apertum. On closer examination of these I found two small dried specimens 

 of this species, which had been temporarily designated by Professor W. Marshall as 

 Hyalonema affine, Marshall. I refer on this point to the brief description which Marshall 

 gives, in his researches on Hexactinellids (1875), of Hyalonema affine, a species which 

 he had erected for a form which had been already examined by Max Schultze and noted 

 by him as " B " and " C." 



The diagnosis which Marshall gives {loc. cit., -p. 234) is as follows: — " Hijalonema 

 affine, if not, as I believe, a distinct species, is at least a specially well defined variety of 

 Hyalonema sieboldii. The tuft is 47 cm. long and only 8 mm. broad; the sponge body 

 proper has a length of 9 cm. Other specimens exhibit, with an axial strand of about the 

 same length, though of greater breadth, a larger sponge-body, which measures for instance 



