REPORT ON THE HEXACTINELLIDA. 229 



surrounded by a circle of radially disposed straight spicules, and as examination witli a low- 

 power at once reveals, represents an oscular opening. The other fragment consists of a 

 somewhat thicker (about 3 mm.) plate, with irregular ragged edges. On one surface 

 smooth-edged oval or roundish pits occur, from which narrow diverticula pass towards the 

 side and towards the interior (PI. XXX. fig. 2). The other surface is rough and 

 apparently damaged. This second specimen undoubtedly forms part of the internal wall 

 of the body, and exhibits the surface limiting the gastral cavity and bearing the openings 

 of the canals. 



An examination of the siliceous elements shows, in the first place, that they are all 

 strikingly slim and delicate, whence my choice of the specific designation tenue. Among 

 the long spicules of the parenchyma, between the numerous slim oxydiacts, one remarks 

 an unusual abundance of oxyhexacts of medium and small size (PL XXX. fig. 8), with 

 thin, gradually pointed smooth rays. Besides these, though not so abundantly, small 

 oxyhexacts occur with perfectly smooth curved rays (PI. XXX. fig. 5). In the external 

 skin, on the smooth hypodermal oxypentacts, and on the tangential oxydiacts, numerous 

 autodermal pentact pinuli are inserted, with four smooth ba-sal rays which are relatively 

 long (0"2 mm.), while the slim, finely pointed distal, beset with minute obliquely inserted 

 teeth, attains a length of almost 1 mm. The amphidiscs of the skin are of medium size 

 (from 0"2 to 0"! mm. in length) and with simple, straight-rayed, eampanulate, medium- 

 sized umbels, occupying one-third of the total length. The umbels never have eight, 

 but always thirteen or twelve smooth, lancet-shaped, umbel rays. The axial rod is beset 

 with nodes, which attain especially in the middle a considerable prominence and a 

 cruciate disposition. The marginalia, which are radially grouped round the oscular 

 opening, attain a length of 1^ to 2 mm. Their pointed proximal end is smooth, and 

 not so long as the likewise pointed distal, which has a length of at least 1 mm. and 

 is beset with oblique lateral teeth. On the boundary between the two rays, four 

 cruciately disposed, globular tubercles project, the rudimentary representatives of the four 

 tangential rays, as is readily demonstrated by the presence of a well-developed axial canal 

 (PI. XXX. fig. 7). 



4. Hyalonema robustum, n. sp. (PL XXXII. figs. 1-10). 



In the west of the North Pacific .(Station 241, lat. 35° 41' N., long. 157° 42' K), 

 from a depth of 2300 flithoms and a red clay bottom, the fragment of a Hyalonema 

 was dredged, which had the form and size of half an apple, and evidently represented 

 about half the entire body of a sponge. On the convex external surface of the hemi- 

 spherical specimen, the dermal membrane is well preserved as a fine-meshed network, 

 while the torn internal surface exhibits a loose, wide-meshed parenchyma, ■with cavities 

 increasing in width towards the interior. 



