HYALONEMA (PRIONEMA) CRASSUM. 
279 
spicule-fur composed of the distal rays of the superficial (dermal and gastral) 
pinules. The dermal and gastral membranes are supported by the lateral 
rays of these pinules and of the hypodermal and hypogastral pentactines. Very 
numerous paratangentially extending amphioxes are also found in them. Many 
of these spicules are very stout and appear as tignules. Hexactine megascleres, 
amphioxes, microhexactines, and amphidiscs occur in the interior. The micro- 
hexactines are exceedingly abundant and appear as dense masses in the sections. 
They form the chief support of the whole sponge. Of amphidiscs four kinds 
can be distinguished: — macramphidiscs with smooth teeth, macramphidiscs with 
serrated teeth, and large and small micramphidiscs. The first- two are not 
frequent and appear to be confined to the superficial parts of the choanosome. 
The large micramphidiscs are also rather rare. The small micramphidiscs, on 
the other hand, are exceedingly abundant and form continuous layers in the 
walls of some of the canals. 
The pinules (Plate 106, figs. 26-30) of the dermal and gastral faces of the 
sponge agree so closely in shape and size that I shall here describe them together. 
All the pinules observed were pentactine. Their distal ray is straight, 110- 
200 m long, most frequently 140-165 n, and 4-5.5 /x thick at the base. The spines 
it bears are small and not numerous. The longest usually arise from the middle- 
part of its length, and here the distal ray, together with the spines, attains a maxi- 
mum diameter of 14-19 m- The lateral rays are spiny, particularly in their 
distal half, and generally conical and pointed, more rarely cylindroconical and 
terminally rounded. They are 20-30 /x long, rarely as much as 35 m- 
In the spicule-preparations I found a few fragments of diadine pinules and 
one whole pinule. Possibly such spicules occur in the above mentioned crest 
separating the dermal and gastral parts of the surface. I, however, failed to 
find any such spicules in situ, so that it appears very doubtful whether the few 
observed are proper to the sponge. 
The hypodermal pentactines (Plate 108, figs. 1, 3-5, 8, 9) have a conical, 
rather blunt-pointed, usually straight, rarely bent apical proximal ray 1-1.7 mm. 
long, and 27-62 m thick at the base. The lateral, paratangential rays are also 
blunt conical. Those of the same spicule are often markedly unequal ; the length 
of the largest is 300-510 m- 
The hypogastral pentactines (Plate 108, figs. 2, 6, 7) are similar to the hypo- 
dermal but have on the whole shorter and somewhat stouter rays. Their 
dimensions are: — length of apical ray 0.75-1.35 mm.; basal thickness of apical 
ray 30-70 /x ; length of lateral rays 230-320 /x. 
