HYALONEMA (PRIOXEMA) 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 IX long, most frequently 140-165 ix, and 4-5.5 fi 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 fx. 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 ix long, rarely as much as 35 m- 



In the spicule-preparations I found a few fragments of diactine 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 n 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 fx; length of lateral rays 230-320 /.. 



