206 HYALONEMA (HYALONEMA) POLYCAULUM. 



and the large and small micramphidiscs of Hyalonema {Hyalonema) obtusum) 

 can be distinguished : — macramphidiscs, large micramphidiscs, and small 

 micramphidiscs. 



The macramphidiscs (Plate 53, figs. 1-3, 13; Plate 54, figs. 28, 29) are 200- 

 365 n long, most frequently about 293 ix. The shaft is cylindrical, straight, 

 6.5-12 n thick, and abruptly thickened in or near the middle to a central tyle 

 12-18 n in diameter. The proportion of the thickness of the adjacent parts of 

 the shaft to the thickness of the tyle is 100 yu to 115-170. A verticil of truncate 

 or blunt-pointed, often irregularly curved spines 3.5-7 m long and 2.5-4 n 

 thick arises from this tyle. Spines similar in shape but smaller (particularly 

 shorter, only 1.5-3 n long and 2-3 ^ thick) are scattered in larger or smaller 

 numbers o^'er the other parts of the shaft. The tips of the spines are smooth 

 or slightly roughened. The terminal anchors are 60-100 m long, usually consid- 

 erably less than a quarter of the whole spicule, and 67-107 ^ broad. The pro- 

 portion of their length to their breadth is 100 to 103.8-125.7, on an average 100: 

 115.5. They consist of ten to twelve teeth. The individual teeth are curved 

 in their (shorter) proximal part and generally nearly straight in their (longer) 

 distal part. The latter usually diverges considerably and encloses an angle of 

 about 20° with the shaft. The teeth are T-shaped in transverse section. Their 

 upper part appears as a band about 10 n broad and is abruptly attenuated 

 to a point at the end. 



The large micramphidiscs (Plate 53, figs. 5, 6; Plate 54, figs. 26, 27) are 

 30-56 M long. The shaft is straight, 1.2-1.7 /^ thick, and gradually thickened 

 in a spindle-shaped manner in or near the middle. It bears a few small cylindri- 

 cal spines. Some of these always arise from the central thickening. The 

 anchors are usually 13.5-17 n long, generally considerably more than one third 

 of the whole spicule, and 8-10 n broad. The distal parts of the individual teeth 

 are fairly straight and generally nearly parallel to the shaft. 



The small micramphidiscs (Plate 53, fig. 7; Plate 54, figs. 21-25) are 13-27 yu 

 long, most frequently about 19.5 m- The shaft is straight, cylindrical, and 

 0.7-1.5 IX thick. Its central part usually bears a few spines. The anchors are 

 4.5-7.5 M long, usually a quarter to a third of the whole spicule, and 5-8 n broad. 

 The individual anchor-teeth, of which there are about eighteen in one anchor, 

 are more strongly curved some distance from the base than elsewhere. The 

 end-part is nearly straight, and diverges \'ery slightly or not at all from the shaft. 



The spiculation of the four hard superficial knobs indicates that the sponge 

 above described had at least two, probably four, distinct and distant stalks, each 

 composed of a separate bundle of spicules. 



