290 HYALONEMA (PRTONEMA) PINULIFUSUM. 



I. Macramphidiscs (1) 

 II. Mesamphidiscs 



A serrated mesamphidiscs 



a large serrated mesamphidiscs (2) 

 b small serrated mesamphidiscs (3) 

 B smooth mesamphidiscs 



a large smooth mesamphidiscs (4) 

 b small smooth mesamphidiscs (5) 

 III. Micramphidiscs. 



A larger short-anchored micramphidiscs (6) 

 B smaller long-anchored micramphidiscs (7) 

 The macramphidiscs (Plate 71, figs. 5-8) are 370^70 m long, most frequently 

 about 425 m- The shaft is straight, for the greater part of its length cylindrical, 

 and 15-22 n thick. It is gradually thickened towards the ends, and generally 

 also slightly and somewhat abruptly thickened near the middle to a central 

 tyle. The ends usually exceed the thinnest part of the shaft by 9-12 yu in thick- 

 ness. The central tyle is small, or absent altogether, and measures, when 

 present, 18-29 m in transverse diameter, that is 1-9.5 m more than the adjacent 

 parts of the shaft. The shaft is very poor in spines. Sometimes it bears no 

 spines at all. Usually one to three cylindrical and truncate, or cylindroconical 

 and terminally rounded spines arise from the central tyle, or, when it is absent, 

 from a corresponding point of the shaft. These spines are 4-11 m long and 

 3-9 n thick. The remaining parts of the shaft are either quite smooth or bear 

 one or a few spines similar to the central ones. 



The anchors are 126-162 n long, about a third of the whole spicule, and 153- 

 177 IX broad. The proportion of their length to their breadth is 100 to 103-138, 

 on an average 100 : 115.3. They are composed of eight teeth. The individual 

 teeth have the usual T-shaped transverse section. The upper (outer) part of 

 the teeth, which corresponds to the upper stroke of the T, is band-shaped, 24- 

 29 n broad, and abruptly pointed or rounded at the end. The margins of these 

 bands, that is the lateral margins of the teeth, are either smooth throughout, 

 or they exhibit slight irregularities, sometimes even an indication of a serration, 

 in their distal part. The lower (inner) part, which corresponds to the lower 

 stroke of the T, is, at the base of the tooth, usually 19-22 ii high. The teeth 

 arise nearly vertically from the shaft, and are curved downward in such manner 

 that their ends are either parallel or convergent. In the latter case the anchor is, 

 at the end, sometimes 17 n narrower than in its broadest part, above. 



