276 HYALONEMA (PRIONEMA) SPINOSUM. 



The abundant normal large macramphidiscs (Plate 48, figs. 14-16; Plate 49, 

 figs. 7-9, 11; Plate 50, figs. 1-5) are 180-298 n long, most frequently about 255 m. 

 The shaft is usually straight, rarely slightly curved, for the most part nearly 

 cylindrical, 3-8 yu thick, and abruptly thickened at or near the middle to a 

 central tyle 6.5-17 yu in transverse diameter. The proportion of the diameter 

 of the adjacent parts of the shaft to the diameter of the tyle is 1 : 1.3 — 1 :3.2, 

 most frequently about 1 :2. From the central tyle a verticil of about eight 

 large spines arises; these are slightly and irregularly curved but on the whole 

 vertical (Plate 48, figs. 14-16; Plate 49, figs. 8, 9, 11). These spines are cylin- 

 drical, rounded or abruptly pointed at the end, and always quite smooth and 

 destitute of secondary spinelets. They are 8-23 y. long and 2-3.5 m thick at the 

 base. The parts of the shaft outside the central tyle and its vicinity bear nu- 

 merous low, cylindrical and truncate, wart-like spines, 0.5-1.5 m high, 1-2 ^l broad, 

 and circular in outline (Plate 48, figs. 15, 16; Plate 49, figs. 8, 9, 11). From the 

 terminal face of each of these spines a cluster of exceedingly minute secondary 

 spinelets arises. 



The terminal anchors, are 68-107 /^ long, considerably more than a third of 

 the whole spicule, and 61-117 n broad. The proportion of length to breadth is 

 100 : 73-100 : 114, on an average 100 : 94. A correlation between the anchor- 

 proportion and the size of the spicule was not noticed. All the anchors counted 

 were composed of eight teeth. 



The individual teeth are considerably curved near the base. Distally the 

 •■curvature decreases. The end is slightly and somewhat abruptly bent inward 

 towards the shaft. The teeth have a T-shaped transverse section. The upper 

 part is band-shaped, 9-13 yu broad near the base, very slightly attenuated distally, 

 and rounded at the end. The lower part is a crest projecting towards the shaft. 

 This crest is 5 m high near the base; distally it gradually becomes lower, and it 

 appears to vanish altogether about 10 ^ from the end of the tooth. The anchor- 

 teeth bear, on their lateral margins, secondary teeth and consequently appear 

 serrated (Plate 49, fig. 7; Plate 50, figs. 1-5). These secondary teeth stand 

 quite close together and extend from the base to within a short distance of the 

 end of the primary tooth, leaving only the rounded end free. The secondary 

 teeth are triangular in outfine, 0.5-1.2 ix long, 1-1.5 yu broad, sharp-pointed, and 

 directed more or less backwards. They resemble shark's teeth. 



Besides the normal spicules above described a few young and also a few 

 ■abnormally large macramphidiscs have been observed. The young forms have a 

 slender shaft, a relatively stout central thickening, and .short and thin anchor- 



