228 
HYALONEMA (HYALONEMA) TENUIFUSUM. 
more rarely, slightly inclined, and measure 5-12 ^ long and 2-4 n thick. From 
the other parts of the shaft arise a greater or smaller number of low truncate 
or terminally rounded protuberances 1-2 ,u long and 2-3 fi thick. The terminal 
anchors are 66-110 about a third of the whole spicule, and 61-97 /j. broad. 
The proportion of their length to their breadth is 100 : 84 to 102, on an average 
100 : 93.6. The anchors in the larger forms are relatively broader than in the 
smaller, the fraction ^en^if being, roughly speaking, in proportion to the length 
of the amphidisc. The anchor-teeth arise vertically from the shaft, and are 
curved concave towards it. This curvature decreases distally, and is on the 
whole such that the ends of the teeth converge more or less. When this conver- 
gence is great the anchor may be, at its end, as much as 10 ^ narrower than in its 
broadest part. The individual teeth are 10-15 m broad, and abruptly and not 
sharply pointed (Plate 67 , figs. 3, 4; Plate 68 , fig. 1 ). 
In specimen ( b ) the large macramphidiscs are similar but have narrower 
anchors. Their dimensions in this specimen are: — length 202-340 n; thickness 
of shaft 5-13 n; diameter of central tyle 8-22 n; length of anchors 46-114 
breadth of anchors 43-98 n ; proportion of anchor-length to -breadth 100 : 65 to 
98, on an average 100 : 80.8. 
The small macramphidiscs (Plate 67 , figs. 13, 14, 22-25; Plate 68 , figs. 22, 
23) are in specimen (a) 129-160 n long, in (6) shorter, only 77-152 ^ long. The 
shaft is straight or, rarely, curved and 2-3 n thick. A cluster of irregularly dis- 
posed, more or less oblique, and often considerably curved, cylindrical, truncate 
spines with a maximum length of 3 n arises from a point in or near the middle 
of the shaft. At this point the shaft is usually, but by no means always, gradu- 
ally thickened to a tyle sometimes 6 n in diameter. The remaining parts of the 
shaft are quite densely covered with smaller spines, generally cylindroconical 
and truncate, which have a maximum length of 2.3 n and are 1 n thick. The 
terminal anchors are somewhat different in the two specimens. In (a) they are 
36-54 fj. long, over one quarter to over two fifths of the whole spicule, and 22-30 m 
broad, the proportion of their length to their breadth being 100 to 48-64, on an 
average 100 : 58.5; in (6) they are 34-63 m long and 18-43 ^ broad, the propor- 
tion of their length to their breadth being 100 to 46-75, on an average 100 : 54. 
Relative to the length of the whole spicule these anchors in specimen (a) are 
considerably shorter than in ( b ). The proportion of the total length of the 
spicule to the anchor-length is in (a) 100 : 27 to 34, on an average 100 : 30.5; in 
(b) 100 : 34 to 44, on an average 100 : 38.8. The individual anchor-teeth are 
strongly curved, concave to the shaft at the base, and only slightly and rather 
