HYALONEMA (HYALONEMA) TYLOSTYLUM. 
233 
remaining parts of the shaft bear a larger or smaller number of similar but much 
shorter and nearly straight spines, which are 3-6 n long, exceptionally 12 n, and 
3-5.5 \x thick. 
The terminal anchors are 95-148 n long, usually a little over a third of the 
whole spicule, and 60-114 n broad. The proportion of their length to their 
breadth is 100 to 57-89, on an average 100 : 73.7. Although both in the larger 
and the smaller of these spicules relatively broad and relatively slender anchors 
are met, yet the relative anchor-breadth is, on the whole, correlated to the 
length of the spicule, so that, roughly speaking, the smaller the amphidisc the 
more slender the anchors. In the largest large macramphidiscs, over 350 n 
in length, the proportion of anchor-length to anchor-breadth is 100 to 62-89, 
on an average 100 : 78; in the smaller large macramphidiscs, under 350 n in 
length, this proportion is 100 to 57-79, on an average 100 : 68.6. 
The anchor consists of eight teeth. The individual teeth arise vertically 
from the shaft, are considerably curved, concave to the shaft in their proximal 
part, and slightly and quite uniformly curved in the same direction in then- 
distal and middle-parts. The curvature is such that the end-parts of the teeth 
are parallel or slightly convergent. In the latter case the end of the anchor is 
of course narrower than a portion of its middle-part. The anchor-breadth 
measurements given above are always the maximum breadths. The anchor- 
end breadth may be 14 m less than the maximum breadth. The teeth have the 
usual T-shaped transverse section. The upper and outer part, which corre- 
sponds to the upper stroke of the T, is a thin band of a fairly uniform breadth of 
13-18 jj., to within a short distance of the end. The end itself is abruptly and 
not sharply pointed. The lower and inner keel, which corresponds to the lower 
stroke of the T, is 13-16 /x high near the base of the tooth and becomes gradually 
narrower towards the tip. 
The small macramphidiscs (Plate 69 , figs. 20-23) are similar to the large 
ones, but have relatively narrower anchors, less distinct central tyles, and more 
spines on the shaft. These spicules are 116-240 ^ long, most frequently 130- 
220 ix. The shaft is 2.2-6 ix thick. The central tyle is 4-14 n in transverse 
diameter, that is 1.8-9 /x more than the adjacent parts of the shaft. It bears a 
verticil of nearly straight, or, more rarely, strongly curved spines, which are 
vertical or oblique to the axis of the shaft. These spines are generally cylindro- 
conical, blunt, and 3-5 /x long. The remaining parts of the shaft are covered 
with much smaller spines. These are the more numerous and the more slender 
the smaller the spicule. 
