264 
HYALONEMA (PRIONEMA) AGUJANUM. 
The rare large micramphidiscs have a stout shaft with an exceptionally 
large, usually somewhat irregular, central tyle. This tyle bears numerous 
minute and slender spines. These are not arranged in a verticillate manner, 
but are scattered over the whole tyle. The remaining parts of the shaft also 
bear minute spines. The anchor-teeth, which arise nearly vertically from the 
end of the shaft, are curved quite uniformly throughout, through an angle of 
about 90°, so that their end-parts are nearly parallel. The dimensions of these 
amphidiscs are : — 
LARGE MICRAMPHIDISCS. 
var. tenuis 
var. lata 
form A 
form B 1 
Total 
length 
limits ju 
51-80 
47,78 
47-64 
most frequently 
about m 
75 
50, 60 
Shaft, thickness p 
1.3-3 
1.7-2. 5 
Central 
tyle 
diameter n 
4-7 
3.5 
5.5 
differences between 
diameter of tyle and 
adjacent parts of 
shaft m 
2.7-4 
3-4 
Anchor 
length, limits p 
18-39 
13,35 
18-24 
breadth, limits p 
17-31 
11,26 
14-20 
Proportion of 
anchor-length to 
anchor-breadth 
limits 100: 
67-100 
74-85 
78-83 
average 100: 
82.5 
79.5 
80.5 
Proportion of 
anchor-length to 
total length of the 
spicule 
limits 1: 
2-3 
2.2, 3.7 
2.3-3 
average 1: 
2.5 
2.9 
2.7 
The srnall micraviphidiscs (Plate 75 , figs. 24-27, 31-34; Plate 77 , fig. 8) 
have a straight shaft, which is either simple, cylindrical, and without any trace 
of a central tyle, or, more rarely, slightly thickened at or near the centre to a 
small central tyle. Such central tyles on the shaft are much more frequent in 
the small micramphidiscs of var. lata than in those of var. tenuis. The shaft is 
covered throughout with more or fewer, sometimes very numerous minute spines. 
Only two seen. 
