216 
HYALONEMA (HYALQNEMA) PLACUNA. 
transverse diameter. The end-breadth is 6-9 n less than the maximum breadth. 
The proportion of the length to the maximum breadth of the anchors is 100 to 
72-107, on an average 100:87.6. There are usually about ten teeth in the 
anchor. The teeth arise nearly vertically from the shaft and are curved rather 
strongly in their proximal part; distally their curvature decreases. Altogether 
it is such that the ends of the teeth converge towards the shaft, with the axis of 
which they enclose angles of about 7°. The teeth are T-shaped in transverse 
section. The distal band-shaped part, which corresponds to the horizontal 
stroke of the T, is uniformly about 12 n broad for the greater part of its length, 
and very blunt-pointed or rounded at the end. 
The dimensions of the single spicule of this kind found in form A are: — 
length 315 /x; thickness of shaft 7 /j.; anchor-length 90 m; maximum anchor- 
breadth 95 ix ; proportion of anchor-length to maximum anchor-breadth 100 : 106. 
The s?nall macramphidiscs with apically narrow anchors of form B (Plate 65 , 
fig. 1) are 296-319 ix, most frequently about 308 fx long, have a shaft 6-8.5 n thick, 
and are abruptly thickened in or near the middle to a central tyle 12-15 fx in 
diameter. Several short truncate cylindrical spines, as much as 9 ^ long and 4 ,u 
thick, arise from this tyle. Low and broad truncate protuberances also occur 
on other parts of the shaft. The terminal anchors are 113-140 fx long, usually 
a little over a third of the whole spicule, and 97-102 fx broad. The proportion 
of their length to their breadth is 100 to 73-87, on an average 100 : 77.3. The 
anchor-teeth are usually arranged in the ordinary, strictly verticillate manner, 
but occasionally an amphidisc of this kind is met in which one of the teeth arises 
at a much lower level than the rest (Plate 65 , fig. 1 ). The anchor-teeth arise 
nearly vertically from the shaft. They are curved more strongly in their basal 
part and less strongly in their distal part than the anchor-teeth of the large 
macramphidiscs with apically broad anchors described above. Their total curva- 
ture is such that their ends usually diverge slightly from the shaft. Sometimes, 
however, their tips are parallel or even slightly convergent. The ends of the 
teeth are usually pointed. 
In form A these spicules (Plate 66, figs. 1, 2, 5) are similar, but on the whole 
smaller. They are here 245-330 ix long; the shaft is 7-10 n thick, and the central 
tyle 13-16 fx. Cylindrical truncate spines 4 n long and 3-4 fx thick arise from 
the latter. The remainder of the shaft usually bears a good many low and broad 
protuberances. The anchors are 95-130 /x long and 80-105 /x broad. The 
proportion of their length to their breadth is 100 to 79-88, on an average 
100:83.6. 
