HYALONEMA (PRJONEMA) SPINOSUM. 
277 
teeth. One of the abnormal forms is represented on Plate 49, fig. 10. This 
spicule is 235 m long, its shaft is 5 ^ thick, central tyle 9 m thick. A verticil of 
short, laterally compressed, distally broadened and truncate, band-shaped 
spines arises from the tyle. The remainder of the shaft bears short, truncate, 
cylindrical spines. The anchors are about 54 n long, 33 m broad. The anchor- 
teeth have serrated margins, are strongly curved in their basal part, but nearly 
straight in their middle- and end-parts. The latter are nearly parallel to the 
shaft. Another similar spicule observed was only 180 ^ long. I have also seen a 
few large macramphidiscs in which the spines on the central tyle were similar 
to the teeth of the terminal anchors, and all curved in one direction, so that the 
verticil formed by them was like a terminal anchor, only smaller. 
The rare small 7nacramphidiscs (Plate 49, figs. 5, 6) differ from the large 
macramphidiscs — apart from their smaller size — chiefly by being destitute 
of long central spines. The small macramphidiscs are 45-126 m long. The shaft 
is 1-3 m thick, and either simply cylindrical (Plate 49, fig. 5) or gradually thick- 
ened at or near the middle (Plate 49, fig. 6) to a tjde sometimes 5.5 m in transverse 
diameter. The proportion of the thickness of the adjacent parts of the shaft to 
the diameter of the tyle is 1 : 1 (when there is no tyle) ; 1 : 2.2 (when the 
tyle is most highly developed). The whole of the shaft is uniformly and densely 
covered with small spines. The spines on the tyle are not larger than the 
others. The anchors are 13-56 ^ long, a third or less of the whole spicule, and 
12-43 /! broad. The proportion of the length to the breadth of the anchors 
is 100 to 77-92, on an average 100 : 86. The individual teeth appear to differ 
from those of the large macramphidiscs only by being smaller. 
The large micramphidiscs are very rare. In fact only two could be measured. 
These are 51 and 56 m long, and have anchors 16 and 19 ^ long and 8.5 and 9 /j. 
broad respectively. The proportion of length to breadth of their anchors is 
100 : 56 and 100 : 44. 
The small micramphidiscs (Plate 48, figs. 28-31; Plate 49, figs. 1-4) are, 
although much more abundant than the other amphidisc-forms, still not nearly 
so frequent as in other hyalonematids. They are 13-29 n long, usually 17-27 n, 
and have a shaft 0.8-1. 7 m thick. The shaft generally bears a larger or a smaller 
number of minute, cylindrical, truncate, vertical or oblique spines. These 
spines are irregularly distributed; often they form a little cluster near the centre 
of the shaft. The anchors are 4-7.5 n long, a fifth to a third of the whole spicule, 
and 5-8 n broad. The proportion of their length to their breadth is 100 to 87- 
175, on an average 100 : 134.8. The individual anchor-teeth are strongly curved 
