HYALONEMA (PHIALONEMA) PATERIFERUM. 
369 
anchors. The large and small micramphidiscs are distinguished biometrically 
by gaps in the frequency-curves pertaining to their length. These gaps lie in 
the different forms in different places, between lengths of 24 and 49 p. Wilson 
also distinguishes four forms of amphidiscs: — macramphidiscs ( = large macram- 
phidiscs), amphidiscs (Wilson, loc. cit., Plate 1, figs. 10 and 11) (= small macram- 
phidiscs), mesamphidiscs ( = large micramphidiscs), and micramphidiscs ( = small 
micramphidiscs). He thinks it possible that the small macramphidiscs (with 
4-6 teeth in each anchor) represent young stages of the large macramphidiscs 
(with 8 teeth in each anchor). I do not think this is so. 
The large macramphidiscs (Plate 50 , fig. 15; Plate 51 , figs. 2, 16-22; Plate 
52 , figs. 3, 4, 9, 10) have a shaft either cylindrical, and of uniform thickness 
throughout (Plate 52 , fig. 10) or thickened towards the ends (Plate 51 , fig. 18). 
In the smaller and medium-sized large macramphidiscs the shaft is usually nearly 
quite smooth (Plate 51 , figs. 17, 19; Plate 52 , fig. 4); in the larger ones it often 
bears a smaller or a larger number of very low and broad, rounded protuber- 
ances which are scattered irregularly over its central part. In the large macram- 
phidiscs (Plate 51, fig. 18) these protuberances are 6 p broad and 2 p high. 
The axial thread is perfectly simple, not thickened in the centre of the spicule, 
and there is no trace of an axial cross (Plate 50 , fig. 15). The anchors are 
remarkably low and composed of from five to twelve teeth, most frequently 
eight. The individual teeth arise nearly vertically from the end of the shaft, 
and are curved concave towards it. The curvature is slight at the base, but 
increases distally, so that the axes of the end-parts of the teeth enclose angles 
of 30°-45° with the shaft-axis. The teeth of the same anchors are usually simi- 
lar (Plate 51 , fig. 22); sometimes, however, particularly in the large macramphi- 
discs with more than eight teeth, one (Plate 51 , fig. 21) or more of them are 
abnormally small. The teeth are T-shaped in transverse section. The upper 
part (of the T) is band-shaped, distally widened, at its broadest point 19-24 p 
in transverse diameter, and abruptly pointed; seen from above the teeth appear 
mitre-shaped. The lower part (of the T) is broad, low, and rounded below. It 
terminates some distance below the end of the teeth. 
The large macramphidiscs of form A and B are, according to Wilson (loc. 
cit.), 100-200 n long. In those of form A the shaft is 8-16 p thick. Their 
anchors are composed of eight teeth. In the large macramphidiscs of form A 
the anchors are about one fifth of the whole spicule in length. Those of form B 
are about one seventh. In form C the large macramphidiscs are 106-186 p long, 
most frequently about 137 p, and have shafts 14-22 p thick, exceptionally only 
