304 
HYALONEMA (PRIONEMA) FIMBRIATUM. 
Plate 62 , fig. 27) form a biometrically homogeneous and well-defined group, 
entirely separated dimensionally from the (larger) macramphidiscs on the one 
hand and the (smaller) large fimbriate amphidiscs on the other. 
The largest fimbriated amphidiscs are 200-323 n long, most frequently 
about 250 n long. The shaft is straight, on the whole cylindrical, and 4-7.5 n 
thick. Its thickness is fairly proportional to the length of the spicule. The 
shaft is thickened slightly and gradually towards the ends, and considerably 
and abruptly somewhere in its middle-part. The latter thickening, the central 
tyle, is usually some distance, occasionally (Plate 60 , fig. 5) very far away from 
the real (geometrical) centre of the shaft, and measures 8-14 n in transverse 
diameter. The proportion between the thickness of the adjacent parts of the 
shaft to the thickness of the tyle is 100 to 160-325. From the central tyle a 
verticillate bunch of spines arises. These spines (Plate 62 , fig. 27) are 5-15 m 
long, at the base 2-2.8 n thick, cylindrical, and terminally simply rounded, or 
attenuated distally and truncate with a cluster of exceedingly minute secondary 
spinelets on the terminal face. The (primary) spines are curved. The curva- 
ture is irregular, and a rather abrupt angular bend usually occurs somewhere 
near the middle of the length of the spine. Generally all the spines of the bunch 
are, as in the macramphidiscs, curved in the same direction longitudinally or 
obliquely (spirally). The parts of the shaft outside the central tyle bear very 
numerous spines, the largest of which are 1 n long, 1.5 ^ broad, cylindrical, and 
provided with a cluster of exceedingly minute secondary spinelets on their flat 
or rounded terminal face (Plate 60 , figs. 5, 6; Plate 62 , fig. 27). The degree 
of development of these scattered (primary) spines is very variable ; often they 
are reduced to hardly perceptible protuberances on the surface of the shaft 
(Plate 60 , fig. 3). 
The two anchors of the same spicule are fairly equal, or rather unequal, in 
size. They usually consist of eight teeth. The anchors are 72-136 n long, and 
43-67 m broad at their broadest point and attenuated distally, their ends meas- 
uring only 32-60 n in transverse diameter. The difference between the maxi- 
mum and end-breadth of the anchors is 3-18, on an average (of 29 measure- 
ments) 7.8 fi. The proportion of the length to the maximum breadth of the 
anchors is 100 to 42-72, on an average (of 29 calculated proportions) 100 : 52.2. 
The largest (longest) anchors are on the whole narrower than the smaller (shorter) 
ones. The average proportion of length to maximum breadth is in the anchors 
over 120 n in length 100 : 47.8, in those under 100 n in length 100 : 55.7. 
The individual anchor-teeth arise nearly vertically from the end of the 
