HYALONEMA (THALLONEMA) GEMINATUM. 
395 
become strongly convergent, the distance between opposite teeth being 6-20 n, 
rarely as much as 32 n, less than the (maximum) breadth of the anchor. 
The small macramphidiscs (Plate 104 , figs. 9, 10, 13, 14) are 88-153 m long, 
most frequently about 112 A good many of the largest, that is of those 136— 
153 fi long, have anchors of only medium length and are consequently transi- 
tional to the large macramphidiscs above described. The shaft is straight, 
cylindrical, and 6-12 n thick. The terminal anchors are 50-72 n long, a third 
to half of the whole spicule, and 70-130 n broad. The proportion of the length 
to the breadth of the anchors is 100 to 146-183, on an average 100 : 161.8. The 
anchors are composed of from ten to sixteen teeth. Roughly speaking, the 
number of teeth is in inverse proportion to the size of the spicule. The teeth 
of the two anchors of the same spicule are often, but by no means always, situ- 
ated alternately. The individual teeth are generally quite uniformly curved 
through a quarter of a circle and abruptly bent inward at the end, so that their 
tips are strongly convergent. The outer band-shaped part of the tooth attains 
its maximum breadth in its distal portion, and is here 12-18 m broad. The end 
is broad, rounded off, sometimes nearly truncate. 
The micramphidiscs (Plate 103 , figs. 37, 38, 49-57) are 16-92 n long, the 
larger ones, to which the conspicuous elevation near the right-hand end of the 
curve pertains, most frequently about 76.5 n long. The shaft is straight or 
only very slightly curved, and 0.7-5 ^ thick. It is simply cylindrical or slightly 
thickened at or near the middle to a central tyle, 0.3-0. 6 n, rarely as much as 
1.5 ii, more than the adjacent parts of the shaft in transverse diameter. Centro- 
tyle forms are more frequent among the larger than among the smaller micram- 
phidiscs. A larger or smaller number of small spines are scattered over the 
whole of the shaft. In the centrotyle forms the spines arising from the central 
tyle are usually larger than the others. The terminal anchors are 3.5-24 n 
long, that is one fifth to two fifths of the whole spicule, and 5.5-30 n broad. The 
proportion of the length to the breadth of the anchors is 100 to 100 200, on an 
average 100 : 150.5. The anchors of the larger forms are on the whole relatively 
broader than those of the smaller. The anchor is composed of a considerable 
number of teeth; in one 24 n broad I counted eighteen. The individual teeth 
are, in the larger micramphidiscs, up to 5 m broad, and pointed at the end. 
Besides the regular micramphidiscs above described I observed a few irregu- 
lar micramphidiscs with terminal anchors on one side much longer than on the 
other. In these anchors the tips of the anchor-teeth lie in an oblique plane enclos- 
ing an angle of about 45° with the axis of the shaft. The longest part of one 
