388 
HYALONEMA (SKIANEMA) UMBRACULUM. 
are 51-93 n long, usually about a third of the whole spicule, and 105-190 n broad. 
The proportion of the length to the breadth of the anchors is 100 to 141-316, 
on an average 100 : 225.3. The number of teeth in the anchor is from eight to 
ten. The two anchors of the same spicule are usually composed of the same 
number of teeth, and in this case the teeth of two anchors are generally regularly 
alternate. Sometimes the number of teeth is not the same in the two anchors 
of the same amphidisc, and in that case they of course do not alternate regularly. 
The individual teeth arise nearly vertically from the ends of the shaft, and are 
curved only slightly in their proximal half, but strongly in their distal half. This 
curvature is so great, that the tips of the teeth become strongly convergent, and 
the distance between the ends of opposite teeth is 12-32 n less than the (maxi- 
mum) breadth of the anchor. The outer band-shaped part of the tooth attains 
its maximum breadth a little distance distally from the middle of its length, and 
is here sometimes 32 n broad. At its distal end the tooth is simply rounded off. 
Besides these regular forms several irregular large macramphidiscs (Plate 101, 
figs. 8-10) have been observed. In these spicules one or both of the terminal 
anchors are irregular, and the shaft bears, besides the terminal anchor-teeth, 
other protuberances which arise — usually in a verticil - from its middle-part. 
All these supernumerary protuberances terminate at the (hypothetical) oval 
wall of the amphidisc-cell, and are here abruptly bent or slightly extended to 
terminal discs. 
The small macramphidiscs (Plate 102 , figs. 3-6; Plate 103 , figs. 24-26) are 
78-128 m long, most frequently about 112 tx. The shaft is straight, cylindrical, 
smooth, and 6-11.5 n thick. The terminal anchors are 37-67 ^ long, about 
half the whole spicule, and 53-104 ^ broad. The proportion of the length to the 
breadth of the anchors is 100 to 138-176, on an average 100 : 150.6. The termi- 
nal anchors consist of ten to thirteen teeth. The number of teeth is, as in the 
large macramphidiscs, not always the same in the two anchors of the same 
spicule. When it is the same the teeth of opposite anchors are usually situated 
alternately; when it is not the same, there is no regular alternation of teeth. 
The teeth arise nearly vertically from the ends of the shaft and are curved quite 
uniformly, approximately through a quarter of a circle, to within a short distance 
of the tip. The anchors are therefore nearly hemispherical in shape. The 
outer band-shaped part of the tooth attains its maximum width of 15-20 m 
some distance distally from the middle of its length. Sometimes its broadest 
part lies quite close to the distal end, and in this case this end is broad and 
rounded (Plate 102 , fig. 3); sometimes it lies some distance from the end, and 
