292 HYALONEMA “(PRIONEMA) PINULIFUSUM. 
The large smooth mesamphidiscs (Plate 72, figs. 3-6) are 122-292 » long. 
Their length frequency-curve has three nearly equal elevations at about 150, 
180, and 240 u. The shaft is nearly always straight, only in two of the hundreds 
observed was it markedly curved. The shaft is for the greater part of its length 
cylindrical, and 4-9 » thick. It is abruptly thickened at or near the middle 
to a central tyle 7-18 » in transverse diameter, that is 2-11 » more than the 
adjacent parts of the shaft. The tyle bears a number of spines which are gen- 
erally arranged in a more or less verticillate manner, sometimes however scat- 
tered indiscriminately over the whole tyle. When these spines form a verticil, 
this is situated in a plane either vertical or oblique to the axis of the shaft. 
The individual spines are usually strongly curved or abruptly bent in their 
distal part, cylindroconical, and truncate or terminally rounded. They are 
2-11 » long, and about 2 u thick at the base. The remaining parts of the shaft 
generally bear numerous small, and often also several large spines, 4-6 u long, 
exceptionally as much as 10». The small spines usually arise vertically; most 
of the large ones are oblique, directed and also curved in a distal direction 
(towards the adjacent anchors, away from the central tyle). 
The anchors are, as in the large serrated amphidiscs, either regular or irreg- 
ular, oblique, with the teeth on one side longer than the teeth on the other. 
The two anchors of the same spicule are generally fairly equal in size; sometimes, 
however, one is considerably larger than the other. In one of the large smooth 
mesamphidises observed, one anchor measured 133 by 78 u, the other only 
112 by 62,4. The anchors are 47-133 u long, usually over two fifths of the 
whole spicule, and 26-78 » broad. The proportion of their length to their 
breadth is 100 to 49-73, on an average 100 : 57.9. The anchors are composed 
of ten to twelve teeth. The individual teeth are curved, more strongly in their 
basal part and often also in their distal than in their middle-part. Their total 
curvature is such that their ends are either parallel or only slightly convergent 
or divergent. In the forms with terminally convergent teeth the end-breadth 
of the anchor is sometimes 7 u less than its maximum breadth. 
The small smooth mesamphidiscs (Plate 72, figs. 7, 8) are similar to the 
large ones, but have not so sharply defined central tyles, and relatively broader 
anchors. Their dimensions are: — length 84-120», most frequently about 
110 »; thickness of shaft 2-5 4; diameter of central tyle 3.4—9 uy, that is 0.6-4 u 
more than that of the adjacent parts of the shaft; anchor-length 30-46 4; anchor- 
breadth 21-40 »; proportion of anchor-length to anchor-breadth 100 to 60-87, 
on an average 100 :73. The anchors of these spicules are composed of about 
ten teeth. 
