HYALONEMA (OONEMA) SEQUOIA. 
353 
In the centrifuge spicule-preparations (Plate 86, fig. 10) I found a few monac- 
tine microhexactine-derivates. This spicule appears as a tylostyle and is spined 
throughout. Its dimensions are: — length 167 n, basal thickness of ray 6 fi, 
diameter of tyle 9 /x- 
The true choanosomal microhexactines have, as above stated, equal rays. 
In the spicule-preparations, however, a large number of small spined hexactines 
are found, in which one ray is considerably larger than the other five. These 
spicules I consider as pinule-like derivates of the regular microhexactines, which 
line the canal-walls, and are therefore to be considered as canalaria. 
These pinule-like microhexactine-derivate canalaria (Plate 88, figs. 5, 6) 
have a longer (distal) ray, 1 15-300 n long, and 5-11 m thick at the base, and 
five shorter (proximal and lateral) rays, 40-95 n long. The proximal ray may 
be longer or slightly shorter than the laterals. All the rays are spined. The 
spines on the distal ray are longer than the spines on the other rays — the more 
so, the more the distal exceeds the other rays in length. They are also for the 
most part directed obliquely upwards towards the tip of the ray. 
The amphidiscs. Morphologically two main kinds of amphidiscs can be 
distinguished: — amphidiscs with broad terminal anchors and a shaft which 
is either quite smooth or provided only with one or a few terminally rounded 
protuberances or spines, and amphidiscs with slender terminal anchors and 
generally spiny shaft. The former are large, 90-550 /x long; the latter are 
small, 17.5-122 ^ long. I consider the former as macramphidiscs, the latter 
as micramphidiscs. 
Among the macramphidiscs two subgroups can be distinguished both 
morphologically and biometrically. In one the anchors are much shorter 
than half the length of the whole spicule, and the anchor-teeth pointed; in the 
other the anchors are about half as long as the whole spicule, and the anchor- 
teeth terminally rounded. The former are larger, 370-550 m long; the latter 
smaller, 90-195 ^ long. The differences in their anchors, and the absence of 
intermediate forms between 195 and 370 n in length, which finds its expres- 
sion in a wide gap in the length frequency-curve, Figure 23, very clearly 
distinguish these two kinds of macramphidiscs from each other. 1 accord- 
ingly divide the macramphidiscs into two subgroups: — large and small 
macramphidiscs. 
The length frequency-curve of the micramphidiscs also shows a great 
depression, which lies at about 57 /x and reaches down to the 0-line. Thus also 
among these spicules a larger and a smaller kind can be distinguished. The 
