HYALONEMA (OONEMA) SEQUOIA. 353 



In the centrifuge spicule-preparations (Plate 86, fig. 10) I found a few monac- 

 tine microhexadme-derivates. This spicule appears as a tylostyle and is spined 

 throughout. Its dimensions are: — length 167 a', basal thickness of ray G n, 

 diameter of tyle 9 u. 



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, 115-300 m long, and 5-11 ^ thick at the base, and 

 five shorter (proximal and lateral) rays, 40-95 ^ 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 a7nphidiscs. 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 ^ long ; the latter are 

 small, 17.5-122 yu 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 yu long; the latter 

 smaller, 90-195 yu long. The differences in their anchors, and the absence of 

 intermediate forms between 195 and 370 ^ in length, which finds its expres- 

 sion in a wide gap in tlie length frequency-curve. Figure 23, very clearly 

 distinguish these two kinds of macramphidiscs from each other. I 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 m and reaches down to the 0-line. Thus also 

 among these spicules a larger and a smaller kind can be distinguished. The 



