320 HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 
in their distal part, more rarely straight throughout. The curvature is such 
that the tangents of the end-parts of the rays enclose angles of 120°-150°, excep- 
tionally only 90°, with the continuation of the axis of their proximal parts. 
The proximal end-part of the rays is smooth for a short distance, the distal end- 
part for a considerable distance. The remaining, middle-part bears spines as 
much as 0.7 » long, which are generally vertical. As stated above, I think it 
probable that the straight-rayed microhexactines are canalaria, and only the 
curved-rayed ones true parenchymalia. 
In specimen b I found a microhexactine-derivate with only one ray. This 
monactine spicule appears as a spined tylostyle curved towards its pointed end. 
Its measurements are:— length 1054; basal thickness of single ray 4.5 u; 
tyle 8.5 pu. 
Morphologically two kinds of amphidiscs can be distinguished : — those with 
stout shaft and relatively broad anchors; and those with slender shaft and rela- 
tively narrow anchors. 
To study them biometrically I measured 275 (134 of specimen a and 
141 of specimen b) and drew Figure 19, in which the length frequency-curves of 
the amphidises are represented as follows:— of specimen a (- -- ----- - ); of speci- 
men b (-—-—); and of both specimens together (———). 
In specimen a the amphidiscs are 18-480 » long. Their length frequency- 
curve (---------- ) exhibits two main elevations at about 33 » and about 164 u, 
a number of small elevations, and three large gaps between 54 and 79 y», between 
90 and 110 uw, and between 200 and 220». The amphidises 18-54 » and 79- 
90 » long are all thin-shafted and narrow-anchored; those 110-200 » and 220- 
480 » long are all thick-shafted and broad-anchored. 
The amphidises of specimen b are 21.5-492 u long. Their length frequency- 
curve exhibits two main elevations corresponding exactly to the two main 
elevations of the curve for specimen 6; a number of small elevations, some 
of which correspond to the small elevations of b, and some of which do not so 
correspond; and three principal gaps between 66 and 79, 87 and 118 uz, 
and 187 and 2124. The amphidises 21.5-66 » and 79-87 uw long all belong 
to the thin-shafted slender-anchored kind, those 118-187 » and 212-492 u 
long to the stout-shafted, broad-anchored kind. 
In both specimens therefore two main groups of amphidiscs can be dis- 
tinguished both morphologically and biometrically: — macramphidiscs with 
stout shaft and broad anchors, in both specimens together 110-492 » long, and 
micramphidises with thin shaft and slender anchors, in both specimens together 
