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 /z 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 105 m; basal thickness of single ray 4.5 yu; 

 tyle 8.5 m- 



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 amphidiscs are represented as follows : — of specimen a ( ) ; of speci- 

 men 6 ( ) ; and of both specimens together ( ) . 



In specimen a the amphidiscs are 18-480 m long. Their length frequency- 

 curve ( ) exhibits two main elevations at about 33 /x and about 164 n, 



a number of ^mall elevations; and three large gaps between 54 and 79 m, between 

 90 and 110 m, and between 200 and 220 m- The amphidiscs 18-54 ^ and 79- 

 90 fi long are all thin-shafted and narrow-anchored; those 110-200 ^ and 220- 

 480 n long are all thick-shafted and broad-anchored. 



The amphidiscs of specimen b are 21.5-492 fi long. Their length frequency- 

 curve exhibits two main elevations corresponding exactly to the two main 

 elevations of the curve for specimen b; 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 ix, 

 and 187 and 212 ix. The amphidiscs 21.5-66 ij. and 79-87 ^ long all belong 

 to the thin-shafted slender-anchored kind, those 118-187 ^ and 212-492 m 

 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 

 micramphidiscs with thin shaft and slender anchors, in both specimens together 



