HYALONEMA (OONEMA) CRASSIPINULUM. 337 



The rays of the ?7iicrohexacimes (Plate 92, figs. 9-15) are usually nearly 

 equal and all quite straight or nearly so. Only rarely microhexactines are 

 found in which one or two of the rays are distinctly cur\'ed in their middle-part. 

 The rays are 3.5-7 fi thick at the base, conical, pointed, and covered with spines. 

 The spines on the proximal half of the ray are sparse, vertical or slightly inclined 

 towards the centre of the spicule, and up to 2 ;u long. The spines on the distal 

 half are more numerous, smaller, and rather strongly inclined towards the centre 

 of the spicule. Most of the microhexactines have rather long and slender rays. 

 These spicules (Plate 92, figs. 9, 10) are 90-220 ^ in total diameter, and the 

 basal thickness of their rays (3.5-6.5 n) is fairly in proportion to their size. 

 Some microhexactines have much shorter and relatively much stouter rays. 

 These spicules (Plate 92, fig. 11) are only 65-80 n in diameter, and have rays 

 as much as 7 m thick at the base. 



The rare monactine microhexactine-derivates appear as strongly spined tylo- 

 styles. They are about 130 /x long, and 8 m thick near the tyle. The terminal 

 tyle itself is about 9 yu in diameter. 



Morphologically four kinds of amphidiscs can be distinguished: — 1, large 

 amphidiscs with fairly smooth shaft and broad and short anchors, about a 

 third of the whole spicule in length; 2, medium amphidiscs with a stout smooth 

 shaft and broad and long anchors, usually a little more than half the whole 

 spicule in length; 3, medium amphidiscs with a slightly spined, rather slender 

 shaft, and long, narrow anchors, more than a third of the whole spicule in length; 

 and 4, small amphidiscs with slender, spined shaft and rather short anchors, 

 only about a third of the whole spicule in length. 



The amphidiscs belonging to the first kind are 375-480 ti long, those belong- 

 ing to the second kind 110-200 /x, those belonging to the third kind 112-137 fi, 

 and those belonging to the fourth kind 31-106 fi. The first and the fourth kinds 

 are accordingly distinguished both morphologically and Isiometrically. The 

 second and third kinds, although distinguished in the same manner from the 

 first and fourth, are distinguished from each other morphologically only, and 

 not biometrically. 



As the measurements given above and the adjoined graph show, the gap 

 in the length frequency-curve separating the fourth from the second and third 

 kinds is much narrower than that separating the second and third from the 

 first kind. In spite of the width of this gap, and the entire absence of transi- 

 tions between the second and third kinds of amphidiscs on the one hand and the 

 first kind of amphidiscs on the other, I am incUned to combine the first, second, 



