254 



HYALONEMA (PRIONEMA) AGUJANUM. 



Diactine, probably marginal pinules (Plate 78, fig. 3) have been observed 

 only in the preparations of var. tenuis, form A, and var. lata. Their distal ray 

 is usually pointed, exceptionally reduced in length, and rounded and thickened 

 at the end (Plate 78, fig. 3). It is covered with rather strongly inclined, distally 

 directed, generally nearly straight spines. The proximal ray is usually more or 

 less spiny, and pointed or rounded at the end. A central tyle, the remnant of 

 the (reduced) lateral rays, is always present. It is irregularly spherical or com- 

 posed of four distinct lobes (ray-rudiments). Generally it bears several large 

 spines which point obliquely upward and outward. 



The dimensions of the diactine pinules are: — 



Pentactine and hexactine spicules with very slender rays have often been 

 observed in the interior of var. lata. I consider these spicules, which are con- 

 nected with the microhexactines l)y numerous transitional forms, as canalar 

 pinules. In these spicules one ray is different from, usually longer, rarely shorter, 

 than, the others. This differentiated ray, which is to be considered as the distal, 

 bears oblique, distally directed spines. The other rays are also spiny, but their 

 spines are much smaller and generally situated vertically. The ray to be con- 

 sidered as the distal is 100-170 /x long, 3.5-7 fj. thick at the base, and in its 



