272 T. IJTMA : HEXACTINELLTDA. T. 



relatively very short (not over 2 mm. in length) and is some- 

 times represented merely by a rounded boss. It enters into the 

 support of the cuft*. 



Of the cruciate, paratangential axes, the one in longitudinal 

 direction is the longest, reachiug up to 30 mm. in length. The 

 superior ray in this axis, i. e., the ray which goes into the com- 

 position of each of the radial sieve-plate beams, is in length about 

 equal to or sliorter than the inferior ray which is imbedded in 

 the parenchyma of the lateral wall. The lateral rays in the 

 transverse axis are always much shorter than either the superior 

 or the inferior ray ; sometimes the}'^ are as short as the distal 

 unpaired ray. Thickness of the rays at base 250-475 ,«. The 

 superior and the inferior rays commonly thicken somewhat at 

 a short distance from the central node, then gradually narrow 

 again toward the finely pointed end. 



The lateral rays, lying along the base of the cuff, run in 

 association with just the same diactin elements as compose the 

 parenchymal bundles of the lateral wall. 



The superior ray is distinguished from all the rest by 

 having a number of obsolete microtubercles widely and sparing- 

 ly distributed over its surface (PI. XI, fig. 7). The microtubercles 

 are frequently only indicated. They disappear entirely to- 

 wards either end of the ray. Along with the ray in question 

 are found in a bundle bow-like oxydiactin-principalia and 

 diactin-comitalia, to complete the parenchymalia of the sieve-plate 

 (PI. XI, fig. 8). Among the comitalia are not uncommonly 

 found small and slender-rayed hexactins, which jDass over into 

 the shorter diactin-comitalia bv a 2;radational series of inter- 

 mediate forms. 



In the Challenger Report F. E. Schulze gave large oxy- 



