Pv. PIKENIX. — SPICULATION. 271 



and the lateral wall, the parcnchymalia are chiefly diactins with 

 an occasional sprinkling of slender thetactins and of similar 

 hexactins which have one axis greatly elongated in excess over 

 the others. 



While the thinner parenchymal strands consist solely of the 

 thin tilamentons spicules, the coarser ones contain large bow- 

 shaped or I)oomerang-like oxydiactins, the principalia, in addition 

 to the much more slender comitalia. The principalia may 

 measure '/) mm. or more in lengtli and 290 « in thickness at the 

 middle which is smooth and either gently curved or bent in an 

 elbow-like manner. The finely attenuated ends are smooth-sur- 

 faced. In forming a bundle, tlie principalia are arranged side 

 by side and one after another in overlapping series, each sur- 

 rounded by a copious quantity of the comitalia. 



The comitalia and all other line parenchymal diactins are 

 either annnlated or cruciately knobbed at the center ; their ends 

 rounded or conically pointed, often swollen and subterminally 

 roughened to a greater or less degree. 



The radial beams of the siere-plale, which are to be con- 

 sidered as outward continuations of the parenchymal bundles, are 

 supported by certain i:)rolonged raj's of large, unequally rayed oxy- 

 peutactins (occasionally oxj'stauractins) arranged in a circle along 

 tiie sieve-plate border. (PI. XI, figs. ~), 6). Similar spicules in 

 the same position and arrangement have been described by 

 F. E. ScHULZE in Dictyaxblus elegant, and by myself in 11. lome- 

 yanwl (see p. 259). The plane of the two complete and 

 cruciately disposed axes is concave on the inner side, and on this 

 side the sixth atrophied ray is always represented by a small, 

 conical protuberance. The outwardly directed, unpaired ray is 



