96 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 81 



usually shorter than hypogastral diactins. They may attain a length 

 of 170/Li and are 16/x wide at the middle. The width is nearly the 

 same throughout, slightly tapering toward the rounded ends, the 

 surface of which is roughened by microspines. The diactins are dis- 

 tributed densely, forming a thickened firm layer 1 mm in thickness. 

 Occasionally diactins that have a central protuberance appear. 

 They are 560fi in length and 20^ to 24)u, wide at the center. The sur- 

 face, except that of the central protuberance, is roughened sparsely. 



Hypogastralia also consist of diactins, which are arranged in loose 

 or compact bundles of variable length, distributed much more 

 sparsely and irregularly. They are generally slenderer than those 

 on the hyjDodermalia but much longer than the latter. They taper 

 very gradually toward both ends, the tip being either simply acumi- 

 nate or conically pointed. Subterminally the surface is sparsely 

 roughened by microspines. Occasionally in the diactins the center 

 shows a gentle swelling, but more frequently four protuberances, like 

 those occurring in the hypogastralia. 



Dermalia are predominantly stauractins (fig. 12, 6), sj^arsely 

 rough all over, nearly plane, not arched ; axial length, 280/x to 360/,i. 

 The rays taper perceptibly toward the conically pointed or rounded 

 tip, or are nearly uniformly thick. They are sometimes provided 

 with a central prominence. The thickne&:s at the middle averages 

 8/x. Occasionally among the dermalia there are found pentactinic 

 forms in which the proximally directed, unpaired ray is somewhat 

 shorter or longer than the paratangentials, 140/i to 200ju, in length. 

 The surface is also sparsely roughened. Besides these common 

 stauractins and pentactins, a smaller and very slender stauractin 

 occasionalh' occurs. Its rays are very slender, measuring 2;u. to 4/x 

 wide at the middle, and are sharply pointed at the ends. 



Gastralia are rough large hexactins (fig. 12, a), irregularly scat- 

 tered. The rays taper slightly outward. The microtubercles on 

 their surface are neither numerous nor strongly developed, so that 

 the roughness on the surface is not prominent. The proximal ray 

 measures 212//, in length; the distal ray 190/a, and the paratangen- 

 tials 175/x.. 



Oxyhexasters consist of normal oxyhexaster (fig. 12, d), hemihex- 

 actinic, and hexactinic forms, the last of which is rarely found in 

 the parenchyme. The normal oxyhexaster may be present in two 

 forms, designated A and B, differing in total size, in the slenderness 

 of the terminals and in the shape of the principals. The variety B 

 (fig. 12, /) frequently occurs in the dermal and gastral layers, as 

 well as abundantly in the parenchyme, intermingled with the 

 other variety. It measures 140fi to 155/x in diameter and has a dis- 

 tinct globular node and short principals, rounded in a knoblike man- 



