AKT. 12 HEXACTINELLID SPONGES OKADA 57 



gradually taper toward the conically or bluntly pointed end. They 

 are beset with small, generally erect prickles, on the end. The 

 proximal ray though occasionally nearly as long as, is usually much 

 shorter than the paratangentials of the same spicule, measuring 100/x 

 in length. The paratangentials usually measure I6O/.1 in length and 

 when subequal to the proximal ray the latter will be found to meas- 

 ure between 120^ and 140/x long. 



The gastralia include both pentactinic and diactinic forms. The 

 diactins in most regions are much the more abundant, and the 

 pentactins are scarcely anywhere more numerous than the diactins. 

 In the pentactins, the distal ray is not represented by a boss; the 

 tangential rays measure 120;U, to 230|U, in length. They have blunt 

 or rounded tubercles on the distal end and are quite straight and not 

 curved inwardly. The proximal ray as a rule is longer than the 

 tangentials, about 200/a to 300ju, long, is of about the same thickness 

 as the tangentials, and tapers evenly to a point above, where it is 

 prominently roughened. Elsewhere it is smooth or has a few scat- 

 tered, weak, minute prickles. Nearly all the rays taper evenly 

 toward the end, which is blunt or rounded. 



The diactins are stout, straight, varying in length from 200/^ 

 to 400(a, and gradually tapering toward the conically pointed ends. 

 They are usually provided with two to eight defined swellings at 

 the center,' measuring 20/x in width, while the ray near the center 

 measures 8|U. in breadth. In some of the diactins, mostly those up 

 to 450^ in length and 12yu broad, the distinct central knobs are not 

 seen. These closely resemble those occurring commonly in other 

 species of A'phrocaUisfes. The roughness of the surface is commonly 

 much more pronounced at the distal ends and sparselj^ scattered 

 on the central knobs and other parts. Occasionally variously 

 developed, prominent microspines cover the entire surface. 



The uncinates show the usual shape, vary considerably in size, 

 extend radially or obliquely, and are usually immersed in the sponge 

 wall without penetrating it. 



The hexasters are of the discohexaster, tylohexaster, and hemi- 

 discohexaster types, as well as of the stout peculiar oxyhexaster 

 type. They are scantily or only fairly abundant, intermixed with 

 one another. The discohexasters are most abundant in the par- 

 enchyme, being nearly spherical, with a diameter of 30/^ to 40/*. 

 Each principal, which is not very short, bears a bunch of two to four 

 or more terminals, which are smooth-surfaced, slightly thickened 

 toward the outer end, and capped by a minute disk, which is 

 divided into two or three clawlike teeth directed backward. 



Occasionally the hexactinic forms may be present in the par- 

 enchj^me. In hexactinic forms the axial length may reach 70/*, 

 showing an increase in diameter over the normal form. The rays 



