ART. 12 HEXACTINELLID SPONGES OKADA 115 



in thickness at the base. The shaft, up to 6.5 mm to 7 mm in lengthy 

 is always the longest of the rays; it is smooth except at the rough- 

 ened end and is not provided with spines. The paratangentials are 

 also nearly smooth on the surface. The stout conical spines occur 

 in a rather regular distribution — in two lateral rows. Those situated 

 on the basal parts of the rays spring vertically, become more or less 

 bent forward near the end of the ray, and bend more strongly toward 

 the extremity. These hypodermal pentactinic spicules may occur 

 singly and not in close groups of two or more, as in some other 

 members of this genus. Occasionally they occur fairly close to- 

 gether. Diactins do not seem to associate with the hypodermal 

 paratangentials in forming the support to the dermal layer. 



The dermalia are mostly stauractins (fig. 16, c), but frequently 

 rough diactins and rarely pentactins, as well as stauractins. The 

 common stauractins appear abundantly in the entire stock. The 

 center of these is generally plain but occasionally shows a gentle 

 swelling on either the external or the internal side or both. The axial 

 length of the spicule may measure 260/^ to 320/a and lOju, thick at the 

 center. The entire surface is slightly roughened, being more pro- 

 nounced at the conically pointed ends. In the diactins the sup- 

 pressed rays are indicated by three knobs in a cruciate arrangement 

 on the center. The rays are rough all over and taper slightly toward 

 the rounded or obtusely conical end. They measure 320ju, to 480/x in 

 total length and 12/x in thickness near the middle. In the tauractins 

 (fig. 16, h) the atrophied paratangential usually leaves a knoblike 

 relic, while the radial rays may or may not be similarly represented. 

 The meshes of the dermalia, which are composed of stauractins, 

 diactins, and pentactins, are more irregular in shape than those of 

 the gastralia. 



The gastralia are rough oxyhexactins (fig. 16, a) of great axial 

 length. The length of the free proximal ray in the most prominent 

 part is 320/a; that of the distal ray, 160/x; that of the paratangentials, 

 180/^ ; thickness of rays near the base, about 10/x, on the average. The 

 microtubercles on all rays are sparsely and uniformly developed but 

 are somewhat strongly pronounced on all the ends. The gastral lace- 

 work shows a regular quadrangular shape, measuring about 140/x by 

 190jU, in length of sides. 



The discoctasters (fig. 16, h) resemble in shape and size those of 

 R. ungniculatus. They are found more abundantly in the ectosome, 

 as well as directly under the dermalia, than in deeper parts. Their 

 diameter is 150/a to 160/a. The principals are entirely smooth on the 

 surface and 16/^ long as measured from the spicular center; in any 

 case they are much longer than in R. unguiculatus. The terminals 

 number 6 to 8 to each principal and form a rather broad, lilylike 

 tuft, expanded at the outer end. Each terminal disk distinctly shows 



