ART. 12 HEXACTINELLID SPONGES — OKADA 101 



occur in the hypodermal and hypogastral layers. They are micro- 

 spined on the entire surface, most pronouncedly so at the end. They 

 are frequently smooth near the center. 



The hypodermal pentactins are somewhat variable in size, the 

 larger ones usually occurring lower down on the sponge, while the 

 small ones, measuring not more than half the size of the larger ones, 

 are situated near the oscular margin. I have found that the small 

 pentactins are generally arranged in the form of a regular cross. 

 This cruciate arrangement of the paratangentials also occurs rather 

 rarely in the larger pentactins lower down on the sponge. The 

 larger pentactins are usually protruded singly from the lower parts 

 of the sponge surface. The paratangentials, which are generally not 

 quite straight but rather wavy, are 4 mm or more long. The straight 

 shaft or the unpaired proximal ray is always much longer than the 

 paratangential in the same spicule. All the rays of the pentactins 

 are at first smooth or very sparsely rough except near the ends, 

 which are minutely rough. They are so in most of the spicules in 

 the hypodermal situation or in the oscular margin; while the older 

 pentactins present a finely shagreenlike surface throughout the lower 

 parts of the entire stock. The roughness is caused by minute, erect, 

 and sharply pointed processes. The fine shagreenlike surface is 

 caused by the same minute and thickly set processes. The micro- 

 spines remind one of those on the prostal pentactins of Staurocalyp- 

 tus dowUngii (Lambe). In general, the surface of the rays in the 

 pentactins is more thickly microspined on the paratangentials and 

 more sparsely so on the proximal unpaired ray. 



The dermalia are mainly rough pentactins. Exceptionally they 

 may be stauractins, rarely hexactins. The pentactins (fig. 13, h) 

 measure 150/x along both the paratangential rays and the unpaired 

 proximal ray, which is somewhat shorter than, or nearly equally as 

 long as, the paratangentials. The thickness at the middle is 8/x. They 

 are straight and taper very slightly toward the rounded or conically 

 pointed ends. All the surfaces of the rays are sparsely roughened. 

 The stauractins are nearly straight on the outside and almost the 

 same size as the pentactins in axial length. The rays are 140ju, to 

 l70/>i long and 8/^ broad at the base. They are entirely rough, and 

 the microtubercles on their surface are more or less prominent. The 

 hexactins are nearly the same as those occurring in the gastralia but 

 are smaller in size. 



The gastralia are fairly large hexactins (fig. 13, a). All six rays 

 in one spicule may sometimes be of nearly equal length, but more 

 frequently the proximal free ray is the longest and the distal the 

 shortest. ^ The length of proximal ray is 100/>t to 250/^; of paratan- 



