AKT. 12 HEXACTINELLID SPONGES — OKADA 75 



The hypodermalia are mainly large oxypentactins (fig. 8, h) with 

 rather strong rays, among which the cliactinic forms are intermixed. 

 The former spicules vary somewhat in size. The paratangentials 

 may be 180/x to l,320;u, or more long, and the straight unpaired 

 proximal ray is always much longer than the paratangentials in 

 the same spicule, measuring 490/x, to 2,000/a in length. The rays at 

 the base may attain a thickness of 70|U. The pointed ends of the rays 

 usually are rough on the surface at a short distance from the end. 

 Somethnes the surface is roughened all over, caused by their being 

 densely covered with tiny microtubercles and lined with a few dis- 

 tinct straight striations. These pentactinic hypodermalia occur sin- 

 gly at the centers of the starlike texturings of the sponge surface. 

 The radiating texture of the surface is formed by the paratangentials 

 and by the slender diactins, described below, which help to support 

 the dermal layer. The diactins, which occur either singly or together 

 with the paratangentials of the oxypentactins forming the small bun- 

 dles, are distinguished by two forms. One, less frequently found, 

 is the shorter and broader diactin and is smooth at the center or, 

 at most, with an annular swelling : its ends are always roughened and 

 conically tapered or rounded to a point. 



The dermalia are slightly rough pentactins (fig. 8, c), occasionally 

 stauractins (fig. 8, d). The rays, measured from the center, average 

 150ja long and 12ju, thick. The unpaired ray is somewhat shorter, 

 measuring 75/a to 145ju, in length. If they taper outward, it is only 

 slightly. The ends are rounded or conically pointed. Not infre- 

 quently the pentactinic form, in which the unpaired ray is always 

 directed proximad, show^s an indication of the sixth distal ray in 

 the form of a knob. The paratangentiai cross is usually straight 

 and not convex. Seen from the surface, the delicate dermal lattice- 

 work presents irregular meshes, though in places these tend to 

 assume a regular quadrate arrangement. Near the oscular margin 

 the latticework may be disturbed, forming a very irregular 

 arrangement. 



The gastralia are rough hexactins (fig. 8, a) wath six long and 

 more sharply pointed rays. The paratangentiai ray is 165/x to 220/i 

 long; breadth at base, 20/^. All the six rays in the same spicule may 

 occasionally be nearly uniform in length, though usually the distal 

 ray is much shorter, measuring 120/^ to 210/a, and the free proximal 

 ray much longer, measuring 300m to 340/^. The microtubercles are 

 more pronounced on the distal parts of the six rays. They are 

 sometimes entirely absent on the basal parts and on the central node 

 of the rays. All the six rays are very gradually tapered distally 

 and sharply pointed at the ends. Frequently the proximal ray (in 

 the case of its ray measuring twice the length of the distal ray) is 

 slightly curved laterally toAvard the proximal end. 



