AKT. 12 HEXACTINELLID SPONGES OKADA 41 



of the framework are smooth on the surface. They are frequently 

 beset with tubercles on the longitudinal beams and are fairly slender, 

 measuring 34/i to 50/x in width, and are curved. The moderately 

 long and curved, free-projecting prongs, or conical pegs, are 4 mm 

 to 1.7 mm long, rough and tubercled on the surface, and project from 

 the inner or outer side, frequently laterally from the median beams. 



The dermal membrane is supported by the four rectangularly 

 intersecting tangential rays of pentactins (fig. 6, a), whose unpaired 

 proximal ray penetrates into the parenchyme vertically. Though the 

 proximal ray is always perfectly straight and slightly roughened on 

 the surface, the tangential rays are somewliat curved inward and 

 more roughened on the surface, with the roughness much more pro- 

 nounced toward the end of the rays. The proximal ray, which is 

 usually much longer than the tangential, measuring 340/x to 510/^ in 

 length and IQ/x to 24/^ broad near the center, is somewhat smooth at 

 a short distance from the center. The tangential rays are usually 

 more or less shorter, 280/x to 320/x long, and slightly curved inward. 

 These pentactins on the dermal membrane are very irregularly 

 arranged, though sometimas they form a quadratic framework. The 

 gastral pentactins agree essentially with the dermal. 



The clavulae are a kind of hooked anchorate. Their size varia- 

 tion is considerable in different regions of the same sponge. This, 

 on the one hand, is chiefly associated with the total sizes of the 

 spicule and, on the other, is partly associated with the number of the 

 protruding teeth on the peripliery of the head. These deviations 

 merge into one another through forms of intermediate size and shape. 



The larger clavulae (fig. 6, c, /), which occur mostly on the dermal 

 Isijer and occasionally on the gastral layer, penetrating obliquely 

 or lying on the surface, are 1 mm to 1.7 mm long. The head, 50/* to 

 70ju, in width, shows a convex, smooth surface with an external, 

 slightly raised swelling at its center. It is usually provided with 

 10 to 14 strong, externally curved or nearly straight teeth 140ju, 

 long, forming a large bunch 200/t broad at the distal expansion. 

 The shaft is gradually attenuated to the conically pointed end, 

 measuring 12/x, to IQ/x broad on parts just below the head and Sfx 

 broad near the end. The curved or nearly straight lateral spines 

 project from the proximal parts of the shaft. They are 80/* to 105/x 

 long, their length gradually decreasing downward. 



The smaller form (fig. 6, b, c, d), measuring 760/t to 850/x long, 

 is much more abundant on the gastral and dermal layers, pene- 

 trating vertically to the surface, exposing only its head from the 

 surface or being immersed entirely into the body wall. The head 

 is much smaller, measuring 20/c in diameter, and its surface is 

 quite smooth and convex or weakly raised at the center. In some 

 of these forms the spines projecting from the periphery of the 



