252 HYALONEMA (PRIONEMA) AGUJANUM. 



also occur slender-i-ayed pentactine and hexactine pinules, and spicules transi- 

 tional between these pinules and the microhexactines. These slender-rayed 

 pinules, and more or less pinule-like transitions to microhexactines, probably 

 occupy the canal-walls, and may be considered as canalar pinules. Acantho- 

 phores are met with in the basal part of the sponge. These vary greatly in 

 thickness. Most of them are tetractine or diactine. Rhabds transitional 

 between the more slender diactine basal acanthophores and the ordinary rhabds 

 of the upper parts of the body are also abundant here. An exceedingly small 

 minority of the short and stout acanthophores in the basal part of the sponge- 

 body are spined not only at the ends of the rays, but entirely. The skeleton of 

 the stalk is continued quite through the body up to the gastral cone (Plate 76, 

 fig. 7). Where it arises from the lower end of the sponge-body, the stalk consists 

 of about a dozen stout and a number of slender rhabds. Of amphidiscs four 

 kinds can be distinguished : — macramphidiscs, serrated amphidiscs, large micr- 

 amphidiscs, and small micramphidiscs. The large micramphidiscs are rare, 

 the others abundant. The skeleton of the Palythoa (Plate 76, figs. 4-6, 34) 

 consists entirely of acanthophores of the sponge. A large majority of these 

 spicules are very short and stout, and entirely spined. These sponge-spicules 

 form an armour of the whole polyp-colony. They occupy in large masses the 

 lateral walls, the oral face, and the stomatodeum of the individual polyps and 

 the superficial part of the coenenchym. 



The dermal and gastral jyimdes (Plate 72, figs. 20-25; Plate 78, figs. 9-11) 

 do not appear to differ from each other appreciably. It is, however, to be noted 

 that the dermal pinules of the basal part of the sponge have, at least in var. 

 tenuis, form A, on the whole shorter distal rays than the other dermal and the 

 gastral pinules. All the gastral and dermal pinules are pentactine. The distal 

 rays are straight and end with a blunt or pointed terminal cone. This cone and 

 the proximal end-part of the distal ray are free from spines. For the greater 

 part of its length the distal ray is covered with nearly straight, mostly rather 

 strongly incUned spines. Generally the spines are simple. Occasionally some of 

 them bear secondary spinelets. The middle-part of the distal ray, together with 

 the spines, is usually nearly cylindrical. The lateral rays are attenuated to- 

 ward the abruptly pointed or blunt end. Distally for one half or two thirds of 

 their length they bear rather large, stout spines. The dermal and gastral pinules 

 of var. tenuis, form B, have more slender distal rays than those of var. tenuis, 

 form A, and var. lata. Apart from this the dermal and gastral pinules of the 

 three groups are very similar. Their dimensions are the following: — 



