252 
HYALONEMA (PRIONEMA) AGUJANUM. 
also occur slender-rayed 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 pinules (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 inclined 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: — • 
