274 HYALONEMA (PRIONEMA) SPINOSUM. 
in the gastral surface. The gastral membrane exhibits, in many places, a 
reticulate structure; in life the mouths of the efferent canals were probably 
covered with nets. 
The skeleton. The surface is, so far as the dermal and gastral membranes 
are intact, covered by a dense pinule-fur (Plate 48, fig. 23). The dermal pinules 
on the outer (lower, convex) side, and the gastral pinules on the inner (upper, 
concave) side are very much alike. The gastral pinule-fur extends quite down 
to the bottom of the grooves above referred to. Lateral, paratangentially 
situated, rays of large (hypodermal and hypogastral) pentactines extend just 
below the level occupied by the lateral pinule-rays. In the gastral membrane 
numerous paratangential amphioxes accompany them. The proximal rays of 
the pentactines point radially inward. Large numbers of stout acanthophores, 
tetractine to monactine, occur in the protuberance from which, in life, the stalk 
arose. 
The interior of the sponge is occupied by dense masses of relatively large 
microhexactines, which evidently form the main support of the whole sponge- 
body. Besides these spicules, rhabd and hexactine megascleres and amphidiscs 
occur in the choanosome. 
The dermal pinules (Plate 48, figs. 17-22) are mostly pentactine, rarely 
hexactine (Plate 48, fig. 20). The distal ray is 100-154 » long, usually 117- 
138 uw, and 3.5-4.5 uw thick at the base. It is straight, regularly conic, and not 
thickened in the middle. The distal end-part of the ray is, for a considerable 
distance, free from spines. The basal part is also smooth. The remaining parts 
of it are covered with sparse spines directed obliquely upward. The spines are 
largest on the middle-part of the ray; they are sometimes 11 » and more long, 
slender, usually only 1-1.3 4 thick, basally cylindrical, distally conical, and 
sharp-pointed. The maximum transverse diameter of the distal ray, together 
with the spines, is 10-17 ». The lateral rays are straight, sparsely spined in their 
distal part, and 20-50 u long, usually 25-40 ». The proximal ray of the hexac- 
tine forms is smooth and rarely more than 15 u long. 
The gastral pinules (Plate 48, figs. 23-27) are similar to the dermal and, like 
these, for the most part pentactine. The distal ray is 100-142 u long, usually 
105-135 yu, and 3.5-5.5 w thick at the base. Its maximum transverse diameter, 
together with the spines, is 11-17 ». The lateral rays are 22-35 u long. 
The hypodermal and hypogastral pentactines (Plate 49, figs. 12-14) have 
smooth, blunt, conic rays. The lateral rays enclose angles of 90° or a little less 
with the apical (proximal) ray. The apical ray is straight, or slightly curved, 
