CAULOPHACELLA TENUIS. 
65 
General structure of the skeleton. Both faces of the lamella are covered 
with pinules occupying the usual position. The pinules on one side are much 
larger than those on the other. The face covered with the larger pinules I 
consider the dermal, the opposite face the gastral. Pentactines, with para- 
tangentially extending lateral rays, and an apical ray directed radially inwards, 
occur under both surfaces. The pentactines underneath the face with the larger 
pinules are much larger than those underneath the opposite face. The former 
are considered as hypodermal, the latter as hypogastral. Numerous slender 
and some large rhabds, a few large hexactines, and dense masses of oxyhexasters 
and hemioxyhexasters occur in the interior (Plate 12, fig. 13). The oxyhexasters 
are much more numerous than the hemioxyhexasters. 
Small hexactines with rays strongly curved at the end ; large sword-shaped 
hexactines with stout and spiny sword-handle ray ; middle sized hexactines with 
cylindrical, terminally rounded, strongly curved rays; and a few other forms 
have also been observed in the spicule-preparations. I consider these spicules 
as foreign to the sponge. 
The rhabds are 3-17 mm. long, 10-34 n thick, rarely 50 /z, and quite sharply 
pointed. 
The rare large hexactines have straight, conic rays, 0.5-1 mm. long and 
20-45 m thick at the base. The rays are smooth for the greater part of their 
length, their tips only being covered with small tubercles. 
The hypodermal and hypogastral pentactines differ only in regard to their 
size. Their lateral rays are straight, conic, and rather sharply pointed. Those 
of the former are 500-1100 n long and 14-32 n thick at the base; the correspond- 
ing measurements of the latter are 110-330 n and 7-14 n. 
The dermal and gastral pinules (Plate 12, figs. 1-8, 14, 15, 19) also differ only 
in size. In both the distal ray is straight, stout at the base, and only slightly 
thickened above. Sparse, small spines arise from its basal part. Towards 
the end the spines become more crowded and larger, the largest attaining a 
length of 7 m in the dermal pinules and a length of 5 m in the gastral. These 
spines are sharp-pointed, directed obliquely upward towards the tip of the ray, 
and also curved in this direction. Their basal part is inclined at an angle of 
about 60° to the ray ; farther on they bend, usually somewhat abruptly, towards 
the ray; so that the angle between their end-part and the ray is 45° or less. 
Usually the spines of the same region are fairly uniform. Sometimes, however, 
adjacent spines differ considerably in position. Occasionally I have observed 
pinules in which the distal spines all tended to one side as if bent by a lateral 
