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HEXACTINELLA MONTICULARIS. 145 
The lamellae separating these tubes consist of a network of beams, mostly 
40-100 » thick, with meshes 100-200 » wide. Some parts of this network are 
quite irregular, others more regular, with more or less quadratic meshes. The 
beams generally bear small, broad, sharp-pointed, conic spines (Plate 28, fig. 22). 
Large, freely terminating, conic protuberances, which are hexactine rays and may 
be designated as thorns, arise from the beams in many places. In the inner part 
of the lamellae these thorns are not numerous; they are small, usually 90-200 u 
long (Plate 28, fig. 22). In their superficial part they are more numerous, more 
or less vertical to the surface of the lamella, and larger, 120-360 » long, and about 
60 u thick at the base. These superficial thorns are covered with spines similar 
to those on the beams, but on the whole larger and more densely crowded. 
The superficial skeleton-net (Plate 28, figs. 21, 27), remnants of which have 
been found in several places, extends paratangentially on the surface. It is 
rather loose and irregular, and consists of pentactines the lateral rays of which 
have been more or less soldered together. 
The loose hexactines (Plate 28, figs. 17, 18) found in the interior are probably 
destined to be soldered together to form the internal skeleton-net. The small, 
probably young forms have straight, or slightly curved, nearly smooth rays, 70— 
100 » long and 3 u thick at the base. In the larger, probably older ones (Plate 
28, figs. 17, 18) the rays are 100-260 » and more long, nearly cylindrical, and 
10-14 » thick. They are, in the same spicule, often unequal and always covered 
with spines. Most of these spines are small, whilst some, which lie irregularly 
scattered between the small ones, attain a very large size and measure 10-50 u 
in length. These large spines, of which each ray bears from five to ten or more, 
increase in size towards the distal end of the ray. The largest of them bear 
small secondary spines. Several, usually three, are situated terminally. These 
are always the largest. The large spines along the length of the rays arise nearly 
vertically, the terminal ones usually point obliquely outward. 
The pentactines (Plate 28, figs. 19, 21, 27) are situated superficially. Their 
lateral rays, which form the superficial net, are 120-200 » long, 4-10 » thick at the 
base, and slightly attenuated towards the end. They are covered throughout 
with vertically arising spines. Young, still free, superficial pentactines (Plate 28, 
fig. 19) have slender rays and very small spines. Older ones, already incor- 
porated in the superficial net (Plate 28, figs. 21, 27), have stouter rays and longer 
spines. 
Of wncinates two kinds, a smaller and a larger, can be distinguished. 
The smaller uncinates (Plate 28, fig. 10), which are very numerous and 
