80 pR.J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [ Jan. 28, 
ment to the primary skeleton-fibres and by their habit of inos- 
culation. 
Beside the auxiliary fibres, there are in some parts of the 
sponge an abundance of true rectangular hexradiate spicula (Plate 
III. fig. 2); but they are rarely found mixed with the auxiliary 
fibres or in the same spaces with them. Although occurring in 
closely packed groups, they never unite with each other, nor are 
they even attached to any parts of the surrounding skeleten-fibre, 
and they always preserve their normal form. They are slender, 
smooth, and their radii are very slightly inclined to become clavate. 
The termination of the elongated basal portion of the spiculum is 
frequently incipiently spinous. Their length is 3'; inch, the expan- 
sion of the lateral radii +4, inch, and the diameter of the axial shaft 
varies from zj5q to today inch. 
The trifurcated attenuato-hexradiate stellate (Plate III. fig. 5) and 
the trifurcated spinulo-hexradiate stellate spicula (Plate III. fig. 4) 
are both very abundant, and in some small masses of sarcode they 
are so numerous and so closely packed together as to render it quite 
impossible to count them. ‘The sarcode appears to have been very 
abundant, as in some parts it completely fills up the reticulations 
of the skeleton; it is of a full amber-yellow colour. 
Thus far we have positive characters by which to discriminate 
this beautiful species of sponge from its nearly allied congeners ; 
but I have been fortunate in finding other characters, which, from 
the mode in which they have been obtained, although not so deci- 
sive in their nature, are yet of such importance that their descrip- 
tion cannot be omitted in treating of this species. 
I carefully examined the half of the type specimen of D. pumi- 
ceus that is in the British Museum in the hope of finding a small 
fragment of the dermal portion of the sponge, but I did not suc- 
ceed in detecting any remains of it on the cup-shaped portion of 
the specimen; but on the basal surface of the pedicel there were 
remains of what appears to have been the basal membrane. It 
consists of a dense yellow incrustation, closely intermingled with 
the basal skeleton-structure, and agreeing in colour and appearance 
with a few very minute specks of the animal matter of the external 
surface of the sponge. I mounted a small portion of this basal mat- 
ter in Canada balsam ; but this material did not render the fragments 
transparent ; yet there were at some portions of their margins unmis- 
takable evidences of their containing spicula. There were also 
fragments of the skeleton-structure of the base of the sponge, the 
reticulations of which were, as might be expected from their situa- 
tion, very close and dense (Plate III. figs. 14 and 15); and along 
with these fragments there was a group of three large and very 
remarkable verticillately spined cylindrical spicula, very closely re- 
sembling in their structure the one represented by fig. 69, plate 3, 
vol. i., ‘ Monograph of British Sponges,’ and also by fig. 23, plate 36, 
Phil. Trans. for 1862, but differing from those figures in being much 
longer in their proportions, and in having a greater number of circles 
of spines (Plate III. fig. 6). Having seen thus much of the dermal 
