1875.] DR. J. S. BOWERBANK ON THE SPONGIAD&. 289 
are projected at right angles to the fibre into the areas, frequently 
in considerable numbers ; a power of about 300 linear is required to 
exhibit them in situ in a satisfactory manner; their length rarely 
exceeds =, inch. 
The acuate skeleton-spicula are distinctly different in their pro- 
portions from those of the dermis; their diameter is twice that of the 
dermal ones. A full-sized one measured 5,155 inch in diameter. 
Since the above description was written I have examined another 
specimen of this species, sent to me from the Straits of Gaspar by 
Commodore Parish. It is, in its external and anatomical characters, 
very like the type one, but rather larger and more strongly deve- 
loped. A remarkable circumstance attending this specimen is that 
it has two very interesting radiate animals seated upon it, the small 
or basal arms of which are so interwoven amidst the branches of the 
sponge as to render it impossible to disentangle them without the 
destruction of the radiate animals, while the larger and longer arms 
for entangling their prey are thrown out above in every direction. 
Their mode of anchoring themselves on the sponge is an interesting 
fact in their natural history. 
HALICHONDRIA RIGIDA, Bowerbank. 
Sponge massive, sessile. Surface very rugged and uneven, full of 
ridges and depressions. Oscula simple, dispersed. Pores incon- 
spicuous. Dermal membrane pellucid, spiculous; tension-spicula 
acuate, the same diameter and nearly the same length as those of the 
skeleton ; retentive spicula bihamate, simple, and contort, rather 
numerous ; and bidentate equianchorate, small, but rather stout, not 
numerous. Skeleton-rete multispiculous, very wide and open, ir- 
regular ; areas very variable in size; spicula purely acuate, rather 
short and stout. Interstitial membranes sparingly spiculous ; spicula 
same as those of the dermis. 
Colour, in the dried state, dull green. 
Hab. Straits of Malacca (Commodore Parish, R.N.). 
Examined in the dried state. 
I obtained this sponge from my friend Commodore Parish, It is 
from the Straits of Malacca. It is 23 inches long, 1 inch wide, and 
rather exceeds half an inch in average thickness. 
_ The dermal membrane is rather sparingly furnished with tension- 
spicula. There is very little difference between these spicula and 
those of the skeleton; the latter are rather the longer of the two ; 
their diameter is about the same. In consequence of the open 
structure of the skeleton-rete there are a considerable number of 
surreptitious spicula of various forms amidst the tissues of this 
sponge ; and fragments of some of these are occasionally incorporated 
in the skeleton-fibre, as in a Dysidea. The spicula in the fibre are 
numerous and closely compacted, and the areas very wide, but by no 
means equal or regular in either form or size. The bihamate 
retentive spicula are not very abundant ; they are rather slender ; 
and the simple and contort forms are about equal in number, and 
Proc. Zoou. Soc.—1875, No. XIX. 19 
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