1876\] siLiCEO-riBiious sponges. 537 



but as it was accompanied by several others obtained by Captain 

 Hunter from the West-Indian Seas, I think it is highly probable that 

 is is from the same locality. It is a fragment, eight lines in length 

 by six in width, of a thin plate of sponge. It is slightly curved at 

 right angles to the primary fibres of the skeleton, which radiate 

 slightly from one end of the sponge ; and from these indications it 

 is probable that it lias formed a portion of a cup-shaped sponge, and 

 probably a rather widely expanded one. A few patches of the dermal 

 membranes remain adhering to the skeleton- fibres ; they are thin and 

 delicate in structure, and many of them are slightly coated with dark 

 amber-coloured sarcode, and not the slightest remains of retentive or 

 other spicula could be detected upon any of them. 



The primary fibres of the skeleton run in nearly parallel lines in 

 the direction of the greatest length ; and the secondary ones are dis- 

 posed at right angles to the primary lines, causing the areas of the 

 skeleton-rete for the greater part to be uniformly square, compara- 

 tively a few only being slightly oblong. The secondary lines of the 

 exterior and interior surfaces of the sponge are very slightly less in 

 diameter than the primary ones ; and there are straggling portions 

 of an intermediate layer of fibres, which are few in number and very 

 much more slender than any portions of the external layers. Both 

 the primary and secondary lines of the two outer surfaces of the ske- 

 leton are very smooth ; on some portions of their fibres no indication 

 of spines can be detected, while on others the faintest possible indi- 

 cations of them are perceptible ; but on some of the straggling inter- 

 vening portions they are much more decidedly produced. On the 

 external or inhalant surface of the sponge there are a few well-produced 

 short stout imbricated conical spicular defences, based on some of the 

 angles of the rete ; but they are of comparatively rare occurrence, 

 and I could not detect them on the inner or exhalant surface. There 

 are also a few long slender conical defensive spines projected from the 

 skeleton-fibres into the interstitial spaces of the sponge ; but, on the 

 whole, the armature of the skeleton-tissues is very meagre, and it 

 requires a linear power of not less than about 100 to render these 

 characters distinctly to the eye. 



The canaliculation of the skeleton-fibres is very unequal and irre- 

 gular ; and they appear to be often projected in opposite directions ; 

 and their ceecoid terminations frequently pass each other without 

 uniting. 



Minute fragments of the interstitial membranes are seen adhering 

 to some of the skeleton-fibres ; they are thin and delicate in structure ; 

 and some of them are slightly coated with dark amber-coloured sar- 

 code ; and not the slightest remains of retentive or other spicula could 

 be detected upon any one of them. 



The gemmules appear to have been very abundant in this sponge, 

 as there are several groups of them attached to the skeleton-fibres, 

 each containing a considerable number closely packed together. They 

 are membranous and smooth, and apparently aspiculous, but so 

 opaque that their contents cannot be seen. They vary slightly in 

 size ; their average diameter measured -\^r> inch. 



