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Show 1876.] SILICEO-FIBROUS S P O N G E S . 537 but as it was accompanied hy 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 has 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 disposed at right angles to the primary lines, causing the areas of the skeleton-rete for the greater part to be uniformly square, comparatively 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 skeleton are very smooth ; on some portions of their fibres no indication of spines can be detected, while on others the faintest possible indications of them are perceptible ; but on some of the straggling intervening 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 irregular; 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 sarcode ; 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 iii size ; their average diameter measured TAro m c n - |
