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Show 26 DR. J. s. B O W E R B A N K O N CEYLONESE SPONGES. [Jan. 7, The normal form is that of a thin, more or less expanded cup, cleft at the edges, as in the one figured; in others the margin is quite perfect; and in all the pedicle is very short and slightly expanded, and the substance of the parietes of the sponge is equally thin and delicate, so thin that if it be held up to the light the radial structures of the primary lines of the skeleton m a y be readily seen by the aid of a lens of two inches focus ; the margin of the cup is very little thicker than a stout sheet of paper, and even near the base it rarely exceeds a line in thickness. The oscula are dispersed on the inner surface of the cup, at nearly equal distances from each other. The circular ones rarely exceed half a line in diameter. In many cases, instead of the usual circular form, they consist of three or four narrow shallow lines radiating from a centre. This variation in their form is remarkable, and I do not recollect ever having seen the like of it before. I could not detect the pores on any of the portions of the outer or inhalant surface of the sponges which were examined. The dermal membrane is very thin and delicate in its structure. The primary lines of the skeleton are very much stouter than the secondary ones. They do not radiate in strictly straight lines, and frequently meander to some extent in their course ; but their general direction is distinctly in lines radiating from the central basal attachment of the sponge. Mr. Holdsworth, in a letter to m e descriptive of its locality, states as follows :-" Spongionella is only found on the 9-fathom line of the large pearl-bank. It is attached to pieces of dead coral or stones. W h e n alive it is of a dark brown ; and when taken out of the water it looks exactly like dirty wet leather. If you soak a bit of one of the dark specimens you will see it with as nearly as possible the original appearance. " This sponge is so strictly confined to the locality above mentioned, that its discovery by the divers is considered the strongest evidence that the outer part of the bank has been reached. " I should mention that the banks, strictly speaking, are only beds of gravel, stones, and dead shells in the midst of the general sea-bottom of fine white sand, and the water is as deep over them as in the neighbourhood." DYSIDEA CONICA, Bowerbank. (Plate VI.) Sponge conical, pedicelled; surface covered with small acutely conical papillse. Oscula simple, large, dispersed. Pores inconspicuous. Dermal membrane thin, pellucid, abundantly arenulous. Skeleton fibro-membranous, unsymmetrical, abundantly arenulous. Interstitial membranes aspiculous. Colour in the living and dead state-pedestal light grey, conical mass dark purple. Hab. Large Pearl-bank, Ceylon, in 8 fathoms (Mr. Holdsworth). Examined from spirit, as it came from the sea. This interesting little species of Dysidea was dredged up by Mr. |