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Show 92 DR. J. s. B O W E R B A N K O N SILICEO-FIBROUS S P O N G E S . [Jan. 28, rounded. Oscula small, slightly elevated, dispersed, very numerous. Pores inconspicuous, dispersed. Expansile dermal system-dermal membrane abundantly spiculous. Connecting spicula furcated, at-tenuato- patento-ternate, large and numerous; heads combining to form an irregular dermal network. Retentive spicula elongo-at-tenuato- stellate ; radii long and slender, rather numerous. Enveloping membrane of rigid skeleton-retentive spicula same as those of the dermal membrane, rather numerous. Skeleton-areas of reticulation round or oval, nearly equable in size ; fibre smooth, but umbonated at intervals ; umbones cylindrical, smooth, short; apices very nearly flat. Gemmules membranous, smooth, sub-globular. Colour, in the dried state, nut-brown. Hab. Madeira (H. N. Mason, Esq.). Examined in the dried state. The form of this sponge is that of a broad, irregularly sinuous, fan-shaped plate about 5 or 6 lines in thickness ; it is 7\ inches high, 12| inches wide, and 3f inches from back to front. On the latter, or inhalant surface, at about the middle of its width, there are three sinuously fan-shaped plates given off, the largest one from about midway between the base and top of the sponge, and two smaller ones from near the base ; the upper one has grown on a plane about parallel to that of the parent sponge, and its inhalant and exhalant surfaces aecord with those of that portion of the specimen. The two lower ones are projected from the large sponge at nearly right angles to its inhalant surface; and they have their inhalant surfaces on their upper sides, and their exhalant ones within the folds of their under ones. The sponge has evidently been sessile: there are no remains of an expanded base, but the attachment has apparently been near the middle of the basal portion of the specimen ; and it appears to have grown on a somewhat elevated piece of rock, as both of the extreme ends of the sponge project below the apparent plane of attachment. It is evidently an old and well-matured specimen, as it has numerous parasites attached to its inhalant surface, among which are several specimens of Vermetus, and three of what is apparently Caryophyllia Smithii, two of which are full-grown, and one of them has numerous parasites on its external surface. The condition of the sponge is excellent: all its organs are evidently in the state they were when it was taken alive from the sea; and it has apparently never undergone the deterioration of immersion in fresh water, as a quantity of salt remains in crystals on its surface. This specimen is therefore especially valuable as leading to a natural elucidation of the general characters of the singular and beautiful class of sponges to which it belongs. The oscula present no very striking characters ; the margins are slightly elevated and rounded ; many of them are completely closed, while others are only partially so ; and through the central orifice on these the enveloping membrane of the rigid skeleton, thickly studded |