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Show 1869.] DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 339 cylindrical spicula, which had every appearance of belonging to the dermal membrane. With this indication, I mounted all the remaining fragments of the sponge in m y possession, and I was fortunate enough to find a small piece of dermal membrane crowded with these minute spicula, and having several of the foliato-peltate spicula attached to its under surface, thus leaving no doubt remaining regarding the presence and nature of the expansile dermal membrane of this singular and beautiful species of siliceo-fibrous sponge (Pl. X X V . fig. 4). The specific characters of the sponge, although few in number, combined with the peculiar and very striking ones derivable from the skeleton, which I have described in detail in treating of the genus, enable us readily to distinguish the species from any other siliceo-fibrous sponge. The cidarate prehensile fibres at the base of the sponge are remarkably curious organs; they proceed at right angles from the crowns of the reversed basal arches, and terminate in stout and acute cones ; and intermediate between their origins and terminations each has a ring of stout round bosses admirably fitting them first to penetrate the fleshy external coat of the coral, and, when once inserted, to securely maintain their position. There is no mistaking the office of these curious and beautiful organs and the admirable adaptation to the nature of the basis on which they were destined to be parasitic (Pl. X X V . fig. 2). The forms of the foliato-peltate heads of the connecting spicula are exceedingly various, passing through every gradation from simple circular plates to the most elaborate foliations. On some of the heads of the detached spicula groups of three or four of the minute fusiform-cylindrical retentive and defensive spicula were attached ; but on some parts of the small fragment of the dermal membrane they were so numerous and so crowded together as to render their individual forms perfectly undistinguishable. The membrane is of a dark brown colour, and can scarcely be said to be transparent, in consequence of the number of the spicula and the density of the sarcode in which they are imbedded. I measured some of the largest and smallest of them, and found their average length not to exceed -^-g inch. The greatest diameter of a large one was -g-j^j-^ inch (Pl. X X V . fig. 5). In these minute spicula the central canal was visible with a linear power of 666 throughout the whole of their lengths, and it occupied about one-sixth of the greatest diameter, so that its own diameter could not exceed about -g-g-Jp-yjj m c n ' FARREA OCCA, Bowerbank. Sponge massive, pedicelled 1 Surface even ? minutely hispid ? Oscula and pores unknown. Dermis furnished with a quadrilateral smooth siliceo-fibrous network, armed at the angles oppositely, externally and internally, with short imbricated conical spicular defences. Skeleton-rete irregularly quadrilateral; fibre cylindrical, more or less minutely tuberculated or spined. Tension-spicula biternate, spiculated biternate, and furcated spiculated biternate, |
