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Show 342 DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [May 13, in considerable numbers around portions of the skeleton-fibres ; and it is probable that the dermal and interstitial membranes were abundantly furnished with them (Pl. X X I V . figs. 2, 3, 4). This remarkable sponge is in its skeleton-structures exactly like those of a Veronyia, its siliceous nature constituting the only essential difference. The specimen is undoubtedly by far the most valuable of the two represented in the plate in the ' Transactions of the Linnean Society.' In conclusion, I must return m y best thanks to m y friend Dr. A . Farre for the repeated opportunities I have had of closely examining its structure. PURISIPHONIA, Bowerbank. Skeleton siliceo-fibrous, reticulate, unsymmetrical; fibres composed of concentric layers of solid silex, with a continuous central canal. This genus is intermediate in its structure between Dactylocalyx, Stutchbury, and Farrea, Bowerbank. Like the latter, its fibres are continuously canaliculated ; but it has not anything approaching the angulated symmetrical arrangement of its skeleton-fibres; on the contrary, it very closely simulates the mode of the distribution of the fibres that prevail in Dactylocalyx. The central canals in the fibres of the species of Purisiphonia on which the genus is founded occupy from about one-fifth to one-third of the entire diameter of the fibre; they are straight and uniform in their own diameter, and have little or no enlargements at their junctions with each other. The reticulations of the skeleton are frequently extremely close, so that the areas do not exceed, or sometimes even equal, the diameters of the fibres bounding them. PURISIPHONIA CLARKEI, Bowerbank. Sponge fistulous, branching; surface of rigid skeleton even. Oscula simple, dispersed over the inner surface of the fistulse. Dermal structures unknown. Skeleton stout, closely reticulated. Interstitial cavities furnished with rectangulated hexradiate spicula. Hab. Wollumbilla, Queensland, Australia (Dr. Clarke). Fossil. There is m u c h greater difficulty in the specific description of a fossil sponge than of a recent one, as a considerable portion of the most decisive specific characters are usually absent, in consequence of the decomposition of the softer parts of the organization previously to fossilization ; and this is doubtless the case with the specimen under consideration ; but although thus deprived of the use of many valuable descriptive characters, there are sufficient remaining to enable us to securely determine its specific identity. It is difficult to say what has been the correct form of the specimen in its unmutilated state; but, judging by its present condition, it has originally been a large fistulous sponge, giving off fistular branches at irregular intervals. The large fistular body of the sponge has been split longitudinally, and a portion 4 inches in length, and of about half of the tube of the sponge, remains, and from the |
