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Show 304 DR. J. S. BOWERBANK ON THE SPONGIAD^E. [May 5, Hab. South Seas. Examined in the dried state. The specimen figured is the only one that I have seen. I obtained it by purchase from a dealer, along with other sponges and specimens of Oculina rosea from the South Seas. The external characters of this sponge at once separate it from the nearly allied species H. ventriculoides. The outer surface exhibits but very faint traces of the primary radial lines of the skeleton that are so prominently exhibited in H. ventriculoides ; and on the inner surface the radial lines are so much depressed as to be scarcely termed elevated. The retiform dermis is abundantly supplied with arenaceous particles of nearly uniform size. The oscula are nearly all obsolete ; the few seen by the aid of a lens of two inches focus were minute simple orifices. The pores are readily to be seen by the aid of the lens ; they are very numerous on the outer or inhalant surface of the sponge, and are equally dispersed on all parts of its surface. The primary lines of the skeleton are abundantly arenulous, the grains of sand usually forming a single series very equable in size. The secondary skeleton-fibres rarely ever contain sand particles ; but a few small fragments of siliceous spicula are occasionally seen in some of them, and they always appear to be disposed in accordance with the axis of the fibre. This species appears to be closely allied to Mantell's Spongus Townsendi, p. 164, tab. xvi. fig. 9, ' Geology of Sussex.' The only portion of the ventriculite sponge in Mantell's figure that is visible is the extremely thin distal margin of the sponge ; and in this character it closely resembles our recent specimen. I have not been fortunate enough to meet with a good specimen of Mantell's S. Townsendi; but I have a portion of what is apparently one of them completely immersed in flint; and, as far as can be judged by a polished section at right angles to its surfaces, it is very similar in its structure to our recent specimen of sponge, and there is a total absence of the sinuous outline that would be exhibited by a similar section of a specimen of Mantell's Fentriculites radiatus. DESCRIPTION OF THE PLATES. PLATE XLVI. Geodia carinata, Bowerbank. Fig. 1 represents the type specimen of the species surrounding the remains of the stem of a large Oorgonia, natural size. 2. Three of the multiangulated cylindrical spicula from the dermal m e m brane, magnified 530 linear. 3. One of the attenuato-spinulate skeleton-spicula, magnified 123 linear. 4. A fully developed aborescent subsphero-stellate retentive spiculum from the interstitial membranes, magnified 530 linear. 5 represents one of the ovaria, magnified 250 linear. Geodia imperfecta, Bowerbank. Fig. 6 represents the type specimen, parasitical on Ocidina rosea, natural size. 7. A n average-sized subfusiformi-acerate skeleton-spiculum, magnified 80 linear. 8,9, 10, 11. Varieties of the undeveloped or malformed attenuato-patento-ternate connecting spicula, magnified 80 linear. |