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Show 1876.] DR. J. S. BOWERBANK ON THE SPONGIAD.E. 771 sponge represented by figure 4. In the specimen represented by figure 5 (Plate LXXIX.) it is apparently the same as in that represented by figure 4 ; but it has not so completely involved the verticillate species, the margins of the plates of which are still uncovered. For the most perfect specimen of these enveloped species of sponges I am indebted to m y late friend Dean Buckland, who could not imagine what it could be, unless it represented an animal allied to the Trilobites, the apparent smooth head and striated body having impreseed that idea upon his mind ; but on m y pointing out to him a small spot on the middle of the smooth end of the mass, which I conjectured might be the basal end of the pedicle, he presented it to me that I might, if possible, clear up our doubts regarding its structure. I accordingly marked it for cutting in such a direction as to make a section of the supposed pedicle, as well as through the centre of the plates of the sponge ; and the result was the production of the specimen represented by figure 4, Plate LXXIX., completely confirming the ideas regarding the nature of these fossils that had previously arisen from m y examinations and comparisons of the fossils with the singular verticillate sponges from the Australian seas. Very few of these enveloped specimens of verticillate sponges are in so perfect a state of preservation as that represented by figure 4. By far the greater number of them appear to have been in a very young state when thus enveloped by the parasitical sponge; and their size has been still further curtailed, and their true form obscured in the fossil state, by the destructive attrition that they have undergone in the diluvial gravel, in which they are by no means scarce. I have in m y own collection 33 specimens of various sizes and states of preservation, among which there is one that is evidently the termination of a fossil specimen quite as large as the recent one figured, the greatest breadth of the spongeous plates being two and a quarter inches. These fossils, from the general character of the siliceous matter in which they are embedded, probably belong to the chalk formation ; but I have never yet obtained one from that deposit, and therefore the formation whence they are derived cannot be positively determined. It is a remarkable circumstance that these diluvial fossils should have their nearest analogues among the recent Australian sponges, and that the same may be said of the fossil fruits of the London-clav formation. OPLITOSPONGIA FUCOIDES, sp. nov. (Plate LXXX.) Sponge pedicellate ; pedicle long, slender, smooth, ramifying and expanding into numerous compressed fucoideal branches disposed in nearly the same plane, so as to be rudely fan-shaped. Surface uneven, minutely hispid. Oscula simple, minute, dispersed. Pores inconspicuous. Dermis irregularly fibro-reticulate; rete abundantly punctiunculate, sparingly spiculous. Dermal membrane abundantly spiculous ; spicula spinulate, smaller, shorter, and more attenuated than those of the skeleton. Skeleton-fibres smooth, |
