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Show 770 DR. J. s. BOWERBANK ON T H E SPONGIADJE. [NOV. 21, appear to be Australian. I have other specimens in my possession of very much greater dimensions, and among them some rather exceeding 3 feet in length, having plates exceeding 5 inches in diameter; and one of the largest, at about the middle of the series of plates, divides, and each stem supports a separate series of plates. The plates of these sponges are not projected from the pedicles at right angles to them; they always assume a more or less ascending direction, so that they form an ascending series of rather irregularly shaped shallow cups. The dermal rete is rather more strongly produced than the skeleton-structures beneath it, and it is quite irregular in form. Very little of the dermal membrane remains ; the small fragments that were apparent were furnished with a few dispersed spicula. The skeleton-structure is rather slender and delicate. The primary lines vary to some extent in their diameter; and in some there are a greater number of spicula than in others. The secondary lines of the skeleton are also variable in the number of their spicula and in their mode of disposition. These singularly formed sponges are interesting, not only on their own account, but also for affording us an explanation of a remarkable series of fossils that are not unfrequently found in a more or less perfect condition in our diluvial gravel, and which have been conjectured by some geologists to have been allied to the Trilobites, while others have believed them to have been Pennatulae. I had longitudinal sections made and polished of several of these fossils ; and on examining them by direct light with a power of 100 linear I found in some of them traces of sponge-structure, but so indistinct as to afford very unsatisfactory evidence of their real nature ; but in some, as in the specimen represented by figure 4, Plate LXXIX., I found unmistakable proofs of a central axial column ; and in this specimen the included sponge was of a nut-brown colour, while the enveloping one was of a milk-white; and the two were cemented together by an intervening thin stratum of semitransparent silex, without any indication of sponge-tissue in it. This peculiarity is strictly in accordance with the natural laws of the Spongiadee, as when two living specimens of the same species touch each other, they unite and become as one sponge; but, however closely two specimens of different species of sponge may envelop each other, they never unite and become one inseparable mass, however closely they may be allied to each other in anatomical structure. In each section of the brown verticillate fossil sponge represented by figure 4, when viewed by direct light with a power of 175 linear, there were unmistakable evidences of a very delicate spongeous reticulation ; while in the white enveloping sponge traces of a very different character of reticulate spongeous structure could be distinctly seen between the leaves of the verticillate sponge. In the latter sponge there are numerous specimens of foraminated shells of various species, such as are frequently found embedded in recent sponges of a similarly complicated structure. The enveloping sponge does not appear to be always of the same species as the |