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Show 1867.] DR. BOWERBANK ON ALCYONCELLUM SPECIOSUM. 351 apical portion of the organ to the distal portions of the area ; while in a smaller one from the same sponge there were only twenty-eight; so that it appears that no two of these organs are furnished with precisely the same number of motive filaments, and that they increase in number as the organ increases in age and size. The fibres on the apices of the oscula of Mr. Lee's specimen, when immersed in water only, were not above half the diameter of those which had been operated upon with caustic potass. The inner membrane of the corium in Mr. Lee's specimen is very thin ; in a portion of it removed and immersed in water for examination there were numerous minute lentiform cells and a considerable number of gemmular bodies, identical in size, form, and structure with those with which we are so familiar in Halichondroid sponges, and which also occur abundantly in the genus Dactylocalyx; but I could not detect any traces of fibro-cellular organs. The more repeatedly and closely we examine the curious protuberant organs on the corium the more strongly we are confirmed in the opinion that every part of Hyalonema mirabile is of a purely spongeous nature. The discrepancy in the numbers of the supposed tentacula beneath the apices of the oscular organs (no two appearing to have anything like the same number of fibres in their circular series), the invariable attachment of both their basal and apical terminations to their respective membranes, their complete immersion in the parietes of the oscular organs, the firm and solid structure of the fibres themselves, and the undoubted keratose structure of the mass on which they are imbedded, all concur in proving them to be anything rather than polypiferous organs. On the contrary, in numerous specimens of Zoanthus sulcatus 1 in my possession, dispersed in patches on the surface of Desmacidon Jeffreysii from Shetland, the structure of the polypidom is widely different from that of the protuberant organs of Hyalonema. In Zoanthus it is simply formed of grains of sand cemented by coagulable lymph, as in the sand-tubes of Terebella, and, like them, rapidly decomposing after the death of the animal. In the polypidoms of the Zoanthus on Desmacidon Jeffreysii no radiating fibres like those in Hyalonema are to be found, nor could I detect any distinct remains of the polypes that once inhabited them. 7. O n Alcyoncellum speciosum. By J. S. B O W E R B A N K , LL.D., F.R.S., F.Z.S. &c. ALCYONCELLUM SPECIOSUM, Quoy et Gaimard. Euplectella aspergillum, Owen, Trans. Zool. Soc. iii. p. 203. E. cucumer, Owen, Trans. Linn. Soc. London, xxii. p. 117, pl. 21. A considerable number of this beautiful sponge have recently been imported, and its natural history has again been the subject of much interest among zoologists. The first notice of its existence occurs |