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Show 1867.] DR. BOWERBANK ON ALCYONCELLU1VI SPECIOSUM. 353 I proposed the following as an amended description of the generic characters: - Sponge fistulate ; fistula single, without a massive base. Skeleton- primary fasciculi radiating from the base in parallel straight or slightly spiral lines; secondary fasciculi at right angles to the primary ones. Oscula congregated, with or without a marginal boundary to their area. I have lately acquired two fine specimens of the sponge, and have been enabledato examine the structure of the skeleton more minutely than I could venture to do that of the rare and beautiful specimen in the possession of the late Mr. Cuming ; and I have ascertained that the skeleton is not composed of fasciculi of spicula, as at that time I believed it to be, but that it is a regular and very delicate siliceo-fibrous structure. This fact necessitates a further correction of the generic characters, which I propose to be as follows :- Sponge fistulate; fistula single, without a massive base. Skeleton siliceo-fibrous; primary lines radiating from the base in parallel straight or slightly spiral lines; secondary lines at right angles to the primary ones. Oscula congregated, with or without a marginal boundary to their area. The siliceo-fibrous structure of the skeleton necessarily removes this genus from the group of genera with which I had placed it, and associates it with Dactylocalyx and other siliceo-fibrous sponges; and this association will be seen, when we consider the specific characters of the sponge, to be in very close accordance with the peculiar interstitial and other remarkable spicula of that beautiful group of sponges. The siliceo-fibrous structure of Alcyoncellum decidedly separates this genus from Polymastia, in which the primary and secondary lines of the skeleton are invariably composed of elongate fasciculi of spicula; and although in the latter genus the general arrangement of the skeleton-structures are so similar to those of the former that slightly magnified drawings of the one could scarcely be distinguished from those of the other, the singularly beautiful forms of interstitial spicula so abundant in Alcyoncellum are entirely absent in the corresponding portions of the structure of Polymastia. I will not repeat my reasons for differing in opinion from Prof. Owen regarding the alteration he has proposed of Quoy and Gaimard's generic name of Alcyoncellum to that of Euqdectella, in his paper on that subject, published in the 'Transactions of the Zoological Society of London,' vol. iii. pt. 2. p. 203, pl. 13, as I have fully discussed that portion of my subject in my paper on the " Anatomy and Physiology of the Spongiadee" (Phil. Trans. Roy. Soc. 1862, p. 1102). Having thus rectified the errors in the descriptions of the genus, I shall proceed to consider the specific,characters of the species Al-cyonellum speciosum, Quoy et Gaimard (Euplectella aspergillum and E. cucumer, Owen) ; and in doing so I may state that my knowledge of the beautiful structures I shall have to describe was derived from the first specimen, imported by the late Mr. Hugh Cuming, who in 1856 obliged me with the loan of the sponge for several weeks that PROC. ZOOL. Soc-1867, No. XXIII. |