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Show 358 DR. BOWERBANK ON ALCYONCELLUM SPECIOSUM. [Mar. 28, its structure can be distinctly made out. It consists of a central primary rectangulated hexradiate spiculum, the rays of which are short and stout, each furnished with three attenuating slightly radiating secondary spicula, which terminate acutely. See ' Philosophical Transactions,' 1858, p. 311, pl. 25. fig. 39, and ' Monograph of British Spongiadee,' vol. i. p. 55, pl. 8. fig. 189. The floricomo-hexradiate form is the most elegant and elaborately constructed spiculum I have ever seen. It consists of six short primary rectangulated central radii of equal length and diameter, the terminations of which are slightly expanded; and from each of these seven or more delicately formed petaloid secondary spicula radiate, but not in straight lines ; each curves slightly outward from its base, and then curves inward again until they nearly meet a little below their distal terminations ; and then again they curve outwards, so as to allow of the full expansion of their beautiful petaloid apices, the margins of which are delicately dentate, the whole structure simulating a beautiful flower. See 'Philosophical Transactions,' 1858, p. 312, pl. 26. figs. 3 and 4, and ' Monograph of British Spongiadee,' vol. i. p. 55, pl. 8. figs. 193 and 194. This form of spiculum is by no means rare in Alcyoncellum, but it is not frequently that a perfect one is obtained. I found them abundantly at the base of the terminal fringe of the sponge, and also at the bases of the diagonal ridges. I have never found any of these complicated forms of hexradiate spicula in any other sponges than the siliceo-fibrous ones. Alcyoncellum speciosum is not the only species of that genus known to science. There is an imperfect specimen of very delicate texture in the Museum of the Jardin des Plantes at Paris, from which I obtained the bifurcated rectangulated hexradiate form of spiculum represented in the 'Transactions of the Royal Society' for 1858, pl. 25. fig. 38, and 'Monograph of British Spongiadee,' vol. i. p. 55, pl. 8. fig. 188. This singular form is peculiar to that species ; and there are other forms of spicula and peculiarities of structure that unmis-takeably stamp it as a distinct species from A. speciosum. The large longitudinal radial lines of the skeleton do not all pass into the great terminal oscular area of the sponge; the greater portion of them terminate when they reach the marginal ring of the oscular area ; about one in every three or four pass the ring and form a portion of the reticulation of that great area. The distal termination of this sponge very closely resembles that of Alcyoncellum speciosum (Eu-jdectella aspergillum, Owen), figured in the ' Transactions of the Zoological Society,' vol. iii. p. 203. The primary or radial lines of the skeleton of this species are symmetrically parallel, and are nearly straight from the lower part of the sponge to its apex. The secondary or transverse series of skeleton-structures pass round its parietes within the primary or radial lines of the skeleton, at about right angles to them. This species is designated by Prof. Valenciennes Alcyoncellum corbicula. It was obtained in 80 fathoms off the Island of Bourbon. There is in the French Museum another specimen of Alcyoncellum, |