358 DR. BOWEUBANK ON ALCYONCELLUM SPECIOSUM. [Mar. 28, 



its structure can be distinctly made out. It consists of a central 

 primary rectangulated liexradiate spiculum, the rays of which are 

 short and stout, each furnished with three attenuating shghtly radia- 

 tino- secondary spicula, which terminate acutely. See ' Philosophical 

 Transactions,' 1858, p. 31 1, pi. 25. fig. 39, and ' Monograph of Bri- 

 tish Spongiadge,' vol. i. p. 55, pi. 8. fig. 189. 



The floricomo-hexradiate form is the most elegant and elaborately 

 constructed spiculum I have ever seen. It consists of six short pri- 

 mary 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, 

 hut 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 simula- 

 ting a beautiful flower. See 'Philosophical Transactions,' 1858, 

 p. 312, pi. 26. figs. 3 and 4, and ' Monograph of British Spongiadse,' 

 vol. i. p. 55, pi. 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 liexradiate 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 ob- 

 tained the bifurcated rectangulated hcxradiate form of spiculum re- 

 presented in the ' Transactions of the Royal Society ' for 1858, pi. 25. 

 fig. 38, and 'Monograph of British Spongiadse,' vol. i. p. 55, pi. 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 

 Sjjonge very closely resembles that of Alcyoncellum speciosum (Eu- 

 plectella asperyillum, 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 secon- 

 dary or transverse series of skeleton-structures pass round its parie- 

 tes 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, 



