1807.] DR. BOWERBANK ON ALCYONCELLUM SPECIOSUM. 357 



code of the sponge. They consist of attenuated rectangulated hex- 

 radiate spicula and of rectanguhited triradiate ones. 



There are two well-characterized descriptions of the attenuated 

 rectangulated hexradiate spicula. The first has the radii compara- 

 tively short and very stout ; this form is exceedingly protean, the 

 full complement of rays being rarely developed. They vary from 

 the form of an inequiacerate spiculum to the completely developed 

 hexradiate one, with intermediate incomplete forms in every imagi- 

 nable variety. They are dispersed abundantly on the outer surface 

 of the skeleton-tissues, especially near the bases of the diagonal 

 ridges. The varieties of this form of spiculum are described in de- 

 tail in the 'Philosophical Transactions of the Royal Society' for 

 1858, p. 309, pi. 25. figs. 24 to 33, and in 'Monograph of British 

 Spongiadae,' vol. i, p. 52, pi. 7. figs. 174 to 183. 



The second form of attenuated rectangulated hexradiate spiculum 

 is much more constant in its development, an incomplete one being 

 of rare occurrence ; their proportions are more equable and slender 

 than those of the first description. Their radii are comparatively 

 long and slender ; and the basal ray of the axial portion is frequently 

 very much elongated, and has its termination somewhat clavate and 

 more or less spinous, while the distal and lateral rays are usually 

 acute and without spines. These spicula in situ are grouped together 

 in considerable numbers in the interstitial spaces of the skeleton, 

 their positions being coincident, and their axes frequently very nearly 

 touch each other. Their office is apparently the same as those of 

 the larger and stouter description of the same form — that of afford- 

 ing points of attachment to the interstitial membranes, so as to pro- 

 duce innumerable surfaces for the multiplication of the nutrimental 

 membranes of the sponge. They are described and figured in the 

 'Philosophical Transactions' for 1858, p. 310, pi. 25. fig. 34, and 

 in 'Monograph of British Spongiadse,' vol. i. p. 260, pi. 7. fig. 184. 



The attenuated rectangulated triradiate spicula are not the trira- 

 diate stage of development of a hexradiate spiculum ; their form is 

 a normal one, and their proportions are distinctly different from either 

 of the hexradiate ones. Sometimes the radii are attenuated and 

 smooth ; but usually the apices of the rays are more or less spinous, 

 and occasionally somewhat clavate. They are not so numerous as 

 the hexradiate forms. They are described and figured in the ' Phi- 

 losophical Transactions' for 1858, p. 313, pi. 26. fig. 7, and in 

 ' Monograph of British Spongiadse,' vol. i. p. 260, pi. 9. fig. 198. 



The sarcode of this sponge affords two of the most elegant and 

 complicated forms of spicula with which we are acquainted — the tri- 

 furcated attenuato-hexradiate, and the floricomo-hexradiate form. 

 The first is not peculiar to AlcyonceUum, as it is also found abun- 

 dantly in the sarcode of Dactylocuhjx pumicea and other siliceo- 

 fibrous sponges. The latter I have never found in any other sponge 

 than the one under consideration. 



The trifurcated attenuato-hexradiate stellate spiculum, with a 

 power not exceeding four or five hundred linear, appears as a simple 

 multiradiate spiculum ; but viewed with a power of about 1000 linear 



