1867.] DR. BOWERBANK ON ALCYONCELLUM SPECIOSUM. 353 



I proposed the following as an aaiended description of the generic 

 characters : — 



Sponge fistulate ; fistula single, without a massire base. Ske- 

 leton — 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 enabled^to examine the structure of the skeleton more minutelv 

 than I could venture to do that of the rare and beautiful specimen 

 in the possession of the late I\Ir. Cuming ; and I have ascertained 

 that the skeleton is not composed of fasciculi of spicula, as at that 

 time T 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. Ske- 

 leton 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 ])laced it, and 

 associates it with Dactylocahjv 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 Pohjmastia, 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 beavitiful forms of inter- 

 stitial spicula so abundant \\\ Alcijoncellum are entirely absent in the 

 corresponding portions of the structure oi Pohjmastia. I will not 

 repeat my reasons for differing in opinion from Prof. Owen regard- 

 ing the alteration he has proposed of Quoy and Gaimard's generic 

 name o{ Alcj/oncenian to that of Euj^lectella, in his paper on that 

 subject, published in the ' Transactions of the Zoological Society of 

 London,' vol. iii. pt. 2. p. 203, pi. 13, as I have fully discussed that 

 portion of my subject in my paper on the " Anatomy and Physiologv 

 of the Spongiadse " (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 asperyillum and 

 JH. 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, wlio in 

 185(3 obliged me with the loan of the sponge for several weeks that 



Proc. Zool. Soc— 1807, No. XXIII. 



