9 



these nor their general arrangement in the sponge structure 

 is very much altered by growth ; hence the diminutive size 

 of the specimens examined by me, seeing that they appear 

 complete in all their parts, is not a sufficient reason foi- 

 this species remaining undescribed. At the next meeting 

 (15th April, 1869) of the Dublin Microscopical Club, after 

 Dr. Wallich had given me the small jDortions of the third 

 specimen above referred to, I exhibited a series of the sjjicules, 

 and stated it as my impression that the species belonged to 

 the section of sponges with silicco-fibrous skeleton and 

 hexradiate spicules called Vitrea by Wyville Thomson, In 

 this I was led astray by some siliceous network, like that 

 met with in Aphrocallistes which was entangled by the body 

 spicules of the little sponge, and I have now little hesitation 

 in referring it to the Corticatse of Oscar Schmidt, suggesting 

 that its affinities are to the genus Stellata, Sdt. I do this for 

 the following reasons : The number of stellate spicules in the 

 outer sarcode layer, which on some portions of the sponge 

 body are so tightly packed together as to form quite a hard 

 layer of silex ; the j^revalence of the large furcate ternate 

 sjaicules, Avhich are certainly most important in the structure 

 of the sponge mass — such spicules (No. 850 — 51 of Bower- 

 bank) are to be met with in Pachymatisma Listeri, Bowk. MS. 

 in Stellata discophora, Sdt., S.Helleri, Sdt., ;S^. mandllaris, Sdt., 

 and S. mucronata, Sdt. So far as I know these two forms of 

 spicules are only met within the same sponge when that sponge 

 belongs to the division Corticatae of O. Schmidt. The genus, 

 however, cannot be easily confounded with any of those 

 placed among the corticates. In some sjaecimens of mud, 

 taken from the same locality by Dr. Wallich, spicules (furcate 

 ternate) occur seven eighths of an inch in length, proving 

 the existence of some enormous specimens of some sponge of 

 this group. Professor Wyville Thomson, who was present at 

 the meeting of our Dublin Microscopical Club at which I ex- 

 hibited this species, stated that he had taken this species, or 

 at least one very closely allied to it, in the same ground that 

 he had taken Holtenia Carpenteri, W. Thomson. 



