194 SPONGES. 



occur abundantly from the Silurian* epoch down to the present time, and 

 when it is remembered that a narrow dredge passing over the deep sea 

 bed of the Atlantic for a few miles, forming a kind of path-way through 

 this vast area like a garden walk, comes up literally crammed with the 

 remains of siliceous sponges, it not only gives us some idea of their 

 plentifulness in this dark and dismal abode, but accounts for the immense 

 quantity of their debris in some of the Mesozoic Strata, and the influence 

 which their Silica when set free has undoubtedly exerted minerally 

 over the composition of these strata. 



Brief as tbis description of the Spongida is, it has been thought 

 desirable to premise something of the kind, before giving the following : — 



List or Sponges dredged by the Birmingham Natural History and 

 Microscopical Society, Falmouth Excursion, 1879, depth 15 — 50 

 fathoms. 

 N.B. — Unless otherwise mentioned, the names of all the following 



sponges are those under which they appear, and are illustrated in 



Dr. Bowerbank's "British Spongiadae," Vol. III., 1874, as this is the 



work most likely to be generally possessed in England. 



Bhaphidonemata. 



l.—Chalina inornata (B. S., PI. 83., figs. 12-16, not that of p. 358.) 

 Three specimens. 



Echinonemata. 



2. — Microciona plumosa, Br. olim. Hymeniacidon plumosa, Bk. (B. S., 

 PI. 26, figs. 7-13.) Obs. — This is Johnston's Halichondria plumosa, and 

 although it sometimes may appear under a laminiform growth like 

 Microciona, its habit is to be massive and erect. The equianchorate 

 flesh spicule is "angulate," (B. S., Vol. 1, PI. 6, fig. 143,) not naviculiform 

 as in Microciona atrosanguinea, Bk. ; and although the red colour of both 

 species may be alike, the spiculation generally, not only differs, but the 

 pungent (? iodine) odour of Halichondria plumosa is quite sufficient to 

 detect it even blindfolded. 



Holorhaphidota. 



3. — Halichondria panicea (B. S., Pis. 39 and 40.) Several speci- 

 mens. 



4:.—Isodictya Normani (B. S., PI. 56, figs. 1-5.) One specimen. Obs. — 

 I can see very little specific difference between this and I. fucorum and 

 I. Alderi, illustrated in the same plate. 



5. — None. 



* In coarse of the discussion which followed the reading of the above paper, 

 Mr. W. J. Harrison remarked that the sponges had even a higher known antiquity 

 than had been assigned to them by Mr. Carter, for their fossil remains had been 

 discovered in rocks of Cambrian age. The researches of Dr. Hick3 (see " Quart. 

 Joorn. Geol. Soc") had brought to light lour species of sponges from tne Menevian 

 Beds of St. David's, in South Wales, and even from strata l.FOOft. lower (corres- 

 ponding to the Longmynd rocks) he had obtained two specirs, which had been 

 named Protospongia Jenestrata and P. major. Hence, as the organic origin of the 

 Laurentian Eozoon was still disputed, the sponges were entitled to rank among the 

 oldest known fossils. 



