266 Geological Society. 



unknown to him elsewhere. He added that the metapodium de- 

 scribed and figured by hiui in 1871, under the name of Acantho- 

 pholis platypus, may perhaps belong to the foot of Macrurosaurus, 

 in which case the latter would probably indicate a modification of 

 the Crocodilian type, and the individual to which the tail belonged 

 would have been about 30 feet long. 



December 20th, 1876.— Prof. P. Martin Duncan, M.B., F.R.S., 

 President, in the Chair. 



" On Pliaretrospongia Straliani, a fossil Holorhaphidote Sponge 

 from the Cambridge Coprolite Bed." By W. J. Sollas, Esq., B.A., 



r.G.s. 



The sponge described by the author, which had been long labelled 

 as a Chenendopora in the Woodwardian Museum at Cambridge, is a 

 fossilized siliceous sponge, characterized by an irregularly reticulate 

 fibrous skeleton, the fibres of which in the living state were composed 

 of a number of siliceous acerate spicules, lying parallel to each other 

 and to the sides of the fibre. These spicules are still sufficiently well 

 prese'rved to be figured and measiired individually, though they have 

 undergone a pseudomorphic change, by which their original com- 

 pcsition has been exchanged for a calcareous one. A similar re- 

 placement has occurred in the case of various species of Manon and 

 Porospongia ; and this fact is of great interest, as showing that the 

 extinct and anomalous order of Calcispongise, which these fossils 

 were supposed to indicate, has no necessarj- existence, since their 

 calcareous nature is a superimposed one, and their original struc- 

 ture agrees completely with that of existing siliceous forms, Pliaretro- 

 spongia Strahani itself exhibits close affinities to an undescribed 

 sponge now living in the Australian seas. 



" On the Remains of a large Crustacean, probably indicative of 

 a new species of Euryptcrus or allied genus {Eurypterus'^ Stevensoni), 

 from the Lower Carboniferous series (Cement-stone group) of Ber- 

 wickshire." By Robert Etheridge, jun., Esq., P.G.S. 



The fragmentary Crustacean-remains described in this paper are 

 referred by the author to a large species of Eiirypterus. They are 

 from a rather lower horizon in the Lower Carboniferous than that 

 from which Eurypterus Scoideri, Hibbert, was obtained. The animal 

 was probably twice the size of E. Scouleri. The remains consist of 

 large scale-like markings and marginal spines which once covered 

 the surface and bordered the head and the hinder edges of the 

 body-segments of a gigantic Crustacean, agreeing in general cha- 

 racters with the same parts in E. Scoideri, but differing in points 

 of detail. For the species, supposing it to be distinct, the author 

 proposes the name of E. Stevensoni, 



