FKOM THE INTEKIOR OOLITE. 551 



Correlation with Continental Species. — In the following table the 

 Inferior-Oolite species here described are correlated with those of 

 Qnenstedt from the Jurassic strata of various continental localities : — 



Correlation of Sponges here described ivith those of Continental 

 Deposits. 



Inferior Oolite, England. Jurassic, Continental. 



Eniploca ovata Siphonia ovata, White Jura d, Heuberge. 



Mastodictymn Whidborni. 



Leptophragrna fragile Textispongia foliata, White Jura (3, Muhlheirn. 



Plectospyris elegans. 

 P. major. 

 Calathiscus variolatus. 



Platychonia elegans Spongites vagans, White Jura S. 



Perouella Metabronnii Scyphia Bronnii, White Jura e. 



Myrineciuru biretiforrue ... S. biretiformis, White Jura 8. 



From this it appears that of the nine species described from 

 our Inferior Oolite, no less than five are closely allied to, if not, 

 indeed, identical with, species occurring on other higher horizons 

 on the continent. 



Depth at which the Sponges lived. — The Inferior Oolite is a shelly 

 limestone, generally admitted to have been formed under shallow- 

 water conditions. The character of its molluscan remains and 

 corals, and the presence of oolitic grains, are all in favour of the 

 generally received belief. 



The sponges we have described — Hexactinellids, Lithistids, and 

 Pharetrones — all occur associated together in the same deposits, 

 and were all alike inhabitants of shallow water. 



From this it follows that the accepted belief in the deep-water 

 character of the ancient Hexactinellids, founded on our incomplete 

 knowledge of their existing bathymetrical distribution, is erroneous ; 

 and next, either that the recent sponges of this group will be found 

 to extend into much shallower water than has hitherto been known 

 to be the case, or that the family has in course of time largely 

 changed its habits. The former alternative appears to be the right 



to be in favour of these and similar sponges having had originally a siliceous 

 composition, though at the same time I felt and expressed serious doubts on 

 the point. The more exact information lately afforded us by Dr. Hinde (Ann. 

 & Mag. Nat. Hist. ser. 5, vol. x. p. 185) on the structure of their fibre, together 

 with Mr. Carter's announcement of tbe discovery of a living calcareous sponge 

 displaying a similar structure to that described by Hinde (Ann. & Mag. JNat. 

 Hist. Jan. 1883), leads me to suspect that full proof of the affinities of these 

 fossil forms with the Calcispongia? will not be long delayed. 



With regard to Pharetrospongia, however, no fresh argument of any weight 

 has been alleged against its having had originally a siliceous composition. Most 

 of Dr. Hinde's arguments on this head bave been fully answered on the zoolo- 

 logical side by Mr. Carter ; and with regard to the mineralogical question 

 raised by Dr. Hinde, I may point out that it overlooks the very heterogeneous 

 origin of the Cambridge fossils, and that Pharetrospongia has evidently been 

 exposed to very different mineral conditions from the Ventriculites of the deposit ; 

 in a word, the Cambridge Greensand is the riddlings of several deposits, and 

 that from which Pharetrospongia was derived was of a very different character 

 from that which furnished the Ventriculites. 



Q.J.G.S. No. 156. 2 b 



