230 PEor. n. a. nicholsot^ and de, j. mueie ow the 



flinty skeleton, were really horny. Nor have our own researches 

 upon the minute structure of the Stromatoporoids at all served 

 to corroborate Von Bosen's view — that these organisms are 

 com230sed of any thing to which the name of '''' fibres " could be 

 properly applied. 



Secondly, the principal observer who of late years has taken 

 the view that the Stromatoporoids are Siliceous Sponges is Mr. 

 Sollas (Ann. & Mag. Nat. Hist, ser. 4, -vol. xix. p. 23), who 

 places Stromatojpora concentrica among the Vitreohexactinellidce. 

 Mr. Sollas, however, has subsequently (Quart. Journ. Geol. Soc. 

 vol. xxxiii. p. 824) stated that he only believes some of the Stro- 

 matoporoids to be of this nature, and that others fall into different 

 groups. As Mr. Sollas has not yet published any of the evidence 

 upon which his views are based, it is, of course, impossible for 

 us to express any opinion in the matter. Two observations only 

 appear to be justifiable : — in the first place, that much will depend 

 upon the question whether the form which Mr. Sollas calls S. 

 concentrica (and which, if it be the S. concentrica of Goldfuss, is 

 really identical with S. jpolymorplia, Groldf.) be truly referable to 

 Stromatopora itself ; and, secondly, that all the evidence derivable 

 from the very extensive series of forms which have passed under 

 our hands is, as we have previously stated at greater length, to 

 our minds absolutely conclusive as to the original calcareous 

 constitution of the Stromatoj^oroids. We should add, however, 

 that we have not had the opportunity of examining personally 

 the original types of Stromatopora concentrica, Goldf. (^=S. poly- 

 morpha, Goldfuss), and have only had the opportunity of study- 

 ing it by means of the excellent figures and descriptions of Von 

 E-osen and Goldfuss. It is possible, therefore, that this form, 

 the type of Stromatopora itself, will prove to be a Hexactinellid 

 Sponge. In that case, however, we should simply have to with- 

 draw all the forms which we have been considering in this 

 memoir under the name of " Stromatoporoids," from any associa- 

 tion with S. polymorpJia, Goldf. ; for we are quite satisfied that, 

 whatever the true nature of these may be, they are not Hexacti- 

 nellidce *. 



* Since our MS. has been lying in the printers' hands, one of us (H. A. 

 Nicholson) has visited the Eifel, and has both collected a large series of Stroma- 

 toporoids from this classical district and examined those in the Bonn Museum. 

 The result of this has been to satisfy us that the Stromatoporoids of the " Eifler- 

 Kalk " are in no respect fundamentally different from those of the Devonian of 

 Devonshire and North America. Further remarks ou this head must be left to 

 another opportunity. 



