116 BRITISH STROMATOPOROIDS. 



genus is therefore a valid one. To mention only the most recent writers on this 

 subject, this view has been maintained by Dr. August Bargatzky (' Die Stromato- 

 poren des rheinischen Devons,' 1881), and by Dr. Carl Riemann (" Die Kalke des 

 Taubensteins bei Wetzlar und ihre Fauna," ' Neues Jahrb. fur Min. Geol. und 

 Pal.,' 1884). Dr. Bargatzky, indeed, not only supports the validity of the genus 

 Caunopora, Phill., but founds the new genus Diapora for certain "Caunopora" 

 colonies in which the " ground-mass " exhibits radial pillars and concentric 

 larninas, instead of being simply reticulate, as it is in the true " Caunopora" of 

 Phillips, as understood by Bargatzky. 



For my own part, I must frankly admit that my views have always been in 

 favour of the validity of " Caunopora" as comprising independent organisms. In 

 pursuit of the present inquiry, however, I have had to make a microscopic exami- 

 nation of a very extensive series of specimens of " Caunopora " and " Diapora " from 

 the Devonian Rocks of Devonshire, Germany, France, and North America, and I 

 have been driven to the conclusion that these names do not correspond with 

 generic divisions, but that the fossils so called are in reality occasional conditions 

 of certain particular species of Stromatoporoids. This does not, however, neces- 

 sarily involve the acceptance of the " commensal theory " of " Caunopora" of which 

 Roemer is the originator, and in which he has been followed by Carter and 

 Champernowne — the theory, namely, that the fossils upon which " Caunopora " is 

 based are really the result of the commensalism of certain types of Stromatoporoids 

 with certain types of Corals. The problem as to the precise nature of the tubes 

 of " Caunopora " has, indeed, proved to be one of such extreme difficulty that it will 

 be best to give here a kind of summary of the ai'guments for and against the 

 different views which might be taken as to this subject, without committing myself 

 finally to any one theory as opposed to the others. In so doing there are three 

 principal theories which I shall pass in review, viz. : — (1) The view that " Caunopora" 

 and " Diapora" are genera of Stromatoporoids; (2) the theory of Roemer that 

 " Caunopora " and "Diapora" are the result of the commensalism of certain Stroma- 

 poroids with certain Corals ; and (3) the theory that the " tubes " of" Caunopora " 

 and " Diapora " belong to the organism in which they are found, but that they repre- 

 sent structures which are only developed in certain colonies or in certain indivi- 

 duals, and that these names, therefore, merely indicate a state of certain 

 Stromatoporoids. 



I. Caunopora and Diapora as Genera. 



The theory that Caunopora, Phill., and Diapora, Barg., are genera of Stromato- 

 poroids may, in the light of presently known facts, be dismissed with comparative 

 brevity. So long as it remained unknown with what particular types of Stromato- 



