GENERAL AND COMPARATIVE STRUCTURE. 43 



as well. At any rate, I feel sure that the difficulty of deter- 

 mining this point in the case of the smaller species is so great 

 that I am right in the formerly expressed opinion that this 

 character alone should not be accepted as an adequate generic 

 distinction between ChcEtetes and Monticulipora (Quart. Journ. 

 Geol. Soc, vol. XXX. p. 500). 



We have at present no evidence as to the existence of 

 " mural pores " in any species of MontiaUipora ; and there is 

 every reason to believe that the walls are really imperforate. 

 So many species of the genus, at any rate, have now been exa- 

 mined by means of thin sections, that it seems very unlikely 

 that mural pores should have escaped notice, had such aper- 

 tures in the walls really existed. This, therefore, is a point 

 upon which the purely negative evidence may be legitimately 

 accepted as of great weight. At the same time, there are some 

 considerations which preclude our regarding the imperforate 

 condition of the walls of the Monticuliporce as a point settled 

 absolutely beyond dispute or doubt. Thus, we find species 

 of the singular genus Stcnopora, Lonsd., in which mural pores 

 can be certainly shown to be present, so that we can hardly 

 suppose any member of the same genus to be without them ; 

 and yet there are well-marked species of Stenopora in which 

 the closest microscopic examination has hitherto failed to reveal 

 the existence of any apertures in the walls. There are also 

 forms (such as Favosites Bowerbanki, E. and H. sp.) which 

 have all the general aspect and structure of the Monticuli- 

 poroids, and which can only be separated from Monticulipora 

 upon the ground that they are known to possess minute mural 

 pores. Upon the whole, therefore, while I think the imper- 

 forate condition of the walls of the Monticuliporoids to be as 

 certain as anything established by merely negative evidence 

 can be, I am not prepared to assert absolutely that mural pores 

 are totally wanting. It is certain, however, that if mural pores 

 do exist in the Monticuliporoids, they must be much more 

 minute, and much more irregular in their distribution, than is 

 the case with these openings in the typical Favositidcc. 



