54 THE GENUS AIONTICULIPORA. 



visceral chamber, but this is never more than a quite occa- 

 sional thing ; and though I cannot satisfactorily explain what 

 these projections may be, there is no reason to regard them as 

 septa. Lastly, Mr Ulrich has separated from Moiiticidipora 

 certain forms for which he has constituted the new eenus 

 Atactopora (Journ. Cincinn. Soc. Nat, Hist., 1879), upon the 

 ground that they possess pseudo-septa. I have only examined 

 one of these forms — viz., Monticulipora{?') Ortoiii, Nich. ; but 

 in its case I find the apparent pseudo-septa to be mere inward 

 protrusions of the wall, due (as in AI. implicata, Ulrich) to 

 the development of " spiniform corallites." 



VII. Epithecal and Opercular Strticttircs. — The only remain- 

 ing point in connection with the general structure of the Mon- 

 ticuliporoids which deserves a few words of notice concerns 

 the development of an epitheca and of opercula to the corallites. 

 An epitheca is, as a rule, only present in those types which pos- 

 sess a discoidal form of corallum ; and in these the concave or 

 flat under surface is normally protected by a thicker or thinner 

 epithecal plate, which is usually concentrically wrinkled, and 

 is sometimes marked with fine radiating strise. In other cases, 

 though no epitheca be present, the mouths of the corallites are 

 liable to become closed, when maturity is reached, by a delicate 

 calcareous membrane which constitutes an opercular growth of 

 variable and partial development. Sometimes, when " mac- 

 ulse," or clusters of small tubes, are present, these alone 

 appear to become sealed up in this way. In other cases (as 

 not uncommonly in the allied group of the FisttLlipord), the 

 small tubes in general become covered by a thin and uniformly 

 diffused opercular membrane, the mouths of the large tubes 

 alone remaining open ; though I cannot say that I have ever 

 noticed this condition of parts in any typical species of JMonti- 

 cnlipora. Lastly, there are cases (as in M. O' Ncalli, James) 

 where certain of the calices become ultimately closed by the 

 development in the mouth of each of a thin calcareous lid or 

 operculum (PI. III., fig. ^i^). This phenomenon is precisely 



