GENERA OF CH.ETETIDyE AND MONTICULIPORID^. 277 



sets of corallites, which must, during life, have been inhabited 

 by different sets of zooids. The existence of minute tubes, 

 either scattered among the larger ones, or aggregated in 

 special groups, has, of course, been long known to palaeontolo- 

 gists ; but these have, for the most part, been regarded either 

 as merely young corallites or as " coenenchymal tubuli." 

 Similarly, palaeontologists have long known that certain species 

 oi Monticulipora {e.g., M. pttlckella, E. and H.) exhibit groups 

 of large tubes distributed at intervals among those of average 

 size ; but the true import of these appearances hardly admitted 

 of recognition save by the light of Mr Moseley's researches 

 upon the living Heliopora. I have, however, now thoroughly 

 satisfied myself that the corallum in Alontictilipora is truly 

 dimorphic, quite as genuinely as in Heliopora or Hcliolites. 

 One set of corallites may be much reduced in number, or may 

 undergo much modification, but I believe that the existence of 

 two different kinds of tubes can almost always be demon- 

 strated ; and the importance of this fact, from a theoretical 

 point of view, can hardly be over-estimated. The relations of 

 the two sets of tubes to one another vary extremely in different 

 forms of Monticulipora, and I shall employ these variations as 

 the basis of a provisional classification of the multitudinous 

 forms included under this head. I shall, therefore, postpone a 

 further consideration of this subject till I come to speak of the 

 different groups which may be comprehended under the general 

 name of Monticulipora. 



I must, however, briefly notice here certain peculiar super- 

 ficial features In different species of Monticulipora, which are 

 in reality due to the dimorphic condition of the corallum just 

 spoken of. The appearances presented by the calices vary 

 according as we have to deal with a form in which the walls of 

 the corallites remain permanently more or less thin throughout 

 their entire extent, or with one In which the tubes undergo a 

 marked thickening before reaching the surface. In the former 

 of these cases the calices are polygonal and sharp-edged, and 

 thus resemble the calices in a Favosites of the normal type. In 



