GENERA OF CH^ETETID^E AND MONTICULIPORID^E. 279 



therefore, be any doubt but that these structures are primitively 

 hollow, though their central cavities often appear to become 

 filled up by a secondary deposit of sclerenchyma, as growth 



Fig- 36. a, Fragment of Monticitli- Fig. 37. Portion of a tangential section of Monti- 



para moniliformis, Nich., from 

 the Hamilton Group of Ontario, 

 enlarged ; b, Portion of surface of 

 same enlarged further ; <r, Portion 

 of surface of M. Barrandi, Nich., 

 enlarged. 



cttlipora moniliformis, Nich., taken just below 

 the surface, showing the intracalicine spines, 

 enlarged fifty times. From the Hamilton 

 Group of Ontario. 



proceeds. In this primordial hollo wness of the spines is to be 

 found, I believe, the real clue to their nature ; and I can hardly 

 doubt that instead of being merely appendages of the corallum, 

 they are truly of the nature of peculiarly modified zooids or coral- 

 lites. The correctness of this view is most readily recognised 

 when we come to examine thin sections of those forms which have 

 usually been separated from Monticulipora under the generic 

 title of Dekayia, E. and H. In these cases (PI. XV., figs, i b, 

 i c} the supposed spines are very much reduced in number, but 

 they are quite exceptionally developed, and they constitute the 

 well-known surface-projections, which are characteristic of the 

 genus. These surface-projections certainly seem to be imper- 

 forate at their apices, but thin sections demonstrate conclusively 

 that they are hollow internally, and that they only differ from 

 the ordinary corallites in the greater thickness and density of 

 their walls and the apparent absence of tabulae. I do not myself 

 entertain any doubt as to these being a peculiar form of coral- 

 lites doubtless tenanted in life by peculiar zooids the mouths 



