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CHAPTER IV. 



RELATIONS OF MONTICULIPORA TO CH^TETES, STENOPORA, 

 TETRADIUM, CERAMOPORA, AND HETERODICTYA. 



We have now considered the structure of Hderopora, Blainv., 

 which, of all other types, is perhaps the one which presents the 

 closest general resemblance to certain forms of the Monti- 

 culiporoids. There are, however, various extinct organisms 

 which are so 'like Monticnlipora, either in appearance or in 

 actual conformation, or in both of these points, that it be- 

 comes necessary to examine how far this likeness is merely 

 superficial, and how far it may be based upon real affinity. 



Amongst the forms which require consideration in this con- 

 nection, the first place must be given to those which are com- 

 prised in the genus Chcetctes, Fischer (Oryct. de Gouv. de 

 Moscou, p. 159, 1837). These forms, in fact, are so similar 

 in most respects to the massive types of MonticiUipora (such 

 as M. undniata, Nich.), that it is only of late years that it has 

 been found possible to indicate definitely the grounds upon 

 which the latter genus might be separated with anything like 

 scientific precision from the former. The corallum in Chcstetes, 

 Fischer, is massive, composed of long irregularly prismatic 

 erect corallites, which are closely contiguous, and are com- 

 pletely amalgamated by means of their walls. The corallites 

 are all of one kind, both as regards size and internal struc- 

 ture, and open upon the surface by irregularly polygonal non- 

 oblique calices. There are no true septa, but the visceral 

 chambers are often partially divided by an imperfect longitu- 



