8o 



THE GENUS MONTICULIPORA. 



dinal partition (or by two such partitions), resulting from the 

 uncompleted fission of the tubes into two young corallites. 

 Complete and remote tabulae are also present. It will be seen 

 from the above description how close is the general likeness 

 between ChcEtetes, Fischer, and the massive forms of Monti- 

 ailipora, D'Orb. ; and there are only two characters by which 

 the two groups may be satisfactorily differentiated. The most 

 important of these characters concerns the structure of the 

 walls of the corallites. Thus, in ChcBtetes it will be seen by 

 thin sections (fig. lo) that the walls of contiguous corallites 



Fig. lo. — A, Tangential section of Clnrtc'tcs radians, Fisclier (var.), from tlie Carboniferous 

 Limestone of Shap, Westmorland, enlarged i8 times; B, Vertical section of the same, 

 similarly enlarged. 



are invariably entirely and undistinguishably amalgamated or 

 fused with one another, all traces of the originally duplex 

 character of the partitions between neighbouring tubes being 

 now lost. It is true that there are species oi Monticnlipora 

 (as, for example, M. tnviida, Phill.) in which the walls of con- 

 tiguous tubes, as seen in tangential sections, are apparently 

 fused with one another ; but in such cases, we have seen that 

 the fusion is only apparent, since rough fractures always 

 expose the exterior of the tubes. In ChcBtetes, Fischer, on the 

 other hand, the amalgamation of the walls of the corallites is 

 shown to be real by the fact, long since pointed out by Lons- 

 dale (Geol. of Russ., vol i. p. 595, 1845), that rough fractures 

 expose the interior of the tubes. Mr Lonsdale at the same 

 time pointed out that the corallum in Chcrictcs increases fissi- 



