io6 THE GENUS MONTICULIPORA. 



thin-walled and polygonal, arid interspersed amongst them are 

 the small angular or sub-angular apertures of the interstitial 

 corallites (PI. VI. fig. \c), the number of which varies much 

 in different specimens, and which are sometimes almost want- 

 ing. The surface always exhibits " monticules," though the 

 extent to which these are developed varies greatly in different 

 examples. In some forms (PI. VI. fig. \a) the monticules are 

 low and rounded, and, though quite recognisable, are certainly 

 not striking features in the corallum. In other specimens, 

 proved by microscopical examination to be identical with the 

 preceding, the monticules are conical, or at other times elon- 

 gated and compressed, in either case rising conspicuously above 

 the general surface (PI. VI. fig. \b). 



As regards the minute structure, the appearances presented 

 by tangential sections vary according to the depth below the 

 surface at which these may be taken. In sections passing just 

 below the actual surface (PI. VI. figs. \d and i^-), the corallites 

 are seen to be moderately thick-walled, and divisible into a 

 series of larg^e tubes and one of small tubes. The laro-e coral- 

 lites are surrounded each by its own ring of laminated scleren- 

 chyma, but they are nevertheless apparently fused with one 

 another at the points where they come in contact. Their form 

 is sub-polygonal, and all the interspaces left between them are 

 occupied by much smaller angular or sub-angular corallites. 

 Intercalated in the thickened walls of the corallites there is, 

 also, a quite considerable number of minute circular, darkly- 

 outlined hollow tubules or " spiniform corallites," the termina- 

 tions of which have not been observed by me. 



In tangential sections taken at a slightly deeper level than 

 the preceding (PI. VI. fig. i/), the appearances to be observed 

 are somewhat different to those above described. The walls 

 of the corallites are now reduced in thickness, causing their 

 cavities to be proportionately increased in size. Hence the 

 large corallites appear to be of somewhat larger size, and 

 more strikingly polygonal, while the dimensions of the small 

 tubes are similarly increased, and the number of the " spini- 



