146 THE GENUS MONTICULIPORA. 



corallites were primitively angular. In other tangential sec- 

 tions, again, the large corallites are bounded each by its own 

 thickened ring-like wall of sclerenchyma, and the small coral- 

 lites seem to have no distinct walls other than those which 

 separate them laterally from one another (fig. 26, b). The 

 laree corallites are never in contact for more than a limited 

 portion of their circumference, and all the interspaces between 

 them are filled with numerous small tubes, which differ from the 

 preceding both in size and in their very irregular though mostly 

 angular shape. Lastly, placed at the angles of junction of the 

 two sets of corallites above noted, or intercalated in the wall 

 between two contiguous tubes, we observe a great number of 

 the dark and dense sections of the " spiniform corallites." 

 These are oval or circular in shape, and, though a central 

 cavity cannot always be detected, they are undoubtedly the 

 sections of strong thick-walled tubes, with a minute median 

 cavity. The upper terminations of these upon the surface 

 can often be recognised as blunt projecting tubercles, placed 

 between contiguous calices, or, I think, sometimes as very 

 minute pore-like apertures. 



Transverse sections of the corallum show that the corallites 

 in the central part of their course (fig. 26, c) are polygonal in 

 shape, and are bounded by very thin and delicate walls. Their 

 size in this region appears to be very variable, numerous small 

 tubes appearing to be intercalated with the larger ones. This, 

 however, is a mere appearance, due to the fact that a section 

 of this kind cuts the different tubes at different levels above 

 their points of origin, and hence at points where their diameter 

 necessarily varies. In reality, the small interstitial corallites 

 do not seem to extend at all Into the axial region of the 

 branches. 



In longitudinal sections (fig. 26, d) the thin-walled corallites 

 of the axis of the branches are nearly, or sometimes quite, free 

 from tabulae ; but these structures are present in moderate 

 quantity in all the corallites in the outer thickened portion of 

 their course. They are always complete and horizontal, or but 



