S UB- GENUS MONO TR YPA . 



189 



and by the presence of numerous clusters of corallites of from 

 one - fourth to nearly one - half larger size than the average. 

 These clusters of large calices can hardly be said to constitute 

 " monticules," in the strict sense of this term, as they are not, so 

 far as I have seen, conspicuously elevated above the surface. 

 There are, moreover, no small calices representing the mouths 

 of a series of interstitial corallites. 



As regards its internal structure, A/. pitlcJiclla, E. and H., 

 exhibits a remarkable simplicity. Thus, in tangential sections 

 (fig. 39, a) the corallites are seen to be regularly polygonal, in 



fi-i- 39- — Thin sections of a typical example of Monticulipora ptikhella, E. and 11., from the 

 Wenlock Limestone of Dudley. A, Part of a tangential section, enlarged eighteen 

 times, not passing through one of the groups of larger corallites ; B, Part of a longitud- 

 inal section, enlarged eighteen times. Both sections show that the wall oi the tubes has 

 the same structure as is characteristic oi 'Favositcs ; and the latter exhibits the remote 

 talndae which intersect tlie cavities of the tubes. 



contact at all points of their circumference, and provided with 

 moderately, but not excessively, thickened walls. Moreover, 

 there is never even an apparent fusion of the walls of con- 

 tiguous corallites, each tube retaining, on the contrary, its 

 own calcareous Investment as a distinct structure. Hence, the 

 wall which separates any two contiguous corallites is always 

 composed of two more or less distinct calcareous laminae, 

 separated by a thin and dark boundary line, which is often 

 conspicuously thickened at the points where three or more 

 tubes come In contact. These nodal thickenings sometimes 

 simulate thick-walled tubes, having a minute central cavity ; 



