82 THE GENUS MONTICULIPORA. 



corallites ; but these lamellae are produced intermittently 

 instead of uniformly, and a marked difference in structure is 

 thus caused. In those MonticuUporce, namely, which possess 

 thickened walls, rough fractures show that the walls of the 

 tubes are approximately smooth and even, while longitudinal 

 sections show that the thickening is uniformly augmented, 

 or remains nearly the same, from the point where the tubes 

 begin to bend outwards to their apertures (see PI. III., figs, i 

 e, I _/). On the other hand^ rough fractures of specimens of 

 Stenopora, Lonsd., show that the thickening of the tubes is 

 periodically effected, so that the outer surfaces of the tubes 

 exhibit a number of annulations or ring-like accretions, separ- 

 ated by intervening flat spaces (fig. ii, b and c). Some 

 species show this feature more conspicuously than others, 

 but almost all (all the typical species) show the same fact in 



^A/- 



Fig. 12. — Minute i.ixwz'iwx'i q{ Stcnopora Ho7i'sii,Kvc\\. (spec, nov.), from the Carboniferous 

 rocks of Redesdale, Northumberland. A, Part of a tangential section, enlarged 

 eighteen times. B, Another part of the same section, similarly enlarged, showing the 

 thick-walled corallites, with the numerous hollow spines in the wall. Some of the tubes 

 also show the pecuHar perforated tabulce. c, Part of the exterior of a transverse section, 

 where the tubes are cut longitudinally, enlarged eighteen times. This section shows the 

 peculiarly thickened moniliform wall which is characteristic of Sieitopora, some of the 

 tabula; being complete, while otliers show a central deficiency. (From the collection of 

 Richard Howse, Esq.) 



an even more striking and instructive manner when examined 

 by means of thin longitudinal sections (fig. 6, a, and fig. 12, 



