1 78 THE GENUS MONTTCULIPORA. 



or defined groups of either large or small corallites. Corallites 

 of one kind only, thin-walled, polygonal in shape, radiating 

 outwards from a basal point towards all parts of the surface. 

 Average diameter of the corallites from i-iooth to i-8oth inch, 

 a few small corallites being occasionally present, but there 

 being no interstitial tubuli. Tabulae almost obsolete, though 

 complete transverse partitions are occasionally developed in 

 certain regions, and generally at corresponding levels in con- 

 tiguous tubes. 



Obs. — This singular species has been excellently described 

 by Mr E. O. Ulrich {Joe. cit. supra), and I am able to corrob- 

 orate most of his observations from a careful investigation 

 of specimens for myself. Its small size, apparently free habit, 

 and nodulated surface (fig. 35, a) are w^ell-marked external 



Fig. 35. — MonticiiUpora irregularis, Ulrich, from the Cincinnati Group of Oliio. A, A speci- 

 men of the natural size ; B, Tangential section of the same, enlarged eighteen times ; c, 

 Vertical section of a few of the tul^ies of the same, similarly enlarged, showing a couple of 

 tabula;. 



characters, though, according to Ulrich, the surface may be 

 nearly smooth. In internal structure, this species belongs to 

 that group of Montiailipor^E which I have associated together 

 under the name of Mono try pa. In tangential sections (fig. 

 35, b) the corallites are seen to be of one kind only, tolerably 

 equal in point of size, thin-walled, polygonal, and wholly with- 

 out minute interstitial tubules of any kind. In longitudinal 

 sections (fig. 35, c) the tubes are seen to preserve the same 

 thin-walled character throughout, the walls being slightly 

 flexuous, but not sharply undulated. In the specimens that 



