GENERA OF FAVOSITID&. 165 



wards the axis of the visceral chamber. Mural pores large, 

 oval, arranged in longitudinal rows between the septa, and 

 separated by intervals as a rule much less than their own 

 diameter. Tabulae numerous, complete, flexuous, often uniting 

 with one another, generally about eight in the space of two 

 lines. 



Obs. The above description is based upon specimens from 

 the Cincinnati group of Ohio, as regards its essential features ; 

 though, as regards one or two characters, I have had in view 

 examples from the corresponding formation in Canada, which 

 I believe to belong to the same species. Thus, in the Canadian 

 examples, the tubes are more liable to show a circular form, 

 and to be at times partially separated near their mouths, than 

 is the case with those from Ohio. On the other hand, the 

 latter usually show polygonal and closely-contiguous tubes. 

 Having fully discussed the structure of this species in dealing 

 with the genus, I need only add that it would seem probable 

 that the Columnopora (Houghtonia) Httronica of Rominger 

 (Foss. Cor. of Michigan, p. 17, PL III., figs. 3 and 4) is really 

 identical with Columnopora cribriformis, Nich. As, however, 

 Dr Rominger's description differs in some important respects 

 from that of the type-species as here given, and as I have not 

 had the opportunity of examining the specimens upon which 

 his account is based, I shall in the meanwhile consider it as a 

 separate species. 



Formation and Locality. In the Cincinnati formation, South- 

 western Ohio. Rare in the corresponding formation (Hudson 

 River group) of the Credit River, Ontario. 



Genus AR^EOPORA, Nich. and Eth. jun., 1879. 

 (Fig. 24.) 



Gen. Char. Corallum massive, Favositiform, of polygonal 

 corallites, which radiate outwards from an imaginary axis to 

 open upon the free surface of the colony. Under surface 



