Paleontology of the Cincinnati Group. 193 



two forms described b)- Ulrich as Amplexopora cingulata and 

 A. robiistata seem to be only this species. The following 

 notes enable the student to judge : 



Aiuplcxopora cingit/ata Ulrich. Corallum ramose, dividing 

 dichotomously at irregular intervals ; branches cylindrical or 

 sub-cylindrical; varying from three to seven lines in diam- 

 eter ; surface smooth and destitute of monticules, but with 

 groups of from seven to fifteen cells, slightly larger than the 

 average, varying from «V to ^V inch in diameter, the ordinary 

 cells being t,V inch in diameter; calices, when well preserved, 

 sub-polygonal, with moderately thin walls and with small 

 granules ; but, as usually found, calices rounded and walls 

 comparatively thick and smooth; in tangential section cells 

 of one kind only ; original polj^gonal walls readily recog- 

 nized, but the internal cavities more or less rounded by sec- 

 ondary deposits of sclerenchyma ; line of junction between 

 walls occupied by numerous small spiniform tubuli ; longitu- 

 dinal sections show corallites with remote horizontal tabulae, 

 and thin walls in the axial region, but as they approach the 

 surface, the walls become thickened and the tabulae are more 

 numerous; a few funnel-shaped tabulae occur in some of the 

 tubes. Beyond having more numerous funnel-shaped tabulae, 

 more conspicuous spiniform tubuli, and slightly thicker walls 

 A. robusta is identical with A. cingulata. It would be a diffi- 

 cult matter indeed to separate a large suite of specimens upon 

 these characters; and while, perhaps, they might merit 

 varietal rank, they should not, according to our views, be 

 regarded as sufficient to constitute distinct species. 



20. — M. AFFiNis Ulrich (sp.), 1890. 



Corallum irregularly dendroid, seldom branching, fifteen 

 mm. thick ; surface smooth, with hardly-appreciable clusters 

 of cells slightly larger than the average ; apertures sub- 

 polygonal ; corallites polygonal, thin-walled; tabulae com- 

 plete and horizontal, twice as numerous in the small as in the 

 large cells and with a few infundibular tabuhe scattered pro- 

 miscuously; spiniform tubuli conspicuous, usually between 

 the corallites, occasionally situated at the angles. (Geol. 

 Sur. Illinois, vol. 8, 1890, p. 450, as Amplexopora ajffiyiis.) 



Locality. — Wilmington, Illinois. 



