50 NORTH AMERICAN INDEX FOSSILS. 



J Epitheca normally wanting in basal portion. 



XXVI. Duncanella. 



\ Epitheca complete (except when denuded) 22. 



22. Septa radial in calyx, rarely uniting or twisted at the 



center, fossula well developed x. 



x. Septa smooth, tabulae well developed. 



(Compare Streplelasma.) II. Zaphrentis. 

 x. Septa carinate. 



40. {Heliophyllum corniculum). 

 22. Septa radial, twisted or united in the center, fossula 

 rarely developed. 



(Compare Zaphrentis.) I. Strepielas?na, 

 22. Septa radial, not twisted at the center. Fossula absent 



xx. 



xx. Septa smooth XIV. Cyathophyllum. 



xx. Septa carinated XVI. Heliophyllitm. 



22. Septa arranged in a bilateral manner xxx. 



xxx. Strong fossula to which the adjoining septa 



converge IV. Aulacophylluiii. 



xxx. Fossula occupied by large cardinal septum, 

 septa uniting into four groups. 



I . Streptelasma profundum. 



2. Coral cylindrical, the tetrameral arrangement obscure... ^. 



33. Fossula and tabulae well developed xxxx. 



xxxx. Septa twisted at the center and with the tabulae 



elevated tent-like V. Acrophyllum. 



xxxx. Septa not twisted or faintly so, sometimes not 



quite reaching center II. Zaphrentis. 



33. Fossula weak or absent, tabulae in central portion only. 



xxxxx. Septa carinated, fossula occasionally devel- 

 oped XVI. Heliophyllum. 



xxxxx. Septa smooth. y. 



y. Septa reaching to center, fossula absent or 

 partly developed and faint. 



XIV. Cyathophyllum. 

 y. Septa not fully reaching center, fossula present 



and faint XV. Campophyllum. 



a. Septa well developed, not reaching to center bb. 



bb. Septa, short strong vertical ridges, tabulae well developed. 



VII. Pycnostylus (single branch). 

 bb. Septa normal, reaching part way to center 3. 



3. Fossula present (rarely absent) 44- 



44. Cylindrical, with numerous often sharp constrictions 

 and well developed tabulae III. Amplexus. 



44. Cylindrical without constrictions, well developed tabu- 

 lae onto which the septa extend to within a short dis- 

 tance of center II. Zaphrentis. 



44. Conico-cylindrical not constricted, often abruptly bent, 



tabulse in cent nl vesicular tissue in peripheral area. 



XV. Ca mpoph yllu m . 



