ii2 NORTH AMERICAN INDEX FOSSILS. 



e. Branches hollow, with irregularly expanding and contracting axial 



tube ; diaphragms few or absent, interspaces with vesicles. 



XXII. Chilotrypa. 

 e. Branches solid ; diaphragms present XVI. Crepipora. 



6. Zoarium bifoliate f. 



f. Lunarium prominent, hood like XIX. Ceramophylla. 



f. Lunarium not prominent, interspaces with vesicles. 



XXIV. Meekopora. 

 III. TREPOSTOMATA. Zoaria compound, with walls of zooecia thickened in the 

 outer region with numerous diaphragms or cystiphragms, and monticules or mac- 

 ulae on surface. Tubes separating upon fracture C. 



C. Cystiphragms always in outer region, acanthopores mostly abundant 6*. 



6* Mesopores few or wanting 7. 



7. Mesopores scattered or absent, acanthopores small and numerous, 



cystiphragms throughout, walls granulose.. XXVI. Monticulipora. 



7. Mesopores few, in clusters, acanthopores generally developed, cysti- 



phragms in outer region only XXVIII. Homotrypa. 



6* Mesopores numerous 8. 



8. Apertures irregularly petaloid XXVII. Atactoporella. 



8. Apertures rounded to polygonal g. 



g. Massive conical or discoidal usually free, with wrinkled epitheca 



on under side dd. 



dd. Zocecia with cystiphragms XXIX. Prasopora. 



dd. Zocecia with oblique or funnel-shaped diaphragms (modified 



cystiphragm) XXXI. Mesotrypa. 



g. Zoarium a thin expansion with epitheca XXX. Aspidopora. 



C Diaphragms instead of cystiphragms in outer region of zocecial tubes J 



\ Mesopores few or absent 7*. 



7* Acanthopores present 9. 



9. A can thopores large h. 



h. Diaphragms of zocecia few or wanting ee. 



ee. Erect, ramose, diaphragms few... XXXVI. Dekayia. 

 ee. Ramose, slender diaphragms practically absent, acan- 

 thopores sometimes wanting.. XXXVIII. Bylhopora. 



h. Diaphragms often numerous ff. 



ff. Zocecia with well-marked division line between walls. 



XXXII. Amplexopora. 



ff. Zooecia with periodically thickened walls in mature 



region XL. Stenopora. 



9. Acanthopores small, few, or wanting i. 



i. Zoceciawith well-marked divisionline. XXXII. Amplexopora. 



i. Zocecia with thick walls XXXIX. Eridotrypa. 



i. Bifoliate with flexuous mesotheca XXXIV. Petalolrypa. 



7* Acanthopores absent 10. 



io. Zocecia with well-marked division line.. XXXIII. Monotrypella. 



10. Zocecia thick-walled, many diaphragms.. XXXIX. Eridotrypa. 

 X Mesopores numerous 8*. 



8* Zoarium ramose, sometimes with anastomosing branches II. 



11. Diaphragms numerous j. 



j. Acanthopores of two sets, large and small. XXXV. Dekayella. 



