TABLE OF CONTENTS 



Terminology 



Summary ......... 



Importance of the Question of Primary Septa 

 Theories of Previous Writers .... 

 Conclusions ........ 



The Two Theories of the Origin of Hexacoralla 

 Theory of Common Ancestry .... 

 Theory of Direct Descent ..... 



Tests of the Theory of Direct Descent from Tetra 



CORALLA 



Geological Occurrence 



So-called Paleozoic Hexacoralla 



Palccacis and its Relation to the Tabulata 

 The Genus Calostylis and its Position in the Classi 

 fication ....... 



Other Peculiar Forms Sometimes Called Hexa- 

 coralla ....... 



Summary of "Paleozoic Hexacoralla" . 

 First Fossil Corals 



Mackenzia of the Middle Cambrian 



First Coral Fauna ...... 



Probable Ancestry of the Tetracoralla . 

 Dominance and Decline of Various Coral Stocks 

 Evolutionary Trends in Tetracoralla 



Plasticity of Tetracoralla in the Late Paleozoic 

 The Columella as an Example of Variability 

 Morphological Significance 

 Steps in Development 

 Summary ...... 



Bibliography 



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