PREFACE. 



This work is the result of studies begun at the University of 

 Michigan in 191 3 under Professor E. C. Case, and continued at 

 Yale Universit}'^ during 1915 and 1916 under Professor Charles 

 Schuchert; in 1916 it was submitted to the Faculty of the 

 Graduate School of Yale University as a dissertation in candi- 

 dacy for the degree of Doctor of Philosophy. Free access to 

 both the Michigan and Yale collections has given the writer the 

 opportunity of examining a large number of Paleozoic corals. 

 In addition to the Yale material, there have been received from 

 Doctor R. G. Carruthers of Edinburgh specimens of Hexaphyllia, 

 Heterophyllia, and Holocystis; from Doctor Gerhard Holm of 

 Stockholm, specimens of Calostylis; from Doctor F. X. Schaffer 

 of the Royal Natural History Museum in Vienna, a number of 

 Hexacoralla from the Alpine Trias ; from Doctor R. S. Bassler, 

 specimens of Calostylis and Palcoacis from the United States 

 National Museum collections ; from Professor Case, the type 

 specimens of Leptopora typa and Conopoterium effusum; from 

 Professor R. R. Rowley of Louisiana, Missouri, specimens of 

 Leptopora and Conopoterium. For all of these loans the writer's 

 thanks are due. 



The writer is indebted to Professor Alexander Petrunkevitch 

 of the Zoological Department of Yale University for assistance 

 in making the photographs which accompany this paper; and 

 to Doctor T. AV. Vaughan of the United States Geological 

 Survey, Professors W. R. Coe and A. E. Verrill of Yale, and 

 Professor T. C. Brown of Bryn Mawr for discussing with him 

 the problem of coral phylogeny. To Professor Case, who first 

 suggested the corals to him as a fruitful field for study, and to 

 Professor Schuchert, whose constant guidance and kindly criti- 

 cism have been of great assistance in the preparation of the 

 paper, the writer hereby acknowledges his indebtedness. 



While the question of the relationship of the Paleozoic and 

 later corals cannot perhaps be definitely settled until a sequence 

 of coral faunas is established representing Permian and Lower 

 Triassic times, still geological occurrence is a factor that cannot 

 be lightly set aside in forming an opinion on the subject. Dur- 



