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INTRODUCTION 



The Ceratopsia Monograph published in 1907 summarized our knowledge of this interesting 

 group of dinosaurs up to about 1905, when the manuscript was completed. It was largely the work 

 of John Bell Hatcher, who actually collected much of the material upon which the monograph was 

 based. He utilized also the brief papers, mainly generic and specific descriptions, which had 

 appeared from time to rime under the authorship of Othniel C. Marsh, as well as the lithographic 

 plates and other illustrations which had been prepared under Professor Marsh's direction in antici- 

 pation of the monograph which the latter had planned to write. It was fitting, therefore, that the 

 names of Hatcher and Marsh should appear as co-authors of the completed work. When Mr. 

 Hatcher died in 1904, several important sections still remained to be finished, including those on 

 the phylogeny, taxonomy, distribution, habits, and environment of the Ceratopsia. He had said 

 that only two weeks more of work on the manuscript were needed, but no notes or other writings 

 regarding the unfinished sections could be found among his effects, and therefore, Professor Osborn, 

 who had succeeded Marsh as the Vertebrate Paleontologist of the United States Geological Survey, 

 assigned to the present author the task of completing the manuscript and seeing it through the press. 



Since that time more material has come to light, largely from the older formations, such as the 

 Belly River and Edmonton of Canada and the Cretaceous of Mongolia, and while new species have 

 been described from these formations, the time seems ripe once more to coordinate and amplify our 

 knowledge of this amazing group in the light of these discoveries. Some problems of generic 

 identity cannot even now be solved in view of the inadequacy of material, especially that from the 

 Judith River of Montana upon which the genera Monoclonius Cope and Ceratops Marsh were 

 based; thus, it cannot now be determined definitely whether or not these genera are synonymous 

 with the better known Belly River forms of equivalent age. Only more extended and detailed 

 collecting of plesiotypes in the Judith River formation can solve these problems in any degree of 

 finality. Enough is known, however, to warrant this study. 



The research upon which this publication is based was rendered possible primarily through the 

 research funds granted to the Sterling Chair of Paleontology at Yale University, which not only 

 made possible the travel incident to the study of widely separated collections, but also provided for 

 a research assistant to aid in the work. 



I very deeply appreciate the generous aid given by the various museums and especially by the 

 several individuals connected with each of them, all of whom were exceedingly generous of free 

 access to the collections as well as of personal aid and advice. My especial acknowledgments are 

 due to Mr. Charles W. Gilmore of the United States National Museum for facilities for study, for 

 photographs and other illustrations, and for the reading and friendly criticism of the manuscript. I 

 am also deeply indebted to Messrs. Barnum Brown and Walter Granger of the American Museum 

 of Natural History for generous aid on several occasions as well as for extraordinary privileges in 

 connection with the rich collections of ceratopsian material. Several photographs were especially 

 taken and others freely furnished for this work. To the authorities of Yale University I am 

 grateful for providing funds for the purchase of the Monoclonius (Centrosaurus) skeleton which 

 forms the basis of our morphologic work and restoration, and to the members of the Peabody 

 Museum staff who aided in the preparation, and in rendering permanent the results of our labors. 



Two of the Canadian Museums have shown the friendliest courtesy, the Royal Ontario Museum 

 of Palaeontology, in Toronto, through Professor Parks, and the National Museum of Canada, in 

 Ottawa, through Messrs. Kindle and Charles M. Sternberg, who granted not only access to the col- 

 lections but the use of several photographs which adorn this volume. The latter institution also 

 aided us in securing through exchange a fine skull of Chasmosaurus belli, and gave the privilege of 

 publishing the interesting restoration of that genus by L. S. Russell. 



My gratitude is also due to President C. C. O'Harra of the South Dakota State School of 

 Mines for measurements and photographs of his Triceratops skull, to Mr. H. H. Lane of the 



