XIY FOREWORD. 



Section 2. Definitions and relationships. General definition of the group and general mor- 

 phology or anatomy as compared with that of other groups. 



Section 3. Geological data. General geological conditions and stratigraphic succession of 

 the stages and horizons in which the remains of the group are found. 



Section 4. Systematic revision. Systematic revision of the types of each taxonomic rank 

 in the chronological order of their original description, including (1) the parts constituting the 

 type and cotype, if any; (2) the locality and geological level so far as recorded; (3) the present 

 location and museum number of the type; (4) the author's original definitions and descrip- 

 tions of the type or types. This method of treatment allows little room for originality, but 

 it is the prerequisite of the monographic research of section 5 ; it disposes once for all of trouble- 

 some questions of priority, and if accurately and impartially done is final and furnishes an 

 invaluable reference work for all future research. This section should precede the original 

 morphologic and taxonomic section, instead of following it as arranged by Marsh in his mono- 

 graph on the Dinocerata. 



Section 5. Morphology and taxonomy. In this section the animals are rearranged in their 

 natural classification according to the observations and conclusions of the authors; they are 

 treated successively, according to their geological sequence, if ascertained, or if not, according 

 to the sequence indicated by increasing specialization of structure; the orders, families, gen- 

 era, and species are redefined if necessary; valid forms are distinguished; the synonymous 

 names are eliminated. The entire structure and functions of different parts of the body of 

 each type are considered and carefully discussed. 



It is evident that section 5 differs from section 4 in containing a large amount of original 

 matter, consisting of the author's conclusions, which are subject to modification by the opinions 

 of others and by future discovery. 



Section 6. Phylogeny and oiology. In this final original section the phylogenetic history 

 of the group is traced from its probable origin. The phylogenetic relationships of the animals 

 to one another and to other forms are now rendered clearer through the full preceding discus- 

 sion of their anatomy. Their environment is considered, their habits, their external form and 

 appearance, and finally the rise and fall of the group, and the probable causes of its extinction. 



Having thus determined upon this general plan of treatment for these monographs, it 

 remained to decide how they could be most carefully and expeditiously prepared. The expe- 

 rience of my predecessor made it apparent that a division of labor was absolutely essential. 

 I therefore invited Mr. F. A. Lucas to undertake the Stegosauria, and Mr. J. B. Hatcher to 

 undertake the Ceratopsia, I myself to undertake the Sauropoda and Brontotheriida?. 



There could be no question as to either the justice or the wisdom of assigning the present 

 monograph on the Ceratopsia to John Bell Hatcher. His discovery and collection of these animals 

 was, with the exception of his explorations in Patagonia, the greatest single achievement of 

 his remarkable life. Under Professor Marsh's direction, he had devoted four most arduous 

 years to bringing together the magnificent specimens of these horned dinosaurs for the United 

 States Geological Survey and National Museum and for the Yale University Museum. 



Mr. Hatcher was delighted to undertake the difficult piece of comparison and research 

 involved in a complete restudy of the Ceratopsia, and entered upon it in Jufy, 1902, with his 

 usual ardor and thoroughness. Except during brief intermissions in the field he worked at 

 this task full time almost daily for two years in addition to discharging his duties during other 

 hours as curator of vertebrate paleontology in the Carnegie Museum. Examining the types, 

 supervising the further preparation of the fossils, visiting all the museums, preparing a very 

 large number of additional drawings, carefully writing and revising his text — this was his 

 occupation for two years. Finally, he was on the very threshold of the pleasantest portion 

 of the work, the conclusion of the systematic and morphological section, and in sight of the 

 rearrangement, classification, and philosophical treatment of the group, when he was stricken 

 down on July 3, 1904. 



