IV PREFACE. 



R. Weber, of the same museum. Most of the wash-drawings that appear in the 

 plates were produced by Mr. Erwin C. Christman of the American Museum of 

 Natural History. 



The thanks of the author are due, first of all, to the Carnegie Institution of 

 Washington for the support it has given him in the preparation of this monograph; 

 in the next place, to Professor H. F. Osborn, of the American Museum of Natural 

 History, New York, for the opportunity to use the materials in that museum; 

 finally', to all the persons and institutions above mentioned and others who have 

 contributed in any way to whatever there may be of value in this work. 



It is not believed to be necessary to append a list of the papers and memoirs 

 consulted in the preparation of this monograph; inasmuch as the writer's Bibliog- 

 raphy and Catalogue of the Fossil Vertebrata of North America, Bulletin 179 of 

 the United States Geological Survey, records the literature of the sub|ect up to the 

 year 1901 and the important writings since published are cited in the text of this 

 monograph. 



Washington, November 20, 1907. 



