Vi : 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 subject up to the 
year 1901 and the important writings since published are cited in the text of this 
monograph. 
WasHINGTON, November 20, 1907. 
