INTRODUCTION 3 



Professor A. S. Romer, and Dr. T. E. White, Museum of Comparative Zoology; Mr. C. M. Stern- 

 berg, National Museum of Canada; Professor E. H. Barbour and Mr. C. B. Schultz, Nebraska 

 State Museum; Professor W. B. Scott, the late Professor W. J. Sinclair, and Dr. G. L. Jepsen, 

 Princeton University; Dr. R. A. Stirton, University of California; Professor E. L. Packard, Oregon 

 State Agricultural College; Mr. C. W. Gilmore, United States National Museum; Professor C. 

 Forster Cooper, University Museum of Zoology, Cambridge University, England; Mr. R. Bruce 

 Horsfall, Washington, D. C; Professor E. C. Case, University of Michigan; and last but not least 

 Professor R. S. Lull and Mr. G. E. Lewis, Yale Peabody Museum. To Professor Lull especially 

 I wish to express my deep gratitude for his continued interest in this research since its inception and 

 for his many favors in connection therewith. 



Many of the drawings of the Yale specimens were made by the late Mr. Rudolf Weber, and 

 others, including the map of oreodont localities, by Mrs. Thaddeus Parr, formerly Miss Joy Stilson. 



I am greatly appreciative of the efforts of Miss Edna M. Gillette in the arduous task of typing 

 the rough manuscript, and of the kindly interest taken by Miss Clara M. LeVene in preparing it 

 for the printer and in seeing it through to publication. Messrs. P. A. Morris and F. C. Herpich 

 have aided greatly in photographic work; and the late Mr. Hugh Gibb, former Chief Preparator, 

 and Mr. F. W. Darby, the present chief, have cleaned and prepared the major portion of the 

 oreodont material, representing more than 2500 individuals, in the Marsh Collection of this 

 Museum. 



I wish also to thank the authorities of Yale University for making possible the publication of 

 this monograph, particularly under the present economic conditions. 



The meaning of abbreviations following the catalogue numbers of fossil specimens is as follows: 



A.M. — Amherst Museum, Amherst, Mass. 



A.M.N.H. — American Museum of Natural History, New York City. 



A.N.S.P. — Academy of Natural Sciences, Philadelphia, Pa. 



C.I.T. — California Institute of Technology, Pasadena, Calif. 



CM. — Carnegie Museum, Pittsburgh, Pa. 



M.C.Z. — Museum of Comparative Zoology, Cambridge, Mass. 



N.M.C.- — National Museum of Canada, Ottawa, Canada. 



N.S.M. — Nebraska State Museum, Lincoln, Neb. 



P.U.M. — Princeton University Museum, Princeton, N. J. 



U.C.M. — University of California Museum, Berkeley, Calif. 



U.O.M.- — University of Oregon Museum, Eugene, Ore. 



U.S.N. M. — United States National Museum, Washington, D. C. 



W.M. — Woodwardian Museum, Cambridge University, England. 



Y.P.M. — Yale Peabody Museum, New Haven, Conn. 



