PREFACE. 



In 1904 Professor Henry Fairfield Osborn requested his assistant, the 

 present writer, to prepare a brief outHne of the history of the ordinal classi- 

 fication of the mammals for use in the Columbia University course on the 

 Evolution of the Mammalia. The preliminary sketch having raised so 

 many interesting problems relating to important principles, Professor 

 Osborn suggested the continuation of the work and very generously assumed 

 the chief expense of the investigation. Part II, dealing with the genetic 

 relations of the mammalian orders, was begun in 1907 and has been carried 

 on through the generosity of Professor Osborn and of Charles Gregory, 

 Esq., to whom the author's cordial acknowledgments are hereby tendered. 



Part I of the present work is offered not as an exhaustive history of the 

 subject but as a series of stages in the history of the ordinal classification of 

 the mammals, i. e., as an outline with sufficient details to make clear the 

 more important steps. 



The main interest of the writer has been centered, however, not so much 

 upon the history as upon the actual problem of ordinal classification, which 

 involves the theme discussed in Part II, namely, the evolution and genetic 

 interrelations of the mammalian orders. This problem in its manifold 

 aspects has long engaged the attention of the writer, especially in connection 

 with his duties as assistant and lecturer in the above mentioned university 

 course on recent and fossil mammals conducted by Professor Osborn. It 

 also continually recurs at the American Museum of Natural History, where 

 during the last decade the writer has had the privilege of working in the 

 midst of a wonderful collection of fossil vertebrates and of assistine: the 

 curator. Professor Osborn, in the monographic revision of the Titanotheres, 

 in the work on the 'Evolution of the Mammahan Molar Teeth' and in many 

 minor studies. The preparation, for the Osborn Library of Vertebrate 

 Palaeontology in the same Museum, of a subject-index including some thou- 

 sands of titles bearing on phylogeny, led into the literature of the subject; 

 while many stimulating discussions with Dr. W. D. Matthew, as well as 

 frequent reference to his numerous palaeontological contributions, have 

 placed the writer under the most lasting obligation. Observations relating 

 to the present work were also made in various other museums, especially 

 the British Museum (Natural History), the Field Museum of Natural History, 

 and the United States National Museum, where the officials extended every 

 courtesy. 



Realizing that phylogenetic speculation has often been rendered nuga- 

 tory by faulty reasoning even more than by insufficient material, the writer. 



