PREFACE 



The present volume is the first of a series of Monographs designed 

 to make known to science the Extinct Vertebrate Life of North America. 

 In the investigation of this subject, the writer has spent the past ten years, 

 much of it in the field, collecting, with no little hardship and danger, the 

 material for study, and the rest in working out the characters and affinities 

 of the ancient forms of life thus discovered. 



During this decade, the field work, extending from the Missouri Eiver 

 to the Pacific Coast, has so predominated, as the subject unfolded, that a 

 plan of gradual publication became a necessity. The more important 

 discoveries were briefly announced soon after they were made, but only 

 where the specimens on which they were based admitted of accurate 

 determination. The principal characters of the new groups were next 

 worked out systematically, and published, with figures of the more 

 important parts. "When the investigation of a group is completed, the 

 results, with full descriptions and illustrations, will be brought together in 

 a monograph. This system has been carried out with the Odontomithes, 

 and will be continued with the other groups. The investigation of several 

 of these is now nearly completed, and the results will soon be ready for 

 publication. 



