X PREFACE 



The entire text has been studied by Dr. W. D. Matthew and Dr. W. K. 

 Gregory, to whom I am indebted for many valuable criticisms and suggestions. 



A liberal appropriation by the trustees of the American Museum of 

 Natural History has facilitated the large amount of special study, which has 

 been devoted to the preparation and illustration of this work. I have also 

 recently been transferred from a teaching to a research professorship in 

 Columbia University. 



Finally, the especial purpose of the work is to spread the knowledge of 



palaeontology in the United States. It will be cause for regret if the 



extended information as to localities, here brought together for the first time, 



should lead to the hasty or untrained collection of fossils, or to the still 



more harmful ill-considered description of new species. All descriptions 



should be preceded by painstaking examination of previous types, and should 



be accompanied by figures and short, clear diagnoses. All type specimens 



should find their way into large central and accessible museums where they 



can be readily examined. 



HENRY FAIRFIELD OSBORN. 



American Museum of Natural History, 

 December 31, 1909. 



