6 R. W. Shufeldt 



ciation of it is rendered all the keener and my gratitude the more 

 profound. 



My thanks are likewise extended to the United States National 

 Museum for the loan of skeletons of existing birds from the collections 

 of that institution, for the purpose of photography and comparison 

 with the fossil material here presented, and for the additional loan of 

 fossil types {Diatrytna, etc.) for the same purpose. Especially am I 

 indebted to Mr. Charles W. Gilmore, Curator of the Fossil Birds and 

 Reptiles of the Division of Palaeontology of that museum, for many 

 courtesies in this connection, and for permitting me to study the 

 museum material, as well as to Doctor Charles W. Richmond, Assistant 

 Curator of the Division of Birds, for similar favors, and for his great 

 kindness in affording me every facility within his power to obtain all 

 the material I needed, to make the comparisons entailed in work of 

 this character. His Aid, Mr. J- H. Riley, also has my thanks for 

 assistance in the matter of carrying out Doctor Richmond's instruc- 

 tions as to the consignment of the specimens, and other details. 

 Indeed, taken as a whole, I feel myself to be under lasting obligations 

 to all those whom I have named; for without their aid the results I 

 here offer would have been impossible of accomplishment. More- 

 over, I am fully sensible of the honor of which I am the recipient 

 through the placing in my custody of material of such incalculable 

 value, and selecting me to be the one to furnish its description for 

 publication. 



The descriptions of the species are arranged geologically, ranging 

 from Cretaceous to Pleistocene. At the close of the article, however, 

 a Summary appears, in which the results of the study are more 

 systematically arranged, and set forth for the reader's convenience. 

 No attempt has been made to submit an elaborate bibliography of 

 the subject, as in initial work of this character it offers no especial 

 value. 



The most of Professor Marsh's descriptions appeared in the Amer- 

 ican Journal of Science and these will be quoted, as well as papers 

 on the subject by other writers and my own. As a matter of fact, 

 the literature on the fossil birds of North America is by no means 

 extensive, and for the reason that, comparatively speaking, so very 

 few of them have fallen into the hands of science. 



After all the above-mentioned material was in my hands. Doctor 

 Schuchert wrote me, on the eighteenth day of April, 1914, that he 

 had sent me "a small registered package with a few ? bird bones from 

 Como, Wyoming, that are from the Morrison = Lower Cretaceous 



