III. THE MIOCENE BEDS OF WESTERN NEBRASKA 



AND EASTERN WYOMING AND THEIR 



VERTEBRATE FAUN^. 1 



By O. A. Peterson. 



During the summers of the years 1 900-1 906 expeditions from 

 the Carnegie Museum have been regularly employed each year in col- 

 lecting fossils in the Tertiary deposits of northwestern Nebraska and 

 eastern Wyoming. Much material has been accumulated, and the 

 collections made contain many species new to science. In view of 

 the general interest at the present time in regard to the geological 

 position of the sediments which overlie the Oligocene of this region 

 it has occurred to the writer that an illustration representing an ideal 

 section showing the formations in proper succession, accompanied by 

 a list of the vertebrates obtained in each, would be of assistance to 

 the student of paleontology. A short preliminary description of new 

 species and additional notes on some forms hitherto little known will 

 follow each list. Statements and observations made in this paper are 

 based almost exclusively upon the collections belonging to the Car- 

 negie Museum, as they were made either directly by the writer or with 

 complete knowledge by him of the geological horizons in which the 

 individual specimens were found. A much more extended list might 

 have been given by adding genera and species which have been col- 

 lected and described by others from time to time, but as the correct 

 geological position of these might, in some cases, be somewhat in 

 doubt, it has been thought best in the present paper to mainly employ 

 data which have been obtained at first hand. 



Since the early Government surveys under Dr. F. V. Hayden, dif- 

 ferent writers have, from time to time, written upon the lithological 

 and geological characters of this region, and they will in the present 



'I take this opportunity to thank Dr. W. J. Holland, the Director of the Car- 

 negie Museum and Curator of Paleontology, for his revision of the manuscript of 

 this article, and for granting me the privilege of describing the splendid material 

 with which it deals. To Mr. Earl Douglass I am indebted for many kind criticisms 

 and suggestions. The drawings for the illustrations were made by Mr. Sidnej 

 Prentice. O. A. Peterson. 



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