Philadelphia, January 20, 1875. 



Sik : The accompanying pages embrace my final report on the vertebrate 

 paleontology of the Cretaceous formations of the West. The greater number 

 of species described has been derived from the beds of the Niobrara (No. 3) 

 and Fort Union (No. 6) epochs. The material has been obtained from the 

 explorations in Kansas by the writer in 1871 ; from similar explorations in 

 Kansas by Prof. B. F. Mudge in the years 1870 and 1872 ; from the explora- 

 tions by the writer in Wyoming in connection with the United States Geolo- 

 gical Survey in 1872; and from a similar expedition in Colorado in 1873. I 

 wish to express here my indebtedness to various friends who have assisted 

 me on these occasions ; especially to General John Pope, commanding the 

 Department of the Smoky Hill, and Captains Butler and Lyman, and Dr. 

 King, stationed at Fort Wallace at the time of my expedition in 1871; to 

 Dr. John H. Janeway, United States Army, of Fort Hays, and Profs. B. F. 

 Mudge and George Merrill, of Kansas, for invaluable specimens of the fossils 

 of the Niobrara group ; and to Capt. E. 0. Clift, Dr. Joseph Corson, and Judge 

 W. E. Carter, of Fort Bridger, Wyoming, for many kindnesses. I am also 

 under obligations to George M. Dawson, geologist of the British North Amer- 

 ican Boundary Commission, for the opportunity of examining fossils from the 

 Fort Union beds of British America ; and to the Smithsonian Institution for 

 facilities in the use of specimens and books. 



Where it has been possible to throw light on questions of stratigraphy, 

 this subject has also been touched upon. 

 I am. with much esteem, 



E. D. COPE, 



Paleontologist. 



Dr. F. V. Hayden, 



Director of the U. S. Geological Survey of the Territories. 



