PHILADELPHIA, January 20, 1875.

      SIR: 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 l872; from the explorations by the writer in Wyoming in connection with the United States Geological 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 Prof. B. F. Mudge and George Merrill, of Kansas, for invaluable specimens of the fossils of the Niobrara group; and to Capt. E. O. 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 American 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,