INTRODUCTORY REMARKS. 



The fossils described and illustrated in this report are from the Cre- 

 taceous and Tertiary rocks of the Upper Missouri country, lying between 

 the British possessions on the north, the north branch of Platte River on the 

 south, the Missouri on the east, and the Rocky Mountains on the west. The 

 original type-specimens were nearly all collected by Dr. Haydeu during a 

 two years' residence in this country on his own account, and subsequently 

 while acting as geologist of Government exploring expeditions under the 

 command of Lieut, (now Major) Gr. K. Warren ; and later in charge of 

 Capt. William F. Raynolds, both of the United States Topographical En- 

 gineers.* 



Preliminary notices of nearly all of the new species were, from time to 

 time, published by the writer, in connection with Dr. Hayden, in the Pro- 

 ceedings of the Academy of Natural Sciences at Philadelphia, chiefly 

 between the years 1856 and 1862, along with remarks on the general 

 geology of this region, including nearly all that is up to this time known on 

 that subject. 



Originally, it was intended that full descriptions of both the species and 

 the genera of most of these fossils would he published with illustrations in 

 Lieutenant Warren's final report on his explorations; but as no appropriation 

 was made l»y Congress for the publication of such report including geological 

 and palseontological results, it was arranged that this palaeontology should be 

 published by the Smithsonian Institution. Consequently, in accordance with 

 this plan, descriptions of all of these collections from older formations than 

 the Cretaceous were, in 1865, published by the Smithsonian Institution in 

 the form of a quarto memoir of one hundred and twenty-eight pages, illus- 

 trated by five lithographed plates. 



* A few of the specimens were collected by Lieut. John JIullan, of the Topographical Engineers, 

 LicuteDaut Balch, of the United States Ordnance, and others by several civilians; all of whom are 

 duly credited in connectiou with the descriptions. 



xix 



