INTRODUCTORY REMARKS. 27 



Niobrara would appear to indicate that the North American continent was at one time emphatically 

 the country of Horses. Proboscidians, Rodents and lusectivores are fairly represented. 



Besides the fossils described as characteristic of extinct species, the various collections submitted to 

 my examination contain fragments indicating a number of others, mostly of Pachyderms, Ruminants 

 and Carnivores, but too imperfect to determine their nature. 



The Mauvaises Terres collections of fossils rarely contained any considerable portions of skeletons 

 preserved in continuity in masses of matrix. With the exception of skulls, a few vertebrae in series, 

 some leg bones together, and several feet, the collections for the most part consisted of isolated bones, 

 and, of the long ones, generally the articular extremities. The absence of more complete parts of 

 skeletons, no doubt, in a measure has depended on the difficulty of removal and transportation of large 

 masses or slabs of rock containing them. They have been reported to exist, and in future, when in the 

 progress of opening up of the country greater facilities will be afforded, they will no doubt be obtained 

 and brought to the investigation of the student. 



The Niobrara fossils, from the nature of the deposit from which they were obtained, in all cases 

 consist of isolated bones and fragments, teeth, and portions of skulls, mingled pell mell. 



In the present work only the more characteristic fossils are described and figured, such as skulls, 

 portions of the same, jaws and fragments of the same, and teeth. Isolated bones and well preserved 

 fragments of others, usually of the extremities, though abundant, have not been represented, and in 

 many instances have not been described, as their peculiarities are too slight to be evident in description 

 without accompanying figures. The pecuniary means at command precluded more complete illustra- 

 tion of the work than is given included in twenty-nine quarto plates. Economy of means, indeed, 

 has been so important a consideration that in many cases views of specimens, when incomplete, have 

 been restored from the opposite side, thus saving the necessity of giving a representation of the two 

 sides of the same specimen. 



