DR. LEIDY’S MEMOIR. 
Tue region of Nebraska Territory of the United States appears to be as rich in 
the remains of Mammalia and Chelonia of the Eocene period as the deposits of the 
same age of the Paris basin. Dr. Hiram A. Prout of St. Louis, described the first 
mammalian fossil from Nebraska, in the American Journal of Science for 1847. 
The specimen indicates a species of Paleotherium, or of a closely allied genus of 
gigantic size, and has been named after its discoverer, Paleeotherium Proutii, Owen, 
Norwood, and Evans. Since the account of this fossil was published, an extraordi- 
nary number of beautiful and highly important specimens, of new species and genera 
of extinct Mammalia and Chelonia have been derived from the same locality, through 
the combined influence and labours of Messrs. Joseph and Thaddeus Culbertson, 
Professor Baird, Drs. D. D. Owen, Norwood, and Evans, and Dr. H. A. Prout and 
Professor O. Loghland. The most valuable collection, obtained by Dr. Owen’s 
survey, forms the basis of the following descriptions, and comprises numerous speci- 
mens of eight species of six genera of Mammalia, and four species of the chelonian 
genus Testudo. 
All the genera of Mammalia are distinct from those now in existence, and half of 
the number are new to Paleontology. 
Among all the specimens which have come under my observation from Nebraska, 
one only belongs to a true carnivorous animal, and this is the Machairodus prime- 
vus, Leidy and Owen. 
All the other mammalian fossils belong to the order Pachydermata, as Paleeothe- 
rium and Rhinoceros, or to this order combined with ruminating characters, as 
in the case of Oreodon and Eucrotaphus; or to the same order in combination with 
decided carnivorous characteristics, as in the Archeotherium. 
Most of the bones and their fragments are in a relatively good state of preserva- 
tion, and are highly mineralized. Those of smaller animals are less fractured and 
‘ mutilated than those of larger animals. The latter in many cases are crushed, 
while the fragments still retain their relative position, and the interstices filled 
