10 INTRODUCTION. 
Mytopon Hartant, Owen: Zool. Voy. Beagle, Pt. I., 1840, 68. 
Megalonyx laqueatus, Harlan: Med. and Phys. Researches, 1855, 354. 
Orycterotherium Missouriense, Harlan: Proc. Am. Phil. Soc., 1841, I. 119; Am. Journ. Se., 1843, 
XLIYV. 69. 
Orycterotherium Oregonensis, Perkins: Am. Journ. Sc., 1848, XLIV. 80. 
EREPTopon priscus, Leidy: Proc. Ac. Nat. Se., 1853, V. 241. 
Eusrapys ANTIQUUS, Leidy: Ibid. 
Megalonyx potens, Leidy: Proc. Ac. Nat. Se., 1852, VI. 117. 
DELPHINUS VERMONTANUS? Thompson: Am. Journ. Sc., 1850, XI. 256. 
TRICHECUS VIRGINIANUS? Dekay: Nat. Hist. New York, 1842, Pt. I., Zool. Mam., 56. 
+ Trichecus. Mitchell, Smith, and Cooper: An. Lyc. Nat. Hist. N. York, 1828, I. 271. 
Trichecus rosmarus (fossilis). Tlarlan: Med. and Phys. Researches, 1835, 277. 
Manarus, Cuvier. Harlan: Journ. Ac. Nat. Sc., 1825, TV. 236; Med. and Phys. Researches, 1835, 278. 
RoRQUALIS AUSTRALIS (fossils). Dekay: Nat. Hist. New York, 1842, Pt. I., Zool. Mam. 99.* 
In addition to the species just enumerated, remains of numerous mammals and 
other vertebrates have been discovered, by Prof. 8. F. Baird, in various caves of 
Pennsylvania and Virginia, and are now deposited in the Museum of the Smith- 
sonian Institution.” The collection contains representatives of nearly all the 
larger recent mammals and turtles of the United States, together with a few 
extinct species. 
The particular object of the present memoir is the description of a large and 
highly important collection of remains of mammalia and chelonia from an exten- 
sive Eocene deposit, which immediately overlies the Green Sand of the Cretaceous 
Period, in the Mauvaises Terres of Nebraska Territory. 
The Mauvaises Terres, or Bad Lands, as they are named, constitute a district of 
country extending along the foot of the Black Hills, a spur of the Rocky Mountains, 
situated between the Platte, or Nebraska, and the Missouri Rivers, at the head of 
certain branches of the latter called the L’Eau-qui-court, White, Cheyenne, and 
Moreau Rivers.* 
Dr. Owen, in describing this region, from notes of a visit made to it by Dr. John 
Evans, in his magnificent “ Report of a Geological Survey of Wisconsin, Iowa, and 
Minnesota, and incidentally of a portion of Nebraska,” observes that it presents one 
of the most extraordinary and picturesque sights that can be found in the whole 
Missouri country.* 
1 The following are erroneously reported as fossil remains :— 
RHINOCEROIDES ALLEGHANIENSIS, Featherstonhaugh: Journ. of Geol. 1831, I. 10. This is no animal 
remain whateyer, but is merely a fragment of stone. See De Blainyille’s Osteographie, article Rhino- 
ceros, p. 172. Further confirmed by Dr. Isaac Hays and Mr. Isaac Lea, who have had an opportunity 
of inspecting the specimen. 
OsTEOPERA PLATYCEPHALA, Harlan: Fauna Amer., 126. - The cranium described under this name is 
now preserved in the Cabinet of the Academy of Natural Sciences, and without the slightest doubt 
belongs to the recent Cologenys paca, Rengger, of South America. 
Equts CABALLUS ? ° 
Equus major, Dekay: Nat. Hist. New York, Pt. I., Zool. Mam., 108. 
Equus curvidens, Owen. Leidy: Proc. Ac. Nat. Sc., 1847, IIL. 262. 
* See Proceedings of the American Association, at Cambridge, 1849, II. 352. 
® See the map accompanying this memoir, for the use of which I am indebted to Dr. D. D. Owen. 
1B, WAG, 
