258 
PEIIISSODACTYLA. 
a greater transverse than longitudinal diameter, and exhibits two approxi¬ 
mated external cusps. There is a single strong internal cusp, and a smaller 
cusp intervenes between it and the anterior external angle. The entire 
base of -the crown is surrounded by a narrow cingulum. Enamel nearly 
smooth. 
Measurements. 
M. 
Length of the bases of the second, third, fourth, fifth, and sixth naolars. 0. 0285 
Length of the crown of the fourth preinolar. 0. 0055 
Width of the crown of the same .. . 0. 0035 
Length of the crown of the penultimate molar. 0. 0065 
Width of the crown of the same... 0. 0050 
Depth of the ramus at the penultimate molar. 0. 0150 
Depth of the ramus at the second premolar .. 0. 0120 
Length of the crown of the third superior premolar. 0. 0050 
Width of the crown of the same . ......... 0. 0060 
Elevation of the crown of the same...... 0. 0035 
This species is dedicated to Oscar Loew, M. D., chemist and mineralo¬ 
gist of the United States Greographical Surveys West of the One hundredth 
' Meridian. 
HYRACOTHERIUM, Owen. 
Hyracotherium, Owen, Transactions of the Geological Society of Ijondon, 1841, pp. 
203-208 5 British Fossil Mammals, p. 419-423.—Gervais, Pal6ontologie Fran- 
9 aise. 
OroMpptis, Marsh, Amer. Jour. Sci. and Arts, 1874, p. 247 (with description); 1. c., 
1872 (name only). 
This genus is a characteristic type of the Lower Eocene, and has many 
near allies. Such are RJiagatherimi, Piet., Lopliiotherimn, Grerv., and others. 
Like the former, the first premolar is separated from the second by a dias¬ 
tema, but, in BJiagatJieriuni, the second and third premolars of the lower jaw 
present three cusps in a single series, a character which distinguishes it at 
once. The mandibular teeth are identical in structure with those of LopMo- 
therium, with the exception that in that genus the first premolar is part of a 
continuous series, while, in Hyracotherium, it is separated by a diastema 
from the second premolar. In comparison with OrotJierium, I find that the 
last premolar is different in structure from the first true molar, while they 
are alike in the last-named genus. The anterior inner tubercle of the molars 
is simple in Hgracotherium, double in Orotkerium. The superior molars 
