PERISSODACTYLA. 
251 
animal than the type of M. armatus, and one probably equal todhe Cory- 
ipliodon radians. Its form approached that of the canines of the JDimcerata 
more nearly than do those of Corypliodon. 
Measurements. 
Long diameter of the tusk. 
Short diameter of the same. 
Diameter of the anterior groove. 
M. 
0. 026 
0. 014 
0. 009 
PERISSODACTYLA. 
This, the second order of hoofed Mammals found in New Mexico during 
the Wasatch Eocene period, was represented by a moderate list of species, 
all of small size. Some of these were very numerous in individuals, so 
that their remains constitute, with those of Coryphodons, a characteristic 
feature of the collections made by the expedition. 
MENISCOTHERIUM, Cope. 
Report "Vert. Foss. New Mexico, IT. S. Geog. Survs. W. of lOOth M., 1874, p. 8. 
Char. gen. —Molars three, with two continuous external crescents and 
two internal tubercles, except on the posterior, where there is but one, the 
anterior conic tubercle. The posterior tubercles on the other molars cres- 
centoid in section. A well-developed crescent between the anterior tubercle 
and anterior crescent, and an oblique crest extending from the latter to the 
adjacent horn of the posterior inner tubercle. Two external crescents on 
the last premolar. 
This genus presents a curious combination in the structure of its molars 
of the character of Palceosyops, Syopotamus, and Hyracotherium. It is 
exceptional among the Ungulates of the same fauna in the number of 
crescents of the molars, being the only genus of the American Eocene 
period yet discovered, which we know to possess the crescent between the 
inner and outer anterior tubercles of the superior molars. Such genera are 
numerous in the Eocene of Europe. It is to be regretted that nothing but 
the superior molar teeth of this genus is known. 
