252 
PERISSODACTYLA. 
Meniscotherium chamense, Cope 
Plate Ixvi, fig. 18. 
Eeport, loc. cit., p. 8. 
Char, specif. —Last molar with the oblique inner posterior crest termi¬ 
nating at the posterior margin of the crown. Prominent external ribs at 
the point of connection of the external crescents of the crown. No cingula; 
enamel entirely smooth. 
Measurements. 
M. 
Length (externally) of the last four molars. 0.029 
Length of the true molars... 0.022 
Length of the penultimate............ 0. 009 
AVidth of the same... 0. 010 
This animal was about the size of the Raccoon, and probably had the 
habits of the Tapirs. 
OROTHERIUM, Marsh. 
Amer. Jour. Sci. and Arts, 1872 [separata^ p. 26). 
This genus has been heretofore known only from partial descriptions 
of the dentition of the inferior series. In these, it has been stated that the 
fourth premolar resembles the first molar in structure, and that the anterior 
inner cusp of the molars is slightly bifid. I have seen a number of speci¬ 
mens possessing one or the other of these characters, which are in other 
respects identical with the genus Hyracotherium. I find the resemblance of 
the fourth premolar to the first true molar to consist in the presence of two 
.tubercles on the posterior part of the crown; in Hyracotlierium, there is 
but a single one, which sends an angular crest forward. The bifid or 
double character of the inner anterior cusp is in some instances so little 
marked as to lead me to regard it as of secondary importance in the defini¬ 
tion of this genus. In the 0. cristonense, the cusps do not display this 
character. The genus Oligotomus^ Cope, differs from Orotherium in the 
possession of one less inferior premolar, while in the details of the inferior 
molars they are alike. 
In the 0. cristonense, the two rami of the mandible display almost the 
entire dentition of those bones. The molars are 4-3, with considerable 
diastemata between the canine and first premolar, and the first and second 
