134 
MESODONTA. 
MESODONTA. 
In my report to Dr, Hayden on the paleontology of the Bridger 
Eocene of Wyoming,* I included six species, viz, Tomitherium rostratum, 
Pantolestes longicaudus, Sarcolemur furcatus^ S. pjgmcBus, Sgopsodus vicarius, 
and H. paulus, Leidy, which belong to this suborder. As many species of 
Mesodonta referred to various orders are described by Dr. Leidy in his 
quarto report in the same series. In my report to you on the Vertebrata 
of the Eocene of New Mexico obtained by the expedition of 1874, eleven 
species are included, none of which had been certainly obtained from 
the Bridger beds. 
A synopsis of the genera is given below, in which the characters are 
derived from the dentition of the lower jaw, the part usually preserved. 
While considerable variety is to be observed in the structure of the teeth, 
they furnish also close approximations, so that their discrimination requires 
careful scrutiny. On examination of Dr. Leidy’s type-specimens, it appears 
that the parts preserved (the last two inferior molars) of his genus Washalcius 
do not differ from corresponding parts of Anaptomorplms of prior description. 
It also appears very probable that MicrosuSj Leidy, is identical with 
Microsgops, Leidy, and, according to rule, should take position as a synonym 
of the latter. The genus AnaptomorpJms, Cope, although included in the 
synopsis, may not belong to the Mesodonta. 
I. Last true molar with cusps in opposing pairs. 
A. Anterior inner cusps, two or a double one, ou some of the molars. 
* Three premolars. 
“ Last premolar without inner tubercle” (Leidy), like the other 
premolars. Omomys. 
Last premolar with inner tubercle like the molars. Microsyops. 
* * Four premolars; last molar heeled. 
Last premolar without inner tubercle; premolars two-rooted ..Pantolestes. 
Last premolar with inner cusp; all the molars with basin- 
shaped heel behind. Tomitherium. 
Last premolars with inner cusp; all the molars with elevated 
cusps behind; the anterior inner bifid ...... Sarcolemur. 
* Ann. Eeport U. S. Geol. Survey Terrs, for 1872, 1873, pp. 546, 607. 
