_Omomys_, Leidy, Journ. Acad. Nat. Sci. Philad., vii., p. 408 (1869).
This genus was established for the first Mammalian fossil--a lower
jaw--described from the Bridger-beds as O. CARTERI. The posterior lower
molar has cusps in opposing pairs; pre-molars, three in number, the two
anterior one-cusped, the posterior two-cusped. The chin was longer and less
rounded than in _Anaptomorphus_.