This genus is represented by five species. Microchærus antiquus (Filhol) is of very small size, and has many affinities with Galago, as exhibited in the well-preserved cranium that has been recovered from the Phosphorites of Central France. The two lower molars have only one root. M. erinaceus, Wood, from the Upper Eocene of Hampshire; M. edwardsi (Filhol), from Central France, a species larger than M. antiquus, presents dental characters similar to the Galagos and the Mouse-Lemurs; M. parvulus (Filhol), and M. zitteli (Schlosser), are both from the Quercy Phosphorites of France; while M. armatus is from the Eocene of Alsace, and M. (Cryptopithecus) siderolithicus from the Bonerg of Frohnstellen.
GENUS MIXODECTES.
Mixodectes, Cope, Proc. Amer. Phil. Soc., p. 447 (1883); id., Rep. U. S. Geol. Surv., iii., p. 240, pl. xxiv. f, figs. 1 and 2.
The members of this genus, founded on fragmentary mandibles from the Puerco (Lower Eocene) strata of New Mexico, have a large front tooth "issuing from the ramus at the symphysis like a rodent incisor, the second tooth being similar but smaller and posterior and external to the first." The genus is represented by two species, M. pungens, Cope, and M. crassiusculus, Cope.
GENUS CYNODONTOMYS.
Cynodontomys, Cope, Palæont. Bull., p. 151 (1882); id., Rep. U. S. Geol. Surv., iii., p. 243, pl. xxiv., fig. 2.
This genus contains but one species, founded on several lower jaws disinterred from the Wasatch beds in the Big-Horn Bad-lands, in Northern Wyoming. The lower incisors, or perhaps, canines, are very large and close to the line of union of the two halves of the jaw; the molars have three cusps in front and a heel behind. The dental characters of the genus "resemble considerably those of Anaptomorphus and Necrolemur [Microchærus] but the large size of the inferior canine or incisor tooth distinguishes it from both." (Cope.) C. latidens, Cope, is the only species.
GENUS OMOMYS.
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.