This genus, which is allied to _Adapis_, is characterised by {121}having its lower incisors with cutting edges; the first and second lower pre-molars with one root; the third with one cusp and a posterior heel, and the fourth an interior lateral cusp in addition. The lower true molars have two anterior cusps (the inner being double) and two posterior. The thigh is long and the knee free from the body as in the _Anthropoidea_, the hand capable of turning freely upwards at the wrist; the hind-limbs longer than the fore-, and "the details of the lower jaw, which is co-ossified in the centre, and teeth similar to that of the lower Monkeys." The remains of the only known species, T. ROSTRATUM (Cope), which was about the size of the Capuchin Monkey (_Cebus capucinus_) of Brazil, were found in the Bridger (Eocene) beds in an isolated spot on Blacks' fork, Wyoming. GENUS MENOTHERIUM. _Menotherium_, Cope, Bull. U. S. Geol. Surv. Territ., 1874, i., p. 22. _Laopithecus_, Marsh, Am. Journ. Sei., 1875, i., p. 240. This genus was established on an under jaw from the Lower Miocene White-river beds of Nebraska. Its molars are successively larger from anterior to posterior; the two pairs of cusps are obliquely opposite, the hinder pair longer than the front pair, and presenting a strong cingulum. Its discovery was the first indication of Lemurs in the Miocene of the United States. M. ROBUSTUM, Marsh, was as large as a Coati; and M. LEMURINUM (Cope) about the size of a domestic Cat. GENUS PELYCODUS. _Pelycodus_, Cope, Cat. Verteb. Eoc. New Mex., p. 13 (1875). _Tomitherium_, Cope, Rep. U. S. Geol. Surv. W. of 100° mer., ii., p. 135 (in part). _Lemuravus_, Marsh, Amer. Journ. Sci., 1875, i., p. 239. {122}This genus is characterised by the second pre-molar having always two roots; the anterior has one root and the third three; the posterior has one external and one internal cusp. Of the true molars, all have two external cusps; the anterior and median have two internal cusps and the posterior has only one; of the lower teeth the posterior pre-molar has an internal cusp and a heel; the next one has no internal cusp; the molars often have the fore inner cusps double; the posterior molar has a strong heel. This genus contains three species, all described by Cope (P. JARROVII, P. TUTUS, P. FRUGIVORUS), with the hind inner cusp of the upper molars distinct from the heel; and P. ANGULATUS, in which that cusp is small and is on the heel. Their remains have been found in the Lower Eocene (Wasatch) beds of New Mexico. P. HELVETICUS has been described from the Upper Eocene of Egerkingen. GENUS MICROSYOPS. _Microsyops_, Leidy, Proc. Acad. Nat. Sci., Philad., 1872, p. 20. _Limnotherium_, Marsh, Amer. Journ. Sci., 1871, ii., p. 43 (in part).