THE MONKEYS AND APES. 2 
Go 
GENUS HYOPSODUS. 
L[Tvopsodus, Leidy, Proc. Acad. Nat. Sci., Philad., 1870, p. 109. 
The present genus is recognised by the front inner cusp of 
the lower molars being single, and their heel presenting a cusp 
at its inner hind angle (except in 7. acolytus). Of the upper pre- 
molars, the median and posterior have an internal cusp; and 
the molars have two outer and two inner cusps with two small 
intermediate tubercles. There are six species known, from the 
Wasatch and Bridger beds of Wyoming and New Mexico, ot 
which H. Aco.ytus is distinguished by having the heel of the 
anterior and median lower molars without an inner hind cusp. 
Professor Cope remarks that though the species of this genus 
are not numerous, individuals of some of them are exceedingly 
common in the Eocene beds of Wyoming. H. PAauLus and 
H. minuscutus, Leidy, H. vicaArius and H. POWELLIANUS, 
Cope, with H. JURENSIS, Rutimeyer, from the Upper Eocene 
of Egerkingen, are the best known species. 
The genera INDRODON, Cope, from the Lower Eocene 
Puerco formation of New Mexico, with three cusped upper 
and four cusped lower molars; OpisrHoromMus, APHELISCUS, 
and SARCOLEMUR, Cope, from the Wasatch of Wyoming ; 
Hieposyus, Leidy ; BATHRopoN, MEsacopon, and STENA- 
copoN, Marsh, from the Middle Eocene Bridger beds; are 
of doubtful affinities. 
Il. THE MONKEYS AND APES—SUB-ORDER 
ANTHROPOIDEA. 
This Sub-order, though containing animals of much higher 
organisation than the Zemuroidea, embraces species presenting 
many different grades of intelligence, and ranging in size from 
the Pigmy Marmoset, not larger than a small Kitten, to the 
