THE MONKEYS AND APES. 123 



GENUS HYOPSODUS. 

 Hyopsodus, 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 H. 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. ACOLYTUS 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. PAULUS and 

 H. MINUSCULUS, Leidy, H. VICARIUS 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 ; OPISTHOTOMUS, APHELISCUS, 

 and SARCOLEMUR, Cope, from the Wasatch of Wyoming ; 

 HIPPOSYUS, Leidy ; BATHRODON, MESACODON, and STENA- 

 CODON, Marsh, from the Middle Eocene Bridger beds; are 

 of doubtful affinities. 



II. THE MONKEYS AND APES SUB-ORDER 

 ANTHROPOIDEA. 



This Sub-order, though containing animals of' much higher 

 organisation than the Lemuroidea, embraces species presenting 

 many different grades of intelligence, and ranging in size from 

 the Pigmy Marmoset, not larger than a small Kitten, to the 



