PEOSIMI^. 239 



and third. The posterior external is obtuse and has a triangular section 

 on all the molars. A crest is continued from the heel of the third molar on 

 the inner side of the crown half way to the anterior inner cusp. 



Measurements. 



M. 



LeDgth of the inferior true molars 0100 



Diameters M. n ^ anteroposterior 0038 



c transverse 0034 



Diameters M.iii^^°*''^°P°^*''™'" 0038 



I transverse 0028 



Depth of ramus at M. ii 



The Microsyops spierianus differs from this species in its smaller size 

 (true molars .008) and in the presence of posterior, internal cusps of the 

 true molars. 



The Hyopsodus acolytus was found by Mr. D. Baldwin, in Northwestern 

 New Mexico. 



PROSIMI^. 



The suborder may be differentiated from the Mesodonta by the posses- 

 sion of an opposable hallux of the posterior foot. This character is, how- 

 ever, not yet demonstrated in the genera of the American Eocene, which I 

 provisionally give to it, nor is the absence of the character known to belong 

 to any of the genera of Mesodonta excepting Pelycodus. It is, iiowever, 

 very probable that the other genera referi-ed to the Mesodonta agree with 

 Pelycodus. It is also possible that some of the genera here referred to the 

 Prosimiag agree with Pelycodus. 



In the uncertainty which exists as to the reference of the genus Cyno- 

 dontomys and its immediate allies, I compare the genera of the Eocene lemu- 

 roids as follows. I premise by observing that the genus Chiromys clearly 

 represents a primary division of the Bunotheria, which occupies a position 

 between the Prosimiae and the Tillodonta. The rodent-like incisors with 

 permanent pulps are those of the Tillodonta, but the opposable hallux of 

 the posterior foot is not found as yet in that suborder. The suborder has 

 been named by Gill* the superfamily Daubentonioidea. 



•Arrangement of the families of Mammals, 1872, p. 54. 



