336 



SYNOPSIS OF THE VERTEBRATE FAUNA OF THE PUERCO SERIES. 



The tritubercular superior molai's and simple premolars show that this species 

 cannot be referred to the genus Hyopsodus. 



The number of the superior premolars of the allied M. mmimus is unknown, so 

 that it may be a Tricentes. In this genus it can be only compared with the T. in- 

 cequidens (Fig. 8), which is of about the same size. But in that species the last 

 molai- is still more reduced than in M. minimus. 



Pig. 7. ~ "^ 



Fig 8. 

 Fig. 7. Tricentes hucculcntus f natural size. Fig. 8. Tricentes inmquideiis f natural size. 



CHRIACUS Cope. 

 Proc. Anier. Phil. Soc, 1883, p. 314 ; Tertiary Vertobrata, 1885, p. 740. 



In the absence of sufficient knowledge of the skeleton in this genus I (ind its 

 distinction from Mioela>nus to rest on dental characters. It differs from that genus in 

 the presence of an internal cusp of the first inferior premolar, which is however but lit- 

 tle developed in some of the species. The molars of the inferior series may be usually 

 easily distinguished from those of Mioclfenus in the well-developed fifth cusp, and 

 in the trihedral cusp of the external side of the lieel, which with the raised internal 

 border gives the heel the basin-like character which is seen in Pel3'codus. The char- 

 acter of the inferior molars graduates into that of Miockenus through such species as 

 M. suhtrigonus and C. scldosseriamis. 



The species are difficult to distinguish with tlie material in my possession. I 

 recognize ten from the Puerco and one from the Wasatch. The former are distin- 

 guished as follows. Owing to the absence of corresponding parts I am obliged to 

 compare the superior and inferior dental series in separate tables : 



Species with Sxtperior Molars. 

 I. Posterior cingulum and its interior cusp large, forming a prominent single of the crown. 



Larger ; true molars .0185 C. pclvidcns. 



Snniller ; true molars .014 (Fig. 9) C. iruncatus. 



n. Posterior cingulum and cusp small or insignificant. 

 «. Superior molars wider than long. 



Largest ; molars .01SJ3 ; depth of ramus at m. i .013 C. jrrisctis. 



Medium ; molars .015 ; depth oi ramus .011 G. schloaserianus. 



Smallest ; molars .010 ; depth of ramus .007 C. simplex. 



aa. Superior molars longer than wide. 

 Medium ; molars .0165 0. ki/ntlianiis. 



