56 



University of California Publications. 



[Geology 



M 1 is small and is narrow transversely. As in Nimravus and 

 Hoplophoneus, it is without an inner protocone lobe. There are 

 apparently three closely connate roots, the inner and antero- 

 external being closely united, and the postero-external much 

 reduced. 



Systematic Position. — This species differs from all of those 

 previously described from the John Day fauna. Like Pogonodon 

 platycopis described by Cope from the John Day, it resembles 

 Hoplophoneus in the large size of the canines, and in the re- 

 duced P- and P 3 . It further resembles Hoplophoneus in the 

 absence of a. deuterocone on P 4 , in the tendency to develop a 

 protostyle on this tooth, and in the reduction of the inner lobe 

 of M 1 . Excepting' the less marked lateral compression of the su- 

 perior canine, the principal characters of the dentition as known 

 are apparently closer to Hoplophoneus than to Deinictis. Affini- 

 ties with Deinictis are more apparent in the skull characters. The 

 root of the zygomatic process of the squamosal is not produced 

 inferiorly, and the posttympanic process is not extended infe- 

 riorly to such an extent as in Hoplophoneus and other highly 

 specialized sabre-tooths with long superior canines. The form of 

 the frontals, nasals, fronto-maxillary suture, paroccipital process, 

 posttympanic process and of the root of the zygomatic process 

 of the squamosal fill approach the characters seen in Deinictis. 

 The very large size of the temporal fossae indicates large tem- 

 poral muscles, and probably a heavy lower jaw with a large 

 coronoid process as in the Deinictis forms. 



This species must be considered a very advanced form of the 

 deinietid group, and finds its closest affinities with the two John 

 Day species platycopis and brachyops, which have been separated 

 from Deinictis as a distinct genus, Pogonodon, by Cope. It differs 

 from 1'. platycopis considerably in size, in the form and propor- 

 tions of the posterior portion of the cranial region, and in the 

 form of the narrow M 1 . "With considerably smaller skull meas- 

 urements in P. davisi. the occiput and sagittal crest are abso- 

 lutely much higher. As the skull is absolutely much smaller, this 

 difference in the cranial region is evidently not due to sex. The 

 relation of the superior outline of the fronto-facial region and 

 sagittal crest to each other seem also different from the arrange- 



