Eaton — John Bay Felichc in Marsh Collection. 435 



had long upper canines. It is not known to what extent 

 the long knife-like upper canines of the true saber-tooth 

 cats were curtained by pendulous upper lips when the 

 mouth was closed in a state of rest : yet obviously such 

 lips would have to be raised to avoid injuring them in 

 the act of biting. Whatever the explanation, the fact 

 remains that in the typical saber-tooth Smilodon the 

 infra-orbital foramina are very large and in the false 

 saber-tooth Nimravus comparatively small. 



The fragment carrying P 4 shows that the mandible at 

 this section is much shallower and broader than the 

 mandible of Nimravus. The vertical and transverse 

 measurements of the mandible of Pogonodon serrulidens, 

 taken immediately behind P 4 , are 23 mm. and 14 mm. 

 respectively, and in P. cismontanus 32 mm. and 14.5 mm. 

 respectively. I can not quote exact corresponding 

 measurements in the types of the several species of 

 Nimravus, but in other material, referred to that genus, 

 the height is uniformly about three times as great as the 

 transverse diameter. Cope evidently thought this 

 character to be of taxonomic value, for he stated of 

 Nimravus gomphodus 11 : "The ramus of the mandible 

 is longer, deeper, and more compressed than in the recent 

 species of Uncia and the Pogonodon platycopis" ; and 

 of Pogonodon platcopis 12 he wrote "The mandibular 

 rami are robust, and not so high and compressed as in 

 Nimravus and its allies." Regarding the form of the 

 anterior portion of the mandible in Pogonodon ser- 

 rulidens, little can be ascertained from the fragment 

 carrying the lower canine ; but the broad and flat anterior 

 surface and the thickness of the bone external to the 

 root of the canine are distinctly favorable to the sup- 

 position that there was a flange for the protection of the 

 upper canine. 



The foramina of the basicranial region, so far as it has 

 been possible to locate them, occur as in Dinietis and 

 Nimravus. The mastoid process, in point of size, 

 resembles Nimravus rather than Dinietis, but it is 

 directed a little more forward than in Nimravus, in this 

 respect being more like Dinietis. The glenoid surfaces 



11 E. D. Cope, Report of the U. S. Geol. Survey of the Territories, vol. 3, 

 965, 1884. 



12 E. D. Cope, Eeport of the U. S. Geol. Survey of the Territories, vol. 3, 

 984, 1884. 



