HISTORY OF THE CARNIVORA 573 



In appearance, ^Oxyoena must have been merely a smaller, 

 lighter and less powerful variant of the Bridger genus, and, no 

 doubt, its habits of life were substantially the same ; but in the 

 details of structure were many minor differences, all of them in 

 the direction of greater primitiveness in the more ancient 

 animal. 



The second phylum of the family was represented in the 

 Uinta- and Bridger stages by a group of small species, which 

 were survivors of still more ancient and primitive progenitors 

 of the family. In the typical genus, ^Limnocyon, the dental 

 formula was the same as in '\Oxywria : i |, c ^, p |, m |, but the 

 first upper molar had its two external cusps well separated and 

 a much lower posterior cutting ridge, while the inner cusp was 

 much larger. The second upper molar, though transversely 

 placed, had all the elements of the primitive tritubercular tooth, 

 the pattern from which all the varied types of fcreodont upper 

 molars were derived by the addition or suppression of parts. 

 The two lower molars were very primitive, having a high an- 

 terior triangle of three cusps, forming an imperfect shearing 

 blade, and a low heel. This dentition was on nearly the same 

 plan as that of the small, contemporary fhysenodonts, but the 

 emphasis of development, so to speak, was differently placed. 

 In the fhysenodonts there were three pairs of sectorials and the 

 best-developed pair was made up of the second upper and third 

 lower molar ; while in fLimnocyon the third molar was lost, and 

 there were but two pairs of sectorials, of which the largest pair 

 was the first upper and second lower molar, as was also true of 

 ^Oxymna and ^Patriojelis. 



The skull of ^Limnocijon had a much longer facial region, and 

 more elongate and slender jaws than in the last-named genera, 

 and the feet must have been quite different, with less spreading 

 digits. -fLimnocyon thus tends to indicate a common origin 

 for the foxysenids and fhysenodonts, though these common 

 ancestors are still unknown. 



A very interesting genus of this series, \Machairoides, of 



