HISTORY OP THE CARNIVORA 557 



tArctocyonidse and fMiacidse, which had sharp claws and 

 uncleft phalanges. 



From this brief description, it is obvious that the fMiacidse 

 occupied a very isolated position among the fcreodonts and, in 

 my judgment, it would be better to transfer that family to the 

 Fissipedia and include the others in a separate order. 



Throughout the Paleocene and Eocene epochs the. fCreo- 

 donta were numerous and varied, the first of the Fissipedia 

 appearing in the upper Eocene. Till then the fcreodonts 

 were the only predaceous mammals in North America and 

 Europe, and they were especially abundant in the former. 

 Most members of the suborder and all the Paleocene forms were 

 of small or moderate size, but some of the Eocene species were 

 very large. In the Uinta the fcreodonts were greatly de- 

 creased in numbers and in the White River there were only 

 two genera of one family, the f Hysenodontidae, and since the 

 Ohgocene the suborder has been extinct. 



1. ^Miacidoe. Fissipede-Kke ^Creodonts 



It is unfortunate that no member of this family is known 

 from a complete skeleton, • but the material collected is suffi- 

 cient to give a fairly adequate conception of these most in- 

 teresting animals. These were the only fcreodonts with a 

 single pair of carnassials, the fourth upper premolar and first 

 lower molar, but in some of the genera the carnassials did not 

 differ greatly from the other teeth. In the various genera the 

 skull differed considerably in length and in the proportions of 

 cranium and face ; the brain-case was larger than in most 

 other fcreodonts and the brain more advanced, though smaller 

 than in the fissipedes, and the sagittal and occipital crests were 

 very prominent ; the tympanic bullae were not ossified. The 

 humerus had the epicondylar foramen and the femur the third 

 trochanter ; in the wrist the scaphoid, lunar and central were 

 separate, almost the only important difference from the Fissi- 

 pedia and merely the primitive stage of the latter. The feet 



