CREODONTA. 343 



It is probable that this genus, in common with the other ArctocijonidcE, 

 stands in ancestral relation to the existing families of the arctoid carnivora. 

 It is, in the restriction of its premolar series, rather less primitive than 

 Ardocyon, and prepares the way for the Procyonidce, the least specialized of 

 the true Carnivora. From this family, by a modification of the fourth pre- 

 molar towards a cai'nassial form, we derive the extinct genus Hycenarctos Falc. 

 of the upper Miocene, and the existing Aeluropoda M. Edw. From the latter 

 the bears have doubtless been derived by a process of divergence from the 

 general carnivorous line, in a special direction of their own. 



Although the Arctoids are well represented in America, an Eocene 

 ancestor has hitherto been a desideratum. It is now happily supplied. 



But one species is known from North America. It is a large and 

 formidable animal. 



ACH^NODON INSOLENS Cope. 



Paleontological Bulletin, No. 17, p. 2, Oct. 25, 1873. Ann. Kep. U. S. Geol. Surv. Terrs. 1873, p. 457, 

 Jour. Acad., Phila., 1874., Fig. 5, p. 10, March. 



Plates LVII and LVII a. • 



The only specimens of this species which I possess consist of mandib- 

 ular rami. The Princeton Exploring Expedition of 1877 discovered a good 

 skull with lower jaw, at the same localit}', and the director of the museum 

 of Princeton College, Professor Guj^ot, kindly permitted me to examine it. 

 I am under obligations to him and to Professors Scott and Osborne for the 

 means of ascertaining the characters of the cranium and superior molar teeth 

 above given. Perhaps before the present article appears, their memoir on this 

 species will have been published. I confine myself to the general characters 

 given, and direct my readers for fuller details to their monograph. 



Judging from the size of the size of the skull, this species was about 

 as large as a lion. It had a muzzle of about the length characteristic of that 

 animal, and a huge sagittal crest. The eyes were remarkably small. 



The rami are robust and rather shallow. The external face is but little 

 convex below the last premolar, but projects much beyond the alveolar 

 border opposite the last two molars. The anterior border of the masseteric 

 fossa is quite prominent, but the fossa shallows out below. The inferior 

 outline of the ramus is gently convex. The symphysis is rather long and 

 rises at an angle of 45°. Its posterior termination is opposite the middle 



