M. R. Thorpe— Arceocyon. 377 



example Hycenognatlius, with Arceocyon. From a survey 

 of the following lists of major characters of the compar- 

 able elements of the two genera, it is seen that there can 

 be no close affinity between the two. 



In conclusion, it is my opinion that there is nothing to 

 preclude the possibility of Arceocyon being an autoch- 

 thonous form, most probably having developed from the 

 trenchant-heeled series, and belonging to this pseudo- 

 canoid line. However, both Professor Lull and the 

 author incline very much more strongly to the theory of 

 migration for this form and its derivation from Old 

 World stock. If the lower jaw upon which Arceocyon is 

 established had been collected in the Pliocene beds of 

 Europe, I should have no hesitancy about referring it to 

 the genus Simocyon, or at most to a subgenus under it. 



If Arceocyon should prove to be a derivative of purely 

 American ancestry, the possibility of which I doubt at 

 present, it will be one of the most remarkable cases of 

 convergence known to the science of vertebrate paleon- 

 tology. 



