I l6 Bulletin American Museum of Natural History. [Vol. XII 



line which we can trace back with tolerable accuracy into the 

 lower Eocene. 



This important connection has been entirely overlooked by 

 previous writers, who have considered Temnocyon to be an abor- 

 tive side-branch of the Canidse. 



The evidence is briefly as follows : 



I. Heels of lower molars trenchant. This unusual character is 

 shared by the recent Icticyon and the John Day genera Oligobunis, 

 Enhydrocyon and Hycenocyon. All of these have dental formulae 

 excluding them from the ancestry of Cyon. 



Fig. 2. Cyon alpitiiis. Upper and tower teeth, three fourths natural size. 

 From a specimen in the American Museum collection. 



2. Postero-internal cusp of superior molars reduced in Tem- 

 nocyon, obsolete in Cyon, antero-internal cone reduced, separated 

 from external cusps by an unusually deep valley, corresponding 

 to the high trenchant heel of the lower molars. 



3. Last lower molar reduced in Temnocyon, absent in Cyon. 

 Last upper molar somewhat reduced in Temnocyon, considerably 



