1879.] NATURAL SCIENCES OF PHILADELPHIA. 119 



Pupil erect ; temporal fossa with simple superior border. 



Vulpes. 

 Pupil erect ; temporal fossa bounded above by a rib-like 

 crest. Urocyon. 



aa. Premolars . 



Inferior sectorial with internal tubercle and cutting heel. 



Enhydrocyon. 

 Inferior sectorial with internal tubercle, and wide tubercu- 

 lar heel. Tomarctus. 

 IY. True molars . 

 a. Premolars %. 



Inferior sectorial with internal tubercle. Speothus. 



Inferior sectorial without internal tubercle (superior molar 

 sometimes one). Synagodus. 



aa. Premolars f . 



Inferior sectorial without internal tubercle (incisors caduc- 

 ous). Dysodus. 

 Y. True molars h- 



Premolars |; inferior sectorial with internal tubercle. 



Icticyon. 



It is discoverable that the series represented b} r the above genera 

 is a part of the greater line of the digitigrade Carnivora, embrac- 

 ing the greater part of it which is less specialized than, or infe- 

 rior to, the part covered by the Hysenidse and Felidse. Without 

 entering into the relations of the Canidee with the civets and 

 Jfustelidse, it may be remarked that the genera display a succes- 

 sive reduction in the number of premolars and molars from the 

 more ancient to modern geologic times. It is interesting to note 

 that the genera presenting the greatest reduction in all respects, 

 Synagodus and Dysodus, are now only known in a domesticated 

 condition. Another reduction is seen in the number of tubercles 

 of the inferior sectorial. 



Amphicyon, Lartet. 



This genus is better represented in Em-ope than in North Ame- 

 rica, but two species being certainly known from the latter. No 

 recent species. 



Thous, Gray, Dusicyon, Smith (nomen nudum). 



Existing species of South America only. 



