I lO Bulletin American Museum of Natural History. [Vol. XII, 



I. — The Short-jawed Dogs of the Eocene. 

 Uintacyon' Lcidy. 



This group of species has been found thus far in the Wasatch, 

 Wind River, and Bridger beds, and is represented so far only by 

 more or less complete specimens of the lower jaws. In one 

 species, Uintacyon vorax from the Bridger, a few fragments of the 

 skeleton are known, but beyond this the materials are very defi- 

 cient. Most of the species which we place in this genus have 

 been referred to Miacis, a genus originally established by Cope 

 upon a jaw fragment from the Bridger.^ It now appears, how- 

 ever, that this first described species, and therefore the genus 

 Afiaa's,is synonymous with the genus Vulpavus, previously estab- 

 lished by Marsh upon a first superior molar.^ The name Miacis 

 will therefore have to be abandoned and the name Uintacyon^ 

 given by Leidy, substituted. Leidy's type of Uintacyoti edax is 

 anomalous, in that it possesses five premolars instead of the nor- 

 mal number four, but this is not open to very serious objection, 

 since the shape and position of the extra tooth will convince 

 almost any one at a glance of its abnormal nature. 



As the genus stands at present no very striking or trenchant 

 characters can be assigned to it which will separate it sharply 

 from its Bridger contemporary, Vulpavus. Although the upper 

 dentition is completely unknown, there can be very little doubt 

 that the most important distinctions between the two will be found 

 to consist in the number of superior molars. In Vulpavus they 

 are reduced to two, as in the modern genus Canis, while there can 

 be very little doubt that the number was three in Uintacyon. The 

 only positively known character by which the two genera can be 

 separated at present, is seen in the thick, heavy lower jaw, 

 together with the abruptly rounded chin. In Vulpavus, on the 

 other hand, the jaw is relatively slender and without the abrupt 

 chin, quite as in the modern Canidae. 



There are apparently several distinct lines of species in this 

 genus reaching from the Wasatch into the Bridger. In one pre- 

 cocious series the jaw is remarkably deep and short, the lower 



^ Proc. Acad. Nat. Sci. Philada. 1872, 277. 

 * Proceed. Amer. Philos. Soc. Aug. 1872, 740. 

 ' Amer. Jour. Science, Aug. 187 1. 



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