Marsh Collection, Peabody Museum. 339 



numerous, yet with sucli imperfect specimens it is not an easy 

 matter to correctly determine their limits and relationships 

 nor to refer other more complete material to them with 

 certainty and exactness. Any attempt must, therefore, be 

 regarded as tentative to a large extent, at least until such time 

 as the acquisition of more complete specimens will throw addi- 

 tional light upon the structure and organization of the types. 



The genera which have been proposed for these dogs are 

 three in number, viz: Vulpavus, proposed by Marsh in 1871 

 upon a first superior molar tooth; Uintacyon, proposed by 

 Leidy in 1872 upon an anomalous lower jaw, with the teeth 

 considerably damaged, and Miacis, proposed by Cope in 1872 

 upon a fragment of a lower jaw bearing the penultimate 

 molar. It will be seen, therefore, that in no case is there asso- 

 ciation of upper and lower teeth in one specimen, so that in 

 the absence of any additional specimens which display charac- 

 ters exactly like the types, the reference of other more or less 

 fragmentary material to them must, at best, be attended with 

 an element of uncertainty. 



In the matter of the synonymy of these generic names I 

 have elsewhere expressed the opinion* that the type specimen 

 of Cope's Miacis belongs to the same genus as that previously 

 described by Marsh under the name of Vulpavus ; but in the 

 absence of superior molars in the former, this cannot be 

 demonstrated with absolute certainty. After the study of a 

 much wider range of specimens than were at my disposal 

 when this conclusion was reached, I can see no reason to ques- 

 tion the correctness of this view. 



Fortunately the relationship of the type species of Uintacyon 

 can now be determined with a reasonable degree of certainty 

 and satisfaction. In the present collection a specimen in which 

 there are upper and lower molars associated, shows that it is 

 quite distinct from Vulpavus. While the number of superior 

 molars cannot now be stated, they may nevertheless be assumed 

 to be three; this assumption is based upon (1) the relative size 

 of the second molar, the presence of which is indicated by its 

 alveolus, and (2) upon its striking resemblance to the three- 

 molared Oligocene Daphcenus series, of which there can be 

 little doubt that it was the forerunner. The main distinction 

 between Vulpavus and Uintacyon has hitherto been supposed 

 to rest upon the number of superior molars. Vulpavus was 

 thought to have but two and Uintacyon three, but it now 

 transpires that some of the species of Vulpavus have a third 

 molar, and it is no doubt true of all of them ; in fact it seems 

 highly improbable that there are any species of Canids in the 

 Bridger which had less than three superior molars. The dis- 



*Bull. Amer. Mus. Nat. History, June 21, 1899, p. 110. 



