120 



molar series. The one in excess of the usual number, without other considera- 

 tion than convenience, I have viewed as a premolar. From its anomalous, or at 

 leasl unusual, form, the fourth of the scries of the premolars may be regarded 

 as the additional tooth. Without it, the jaw would indicate a small canine 

 animal, or at least a species of a closely allied genus. The animal was about 

 half the size of the common fox. 



UlNTACYON VORAX. 



Perhaps a larger species of the genus just named is indicated by the jaw- 

 fragment represented in Fig. 11, Plate XXVII. The specimen was obtained 

 on Henry's Fork of Green River, during Professor Hayden's expedition of 

 1870. 



The jaw-fragment agrees in form with the corresponding part of the jaw- 

 specimen of U. edax, but from its proportions belonged to an animal twice the 

 size. It contains the penultimate molar, the heel of the one in advance, and 

 the alveolus of the last molar. The teeth agree in their proportions with 

 those of U. edax, and the penultimate molar, represented in Figs. 12, 13, 

 sufficiently resembles that of the latter to belong to the same genus. The 

 breadth of the penultimate molar is 2f lines. 



Order Insectivorn. 



OMOMYS. 



Omomys Carteri. 



The first mammalian fossil described from the Bridger Tertiary beds con- 

 sists of the fragment of a lower jaw with teeth, discovered by Dr. Carter on 

 Twin Butte, about one mile from Fort Bridger. The specimen is repre- 

 sented in Figs. 13, 14, Plate XXIX, of ''The Extinct Mammalian Fauna 

 of Dakota and Nebraska," published as the seventh volume of the Journal of 

 the Academy of Natural Sciences of Philadelphia for 1869, and is described 

 on page 408 of that work. 



The jaw-specimen was accompanied with fragments of the cranium, for the 

 most part too much broken to determine anything from them. They would 

 appear to indicate a skull about the size of that of the common weasel, but 

 with weaker jaws. 



A fragment of the cranium retains a straight linear sagittal crest about 14 



