1899 ] Wortman and Matthew^ Ancestry of the CanidcE, etc. I 1 T 



canines laterally flattened, and the anterior premolars much 

 reduced. In another line the jaw is somewhat more slender but 

 still very short, the lower canines laterally compressed, but the 

 premolars are not especially reduced in size. A third section in- 

 cludes a single very small species from the Bridger in which the 

 jaw is very short and deep, the canines not flattened, and the pre- 

 molars unreduced. In a fourth section the jaw is much more 

 elongated and shallower, the canines not flattened, and the pre- 

 molars are not reduced. 



The dentition of the lower jaw is I. -3, C. y, Pm. y, M. -j. The 

 second pair of incisors is much displaced, being pushed back out 

 of the transverse line. The sectorial is made up of an elongated 

 trigon and a basin-shaped heel ; the second molar exhibits a 

 crown of similar composition, but the trigon is much lower and 

 the anterior cusp considerably reduced. In some species the last 

 molar is very small and single-rooted, while in others it is larger 

 and is implanted by two distinct roots. One peculiar feature of 

 all the short-jawed species of the genus is the great length of the 

 molar as compared with the premolar series. In many the 

 molars occupy quite one half of the tooth-line of the jaw. 



Uintacyon promicrodon, sp. nov. 



This species is represented in the collection by a single specimen 

 of an almost complete lower jaw (No. 83), in which the sectorial 

 and fourth premolar are in good state of preservation ; portions 

 of the third premolar and second molar, as well as the roots and 

 alveoli of all the remaining teeth, are present. The species be- 

 longs in the first section of the genus mentioned above, and is its 

 oldest known representative, coming as it does from the Wasatch. 

 The chief distinctions between it and U. canavus from the Wind 

 River is seen in the size of the fourth lower premolar in com- 

 parison with that of the first molar. In the species under con- 

 sideration it is of normal size and holds about the same relations 

 to the succeeding tooth in this respect as is commonly observed 

 in the modern Canidae, whereas in U. canavus this tooth is much 

 more reduced. 



The remaining premolars were remarkably small and weak, if 

 we can judge by the size of the roots ; the first was implanted by 

 a sinde root, while the second and third each had two. The 



