117 



Hyaenodon than in the fox. It is proportionately longer and narrower than 

 in the latter, and the accessory cusp at the back border of the principal one 

 in the fox is nearly obsolete in the fossil. The heel of the crown is better 

 developed than in the fox. It forms a median acute ridge, and slopes off on 

 each side to the rounded base of the crown. 



The first molar, as before intimated, is smaller than the last premolar. It 

 is as wide as the second molar, but not so thick, and is slightly wider than 

 the last molar. It is proportionately better developed in its relation with the 

 succeeding molars than in Hyaenodon. Its crown is intermediate in form 

 and in the development of its parts to that in the fox on the one hand and the 

 raccoon and badger on the other. The fore part of the crown, consisting of 

 rather more than one-half, corresponds with the sectorial portion of the same 

 tooth in the fox, but accords more in shape and the relative position and de- 

 velopment of its points with the homologous portion in the raccoon and bad- 

 ger. The heel of the crown is bordered by a horseshoe-shaped ridge inclos- 

 ing a cup-like concavity. 



The heel of the second molar, the only portion of the crown retained in 

 the specimen, is stouter than in the first molar, but has the same shape. The 

 width of the crown is about equal to that of the tooth in advance, but has 

 been slightly thicker. 



The last molar is a two-fanged tooth like those in advance, but is not quite 

 so wide, and a small portion of the back of the crown indicates it to have 

 been of less thickness. 



The base of the jaw-fragment is broken away in the specimen. The por- 

 tion preserved presents nothing peculiar. 



Measurements of the fossil are as follows : 



Lines. 



Space occupied by the last premolar aiid molars 15 



Space occupied by the molars 11 



Breadth of crown of last premolar 4 



Length of crown of last premolar at middle 3£ 



Breadth of crown of first molar 4 



Length of crown of first molar at principal cusp 2| 



Thickness of crown of first molar at heel 2 



Breadth of crown of second molar . 4 



Thickness of crown of second molar at heel 2£ 



Breadth of crown of last molar 3£ 



The name Sinopa, applied to the extinct genus, according to Professor 

 Hayden, is aboriginal, and is applied by the Blackfeet Indians to a small fox 



