the Marsh Collection, etc. 437 



a slight increase in length and robustness with a jaw 

 shortening. The premolar reduction might well result 

 from this form in a few generations. 



Measurements of Holotype. 



mm. 



Lower dentition, P x -M 2 81.5 



Lower premolars, P^P^ 43. 



Lower molars, Mj-Mg 41. 



P 2 , ant. -post, diameter 11. ; transverse diameter 7. 



P 3 , ant.-post. diameter 13.2 ; transverse diameter 8.5 



P 4 , ant.-post. diameter 19. ; transverse diameter 10. 



M-l, ant.-post. diameter 30.3 ; transverse diameter 12.1 



M.,, ant.-post. diameter 11.2 ; transverse diameter 8.5 



Depth of jaw beneath M 2 30.7 



Depth of jaw beneath P 2 29.1 



This species may be referable to the genus Tomarctus 

 Cope 1873, and in fact it is possible that Tephrocyon may 

 be synonymous with Cope's genus. The holotype of the 

 type species, Tomarctus brevirostris Cope, was collected 

 near Pawnee Buttes, Colorado, in the Middle Miocene 

 Pawnee Creek beds. It consists of "an immature jaw, 

 the carnassial about half emerged, and the anterior part 

 of the jaw so broken that it is not at all certain that the 

 premolars w^ere, as Cope considered them, reduced in 

 number" (Cope-Matthew 1915, pi. CXIXc). 



This type retains only the carnassial, but if the draw- 

 ing of this be correct, then it apparently bears a strong 

 resemblance to the analogous tooth in Tephrocyon. 



Leptocyonvafer (Leidy). 



Several lower jaws, with teeth, in the Marsh Collection 

 are referred to this slender-jawed genus. The premolars 

 are compressed and not crowded, and the heel of M x 

 shows the low entoconid crest obscurely divided into two 

 cusps as stated by Matthew. 



Amphicyon americanus Wortman. 



_ The type of this species, Cat. No. 10061, Y. P. M., con- 

 sists of a palatal portion of a skull with the teeth, except 

 the incisors and first premolar. It was very fully 

 described by J. L. Wortman in 1901. 



