Peterson : Miocene Beds of Nebraska and Wyoming. 65 



No. 1306 

 mm. 



Length of molar series 92 



Antero-posterior diameter of P T 18 



Transverse diameter of P T io 



Antero-posterior diameter of P% 17 



Transverse diameter of P^ 9 



Antero-posterior diameter of P3 19 



Transverse diameter of P3 10 



Antero-posterior diameter of P ? 19 



Transverse diameter of P^ 1 1 



Antero-posterior diameter of M T 19 



Transverse diameler of M T 16 



Antero-posterior diameter of M^ 29 



Transverse diameter of M ^ l l 



Antero-posterior diameter of M ¥ 41 



Transverse diameter of M-g- 17 



Merychyus medius Leidy. 



A number of incomplete specimens, Nos. 1049, x 337j an ^ I 4 IT > 

 from the Upper Harrison beds are provisionally referred to this species, 

 inasmuch as in size and dentition they nearly agree with Leidy's type. 

 (The Extinct Mammalian Fauna of Dakota and Nebraska, PI. XL, 

 Figs. 12, 13, 14). Very careful comparison with the types of Me?y- 

 chyus medius, Merycochcerus rusticus, and the specimens in the Car- 

 negie Museum shows that the dentition is so nearly identical as not to 

 warrant separation. Other features of the cranium of the type speci- 

 men of Merycochcerus rusticus, however, differ from the specimens 

 here referred to Merychyus medius in having the muzzle more produced 

 in front of the nasals, and the infraorbital foramen placed further back 

 as in Merycochcerus proprius. The type of M. rusticus was found on 

 the Sweetwater River in Wyoming and may belong to a different 

 geological horizon. 



Among the specimens referred to Merychyus medius a fragment of a 

 skull (No. 1409) presents a prominent sagittal crest which extends 

 well forward. The temporal ridge is quite prominent posteriorly, 

 but gradually fades away before reaching the orbit, which is incom- 

 plete through crushing. The frontals are slightly convex from side 

 to side, except in the median line near the junction with the nasals, 

 where they are slightly concave laterally. The nasals are not complete, 

 but the contact of the naso-maxillary suture indicates that they are of 

 a relatively greater length than in Merycochcerus. The brain cavity 



