1884-1 O^D [Cope. 



Measurements. M. 



Length of molar series 081 



" " premolars on bases 041 



Width of canine posteriorly 010 



Diameters P-m. iv { anteroposterior 010 



I- transverse 012 



Of this species I have but two specimens, which were obtained from the 

 Ticholeptus beds of Deep river, Montana, by my assistant, J. C. Isaac. 



Merychyus elegans Leidy. 



Proceedings Academy Philada., 1858, p. 24. Extinct Mammalia 

 Dakota and Nebraska, 1869, p. 118, PI. XI, figs. 1-11. 



Niobrara river, Nebraska. 



Merychyus zygomaticus Cope. 



Ticholeptus zygomaticus Cope, American Naturalist, Feb. 1878. Bulle- 

 tin U. S. Geolog. Survey Territories, 1878, p. 380. 



This species is peculiar in having the posterior expansion of its zygo- 

 matic arch horizontal instead of vertical. It has a thickened external edge 

 which continues into a strong posterior angle which projects behind the 

 posterior margin of the postglenoid process. The auricular meatus is 

 directed posteriorly in a way quite peculiar, resembling somewhat the 

 position seen in some of the hogs. The malar bone is very prominent. 

 The infraorbital foramen is above the contact of the third and fourth 

 superior premolars. The larmier is large and its maxillary border descends 

 posteriorly. 



In size this species is between the M. elegans and the M. medius. If 

 my identification of New Mexican specimens is correct, this species diflers 

 from the M. medius in the much less production of the premaxillary re- 

 gion, besides the smaller size. 



Ticholeptus beds of Deep river, Montana ; J. C. Isaac. 



Merychyus medius Leidy. 



Proceedings Academy Philad'a, 1858, p. 25. Extinct Mammalia, 

 Dakota and Nebraska, 1869, p. 119, PI. XI, figs. 12-14. Cope U. S. Expl. 

 Surv. W. of 100th Mer., G. M. Wheeler, iv, pt. ii, p. 324. 



Niobrara river, Nebraska, Hayden ; Santa Fe, New Mexico, Cope. 



Merychyus major Leidy. 



Proceedings Academy Philada., 1858, p. 26. Extinct Mammalia, Da- 

 kota and Nebraska, 1869, p. 121, PL X, figs. 15-16. 



This species, known hitherto from Leidy's descriptions of four of the 

 superior molars, is the largest of the genus, and perhaps of the family. 

 More information regarding it is much to be desired. 



Headwaters of the Niobrara river ; from Loup Fork beds, according to 

 Hayden. 



