1884.J ODD [Cope., 



Measurements. M. 



Length of dental series (straight line) 4 191 



" from last molar to apex of coronoid 0735 



" of premolar series 085 



" " true molar series 084 



" " second premolar on base 021 



" first premolar on base 0225 



Depth of ramus at coronoid 044 



" " end of m. iii 073 



" " middle m. i 056 



" " P-m. i. vertically 034 



The specimens of this species were found by Mr. J. C. Isaac in the 

 Ticholeptus beds of Deep river, Montana, during his Expedition of 1880. 



Merycochcerus rusticus Leidy. 



Report U. S. Geological Survey Terrs., 1873, i,' p. 199, PI. Ill, figs. 1-3 ; 

 VII, figs. 1-5 ; XX, figs. 9-81. Proceedings Academy Philadelphia, 1870, 

 109. 



The smallest species, characterized among other things by the closure 

 of that part of the nareal fissure which separates the premaxillary bones 

 below. According to Leidy's figure above quoted, the depth of the middle 

 line of the undivided premaxillary is greater than the width of the bone, 

 a state of things not approached by any of the species of this genus de- 

 scribed in the preceding pages. The premaxillary in the M. proprius is 

 not described. 



From the ? Ticholeptus beds of the Sweetwater river, Wyoming. 



Merycochoerus proprius Leidy. 



Proceedings Academy Philadelphia, 1858, p. 24 ; Extinct Mammalia 

 Dakota and Nebraska 1869, p. 110 ; PI. X. 



This large species represents the extreme form of the genus in the ante- 

 rior position of its dental series as compared with the braincase. The 

 zygomatic arch and infraorbital foramen are therefore more posteriorly 

 placed than in any other species. The premaxillary bone is more promi- 

 nent than in any other, and the incisor teeth have relatively larger dimen- 

 sions. The size is about that of the M. superbus. I have not seen any 

 other than the typical specimen. 



From the Ticholeptus beds at the head waters of the Niobrara river, 

 Nebraska. 



MERYCHYUS Leidy. 



Proceedings Academy Philad'a, 1858, p. 24, (nomen nudum). Extinct 

 Mammalia Dakota and Nebraska, 1869, 115. Report U. S. Geological 

 Survey Terrs, i, 1873, p. 202. Cope, American Naturalist, 1884, p. 281. 

 Ticholeptus Cope, Bulletin U. S. Geolog. Survey Terrs., 1878, p. 380. 



Premaxillary bones coossified ; otic bulla swollen ; a vacuity between 



