88 Annals of the Carnegie Museum. 



of careful definition. This is important as the species was made the 

 type of Pr ornery cochoerus^ when that genus was separated from Mery- 

 cochce.rus. 



When Cope wrote his Synopsis of the Oreodontidce, he was unable to 

 give real distinguishing characters to the genus Merycochoerus as he 

 employed the name. In his key to the species, however, he made 

 some divisions which are interesting. He divided the group into three 

 sections. 



In section I. the infraorbital foramen is above the middle of the 

 fourth superior premolar, the posterior part of the zygoma is ex- 

 panded, and the palate is moderately produced posteriorly. Species : 

 "Merycochoerus siperbus, M. leidyi, and M. chelydra." 



Sec. II. Infraorbital foramen above first true molar ; palate greatly 

 produced posteriorly. "Merycochoerus macrostegus ? and M. montanus. ' ' 



Sec. III. Infraorbital foramen above the anterior border of the 

 second true molars. ' ' Merycochoerus rusticus and M. proprius. ' ' 



The two latter are distinguished as follows : 



In Merycochcerus rusticus the zygoma originates above the second 

 molar ; size large ; incisors small. 



In Merycochoerus proprius. the zygomatic arch originates above the 

 third true molar ; size larger ; incisors large. 



On page 535 of the same paper, Cope gives some of the distinguish- 

 ing characters of Merycochoerus proprius and Merycochoerus rusticus. 

 Of the former he says : 



"This large species represents the extreme form of the genus in 

 the anterior position of its dental series as compared with the brain- 

 case. The zygomatic arch and infraorbital foramen are therefore 

 more posteriorly placed than in any other species. The premaxil- 

 lary bone is more prominent than in any other, and the incisor teeth 

 have relatively larger dimensions. The size is about that of M. 

 superbus. I have not seen any other than the typical specimen." 



Of Merycochoerus rusticus he says : 



"The smallest species, characterized among other things by the 

 closure of that part of the narial fissure which separates the premaxil- 

 lary 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 



6 Amer. Jour. Sci., Vol. XL, 1901, p. 82. See also Matthew's "Fossil Mam- 

 mals of Colorado," Mem. Amer. Mus. Nat. Hist., Vol. VII., p. 398. 



