Cope.] 5ob L Jan . 1S- 



the maxillary, lachrymal, and nasal bones, or larmier. Nasal bones nor- 

 mal. First inferior premolar caniniform. 



This genus has not been defined prior to the present article, although 

 some characters common to the species of the genus known to him, have 

 been given by Leidy. As now defined it is identical with genus Ticholep- 

 tus Cope. This group was distinguished by the presence of a larmier, a 

 character whose presence in the species of Merychyus has been hitherto 

 unknown. It is not yet reported indeed as present in any of the original 

 species of the latter, but I think that there can be no reasonable doubt of 

 its presence there. A character found by Leidy in the M. major I find to 

 be present in one or more of the superior molar teeth in all the species. 

 The posterior horn of the anterior internal crescent cuts off the adjacent 

 or anterior horn of the posterior internal crescent from contact with -the 

 inner side of the external wall of the crown. It is the anterior horn of the 

 posterior internal crescent which reaches the external wall, in the genera 

 Merycochoerus, Eucrotaphus and Oreoden. In Leptauchenia the arrange- 

 ment is generally as in Merychyus ; see under the head of that genus. 



This genus is confined to the Upper Miocene beds, the Ticholeptus and 

 Loup Fork epochs. In size the species range from medium to large, the 

 M. major equaling any species of the family in dimensions. They are 

 distinguished as follows : 



I. True molar teeth not prismatic. 



Infraorbital foramen above fourth premolar ; malar bone shal- 

 low ; squamosal with superior zygomatic angle anterior ; 

 true molars M. .042 M. pariogonus. 



II. True molar teeth more or less prismatic. 

 a- Infraorbital foramen above third premolar. 



Larmier a slit ; front narrow M. arenarum leptorhyn chits. 



aa- Infraorbital foramen above fourth premolar. 



p. Zygomatic arch vertical, and with posterior angle small and rounded. 

 Larmier triangular; front wide; true molar series M. .044; 



face convex M. arenarum arenarum. 



{3(3. Zygomatic arch expanded horizontally ; posterior angle strong, 

 acute. 

 Larmier large ; true molars .051 M. zygomaticus. 



ft(3. Zygomatic arch unknown. 



Facial plate generally concave ; true molars M. .045 M. elegans. 



True (inferior) molars, M. .069 M. medius. 



True (superior) molars (m. iii inferred), M. .095 M. major. 



Of the above species, the M. arenarum and M. zygomaticus are known 

 from entire skulls. In the first named, the foramen infraorbitale appears 

 to be partly above -.the posterior edge of the third premolar, as well as 

 above the anterior edge of the fourth. 



