el 
Cope.] 536 |Jan, 18, 
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 MZ 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 
Merycochcerus, 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 ; 
TUS MOMATE NM Oder 6 elitis sa el olhnie aint seuecerees dM, pariogonus, 
II. True molar teeth more or less prismatic. 
a. Infraorbital foramen above third premolar. 
Larmier a slit ; front marrow......+.ssseeeee- dh, arenarum leptorhynchus. 
aa. Infraorbital foramen above fourth premolar. 
f. Zygomatic arch vertical, and with posterior angle small and rounded, 
Larmier triangular; front wide; true molar series M, .044; 
THCE CONVER  driescis vsvin's Wei y vc eby 4 vlalnnsy vie es QTOMAIUI UNeOmUNt. 
£8. Zygomatic arch expanded horizontally; posterior angle strong, 
acute. 
Larmuer large; trie molars 061... . 0. even seers ernest oe Lt) CYQOMANICUS. 
6B. Zygomatic arch unknown. 
Facial plate generally concave ; true molars M. .045..........0 elegans. 
True Gurenior) molars, MinQOve es niseravaiibnuewinvars socrevedd, medvus, 
True (superior) molars (m. ili inferred), M. .095...............M. major. 
Of the above species, the M. arenarwm and M. eygomaticus 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, 
