324 
. ARTIODACTYLA. 
ARTIODACTYLA. 
MERYCOYUS, Leidy. 
Proc. Acad. Phila., 1858, p. 24; Extinct Mammalia Dakota and Nebraska, 1869, p. 115. 
Merychyus medius, Leidy. 
Leidy, Proc. Phila. Acad., 1858, p. 25; Extinct Mammalia Dakota and Nebraska, p. 
119.—Cope, Ann. Rept. Chief of Engineers, 1875, ii, p. 990. 
The greater part of the premaxillary and maxillary bones of the right 
side of a single individual represent this species. The third, fourth, sixth, 
and seventh molars are well preserved, while the other teeth are fragmentary 
or wanting. 
One of the characters of this and other species of Merychyus is the 
production forward of the anterior part of the jaws, beyond the postero¬ 
lateral border of the nares; the premaxillary being prolonged in front of 
this border further than the latter is in advance of the infraorbital foramen. 
The premaxillary is small, indicating a narrow upper lip, and contains three 
alveoli. It is coosified with the maxillary. The side of the maxillary above 
and in front of the infraorbital foramen is openly concave, in a manner not 
seen in Oreodon culbertsonii. There is a pronounced lachrymal fossa imme¬ 
diately in front of the orbit. The anterior border of the latter is above the 
middle of the posterior lobe of the penultimate molar. The infraorbital 
foramen issues above the middle of the last premolar. As in M. major 
and M. elegans, the third premolar has two internal lobes while the 
fourth has but one. The crowns are all well worn, indicating the maturity 
of the animal. Their inner lobes are convex and the external ones 
slightly concave, the lobes separated by a well-marked rib. There 
are no cingula, except a trace on the base of the external lobes of the true 
molars, and the enamel is wanting on the adjacent sides of the crowns. It 
is also wanting on the inner boundary of the central lakes of the true 
molars. The measurements agree very nearly with those given by Dr. 
Leidy. 
Measurements. 
M. 
Length of the superior dental series. .. 0.1215 
Length of the superior molar series . 0.1020 
Length of the true molar series . 0. 059 
Length of the second true molar. 0.023 
