NATURAL SCIENCES OF PHILADELPHIA. 
26 
of a large animal, discovered by Dr. Hayden in the red grit bed of Niobrara, 
near Fort Laramie, Nebraska. The formula of dentition and relative position 
of the teeth with one another are the same as in Oreodon. The true molars 
present a repetition of the form and structure of those of the latter genus, and 
the premolars nearly so. The upper anterior two premolars have a greater 
breadth in relation with their length and thickness than in Oreodon ; and the 
anterior two lower ones are more crowded in position. 
The side of the face turns rather abruptly outward and backward from above 
the position of the true molars, more even than in the Hog, whereas, in the 
three described species of Oreodon^ it slopes gradually backward aud outward, 
more as the Wolf. The infra-orbital foramen is above the interval of the 
first and second true molars, while in Oreodon it is above the third premolar. 
The malar bone below the orbit is, relatively to the size of the animal, deeper 
than in the Hog, but in Oreodon it is not more so than in the Wolf. 
Length of upper series of molars, 74 lines. 
Length of lower series of molars 69 " 
Length of upper series of true molars, 43 " 
Length of lower series of true molars. 45 " 
Merychyus, Leidy. 
The formula of dentition, and the relative position, structure, and form of 
the teeth are nearly the same as in Lbptauchenia. In this genus, of which 
the remains of two species, L. decora and L. major, were discovered by Dr. 
Hayden in the upper miocene beds of White River, near Eagle Nest Butte, 
Nebraska, the formula of dentition and relative position of the teeth with 
one another are the same as in Oreodon. The crowns of the molars are rela- 
tively much longer, and at their outer part are more vertical than in the latter, 
differing in these respects very much as the molars of the Ox and the Deer. The 
outer lobes of the upper true molars are separated quite to the fangs by narrow, 
deep, vertical folds inclining forward. The inner lobes of the lower true molars 
are separated by narrow, overlapping folds, and present internal plane sur- 
faces, while those of Oreodon are folded as in the Deer. The premolars are 
more crowded than in Oreodon ; and in the case of the upper ones, the most 
elevated point of the triturating surface is much more anterior than in tlie 
latter. The enamel pits of the triturating surfaces of the true molars are very 
narrow in comparison with those of Oreodon, and in the lower teeth are quickly 
obliterated. The canines are relatively small in comparison with those of the 
latter genus. 
In Merychyus, of which there appear to be three species, as indicated by the 
remains discovered by Dr. Hayden in the pliocene deposit of Niobrara, the 
folds separating the outer lobes of the upper true molars have the same form 
as in Leptauchenia, but are not so deep, do not incline forward, and do not 
divide the crown through its base. The lower true molars have their inner 
surfaces as plane as in the Camel, and have their lobes but feebly separated 
in comparison with the condition in Leptauchenia. The canines are as well 
developed as in Oreodon. 
Merychyus elegans, Leidy. 
This species is founded on several halves of upper and lower jaws, contain- 
ing admirably preserved series of teeth. The animal was nearly the same size 
as Leptauchenia major. 
Length of the upper jaw, from the back molar tooth to 
the front of the incisors, 43 lines. 
Length of upper series of seven molars, 37 " 
Length of lower series of six molars 34 
Length of upper series of true molars, 22 " 
Length of lower series of true molars 23 " 
Depth of lower jaw at first true molar, 11 
Depth of lower jaw at last true molar 15 " 
1858.] 
