1884. ] 537 |Cope. 
Merychyus arenarum Cope, sp. nov, Sub-species leptorhyn- 
chus Cope. 
This species is represented by a skull which lacks of completeness only 
the extremity of the muzzle and the angles of the lower jaw. Its size is 
about that of the Oreodon culbertsoni or of the Merychyus elegans. The 
confluence of the premaxillary bones shows that the place of the species 
is with the last-named genus, and the sigmoid flexure of the masticating 
line of the superior dentition is a point of resemblance to the species of 
the same. The position of the external infraorbital foramen is one de- 
gree further posterior than in the species of Oreodon, and agrees with 
the position in two other species of Merychyus (1. arenarum and M, 
pariogonus), which is more anterior than in the other species of the 
genus. ‘The foramen is in fact quite identical in position with that seen 
in most of the species of Hucrotaphus, to which genus the above named 
species must be regarded as the nearest in the genus to which they belong. 
As in other species of the genus, the malar bone is deeper and less prom- 
inent laterally than in those of Oreodon. The preorbital fossa is wider 
and shallower. The orbit is closed behind. 
The premaxillaries are convex in every direction, least so transversly. 
The fissure which separates them is quite narrow, and is separated from 
the alveolar border by a rather narrow isthmus of uninterrupted bone. 
At the canine tooth the direction of the surface becomes longitudinal by 
an abrupt turn, and the side of the face above the second premolar is un- 
interruptedly gently concave. The lateral convexity which bounds the 
preorbital fossa below, appears above the third superior premolar, and be- 
comes more prominent posteriorly as it passes into the flat surface of the 
malar bone. The anterior orbital border is prominent and thin, and does not 
develop a distinct tubercle, although its edge is roughened. The profile of 
the muzzle is astraight line descending gently from the interorbital region. 
Above the middle of the orbits the frontal bones are gently convex; on 
the line of their anterior border, there is a concavity of the median line. 
The superior face of the nasal bones is flat, and is peculiarly narrowed, 
especially posteriorly, where the large preorbital fossee approach each 
other, 
The anterior temporal ridges are well marked, and after a gradual 
approach unite into a sagittal crest, which has a gently convex ris- 
ing profile. After the posterior bifiurcation of the latter, the convex 
posterior tempofal crests do not project beyond the occipital condyles 
when the inferior edge of the lower jaw rests on a horizontal plane, 
as in so many other species of this genus and of its allies. These 
crests continue without interruption above the auricular meatus to the 
posterior base of the postglenoid process. As compared with the 
Oreodon culbertsont, the postorbital part of the cranium is short; it is 
also shorter than in any other species of Merychyus. Thus the 
length from the posterior border of the orbit to the convexity of the 
