HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 239 
about opposite the glenoid cavity of the squamosals, then passing backward to 
the occipital plate. The supra-orbital ridges are light in M. elatus and M. petersoni 
and in their backward course come close together in the former, but not in the 
latter species. In M. elatus without uniting they form an inconspicuous sagittal 
crest, but again are divided by the triangular interparietal before they unite with 
the lambdoidal crest. On the posterior portion of the parietals are a number of 
foramina similar to those in other Ungulata (Hquus), in fact this region of the 
cranium is quite suggestive of the horse, except in the lack of the emarginated 
area below the lambdoidal ridges beneath the inion. 
The squamosal furnishes a considerable portion of the lateral walls of the 
brain-case. Posteriorly and inferiorly the sutures are not very distinct in the 
material before us. However, the squamosals appear to form the base of the 
lambdoidal crests for about five and a half centimeters back of the external auditory 
meatus. The zygomatic process is quite heavy and does not extend forward as 
far as in the horse or the rhinoceros, in the former of which it enters into the lower 
posterior margin of the orbit. In this respect Moropus more nearly presents the 
condition found in the tapir. The postglenoid process suggests that of the horse, 
though proportionally much heavier and especially well developed in its transverse 
diameter, in this respect somewhat closely resembling the genus Phenacodus. 
In the tapir the postglenoid process lies obliquely to the long axis of the skull, 
while in Moropus it lies nearly at right-angles to the axis. In the rhinoceros 
(R. bicornis, and simus) it is very prominent and elongated. The glenoid cavity of 
Moropus is a broad flat surface which gradually shades into the inferior border of 
the zygomatic arch without much indication of a well-defined anterior border 
of the articulating surface, such as is found in the horse, and other recent 
Perissodactyla. 
The frontal bone has a triangular outline with the sutures well indicated 
in the material before us. Anteriorly the sutures of the two bones together form a 
sinuous curve across the face, the median portions of the bones projecting the 
farthest forward, somewhat more so than in the recent horse. Laterally the 
superior border of the orbit is heavily developed, overhanging, and perforated by 
a large foramen somewhat similar to that occurring in the skull of the horse, as 
already mentioned by Peterson in an earlier publication,” the superciliary ridge 
being, however, much heavier than in the horse. There is a slightly developed 
postorbital process. The orbit is, however, open posteriorly, as in the rhinoceros 
and tapir, and as in these genera is located well forward in comparison with the 
™@ Peterson, O. A., Amer. Naturalist, Vol. XLI, 1907, pp. 737-738. 
