The _Mandible_ is long, stout, but comparatively shallow. It is of nearly uniform thickness throughout, and does not exhibit the thickening of the alveolus and thinning, of the lower margin, which is shown in _Palæosyops_, especially in _P. major_; and the downward and inward arching of the alveolar border is not marked to the same extent as in that species. The lower border is nearly straight, and has but one slight emargination just behind the symphysis. The ascending portion of the ramus rises near the last molar quite abruptly, and makes an angle of nearly 90° with the horizontal portion. The masseteric fossa is shallow and obscure, and the anterior bounding ridge is almost obsolete. This part of the jaw is very different from any of the species of _Palæosyops_. The symphysis is quite long, and extends back as far as the second premolar; the chin is probably rounded. The dental foramen is situated high up in the ascending portion of the ramus; the mental foramen is placed below the second premolar; it is large and single. _Cranial Measurements._ M. Breadth of frontal at postorbital process ·045 Breadth of frontal in front of postorbital ·030 Breadth of nasal just in front of orbit ·032 Length from angle of nares to end of premaxillary ·1235 Length of premaxillary ·056 Length of maxillary ·230 Breadth of palatine process at canine ·026 Breadth of palatine process at second premolar ·029 Vertical height of maxillary at angle of nares ·064 Breadth of maxillary across floor of orbit ·058 Fore-and-aft diameter of orbit ·054 Length of malar along maxillary ·094 Vertical diameter of malar behind maxillary ·029 Transverse diameter of malar behind maxillary ·033 Fore-and-aft diameter of glenoid cavity (about) ·029 Vertical diameter of squamosal at end of malar articulation ·032 Transverse diameter of squamosal at end of malar articulation ·0325 Length of ramus mandibuli from symphysis to ascending portion ·177 Depth of jaw at last molar ·068 Depth of jaw at second premolar ·061 DENTITION. Upper Jaw.--The incisors, three in number, are placed close together in a nearly straight line, which does not make so great an angle with the line of molars as in _Palæosyops_. They increase regularly in size from the first to the third, which is very large. They all have stout rounded fangs, and sharp pyramidal crowns, with strong basal ridges separated from the acute blades by deep clefts. Between the incisors and the canine there is a long diastema.