112 ON THE EXTINCT MAMMALIA OF 



The incisive border of the jaw is of great relative depth, whether compared with 

 its condition in Oreodon, the ruminants generally, or the suilline animals. It recalls 

 to mind the corresponding deep convexity of the fore-part of the upper jaw in the 

 Horse and Tapir, though it projects comparatively little in advance of the canines. 

 Within the position of the incisive portion of the premaxillaries, in conjunction with 

 the contiguous portion of the maxillaries, the bone is excavated with a broad con- 

 cavity, which appears to be part of a basin-like expansion from the incisive foramina. 

 This expansion has been at least an inch in diameter, whereas in Oreodon the incisive 

 foramina are two small elliptical apertures opening directly on a level with the hard 

 palate. The premaxillaries appear to have been completely co-ossified in the adult 

 state. 



The lower jaw has the same form nearly as the corresponding portion of that of 

 Oreodon. The symphysial portion or fore-part is relatively wider and deeper, 

 apparently in accordance with a more robust character of the canines and incisors. 

 A ridge, descending in the course of the canine alveolus, sweeps backward and 

 gradually subsides along the base of the jaw. The presence of the ridge produces a 

 concave condition of the surface below the anterior molar teeth. In Oreodon the 

 corresponding portion of the jaw forms a continuous convexity with that of the 

 symphysis. The mental foramen is situated below the interval of the second and 

 third premolars. 



As befoi'e mentioned, the teeth o( Merycochoerus are like those of Oreodon, but they, 

 together with the jaws, are proportionately more robust in comparison with the size 

 of the skull than in the latter. 



The differences indicated between the fossils referred to Iferycochcerus and the 

 corresponding parts of Oreodon may by other naturalists be considered as insufficient 

 to separate the former from the latter otherwise than sjjecifically. Under such a 

 view the remains would indicate a well-marked fourth species, with the name of 

 Oreodon proprius. 



In comparing the remains oi Merycochcerus proprius vf'iih. those of Oreodon major, 

 it would appear as if one might readily have been derived from the other on the 

 Darwinian theory of selection. 



The fossil specimens oi Merycochoerus propritis which I have had the opportunity of 

 examining are as follows : 



1. The greater portions of the upper and lower jaws, with nearly all the teeth. 

 Those of the left side, partially restored from those of the right, are represented, two- 

 thirds the natural size, in figures 1, 2, plate X. The triturating surfaces of the teeth 

 are represented of the natural size in figures 3, 4 of the same plate. 



The molar teeth are about half worn away, and are repetitions in form of those of 

 Oreodon. 



