136 ON THE EXTINCT MAMMALIA OF 



inion to the forehead, as formed by the frontals. Its bifurcation anteriorly is acute 

 and remarkably prominent, but the diverging temporal ridges gradually subside 

 ai^proaching the post-orbital processes. 



The fronto- parietal suture is more advanced in position than is usual in Oreodon 

 Oulhertsoni. Commencing at the bottom of the notch formed by the bifurcation of the 

 sagittal crest, it curves forward and outward, crosses the temporal ridge just back of 

 its middle, descends a short distance at the side of the cranium about midway 

 between its narrowest part and the post-orbital process, and then curves backward 

 and downward to the alisphenoid. 



Both the squamosals and parietals are rather wider, fore and aft, than in Oreodon 

 Calbertsoni, and tlie back part of the latter above the former are more depressed than 

 is usual in the animal just named. 



The inion appears to have been proportionately wider and lower, and to have had 

 a wider summit than in Oreodon Culbertsoni. The sides of the inion in the latter 

 incline outwardly to the acute border formed by the squamosal. In the skull of J.. 

 latifrons the outer part of these lateral surfaces presents a long, deep and wide fossa, 

 bounded in front by the acute border of the squamosal, and behind by the prominent 

 sub-acute border of the ex-occipital. The bottom of the fossa is occupied by the mas- 

 toid, which is more exposed than in Oreodon Culbertsoni, and appears as a clavate 

 surface widest above, narrowing below, and terminating in a somewhat wider exti'e- 

 mity constituting the mastoid process, which is also thicker, though not more 

 prominent inferiorly, than in 0. Oalbertsoni. In the latter the margin of the ex- 

 occipital is not prominent, and the mastoid continues on the same inclined plane with 

 it to the border of the squamosal, so that the large conspicuous fossa at the side of 

 the inion of A. latifrons is not existent in 0. Oulhertsoni. A smaller fossa, however, 

 exists in a nearly corresponding position between the upper end of the mastoid and 

 the ex- and supra-occipitals. 



The paramastoids or par-occipitals are long, strong, and curved tapering processes, 

 resting at their base against the auditory buUiB. 



The post-auditory process of the squamosal is much thicker than in Oreodon, and 

 projects more inferiorly than the mastoid pi'ocess. 



The post-glenoid tubercle has the same form and robust character as in Oreodon, 

 and the glenoid articulation likewise appears to have the same form and construction. 



The auditory bulla is fore and aft oval, and measures an inch in that direction, 

 about eight lines in depth, and about seven in width. The back part of its base turns 

 outwardly to articulate with the base of the par-occipital. 



The space between the post-glenoid tubercle and the par-occipital is relatively much 

 wider than in Oreodon, mainly to accommodate the more robust post-auditory and 

 mastoid processes. 



