1884.1 561 [Cope. 



Agriochoerus trifrons sp. nov. 



This species is known to me by a single cranium of an immature indi- 

 vidual. It lacks of perfection only the basioccipital, the pterygoid, and 

 the alveolar border of the premaxillary bones. It retains the third and 

 fourth deciduous premolars, while the third true molar is still in its alveo- 

 lus, where it is exposed in place. 



Although the specimen is immature, its characters will not permit me to 

 place it with any other species known to me. I have specimens of like age 

 of the A. guyotianus, and these are quite different. From A. ryderanus 

 it differs in the form of its otic bulla, etc. 



The muzzle and front form a flat horizontal profile, while the parietal re- 

 gion is convex. The profile descends gently to the supraoccipital border, 

 or inion. The muzzle is compressed above and below the canine alveolus, 

 and there is a concavity above the third and fourth premolars, and behind 

 the foramen infraorbitale above this fossa the lachrymal region is con- 

 vex. The nasal bones are lost, so that the form of their posterior suture 

 cannot be ascertained. The frontal bones are gently concave in transverse 

 section between two lines produced forwards from the anterior extremities 

 of the temporal ridges, that is at the postorbital constriction of the cranium. 

 These lines are represented by a rounded longitudinal angle, from which 

 the frontal bone descends to the superciliary border on each side. A trace 

 of this form is seen the A. ryderanus. The supraorbital borders diverge 

 outwards and backwards to the postorbital processes. These are prominent 

 horizontally, and are abruptly decurved at the apex. The temporal ridges 

 enclose an urceolate area, having a gentle convexity in their direction be- 

 fore they unite at a point more posterior than in the other species, that is 

 above a line connecting the anterior borders of the postglenoid processes. 



The malar bone is slightly concave on the external face, and is mode- 

 rately deep, and not thick. The squamosal part of the zygoma is rather 

 slender, and does not rise above the postglenoid process. Its superior edge 

 continues without interruption into the posterior temporal crests, and so 

 into the supraoccipital. The postglenoid process is like that of A. guyo- 

 tianus, narrow and produced downwards. Paroccipital lost. The otic 

 bulla is large, its anterior edge extending anterior to the postglenoid pro- 

 cess. It is nearly twice as large as in M. guyotianus, and extends much 

 further forwards. It presents two flat sides, one external, the other out- 

 wards and forwards, and a convex side inwards and backwards. These 

 sides meet at an angular edge below, which runs outwards and backwards. 

 The sphenoid bone is convex between the bullae. Basioccipital lost. The 

 palatonareal border is convex, and is opposite the middle of the second 

 true molar. In the mature skull it would be probably more posterior. The 

 palate is everywhere concave in transverse section. 



The frontoparietal suture is broadly convex, and is opposite the anterior 

 edge of the glenoid surface, and 25 mm. in advance of the sagittal crest. 

 The anterior processes of the bone on each side of the nasals are wide and 

 truncate, and do not extend beyond the interior suture of the lachrymal 



