Cope.] 53® [Jan. 18, 



posterior temporal crest, is as long as from the former point to the 

 anterior base of the first premolar. In the Oreodon culbertsoni, the same 

 measurement is equal to the length from the same point to the anterior 

 base of the third incisor. This shortening posterior to the orbit is seen to 

 involve the zygomatic fossa as well as the region posterior to it. Thus the 

 horizontal diameter of the orbit in the M. leptorhynchus is exactly equal 

 to the distance between the posterior border of the same and the anterior 

 edge of the glenoid cavity. The posterior part of the superior edge of 

 the squamosal zygomatic process is thin and strongly convex. The apex 

 of the convexity is above a point just anterior to the posterior border of 

 the glenoid cavity. The posterior edge of the process is nearly vertical, 

 and if continued would reach the middle of the base of the postglenoid 

 process. The latter is compressed and rather elongate, and its convex 

 edge has considerable transverse extent. The paroccipital process is long 

 and is flat on its posterior face. The postorbital process of the frontal is 

 elongate wedge-shaped, with its truncate apex below joining a slight ele- 

 vation of the malar bone, which is much less prominent than in Oreodon 

 culbertsoni. It presents an angle outwards and forwards, as the orbital 

 border. The anterior half of the zygomatic process of the malar bone is 

 rounded- truncate below. The glenoid surface is plane transversely, and 

 slightly convex, rising backwards, anteroposteriorly. The anterior border 

 of the squamosal bone is not developed into a ridge. 



The frontal bone extends forwards on either side of the nasals, forming 

 a narrow process above the lachrymal bones. It overlaps the superior 

 edge of the maxillary, of which a narrow splint appears between it and 

 the nasal. The nasals are rather narrow, and each has the posterior bor- 

 der rounded. The latter fall above the middle of the first true molar 

 tooth when the inferior edge of the mandible is horizontal. The lachry- 

 mal bone has greater anteroposterior than vertical diameter, extending 

 nearly to the line of the infraorbital foramen, or much in advance of its 

 position in Oreodon culbertsoni, Eucrotaphvs jacJcsoni, or Merycochcerus 

 superbus. The malar bone has a correspondingly large anterior extension, 

 reaching to above the posterior part of the fourth premolar. It does not 

 extend so far in the three species just named. The zygomatic process of 

 the squamosal is more deeply received into the malar bone than in any of 

 the three species mentioned, reaching to below the posterior third of the 

 orbit. 



The larmier in this species is small, and its anteroposterior diameter is 

 more than twice as long as the vertical. More than halt of its inferior bor- 

 der is formed by the maxillary bone. As it is exhibited in the specimen, 

 its superior border is formed by the ascending process of the maxillary 

 bone ; whether this is overlapped by the laminar process of the frontal so 

 as to bound the foramen, when in a perfect condition, is uncertain. The 

 posterior edge of the larmier is the lachrymal bone. The external foramen 

 infraorbitale is on' one side double. The supraorbital foramina form 

 notches at the anterior edge of the supraorbital border. The frontal 



