210 



the merycoidodontim: 



to the last molars. The basicranial axis is very shallow. The glenoid surface is wide, nearly flat 

 externally, and convex inwardly. The postglenoid process is remarkably thin anteroposteriorly. It is 

 short and about half of the total transverse extent of the glenoid surface. 



Mandible: The symphysis is strong and noticeably concave vertically. The chin is unusually 

 straight, with a symphysiodental angle of 55°. There is a small tubercle at the base of the sym- 

 physis. The depth of the ramus below the tooth row is moderately uniform, except for a very 

 gradual increase in depth posteriorly. 



Foramina: The infraorbital foramen is located above P 4 . The supraorbitals are nearer to the 

 sagittal suture, being 29 mm. apart, than to the supraorbital margin. 



Fig. 152. — Metoreodon frojectiu Matthew and Cook. Mandible. HT. Cat. 



(After Matthew and Cook, 1909.) 



No. 14-055 A.M.N.H. 2/3 nat. size. 



Dentition: The teeth are strongly hypsodont. Superior: The incisors are small, with I 3 twice 

 the diameter of I 2 . The canines are relatively much reduced. The first three premolars have the 

 appearance of sloping backward, as in Merychyus. P 1 is rather oblique in position, while P 2 is also 

 oblique, though to a much less extent. These anterior three premolars are reduced in the anterior 

 part and have developed a prominent tubercle in the anterior basin. The posterior crescent is well 

 developed on P 3 and diminishes proportionally on the two preceding teeth. The molars are large, 

 with M 2 and M 3 nearer of a length than are M 1 and M 2 , a characteristic tendency in Ticholeptus. 

 The parastyle and mesostyle of M 2 appear to be relatively heavier than those of either M 1 or M 3 , 

 those of M 3 being fully as prominent but slenderer. The metastyle is well developed, and the 

 posterior termination of M 3 is bifid, as in Merychyus. 



Inferior: Matthew and Cook stated that the anterior teeth increase uniformly in size from I 2 

 to P 3 and form a progressive series in their structure, which is almost identical with the condition in 

 M. relictus, allowing for some difference in wear. The anterior premolars seem to be somewhat 

 more oblique, and the posterointermediate crest is not so well developed as in the latter species. 

 Ml 2 are proportionally larger than in Merychyus, and the metastylid of M 3 is aligned with the 

 inner edge of the molar, as in the genoholotype. The plesiotype lower jaw differs from the holo- 

 type mainly in the greater size of Pi, which may well be a sex difference, and in that the inner and 

 outer crescents of M 3 do not appear to be partially separate. The plesiotype jaw is that of a very 

 young animal, with M 3 not fully erupted, while the molars and premolars of the holotype are well 

 worn, which may explain the seeming discrepancies. 



Discussion: I believe that the recession of the nares emphasizes what appears to be a relative 

 enlargement of the maxilhe. Barbour and Cook (1917, p. 170) state that the maxillaries are rela- 

 tively longer and heavier than in the earlier types. They may well be heavier to afford sufficient 



