230 THE merycoidodontid;e 



death. The frontal bones appear to be quite flat, which again is probably the result of the crushing 

 which this specimen has suffered. The orbits, which look chiefly outward, are closed by a relatively 

 slender bar. The temporal ridges unite over the anterior part of the glenoid surfaces to form a low 

 sagittal crest, less than one-third of the skull length. The supraoccipital crest overhangs the occipital 

 condyles, and the wings diverge at an angle of about 45°. The occiput is deeply excavated above 

 the foramen magnum. 



The brain case is low and moderately wide, with a marked ridge along the parietosquamosal 

 suture. The external auditory meatus is directed mostly outward, but somewhat backward and 

 upward. The palate is moderately wide and slightly vaulted. The U-shaped palatonarial border 

 is on a line with the end of M 3 . The basicranial axis is gently curved. The glenoid surface is 

 nearly flat. The postglenoid process is cone-shaped and relatively small. The bullas are large and 



Fig. 168. — Merychyus harrisonensis Peterson. Inferior view of skull. HT. Cat. No. 1341 CM. 1/2 nat. size. 



(After Peterson, 1906.) 



have, as Peterson states it, "a peculiarly depressed and flask-like form. There is a conical swelling 

 on the posteroexternal angle of the bulla, and a deep emargination or pit near this eminence for 

 the tympanohyal which constricts the otherwise broad tube of the external ear." The paroccipital 

 process is in contact with the posterior part of the bulla. This process is moderately large and 

 directed markedly outward as well as downward. Index: 0.54. 



Foramina: The infraorbital foramina are above the anterior part of P 4 . The supraorbitals lie 

 about 9 mm. on either side of the sagittal suture. The foramen ovale is large and situated just 

 anteroexternally to the large foramen lacerum medium. There seems to be no trace of a foramen 

 rotundum. The posterior palatine foramina are opposite the extreme anterior parts of M 1 . 



Dentition: As the specimen is an old animal, the teeth are considerably worn. The premolars 

 2 and 3 do not have the appearance of being set at such an oblique angle as they do in Merychyus 

 generally. The anterior of P 3 is not quite so much reduced, and the parastyle and mesostyle on M 3 

 appear to be heavier than usual. These variations from the normal may well be due to age or sex, 

 but they are more probably due to the fact that this species is nearer than some of its contemporaries 

 to the form of the stem stock, and of course these divergences become greater when compared with 

 later forms, such as M. elegans. The proportions and construction are much nearer the Merychyus 

 pattern than that of Ticholeptus, although the teeth are not so hypsodont as the later forms of the 

 former genus. The molar-premolar index is 0.77. 



Discussion: As the position of this species has been a matter of controversy, it is worth while to 

 review the reasons for this. Loomis (1923, p. 227) is inclined to place the species in Ticholeptus on 

 the grounds that the skull is too heavy, too wide, and too long for Merychyus. He states, however, 

 that this reference can not be definitely settled until the limbs are found. In 1917 (p. 165), Barbour 

 and Cook considered this species as typical of the lower Miocene forms of Merychyus. Schlaikjer 



