148 



the merycoidodontim: 



Specific Characters: The skull is similar in length to that of P. carrikeri but is narrower 

 across the arches. The maximum zygomatic expansion is opposite the middle of the zygomatic 

 foramina. The malar is moderately shallow beneath the middle of the orbit but attains considerable 

 depth beneath the postorbital bar. The convexity leading forward from the anterior zygomatic 

 pedicle soon dies out anterosuperiorly from the infraorbital foramen. The squamosal portion of the 

 zygoma is moderately robust, flares outward near the postorbital bar, descends sharply and becomes 

 first thicker and then thinner as it rises to the vertical crest above the postglenoid process. It rises 

 to a level above the orbit. The nasal bones are narrow and extend forward as far as a plane through 

 the middle of the canines. They are somewhat anteriorly decurved and transversely convex. The 



Fig. 108. — Promerycochcerus vantasselensis Peterson. Skull. HT. Cat. No. 1230 CM. 2/5 nat. size. (After 



Peterson, 1906.) 



lacrimal fossa is large and moderately deep. The wide frontals rise posteriorly and are moderately 

 flat transversely, with a strong supraorbital decurvature. The bone of the supraorbital and post- 

 orbital margins is rugose. The orbits are of medium size and are nearly circular. The temporal 

 ridges unite above the anterior part of the glenoid surfaces to form a high sagittal crest, with a 

 thickened border and equal in length to about a fourth of the skull. The supraoccipital crest is well 

 produced aft, and the wings are open. The small brain case has a prominent lateral convexity and a 

 secondary anterosuperior one less prominent. The external auditory meatus is unusually small. The 

 basicranial axis is not steep. The wide palate is but slightly vaulted, and the V-shaped palatonarial 

 border is well aft, somewhat less than half the distance between the last molar and the anterior of 

 the glenoid surface. The posterior palatal margin is slightly notched. The glenoid articular sur- 

 faces are twice the transverse dimension over the anteroposterior and are slightly oblique to the 

 sagittal plane. The postglenoid processes are small and anteroposteriorly compressed and have an 

 oblique border. The bulla; are relatively large, are subcircular in outline, and extend slightly below 

 the inferior surface of the postglenoid process and anteroposteriorly in advance of those processes. 

 The paroccipital process is transversely wide at the base and is not in contact with the bulla nor does 

 it approach closely to the postglenoid process, and its outer margin is in part strongly twisted forward. 

 Index: 0.70. 



Mandible: The chin profile is very gently concave and the symphysiodental angle approxi- 

 mately 40°. The mental tubercle is small, and, from that point to the medium-sized angle, the 

 inferior border of the ramus is slightly concave. The posterior components show no unusual devia- 

 tions from the generic type. 



