PROMERYCOCHCERUS 



129 



Specific Characters: This is a medium-sized skull, somewhat shorter than that of P. chelydra 

 or of P. hollandi and much narrower than either. The maximum zygomatic expansion is opposite 

 the anterior glenoid surface. The malar is deep below the orbit and extends backward to the 

 glenoid surface, and the strong anterior convexity from the anterior zygomatic pedicle soon dies out 

 on the side of the face. The malar is nearly horizontal and is inferiorly grooved. The squamous 

 portion of the arch is moderately slender. Its anterior portion extends forward to a point beneath 

 the posterior third of the orbit. It rises posteriorly to the crest, which turns backward internally and 

 overhangs a position posterior to the postglenoid process. In side view the arch forms a wide, 

 shallow U, which rises aft to the level of the superior fourth of the orbit. The nasal bones are 



Fig. 84. — Promerycochcerus leidyi (Bettany). Skull and jaw. HT. Cat. No. C.3299 W.M. 3/8 nat. size. (Redrawn 

 from Bettany, 1876, and from photographs from Cambridge University.) 



wide and unreduced, transversely convex, and posteriorly very bluntly pointed. The lacrimal fossa 

 is deep and large, the pars facialis of the lacrimal is subquadrangular in outline, and there is a 

 moderate-sized lacrimal tubercle on the antorbital margin. The frontals are wide and flat and rise 

 gently posteriorly, with but a slight supraorbital decurvature. The medium-sized orbits are sub- 

 circular to suboval, with the vertical diameter the greater, and are highly placed. The temporal 

 ridges unite above the anterior of the glenoid surfaces to form a very high and thin sagittal crest, 

 about a fourth of the skull length. The supraoccipital crest is well produced aft, and the wings are 

 very close together. The occipital pillar is strong, but the lateral fossa; are moderately shallow. 



The small brain case is low but moderately wide and has no pronounced lateral ridge, except 

 in the anterior portion. The external auditory meatus is small and is directed posteriorly, as well as 

 upward and outward. The basicranial axis is comparatively shallow. The palate is moderately 

 wide, is vaulted, and is not posteriorly notched, while the U-shaped palatonarial border is well behind 

 the last molars and almost beneath the postorbital constriction. The glenoid articular surface is 

 somewhat oblique to the sagittal plane and is strongly convex, being 48 mm. in transverse, and 

 22 mm. in anteroposterior diameter. The postglenoid processes are anteroposteriorly compressed, 

 26 mm. transversely and 1 8 mm. anteroposteriorly, are moderately deep, and have a nearly vertical 

 external border. The bulla; are large and oval in section, with a pitted surface, and extend some- 

 what below the level of the postglenoid process and forward to the midline of the glenoid surface. 



