PROMERYCOCHCERUS 139 



developed high sagittal crest, whose straight superior border is not thickened. In length it is about 

 one fourth that of the skull. The supraoccipital crest is very much produced beyond the occipital 

 condyles, and the wings are moderately close together. 



The brain case is narrow and elongate, with a prominent lateral ridge. The external auditory 

 meatus is small. The basicranial axis is steep. The palate is relatively narrow, and the palatonarial 

 border lies about midway between the last molars and the foramen magnum, according to Cope. 

 This area is badly damaged. The glenoid articular surface is somewhat oblique to the sagittal plane 

 and is about twice as long transversely as it is wide anteroposteriorly. The postglenoid process is 

 robust and has a convex posterior face. The large bulla; are laterally compressed and extend from 

 their contact with the paroccipital processes well in advance of the postglenoid processes, nearly to 

 the glenoid surface. The long, acuminate paroccipital process is directed well forward, so that its tip 

 is approximately in the plane of the anterior surface of the postglenoid process. An external basal 

 ridge of the paroccipital partially surrounds the external auditory meatus before curving forward and 

 downward to form the anterior edge of the process, which closely approaches the postglenoid process. 

 The occipital pillar is narrow but strongly convex and is flanked on either side by a deep fossa. 



Mandible: The chin profile is concave but less so than that of P. macrostegus, the posterior 

 part of the symphysis is below P 3 , as in the latter, and the symphysiodental angle is approximately 

 the same in both. The inferior border of the horizontal ramus is nearly straight. The masseteric 

 fossa is small; the coronoid process is low, broad, and small; and the wide sigmoid notch is shallow. 

 The condyle is normal; the angle is not especially prominent. 



Foramina: The infraorbital foramina are large and lie above the extreme anterior part of Mi. 

 The supraorbitals are about 30 mm. apart. The foramen ovale is large. 



Dentition: Superior: The metastyle of M 3 is small. No internal cingulum is present on the 

 molars, but cingula are present on the inner bases of the protocones and hypocones. Inferior: The 

 metastylid of M 3 is well developed. There are cingula corresponding to those on the superior 

 molars. The last three premolars are typical of the genus. Pi is very robust and lenticular in 

 section. The incisors are considerably larger than the superior ones. The superior molar-premolar 

 index is 0.84 and the inferior, from Cope's second specimen, 1.00. 



Promerycochoerus montanus grandis Douglass 1907 

 Figs. 4, 96; PI. XVIII 



Original Reference: Some new merycoidodonts. Ann. Carnegie Mus., IV, pp. 104-106, pi. XXVII. 

 Type Locality: Canon Ferry on the Missouri River, about 20 miles east of Helena, Montana. 

 Geologic Horizon: Lower Miocene (lower Harrison). 



Type: Holotype, Cat. No. 990 CM., well-preserved skull and jaws, cervical and lumbar vertebra?, femur, 

 humerus, portions of scapula, radius, ulna, pelvis, and tibia. Collected by E. Douglass in 1902. 



Specific Characters: This skull is among the longer ones in the genus and is dolicho- 

 cephalic, with a long, narrow face and with the superior contour nearly straight. The maximum 

 expansion of the zygomatic arches is just in front of the glenoid surface. The malar is deep below 

 the orbit, and a broad convex ridge extends forward and upward from the anterior zygomatic pedicle. 

 Below this ridge is a concavity. The squamosal portion is slender, extends forward to a position 

 beneath the postorbital bar, and rises nearly vertically aft. It is neither heavy nor high. The nasal 

 bones are narrow and posteriorly pointed. The anterior part is restored. The pars facialis of the 

 lacrimal is large, and the lacrimal fossa is deep but small. The narrow frontals are unreduced and 

 extend in advance of the lacrimal bone. They are for the most part transversely convex. The orbits 

 are medium in size, and the vertical diameter is the greater. The temporal ridges unite just aft 

 of the postorbital constriction to form a high and thin sagittal crest, somewhat less than a fourth of 

 the skull length. The paroccipital crest is moderately produced, and the wings are widespread. 



