132 THE MERYCOIDODONTIMi 



oblong to square in section. They, together with the postglenoid processes, nearly close the auricu- 

 lar fossa below. The occipital pillar above the foramen magnum is very narrow and convex, with 

 exceedingly deep lateral fossa. Index: 0.515. 



Mandible: The chin profile is almost straight, with a symphysiodental angle of 40°. The 

 mental tubercle is large. The angle is prominent, and the posterior edge of the ascending ramus is 

 nearly vertical. The coronoid process is thin and very low and flares somewhat outwardly. The 

 sigmoid notch is very shallow and the condyle low. 



Foramina: The small infraorbital foramina are located above P\ The supraoccipitals are 

 about 1 5 mm. apart. The posterior palatines cannot be seen. 



Dentition: Superior: The metastyle of M 3 is very small, and there are no internal cingula on 

 M 1 and M 2 , but there is a faint one on M 3 and on P 4 . P 4 has an anteroexternal pit. P 3 has a strong 

 anterointermediate crest but a very weak median crest or none at all. P 1 is strongly isolated. The 

 canines are large and the incisors very small and spaced. Inferior: The metastylid on M 3 is fairly 

 large. Pi is very large and very narrow, and P 2 and P 3 are laterally compressed and slightly over- 

 lapping. The incisors are crowded. The superior molar-premolar index is 0.87, and that of the 

 lower series is 0.95. 



Skeleton: The stylohyals of this species show the same characters as those exhibited by the 

 corresponding bones of M. culbertsonii. They are 67.5 mm. in length. 



Promerycochoerus macrostegus (Cope) 1884 

 Figs. 89-90 ; PI. XIII, fig. 3 



Original Reference: Synopsis of the species of Oreodontidas. Proc. Amer. Philos. Soc, XXI, pp. 

 526-531 {Meryco cheer us macrostegus). 



Type Locality: Bridge Creek, John Day Valley, Oregon. 



Geologic Horizon: Lower Miocene (upper John Day). 



Types: Holotype, Cat. No. 7444 A.M.N.H., well-preserved skull and jaws. Plesiotypes, Cat. Nos. 

 10955 and 10957 Y.P.M., skulls and jaws, together with several skeletal elements. 



Specific Characters: The skull is large, longer than that of P. superbus but not so robust 

 as that of either P. chelydra or P. c. latidens. It is on the borderline between mesocephaly and 

 brachycephaly. The face is very long and strongly convex above the infraorbital foramen, on 

 account of a ridge which slopes upward from the anterior zygomatic pedicle to the nasals. The 

 maximum width of the zygomata is at the posterior of the glenoid surface. The malar is deep, 

 while the squamous portion of the arch is heavy, rugose, and U-shaped, with a truncated edge. 

 The posterior part rises to the plane of the summit of the sagittal crest, which is not true of any other 

 species in this genus. Its apex is above the external base of the postglenoid process. The origin of 

 the zygoma above M 2 turns outward abruptly, while again just behind the postorbital bar there is 

 a very markedly abrupt outward flare, which soon turns directly backward. The width of the skull 

 is equal to the length from the occipital condyles to P 4 . The nasal bones are long but proportion- 

 ally reduced. They extend anteriorly to a line just posterior to the canines, and their truncated 

 posterior terminations are well in advance of the antorbital margins. They are moderately narrow. 

 The lacrimal bones appear to be small, and the lacrimal pits are moderately deep but very small. 

 The frontal plane is flat and medium in width, apparently extending in advance of the lacrimals, 

 although the type is an old individual, with sutures closed. The small orbits are situated high on the 

 skull and are deeper than wide. The temporal ridges unite at the postorbital constriction to form a 

 narrow, high, and straight sagittal crest, somewhat longer than a fifth of the skull length. The 

 supraoccipital crest is much produced beyond the occipital condyles and is very slender, with the 

 wings widespread. 



