242 M. R. Thorpe — John Day Promerycochwri, 



zygomatic arch narrow immediately in advance of the 

 glenoid process, continuing forward and upward in a 

 strong convexity on the side of face, more as iiiEporeodon 

 than in P r ornery co choeriis ; lacrymal fossae deep but 

 small ; depth of malar below orbit, 29 mm. ; hypocone of 

 M3 noticeably smaller than protocone ; internal cingulum 

 on superior molars but faintly developed; transverse 

 crests near together; very strong convexity above fora- 

 men magnum; crest of zygoma low and directly above 

 glenoid process. Shape of the canine more like that of a 

 carnivore than an herbivore. 



The holotype, consisting of the skull and jaws, appears 

 to be one of the earliest Promerycochoeri, and apparently 

 connects the Eporeodons mth this genus. The total 

 length of the skull is but about 30 mm. longer than the 

 largest Eporeodon. It differs, however, from Eporeodon 

 in the following features: (1) the postglenoid processes 

 are robust and prominent; (2) the bulliB are large and 

 laterally compressed, but less prominent than the post- 

 glenoid processes, whereas in Eporeodon the bullae are 

 very large and the postglenoids always relatively very 

 small; (3) the condyles are heavier, of different shape, 

 and more widely separated at the basion; (4) in Epore-' 

 odon the highest point of the zygoma is near the middle 

 of the temporal fossa, but in this species, the squamous 

 part trends upward, as in the other Promerycochoeri, 

 above or just in advance of the glenoid articular surface ; 

 (5) the infra-orbital foramen is above the posterior part 

 of P^, while in Eporeodon it is normally above the anter- 

 ior part of P-% and in the other species of Promerycochoe- 

 rus, either above P^ or above the interval between P^ and 

 M^ ; (6) the basicranial axis is steep, a condition fre- 

 quently found in P r ornery cochcerus , but not in Eporeodon. 



This species resembles Eporeodon in that (1) the metas- 

 tyle of ]\P is not rotated as far inward as is usual in 

 P r ornery CO choer us, but has more the position found in 

 the other genus; (2) the hypocone of M^ is smaller than 

 the protocone, whereas in the other species they are 

 normally nearly equal in size; (3) its size is close to 

 that of the larger Eporeodons ; (4) the inferior border of 

 the ramus does not so closely parallel the alveolar border 

 as in the latter genus (in Pr ornery co choer us the inferior 

 border projects do\\mward toward the angle gradually, 

 beginning beneath the posterior portion of M-^) ; (5) the 



