234: M. R. Thorpe — John Bay Promerycochoeri, 



prominent. The inferior surfaces of the bullae are deeply 

 pitted. These bullae are proportionally small and com- 

 pressed; in P. macrostegus they are the smallest in the 

 genus and are cone-shaped, while in P. latidens they 

 extend from the anterior third of the paroccipital process 

 to a line passing through the middle of the glenoid arti- 

 cular surface, but in P. chelydra they are small and sub- 

 conical. The bull^ extend as far as, but not below, the 

 inferior edge of the postgienoid, in which they differ from 

 those both in the last named species and in P. macros- 

 tegus. The surface of the glenoid articulation is 70 mm. 

 in length, while in the latter species, one of the longest 

 of the genus, it is somewhat less than 60 mm. 



The occiput is much more overhanging and the trans- 

 verse crests spread much farther apart than in P. macros- 

 tegus. The height of the occiput above the base of the 

 occipital condyles is 110 nnn. in the latter species and 120 

 mm. in P. latidens. There is a very strong convexity above 

 the foramen magnum, as in P. macrostegus, whereas 

 in P. chelydra the convexity is wide and shallow. This 

 convexity is separated from the posterior temporal angles 

 by very deep lateral fossae. The coossified mastoid and 

 paramastoid processes do not close the auricular fossa 

 below in P. m.acrostegus, but in this species they come 

 extremely close to the postgienoid, although not actually 

 forming a contact. The paramastoids are triangular 

 shaped and robust ; not nearly so slender as in P. macros- 

 tegus. They abut directly against the bullae. 



Measurements of Holotype. 



mm. 



Total leng-th of skull, approx. , 385 



Bipostglenoid diameter 143.5 



Bizygomatic diameter 274 



Length of superior molar series 79 



Length of superior premolar series 69.5 



Max. width of cranium 113.5 



Diameter of post orbital constriction , 72.3 



Max. height of zygoma above glenoid surface 65.7 



Width of frontal above middle of orbit 121.5 



Width of face at infra-orbital foramina 87 



Distance from M" to posterior margin of occipital condyles 



in median plane 148 



Ant.-post. diameter of M"^ 36 



