104 THE MERYCOIDODONTID/E 



Specific Characters: Compared with M. chelonyx and M. megalodon, the skull is intermedi- 

 ate between these two species, but it is longer and much wider than either, having an index of 0.74. 

 The posterior part of the zygomatic arch is heavier, and the face is somewhat broader. The sagittal 

 crest is long. The radius and tibia are proportionately short, the metatarsus shortened, and the 

 remainder of the skeleton intermediate in size between the two previously described species. The 

 index of the superior molar-premolar series is 0.81 and of the lower series 0.84. 



Discussion: The skull is of somewhat less depth than that of M. megalodon, the limbs are 

 shorter, and the scapula is narrower, but the total length of the skeleton is approximately the same 

 as that of the Peterson species or even slightly greater. 



This is the largest species of the genus so far described. It is quite possible that it may prove 

 to be the male of M. megalodon, for the larger size, the heavier and broader skull, and the shorter 

 limbs are in keeping with a male of that species. Both Scott and Loomis have found a considerable 

 range of variation in the older species of this genus that they attribute to sexual variation. 



Genus PROMERYCOCHCERUS Douglass 1901 

 Tables 5-7 



Original Reference: New species of Merycochcerus in Montana. Part II. Amer. Jour. Sci. (4), XI, 

 p. 82. 



Synonyms: Paracotylops Matthew 1901; Desmatochcerus Thorpe 1921; Hypselochcerus Loomis 1924. 



Genotype: Promerycochcerus suferbus (Leidy) 1870. 



Genocotypes: Cat. Nos. 516 U.O.M., 10151, 10152, 10153, 10967, and 10968 Y.P.M., fragmentary 

 parts of rami and skulls, some with teeth. 



Distinguishing Characters: Skull large, ranging from 253 mm. to 41 1 mm., mainly meso- 

 cephalic but in a very few instances brachycephalic or dolichocephalic, with an average index slightly 

 below 0.65; all sutures apparently closed very early; nasal bones long and unreduced; premaxil- 

 laries large, not coossified, transversely wide at base, and long diameter changing upward from 

 transverse to anteroposterior; muzzle narrow to moderately broad; face with orbits fully half of 

 skull length; orbits medium to small for size of skull; antorbital fossa small and deep to iarge and 

 shallow; frontals wide and unreduced; brain case small on the average; supraoccipitals prolonged 

 and occiput narrow; malar deep and zygomatic arch light to medium aft; bullse small in relation to 

 size of skull but large for the family; mandible medium in depth, symphysis strong, ascending ramus 

 wide, and coronoid process low; infraorbital foramen above P 4 in majority of species, but above 

 interval between P 4 and M 1 in several, in one species above P 3 , and in another, above interval 

 between P 3 and P 4 ; posterior palatine foramina small or obsolete and seldom plainly visible. 



Dentition: Subhypsodont. In the superior premolars the anterior and posterior crescents are 

 well developed, with the latter normally larger than the former, and the anterointermediate and 

 median crests are weak. Occasionally there is a small pit on the anteroexternal corner of P 4 . The 

 inferior premolars are narrow and compressed, with a prominent posterointermediate crest which 

 subdivides the posterior basin. P 4 is characteristic, with the presence of a large pillar-like cusp at the 

 junction of the median crest and the posterior crescent, which remains distinct from both until the 

 tooth is considerably worn. There is also an enlargement on the posterior crest of this tooth which 

 may occasionally appear like a smaller cusp. P 2 and P 3 lack the anterior crescent but have a weak 

 posterior one. 



Skeleton: This ranges in length from 1370 mm. to 1720 mm. and in height from 610 mm. to 

 725 mm., as now known. 



Discussion: There is a greater variation between specimens of this genus than is shown in any 

 other division of the family. Hardly any two skulls are really closely alike. This perhaps is 

 somewhat understandable when we remember that Eporeodon was also very widespread and very 



