56 THE MERYCOIDODONTID/E 



The malar is not deep but is moderately robust beneath the orbit. The nasals are posteriorly acute, 

 anteroposteriorly straight, transversely but very slightly convex, and of normal width. The 

 lacrimal has a medium-sized -pars facialis, with a large and deep antorbital fossa. The frontals are 

 wide and unreduced. Anteroposteriorly they are convex, while transversely they are sharply 

 depressed along the sagittal suture for more than half their length and are convex between the 

 depression and the supraorbital margin. The frontal is produced forward of the lacrimal and termi- 

 nates in an acute apex between the nasal and maxillary. The orbits are small and subcircular. The 

 temporal ridges unite just back of the postorbital constriction. The sagittal crest is moderately high 

 and about a third of the skull length. The supraoccipital crest is moderately produced, and the 

 wings are wide open. The brain case is well rounded, with the usual convexities. The large 

 trumpet-shaped auditory meatus is directed upward and backward. The basicranial axis is steep. 

 The palate is wide and very gently vaulted, with the palatonarial border on a line with the posterior 

 of the last molars. The glenoid articular surface is moderately wide anteroposteriorly and slightly 

 convex, and the postglenoid process is robust. The large paroccipital process is triangular in cross 

 section, extending downward well below the level of the occipital condyles. The bullas are very 

 small. Index: 0.56a. 



Mandible: The symphysiodental angle is 43°, and the chin profile is very slightly concave, 

 with a small mental tubercle. The horizontal ramus has a nearly straight inferior border. The 

 angle is prominent. The condyle is strongly convex, and the coronoid process is slender and rises 

 moderately above the strongly convex condyle. The sigmoid notch is shallow and wide open. 



Foramina: The infraorbitals lie above the anterior portion of P 3 . The supraorbitals are unusu- 

 ally close together, being only about 5 mm. apart. The foramen ovale is large, and the foramen 

 rotundum small. The posterior palatine foramina are opposite P 4 . 



Dentition: The teeth are so much like those of M. culbertsonii that they need no description. 

 The superior molar-premolar index is 0.87, and that of the inferior series is 0.84. 



Discussion : This subspecies probably should be considered as a geographic variant or mutant 

 confined mainly to Colorado, although a few specimens have been collected in Wyoming and 

 Nebraska. Except for its smaller size, it differs so little from Af . culbertsonii that it might well be 

 considered as the female form of that species, but the geographic distribution seems to be opposed to 

 this conclusion. 



The age at which death occurred in forty specimens in the Marsh Collection is as follows: 

 15 per cent with milk dentition; 65 per cent in the prime of life j 15 per cent past middle age; 

 and 5 per cent in old age. 



Merycoidodon gracilis (Leidy) 1851 

 Fig. 7; PI. I, figs. 4-5; PI. Ill, figs. 3-5; PI. XLI 



Original Reference: Descriptions of fossil ruminant ungulates from Nebraska. Proc. Acad. Nat. Sci. 

 Phila., V, p. 239 {Oreodon gracile). 



Synonyms: Oreodon gracilis coloradoensis Cope 1884; Oreodon minor Cope 1888, nomen nudum. 



Type Localities: White River, South Dakota; Nebraska. 



Geologic Horizon: Middle Oligocene (lower Brule). 



Types: Cotypes, Cat. Nos. 10682-10691 A.N.S.P., several fragments of rami and maxilla; with teeth, 

 together with skulls. Plesiotype, Cat. No. 136 U.S.N.M., skull and jaws. Cat. No. 6404 A.M.N.H., holotype 

 skull of M. gracilis coloradoensis (Cope). 



Specific Characters: The skull is small, about two-thirds the size of that of M. culbert- 

 sonii. The maximum expansion of the zygomata is about at the middle of the zygomatic foramina. 

 The malar is medium in depth, and posteriorly the arch rises gradually. The nasals are posteriorly 

 rounded, about uniform in width and very slightly convex in both diameters, and extend forward 

 almost as far as the incisive border. The large lacrimal bone is triangular in outline, and the 

 lacrimal fossa is well marked but not deep. The frontal bones are wide and convex above the orbits 



