MERYCOCHCERUS 157 



rather narrow. The glenoid surface is wide. The paroccipital process is moderately slender and 

 directed nearly straight downward. Index: 0.73. 



Mandible: The symphysis is strong, and the symphysiodental angle is about 30°. The inferior 

 border of the ramus is slightly shallower and is nearly straight between the rounded eminence at 

 the base of the symphysis and the angle, both of which are of relatively slight prominence. The 

 posterior depth is normal. The coronoid process is wide at the base, diminishing rapidly near the top, 

 which is relatively small. The sigmoid notch is small, shallow, and wide open. 



Foramina: The infraorbitals lie above the anterior part of M 2 . The supraorbitals are approxi- 

 mately 39 mm. apart. 



Dentition: The molars are hypsodont, and the crowns of all the teeth, except M 3 , are much 

 worn. The superior premolars and molars, especially the latter, seem to be rather broad, but when 

 the skull and jaws are separated this statement may need qualification. The superior molar-pre- 

 molar index is 0.74. 



Skeleton: The limbs and feet are relatively long rather than short and stocky, as in M. magnus 

 or as is typical for this genus. 



Discussion: While this species is a true Merycochcerus, it seems to be less specialized than 

 M. proprius in certain respects. It may represent a female, or it may be a side branch from the 

 main stem that is slenderer, more delicately constructed, and longer legged. 



M. magnus, on the other hand, may well be a male or the representative of a heavy, stocky 

 line, but in any event it is more typical of the Merycochcerus genus. 



Merycochcerus proprius Leidy 1858 

 PI. XXII; PI. XXIII, figs. 1-3 



Original Reference: Notice of remains of extinct Vertebrata. Proc. Acad. Nat. Sci. Phila., X, pp. 

 24-25. 



Type Localities: Genoholotype, near the headwaters of the Niobrara River, not far from Fort Laramie, 

 Wyoming. Plesiotypes, the Pawnee Creek area of northeastern Colorado. 



Geologic Horizon: Middle Miocene (GHT, Hayden's Bed D, in a stratum of "dull reddish-brown 

 grit"); upper Miocene (PLTs, Pawnee Creek beds). 



Types: Genoholotype, Cat. No. 156 U.S.N.M., upper and lower jaws, containing nearly complete denti- 

 tion (figured by Leidy 1869, pi. 10, figs. 1-4). Paratype, Cat. No. 445 U.S.N.M., last left upper molar, from 

 same horizon and locality as GHT. Plesiotypes, Cat. No. 8968 A.M.N.H., skull, jaws, and all parts of skeleton 

 of one adult, probably a male, and of four juveniles found together in the fine pinkish-buff clays; Cat. No. 9052 

 A.M.N.H., complete skull of adult, probably a female, and skeletal fragments; Cat. No. 9064 A.M.N.H., teeth, 

 parts of jaw and fore limb, vertebrae, and other fragments, the latter collected in Hayden's Beds D and E, similar 

 to the stratum in which the genoholotype was found. 



Specific Characters: This is evidently the smallest species so far described, but we do not 

 know a complete skull of M. buwaldi nor any skull material of M. ccenopus. As seen from above 

 the general outline of the skull is triangular, and from the side it is roughly right-triangular. The 

 cranial region is greatly foreshortened. The maximum skull width is about the same as that of 

 Promerycochcerus. The face is abruptly narrowed anterior to M 2 , on account of the excavation of the 

 lacrimals and maxillse. The zygomata attain their maximum expansion at the glenoid articular sur- 

 faces, and the malars have an extreme depth of about two inches below the orbits. The squamosal 

 portion of the zygoma extends forward as far as a point opposite the posterior part of M 3 . From 

 this point it extends posteriorly in a gentle upward curve, reaching vertically in a plane somewhat in 

 advance of the occipital condyles. As seen from above the zygoma trends outward in nearly the 

 same plane as the malar, as far aft as the glenoid surface, and then curves inward. The curve of the 



