234 THE MERYCOIDODONTID^E 



Merychyus species Peterson 1906 



Original Reference: The Miocene beds of western Nebraska and eastern Wyoming and their vertebrate 

 fauna?. Ann. Carnegie Mus., IV, pp. 40-41. 



Discussion: A nearly complete tibia, with the middle part of the shaft of the fibula adhering to 

 it, together with the astragalus, cuboid, navicular, cuneiform, and the major part of the metatarsals, 

 was collected in the lower Harrison beds, on Squaw Butte, Sioux County, Nebraska. This material 

 bears Cat. No. 1284 CM. Unfortunately no teeth nor skull parts were found with it. 



These bones represent an animal larger than M. a. minimus, but with long, slender legs. The 

 feet are rather long, but Mts. Ill and IV are proportionally smaller and probably shorter than in 

 M. a. minimus. These specimens may be referred to M. siouxensis, but in any event they seem to 

 belong to the genus Merychyus, and we shall have to await the discovery of comparable material 

 with an associated skull before making a definite assignment. 



Oreodont cf. Merychyus Maxson 1930 



Original Reference: A Tertiary mammalian fauna from the Mint Canyon formation of southern 

 California. Carnegie Inst. Wash. Publ. No. 404, p. 1 1 1, fig. 18. 



Discussion: Maxson described and figured the posterior part of a left ramus with part of a 

 worn Mi and an unworn M 3 found in the Mint Canyon beds. 



I believe there is no doubt that it is impossible to refer this specimen to any genus of the mery- 

 coidodonts. I agree with Stirton that it belongs in the Antilocapridse and is not far from Merycodus. 



LEPTAUCHENIA-CYCLOPIDIUS STOCK 



Genus LEPTAUCHENIA Leidy 1856 

 Table 13 



Original Reference: Notices of remains of extinct Mammalia. Proc. Acad. Nat. Sci. Phila., VIII, 

 p. 88. 



Genotype: Leftauchenla decora Leidy. 



Genocotypes and Genoparatypes not differentiated; Cat. Nos. 10875-10940 A.N.S.P., fragmentary 

 upper and lower jaws, with teeth and a badly damaged skull. 



Distinguishing Characters: Skull small} facial vacuities large, averaging less penetration 

 of the frontals than in Cyclopidius; form brachycephalic (indices 0.68-0.71); premaxillaries small 

 and somewhat rotated; nasals, frontals, and maxillaries somewhat reduced; malar moderately deep 

 but light, and zygomatic arch light; basicranial area foreshortened, with enormous bulla; which 

 underlie the postglenoid articular surfaces somewhat more than in Cyclopidius; external auditory 

 meatus large, elevated, and posteriorly directed; postglenoid process compound; frontal complete 

 between the orbits; chin less vertical than in Cyclopidius; orbits large and elevated; posterior of 

 cranium very wide, because of great lateral expansion of exoccipitals and zygomatic processes; basi- 

 occipital and basisphenoid reduced almost to bony ridges; sagittal crest low; symphysis coossified; 

 ascending ramus very deep and coronoid process small, scarcely projecting above the small condyles, 

 in which the transverse diameter is but slightly more than the anteroposterior; dentition hypsodont; 

 1 1 ; premolars appearing to slant backward. 



Discussion: The genera Leptauchenia and Cyclopidius are the most peculiar of all the Mery- 

 coidodontidas. It is difficult to separate the two, the latter being the more exaggerated form. The 

 former is the older geologically. They represent a group which appeared suddenly in late Oligocene 

 times and vanished as suddenly in the middle or upper Miocene (Deep River). Leptauchenia 

 averages smaller in size and is of lighter build and less specialized. 



