222 THE MERYCOIDODONTID^E 



nently developed external supracondylar ridge; the supracondylar fossa is unusually large and its anterior border 

 apparently separates the supracondylar ridge from the external tuberosities of the distal end. 



The upper portion of the patella is relatively thick anteroposteriorly, but tapers rapidly towards the lower 

 end. The trochlear articulations are of equal size and are separated by a prominent ridge. 



The tibia is relatively slightly longer than in Merycoidodon and considerably longer and slenderer than in 

 Phenacoccelus. The most characteristic feature of this bone is the short, though stout, cnemial crest; thus differ- 

 ing markedly from most of the oreodonts and again suggesting that it was more fleet-footed. 



The fibula was thin and slender and the shaft complete. 



Of the pes Peterson says: 



It is as much specialized in the direction of a cursorial habit as the forefoot. The tuber of the calcaneum is 

 shortened. The tarsus and metatarsus are actually or very nearly the same length as those in the skeleton of 

 Merycoidodon culbertsoni. . . . while the transverse diameters of the shafts, especially of Mt. Ill and IV, are 

 only very little more than half as great as in M. culbertsoni. In their general proportions the lateral digits are, 

 however, not much reduced, not as much as one might expect, judging from the change in the tibia and other 

 features of the limbs. The phalanges of metatarsals II and V function very nearly, if not identically, as those in 

 Merycoidodon. The phalanges are on the whole possibly somewhat reduced in length. 



The mounted skeleton he describes as follows: 



The most striking feature ... is its relatively high stature in comparison with its small size and the general 

 reduction of its caudal region, when compared with Merycoidodon. The tail in the different genera of this family 



found in the later Tertiary, so far as we now know, seems to be much reduced, In the present genus it is 



very evident that the limbs were specialized in the direction of a cursorial habit. The thorax is also well propor- 

 tioned in size, while the head is perhaps somewhat large for an animal which possibly inhabited open country. The 

 robustness of the upper and lower jaws and their large teeth indicate the power of masticating coarse vegetation. 

 They did not require the incisors specially adapted to cropping grasses seen in other contemporary Artiodactyla. 

 Tall grasses and shrubbery in close vicinity to streams perhaps furnished their pabulum. 



Discussion: This form was originally described by Peterson as a subspecies of M. elegans. In 

 size it is somewhat shorter, with a premolar series relatively a trifle longer, the molar-premolar index 

 being 0.74. The skull is relatively a shade more brachycephalic (index 0.55). With M. a. lepto- 

 rhynchus the agreement is much closer in size and in general structure. The shape of the ramus, 

 with the depth increasing regularly aft, is like that in Cope's species, whereas in M. elegans the depth 

 is more uniform beneath the tooth row. Both the latter forms are lower Miocene in age, Cope's 

 form having been collected in Wyoming and Peterson's in Nebraska, about one hundred miles apart. 

 The differences between these two seem to be mainly connected with size, M. a. minimus being the 



smaller. 



I am reminded again of what we should expect to find in a female, i.e., the same characters 

 that M. a. leptorhynchus seems to show. M. elegans is from the upper Miocene and not contem- 

 poraneous with these other two, and therefore M. a. minimus could not represent the female of that 

 species sensu stricto. Peterson's species might be considered as a geographical variant of equal rank 

 with M. a. leptorhynchus, but if both are females, as I believe, I should include them as such under 

 M. arenarum. 



Merychyus curtus Loomis 1924 

 Figs. 162-163; PI. XXXIV, figs. 1-3; PI. XLVIII, fig. 1 

 Original Reference: Miocene oreodonts in the American Museum. Bull. Amer. Mus. Nat. Hist., LI, 



Art. 1, pp. 31-33, figs. 19-20. 



Type Locality: Ten miles east of Kyle, Porcupine Creek, South Dakota. 



Geologic Horizon: Lower Miocene (lower Rosebud). 



Types: Holotype, Cat. No. 13817 A.M.N.H., well-preserved skull and jaws. In the same locality and 

 geologic horizon a skull, jaws, and the major part of a skeleton were found in 1931 by an Amherst College field 

 party." This specimen now becomes the plesiotype, Cat. No. 31-31 A.M. 



