228 THE MERYCOIDODONTID/E 



Matthew (1901 A, p. 419) compares the teeth with those of M. arenarum. The former show 

 more advanced hypsodonty. He says: 



The second and third upper premolars are not as wide and scarcely so long as in M. arenarum and the 

 external wall of the third is slightly convex antero-posteriorly toward the base of the enamel, instead of uniformly 

 concave as in M. arenarum. The fourth premolar has less transverse diameter. The outer walls of the outer 

 crescents of m 3 are uniformly concave in some individuals and have a median ridge, variably prominent in others; 

 this character is also variable in M. arenarum and is probably not of specific value. The third and fourth lower 

 premolars are narrower than in M. arenarum and the external notch between protoconid and heel is deeper on 

 P 4 (more molariform). 



Skeleton: The limbs and feet are longer and slenderer than in M. arenarum. Matthew 

 (1901 A, p. 420) describes them thus: 



The radius and ulna are more closely conjoined, the fibula more reduced, the carpus narrower and more 

 rounded than in other Oreodonts, and the ungues are narrow and pointed. The trapezoid is a small, laterally 

 compressed bone, suggesting the trapezium of Oreodon in its shape ; it has a distal facet for mc II, and a smaller 

 distal external facet for mc III. There seems to have been a small nodular trapezium, but its facets are indistinct 

 if present. The metacarpals are rather closely compact, the lateral ones one fifth shorter and one fourth slenderer 

 than the median pair. There was therefore no tendency to functional didactylism of the fore foot, in spite of its 

 extreme (for an Oreodont) slenderness. The unguals are long, pointed, as high as they are wide, except toward 

 the distal end. 



The hind limb is similar to that of M. arenarum, but uniformly more slender. The tibia has a deep 

 trochlea and rather small malleolus. The fibula is unusually small, laterally compressed, with a small calcaneal 

 facet, and above this it is flattened to a thin-edged plate, closely united to the tibia, though not coossified. The 

 shaft is reduced to a mere thread and is again united to the tibia for the second fifth of the distance up the shaft; 

 whether it extended free from the tibia above this point our specimens do not show. 



The toes were hoofed, with four on the manus. 



Discussion: The ramus of this species appears to be a trifle longer than that of M. elegans, 

 and the angle is more pronounced, but the depth below the tooth row is approximately the same. 

 The length of the individual molar and premolar series in both is very nearly the same, and so is the 

 combined length. Pi (caniniform premolar) is about the same size in both, and so is P 2 . P3 is 

 slightly larger in M. e. paniensis, and P 4 is a trifle smaller than in M. elegans. The molars are all a 

 little shorter and narrower than in the latter species. The posterior lobe of M 3 is relatively larger 

 in M. e. paniensis, and there is a slight diastema between Pi and the C, which appears to be absent in 

 M. elegans. The paratype jaw, Cat. No. 9045, is slightly longer than that of the holotype, and the 

 jaw has a little greater depth. 



There are some differences between this species and M. elegans and many points of similarity. 

 It appears to be a somewhat longer jawed animal and yet a little slenderer, both in teeth and ramus. 

 The differences do not seem to be attributable to sex. The male, as designated by Matthew, is closer 

 to M. elegans than the female, the latter rather emphasizing the differences. 



The geologic age is the same, but there is a different geographic locality, Colorado for M. e. 

 paniensis and Nebraska for the genotype. 



The mature skull, when known, will undoubtedly help to define this species more accurately 

 or will point to its closer similarity to M . elegans. I expect that the latter will be true. 



My present opinion is that Loomis' M. paniensis should be considered as a geographic subspecies 

 under M. elegans, since the differences now demonstrable seem not to be of high specific value. 



Merychyus euryops (Cope) 



In 1899 Matthew published this name in his list of Tertiary vertebrate fossils, stating that the 

 supposed type was collected near Laramie Peak, Wyoming, from beds of Loup Fork age, and that 

 it was in the American Museum of Natural History. 



