146 THE MAMMALIA OF THE DEEP RIVER BEDS. 



the preceding species, these bones are decidedly longer and more slender, with the 

 carina? of the distal trochleas more extended anteriorly. In their proportions and in 

 their carpal facets these hones closely approximate those of Merychyus, though the 

 trapezoid facet of mc. iii is smaller. 



The second specimen (PI. V, Fig. 44) consists of isolated phalanges. Those 

 of the proximal row are much more slender and arched forward than in M. chehnyx. 

 The unguals are extremely like those of [Merychyus, but are somewhat more obtusely 

 pointed. 



Measurements. 



M. 



Metacarpal iii, length 069 



Metacarpal iii, width of proximal end 015 



Metacarpal iii, width of distal end . .014 



Metacarpal iii, width of shaft below head Oil 



Metacarpal iv, width of proximal end 013 



Metacarpal iv, width of shaft below head Oil 



First phalanx of third digit, length (pes) 023 



First phalanx of third digit, width of proximal end 012 



Third phalanx of third digit, length 017 



Third phalanx of third digit, width of proximal end 008 



MEEYCHYUS Leidy. 



Froc. Acad. Nat. Sci. Phila., 1858, p. 24. 



Merychyus zygomaticus Cope. 



(Syn. TichoUptus zygomaticus Cope, Amer. Naturalist, Vol. XII, p. 129.) 



The type specimen of this species is a much crushed and distorted skull, of 

 which, through the courtesy of Prof. Cope, I present a drawing (PI. V, Fig. 45), 

 corrected so far as is possible by the aid of other material. On comparing this 

 skull with that of 3Iesoreodon, we are at onee struck by the great increase in vertical 

 height, both relative and actual, wjjich it has undergone, the height measured verti- 

 cally from the lower border of the mandible to the upper line of the forehead above 

 the orbit being to the total length of the skull about as 7 : 11, while in Mesoreodon 

 the height barely exceeds one-half of the length. The face has also become some- 

 what shortened and the cranium relatively longer. The orbits do not extend so 

 nearly to the upper line of the skull, the forehead rising much more above them and 

 is more convex, which appears to be due to a greater development of the frontal 

 sinuses. The supraorbital ridges converge less rapidly, and the forehead is thus 

 longer, higher and more arched, and the sagittal crest is shorter. The upper contour 

 of the skull is more arched from before backward, and in all probability the great 



