s 



11 



smaller than those of the species before mentioned. There is a considerable popliteal cal- 

 lus, and, what is especially characteristic, the crest is divided by a vertical median groove, 

 as in the genera Aphelops and Rhiuocerus. This type of tibia corresponds to that of some 

 of the species of Symborodon, e. g., S. bucco, and perhaps others. There is no tibia nor any 

 other bone, except perhaps part of a humerus, which corresponds with the smallest astra- 

 galus. 



The bones of the two largest species are probably those of the M. americanus and 31. 

 proutii, but which belongs to which I cannot certainly determine. As the M. americanus 

 is, in the characters of its muzzle and horns, the nearest to the M. angustigenis, it will be 

 probably safe to refer to it the tibia which approaches the corresponding bone of that 

 species. That will be the second of the above description The third corresponds in size 

 to the M. angustigenis, and agrees with it in approaching the species of Symborodon in 

 some respects. I give corresponding measurements of the tibite, astragalus and calcanea 

 of the two species : — 



I. Tibia. 



M. proutii. M. americanus. 

 Total length 387 355 



f Anteroposterior 135 150 



Diameters of head-! 



(Transverse 144 135 



f Anteroposterior 60 55 



Diameters of shaft-] 



( Transverse 60 60 



C Anteroposterior 72 65 



Distal diameters..-! 



(.Transverse 100 100 1 



II. Calcaneus!. 



Length 155 135 



Length of tuber 90 SO 



Width distally 75 57 



(Vertical 35 42 



Diameters of cuboid facet-! 



(Transverse • 55 30 



III. Astragalus. 

 f Transverse 80 



Diameters of trochlea -{ f External roller 70 



| Anteroposterior -J 



L I Internal roller 57 



(Vertical 54 



Diameters of navicular facet 1 



( Transverse 49 



Oblique length of cuboid facet 47 



From the above it is evident that the hind foot of the M. americanus is relatively and 

 absolutely larger than in the M. proutii. In the former the external cotylus has a greater 

 transverse, and the internal a smaller anteroposterior diameter than in that of the M. 

 proutii. 



1 Partly restored. 



