70 



THE DESEADO FORMATION OF PATAGONIA 



the second series, all associated, which probably indicates 

 the full number of the toes. The ungual phalanges are 

 proximally narrow and high, then expand toward the tip, 

 developing into marginal expansions. There is but a trace 

 of a cleft in the end of these ungual phalanges. 



Measurements 



Skull, greatest length 



Upper dentition, length inc. I to m. 3 



Upper dentition, length pm. I to m. 3 



Upper dentition, incisor 1, width 



Upper dentition, molar 1, length 



Upper dentition, molar, width 



Mandible, greatest length 



Lower dentition, length inc. 1 to m. 3 



Lower dentition, length pm. 1 to m. 3 



Lower dentition, molar 1, length 



Lower dentition, molar, width 



Third metacarpus, greatest length 



Pelvis, length front to back 



Femur, greatest length (computed) 



Femur, diameter of middle of shaft 



Tibia, greatest length 



Astragulus, length 



Astragulus, width 



Calcaneum, length 



Metatarsus III, length 



First phalanx of digit III, length 



Ungual palanx of digit III, length 



To make the similarity of Prosotherium with Pachy- 

 rukhos clearer, I have restored Prosotherium, figure 40, 

 from which it will be seen that this genus is also a hopping 

 form with a plantigrade hind foot and a semidigitigrade 

 front foot. In general it compares very closely with Pachy- 

 rukhos, but the limbs are shorter and the grade of speciali- 

 zation is not quite as high. It is, however, very evidently 

 the ancestor of Pachyrukhos. 



