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UINTA SELENODONTS 



ences may be mentioned the following : In Protylopus the nasals extend 

 farther backward and in front they are pointed, reaching beyond the premax- 

 illaries ; the supraorbital foramina have not shifted so far towards the median 

 line, and the grooves leading from them are much shallower, as are also the 

 supraorbital notches. The mandible has a shorter horizontal ramus and a 

 lower ascending ramus, but a higher, more recurved, and more ruminant-like 

 coronoid ; the peculiar shape of the angle is much the same in both genera. 



It would be interesting in the highest degree to compare the cervical 

 vertebras of the two forms, but, unfortunately, only the atlas of the Uinta 

 genus is known, and that is not sufficiently characteristic for the purpose. 

 The other vertebra? in the latter are somewhat more slender and delicate 

 than in Poebrotherium, but are essentially like them. 



The scapula of Protylopus is higher, narrower, and more slender than that 

 of its White River successor. The spine is lower and the acromion very 

 much shorter and more pointed. The humerus is lighter, but otherwise very 

 similar, but the fore-arm bones remain separate, except in aged individuals, 

 and though the radius is enlarged and the ulna reduced, the change is less 

 than in Poebrotherium, in which anchylosis is complete. The manus is farther 

 removed from that of the White River genus (in which both fore- and hind- 

 foot have attained the same stage of reduction) than might have been expected 

 from the advanced development of the dentition, skull, and pes. The carpus is 

 very much as in the White River genus, except that the distal elements have 

 not yet been so much shortened proximo-distally. Four functional members 

 compose the metacarpus, though the lateral elements are very slender and are 

 more reduced than in other Uinta selenodonts, but in Poebrotherium they are 

 mere vestigial nodules. The carpo-metacarpal articulations are in a state trans- 

 itional to the " adaptive " mode of reduction ; mc. ii. still clings to the trape- 

 zoid, which mc. iii. has not yet reached, but the former has lost its connection 

 with the magnum. The whole manus is relatively very short. 



It is a suggestive fact that the fore-limb of Leptomeryx has many resem- 

 blances to that of Protylopus, and that almost the only important difference 

 between them is the coalescence of the trapezoid and magnum in the former. 



Pelvis and femur differ very little from those of Poebrotherium, and the 

 tibia is also much the same, except that it is proportionately shorter and more 

 slender, and the fibular shaft, though reduced to a mere thread, appears to be 

 still complete. The tarsus differs so little from that of the White River type 

 that it might almost be described as that of Poebrotherium in miniature ; the 



