No. 2.] THE RELATIONS OF PROTOCERAS. 365 



In Hypertragnlus we find certain characteristics peculiar to 

 itself, such as the retention by the lower canine of its original 

 form and function, the loss of the first and isolation by diaste- 

 mata of the second lower premolar, and the coossification of 

 the ulna and radius, but the general resemblance to Leptomeryx 

 is close. The structure of the cranium and position of the 

 orbits are the same in both, but the elongated, constricted, and 

 slender muzzle, the large and irregular fontanelles which en- 

 croach upon the nasals, the character of the palate, the shape 

 and position of the posterior nares, the aspect of the base of 

 the skull, with auditory bullae and glenoid cavities, are all 

 suggestively like what we find in Pr-otoceras. The premolars 

 have the same simple structure found in the latter, but are not 

 so much elongated antero-posteriorly. The pes is like that of 

 Protoceras, except for the coossification of cuboid and navicu- 

 lar. In size Hypertraguhis somewhat exceeds Leptomeryx, but 

 is much inferior to Protocet'as. Still another genus of appar- 

 ently this same group is the curious little Hypisodus, from the 

 White River, with its hypsodont molars and ten functional 

 lower incisors, made up of the incisors proper, the canines, and 

 first premolars. The distal end of the fibula is coossified with 

 the tibia, and the feet, so far as known, resemble those of 

 Lepto7Jteryx. 



This family represents a group of White River selenodonts, 

 each of whose genera has become more or less specialized in a 

 way peculiar to itself, and with a tendency to simulate the 

 Pecora in some respect or other, yet always retaining a num- 

 ber of primitive features. I cannot but believe that Protoceras 

 represents a divergent offshoot of the same stock which, retain- 

 ing in most respects the foot-structure belonging to the com- 

 mon ancestor of all these genera, has, at the same time, 

 wonderfully paralleled the higher Pecora in many features of 

 the skull. We have yet to find the forerunners of this genus 

 in the two lower divisions of the White River formation, the 

 Oreodon and TitanotJierumi beds, but one of these forerunners 

 may prove to be the problematical genus Stibarits. The 

 Uinta formation may be expected to yield the ancestor com- 

 mon to the entire group, and when it is found we shall prob- 



