164 THE MERYCGIDODONTID/E 



nent ridge. In pm 4 the ridge has become a prominent element of the tooth, being separated from the other part 

 by a large posterior fossa and the extension backward to meet it of the anterior interior fossa. In this tooth the 

 posterior concavity above mentioned has become quite a deep trough and is more nearly central. The unworn 

 and nearly perfect condition of the premolars gives an excellent opportunity for the study of their development 

 and their conditions before wear. If worn to the same extent they would not differ so greatly from those of 

 M. laticep. 



In general the teeth of this species, although unworn, were apparently more hypsodont, nar- 

 rower, and with sharper cusps and ridges than the teeth of P. laticefs. 



Fig. 117. — Pronomotherium elrodi (Douglass). Fragmentary ramus. HT. Cat. No. 818 CM. 1/3 nat. size. 



(After Douglass, 1901.) 



Pronomotherium elrodi (Douglass) 1901 

 Fig. 117; PI. XXIV, fig. 4 



Original Reference: New species of Merycochcerus in Montana. Pt. II. Amer. Jour. Sci. (4), XI, 

 p. 78, fig. 3 (Merycochcerus elrodi). 



Type Locality: At Big Round Top, on the east side of the lower Madison Valley, about seven miles 

 south of Logan, Montana. 



Geologic Horizon: Upper Miocene (Madison Valley). Indurated clay formation. 



Type: Holotype, Cat. No. 818 CM., posterior portion of left ramus with M 2 and M 3 . Collected by 

 E. Douglass and named in honor of Professor M. J. Elrod of the State University of Montana. 



Specific Characters and Discussion: Douglass compared this fragment of a mandible with 

 P. madisonium y P. laticeps, and P. altiramus, all species which were originally placed in Meryco- 

 chcerus and subsequently removed to Pronomotherium. In so far as comparison is possible, the type 

 of this species most nearly resembles P. madisonium. Douglass noted that the ramus is deeper but 

 not so thick, the difference being most marked near the lower border. The inferior border is less 

 flat, with an angular ridge near the external edge. Beneath Mi the ramus is nearly flat, and the 

 crescent-shaped convexity is lacking on the external surface. Douglass said that the contour of the 

 lower border of the ramus differs from that of P. laticeps in that the beginning of the descent to the 

 angle is farther aft and the angle itself is not so deep. The masseteric fossa, he noted, had evi- 

 dently about the same position and shape as in P. altiramus. There is a shallow trough extending 

 downward and forward from that fossa to the middle of the ramus beneath M 2 . In P. altiramus 

 and P. laticeps there are traces of a similar trough. 



Dentition: In comparison with P. madisonium the crowns of the two molars in the present 

 species are higher, but this may be accounted for by the lesser amount of wear. There is no cingu- 

 Jum between the inner lobes of M 2 , and the tooth is somewhat longer and wider, though of about 

 the same proportions, in this species. A cingulum is present on the anterior face of both M 2 and M 3 . 



