PRONOMOTHERIUM 1 67 



Inferior: T is lacking. I 2 , 3 are laterally compressed at the roots and spaced, although the 

 latter is close to the true canine. The canine is small and is triangular in cross section. Pi is about 

 the size of the upper canine and has a longitudinal groove on the outside of the root. All of the 

 premolars are crowded but do not overlap, nor are they set obliquely, except P>, which is slightly 

 oblique in position. 



Pronomotherium madisonium (Douglass) 1901 

 Fig. 119; PI. XXIV, fig. 5 



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

 pp. 75-77, fig. 2 {Merycochaerus madisonius). 



Type Locality: Lower Madison Valley, Montana. 



Geologic Horizon: Upper Miocene (Madison Valley). 



Type: Holotype, Cat. No. 800 CM., part of right mandible, with anterior lobe of M 3 , nearly complete 

 Mi, 2 , and roots of premolars; crowns of teeth considerably worn. 



Specific Characters: Smaller than P. laticeps and close in size to P. siouense. It also 

 resembles the latter in that there is no abrupt descent beneath M 2 or M 3 but apparently a gradual 

 downward curve. The angle of the chin is beneath the posterior part of P 3 in both species. 



Fie. 119. — Pronomotherium madisonium (Douglass). Fragmentary ramus. HT. Cat. No. 800 CM. 1/2 nat. size. 



(After Douglass, 1901.) 



Owing to the broken and worn condition of the teeth, almost nothing of the crown patterns can 

 be discerned. The premolars were crowded, and P 2 is set obliquely. From the root of Pi it would 

 seem that the transverse diameter of the crown was greater than the anteroposterior. 



Discussion: From the same locality and horizon Douglass referred provisionally to this genus 

 and species a fragment of an upper jaw bearing the molars. The length of the molar series is 

 almost exactly that of P. siouense, and in many other characters it resembles the latter and in the same 

 features it differs from P. laticeps. The face apparently contracted sharply and was short. 



If we had more complete material of P. madisonium, I believe that it would be very close to 

 P. siouense, in fact so close that they might well be the same species or at most geographic variants. 

 Should this prove to be true with adequate materials for comparison, then P. siouense would have to 

 be abandoned in favor of the earlier species of Douglass. For the present, however, both forms 

 should be allowed to stand. P. madisonium, as far as can be determined at present, is a valid species. 

 Douglass compared the lower jaw with that of P. laticeps, which he said it very much resembled, 

 but the upper jaw fragment was more Merycochcerus-Y\ke.. In P. siouense there is a very close 

 approximation to these seemingly divergent characters. 



