204 



THE MERYCOIDODONTIME 



and cingulum correspond closely to those of the latter species. All of these teeth have external 

 cingula, as well as anterointernal ones, and they, like the molars, are hypsodont. The canine is 

 reduced, which is a character normal for this genus. 



Discussion: Merriam thought that this species represented an advanced Merycochcerus, though 

 in some respects approaching Pronomotherium. The characters of both the skull and the dentition, 

 however, resemble much more closely the diagnostic features of Metoreodon than those of either 

 Merycochcerus or Pronomotherium. The shortening of the premolar series shows more advance- 

 ment in that element than in any other species of Metoreodon, but the development of the premolar 



Fig. 147. — Metoreodon calijornicus (Merriam). Superior molars. HT. Cat. No. 21351 U.C.M. Nat. size. 



(Redrawn from Merriam, 1919.) 



pattern has not advanced to the stage seen in M. novomexicanus. Merycochcerus fro-prius has a 

 molar-premolar index of 0.85, Pronomotherium latice-ps of 0.70, and P. altiramus of 0.77, so that it 

 is evident that the anterior shortening has progressed farther than in Pronomotherium and much 

 farther than in Merycochcerus. It is, however, not much below the average of 0.66 for Metoreodon. 

 Matthew (1924A, p. 182) suspected that this species belonged in Metoreodon because, as he 

 said, "The upper premolars agree more closely with Metoreodon than they do with Pronomotherium 

 and the infraorbital foramen has the same position as in P. frofectus and relictus, whereas in 

 Pronomotherium- it is much farther back, approximately over m 2 or m 3 ." I thoroughly agree with 

 Matthew's view. 



Metoreodon compressidens (Douglass) 1901 

 Fig. 148 



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

 pp. 79-80, fig. 4 (Merycochcerus compressidens) . 



Type Locality: East side of the lower Madison Valley, Montana. 



Geologic Horizon: Upper Miocene (Madison Valley). 



Type: Holotype, Cat. No. 801 CM., left mandibular ramus, from alveolar parapet of Ij through middle 

 of M 3 . Premolars and first two molars nearly complete. Collected by Earl Douglass. 



Specific Characters: In its form this ramus closely resembles that of M. frofectus. It is 

 thick in the symphysial region, making the symphysis, especially the inferior half, very broad. 

 Posterior to the symphysis the ramus is somewhat thinner, then thicker again under the molars, thus 

 forming a large convexity on the inner side of the ramus, which does not, however, extend to the 

 inferior margin. This convexity is bounded inferoposteriorly by the inner fossa. There is a broad 

 tubercle at the angle of the chin, back of which the inferior border of the ramus, so far as preserved, 

 is nearly straight. The mental foramen is small and nearly round. 



Dentition: The line of the molar-premolar series is that of a slight sigmoid curve when viewed 

 from above. All the teeth are closely crowded, with the premolars overlapping. The incisors are 

 laterally compressed. The true canine is nearly circular in section at the alveolar parapet. Pi, 

 although considerably worn, is much reduced in original size, and its long diameter is oblique. The 

 tooth has well-marked anterointernal and posteroexternal angles, between which it is broadly con- 



