160 the merycoidodontim: 



The succession of the eruption of the teeth, according to Matthew, is MJ, P 1 , Mo, C 1 , 



p T 1-3 f p2-4 



1 1) - 1 1 -35 ^l) r 2-4- 



As is to be expected in the young, the limb bones are proportionately shorter than in the adult. 



Discussion: Under Metoreodon profectus I have discussed the last upper left molar, figured 

 by Leidy (1869, pi. 10, fig. 5), which is the paratype of Merycochoerus proprius (Cat. No. 445 

 U.S.N. M.). The smaller relative transverse diameter of the hypocone is also seen in M. buwaldi 

 and in the holotype of M. ma gnus. The apparently greater size of the metastyle is due, I believe, 

 to the fact that it has suffered considerable wear. This structure enlarges as it nears the roots, that 

 is, it is constructed after the manner of a cone. The tooth may have belonged to a male, as it is very 

 robust and heavy. The accessory cusp on the posterior of the hypocone is, to my mind, an individual 

 variation. I prefer to regard this isolated tooth as certainly belonging to a merycochcerid and most 

 probably to M. proprius, as considered by Leidy. 



Leidy ( 1 869, p. Ill) proposed placing this species in the genus Oreodon, since he was not com- 

 pletely satisfied that the characters of Merycochosrus as then known were of sufficient value to hold 

 the genus. 



Genus PRONOMOTHERIUM Douglass 1907 

 Table 8 



Original Reference: Merycochoerus, and a new genus of merycoidodonts, with some notes on other 

 Agriochcerida?. Ann. Carnegie Mus., IV, pp. 94-95. 

 Genotype: P. laticefs (Douglass) 1900. 

 Genoholotype: Cat. No. 796 CM., nearly complete skull and mandible, collected by Earl Douglass in 1899. 



Distinguishing Characters: Skull moderately large (250 approx.-335 mm.) but broad and 

 low, normally brachycephalic (P. siouense more mesocephalic) , nasal bones greatly shortened and 

 upwardly directed forward; premaxillaries and maxillaries coalesced; face elongate, pars facialis 

 very small or lacking and sides of face concave; brain case rather small, with great foreshortening 

 of basicranial region; basicranial axis very steep; malar deep but squamosal part of zygoma light, 

 although well expanded; frontals flat and somewhat reduced by intrusion of nasal bones; antorbital 

 fossa deep and large; bulla; small and cylindrical; mandible of great posterior depth ; infraorbital 

 foramen over M 2 ; dentition hypsodont; average superior molar-premolar index 0.68 and average 

 lower index 0.65; P 3 having weak median crest, anterior and posterior basins confluent, and traces 

 of small intermediate crests; average length of upper premolar series equalling combined length of 

 M 1 , M 2 , and nearly half of M 3 ; lower premolars somewhat shortened and crowded; P 3 having 

 anterior part prolonged, median crest well developed, anterior crescent weak, and intermediate 

 crests lacking; P 4 with strong median crest and cusp-like pillar at junction of crest and posterior 

 crescent; length of premolar series equalling average combined lengths of Mi, M 2 , and half of 

 anterior lobe of M ; limbs short and stocky. 



Discussion: The structure of the skull in this genus assuredly indicates either a lengthened 

 snout or, what is more probable, a proboscis longer than that of the modern tapir. 



The incisors are very small and, curiously enough, the first incisor is missing in the lower series 

 of all the species. Whether that incisor has permanently dropped out or is missing as a result of 

 postmortem injury I cannot determine. The maximum space in which it could have been lodged is 

 indeed very small, and I am inclined to believe that it had already been permanently lost or was 

 rapidly approaching that state. There is no question about the three incisors having been present in 

 the superior series. 



While in some of its characters this genus resembles Merycochoerus, I believe that the funda- 

 mental structure of the former was not derived from the latter but rather from some form ante- 



