FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 147 



transversely but otherwise similar. P4 has a metaconid. M1.2 are 

 much like Paromomys. The third lobe on M3 is narrower than in 

 P. maturus but closely approached in P. depressidens. The cheek 

 teeth throughout are very close to Palaechthon but lower, broader, 

 and heavier. Palaeddhon is an admirable structural ancestor for 

 Trogolemur, although the time gap is too great for definite decision. 



Uintalestes is very poorly known but is evidently related to Tro- 

 golemur from which it differs essentially only in the further dental 

 reduction, having only seven teeth in the lower jaw, and the narrower 

 heel of P4. 



The lower molars of Phenacolemur could readily be derived from 

 the Paromomys type but are heavier and more quadrate. P4 is also 

 similar but is much enlarged and likewise heavier and more quadrate. 

 The much heavier incisor and the complete loss of all teeth between 

 it and P4 sharply distinguish Phenacolemur, however, and the time 

 gap is far too short for derivation from Paromomys. The molar 

 resemblance may, therefore, be misleading. P^ has a much stronger 

 posteroexternal cusp than in Paromomys, and the internal groove is 

 absent on the upper molars, but they have an equally and similarly 

 expanded posterointernal basin and in general are as close to those of 

 Paromomys as are the lower molars. 



Resemblances to the Carpolestes and the Plesiadapis phyla are dis- 

 cussed in dealing with the contemporary members of the latter, 

 Elphidotarsius and Pronothodectes , but the adaptively related group 

 Apatemyidae has no known representative before the upper Paleocene. 

 They may, however, be summarily dismissed as possible close relatives 

 of the Fort Union forms, as none of their peculiar distinctions are 

 foreshadowed in the latter. The apatemyids, as redefined by Jepsen 

 (1934), have an enlarged incisor, larger than in Carpolestes or Plesia- 

 dapis, which more nearly resemble Paromomys and its allies in this 

 respect, and early lose all teeth between this and P3, at least two of 

 which are retained in Paromomys and in the other two groups men- 

 tioned. P3 becomes 1-rooted and pecuHarly bladed. P4 is markedly 

 reduced even in the upper Paleocene and becomes vestigial in later 

 forms. The molars have a quadrate trigonid, as in many early 

 primates, but, especially on Mi, it is much more elongate anteropos- 

 teriorly than in Paromomys and its allies. The upper teeth are 

 equally divergent. 



Gidley (1923, pp. 3-4, 8-9) noted the resemblance of Paromomys and 

 Palaechthon to the Notharctinae in the lengthened heel of M3, the 

 trigonids consisting chiefiy of protoconid and metaconid connected 

 by a loph and with an anterior shelf, and the posterointernal expan- 

 sion and basining of the upper molars. He added, however, that 

 these are not exclusively notharctine characters and concluded that 

 they did not indicate close affinity in this case. The resemblance is. 



