1902.] Osboniy American Eocene Primates. 195 



(Sp. 45) Notharctus nunienus Cope. — Includes the smaller 

 Wind River forms (mj-mg — 15 mm.). We find a strong 

 deuterocone (internal cusp) on pm^. 



(Sp. 58) Notharctus venticolus, Sp. nov. 



A much larger monkey (No. 47156, Am. Mus.) was referred 

 by Cope to P . tutus but is clearly distinguished from this 

 older Wasatch species by the presence of a mesostyle in the 

 upper molars, and by the more progressive character of the 

 grinding teeth throughout m — nig = 17. The type (No. 

 4715 6) was figured by Cope, ' Tertiary Vertebrata,' PL xxv, 

 figs. I, 2. Other specimens are No. 4726 {op. cit. fig. 3), Nos. 

 4728, 4738. 



3. Bridger (Bartonien) Stage. 



The gradual steps toward sexituberculy in the upper molars 

 and quadrituberculy in the lower, begun in Pelycodus, lead 

 directly into a number of Middle Eocene (Bridger) forms, 

 mostly of larger size and on a higher plane of general develop- 

 ment, baptized by Leidy, Cope, and Marsh with an unusual 

 number and variety of names, as shown in the chronological 

 table of species above. The identification of all these genera, 

 however, needs confirmation by further comparison of types. 



Unfortunately we have an incomplete record of the levels 

 at which the types of these species and genera were found, 

 but it is important to remember that the Bridger was a 

 very long period, with time for the marked progression in 

 dental structure observed in various specimens which may 

 provisionally be referred to the single genus Notharctus. While 

 there was considerable range of progression from the lower 

 to the higher forms we cannot at present specify any single 

 generic character which will enable us to clearly subdivide 

 the Bridger species into different genera, because the pro- 

 gression although on a higher scale, is precisely analogous to 

 that observed in the transition from Pelycodus frugivorus to 

 P. tutus. 



