196 Bulletin American Museum of Natural History. [Vol. XVI, 



Notharctus has the same dental formula as Pelycodus but is 

 readily distinguished by the coossified mandibular symphysis, 

 the chisel-shaped incisors, the usually single fang of the first 

 and sometimes of the second lower premolar, the compara- 

 tively well developed hypocone and the subquadrate shape of 

 the upper molars; the usually marked reduction or absence 

 of the paraconid in the lower molars. 



p.3 pA m.l m:2 m.3 



Fig. 23. Notharctus sp. indet. Princeton Mus. No. 10,020. 



Thanks to the excellent type selected by Leidy, A^. tene- 

 brosus, to the beautiful specimen of T. rostratum (Am. Mus. 

 No. 5009), and to the very complete series belonging to the 

 Yale Museum, this genus is by far the best represented of all 

 the American Primates, or in fact of any sub-Pliocene form 

 excepting possibly Adapts. It is most interesting to observe 

 the exact homoplasy between the variations in the cheek 

 teeth with those seen in the early Ungulates. 



(Sp. 4) N. tenebrosus Leidy. — The type (Phila. Acad.) is a 

 relatively primitive species in which the second premolar is 

 still bifanged, and there are traces of the paraconid on all the 

 true molars ; the third lower molar has a well developed heel 

 or hypoconulid, the fourth premolar is sub-molariform. On 

 the other hand its progressive specialization is marked by 

 the low uniform wearing surface of the molars, the primitive 

 trigonid being almost as depressed as the talonid; also by 

 the large erect canine (probably indicating a male individual), 

 by the well defined chin, by the unbroken dental series, and 

 by the elevated condyle. 



First Stage f Lower Bridger. 

 A stage beyond .V. tenebrosus is the species or variety 



