GREGORY: NOrilARCTUS, AN AMERICAN EOCENE PRIMATE 



189 



arctiden zu suchen als bei den Adapiden. Aber zur Formulierung eines zuverliissigen Schlusses bietet unsere gegenwartige 

 Kenntniss des Genus noch nicht hinlangliche Anhaltspunkte. 



Weder im europiiischen noch im nordamericanischen Untereocaen ist also vorderhand die Wurzelgruppe der Ada- 

 piden zu finden; die Frage naeh der Herkunft (lersell)en blcMbt bis auf weiteres unbeantwortet. 



To the writer it appears that the general purport of Dr. StehUn's views in 1912 was that the Adapidse 

 and Notharctidfp followed divergent trends of evolution in the dentition, that the common characters 

 might well be ])rimitive, inherited from the stem forms of all primate stocks and giving very little evi- 

 dence for a near connection of these two families. 



The writer's error in regarding Protoadapis as a primitive member of the Adapina? (1915, p. 423) 



Fig. 70. Lower jaws and t(-rtli of Profoadapis. After Stehlin. 



1. Left ramus of the lower jaw of Protoailn pis liraclnjiinjruii u.-:. Natural size. Phosphorites, Prajons (Lot). After Stehlin. 



2. Risht i-aiiuis of the lower jaw of FrohHula pis reel icuspid ens. Lower Eocene (Ypresien), France. Three times natural size. 

 After Stehlin. 



has been corrected by Dr. Stehlin (1910, p. 1520). He also shows (1912, p. 1286) that this puzzling 

 genus in the structure of the fourth lower premolar and lower molars approaches Pronycticebus Gaudryi, 

 which the writer regards as i:ierhaps the most generalized of all the European Eocene primates: structur- 

 ally allied on the one hand with the Tarsius-\ike group, in another direction with the Lorisidae, and thirdly 

 with the Adapidse. Dr. Stehlin also shows (1912, p. 1289) that in the characters of its lower molars 

 Protoadapis approaches the Notharctidse rather than the Adapidse. 



The existence in the Eocene of Europe of other genera (e. g., Plesiadapis, Anchomomys) that exhibit 

 structural affinities with the primates of the Eocene of America tend to support the hypothesis that 

 these two " Entwicklungsherden " are divergent derivatives of a Paleocene or Upper Cretaceous com- 

 mon stock, of uncertain geographic location. 



In another passage of the 1915 paper cited above, the writer said (p. 423): "The oldest forms of 

 Pelycodus, which have recently been described by Doctor Matthew,' have extremely primitive trituber- 

 cular upper molars, without any posterointernal cusp, and they have a pattern which, according to 

 accepted principles of dental evolution, is structurally ancestral to the two divergent lines seen in the 

 Notharctinse and Adapinse." 



1 1915, Bull. Amer. Mus, Nat. Hist., XXXIV, pp. 429-483. 



