132 



Gregory: notharctus, an American eocene primate 



flattened, the latter being much the larger. The external cingulum rises anteriorly into a low parastyle 

 and posteriorly into a prominent metastyle. The anterolabial surface is slightly convex but the pos- 

 terolabial surface is gently concave. Thus the chief features of p'* are foreshadowed in p'^, the main differ- 

 ence being in the small size and low position of the protocone or internal cusp, and the feeble develop- 



Fig. 37. Diagram of the left upper and right lower molars and last two premolars of Noiharcius, showing the names 

 of the principal cusps and crests. 



ment of the parastyle. In N. osborni the protocone is extremely small, narrow, and located more to the 

 rear; this is possibly a conservative condition; in the progressive N. crassus the protocone region is wider 

 and the crown is approaching the general form of p"*. 



With regard to its functional relations with the lower teeth, the outer side view in N. venticolus shows 

 the simple conical paracone, articulating by its anterior slope with the posterior slope of the conical p2 

 in a very primitive fashion. Its posterior slope articulates with the anterior slope (crista anterior) of p4, 

 its protocone spur partly with the talonid of ps and partly with the paraconid of p4. Similar relations 

 are observed in N. crassus. In N. osborni the small size and backward displacement of the protocone 

 results in its articulating solely with the trigonid of p4 and not at all with the talonid of ps. This is pos- 

 sibly a retrogressive condition. 



P'^ is not w^ell known in the earlier species of the Notharctinse. In Pelycodus jarrovii it appears to be 

 similar to that of N. venticolus. 



In Adapis parisiensis p'* is less like p'* than it is in Notharctus; it is biconvex with a heavy internal 

 cingulum, representing the reduced protocone spur. In Adapis magnus on the other hand p'^ is a wide 

 tooth with a large protocone and an almost bicuspid general contour. Thus, in the characters of p^, 

 both these divergent phyla of the Adapinae are obviously more specialized than the primitive members 

 of the Notharctinffi in which p'^ approximates the primitive placental type which is seen in many Eocene 

 carnivores and insectivores. In the primitive Adapis riitimeyeri (Stehlin, 1916, Taf. xxi, fig. 18) p^ 

 is more primitive than that of A . magnus, its protocone being less expanded and the contour of the crown 

 view more oblique. 



paracone 



