140 



gre(X)ry: notharctus, an American eocene primate 



placed posteriorly, so that the distance from the mesostyle to the metastyle is decidedly less than the 

 distance from the mesostyle to the prominent parastyle; in correlation with this backward position of 

 the mesostyle the sharp groove for the hypoconid runs obliciuely inward and forward; the metastyle is 

 prominent, at least in little-worn teeth; the metaconule is low and inconspicuous, more so on m- than 

 on m^ (Plate XXXV.) 



In N. crassus, the largest and latest known membei' of the subfamily, from the Upper Bridger forma- 

 tion, m\ m^ have increased their anteroposterior diameter and the mesostyles, paracones, metacones, 

 and pseudohypocones are a little larger; but otherwise these molars resemble those of N. pugnax. 

 (Plate XXXV.) 



To recapitulate the evolution of m^ m'- in the Notharctinse, the earliest forms had tritubercular molars, 

 wide transversely and with a bare suggestion of the mesostyle and pseudohypocones. These evolve by 

 small gradations, through the ascending levels of the Lower and Middle Eocene into the large subquad- 

 rate molars of A^ofharctus crassus, with large mesostyles and large pseudohypocones. The pseudohypo- 

 cones appear in a region which articulates lingually with the entoconids, labially with the paraconids and 

 posteriorly with the metaconids of the lower molars. The excursion of the 

 mandi]:)le in the earlier forms was somewhat more vertical, in the later forms 

 it was somewhat more transverse. 



In Ada pis parisiensis, m^ and nr are very different from the corre- 

 sponding teeth in any known member of the Notharctinse. Not only do 

 they lack the mesostyle and the pseudohypocone and possess a true hypocone 

 derived from the cingulum, but they are distinctly more elongate antero- 

 posteriorly, the para- and metacones are widely separated, the ectoloph is 

 flatter and obliquely placed, the metaconule is reduced or absent, the pro- 

 tocone is high and the oblique protocone-parastyle crest is prominent and 

 sharp. 



In Adapts magnus (Amer. Mus. No. 10511) the fundamental pattern is 

 the same as in Adapis parisiensis but the molars are relatively wider. The 

 sharp protocone-parastyle crest is opposed by the protoconid-metaconid 

 ridge of the lower molars; the rounded hypocone projected above the tri- 

 gonid but did not fit into it; the large central fossa received the hypoconid 

 while the meta- and paracones opposed the middle valley and lower molar 

 interv alley respectively. The upper molars of Adapis sciureus (Stehlin, 

 tS^^^'^^^^^^^^ 1916, p. 1514, fig. 368) were much more primitive with the crown less 

 ^^^^^^p**^ elongate anteroposteriorly, the para- and metacones less separated and more 



conical, the proto- and metaconule large and the trigonid of the crown dis- 

 tinctly tritubercular; the hypocone is a prominent upgrowth from the 

 cingulum. As first noted by Stehlin (1912, p. 1289) the latter character 

 sharply separates this species from all the Notharctinse. In Adapis 

 riitimeyeri (Stehlin, 1916, Taf. xxi, figs. 27-31) m' and m'^ in pattern sug- 

 gest those of A. magnus but they are relatively wider and when little worn 

 have more of the tritubercular stamp even though the hypocone is larger. 

 The metaconule in the specimen illustrated in Taf. xxi, fig. 31 is better 

 developed than in others referred to the same species. Even at this early 



Fig. 41. T'pper ain 

 teeth of Adapik- ri'iti 

 After Stehlin. X § 



1. F-, p- and alveolus of p\ 

 right .side. 



2. P\ ni\ right. 

 .3. M'-m\ right. 



4. P", m^, m-, left. 



5. P?, p!, pi, nil, right; al- 

 veoli of c and pi. 



