Gregory: notharctus, an American eocene primate 



131 



that observed in N. osborni. In Adapts parisiensis \r is more compressed and swollen than in Notharctus 

 and has a sharp cutting edge; in A. magnus it is wider and more hke p\ In Adapts riitimeyeri (Stehlin, 

 1916, Taf. XXI, fig. 18) the premolars are all relatively primitive, but not so much so as in the Notharc- 

 tinse. P" suggests that of A. magnus in that it is less compressed than in A. parisiensis. 



Fig. 36. IJ)iagram illustrating progressive complication of the premolar-molar series and the interlocking relations 

 of the upper and lower teeth in a generalized mammal. The crown pattern of the lower teeth is shown in heavy black lines. 



According to the view adopted provisionally by the author the protocone of the upper molars arose from a lingual extension from 

 the basal cingulum, as it did later in the premolars, the primitive tip of the crown being represented by the para + metacone. The para- 

 and metacones probably became separated pari passu with the transverse widening of the talonid and the upgrowth of the hypoconid. 



Second Lower Premolar 

 Plates XXXVI, XXXVII 



P2 exhibits considerable variation in form in the Notharctinse ; in the more progressive larger species 

 A^. rostratus, N. pugnax, N. crassus it is quite different from ps, being much smaller and simpler, with a 

 tendency toward the fusion of the roots. This character is marked also in N. oshorni and N. motthewi. 

 On the other hand in N. venticolus, N. nunienus, P. trigonodus, and P. ralstoni there is a more even 

 gradation in form as we pass from ps to ps; this has every appearance of being the primitive condi- 

 tion seen in Eocene carnivores and taken in connection with other evidence it suggests that the simple 

 character of p| in N. oshorni and of po in Pelycodus relictus is partly retrogressive. 



The anterolabial crest (crista anterior) of po articulates with the posterolingual crest and surface 

 of p^. Its posterolingual surface probably articulated with the anterolabial surface of p'^. In A^. venti- 

 colus the crista anterior of po is partly worn, probably by articulation with p". In Adapis parisiensis 

 (Amer. Mus. No. 10006) p2 is more compressed and elongate than pi, and shows all the premolariform 

 characters more distinctly. It is obviously much more specialized than the corresponding tooth in 

 Pelycodus trigojiodus (Amer. Mus. No. 16843). In Adapis magnus (Stehlin, 1912, p. 1242, fig. 270) ps is 

 thicker transversely than in A. parisiensis and far thicker than in primitive Notharctinse. In Adapis 

 sciureus (Stehlin, 1916, p. 1515, fig. 369) ps is more primitive than in either of the other species, but is essen- 

 tially adapine in its low, obliquely placed crown. In A. riitimeyeri this tooth retains an incipient hypo- 

 conid. 



Third Upper Premolar 

 Plate XXXV; Text Fig. 35 

 P^ in N. venticolus, N. oshorni, and N. crassus shows a distinct advance toward the pattern of p"*. 

 It is roundly triangular in section, the rounded apex of the triangle forming a low internal projection or 

 protocone supported by a stout root; there is a single main cusp homologous with the paracone of the 

 molars, with a crista anterior and a crista posterior; the anterolingual and posterolingual faces are 



