Gregory: notharctvs, an American eocene primate 



141 



stage the true adapine characters are ah-eady more or less clearly indicated in ni\ ni", just as the true 

 notharctine characters are foreshadowed even in the corresponding teeth of the oldest known Pehjcodus. 



First and Second Lower Alolars 

 Plates XXXVI-XXXVIII, XLI; Text Fig. 39 



In Pelycodus ralstoni the construction of nii, nio approaches that of the more primitive Eocene In- 

 sectivores and Creodonts; the trigonid comprises a small triad of rather delicate more or less pointed 

 cusps, followed on a much lower level by the wide talonid, which consists of a large projecting hypoconid, 

 bearing the posterior cutting V and a small low entoconid, which projects gently on the lingual border. 

 The anterior and posterior roots are not subdivided longitudinally. The paraconid on nii juts forward; 

 that on nio is near the metaconid. The crown as a whole is relatively narrow; m2 is notably larger than 

 nil. The external cingulum is irregularly arranged and does not extend across both talonid and trigonid 

 as a sharp ridge. (Plate XXXVI.) 



In the latest and most progressive members of the subfamily nii, ms are of large size, low crowned, 

 with swollen cusps; the trigonid decidedly less elevated above the level of the talonid; the crow^n as a 

 whole is shorter, wider and rounder as seen from above; the paraconid on nii is small, on nio it is reduced 

 or wanting; the metaconid more nearly internal to the protoconid; the proto-paraconid crest short and 

 inconspicuous; the entoconid is notably larger and more in line with the metaconid; a small hypoconulid 

 has appeared at the junction of the posterior V with the posterior cingulum. The sharp external cingulum 

 is continued across both talonid and trigonid. The main anterior and posterior roots are subdivided 

 longitudinally with the inner and outer branches more or less divergent, especially in old animals. Be- 

 tween these two extremes in the construction of nii, m2 in the earliest and latest types there are several 

 successive stages from ascending horizons of the Lower Eocene, passing from Pelycodus ralstoni to P. 

 trigonodus and P. frugivorus and thence on the one hand to P. jarrovii and perhaps to Notharctus venticolus, 

 N. pugna.T, N. crassus, and on the other hand to Notharctus nunienus and perhaps A^. oshorni. (Plate 

 XXXVL) 



The general articulating relations of m2 in the Notharctinse are shown in Figs. 38, 40; Plate XLI; 

 they are essentially the same as in all primitive mammals with tuberculosectorial lower molars. In the 

 oldest forms the motion of the lower jaw and the consequent impact of the lower molars seem to have 

 been somewhat more vertical and less transverse than in the latest types. The molars of the early forms 

 accordingly seem to be adapted to a more or less insectivorous diet, those of the later members rather 

 for vegetable food, especially leaves and fruits, perhaps more or less varied with insects, eggs, etc. 



In Adapis parisiensis nii, m2 show a certain analogy with the corresponding teeth of primitive peris- 

 sodactyls and other ungulates, inasmuch as they bear two cross crests, corresponding to the protolophid 

 and metalophid; the paraconid also is absent, and the crista obliqua (interior limb of the posterior V) 

 joins the protolophid half way between the protoconid and the metaconid; a metacristid (not metastylid, 

 since it does not arise from a Assuring of the metaconid tip) is present on the slope leading down from the 

 metaconid to the talonid; the talonid fossa is continued labially as a deep notch between the meta- 

 cristid and the low entoconid; into this notch fitted the labial face of the protocone; the crown as seen 

 from above does not bulge sharply in the rear but the trigonid is nearly as wide as the talonid. These 

 teeth are of small size and comparatively narrow in proportion to the size of the jaw and to the great 

 strength of the jaw muscles and must have been very effective in cutting tough vegetable fibre. The 

 protolophid is obliquely placed, and its edge is worn posteriorly from shearing past the sharp protocone- 



