142 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



protoconule crest of the upper molar. The chief difference from the molar pattern of such Eocene peris- 

 sodactyls as Lamhdotherium and Telmatherium is that the anterior limb of the anterior V is nearly lacking, 

 the protoconid lies nearer the anterior end of the crown and the protolophid points more obliquely backward. 



More in detail the articulating relations of nii, nio with m^, nr, as shown in American Museum speci- 

 mens (Nos. 10001-10017) are as follows: the small trigonid fossa came opposite to but did not touch the 

 jutting hypocone of the upper molar; this is the normal primitive mammahan relation of the trigonid 

 fossa and contrasts with the relations of the trigonid fossa in the Notharctinse, which articulated quite 

 behind the pseudohypocone. The sharp protoconid was received into a small fossa immediately behind 

 the metacone of the preceding upper molar and in front of the anteroexternal part of the protoloph crest 

 of the corresponding upper molar. The high metaconid sheared in front of the protocone and its tip was 

 received in a shallow fossa between the protocone and the anteroexternal corner of the internal cingu- 

 lum.^ The metacristid ridge is the continuation of the protolophid and shears past the labial slope of 

 the protocone ; the lingual slope of the large hypoconid articulates with the labial slope of the wide proto- 

 cone; the low small entoconid comes opposite the notch between the protocone and the low hypocone; 

 the notch between the entoconid and the metacristid as above noted is lingual to the tip of the protocone. 

 The anterior slope of the metalophid (hypoconid-entoconid crest) articulates with the posterior slope 

 of the protocone. (Plates XXXVIII, XXXIX, XLI.) 



In Adapts ■magmis (Amer. Mus. No. 10511) the general plan of nii, m^ is identical with that in A. 

 parisiensis but the crowns are relatively wider and much larger; the cristids are \'ery prominent and 

 the sharp protoloph crest is wider; the entoconids are low. The articulating relations with the upper 

 teeth are identical with those described above in A. parisiensis. 



In the very primitive Adapts riitimeyeri (Stehlin, 1916, Taf. xxi) the anterior limb of the anterior 

 V is still present although the paraconids have already been lost ; the protolophid is less oblique and the 

 metacristid has not yet developed. The notch between the metaconid and the entoconid is not so deep. 

 But the interlocking relations, as may be seen by comparison with the upper molars, already foreshadowed 

 the adapine conditions. The lower molars of Adapts riitimeyeri together with those of Adapis sciureus 

 represent early stages of the adapine phylum which might readily be derived from a much more primi- 

 tive pattern that is preserved in most respects in Pronydicebus (Fig. 80, p. 231). 



Third Upper Molar 

 Plates XXXV, XLI 



M'^ in Pelycodus ralstoni has a small wide asymmetrical tritubercular crown, the paracone higher 

 than the metacone, the protoloph sharp ; while there is no trace of a pseudohypocone the posterior slope 

 of the protocone is worn fiat by the entoconid of m.z. Parastyle and metastyle not present, mesostyle 

 incipient; cristse of conical paracone and metacone arranged anteroposteriorly and with very little tend- 

 ency to form a V. Metacone without crista posterior. Internal and posterior cingula well marked; 

 no hypocone on cingulum. Lingual face of paracone pyramidal rather than conical, proto- and meta- 

 conules with blunt transverse crests. 



In the latest of the phylum, N. crassus, m'^ is relatively larger, more symmetrical, subquadrate with 

 an increased anteroposterior diameter, a large mesostyle, low roundly conical para- and metacones, blunt 



1 A somewhat analogous fossa is present in the lower molars of opossums on the anteroexternal wall of the trigonid, for the tip of 

 the enlarged metacone. 



