130 



GREGORY: NOTHARCTU^, AN AMERK AN EOCENE PRIMATE 



moiety, or talonid; the trigonid is represented by the conical tip (protoconid) , by the crista anterior, 

 which faces rather inward than forward, and by the flattened posterolingual face of the protoconid, 

 foreshadowing the posterior face of the trigonid; the talonid basin is represented by the shallow fossa at 

 the posteroUngual base, while the posterior valley is represented by a still fainter fossa on the postero- 

 labial slope; the whole posterior V of the molar type is represented by the slight swelling at the postero- 

 basal tip of the crista posterior. These indications are very faint in N. osborni, as well as in Pelycodus 

 relictus; but they are more distinct both in the progressive N. pugnax and in the primitive Notharctus 

 venticolus, which also shows a slight grooving of the root. In Pelycodus ralstoni pi, to judge from its 

 alveolus, must have been a very simple tooth, which is perhaps correlated vnth the crowding together 

 of c, pi and ps in that otherwise primitive species. 



The evidence, then, by no means indicates that there was a stage in the remote ancestry of Notharctus 

 in which pi had two distinct roots and a more premolariform crown; to the present writer, indeed, it 

 seems more likely that in a pre-Pelycodus stage there was some variation in form both of the canines and 

 of pi, and that both were always somewhat different from each other and from po. This would be partly 

 conditioned by their different distances from the fulcrum of the jaw, partly by the fact that the upper 

 canine, with which the lower articulated, was always the first tooth behind the premaxillo-maxillary 

 suture and therefore subject to conditions of use and growth that Avere considerably different from those 

 affecting p^ and pi; thirdly, these last named teeth appear to be serially homologous rather with the 

 deciduous canines, deciduous molars and true molars than with the permanent canines and premolars. 

 For these reasons I infer that in the unknown Paleocene ancestors of the Notharctinse pi were simple 

 teeth with only a bare suggestion of true premolariform character. 



In N. osborni, pi articulated by its anterior crest with the posterior edge of the upper canine; it 

 barely touched p2. In N. venticolus, pi articulated both with the upper canine and apparently also with p^. 



Pi in Adapts parisiensis (Amer. Mus. No. 10006) is a low-crowned, sharp-edged tooth of asymmetri- 

 cal form A\ith an incipient talonid a.t the base of the posterolingual fossa. It has all the elements in a 

 barely incipient stage of the typical premolariform crown, namely sharp external and internal cingula, 

 incipient differentiation into trigonid and talonid and incipient metaconid ridge. In the opinion of the 

 wTiter it is more a specialized tooth than pi in the earliest Notharctinse. In A. magnus pi is more com- 

 pressed with a smaller internal basal extension. In Adapts sciureus (Stehlin, 1916, p. 1515, fig. 369) pi 

 is less extended transversely than in A. parisiensis or even than in A. magnus; its internal cingulum is 

 more pronounced than in Notharctus. 



Second Upper Premolar 

 Text Fig. 35 



P^ is likewise known in very few specimens of the Notharctinse. In the type of N. osborni it is a 

 conical tooth about 2.5 mm. in length by 2 in breadth, at the base of the crown; it is supported by two 

 roots of which the posterior is the wider transversely, the anterior root being decidedly smaller. Like 

 p^ it lacks an internal extension, but on the whole it represents a slight advance toward the true premolar 

 shape. Its apex corresponds with the paracone of succeeding teeth; its crista posterior corresponds with 

 the paracone-metastyle ridge of p'^; the slight depression or fossa on the posterolingual base, guarded by 

 the posterointernal cingulum, is all that represents the internal spur or ledge. In an old male of 

 Notharctus venticolus is much larger than in N. osborni; its crown is compressed and the two large 

 and nearly subequal roots are widely separated. This is very possibly a more primitive condition than 



