GREGORY: NOrHARCTUS, AN AMERICAN EOCENE PRIMATE 



143 



protoloph and obscurely defined protoconule. Posterior cingulum very thick, giving rise to a hypocone. 

 All cusps coarse, para- and metacones conic, their cristse tending to form a W. 



Between these extremes the species from ascending horizons furnish a series of intermediate con- 

 ditions. The interlocking relations of nr^ will be discussed below. 



In Adapts parisiefisis (Amer. Mus. No. 10005) m''' differs from nr as described above (p. 140) chiefly 

 in the absence of a hypocone, in the somewhat smaller size of the crown, which is less extended antero- 

 posteriorly; protoloph sharp and high, metacone smaller than in nr; internal cingulum delicate; no 

 metaconule. In some of the varieties of A. parisiensis as figured by Stehlin (1912) m' has a low hypocone- 

 cingulum. In Adapts magnus (Amer. Mus. No. 10511) m'* is tritubercular with barely incipient hypo- 

 cone, with conical para- and metacones, and a prominent sharp protoloph, which is, however, less ele- 

 vated than in ^4. parisiensis. The crown is less elongate anteroposteriorly than in that species. Adapis 

 rutimeyeri (Stehlin, 1916, Taf. xxi, fig. 31) has a very primitive m^ which approaches those of Pronycti- 

 cehus and Pelycodus ralstoni. The crown is wide transversely, the paracone much larger than the meta- 

 cone, the protoloph low and interrupted by the large protoconule; the hypocone swelling of the cingulum 

 is much more distinct than in either A. magnus or A. parisiensis. 



Third Lower Molar 

 Plates XXXVI, XXXVII 



Ms in Pelycodus ralstoni (Amer. Mus. No. 16096) is elongate anteroposteriorly with a wide trigonid 

 and a long tapering talonid; paraconid small, near the metaconid, protoconid-metaconid crest low, ento- 

 conid very small, hypoconulid small; hypoconid crests not forming a distinct V. (Plate XXXVI,) 



This very jjrimitive form of nia which recalls that of Protiydicehus, leads through the intermediate 

 species to the pattern of m.^ in N. crassus, which is as follows: talonid as wide as trigonid, entoconid 

 large, paraconid reduced; anterior cingulum thick, hypoconulid large, hypoconid crests forming a widely 

 open V; one or more small accessory cusps on the ridge connecting the hypoconulid with the entoconid; 

 all cusps with very thick enamel. 



The occlusion of nis with the upper teeth has been studied in Pelycodus irigonodus (Amer. Mus. No. 

 15017),. A/", venticolus (14655), N. oshorni (11466) and A^. crassus. The small size and peculiar character 

 of m^ and ms are doubtless conditioned by the fact that they lie nearer to the fulcrum than the other 

 teeth, which enables them to exert great pressure, the smaller size further increasing their penetrating 

 power. The narrow hypoconulid of would be well adapted for piercing or breaking resistant objects; 

 together with the entoconid it presses against the posterior slope of the protocone of m^ The remaining 

 parts of ml articulate much as they do in the other molars. (Plate XLI ; Figs. 39, 40.) 



In this subfamily the subcrescentic shape of the para- and metacones and many other features are 

 connected with the lateral sweep of the lower molars across the upper. In the later Notharctin?e mi 

 could apparently be used as a pivot for this lateral motion. The animals could exert great pressure on 

 one side or the other by pressing together the outer parts of the teeth and then pushing the lower teeth 

 up the slopes of the upper teeth as the mandible passed inward. This motion was essentially the same 

 as it was in Lamhdotherium, Tapirus and many other mammals investigated by the writer. 



In Adapis magnus (Amer. Mus. No. 10511) the pattern is essentially similar but the tooth is wider; 

 the entoconid is absent; metacristid ^'ery prominent. In Adapis sciureus (Stehlin, 1916, p. 1515, fig. 368) 

 the protolophid is small, metacristid absent, entoconid distinct, hypoconulid short and narrow. In 



