Gregory: notharctvs, ax American eocene primate 



139 



P. jarrovii from the Upper Gray Bull beds (Amer. Mus. Nos. 4174, 15041) is considerably larger; 

 the pseudohypocone of m'^ wears into small round cusps connected by a short neck with the protocone, 

 and the contour of the crown is becoming more or less quadrate; although it is less elongate antero- 

 posteriorly than in the later stages the mesostyle is more (Amer. Mus. No. 15041) or less (4174) distinct, 

 so that on the whole this species approaches Nothardus. (Plate XXXV.) 



The most primitive species of Nothardus, N. nunienus (Amer. Mus. No. 4735) from the Lost Cabin 

 formation of the Wind River Basin, differs from Pelycodus jarrovii in having the pseudohypocones of m^ 

 and m- slightly more advanced; the mesostyles though small are distinct bead-like cusps and nr is pos- 

 sibly a little less wide transversely in proportion to its anteroposterior diameter. (Plate XXXV.) 



Nothardus venticolus from the Lost Cabin beds, Wind River Basin, is a large and relatively progres- 

 sive species with large and distinct pseudohypocones, quadrate molars and large mesostyles (Amer. Mus. 

 Nos. 14637, 14655), so that it foreshadows the still larger and more progressive species of the Bridger 

 (A'', pugnax, N. crassus). A primitive character, howe\'er, is the greater relative width of nr and the 

 relatively smaller anteroposterior diameter of m\ nr. Other parts of the crown are more advanced, as 

 compared with earlier species in the following details: the protoconule is now associated almost exclu- 

 sively with the protoloph and has nearly lost the posterior limb of its originally V-shaped crown. The 

 metaconule of m^ is relatively large and is of truncate pyramidal shape. The cingulum is fairly hea\'y 

 all around the tooth, except opposite the protocone of m^ The pseudohypocone in m^ is roundly coni- 

 cal and the neck that joins it with the protocone is narrow. A deep fissure on the labial side separates 

 it from the protocone. In m" the pseudohypocone is a little less advanced than in m^ (Plate XXXV.) 



No. 14637 shows the wearing facets little worn and No. 14655 shows them greatly worn, and is more- 

 over associated with the lower jaw; so that a careful study of the movement of the jaw and articulating 

 relations of the teeth was made possible. The parastyle and labial part of the anterior cingulum of m'^ 

 was worn by the protoconid of mi; the mesostyle by the hypoconid of nii, which also slid down into 

 the central fossa, leaving in No. 14655 a wide groove extending from the mesostyle inward and forward 

 to the back of the protoconule (Fig. 40) and showing that in this stage a markedly transverse excursion 

 of the mandible had become established. In the little-worn state the constriction between the pro- 

 tocone and the pseudohypocone bore on its lingual side a groove for the entoconid; in the old stage the 

 labial slope of the pseudohypocone of m^ is scarred by the paraconid of m2. In the young stage there 

 was perhaps more vertical and less transverse movement of the mandible than in the old stage. 



Accordingly, the Notharctinse of the Bridger formation show a considerable range of variation in 

 the pattern of m\ nr. In the conservative Pelycodus relidus these teeth are as small as they are in Pely- 

 codtis trigonodus, but are narrower; the pseudohypocones are small, but the mesostyles are distinct and 

 the contour of the crown is more quadrate than in any true Pelycodus. In Nothardus osborni (Amer. 

 Mus. No. 11466) m\ m^ are notably longer in anteroposterior diameter than in the species of Pelycodus; 

 m- is not greatly wider than m\ the mesostyles are large and the contour of the crown is subquadrate. 

 But the pseudohjqoocones do not project upon the labial border of the tooth. The internal cingulum 

 is delicate. The articulating relations of m'^, m'- have been closely studied and are indicated in Figs. 39, 40. 

 In m^ and nr the constriction between the protocone and the pseudohypocone and the valley that marks 

 this separation on the lingual border of the crown engage the entoconids of the lower molars m2, 1113. The 

 tip of the pseudohypocone articulates with the paraconid; the posterolingual slope is pressed by the 

 metaconid. 



In the very progressive N. jmgnax (Amer. Mus. No. 14567) the pseudohypocone of m^ is worn into 

 a large circular surface which fills the whole posterolingual corner of the crown; the mesostyle is dis- 



