GREGORY: XOTHARCTVS, AN AMERICAN EOCENE PRIMATE 



125 



is; in the upper jaw the tip of the enlarged lower canine occupies the space which would be filled by i^ 

 if present, and this is true even in female skulls with small canines. 



Canines 

 Plate XLII; Text Figs. 30-32, 35 

 The large upper canines in supposed males have a long, nearly straight, pointed crown and a mas- 

 sive root. In a specimen of N. venticolus (Amer. Mus. No. 14655) the crown and root together measure 

 22 mm. in length. In the earlier species of Pelycodus the canines of supposed males were less robust in 

 proportion to the size of the jaw; in the latest species of 

 Notharctus (N. crassus) the crown was thicker at the base 

 than that of A^. venticolus and the lower end of the tooth was 

 more recurved. It is thus apparent that the base of the 

 upper canine crowns in males becomes thicker as w^e pass 

 from lower to higher levels of the Eocene. In old animals 

 the front face of the crown is flattened by the wear of the 

 lower canine; in N. crassus (Amer. AIus. No. 11982) the 

 lateral (external) face is marked by a deep vertical groove, 

 flanked by a faint shallow groove in front and another 

 behind. On the posterolingual side of the crown there is a 

 deeper groove and near the root faint grooves or plications 

 appear on all sides of the crown. This condition is fore- 

 shadowed in A^. venticolus. The posterior cutting ridge of 

 the canine is sharply defined in that species, less so in N. 

 crassus. 



In a supposed female (type of A^. oshorni, Amer. Mus. 

 No. 11466) the upper canine is quite small, its crown hav- 

 ing a length of only 4.5 mm., as compared with 10-12 mm. 

 in a male N. venticolus. The crown is decidedly less canini- 

 form and somewhat more premolariform than that of the 

 male. It is essentially, however, a weak variant of the male 

 canine, with a slightly recurved tip which differentiates it 

 from the premolars. It is ciuite cUssimilar to the upper 

 incisors. In Ada pis an analogous difference between the 

 canines of supposed males and females has been observed by 

 Stehlin (1912, p. 1171). 



The lower canines of males are more slender at the base 

 of the crown than the corresponding upper canines. The 

 root is very massive and is more or less strongly recurved. 

 As noted above it crowds the roots for the incisors. In N. 

 venticolus and A^. tenehrosus the crown is convex labially and 

 flattened to concave on the lingual side. Posteriorly it is 

 flattened and worn where it works against the upper canine. 

 It has a faint anterior ridge, homologous with that of the 



Fig. 31. Fragment of the left premaxilla, 

 nasal and maxilla, ^vith incisors and canine 

 of Xoiharctui- rciificohis. Amer. Mus. No. 

 1465G. Lower Eocene, Lost Cabin beds, 

 Wind River Basin, Wyoming. Twice natural 

 size. Lateral, inferior and medial aspects. 



