154 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



molar came in before the deciduous molars were shed as in Adapts and the modern lemurs, while in the 

 New World and Old World monkeys ms is delayed until after the deciduous molars have been replaced 

 by the premolars. 



From the relations of m'* and nis and the other teeth it appears that Amer. Mus. specimen No. 13025 

 (Plate XLII, figs. 7, 8) is in a stage between 2 and 3 of Adapis as defined by Stehlin, since p\ m^, m- 

 and all the deciduous molars are in place but m^ is not yet up. The first lower jaw (Amer. Mus. No. 

 13029) is at the beginning of stage 3, since m3 is just coming in, and the second lower jaw (No. 12578) 

 is perhaps in the middle of stage 3, since the permanent canine is beginning to come in. Possibly the 

 permanent incisors were already in place as apparently indicated by the presence of a pit in front of the 

 canine tip, but the evidence is not altogether clear; p4 is quite close to the surface preparing to push 

 out dp4. (Plate XLII, figs. 9, 10.) 



THE SKULL AND BRAIN CAST OF NOTIJARCTrS; COAIPARISON WITH ADAPIS 

 , Skull 



Text Figs. 48, 49, 51, 52, 56, 58, 62 



The general form of the skull in the two subfamilies is summarized below (page 185). The detailed 

 description of the parts is as follows: 



The face of Notharctus osborni, measured on the fine joining the postorbital process of the front als 

 to the projection of the premaxillary, is about as long as the brain-case, while in Adapis, although varying 

 in different species, it is distinctly shorter than the brain-case. The orbit is larger than it is in Adapis 

 magmis or A. parisiensis and the malar is smaller. The postorbital constriction in Notharctus osborni 

 is much less pronounced than in Adapis, but in the older Notharctus venticolus the sharper postorbital 

 constriction recalls that of Adapis magnus leenhardti (Stehlin, 1912, p. 1278, fig. 286). The sagittal and 

 lambdoidal crests of Notharctus are less elevated than those of Adapis. The greatest difference is in the 

 lower jaw, which has a strongly expanded angle in Adapis and a very primitive projecting angle in the 

 Notharctinse. The horizontal ramus of the mandible is also much deeper in Adapis in proportion to its 

 length. These differences, as well as the heavy zygoma and prominent masseter tubercle of Adapis, 

 are correlated with its more voluminous temporal, masseter and internal pterygoid muscles. (Figs. 48-50.) 



Very little is known of the structure of the skull in the older Notharctinse. Fragments of the maxillary 

 preserved in Pelycodus ralstoni, P. trigonodus and P. jarrovii (Amer. Mus. No. 4174) indicate that, at least 

 in the females, the malar below the orbit was not as deep as it is in Notharctus; probably in these smaller 

 forms of Pelycodus, the orbits were a little larger, with more slender postorbital rims (P. trigonodus. No. 

 15017). The opposite rows of cheek teeth converged more toward the midline than in the later forms 

 with heavy canines and the muzzle was probably somewhat shorter and narrower. This is a step back- 

 ward toward the hypothetical stem form of the Notharctinse and Adapinse, which presumably had fairly 

 large orbits, a more delicate muzzle and less developed muscular crests. 



Premaxillse 

 Text Figs. 52, 58 



Except for their palatal processes these elements are preserved in Notharctus venticolus (No. 14656) 

 and in N. osborni (No. 11466). (Fig. 52.) They are strikingly like those of Adapis and have similar 

 relations with the nasals and maxillaries. The gentle inclination of the opposite premaxillaries toward 

 the midline was probably similar to that of Adapis parisiensis var. bruni (Stehlin, 1912, p. 1201, fig. 259). 



