150 



GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



(8) The writer's original statement (1915, p. 423) that in the Notharctinse "the progressive develop- 

 ment of the mesostyle is also correlated with a partly transverse excursion of the mandible and 

 with the V-like modification of the para- and metacones," can now hardly be questioned in the 

 hght of all the evidence cited in this paper and of the analogous cases among other groups of 

 mammals (e. g., Lamhdotherium , Propithecus, Moropus, etc.) which the writer has investigated. 



(9) No less decisive is the evidence cited above (pages 137, 142, 144, 159) that in the Adapinae the 

 motion of the jaw was more orthal than it was in the Notharctinse and that this more orthal 

 movement is found in association with the lack of V-shaped para- and metacones, the total 

 absence of mesostyles, the emphasis of the protoloph and of the protolophid (protoconid- 

 metaconid crest). 



In reference to the writer's statement (1915, pp. 422, 423) to the effect that by fitting the upper and 

 lower teeth together it was observed that the movement of the mandible must be more transverse in 

 Nothardus and more vertical in Adapis, Dr. Stehhn (1916, p. 1539) says: "Da ich keine Gelegenheit 

 gehabt habe, das Kiefergelenk von Notharctiden zu untersuchen, kann ich mich nicht zu der Frage aus- 

 sern, ob eine solche Differenz in Kaumechanismus besteht oder nicht." 



The appended photographs (Fig. 42, p. 144) of the condylar region of Notharctus and of Adapis 

 may partly supply this need, although it must be stated that there is nothing so demonstrative on this 

 point as the fitting together of specimens and the study of the actual movements of the lower teeth when 

 they are pressed against the upper teeth in their natural positions. These may readily be determined 

 by fitting the protocone of the first upper molar into the talonid basin of the first lower molar. When 

 this is done the remaining parts of the teeth will exhibit the spatial relations which were summarized 

 by the writer in 1910.^ 



Deciduous Dentition 

 Plate XLII 



The upper milk molars of Notharctus cf. tyrannm are preserved in Amer. Mus. No. 13025, from the 

 Bridger Basin, Horizon B. This specimen shows the alveolus of p\ and the well-preserved dp'-, dp'', 

 dp^ followed by m\ nr all in place. lies in the bone beneath the last milk molar (dp^), while p'' Ues 

 beneath dp'^; impression made by p- against the maxillary is shown beneath dm\ The alveolus of p^ 

 (which, as in most mammals, appeared with the deciduous molars) is at the intersection of lines drawn 

 through the base of the crowns of the milk series and through the permanent series of premolars beneath 

 them. It thus may be possible that p^ originally belongs with the permanent series, but has been forced 

 into association with the deciduous set through the early eruption of the permanent canine, and that 

 the deciduous predecessors of p^ have been lost. is also present; it is just beginning to erupt and must 

 have been nearly covered by bone. The specimen thus shows that m\ m- were fully in place and that 

 m'^ was also on the point of erupting while the deciduous molars were firmly in place. (Plate XLII, figs. 

 7, 8.) 



As usual among mammals the last milk molar (dp"*) was much more molariform than p*. It has two 

 widely separated external cusps, with a distinct mesostyle; it also has a small but distinct pseudohypo- 

 cone. Its protoloph is very oblique, and the protocone is low. (Stehlin, 1912, p. 1178, fig. 248). Except 

 that it has both pseudohypocone and mesostyle it is much like the corresponding deciduous tooth in Adapis 

 parisiensis, whereas the tooth that succeeds it (p^) is quite unlike that of Adapis. (Plate XLII, figs. 6-8.) 



^Bull. Amer. Mus. Nat. Hist., XXVII, pp. 190, 191. 



