OREfiORY: XOTIIAm'TI'S, AN AMERICAN EOCENE PRIMATE 



123 



THE DFNTITION ANT) MANDTBLE OE XOTJIARCTVS AND ITS AI.EIES; ( OMPARISOX 



WITH Tin<: ADAPLN.E 



Adult Dentition ^ 



In order to place on record a detailed description of the dentition of the Notharctinfe and at the 

 same time to interpret the facts from an evolutionary viewpoint, the writer has endeavored to trace the 

 evolution of each tooth, in so far as it is shown in the species of Notharctinfe from successive horizons 

 of the Lower and Middle Eocene. Next, the mechanical relations of each tooth, with the articulating 

 teeth of the opposite jaw are considered. Then, the structure, evolution, and mechanical relations of 

 the corresponding teeth of the Adapina^ are treated in order to exhibit the evidence for th(^ common 

 origin and diverse trends of (n^ohition of the two subfamilies. 



Incisors 

 Text Ki,^s. 30, •?,], 32, 35 



The central upper incisor (i^ ) is preserved /// nit a in a specimen of Notharctus venticolus (Amer. Mus. 

 No. 14650). It has a compressed oval crown 4.2 mm. in length and 1.9 mm. in l)readth, the long axis 

 running obliciuely from the lingual to the labial side. The crown is gently convex and smooth on the 

 labial side, which is sharply truncate below by the elongate cutting edge, which runs forward to the bluntly 

 worn anterior tip; the gentle concavity of the lingual surface of the crown is interrupted by a downwai-dly 

 pointing V-shaped region of low relief. The crown is supported ])y a long i)rocumbent cylindrical root, 

 which in side view is sharply inclined to the anteroposteiior axis of the crown. By comparison with 

 Aclapis, Propithecus and Chirogale it seems improbable that the central upper incisor touched its fellow 

 of the opposite side; in other words, there was very probably a small median diastema. The central 

 incisor is obviously less si:)ecialized than that of Adapts parisiensis, in which the cutting edge has become 

 much more extended. 



Ei-. 30. Skull and hnxw jaw of Xofl.anlN.s r.st;„nii. Anicr. Mus. No. WAm. Mid, lie Eocviie {\mxvv Brid-cT beds) 

 Brid>;('r i'asiu, \V\ oniiTi.u. Natural size. 



l acryiual ivi;i(>n and incisors jiartly restored from other specimens. 



The lateral upper incisor (r) is preser^'ed in N. venticolus (No. 14656) and in the type of Notharctus, 

 oshorni (No. 1146()). Its ci-own is small, low and asymmetrical, the tip low and obtuse, the labial sur- 

 face strongly convex, the lingual surface gently concave or flattened, but bearing a slight central ridge 



' For a siiniinary of the elianieters of (lie dciitilion see pages ISI, 22.5. 



