GREGORY: NOTHAlK'TrS, AN AMERICAN EOCENE PRIMATE 



207 



expanded angle and usually coalesced symphysis; the condyle is conyex anteroposteriorly but more 

 flattened transversely. In the Lemuridae the mandible appears to represent a more or less degenerate 

 derivative of the Adapine type, w'lih an excessively sloping symphysis, a usually slender ramus with a 

 straight lower border and a more or less delicate angle. The condyle is flattened transversely, l^ut in 

 Lepilemur it has also a deep posterior vertical extension \vhich articulates with the large postglenoid 

 process. In Myoxicebus simus the mandible in correlation with its heavy zygomata and wide crushing 

 molars retains considerable resemblance to the Adapine type, as seen especially in the expanded angle, 

 stout ramus and fairly convex chin. 



Dr. Stehlin (1912, p. 1294) regards the early coalescence of the opposite rami of the mandible as one 

 of five important specializations which tend to exclude the Adapina? from further evolution in the direc- 

 tion of the recent and subfossil Lemurida, the latter term being apparently used in a very inclusive sense. 

 The writer, on the contrary, would be inclined to associate the failure of the rami to coalesce in the typi- 

 cal Lemuridse partly with the largely degenerate and feeble character of the canines and with the retro- 

 gressive character of all the muscle areas. According to this hypothesis a lemur with massive jaws and 

 expanded muscle areas analogous with those of Ada pis ought to exhibit an early coalescence of the rami 

 and this is actually the case in a young jaw of Megaladapis grandidieri described by Standing.^ As 

 retrogressive changes often involve the permanent retention of originally transitory juvenile or infantile 

 characters there is no apparently valid a priori reason why a race with normally coalesced rami should 

 be incapable of giving rise to a race with a weak jaw and a persistent symphyseal suture. In this con- 

 nection it is noteworthy that even in the Adapinse there was considerable variation in the age of coalescence 

 of the rami, as the following passage shows: "Die Symphysalnaht [of Adapts magnus] erlischt offenbar 

 spater als bei Adapis parisiensis, denn es liegen mir verschiedene Mandibelhalften adulter Individuen 

 vor, an welchen die Verwaschsung eben erst begonnen hat" (Stehlin, 1912, p. 1259). 



Mental Foramina 



The position of the mental foramina of certain modern Lemuridse in comparison with the Notharc- 

 tinse and Adapinse is as follows. 



Beneath 





c 



Pi 



]> 



P3 



P4 



nil 



Fcljicodus frugironis 





X 



X 







X 





Xofhnrcfii.'i rrniicnhi^ 





X X 





X 





" pin/iDi.v 





X 







X 



X 



(X) 



Adfijji.s- par/sicii.'ii.s 



X 



X 





X 





" iiKigini.s' 







X 







X 



" .-.■rnirru.s 





X 







X 







Lvpilnnur mu.slrVnius 



X 









X 



XX 



X 









X 





X 



X 





Lrmur rariu. 



X 





XX 





> 









X 





X 





X 







" iiiongoz 



X 









X 













X 





X 







Mirrorrbu.s 



X 













X 













X 



X 





Chirogair 



X 











X 



X 



AfUHninir 



X 













X 



Mi/o.V!rrl)us fiiiiui.s 



X 









X 



X 





1 On recently discovered subfossil Primates from Madagascar. 1908, Trans. Zool. Soc. London, XVHI, part 2, p. 115. 



