158 



BULLETIN 16 9, UNITED STATES NATION.\L MUSEUM 



the same size, the status of these upper jaws is dubious, although the 

 lower jaws are quite distinct, and it is unfortunate that one type is 

 an upper jaw and the other a lower. The upper jaws are, however, 

 probably distinct and correctly associated with the lower jaws as 

 determined by Gidley. Those placed in Palaechthon alticuspis are 

 very slightly smaller, molars definitely more transverse, and the pos- 

 terointernal basin probably less developed. It seems justifiable, in 

 the absence of definite evidence to the contrary, to accept the identi- 

 fications established and thus avoid changing the nomenclature, con- 

 sidering the separation of the species and genera as validated by the 

 lower jaws and, for the present, overlooking the fact that one type is, 

 in fact, an upper jaw and of doubtful status. 



Table 33. — Numerical data on Palaechthon alticuspis 



R 



1. 9 -2. 1 

 1. 5 -1. 7 

 1. 9 -2. 2 

 1. 5 -I. 8 

 1. 17-1. 40 



M 



2. 030 ±0. 025 

 L 567 ±0. 022 

 2. 067 ±0. 024 

 1. 682 ±0. 025 

 1. 231 ±0. 021 



0. 078 ±0. 017 

 0. 066 ±0. 016 

 0. 085 ±0. 017 

 0. 084 ±0. 018 

 0. 070 ±0. 015 



3. 8±0. 9 



4. 2±L 



4. 1±0. 8 



5. Oil. 1 



Table 34. — Individual measurements of Palaechthon alticuspis 

 Typk and Characteristic Lower Jaws 



Upper Jaws (only two are known) 



Genus PALENOCHTHA Simpson 



a lenochtha Simpson, 1935d, p. 231. 



Type. — Palaechthon minor Gidley. 



Distribution. — Middle Paleocene, Fort Union, Montana. 



