320 University of California Publications in Geology [Vol.7 



Leidy 's figure 1 of the plate to which reference is made above 

 the identical P 4 represented in figure 2 seems to show almost no 

 external groove. 



In the type of Auchenia he stoma, M 1 and M 2 are both very 

 considerably larger than in specimen 20028, and M 2 seems rela- 

 tively much larger, especially compared with M 3 . In specimen 

 20040 the dimensions of P 4 and M 3 are practically identical with 

 those in the type of A. hesterna. M- is only seven per cent 

 smaller, and M 2 eleven per cent smaller. The slight differences 

 between specimen 20040 and the type of A. hesterna seem to the 

 writer of less than specific value, and the Kancho La Brea form 

 may be considered as typifying that species. The differences 

 between nos. 20040 and 20028 are greater than between 20040 

 and the type of hesterna, but considering the close similarity in 

 form and dimensions of the skull, together with the evident 

 difference in age of the two individuals, the writer is not inclined 

 to believe the difference in tooth measurement as of specific rank. 

 No. 20028 represents a much older animal than no. 20040. During 

 a considerable period in the life history of each individual P 4 

 and M 3 increase in anteroposterior diameter of the crushing face 

 as the crowns wear down ; while M : and M 2 , with crowns narrow- 

 ing inferiorly much earlier than the other teeth, shorten the 

 anteroposterior diameter of the occlusal surface. There seems 

 also to be some individual variation in tooth dimensions, so that 

 age, with sex and individual variation, may produce rather large 

 differences in relative size of the teeth. 



The upper molar of Auchenia hestcrna figured by Leidy does 

 not differ greatly from M 2 of the Rancho La Brea form. 



A California species described by Leidy 1 " as Auchenia califor- 

 nica previous to the publication of A. hesterna may be identical 

 with hesterna, and may therefore include the specimens here 

 described. This can best be determined by a careful comparative 

 study of all skeletal material obtained, as A. californica was 

 based solely upon limb and arch bones of very large size. If we 

 give full value to the statement on the label accompanying the 

 type specimen of A. californica, to the effect that it came from 

 beneath the lavas at Table Mountain, it is probable that this 



-^Leidr, J., Proc. Acad. Nat. Sci., Phila., 1870, p. 126. 



