PLATE X. 

 Teeth of Bison americanus, showing different stages of attrition, etc. (All the figures natural rise.) 



Fig. 1. Left lower molars, seen from above, of a very old specimen from the plains of Kansas (No. 10), 



showing an extreme stage of attrition. 

 Fig. 2. The same, seen from the outside. 

 Fig. 3. Left lower molars, seen from above, of an aged specimen from the plains of Kansas (spec. 



No. 105), showing a less advanced stage of attrition. 

 Fig. 4. The same, seen from the outside. 

 Fig. 5. Right lower molars, seen from above, of a middle-aged specimen from Big-Bone Lick, Kentticky 



(No. 2046), showing the small amount of attrition. 

 Fig. fi. The same, from the outside, showing the deeply serrated outlines of the crown surface of the 



molars. 

 Fig. 7. Left upper molars, from above, of a middle-aged specimen from Big-Bone Lick. Kentucky 



(No. 2132), showing the small amount of attrition. 

 Fig. 8. The same, from the outside, showing the deeply serrated outline of the crown surface of the 



molar.-. 

 Fig. 9. Bight lower molars, seen from above, of a rather young or middle-aged specimen from the plains 



of Kansas (No. 102). 

 Fig. 10. The same, from the outside, showing the nearly even outlines of the crown surface of the molars. 

 Fig. 11. Upper molars of the same specimen, Been from above. 

 Kg. i -. Thi »me, from the outside, showing the nearly even outlines of the crown surface. 



N. B. Fig-. 1 1 and 12 are strictly comparable, as respects the age of the specimens, with Fig-. :> and 10, 

 If there is any difference, the specimen illustrated by Figs. 1 1 and 12 is younger, rather than older, than 



the specimens from which Pigs. U and IO were made. 



to short the mature dentation of B. americanus. 



