1916] Chandler: Skull and Dentition of Bison antiquus 



135 



tween the second and third lobes, but not as well developed as that 

 between the first and second lobes. The third lobe is very simple. 



Milk teeth are present in a number of jaws. Dm 3 somewhat re- 

 sembles permanent P 3 , having two open interior valleys and a single 

 outer one ; it is considerably smaller, however. Dm 4 resembles perma- 

 nent P 4 in size, but differs from it in having the posterior inner valley 

 closed, forming a lake (fig. 12a). Dm 4 is trilobed, having large tri- 

 angular outer lobes between the first and second and between the 

 second and third main lobes, as well shown in fig. 12a, representing 

 a Dm 4 about to be shed, as can be seen from fig. 12&. When unworn 

 Dm 4 is almost as large as permanent M 3 . 



The sequence with which the permanent teeth come into function 

 is as follows : M 1 , M 2 , P 2 , then almost simultaneously P 3 and M 3 , and 

 finally P 4 . 



Conclusions 



Bison antiquus, as represented by an excellent series from Rancho 

 La Brea, and by other specimens, is subject to approximately the same 

 sort of individual and sexual variation as is found in the modern 

 species. Individual variation occurs in size and relative measurements 

 of the skull to the extent of about 20 per cent or less, while the sexual 

 difference in these respects is small, apparently less in B. antiquus 

 than in B. bison or B. bonasus. The horn-cores show approximately 

 similar individual variation within a sex, but the average length in 

 females is about 25 per cent less, while the basal circumference is about 

 33 per cent less, with no individual overlap in either case. From 

 this it is evident that the females have not only smaller, but more 

 slender horns. This corresponds to the condition in the existing species. 

 The variation in general form, curvature, and angle of insertion of 

 the horn-cores is very slight, and these make reliable specific characters. 



The dentition varies so little in different species, that specific 

 identification by means of the teeth is almost impossible. The size of 

 the teeth, and the amount of indenting or folding of the enamel walls 

 of the lakes varies to some extent in different species, but it is ap- 

 parently so variable within a species as to be of very little taxonomic 

 value. In general the teeth of B. antiquus have the enamel walls of 

 the lakes more complicated than have modern specimens of B. bison. 



Transmitted June 21, 1915. 



