134 University of California Publications in Geology [Vol. 9 



important details from that of B. bison, except that the posterior inner 

 tubercules of all of them are better developed, in slightly worn teeth, 

 (e.g., 21152) forming a minute lake posterior to the main one. See 

 figs. 8, 9 and 10. 



M 1 when once worn fiat is almost square with the lakes very 

 narrow and V-shaped, in well-worn teeth the anterior horn of the 

 posterior lake and the posterior horn of the anterior lake reaching 

 relatively far toward the outside (fig. 10). 



The sides of the lakes are very slightly indented on 21152 and 

 21414 (see figs. 8 and 9), while in 21183 there is an invaginating lobe 

 on the anterior side of the posterior lake as in Allen's pi. 10, fig. 7, 

 ascribed to a fossil B. bison. M 2 has wider lakes than M 1 , with a more 

 or less Avell developed invagination of the enamel on the posterior side 

 of the posterior lake compare 21152 (fig. 9) and 21443 (fig. 10), the 

 latter also having an invagination on the anterior side of the anterior 

 lake while on more worn teeth (21183 and 21185) there is no such 

 invagination to be seen. Upper milk molars 2 and 3 are present in 

 21188, and but slightly worn. They resemble permanent molars, ex- 

 cept for their smaller size, and the relatively greater size and different 

 form of the small inner lobe between the protocone and hypocone. In 

 Dm 3 of 21188 this lobe is long and tongue-like, about 8 mm. long, with 

 its widest anteroposterior diameter only about 2.5 mm. It is less con- 

 spicuous in Dm 2 . 



The teeth of the lower jaw vary in much the same way as those of 

 the upper, and show the same differences relative to B. bison. There 

 are specimens showing teeth in all stages of wear, from unworn milk 

 molars to permanent molars which have been worn below the level of 

 the lakes. Figure 11 shows the lower teeth of 21189, of moderate age. 

 P„ is a very simple tooth with an inner and outer furrow, slightly 

 nearer the posterior end of the tooth. P 3 has two open interior valleys 

 and a slight posterior outer furrow, the anterior inner furrow being 

 more or less bilobed in some specimens, especially in 21181. In P 4 

 there are large open anterior and posterior valleys on the inner side 

 and a smaller one on the anterior inside corner. There is also an outer 

 furrow, situated rather posteriorly. M t and M 2 have very narrow 

 crescentic lakes, the outer side of the crescent being slightly pushed in. 

 The outer pillar, when moderately worn, becomes connected with both 

 the protoconid and hypoconid. It is not as large as the inner pillars of 

 the upper molars. In M, the pushing in on the base of the crescents 

 is still more prominent. In this tooth there is a slight outer lobe be- 



