ART. 5. 



BISON OCCIDENTALIS FROM MINNESOTA HAY. 



will show that this is a long-faced, narrow-headed species. B, occi- 

 dentalis is a broad-headed form, surpassing B. bison in this respect. 



Indices for the horn-cores (pis. 1, 2) are obtained by dividing 

 the length along the lower curve by the distance from the base of the 

 horn-core on the upper side to the tip in a straight line. The fol- 

 lowing table presents the indices as obtained : 



It will be seen that there is a wide range of curvature in B, 

 occidentalis. There is no less in B. bison. Five individuals of 

 the latter had this index varying from 128 to 145. From the curva- 

 ture alone B. bison can not be distinguished from B. occidentalis. 

 Nevertheless, their horn-cores are very different, those of the ex- 

 isting bison being short and stubby, those of B. occidentalis much 

 longer and relatively slenderer. It will be observed, too, that the 

 index of the curvature of B. alleni is low ; that of B. bonasus, very 

 high, at least as shown by the specimen at hand. 



Formerly the writer proposed,^ in view of the imperfection of 

 most skulls of bisons, to make the distance from the lower lip 

 of the foramen magnum to the rear of the nasals a unit for measure- 

 ments. This unit has been applied in the case of the skulls studied 

 for this paper, but the results have not been satisfactory. 



A full face view of the skulls of B. occidentalis (pi. 1, fig. 1) shows 

 that the face is more narrowed in front of the orbits than it is in 

 B. bison. This may be tested by dividing the width at the rear of 

 the orbits into the w^idth on the maxillary ridge at the maxillomalar 

 suture and multiplying the result by 100. The following results 

 are obtained: o 



Of these skulls here measured the first three belong to B. occi- 

 dentalis. That of the fourth column accompanies the materials from 

 Minnesota and is in good condition, except that the muzzle is in- 

 jured. The fifth, sixth, seventh, and eighth columns belong, respec- 



a Tioc. U. S. Nat. Mus., vol. 46, p. 163. 



