DAKOTA AND NEBRASKA. 



285 



Antero-posterior diameter, 



1st superior molar. 

 Lines. 



. Hi 



2d. 



Lines. 

 IIJ 



5th.l 

 Lines. 



10 



Transverse diameter, . 





11 



10 



Length externally, 

 Length internally. 

 Breadth of internal column, 



.21 



18 

 14 



Si 



20 

 15 



21 



3. Five upper molars, apparently from the same individual, consisting of the first, 

 third, and fourth, of the left side, and the second and last of the right side. The 

 specimens are somewhat weather-worn; the fourth is mutilated, and the sixth, 

 which had not long protruded, has lost its outer portion. A series, from the first to 

 the fourth inclusive, is represented in figures 7 — 10. 



They are less worn than the preceding specimens, hut independently of this cir- 

 cumstance the first molar is proportionately larger, while the others nearly agree in 

 proportions. The internal column of the crown is rather wider towards the bottom, 

 and partakes less of the lozenge-shaped character, or is more elliptical in transverse 

 section. 



The arrangement of the enamel, as seen on the triturating surface of the first 

 molar, figure 7, is almost exactly hke that of the preceding specimen, figure 6. In 

 the second molar, figure 8, the enamel is more folded on the contiguous sides of the 

 median lakes than in the corresponding tooth, figure 11, above described, but not in 

 a remarkable degree. In the third molar the triturating surface, figure 9, nearly re- 

 sembles that of the second, but the section of its internal column appears renifonn 

 instead of ellijitical. The fourth molar, figure 10, agrees in its characters with the 

 corresponding teeth above described sufficiently to refer it to the same species. 



In most all the Hipparmi teeth previously described to the specimens under con- 

 sideration, the internal column of the crown is of pretty unifox'm diameter, but in 

 these it is narrow at the triturating surface, and gradually but slightly widens 

 towards the bottom. 



By comparing the views of the triturating surfaces (figures 7 — 10) of these teeth 

 with those (figures 1 — o)'oi Hipparion occidentale, they will be observed to be difier- 

 ent in appearance, — too much so to render it probable that they should belong to the 

 same species. 



The measurements of the specimens are as follow : 



Antero-posterior diameter, . 

 Transverse diameter. 

 Length externally. 

 Length internally, . 

 Breadth of internal column, 

 Breadth of do. at bottom, . 



or molar. 



2d. 



3d. 



4th. 



6th. 



Lines. 



Lines. 



Lines. 



Lines. 



Lines 



13 



Hi 



11 



lOi 



9 



10 



10} 



10 



10 





17 to 20 



21 



23 







13 



16 



17 



14 



17 



3 



8 



3} 



31 



3 



4 



4 



4} 



4i 



4 



