DAKOTA AND NEBRASKA. 319 



Lines. 



Third molar, breadth of crown, . . . . . .9 



Fourth molar, " " . . . . . .Si 



Fifth molar, " " ...... 10 



Fifth molar, " " near middle, . . . .9 



9. A number of molars, fitting in pairs, from different individuals and ages, proba- 

 bly belong to the same species as the preceding series. Figure 7 represents the 

 triturating surface of the posterior two of the series ; figure 8, the fourth and fifth of 

 another series ; figure 9, the second and third of a series, which are contained in a 

 fragment of the jaw; and figure 10 an anterior pair. Figure 2 also represents a last 

 molar, probably of the same species. 



10. A series of the back three molars, apparently belonging together, and repre- 

 sented in figure 5. They appear to be less than half worn away, and nearly agree in 

 size and proportions with the teeth above described. The arrangement of the enamel 

 on the triturating surface differs in an important manner, and they probably belong 

 to a different animal, — probably Protohi];>])us perdUus. In the teeth previously de- 

 scribed, at the fore part of the crown externally there is a narrow longitudinal fold 

 with a more or less free summit. "When the teeth were slightly worn, the latter 

 appeared on the triturating surface as an islet, but soon became an outward extension 

 of the more important fold directed inwardly. In the teeth under inspection, the 

 external fold at the fore part of the crown is rudimental, or substituted by a ridge of 

 enamel as in the Horse, and does not appear on the triturating surface, as an outer 

 extension of the large internal enamel fold, in any stage of abrasion. 



The measurements of the teeth are as follow : 



Lines. 



Space occupied by the three molars, . . . . .29 



Breadth of fourth molar, . . . . . . .9 



Breadth of last molar, . . . . . . .11 



Length of crown of fourth molar externally, . . . .11 



Length of crown of last molar externally, . . . . .11 



11. A series of the back three molars, apparently from the same animal, which had 

 scarcely reached adult age, as the last tooth is unworn. Their triturating surfaces 

 are represented in figure 11, and nearly resemble those of the series last described, 

 but are even simpler in the arrangement of the enamel folds internally. 



The measurements of the teeth are as follow : 



Lines. 



Space occupied by the three molars, . . . . .31 



Breadth of fourth molar at triturating surface, . . . .10 



Breadth of fourth molar near bottom, . . . . . 7i 



