Ant.-post. diam. 



Trans, diam 



Lines. 



Lines. 



14i 



7 



13 



5 



DAKOTA AND NEBRASKA. 269 



other side, and are moderately worn. They are rather smaller than those above 

 described, especially the last one. The series from the second to the sixth, at their 

 triturating surfaces, together occupy a space of about six inches from before back- 

 ward. Measurements of two of the specimens, independent of the investing 

 cementum, are as follow : 



Length of crown. 



Lines. 



Second molar, . . . .31 



Last molar, . . . .22 



5. Two inferior first molars, one from Pawnee Loup River, the other from the Nio- 

 brara. They are between a third and a half worn, and agree closely in character 

 with the corresponding teeth of the recent Horse. Their measurements are as follow: 



Lines. Lines. 



Length of the crown at the middle internally, . . .19 22 



Antero-postero diameter of the triturating surface, . .16 15 



Transverse do. independent of the cementum, . . .7 7i 



6. Six inferior molars, one from Pawnee Loup, the others from the Niobrara River. 

 Three are the third, fifth and sixth of the series, and are two-thirds worn down. The 

 others are less worn, and of different ages. They all agree in character with those of 

 the recent Horse. 



7. A series of three lower temporary molars, from the Niobrara River. The first 

 is but little worn ; the others belonged to a different individual, and are more worn. 

 The measurements of the specimens at or near the triturating surface, as defined by 

 the exterior enamel, are as follow : 



Ant.-post. diam. Trans, diam. 



Lines. Lines. 



First temporary molar, ..... 16i 5 



Second ""..... 15 6 



Third " « 16J 5J 



8. Tour symphysial fragments of as many lower jaws, from the Niobrara River. 

 They agree in form with the corresponding portion of the lower jaw of the recent 

 Horse. One of them retains the bottoms of the six incisive alveoli, and the contigu- 

 ous canine alveoli. 



9. An unworn and a much worn incisor, from the Niobrara, agreeing with corres- 

 ponding teeth of the recent Horse. 



10. The greater part of a mutilated occiput, about the size and form of that of the 

 ordinary Horse, from the Niobrara River. The breadth of the specimen at the para- 

 mastoid processes is estimated to have been about four and a quarter inches. The 

 occipital foramen is about seventeen lines in diameter transversely about the middle, 



