DAKOTA AND NEBRASKA. 



291 



4. A first superior temporary molar, nearly as large as the preceding specimen, and 

 sufiiciently resembling it to render it probable that it may belong to the same species. 

 It is apparently about one-third worn away, and is represented in figure 36. The 

 triturating surface presents nearly as much complexity of arrangement of the enamel 

 as in the preceding sjiecimen. The central lakes are deficient in cementum at their 

 centre. The internal column is elliptical in transverse section. The measurements 

 of the specimen are as follow : 



Lines. 



Length externally, . . . . . . . . 6J 



Length internally, ........ 4J 



Antero-posterior diameter, . . . . . . .12 



Transverse diameter, . . . . . . . 7i 



Breadth of internal column, . . . . . . 2J 



5. A first superior temporary molar, remarkable for its narrowness transversely 

 compared with its breadth antero-posteriorly. It is represented in figure 37, and is 

 so peculiar in appearance as to suggest the idea that it may belong to an unknown 

 equine genus. The central lakes of the triturating surface partake of the proportion- 

 ate breadth of the tooth, and are unoccupied with cementum centrally. The 

 surrounding enamel is delicate, and folded with a medium degree of complexity. 

 The fore part of the tooth is extended by a pair of accessory columns, instead of one 

 as usual in Equus and Hipparion. The inner of the two accessory columns, in 

 section, as seen on the triturating surface, is uncinate. The internal column of the 

 crown increases in breadth towards the bottom, and is ellipsoid in section on the 

 triturating surface, with a small beak directed towards the antero-median column. 

 The measurements of the specimen are as follow : 



Lines. 



Length externally, . . . . . . , . . 6i 



Length internally, . . . . . . . .4 



Antero-posterior diameter, . . . . . . .16 



Transverse diameter, . . . . . . .8 



Breadth of internal column, . . . . . .2;^ 



5. Two isolated temporary molars, slightly water-worn. They are sufficiently 

 alike in size and construction to be the second and third of the same individual. 

 They likewise bear sufficient resemblance to the specimen last described, notwith- 

 standing the great difference in antero-posterior measurement, as to lead to the sus- 

 picion that they may belong together. 



The teeth are considerably wider from before backward than from side to side, 

 The central lakes of the triturating surface, as represented in figure 38, are of com- 

 paratively simple construction. The internal column is elliptical in section, and 



