290 



ON THE EXTINCT MAMMALIA OF 



These teeth appear as intermediate varieties between those referred to H. speciosum 

 and H. occidentaU, and favor an impression that all the specimens together belong to 

 the same species. Their measurements are as follow : 



2d superior molar. 2d. 3d. 



Lines. 



Lines. 



Lines. 



Antero-posterior diameter, 





11 



Hi 



Transverse diameter, . 





10 



11 



Length externally, 





19 



15 



Length internally, 



. 15 



15 





Width of internal column. 



. 4 



U 



4J 



"Width of do. at bottom, 



. 4 



4 





2. A first superior molar tooth, apparently belonging to a different species of 

 nipparion from any before indicated. It is about half worn away, and is represented 

 in figure 34. The triturating surface bears a near resemblance to that of the corres- 

 ponding tooth (4) oi H. occidentcde, but the tooth is of much smaller proportions, 

 being intermediate in size to the former and that of H. gratum. The central lakes of 

 the triturating surface are almost as complex; and the internal column is reniform 

 in transverse section, as in H. occidentale. The measurements of the specimen are 

 as follow : 



Lines. 



Length externally, ...... 



. 7 



Length internally, ...... 



. U 



Antero-posterior diameter, ..... 



. 12* 



Transverse diameter, ..... 



. 9 



Breadth of internal column, .... 



. U 



3. A second or third superior molar, probably of the temporary set, though of this 

 latter point I feel uncertain. Its proportions are nearly as gi'eat as in Hipparion 

 occidentale, and the arrangement of the enamel, as seen on the triturating surface 

 represented in figure 35, is quite as complex as in that species. The tooth also bears 

 some resemblance to the temporary molars of MerycMppus mirabilis, hereafter to be 

 described. I suspect it to be the third temporary molar of Hipparion spexiiosum. The 

 measurements of the specimen are as follow : 



Lines. 



Length externally, . . . . . . . .8 



Length internally, . . . . . . , . 6J 



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



Transverse diameter, . . . . . . .7* 



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



