328 ON THE EXTINCT MAMMALIA OF 



LiDca. 



Length of crown externally at middle, . . . . ,18 



Breadth at triturating surface, . . . . . .10 



Breadth near fangs, . . . . . . .8 



Width, transversely, . . . . . . .10 



6. Two first upper molars, from animals about the same size but of slightly differ- 

 ent ages. The specimens, represented in figures 6, 7, plate XXVII, are sufficiently 

 different in appearance to belong to different species, and approach most nearly in 

 character those referred to Protohippus placidus, represented in figures 40, 41, 42, 

 plate XVIII. Their measurements are as follow : 



Lines. Lines. 



Length at middle externally, . . . .. .IIJ 13J 



Breadth, . . . . ... . . 9^ 10 



Width obliquely across the middle, . . . .8 7i 



7. Three isolated upper molars, larger than any of the above from the same 

 locality. One of them is an unworn first molar, which had not yet protruded from 

 the jaw. Its length antero-externally is nearly two inches ; its breadth is thirteen 

 lines ; its width ten and a half lines. The other two specimens, from intermediate 

 positions in the series, are represented in figures 3, 4, plate XXVII. In structure 

 they bear a resemblance to those of Protohippus perditus more than to those of any of 

 the other equine species indicated, but they are much larger, and probably belong to 

 another species of the genus. In one of the specimens, figure 4, comparatively but 

 little worn, the section of the internal median column on the triturating surface 

 appears isolated as in Hipparion, but a prolongation exists at its fore part, indicating 

 an early conjunction with the antero-median column of the tooth, as in P-otoMppus 

 and Equus. Though I am apprehensive of having fallen into the error of multiply- 

 ing species on insufficient grounds, I feel persuaded that the specimens just described 

 indicate a larger species of Protohip)piis than those previously named, and therefore 

 propose to distinguish it with the name oi Protohippus supremus. 



The measurements of the two worn molars are as follow : 



Lines. Lines. 



Length at middle externally, .... 



Breadth at triturating surface, .... 



Breadth near fangs, ...... 



Width at middle of triturating surface, 



8. A portion of the left side of a lower jaw of a young animal, containing the three 

 temporary molars in functional position, and about one-half worn. The fourth per- 

 manent molar was yet entirely concealed within the jaw. In advance of the teeth 

 there exists a minute conical socket, from which a small premolar has been shed. 

 The measurements of the specimen are as follow : 



22 



26 



12 



13J 



9 



10 



12 



11 



