284 ON THE EXTINCT MAMMALIA OF 



The measurements of the three specimens, in comparison with the most perfect 



Bijou Hill specimen, are as follow : 



4th superior molar. 4th. 5th. 5th Bijou. 

 Lines. Lineg. Lines. Lines. 



Antero-posterior diameter, . . .lOi 9J 9J 9 



9} 9 8i 8i 



17 14 16 17 



9 lOJ 10 10 



3 3i 3 3 



Transverse diameter. 

 Length externally, . 

 Length internally, . 

 Breadth of internal column, 



2. Three upper molars, apparently from the same individual, consisting of an im- 

 perfect first, a second, and a fourth or fifth of the series. Their triturating surfaces, 

 represented in figures 6, 11, 12, plate XVIII, exhibit an arrangement of the enamel 

 which has led me to suspect that they belong to the same species as the preceding 

 specimens. 



The fourth or fifth molar (12), the only tooth corresponding with any of the above 

 specimens (13, 14), approximates them in the folding of the enamel. In comparison 

 with them it appears proportionately too large for a fifth molar, and agrees better in 

 this respect with the fourth molars. In relation with its two companions, however, 

 judging from its proportionate length, it appears rather to be the fifth of the series. 

 It is less worn than any of the worn specimens above described, and is therefore 

 longer and slightly broader on the masticating surface. 



In the three specimens under consideration, as observed on the masticating 

 surfaces, the arrangement of the enamel is simple in comparison with its condition in 

 previously recognized species of Hipparion, and indeed is nearly as simple as in the 

 Horse and Ass. A comparison between the specimens and those oi H. occidentale 

 exhibits a striking difference, rendering it improbable that they should belong to the 

 same species. 



The internal column of the cro'wn is narrow and rather lozenge-like ellipsoidal in 

 transverse section. 



In what may be considered to be the fifth molar (12), the fold of enamel, at the 

 inner side of the triturating surface, extending towards the ellipsoidal islet, is simple ; 

 and in the second molar (11) is bi-lobed. 



In the first molar (6), which has lost its outer portion, the two central lakes of the 

 masticating surface communicate by their contiguous arms, and the anterior one 

 opens into the interval bordering on the internal ellipsoidal lake or islet. 



The measurements of the specimens are as follow : 



