320 



ON THE EXTINCT MAMMALIA OF 



Lines. 



Breadth of last molar, ....... 10 J 



Length of fourth molar externally, ...... 16 J 



Length of fifth molar externally, . . . . . .19 



12. A series of the anterior four molars, inserted in a portion of the jaw. The 

 teeth appear to be about a third worn away, and they nearly agree in proportions 

 with those previously described. Their triturating surfaces are represented in figure 

 12, and are intermediate in character with those of the last two series described and 

 the previous ones. The narrow external fold or ridge at the fore part of the crown is 

 rather better developed than in the last two series indicated, but not so well as in the 

 others. 



The measurements of the teeth are as follow : 



Lines. 



Space occupied by the four molars, . . . . . .361 



Space occupied by the anterior three molars, 



Breadth of first molar, 



Breadth of do. near bottom, 



Length of do.. 



Breadth of third molar. 



Breadth of do. near bottom, 



Length of do.. 



Breadth of fourth molar. 



Breadth of do. near bottom. 



Length of do.. 



28J 



9i 



8 



9 



9 



8 

 14 



Si 



7i 

 12 



ts length in relation with 



13. A last molar of the left side, narrow in proportion to 

 the corresponding teeth previously described. Its triturating surface is represented in 

 figure 15, and is nine lines in breadth, while the length of the crown at the middle 

 externally is twenty lines. 



14. A fourth or fifth molar of the right side, from Bijou Hill. The triturating 

 surface is represented in figure 1, and resembles in the arrangement of its enamel the 

 series of figure 5, supposed to belong to Protohippus. At the lower four-fifths of the 

 specimen, however, the narrow external fold at the fore part of the crown is as well 

 developed as in the teeth supposed to belong to Hipparion, and, as in them, at a later 

 stage of attrition would have exhibited itself on the triturating surface. 



It is this specimen which is among the number mentioned under the head of 

 Hipparion {Hippodon) speciosum, in the Proceedings of the Academy for 1856, p. 311. 



15. A number of isolated molars, represented in figures 19 — 23 The specimen of 

 the last figure is from Bijou Hill, and appeared so peculiar that when first seen it was 



