3d superior molar. 



4tli. 



6th. 



6tli. 



Lines. 



Lines. 



Lines. 



Lines 



. 6 



5 



5 



5i 



. 2 



2 



U 



2J 



. lOi 



9 



9i 



IIJ 



. 12i 



Hi 



12 



11 



302 ON THE EXTINCT MAMMALIA OF 



fragment referred to Merycliippus it holds a more advanced position, being placed 

 above the fore part of the third temporary molar. 

 The measurements of the teeth contained in the specimen are as follow : 



Length externally, 

 Length internally, 

 Antero-posterior diameter. 

 Transverse diameter, 



5. Two last superior molars. One of them is worn about as much as that of the 

 fossil last described, and presents nearly the same proportions and appearance, as 

 represented in figure 56, plate XVIIL It is six lines externally along its median 

 ridge, and three lines along the internal column. Its antero-posterior diameter is 

 twelve lines, and its transverse diameter ten and a half lines. 



The other specimen is much less worn, and is of larger proportions. The tritu- 

 rating surface, as represented in figure 55, plate XVIII, resembles in its anatomical 

 character the two corresponding teeth above described. Its length externally is 

 thirteen lines; internally eight lines. Its antero-posterior diameter at the triturating 

 surface is twelve and a half lines ; the transverse diameter eleven lines. On the same 

 level as the corresponding tooth in the jaw fragment above desci'ibed, it is nearly 

 thirteen lines in antero-posterior diameter, and twelve lines in transverse diameter. 



6. The outer portion of a last superior molar, from White River, This was found 

 in association with the teeth of Hipparion occidentale, from the same locality, and at 

 first was suspected to belong to that animal, notwithstanding the comparative sim- 

 plicity in its construction. It is very much less worn than in any of the correspond, 

 ing teeth referred to MerycMppus, but resembles them in the character of its 

 triturating surface. At the same age it would have had nearly the same proportions 

 and appearance as the last molar in the jaw fragment of Mei-ycliippus mirabilis. The 

 length of the tooth following the curve of the antero-external ridge is twenty-two 

 lines; along the external median ridge, nineteen lines. The antero-posterior diameter 

 of the triturating surface is ten lines ; at the bottom of the crown eleven lines. 



ANCEITEERIDM 



The Anchitheridce, an extinct family of solipeds, has for its type the genus Anchi- 

 therium, first established on the remains of a species, the A. aurelianense, from the 

 medial tertiary deposits of France. 



The Ancliitheridce have six large molar teeth on each side of both jaws, besides a 

 small premolar, as in the Horse. 



