EXPLANATION OF PLATE XXII. 



Fig. 1-4. Mastodon obscukus: 



Fragments of a lower jaw, from near Santa F6, New Mexico, presented to the Smithsonian 

 Institution by W. F. M. Arny. 



Fig. 1. Portion of the jaw containing the greater part of the last inolar tooth. Fig. 2. Por- 

 tion of the symphysis. The two fragments placed in their relative position, and reduced 

 to one-sixth the natural size. 



Fig. 3. Inferior view of the symphysial fragment, exhibiting exposed portions of the incis- 

 ors. One-fourth the natural size. 



Fig 4. The last inferior molar, natural size, seen on the triturating surface. The back por- 

 tion, consisting of another division and the heel, are broken away. 



Figs. 5, 6. Mastodon americanus. An anomalous molar tooth, natural size. 

 Fig. 5. View of the triturating surface. 

 Fig. 6. Side view. 



Fig. 7. Graphiodon vinearius. A tooth of the natural size. Specimen from the Miocene of Martha's 

 Vineyard, belonging to the museum of the Smithsonian Institution. 



