32 THE MASTODON. 



10. M. Buffonis. This is characterized by short teeth. 



11. M. Brevirostris. The M. Brevirostris has a short 

 lower jaw, the lower tusks wanting, and the molar similar 

 to M. longirostris, with secondary tubercles between the 

 ridges. 



12. M. Productus. M. Productus belongs to that class 

 of the genus in which the transverse valleys are inter- 

 rupted by tubercles or cones. 



13. M. Obscurus. This species rests upon the tooth 

 known as the "Baltimore tooth," discovered in Caroline 

 County, Maryland, in 1840. The tooth bears some resem- 

 blance to the last inferior molar of M. productus, but 

 narrower, and displaying a stronger tendency to alternation, 

 and less tubercular. 



14. M. Shepardi. Dr. Leidy thinks it probable that 

 M. Shepardi and M. obscurus belong to one and the same 

 species. M. Shepardi was discovered in California by Dr. 

 L. G. Gates, who sent the specimens to Professor C. U. 

 Shepard, of Amherst, Massachusetts, who in turn sent them 

 to Dr. Leidy. The last named it in honor of Professor 

 Shepard. 



15. M. Campester. This is a species recently discovered 

 by R. S. Hill, in the Loup Fork beds of Kansas and named 

 by Professor Cope. It belongs to the tetralophodon type, 

 and is somewhat allied to the M. Sivalensis and M. longiros- 

 tris. There is no indication of tusks in the symphysis, and 

 the superior tusks have a broad band of enamel. In size, 

 it was about that of the African elephant. 



[X. GEOLOGY. 



i / The mastodon lived during three distinct periods of the 



* world's history, viz., Miocene, Pliocene, and Alluvial. As 



the Glacial period is placed between the Pliocene and 



Alluvial, a fourth age must be added. It experienced great 



changes in the climate, as well as having lived during the 



