EXPLANATION OF PLATE XXVIII. 



Figs. 1,2. UlNTATIIKUIUM R0BU8TUM : 



Fig. 1. Outline taken from Professor Marsh's Fig. 1, Plato II, of D'moceras mirabilis, in tbo 

 Am. Jour. Sciouco, 1873, enlarged so as to accord with one-sixth of tho size of the frag- 

 ments introduced in the figure, which correspond with thoso of Figs. 1 and 8, Plato XXV, 

 and Fig. 1, Plato XXVI. 



Fig. 2, View of the base of tho cranial specimen also represented in Fig. 1, Plato XXVI. 

 One-sixth the diameter of nature. 



Fig. 3. Large osseous protuberance, one-half the size of nature, resembling the similar 

 osseous protuberances of tho specimen of Mcyaccrops, represented in Figs. 2, 3, Plato 1. 

 The specimen is from the Mauvaises Torres of White River, Dakota, and was originally 

 suspected to belong to Titanothmum. 



Figs. 4-8. Bison latikhons: 



Figs. 4,5. Cranium from Pilarcitos Valley, California, discovered by Messrs. Calvin and 

 Wilfred Brown, and presented to tho Academy of Natural Sciences of Philadelphia. One- 

 fifth the natural size. 



Fig. 4. Upper view. Fig. 5. Posterior view. 



Figs. G, 7. The second and last upper molars seen on their triturating surfaces. Natural size. 

 Specimens from California, belonging to Wabash Collogo, Indian;). 



Fig. H. An upper second molar of the left side, considerably worn, and soon on its triturat- 

 ing surface. Natural size. From Luzerne County, Pennsylvania. 



Fig. 9. Mastodon amkuicanus: 



A first lower premolar of tho right sido, natural size. Found with (lie preceding. 



