EXPLANATION OF THE PLATES. 121 



PLATE VI. 



All the figures are of the natural size. 



Figs. 1—7. Oreodon gracilis. 



Fig. 1. Upper view of a broken skull. 



Fig. 2. Base view of the same specimen. On the right side the jaw contains entire the last premolar 

 and all the true molars of the permanent series. 



Fig. 3. View of the right side of the same specimen as the last. 



Fig. 4. View of the left side of a face and lower jaw of another adult specimen. The upper jaw exhibits 

 the last two molars, and the lower jaw the last premolar and all the true molars. The orbit is entire. 



Fig. 5. View of the masticating surfaces of the lower molars of the specimen last indicated. 



Fig. 6. View of the left side of the skull and lower jaw of a young individual, being the same specimen 

 represented in Figs. 3, 4, Plate V. The orbit is nearly entire. The upper jaw exhibits a series of the first 

 premolar restored, the three temporary molars, and the anterior two permanent true molars. The lower 

 jaw contains two temporary molars and the succeeding two permanent true molars. 



Fig. 7 represents the masticating surfaces of the inferior teeth last mentioned. 



Figs. 8—11. Oreodon Culbertsonii. 



Fig. 8. Masticating surfaces of the inferior posterior five molars of the left side, very much worn. 



Fig. 9. Inner view of the same teeth as those last indicated. 



Fig. 10. Fragment of the lower jaw of the right side of a young animal. It contains the broken canine, 

 and the entire last temporary molar and the succeeding two permanent true molars. 



Fig. 11. Outer view of the same specimen as the last. 



PLATE VII. 



Figures all the size of nature. 



Figs. 1-3. Eiicrotaphus aurilus. 



Fig. 1. View of the left side of a portion of the cranium, exhibiting the jwrs squamosa and the parietal 

 bone. 



Fig. 2. Upper view of the same specimen. 



Fig. 3. View of the base of the same specimen, exhibiting the large ossa tympanica, portions of the 

 glenoid articulations, and the occipital and sphenoidal bodies. 



Figs. 4-6. Eiicrotaplms Jacksoni. 



Fig. 4. View of the right side of a portion of the cranium, exhibiting the pars squamosa, the post glenoid 

 tubercle, the meatus auditorius externus, and part of the parietal bone. 



Fig. 5. Upper view of the same specimen as the last. The parietal crest is broken away. 



Fig. 6. View of the base of the same specimen. It exhibits one os tympanica with its superficies broken 

 ofi^, one glenoid articulation, and the occipital and sphenoidal bodies. 



PLATE VIII. 



Figures of the natural size. 



Arcliaeotlieriwn Blortoni. 



Fig. 1. View of the base of the skull of a young animal. The deciduous teeth had not yet been shed, 

 and only the first two permanent true molars had protruded. Upon the left side are exhibited the last two 

 permanent premolars, exposed by breaking away deciduous teeth occupying a corresponding position; the 

 first two permanent true molars, which are in place; and the last molar, which was exposed by breaking 

 away the bone. Upon the right side are exhibited the last two deciduous molars, succeeded by the three 

 permanent true molars. 



