EXPLANATION OF THE PLATES/ 



PLATE I. 



All the figures are of the natural size. 



Figs. 1-4. Pocbi-otlierium Wilsoni. 



Fig. 1. View of the right side of the face. The top of the head and the cranium proper are broken 

 away. To the left is represented the angular apophysis, and in the concavity above this is the very large os 

 tympanica. The upper jaw contains the first premolar, separated from the others by a hiatus, the temporary 

 molars, and the permanent true molars. The lower jaw contains the temporary molars and the permanent 

 true molars. 



Fig. 2. Upper view of the nasal extremity of the face, exhibiting its great narrowness. 



Fig. 3. View of the masticating surfaces of the upper molars of the specimen 1. 



Fig. 4. View of the masticating surfaces of the lower molars of the specimen 1. 



Figs. 5-10. Ayriochoeriis anliquus. 



Fig. 5. View of the right side of the face. The specimen is much mutilated, but the orbit is observed 

 not to be closed by an arch posteriorly. In the upper jaw the inner part of the second premolar of the left 

 side is visible, and succeeding it upon the right side the posterior two premolars and the true molars. In 

 the portion of lower jaw are visible the posterior two premolars and the true molars. 



Fig. 6. Inferior view of the upper jaw, exhibiting the triturating surfaces of the molars, five of which 

 are preserved on the right side and six upon the left. The hard-palate is obscured by a mass of very dense 

 matrix, which would endanger the integrity of the specimen to remove. 



Figs. 7, 8. Triturating surfaces of the posterior five inferior molars of the right and left sides. 



Fig. 9. Triturating surfaces of the first and second true inferior molars of the left side, somewhat worn. 



Fig. 10. Triturating surfaces of the posterior two true superior molars of the left side, a little worn, and 

 probably belonging to the same individual as the last specimen. 



PLATE II. 



Figures of the natural size. 



Oreodon Culhertsonii. 



Fig. 1. The right side of a much fractured skull with the lower jaw, of an adult, containing the full 

 complement of teeth quite perfect. In the upper jaw are three incisors, the canine, four premolars, and 

 three true molars; in the lower jaw, four incisors, the canine, three premolars, and three true molars. 



Fig. 2. Front view of the three upper and four lower incisors of the right side, from the same specimen 

 as the preceding figure. 



Fig. 3. The left side of another adult specimen, which is in a comparatively fine state of preservation. 

 It has lost the nasal extremity, post-orbital arch, and zygoma; the latter, however, was entire when the 

 specimen was received, but was afterwards accidentally broken off' and lost. The upper jaw contains the 

 seven molars, and the lower jaw the canine and sis molars. 



' All the Plates are drawn directly from Natm-e, on stone. Plates 1, 2, 3, 8, 9, 10, 11, 13, are by Mr. A. Sonrel, of 

 Woburn, Mass. : Plates 4, 7, 13, 14, 16, 20, 21, 22, 23, 24, by Mr. A. Frey, of Philadelphia: Plates 5, 6, 12, by Mr. 

 A. J. Ibbotson, of Philadelphia: Plates 18, 19, by Mr. F. Sohell, of Philadelphia: and Plate 17 by Mr. J. Butler, of 

 Philadelphia. 



