KEFERENCES TO THE PLATES. 469 



Figs. 14-20. PALiEOLAGUS Haydeni. See page 331. Triturating surfaces of the upper and lower 

 molar teeth, all magnified three diameters. 



Figs. 14-16. Upper molar teeth. 



Fig. 14. From a young specimen, containing the temporary teeth 1, 2, 3, and the following two per- 

 manent teeth, 4, 5, of the left side. The temporary molars were nearly ready to be displaced, their 

 crowns being much worn and inserted alone by fangs. 



Fig. 15. From an adult specimen, coutaining the four intermediate permanent teeth, 2-5, of the 

 right side. 



Fig. 16. The four intermediate molars, 2-5, of the right side, from an old animal. 



Figs. 17-20. Lower molar teeth. 



Fig. 17. A full series of molars of the right side, from a young adult specimen. 



Fig. 18. The anterior four molars of the left side, from an older specimen than the preceding. 



Fig. 19. The anterior three molars of the right side, from another specimen. 



Fig. 20. The anterior three molars of the left side, from an old animal. 



Figs. 21, 22. Castor tortus. See page 341. 



Fig. 21. Under view of the upper jaw, containing the anterior three molars on both sides and part of 

 the incisors, the natural size. 



Fig. 22. Inferior view of the molars of the right side, from the same specimen as the last, twice the 

 diameter of nature. 



Figs. 23, 24. Hystkix venustus. See page 343. One and a half times the diameter of nature. 



Fig. 23. First upper molar of the right side. 



Fig. 24. Section near the triturating surface of an unworn molar, probably from the same animal. 



Figs. 25-28. Leptictis Haydeni. See page 345. All the figures of the natural size except the 

 last one. 



Fig. 25. View of the left side of the skull. Fig. 26. Inferior view of the left half of the skull. Fig. 

 27. Superior view of the skull. 



Fig. 28. Inferior view of the third and fourth premolars of the right side, magnified three diameters. 



Figs. 29, 30. IcTOPS dakotensis. See page 351. 



Fig. 29. Inferior view of the third, fourth and fifth molars, magnified three diameters. 



Fig. 30. Superior view of the facial portion of a skull, of the natural size. 



PLATE XXVII. 



All the figures are of the natural size except Figs. 10, 13-16, which are one-half the diameter. 



Fig. 1. Merychippus mirabilis? See page 327. Series of upper molars of the left side, partially 

 restored. 



Fig. 2. Hipparion occidentale. See page 326. Triturating surfaces of the second and third 

 upper molar.s of the left side. 



Figs. 3, 4. Protohippus SUPREMUS. See page 328. Triturating surfaces of left upper molars, from 

 an intermediate position of the series. 



Fig. 5. Protohippus perditus. See page 327. An upper fourth molar of the left side. 



Figs. 6, 7. Protohippus placidus? See page 328. Two upper first molars of the right and left 

 side, from different individuals, perhaps different species. 



Figs. 8-11. Elotherium ingens. See page 192. 



Figs. 8, 9. Crown of an inferior true molar of the right side. Fig. 8. External view. Fig. 9. View 

 of the triturating surface. Of the natural size. 



