EXPLANATION OF PLATE XVIII. 



All the figure* are of the natural size except Figs. 51, 52. 



Figs. 1-14. Ptychodus Moktoni: 



Figs. 1, 2. Upper and posterior views of a large tooth from Kansas, obtained by Dr. George 



M. Sternberg. 

 Figs. 3, 4. Upper and posterior views of another tooth, apparently from the same individual. 

 Figs. 5, 6. Upper and posterior views of another tooth from the same locality. 

 Figs. 7, 8. Upper and posterior views of another tooth from the same locality. 

 Figs. 9, 10. Upper and posterior views of another tooth from the same locality. 

 Figs. 11, 12. Upper and anterior views of a large tooth from near Columbus, Mississippi, 



found by Dr. William Spillman. 

 Figs. 13, 14. Upper and posterior views of a tooth from Green County, Alabama, obtained 



by Professor Joseph Jones. 



Figs. 15-18. Ptychodus occidentals. Specimen obtained near Tort Hays, Kansas, by Dr. John L. 

 Le Conte. 

 Figs. 15, 1G. Upper and posterior views of a worn tooth. 

 Figs. 17, 18. Upper views of two small teeth. 



Figs. 19, 20. Ptychodus Whippleyi. The specimen obtained in the Cretaceous formation of Texas, by 

 Dr. Benjamin F. Shumard. 

 Fig. 19. Upper view of a tooth. 

 - Fig. 20. Posterior view of the same tooth. 



Figs. 21-25. Oxyrhina extent a : 



Figs. 21-23. Views, external or anterior, of three teeth from the Cretaceous formation of 

 Kansas, obtained by Dr. George M. Sternberg. 

 * Figs. 24, 25. External views of two teeth, from the Cretaceous formation near Columbus, 

 Mississippi, obtained by Dr. William Spillman. 



Figs. 26-28. Otodus divaricatus. The specimen from Texas, probably from a Cretaceous formation. 

 Loaned for examination by Dr. William Spillman. 

 Fig. 26. External or anterior view of the tooth. 

 Fig. 27. Lateral view reversed. 

 Fig. 28. Internal or posterior view.. 



Figs. 29-40. Galeocerdo falcatus'. External views of teeth. 



Figs. 29-31. Specimens from the Cretaceous of Kansas, collected by Dr. George M. Sternberg. 

 Figs. 32-36. Specimens from the Cretaceous, near Columbus, Mississippi, collected by Dr. 



William Spillman. 

 Figs. 37-40. Specimens from the Cretaceous, near Fort Hays, Kansas, collected by Dr. John 



L. Lo Conte. 

 Figs. 41, 42. Specimens from the Cretaceous of Texas, collected by Dr. Benjamin F. Shumard. 

 Fig. 43. Specimen from the chalk of Sussex, England. 



Figs. 44, 45. Lamna : 



Fig. 44. External view of a tooth, from the "Cretaceous, near Fort Hays, Kansas, found by Dr. 



John L. Le Conte. 

 Fig. 45. External view of a similar but smaller tooth, from the chalk of Sussex, England. 



Figs. 46-49. Lamna : 



Figs. 46, 47. Specimens from the Cretaceous of Now Jersey. Fig. 46. Lateral view of a tooth. 

 Fig. 47. External view of another specimen. 



Figs. 48, 49. Specimens from the Cretaceous of Mississippi, collected by Dr. William Spill- 

 man. Fig. 48. Lateral view of a tooth. Fig. 45. External view of another tooth. 



Fig. 50. Outer view of a tooth. Specimen from the Cretaceous of Kansas, collected by Pro- 

 fessor Hayden. 



Figs. 51, 52. Paobosyops paludosus. One-half the natural size. 



Fig. 51. Side view of the face; from the same specimen as the teeth of Fig. 3, Plate IV. 

 Fig. 52. Lower jaw; repealed from the same specimen as Fig. 11, Plate V. 



