EXPLANATION OF PLATE XXXV. 



All the figures one-half the natural size except Fig. 14, which is of the natural size. 



Figs. 1-11. Tylosaurus dyspelor. Specimens from the Cretaceous of New Mexico, and belonging to 

 the Smithsonian Institution. 



Fig. 1. Articular ball of a posterior dorsal centrum. 



Fig. 2, 3. The same of two other specimens, exhibiting a successive increase of compression 



from above downward. 

 Fig. 4. Articular ball of a caudtll. centrum. 

 Fig. 5. Left lateral view of the same. 

 Fig. 6. Articular ball of a more posterior caudal centrum. 

 Fig. 7. Left lateral view of the same specimen, exhibiting the reduction in the size of the 



diapophysis. 

 Fig. 8. Left lateral view of a more posterior caudal vertebra, devoid of diapophyses. 

 Fig. 9. Supposed femur, posterior view. 

 Fig. 10. Supposed fibula. 

 Fig. 11. Supposed tibia. 



Figs. 12, 13. Tylosaurus proriger. Specimens from the Cretaceous of Kansas, belonging to tbe 

 Smithsonian Institution. 



Fig. 12. Extremity of the snout, or of the premaxillary. 



Fig. 13. Posterior articular surface of the left splenial bone of the lower jaw. 



Fig. 14. Tooth of a mosasauroid, natural size, from the Cretaceous of L'Eau qui Court 

 County, Nebraska. Tbe crown is compressed, conical, with acute borders and smooth sur- 

 faces. The base is compressed oval, and it exhibits on its inner side a small concavity for 

 the accommodation of a successor. 



