REFERENCES TO THE PLATES. I35 



Eig. 4. Three marginal plates of the left side of Plalemys sulcatus, one-half the diameter of the 

 originals. From Tinton Falls, Monmouth County, New Jersey, and belonging to the same collec- 

 tion as the preceding. 



Fig. 5. Four marginal plates of the left side of Chelone sopita, one-half the diameter of the 

 originals. From Mullica Hill, Gloucester County, New Jersey, a, Portion of a marginal plate ; 

 b, c, d, the three succeeding plates ; e, large notch between two of the plates ; /, suture for articula- 

 tion with the next plate ; g rounded unarticulating border ; h, inner border of the plates ; i, outline 

 of the scutes. 



Fig. 6. Anterior extremity of the upper jaw of Mosasaurus, from Monmouth County,New Jersey, 

 one-half the diameter of the original. From the collection of Rutgers College, a, Intermaxillary, 

 occupied by two teeth on each side ; h, portion of the right maxillary ; c, fore part of the maxillary, 

 imperfect ; the space which was originally occupied by a tooth being now filled with an artificial 

 cement. 



Fig. T. Mosasauroid tooth, natural size, from near Marion, Alabama. The specimen from which 

 the tooth was drawn belongs to the Smithsonian Institution, and strongly resembles, in general 

 appearance, llosasaicroid fossils from near Columbus, Mississippi. 



Fig. 8. Tooth of Piratosaurus iMcatus, of the size of the original. From the Red River of the 

 North, and belonging to the collection of the Smithsonian Institution. 



PLATE XX. 



Fig. 1. Transverse section of a tooth of Hadrosaurus Foulkii, highly magnified, a, Enamel ; 

 h, isolated streak of the same ; c, the interior dentine ; d, exterior layer of vaso-dentine. 



Fig. 2. Transverse section of a small portion of the vaso-dentine of the tooth of Hadrosaurus, 

 more highly magnified, a, The dentine ; 6, network of vaso-dentinal tissue. 



Fig. 3. Diagram representing the arrangement of structure seen in a vertical section of the teeth 

 of Mosasaurus. a, The crown, composed of interior dentine with a thin investment of enamel ; b, the 

 fang, composed of cementum ; c, the pulp cavity ; d, the communication of the latter with the exte- 

 rior occupied by a coarser structure of cementum, pervaded by large vaso-neural canals ; e, line of 

 cessation of the dentine ; f, cavity for a successional tooth ; g, position from which the section was 

 taken forming the subject of the next figure. 



Fig. 4. Section from the tooth of Mosasaurus, taken from the position marked g in the preceding 

 figure, and highly magnified, a, dentine of the crown ; 6, cement of the fang. 



Fig. 5. A smaller section similar to the last, more highly magnified, a, dentine ; b, cement. 



Fig. 6. A similar section still more highly magnified, a, dentine ; 6, cement. 



Figs. 7-9. Tooth of Tomodon horrificus, from Mullica Hill, Gloucester County, New Jersey, of 

 the natural size. 



Fig. t. Outer view. 



Fig. 8. Inner view. 



Fig. 9. Lateral view. 



Fig. 10. Transverse section of the tooth of ' Astrodon Johnstoni, highly magrified, from a prepa- 

 ration made and loaned by Dr. Christopher Johnston. 



PUBLISHED BY THE SMITHSONIAN INSTITUTION, 



WASHINGTON CITY, 



MAY, 1865. 



