PLATE XV. 



PAGE. 

 PSAMMODUS GBANDIS, St. J. and \V 211 



Fig. 1 a. Mandibular tooth, from above, showing a fragment of a very large example, 

 the trituating surface but slightly worn, restored in outline; 1 1>. do., 

 from the posterior margin; 1 c. do., anterior margin; 1 d. do., profile sec- 

 tion. Keokuk; Keokuk, Iowa. Prof. Worthen. 



Pig. 2 a. Maxillary tooth, view from above, outline restored, coronal surface worn 

 during use; 2 b. do., from the posterior margin; 2 c. do., profile section. 

 Keokuk; Keokuk, Iowa. Mr. Cox. 



Fig. 3 a. A small worn example of the same form, view from above, outline partially 

 restored; 35. do., from the posterior margin; 3 c. do.' from the inner ar- 

 ticular border. Keokuk; Bentonsport. Iowa. Mr. Spriager. 



PSAMMODUS TUBGIDUS, St. J. and W 206 



Fig. 4 a. Maxillary tooth, view from above, outline partially restored; 4 b. do., from 

 the posterior margin: 4 c. do., anterior margin; 4 d. do., inner articular 

 border; 4 e. do,, from the exterior border. U. B. limestone fish-bed; Des 

 Moines county, Iowa. 



