PLATE XVI. 



PAGE. 

 Fig. 1-4 PSAMMODUS PLENUS, St. J. and W 213 



1 a. Mandibular tooth, view from above; 1 b, do., from the articular border; 1 c, 



do., exterior border; 1 d, do., posterior margin; 1 e, do., anterior margin; 

 /, do., inferior surface. St. Louis limestone; Alton, Ills. Mr. Van Horne. 



2 a. A similar example of the same form, from above, outline partially restored; 



2 b. do., inferior surface; 2 c, do., showing the channeled exterior border. 

 St. Louis limestone; Monroe county. Ills. Prof. Worthen. 



3 a, b. A nearly perfect specimen of the same form, view from above and the ar- 



ticular border, showing a faint marginal sulcation round the articular, 

 posterior and anterior margins of the crown. St. Louis limestone; Alton. 

 Ills. Mr. Van Horne. 



4 a. View from above of a fragment of a very large maxillary tooth, partially 



restored in outline; 4 b, do., from the posterior margin; 4 v, do., articular 

 inner border. St. Louis limestone; Alton. Mr. Alex. Butters. 



