PLATE XVII. 



PAGE. 

 PSAMMODUS PLENUS, St. J. and W 213 



Fig. 1 a. View from above of a small maxillary tooth; 1 b. do., posterior margin; 1 c. 

 do., anterior margin, 1 d, do., inner articular border; 1 e. do., exterior bor- 

 der; If. do., inferior surface. St. Louis limestone; Alton. Mr. Van Home. 



Fig. 2 a, b. c. d. e.f. Similar views of a medium-size example of the same form, out- 

 line partially restored. Alton; Mr. Van Home. 



Fig. 3 a. A larger specimen of the same form, view from above, showing more pro- 

 duced basal rim along the exterior border; 3 &. do., from posterior margin; 

 3 c. do., articular border; 3 d, do., exterior border. St. Louis limestone; Al- 

 ton. Mr. Van Home. 



Fig. 4 o. A very wide mandibular tooth, from above; 4 b. do., from the posterior mar- 

 gin; 4 c. do., anterior margin; 4 d. do., longitudinal profile from the exterior 

 border; 4 e. do., articular border. St. Louis limestone; St. Louis. Mr. St. 

 John. 



