Plate Xa. — Continued. 



I'AGE . 



Fig. 20 22. Lisgodus cuhtus, St, J. and W 364 



20 a. Convex face of worn, laterally elongated tooth ; Upper Burlington ; Louisa county, 



Iowa. 



21 a,b,c. Views of concave and convex faces, and profile section, of specimen of normal 



form, enlarged two diameters. Same horizon and locality. 



22 a, b, c. Similar views of sinall"r, vertically elongated tooth, enlarged two diameters. 



Same horizon and locality. 

 Fig. 23. PoLYitinzonus WIUJAMSI. St J. and W 384 



23 a. View from the basal sido of a small worn tooth. ; 23 b, profile section. Keokuk 



limestone; Keokuk, Iowa. 

 Fig. 24,23. Polyuhizouus CAUiioxARitJS; St. J. and "W 369 



24 a, b. Sketch of concave, and convex faces, restoration of fig. 10, PI. 13. Coal Measures; 



Belleville, Illinois 



25 a, b, c. Concave ami convex faces and profile sectioa, of smaller tooth.. Upper Coal Mea- 



sures; near Sprin-lieM, Illinois. 



Fig. 26. . Ctenol'ICTai.us mkdius, St. J. and "W 400 



26 a. Convex face; -26 b, s'cadi of the ujntuve aspect; 26 c, profile section. Chester 



limestone; Chester, Illinois', 



Fig. 27. CiEvm j nanus prktkxuis, St. J- and W 382 



27 a. View of concave face, enlarged two diameters; 27 5, convex face; 27 c, profile seo- 



tion. Chester limestone, lower fish bed; Chester, Illinois. 



