318 THOMAS J. HEADLEE. 



EXPLANATION OF PLATE XII. 



FIG. I. Right and left valves of Uniofabalis. 



FIG. 2. Right and left valves of Unio glans. 



FIG. 3. Right and left valves of Unio subrostratus. 



FIG. 4. Right and left valves of Unio rubiginosus. 



FIG. 5. Right and left valves of Afargaritana marginata. 



FIG. 6. Right and left valves of Unio luteolus. 



FIG. 7. Right and left valves of Anodonta grandis. 



FIG. 8. Right and left valves of Anodonta edentula. 



FIGS. 9-15. Side view of a series showing gradations in form, color, and size from 

 the small light- colored variety to the large dark-colored variety of Unio luteolus. 



FIGS. 16-19. Dorsal view of a series of Unio luteolus including both males and 

 females and showing the gradations in form and size from the small light-colored to 

 the large dark-colored variety. 



Note. The shell represented in FIG. 7 is 2.75 in. from dorsal to ventral surface 

 and 4.5 in. from anterior to posterior end. The reduction of FIGS. 1-19 is the same 

 as that of FIG. 7. 



