EXPLANATION TO PLATE 6L 



Map of the Tennessee River to show the location of the groups of shells used in the quan- 

 titative studies. The numbers from 1 to 27 show the location of the groups. By comparison 

 with appropriate plates, plates 28-55, one may at a glance get an idea of the shell poj^ulation 

 in rej^resentative parts of the rivers. 



184 



