Bull. U. S. B. F., 1917 i8. 



Plati^ 111. 



Upper and middle: Nigf^erhead, Quadrula ebcnus (Lea), from Mississippi River. (See p. 20.) 

 Lower pair: Hickory-nut, Obovaria ellipsis (Lea), irom Mississippi River. (See p. 22.) 



