PLATE VI. 
a, Pimple-back, Quadrula pustulata (I.ea) (p. 23); b and c, purple pimple-back, Quadrula granifera (Lea), from Mississippi River 
(p. 24); d, three-horned warty-back, Obliquaria reflexa (Rafinesque) (p. 24); e, _pimple-back, Quadrula cooperiana (1,ea), 
from Cumberland River (p. 23); f, purple pimple-back, Quadrula tuberculata (Rafinesque) (p. 24). 
