Bull. U. S. B. F., 1917-18- 



Plate VI. 



a, Piinple-back, Quadnila pzistulaia (Lea) (p. 23); h and c, purple pimple-back, Quadrula granifcra (Lea) from Mississippi River 

 (p. 24); d, three-homed warty-back, Obliquaria reflcxa (Rafinesque) (p. 24); e, pimple-back, Quadrula cooper lana (.Leaj, 

 from Cumberland River (p. 23);/, purple pimple-back, Quadnila tuherculata (Rafinesque) (p. 24). 



