352 ■ MEMOIRS OF THE CARNEGIE MUSEUM. 



EXPLANATION OF PLATE V. 



All figures are three-fourths natural size, a, lateral view; h, dorsal view. 



Fig. 1. Quadrula cylindrica (Saj-). Normal individual, from the Allegheny River, 

 Godfrey, Armstrong Co., Pennsylvania, collected August 10, 1909; C. M. Cat. No. 

 61.4358. 



Fig. 2. Quadrula cylindrica (Say). Intergrade toward the smooth form, with 

 tubercles greatly reduced, but shell not much compressed, from French Creek, Coch- 

 ranton, Crawford Co., Pennsylvania, collected September 2, 1908; C. M. Cat. No. 

 61.3851. 



Fig. 3. Quadrula cylindrica (Say). Smooth and compressed form, characteristic 

 for the headwaters of the Ohio, from French Creek, Meadville, Crawford Co., Penn- 

 sylvania, collected September 1, 1908; C. M. Cat. No. 61.3850. 



Fig. 4. Rotundaria tuherculata (Rafinesque). Female from the Allegheny River, 

 Godfrey, Armstrong Co., Pennsylvania, collected August 10, 1909; C. M. Cat. No. 

 61.4411. 



. Fig. 5. Plethobasus cooperianus (Lea). Normal individual from the Ohio River, 

 Industry, Beaver Co., Penn.sylvania, collected October 22, 1908; C. M. Cat. No. 61.3882. 



Fig. 6. Plethobasus cyphyus (Rafinesque). Large specimen of normal shape, 

 from the Allegheny River, Kelly, Armstrong Co., Pennsylvania, collected September 27, 

 1907; C. M. Cat. No. 61.3065. 



