PLATE I. 



Fig. 1. Pisidium abditmn, Haldeman, (x 2), Reaclville, 

 Mass., p. 306. 



Fig. 2. Pisidium coniprcssiiiii. Prime, (x 2), Mohawk, N. Y., 

 p. 306. 



Fig. 3. Musculium raymondi, J. B. Cooper, (x 2), Likely, 

 Pitt River Valley, Cal., p. 306. 



Fig. 4. Marganiana margaritifera, Linne, (x 3/3), San Lo- 

 renzo River, Felton, Cal. p. 301. 



Fig. 5. Musculiniii /^arfiiiuciiiin. Say. (x 2). Staten Island, 

 X. Y., p. 305. 



Fig. 6. Physa hetcrosfropha, Say, (form known as P. hwdi), 

 (X 1), Chelsea, Quebec Province, Canada, p. 312. 



