Sterki: North American Sph.eriid/e. 453 



33. Pisidium variabile Prime. 



Pisidium variabile Prime, Boston Proc, IV, 1851, p. 163; Mon. Coib., 1865, p. 66. 

 Pisidium mirahile (Whittemore) Clessin, Monogr. Cydadeen in Martini-Chem- 

 nitz, 1879. p. 49. PI- 6, figs. 1-3. 19-21. 



Rather variable. 



Habitat. — Widely distributed over the continent, except, apparently, 

 in the South; common in the Northeast, ranging from New England 

 and New York to Michigan. 



Fossil. — IMaine, New Jersey, Ohio, Michigan, Ontario, Illinois, 

 South Dakota. 



34. Pisidium variabile cicer Prime. 



Pisidium ciccr Prime, Ann. N. Y. Lye, VI, 1853, p. 65, PI. I, fig. i. Synonym of 

 P. compressum. Prime, Mon. Corb., 1865, p. 65. 



A form of variabile, not of cofupressum, as is proved by the specimens 

 in the collection of T. Prime, preserved in the Museum of Comparative 

 Zoology, and in other collections. 



Habitat. — Massachusetts, Maine; 



35. Pisidium variabile brevius Sterki. 



Pisidium. variabile var. brevius Sterki, Nautilus, XIX, 1906, p. 118. 

 Habitat. — Ohio and Michigan to South Dakota, Keewatin. 

 Fossil. — Michigan, Ontario. 



36. Pisidium variabile magnum var. no v. 



Considerably larger than any eastern form, strongly inflated, shell 

 and hinge slighter. 



Habitat. — Washington, Montana. 



37. Pisidium variabile hybridum Sterki. 



Pisidium variabile var. hybridum Sterki, Nautilus, XIX, 1906, p. 118. 

 Apparently a perpetuated hybrid, P. variabile X crquilatcrale. 

 Habitat. — Herkimer County, New York. 



38. Pisidium minusculum Sterki. 



Pisidium minusculum Sterki, Nautilus, XX, 1906, p. 17. 

 Habitat. — Wisconsin, Ohio. 



'A number of specimens labelled "P. mirabile Whittemore, Mass.," evidently 

 authentic, are contained in the Anthony Collection in the Museum of Comparative 

 Zoology. They aie not distinct fiom P. variabile, and Clessin's description and 

 figure also differ very little. 



