APA

Hershler R., . (1994). A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae). Washington, D.C: Smithsonian Institution Press.

Chicago

Hershler Robert, . 1994. A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae). Washington, D.C: Smithsonian Institution Press.

Harvard

Hershler R., . (1994). A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae). Washington, D.C: Smithsonian Institution Press.

MLA

Hershler Robert, . A review of the North American freshwater snail genus Pyrgulopsis (Hydrobiidae). Washington, D.C: Smithsonian Institution Press. 1994.