Não informado. (1919). University of Iowa Studies in Natural History. University of Iowa.
Chicago-referens (17:e uppl.)Não informado. University of Iowa Studies in Natural History. Iowa City, Iowa: University of Iowa, 1919.
MLA-referens (8:e uppl.)Não informado. University of Iowa Studies in Natural History. University of Iowa, 1919.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.