Since 1900, the major taxonomic studies on "Amphidromus" have been faunistic (a study of the fauna of some territory or area) in scope. The papers of American malacologist Paul Bartsch (1917, 1918, 1919) on the Philippine species, Bernhard Rensch (1932) on the Lesser Sunda Islands forms, and Tera van Benthem Jutting (1950, 1959) on Javan and Sumatran populations are especially comprehensive. Potentially the most valuable contribution is that of Curt Haniel (1921), who discussed the variation within "A. contrarius" and "A. reflexilabris" on Timor; the variations in color and form were well illustrated in a series of color plates.