Part 3 of this study is concerned with bryozoan species from four limestone units (Mifflin, Quimbys Mill, Guttenberg, and Ion Formations); these rock units of Champlainian age (Middle Ordovician) are exposed in northwestern Illinois and adjacent parts of Iowa and Wisconsin. Representatives of the following genera are discussed: Homotrypa Ulrich (including 6 species, 2 variants), Orbignyella Ulrich and Bassler (one species), Prasopora Nicholson and Etheridge (2 species), Monticulipora d'Orbigny and Cyphotrypa Ulrich and Bassler (one species each).