Boston, J.S., Ikenga Figures among the North-West Igbo and Igala, 1977; Cornet, J., Art of Africa. Treasures from the Congo, 1971; Fagg, W. & Plass, M., African Sculpture, 1964; Meauzé, P., African Art, 1968; Sweeney, J.J., African Sculpture, 1970; Thompson, R.F., Black Gods and Kings, Yoruba Art at UCLA, 1971; and sixteen others of similar interest (22)