Loeblich, A. R., Tappan, H. N., 1987: Foraminiferal genera and their classification. Van Nostrand, Reinhold Co. New York 1728 pp. Plate 21, Fig. 3: Ordovician, Estonia. Exterior, x 95 (from Eisenack, 1954). courtesy of Michael Hesemann https://foraminifera.eu