Loeblich, A. R., Tappan, H. N., 1987: Foraminiferal genera and their classification. Van Nostrand, Reinhold Co. New York 1728 pp. Plate 268, Fig. 1: U. Carboniferous (Kasimovian), Donbas, Ukraine. Axial section, x 20 (from Rauzer-Chernousova and Fursenko, 1959). courtesy of Michael Hesemann https://foraminifera.eu