Diagnosis
provided by World Register of Marine Species
Test ovate in outline, discoidal to biconvex, periphery broadly rounded, with two rapidly enlarging chambers per whorl added in planes less than 180¡ apart to result in an early sigmoid arrangement as seen in section, later with up to five chambers per whorl added in a single plane, lateral wall extensions from each chamber overlap the umbilical region and entirely cover the earliest chambers but do not completely cover the peripheral region of the penultimate chamber, thus sectioned specimens with three to five chambers per whorl show an equal number of lamellae per whorl; wall thick, calcareous, imperforate, porcelaneous, surface smooth and polished; aperture large, semicircular to subtriangular at the end of the final chamber, with a distinct broad flap. M. Miocene (Tortonian) to Holocene; Europe; Atlantic; Pacific. (Loeblich & Tappan, 1987, Foraminiferal Genera and Their Classification)
Loeblich, A. R.; Tappan, H. (1987). Foraminiferal Genera and their Classification. Van Nostrand Reinhold Company, New York. 970pp.
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