Cassidulina is a genus of foraminifera described in the Treatise Part C. (Loeblich & Tappan, 1964), as having a free, lenticular test, with central boss of clear calcite on either side. Chambers are biserially arranged, enrolled planispirally with a subangular to keeled periphery. The wall is calcareous, hyaline (glassy), optically granular, perforate. The surface is smooth with a polished appearance. Sutures are radial to oblique, straight or curved. The aperture is a narrow arched slip at the base of the apertural face, partly closed by an apertural place. (Loeblich and Tappan 1988)

The taxonomy of Cassidulina is rather stable, and is included in the Cassidulinidae at least as far back as Cushman, 1950. Related genera include Cassidulinella, Favocassidulina, Globocassidulina, and Buriela. Cassidulina, itself, is cosmopolitan, with a stratigraphic range extending from the Upper Eocene to recent.

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