Sigmoilinita is a miliolid genus (Foraminifera) with an ovate to fusiform test that becomes flattened with growth. Chambers are tubular, one-half coil in length, at first added in a sigmoiline (S-shaped) series starting at slightly more than 180ð apart. the angle gradually decreasing until the later whorls are planispiral. Chambers are numerous, the wall narrow. imperforate, porcelaneous. The aperture at the end of the final chamber may have a weakly developed tooth.