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 180° apart.
the angle gradually decreasing until the later whorls are planispiral.
Chambers are numerous, the wall narrow.
The aperture at the end of the final chamber may have a weakly developed tooth.