Genera of order “Rotaliida”

Cibicidoides

Test in a low trochospiral coil, spiral side flattened but slightly involute, final whorl slightly elevated and partly overlapping the preceding one.

Elphidium

Test planispiral, bilaterally symmetrical; sutural canal system opens into a single row of pores; septal bridges usually hollow and contain a retral process; aperture a series of large circular pores at base of aperture face.

Neorotalia

Single or compound umbilical plug, aperture restricted by a toothplate that protrudes with a free edge into the aperture and forms an umbilical spiral canal.

Nonionella

Low trochospiral test, slightly compressed, rounded periphery, spiral side partially evolute around an umbonal boss, umbilical side involute, chambers with flaplike projections overhanging the umbilicus.

Operculina

Test planispiral and evolute, flattened, numerous narrow chambers in many rapidly expanding whorls, sutures strongly curved back at the periphery.

Operculinella

Smooth exterior, undivided chambers. External similarities in shape to N. venosus but is distinguished by the latter by the possession of trabeculae. Thick lenticular central part and flat final chambers in large individuals.

Oridorsalis

Lenticular, low trochospiral test, spiral side evolute with three slowly enlarging whorls, four to five chambers in the final whorl, umbilical side involute.

Trifarina

Elongate test, sharply triangular in section and early stage triserial, later uniserial and rectangular. Aperture surrounded by a low collar.

Virgulinella

Test elongate, early stage triserial, later biserial. Chambers slightly inflated and strongly over-lapping, final pair comprising about two-thirds the test length, lower margin of chambers with numerous narrow bridgelike projections that cross the slightly constricted sutures; wall calcareous, finely perforate. Aperture an oblique loop in the apertural face, provided with a reduced toothplate that commences near the previous foramen and attaches to the lower part of the chamber wall, continuing to the lower border of the aperture, wjth supplementary sutural openings between the sutural bridges.