Genera of family “Nummulitidae”

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.