Large, hollow, oblate sphere of toned red-copper made by the Jonga (incl. Nkutshu, Mongo, Mbole), Congo River region.  Mostly soccer ball size, some larger.  Worn at the ankle and used in dowry.  Ballarini The Perfect Form p. 288-289 lists five named denominations by size, though observed specimens are quite variable in size and weight. Opitz An Ethnographic Study of Primitive Money (2000) p. 201.  I do not know when these were made or used but from the appearance of the copper I would guess 19th to early 20th century.  AAs with most legband currencies, these were worn for many years and removed at death by blacksmiths, so many specimens have flat spots from impacts and/or cracks in the edge.  "Perfect" specimens are suspect and may have been made after the period of actual use;