IBO. A Southern Nigerian tribe comprising 33 sub-tribes, inhabiting the provinces of Benin, Ogoja, Onitsha, Owerri and Warri, whose language is related to Ibibio. The Ibo on the west of the Niger were long subject to the Edo : the rest lived in inde pendent towns or villages under a paramount chief and a chief for each quarter. The extended family groups lived together in the same quarter. Marriage rules vary : marriage is usually prohibited between members of the same extended family and between near relations. Marriage by exchange is frequent. Descent is patri lineal. Age classes and secret societies flourish.