Wolf, Paul Polydoor de (1971)
The Noun Class System of Proto-Benue-Congo
(Thesis, Leiden University). The Hague/Paris: Mouton.
Williamson, Kay (1989) 'Benue-Congo Overview', pp. 248–274 in Bendor-Samuel, John & Rhonda L. Hartell (eds.)
The Niger-Congo Languages — A classification and description of Africa’s largest language family
. Lanham, Maryland: University Press of America.