122-133. Williamson, Kay. 1969. 'Igbo' and 'Ịjọ', chapters 7 and 8 in: Twelve Nigerian Languages, ed. by E. Dunstan. Longmans. Williamson, Kay. 1971. Animal names in Ịjọ. Afr. Notes 6, no. 2, 53-61. Williamson, Kay. 1973. Some reduced vowel harmony systems. Research Notes 6:1-3. 145-169. Williamson, Kay. 1977. Multivalued features for consonants. Language 53.843-871. Williamson, Kay. 1978. From tone to pitch-accent: the case of Ịjọ. Kiabàrà 1:2.116-125. Williamson, Kay. 1979. Consonant distribution in Ịjọ. In: Linguistic and literary studies presented to Archibald Hill, ed. E.C. Polome and W. Winter, 3.341-353. Lisse, Netherlands: Peter de Ridder Press. Williamson, Kay. 1979. Medial consonants in Proto-Ịjọ. Journal of African Languages and Linguistics 1.73-94. Williamson, Kay. 1987. Nasality in Ịjọ. In: Current trends in African linguistics, 4, ed. by David Odden, 397-415. Williamson, Kay. 1989. Tone and accent in Ịjọ. In Pitch accent systems, ed. by Harry v.d. Hulst and Norval Smith, 253-278. Foris Publications. Williamson, Kay. 2004. The language situation in the Niger Delta. Chapter 2 in: The development of Ịzọn language, edited by Martha L. Akpana, 9-13. Williamson, Kay, and A. O. Timitimi. 1970. A note on number symbolism in Ịjọ. African Notes (Ibadan) 5:3. 9-16. Williamson, Kay & Timitime, A.O. (197?) 'A note on Ijo number symbolism', African Notes, 5, 3, 9-16. Filatei, Akpodigha. 2006. The Ijaw Language Project. (Editor of www.ijawdictionary.com). www.ijawdictionary.com On specific languages Williamson, Kay. 1962. (Republished by Bobbs-Merrill Reprints 1971.). Changes in the marriage system of the Okrika Ịjọ. Africa 32.53-60. Orupabo, G. J., and Kay Williamson. 1980. Okrika. In West African language data sheets, Volume II, edited by M.E. Kropp Dakubu. Leiden: West African Linguistic Society and African Studies Centre. External links The Ijaw Dictionary Online Languages of Nigeria Indigenous languages of Rivers State Subject–object–verb languages