Ewa-Oboho (1993), Ewa-Oboho & Abby-Kalio (1994), Rodríguez-Tovar et al. (2014)†, Snowden & Ekweozor (1987), Snowden & Ekweozor (1990), Spivak & Cuesta (2009)†
Entries marked with † represent indirect references to location through citation.