Williams, E. H., and L. Bunkley-Williams. “Three Anomalies: A Scythebill in the Greater Antillean Grackle (blackbird), a Crown Pattern in the Rock Beauty (angelfish), and a Double Spot in the Butter Hamlet (grouper), and Their Possible Genetic Significance”. Revista De Biología Tropical, vol. 54, no. S3, Dec. 2006, pp. 161–169, doi:10.15517/rbt.v54i3.26910.