Ruiz, A. and Alfaro, M. 1959. Notes on Costa Rican Opalinids. Il. Zelleriella antillensis ( Metcalf) and Z. bufoxena Metcalf. Revista de Biología Tropical. 7, 2 (Dec. 1959), 219. DOI:https://doi.org/10.15517/rev.biol.trop.1959.29949.