Wieland, George R. (1923). "A new Paraná pleurodiran". American Journal of Science, Series 5, 5: 1–14.
Rhodin, Anders G.J.; Mittermeier, Russell A. (1983). "Description of Phrynops williamsi, a new species of chelid turtle of the South American P. geoffroanus complex". pp. 58-73. In: Rhodin, A.G.J.; Miyata, K. (Editors) (1983). Advances in Herpetology and Evolutionary Biology. Essays in Honor of Ernest E. Williams. Cambridge, Massachusetts: Museum of Comparative Zoology.