Phrynops williamsi, also known commonly as Williams' side-necked turtle, Williams' South American sideneck turtle, William's [sic] South American side-necked turtle, William's [sic] toadhead turtle, and Williams' toadhead turtle, is a species of turtle in the familyChelidae. The species is endemic to South America.
^Rhodin, Anders G.J., and 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., and Miyata, K. (Editors) (1983). Advances in Herpetology and Evolutionary Biology. Essays in Honor of Ernest E. Williams. Cambridge, Massachusetts: Museum of Comparative Zoology.
^van Dijk, Peter Paul, John B. Iverson, H. Bradley Shaffer, Roger Bour, and Anders G.J. Rhodin (2012). "Turtles of the World, 2012 Update: Annotated Checklist of Taxonomy, Synonymy, Distribution, and Conservation Status". Chelonian Research Monographs No. 5, pp. 000.243–000.328.
^Beolens, Bo, Michael Watkins, and Michael Grayson (2011). The Eponym Dictionary of Reptiles. Baltimore, Maryland: Johns Hopkins University Press. xiii + 296 pp. ISBN978-1-4214-0135-5. (Phrynops williamsi, p. 286).
Borteiro, Claudio; Kolenc, Francisco; Prigioni, Carlos (2015). "A new noteworthy record of Phrynops williamsi Rhodin & Mittermeier (Testudines, Chelidae) in Uruguay". Cuadernos de Herpetología29 (1): 95–96.
Buskirk, James R. (1989). "Field observations on Phrynops williamsi and other Uruguayan chelonians". Vivarium1 (4): 8–11.
Cabrera, Mario R. (1993). "Phrynops williamsi (Williams' South American Sideneck Turtle). Argentina: Corrientes". Herpetological Review24 (2): 65–66.