Christiane Sourvinou-Inwood, «Reading» Greek Death (Oxford University Press, 1996), p. 359 online and p. 390 online.
jstor.org
Grinsell, L. V. (1957). «The Ferryman and His Fee: A Study in Ethnology, Archaeology, and Tradition». Folklore. 68 (1): 257–269 [p. 261]. JSTOR1258157.