Muntz, W.R.A. (1973)
Yellow filters and the absorption of light by the visual pigments of some amazonian fishes. Vision Research, 13(12), 2235–2254
DOI: 10.1016/0042-6989(73)90225-3

Muntz, W.R.A. & Church, E. & Dartnall, H.J.A. (1973)
Visual Pigment of the Freshwater Stingray, Paratrygon motoro. Nature, 246(5434), 517
DOI: 10.1038/246517a0

Ali, M.A. & Anctil, M. (1974)
Retinas of the electric ray (Narcine brasiliensis) and the freshwater stingray (Paratrygon motoro). Vision Research, 14(7), 587–588
DOI: 10.1016/0042-6989(74)90048-0