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Shippey, Tom. The Road to Middle-earth. London: HarperCollins, 1992 (rev.). ISBN 0-261-10275-3
South, Malcom, ed. Mythical and Fabulous Creatures: A Source Book and Research Guide. Westport, CT: Greenwood Press, 1987. Reprint, New York: Peter Bedrick Books, 1988. ISBN 0-87226-208-1
