↑Say, T. (1823) In James, E. Account of an expedition from Pittsburgh to the Rocky Mountains, performed in the years 1819, '20, by order of the Hon. J. C. Calhoun, Secretary of War, under the command of Major Stephen H. Long. Vol. 2., Philadelphia, H. C. Carey & I. Lea.
↑Baird, S. F. and C. Girard. (1853) Catalogue of North American Reptiles in the Museum of the Smithsonian Institution. Part 1.-Serpents., Smithsonian Inst., Washington, xvi + 172 pp.