Central North America, Fourth Edition. Boston and New York: Houghton Mifflin Harcourt. xiv + 494 pp. . (Opheodrys vernalis, pp. 382–383 + Plate 35). Zim, H.S.; Smith, H.M. (1956). Reptiles and Amphibians: A Guide to Familiar American Species: A Golden Nature Guide. New York: Simon and Schuster. 160 pp. (Opheodrys vernalis, pp. 77, 156). External links Smooth Green Snake, Reptiles and Amphibians of Iowa. Smooth Green Snake, Michigan Department of Natural Resources. Opheodrys vernalis, Illinois Natural History Survey. Opheodrys Snakes of North America Reptiles of Mexico Reptiles of the United States Reptiles of Ontario Fauna of the Eastern United States Fauna of the Great Lakes region (North America) Fauna of the Great Plains Fauna of the Plains-Midwest (United States) Reptiles described in 1827 Taxa named by Richard Harlan