The Chimalcoatl, “shield snake”, is a long, thick Mexican snake. It earns its name from the fleshy, colorful shield on its back. Its appearance is an omen of death or prosperity and fortune in war, depending on the occasion.
Nuttall, Z. (1895) A Note on Ancient Mexican Folk-lore. The Journal of American Folklore, v. 8, no. 29, pp. 117-129.