Mexican Horned Pit Viper

Adults grow to 55–70 centimetres (21+5⁄8–27+1⁄2 inches) in length and are moderately stout. Elongated supraocular scales form a pair of "horns" or "spines" over the eyes. The color pattern consists of a silvery-gray ground color overlaid with a series of black dorsal blotches that merge to form a broad wavy stripe. Black speckling is present on the flanks. The top of the head is black.

Found in the mountains of central and southern Mexico (Hidalgo, Veracruz, Oaxaca and Guerrero) west of the Isthmus of Tehuantepec at elevations of 1,800–2,800 m (5,900–9,200 ft). The type locality given is "Messico" (Mexico). H.M. Smith & Taylor (1950) proposed that it be restricted to "Orizaba, Veracruz, Mexico."

Night-time temperatures throughout its range are low, and this species only seems to be active during the day. Individuals have frequently been seen coiled on or near fallen logs, as well as in bushes and small trees 1–4 m (3.3–13.1 ft) above the ground.