Ophryacus undulatus is a venomous pitviper species found in the mountains of central and southern Mexico.

[2] Elongated supraocular scales form a pair of "horns" or "spines" over the eyes.

[3] 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).

[5] A species is listed as such when the best available evidence indicates that the geographic range, in the form of extent of occurrence, is estimated to be less than 20,000 km2, that estimates indicate it to be severely fragmented or known to exist at no more than 10 locations, and that a continuing decline has been observed, inferred or projected, in area, extent and/or quality of habitat.

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.