Lachesis melanocephala is a venomous pit viper species found in Costa Rica. No subspecies are currently recognized.
Adults frequently grow to 1.9–2 m (6.2–6.6 ft) in total length. The largest reported specimens were 2.3 m (7.5 ft) by Solórzano (2004), and 2.4 m (7.9 ft) by Ripa (2001).
The top of the head is uniform black in color, to which the specific name, melanocephala, refers.
Found in Costa Rica on the Pacific versant of southeastern Puntarenas province from near sea level to about 1500 m (about 4,900 feet). The type locality given is "tropical rainforest 9 km northern of Ciudad Neily in southeastern Provincia de Puntarenas, Costa Rica."
Campbell and Lamar (2004) describe its range as southwestern Costa Rica and possibly extreme western Panama, but state that almost all locality records are from Puntarenas province.
