Crotalus simus is a venomous pit viper species found in Mexico and Central America. The specific epithet is Latin for "flat-nosed", likely because its head is blunt compared with lanceheads (Bothrops). Three subspecies are recognized, including the nominate subspecies described here. Adults commonly exceed 130 cm (51 in) in length, with males growing larger than females. Large males reach 140-160 cm (55-63 in) in some populations. The maximum length is 180 cm (71 in).