The eastern diamondback rattlesnake (Crotalus adamanteus) is a species of pit viper in the family Viperidae. The species is endemic to the Southeastern United States. It is one of the heaviest venomous snakes in the Americas and the largest rattlesnake. No subspecies are recognized. Description The eastern diamondback rattlesnake is the largest rattlesnake species and is one of the heaviest known species of venomous snake, with one specimen shot in 1946 measuring in length and weighing . However, other venomous snakes may rival this species in weight such as the much longer but more slender king cobra and the shorter but even bulkier Gaboon viper. Maximum reported lengths for the eastern diamondback rattlesnake are and . However, the stated maximum sizes have been called into question due to a lack of voucher specimens. Males are typically larger than females, which is rare among snakes (females are usually larger than males). Specimens over are rare, but well documented. Klauber (1998) included a letter he received from E. Ross Allen in 1953, in which Allen explains how for years he offered a reward of $100, and later $200, for an specimen, dead or alive. The reward was never claimed. He did receive a number of range specimens and some skins, but said such skins can be taken from specimens as short as . A specimen was caught and killed outside a neighborhood in St. Augustine, Florida in September 2009. The average size is much less. Specimens are rarely found over 6 feet in length. Lengths of , and are given. One study found an average length of based on 31 males and 43 females. The average body mass is roughly . The average weight of 9 laboratory-kept specimens was , with a range of . Few specimens can exceed , although exceptional specimens can weigh or more. The scalation includes 25–31 (usually 29) rows of dorsal scales at midbody, 165–176/170–187 ventral scales in males/females and 27–33/20–26 subcaudal scales in males/females, respectively. On the head, the rostral scale is higher than it is wide and contacts two internasal scales. There are 10–21 scales in the internasal-prefrontal region and 5–11 (usually 7–8) intersupraocular scales. Usually, there are two loreal scales between preoculars and the postnasal. There are 12–17 (usually 14–15) supralabial scales, the first of which is in broad contact with the prenasal, and 15–21 (usually 17–18) sublabial scales. The color pattern consists of