Crotalinae

Crotalinae is a subfamily of Viperidae and consists of the pit vipers. They have a large heat-sensitive pit on either side of the head. They are usually viviparous though some genera are oviparous. Genera include Agkistrodon, Bothriechis (palm vipers), Bothriopsis, Bothrops, Calloselasma, Crotalus (most rattlesnakes), Deinagkistrodon, Hypnale (hump-nosed vipers), Lachesis, Ophryacus, Porthidium, Sistrurus, Trimeresurus and Tropidolaemus.