Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Sauria
Family: Helodermatidae
Helodermatidae is the lizard family that contains the only two venemous lizard species. Both of these are of the genus Heloderma:
The above wus give an excellent description of these two species, so the rest of this writeup is concerned primarily with the venom delivering mechanism common to both of them.
Unlike venomous snakes, the venom glands (modified salivary glands) of these lizards are located in their lower jaws. The venom delivering teeth are not long and pointed, instead they are large and serrated, with a channel down them. When a victim is bitten venom is not "injected" as it is in a case of snake envenomation. Instead, it is though that capillary action draws some of the venom from the lizard's venom glands up through the teeth, where it is introduced to the wound.
With a single bite only a very small quantity of venom will be introduced, so to ensure adequate envenomation the lizard is likely to latch on, and chew. It should be noted that the venom of these creatures is thought to have evolved as a defence mechanism, as it is far from necessary in the aquisition of prey animals. Although cases of human envenomation are exceedingly rare, the following syptoms may occur following a bite:
Because the two species responsible for these bites are not thought of as threatening to man, there is no antivenom for their bites. Treatment must be symptomatic. Thankfully there are no reported deaths from Heloderma bites, and full recovery is very likely.
Sources:
Lizards of the World: Mattison
http://mason.gmu.edu/
http://americazoo.com