What lizard has a black underbelly?

It may be a Gila monster if it has beaded like skin. They are deadly if you get bitten by it and may kill you. It also may be a Leopard gecko if its tail does not taper and it seems to get larger near the end, but they are not poison. There are only 2 venomous lizards native to North America, the Gila monster and the Bearded Dragon.