I am stuck on three
4D agile long-legged rodent with hoof like claws 6 letters A-o---
15 across - monster, a large venomous lizars inhabiting deserts of the united states and Mexico 4letter G--a
26D a silvery-white metallic element, used in jewellery 8 letters T--t-n-m
thanks I know they are probably obvious but the brain is not working properly this afternoon