The purreus is the Den's gold coin, plural purrei, struck with Lupa in profile on the obverse and a pawprint on the reverse, around which runs the house motto: Si vis pats, para bellyrub. If you want pats, prepare a bellyrub.
The denarius is the Den's silver coin, so called because it is the Den's. Twelve of them make a purreus. The obolus floofus is a small copper coin used for tips, the lift and the water feature in the lobby, which is full of them.