You have what appears to be a Belgian Velo Dog revolver, of which any number of small Belgian gun firms made untold hundreds, if not thousands.
The velo-dog genre is characterised by small size, slab profile, enclosed hammer, folding trigger, and a safety-catch: all essential requirements for quick-accessibility from the waist-coat pocket while riding a velocipede (bicycle).
Most were chambered for the 5.5 mm Velodog cartridge - unobtainium.
I would put it's wall hanger value (they are unsafe to shoot) at $150-$200.
Here is one, in almost perfect condition, F/S at a normally high-priced website for $330: