It may be Belgian, but it was more likely German or at least made for sale in Germany where safeties were required. Neither that gun nor the one in the link are true "Velo Dog" revolvers since the cylinders are not long enough to the Velo Dog cartridge, which looks liike a .22 WMR. Those guns were the European equivalent of our cheap double action pocket revolvers, and date from the same era, roughly 1880-1914 (the start of WWI). Today in the US they are mainly curiosities, though there is a mild collector interest if in top condition. The grips are probably genuine ivory, common and cheap at the time it was made, now scarce due to both scarcity of elephants and laws protecting them from ivory hunters.
I would value that gun at $200, but it could go for more. Caliber could be one of several, but .25 ACP or .32 ACP would be my first thought. I know those are auto pistol cartridges, but both were quite common in those little guns.
Jim