you see them from time to time, rare and this one is especially in good condition. pinfire revolver and by the size I think its for the 9 mm cartridge.
with a 12 rounds cylinder it was the ultimate self defense gun around 1870. would like to shoot this one it looks well made and handy.

http://www.lauritz.com/da/auktion/belgisk-12-skuds-revolver/i4769201/#