These were marketed in France as 'Velo-dog' revolvers. I have one that is very similar with a slightly longer barrel. It came to me heavily worn - I think it had been dug up in someone's garden but I managed to get it to operate, main spring from biro, assorted BA screws etc. I think it is sub-.22 calibre, perhaps 4mm, 6 shot. The construction is fairly cheap and nasty. Some of them were 'hammerless' or more correctly had a shrouded hammer so as not to catch on clothing when drawn from a pocket while awheel presumably.
I rather think that these are more correctly pocket or ladies' revolvers and the dog scarers were more likely to be single shot models.
But for proper dog slaughtering advice I usually refer to Richard's Bicycle Book.