"Velo-dog" was sort of a generic name, sort of like calling a small revolver a "snubnose"; they ran the gamut in terms of quality, just like any other type of gun. The name comes from the French name for "bicycle" - "velocipede", and they were originally designed to be sold to bicyclists who wanted to be able to drive off vicious dogs. Here's a picture showing one of the most popular chamberings for these things, that looks sort of like a centrefire 22 Magnum.
