Re: Cowles & Son 22 Darrenger
The picture is too poor to determine the condition, but with the silver gone and the barrel in poor shape, it would probably bring around $350 or so. According the Flayderman, guns marked "WW COWLES DEAN & CO." or "SMITH & DEANE" will bring a premium.
.30 rimfire is unobtainable except in collector quantities and collector prices. A .22 would fire .22 Short, but I recommend against firing that old gun. If you choose to do so, I strongly suggest using only .22 CB Caps; modern .22 Shorts are too powerful and may damage the gun.