Frank Wesson Superposed Pistol. They were made in small, medium and large frame versions. .22, .32 and .41 rimfire respectively. Yours appears to be of the medium (.32 rim.) "third type" given the full length fluted barrels. Some were made with a small sliding knife blade between the barrels. Mfg. 1868 to 1880. Nice condition on yours with the exception of the overpolished brass frame. I don't believe many survived in that condition, last book price I have is $1500. in "good" condition. No prices stated above that.