This is a Bb double bell euphonium made by C.G. Conn in Elkhart Indiana, USA around 1936. This is a unique novelty instrument with with fifth piston controlling the player's choice of whether their sound emanates from the smaller or larger bell. The fifth piston is operated by the first finger of the player's left hand. Other than that, this plays like a standard American-style euphonium. This is the model 60I. The conical parts of this euphonium are all made of gold brass. It's subtle but you can see it as the brass ferrules and bell connecting rings.
The condition is very good. The lacquer is intact though it's pitted and marked with age. All slides and valves work fine. Any dentiness or repairs are really minor. The horn has been professionally cleaned and tuned and is ready for another generation of use.
Hard case is included. Uses small shank trombone-baritone mouthpiece.