That's a baritone horn, although no tag existed for it yet. I'll add it to the other image as well. It's basically a small tuba that plays in a slightly higher register, and the silvery colour is also quite typical, although they also come in the more traditional brass colour.

I'm changing the tag to euphonium. I still think it's a baritone, because of the valve placement, but the two instruments are basically identical and the euphonium already has a tag.