The mellophone is a brass instrument, used to replace the French horn in marching. It is different from the French horn in that its bell faces the front and it uses piston valves instead of rotary valves.
This video is the Ohio State mellophone section playing Kansas' Carry On My Wayward Son
The mandolin is a string instrument in the lute family. The soundboard comes in many different shapes but typically the round or teardrop shaped. Modern mandolins originated from Naples, Italy in the late 18th century. They have 4 pairs of metal strings.
This is a solo by Chris Thile from the band Nickel Creek