The Gemshorn is an early form of recorder, made of a cow horn with a cedar fipple inserted at the wide end. It has an incredibly sweet sound due to the conical shape of the horn. They have 7 finger holes and 1 thumbhole, and play similar to a recorder (the soprano has 5 finger holes plus 1 thumbhole and fingers like an ocarina).
They have a range of one octave and one note. During the 15th c. it must have been a fairly common instrument, as there existed an organ stop of that name.