This unusually shaped Eb Tuba is carried on both shoulders- with the head of the player inserted in the middle. It employs American String rotary valves. These were produced around the time of the US centennial in 1876.   The analagy to a "toilet seat" can easily be imagined.  These tuba  are relatively rare.  This one is owned by Karl Megules of Trenton N.J.  Karl is principal tubist with the Greater Trenton Symphony Orchestra), and the Delaware Valley Philharmonic Orchestra.