While browsing the Bodleian Ballads (again) I came across the following notes on a song sheet.

The renowned Jack Sheppard. A new comic medley sold by G. Green, at his Music Stall, near the Turnpike, City Road, Accordians Harmonicons & concertinas repaired Written music figured in an easy style for concertina

Do any of the musical historians here have details of G. Green's 'easy style'? And what was a 'Harmonicon'?