In response to Rob Drake - this recently sold on eBay:-

Bassix bass banjo

Alan Middleton (Fleetwood Folk Club) has a much older bass banjo which appears occasionally. I presume there were matching instruments of various sizes, corresponding to violin, viola, cello and double bass, probably intended to be played in quartets. I have seen equivalent instruments based on the Gibson "A" style mandolin shape. The bass mandolin was a magnificent instrument, seen in a pawnshop in Toronto more than twenty five years ago, regrettably not for sale!

As for Ole Bull violins, I may be on the track of one - I'll let you know.

Ross