[Peter B]

I think this must be Adolphe Sax's original prototype !!

http://www.ebay.co.uk/itm/saxophone-alto-/160674471459?pt=UK_Woodwind_Instruments&hash=item2568f1de23

 

[milandro]

there are many of these types of saxophones around (generally French or Belgian made), this is a particularly turned down version and with some damaged keys.
I don't think it was a Adolphe sax alto although it certainly shares some of the characteristics. as for the date it is certainly made before of the end of the 19th century but if made by another maker more towards the end than obviously the date of its invention.