Feather brooch Silver with Rose cut diamonds and gold

In my country we call such a brooch a Feather brooch. But I'v heard sometimes this kind of jewelry is also named Halley brooch. Whatever it is called I think it's beautiful.
Rose cut diamond silver on top and backed with 14K yellow gold. The makers mark J5 (??) and an old Dutch silvermark (sword).
Is there a fellow collector who knows the maker's name perhaps ?? I'v the idea that the trompet clasp was made later for security reasons. This brooch dated Late Victorian, do you agree?