The silverware of Venice is often falsified, but in this case I would say that it is a genuine piece.
The mark of the "sazador" (assayer) seems to be the one present on the reliquary of S. Bartolomeo http://www.beweb.chiesacattolica.it/ben ... =TRIVENETO
There are a couple of silversmiths who have the mark B.N and several others who have B dot something.
Unfortunately they are all unknown and we only know that they are from the late eighteenth or early nineteenth century.
I hope this helps