French silver snuff box

[rat-tail]

Hi All - would appreciate any help identifying the maker and working period of this large French silver snuff box. Engraved all over, it has a first standard post 1838 (I think) guarentee mark on the one side of the lip on the lid, and a maker's mark I can't make out on the other. Something smudged over something over B. My guess would be C1840s. Many thanks Frank