Cruet with 4 dates and Pat D' ???

[torysemo]

Have a lovely cruet stand with bottles 2 hinged lids, 2 cruets, and a salt and a pepper. There is a curious bell at the top. The only apparent marks are around two rings on the knob for the bell. (It's almost a finial.) The top ring says "PAT D' AUG 26, 1868. AUG 8, 1866" The lower ring says "APR 8 1870, FEB 8 1874" The print is too small to for my camera to pick up. (I almost misssed seeing the lettering, it was so small.) Has anyone ever seen something like this before? Are the dates likely to be patent dates for the bell and set or???

Without more marks, I can't begin to tell whether this is silver, silverplate or ?? Guess I'll have to get it tested.

Photos below: