It is a garment clasp, originally patented by Byron G. Clark.. Clark Manufacturing Company located in Boston .. in 1899. It was renewed again with revisions in 1902. It may have been reissued in 1907 as well.
I meant to say clasp,..but I couldn't think of that word at the time,..It won't let me edit the title,..I believe it is a garment clasp..back then they didn't have the elastics that we have today.
Nice clasp! When I first started metal detecting I found a very similar nickel or silver plated one, with "Pat Aug 1 1899" written on it, the same exact patent as the one posted above. I remember reading that it was for garters or stockings when I did research about it.