Dragonflies were very popular during the Victorian times; especially Art Nouveau era. At this point, I agree with Okie in that it looks like a buckle, but can't say for sure without more pics & info. I'd like to see a clearer pic of the front & back and to know the dimensions. Is it made of brass? Have you cleaned it, if so, what color was it when you dug it? After this information, we can probably give you a more accurate date. Nice find, Breezie