I have a piece which looks very like this from the side, though the pattern is different. A thick edge indicates an early date I believe, and I know mine is circa 1840 or earlier. I would guess yours is quite likely pre 1850. I have had a look through a couple of my books on Sandwich glass - American lacy plates - and I do not see your design there. Are there any signs of letters hidden in the lacy dots? Some of these are marked with a "W" or "D" or "WR"