The coin is a spanish reale of some denomination. I *think* it's a half reale because of what the inscription on the reverse appears to say (ET * IND * R * M0 * F * M) but the coin is pretty worn. It's hard to tell since there isn't any other coin in the picture to judge the size by. If it's the size of a dime, it's a half reale, if it's bigger than a penny but slightly smaller than a nickel it's a 1 reale. If it's larger than that (like the size of a quarter or bigger) it's a 2 reale or higher denomination. Some times on the reverse they will say R 1 or R 2 or something similar, but it depends on the series. I have a 1776 half reale I found in a field here in mass a couple years ago (I'm also from eastern massachusetts). It doesn't have any mention of the denomination.
I'm guessing this is your first reale since you didn't know what it was offhand. Well, now you know : ). The first time I found one, I didn't know what it was either. The guy on it is king charles III (aka carlos the third) (on the coin it says CAROLUS III). He ruled spain from 1759-1788. It's a nice find, and I hope you go back and find another. Not worth much money, no more than $20-25 in the condition it's in, but a nice trophy none the less.
