Early 1900s vintage J &G Meakin semi-porcelain (ironstone china) made in England - this is a platter in the Eldorado pattern, green on white.
It's 14 1/2" long, nicely sized for a tray, or to hold a chicken or roast or ham. It's showing some age and wear, has crazing and scratching / utensil marks, and an old chip to the rim.