It is the early developmental stage of a Dryadd Saddle commonly called Pheasant Back mushroom. Edible and some people like them. I give them a \"2\" on a scale of 1 to 10 on a \"Choice\" edible scale. They will develope a 3/4 moon like shape and can often be the size of a trashcan lid. They smell like a cross between cucumbers and water-mellon.
Not a big fan of them.