Slice mushrooms length-wise. Pound the scallops until thin and even. Salt and pepper scallops and drop one at a time into a bag with the flour. Shake until lightly coated. Melt 3 tablespoons of butter in skillet over medium heat. As soon as butter begins to melt, add the mushrooms and teaspoon of the lemon juice. Once mushrooms are wilted, pour entire contents into a shallow bowl and quickly wipe skillet. Place skillet back on the burner to re-heat. Once skillet is hot, add the remaining three tablespoons of butter. Quickly cook the scallops until they are brown only at the edges. Remove to a serving platter. Add the wine or vermouth and stir, being sure to incorporate the pan drippings. Return the mushroom and lemon juice mixture to the skillet and allow to simmer for a minute or two, then pour over the meat. Garnish with lemon slices and parsley.