Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9 inch pie plate.
Bring a pot of water to a rolling boil. Rinse the scallops, and drop them into the boiling water; cook for 2 minutes. Remove the scallops with a slotted spoon, and pat dry. Place on the bottom of the prepared pie plate.
In a small saucepan, melt the butter, and stir in the flour. Cook over low heat for 3 minutes. Whisk in heavy cream and 1/4 cup Parmesan cheese. Season with salt and pepper to taste. Cook for another 2 to 3 minutes, stirring constantly, or until thick.
Squeeze the spinach dry, and spread over the scallops. Pour the cream sauce over the spinach, and top with mozzarella cheese, 1/4 cup Parmesan cheese, and bread crumbs. Sprinkle Old Bay Seasoning over the bread crumbs.
Bake in preheated oven for 15 minutes, or until browned and bubbly.