Oysters on Spinach

 Makes 10, 4 a piece? I do not understand the notation but here is the recipe. 

"Wash and cook, uncovered, 2 pounds spinach. As soon as leaves are withered remove from fire and chop very fine. Add 1/2 small onion, chopped fine, a 1/2 cup thin white sauce, 1/8 teaspoon Mace, pinch of garlic salt, salt, pepper and 1 teaspoon Brandy. Put in the top of a double boiler over fire. Take oysters out of shell and lay on good firm bed of spinach with in shell oyster on top. Cover each with seasoned white sauce, sprinkle with mace, and set all in oven to bake bedded in pan, already heated with rock salt. Bake ten minutes. Serve Immediately. "