Soak the spinach in several changes of water until completely free of grit; set aside for later.
In a 4-quart saucepan, set a vegetable steamer over 2 inches of water and bring the water to a boil. Add the clams to the steamer, cover and steam for 5 minutes or until they open. Remove the clams from their shells and reserve for later.
In a 12-inch skillet over low heat, cook the bacon until it begins to render its fat. Increase the heat to medium and cook the bacon until it is crisp. Discard the fat in the skillet and add the butter to the remaining cooked bacon bits in the skillet. Over medium heat, heat the butter. Add the shallots and saut, for 3 to 4 minutes, stirring on occasion, or until tender.
Add the vermouth to the shallots and boil until almost evaporated. Hold a strainer over the skillet and strain the oysters' juices into the skillet. Reserve the oysters for later. Simmer the juices until almost evaporated.
Add the spinach to the skillet, cover and cook for a minute or until just wilted. Season with salt and pepper to taste. Add the oysters and clams you reserved to the spinach and cook them, uncovered, for 30 seconds or until the edges of the oysters curl.
With tongs set some spinach on four appetizer dishes. Place 3 oysters and 3 clams per person on top of the spinach, then spoon the skillet juices and bacon bits over the shellfish and spinach. Serve immediately.
Per serving: 648 Calories (kcal); 40g Total Fat; (55% calories from fat); 35g Protein; 37g Carbohydrate; 137mg Cholesterol; 1401mg Sodium Food Exchanges: 1/2 Grain(Starch); 2 Lean Meat; 5 Vegetable; 0 Fruit; 6 1/2 Fat; 0 Other Carbohydrates