Preheat oven to 400˚F (200˚C).
In a large pot of boiling salted water, cook potatoes until just tender and parboiled, about 10-13 minutes. Stir in corn during the last 5 minutes of cooking time and drain well.
In a small bowl, combine butter, garlic, and Old Bay Seasoning.
Place potatoes, corn, shrimp and sausage in a single layer onto a greased baking sheet. Gently toss with the butter mixture.
Bake for 12-15 minutes, or until the shrimp are opaque and corn is tender.
Serve immediately with lemon wedges, and sprinkle with parsley.