Place shrimp and scallops in a large resealable plastic bag. In a microwave-safe bowl, combine th butter, lemon juice, Worcestershire sauce, garlic powder, and paprika. Microwave at 50% power for 1-1/2 minutes or until butter is melted. Stir to blend; set aside 1/3 cup for basting. Pour remaining marinade over shrimp ans scallops. Seal bag and turn to coat; refrigerate for 1 hour, turning occasionally.
Drain and discard marinade. Alternately thread shrimp and scallops on metal or soaked wooden skewers. Grill, uncovered, over medium-hot heat for 6 minutes, turning once. Brush with reserved marinade. Grill 8-10 minutes longer or until shrimp turn pink and scallops are opaque.