In a heavy deep pan heat 2-inches of peanut oil to 350 degrees F. Season the cr abs with salt and pepper. Dust the crabs with flour, shaking off any excess. Co at and fry crabs two at a time. Dip each crab into the beer batter and allow ex tra batter to drip back into bowl. Carefully lower the crabs into the heated oi l and fry until golden brown, turning once, about 2 minutes per side. Transfer fried crabs to paper towels to drain. Repeat process with remaining two crabs. Arrange crabs on individual serving plates. Garnish with scallion brushes, cila ntro sprigs and lime wedges. Serve immediately with dipping sauce on the side.