1. In a small bowl, combine rice vinegar, lime juice, ginger, parsley, garlic, and salt. Set mignonette aside.
2. Gently lift (but don't detach) each side of the back shell of the crab and pull off and discard the soft gills; lay shell back in place. Rinse crab and pat dry. Coat crab with flour and shake off excess.
3. Melt butter in an 11- to 12-inch nonstick frying pan over medium-high heat. Add crabs and brown well, turning once or twice, about 7 minutes total. Lift from pan and drain briefly on paper towels.
4. Serve crabs hot and drizzle to taste with mignonette.
Nutritional analysis per crab.