Mix flour, cornmeal, chili powder, cayenne, cumin, ground coriander, and salt in shallow bowl.
Heat 2 inches of oil in deep fryer to 350 degrees.
Coat crabs thoroughly with flour mixture and fry 2 at a time, turning once, until golden brown, about 5 minutes. Drip and serve hot with dipping sauce.
To make dipping sauce, mix last 12 ingredients in small bowl.