1. Remove meat from crab legs. Slice in thin strips 5 inches long, cover, and refrigerate.

2. Cut mango flesh into strips 1/2 inch-by-2 1/2 inches. Cut lettuce leaves in half, discarding center ribs. Trim each scallion into two 5-inch lengths; slice lengthwise into very thin strips.

3. Bring a pot of water to a boil. Add salt and rice vermicelli to boiling water, and cook until tender, 2 to 3 minutes. Drain, and rinse in cold water.

4. Transfer rice paper to a plastic bag. Place 2 paper towels, one on top of the other, on a work surface; dampen them slightly. Lay a sheet of rice paper on top. Cover with 2 more damp paper towels. Removing 1 sheet of rice paper at a time, repeat until you have 10 layers. Let stand until pliable, 10 to 15 minutes. Meanwhile, line a baking sheet with plastic wrap.

5. Across the bottom third of 1 sheet of rice paper place 2 pieces of lettuce; 4 cilantro leaves; 4 mint leaves; 1 piece of crab (if using lump crabmeat, 2 tablespoons); 2 pieces of mango, end to end; and 1/4 cup vermicelli. Cover with 4 strips of scallion, 4 cilantro leaves, and 4 mint leaves. Roll rice paper into a cylinder, stopping halfway. Fold left and right sides into the middle; finish rolling.

6. Place on prepared baking sheet, cover, and refrigerate. Repeat entire process, making 10 rolls. To serve, trim ends with a sharp knife and cut the roll into 4 pieces. Serve dipping sauce on the side.