Lime Marmalade: Remove the zest from the limes in thin strips (use a citrus zester, not a microplane). Slice the tops and bottoms off the limes and stand them on a cutting board. Cut off the pith in vertical strips, slicing just beneath the white layer, then slice the limes in half-inch-thick rounds and cut each round in quarters.

Bring the sugar, water, lime zest, and salt to a boil in a small saucepan. Drop in the lime pieces and boil, uncovered and without stirring, for eight minutes. Allow the marmalade to cool at room temperature (it will thicken and gel).

Assembly: Work with one slice of prosciutto at a time. Cut it in half and spread the middle of each portion with a half-teaspoonful of marmalade. Lay several sprigs of cilantro across each piece, allowing the leaves to extend over the edges, and top with a melon slice. Wrap the prosciutto around the melon.

Note: These are best served as soon as possible; the melon slices will weep as they sit.