Agathotoma candidissima, common name Cox's mangelia, is a species of sea snail, a marine gastropod mollusc in the family Mangeliidae.

The white, oblong, turreted shell features 7 to 8 whorls, with the protoconch missing in the specimen described.

The aperture is elongate-ovate, accounting for approximately 3/7 of the shell's total length.

The outer lip is thickened and slightly insinuate at the top.

[2] This species occurs in the Caribbean Sea, the Gulf of Mexico and the Lesser Antilles.