Ostracion

from The Century Dictionary.

• noun A genus of fishes with an exoskeleton of juxtaposed hexagonal plates forming a hard shell of bone, typical of the family Ostraciontidæ They are known as cow-fishes, trunk-fishes, and coffer-fishes. See cut under cow-fish.
• noun [lowercase] A fish of this genus; an ostraciont.

from the GNU version of the Collaborative International Dictionary of English.

• proper noun (Zoöl.) A genus of plectognath fishes of the family Ostraciontidae having the body covered with solid, immovable, bony plates. It includes the trunkfishes (also called boxfish).