manducus

from The Century Dictionary.

• noun In Roman antiquity, a comic character of Italic origin, wearing a mask with gaping jaws set with great teeth, which were made to clash against each other.

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

• noun (Gr. & Rom. Antiq.) A grotesque mask, representing a person chewing or grimacing, worn in processions and by comic actors on the stage.