What is "calygreyhound"

The calygreyhound is a mythical creature, that appears on Medieval heraldry. The de Vere family, who were the Earls of Oxford, used the calygreyhound in their coat of arms in the 15th and 16th centuries. The calygreyhound may be unique to the de Veres, and unlike most heraldic monsters, it made no attempt to seem realistic. A similar monster is the caretyne.