Canton is in Ordinaries.
Canton. A small rectangle in the top left corner.
Fox Arms. Ermine, on a chevron azure three fox's heads and necks erased or on a canton of the second a fleur de lys of the third. The canton is an augmentation of honour to his paternal arms, granted out of the Royal Arms as a mark of esteem to him and his heirs forever, by King Charles II following the Restoration of the Monarchy. Source.