The chief is the upper third of the shield, here apparently formed by a roll of parchment. It is rare for the crest to consist of the same object as is depicted on the shield.
I ber a pilch of ermyn
Poudert with a catt-skyn;
The chefe is of pechmyn
That stondis on the creste. fur (coat); ermine
chief; [roll of] parchment
crest