The Yerkes Family Crest

as described in
Chronicle of the Yerkes Family With Notes on the Leech and Rutter Families
by Josiah Granville Leech, L.L.B.
Private publishing, 1904.

"Party per fess in chief gu. a fess wavy arg. in base ermine"
Party Parted: divided. Used in reference to any division of a field or charge. When a field is divided toward an ordinary it is said to be "party per" that ordinary.
Ordinary An ordinary is considered to be a charge, or bearing, of simple form.
The ordinaries, or as they are called by the majority of heraldic writers, honorable ordinaries, are thought to be nine in number as follows: Chief, Cross, Pale, Saltire, Fesse, Pile, Chevron, Quarter, and Bend.
Fess A division of a shield formed by two lines drawn horizontally and occupying one third of it
Party Per Fesse Divided by a horizontal line in the center of the shield.
Chief The head or upper part of the shield, containing a third of the field, and is divided off by one line, either straight or crenellé (indented). Stands for authority and domination of will.
In Chief Anything borne in the chief.
Gules (gu.) Red
Wavy A line of partition formed like waves. Represents the sea or water. Also undée, ondée, or undy.
Argent (arg.) The metal silver, shown as white in heraldic illustration.
Base The lower part of a shield.
Ermine White fur with black spots. Denotes nobility.