Chesapecten jeffersonius is the fossilized form of an extinct scallop, which lived in the early Pliocene epoch between four and five million years ago on Virginia's coastal plain. Chesapecten jeffersonius are commonly found in strata exposed along Coastal Plain cliffs along major rivers in southeastern Virginia and eastern North Carolina, and it is the index fossil for the Lower Yorktown Formation. It is the state fossil of the State of Virginia in the United States.