Barnes accepted Clark’s offer to sell to him a portion of Clark’s coin collection. Clark forgot that his prized $20 gold piece at the time of the offer and acceptance was included in the portion which he offered to sell to Barnes. Clark did not intend to include the gold piece in the sale. Barnes, at the time of inspecting the offered portion of the collection, and prior to accepting the offer, saw the gold piece. Is Barnes entitled to the $20 gold piece?