The county treasurer, upon receipt of the statement from the State Lands Commission showing the amounts paid by each purchaser of swamp and overflowed lands in the district, shall, after deducting all amounts chargeable against the lands in the district by reason of moneys drawn from the “swamp-land fund” of the county, pay the balance thereof pro rata to the original purchasers of land in the district, or their heirs, executors, administrators, successors or assigns.