Issurer Isthmian Canal Commission. This was the U.S. government entity set up by Congress to build the canal. Numbers were issued from 1 to 99999 in this variety. See the historical note for more details. Manufacturer AM.RY.S.CO., NEW YORK which was the American Railway Supply Company.
Some checks have two additional small holes as in the example below.
If the lettering and numbers are undamaged, there is no reduction in value for these holes. By 1912 about 165,000 had been issued to various timekeepers.