In all counties containing a population of not more than twenty-three thousand, eight hundred and ninety (23,890) and not less than twenty-three thousand, eight hundred and eighty (23,880) according to the Federal Census of 1930, and containing a scholastic population of not more than six thousand and ten (6,010) and not less than six thousand (6,000) according to the 1938-1939 Public School Directory of the State Department of Education, the County Superintendent of Schools shall receive from the Available School Fund of their respective counties an annual salary of not less than Two Thousand, Two Hundred Dollars ($2,200) nor more than Two Thousand, Four Hundred Dollars ($2,400), said salary to be fixed by the County Board of School Trustees of the respective counties.