The minimum salaries of all county superintendents for their terms which shall begin on the first Monday of July, one thousand nine hundred thirty-four, shall be the following: County superintendents of counties having a population of less than twenty thousand (20,000), minimum annual salary, two thousand seven hundred dollars ($2,700); county superintendents of counties having a population of twenty thousand (20,000) and more, but less than forty-five thousand (45,000), minimum annual salary, three thousand one hundred and fifty dollars ($3,150); county superintendents of counties having a population of forty-five thousand and more, but less than one hundred and fifty thousand (150,000), minimum annual salary, three thousand six hundred dollars ($3,600); county superintendents of counties having a population of one hundred and fifty thousand, or more, minimum annual salary, four thousand fifty dollars ($4,050).