The district attorney of the Sixteenth Judicial District of this state shall receive, in addition to the salary now paid him by the state, an annual salary of nine thousand dollars, payable monthly on his own warrant by the parishes of St. Martin, St. Mary, and Iberia, comprising the Sixteenth Judicial District, apportioned as follows:
(1) By the parish of Iberia, the sum of three thousand dollars per annum.
(2) By the parish of St. Martin, the sum of three thousand dollars per annum.
(3) By the parish of St. Mary, the sum of three thousand dollars per annum.