There are four types of elections in Spain: general elections, elections to the legislatures of the autonomous communities (regional elections), local elections and elections to the European Parliament. General elections and elections to the legislatures of the autonomous communities are called after the mandate of the national or regional legislature expires, usually four years after the last election, although early elections may occur. Elections to local councils (municipal and insular) and to the European Parliament are held on fixed dates but some local government bodies (including provincial councils) are not directly elected. For most elections party list PR is used, but the plurality system is used for the Senate. General elections General elections are elections held for the national legislature, which is called in Spain Cortes Generales (Spanish for "General Courts") and consists of two chambers, the Congress of Deputies and the Senate. The Congress and Senate usually serve concurrent terms that run for a maximum of four years. However, the Prime Minister has the prerogative to dissolve both Houses at any given time either jointly or separately. Congress of Deputies The Congress is composed of 350 members directly elected by universal adult suffrage for a four-year term of office. Each one of Spain's fifty provinces is a constituency entitled to an initial minimum of two seats; the cities of Ceuta and Melilla elect one member each. The remaining 248 seats are allocated among the fifty provinces in proportion to their populations. Parties, federations, coalitions and agrupaciones de electores (electors' groups) may present candidates or lists of candidates. The lists are closed, so electors may not choose individual candidates in or alter the order of such lists. Electors cast a ballot for a single list, or for a single candidate in Ceuta and Melilla. The seats in each constituency are apportioned according to the largest average method of proportional representation (PR), conceived by the Belgian mathematician Victor d'Hondt in 1899 (d'Hondt method). However, in order to participate in the allocation of seats, a list must receive at least three percent of all valid votes cast in the constituency, including blank ballots. The single-member seats in Ceuta and Melilla are filled by the plurality or first-past-the-post method, under which the candidate obtaining the largest number of votes in the constituency is elected. Seat allocation in Congress To illustrate the functioning of the system, the allocation of seats in the three provinces