We determine, for all genus g ≥ 2 the Riemann surfaces of genus g with 4g automorphisms. For g = 3, 6, 12, 15 or 30, this surfaces form a real Riemann surface F g in the moduli space M g : the Riemann sphere with three punctures. The set of real Riemann surfaces in F g consists of three intervals its closure in the Deligne-Mumford compactification of M g is a closed Jordan curve.