Yotsugana

Yotsugana (四つ仮名?, literally "four kana") refers to four specific kana ジ, ヂ, ズ, ヅ (Nihon-shiki: zi, di, zu, du; Kunrei: zi, zi, zu, zu) of the Japanese script. While they used to represent four distinct phonemes, currently they are either one, two, three, or four distinct phonemes depending on dialect. In the current dialect of Tokyo, it is two phonemes as represented in Hepburn romanization.