Diplomystus is an extinct genus of freshwater clupeomorph fish distantly related to modern-day extant herrings, alewives, and sardines. The genus was first named and described by Edward Drinker Cope in 1877. There are seven species of Diplomystus: D. dentatus (Cope, 1877), D. birdii, D. dubetreiti, D. shengliensis (Chang 1983), D. kokuraensis (Uyeno 1979), D. primotinus (Uyeno 1979), and D. altiformis.