Plagiogeneion i is a genus of marine ray-finned fishes belonging to the family Emmelichthyidae, the rovers, bonnetmouths or rubyfishes.

The fishes in this genus are found in the southeastern Atlantic, Indian, and Pacific Oceans.

Plagiogeneion was first proposed as a monospecific genus in 1890 by the Scottish explorer, ornithologist, and botanist Henry Ogg Forbes with Therapon rubiginosus, which had been described in 1875 by Frederick W. Hutton from New Zealand,[2] as its only species.

[1] The genus is classified in the small family Emmelichthyidae which is included in the order Acanthuriformes.

[4] There are currently five recognized species in this genus:[5] Plagiogeneion rubyfishes have a body which has a standard length of 2.8 to 3.6 times its depth.