Martinichthys is an extinct genus of plethodid fish from the Cretaceous of North America.

[3] It is named after one H. T. Martin, who collected the most complete specimen at the time of description.

[2] Two species are known, the short-snouted M. brevis and the long-snouted M. ziphioides; multiple other species previously described have been synonymized with M. ziphioides.

[4] With its long rostrum, the genus shows notable morphological convergence with modern billfish and the co-occurring pachycormid fish Protosphyraena, although not to the extent of its close relative, Rhamphoichthys.

This article about a prehistoric ray-finned fish is a stub.