Triplomystus applegatei, sp. nov., is described as a new clupeomorph fish belonging to the order Ellimmichthyiformes, based on a single specimen collected from the Early Cretaceous (Albian) limestones of El Espinal quarry, near Ocozocuautla de Espinosa, Chiapas, southeastern Mexico. T. applegatei is differentiated from the other two species of the genus on the basis of body proportions and meristic data, as well as a peculiar development of a complex shape and articulation between the last scutes in the posterodorsal series. This species extends the geographical and geological domain of this genus from the Cenomanian Eastern Tethys Sea to Albian western Tethys Sea.