On the invalid resurrection of the lamprey genus Exomegas Gill, 1883

The lamprey genus Exomegas Gill, 1883, was erected on the assumption that it was distinguishable from Geotria Gray, 1851, by possessing three rather than two cusps on the transverse lingual lamina (TLL). Based on literature review and examination of holotypes and new data, the authors reaffirm that the TLL of Geotria possesses two or three cusps in the adult stage. The reduction or disappearance of the middle cusp at the beginning or during the spawning run constitutes a key feature of Geotria. The resurrection of Exomegas by Firpo Lacoste, Fernandez and Scioscia, Journal of Fish Biology, 2021, 1-6, 1507-1512, is therefore unjustified and not supported.