The taxonomy of the South American genus Exomegas Gill 1883 has been unstable owing to the unknown status of the type specimen of its type species, Petromyzon macrostomus Burmeister 1868. Here the authors announce the finding of the holotype in the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" ichthyology collection. Whereas Exomegas type species is recognized based on its holotype, Exomegas gallegensis (Smitt 1901) new status is proposed. These preliminary results resolve a century-long taxonomic uncertainty and foster a nomenclatural arrangement for a Southern Hemisphere lamprey genus.