Identification of long-preserved specimens reveals the historical geographic range of the Patagonian lamprey Geotria macrostoma (Burmeister, 1868) in southern South America.

The lamprey genus Geotria Gray, 1851 currently includes only two species: G. australis and G. macrostoma.

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.

Morphometric and physical characteristics distinguishing adult Patagonian lamprey, Geotria macrostoma from the pouched lamprey, Geotria australis.

The pouched lamprey, Geotria australis Gray, 1851, has long been considered monotypic in the Geotriidae family with a wide southern temperate distribution across Australasia and South America. Recent studies have provided molecular and morphological evidence for a second Geotria species in South America; Geotria macrostoma (Burmeister, 1868). The aim of this study was to determine morphometric and physical characteristics of adult G.