A new fossil species of mayfly of the genus CloeonLeach, 1815 (Ephemeroptera, Baetidae) is described. The type material comprises female imagines from 24 amber inclusions, from Miocene strata of Chiapas in southern Mexico. The fossil species, Cloeon tzeltal sp. nov., closely resembles those in the genus Cloeon by the following diagnostic characters: absence of hind wings; two major crossveins between R1 and R2 not in line with the crossveins below them; single marginal intercalaries; and basal crossveins between veins R and Rs situated more basally than the following vein. The new species can be distinguished from extant species of Cloeon by the absence of colored costal and subcostal fields in the forewings and the absence of transversal veins in vitta broadly bordered with white. Extant species of the genus Cloeon in America have an exclusive distribution in the northern part of the continent; with the exception of one introduced taxon, no valid species have been recorded in the tropics. As such, the fossil record of Cloeon in the southernmost part of North America suggests a broader geographic distribution of this genus in the geological past, including the southernmost part of North America.

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