A new species, Eltxo grimaldii sp. nov., is described from Spanish Lower Cretaceous (middle Albian) amber from El Soplao, based on a single female. The new species is compared with the other only known species of the genus, Eltxo cretaceus Arillo & Nel, 2000, based on a single male specimen also found in Spanish amber, but slightly younger (Peñacerrada I amber; upper Albian). The holotype of E. cretaceus is reviewed and its description corrected and expanded, providing the first micrographs of its anatomical features. The holotype of the new fossil species is the only female specimen known of the cecidomyiid tribe Amediini Jaschhof, 2021, a tribe recently described after changes of taxonomic attribution of the genus Eltxo during the last 20 years.