A new Liolaemus species related to L. thermarum from Peteroa volcano region and also lacking precloacal pores in adult males, has been described from the frontier area of Pehuenche pass, Malargiie dept., Mendoza province. It lives at about 2500 meters of altitude, in a rocky habitat with streamlets and thermal springs. Morphological and ecological data suggest to establish a peculiar Andean species group, the "’neuquensis" group, assembling the new species, L. thermarum and L. cristiani from Chile, at the same latitude, besides L. coeruleus and L. neuquensis from the close frontier mountains of Neuquen. Their habitat is a volcanic landscape scattered with thermal springs and isolated clusters of Araucaria woods, relic of a primeval antantandic biome, fossil in the above cited Andean district of Mendoza province. Differences between the "neuquensis"' and “elongatus" groups are outlined, but the ancestral phyletic relationships of these liolaemine lizards are also taken into account.