Holcosus undulatus, also known commonly as the barred whiptail, the metallic ameiva, and the rainbow ameiva, is a species of lizard in the family Teiidae. The species is endemic to Mexico. There are three recognized subspecies.
H. undulatus is brown-coloured, with a series of darker zig-zag bars running down the sides, often with light blue and green markings along the sides and underside. It is similar to the Middle American ameiva (H. festivus).
H. undulatus lives in litter in open habitats.
The following three subspecies, including the nominotypical subspecies, are recognized as being valid.
A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Holcosus.