A new genus and species of colubroid snake is described from the isolated highlands of western Chiapas. This enigmatic little snake possesses a unique suite of characters that defies placing it in any known genus and clearly distinguishes it from all known genera. Several of the most unusual features include subcaudals undivided throughout the length of the tail and a simple hemipenis completely adorned with calyces and having a sulcus spermaticus that remains unbifurcated until the apical portion of the organ. Neither of these characteristics is known for any other colubroid of the Western Hemisphere. Consideration of morphology places the new snake in the Dipsadidae and suggests that Adelphicos, Atractus, Geophis, and Chapinophis are among its closest relatives.