The Coelocybinae (Hymenoptera: Pteromalidae) of the southern parts of the New World are reviewed. Ariasina Heydon n. gen. is described for Ar. adusta Heydon n. sp. and Ar. gigas Heydon n. sp. Other new species described are Ambogaster karooi Heydon n. sp., Lanthanomyia bockleri Heydon n. sp. and L. pardos Heydon n. sp. Updated information on distributional records, new host plant information, and a key to all included genera and species of the Coelocybinae of Chile and Argentina are presented.