Problems in taxonomy of the Polymorphidae are discussed, with particular reference to trunk spines. Andracantha gen. n. is proposed for species with genital spines and 2 fields of trunk spines. Corynosoma gravida Alegret 1941, C. mergi Lundstroöm 1941 and C. phalacrocoracis Yamaguti 1939 are redescribed and placed in Andracantha, with A. gravida (Alegret, 1941) comb. n. designated as type species.