The extinct drepanidine genus Ciridops is known from five historically taken specimens of Ciridops anna from the island of Hawaii, the last in 1892, and from fossil populations on Molokai, Oahu, and Kauai. The origins of the historical specimens and the taxonomic history of the genus are reviewed. The plumages of C. anna are interpreted as highly sexually dimorphic (red males vs. greenish females); the juvenile plumage of males included brownish feathers that appear to have been retained and mixed with the incoming definitive plumage. The thigh musculature and pelvic and hindlimb osteology show that the strong legs and feet of Ciridops were probably used to move plant debris in search of insects. The closest living analog may be the Yellowhead (Mohoua ochrocephala) of New Zealand. Analysis of stomach contents of the single fluid-preserved specimen of C. anna disclosed remains of insects that are widely distributed in Hawaiian forest ecosystems. The traditionally claimed association of Ciridops anna with palms of the genus Pritchardia suggests that Ciridops may have fed in the accumulated debris in the axils of palm leaves. The patchy distribution of fossils of Ciridops may result from the birds being associated with nearly pure stands of Pritchardia that were in turn patchily distributed. Vulnerability of Pritchardia to introduced seed predators, including rats and humans, and to destruction of lowland habitats by cutting and burning, may have caused the prehistoric extinction of Ciridops on all islands except Hawaii.