Two extinct taxa, Moorea Sandpiper Prosobonia ellisi and Tahiti Sandpiper P. leucoptera, once occurred on Moorea and Tahiti, respectively. Four illustrations of Prosobonia from the second and third Cook expeditions (1772–75 and 1776–80) exist, of which one was the model for P. ellisi, whilst two others depict P. leucoptera and one Kiritimati Sandpiper P. cancellata. Considerable confusion exists as to whether P. ellisi is a valid species or an intraspecific variant of P. leucoptera. We examined the Tahiti / Moorea illustrations and original notes by crew of the Cook expeditions. We conclude that P. ellisi should be regarded as a junior synonym of P. leucoptera, as the differences between them may represent age-related, sexual, seasonal or even inter-island variation.