The species in the sipunculan genus Nephasoma (formerly a subgenus of Golfingia) are reviewed and evaluated in light of a critical examination of 13 historically used morphological characters. Whenever possible, type material was examined. The monograph of Stephen and Edmonds (1972) was used as a starting point. Of the 46 putative species listed in that work or described since then, 23 remain as valid species, three are reduced to subspecific rank, five are considered either species inquirendum or incertae sedis, and the remainder are considered junior synonyms. One new subspecies is described (N. diaphanes corrugatum). The known distribution of each species is summarized. A key to all species is provided.