Redescriptions of Notomastus hemipodus and N. tenuis are provided based on the examination of type specimens and supplemental material. Details of important morphological characters such as epithelial texture, lateral organs, genital pores, shape of the hooded hooks, and methyl green stain pattern are provided for both species. The two species, widely reported along the east, west, and Gulf coasts of North America, the Caribbean, and even Nigeria, have been confused since the 1960s. Notomastus americanus is newly synonymized with N. hemipodus due to the similarity in the characters of epithelial texture, first uniramous chaetiger, presence of an anterior palpode, and hooded hooks as well as identical methyl green stain patterns.