Species and genera of Bairdiidae can be difficult to discriminate, because of the somewhat limited morphological range of the carapace and limbs and the prevalence of homeomorphy. Attention to the esophageal flapper valve, an uncalcified but relatively well sclerotized structure, may contribute to more reliable identifications. Living species of Neonesidea exhibit sufficient variability in the architecture of this structure to suggest that it may have taxonomic value. Twelve named and three new species are examined to test this premise: N. bacata, N. caraionae n. sp., N. decipiens, N. credibilis n. sp., N. forea n. sp., N. edentulata, N. gerda, N. holdeni, N. longisetosa, N. manningi, N. mediterranea, N. omnivaga, N. plumulosa, N. schulzi, N. tenera. The geographic range of N. gerda is extended across the Gulf of Mexico, while the ranges of N. longisetosa and N. dinochelata are restricted. This supplemental information helps to clarify the relationships of several poorly known species from carbonate environments of Bermuda, the Bahamas, Florida, the Gulf of Mexico, and the Caribbean.