One species of the genus Masoncus (Araneae, Linyphiidae) is described and illustrated . Masoncus pogonophilus new species has been collected exclusively inside the nests of the Florida harvester ant, Pogonomyrmexbadius (Latreille) (Hymenoptera, Formicidae) and is, therefore, considered a myrmecophile, or obligate ant associate. Morphological characters separating this new species from two of the three described congeners(M. arienus and M. conspectus) are noted .
