The Appalachian troglobite Porrhomma cavernicola (Keyserling 1886) is redescribed. Porrhomma emertoni Roewer 1942 is a junior synonym (new synonymy). An unusual stridulatory organ with the plectrum on trochanter II and the striae on coxa I is found in both sexes of this species. Porrhomma cavernicola is widespread in Appalachian caves. By contrast, Appalachian Nesticus (Nesticidae) troglobites tend to be highly endemic. This despite the fact that both groups of spiders are web-builders that may be found in the same caves. Porrhomma cavernicola is added to a previous phylogenetic analysis of linyphiid spiders. Implications of this analysis for the phylogenetic structure of linyphiid spiders is discussed.