The New World species of the subgenera Allotrichoma Becker and Neotrichoma (new subgenus) are revised, including a phylogenetic analysis of the species groups and subgenera within the genus Allotrichoma. For phylogenetic perspective and to document the monophyly of the genus Allotrichoma and its included subgenera and species groups, we also provide a cladistic analysis of genera within the tribe Hecamedini. The ingroup included seven exemplar congeners from within Allotrichoma. Outgroup sampling included exemplars of other genera within Hecamedini and from the putative sister group, Lipochaetini, and to root the analysis, we used an exemplar of the tribe Discocerinini. Analyses with successive weighting and implied weighting recovered a monophyletic Allotrichoma and indicated clades within the genus. Eight new species are described (type locality in parenthesis): A. bifurcatum (Utah. Utah: Lake Shore (40°06.9'N, 111°41.8'W; 1370 m)), A. dynatum (Oregon. Benton: Finley National Wildlife Refuge (44°24.6'N, 123°19.5'W)), A. occidentale (Oregon. Lake: Lakeview (44 km E; Drake Creek; 42°11'N, 119°59.3'W)), A. robustum (California. Kern: Kern River (35°16.1'N, 119°18.4'W)), A. sabroskyi (New Mexico. Sandoval: La Cueva (Junction of Highways 126 and 4; 35°52'N, 106°38.4'W; 2342 m)), A. wallowa (Oregon Baker: Goose Creek (35 km E Baker City; 44°49.2'N, 117°27.79'W; 825 m)), A. baliops (Florida. Monroe: Key West (Willie Ward Park; 24°32.9'N, 81°47.9'W)), and A. insulare (Dominica. Cabrits Swamp (15°35'N, 61°29'W)). Within Allotrichoma, we recognize three subgenera of which one, Neotrichoma (type species: A. atrilabre), is newly described. All known species from the New World are described with an emphasis on structures of the male terminalia, which are fully illustrated. Detailed locality data and distribution maps for the New World species are provided. A lectotype is designated for Discocerina simplex Loew and a neotype is designated for Allotrichoma bezzii Becker. Allotrichoma filiforme Becker, A. trispinum Becker, and A. dahli Beschovski are reported as new synonyms of A. simplex (Loew) and A. yosemite Cresson is a new synonym of A. atrilabre Cresson. We also clarify the status of previously described species, including those with Holarctic distributions. For perspective and to facilitate genus-group and species-group recognition, the tribe Hecamedini is diagnosed and a key to included genera is provided.
