A revision of the New World species of Gymnoclasiopa Hendel (Diptera, Ephydridae)

Species of the shore-fly genus Gymnoclasiopa Hendel from the New World are revised, including G. grecorum sp. n. (Alaska. Juneau: Gastineau Channel, Thane Road (S Juneau; 58 degrees 16.9'N, 134 degrees 22.4'W)) and G. matanuska sp. n. (Alaska. Matanuska-Susitna: Palmer (Matanuska River; 61 degrees 36.5'N, 149 degrees 04.1'W)). We also clarify the status of previously described species, including those now discovered to have Holarctic distributions and/or for which sexual dimorphism was not appreciated and the species was described twice, including G. montana (Cresson) as a syn. n. of G. bohemanni (Becker). Two species, G. bella (Mathis), comb. n., and G. chiapas (Mathis), comb. n., are transferred from Ditrichophora to Gymnoclasiopa, and D. cana Cresson stat. rev. and D. canifrons Cresson, stat. rev. are returned to Ditrichophora, the genus in which Cresson originally described them. A neotype is designated for G. tacoma to stabilize the nomenclature of this species. The two excluded species, D. cana and D. canifrons, are diagnosed and distributional data are also provided. For all known New World species of Gymnoclasiopa, structures of the male terminalia are described for the first time and are fully illustrated. Detailed locality data and distribution maps are also included. To provide context and also to facilitate identification, diagnoses are included for the tribe Discocerinini and genus in addition to a key to the genera and species occurring in the New World.