Cladotanytarsus crassus, a new North American non-biting midge with a distinctive hypopygial digitus (Diptera: Chironomidae)

Cladotanytarsus (Cladotanytarsus) crassus sp. n. is described from the USA (Oregon, Wyoming) and Canada (Ontario). The distinctive structure of the adult male hypopygium, bearing a thickset digitus and a stout elongated superior volsella, is presented. Intraspecific morphological variations are described in order to compare C. crassus and C. nigrovittatus (Goetghebuer, 1922), treated as close relatives. The geographical distribution and ecology of the two species are commented on.