A review of available information on the tribe Diamesini led to the construction of generic keys to most life stages. Serra-Tosio (1971b) first described Potthastia iberica from an adult male from the Spanish Pyrenees. Evaluation of specimens collected in the Nearctic, from Idaho (in 1967) and Georgia (in 1981 and 1983), indicate that this species is extant in eastern and western highland streams that appear to be typical trout streams. This new group of specimens contained a mature male and female pupa and immatures, and associations made it possible to describe the female and the immatures for the first time. Adult specimens conform very closely to the holotype. The known species of Potthastia are keyed.