The following is a description of a new species of leafhopper from Eastern Canada of the subgenus Cloanthanus of the genus Scaphytopius. A key to the known Canadian species of Cloanthanus is included. Two of these species, angustatus (Osb.) and argutus DeL., do not appear to have been recorded previously for Canada. The key is based primarily on structures of the male genitalia, as these show the most reliable specific characters. External characters of colour, markings, and structure are often unreliable, because of the variation that occurs. There is occasionally some variation in the genitalic characters, notably in the degrees of curvature of the paraphyses, but the general shape of each structure is sufficiently constant to provide reliable specific characters. This subgenus, which was revised by Hepner (1947), is poorly represented in Canada, as the majority of the species have southerly distributions in North America. The common Canadian species is acutus (Say), followed by latus (Baker); the remaining species are more restricted in their ranges and distributions in Canada.