The genera of the aphids of Canada

The chaetotaxy of the disc of the head is variable throughout the Aphidodea. [...] Taxonomic characters of the rostrum are largely confined to the length and shape and to the chaetotaxy of the apical segment. [...] The length of the rostrum is measured by the distance between the base and apex of the stylets. [...] The small portion of the apical rostral segment that occurs distad of the apical primary setae varies greatly in shape; in some genera, such as Cinara Curtis it is separated from the rest of the apical segment by a membranous, articular area immediately distad of the apical primary setae (Fig. [...] This structure is usually separated from the rest ofthe head capsule by a membrane that permits the rostrum to extend forwards, but fusion of the frontal area of the head capsule and the anterior margin of the clypeal structure does occur (as in Drepanaphls Del Guercio, Fig.