Psocoptera (Copeognatha, Corrodentia: Booklice or Psocids and their allies)

Hemipteroid insects with long, filiform antennae of 12-50 segments, sometimes secondarily annulate. Head with Y-shaped 'epicranial' suture usually present; post-clypus inflated. Maxilla with 4-segmented palp and a rod-like lacinia which is partially sunk into head-capsule; labial palps much reduced, 1- or 2- segmented. Prothorax genertally small; wing-veination simple, with a few cross veins, but often with characteristic anastomes between Rs and M and between M and Cu 1a. Tarsi 2- or 3-segmented. External genitalia inconspicuous, cerci absent.