Orthosia incerta may be complete or broken up into three blotches; upper stigmata large, the reniform generally dark, both edged with pale; a strong thick median shade, sometimes bent at middle and entire, often marked only at costa and inner margin; hindwing pale or dark grey with dark cellspot and pale fringe. The markings are all clearer in the grey unsuffused forms: of these the chief are pallida Lampa from Sweden with the ground colour pale grey, finely striated with dark, and the two dotted cross lines;- "coerulescens" Tutt with the ground colour pale bluish grey; — "subsetaceus" Haw.which is dark slaty
Pale crag martin often treated as the small, pale northern subspecies of the rock martin, but it is now usually considered to be a separate species. The changes in size and colour are continuous, so the evidence for separate species is not strong, although some rock martins can weigh more than twice as much as the smallest subspecies of the pale crag martin. The average weight for "P. o. fusciventris" is 22.4 g (0.79 oz) against 10 g (0.35 oz) for "P. o. obsoleta". There do not appear to be any intermediate forms where pale crag martins and rock martin populations breed close