This is the Acidalia osseata W.V. of Robson, which he calls 'Dark Cream Wave'. He admits to being unsure of his taxonomy which, in this group, was not fully understood in his time. The form which he mentions as having seen in southern collections was most probably Idaea humiiata Hufn., which is only found in this country in a small area on the Isle of Wight, a most unlikely candidate for the North-East. In addition to Robson's remarks on its distribution here, most recent records are from the Derwent Valley with outliers along the railway south of Hawthorn Dene (J. W. H. Harrison) [...] The insect may be more common than these records show, due to confusion with other species of Idaea.