J. W. H. Harrison 



209 



actual truth. Furthermore, these phenomena afford, with other similar 

 cases in many genera like Lycaena and Taeniocampa, some degree of 

 proof of the principle. 



TABLE II. 



Summary of characters differentiating Oporabia dilutata and O. christyi. 



(6) The Evolution of the Subspecies Oporabia filigrammaria. 



Evolved as we have seen from Venusia cambrica, whose life history 

 was interwoven inextricably with that of the northern tree Pyrus ancu- 

 paria, Oporabia autumnata accepted birch as a food and was thus enabled 

 to colonise much of the Boreal circumpolar continent of Mid Tertiary 

 times, just as had many of its contemporaries like Lycia hirtaria and 

 Poecilopsis lapponaria. So like that of P. lapponaria, Nyssia zonaria, 

 Anthrocera purpuralis, A. achilleae and Platyptilia tessaradactyla are 

 many points of its history that, in view of my detailed treatment of the 

 Bistoninae elsewhere \ no repetition is necessary here. 



Only one fact must be singled out, and that is, that as with the last 

 mentioned five insects, the climax of glacial conditions saw the insect in 

 Europe split into two widely separated colonies, one located in South 

 Eastern Europe and the other in stations far to the west of the British 

 Islands of today. 



With these preliminaries we have reached a stage at which the 

 modern history of what now represents the original 0. autumnata may 

 be regarded as commencing. 



' Harrison, "The Geographical Distribution of the Moths of the Geometrid Subfamily 

 Bistoninae," Naturalist, pp. 164—166, 194—198, 273—278, 377—382 (1916). 



