Distribution of Moths of the Sub-family Bistonince. 313 



supposed that such species are what we have termed or have 

 come to regard as " representative species ; the departure 

 from type is too great for that. 



In our studies in the genus Amphidasys we concluded that 

 it arose in time when the climatic conditions to the north 

 and to the south, to the east and to the west, were so uniform 

 as to cause animals and plants throughout that vast area to 

 be specifically the same. From this we gather that Phigalia 

 spread seemingly when these conditions were breaking down, 

 and when climatic variations were able to work their will in 

 the moulding of new species from plastic genera — and this 

 conclusion demands in its turn that Phigalia colonised new 

 ground in later times by far than Amphidasys, and times 

 when inroads of the sea and various other contributory factors 

 were adversely affecting the geographical and climatic con- 

 ditions of the more northern regions. Such a period, never- 

 theless, must have been one when free access existed for 

 insects feeding on oak and trees of a similar type to America 

 from North-western Eurasia. 



In other words the period must have been when the sub- 

 polar temperate belt rejoiced in a sylva comprising not such 

 trees as Magnolia, Sassafras, Liriodendron, but consisting of 

 members of the genera Querciis, Ulmus, Fraxinus, etc., whence 

 we decide that our genus was moving in early or middle 

 Pliocene times — a period indicated independently by the 

 demonstrably later evolution of Phigalia as compared with 

 Amphidasys. 



Here we must direct our attention to the individual species 

 of the genus which is so homogeneous that, at first sight, one 

 can scarcely grasp, making due allowance for geographical 

 and climatic agencies, differences tangible enough to aid us 

 in fixing upon any one species as the earliest form. However, 

 dissection of the male genitalia reveals that the vesica in 

 Phigalia titea bears an enormous finger-like cornutus, not 

 undeveloped in the others, for its positions can be discerned, 

 but lost. The possession of this cornutus brings us once more 

 toward the Boarmiince, and also very near the next genus 

 Microbiston, a genus barely younger that Phigalia but actually 

 so, as its excised genital valves and its enormous abdominal 

 development of spines demonstrate. Since Phigalia has 

 yielded Microbiston, whilst Phigalia both in Eurasia and 

 America once possessed this exaggerated spine, it follows 

 that Phigalia titea more nearly approaches the original form. 

 Furthermore, this same conclusion would have been gained 

 had we made a minute examination of such minor features 

 as the greater or less elaboration of wing pattern, and the 

 nearness of such patterns to those of the primitive Boarmia 

 and Amphidasyd wing. 



