380 = Distribution of Moths of the Sub-family Bistonine. 
the conditions periodically tended to deteriorate. But let 
us pause ; under what conditions had these species persisted 
over the long stream of centuries? Century after century, 
they had been under maritime conditions, and these had 
become part and parcel of their being ; species normally of 
general occurrence were now restricted to areas with an oceanic 
climate. Their endeavours to reconquer ground would have 
most success along the reopened coasts to the north, and 
thither a move was made. Now, however, the ocean was 
fretting away the land, and gradually our species was forced 
back until it occupied a coast line of West Britain following 
a line passing outside the Hebrides and the various isles of 
Western Ireland. Along it, on the coast sandhills, N. zonaria 
increased and multiplied. Still the Atlantic rollers pressed 
on, wearing away without cessation our western shores, and 
thus the Outer Hebrides, Clare and Arran Islands came into 
being ; on them, isolated colonies were marooned. No respite 
was given; the waves must have their way. First the Irish 
Sea appeared as a huge landlocked gulf from the south; and 
resistance in the north was not prolonged, the huge basaltic 
barrier binding Ireland to Scotland gave way, and now Ireland 
was anisland. On it, zonaria could only wend its way eastward, 
and that with difficulty, along the northern shore, reaching 
the Antrim coast ere its momentum was lost. The portion 
cut off in Scotland was in no better plight. Little colonies 
stayed behind on each little isle as it was formed, but the 
main body tried to gain ground on the mainland and with 
much success. Utilising the virgin and more favourable 
coast of South-western Scotland, it progressed, passing by 
degrees along the South of that country until England was 
reached. The same slow gain of ground was made and ever 
along the coast; finally, its outposts took their final stand 
on the Welsh coast of Carnarvonshire, 
Thus we have traced the course of events which have 
caused N. zonaria and other insects and plants, which are 
not fastidious as to ground on the continent, to be maritime 
and western in their distribution in the British Isles. Of 
these, none are more significant in elucidating the past history 
of such forms than the moths Anthrocera purpuralis, Anthrocera 
achilleae and Platyptilia tessaradactyla. 
Let us now examine the course of events in the east. Here 
we left a colony penned up in the South east of Europe and 
in Asia Minor. Soon after it arrived in Asia Minor, the Atgean 
Sea was formed, and with the steady wash of its waves, it 
bored its way into the Black Sea, and thus the fate of the 
western refugees was repeated. Two divisions now existed. 
With the advent of better conditions, very slowly, much more 
slowly than depicted in the case of Poecilopsis pomonaria, 
Naturalist, 
