256 Distribution of Moths of the Sub-family Bistonince. 



chain itself, militated against it. Probably Sequoia worked 

 its way down the mountains and to its present, and very 

 obviously, favourable stations. 



Returning now to Amphidasys cognataria, we must picture 

 it as driven southward and surviving the Glacial period in 

 the Southern Atlantic United States, and in the Chinese area, 

 with all the forms discussed above. With the appearance of 

 more genial times, its course to recover lost ground was just 

 that mapped out in the case of Lycia ursaria ; therefore its 

 distribution to-day in America is co-extensive with that of 

 that insect. In China, too, its course was gradually northward 

 and along the river valleys until its ' present stations were 

 attained. 



Now it will be noted that this form occurs in Turkestan, 

 and crops up casually in Asia Minor. This may occur in two 

 ways ; we may have a reversal to type of the neotypical 

 A. betularia or, otherwise, there has been, in some portion of 

 Eurasia, a further refuge for Tertiary insects. If the former 

 supposition were justifiable, then at any point in the range 

 of A. betularia, cognataria forms should occasionally appear, 

 and this is not the case ; whence we must assume that the 

 second supposition is the correct one. 



This then involves the corollary that we ought to be able 

 to produce species of similar history ; and some of these should 

 occur in North America. Such instances are easily adduced, 

 and these in weighty and remarkable examples. Amongst 

 them are the two Mud-fishes, Umbra limi in the Danube, and 

 U. krameri in the Mississipi, the Walnuts — the genus Juglans — ■ 

 found in all three stated refuges of Tertiary relicts, Atlantic 

 America, Eastern Asia and Asia Minor and, possibly, a fourth, 

 Turkestan, unless it is to be regarded (correctly in my view) 

 as part and parcel of the third. Thus, in a round-about manner, 

 the history and geography of the palseotypical form of 

 A. betularia has been traced. 



Taking now the case of the neotypical and nymotypical 

 form A. betularia, we find that it appears throughout the 

 Pakearctic area from Japan to Britain ; but, of course, is more 

 or less of a northern insect, as its name ' betularia,' derived 

 from that of its chief food-plant birch (B etui a alba), would 

 cause one to surmise. Obviously, as it comes into intimate con- 

 tact with A. cognataria in Southern Siberia, it has arisen from 

 that species in that area, and, favoured by the slightly delayed 

 advent of Glacial conditions there, has soon after its evolution, 

 worked its way both to the east and to the west along the 

 birch-clad foot-hills of the mountains of Central Asia where, 

 in turn, it has given birth to the species Amphidasys huberaria. 

 Thus, when an entrance was possible to Europe across the bed 

 of the older and more extensive Caspian Sea, it pressed onward 



Naturalist, 



