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THE GEOGRAPHICAL DISTRIBUTION OF THE 

 MOTHS OF THE SUBFAMILY BISTONINAE. 



J. W. HESLOP HARRISON. D.Sc. 



X.— THE GENUS AMPHIDASYS (TREITSCHKE). 



Amphidasys b etui aria (Linn). 



Palfeotypical form, A. cognataria (Gn.). Distribution : — 

 In North America : Northern Atlantic States, Quebec, 

 extending in Canada as far west as the Rocky Mountains. 

 In Asia : Ussuri and Amur Districts, West Central China to 

 the Thian Shan Mountains, occasionally in Armenia. 



Neotypical form, A. betularia (L.). Central Europe (ex- 

 cluding the Polar Regions and the Balcan Peninsula), Siberia, 

 Japan, Armenia. 



Amphidasys huberaria (Ballion). Western Siberia, Tibet. 



Amphidasys thoracicaria (Obthr.). Ussuri District, Corea 

 and China. 



Amphidasys tortuosa (Wileman). Japan. 



In discussing the geographical distribution of forms of such 

 (apparently) erratic occurrence as Amphidasys cognataria, a 

 mere consideration of present day geographical conditions is 

 utterly futile. We have, if possible, to reconstruct for ourselves 

 the position of the main land masses on the earth's surface 

 when the forerunner of the form had occupied its maximum 

 area, and then, from the possibilities there presented to us, 

 draw the necessary conclusions. 



Direct appeal to the geological record for fossil evidence, 

 is, in the case of insects, almost useless from the very nature 

 of things ; only in very rare and exceptional cases, exemplified 

 by the Miocene shales of Florissant in Colorado, do such 

 remains appear in any quantity. We can, however, argue 

 from the fossils of less perishable forms which existed in the 

 times we must consider, and which at the present time display 

 the same range as the objects of our studies. 



But before doing so, let us look at the structure of the 

 continental masses of the Tertiary Period. Throughout 

 Miocene time, and very probably in the Eocene and the 

 Oligocene also, the continental areas of the Northern Hemi- 

 sphere were much more extensive than at present. Almost 

 certainly the only gaps in the huge circumpolar continent (if 

 one may call a continent stretching as far south as the Gulf 

 of Mexico circumpolar) were one to the east of the Japanese 

 area, a second in Central Asia and another which, of a certainty, 

 existed in Eocene times and probably, in part, far into Pliocene 

 times along the Western Coast of North America. If others 

 occurred they do not concern us here. The last-mentioned 

 marine basin almost coincided in position with the land now 



Naturalist, 



