The relationship between the palaearctic and nearctic faunas 



305 



FIG. 59. Bembidion trans- 

 parens Gebl. Distribution of 

 long- and short-winged speci- 

 mens in Newfoundland. For 

 explanation, vide figs. 57, 58. 



ledge. The Cordilleras of western North America are against boreoalpine distribu- 

 tion but in the northeast the St. Lawrence Valley cuts off from the main area an 

 arctic-subarctic fauna on the highest mountains of New England, especially in 

 the White Mountains of New Hampshire (Darlington, 1943). In some Diurnal 

 Lepidoptera (Butterflies) the southern component of a boreoalpine species is 

 supplemented or replaced by one or more subspecies ecologically connected with 

 mires and bogs (Petersen, 1954). 



The distribution of wing-dimorphic insects, here as in many other cases, may 

 allow partial reconstruction of the troublesome history of circumpolar species. 



The tiny Carabid beetle Bembidion transparens Gebl. [sulcatum Lee.) (fig. 57) 

 apparently has an uninterrupted transamerican distribution and a traditional map 

 of its area does not preclude the interpretation of a successive spread in a west- 

 east direction across North America in Postglacial time. The distribution of 

 long- and short-winged individuals (fig. 58) gives a contrary impression. From 

 the western half of North America, west of longitude 100°, only macropterous 

 specimens are known; the westernmost brachypterous specimen seen is from 

 Aweme, Manitoba. A predominance of this form occurs only in Nova Scotia and 

 Newfoundland and this region should therefore be regarded as a secondary centre 

 of distribution. The picture may become slightly, but not decisively, altered if 



20 — 565597 Lindroth 



