242 



H. H. KOSS 



offers evidence of only one Intercontinental dispersal, it is impossible 

 to approximate the date of arrival of these lines in North America. 

 We should not forget that during this Cenozoic period many 

 lines were almost certainly already present and evolving in the 

 cooler habitats of western North America. In the montane caddisflies 

 some of these lines apparently remained in the area (e.g., the 







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clasp, apical 

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a.s. lost 



Fig. 8. Phylogenetic diagram of the caddisfly genus Himalopsyche. 

 Note that all the species occur In Asia except the one shown at the extreme 

 left, phryganea, which represents the only known dispersal of the genus 

 into North America. (From Ross, 1956.) 



Rhyacophila verrula and vagrita groups), whereas others (Fig. 9) 

 seemingly gave rise to species that spread into eastern North 

 America, e.g., the Rhyacophila invaria and Carolina groups, or into 

 Eurasia, e.g., the Rhyacophila glareosa and pepingensis branches. 

 The climatic and geologic changes in late Pliocene and the 

 Pleistocene are associated with what appears to have been a whole- 

 sale redispersal of many cool-adapted insects throughout the Hol- 

 arctic region. This phenomenon is especially well illustrated in the 



