INSECTS OF WESTERN NORTH AMERICA 235 



eastern Asia, it is plausible to assume that this genus and others of 

 similar range characteristics were former denizens of the American 

 Northwest. 



A few cases drawn entirely from the distribution of living forms 

 give practically conclusive proof of the same phenomenon. An 

 example is the subgenus Doloclanes of the caddisfly genus Wormaldia 

 (Ross, 1956). The main group of species involved in this subgenus 

 evolved in and is now restricted to the eastern part of Asia (Fig. 

 2), but one species (most closely allied to one in Japan) occurs in the 

 Great Smoky Mountains of eastern North America. The only 

 logical explanation for this set of circumstances is that a northeastern 

 Asiatic species spread across North America and ultimately became 

 established in the Smoky Mountains. During this dispersal, we 

 must assume that a species of Doloclanes lived in northwestern 

 North America, although we have no definite records for this 

 subgenus there. 



Some insect fossils from western localities represent highly 

 specialized genera not known from living species and undoubtedly 

 have become extinct. The existence of such extinct "side branches" 

 of phylogenetic trees cannot be deduced from the study of living 

 forms, hence how many of them existed in the past we do not know. 



PRESENT INHABITANTS OF THE WEST 



The oldest dispersals of northern insects involved in the origin 

 of the present western North American fauna for which we have 

 evidence seem to have been in middle Cretaceous. It may be in- 

 ferred that the caddisfly genus Sortosa dispersed at that time to 

 almost every continental land mass and that after this great spread, 

 many populations of Sortosa became isolated in and persisted in 

 various parts of the world. In western North America five species, 

 comprising the subgenera Sisko and Fumonta, represent this old 

 movement (Fig. 3). It is highly likely that several archaic western 

 genera of limnephilid caddisflies, including Dicosmoecus, Ecclisomyia, 

 Farula, and Pedomoecus, also are surviving lines dating back to this 

 same mid-Cretaceous dispersal (Schmid, 1955). All five of these 

 caddisfly genera frequent streams in the extreme north or at higher 

 elevations in mountains. 



Judged from their known present distributions, most of these north- 

 western genera or subgenera have either remained isolated in moun- 



