1919] Distribution of Insects 7 



The lower belt of that fauna, that found within the fir zone, is 

 generally spoken of as the Canadian, that immediately above 

 it and in the more barren treeless areas as the Hudsonian, and 

 that on the tops of the high peaks as the Arctic. These faunas 

 are in reality marginal or fringing faunas. They fringe the snow 

 fields of the mountains and the barren wastes of the north, 

 advancing and retreating with them, and have done so not 

 only during the present period, but undoubtedly during the 

 entire portion of the Great Ice Age, and I believe even before 

 that were only to be found in the cooler areas of the north. 

 During the period of greatest ice development, the Pleistocene, 

 they were, driven down to the lower levels and forced much 

 farther south than they were before. With the decline of this 

 period, they retreated both upwards and northward. At the 

 more southern limits of their distribution their retreat was often 

 prevented by breaks in the ranges or by the lowness of the 

 mountains so that their continuity was interrupted leaving as 

 we find today little islands of fauna here and there restricted 

 to the more elevated parts of the high mountains. 



The first of these, the Canadian, is in the west almost entirely 

 a forest loving fauna. Where it comes in contact with the 

 Vancouveran and Sierran, it blends to some extent with them 

 and as a result is often hard to separate. It has also borrowed 

 many species from these as they have from it. It commences 

 in the north as a continuation on to the mountains of that 

 extensive lowland fauna which populates the vast areas of 

 western Canada. Then it continues south along the mountains, 

 at first as a rather broad belt, later as a much narrower one, 

 and wedged in between the Vancouveran and Sierran, and the 

 Hudsonian on the west slopes; and the Great Basin fauna, a 

 portion of the so-called Upper Sonoran, and the Hudsonian 

 when the mountains are sufficiently high for that, on the east 

 side. Its forest types of Coleoptera are fairly characteristic,, 

 such as many of its ElateridcE and CerambycidcB, but its CarabidcB- 

 are less so. Pterostichus protr actus Lee. and Platynus bogemanni 

 Gyll. are, however, quite distinctive of it in the more southerrt 

 Cascades and the Sierras. 



The Hudsonian is in most places a very narrow zone, but 

 it is very distinct. In Alaska, it is found on the uplands of the 

 Aleutian Islands, on the mountains and the north side of the 

 Alaska Peninsula, to quite an extent about the Kenai Peninsula, 



