DERMAPTERA AND ORTHOPTERA 257 



species, was recently described from Madera County, California, 

 in the Sierras at an elevation of 4,300-5,000 feet. The components 

 of the Tetrix ornata line, which is confined to North America, are of 

 particular interest, as they clearly show reactions to the varying 

 aspects of Postglacial climate, as well as the probable results of 

 Glacial control. Two subspecies, dominant in eastern and middle 

 North America, namely Tetrix ornata ornata and T. o. hancocki, are 

 clearly differentiated in certain areas, and are less sharply, probably 

 environmentally, segregated in others. The more predominantly 

 eastern of the two, T. o. ornata, is far less frequent in large series 

 that represent many localities in the western United States and 

 Canada, whereas the other, T. o. hancocki, which seems to be more 

 partial to steppe country or coniferous forest lands and also is more 

 frequent at higher elevations, is the prevailing form in the broad 

 sweep of the Great Plains and the Cordilleran region. The Post- 

 glacial ebb and flow of prairie land and coniferous and deciduous 

 forests appears to account for the mosaic pattern of distribution 

 presented by these two elements of this species over a large part of 

 its range. However, an isolated subspecies, T. o. ifisolens, is known 

 only from the western slopes of the Sierras in California, and is 

 broadly isolated from the other localities where the species occurs. 

 Another subspecies, T. o. occidua, is limited to the Snake River and 

 Columbia River region of Idaho and Washington, reaching north- 

 ward to Lake Okanagan in southern British Columbia, in the 

 general vicinity of which it intergrades with T. o. hancocki of the 

 higher levels about the Okanagan area. It is probable that the 

 Columbia-Snake River subspecies represents survival in an area of 

 relative aridity of a species once more uniformly distributed, and 

 which normally requires a greater degree of humidity. 



The last incursion of the genus Tetrix may have been Inter- 

 glacial or even Postglacial, as New World and Old World individuals 

 of the one species involved, T. subidata, are inseparable. In the 

 New World it is broadly distributed north to the northern border 

 of the Subarctic, reaching southward in western America to the 

 southern Sierras of California, to relatively high mountain areas in 

 southern Arizona and New Mexico, and even to the Sierra Madre 

 region of northern Chihuahua, Mexico. In eastern North America it 

 does not range south of eastern Pennsylvania and southern New 

 Jersey. Another line of the genus developed in North America a 



