258 J. A. G. REHN 



species, T. brunnen, which is found in Hudsonian and Boreal 

 conditions extending from Alaska to New Brunswick and Quebec, 

 north to the northern hmits of the Subarctic and south in western 

 North America in mountain areas as far as the Cascades of central 

 Oregon and the Rockies of south-central Utah and central Colorado; 

 in the eastern United States it is known to occur only in the upper 

 Great Lakes region and the Adirondacks; a closely related, or 

 possibly inseparable, analog is now known from extreme eastern 

 Siberia. It would appear that the brunneri line of Tetrix may owe 

 the base pattern of its distribution to the same activating causes 

 as the members of the acridoid genus Zubovskya and the blattid 

 Cryptocercus, discussed beyond. 



Paratettix is the most widely distributed genus of the Tetrigidae, 

 occurring in both hemispheres but not reaching as far northward as 

 Tetrix. All representatives of the genus in North America are now 

 regarded as developments of lines that have reached us from the 

 Neotropical Region. Whether the four chief lines of the genus in 

 western North America moved from a developmental point in 

 southern Mexico and Central America northward into the truly 

 Sonoran areas of more northern Mexico and the western United 

 States, or whether they evolved in the latter, at present rela- 

 tively more arid district, and then spread southward, can hardly 

 be determined from present knowledge. The more pluvial conditions 

 which prevailed over much of that country during the late Pleisto- 

 cene and/or early Recent clearly were more favorable for tetrigids 

 than the severe restrictions of suitable environment there today. 

 One North American member of Paratettix, P. cucullatus, has a 

 very broad distribution, reaching from southwestern Ontario and 

 the northeastern United States to north-central peninsular Florida 

 and westward broadly to the lower Rio Grande in Texas and the 

 eastern border of the Great Plains to the northward. However, it 

 apparently spread, Postglacially in a period of greater precipitation, 

 from the Platte drainage across the non-mountainous Wyoming 

 Basin into the drainages of the Green and Colorado rivers and certain 

 of their tributaries, and also to the Bear and Snake rivers, and 

 eventually to the Columbia in northern Oregon and southern 

 Washington. In these immediate areas P. cucullatus and the quite 

 distinct P. aztecus are the sole members of the genus. The species 

 aztecus has clearly reached the northwestern United States from its 



