DERMAPTERA AND ORTHOPTERA 271 



have spread northward over the Great Plains and entered the Great 

 Basin, in which area Derotmema has developed a very distinctive 

 type {D. piiite). Hadrotettix, Tropidolophus, and Platyladista are 

 also Sonoran. The first two extend to varying degrees northward 

 over the Great Plains. Hadrotettix is also known from relict grassland 

 areas in northern Arizona. 



The more dominantly eastern genus Spharagemon probably had 

 its origin in the eastern United States, where it now has three dis- 

 tinct lines. Two of these lines extend westward, but the extent of 

 the genus in that direction is virtually limited by the Rockies. 

 Spharagemon has four well-marked lines in the Great Plains and in 

 Texas, of which two also occur in the eastern United States. The 

 genus Dissosteira is widely spread over the United States, narrowly 

 entering Canada. One of its species is almost ubiquitous in the east- 

 ern United States, but west of the Rockies it chiefly occurs in the 

 Transition zone. A second species is basically a Great Plains form, 

 a third is largely Californian and Great Basin, and a fourth occurs 

 locally only in California. The genus is apparently of Sonoran origin, 

 and the same may be true of the related Scirtetica, which has one 

 locally distributed stock in coastal areas of the eastern and south- 

 eastern United States and in the Great Lakes sections of the 

 United States and southeastern Canada, while another stock is 

 isolated in the mountains of southern Arizona, with no representa- 

 tives known from the interv^ening sections of the territory the pres- 

 ent symposium is covering, or as yet from Mexico. The strange 

 little genus Microtes is an autochthon of the Californian coastal 

 mountains and adjacent valleys, with no very close relatives, and is 

 probably an old type. Lactista and Tomonotus are clearly Mexican 

 Sonoran entities rather narrowly intrusive in our border states. 



The genera Trepidulus, Shotwellia, and Ciholacris are relatively 

 arid land Sonoran types. The last is also coastal in southern Cali- 

 fornia. All three probably range into northern Mexico, and doubtless 

 all had their origin in that great area on both sides of the inter- 

 national lioundary which, even in its diversity of surface features, 

 has to a considerable degree had a similar faunistic history. The 

 genera Mestobregma and Metator are clearly of Sonoran origin ; each 

 extends northward over the Great Plains and the Great Basin, with 

 distinctive lines in each of these areas, indicating a considerable 

 period of time for divergence and development of differentiating 



