278 J. A. G. REHN 



to the Dakotas and western Iowa. A single very distinctive species 

 is isolated in the extreme southeastern United States. The greatest 

 specific diversity of Arethaea is in southwestern Texas and adjacent 

 Mexico, and only one species reaches westward to southern Cali- 

 fornia and southern Nevada. Another genus with a similar, and 

 clearly Sonoran, pattern of development and distribution is 

 Dichopetala, a thamnophilous flightless genus of nearly a score of 

 species, which range from Oklahoma, Texas, New Mexico, southern 

 Arizona, and southern California southward to the Rio Balsas 

 Valley and northern Vera Cruz, Mexico, with several species simi- 

 larly referred generically from Peru and Ecuador. However, its 

 greatest specific development is in southern Texas and the north 

 and central parts of the Mexican tableland and its bordering 

 eastern Cordillera. It is possible that the South American species 

 may require generic separation or that they represent a southward 

 extension of the genus across the "Panama fault," rather than the 

 more usually postulated one of a reverse movement. However, the 

 maximum diversity of Dichopetala is clearly in the Sonoran region, 

 very largely east of the Continental Divide. 



The genus Scudderia, which apparently developed from a Neo- 

 tropical center, includes a certain number of species limited to 

 Central America, and others intrusive into the western United 

 States from Mexico. However, a secondary evolutionary center 

 most certainly developed in the southeastern United States. From 

 that area, apparently some of the most distinctive members of the 

 genus extended. Several broadened their range into the western 

 United States, reaching the Pacific Coast, and also into southern 

 Canada. The genus Amblycorypha, which probably came from a 

 Neotropical ancestral stock, developed an evolutionary center in the 

 eastern and southeastern United States. Four of its five lines center 

 there, whereas only one is definitely Sonoran. The Sonoran line ex- 

 tends narrowly along the Mexican border area from western Texas 

 and Coahuila to southern Arizona. The broad north to south range of 

 Amblycorypha in western North America reaches from southern 

 Manitoba and Wyoming to Zacatecas, Mexico. 



The subfamily Pseudophyllinae, which is a greatly diversified 

 and remarkably developed, almost entirely pantropical, assemblage 

 is represented in North America by a single tribe, the Pterophyllini, 

 which may be called the "true katydids." This tribe is a Neogaeic 



