276 J. A. G. REHN 



found off of it. It clearly developed in the area of our Mexican 

 border. One species occurs on the Pacific side of the more elevated 

 Continental Divide, the other on the Atlantic side; both are known 

 to extend southward, with their host plant, into Mexico. 



The genera Esselenia and Eupnigodes are Californian endemics. 

 The former is found only in the central section of the Coast Range 

 region, and has no known close relatives. On the other hand 

 Eupnigodes, which is more broadly distributed over the San Joaquin 

 Valley and the lower western slopes of the Sierra Nevada, is rela- 

 tively close to Ageneotettix, which is a quite widely dispersed 

 Sonoran genus, and clearly the stock from which Eupnigodes 

 developed in relatively recent times. Another apparent development 

 from the Ageneotettix line is Zapata, of which a few species are quite 

 locally distributed in southern Arizona, western Texas, and northern 

 Mexico. A genus almost exclusively Texan Sonoran is Mesochloa, 

 which is clearly derived from Eritettix. The latter, probably also of 

 Sonoran origin, is broadly distributed northward over the Great 

 Plains and westward along sections of the Mexican borderland. 

 One species of Eritettix has deeply penetrated into the central and 

 eastern United States, where it occurs from New England and 

 Nebraska southward. A related, and apparently derived, endemic 

 genus, Macneillia, is restricted to peninsular Florida. 



The genus Dichromorpha is probably of Sonoran origin, but 

 ranges northward over most of the central and eastern United 

 States, with several species in Mexico, while to the southward, after 

 a gap of some thousands of miles, it reappears in areas of Paraguay 

 and northern Argentina. It is a grassland type and its distribution, 

 like that of the mantid Briinneria, probably reflects the much 

 broader extent of grasslands in the Pliocene, and their later restric- 

 tion by the moister and colder Pleistocene, with its greater develop- 

 ment of forests. 



A dominant genus of largely arid or semi-arid sections of the 

 whole Sonoran region, also occasionally entering the Transition Life 

 Zone, is Psoloessa, one line of which extends as far northward in 

 the Upper Sonoran as the Okanagan Lake country of extreme 

 southern British Columbia, and also to sections of the Great Plains 

 of southern Alberta, Saskatchewan, and Manitoba. Southward one 

 line of Psoloessa reaches as far as the Mexican states of San Luis 

 Potosi, Guadalajara, and Mexico. Psoloessa is probably one of the 



