272 J. A. G. REHN 



stocks. Trachyrhachts, which clearly has had a similar history, has 

 also extended the range of one of its species eastward, probably 

 Postglacially, to parts of the Appalachian uplift in the eastern 

 United States. The genus Rehnita is an additional Sonoran type, 

 probably derived from the same basic stock as Mestobregma. 



The genus Conozoa has more affinity to Trimerotropis, which has 

 already been mentioned, than to any other member of the sub- 

 family, and it may represent an offshoot from the same stock. If so, 

 its divergence was not recent. The genus occurs entirely within the 

 area of our coverage, only rarely east of the Continental Divide. 

 The chiefly Boreal and generally montane genus Circotettix may also 

 originally have been derived from the basic Trimerotropis stock. 

 Its distribution is often discontinuous, extending eastward across 

 southern Canada and the northern United States into Boreal areas 

 in eastern North America. Its species are among the few grasshoppers 

 that perform aerial stridulating dances. Another genus with the same 

 proclivities, that may be related in some degree to the Eurasian 

 genus Bryodema, is Aerochoreutes, which occurs in Upper Austral 

 and even Transition areas of the northern Great Plains, northern 

 Great Basin, and the Columbia-Snake River semi-arid hills. 



The extremely arid sections of the Lower Sonoran life zone are the 

 home of the genus Anconia, which also occurs some distance south- 

 ward into northern Mexico. It would appear to be endemic in the 

 territory where it now occurs. Its only known relative is Spaniacris, 

 which lives in limited, and intensely arid, sections of the same area 

 in southern California and extreme western Arizona. These two 

 genera clearly are old desert types, with no close relatives, markedly 

 specialized in a number of respects, and with distinctive habitat 

 preferences. The genera Xeracris and Coniana, smaller desert types 

 known only from the most arid sections of the Colorado, Yuma, and 

 Mohave Deserts, are similar to Spaniacris in distribution, but 

 are of different affinities. They are clearly authochthons without 

 any very close relatives, although further study on this matter is 

 required. 



The genus Heliastus is a Mexican and Central American type, 

 which reaches even to northern South America, but in our territory 

 is found only narrowly and locally in southern Arizona and coastal 

 Texas. This is clearly a Sonoran genus which has spread southward — 

 a less frequent pattern. A Sonoran type of higher levels, largely 



