266 J. A. G. REHN 



Argentina and Chile, thus well over one hundred degrees of latitude, 

 and occupy stations ranging from extremely arid ones below sea- 

 level to others as high as Arctic-Alpine in North America and the 

 Paramo in South America. Three major centers of evolution of the 

 Melanoplini in the Americas have clearly been indicated: (1) North 

 America south to the Isthmus of Tehuantepec; (2) the Venezuelan 

 Andes and adjacent, chiefly montane, areas in northern and eastern 

 Columbia; and (3) South America from approximately 15° south 

 latitude southward. Few genera of the tribe occur over the inter- 

 vening areas. In the Old World the tribe is much more circum- 

 scribed, for it is absent from the Ethiopian region, from most of the 

 Oriental region and from all the Australasian region. In Eurasia 

 twenty-seven genera occur, three of which are also in the Nearctic. 

 In the Nearctic and Neotropical combined, we find 59 genera, 

 including the three occurring also in Eurasia. In the New World 

 forty genera are known north of the Isthmus of Tehuantepec, the 

 majority only north of the Mexican boundary. 



Within the northern United States we find one line of the Melano- 

 plini, the genus Podisma, which clearly is of Old World relationship, 

 for it has numerous species in Eurasia and only one in North 

 America, P. hesperus, in the Cascades of Oregon, the nearest relative 

 of which appears to be a species of northern Japan, P. sapporensis. 

 It is probable that the ancestral stock of this species reached our 

 continent in the Pleistocene, perhaps Interglacially, or even earlier. 

 Another line in North America, comprising the genera Dendro- 

 tettix and Appalachia, also represents an older invasion of the same 

 stock. (This line is not now present in western North America; 

 its two generic members occur, so far known discontinuously, in 

 the eastern and central parts of the United States.) These 

 two genera clearly developed within our territory. A third line, 

 including the single flightless genus Zubovskya, which occurs dis- 

 continuously in eastern forested areas of North America and in the 

 Cascades of Oregon, is also represented in a limited section of 

 eastern Asia by several distinct species. Whether Zubovskya is an 

 Asiatic genus that has traveled to North America and spread 

 broadly there, or is of North American origin and has narrowly 

 entered the Old World, remains to be determined. Clearly, however, 

 it has been present in North America since before the Glacial 

 period, as there can be little question but that the present dis- 



