DERMAPTERA AND ORTHOPTERA 267 



continuous distribution of the genus in our continent reveals the 

 part the ice-sheets had in separating the eastern form of this forest 

 land genus from that now occurring in the Oregon Cascades. A 

 largely parallel case of discontinuous distribution of this type, 

 with apparently the same origin, is that of the flightless wood- 

 boring cockroach Cryptocercus. 



It seems that all the other numerous lines of the Melanoplini in 

 western North America have developed within our territory, and 

 that a single species of the genus Melanoplus has crossed into the 

 Old World. The genus Melanoplus developed a considerable number 

 of specific lines in North America, with a very marked center of 

 speciation in the southern Appalachians and the adjacent lowlands, 

 while other lines, clearly representing evolutionary phyla, have 

 centered in the grasslands of the Great Plains, the Transition and 

 Canadian areas of the Rockies, the Great Basin region and its 

 various mountain areas, the Lower Sonoran Deserts of the south- 

 western United States and northern Mexico, the Sierra Nevadas, 

 and the coastal ranges of California and Oregon. In each of these 

 areas one or more definite lines of development of the genus will be 

 found. Some lines reach as high in their distribution as Hudsonian or 

 even Arctic-Alpine conditions, often with some species quite local- 

 ized. To the southward the genus Melanoplus enters Mexico, 

 where there is a considerable number of more broadly ranging and 

 endemic species, but the genus does not extend south of that country. 

 The Melanoplini of Mexico are rich in species and work now under 

 way will shortly give us a clearer picture of the richness of that 

 fauna, which with the western part of North America has been a 

 major site in the evolution of the Melanoplini. 



Of the other genera of the Melanoplini in western North America, 

 the Campestran Great Plains apparently produced at least four, 

 Campylacantha, Argiacris, Phoetaliotes, and Hypochlora. Phoetaliotes 

 is more widely distributed in grassland areas (formerly of greater 

 extent, perhaps in the Pliocene, a grassland optimum), and relict 

 populations remain in sections of southern Arizona and certain 

 other areas. The genus Dactylolum, now widely distributed in 

 Sonoran situations in western North America, is doubtless of Mexi- 

 can origin, as there the genus has developed a broader specific 

 diversity than it has north of the Mexican line, although in the 

 latter territory its range is much more extensive. The same is prob- 



