DERMAPTERA AND ORTHOPTERA 273 



Upper Sonoran, is the genus Heliaula, which extends northward 

 over the Great Plains as far as eastern Colorado, but does not go 

 far west of the Continental Divide. 



(4) Subfamily Acridinae. The Acridinae, or slant-faced grass- 

 hoppers, which in our section of the world are in considerable part 

 grassland forms, are very well represented in our fauna, and the 

 greater part of the forty or more genera reviewed clearly have 

 developed within North America west of the Mississippi. Two 

 genera, Chorthippus and Stethophyma, are certainly relatively 

 recent Palearctic intrusives in North America, the former so recent 

 that the single species we have is also widely distributed in Eurasia. 

 Chorthippus has a large number of Old World species, and it is possi- 

 ble we received C. longicornis in an Interglacial period. Our three 

 species of Stethophyma are endemic, two with preferences for Boreal 

 or sub-boreal conditions, the other of infrequent and very local 

 occurrence over a broad section of eastern North America. The 

 species of sub-boreal preferences occurs in widely separated parts of 

 western North America, but has been taken at only a few localities. 

 Presumably Stethophyma reached North America from Eurasia 

 prior to the advent of Chorthippus, as its species are well differenti- 

 ated from Old World forms. 



One set of three genera, representing the group Chrysochraontes, 

 has presumably also been derived from Eurasia, probably through a 

 succession of waves. The earliest invasion was probably that of 

 an ancestral stock of the genus Chloealtis, which today is chiefly an 

 inhabitant of the more northern parts of eastern North America, 

 although it narrowly reaches our included territory in eastern 

 Colorado. Apparently a second intrusive line of the same group is 

 represented by Chrysochraon, which occurs broadly in the Pale- 

 arctic, and of which we have a single endemic species in Cordilleran 

 montane localities. A third line of the same group comprises the 

 equally endemic genus Napaia of Coastal Range mountains of 

 southern Oregon and California, as well as the San Gabriel Range in 

 the latter state. The members of the Chrysochraontes are peculiar 

 in that they usually oviposit in dead wood, an unusual situation for 

 acridids. Another genus of Palearctic relationship is Aeropedellus 

 a Cordilleran and high Great Plains genus, which clearly has been 

 derived from the same stock as a number of Palearctic genera 

 related to, and including, Gomphocerus and Aeropus. A distant 



