203 



It now remains to compare the Illinois sand regions with 

 the sand-hills of western Nebraska. Unfortunately, I have not 

 a definite list for the latter locality. The general Nebraska 

 list shows that all the Acridiidce of the Illinois valley sand dis- 

 trict are found in that state with the exception of the southern 

 Melanoplus impudicus and Eritettix virgatus, and about half of 

 them in the western part, but that a number of additional sand 

 species appear in that part of the state. As to the intervening- 

 states, Missouri and Iowa, we have only an old list of about 41 

 Acridiidce for Iowa (Osborn '92), in which 19 of the 30 Illinois- 

 Nebraska sand species are lacking. Further knowledge of the 

 Orthoptera of these states is very desirable. The occurrence of 

 Melanoplus impudicus and Eritettix ririjutiis in our district gives 

 force to Morse's suggestion ('99, p. 316) that a southern species 

 of sandy or light-soil situations may have a more elastic north- 

 ern limit than one of damp and heavy soil. 



So far, therefore, as the Orthoptera are concerned, the evi- 

 dence indicates that the fauna of the Illinois valley sand region 

 has much stronger western affinities than that of the south end 

 of Lake Michigan; that it is quite closely allied with that of 

 the eastern part of Nebraska, which is within the Carolinian 

 life zone, but can hardly be called Sonoran; and that it is of 

 western derivation, and migrated eastward, probably by way 

 of the glacial outwash in Iowa, at an early period. 



Our entire list of western Illinois sand insects numbers 596 

 species. From these has been selected the following list of 85 

 species which seem to be not generally distributed east of the 

 Rocky Mountains. These, of course, are the significant ones in a 

 study of distribution. They fall into six classes with regard to 

 the extent and direction of their range outside of western Illi- 

 nois, the scattering, the local, the northern, the southern, the 

 eastern, and the western species, and are correspondingly listed 

 in this connection as being of especial interest, a summary state- 

 ment of their previously known distribution being appended to 

 each species. The last two groups are divided into near and 

 distant species, the distinction being based on their presence 

 or absence, so far as known, in states adjoining Illinois. 



