208 



piiti !<iiiitlii. (Jpati'ijuta nutius, and SplHrrupthalnui hannoiiia, are 

 probably true eastern species, the Pentafonia and Opa f r inns giv- 

 ing wa,y in the arid region to otlier dominant species, though the 

 former has lately been found to occur in Colorado. Sixty-four 

 percent [il species ) are western, most of them definitely so, 

 and over 42 percent (31 species) have not even been recorded 

 from any adjacent state.* Four of the Heferopferti, however, 

 have each been listed once at the Atlantic coast, three of them 

 in Florida; and there is no apparent reason, except that of 

 greater distance, why the eastern sand areas should not acquire 

 species of the arid West in the same way as is assumed for 

 Illinois. 



Several species of the Illinois valley sand region — Campy- 

 l(ir<infli(i o/ii-(ii-r<(, llisperotettix pratensis, H. speciosiis, and Srhis- 

 forcrni (ihitacra — are not rare on the dry soils of the Illinoian 

 glaciation in southern Illinois, and last season (1905) the ('(uh- 

 IHjIdcaiitlni was actually abundant there, in both the western and 

 the eastern portions, on the common Ainbrosia of that district, 

 ^-1. hiihnfiifd. These species probably do not exist on the black 

 soil of central Illinois. 



The presence in the Illinois valley sand region, as reported 

 by Ml-, (xleason, of several characteristic plants of the tlreat 

 Plains flora, would doubtless attract their own insect fauna, 

 and thus may directly account for the presence of a number of 

 insect species. 



Sand as a Factor of Animal Environment. 



It has already been stated herein that the presence of sand 

 in the soil has little effect on the fauna — and this is true of the 

 flora also — until the sand reaches a stage of purity which per- 

 mits it to dry readily and to drift gradually with the wind, in 

 which condition it is called blow-sand; and that except for 

 brief periods at times of rain or melting snow, this is dry and 

 loose at the surface, but always moist a short distance below. 



In what way these blow-sand conditions have so marked 



* A comparison of these data with those independently obtained from the flora by 

 Mr. Gleason, on p. 191, second paragraph, will be of especial interest. 



