208 



pus smithi, Opatrinus notus, and Sphceropthalma harmonia, are 

 probably true eastern species, the Pentatoma and Opatrinus giv- 

 ing way in the arid region to other dominant species, though the 

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

 percent (47 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 Heteroptera, 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- 

 lacantha olivacea, Hesperotettix pratensis, II. speciosus, and Schis- 

 tocerca alutacea — are not rare on the dry soils of the Illinoian 

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

 pylacantha was actually abundant there, in both the western and 

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

 A. bidentata. These species probably do not exist on the black 

 soil of central Illinois. 



The presence in the Illinois valley sand region, as reported 

 by Mr. (Ileason, of several characteristic plants of the Great 

 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. 



