198 The Rocky Mountain Locust. 



spretus seen. The several specimens obtained from Ford 

 county were all Atlanis / a single specimen received from 

 Mr. H. J. Dunlap, of Champaign, was a male femur - 

 rubrum ; while specimens taken by Prof. Burrill, of the 

 Industrial University, at the same place, as well as others 

 from Norwood, Mercer county, sent to Prof. Thomas, were 

 differentialis. The parties capturing these specimens are 

 not apt to fall into error, and are all positive that the 

 specimens submitted were from the flying bevies. 



From these facts it results that two species, viz., femur - 

 rubrum and differentialis, though normally having no 

 migratory habit, and, as I believe, incapable of extended 

 flights, can actually assist in such flights. That the bulk 

 of these Illinois swarms was composed, however, of At- 

 lanis, scarcely admits of a doubt. The other two, less 

 able to sustain lengthened flight, would naturally be most 

 near the ground and most often captured ; while Atlanis, 

 which we now know to occur in this part of the country 

 as well as East, and to often display the migratory habit, 

 would fly higher. 



There are two facts which it will be well to bear in mind 

 in this connection, as explaining the above phenomena. 

 The first is, that Atlanis was very common in Missouri, 

 even in fields where it had never been noticed before. It 

 prevailed to such an extent in Illinois, that around Carbon- 

 dale Prof. Thomas could not find a single specimen of the 

 typical femur-rubrum, and there was not a single specimen 

 of it among a number which he caused to be collected for 

 me. 



The second fact is, that differentialis was also unusually 

 abundant. A letter from Mr. M. Brinkerhoff, of Onarga, 

 Illinois, dated October 18, 1875, and accompanied by speci- 

 mens, describes them as in great numbers there, filling the 



