the generic name of these insects, no typographical error being evi- 

 dent. Four common names for the members of this group are known 

 to the writer, viz.: Aleyrodes, white fly, mealy wing and snowy fly, 

 the latter name apparently being in use only in England. The com- 

 mon name, Aleyrodes, derived directly from the name of the genus, 

 will be used hereafter in this paper in preference to the others. 



The bibliography of each species is numbered, and whenever I 

 have had occasion to mention any of those writings I have referred 

 to them by their number only. Other references are found in the 

 foot notes. 



This paper represents a little more than half of a thesis pre- 

 sented to the faculty of the Massachusetts Agricultural College in 

 June, 1903, for the degree of Doctor of Philosophy. I wish to ac- 

 knowledge here my obligations to Professors C. H. and H. T. Fer- 

 nald, under whose able supervision and direction I have pursued my 

 graduate studies in the Entomological Laboratory of the college dur- 

 ing the past three years. 



