1910] Key to the Genera of Aphidinae 315 



In working up synonomy from a standpoint of literature 

 there seems to be a great difference of opinion. However since 

 an International Code has been established there seems to be 

 but one correct plan and if followed in all cases the troubles 

 of the systematist must soon disappear. One of the rules of 

 the code in substance states that if a number of species belonging 

 to distinct different genera are arranged under a certain genus 

 without a type being set by the maker of the genus then the 

 type may be any one of the original species. If all the species 

 but one are removed without a type being set then the last 

 species is the type. 



In 1758 Linnaeus formed the genus Aphis without setting 

 a type. In this genus he included a large number of species 

 which have been placed in various different genera, and Aphis 

 sambiici is now generally taken as the type of the original 

 genus. In 1801 Lamarck* set Aphis ulmi as the type and Aphis 

 sambiici was not set until a year later by Latreille.f 



Aphis ulmi L. is the species generally known as Tetraneura 

 ulmi DeGeer. This species was first described and figured by 

 Reaumer previous to the 10th Edition of Linnaeus. Linnaeus 

 and DeGeer give the same citation, so the species does not 

 belong to DeGeer. Schizoneura ulmi Linn, is the species 

 designated by himself as Chermes ulmi. 



The author of this paper will not at this time .attempt to 

 say that any of the above names should be changed, but it 

 seems that a decision of some kind as to the disposal of the 

 above should be made. 



In making the ke^^ type species of each genera were used 

 and more or less detailed descriptions taken of the external 

 characters. In several instances wide variations were noticed 

 among the species included in certain genera and some were 

 separated to form new genera. 



In studying closely related genera the development of exter- 

 nal characters may be placed in five divisions. 1. The antennae 

 and spur. 2. The antennal tubercles. 3. The development 

 of the nectaries. 4. The development of the cauda. 5. The 

 development of the wing venation. In a group of insects as 

 pliable as the present one, any one or two of these characters 



■■' Systeme des animaux sans vertebres, ou Tab. gen. classes, des orders et generes aniraaux 

 A. Paris, an. IX, p. 300. 1801. 



t Histore Naturelle Gen. et par. Des Crus. et Ins. Tome III, p. 264. 1S02. ' 



