1909J Observations on a Gall Aphid 95 



hand. Since every gradation exists in the degree of the bulge in 

 the cornicles of the genus Siphocoryne from forms like 5. salicis 

 Monell down to 5. avenae Fab. which is scarcely incrassate at 

 all and that on the inner side, I cannot recognize either Sipho- 

 coryne or Hayhurstia as valid genera, but w^ould rank them both 

 as subgenera of the genus Aphis. I therefore consider the follow- 

 ing grouping of those species of Aphis and Siphocoryne with a dis- 

 tinct Cauda worth testing. This is modified from Del Guercio's 

 revision oi Aphis (Redia, Firenze Vol. 4, Fasc. i, 1906, pp. 191-2.) 



1. Cornicles longer than cauda. 



a. Cornicles cylindrical or gradually attenuated from base. 



Subgentis Aphis L. (Fig. 13.) 

 Aphis sambuci L. 



b. Cornicles clavale or incrassate at or beyond base. 



Subgenus Siphocoryne Pass. (Fig. 11.) 

 Aphis nymphaeae L. 



2. Cornicles ecjual to caurla or shorter. 



a. Cornicles cylindrical or gradually attenuated from base. 



1. Cornicles shorter than style. 



Subgenus Uraphis Del G. 



Aphis genistae Koch. 



2. Cornicles equal ti_) style. 



Subgentis Microsiphon Del G. 



Aphis tarmentillae Pass. 



b. Cornicles incrassate. 



N. Subgenus Hayhurstia Del G. (Fig. 12.) 

 Aphis atriplicis L. 



Aphis atriplicis L. seems never to have been carefully 

 described. In the following descriptions all colors were taken 

 from the living insects with a high power hand lens, daylight, 

 and many individuals were compared. All measurements of the 

 bodies are from formalin material and are therefore reliable, while 

 those of the appendages are from balsam mounts; the lengths 

 given are averages of six or more representative specimens. Fig- 

 ures in parentheses are extremes. Del Guercio states that the 

 colors especially of the wingless viviparae in Italy vary greatly 

 according to the host and other conditions so that "now greenish- 

 yellow forms preponderate, and now those of a 3^ellowish-green, 

 green, olive green and olive color, sometimes, indeed, so deep in 

 tint as to seem brownish with greenish reflections." 



The lobes of the mesothorax are figured for clearness, because 

 they are not generally mentioned individually by authors (Fig. 2). 

 Their color is here treated as of specific \'alue, but their form is 

 not described for this purpose. Their structural details present 

 marked constant differences, which have apparently never been 

 •carefully studied. They are already called the prcscutum, scu- 



