A SYNOPSIS OF THE APHIDIDAE 141 



38. Genus Trifidaphis Del Guercio 



Del Guercio, Eiv. di patal. veg., vol. 3, p. 20, 1909. Type Pemphigus radi- 

 cicola Essig. 



163. Trifidaphis radicicola Essig 



Essig, Pom. Jour. Ent., vol. 1, p. 8, 1909. Pemphigus (orig. desc.). 

 Baker, Pom. Jour. Ent., vol. 1, p. 74, 1909. (Translation of Del Guer- 

 cio 's description of the genus.) 

 Essig, Pom. Jour. Ent., vol. 2, p. 283, 1910 (list). 

 Essig, Pom. Jour. Ent., vol. 4, p. 699, 1912 (list). 



Eecords. Amaranthus retroflexus, Solanum douglasii; Claremont, Santa Paula 

 (Essig). 



Essig described this species from specimens taken on the roots of 

 Amaranthus retroflexus and Solanum douglasii in Santa Paula and 

 Claremont. Later Del Guercio described a new genus for this species 

 based on the venation and the antennae. It seems that the type speci- 

 men of this species had but five-jointed antennae and so of course 

 it could not belong to the genus Pemphigus. On an examination of 

 eight specimens, including the type specimen and seven cotypes, the 

 author finds that the number of joints in the antennae are variable. 

 The type specimens had both antennae with but five joints. Six 

 antennae had but five joints, six had six distinct joints, and four had 

 five joints in which the division into six could be made out. This 

 divison was in the third joint at about one-third the distance from the 

 apex. Consequently one could say that this species was typically five- 

 jointed, but with some specimens with the third joint divided into two, 

 or it could be said that it was typically six-jointed, but in some speci- 

 mens a reducton occurred through the joining of the third and fourth 

 segments. As but a few specimens were examined the author is not 

 willing to state which is the more common, hence leaves this as a valid 

 genus, although he is of the opinion that this really belongs to the 

 genus Prociphilus Koch. 



39. Genus Pemphigus Hartig 



Hartig, Jahresb. u. d. Fortschr. d. Forstwiss. u. forstliche Naturk., vol. 1, 

 p. 645, 1837. Type Aphis bursarius Linn. 



This genus is represented in California by three well known 

 species, 26 P. betae Doane, P. populi-caulis Fitch, and P. populi-trans- 



26 There has been taken several times a species forming elongate leaf galls on 

 Populus fremontii, both in the San Francisco Bay region by Davidson and in San 

 Diego County by the author, that structurally seems to be identical with P. populi- 

 caulis Fitch, but its gall is quite distinct, being more or less similar to that of 

 P. betae Doane. Further study may reveal the identity of this form. 



