SANBORN : KANSAS APHIDID.E. 45 



larly the wing venation was not clear to him. On account of 

 abundance of material, I can say that his statements were all 

 true, except the third discoidal of the cubitus in his specimen 

 must have been slightly abnormal. I think that the elimina- 

 tion of one joint in the antenucp is brought about by the non- 

 division of the third and fourth, because in all aphids that I 

 have examined the winged form has a constant distal sensorium 

 on the fifth segment. In this form this is present on the fourth, 

 which, together with the arrangement of the sensoria on the 

 distal end of the fifth, which corresponds to the normal arrange- 

 ment of the sixth segment in the genus Apliu, furnishes proof 

 that the fourth and fifth joints of this form correspond to the 

 fifth and sixth in Aphis. Furthermore, I have an example of 

 the gradual elimination of one joint by the coalition of the third 

 and fourth. It is shown in plate XXII, figure 100, and de- 

 scribed as a transitional form. 



Drepanosiphum acerifolii Thomas. Plate XX, fig. 94. 



Head brownish yellow. Antennse paler than the head, except 

 the distal end of the third, both ends of the fourth, fifth, sixth, 

 and the base of the seventh, which are all black ; all slightly 

 hirsute; length of joints: I, 0.21 mm.; II, 0.05 mm.; Ill, 

 0.86 mm. ; IV, 0.59 mm. ; V, 0.55 mm. ; VI, 0.13 mm. ; VII, 

 0.90 mm. ; total length, about 3.17 mm. (These measurements 

 are not constant.) Sensoria circular; of the third, eight to 

 eleven, somewhat large, raised and in a single row, mostly on 

 the basal half of the segment. The usual large sensoria present 

 near th-e distal end of the fifth joint. Three large sensoria in a 

 longitudinal row near the distal end of the sixth joint. Eyes 

 red ; ocular tubercles present. Ocelli prominent, with a dark 

 border. Beak dark, 0,36 mm. long, and extending nearly to 

 the mesocoxse, 



Prothorax as wide as the head, pale black. Thorax brown- 

 ish yellow, sclerites sometimes with dark longitudinal centers. 

 Wings hyaline in places, venation frail, greenish yellow ; stigma 

 somewhat mottled, ranging from a clear color to a dark brown ; 

 in length, 0.59 mm., and breadth, 0.21 mm. All the veins 

 have a smoky border as shown in the illustration. Total wing 

 expansion, 4.70 mm. Legs pilose, pale brown, and small in 

 proportion to the body. 



