iQog] Observations on a Gall Aphid 97 



lations except 4 or 5 small dusky spots forming a dorso-lateral longi- 

 tudinal row continuous with the thoracic spots, the last distinct spot 

 on about the 5th segment ; one indistinct spot just mesal to the cornicle, 

 often absent. Cornicles yellowish with apex dusky, the entire appen- 

 dage usually not dusky. Whole body lightly pulverulent. Other- 

 wise as in winged vivipara. 



Measurements — Length of body, 1.5-4 mm. (1.35-1.70), width, 

 .609 (.522-.696). Antennae .584 (.516-.705); III .20, IV, .077, V 

 .09, VI (scape) .077, filament .142. Cornicles, .114, cauda, .172. 



Ovipara. This form can be easily told with a hand-lens from the 

 wingless vivipara by the dusky incrassate hind tibiae with many 

 sensoria and the blackish vaginal plate. Detailed description as fol- 

 lows: Eyes black, rarely reddish black. Legs dusky except the yel- 

 lowish-brown base of femora and greater proximal portion of fore and 

 middle tibiae, hind tibiae dusky, proximal half swollen, 30-40 nearly 

 circular sensoria on both anterior and posterior aspects (Fig. 4) . Cor- 

 nicles dusky: Cauda pale yellowish distally, or entirely dusky; often 

 not constricted. Otherwise similar to the wingless vivipara. 



Measurements. Length of body, 1.45 mm. (1.24-1.70), width 

 .565 (.478-.652). Antennae .553 (.516-.671); III .129, IV .06, V 

 .0774, VI (scape) .077, filament, .122. Cornicles, .112, cauda, .146. 

 Wingless male. Head and antennae dusky to blackish. Antennae 

 (Fig. 17 j with average number of sensoria as follows (extremes in 

 parentheses): joint III, 14-15 (11-24); IV, 9-10 (7-14); V, 10-11 

 (10-14) ; VI, usual group at apex of scape, often with a single sensor- 

 ium near its middle. Eyes blackish red; ocelli conspicuous. 

 Beak extending just beyond mesocoxae. Pronotiim dusky, lateral 

 tubercle distinct, meso thoracic lobes brownish to dusky, traceable as 

 in Fig. 3; in several specimens they are reduced to irregular dusky 

 marks. Legs dusky to blackish. Abdomen dusky yellow, very varia- 

 able in the tint of yellow, dorsum with irregular, variable dusky marks, 

 usually resembling Fig. 3. Lateral tubercles relatively more pro- 

 nounced than in the females. Cornicles dusky. Cauda dusky, not 

 constricted (Fig. 19). Otherwise as in winged vivipara. 



Measurements. Length of bodv, 1 mm. (.957-1.04), w4dth, .481 

 (.430-.550). Antennae .89 (.72-1.02); III, .258; IV, .142; V, .142, 

 VI (scape) .094, filament, .215. Cornicles, .066; cauda, .113. 



Eggs, oval, shining black, .60 x .327 mm. Dissection of many 

 oviparae collected Oct. 9th, showed that each individual contained 

 from one to eight eggs. The number evidently depended on the size 

 as well as the age, since some large specimens were opened that 

 contained no eggs. The usual number was two to six. 



The common black aphid infesting the Chenopodiums, as stated 

 above, is entirely distinct from Aphis atriplicis L. For the sake of 

 comparison I have drawn the principal systematic differences which 

 may be summarized as follows: 



Winged vivipara — Antenna with many (fully 15-16) sensoria on 

 joint III; 4-5 on IV (Fig. 16). Basal half of costal vein of fore-wing 

 strongly bent anteriorly, bases of 1st and 2nd discoidals always com- 



