KEY TO SYRPHID^E. 



Face without orbital grooves; black, with more or 

 less metallic green or blue and with yellowish, reddish 

 or metallic cross-bands on abdomen. Wings not longer 

 than the abdomen: Pyroph&na. Wings longer than the 

 abdomen: Platychirus (Plate LXVIII; front legs of males 

 with tarsi and end of tibiae dilated) and Melanostoma 

 (these joints slender in both sexes). Common at flowers. 

 10. Abdomen much narrowed toward the base, distinctly 

 club-shaped or spatulate in outline. Hind femora slender: 

 Baccha; frequently hover near flowers and tips of branches, 

 especially of pine. Hind femora thickened: Spliegina 

 (third joint of antennas rounded) and Neoascia (this joint 

 not rounded). 



Abdomen oval or slender, not club-shaped or spatu- 

 late ii. 



n. Side-margins of thorax yellow 12. 



Side-margins of thorax not yellow. Abdomen 

 without several definite yellow cross-bands: several not 

 very common genera, including Leucozona (thickly pilose; 

 a broad yellow band at base of black abdomen). Abdo- 

 men with several definite, yellow cross-bands 13. 



12. A median, ashy line on thorax. Mesogramma (Plate 

 LXVIII). The larva? feed on aphids, although those of 

 polita are said to feed on corn-pollen. 



No median ashy line on thorax. Spli<zrophoria 

 (Plate LXVIII; face projecting below) and Xanthogramma 

 (face receding). 



13. Hind femora much thickened. Syritta. 



Hind femora slender. Third longitudinal vein with a 

 distinct bend into the first posterior cell: Didea. This 

 vein straight or only gently curved 14. 



14. Margin of mouth produced into a long snout. . .Rhin- 

 gia. 



Margin of mouth not produced. Syrphus (see 

 below). 



15. Arista plumose 16. 



Arista bare or merely pubescent 17. 



16. Antennae elongate, the third joint more than twice 

 as long as wide. Volucella (see below). 



Antennae short, the third joint not so proportionately 

 long. Sericomyia. 



255 



