274 BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



habits? Certainly some of the pilose-eyed forms are the less active of 

 the family. 



The scutellum presents few structural characters. In Chri/sof/aster, 

 Pipiza, and Chilosia its thinness may be of generic value. In Chalcomyia 

 and Solenaspis O. S., its size and width are ])eculiar. Strangely, both 

 these genera, though widely separated, must present a singular re- 

 semblance. In Mkrodon the sluipe and spines are characteristic. In 

 all the other genera the scutellum is usually hemispherically convex, 

 and but little variable. 



In the wing numerous characters appear, in nearly all parts. The 

 shape and termination of the second longitudinal vein, the curvature of 

 the third, the position and shape of the cross-veins, the shape of the 

 sixth longitudinal vein in the Eristaloid genera, and the termination in 

 the Milesoid forms, all form the basis of our classification. In the Syr- 

 ])hoid neuration the veins are usually weak, the wings light and thin; 

 such are mostly adapted to terial flight and soaring. In the species 

 with inflected veins and more or less elongated antenmie we find the 

 venation usually stouter and the wing heavier, the posterior part un- 

 supported; such species are more sluggish and less active in flight. 

 Finally, speed and strength are united in the Eristalim, Xi/lotini, and 

 Milesini. The wings here have moderately strong veins, with the outer 

 and posterior portions stronger. iSyritta differs most in the position of 

 the cross- vein, and its habits are more nearly like the Syrphoid species. 



In the abdomen the shape, flattening and elongation ofler the greatest 

 diversity, and aflbrd both generic and specific characters, but the former 

 are not easily limited. Some of the smaller, more slender, species are 

 noted for their quick flight, as AUograpta, Splmroplioria, Mesograpta, 

 Syritta, otc. Those with a short, thick-set abdomen will usually be 

 found resting upon flowers, and never soaring; those with an oval de- 

 l>ressed abdomen, as in Syrjyhus, are the most delicate in their structure, 

 and at the same time very quick and active in flight. The extremes of 

 shape are found in Baccha, where it is sometimes extremely slender, or 

 clavate; in Syrphus, where it is most depressed ; in the Mallofa group, 

 and VoluceUuii, with the greatest convexity and shortness, and in Seno- 

 gaster, with the remarkable contraction of the median segments. The 

 hypopygium is usually inconspicuous, especially in the Syrphini, but in 

 species of Splicer oplioria^ and many of the Xylotini and EristaUni, it is 

 enlarged and conspicuous. In EupeoiUs the peculiar development of 

 the two slender processes is remarkable. The structure of Kausigaster 

 abdomen is the most peculiar; here the fourth segment is extraordinarily 

 developed and arched, wholly excluding from sight the following seg- 

 ments and inclosing the terminal organs in a deep ventral cavity. 



The legs, outside of secondary sexual characters, which will be spoken 

 of further on, do not^ offer a very great deal of structural differences. 

 They find their greatest slenderness in the SyrpMni, Melanostomini, 

 and here rarely have any thickened parts, and then usually in the feet. 

 In the EHstalini and Xylotini they are usually stouter, and very often 



