6Q BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



SYRPHUS. 



Syrphus F'jibricius, Syst. Entom., I77r>. 



Scteva FaltiiciuH, Sy.st. Autl., 1805. 



Lasiophticiis Rondani, Dipt. ItaL, Prodr., i, 51, 1856. 



AncycloHijrphus Bigot, Soc. Eut. Fr., 1882, Bull, biiueus., No. 6, 78. 



Iscluirosyrphus Bigot, Soc. Ent. Fr., 1882, Bull, bimeus., No. 6, 78. 



Medium to large-sized species, tbiuly pilose, black, or metallic green 

 or blue, the abdomen with yellow bands or spots. Head hemispherical, 

 as broad or a little broader than the thorax. Antennai shorter than 

 the head, the third joint oval, as long or scarcely longer than the first 

 two together; arista basal, bare. Face perpendicular, produced but 

 little below the eyes, broad, either wholly yellow or with a black median 

 stripe, often with black cheeks, never* wholly black; tubercle obtuse, 

 scarcely at all concave above it in profile, but below always receding. 

 Eyes bare or pubescent, contiguous in the male. Thorax large, moder- 

 ately convex above, never with distinct yellow lateral stripes. Scutel- 

 lum more or less translucent, yellow, or yellowish and bluish or green- 

 ish. Abdomen oval, broader than the thorax, sometimes with nearly 

 parallel sides and scarcely wider than the thorax, more than twice as 

 long. Legs slender. Third longitudinal vein of the wing nearly straight 

 or gently curved ; anterior cross- vein near the base of discal cell; an- 

 terior outer angle of the first posterior cell always acute; marginal cell 

 broadly open. 



The present genus is one of the most difficult in the family to study. 

 Many of the species are so closely allied that only a large amount of 

 material will determine their limits. Thanks to the careful study which 

 they have received in this country from Baron Osten Sackeu, the labor 

 has been much lessened. Still, much remains to be done by local stu- 

 dents who shall make large collections and study them thoroughly 

 while they are in a fresh or at least uninjured condition. All but two 

 or three of the species of our fauna now known have been examined by 

 me. Still, I have thought best to reproduce the larger part of Baron 

 Osten Sacken's descriptions, with my own notes or additions appended. 



TABLE OF SPECIES. 



1. — Three principal yellow bands of abdomen interrupted 2 



Three principal bauds entire 24 



First cross band interrupted ; the others entire 12 



2. — Eyes pubescent or pilose 3 



Eyes bare 9 



3. — Abdominal spots crescentric or arcuate, sometimes dissolved into spots . . 4 

 Abdominal spots straight and transverse 7 



4. — The abdominal spots do not come in contact with the lateral margin ... 5 



The abdominal spots reach quite to tbe margin, or, if not, the spots are but little 



oblique ; emargiuate in front, often broken up into smaller spots ... 6 



* Syrphua simplex from the West Indies is an exception. 



