14 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.64 



Thorax of female not so extensively darkened as of male; lamellae much flattened, 

 broad at base, then rapidly narrowing and again gradually broadening out to the 

 rounded tip, where on the lower inner side they bear a cluster of black spines, 

 their hind margin ciliate with long hairs. (England) verticalis Collin. 



4. Palpi usually entirely yellow; third joint of antennae usually yellow. 



johnsoni Malloch, e. str. 

 Palpi and thii'd joint of antennae largely or wholly black. 



johnsoni, form nigripalpis Malloch. 



5. Legs, including coxae, entirely piceous black; thorax and abdomen black, the 



humeri yellow; face, cheeks, antennae, and mouthparts yellowish. (N.Mex.) 



nigra, new species. 



Legs, at least in part, pale, usually only the first or second joints of front tarsi 



black 6 



6. Normally three fronto-orbitals; hypopygium small, the valves short and rounded; 



vibrissae long and nearly straight, buccal hairs strong; thorax of female usually 



paler than of male. (Eur.; U. S.) {albimana Meigen) 7 



Normally two fronto-orbitals; hypopygium larger; vibrissae shorter and incurved, 

 buccal hairs fine; thorax of both sexes colored alike; antennae pale 8 



7. Face, cheeks, mouthparts, and antennae yellow; notum and pleurae reddish; legs 



largely yellow; average length 3.5 mm albimana, form pallidior Loew. 



Face, mouthparts, third joint of antennae, notum largely, pleurae, and most of 

 legs blackish; average length 4 mm albimana, form obscurior Loew. 



8. Hypopygial lamellae about twice as long as greatest breadth, the recurved apical 



portion half as wide as the basal part, haii's of lamellae short; face and palpi 



yellow; notum blackish. (Scotland) caledonica Collin. 



Lamellae shorter, broader and more flattened at end and not recurved at tip 9 



9. Palpi black, face yellowish, notum rufous, upper pleurae brown, posterior legs 



pale. (Eastern U.S.) americana Malloch. 



Palpi yellow, face somewhat darkened, thorax piceous, posterior legs extensively 

 darkened. (England) gentilis Collin. 



10. Postverticals absent; cloud of wing commencing at end of first vein; thorax 



brownish yellow, with front margin, two vittae, scutellum and upper pleurae 

 blackish; front tarsi and apices of front and hind tibiae infuscated. (Me.) 



orbitalis Malloch. 

 Postverticals present 11 



11. Mesonotum reddish, sometimes \'ittate posteriorly; pleurae mostly or entirely 



yellow; legs entirely yellowish 12 



Mesonotum and pleurae mostly black, the sides of mesonotum narrowly yellow; 

 legs partly dusky or dark 15 



12. Face of male black; one, two, or more pairs of strong porrect vibrissae; female 



with face pale and single normal vibrissa; mesonotum usually without dark 

 stripes, uppermost pleurae vittate; hypopygium large, globose, the valves 

 large, flat, trapezoidal, uncinate apically and glabrous. (N. Amer.) (mela- 



nostoma Loew) 13 



Face of both sexes not black; only one vibrissa 14 



13. Vibrissa single; usually three fronto-orbitals melanostoma Loew, s. str. 



Vibrissae of male plural; usually two fronto-orbitals. 



melanostoma, form dupllcata Malloch. 



14. Face reddish; notum with four blackish stripes; pleurae not vittate; antennae 



brownish. (Eur.) nubila Meigen. 



Face pale yellow; notum with two dark stripes; upper pleurae vittate; antennae 

 yellow, in female brownish at base of arista. (Eur.; Can.). .nificoUis Meigen. 



