SYNOPSIS OF NORTH AMJIRICAN SYRPHID^E. 203 



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$ ,9 . Length, 13 to W""°. Eyes bare, contiguous for a short dis- 

 tance below the ocelli in the male. Front in female narrowed above, 

 black, shining, except on the sides below the ocelli, where it is narrowly 

 but thickly dusted, like the face; pile black, intermixed with yellowish 

 across the middle and at the vertex. In the male the frontal triangle 

 is thickly dusted like the face, except just above the base of the an- 

 tenna? ; the pile is usually black, sometimes almost wholly yellowish. 

 Face deeply concave below the antennsB to tip of tubercle, produced 

 moderately downward, thickly covered on the sides with grayish or 

 whitish pollen, leaving a broad median stripe and cheeks shining black. 

 Antennte brownish-black, the third joint somewhat reddish ; arista 

 reddish. Posterior orbits thickly dusted with whitish. Dorsum of 

 thorax in its ground color moderately shining on the disk, pollinose in 

 front, the color concealed beneath thick, furry, light-yellow pile. Scu- 

 tellum light yellow, with similar colored pile; pile of pleurae thicker and 

 a little lighter colored. Abdomen short, convex, obtusely conical, deep 

 shining black, with short, erect, black pile, longer towards the tip ; the 

 first segment is grayish pollinose, and the pile slightly intermixed with 

 whitish; venter black, the basal segments more or less pale. Legs 

 deep black, with black pile, the tarsi dark reddish, slightly or not all 

 so, however, on the hind pair ; posterior femora very much thickened ; 

 in the male extraordinarily so, and arcuated ; posterior tibiae com- 

 pressed, especially in the male. Wings hyaline, sometimes with a dis- 

 tinct brown spot near the furcation of the second and third veins and 

 the tip of the auxiliary vein. 



Form cimbiciformis. Hind tibiae in male moderately compressed, 

 wholly without a spur in the middle ; usually smaller specimens. 



Form Bautias. Hind tibiae in the male extraordinarily compressed, 

 and with a stout angular projection in the middle, which, when the 

 tibia is flexed, lies on the outer side of the femur ; usually larger speci- 

 mens. 



A very singular species, which is apparently dimorphic in the male. 

 Of the form without the spur I have two males taken in company with 

 two other males of the spurred form, June 20, near New Haven, about 

 the blossoms of Coryms paniculata. They are smaller than the smallest 

 of all my spurred specimens, but otherwise I can see no differences 

 whatever. With these four males just mentioned I captured four fe- 

 males, all of which were larger than the unspurred males. A single 

 female from Indiana, however, agrees very well in size with these un- 

 spurred males, but shows no other differences from the other females. 

 I have also six males and an equal number of females, all of them large 

 and all of the males with spurs, collected near the base of Mount Wash- 

 ington, July 25-28. Another spurred male I have seen from Pennsyl- 

 vania (E. Keen) and a female from Canada (William Brodie). 



There are some minor differences in tnese specimens which it will be 

 worth while to notice. The pile of the legs is usually wholly black, at 



