North American Dii-tera. 47 



38. All femora sUmkUt, alKloininal si'gnieuts with bristles before the 



hind margin Liaxcalus 



Fore femora incrassated towards the basis. ... 39 



39. Fore tibia; with long thorns Scellus 



Fore tibiai with very short little tiiorns. IIydkophokus 



40. Arista ai)ioal, or at least subapieal 41 



Arista distinctly dorsal. ....... 42 



41 Third and fourth longitudinal veins strongly convergent. 



Medeteros 



Third and fourtii longitudinal veins parallel. Ciirysotimus 



42. Male abdomen with si.\ distinct segments. Xaxtiiochlorus 



Male abdomen witii five distinct segments. S.vicROPrs 



"Face of the male prolonged downward, and dependent in the 

 shape of a silvery sheet or ribbon ; in length, this ribbon is about 

 equal to the upper part of the face l)etween the antenna? and the 

 lower end of the eye. In life, the ribbon is straight ; in dried speci- 

 mens its end is usually bent inwards. Cilia of the very small tegula; 

 in the male unusually long (bent backward, they would almost reach 

 the end of the second abdominal segment); they can be folded like 

 a fan, and then form a long tapering horn or spine-like body." 



POLYMEDON 



" Hypopygium of male with four strong setulae; tarsi without 

 elongate pulvilli ; distal portion of fourth longitudinal vein inter- 

 rupted ; posterior transverse vein remote from the border ; other- 

 wise similar to Diaphorus." . . . . Asyndetus 



"First antennal joint bristly above, second rudimentary, third 

 small,, with an extraordinarily elongated dorsal bristle, which is di- 

 lated shovel-shaped at the end. Face descending below the angle 

 of the eyes. Hind femora in front with only one preapical bristle ; 

 hind metatarsi unarmed. Hypopygium free ; the exterior processes 

 lamelliform. Last section of the fourth longitudinal vein strongly 

 convergent toward the third, so that the terminations of the two 

 veins are close together. M. (T a c h y t r e c h u s) m ae c h u s Loew." 



< Macellocerus. 



SYRPHIDiE. 



Rather large to rather small, thickly or thinly pilose, often brightly 

 colored flies. Ocelli present; males holoptic or dichoptic. Third 

 joint of antennae simple; with a dorsal bristle, or rarely a terminal 

 style. Abdomen very variable in shape. Legs often with structural 

 sexual peculiarities ; empodia not developed. Three basal cells of 

 wing large ; first posterior cell closed near or at some distance before 

 the margin of the wing; between the third and the fourth longitud- 



