92 xoirni amehtcan diitkra. 



About forty species of this family are known from i*^orth 

 America. Tliey are all flower-flies, not very quick in flight. 

 Flies of some of the genera (Conops, Pltj/socejyhala and Tropido- 

 rnyia) have a curious resemblance to certain wasps, and yet 

 more to the species of Cerla among the Syrphida?. The genus 

 Sti/logaster is remarkable for the very long ovipositor of the 

 female and the elongate proboscis in both sexes. The four 

 known species are from Africa, ISTorth and South America. 



So far as known, the larvte of this family are parasitic upon 

 adult hymenoptera (wasps and humble-bees) and orthoptera. 

 The eggs of the female are laid directly upon the bodies of 

 the bees or wasps during fliglit. The young larvae burrow- 

 within the abdominal cavity of their host, and there remain, 

 the posterior end directed toward the base of the abdomen, 

 feeding upon the non-vital portions, until ready to transform 

 into the mature fly, when they escape from between the 

 abdominal rings of the insect. The larvye of ConopidaB 

 are oval or pear-shaped, Avith distinctly differentiated seg- 

 ments, which are capable of extension or contraction. The 

 antennae are wart-like, with two chitinous, ocellus-like rings at 

 the extremity. The mouth-hooklets are strongly bent. On 

 the last segment there are two, large, round or kidney-shaped 

 stigmatic plates, arched like a watch crystal. The puparium 

 is oval, with button-like, slightly projecting anterior stigmata 

 and the posterior pair as in the larvte. They remain within 

 the body of tlieir host during the winter. 



TABLE OF GEN EH A. 



1. iViiteima' with a tiTininal style; proboscis direftcd forward, without me- 

 dian hinge ; abdomen foiistrietod toward tho t)ase. . . 2 

 Antennae witii a dorsal or subdorsal arista. ..... 4 



L'. Face witli a median rid^c, without _\^-s]ia]ied <;rooves (Central and South 

 America.) ....... Thopioomvia Williston. 



Face with a well-marked \-sliapci] groove. .....•> 



.'5. Femora and tibia' not thickened or dilated, or, if so, the thickening reg- 

 ular ; small cros.s-vein of the wings nearly opi)osite the tip of the 

 Muxiliarv vein, and near the middle of the discal cell. Con-ops Linne. 



