254 Illinois State Laboratory of Natural Ilistory. 



10 upon a reed stem, mutilating an Odontomyia egg 

 mass. The lower part of the mass was gone, and in its 

 place stood the chalcid with its jaws apparently working 

 at the low-er edge of the remaining portion, where many 

 of the eggs were evidently roughly displaced. July 15 

 I found an example of S. microgaster resting on a Sagit- 

 taria leaf at Station A, and another appeared in my dip- 

 net August 20 at D. Megilla maculata, a coccinellid 

 beetle, has been found by us eating Odontomyia eggs. 



These two Odontomyia larvae may readily be dis- 

 tinguished from the Stratiomyia, not only by their shape, 

 but also by their green or browm colors when not black- 

 ■ened by exposure, and by the presence of one or more 

 pairs of ventral hooks on the posterior margins of seg- 

 ments nine and ten. They differ from each other as fol- 

 lows: 



KEY TO LARV^ OF ODONTOMYIA. 



Surface covered with minute peltate scales; ventral lines 

 of segments 9 and 10 distinct, basal (Fig. 59) ; dor- 

 sal pale lines parallel posteriorly, continued upon 

 last segment dncta. 



Surface naked, with a few bristles; ventral lines of seg- 

 ments 9 and 10 discal (Fig. 60) ; dorsal pale lines con- 

 verging behind and vanishing, on last segment 

 obliterated, the dark stripes there confluent into one 

 broad dorsal stripe [Fig. 60] vertebrata. 



Mr. Day's key to the imagos* is a purely artificial one 

 based on color characters, and the close relationship of 

 dncta {extremis) and vertehrata {wilUstoni) there indicated 

 is misleading. Their true groupings in the genus may be 

 «een by the following tabulation of our Illinois species, 

 based primarily on structural characters. 



• Proc Acad. Nat. ScL PhU., 1882, p. 74. 



