AMERICAN DIPTERA. 



327 



EXPLANATION OF PLATES. 

 All the figures given were drawn by the aid of the camera lucida, 

 and are merely outlines showing general form of the antennae, geni- 

 talia, wings, etc. As much depends upon the angle in which objects 

 are viewed, this must be taken into account when referring to these 

 figures, especially of the genitalia. Also in many cases of the wing 

 drawings, the apparent fold between the third and fourth veins, 

 makes the anterior cross-vein appear shorter in proportion. On each 

 plate is a scale representing about one millimeter, which will be a 

 guide for ascertaining the relative lengths of the objects. 



