THE SYRPHIDAE OF OHIO 33 



Most of the males are holoptic. In a few genera {Microdon, Chal- 

 comyia, Triodonta, Mallota, Helophihis) the males are dichoptic; but 

 even then the front is different, always narrower and forming some an- 

 gularity with the eyes, in the male, broader and with the margins straight 

 in the female. 



In the legs are found the most important secondary sexual charac- 

 ters; it is the male legs which are modified. Some of these specializations 

 are probably of value as seizing or clasping organs during copulation, 

 and hence, unlike most of the others, present some evident utility. The 

 front pair are modified in a few cases (notabaly Platychirus) ; the middle 

 ones rarely; the hind ones most extensively. 



In coloration and vestiture there are very frequent secondary sexual 

 differences. In general, where there is any difference, the male is more 

 strongly or brightly colored, though the females are by no means somber 

 in this family. The male is also frequently more strongly or thickly 

 pilose. 



CHARACTERS AVAILABLE FOR CLASSIFICATION 



In adult Syrphidac one finds a great variety of characters peculiar to 

 genera and species and hence available for the purpose of bringing related 

 forms together. Apparently the most fundamental are those of the wing. 

 The various features of the head are of constant service. The legs 

 present a number of excellent characters. The abdomen (shape and 

 especially color pattern ) has constantly to be drawn upon for specific 

 characters. While in not a few cases the thoracic features are of value. 



The characters of the neuration of the wing are especiall>- constant 

 and reliable and have been extensively used. The position of the cross- 

 veins, and the shape, curvature and termination of the second, third and 

 sixth longitudinal veins, are of fundamental value; while the size and 

 shape of certain cells can often be used to advantage in the separation of 

 closel}' allied forms. 



Probably more characters are derived from the head than from all 

 other parts of the body. Characters of the anteimae, of the front and 

 face, and of the eyes are all much used. 



The antennae as a whole may be elongate or short: the third seg- 

 ment varies much in size and shape, ma>- bear a st>le or an arista, and 

 the arista varies in position and in vestiture. from bare to pubescent, 

 pilose, or plumose. Williston notes that species with elongate antennae 

 are not very active in habits. On the front and face are to be noted 

 length, breadth, projections, wrinkles and grooves. The size and shape 



