110 NORTH AMERICAN DIPTERA. 



On account of its robust appearance and the general shape of the 

 head and abdomen, it seems to form, with the genus Metatrichia, a 

 separate group, wherein Metatrichia differs in its closed first poste- 

 rior cell. 



In some species the sexes vary considerably in size, the male being 

 the smaller; even the same sex will vary, thus making this charac 

 ter very unreliable. In species where the female shows some white 

 on the posterior margins of the abdominal segments, the male is 

 very likely to have several segments entirely white. 



TABLE OF SPECIES. 



1. Third and fourth veins at their apices parallel to each other; last section of 



third vein about three-fifths as long as the preceding section ; front 



rough; femora black liubilipes Say, %,^ . 



These veins converge as they approach the costa; last section of third vein not 

 shorter than the preceding section 2. 



2. Front polished, not pitted, except sometimes near the antennje. 



glabrifrons Meig., S , 9 • 



Front rough, pitted, polished only in a narrow median furrow and narrowly 



along the orbits f'enestralis Linn., %,, ^. 



The species alhidipennis Loew I have not seen, but I give the 

 reference and a translation of the typical description further on. 



^iceiiopinus fenestralis Linn., PI. II, fig. 1. 



This is the typical species of the family, and is commonly known 

 as the " window- fly ; " the larvae are often found under carpets and 

 are supposed to feed upon the larvse of the carpet moth. 



Generally black. Front minutely rugose, giving it a sub-opaque appearance, 

 but is narrowly polished along the orbits and in a narrow median furrow. Thorax 

 marked with minute furrows; pleurse more shining. Scutellum also furrowed. 

 Abdomen shining, posterior margins of second to fifth segments of male generally 

 narrowly whitened. Knobs of halteres white, brown above. L«!gs generally 

 yellow, but the femora and tibias, especially the hind pair, dark to nearly black, 

 knees yellow, apices of all tarsi infuscated. The third and fourth veins of the 

 wing are not parallel before they enter the costa, but converge their entire length 

 from the cross-veins; last section of third vein longer than the preceding section. 

 Length ranging from 4-6 mm. 



With older and dried out specimens the color becomes more dis- 

 tinct, ranging from black through bi'own to nearly rufous. 



Sceiiopiniis glabrifrons Meig. 



In general similar to fenestralis, but the front is entirely polished, 

 excepting sometimes a little rough just above the antennae ; the 



