second longitudinal vein wanting, the third arising from 

 the first; third vein sometimes furcate;* fourth usually 

 furcate ; first basal and often the second basal cells com- 

 plete; anal cell rarely closed; posterior cross-vein always 

 wanting. 



The relationships of this small family of nematocerous 

 flies are very close with the Mycetophilidae through the 

 Pachyneurinae and Scatopsinae ; indeed there is greater 

 difference between some genera included in the family 

 than between the families themselves. One of these 

 annectant genera is Hesperodes described a few years ago 

 by Coquillett. Because of the presence of a distinct sec- 

 ond basal cell, and the resemblance of its venation to 

 Hespennus, it would seem better placed here than among 

 the Mycetophilidae, where its author placed it. A glance, 

 however, at the different types of venation in the figures 

 will show how composite a group the family is, as at 

 present recognized. 



Such larvae as are known are cylindrical, footless, with 

 transverse rows of bristles, usually with eyes; they feed 

 upon excrementitious or vegetable substances, especially 

 on the roots of grass. The pupae are inactive, for the 

 most part free, living in excavated, smooth oval cavities 

 near the surface of the ground, which the larvae have 

 prepared before undergoing their metamophosis, and 

 where the pupae remain before emerging in the perfect 

 state. 



In some species the male flies differ very noticeably in 

 coloration from the females, so much so that they are 

 commonly mistaken for different species. Some of the 

 species, especially Bibio albipennis, are very abundant in 

 early spring, in meadows, about willows, upon the win- 



'' The anterior branch is in reality the second vein. 

 15 



