NOTES ON NEARCTIC BIBIONID FLIES. 



By W. L. McAtee, 

 Of the United States Biological Survey. 



INTRODUCTION. 



Wishing to identify some Bibionidae and finding no keys available 

 the writer decided to make some. The resulting keys and notes are 

 based largely on the collections of the United States National Mu- 

 seum, and it is hoped that they will be useful to others desiring to 

 study this neglected family. Among Nemocera in general the 

 Bibionidae are distinguished by absence of transverse suture in 

 mesonotum and of discal cell in wing, forking of the radial sector 

 beyond the discal cross vein, and presence of three large ocelli on a 

 well-developed ocellar prominence. Eliminating the flies properly 

 separable as the family Scatopsidae, the Bibionidae may be separated 

 from their nearer relatives with fair satisfaction. From all but the 

 most primitive Mycetophilidae {Paleoplatyura, Apemon, etc.) they 

 are distinguished by possession of two basal cells in the wing; most 

 of them have short and compact (even if many-jointed) antennae, 

 again in contrast to the majority of Mycetophilidae. The latter 

 usuall}'' have all of the tibiae conspicuously spurred, while in the 

 Bibionidae spurs of any magnitude are confined to the front tibiae. 

 The Scatopsidae differ from the Bibionidae in much smaller average 

 size, in possession of but one basal cell, and general reduction in 

 venation. In these characters again they approach the Myceto- 

 philidae, which differ, however, in the elongation of the coxae, and 

 usually of the other leg joints and antennae. 



In identifying various Bibionidae it is especially desirable, some- 

 times necessary, to have associated sexes of the species. By bear- 

 ing this in mind collectors can greatly help the study of this family. 

 Bibionidae exhibit what is apparently more than a fair share of 

 injuries and malformations which may be connected with emergence 

 from the soil. Distorted tarsal joints are not rare, and in the course 

 of the present study the following more important abnormalities 

 were observed: Bihio femoratus Wiedemann, a female from Plum- 

 mers Island, Maryland, April 30, 1911 (W. L. McAtee), has the left 

 front leg lacking a tarsus, the tibia being only about half the nor- 



No. 2406— Proceedings U. S. National Museum, Vol. 60, Art. I i. 



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