38 NORTH AMERICAN DIPTERA. 



occurs early in the spring, in great numbers, especially about 

 willows, and in gardens. It is conspicuous for its white wings 

 and black color, and like most other members of the family is 

 slow in its movements, flying heavily. B. femorata, a com- 

 mon species, is of a deep red color with black wings. B. tristis 

 has been observed in large numbers in many Kansas wheat- 

 fields, during the last week of April, apparently without 

 causing damage. 



1. Second basal cell present. ."' 2 



Second basal cell wanting. . ' 5 



2. Third longitudinal vein furcate. . . , ~ . . . . 3 

 Third vein not furcate 4 



3. Palpi four-jointed ; first antennal joint elongate. HESPERINUS Walker. 

 Palpi five-jointed. PLECIA Wiedemann. 



4. Front tibise with a stout, spine-like process at the tip. BIBIO Geoffrey. 

 Front tibiae with a terminal coronet of spines. DILOPHUS Meigen. 



5. Front tibia? ending in a spine-like process. . . ASPISTES Meigen. 

 Front tibiae of the usual structure; third vein not furcate; hind meta- 

 tarsi shorter than the remaining joints together. SCATOPSE Geoffrey. 



11. SIMULIID^E. 



Small flies, from three to six mm. in length, with thick, 

 compressed, short legs. Head hemispherical ; face short ; 

 eyes round or reniform, holoptic in the male ; no ocelli. 

 Antennae scarcely longer than the head, cylindrical, ten- 

 jointed; the two basal joints differentiated, the others closely 

 united. Proboscis not elongated, with small, horny labella ; 

 palpi incurvate, four-jointed; the first joint short and the two 

 following of equal length ; the last one longer and more slen- 

 der than the preceding. Thorax ovate, without suture ; the 

 scutellum small. Abdomen cylindrical, composed of seven or 

 eight segments ; genitalia concealed ; legs strong and not elon- 

 gated ; femora broad and flat ; tibiae without terminal spurs ; 

 first joint of the tarsi longer than the following and usually 



