311 



2. Prothorax with a large aperture mesad of and connected with the 



spiracle Tabanidae (p. 355) . 



— Prothorax without an aperture mesad of the spiracle 3 



3. Head without strong forwardly directed thorns, at most with one 



thorn on base of antenna which is directed laterad; abdominal 

 armature weak, becoming gradually stronger towards apex of 

 abdomen ; wings short, extending to or very slightly beyond apex 

 of basal abdominal segment ; apices of hind tarsi at most extend- 

 ing slightly beyond apices of wings; abdomen with 7 pairs of 

 spiracles 4 



— Head usually with strong thorns, or if these are absent the ab- 



dominal armature is stronger on basal or second segment than it 

 is on apical or there are less than 7 pairs of abdominal spiracles 

 present; apices of hind tarsi usually extending distinctly beyond 

 apices" of wings 6 



4. Antenna! sheaths much thickened at bases, apical portion slender, 



stylif orm, the whole directed almost straight downward 



Leptidae (p. 362). 



— Antennal sheaths thickened throughout their length, the apical por- 



tion generally more or less distinctly annulated, the whole direct- 

 ed either straight laterad or in a slightly downward direction . . 5 



5. Antennal sheaths very stout, not over twice as long as their basal 



breadth ; face with a small sharp protuberance on each side a 

 little mesad of the vertical line of apices of antennae and slightly 

 above middle of face, and at the base of each are 2 short hairs 

 on their inner side ; 2 very strong postspiracular abdominal 

 bristles on each segment Coenomyiidae (p. 351). 



— Antennal sheaths distinctly annulated, slender, about 4 times as long 



as their basal breadth ; face without protuberance ; postspiracular 



abdominal bristles slender, 8-10 on each segment 



Xylophagidae (p. 346) . 



6. Head without strong thorns ; abdomen with 3-4 distinct pairs of 



spiracles and without spinose armature Cyrtidae (p. 368). 



— Head usually with strong thorns, at least with elevated ridge-like 



antennal sheath and several small carinated elevations ; abdomen 

 with 7 pairs of spiracles and spinose armature 7 



7. Head with 2 thorns 8 



— Head with more than 2 thorns or with several short tubercles 9 



8. Abdomen with a single transverse series of spines on each dorsal 



segment ; wing with a long thorn at base .... Therevidae (p. 396) . 



— Abdomen with 2 transverse series of spines on each dorsal segment; 



wing without thorn at base Scenopinidae (p. 398). 



9. Upper pair of cephalic thorns directed laterad and slightly upward; 



apices of wings extending to or very slightly beyond apex of first 

 abdominal segment ; apices of middle tarsi not extending to apices 

 of wings Mydaidae (p. 370). 



