184 



larvae retain their hold upon rocks, etc., in the streams where 

 they are found Simuliidae (p. 302) . 



— Larvae with distinct though sometimes small abdominal spiracles; 



mouth without fan-like processes ; posterior abdominal segments 

 not noticeably dilated, the last without sucker-like disc ; terrestrial 

 species 8 



8. Antennae elongate; body armed with conspicuous bristles or hairs 



9 



— Antennae usually short and inconspicuous, sometimes apparently 



absent ; body without conspicuous bristles 10 



9. Anal spiracles at the apices of a pair of long stalk-like processes .... 



Scatopsidae (p. 300). 



— Anal spiracles not noticeably elevated, situated near base of dorsal 



surface of apical segment Bibionidae (p. 298). 



10. Dorsal, or clypeal, sclerite of head not conspicuously tapered pos- 



teriorly ; antennae well developed Bolitophilidae (p. 247). 



— Dorsal, or clypeal, sclerite of head conspicuously tapered pos- 



teriorly; antennae almost indistinguishable 11 



11. Lateral sclerites of head meeting on ventral line only for a short 



space immediately caudad of mouth-opening, not connected at 

 posterior margin Mycetophilidae (p. 248) . 



— Lateral sclerites of head connected for a very short space behind 



mouth-opening and again near posterior margin 



Sciaridae (p. 258) 



12. Dorsal surface of first and second abdominal segments each with 2 



Avart-like elevations somewhat resembling pseudopods, the apices 

 of which are armed with numerous small hook-like setae ; larvae 

 aquatic, amphipneustic Dixidae (p. 279). 



— Dorsal surface of first and second abdominal segments without ele- 



vated processes 13 



13. All or some of the dorsal segments with narrow, chitinized, strap- 



like transverse bands, or the apical segment in the form of a 

 short chitinized tube ; rarely the ventral abdominal segments bear 

 a central series of sucker-like discs Psychodioae (p. 264). 



— Dorsum without narrow, chitinized, strap-like bands, apical segment 



not in the form of a short chitinized tube ; ventral abdominal seg- 

 ments never with sucker-like discs 14 



14. Apical abdominal segment with long, slender respiratory tube .... 



Ptychopteridae (p. 238) . 



— Apical abdominal segment without long respiratory tube 15 



15. Antennae undeveloped, appearing as pale round spots on sides of 



head ; ventral surface of head with the sclerites contiguous ante- 

 riorly, widely separated posteriorly 16 



— Antennae pedunculate, usually well developed; ventral surface of 



head with sclerite contiguous on entire length, not separated 

 widely posteriorly 17 



