187 



11. Thoracic respiratory organs lamelliform, consisting of 4 flat plates, 



the broad sides of which are contiguous 



Blepharoceridae (p. 274) . 



— Thoracic respiratory organs simple, tube-like 



PSYCHODIDAE, pt. (p. 264) . 



12. Apical abdominal segment terminating in 2 or 4 paddle- or fin- 



shaped organs which are fringed on all or a part of their outer 

 surfaces with strap-like hairs ; or if the apical segment terminates 

 in 2 long subconical processes the tarsi are, as in the other group, 

 recurved against the ventral surface of the base of abdomen and 

 apex of thorax so that they do not extend beyond the apices of 

 wings 13 



— Apical abdominal segment obtuse, armed with short or elongate 



spines or thorns, or if ending in a pair of long, slender processes 

 these are more or less oval or circular in transverse section and 

 without strap-like hairs; tarsi generally entirely straight, rarely 

 the apices of the hind pair incurved slightly, but they are never 

 recurved as above 18 



13. Thoracic respiratory organs terminating in numerous thread-like 



filaments Chironomidae, pt. (p. 284) . 



— Thoracic respiratory organs consisting of a single stem, in some 



cases with a few long, or many short, scale-like surface hairs, but 

 never terminating in numerous thread-like filaments; or occa- 

 sionally the thoracic respiratory organs are not elevated 14 



14. Thoracic respiratory organs not elevated, sternopleura exposed .... 



Chironomidae, pt. (p. 284) . 



— Thoracic respiratory organs conspicuously elevated 15 



15. Thoracic respiratory organs situated close to anterior margin of 



thorax ; thorax and abdomen without stellate hairs 



Chironomidae, pt. (p. 284) . 



— Thoracic respiratory organs situated close to middle of thoracic dor- 



sum 16 



16. Apical abdominal segment ending in 2 or 4 broad, flat, paddle-like 



plates Culicidae, pt. (p. 276). 



— Apical abdominal segment ending in 2 long subconical processes . . 17 



17. Apical processes armed at apices and on middle of their outer mar- 



gin with short hairs (3:1) Culicidae, pt. (p. 276) . 



— Apical processes unarmed Dixidae (p. 279). 



18. Apices of legs not extending beyond apices of wings 19 



— Apices of posterior legs at least extending beyond apices of wings 



20 



19. Apical abdominal segment ending in 2 conical processes 



Ceratopogonidae (p. 281 ) . 



— Apical abdominal segment ending in 2 upper and 2 lower short 



thorns Psychodidae, pt. (p. 264) . 



