188 



20. Thoracic respiratory organs long, bifid; apical abdominal segment 



rounded, without processes ; abdominal spiracles pedunculate .... 



SCATOPSIDAE (p. 300) . 



— Thoracic respiratory organs simple; apical abdominal segment not 



rounded, generally armed with protuberances .21 



21. Thoracic respiratory organs elevated but little above the level of 



disc of thorax ; tarsi of the fore legs overlapping those of mid pair, 

 the latter overlapping those of hind pair, all rather closely fused 

 together and to wings Rhyphidae (p. 241). 



— Thoracic respiratory organs very conspicuously elevated ; legs not as 



above 22 



22. Thoracic respiratory organs equal in length, rarely with one twice 



as long as the other ; anterior, middle, and posterior tarsi distinct 

 23 



— Thoracic respiratory organs of conspicuously unequal length, one 



many times as long as the other ; anterior tarsi overlapping mid- 

 dle pair Ptychopteridae (p. 238). 



23. Abdominal segments each with 1 transverse row, sometimes 2 such 



rows, of thorn-like protuberances ; palpi recurved at apices 



Tipulidae (p. 191). 



— Abdominal segments rarely with distinct thorn-like protuberances, 



usually with weak hairs; palpi straight, not recurved at apices. . 

 Limnobiidae (p. 207). 



IMAGINES 



1. Wing with at least 9 veins extending to the margin (exclusive of the 



anal vein) ; if there are only 8 such veins the radius is 3-branched, 

 the second branch having its base proximad of the radio-medial 

 cross-vein 2 



— Wing with loss than 9 veins extending to the margin, or the vena- 



tion not as above 8 



2. Mesonotum with a more or less distinct V-shaped suture; male 



hypopygium generally very large, chitinous ; female ovipositor 

 conical, chitinized, and generally protruded 3 



— Mesonotum without distinct suture, or if there is a poorly defined 



suture it is not V-shaped 5 



3. Wing with 2 anal veins 4 



— Wing with 1 anal vein Ptychopteridae (p. 238). 



4. Last palpal joint slender, much longer than the combined lengths of 



the 3 preceding joints ; auxiliary vein terminating in first vein . . . 

 Tipulidae (p. 191) . 



— Last palpal joint at most but little longer than the combined lengths 



of the preceding joints; auxiliary vein usually terminating in 



costa, connected with first vein by a cross-vein 



Limnobiidae (p. 207). 



5. Costa continued around the hind margin of the wing 6 



— Costa discontinued at apex of wing Rhyphidae, pt. (p. 241). 



