183 



Keys to Families 



LARVAE 



1. Head incomplete; thorax and abdomen combined consisting of 13 



segments; larvae peripneustic ; usually with a chitinized plate 

 (very distinct in mature larvae) on ventral surface of second 

 thoracic segment Cecidomyiidae (p. 293) . 



— Without the above combination of characters 2 



2. Head and thoracic and first and second abdominal segments fused; 



larvae with minute abdominal spiracles; abdomen with a ventral 



longitudinal series of sucker-like discs 



Blepharoceridae (p. 274) . 



— Head free, or if retracted within or fused with prothoracic segment 



the other thoracic segments are distinct 3 



3. Head complete, enclosing first ganglion ; mandibles opposed 5 



— Head incomplete posteriorly, either with 3 deep wedge-shaped slits, 



2 on dorsum and 1 on venter, or the ventral surface very poorly 

 chitinized and the dorsal one posteriorly in the form of 4 slender 

 heavily chitinized rods, with a weakly chitinized divided plate on 

 anterior half of the dorsum 4 



4. Apical abdominal segment with 6 radiating protuberances, which 



are rarely poorly developed but frequently unequally so; body 

 segments with regularly placed bristles, as shown in Figure 1, 

 Plate XXVIII ; head heavily chitinized, dorsally slightly arcuate 

 and with 2 longitudinal slits, ventrally slightly rounded and with 

 a central slit ; antennae longer than maxillary palpi ; labium 

 pointed, not divided into 2 plates, the anterior margin dentate; 

 mandibles very stout, with only 2 teeth (at apex) in species with- 

 out apical processes Tipulidae (p. 191). 



— Apical abdominal segment with at most 5 radiating teeth, or if 6 



are present the labium is subdivided centrally ; body usually with- 

 out regularly placed bristles, frequently with dense surface 

 pilosity; head sometimes weakly chitinized and without distinct 

 labium ; antennae sometimes short and slender and not as long as 

 maxillaiy lobe (not palpus) ; labium frequently subdivided into 

 2 plates; mandibles never with only 2 teeth. Limnobiidae (p. 207). 



5. Thoracic segments fused and dilated, forming a complex mass .... 



Culicidae (p. 276) . 



— Thoracic segments not fused, distinct 6 



6. Larvae peripneustic, or with at least rudimentary abdominal 



spiracles 7 



— Larvae amphipneustie or metapneustic 12 



7. Larvae with rudimentary abdominal spiracles ; mouth with a large 



articulated process on each side which bears a number of long 

 hairs and closes, fan-like, when at rest; posterior abdominal seg- 

 ments dilated, the last one armed on venter with a sucker-like disc 

 which bears concentric series of bristles, by means of which the 



