8 Key to Families oj North American Insects. 



21. Prothorax small or only moderately long 22 



Prothorax very long and cylindrical; antennae many-jointed; crossveins nu- 

 merous RAPHIDIOIDEA (Pagt 44) 



22. Wings similar, with many veins and crossveins, costal cell almost always filled 



with crossveins; prothorax more or less free. If the neuration is very rarely 

 reduced (Coniopteryx) the vraigs are powdered. .KEUROPTERA. (Page 45) 

 Wings with relatively few angular cells, the costal cell without crossveins; hind 

 wings smaller than the fore pair; prothorax fused with the mesothorax; 

 abdomen usually constricted at the base and ending in a sting or specialized 

 ovipositor. Wasps, Bees, etc HYMENOPTERA (Page 19) 



23. Prothorax well developed; wings equal in size, held superimposed on the abdo- 



men when at rest 24 



Prothorax inconspicuous; hind wings smaller than the fore wings; tarsi two- 

 or three-jointed; wings at rest held roof-like against the abdomen 



CORRODENTIA (Page 17) 



24. Tarsi apparently four-jointed; social species, living in colonies 



ISOPTERA (Page 17) 

 Tarsi three-jointed, the front metatarsi swollen; solitary; southern species 



EMBnDINA (Page 42) 



25. Wings not covered with scales, usually transparent, not outspread when at 



rest; prothorax large; antennae with few joints 26 



Wings and body covered with scales, the wings well developed and pictured; 

 prothorax small; antennae many-jointed. Moths and Butterflies 



LEPmOPTERA (Page 48) 



26. Beak arising from the back of the head HOMOPTERA (Page 73) 



Beak arising from the front part of the head HEMIPTERA (Page 76) 



27. Mouth not functional; abdomen furnished with a pair of caudal filaments. .28 

 Mouth-parts forming a proboscis, only exceptionally vestigial; abdomen with- 

 out caudal filaments; hind wings replaced by knobbed halteres. Flies, 

 Mosquitoes, Midges DIPTERA (Page 61) 



28. No halteres; antennae inconspicuous; crossveins abundant. A few rare Maj'- 



flies PLECTOPTERA (Page 43) 



Hind wings represented by minute hook-like halteres; antennae evident; cross- 

 vems lacking. Males of Scale-insects HOMOPTERA (Page 73) 



29. Body more or less insect-like, i. e. with more or less distinct head, thorax and 



abdomen, and jointed legs, and capable of locomotion 30 



Without distinct body parts, or without jointed legs, or incapable of locomo- 

 tion 70 



30. Terrestrial, breathing through spiracles 31 



Living in the water; usually gill-breathing, larval forms 59 



Parasites on warm-blooded animals 65 



31. Mouthparts vestigial, retracted in the head and scarcely or not at all visible; 



underside of the abdomen with styles or other appendages; very delicate 



small or minute insects 32 



Mouthparts mandibulate, formed for chewing 38 



Mouthparts haustellate, formed for sucking 55 



