20 Key to Families of North American Insects. 



5. Fore wings with only two cubital cells; antennae inserted much below the lower 



margin of the eyes, beneath a frontal ridge; vertex tuberculate. (Oryssus) 



ORYSSIDJE 

 Fore wings with three or four cubital cells 6 



6. Pronotum nearly truncate or weakly emarginate behind; mesonotum short? 



not extending much beyond the anterior margin of the tegulae; abdomen 

 more or less compressed; antennas filiform, many-jointed. (Cephus [C. 



pygmcnts, Wheat-stem Saw-fly], Janus.) CEPHID^ 



Pronotum deeply curved or emarginate behind; mesonotum longer, extending 

 well beyond the anterior margin of the tegulae 7 



7. Parapsidal furrows present; fore wings with a transverse intercostal vein; no 



triangular plate at the apex of the abdomen; prothorax conical. (Xiphydria.) 



XIPHYDRinXE 



Parapsidal furrows absent; fore wings without an intercostal vein; apex of 

 abdomen with a triangularly shaped plate; prothorax subquadrate. (Tre- 

 mex, Sirex, Paurfcrus) (PI. 3, fig. 39) (UROCERIDft) SIRICnXE 



8. First parapterum (a small, more or less triangular plate just behind the pro' 



thoracic spiracle and above the mesopleura) present 9 



First parapterum absent; mesosternum not separated from the mesopleura by 

 an impressed line (Acordulecera) PTERYGOPHORID.flJ 



9. Abdomen angled laterally so that the dorsal sclerites are sharply divided into 



a dorsal and ventral surface; antennae clubbed. (Cimbex \C. americana, 



Willow Saw-fly], Trichiosdma, Zaraea) CIMBICIIXE 



Abdomen not sharply angled laterally; antennae not clubbed 10 



10. Mesopleura separated from the mesosternum by an impressed line; antennae 



three- jointed, the third joint very long (Hylotoma(= Arge), Sterictiphora) 



HYLOTOMHXE 



Mesopleura not separated by an impressed line; antennae with more than six 

 joints 11 



11. Antennae serrate (female) or pectinate (male), eighteen- to twenty-six-jointed. 



(Diprion (= Lophyrus) [Pine Saw-flies] DIPRIONHXE; 



Antennae filamentous, with seven to twelve, usually nine, joints. (Dolerus, 

 Nematus, Macrophya, Tenthredella) (PI. 3, fig. 37). .TENTHREDINID^; 



12. Hypopygidium divided, or never closely united with the pygidium, the ovi- 



positor issuing some distance before the tip of the abdomen, from its ventral 



surface (PI. 4, fig. 79) 13 



Hypopygium entire and closely united with the pygidium, the sting or qvi- 

 positor always issuing from the tip of the abdomen (PI. 4, fig. 82) 44 



13. Winged 14 



Wingless 25 



14. Fore wings with a stigma which is rarely very slender or linear; costal vein 



well developed as far as the stigma (PI. 3, figs. 42, 43); abdomen usually 

 with the ventral segments membranous and with a median fold; antennae 

 usually with more than sixteen joints; wing venation ordinarily well de- 

 veloped. (ICHNEUMON01DEA.) 15 



