28 Key to Families of North American Insects. 



Fore wings with three cubital cells; second often petiolate; abdomen sessile or 

 subsessile, usually constricted between the segments; eyes rarely emargin- 

 ate (PI. 3, fig. 54). (Philanthus, Cerceris, Eucerceris.). . PHILANTHID.S: 



83. Abdomen sessile 84. 



Abdomen petiolate or subpetiolate; two or three cubital cells, transverse median 



nervure not S-shaped, hind wing usually twice emarginate on the basal half 

 of the posterior border; usually rather small black species. (Psen, Cemonus, 

 Stigmus, Passaloecus.) (Including Mimesid,e and Pemphredoxid.e.) 



PSENID.E 



84. Labrum large, free, triangularly elongated beyond the clj^peus, much longer 



than wide; radial cell not divided near the apex; oceUi more or less aborted 



(PI. 3, fig. 5i). (Bembex, Monedula, Microbembex.) BEMBEClDiE 



Labrum small, usually entirely concealed by the clypeus; radial cell usually 

 divided by a crossvein near apex, the portion beyond the crossvein less 

 clearly defined; at least the front ocellus perfectly formed 85 



85. Second cubital cell petiolate, very rarely absent; third either present or absent; 



three perfectly formed ocelli; small species. (Miscophus, Plenoculus.) 



NITELID^ 

 Second cubital cell present not petiolate; hind ocelli frequently aborted (PI. 



3, fig. 51; PI. 5, figs. 87, 89). (Astata, Lyroda, Tachysphex, Tachytes.) 



LARRID^ 



86. Abdomen with a more or less distinct constriction between the first and second 



segments, the first segment broader at tip than at base; middle coxae in 

 contact; second cubital cell not receiving a reciurent nervure; rare species. 



(Mellinus.) MELLINID^ 



Abdomen not constricted between the first and second segments; middle coxae 

 separated by the sternum (some metallic green Chrysididse (see couplet 57) 

 may lead out here; they have the abdomen sessile, with less than six dorsal 

 segments, and the pronotum though long does not quite reach the tegula?) . 87 



87. Mesosternum produced into a forked process posteriorly, the mesepisternum 



not separated; parapsidal furrows distinct; pronotum conically produced 



in front. (Rhinopsis.) AMPULICIDjE 



Mesosternum not produced backwards, the mesepisternum separated; parap- 

 sidal furrows indistinct or absent; pronotum not conically produced 88 



88. Abdomen with a distinct slender, nearly cylindrical petiole (PI. 3, fig. 57; PI. 



4, figs. 75, 77). (Chalybion, Sceliphron { = Pelopwus) Sphex {= Ammd-phila) . 

 Chlorion {=Sphcx, Priononyx, Isodontia) SPHECIDjiE 



Abdomen sessile or subsessile, never with a slender petiole 89 



89. Labrum free, well developed, triangular or semicircular, wider than long. 



(Stizus, Sphecius.) STIZIDjE 



Labrum short, not or scarcely exserted beyond the clypeus 90 



90. Marginal cell broadly truncate at apex and prolonged as a small, weakly defined 



cell; antennae inserted close to the clypeus or very close to the clypeal suture. 



(Astata, Diploplectron) Subfamily AsT.\TiN^ of the NYSSONED.^ 



Marginal cell pointed at apex, not appendiculate; antennae inserted far above 

 the clypeus, always away from the clypeal suture 91 



