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). (PhMnthus, Cerceris, Eucerceris.) . . PHILANTHIIXS 



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, Cemfinus, 

 Stigmus, Passaloecus.) (Including MIMESID.E and PEMPHREDOXID^E.) 



84. Labrum large, free, triangularly elongated beyond the clypeus, much longer 



than wide; radial cell not di vided near the apex; ocelli more or less aborted 

 (PI. 3, fig. 52). (Bembex, Monedula, Microbembex.) ....... BEMBECIIXE 



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^E 



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

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



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 recurrent nervure; rare species. 

 (Mellinus.) ............................................ MELLINnXE 



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

 separated by the sternum (some metallic green Chrysididae (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 tegulse) . 87 



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



not separated; parapsidal furrows distinct; pronotum conically produced 

 in front. (Rhin6psis.) ................................. AMPULICID^ 



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 (=Pelopceus) Sphex (= Amm6phila) . 

 Chlorton (= Sphex, Priondnyx, Isod6ntid) .................. SPHECDX& 



Abdomen sessile or subsessile, never with a slender petiole ................ 89 



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



(Stizus, Sphecius.) ........................................ STIZID^E 



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 ASTATINE of the NYSSONTD-flS 



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

 the clypeus, always away from the clypeal suture .................... 91 



