236 G. E. J. NIXON 



- Anterior margin of the postscutellum not closely applied to the posterior margin of the 



scutellum so that, laterally, the phragma of the scutellum is narrowly visible (Text- 

 fig. 321) ; lateral sulci of tergite 2 enclosing an elongate, subtriangular field that is 

 slightly widened behind. 



Tergite 1 strongly narrowed behind, wedge-shaped ; 1st abscissa of the dis- 

 coideus very distinctly shorter than the 2nd ; 2nd transverse cubitus arising from 

 the base of the 2nd abscissa of the radius ; 1st abscissa of the radius much longer 

 than the 2nd. Europe. Philippines .... marginatus- group (p. 239) 



6 Stigma emitting radius much distal to middle (Text-fig. 331) ; tergite 1 very long, 



narrow, constricted medially and dilated apically. 



1st abscissa of the discoideus much shorter than the 2nd .... 7 



Stigma emitting radius at most slightly beyond middle ; tergite 1 never of this form 8 



7 2nd transverse cubitus more or less interstitial with the 1st abscissa of the radius so 



that the areolet is virtually 3-sided (Text-fig. 331) ; stigma bright yellow on at 

 least basal half ; hind coxa yellow, polished ; tergite 2 without a clearly de- 

 limited, median field. N. America .... calliptera-Qroup (p. 261) 



- 2nd transverse cubitus joined with the 2nd abscissa of the radius so that the areolet is 



very large, 4-sided (Text-fig. 335) ; stigma black ; hind coxa black, very large, its 

 upper surface extremely coarsely reticulate ; tergite 2 with an extremely narrow 

 median field that abruptly dilates apically. 



Disc of scutellum thickly covered with almost golden, setiform hairs. Brazil 



ippis- group (p. 263) 



8 Tergite 2 with a more or less distinct median field that varies in shape from longi- 



tudinal-oval to long, narrow, more or less parallel-sided but is never triangularly 

 widened posteriorly, though sometimes widened anteriorly. 



This field is not enclosed by the normal lateral sulci of tergite 2 ; these are 

 usually indicated by a pit or small elongate depression but may sometimes form, 

 as in the pyrene-subgrowp, deeply channelled grooves bordering the tergite as far 

 as the 2nd suture. Old and New World, mainly tropical . xanthaspis- group (p. 240) 



Almost all species have the mesoscutum and disc of scutellum heavily punctate ; 

 sometimes the grooves that enclose the median field of tergite 2 curve outwards 

 posteriorly towards the lateral margin of the tergite so that the tergite appears to be 

 divided into three parts ; in such cases, tergite 1 is narrow and more or less parallel- 

 sided and tergite 3 is always smooth. 



- Tergite 2 either without such a delimited field or if one is present then tergite 1 is short 



and triangularly widened posteriorly ........ 9 



9 Tergite 2 divided by two curved, more or less rugose furrows into three fields of 



which the middle one is triangular and narrowest behind (Text-fig. 319). 



Tergite 1 short, very broad, strongly widened behind ; antenna of female very 

 short, with segments 10-12 hardly longer than wide ; metacarp hardly one and a 

 half times longer than its distance from the apex of the radial cell ; stigma short, 

 broad ; scape long ; tergite 3 always polished. Old World . spretus- group (p. 255) 



- If tergite 2 shows any indication of such a division into three fields (as in scotica- 



group), then tergite 3 shows considerable rugosity and/or the antenna of the female 



is normal ............. 10 



10 Tergite 2 smooth, polished (though often with more weakly sclerotised areas laterally) 



the lateral sulci indicated at most by short furrows at base of segment . . 11 



- Tergite 2 rugose more or less all over . . . ..... 13 



1 1 Tergite 1 about as wide as long, strongly, triangularly widened behind ; tergite 2 (as 



delimited by the 2nd suture which is itself convex in the anterior direction) trans- 

 verse without any indication of a median field and appearing as a polished, evenly 

 sclerotised segment that occupies the full width of the gaster ; side of pronotum 

 polished and with deep, dorsal furrow (Text-fig. 320). 



