12 R. W. CROSSKEY 
or more supernumerary postalar setae (in addition to the basic two) has evidently 
occurred several times over in different evolutionary lines—hence different genera 
and subgenera have either three or four (+) postalars, and the common possession of 
either of these numbers does not indicate that the genus-group taxa involved are 
necessarily phyletically close. Unfortunately the number of postalar setae is not 
absolutely dependable in every specimen, for very rarely specimens do occur in which 
the postalar callus has three setae on one side and four on the other (in this case it 
seems from other characters that such specimens always, or nearly always, belong 
to taxa in which 4+ is the norm for postalar setae). The sternopleural setae provide 
some useful supporting characters in the definition of genus-group segregates, some 
typically having only a single (posterior) stp] seta and others having either I + 1 
or 2 + 1 stpl, but some variability occurs; for example groups normally having 2 + 1 
may lack one of the anterior pair in some specimens or on one side of a specimen, and 
groups normally having I + 1 stpl may have the anterior one virtually indistinguish- 
able from the sternopleural hairing (especially in the male). No taxonomic charac- 
ters have been discovered in the mesopleural, hypopleural, propleural or prostig- 
matic setae; there is no definite pteropleural seta differentiated from the tuft of long 
strong pteropleural hairing below the wing-base in any Rutiliini. 
The scutellar setae show characters of value in the definition of genera and sub- 
genera. The number and strength of marginal scutellar setae vary much, but the 
position of the apical pair (whether inserted lower than or level with the other 
marginals) provides a very dependable character (in all Formosia s.1. for example the 
apical scutellars are level with the other marginal scutellar setae, whereas in Rutilia 
s.l. they are set at an obviously lower level on the tip of the scutellum). In some 
segregates the scutellum carries a transverse row of small but distinct preapical 
setae lying in the same horizontal plane as the marginals, and these provide a useful 
character (though there is some variability in their number and size it is nearly 
always certain whether they can be classed as present or absent). 
In some forms the thoracic setae (especially the supernumerary prescutellars, if 
present, the scutellars, the postalars and some setae on the venter of the sternopleura 
in front of the middle coxae) are markedly spiniform; in this case they are usually 
stiffer, straighter and relatively shorter than in other forms. In some genus-group 
segregates (notably Formosia s.l. and Rutilia s.str.) the development of strong 
spiniform setae can be very striking, but it is difficult—because of intergradation 
with forms with more normal bristling—to use the spiniform nature of the setae as a 
taxonomic character. 
Leg chaetotaxy. The legs provide few useful taxonomic characters. The setae 
of the fore and mid legs (such as the pv setae of the fore tibia and ad setae of the 
mid tibia) may vary in size and number and no useful features have been found. 
Some forms have very heavy spiniform bristling on the mid and hind coxa but this 
cannot be used as a dependable character. The development of the ad fringe of 
the hind tibia, whether formed as a regular close-set comb or as a sparse irregular 
row of ad setae and setulae, sometimes provides a helpful character, and is some- 
times correlated with a different number of fd setae on the hind tibia (though this 
can be intraspecifically variable or show sexual differences, e.g. pd setae absent in 
