44 Rk. W. CROSSKE Y 
factorily in any particular segregate, it is generally true that the great majority of 
species can be placed alongside obviously allied species where together they form 
natural subdivisions of the genus, each of which can be reasonably well charac- 
terized and differentiated from other such segregates. It is here considered best to 
treat these major groupings of the species as subgenera, a course which has not 
previously been adopted with Rutilia (except for Malloch’s (1936) recognition of his 
new species simplex as representing a new subgenus, and his recognition of subgenus 
Microrutilia in the same paper). The seven subgenera recognized can be distin- 
guished by the accompanying key and diagnoses, but it may be useful to draw 
attention here to some general conclusions to which I have come before formulating 
these subgenera. 
It is certainly unwise in Rutilia (as indeed generally in the Tachinidae) to aggre- 
gate species into a defined taxon merely on the common possession of a single 
character, or to attach too great an importance to some single striking attribute that 
may well have, and usually almost certainly has, been evolved more than once within 
the whole complex of forms. This course forced Malloch to place species such as 
confusa Malloch and cingulata Malloch out of Rutilia and in Formosia instead, 
simply because on the single character of bare suprasquamal ridge they are atypical 
for Rutilia, though on their overall totality of characters these species clearly fit 
Rutila and not Formosia. Yet within Rutilia the rest of the characters shown by 
confusa and cingulata leave little doubt that these two species are not closely allied, 
and an unnatural group would be formed by defining a taxon (subgenus or species- 
group) which brought these species together: it seems certain that bareness of the 
suprasquamal ridge has arisen more than once within Rutilia, so that while the charac- 
ter can be usefully used as one of the characters of an infrageneric taxon it cannot 
be used as an exclusive diagnostic feature. Similarly, the depression in the last 
visible abdominal tergite (T5), which is such a conspicuous feature of many Rutilia 
species and was used as a generic character by Enderlein, has undoubtedly in my 
view arisen at least twice in separate lines of evolutionary development in the 
genus: it occurs principally in the subgenus Donovanius but is also found in Rutilia 
s.str., groups which seem to resemble each other convergently but differ much when 
all their characters are taken into account. 
In Rutilia the chaetotaxy is often very variable, the number of setae and their 
degree of development often showing great inconstancy within a species and between 
sexes (females normally have a stronger chaetotaxy and may show development of 
certain setae that are usually totally lacking in males), and also sometimes showing 
imperfect bilateral symmetry. Hence chaetotactic characters must be used with 
great caution and long series of specimens require study before any conclusions can 
be made about which setae, if any, are more or less dependable. The acrostichal, 
dorsocentral, intra-alar and supra-alar setae are, speaking generally, too inconstant 
in number and strength to be of real value in providing group characters or specific 
characters, and the sternopleural and posthumeral setae (especially the latter) show 
some variability which makes their usefulness limited (though the sternopleurals can 
usefully be used, and are here used, as a supporting character in defining the sub- 
genera). The humeral callus has two moderately strong setae on the outer half in 
