80 
REVIEWS. 
tematic arrangement of the Diptera that has yet been proposed ; meaning, 
of course, within the limits in which only this* can be predicated of a 
system based upon a local fauna. If there be other systems, as, for 
instance, that of Mr. Macquart, in his Dipteres Exotiques, liable to fewer 
criticisms, the reason is, that the families are taken there in a much more 
restricted scope, which has made it greatly easier to circumscribe and 
characterise them. 
We proceed next to take a glance at the genera given by Mr. Walker, 
their composition and contents. There is a great want of uniformity here, 
in the extent assigned to particular genera. While a judicious medium 
has been observed in the majority of families, the sub-division in some 
cases, as, for instance, in the sub-family, Hydromyzides , is carried on to a 
degree of minuteness almost frivolous; while, in other instances,- it stops 
far short of the measure, and presents (as in the Muscidce) genera of 
such unwieldy bulk as greatly to impair the usefulness of the work. It is 
fair to say that a complete analysis of the system of Diptera, up to its 
ultimate members, is not an undertaking to be disposed of incidentally in 
the treatment of a particular Fauna. Accordingly, such a work will 
naturally be more complete in those portions which have formed the sub¬ 
ject of able Monographs, or which have obtained the special attention of 
the author himself, than in others, where neither of these has been the 
case. It is no blame to Mi'. Walker that it is so with the present work; 
but it seems to us that he has, in some instances, stopped short of what 
his predecessors had already accomplished, and which he need only have 
adopted from them. If not disposed to follow the precedent set by the 
French Dipterists (Macquart in particular), in the much needed sub-divi¬ 
sion of the genera Tachina , Musca , Dexia , and Anthomyia —and from 
this he may have been deterred by not unreasonable scruples against the 
excessive multiplication and often indefinite character of the new genera— 
yet, surely he might have adopted the chief part of those which Meigen 
has admitted in his seventh volume. His work would have gained 
much by this, both as to uniformity and practical utility. The 
study of such genera also as Limnohia , Ceratapogon , Chironomus , and 
Cecidomyia , would have been facilitated by their distribution under 
smaller genera. The characters of many of the genera are very well 
drawn; in other cases as much cannot be said of them ; and there are two 
opposite faults which invite remark by their frequent recurrence. One 
of these is the introduction of mere specific differences into the generic 
character; the other, that this is made to embrace propositions applicable 
