70 
REVIEWS. 
requires some amendments. Thus, for example, in the determination of 
the family to which a Dioctria belongs, the student would be directed, not 
to the Asilidce , but the Xylophagidce; and, again, to the Conopidce , instead 
of the Stratiomydce , in the case of a Stratiomys with simple cubital vein. 
These, however, are but trivial blemishes, which may easily be remedied, 
and which, in the meantime, scarcely detract from the usefulness of 
the book. 
The characteristic of the families is framed with reference only to the 
European species, or, more strictly, only to those indigenous to Britain. 
Readily as we concede to Mr. Walker, with a view to the special object 
for which he has written, the privilege of disregarding many peculiarities 
and singularities of the exotic forms, and of applying himself by preference 
to the characters of the native species ; yet we cannot give an unqualified 
approval to the exclusive consideration of the latter. The author should 
have asked himself, and have answered the question decidedly, whether he 
proposed to give a characteristic of the families, or a mere recapitulation 
of the accidental distinctive marks by which the British species of one 
family may be known from those of another. If the former were his 
object—and he has given enough to make it appear that it was—then 
the exotic genera and species ought to have been regarded. The family 
character is no product of the casual fauna of a particular district, but 
the result of the comparative knowledge of the entire family, so far as 
this has been attained ; not different for every country and province, 
but the same, and a common property of science everywhere. On the 
other hand, if he intended only to give the distinctive marks by which 
the British species of one family may be separated from those of another 
*—and it seems that this might have been enough for the object of his 
book—then he was fully entitled to consider only what lay within the 
limits of the fauna which he had to treat of. But, then, he should have 
expressed this intention clearly, and adhered to it consistently. The 
indecision in which Mr. Walker has remained as to his own purpose 
has led to this result, that for those families which have numerous repre¬ 
sentatives in the British fauna, a tolerably full, and in several instances— 
as, for example, in the Syrphidce , and more especially in the Dolichopidce 
■—a well-constructed family character is given, which approaches the more 
nearly to the true family character in proportion as there are found among 
exotic forms few that differ materially from the indigenous ; while, on the 
other hand, for the families which are sparingly represented therein, we 
have, instead of this, distinctive marks applicable only to the British 
