Vi INTRODUCTION. 
The Dytiscide and Hydrophilide, as mentioned above, consist together of over 
300 species. I shall not, however, make any general remarks on these insects, for 
though this number of species is far from inconsiderable, the two families are but little 
adapted for consideration in questions of zoo-geography. The Dytiscide are appa- 
rently subject to different laws of distribution from other Coleoptera, illustrating in 
this respect what I believe is the case with aquatic organisms generally, viz. diminished 
endemicity ; and though the family Hydrophilide is not so purely aquatic as the 
Dytiscide, yet, on the other hand, it is one of the most neglected of all the families of 
Coleoptera. Moreover there is another reason why water-beetles, though possessing a 
special interest in certain respects, should be at present omitted in the discussion of 
faunistic questions, viz. that they require special apparatus to obtain them, and so they 
are very unequally collected—the collector rarely troubling himself to carry a water-net 
in addition to his other implements, so that they are frequently passed over and not 
procured even in spots where they are really numerous. 
By far the larger part of the volume is occupied with the great family Staphylinide, 
of which we register 1405 species. In the temperate regions of the world this family 
is more numerous in species than the Carabide, and is about equal in this respect to 
the Curculionide ; but it has been hitherto supposed to be less numerous in species in 
the tropics. There are undoubtedly some tropical regions, especially such as possess 
an arid climate, that are deficient in Staphylinide; but taking the world all over, I 
believe the family will be found to maintain its supremacy of specific multiplicity with- 
out much diminution. Actually, however, statistics would not show this to be the 
case; for the total number of described species of Staphylinide outside the Nearctic 
and Palearctic regions cannot at present, I should think, amount to 3000 species. 
The study of this great family is therefore practically in its infancy, and very little can 
be done with advantage in the comparison of our Staphylinide with those of other 
regions. ‘The South-American Staphylinide are very little known; and the North- 
American list, though it comprises upwards of 900 species, is very incomplete. 
The 1400 species ascertained to exist in the Mexican or (as I think it would be better 
called) the Central-American subregion can be actually but a small part of its true 
Staphylinid-fauna, which if exhaustively explored would probably be found to be 
nearer 4000 than 3000 species. In order to procure the insects composing this family 
a skilful and persevering collector is absolutely necessary: our Editors were fortunate 
in securing such a one in the person of Mr. Champion ; but for the provinces of our 
subregion not visited by him our records are comparatively very imperfect. In order 
